CA2222384A1 - Paging channel control method and apparatus - Google Patents
Paging channel control method and apparatus Download PDFInfo
- Publication number
- CA2222384A1 CA2222384A1 CA002222384A CA2222384A CA2222384A1 CA 2222384 A1 CA2222384 A1 CA 2222384A1 CA 002222384 A CA002222384 A CA 002222384A CA 2222384 A CA2222384 A CA 2222384A CA 2222384 A1 CA2222384 A1 CA 2222384A1
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- Prior art keywords
- channel
- receiver
- channels
- controlling
- traffic
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W68/00—User notification, e.g. alerting and paging, for incoming communication, change of service or the like
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- 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
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
- H04B7/18567—Arrangements for providing additional services to the basic mobile satellite telephony service
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
- H04W84/022—One-way selective calling networks, e.g. wide area paging
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/02—Power saving arrangements
- H04W52/0209—Power saving arrangements in terminal devices
- H04W52/0212—Power saving arrangements in terminal devices managed by the network, e.g. network or access point is master and terminal is slave
- H04W52/0216—Power saving arrangements in terminal devices managed by the network, e.g. network or access point is master and terminal is slave using a pre-established activity schedule, e.g. traffic indication frame
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
In a messaging system, message traffic is transmitted on one or more traffic channels T1, T2 and the allocation of groups S1, S2 of receivers to the traffic channels T1, T2 is controlled by information transmitted on a bulletin board channel BB. A predetermined number of frames before a change in the traffic channel allocation, a countdown value is transmitted in the relevant traffic channel T1 and the countdown value is decremented in each subsequent frame. Before the countdown value reaches zero, the groups of receivers S1, S2 retune to the bulletin board channel, receive their new channel allocations and retune to the traffic channel indicated for their group.
The frame timings of the different traffic channels T1, T2, are staggered to reduce the peak power required to transmit message bursts in these channels.
The frame timings of the different traffic channels T1, T2, are staggered to reduce the peak power required to transmit message bursts in these channels.
Description
Paging Channel Control Method and Apparatus The present invention relates to a channel control method and apparatus, and particularly, though not exclusively, to a method and apparatus for implementing a radio frequency messaging or paging system.
Paging systems generally include at least one transmitterwhich receives messages addressed to different paging receivers and transmits each message with data identifying the receiver for which the message is intended. Each paging receiver monitors the transmission channel or channels and, when a message addressed to the paging receiver is identified, the receiver stores and displays the message for the user. The message may be a simple alert, or a numeric or alphanumeric string.
In most terrestrial local paging systems, the receiver or pager is tuned to a single frequency channel which is fixed during manufacture, and messages addressed to the receiver are transmitted on this channel. The capacity of such systems is limited by the bandwidth of the single frequency channel.
The capacity may be increased by using more than one transmit frequency and allocating one of these frequencies to each receiver.
The European Radio Messaging System (ERMES), defined by the European Telecommunication Standard 300 13 3, allows each paging receiver to monitor 16 different frequency channels in turn according to a predetermined schedule, to detect messages addressed to the receiver on any one of these channels. The ERMES system allows the user to roam between different networks and countries in which different frequency channels may need to be used for transmission of paging messages.
However, neither of the above methods is suitable for mess~ginP or paging systems in which bandwidth usage and transmit power must be kept to a S minimum such as, for example, a satellite-based me~.s~ging system. Moreover, these methods are inflexible as they do not easily allow reallocation of frequency channels, such as adding a new frequency channel to allow an increase in traffic, discontinuing use of a frequency channel when traffic is reduced, or ch~nging frequency channel allocations according to operational 1 0 constraints.
In many types of radio frequency communication system, channel assignment information is transmitted on a common channel, to which receivers are normally tuned. When a receiver receives a command on the common channel, it retunes to another channel to receive or transmit a message. While 15 this method is suitable for a communication system in which a different traff1c channel may need to be used by a receiver for each message, it is not well suited to paging or mess~ging systems in which the re-allocation of frequencies to receivers is only required occasionally.
The document US 4,849,750 discloses a paging receiver which is 20 responsive to received commands to retune to different message channels.
The document GB 2,284,496A discloses a paging system in which base stations receive and retransmit paging messages. A first set of the base stations retransmits promptly following receipt, while a second set delays retransmissionso as not to retransmit simultaneouslywith the first set.
The document US 5,206,855 discloses a multiple frequency mess~ging system in which the same paging channel is offset by one slot from one frequency to the next, so that a receiver can receive a message by sequentially sc~nning the frequencies.
Summary of the Invention According to one aspect of the present invention, there is provided a paging system in which paging messages are transmitted on a first traffic channel and system control information is transmitted on a control channel. In order to alert paging receivers to new system control information, change indication information is transmitted on the first traffic channel. In responseto the change indication information, at least some of the paging receivers tuned to the first traffic channel retune to the control channel and, in response to the new system control information, retune to a second traffic channel. In this way, receivers may be tuned for the majority of the time to traffic channels on whichmessages can be received, and may be reassigned to different traffic channels.
The receivers only need retune to the control channel when traffic channels are reasslgned.
Preferably, the change indication information is transmitted more than once before the receivers are required to retune to the control channel, so as to reduce the possibility that some of the receivers may not receive the change indication information because of interference. Preferably, each repetition of the change inforrnation indicates the period remaining until the receivers should retune to the control channel, so that the retuning of the receivers may be synchronised even if the receivers do not receive all of the change indication S signals.
According to another aspect of the present invention, there is provided a communication system in which first and second traffic channels are transmiKed to a plurality of receivers, the first and second traffic channels including messages addressed to selected ones of the receivers. Signals in the first and 10 second traffic channels are transmitted in a periodic frame structure with any messages being transmitted sequentially within the frame. The beginning of the second traffic frame is delayed by a period less than the frarne period with respect to the beginning of the first traffic frame. In this way, the peak transmission power can be reduced.
Where the traffic frames are transmitted via satellite, the above aspect is particularly advantageous, since the peak power output of a satellite is limited by the satellite power sources.
In another aspect, a control channel is transmitted together with first and second traffic channels each having a periodic frame structure with the second 20 traffie channel frames delayed relative to the first.
The eontrol ehannel includes first and second traffic channel data indieating properties of the first and seeond traffie ehannel respeetively, transmitted sequentially. The order of transmission of the first and second traffic channel data is the same as the order of the beginning of the first and second traffic frames. Thus, the interval between receiving traffic channel data on thecontrol channel and tuning to the correspondingtraffic frame is substantiallythesame for all traffic channels and may be set as short as possible while still ensuring that all receivers are able to retune to their respective traffic channels before the beginning of the next traffic frame.
The present invention extends to components of the above systems and methods performed thereby.
Brief Description of the Dra~vin~s Specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is a schematic diagram of a satellite messaging system in an embodiment of the present invention;
Figure 2 is a schematic diagram showing bulletin board and traffic channels transmitted from the earth station to the message terminal of Figure 1;Figure 3 shows the functions of the earth station in greater detail;
Figure 4 shows the functions of the message terminal in greater detail;
Figure 5 shows the structure of a frame of one of the traffic channels;
Figure 6 shows the structure of a frame of the bulletin board channel;
Figure 7 shows the time alignrnent between the bulletin board channel and the traffic channels;
Figure 8 is a diagram showing the addition of a new traffic channel;
Figure 9 is a diagram showing the removal of a traffic channel; and Figure 10 is a diagram showing reallocation of a traffic channel frequency.
5 Specific Description of an Embodiment Figure 1 shows the structure of a satellite based store and forward me~s~ging system, in which messages are sent from a caller 2 to a selected user 18. The messages are initially sent to a service provider 4, which routes the message to the appropriate earth station 8. The service area of the mess~ging 10 system is covered by a plurality of satellites 12, such as the Inrnarsat-3 TM
satellites which are geostationary repeater satellites which relay data from earth stations to a selected area of the earth's surface covered by one of the spot beams generated by the satellite antennas. Each satellite 12 is able to receive and relay signals from more than one earth station located within its field of 15 view. Messages are transmitted from the earth station 8 to the satellite 12, which relays the messages down to a selected area. If a message terminal 14 is within that area, it receives the messages and decodes those message which carry its identity code. The decoded messages are displayed to the user 18.
The messages are sent by means of a three-stage process, as explained 20 below.
Caller to Service Provider The caller 2 sends a message to the service provider 4, for example by telephoning an operator and dictating the message, or by encoding the message and sending it over a network, for example by means of a modem connected to a PSTN. The message may comprise an alphanumeric or numeric string, a 5 simple alert code, or binary data, which is passed transparently from the caller 2 to the user 18. Additionally, the caller specifies the identity of the user 18 and optionally the user's approximate location.
The service provider 4 consists of a facility which allows reception of messages from callers, storage of the messages in a service provider store 6 and 10 routing of the messages; the service provider 4 is analouous in this way to service providers which are conventionally provided in terrestrial paging systems.
Service Provider To Earth Station The service provider 4 formats the message and the user identity to 15 generate a paging request message. The service provider 4 routes the paging request message to the earth station 8 which serves the satellite 12 which covers the region in which the user 18 is expected to be. This region may be indicated by the caller 2 or may be determined from a location register stored at the service provider, which is updated by the user 18 calling the service providér 4.
20 The paging request message may be routed to more than one earth station serving more than one satellite if there is uncertainty as to the location of the user 1 8.
Earth Station to Message Terminal The earth station 8 receives the paging request message and stores it in an earth station store 10, which buffers messages prior to transmission over the satellite 12. The paging request message is converted to a format for 5 tr~n~mi~ion and transmitted to the satellite 12, which retransmits the message over one of the spot beams selected by the earth station 8.
If the message terminal 14 is switched on, is tuned to the correct traffic channel and is within the coverage area of the selected spot beam. it detects that an address portion of the message matches an identity code assigned to the 10 message terminal and decodes the message following this address portion. The decoded message is stored in a message terminal store 16 and is displayed to the user 1 8.
Channel Types In addition to traffic channels on which the messages are sent. the 15 satellite 12 also broadcasts a bulletin board channel on a fixed frequency, on a global beam which has a coverage area substantially encompassin~ the coverage areas of all the spot beams of the satellite. When the terminal 14 is switched on, it initially tunes to the bulletin board channel, which carries all the information needed by the terminal to retune to the frequency of the traffic channel on which 20 it can expect messages to be transmitted.
As shown schematically in Figure 2, network information concerning the traffic channel frequency allocations is submitted from a network management system 20, which determines which frequencies are assigned to each earth station 8. The information is used to generate the bulletin board channel information, which is transmitted in the bulletin board channel BB from the earth station 8 via the satellite 12 to the terminal 14. A receiver 22 in the 5 terminal 14 is selectively tunable to either the bulletin board channel frequency or any designated one of a set of traffic channel frequencies.
Earth Station Figure 3 shows the functional portions of the earth station 8. An 10 interface 24 is adapted to receive paging request signals from the ser~ice provider transmitted over a network, such as an ISDN and to convert them to data for use within the earth station 8 . The data is input to a controller 26 u-hich stores the data in the message store 10 until the data is scheduled for transmission. The controller 26 then reads the data from the message store 10 15 and outputs it to a transmitter 30 in a channel format as described below, uith a timing determined by means of a clock 28. The controller 26 controls the frequency of tr~n~mi~.~ion of the transmitter 30 in accordance with the information received from the network management system 20 in order to transmit the paging messages on the allocated traffic channels via an antenna 20 32. The controller 26 also generates the bulletin board channel information in a bulletin board channel format as described below, and controls the transmitter 30 to transmit the bulletin board channel information at the bulletin board channel frequency.
Satellite The satellite 12 receives signals transmitted by the earth station 8 and translates each received frequency channel to a corresponding transmitted frequency channel without affecting the signal content; the satellite acts as a transparent repeater. Different groups of received frequency channels are mapped onto different transmitted spot beams and one or more of the received frequency channels are mapped onto the global beam.
Messa~e Terminal Figure 4 shows the functional portions of the message terminal 14, which comprises an antenna 34 connected to the receiver 22. A controller 36 receives message data from the receiver 22. The controller 36 has a clock 44 which enables tuning of the receiver 22 to a predetermined frequency at a predeterrnined time, as described in more detail below. Messages addressed to the message terminal 14 are stored in the message terminal store 16 and retrieved therefrom under the control of the controller 36. The controller 36 isconnected to a keypad 38 to allow the user to select a message which is displayed on a display 40, which may be a liquid crystal display (LCD). The controller 36 is also connected to an alerting device 42 to alert the user 18 when a new message has been received, by generating an audible tone, fl~.~hing an LED or by other suitable means. The user 18 may then operate a key on the key pad 38 to actuate display of the new message. Previously received messages may also be displayed.
The terminal 14 may be a simple message receiver or may be integrated with other functions, such as in a duplex voice and/or data terminal.
5 Traffic Channel Structure Each traffic channel is transmitted at a corresponding traffic channel frequency. The traffic channel transmissions are arranged in repeating frames of data symbols, each data symbol comprising five bits. Each frame may have a length FL of 960 symbols, corresponding to 4 minutes' duration, for exarnple.
The structure of each frame is shown in Figure 5. The frame TF begins with a frame header TH of fixed length which contains synchronisation information to assist the terminals 14 to acquire the timing and frequency of the traffic channel. There follows a frame identity block TID which contains general system information, such as the identity code of the transmitting earth 15 station 8 and the serial number of the frame, and includes a changeover countdown field, which is used to indicate an imminent change in frequency allocation and will be described in detail below.
Next, the frame F contains a control block CB cont~ining control information, followed by a message block MB containing one or more 20 messages addressed to individual tennin~ 14. Each message is of variable length and includes an identity code indicating the terminal 14 to which the message is addressed, a message type code indicating the message type and the message itself. If insufficient messages are available to fill the message blockfield MB, transmission in the traffic channel ceases at the end of the messages until the beginning of the next frame TF.
Bulletin Board Channel Structure S The bulletin board channel is transmitted continuously at a fixed frequency. Transmissions in the bulletin board channel may be arranged in a frame structure with a length FL of 960 5-bit symbols, lasting four minutes for example.
As shown in Figure 6, each bulletin board frame BBF comprises a frame header BBH, a bulletin board identity BBID and an allocation table AT.
The frame header BBH comprises synchronisation information to assist terminals in acquiring the bulletin board channel. The bulletin board ID field BBID contains general information such as the identity of the earth station 8 transmitting the bulletin board channel, the date and time, and the version number of the bulletin board, which is changed every time a change occurs in the information transmitted in the allocation table AT.
The allocation table AT comprises a set of entries transmitted sequentially, each relating to one traffic channel. Each entry comprises the following information:
1. A service ID indicating a specific service using the relevant traffic channel. The service corresponds to one specific service provided by one of the service providers 4.
5 2. A satellite beam ID identifying the satellite beam over which the traff~c channel is transmitted.
3. A pager subset number range, indicating the group of terminals 14 allocated to that traffic channel. Each terminal 14 is pre-prograrnmed with the different subsets into which it falls.
4. A channel number, which indicates the frequency assigned to that traffic channel.
15 Unused entry fields are filled with idle codes, so that the transmission on the bulletin board channel is continuous.
Frame Timin Since the message blocks MB of the traffic channel frames are not always completely filled, the traffic channels are transmitted as bursts of up to 20 four minutes duration every four minutes. Multiple traffic channels are transmitted by each satellite 12, so that the transmit power used by the satellite 12 to transmit the traffic channels varies as the sum of the instantaneous power required to transmit the bursts of each channel. If all the traffic channels were synchronised so that their frames commenced at the same moment, the total transmit power at the start of the frames would be the total power required to transmit all the channels in use. As the bursts on the different traffic channels 5 ended, so the total transmit power would fall until the beginning of the next frame, when the power would rise to the maximum once again. This method would lead to a high peak transmit power requirement and large power fluctuations in the satellite.
Moreover, if the bulletin board frames were synchronised to begin at the 10 same time as the traffic channel frames, there would be a considerable delay in some cases between a terminal 14 receiving the relevant entry in the bulletin board channel and the start of the next frame of the traffic charmel indicated by that entry. In the extreme case, where the entry is the first entry of the allocation table AT, the delay would be nearly four minutes.
In order to avoid the above problems, the time alignment between the bulletin board frames and the traffic channel frames is as sho~n in Figure 7. At the top row of the figure, the bulletin board header and identity BBH, BBID is shown followed by each of the entries in the allocation table AT. The first four entries ATI to AT4 correspond to traffic channels Tl to T4, shown in 20 successive rows below.
The start of each traffic channel frame header TH is delayed relative to the start of the bulletin board &ame header BBH by a different multiple of 32 symbols, corresponding to eight seconds. For example, the start of the first traffic channel header TH 1 is delayed by 8 seconds, the second channel header TH2 by 16 seconds, the third TH3 by 24 seconds and the fourth by 32 seconds, and so until the last traffic channel n delayed by n x 8 seconds.
The timing of the traffic and bulletin board channels is referenced to the satellite 12, so that each earth station 8 transmits its traffic channels with atiming determined according to the propagation delay to the satellite 12 and thetransmission of the traffic channels from the satellite is timed as described above, regardless of which earth station 8 transmitted that channel.
The delay between the start of the bulletin board frame and the start of each traffic frame may be a multiple of the order of the entry in the allocationtable AT for that traffic frame, although the order of entries in the allocationtable AT need not be exactly the same as the order of starting of the corresponding traffic frames. The order of entries is arranged so that there is a minimum delay between the end of tr~n.smission of an entry and the start of the corresponding traffic frame, which is sufficient to allow the terrninal to retune from the bulletin board to the correct traffic channel, but the maximum delay isnever more than a small fraction of the frame period.
In other embodiments, the delay may be chosen according to the number of traffic channels and the frame period, so as to reduce the peak transmit power of the satellite and/or keep the delay between a channel entry in the bulletin board channel and the start of the corresponding traffic channel frame between aminimum and a maximum value for any channel.
Frequency Allocation When the terminal 14 is switched on, it automatically tunes to the fixed frequency of the bulletin board channel and receives the allocation table AT
entries until an entry corresponding to a pager subset number of the terminal 14and a service ID indicating a service subscribed to by the user 18 is received.
The terminal then retunes to the traffic channel indicated by that entry. The bulletin board information may change while the terminal is tuned to the previously indicated traffic channel. It is therefore necessary to alert the terminal to changes in channel allocation which may affect it.
The terminal is alerted in the following manner. The changeover countdown field in the identity block TID of the traffic channel frame is normally set to zero, but a predetermined number of frames before a change in frequency allocation which affects the terminals tuned to that traffic channel, the changeover countdown field is set to that predeterrnined number and is decremented in each subsequent frame until the terrninals must retune to the new channel. Meanwhile the new channel is signalled on the bulletin board channel.
Three different situations in which this method is employed will now be described.
Additional Traffic Channel In the example shown in Figure 8, two subsets of terminals Sl and S2 are tuned to traffic channel Tl . Within the frame divisions of Tl are shown the value of the changeover countdown field for that frame, while the version number of the bulletin board is shown within the frame boundaries of the S bulletin board channel. At the third frame before the allocation changeover, the version of the bulletin board changes from N to M. After the third last frame of the traffic channel T1, all the terminals of subsets S1 and S2 retune to the bulletin board channel BB as indicated by the arrow in Figure 8 and receive the new allocation entries for their subsets. In this example, subset S 1 is to remain 10 on traffic channel T1 while subset S2 is to change to traffic channel T2. The changeover countdown field of traffic channel T2, as sho~n between frame boundaries, remains at zero.
Meanwhile, in the last two frames before the channel changeover, no messages are sent in the traffic channel T1 as the terminals should now be tuned 15 to the bulletin board channel BB. Tr~n~mi.~sion also begins in the new traffic channel T2 but no messages are sent until the point of changeover. At the point of changeover, as indicated by the arrows in Figure 8, the subset Sl of pagers retune to traffic channel T1 while the subset S2 tune to the new traffic channel T2, and tr~n~mi~sion of messages in the traffic channel T2 for the subset S2 20 begins.
Since the frame boundaries of the traffic channels and the bulletin board channel are not time aligned but are delayed as described above, a two frarne period is allowed between the time when the terminals should tune to the bulletin board and the time when the terminals tune to the new channel, to ensure that none of the terminals fail to receive the necessary information.
The precise time at which the terminals 14 tune to the new channel T2 is 5 aligned with the start of the bulletin board frame BBF. The internal clock 44 is synchronized with the start of the bulletin board frame and set according to the date and time information when the terminal is tuned to the bulletin board channel.
However, this method may also be applied to systems in which frame 10 boundaries are aligned between different channels.
Removal of Traffic Channel Figure 9 shows another example in which a traffic channel is removed and terminals tuned to that channel are assigned to another e:~isting channel.
Initially, subset S I are tuned to traffic channel T1 while subset S2 are tuned to 15 traffic channel T2. Fifteen frarnes before the point of changeover, the changeover countdown field of traffic channel T2 is set to 15 and is decremented at each subsequent frame. After the value of the changeover countdown field is reduced to 3, the subset S2 retune to the bulletin board channel. At the third from last frame before the changeover. the bulletin board 20 version changes from N to M and the new allocation of the subset S2 is indicated in the allocation table AT.
The subset S2 detect the new channel allocation and retune to the traffic channel Tl at the time of changeover. Subsequently, traffic channel Tl carries messages for both subset S 1 and S2. Traffic channel T2 carries no messages for the last two frames before the allocation change, and no transmissions take 5 place after the change.
In this example, the changeover countdown field value for traffic channel Tl is set to zero throughout the allocation change, because the change does not require the subset S 1 to retune.
Change of Traffic Channel Frequency Allocation Figure 10 shows an example in which all the terrninals tuned to one traffic channel are retuned to another traffic channel.
Initially, subset Sl are tuned to traffic channel T1. As in the other examples, the changeover countdown field indicates that the channel allocation for these terrninals is about to change. Before the change, the bulletin board 15 version is changed and indicates the new traffic channel T2 assigned to all the subset S 1. Two frames before the changeover, the terminals 14 of the subset S 1 retune to the bulletin board channel BB and receive the new allocation entry from the allocation table AT. At the same time, transmission begins in the new traffic channel T2 but no messages are transmitted until the change. After the 20 change, tr~n~mi.~sionceases on the traffic channel T1.
The above methods provide a very robust method of controlling reallocation of terminals to traffic channels, since any terrninal need only receive one changeover countdown field out of the 15 non-zero countdown fields and may still determine that a channel reallocation is required and when the reallocationshould take place. If, however, a terminal is unable to receive 15 consecutive frames. it then automatically retunes to the bulletin board channel in S order to determine whether any channel reallocation has taken place for the relevant subset.
Although the above embodiments have been described ~ ith reference to a satellite messaging system, aspects of the present invention are also applicable to terrestrial paging systems, particularly power limited systems or systems in 10 which blockage of traffic channels may occur, and to paging systems with enhancements such as acknowledgement of messages by recei- ers. Aspects of the present invention may also be applied to combined satellite and terrestrial paging systems in which messages are relayed via satellite to terrestrial stations which retransmit the messages to paging receivers.
Aspects of the present invention are applicable to satellite communications systems using satellites other than geostationary satellites, in which case the allocation of earth stations to satellites will change as the satellites come into or go out of view of different earth stations.
It will be appreciated that individual elements of a mess~ging or paging 20 system may be located in different jurisdictions or in space. The present invention e~ctends to any such element which contributes to the aspects of the invention as herein defined.
Paging systems generally include at least one transmitterwhich receives messages addressed to different paging receivers and transmits each message with data identifying the receiver for which the message is intended. Each paging receiver monitors the transmission channel or channels and, when a message addressed to the paging receiver is identified, the receiver stores and displays the message for the user. The message may be a simple alert, or a numeric or alphanumeric string.
In most terrestrial local paging systems, the receiver or pager is tuned to a single frequency channel which is fixed during manufacture, and messages addressed to the receiver are transmitted on this channel. The capacity of such systems is limited by the bandwidth of the single frequency channel.
The capacity may be increased by using more than one transmit frequency and allocating one of these frequencies to each receiver.
The European Radio Messaging System (ERMES), defined by the European Telecommunication Standard 300 13 3, allows each paging receiver to monitor 16 different frequency channels in turn according to a predetermined schedule, to detect messages addressed to the receiver on any one of these channels. The ERMES system allows the user to roam between different networks and countries in which different frequency channels may need to be used for transmission of paging messages.
However, neither of the above methods is suitable for mess~ginP or paging systems in which bandwidth usage and transmit power must be kept to a S minimum such as, for example, a satellite-based me~.s~ging system. Moreover, these methods are inflexible as they do not easily allow reallocation of frequency channels, such as adding a new frequency channel to allow an increase in traffic, discontinuing use of a frequency channel when traffic is reduced, or ch~nging frequency channel allocations according to operational 1 0 constraints.
In many types of radio frequency communication system, channel assignment information is transmitted on a common channel, to which receivers are normally tuned. When a receiver receives a command on the common channel, it retunes to another channel to receive or transmit a message. While 15 this method is suitable for a communication system in which a different traff1c channel may need to be used by a receiver for each message, it is not well suited to paging or mess~ging systems in which the re-allocation of frequencies to receivers is only required occasionally.
The document US 4,849,750 discloses a paging receiver which is 20 responsive to received commands to retune to different message channels.
The document GB 2,284,496A discloses a paging system in which base stations receive and retransmit paging messages. A first set of the base stations retransmits promptly following receipt, while a second set delays retransmissionso as not to retransmit simultaneouslywith the first set.
The document US 5,206,855 discloses a multiple frequency mess~ging system in which the same paging channel is offset by one slot from one frequency to the next, so that a receiver can receive a message by sequentially sc~nning the frequencies.
Summary of the Invention According to one aspect of the present invention, there is provided a paging system in which paging messages are transmitted on a first traffic channel and system control information is transmitted on a control channel. In order to alert paging receivers to new system control information, change indication information is transmitted on the first traffic channel. In responseto the change indication information, at least some of the paging receivers tuned to the first traffic channel retune to the control channel and, in response to the new system control information, retune to a second traffic channel. In this way, receivers may be tuned for the majority of the time to traffic channels on whichmessages can be received, and may be reassigned to different traffic channels.
The receivers only need retune to the control channel when traffic channels are reasslgned.
Preferably, the change indication information is transmitted more than once before the receivers are required to retune to the control channel, so as to reduce the possibility that some of the receivers may not receive the change indication information because of interference. Preferably, each repetition of the change inforrnation indicates the period remaining until the receivers should retune to the control channel, so that the retuning of the receivers may be synchronised even if the receivers do not receive all of the change indication S signals.
According to another aspect of the present invention, there is provided a communication system in which first and second traffic channels are transmiKed to a plurality of receivers, the first and second traffic channels including messages addressed to selected ones of the receivers. Signals in the first and 10 second traffic channels are transmitted in a periodic frame structure with any messages being transmitted sequentially within the frame. The beginning of the second traffic frame is delayed by a period less than the frarne period with respect to the beginning of the first traffic frame. In this way, the peak transmission power can be reduced.
Where the traffic frames are transmitted via satellite, the above aspect is particularly advantageous, since the peak power output of a satellite is limited by the satellite power sources.
In another aspect, a control channel is transmitted together with first and second traffic channels each having a periodic frame structure with the second 20 traffie channel frames delayed relative to the first.
The eontrol ehannel includes first and second traffic channel data indieating properties of the first and seeond traffie ehannel respeetively, transmitted sequentially. The order of transmission of the first and second traffic channel data is the same as the order of the beginning of the first and second traffic frames. Thus, the interval between receiving traffic channel data on thecontrol channel and tuning to the correspondingtraffic frame is substantiallythesame for all traffic channels and may be set as short as possible while still ensuring that all receivers are able to retune to their respective traffic channels before the beginning of the next traffic frame.
The present invention extends to components of the above systems and methods performed thereby.
Brief Description of the Dra~vin~s Specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is a schematic diagram of a satellite messaging system in an embodiment of the present invention;
Figure 2 is a schematic diagram showing bulletin board and traffic channels transmitted from the earth station to the message terminal of Figure 1;Figure 3 shows the functions of the earth station in greater detail;
Figure 4 shows the functions of the message terminal in greater detail;
Figure 5 shows the structure of a frame of one of the traffic channels;
Figure 6 shows the structure of a frame of the bulletin board channel;
Figure 7 shows the time alignrnent between the bulletin board channel and the traffic channels;
Figure 8 is a diagram showing the addition of a new traffic channel;
Figure 9 is a diagram showing the removal of a traffic channel; and Figure 10 is a diagram showing reallocation of a traffic channel frequency.
5 Specific Description of an Embodiment Figure 1 shows the structure of a satellite based store and forward me~s~ging system, in which messages are sent from a caller 2 to a selected user 18. The messages are initially sent to a service provider 4, which routes the message to the appropriate earth station 8. The service area of the mess~ging 10 system is covered by a plurality of satellites 12, such as the Inrnarsat-3 TM
satellites which are geostationary repeater satellites which relay data from earth stations to a selected area of the earth's surface covered by one of the spot beams generated by the satellite antennas. Each satellite 12 is able to receive and relay signals from more than one earth station located within its field of 15 view. Messages are transmitted from the earth station 8 to the satellite 12, which relays the messages down to a selected area. If a message terminal 14 is within that area, it receives the messages and decodes those message which carry its identity code. The decoded messages are displayed to the user 18.
The messages are sent by means of a three-stage process, as explained 20 below.
Caller to Service Provider The caller 2 sends a message to the service provider 4, for example by telephoning an operator and dictating the message, or by encoding the message and sending it over a network, for example by means of a modem connected to a PSTN. The message may comprise an alphanumeric or numeric string, a 5 simple alert code, or binary data, which is passed transparently from the caller 2 to the user 18. Additionally, the caller specifies the identity of the user 18 and optionally the user's approximate location.
The service provider 4 consists of a facility which allows reception of messages from callers, storage of the messages in a service provider store 6 and 10 routing of the messages; the service provider 4 is analouous in this way to service providers which are conventionally provided in terrestrial paging systems.
Service Provider To Earth Station The service provider 4 formats the message and the user identity to 15 generate a paging request message. The service provider 4 routes the paging request message to the earth station 8 which serves the satellite 12 which covers the region in which the user 18 is expected to be. This region may be indicated by the caller 2 or may be determined from a location register stored at the service provider, which is updated by the user 18 calling the service providér 4.
20 The paging request message may be routed to more than one earth station serving more than one satellite if there is uncertainty as to the location of the user 1 8.
Earth Station to Message Terminal The earth station 8 receives the paging request message and stores it in an earth station store 10, which buffers messages prior to transmission over the satellite 12. The paging request message is converted to a format for 5 tr~n~mi~ion and transmitted to the satellite 12, which retransmits the message over one of the spot beams selected by the earth station 8.
If the message terminal 14 is switched on, is tuned to the correct traffic channel and is within the coverage area of the selected spot beam. it detects that an address portion of the message matches an identity code assigned to the 10 message terminal and decodes the message following this address portion. The decoded message is stored in a message terminal store 16 and is displayed to the user 1 8.
Channel Types In addition to traffic channels on which the messages are sent. the 15 satellite 12 also broadcasts a bulletin board channel on a fixed frequency, on a global beam which has a coverage area substantially encompassin~ the coverage areas of all the spot beams of the satellite. When the terminal 14 is switched on, it initially tunes to the bulletin board channel, which carries all the information needed by the terminal to retune to the frequency of the traffic channel on which 20 it can expect messages to be transmitted.
As shown schematically in Figure 2, network information concerning the traffic channel frequency allocations is submitted from a network management system 20, which determines which frequencies are assigned to each earth station 8. The information is used to generate the bulletin board channel information, which is transmitted in the bulletin board channel BB from the earth station 8 via the satellite 12 to the terminal 14. A receiver 22 in the 5 terminal 14 is selectively tunable to either the bulletin board channel frequency or any designated one of a set of traffic channel frequencies.
Earth Station Figure 3 shows the functional portions of the earth station 8. An 10 interface 24 is adapted to receive paging request signals from the ser~ice provider transmitted over a network, such as an ISDN and to convert them to data for use within the earth station 8 . The data is input to a controller 26 u-hich stores the data in the message store 10 until the data is scheduled for transmission. The controller 26 then reads the data from the message store 10 15 and outputs it to a transmitter 30 in a channel format as described below, uith a timing determined by means of a clock 28. The controller 26 controls the frequency of tr~n~mi~.~ion of the transmitter 30 in accordance with the information received from the network management system 20 in order to transmit the paging messages on the allocated traffic channels via an antenna 20 32. The controller 26 also generates the bulletin board channel information in a bulletin board channel format as described below, and controls the transmitter 30 to transmit the bulletin board channel information at the bulletin board channel frequency.
Satellite The satellite 12 receives signals transmitted by the earth station 8 and translates each received frequency channel to a corresponding transmitted frequency channel without affecting the signal content; the satellite acts as a transparent repeater. Different groups of received frequency channels are mapped onto different transmitted spot beams and one or more of the received frequency channels are mapped onto the global beam.
Messa~e Terminal Figure 4 shows the functional portions of the message terminal 14, which comprises an antenna 34 connected to the receiver 22. A controller 36 receives message data from the receiver 22. The controller 36 has a clock 44 which enables tuning of the receiver 22 to a predetermined frequency at a predeterrnined time, as described in more detail below. Messages addressed to the message terminal 14 are stored in the message terminal store 16 and retrieved therefrom under the control of the controller 36. The controller 36 isconnected to a keypad 38 to allow the user to select a message which is displayed on a display 40, which may be a liquid crystal display (LCD). The controller 36 is also connected to an alerting device 42 to alert the user 18 when a new message has been received, by generating an audible tone, fl~.~hing an LED or by other suitable means. The user 18 may then operate a key on the key pad 38 to actuate display of the new message. Previously received messages may also be displayed.
The terminal 14 may be a simple message receiver or may be integrated with other functions, such as in a duplex voice and/or data terminal.
5 Traffic Channel Structure Each traffic channel is transmitted at a corresponding traffic channel frequency. The traffic channel transmissions are arranged in repeating frames of data symbols, each data symbol comprising five bits. Each frame may have a length FL of 960 symbols, corresponding to 4 minutes' duration, for exarnple.
The structure of each frame is shown in Figure 5. The frame TF begins with a frame header TH of fixed length which contains synchronisation information to assist the terminals 14 to acquire the timing and frequency of the traffic channel. There follows a frame identity block TID which contains general system information, such as the identity code of the transmitting earth 15 station 8 and the serial number of the frame, and includes a changeover countdown field, which is used to indicate an imminent change in frequency allocation and will be described in detail below.
Next, the frame F contains a control block CB cont~ining control information, followed by a message block MB containing one or more 20 messages addressed to individual tennin~ 14. Each message is of variable length and includes an identity code indicating the terminal 14 to which the message is addressed, a message type code indicating the message type and the message itself. If insufficient messages are available to fill the message blockfield MB, transmission in the traffic channel ceases at the end of the messages until the beginning of the next frame TF.
Bulletin Board Channel Structure S The bulletin board channel is transmitted continuously at a fixed frequency. Transmissions in the bulletin board channel may be arranged in a frame structure with a length FL of 960 5-bit symbols, lasting four minutes for example.
As shown in Figure 6, each bulletin board frame BBF comprises a frame header BBH, a bulletin board identity BBID and an allocation table AT.
The frame header BBH comprises synchronisation information to assist terminals in acquiring the bulletin board channel. The bulletin board ID field BBID contains general information such as the identity of the earth station 8 transmitting the bulletin board channel, the date and time, and the version number of the bulletin board, which is changed every time a change occurs in the information transmitted in the allocation table AT.
The allocation table AT comprises a set of entries transmitted sequentially, each relating to one traffic channel. Each entry comprises the following information:
1. A service ID indicating a specific service using the relevant traffic channel. The service corresponds to one specific service provided by one of the service providers 4.
5 2. A satellite beam ID identifying the satellite beam over which the traff~c channel is transmitted.
3. A pager subset number range, indicating the group of terminals 14 allocated to that traffic channel. Each terminal 14 is pre-prograrnmed with the different subsets into which it falls.
4. A channel number, which indicates the frequency assigned to that traffic channel.
15 Unused entry fields are filled with idle codes, so that the transmission on the bulletin board channel is continuous.
Frame Timin Since the message blocks MB of the traffic channel frames are not always completely filled, the traffic channels are transmitted as bursts of up to 20 four minutes duration every four minutes. Multiple traffic channels are transmitted by each satellite 12, so that the transmit power used by the satellite 12 to transmit the traffic channels varies as the sum of the instantaneous power required to transmit the bursts of each channel. If all the traffic channels were synchronised so that their frames commenced at the same moment, the total transmit power at the start of the frames would be the total power required to transmit all the channels in use. As the bursts on the different traffic channels 5 ended, so the total transmit power would fall until the beginning of the next frame, when the power would rise to the maximum once again. This method would lead to a high peak transmit power requirement and large power fluctuations in the satellite.
Moreover, if the bulletin board frames were synchronised to begin at the 10 same time as the traffic channel frames, there would be a considerable delay in some cases between a terminal 14 receiving the relevant entry in the bulletin board channel and the start of the next frame of the traffic charmel indicated by that entry. In the extreme case, where the entry is the first entry of the allocation table AT, the delay would be nearly four minutes.
In order to avoid the above problems, the time alignment between the bulletin board frames and the traffic channel frames is as sho~n in Figure 7. At the top row of the figure, the bulletin board header and identity BBH, BBID is shown followed by each of the entries in the allocation table AT. The first four entries ATI to AT4 correspond to traffic channels Tl to T4, shown in 20 successive rows below.
The start of each traffic channel frame header TH is delayed relative to the start of the bulletin board &ame header BBH by a different multiple of 32 symbols, corresponding to eight seconds. For example, the start of the first traffic channel header TH 1 is delayed by 8 seconds, the second channel header TH2 by 16 seconds, the third TH3 by 24 seconds and the fourth by 32 seconds, and so until the last traffic channel n delayed by n x 8 seconds.
The timing of the traffic and bulletin board channels is referenced to the satellite 12, so that each earth station 8 transmits its traffic channels with atiming determined according to the propagation delay to the satellite 12 and thetransmission of the traffic channels from the satellite is timed as described above, regardless of which earth station 8 transmitted that channel.
The delay between the start of the bulletin board frame and the start of each traffic frame may be a multiple of the order of the entry in the allocationtable AT for that traffic frame, although the order of entries in the allocationtable AT need not be exactly the same as the order of starting of the corresponding traffic frames. The order of entries is arranged so that there is a minimum delay between the end of tr~n.smission of an entry and the start of the corresponding traffic frame, which is sufficient to allow the terrninal to retune from the bulletin board to the correct traffic channel, but the maximum delay isnever more than a small fraction of the frame period.
In other embodiments, the delay may be chosen according to the number of traffic channels and the frame period, so as to reduce the peak transmit power of the satellite and/or keep the delay between a channel entry in the bulletin board channel and the start of the corresponding traffic channel frame between aminimum and a maximum value for any channel.
Frequency Allocation When the terminal 14 is switched on, it automatically tunes to the fixed frequency of the bulletin board channel and receives the allocation table AT
entries until an entry corresponding to a pager subset number of the terminal 14and a service ID indicating a service subscribed to by the user 18 is received.
The terminal then retunes to the traffic channel indicated by that entry. The bulletin board information may change while the terminal is tuned to the previously indicated traffic channel. It is therefore necessary to alert the terminal to changes in channel allocation which may affect it.
The terminal is alerted in the following manner. The changeover countdown field in the identity block TID of the traffic channel frame is normally set to zero, but a predetermined number of frames before a change in frequency allocation which affects the terminals tuned to that traffic channel, the changeover countdown field is set to that predeterrnined number and is decremented in each subsequent frame until the terrninals must retune to the new channel. Meanwhile the new channel is signalled on the bulletin board channel.
Three different situations in which this method is employed will now be described.
Additional Traffic Channel In the example shown in Figure 8, two subsets of terminals Sl and S2 are tuned to traffic channel Tl . Within the frame divisions of Tl are shown the value of the changeover countdown field for that frame, while the version number of the bulletin board is shown within the frame boundaries of the S bulletin board channel. At the third frame before the allocation changeover, the version of the bulletin board changes from N to M. After the third last frame of the traffic channel T1, all the terminals of subsets S1 and S2 retune to the bulletin board channel BB as indicated by the arrow in Figure 8 and receive the new allocation entries for their subsets. In this example, subset S 1 is to remain 10 on traffic channel T1 while subset S2 is to change to traffic channel T2. The changeover countdown field of traffic channel T2, as sho~n between frame boundaries, remains at zero.
Meanwhile, in the last two frames before the channel changeover, no messages are sent in the traffic channel T1 as the terminals should now be tuned 15 to the bulletin board channel BB. Tr~n~mi.~sion also begins in the new traffic channel T2 but no messages are sent until the point of changeover. At the point of changeover, as indicated by the arrows in Figure 8, the subset Sl of pagers retune to traffic channel T1 while the subset S2 tune to the new traffic channel T2, and tr~n~mi~sion of messages in the traffic channel T2 for the subset S2 20 begins.
Since the frame boundaries of the traffic channels and the bulletin board channel are not time aligned but are delayed as described above, a two frarne period is allowed between the time when the terminals should tune to the bulletin board and the time when the terminals tune to the new channel, to ensure that none of the terminals fail to receive the necessary information.
The precise time at which the terminals 14 tune to the new channel T2 is 5 aligned with the start of the bulletin board frame BBF. The internal clock 44 is synchronized with the start of the bulletin board frame and set according to the date and time information when the terminal is tuned to the bulletin board channel.
However, this method may also be applied to systems in which frame 10 boundaries are aligned between different channels.
Removal of Traffic Channel Figure 9 shows another example in which a traffic channel is removed and terminals tuned to that channel are assigned to another e:~isting channel.
Initially, subset S I are tuned to traffic channel T1 while subset S2 are tuned to 15 traffic channel T2. Fifteen frarnes before the point of changeover, the changeover countdown field of traffic channel T2 is set to 15 and is decremented at each subsequent frame. After the value of the changeover countdown field is reduced to 3, the subset S2 retune to the bulletin board channel. At the third from last frame before the changeover. the bulletin board 20 version changes from N to M and the new allocation of the subset S2 is indicated in the allocation table AT.
The subset S2 detect the new channel allocation and retune to the traffic channel Tl at the time of changeover. Subsequently, traffic channel Tl carries messages for both subset S 1 and S2. Traffic channel T2 carries no messages for the last two frames before the allocation change, and no transmissions take 5 place after the change.
In this example, the changeover countdown field value for traffic channel Tl is set to zero throughout the allocation change, because the change does not require the subset S 1 to retune.
Change of Traffic Channel Frequency Allocation Figure 10 shows an example in which all the terrninals tuned to one traffic channel are retuned to another traffic channel.
Initially, subset Sl are tuned to traffic channel T1. As in the other examples, the changeover countdown field indicates that the channel allocation for these terrninals is about to change. Before the change, the bulletin board 15 version is changed and indicates the new traffic channel T2 assigned to all the subset S 1. Two frames before the changeover, the terminals 14 of the subset S 1 retune to the bulletin board channel BB and receive the new allocation entry from the allocation table AT. At the same time, transmission begins in the new traffic channel T2 but no messages are transmitted until the change. After the 20 change, tr~n~mi.~sionceases on the traffic channel T1.
The above methods provide a very robust method of controlling reallocation of terminals to traffic channels, since any terrninal need only receive one changeover countdown field out of the 15 non-zero countdown fields and may still determine that a channel reallocation is required and when the reallocationshould take place. If, however, a terminal is unable to receive 15 consecutive frames. it then automatically retunes to the bulletin board channel in S order to determine whether any channel reallocation has taken place for the relevant subset.
Although the above embodiments have been described ~ ith reference to a satellite messaging system, aspects of the present invention are also applicable to terrestrial paging systems, particularly power limited systems or systems in 10 which blockage of traffic channels may occur, and to paging systems with enhancements such as acknowledgement of messages by recei- ers. Aspects of the present invention may also be applied to combined satellite and terrestrial paging systems in which messages are relayed via satellite to terrestrial stations which retransmit the messages to paging receivers.
Aspects of the present invention are applicable to satellite communications systems using satellites other than geostationary satellites, in which case the allocation of earth stations to satellites will change as the satellites come into or go out of view of different earth stations.
It will be appreciated that individual elements of a mess~ging or paging 20 system may be located in different jurisdictions or in space. The present invention e~ctends to any such element which contributes to the aspects of the invention as herein defined.
Claims (33)
1. A method of controlling the transmission of a plurality of frequency channels, each of which has a frame format of substantially the same constant frame period, with each frame comprising a transmission burst of variable duration, comprising:
controlling the timing of transmission of the frames of each of said frequency channels such that the start of the transmission burst of one of said channels is delayed relative to the start of the transmission burst of another one of said channels.
controlling the timing of transmission of the frames of each of said frequency channels such that the start of the transmission burst of one of said channels is delayed relative to the start of the transmission burst of another one of said channels.
2. A method as claimed in claim 1, wherein the start timing of the transmission burst of each of said frequency channels is different from that of the other ones of said channels.
3. A method of controlling the transmission of a plurality of frequency channels, each of which has a frame format of substantially the same constant frame period, comprising controlling the timing of transmission of said frequency channels such that the start timing of the frames of each of said channels differs from that of the other ones of said channels, the method further comprising controlling the transmission of a control channel including a plurality of sets of channel control data each relating to a corresponding one of said plurality of channels such that said sets are transmitted sequentially and the order of starting of said frames of said frequency channels substantially corresponds to the order of transmission of said sets of said channel control data.
4. A method as claimed in any preceding claim, wherein said plurality of frequency channels are each message traffic channels carrying one or more messages for selective message receivers.
5. Apparatus for controlling the transmission of a plurality of frequency channels, each of which has a frame format of substantially the same constant frame period, with each frame comprising a transmission burst of variable length, comprising:
means for controlling the timing of transmission of the frames of each of said frequency channels such that the start of the transmission burst of one of said channels is delayed relative to the start of the transmission burst of another one of said channels.
means for controlling the timing of transmission of the frames of each of said frequency channels such that the start of the transmission burst of one of said channels is delayed relative to the start of the transmission burst of another one of said channels.
6. Apparatus as claimed in claim 5, wherein the means for controlling is arranged to control the start timing of the transmission burst of each of said frequency channels to be different from that of the other ones of said channels.
7. Apparatus for controlling the transmission of a plurality of frequency channels, each of which has a frame format of substantially the same constant frame period, comprising:
means for controlling the timing of transmission of said frequency channels such that the start timing of the frames of each of said channels differs from that of the other ones of said channels, the apparatus further comprising means for controlling the transmission of a control channel including a plurality of sets of channel control data each relating to a corresponding one of said plurality of frequency channels such that said sets are transmitted sequentiallyand the order of starting of said frames of said frequency channels substantially corresponds to the order of transmission of said sets of said channel control data.
means for controlling the timing of transmission of said frequency channels such that the start timing of the frames of each of said channels differs from that of the other ones of said channels, the apparatus further comprising means for controlling the transmission of a control channel including a plurality of sets of channel control data each relating to a corresponding one of said plurality of frequency channels such that said sets are transmitted sequentiallyand the order of starting of said frames of said frequency channels substantially corresponds to the order of transmission of said sets of said channel control data.
8. Apparatus as claimed in any one of claims 5 to 7, wherein said plurality of frequency channels are each message traffic channels carrying one or more messages for selective message receivers.
9. A method of controlling the channel allocation of a receiver, comprising:
controlling the transmission of a control channel indicating the current channel allocation of the receiver; whereby the current channel allocation is modified from a first traffic channel to a second traffic channel;
controlling the transmission of the first traffic channel allocated to the receiver such that a channel change indication is transmitted to the receiver and the receiver is caused to receive said control channel so as to receive said indication of said modified allocation to the second traffic channel.
controlling the transmission of a control channel indicating the current channel allocation of the receiver; whereby the current channel allocation is modified from a first traffic channel to a second traffic channel;
controlling the transmission of the first traffic channel allocated to the receiver such that a channel change indication is transmitted to the receiver and the receiver is caused to receive said control channel so as to receive said indication of said modified allocation to the second traffic channel.
10. A method as claimed in claim 9, wherein the channel change indication is transmitted more than once before the receiver is required to receive said control channel.
11. A method as claimed in claim 10, wherein each of said channel change indications indicates when the current channel allocation of the receiver will be modified.
12. A method as claimed in any one claims 9 to 11, wherein said first traffic channel has a repeating frame structure, the channel change indications each being transmitted in a respective frame and indicating the number of frames remaining before the current channel allocation will be modified.
13. A method as claimed in any one of claims 9 to 12, whereby the receiver is caused to receive said second traffic channel after receiving said control channel with a timing determined by said channel change indication.
14. Apparatus for controlling the channel allocation of a receiver, comprising:
means for controlling the transmission of a control channel indicating the current channel allocation of the receiver, whereby the current channel allocation is modified from a first traffic channel to a second traffic channel; and means for controlling the transmission of the first traffic channel allocated to the receiver such that a channel change indication is transmitted to the receiver and the receiver is caused to receive said control channel so as to receive said indication of said modified allocation to the second traffic channel.
means for controlling the transmission of a control channel indicating the current channel allocation of the receiver, whereby the current channel allocation is modified from a first traffic channel to a second traffic channel; and means for controlling the transmission of the first traffic channel allocated to the receiver such that a channel change indication is transmitted to the receiver and the receiver is caused to receive said control channel so as to receive said indication of said modified allocation to the second traffic channel.
15. Apparatus as claimed in claim 14, wherein the means for controlling the transmission of the control channel is arranged so that the channel change indication is transmitted more than once before the receiver is required to receive said control channel.
16. Apparatus as claimed in claim 15, wherein the means for controlling the transmission of the control channel is arranged so that each of said channel change indications indicates when the channel allocation of the receiver will be modified.
17. Apparatus as claimed in claim 15 or 16, wherein said means for controlling the transmission of the first traffic channel is arranged so that the first traffic channel has a repeating frame structure, the channel change indications being each transmitted in a respective frame and indicating the number of frames remaining before the current channel allocation will be modified.
18. A method as claimed in any one of claims 1 to 4 or 9 to 13. wherein said steps of controlling transmission of said channels comprises transmitting signals to a relay station such that the relay station transmits said channels with said corresponding timing relationships.
19. A method as claimed in any one of claims 1 to 4 or 9 to 13. wherein said steps of controlling transmission of said channels include transmitting said channels.
20. Apparatus as claimed in any one of claims 5 to 7 or 14 to 17, wherein said means for controlling transmission of said channels includes means for transmitting signals to a relay station such that the relay station transmits said channels with said corresponding timing relationships.
21. Apparatus as claimed in any one of claims 5 to 7 or 14 to 17 including means for transmitting said channels.
22. A satellite earth station including apparatus as claimed in any one of claims 5 to 7, 14 to 17 or 20.
23. A terrestrial base station including apparatus as claimed in any one of claims 5 to 7, 14 to 17 or 21.
24. A method of changing channel reception in a receiver, comprising:
receiving a first traffic channel;
detecting in said first traffic channel a channel change indication;
receiving a control channel in response to said channel change indication;
detecting a channel indication relating to the receiver in said control channel; and receiving a second traffic channel designated by said channel indication.
receiving a first traffic channel;
detecting in said first traffic channel a channel change indication;
receiving a control channel in response to said channel change indication;
detecting a channel indication relating to the receiver in said control channel; and receiving a second traffic channel designated by said channel indication.
25. A method as claimed in claim 24, wherein the receiver begins to receive said second traffic channel at a time indicated by said channel change indication.
26. A method as claimed in claim 24 or 25, wherein the receiver begins to receive the control channel at a time indicated by said channel change indication, before receiving the second traffic channel.
27. A method as claimed in any one of claims 24 to 26, wherein the control channel includes a plurality of channel indications and a plurality of receiver indications, and the receiver receives the second traffic channel indicated by one of the channel indications corresponding to one of the receiver indications which corresponds to said receiver.
28. A receiver, comprising:
means for controlling the receiver to receive a first traffic channel;
means for detecting in said first traffic channel a channel change indication;
means for controlling the receiver to receive a control channel in response to said channel change indication;
means for detecting a channel indication relating to the receiver in said control channel; and means for controlling the receiver to receive a second traffic channel designated by said channel indication.
means for controlling the receiver to receive a first traffic channel;
means for detecting in said first traffic channel a channel change indication;
means for controlling the receiver to receive a control channel in response to said channel change indication;
means for detecting a channel indication relating to the receiver in said control channel; and means for controlling the receiver to receive a second traffic channel designated by said channel indication.
29. A receiver as claimed in claim 28, wherein the means for controlling the receiver to receive the second traffic channel is arranged so that the receiver begins to receive said traffic channel at a time indicated by said channel change indication.
30. A receiver as claimed in claim 28 or 29, wherein the means for controlling the receiver to receive the control channel is arranged so that the receiver begins to receive the control channel at a time indicated by said channel change indication, before receiving the second traffic channel.
31. A receiver as claimed in any one of claims 28 to 30, wherein the control channel includes a plurality of channel indications and a plurality of receiver indications, and the means for controlling the receiver to receive the second traffic channel is arranged so that the receiver receives the second traffic channel indicated by one of the channel indications corresponding to one of the receiver indications corresponding to said receiver.
32. A receiver as claimed in any one of claims 28 to 31 arranged to receive only one channel at any one time.
33. A message terminal including a receiver as claimed in any one of claims 28 to 32.
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Families Citing this family (5)
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|---|---|---|---|---|
| US6711398B1 (en) * | 2000-04-19 | 2004-03-23 | Hughes Electronics Corporation | Radio signal broadcast system and method |
| US7043259B1 (en) * | 2000-09-29 | 2006-05-09 | Arraycomm, Inc. | Repetitive paging from a wireless data base station having a smart antenna system |
| US20060039698A1 (en) * | 2004-08-18 | 2006-02-23 | Pautler James A | System and method of communications with traffic signals |
| EP2254266A1 (en) * | 2009-05-20 | 2010-11-24 | Astrium Limited | Content broadcast |
| US11616566B2 (en) * | 2020-12-30 | 2023-03-28 | Hughes Network Systems, Llc | Satellite beam selection |
Family Cites Families (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4686672A (en) * | 1983-10-13 | 1987-08-11 | Nec Corporation | TDMA communications apparatus having adaptive burst duration |
| US4849750A (en) | 1987-10-20 | 1989-07-18 | Telefind Corp. | Paging receiver with dynamically programmable channel frequencies and functionality |
| DE69025311T2 (en) * | 1989-08-25 | 1996-08-22 | Nippon Telegraph & Telephone | CONTROL METHOD OF A RADIO CHANNEL SWITCH |
| US5228029A (en) * | 1990-02-27 | 1993-07-13 | Motorola, Inc. | Cellular tdm communication system employing offset frame synchronization |
| US5206855A (en) * | 1990-04-06 | 1993-04-27 | Motorola, Inc. | Multiple frequency message system |
| US5309439A (en) * | 1991-11-29 | 1994-05-03 | Hughes Aircraft Company | TDMA system with a virtual reference |
| SE9300681D0 (en) * | 1993-03-01 | 1993-03-01 | Ericsson Telefon Ab L M | A METHOD AND APPARATUS FOR HANDING OFF A MOBILE STATION FROM A FIRST TO A SECOND CHANNEL IN A MOBILE COMMUNICATION SYSTEM |
| FR2708813B1 (en) * | 1993-07-30 | 1995-09-01 | Alcatel Mobile Comm France | Cellular radio system. |
| US5448621A (en) * | 1993-08-02 | 1995-09-05 | Motorola, Inc. | Dynamic reallocation of spectral capacity in cellular communication systems |
| GB2284496B (en) * | 1993-12-03 | 1997-11-05 | Motorola Gmbh | Store and forward paging system |
| FR2713850B1 (en) * | 1993-12-14 | 1996-01-05 | France Telecom | Method for allocating a communication channel in a satellite network. |
| GB2299695B (en) * | 1995-04-07 | 1998-12-02 | Centrepoint Technology Limited | Vehicle security systems |
| US5781540A (en) * | 1995-06-30 | 1998-07-14 | Hughes Electronics | Device and method for communicating in a mobile satellite system |
| US5930706A (en) * | 1995-11-29 | 1999-07-27 | Ericsson Inc. | Detecting messages transmitted over a communications channel such as a paging channel |
| US5812545A (en) * | 1996-01-04 | 1998-09-22 | Orion Atlantic, L.P. | Full mesh satellite-based multimedia networking system |
| US5740165A (en) * | 1996-02-29 | 1998-04-14 | Lucent Technologies Inc. | Wireless TDMA transmitter with reduced interference |
-
1996
- 1996-12-03 GB GB9625256A patent/GB2320118A/en not_active Withdrawn
-
1997
- 1997-11-27 CA CA002222384A patent/CA2222384A1/en not_active Abandoned
- 1997-12-02 DE DE69715790T patent/DE69715790T2/en not_active Expired - Lifetime
- 1997-12-02 DE DE69724479T patent/DE69724479T2/en not_active Expired - Lifetime
- 1997-12-02 EP EP97309703A patent/EP0847148B1/en not_active Expired - Lifetime
- 1997-12-02 EP EP01202118A patent/EP1134914B1/en not_active Expired - Lifetime
- 1997-12-03 JP JP9366104A patent/JPH10271548A/en active Pending
- 1997-12-03 US US08/984,325 patent/US6600757B1/en not_active Expired - Lifetime
-
2003
- 2003-06-25 US US10/602,766 patent/US20040087330A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| GB2320118A (en) | 1998-06-10 |
| DE69715790T2 (en) | 2003-02-13 |
| EP1134914A2 (en) | 2001-09-19 |
| EP1134914B1 (en) | 2003-08-27 |
| EP1134914A3 (en) | 2002-02-27 |
| DE69715790D1 (en) | 2002-10-31 |
| EP0847148B1 (en) | 2002-09-25 |
| US20040087330A1 (en) | 2004-05-06 |
| US6600757B1 (en) | 2003-07-29 |
| EP0847148A2 (en) | 1998-06-10 |
| GB9625256D0 (en) | 1997-01-22 |
| DE69724479D1 (en) | 2003-10-02 |
| DE69724479T2 (en) | 2004-06-17 |
| EP0847148A3 (en) | 2000-05-03 |
| JPH10271548A (en) | 1998-10-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20070228 |