CA1258324A - Synchronization control capable of establishing synchronization without transmission of distance information between control and local earth stations - Google Patents
Synchronization control capable of establishing synchronization without transmission of distance information between control and local earth stationsInfo
- Publication number
- CA1258324A CA1258324A CA000532115A CA532115A CA1258324A CA 1258324 A CA1258324 A CA 1258324A CA 000532115 A CA000532115 A CA 000532115A CA 532115 A CA532115 A CA 532115A CA 1258324 A CA1258324 A CA 1258324A
- Authority
- CA
- Canada
- Prior art keywords
- earth station
- time
- control
- reception
- transmission
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/204—Multiple access
- H04B7/212—Time-division multiple access [TDMA]
- H04B7/2125—Synchronisation
Abstract
Abstract of the Disclosure:
In a TDMA satellite communication network comprising control and local earth stations communicable with one another through a satellite, a time difference between transmission and reception of a reference burst is measured at the control earth station to detect a time deviation (Tb) from a standard offset time (SO) predetermined for the control earth station. In the control earth station, the time deviation is doubled and added to the standard offset time to provide a reception time instant (t4) for the local earth station. Thus, the reception time instant is varied and predicted in the control earth station with reference to the time deviation detected in the control earth station. The local earth station determines a transmission time instant (t2 or t2') by delaying a reception timing signal by a predetermined time interval (Ta).
In a TDMA satellite communication network comprising control and local earth stations communicable with one another through a satellite, a time difference between transmission and reception of a reference burst is measured at the control earth station to detect a time deviation (Tb) from a standard offset time (SO) predetermined for the control earth station. In the control earth station, the time deviation is doubled and added to the standard offset time to provide a reception time instant (t4) for the local earth station. Thus, the reception time instant is varied and predicted in the control earth station with reference to the time deviation detected in the control earth station. The local earth station determines a transmission time instant (t2 or t2') by delaying a reception timing signal by a predetermined time interval (Ta).
Description
1;~5~
SYNCHRONIZATION CONTROL CAPABLE OF ESTABLISHING
SYNCHRONIZATION WITHOUT TRANSMISSION OF DISTANCE
INFORMATION BETWEEN CONTROL AND LOCAL EARTH STATIONS
Background of the Invention:
This invention relates to an earth station for use in a time division multiple access toften abbreviated to TDMA) satellite communication network.
A TDMA satellite CQmmUniCatiOn network comprises a plurality of earth stations communicable with one another through a geostationary satellite (hereafter referred to simply as a satellite) in a time division fashion. Such communication is carried out in each 10 earth station by sending an up-link signal to the satellite and by re¢eiving a down-link signal from the satellite. Each of the up-link and the down-link signals is divisible into a succession of frames. Each frame includes a plurality of time slots to which bursts 15 are assigned by the respective earth stations.
In such a communication network, accurate synchronization must be established in relation to the -
SYNCHRONIZATION CONTROL CAPABLE OF ESTABLISHING
SYNCHRONIZATION WITHOUT TRANSMISSION OF DISTANCE
INFORMATION BETWEEN CONTROL AND LOCAL EARTH STATIONS
Background of the Invention:
This invention relates to an earth station for use in a time division multiple access toften abbreviated to TDMA) satellite communication network.
A TDMA satellite CQmmUniCatiOn network comprises a plurality of earth stations communicable with one another through a geostationary satellite (hereafter referred to simply as a satellite) in a time division fashion. Such communication is carried out in each 10 earth station by sending an up-link signal to the satellite and by re¢eiving a down-link signal from the satellite. Each of the up-link and the down-link signals is divisible into a succession of frames. Each frame includes a plurality of time slots to which bursts 15 are assigned by the respective earth stations.
In such a communication network, accurate synchronization must be established in relation to the -
2 1258;~2~
frames and the bursts of each of the up-link and the down-link signals. Otherwise, overlap takes place between two adjacent ones of the bursts.
One of the earth stations is selected as a 5 control or reference earth station for producing a succession of reference bursts which define the frames in the up-link signal sent from the control earth station and which may collectively be called a transmission reference timing signal. The reference 10 bursts appear through the satellite in the down-link signal and are delivered to each earth station as a reception timing signal. The earth stations establish frame synchronization with reference to the reception timing signal and thereafter carry out reception and 15 transmission. In addition, transmission timing is also determined in each earth station in relation to the reception timing signal.
On receiving a burst from the down-link signal within an assigned one of the down-link signal after 20 establishment of the frame synchronization, each earth station detects a fixed pattern by monitoring autocorrelation between the fixed pattern and a received pattern included in a received one of the bursts.
However, false or wrong detection of the fixed pattern 25 often takes place due to thermal noise and the like.
In order to avoid such false detection, each earth station is controlled so as to intermittently open a window at a predicted time location at which a burst
frames and the bursts of each of the up-link and the down-link signals. Otherwise, overlap takes place between two adjacent ones of the bursts.
One of the earth stations is selected as a 5 control or reference earth station for producing a succession of reference bursts which define the frames in the up-link signal sent from the control earth station and which may collectively be called a transmission reference timing signal. The reference 10 bursts appear through the satellite in the down-link signal and are delivered to each earth station as a reception timing signal. The earth stations establish frame synchronization with reference to the reception timing signal and thereafter carry out reception and 15 transmission. In addition, transmission timing is also determined in each earth station in relation to the reception timing signal.
On receiving a burst from the down-link signal within an assigned one of the down-link signal after 20 establishment of the frame synchronization, each earth station detects a fixed pattern by monitoring autocorrelation between the fixed pattern and a received pattern included in a received one of the bursts.
However, false or wrong detection of the fixed pattern 25 often takes place due to thermal noise and the like.
In order to avoid such false detection, each earth station is controlled so as to intermittently open a window at a predicted time location at which a burst
3 1~ 4 might be received, In this event, detection of the fixed pattern is valid only when the window is opened.
As a result, superfluous or false detection of the fixed pattern becomes invalid in each earth station, In the meanwhile, a distance is variable between the satellite and each earth station in the TDMA
satellite communication because the satellite fluctuates from a standard position to a deviated position with time with a spatial deviation left between the standard 10 and the deviated positions. It is therefore necessary to control or adjust synchronization of each earth station in consideration of a variation or deviation of a distance between the satellite and the earth station under consideration.
In a conventional TDMA satellite communication network, synchronization of each earth station is carried out so that the reception timing signal is received within the window by controlling the transmission timing.
More particularly, each earth station determines its own reception time slots with reference to the reference bursts to,open the windows at the reception time locations. Under the circumstances, the transmission timing of each earth station is controlled 25 so as to carry out reception within the windows. For example, it is assumed that a certain earth station can transmit its own burst to the satellite and receive the own burst in question as a reception burst. In this ~:~5~:~24 event, a time relationship between the reference burst and the own burst is monitored to control the transmission timing which might vary due to fluctuation of the satellite. On the other hand, when an earth 5 station can not receive the own burst, the transmission timing is adjusted in the earth station in response to an information signal which is indicative of fluctuation of the satellite and which is given from any other earth station. Such an information signal may be either a 10 position error signal representative of a difference between the standard position and the deviated one or a distance signal representative of a distance between the deviated position of the satellite and each earth station.
As mentioned before, each earth station must carry out operation so as to adjust synchroni~ation and to correct fluctuation or variation of the satellite when the transmission timing is controlled in each earth station. Moreover, either the position error signal or 20 the distance signal should be sent from any other station to the earth station when the earth station in question can not receive its own transmission burst.
Thus, a superfluous information signal must be transmitted between the earth stations. Transmission of 25 a superfluous information signal gives rise to a reduction of througbput in the satellite communication network.
,. , ,:
5 1;~5~;324 Moreover, communication control is widely distributed to the local earth stations in addition to the control earth station. This means concentration of communication control difficult.
At any rate, an expensive and complicated transmission timing control device must be included in each local earth station to control the transmission timing and results in an increase of costs of the local earth station and in an increase of a load in the local 10 earth station.
Summary of the Invention:
It is an object of this invention to provide a time division multiple access (TDMA) satellite communication network which is capable of establishing 15 synchronization without transmission of distance information between control and local earth stations so as to increase throughput of the network.
It is another object of this invention to provide an earth station which is used in a TDMA
20 satellite communication network of the type described and which makes control of transmission timing unnecessary.
It is a further object of this invention to provide an earth station of the type described which is 25 operable as a control earth station and which favorably controls synchronization of the TDMA satellite communication network.
~ .
6 1;~ 4 It .is a still further object of this invention to provide an earth s-tation of the type described, which is operable as a local earth station and which is simple in structure and inexpensive.
A control earth station to which this invention is applicable is for use in a time division multiple access network to communicate with a local earth station through a geostationary satellite which fluctuates from a standard position into a deviated position with time 10 with a spatial deviation left between the standard and the deviated positions. The control earth station comprises transmission timing means for transmitting a transmission reference timing signal towards the geostationary satellite, detecting means for receiving a 15 reception timing signal which results from the transmission reference timing signal sent back from the satellite, and reception timing control means coupled to the transmission timing means and the detecting means for controlling a reception time instant determined for 20 the local earth station. According to this invention, the reception timing control means comprises measuring means responsive to the reception timing signal for measuring a time difference between the transmission reference timing signal and the reception signal to 25 determine an actual distance between the control earth station and the satellite, standard delay providing means for providing a standard delay time determined by a standard distance between the control earth station 1;~58;3Z4 and the standard position of the satellite, detecting means coupled to the measuring means and the standard delay providing means for detecting a time deviation resulting from the spatial deviation of the satellite with reference to the time difference and the standard delay time, and varying means coupled to the detecting means and the standard delay providing means for varying the reception time instant for the local earth station with reference to the standard delay time and the time deviation.
According to another aspect of the invention there is provided, in a local earth station for use in a time division multiple access network to communicate with a control earth station through a geostationary satellite, said local earth station being supplied with a reception timing signal from said control earth station through said geostationary satellite, and carrying out transmission in synchronism with a local transmission timing signal, the improvement wherein said local earth station comprises:
delay means responsive to said reception timing signal for delaying said reception timing signal by a predetermined duration to produce a delayed timing signal, said predetermined duration being determined in said local earth station; and means for providin~g said delayed timing signal as said local transmission timing signal.
Brief DescriPtion of the Drawinq:
Fig. 1 is a time chart for use in describing operation of a conventlonal TDMA satellite communication network;
Fig. 2 is a time chart for use in describing a principle of this invention;
1;~58~324 7a 64768-145 Fig. 3 is a block diagram of a control earth station according to a preferred embodiment of this invention;
Fig. 4 is a block diagram for use in describing a part of the control earth station illustrated in Fig. 3 in detail; and Fig. 5 is a block diagram of a local earth station communicable with the control earth station illustrated in Figs. 3 and 4.
lZ58;~Z4 Description of the Preferred Embodiment:
Prior Art Referring to Fig. 1, a conventional synchronization control method will be described for a 5 better understanding of this invention. Such a control method is applicable to a time division multiple access (TDMA) satellite communication network comprising a plurality of earth stations one of which is operable as a control or reference earth station 11 the remaining 10 ones of which are operable as local or peripheral earth stations exemplified by a single local earth station 12.
Each of the control and the local earth stations 11 and 12 is communicable with one another through a satellite 13.
The control earth station 11 can transmit a reference burst to the satellite 13 in the form of an up-link signal to deliver the reference burst to the respective earth stations in the form of a down-link signal.
The satellite 13 might undesirably move from a standard position to a deviated position with a spatial deviation or distance variation left between the standard and the deviated positions, although the satellite is placed on a geostationary orbit.
25 Therefore, the control earth station 11 measures a distance between the satellite 13 and one or a plurality of the earth stations in the illustrated satellite communication network. The measured distance may be 9 125~3324 either a distance between the earth station or stations and the standard position of the satellite 13 or a distance between the earth station or stations and the deviated position of the satellite 13. Anyway, the 5 measured distance indicates an actual distance between the earth station or stations and the satellite 13. The measured distance i5 produced from the control earth station 11 as a distance information signal representative of the measured distance, although 10 description will be made only as the position information signal. Since the measured distance may be indicative of a position of the satellite 13, the measured distance may be produced as a position information signal. In addition, the illustrated 15 control station 11 can measure the spatial deviation between the standard and the deviated positions to produce a position error signal indicative of the spatial deviation.
On the other hand, it is assumed that each of 20 the local earth stations 12 can control and correct a transmission timing assigned thereto in response to the distance or position information signal and the position error signal. When the local earth station in question can not receive its own transmission burst through the 25 satellite 13, the position error signal must be delivered to the local earth station in question.
Otherwise, delivery of the position error signal is unnecessary. In the example being illustrated, the 1;~5~;324 illustrated local earth station 12 can not receive its own transmission burst.
On initiallization of the network, the reference burst is sent as a reference timing signal RT from the 5 control earth station 11 through the satellite 13 to the illustrated local earth station 12. In this event, the position information signal is also given from the control earth station 11 to the local earth station 12.
Responsive to the reference timing signal RT, the local 10 earth station 12 determines an actual transmission timing AT with reference to a reception timing of the reference timing signal RT. For this purpose, the local earth station 12 previously calculates a standard offset time value SO determined by the distance between the 15 local earth station 12 and the standard position of the satellite 13. The local earth station 12 adjusts the standard offset time value SO in response to the position information signal. Specifically, a correction value CV is calculated from the position information 20 signal in the local earth station 12 and is added to or subtracted from the standard offset time value SO. In consequence, an actual offset time value AO is obtained by the local earth station 12 to determine the actual transmission timing AT. The transmission burst is 25 transmitted from the local earth station 12 at the actual transmission timing and is received by the control earth station 11 through the satellite 13. In the illustrated example, the correction value CV is .
5~ 4 subtracted from the standard offset time value SO. This shows that the satellite 13 becomes nearer to the local earth station 12 than the standard position.
Once synchronization is established among the 5 earth stations, the control earth station 11 receives the transmission burst transmitted from each local station together with the reference burst (depictd at RB) returned back from the satellite 13. In Fig. 1, the transmission burst is assumed to be transmitted at 10 another transmission timing depicted at ATl with reference to the reference burst RB and is received through the satellite 13 at an actual reception time instant RTl. If the transmission burst is to be received by the control earth station 11 at a normal 15 reception time instant RTn, a time deviation TD takes place between the normal and the actual reception time instants RTn and RTl and might be equal to the correction value CV. The control earth station 11 monitors the time deviation TD between the normal and 20 the actual reception time instants RTn and RTl in response to the reference burst sent back from the satellite 13. The time deviation TD is delivered in the form of the position error signal from the control earth station 11 to the illustrated local earth stations 12 25 through the satellite 13. The local earth station 12 controls the transmission timing in response to the time deviation TD so that the transmission burst of the local 12 1;~5~:324 earth station 12 is received at the normal reception time instant RTn.
In any event, the transmission timing should be varied by the use of a transmission timing control 5 device in each local earth station. In addition, a superfluous information signal, such as the position information signal and the position error signal, must be transmitted among the earth stations. This results in a reduction of throughput in the TDMA satellite 10 communication network.
Principle of the Invention Referring to Fig. 2, a principle of this invention will be described so as to facilitate an understanding of this invention. This invention is 15 applicable to a TDMA satellite communication network comprising a plurality of earth stations which are divisible into a control earth station 11' and local earth stations 12' and which are communicable with one another through a satellite (not shown in this figure), 20 like in Fig. 1. The satellite is placed on an orbit which is spaced apart from the earth's surface by an altitude of about 36,000 km. The earth stations are distributed on the earth's surface with a spatial interval or distance left between two adjacent ones of 25 the earth stations. The spatial interval is several thousands of kilometers at most and is very shorter than the altitude of the satellite.
`:
13 1 ~ 5 832 4 Distances between the earth stations and the satellite are different from one another and are variable with time, as mentioned in conjunction with Fig. 1.
This means that delay times between the earth stations and the satellite are also different from one another and variable with time. However, it is to be noted that differences and variations of the delay times can be very shorter than a width of a window opened for 10 synchronization of the respective earth stations. Such differences and variations of the delay times may therefore be absorbed by substituting a time variation of the delay time measured at the control earth station 11' for the time variations of delay times measured at 15 the respective earth stations and by selecting the width of the window. A time variation of the control earth station 11' may be called a selected time variation.
Such substitution of the selected time variation of delay time in question scarcely influences 20 synchronization when differences between the selected time variation and the other time variations are smaller than the widths of the windows.
In order to carry out the above-mentioned substitution of the time variation, the control earth 25 station 11' comprises a distance measurement device 15 for measuring the actual distance between the control earth station 11' and the satellite by detecting a time difference between transmission of the reference burst 14 1;~5~3'~4 and reception of the reference burst returned back to the control earth station 11 through the satellite.
In Fig. 2, a reference burst is transmitted from the control earth station 11 to the respective earth 5 stations through the satellite as a transmission reference timing signal RE at a predetermined period of, for example, 210 milliseconds. The control earth station 11 has a standard offset time value SO
previously calculated with reference to a standard 10 distance between the control earth station 11' and the standard position of the satellite.
Let a delay time between the satellite and the control earth station 11' be equal to the standard offset time value SO. In this event, operation is 15 carried out in a manner as shown at dot-and-dash lines in Fig. 2.
More specifically, each reference burst RE is received by the control earth station 11' through the satellite at a reference time instant tr after lapse of 20 a standard offset time which is equal to the standard offset time value SO. Likewise, the refernece burst RE
is also received by~the local earth stations 12' after lapse of each local offset time which may slightly be different from the standard offset time and which is 25 determined by the distance between each earth station and the satellite.
The illustrated local station 12' receives the reference burst RE at a local reception time instant t 1~5~33;~4 as a reception timing signal and determines a local transmission time instant t2 with reference to the local reception time instant tl. In the example being illustrated, the local transmission time instant t2 5 appears after lapse of a predetermined time interval Ta.
The predetermined time interval Ta is defined at every local earth station 12' in consideration of the time variation or time difference of the delay times between the control earth station 11' and the local earth 10 station 12'.
Transmission is carried out at the local transmission time instant t2 in a direction from the local earth station 12' to the control earth station 11'. Reception is made at the control earth station 11' 15 within a window opened for the reception.
Let variations of delay times ta~e place between the control and the local earth stations 11' and 12' as a result of movement of the satellite from the standard position to the deviated one. In this situation, it is 20 assumed that the reference burst RE is received as a reception timing signal at a control reception time instant t3 after a delay time Tb which corresponds to twice the spatial variation left between the standard and the deviated positions of the satellite and which 25 may be referred to as the twice variation of the delay time in the control earth station 11'. Anyway, the distance measurement device in the control earth station 11' determines the distance between the control earth 1'~583z4 station 11' and the deviated position of the satellite by measuring a time difference between the transmission reference timing signal (defined by the reference burst RE) and the control reception time instant t3.
Suppose that a distance between the local earth station 12' and the deviated position of the satellite is longer than the distance between the control earth station 11' and the deviated position. Operation is carried out in a manner as depicted at solid lines.
10 More particularly, arrival of the reference burst RE at the local earth station 12' is delayed relative to its arrival at the control earth station 11'. As a result, the reference burst RE is received as a reception timing signal at a delayed reception time instant tl' delayed 15 relative to the control reception time instant t3 by an actual time interval Tc. The actual time interval Tc corresponds to twice a difference of the distances between the control earth station 11' and the deviated position of the satellite and between the local earth 20 station 12' and the deviated position.
A reception offset time TO for the local earth station 12' is specified by a total delay time equal to a sum of the standard offset time SO, the time variation Tb, and the actual time interval Tc. It is to be noted 25 that the standard offset time SO and the time variation Tb are actually measured at the control earth station 11' while the actual time interval Tc is determined for the local earth station 12' without any measurement.
~' ~
., , 17 1~ 5 ~32 4 The local earth station 12' provides a delayed transmission time instant t2' when the predetermined time interval Ta lapses after the delayed reception time instant tl'. At the delayed transmission time instant 5 t2', transmission is made from the local earth station 12 to the control earth station 11'.
In order to respond to the transmission carried out at the delayed transmission time instant t2', the window must be opened in the control earth station 11' 10 at a reception timing. For this purpose, the reception timing of the control earth station 11' is varied by substituting an additional time variation Tb' in the control earth station 11' for the actual time interval Tc in the local earth station 12'. In other words, the 15 actual time interval Tc in the local earth station 12' is simulated by the additional time variation Tb' in the control earth station 11' to determine the reception timing. In the illustrated example, the additional time variation Tb' is selected so that it becomes equal to 20 the time variation Tb, although the additional time variation Tb' is somewhat different from the actual time interval Tc of the local earth station 12'.
Consequently, the window for the local earth station 12' is opened for a preselected duration of, for 25 example, 80 microseconds after an additional reception time instant t4 which is delayed by the additional time deviation Tb' relative to the control reception time instant t3 and which defines the reception timing.
18 1;~5~33'~4 Thus, the location of the window is predicted in the control earth station 11' by adding twice the delay time Tb to the standard offset time (SO).
Reception might be made at the control earth 5 station 11' with a time error Td left between the reception timing and an actual reception timing, as illustrated along the third line. However, it is possible to shorten the time error Td in comparison with the width of each window because the space intervals 10 among the earth stations are considerably shorter than the distance between the satellite and each earth station. Accordingly, synchronization is readily established by using the additional time deviation Tb' in the control earth station 11' instead of the actual 15 delay time Tc in the local earth station 12'.
Preferred Embodiment Referring to Fig. 3, the control earth station 11' which can carry out the operation described in conjunction with Fig. 2 comprises a transmitter section 20 21 supplied with a sequence of transmission data signals DT from a substation or substations (not shown) connected to the control earth station 11'. The transmitter section 21 comprises a transmission interface 22, a transmission controller 23, and a 25 modulator 24, all of which are similar to those known in the art and which will not be described any longer. At any rate, the transmission data signal sèquence DT is sent through the transmission interface 22, the 19 1'~58~
transmission controller 23, and the modulator to the satellite in the form of a data burst.
The transmission controller 23 is coupled to a transmission timing generator 26' given an oscillation 5 signal of a predetermined frequency from an oscillator 27. The transmission timing controller 26 produces a transmission reference timing signal TRS in cooperation with the oscillator 27. The transmission reference timing signal TRS is delivered at a predetermined period 10 of, for example, 210 milliseconds to the transmission controller 23 to be sent to the satellite as a sequence of reference bursts RE shown in Fig. 2.
The reference burst RE is delivered to the local earth stations (not shown in Fig. 3) through the 15 satellite and sent back from the satellite to the control earth station 11' as a reflected burst RF. The reflected burst RF carries the transmission reference timing signal TRS. Although the reflected burst RF may include any other data signals destined to the control 20 earth station 11', such data signals might be left out of consideration.
The reflected burst RF is supplied to a detecting circuit 31 comprising a first demodulator 32, a unique word detector 33, and a frame synchronization 25 circuit 34, all of which are known in the art. The detecting circuit 31 is operable to monitor the reflected burst RF and to establish sychronization. To this end, a unique word is detected by the unique word .~ .
20 1Z58;~
detector 33 and is sent to the frame ~ynchronization circuit 34. The frame synchronization circuit 34 produces a reception timing signal RTS which results from the transmission reference timing signal TRS.
The reception timing signal RTS is sent to a distance measuring circuit 36 for measuring a distance between the control earth station 11' and the satellite of which the position might be variable. The distance measuring circuit 36 comprises a counter 37 operable in 10 response to the transmission reference timing signal TRS
and the reception timing signal RTS and a reception timing predictor 38 operable in a manner to be described later. The counter 37 starts counting a clock pulse sequence in response to the transmission reference 15 timing signal TRS and stops counting in response to the reception timing signal RTS. The counter 36 therefore has a count indicative of a time difference between the transmission reference timing signal TRS and the reception timing signal RTS and specifies twice the 20 distance between the control earth station 11' and the satellite. The time difference is equal to the standard offset time (SO) or,a sum of the standard offset time (SO) and the time deviation Tb, both of which are described in conjunction with Fig. 2. When the 25 satellite is moved from the standard position to the deviated position, the counter 36 serves to measure twice the actual distance between the control earth station 11' and the satellite and therefore determines 1~58:~;24 the distance between the control earth station 11' and the satellite.
Referring to Fig. 4 together with Fig. 3, the reception timing predictor 38 is supplied with the count 5 of the counter 37 as a time difference signal TM
representative of the above-mentioned twice difference.
In the reception timing predictor 38, a standard delay circuit 41 produces a standard offset signal indicative of the standard offset time value SO (Fig. 2). The 10 standard offset time (SO) indicates a standard distance between the control earth station 11' and the standard position of the satellite, as mentioned before.
A subtractor 42 subtracts the time difference (TM) from the standard offset time (SO) to detect the 15 time delay or time deviation Tb resulting from a movement of the satellite from the standard position to the deviated position. The time deviation Tb is delivered to a multiplier 43 as a time deviation signal.
The multiplier 43 multiplies the time deviation 20 Tb by a factor of two to calculate twice the time deviation Tb as a prediction time deviation. The prediction time dev,iation is added by an adder 44 to the standard offset time (SO) to specify the additionial reception time instant or reception time instant t4, 25 described in connection with Fig. 2. Thus, a combination of the multiplier 43 and the adder 44 is operable to calculate and vary the reception time 22 lZ5~ 4 instant t4 and may be named a varying circuit 45 for varying the reception time instant.
The reception offset time TO between the transmission of the reference burst RE and the reception 5 time instant t4 is equal to a sum of the standard offset time (SO) and a couple of the time deviations Tb, as mentioned before. The reception time instant therefore indicated by a reception offset time signal TO
representative of the reception offset time.
In Fig. 3, a reception timing generator 46 is supplied with the transmission reference timing signal TRS and the reception offset time signal TO. A
reception timing signal is produced from the reception timing generator 46 when the reception offset time 15 signal TO is received after reception of the transmission reference timing signal TRS.
A receiver section 51 comprises a second demodulator 52, a reception controller 53, and a reception interface 54, which are all known in the art.
20 The reception burst RC is sent from the local earth station 12' through the second demodulator 52 to the reception controller 53 supplied with the reception timing signal. When the window is opened in response to the reception timing signal, reception synchronization 25 is established in the control earth station 11'.
Referring to Fig. 5, the local earth station 12' is communicable with the control earth station 11' illustrated in Figs. 2 through 4 and comprises a ~3 1Z5~
reception portion 61 and a transmission portion 62 which are coupled through the satellite (not shown) to the control earth station 11'.
A reception burst is sent from the control earth 5 station 11' to the receiver portion 61 of the local earth station 12' and is sent through a third demodulator 63 and a unique word detector 64 to a reception control section 65. The unique word detector 64 detects a unique word assigned to the control earth 10 station 11' and produces a local reception timing signal LRT on detection of the unique word. After establishment of synchronization, a reception data signal D~L is sent through a reception interface 66 to a terminal end (not shown).
The local reception timing signal LRT is given to a timing delay circuit 67. The timing delay circuit 67 delays the local reception timing signal LRT by the predetermined time interval Ta illustrated in Fig. 3 and supplies the transmission portion 62 with a delayed 20 local reception timing signal as a local transmission timing signal LTT.
The transmission portion 62 comprises a transmission interface 68, a transmission controller 69, and a modulator 70. The transmission controller 69 is 25 controlled by the local transmission timing signal LTT
to be put into a synchronized state. Thereafter, a local transmission data signal DTL is sent through the 24 1;25~3324 transmission interface 68, the transmission controller 69, and the modulator 70 to the satellite.
In Fig. 5, description has been made on the assumption that the illustrated local earth station 12' S can not receive a transmission burst sent from the local earth station 12' itself. However, this invention is also applicable in the case where the local earth station 12' can receive its own transmission burst.
Thus, the control earth station 11' controls 10 reception synchronization in consideration of the time deviation related to the local earth stations 12'. This dispenses with control operation of transmission timings in the local earth stations 12' and with delivery or broadcast of distance information of the satellite to 15 the local earth stations 12'. The local earth stations 12' become simple in structure due to a light load of processing.
While this invention has thus far been described in conjunction with a preferred embodiment thereof, it 20 will readily be possible for those skilled in the art to put this invention into practice in various other manners. For examp,le, the additional time deviation Tb' may not be equal to the time deviation Tb. In addition, a plurality of the local earth stations may be included 25 in the satellite communication network.
As a result, superfluous or false detection of the fixed pattern becomes invalid in each earth station, In the meanwhile, a distance is variable between the satellite and each earth station in the TDMA
satellite communication because the satellite fluctuates from a standard position to a deviated position with time with a spatial deviation left between the standard 10 and the deviated positions. It is therefore necessary to control or adjust synchronization of each earth station in consideration of a variation or deviation of a distance between the satellite and the earth station under consideration.
In a conventional TDMA satellite communication network, synchronization of each earth station is carried out so that the reception timing signal is received within the window by controlling the transmission timing.
More particularly, each earth station determines its own reception time slots with reference to the reference bursts to,open the windows at the reception time locations. Under the circumstances, the transmission timing of each earth station is controlled 25 so as to carry out reception within the windows. For example, it is assumed that a certain earth station can transmit its own burst to the satellite and receive the own burst in question as a reception burst. In this ~:~5~:~24 event, a time relationship between the reference burst and the own burst is monitored to control the transmission timing which might vary due to fluctuation of the satellite. On the other hand, when an earth 5 station can not receive the own burst, the transmission timing is adjusted in the earth station in response to an information signal which is indicative of fluctuation of the satellite and which is given from any other earth station. Such an information signal may be either a 10 position error signal representative of a difference between the standard position and the deviated one or a distance signal representative of a distance between the deviated position of the satellite and each earth station.
As mentioned before, each earth station must carry out operation so as to adjust synchroni~ation and to correct fluctuation or variation of the satellite when the transmission timing is controlled in each earth station. Moreover, either the position error signal or 20 the distance signal should be sent from any other station to the earth station when the earth station in question can not receive its own transmission burst.
Thus, a superfluous information signal must be transmitted between the earth stations. Transmission of 25 a superfluous information signal gives rise to a reduction of througbput in the satellite communication network.
,. , ,:
5 1;~5~;324 Moreover, communication control is widely distributed to the local earth stations in addition to the control earth station. This means concentration of communication control difficult.
At any rate, an expensive and complicated transmission timing control device must be included in each local earth station to control the transmission timing and results in an increase of costs of the local earth station and in an increase of a load in the local 10 earth station.
Summary of the Invention:
It is an object of this invention to provide a time division multiple access (TDMA) satellite communication network which is capable of establishing 15 synchronization without transmission of distance information between control and local earth stations so as to increase throughput of the network.
It is another object of this invention to provide an earth station which is used in a TDMA
20 satellite communication network of the type described and which makes control of transmission timing unnecessary.
It is a further object of this invention to provide an earth station of the type described which is 25 operable as a control earth station and which favorably controls synchronization of the TDMA satellite communication network.
~ .
6 1;~ 4 It .is a still further object of this invention to provide an earth s-tation of the type described, which is operable as a local earth station and which is simple in structure and inexpensive.
A control earth station to which this invention is applicable is for use in a time division multiple access network to communicate with a local earth station through a geostationary satellite which fluctuates from a standard position into a deviated position with time 10 with a spatial deviation left between the standard and the deviated positions. The control earth station comprises transmission timing means for transmitting a transmission reference timing signal towards the geostationary satellite, detecting means for receiving a 15 reception timing signal which results from the transmission reference timing signal sent back from the satellite, and reception timing control means coupled to the transmission timing means and the detecting means for controlling a reception time instant determined for 20 the local earth station. According to this invention, the reception timing control means comprises measuring means responsive to the reception timing signal for measuring a time difference between the transmission reference timing signal and the reception signal to 25 determine an actual distance between the control earth station and the satellite, standard delay providing means for providing a standard delay time determined by a standard distance between the control earth station 1;~58;3Z4 and the standard position of the satellite, detecting means coupled to the measuring means and the standard delay providing means for detecting a time deviation resulting from the spatial deviation of the satellite with reference to the time difference and the standard delay time, and varying means coupled to the detecting means and the standard delay providing means for varying the reception time instant for the local earth station with reference to the standard delay time and the time deviation.
According to another aspect of the invention there is provided, in a local earth station for use in a time division multiple access network to communicate with a control earth station through a geostationary satellite, said local earth station being supplied with a reception timing signal from said control earth station through said geostationary satellite, and carrying out transmission in synchronism with a local transmission timing signal, the improvement wherein said local earth station comprises:
delay means responsive to said reception timing signal for delaying said reception timing signal by a predetermined duration to produce a delayed timing signal, said predetermined duration being determined in said local earth station; and means for providin~g said delayed timing signal as said local transmission timing signal.
Brief DescriPtion of the Drawinq:
Fig. 1 is a time chart for use in describing operation of a conventlonal TDMA satellite communication network;
Fig. 2 is a time chart for use in describing a principle of this invention;
1;~58~324 7a 64768-145 Fig. 3 is a block diagram of a control earth station according to a preferred embodiment of this invention;
Fig. 4 is a block diagram for use in describing a part of the control earth station illustrated in Fig. 3 in detail; and Fig. 5 is a block diagram of a local earth station communicable with the control earth station illustrated in Figs. 3 and 4.
lZ58;~Z4 Description of the Preferred Embodiment:
Prior Art Referring to Fig. 1, a conventional synchronization control method will be described for a 5 better understanding of this invention. Such a control method is applicable to a time division multiple access (TDMA) satellite communication network comprising a plurality of earth stations one of which is operable as a control or reference earth station 11 the remaining 10 ones of which are operable as local or peripheral earth stations exemplified by a single local earth station 12.
Each of the control and the local earth stations 11 and 12 is communicable with one another through a satellite 13.
The control earth station 11 can transmit a reference burst to the satellite 13 in the form of an up-link signal to deliver the reference burst to the respective earth stations in the form of a down-link signal.
The satellite 13 might undesirably move from a standard position to a deviated position with a spatial deviation or distance variation left between the standard and the deviated positions, although the satellite is placed on a geostationary orbit.
25 Therefore, the control earth station 11 measures a distance between the satellite 13 and one or a plurality of the earth stations in the illustrated satellite communication network. The measured distance may be 9 125~3324 either a distance between the earth station or stations and the standard position of the satellite 13 or a distance between the earth station or stations and the deviated position of the satellite 13. Anyway, the 5 measured distance indicates an actual distance between the earth station or stations and the satellite 13. The measured distance i5 produced from the control earth station 11 as a distance information signal representative of the measured distance, although 10 description will be made only as the position information signal. Since the measured distance may be indicative of a position of the satellite 13, the measured distance may be produced as a position information signal. In addition, the illustrated 15 control station 11 can measure the spatial deviation between the standard and the deviated positions to produce a position error signal indicative of the spatial deviation.
On the other hand, it is assumed that each of 20 the local earth stations 12 can control and correct a transmission timing assigned thereto in response to the distance or position information signal and the position error signal. When the local earth station in question can not receive its own transmission burst through the 25 satellite 13, the position error signal must be delivered to the local earth station in question.
Otherwise, delivery of the position error signal is unnecessary. In the example being illustrated, the 1;~5~;324 illustrated local earth station 12 can not receive its own transmission burst.
On initiallization of the network, the reference burst is sent as a reference timing signal RT from the 5 control earth station 11 through the satellite 13 to the illustrated local earth station 12. In this event, the position information signal is also given from the control earth station 11 to the local earth station 12.
Responsive to the reference timing signal RT, the local 10 earth station 12 determines an actual transmission timing AT with reference to a reception timing of the reference timing signal RT. For this purpose, the local earth station 12 previously calculates a standard offset time value SO determined by the distance between the 15 local earth station 12 and the standard position of the satellite 13. The local earth station 12 adjusts the standard offset time value SO in response to the position information signal. Specifically, a correction value CV is calculated from the position information 20 signal in the local earth station 12 and is added to or subtracted from the standard offset time value SO. In consequence, an actual offset time value AO is obtained by the local earth station 12 to determine the actual transmission timing AT. The transmission burst is 25 transmitted from the local earth station 12 at the actual transmission timing and is received by the control earth station 11 through the satellite 13. In the illustrated example, the correction value CV is .
5~ 4 subtracted from the standard offset time value SO. This shows that the satellite 13 becomes nearer to the local earth station 12 than the standard position.
Once synchronization is established among the 5 earth stations, the control earth station 11 receives the transmission burst transmitted from each local station together with the reference burst (depictd at RB) returned back from the satellite 13. In Fig. 1, the transmission burst is assumed to be transmitted at 10 another transmission timing depicted at ATl with reference to the reference burst RB and is received through the satellite 13 at an actual reception time instant RTl. If the transmission burst is to be received by the control earth station 11 at a normal 15 reception time instant RTn, a time deviation TD takes place between the normal and the actual reception time instants RTn and RTl and might be equal to the correction value CV. The control earth station 11 monitors the time deviation TD between the normal and 20 the actual reception time instants RTn and RTl in response to the reference burst sent back from the satellite 13. The time deviation TD is delivered in the form of the position error signal from the control earth station 11 to the illustrated local earth stations 12 25 through the satellite 13. The local earth station 12 controls the transmission timing in response to the time deviation TD so that the transmission burst of the local 12 1;~5~:324 earth station 12 is received at the normal reception time instant RTn.
In any event, the transmission timing should be varied by the use of a transmission timing control 5 device in each local earth station. In addition, a superfluous information signal, such as the position information signal and the position error signal, must be transmitted among the earth stations. This results in a reduction of throughput in the TDMA satellite 10 communication network.
Principle of the Invention Referring to Fig. 2, a principle of this invention will be described so as to facilitate an understanding of this invention. This invention is 15 applicable to a TDMA satellite communication network comprising a plurality of earth stations which are divisible into a control earth station 11' and local earth stations 12' and which are communicable with one another through a satellite (not shown in this figure), 20 like in Fig. 1. The satellite is placed on an orbit which is spaced apart from the earth's surface by an altitude of about 36,000 km. The earth stations are distributed on the earth's surface with a spatial interval or distance left between two adjacent ones of 25 the earth stations. The spatial interval is several thousands of kilometers at most and is very shorter than the altitude of the satellite.
`:
13 1 ~ 5 832 4 Distances between the earth stations and the satellite are different from one another and are variable with time, as mentioned in conjunction with Fig. 1.
This means that delay times between the earth stations and the satellite are also different from one another and variable with time. However, it is to be noted that differences and variations of the delay times can be very shorter than a width of a window opened for 10 synchronization of the respective earth stations. Such differences and variations of the delay times may therefore be absorbed by substituting a time variation of the delay time measured at the control earth station 11' for the time variations of delay times measured at 15 the respective earth stations and by selecting the width of the window. A time variation of the control earth station 11' may be called a selected time variation.
Such substitution of the selected time variation of delay time in question scarcely influences 20 synchronization when differences between the selected time variation and the other time variations are smaller than the widths of the windows.
In order to carry out the above-mentioned substitution of the time variation, the control earth 25 station 11' comprises a distance measurement device 15 for measuring the actual distance between the control earth station 11' and the satellite by detecting a time difference between transmission of the reference burst 14 1;~5~3'~4 and reception of the reference burst returned back to the control earth station 11 through the satellite.
In Fig. 2, a reference burst is transmitted from the control earth station 11 to the respective earth 5 stations through the satellite as a transmission reference timing signal RE at a predetermined period of, for example, 210 milliseconds. The control earth station 11 has a standard offset time value SO
previously calculated with reference to a standard 10 distance between the control earth station 11' and the standard position of the satellite.
Let a delay time between the satellite and the control earth station 11' be equal to the standard offset time value SO. In this event, operation is 15 carried out in a manner as shown at dot-and-dash lines in Fig. 2.
More specifically, each reference burst RE is received by the control earth station 11' through the satellite at a reference time instant tr after lapse of 20 a standard offset time which is equal to the standard offset time value SO. Likewise, the refernece burst RE
is also received by~the local earth stations 12' after lapse of each local offset time which may slightly be different from the standard offset time and which is 25 determined by the distance between each earth station and the satellite.
The illustrated local station 12' receives the reference burst RE at a local reception time instant t 1~5~33;~4 as a reception timing signal and determines a local transmission time instant t2 with reference to the local reception time instant tl. In the example being illustrated, the local transmission time instant t2 5 appears after lapse of a predetermined time interval Ta.
The predetermined time interval Ta is defined at every local earth station 12' in consideration of the time variation or time difference of the delay times between the control earth station 11' and the local earth 10 station 12'.
Transmission is carried out at the local transmission time instant t2 in a direction from the local earth station 12' to the control earth station 11'. Reception is made at the control earth station 11' 15 within a window opened for the reception.
Let variations of delay times ta~e place between the control and the local earth stations 11' and 12' as a result of movement of the satellite from the standard position to the deviated one. In this situation, it is 20 assumed that the reference burst RE is received as a reception timing signal at a control reception time instant t3 after a delay time Tb which corresponds to twice the spatial variation left between the standard and the deviated positions of the satellite and which 25 may be referred to as the twice variation of the delay time in the control earth station 11'. Anyway, the distance measurement device in the control earth station 11' determines the distance between the control earth 1'~583z4 station 11' and the deviated position of the satellite by measuring a time difference between the transmission reference timing signal (defined by the reference burst RE) and the control reception time instant t3.
Suppose that a distance between the local earth station 12' and the deviated position of the satellite is longer than the distance between the control earth station 11' and the deviated position. Operation is carried out in a manner as depicted at solid lines.
10 More particularly, arrival of the reference burst RE at the local earth station 12' is delayed relative to its arrival at the control earth station 11'. As a result, the reference burst RE is received as a reception timing signal at a delayed reception time instant tl' delayed 15 relative to the control reception time instant t3 by an actual time interval Tc. The actual time interval Tc corresponds to twice a difference of the distances between the control earth station 11' and the deviated position of the satellite and between the local earth 20 station 12' and the deviated position.
A reception offset time TO for the local earth station 12' is specified by a total delay time equal to a sum of the standard offset time SO, the time variation Tb, and the actual time interval Tc. It is to be noted 25 that the standard offset time SO and the time variation Tb are actually measured at the control earth station 11' while the actual time interval Tc is determined for the local earth station 12' without any measurement.
~' ~
., , 17 1~ 5 ~32 4 The local earth station 12' provides a delayed transmission time instant t2' when the predetermined time interval Ta lapses after the delayed reception time instant tl'. At the delayed transmission time instant 5 t2', transmission is made from the local earth station 12 to the control earth station 11'.
In order to respond to the transmission carried out at the delayed transmission time instant t2', the window must be opened in the control earth station 11' 10 at a reception timing. For this purpose, the reception timing of the control earth station 11' is varied by substituting an additional time variation Tb' in the control earth station 11' for the actual time interval Tc in the local earth station 12'. In other words, the 15 actual time interval Tc in the local earth station 12' is simulated by the additional time variation Tb' in the control earth station 11' to determine the reception timing. In the illustrated example, the additional time variation Tb' is selected so that it becomes equal to 20 the time variation Tb, although the additional time variation Tb' is somewhat different from the actual time interval Tc of the local earth station 12'.
Consequently, the window for the local earth station 12' is opened for a preselected duration of, for 25 example, 80 microseconds after an additional reception time instant t4 which is delayed by the additional time deviation Tb' relative to the control reception time instant t3 and which defines the reception timing.
18 1;~5~33'~4 Thus, the location of the window is predicted in the control earth station 11' by adding twice the delay time Tb to the standard offset time (SO).
Reception might be made at the control earth 5 station 11' with a time error Td left between the reception timing and an actual reception timing, as illustrated along the third line. However, it is possible to shorten the time error Td in comparison with the width of each window because the space intervals 10 among the earth stations are considerably shorter than the distance between the satellite and each earth station. Accordingly, synchronization is readily established by using the additional time deviation Tb' in the control earth station 11' instead of the actual 15 delay time Tc in the local earth station 12'.
Preferred Embodiment Referring to Fig. 3, the control earth station 11' which can carry out the operation described in conjunction with Fig. 2 comprises a transmitter section 20 21 supplied with a sequence of transmission data signals DT from a substation or substations (not shown) connected to the control earth station 11'. The transmitter section 21 comprises a transmission interface 22, a transmission controller 23, and a 25 modulator 24, all of which are similar to those known in the art and which will not be described any longer. At any rate, the transmission data signal sèquence DT is sent through the transmission interface 22, the 19 1'~58~
transmission controller 23, and the modulator to the satellite in the form of a data burst.
The transmission controller 23 is coupled to a transmission timing generator 26' given an oscillation 5 signal of a predetermined frequency from an oscillator 27. The transmission timing controller 26 produces a transmission reference timing signal TRS in cooperation with the oscillator 27. The transmission reference timing signal TRS is delivered at a predetermined period 10 of, for example, 210 milliseconds to the transmission controller 23 to be sent to the satellite as a sequence of reference bursts RE shown in Fig. 2.
The reference burst RE is delivered to the local earth stations (not shown in Fig. 3) through the 15 satellite and sent back from the satellite to the control earth station 11' as a reflected burst RF. The reflected burst RF carries the transmission reference timing signal TRS. Although the reflected burst RF may include any other data signals destined to the control 20 earth station 11', such data signals might be left out of consideration.
The reflected burst RF is supplied to a detecting circuit 31 comprising a first demodulator 32, a unique word detector 33, and a frame synchronization 25 circuit 34, all of which are known in the art. The detecting circuit 31 is operable to monitor the reflected burst RF and to establish sychronization. To this end, a unique word is detected by the unique word .~ .
20 1Z58;~
detector 33 and is sent to the frame ~ynchronization circuit 34. The frame synchronization circuit 34 produces a reception timing signal RTS which results from the transmission reference timing signal TRS.
The reception timing signal RTS is sent to a distance measuring circuit 36 for measuring a distance between the control earth station 11' and the satellite of which the position might be variable. The distance measuring circuit 36 comprises a counter 37 operable in 10 response to the transmission reference timing signal TRS
and the reception timing signal RTS and a reception timing predictor 38 operable in a manner to be described later. The counter 37 starts counting a clock pulse sequence in response to the transmission reference 15 timing signal TRS and stops counting in response to the reception timing signal RTS. The counter 36 therefore has a count indicative of a time difference between the transmission reference timing signal TRS and the reception timing signal RTS and specifies twice the 20 distance between the control earth station 11' and the satellite. The time difference is equal to the standard offset time (SO) or,a sum of the standard offset time (SO) and the time deviation Tb, both of which are described in conjunction with Fig. 2. When the 25 satellite is moved from the standard position to the deviated position, the counter 36 serves to measure twice the actual distance between the control earth station 11' and the satellite and therefore determines 1~58:~;24 the distance between the control earth station 11' and the satellite.
Referring to Fig. 4 together with Fig. 3, the reception timing predictor 38 is supplied with the count 5 of the counter 37 as a time difference signal TM
representative of the above-mentioned twice difference.
In the reception timing predictor 38, a standard delay circuit 41 produces a standard offset signal indicative of the standard offset time value SO (Fig. 2). The 10 standard offset time (SO) indicates a standard distance between the control earth station 11' and the standard position of the satellite, as mentioned before.
A subtractor 42 subtracts the time difference (TM) from the standard offset time (SO) to detect the 15 time delay or time deviation Tb resulting from a movement of the satellite from the standard position to the deviated position. The time deviation Tb is delivered to a multiplier 43 as a time deviation signal.
The multiplier 43 multiplies the time deviation 20 Tb by a factor of two to calculate twice the time deviation Tb as a prediction time deviation. The prediction time dev,iation is added by an adder 44 to the standard offset time (SO) to specify the additionial reception time instant or reception time instant t4, 25 described in connection with Fig. 2. Thus, a combination of the multiplier 43 and the adder 44 is operable to calculate and vary the reception time 22 lZ5~ 4 instant t4 and may be named a varying circuit 45 for varying the reception time instant.
The reception offset time TO between the transmission of the reference burst RE and the reception 5 time instant t4 is equal to a sum of the standard offset time (SO) and a couple of the time deviations Tb, as mentioned before. The reception time instant therefore indicated by a reception offset time signal TO
representative of the reception offset time.
In Fig. 3, a reception timing generator 46 is supplied with the transmission reference timing signal TRS and the reception offset time signal TO. A
reception timing signal is produced from the reception timing generator 46 when the reception offset time 15 signal TO is received after reception of the transmission reference timing signal TRS.
A receiver section 51 comprises a second demodulator 52, a reception controller 53, and a reception interface 54, which are all known in the art.
20 The reception burst RC is sent from the local earth station 12' through the second demodulator 52 to the reception controller 53 supplied with the reception timing signal. When the window is opened in response to the reception timing signal, reception synchronization 25 is established in the control earth station 11'.
Referring to Fig. 5, the local earth station 12' is communicable with the control earth station 11' illustrated in Figs. 2 through 4 and comprises a ~3 1Z5~
reception portion 61 and a transmission portion 62 which are coupled through the satellite (not shown) to the control earth station 11'.
A reception burst is sent from the control earth 5 station 11' to the receiver portion 61 of the local earth station 12' and is sent through a third demodulator 63 and a unique word detector 64 to a reception control section 65. The unique word detector 64 detects a unique word assigned to the control earth 10 station 11' and produces a local reception timing signal LRT on detection of the unique word. After establishment of synchronization, a reception data signal D~L is sent through a reception interface 66 to a terminal end (not shown).
The local reception timing signal LRT is given to a timing delay circuit 67. The timing delay circuit 67 delays the local reception timing signal LRT by the predetermined time interval Ta illustrated in Fig. 3 and supplies the transmission portion 62 with a delayed 20 local reception timing signal as a local transmission timing signal LTT.
The transmission portion 62 comprises a transmission interface 68, a transmission controller 69, and a modulator 70. The transmission controller 69 is 25 controlled by the local transmission timing signal LTT
to be put into a synchronized state. Thereafter, a local transmission data signal DTL is sent through the 24 1;25~3324 transmission interface 68, the transmission controller 69, and the modulator 70 to the satellite.
In Fig. 5, description has been made on the assumption that the illustrated local earth station 12' S can not receive a transmission burst sent from the local earth station 12' itself. However, this invention is also applicable in the case where the local earth station 12' can receive its own transmission burst.
Thus, the control earth station 11' controls 10 reception synchronization in consideration of the time deviation related to the local earth stations 12'. This dispenses with control operation of transmission timings in the local earth stations 12' and with delivery or broadcast of distance information of the satellite to 15 the local earth stations 12'. The local earth stations 12' become simple in structure due to a light load of processing.
While this invention has thus far been described in conjunction with a preferred embodiment thereof, it 20 will readily be possible for those skilled in the art to put this invention into practice in various other manners. For examp,le, the additional time deviation Tb' may not be equal to the time deviation Tb. In addition, a plurality of the local earth stations may be included 25 in the satellite communication network.
Claims (4)
1. In a control earth station for use in a time division multiple access network to communicate with a local earth station through a geostationary satellite which fluctuates from a standard position into a deviated position with time with a spatial deviation left between said standard and said deviated positions, said control earth station comprising transmission timing means for transmitting a transmission reference timing signal towards said geostationary satellite, detecting means for receiving a reception timing signal which results from the transmission reference timing signal sent back from said satellite, and reception timing control means coupled to said transmission timing means and said detecting means for controlling a reception time instant determined for said local earth station, the improvement wherein said reception timing control means comprises:
measuring means responsive to said reception timing signal for measuring a time difference between said transmission reference timing signal and said reception signal to determine an actual distance between said control earth station and said satellite;
standard delay providing means for providing a standard delay time determined by a standard distance between said control earth station and said standard position of the satellite;
(Claim 1 continued) detecting means coupled to said measuring means and said standard delay providing means for detecting a time deviation resulting from said spatial deviation of the satellite, with reference to said time difference and said standard delay time; and varying means coupled to said detecting means and said standard delay providing means for varying said reception time instant for the local earth station with reference to said standard delay time and said time deviation.
measuring means responsive to said reception timing signal for measuring a time difference between said transmission reference timing signal and said reception signal to determine an actual distance between said control earth station and said satellite;
standard delay providing means for providing a standard delay time determined by a standard distance between said control earth station and said standard position of the satellite;
(Claim 1 continued) detecting means coupled to said measuring means and said standard delay providing means for detecting a time deviation resulting from said spatial deviation of the satellite, with reference to said time difference and said standard delay time; and varying means coupled to said detecting means and said standard delay providing means for varying said reception time instant for the local earth station with reference to said standard delay time and said time deviation.
2. A control earth station as claimed in Claim 1, wherein said varying means comprises:
calculating means coupled to said detecting means for calculating twice the time deviation as a result of calculation;
adding means coupled to said caluculating means and said standard delay providing means for adding said result of the calculation to said standard delay time to provide a total delay time equal to a sum of said result of the calculation and said standard delay time; and means coupled to said transmission timing means and said adding means for delaying said transmission reference timing signal by said total delay time to provide said reception time instant.
calculating means coupled to said detecting means for calculating twice the time deviation as a result of calculation;
adding means coupled to said caluculating means and said standard delay providing means for adding said result of the calculation to said standard delay time to provide a total delay time equal to a sum of said result of the calculation and said standard delay time; and means coupled to said transmission timing means and said adding means for delaying said transmission reference timing signal by said total delay time to provide said reception time instant.
3. A control station as claimed in Claim 1, wherein said transmission reference timing signal is produced at an invariable period.
4. In a local earth station for use in a time division multiple access network to communicate with a control earth station through a geostationary satellite, said local earth station being supplied with a reception timing signal from said control earth station through said geostationary satellite, and carrying out transmission in synchronism with a local transmission timing signal, the improvement wherein said local earth station comprises:
delay means responsive to said reception timing signal for delaying said reception timing signal by a predetermined duration to produce a delayed timing signal, said predetermined duation being determined in said local earth station; and means for providing said delayed timing signal as said local transmission timing signal.
delay means responsive to said reception timing signal for delaying said reception timing signal by a predetermined duration to produce a delayed timing signal, said predetermined duation being determined in said local earth station; and means for providing said delayed timing signal as said local transmission timing signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61056086A JPS62214739A (en) | 1986-03-15 | 1986-03-15 | Synchronization control system |
| JP56086/1986 | 1986-03-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1258324A true CA1258324A (en) | 1989-08-08 |
Family
ID=13017279
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000532115A Expired CA1258324A (en) | 1986-03-15 | 1987-03-16 | Synchronization control capable of establishing synchronization without transmission of distance information between control and local earth stations |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4800560A (en) |
| EP (1) | EP0237972B1 (en) |
| JP (1) | JPS62214739A (en) |
| AU (1) | AU586774B2 (en) |
| CA (1) | CA1258324A (en) |
| DE (1) | DE3787906T2 (en) |
Families Citing this family (46)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6214546A (en) * | 1985-07-12 | 1987-01-23 | Nec Corp | Quasi-synchronous buffer control system |
| US4937819A (en) * | 1988-09-26 | 1990-06-26 | A.T. & T. Paradyne | Time orthogonal multiple virtual dce for use in analog and digital networks |
| JPH0683172B2 (en) * | 1988-09-27 | 1994-10-19 | 日本電気株式会社 | Frame alignment method |
| US5638375A (en) * | 1988-11-30 | 1997-06-10 | Motorola, Inc. | AGC isolation of information in TDMA systems |
| JPH02256329A (en) * | 1988-12-01 | 1990-10-17 | Nec Corp | Demodulator control system |
| FR2646302B1 (en) * | 1989-04-25 | 1993-01-15 | Matra Communication | PSEUDO-SYNCHRONIZATION METHOD OF A TIME MULTIPLEXED COMMUNICATION NETWORK AND APPLICATIONS |
| US5105439A (en) * | 1989-08-11 | 1992-04-14 | Motorola, Inc. | Delay equalization detector |
| AU647062B2 (en) * | 1989-12-27 | 1994-03-17 | Nec Corporation | Frame synchronization system among multiple radio base stations for TDMA digital mobile communications system |
| US5228029A (en) * | 1990-02-27 | 1993-07-13 | Motorola, Inc. | Cellular tdm communication system employing offset frame synchronization |
| JP2723691B2 (en) * | 1991-04-30 | 1998-03-09 | 日本電気株式会社 | Variable timing signal generation circuit |
| ATE151581T1 (en) * | 1992-01-31 | 1997-04-15 | Cit Alcatel | METHOD FOR DETERMINING THE DELIVERY TIME BETWEEN A REMOTE TERMINAL STATION AND A CENTRAL TERMINAL STATION, IN A BIDIRECTIONAL POINT-TO-MULTIPOINT TRANSMISSION SYSTEM |
| US5245634A (en) * | 1992-03-23 | 1993-09-14 | Motorola, Inc. | Base-site synchronization in a communication system |
| GB2267200B (en) * | 1992-05-19 | 1995-10-25 | Dowty Communications Ltd | Packet transmission system |
| US5363368A (en) * | 1992-05-26 | 1994-11-08 | Motorola, Inc. | Simultaneous TDMA communication system |
| JPH0629910A (en) * | 1992-07-09 | 1994-02-04 | Nec Corp | Inter radio base station synchronization system |
| JPH0738606B2 (en) * | 1992-10-30 | 1995-04-26 | 日本電気株式会社 | Satellite communication system |
| US5406559A (en) * | 1992-11-02 | 1995-04-11 | National Semiconductor Corporation | Isochronous link protocol |
| EP0596651A1 (en) | 1992-11-02 | 1994-05-11 | National Semiconductor Corporation | Network for data communication with isochronous capability |
| USRE39116E1 (en) | 1992-11-02 | 2006-06-06 | Negotiated Data Solutions Llc | Network link detection and generation |
| USRE39395E1 (en) | 1992-11-02 | 2006-11-14 | Negotiated Data Solutions Llc | Data communication network with transfer port, cascade port and/or frame synchronizing signal |
| EP0596648A1 (en) | 1992-11-02 | 1994-05-11 | National Semiconductor Corporation | Network link endpoint capability detection |
| JPH0828754B2 (en) * | 1993-06-30 | 1996-03-21 | 日本電気株式会社 | Frame synchronization method |
| JPH0787424B2 (en) * | 1993-06-30 | 1995-09-20 | 日本電気株式会社 | Burst signal transmission system |
| FI106824B (en) * | 1993-07-05 | 2001-04-12 | Nokia Networks Oy | The base station |
| US5697082A (en) * | 1993-10-01 | 1997-12-09 | Greer; Steven Craig | Self-calibrating frequency standard system |
| US5469467A (en) * | 1993-10-15 | 1995-11-21 | At&T Corp. | Method for synchronizing the reference frequency oscillator of a metallic-based microcell to a master oscillator |
| US5440562A (en) * | 1993-12-27 | 1995-08-08 | Motorola, Inc. | Communication through a channel having a variable propagation delay |
| US5450394A (en) * | 1994-03-10 | 1995-09-12 | Northern Telecom Limited | Delay monitoring of telecommunication networks |
| JP2800679B2 (en) * | 1994-06-01 | 1998-09-21 | 日本電気株式会社 | Communications system |
| US5533018A (en) | 1994-12-21 | 1996-07-02 | National Semiconductor Corporation | Multi-protocol packet framing over an isochronous network |
| CA2191221A1 (en) | 1995-03-24 | 1996-10-03 | Brian George Flowers | A conferencing system |
| GB2301734B (en) * | 1995-05-31 | 1999-10-20 | Motorola Ltd | Communications system and method of operation |
| US5790939A (en) * | 1995-06-29 | 1998-08-04 | Hughes Electronics Corporation | Method and system of frame timing synchronization in TDMA based mobile satellite communication system |
| JP3435908B2 (en) * | 1995-07-05 | 2003-08-11 | 松下電器産業株式会社 | Digital wireless communication device |
| US5937357A (en) * | 1996-05-15 | 1999-08-10 | Nec Corporation | Network comprising base stations for selectivity calling mobile units by call radio signals of different bit rates in phase coincidence |
| US5878034A (en) * | 1996-05-29 | 1999-03-02 | Lockheed Martin Corporation | Spacecraft TDMA communications system with synchronization by spread spectrum overlay channel |
| US5805597A (en) * | 1996-06-04 | 1998-09-08 | National Semiconductor Corporation | Method and apparatus for providing low power basic telephony type service over a twisted pair ethernet physical layer |
| FR2750559A1 (en) * | 1996-06-28 | 1998-01-02 | Alcatel Telspace | TERMINAL FOR RADIOTELEPHONE SYSTEM AND SYSTEM AND METHOD USING THE TERMINAL |
| ZA978516B (en) * | 1996-09-30 | 1998-06-10 | Qualcomm Inc | Method and apparatus for precorrecting timing and frequency in communication systems. |
| JPH11146444A (en) * | 1997-11-11 | 1999-05-28 | Nec Corp | Synchronization establishing system for mobile communication base station network |
| US6674730B1 (en) * | 1998-08-04 | 2004-01-06 | Tachyon, Inc. | Method of and apparatus for time synchronization in a communication system |
| EP1528692A1 (en) * | 1998-08-04 | 2005-05-04 | Tachyon, Inc. | Method of and apparatus for time synchronization in a communication system |
| DE602004013592D1 (en) * | 2003-07-11 | 2008-06-19 | Qualcomm Inc | DYNAMIC COMMONLY USED FORWARD CARD |
| US20050095982A1 (en) * | 2003-11-05 | 2005-05-05 | Blanchard Scott D. | MSS user equipment and methods for synchronizing MSS user equipment |
| GB0329783D0 (en) * | 2003-12-23 | 2004-01-28 | Roke Manor Research | TDD for satcom application |
| CN101406076B (en) * | 2007-02-28 | 2010-06-02 | 华为技术有限公司 | System and method for confirming transmission time in radio communication system |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3320611A (en) * | 1964-04-11 | 1967-05-16 | Nippon Electric Co | Time-division radio relay communication system |
| JPS5324761B1 (en) * | 1968-10-11 | 1978-07-22 | ||
| US3566267A (en) * | 1968-10-30 | 1971-02-23 | Communications Satellite Corp | Burst synchronization method and apparatus |
| JPS61184014A (en) * | 1985-02-08 | 1986-08-16 | Nec Corp | System and apparatus of initial connection in time division multiple access communciation |
-
1986
- 1986-03-15 JP JP61056086A patent/JPS62214739A/en active Pending
-
1987
- 1987-03-13 EP EP87103639A patent/EP0237972B1/en not_active Expired - Lifetime
- 1987-03-13 AU AU69996/87A patent/AU586774B2/en not_active Ceased
- 1987-03-13 DE DE87103639T patent/DE3787906T2/en not_active Expired - Fee Related
- 1987-03-13 US US07/025,342 patent/US4800560A/en not_active Expired - Fee Related
- 1987-03-16 CA CA000532115A patent/CA1258324A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4800560A (en) | 1989-01-24 |
| EP0237972B1 (en) | 1993-10-27 |
| JPS62214739A (en) | 1987-09-21 |
| AU586774B2 (en) | 1989-07-20 |
| EP0237972A2 (en) | 1987-09-23 |
| DE3787906T2 (en) | 1994-03-24 |
| EP0237972A3 (en) | 1989-11-02 |
| DE3787906D1 (en) | 1993-12-02 |
| AU6999687A (en) | 1987-09-17 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1258324A (en) | Synchronization control capable of establishing synchronization without transmission of distance information between control and local earth stations | |
| EP0511861B1 (en) | Digital mobile station using presettable timeslot counter for compensating for propagation delay time | |
| EP0437835B1 (en) | Frame synchronization system among multiple radio base stations for TDMA digital mobile communication system | |
| CA2406415C (en) | Synchronization of timing advance and deviation | |
| CA1130026A (en) | Space diversity system in tdma communication system | |
| US5124698A (en) | Method and apparatus for synchronizing radio transmitters in a paging network | |
| EP1605610B1 (en) | Base station synchronization for wireless communication systems | |
| JP2556254B2 (en) | Burst transmission timing control method | |
| EP1201050B1 (en) | Method and apparatus for sequentially synchronizing a radio network | |
| GB2310111A (en) | Synchronising Base Stations via Wired Timing Control Centre | |
| US3654395A (en) | Synchronization of tdma space division satellite system | |
| EP0190771B1 (en) | Method of initially establishing burst acquisition in tdma satellite communications system and arrangement therefor | |
| US4262356A (en) | Method and system for synchronizing a TDMA communication network comprising a satellite equipped with several directional beam antennas transmitting signals at various frequencies | |
| US5309439A (en) | TDMA system with a virtual reference | |
| US5991280A (en) | Method and system for controlling TDMA timing in satellite communication network | |
| JP2638295B2 (en) | TDMA digital mobile communication system | |
| EP0257634B1 (en) | Synchronisation burst transmit phase control system | |
| JPH07264673A (en) | Method and equipment for automatic synchronization of data burst | |
| JP2967738B2 (en) | TDMA timing control system and method in satellite communication network | |
| JP3211129B2 (en) | Frame phase synchronization method between base stations | |
| JPS6269735A (en) | Butst synchronization system in time division multiple access communication system | |
| JPS6327133A (en) | System for synchronizing phase of transmission signal from plural stations | |
| JP2731640B2 (en) | TDMA frame synchronization method between multiple radio base stations | |
| JP2953174B2 (en) | Access delay control apparatus and method | |
| JP2799476B2 (en) | Receive aperture control method |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |