CA1299781C - Reuse groups for scan monitoring in digital cellular systems - Google Patents
Reuse groups for scan monitoring in digital cellular systemsInfo
- Publication number
- CA1299781C CA1299781C CA000584960A CA584960A CA1299781C CA 1299781 C CA1299781 C CA 1299781C CA 000584960 A CA000584960 A CA 000584960A CA 584960 A CA584960 A CA 584960A CA 1299781 C CA1299781 C CA 1299781C
- Authority
- CA
- Canada
- Prior art keywords
- radiotelephone
- frequencies
- base site
- monitoring
- frequency
- 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 - Lifetime
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
- H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
- H04B7/2643—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W24/00—Supervisory, monitoring or testing arrangements
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/08—Access point devices
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/50—Allocation or scheduling criteria for wireless resources
- H04W72/56—Allocation or scheduling criteria for wireless resources based on priority criteria
- H04W72/563—Allocation or scheduling criteria for wireless resources based on priority criteria of the wireless resources
-
- 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]
- H04W84/04—Large scale networks; Deep hierarchical networks
- H04W84/042—Public Land Mobile systems, e.g. cellular systems
Abstract
CE12r Abstract of the Disclosure An improved TDMA radiotelephone cellular communication system employs an improved cell site scan monitoring technique. The technique includes monitoring radiotelephone calls, and tracking and recording their signal qualities. The records are used to maintain and determine which frequencies and which time partitions at the base site equipment are being utilized for radiotelephone communication. When a new call assignment is required at a cell site, it is assigned to a time partition of a base site equipment frequency in a frequency prioritized manner such that radiotelephone calls are concentrated within each frequency so as to reduce the number of frequencies carrying radiotelephone calls.
Description
~2~
REUSE GROUPS FOR SCAN MONITORING IN
DIGITAL CELLUL~R SYSTEMS
Field of the Invention The present invention relate~ generally to radio communication systems, and~ more particularly, to digital cellular communication systems and a technique for improving the channel usage efficiency in such systems during the process of assigning channels and performing "handoffs", i.e., transferring a radiotelephone call ~rom a voice channel withln one coverage area to a voice channel within an adjacent coverage area.
BacXground In conventional analog cellular communication systems, a plurality of base sites are used to provide associated geographical co~erage areas within which radiotelephones coT~municate. Each base site is controlled by the system's central switch controller.
When a radiotelephone call is to be handed-off from a communication channel at the host base site (the base site currently sustaining the call) to a comTnunication channel at an adjacent base site, the system must ~2~
REUSE GROUPS FOR SCAN MONITORING IN
DIGITAL CELLUL~R SYSTEMS
Field of the Invention The present invention relate~ generally to radio communication systems, and~ more particularly, to digital cellular communication systems and a technique for improving the channel usage efficiency in such systems during the process of assigning channels and performing "handoffs", i.e., transferring a radiotelephone call ~rom a voice channel withln one coverage area to a voice channel within an adjacent coverage area.
BacXground In conventional analog cellular communication systems, a plurality of base sites are used to provide associated geographical co~erage areas within which radiotelephones coT~municate. Each base site is controlled by the system's central switch controller.
When a radiotelephone call is to be handed-off from a communication channel at the host base site (the base site currently sustaining the call) to a comTnunication channel at an adjacent base site, the system must ~2~
- 2 - CE12r determine which adjacent base site provicles the best coverage area for the handoff. This is typically accomplished by instructing the equipment at each adjacent base site to monitor the channel used by the radiotelephone to be handed-off Using scan receivers to monitor tha radiotelephone channels, the equipment at each adjacent base site reports the signal strength of the radiotelephone's signal to the system's switch controller~ The switch controller then compares the lo strongest reported signal strength with the signal strength from the radiotelephone at the host bass site.
When the latter falls below that of the former, tha radiotelephone is instructed to reconfigure its transceiver to effect the handoff.
In a time division multiplex access (TDMA) cellular communication system, there are typically a plurality of radio frequencies employed at each base site to provide the appropriate allocation of voice communication channels for the base site's associated coverage area.
Each frequency i~ time partitioned into several time slots, each of which may carry radiotelephone communication.
When a radiotelephone call is to be handed-of~
between coverage areas in a TDMA cellular communication system, the system also determines to which base site the call should be handed-off by the adjacent base sites monitoring the channel used by the radlotelephone.
However, because each frequency may be carrying a radiotelephone communication, the base sitesi scan receivers can become excessively busy monitoring each time slot in each frequency for each radiotelephone's signal strength.
This problem is aggravated when each base site includes only a few scan receivers which are time shared 7~3~
~ 3 ~ CE12r to monitor the fre~lencias. For each fre~uency on which at least one radiotelephone i~ a hando~f candidate, the scan receiver must ad~ust its oscillator to that frequency and receive the information transmitted thereon. Such oscillator adjustment introduces a significant delay which i~ inherent in mo~t every receiver. As the number of potential handoff candidates increases, this inherent delay can become unacceptable.
Accordingly, a scan receivex monitoring technique for ~uch base site~ in a TD~A cellular communication ~ystem i5 needed which overcome the above described deficiencies.
Objects of the Present Invention It is a general object o~ the present invention to provide a TDM~ cellular communication system which overcomes the above described shortcomings.
It is a more particular ob~ect o~ the present invention to provide a cell~lar communication system which increase~ the usage e~iciency of scan receivers in such systems by assigning radiotelephone calls to time partitions of the c211 sites in a frequency prioritized manner such that radiotelephone calls are concentrated within each fre~uency so as to reduce the number of ~requencies carrying radiotelephone calls.
An additional ob~ect o~ the prasent lnvention includes increasing the usage efficiency o~ scan receivers in a radiotelephone ~reguency hopping TDMA
cellular system by assigning radiotelephona calls to time partitions of the cell site~s freqùencies in a ~requency prioritized manner and by measuring radiotelephone call signals by the scan receiver in a delayed manner such that the amount of frequency programming to each scan receiver is minimized.
~!
- 4 - CE12r BriPf Descriptio of the Drawin~
The features of the present invention whiah are believed to be novel are set forth with partiaularity in the appended claims. ~he invention, together with further objects and advantages thereo~, may best be understood by making re~erence to the ~ollowing description taken together with th~ accompanying drawings, in which reference numerals identify the elements, and wherein:
Fig. la is a diagram of a cellular communication system including two base sites and their respective equipment, according to the present invention;
Fig. lb is an expanded diagram of the base site equipment 115 or 119 of Fig. la., according to thQ
present invantion:
Fig. 2 is a diagram illustrating a frequency assignment for the scan receiver 146 or 1~8 of F~g. lb, according to the present invention:
Fig. 3 is a flowchart illu~trating a frequency assignment for the scan receiver 146 or 148 of Fig. lb, according to the present invention;
Fig. 4 is a flowchart illustrating a switch controller technique for executing time slot and frequency as~ignments for the scan receiver 146 or 148 of Fig. lb, according to the present invention: and Fig. 5 is a flowchart illustrating an alternative ~requency assignment for the scan receiver 146 or 148 of Fig. lb, according to the present invention.
7~1~
- 5 - CE12r Detailed DPscri~ f~the Preferred _ bodiment The arrangement disclosed in this specification has particular use for handing-off radiotelephonQ calls between cells in a TDMA cellular telephone infrastructure. More particularly, the arrangement disclosed herein is directed to improving the usage efficiency o~ scan receivers with respect to channel assignements in such systems for call initiations and handoffs.
Fig. la illustrates a novel cellular system which includes base site eguipment 115 and 119 for two geographic radio frequency (R~) coverage area (cells) 110 and 112, respectively. For cell 110, the base site equipment 115 includes a set of base transceivers 114 and a base site (1) controller 116. For cell 112, the base rite equipment 119 includes a set o~ base transceivers 118 and a base site (2) controller 120 with substantially identical circui~ry as the base site eguipment 115.
For purposes of exemplifying a handoff operation according to the present invention, a radiotelephone unit 130 is depicted in transition from cell 110 to cell 112.
Overall control of the base ~ite equipment 115 and 119 is provided by a signal processing unit 121 of a cellular switch controller 122. ~he switch controller 122 also ir.cludes a digital switching network 123 for controlling the call switching operation between a public switched telephone network (PSTN) 131 and the base si~e equipment 115 and 119. A set of pulse code modulation tPCM) converters 125 are included in the cellular switch controller 122 for interfacing the system to the PSTN
131. For general details of a conventional cellular system, reference may be made to "Cellular Voice and Data Radiotelephone System", Labedz et. al., U.S. patent no.
7~ ~
- 6 - CE12r 4,654,8~7. For ~urther details o~ a conventional cellular switch controller, re~erence may be made to U.S.
Pat. No. ~,268,722, Li~ e~ al. Both o~ the above U.S.
patents are assigned to the same assignee.
In Flg. lb, the base site equipment 115 or 119 i5 shown in expanded ~orm. The radio portion o~ the base site e~uipment is conventional. It include~ a set of transmit antenna~ 132, a ~et o~ receive antenna~ 134, a transmitter-combiner 136, a receiver interface equipment 138, a tran ceiver 140 and audio path3 141 directed to/Prom tha switch controller 122 of Fig. la.
Transceiver functions such as ~requency programming, transmit keying, tran~mit power control, alarm and status monitoring, and message passing are controlled by a microcomputer 142 through a microcomputer inter~ace 144.
A conventional scan receiver 146 or 148 monitor~ th~
signal strength o~ radiotelephone tran~missions in ad~acent cells and provide~ an output 150 which i~ used by ~he microcomputer 142 to determine when radiotelephones in such ad~a¢ent cells are handof~
candidates. Measuring radiotelephone signal strength with scan receivers i~ typical in mo~t analog cellular systemR. For example, in U.S. Pat. No. 4,485,486, Webb e~ al., a scan receiver implementation ~or such a system is described. For ~urther details oP conventlonal base site equipment, re~erence may be made to U.S. Pat. No.
4,485,486. Both oP the above referenced U.S. patents are assigned to the same asslgnee.
According to the present lnvention, the microcomputer 142 also controls the scan receivers 1~5 and 148. The particular method o~ control, which i5 unique to the present invention, is discussed in more detail with Figs.
~2~
- 7 - CE12r 2, 3 and ~. An analog to digital converter (ADC) 152 :ls used to convert the outputs 150 provided by tha scan receivers 146 and 148 to digital form for analysis by the microcomputer 142.
Each scan raceiver 146 or 148 generates an additional (audio) output 154 which i~ used by a preamble detector 156 or 158 to detect the beginning of a radiotelephone transmission. In a TDMA cellular communication system, the radiotelephones are typically synchronized with the base site equipment at each of the cell sites. A
radiotelephone transmits and receive~ messages by accessing a timeslot of a particular frequency, as assigned by the base site equipment. Each message, received or transmitted, begins with a preamble consisting of a predeterminad signal pattern. For more detail, reference may be made to "A Digital FD/TDMA
System fox a New Generation", pages 41-46 of "Primer for the Future ... DIGITAL TECHNOLOGY", L.M. Ericsson Telephone Company, June, 1987. The pr~-amble detector 156 or 158 may implemented using a conventional multi-bit digital comparator circuit.
Accordingly, the preamble detector 156 or 158 detects the preamble of each radiotelephone message received by the respective scan receiver 146 or 148. After each such detection, the preamble detector 156 or 158 informs the microcomputer 142, via the microcomputer interface 144, so that ths microcomputer knows when the signal strength should be measured from the received data at the outputs 150 of the scan receivers. Measurements performed by the microcomputer 142 are stored in a database in a memory circuit 143.
12~7~
- 8 - CE12r The microcomputer 142 operation for the scan receiver 146 or 148 is illustrated in Fig. 2 and in the corresponding flowchart of Figure 3. The illustrations in Figs. 2 and 3 particularly involve the operation of a TDMA cellular communioation ~ystem in which radiotelephone frequency hopping i5 employed, i.e., where radiotelephones communicate on the system in a designated time slot while rotating between a predetermined group of frequencies. Such a system is described in more detail in "A Digital FD/TDMA System for a New Generation"~
supra.
The flowchart of FigO 3 begins at block 310 where the microcomputer establishes the frequency hopping patterns and groups for radiotelephone communication within the associated coverage area. Fig. 2 illustrates an example of a system frequency hopping group assignment, according to the present invention, for N groups in which M
frequencies per hopping pattern (group) are employed.
Each employed frequency include~ 8 time ~lots tTl ~
T8). In this example, the 8 time slots (Tl - T8) establish a set which is equal to 1 frame. There are a total of (N x M) frequencies used. A solid line 210, which rotates through each frequency in each group from left to right and top to bottom i8 depicted to represent the flow of the scan receiver through each time slot and each frequency. Mathematically, the scan receiver assignment changes from frequency fxy to frequency fx+l,y with X being reinitialized to 1 after the Mth fre~uency. A series of vertical dotted line~ 220, are depicted to illustxata the frequency transition for a hopping radiotelephone in a particular time slot of a group during communication.
From block 310, flow proceeds to block 312 where the frequency of the scan receiver is set to the first frequency of group 1 (fll of Fig. 2).
'7~l - g - CE12r At block 314, a software timer (internal to the microcomputer 144 of Fig. lb) is ~et to begin timing a time interval equal to the time requlred to receive 1 frame of data. This timer is used to limit the length of time that the scan receiver will r~main on any given freguency to receive data in a designated frameO
At block 316, tests are repeatedly perfo~med to determine if either the timer has timed out or if the preestablished preamble has been detected in the received signal. As previously discussed, each radiotelephone transmisslon is preceded by a predetermined data pattern dafining the preamble. However, although a transmission will be expected, there may not be a transmission on every time slot of a given frame.
If the preamble is detected before the timer times out, flow procaeds to block 318. At block 318, because the preamble has been detected, the microcomputer presumes that a valid radiotelephone transmission has been received. The quality of the data following the preamble is tested for signal strength and signal "integrity" (i.e., the data legibility or data bit error ratio) using conventional digital analysis methods. In addition, the microcomputer examines the data to determine the base station's unique identification code (to identify the radiotelephone's site), and determines in which time slot the transmission was made. The particular time slot can be determined from the local base equipment r~ference timing if the system has synchronized base stations.
If the system does not have synchronized base stations, the time slot can be determined by extracting time slot informatlon from the received message. E.g., the radiotelephone's unique identification (ID) code can be extracted from the preamble and passed to the - 10 - CE12r microcomputer which can then identify the time slot using a conventional memory look-up technique with the ID code as the address.
From block 318, flow proceeds to block 320 where the microcomputer's data base ia updated to indicate the presence o~ a radiotelephone transmission in the detected time slot, and the measurements for that transmission are stored accordingly. From block 320, flow returns to block 316 so that a transmission in the next time slot can be detected.
I~ the preamble is not detected before the timer times out, flow proceeds from block 316 to block 322 where a test is performed to determine if the scan receiver has just finished receiving data in tha frame of the last group. In Fig. 2, this test is satisfied after the scan receiver receives data from the eigh~h time slot of the Nth group.
If the scan receiver has not ~inished receiving data from the frame of the last group, flow proceeds from block 322 to block 324 where the scan receiver is assigned to the frequency of the next group. In Fig. 2, this is a horizontal mov~ along the solid line from the left to the right. From block 324, flow returns to block 314 so that the scan receiver can begin receiving data for a new frame.
If the scan receiver has finished receiving data for the frame of the last group, flow proceeds from block 322 to block 328 where a test is performed to determine if the scan receiver has completed receiving data from the frame of the last group. In Fig. 2, this test would comprise a determination as to whether or not the frequency being monitored is f~. If the scan receiver is not monitoring fre~uency fNM at this point, flow proceeds to block 330 where the scan receiver is assigned ~8 1 !
~ CE12r to the next ~requency of tha ~irst group. IP khe frequency is e~ual to ~NM at this point, ~low returns to block 312 where tha entire proce~s i~ reinitiated ~rom tha first ~requency o~ the first group.
As this process continuas, the microcomputer's data base, as indicated at ~lock 320, is continuously updated.
Because the data base i5 be1ng updated with measurements of signal quality and strength for any radiotelephone's trans~ission from an ad;acent ~ell, the switch controller (Fig la) is provided acc2ss with an up-to-date status of a radiotelephone's potential to be handed-o~ to the as~ociated call s$te.
This staku~ information can ba used in a conventional handof~ process such as the ones de~cribed ln U.S. Pat.
Nos. 4,485,486 (Webb et al.), 4,654,867 (Labedz) and 4,696,027 (Bonta et a~ ach assign~d to the same assignee. It should be pointed out, however, that because this information is immediately available to the switch controller, the switch controller does not have to raquest the base ~ite equipment at ad~acent calls to first perform the requisite monitoring ~or each hando~ candidate radiotelephone. The switch controller merely queries the ad~acent cell ~ite eguipment to provide the in~ormation already stored in the database. Alternatively, the ad~acent cell site equipment can continually provide this accumulated signal information to the switch controller to alleviate the extra step of having the switch controller first make the request. Using either implementation, this provides a signi~icant advantage over known system san monitoring techniques because it substantially reduces the time otherwise necessary to detexmine where and when to make a handoff.
Another aspect o~ the present invention involves the $?~
~2~
- 12 - CE12r manner in which con~unication frequencies (channels) are assigned at each of the cell sites. As indicated previously, each time a scan receiver is assigned a new frequency, an inherent delay occurs before the scan receiver can actually receive data on the new frequency.
In a frequency hopping TDMA cellular system, a significant amount of data can be missed by a scan receiver if thi~ delay becomes excessive.
To overcome this problem, the present invention employs a novel radiotelephone time slot/frequency assignment. Referring to Fig. 2, this asRignment involves selecting an open time slot from a group frame such that the group frames are filled one fram~ at a time, and that each group is filled before another group is filled.
For example, presume that at a particular time the base site targetted for a handoff includes two designated groups ~Gl and G2), and ~our corresponding frequencies (F11, F12, F21, F22). Further, at a given point in time presume that in the group frame Fll, radiotelephone calls are active in frames 1, 3, 5, 6, 7 and 8 in the group frame F12 radiotelephone calls are active in frames 1, 2 and 3: and in the group frames F21 and F22, there are no active radiotelephona calls.
According to the present invention, the first open time slot in this given frequency assignmant (for a radiotelephone candidate or for a radiotelephone call initiation? is the second time slot of the group frame designated Fll. Thus, the second time slot of the group frame designated Fl1 will be chosen.
The next radiotelephone call assignment at this site will be (presuming the same active calls as described earlier) the fourth time slot of the group frame designated Fl1. Once the entire frame F11 contains '7~
- 13 - CE12r active calls, time ~lot from frame F12 will ha chosen from left to right, and then time 810t~ ~rom F21 and then F22.
As radiotelephone calls are dropped or handed off to 5 adjacent cell sitas, time slots from the group ~rames (Fll, F12, F21, F22) will become free to enable additional radiotelephone call time slot assignments in a similar manner.
Additionally, tha present invention provides a method 10 O~ minimi~ing the a~ount of data passed between the base ~ites, while, at ths ~ame time, allowing aach bas2 site to ~ore effectively scan the active communication fre~uencies of a particular group. A~ each new group (comprising at least one time partitioned ~rams) i~
15 established for comm~!nlcation use at ~ach ba~ 6ite, a message is passed to the adjacent cell sites to inform them that the new group should be scan monitored. This allows ~he ~ystem to monitor aotivQ call , or those calls about to become active, without rQquiring that all 20 frequencies be scanned and w~thout re~u~ring in~tructions for scan monitoring to the ad~acent cell sites each time a new active call i8 establish~d. Similarly, a5 groups become unused (idle) a single m~esage ~s communicated to the ad-Jacent base ~ite~ to ~top scanning the unused 25 group.
In Fig. 4, a ~low chart illustrates an example of the r switch controller (Fig. la) directing a handoff from site 1 to site 2 (re~erring to Fig. la), according to ~he pxesent invention and con5i5tant with the previous 30 examples. The ~low chart b~gins at block 410 where a test is performed to datermine if there i5 a handoff candidate present at th~ site 1. If there i5 not a handoff candidate present, the procedure ends and similar tests are performed at another site~
. .
- 14 CE12r If a hando~f candidat~ is present a~ site 1, rlow proceeds from block 410 to block 420 where th~ 3witch controller requssts the relevent data base signal measurement lnformation for the radiotelephone ~rom the cell site that i~ ad~acent the host cell site (site 2).
As discussed previously ~with blocks 31~ and 320 of Fig.
When the latter falls below that of the former, tha radiotelephone is instructed to reconfigure its transceiver to effect the handoff.
In a time division multiplex access (TDMA) cellular communication system, there are typically a plurality of radio frequencies employed at each base site to provide the appropriate allocation of voice communication channels for the base site's associated coverage area.
Each frequency i~ time partitioned into several time slots, each of which may carry radiotelephone communication.
When a radiotelephone call is to be handed-of~
between coverage areas in a TDMA cellular communication system, the system also determines to which base site the call should be handed-off by the adjacent base sites monitoring the channel used by the radlotelephone.
However, because each frequency may be carrying a radiotelephone communication, the base sitesi scan receivers can become excessively busy monitoring each time slot in each frequency for each radiotelephone's signal strength.
This problem is aggravated when each base site includes only a few scan receivers which are time shared 7~3~
~ 3 ~ CE12r to monitor the fre~lencias. For each fre~uency on which at least one radiotelephone i~ a hando~f candidate, the scan receiver must ad~ust its oscillator to that frequency and receive the information transmitted thereon. Such oscillator adjustment introduces a significant delay which i~ inherent in mo~t every receiver. As the number of potential handoff candidates increases, this inherent delay can become unacceptable.
Accordingly, a scan receivex monitoring technique for ~uch base site~ in a TD~A cellular communication ~ystem i5 needed which overcome the above described deficiencies.
Objects of the Present Invention It is a general object o~ the present invention to provide a TDM~ cellular communication system which overcomes the above described shortcomings.
It is a more particular ob~ect o~ the present invention to provide a cell~lar communication system which increase~ the usage e~iciency of scan receivers in such systems by assigning radiotelephone calls to time partitions of the c211 sites in a frequency prioritized manner such that radiotelephone calls are concentrated within each fre~uency so as to reduce the number of ~requencies carrying radiotelephone calls.
An additional ob~ect o~ the prasent lnvention includes increasing the usage efficiency o~ scan receivers in a radiotelephone ~reguency hopping TDMA
cellular system by assigning radiotelephona calls to time partitions of the cell site~s freqùencies in a ~requency prioritized manner and by measuring radiotelephone call signals by the scan receiver in a delayed manner such that the amount of frequency programming to each scan receiver is minimized.
~!
- 4 - CE12r BriPf Descriptio of the Drawin~
The features of the present invention whiah are believed to be novel are set forth with partiaularity in the appended claims. ~he invention, together with further objects and advantages thereo~, may best be understood by making re~erence to the ~ollowing description taken together with th~ accompanying drawings, in which reference numerals identify the elements, and wherein:
Fig. la is a diagram of a cellular communication system including two base sites and their respective equipment, according to the present invention;
Fig. lb is an expanded diagram of the base site equipment 115 or 119 of Fig. la., according to thQ
present invantion:
Fig. 2 is a diagram illustrating a frequency assignment for the scan receiver 146 or 1~8 of F~g. lb, according to the present invention:
Fig. 3 is a flowchart illu~trating a frequency assignment for the scan receiver 146 or 148 of Fig. lb, according to the present invention;
Fig. 4 is a flowchart illustrating a switch controller technique for executing time slot and frequency as~ignments for the scan receiver 146 or 148 of Fig. lb, according to the present invention: and Fig. 5 is a flowchart illustrating an alternative ~requency assignment for the scan receiver 146 or 148 of Fig. lb, according to the present invention.
7~1~
- 5 - CE12r Detailed DPscri~ f~the Preferred _ bodiment The arrangement disclosed in this specification has particular use for handing-off radiotelephonQ calls between cells in a TDMA cellular telephone infrastructure. More particularly, the arrangement disclosed herein is directed to improving the usage efficiency o~ scan receivers with respect to channel assignements in such systems for call initiations and handoffs.
Fig. la illustrates a novel cellular system which includes base site eguipment 115 and 119 for two geographic radio frequency (R~) coverage area (cells) 110 and 112, respectively. For cell 110, the base site equipment 115 includes a set of base transceivers 114 and a base site (1) controller 116. For cell 112, the base rite equipment 119 includes a set o~ base transceivers 118 and a base site (2) controller 120 with substantially identical circui~ry as the base site eguipment 115.
For purposes of exemplifying a handoff operation according to the present invention, a radiotelephone unit 130 is depicted in transition from cell 110 to cell 112.
Overall control of the base ~ite equipment 115 and 119 is provided by a signal processing unit 121 of a cellular switch controller 122. ~he switch controller 122 also ir.cludes a digital switching network 123 for controlling the call switching operation between a public switched telephone network (PSTN) 131 and the base si~e equipment 115 and 119. A set of pulse code modulation tPCM) converters 125 are included in the cellular switch controller 122 for interfacing the system to the PSTN
131. For general details of a conventional cellular system, reference may be made to "Cellular Voice and Data Radiotelephone System", Labedz et. al., U.S. patent no.
7~ ~
- 6 - CE12r 4,654,8~7. For ~urther details o~ a conventional cellular switch controller, re~erence may be made to U.S.
Pat. No. ~,268,722, Li~ e~ al. Both o~ the above U.S.
patents are assigned to the same assignee.
In Flg. lb, the base site equipment 115 or 119 i5 shown in expanded ~orm. The radio portion o~ the base site e~uipment is conventional. It include~ a set of transmit antenna~ 132, a ~et o~ receive antenna~ 134, a transmitter-combiner 136, a receiver interface equipment 138, a tran ceiver 140 and audio path3 141 directed to/Prom tha switch controller 122 of Fig. la.
Transceiver functions such as ~requency programming, transmit keying, tran~mit power control, alarm and status monitoring, and message passing are controlled by a microcomputer 142 through a microcomputer inter~ace 144.
A conventional scan receiver 146 or 148 monitor~ th~
signal strength o~ radiotelephone tran~missions in ad~acent cells and provide~ an output 150 which i~ used by ~he microcomputer 142 to determine when radiotelephones in such ad~a¢ent cells are handof~
candidates. Measuring radiotelephone signal strength with scan receivers i~ typical in mo~t analog cellular systemR. For example, in U.S. Pat. No. 4,485,486, Webb e~ al., a scan receiver implementation ~or such a system is described. For ~urther details oP conventlonal base site equipment, re~erence may be made to U.S. Pat. No.
4,485,486. Both oP the above referenced U.S. patents are assigned to the same asslgnee.
According to the present lnvention, the microcomputer 142 also controls the scan receivers 1~5 and 148. The particular method o~ control, which i5 unique to the present invention, is discussed in more detail with Figs.
~2~
- 7 - CE12r 2, 3 and ~. An analog to digital converter (ADC) 152 :ls used to convert the outputs 150 provided by tha scan receivers 146 and 148 to digital form for analysis by the microcomputer 142.
Each scan raceiver 146 or 148 generates an additional (audio) output 154 which i~ used by a preamble detector 156 or 158 to detect the beginning of a radiotelephone transmission. In a TDMA cellular communication system, the radiotelephones are typically synchronized with the base site equipment at each of the cell sites. A
radiotelephone transmits and receive~ messages by accessing a timeslot of a particular frequency, as assigned by the base site equipment. Each message, received or transmitted, begins with a preamble consisting of a predeterminad signal pattern. For more detail, reference may be made to "A Digital FD/TDMA
System fox a New Generation", pages 41-46 of "Primer for the Future ... DIGITAL TECHNOLOGY", L.M. Ericsson Telephone Company, June, 1987. The pr~-amble detector 156 or 158 may implemented using a conventional multi-bit digital comparator circuit.
Accordingly, the preamble detector 156 or 158 detects the preamble of each radiotelephone message received by the respective scan receiver 146 or 148. After each such detection, the preamble detector 156 or 158 informs the microcomputer 142, via the microcomputer interface 144, so that ths microcomputer knows when the signal strength should be measured from the received data at the outputs 150 of the scan receivers. Measurements performed by the microcomputer 142 are stored in a database in a memory circuit 143.
12~7~
- 8 - CE12r The microcomputer 142 operation for the scan receiver 146 or 148 is illustrated in Fig. 2 and in the corresponding flowchart of Figure 3. The illustrations in Figs. 2 and 3 particularly involve the operation of a TDMA cellular communioation ~ystem in which radiotelephone frequency hopping i5 employed, i.e., where radiotelephones communicate on the system in a designated time slot while rotating between a predetermined group of frequencies. Such a system is described in more detail in "A Digital FD/TDMA System for a New Generation"~
supra.
The flowchart of FigO 3 begins at block 310 where the microcomputer establishes the frequency hopping patterns and groups for radiotelephone communication within the associated coverage area. Fig. 2 illustrates an example of a system frequency hopping group assignment, according to the present invention, for N groups in which M
frequencies per hopping pattern (group) are employed.
Each employed frequency include~ 8 time ~lots tTl ~
T8). In this example, the 8 time slots (Tl - T8) establish a set which is equal to 1 frame. There are a total of (N x M) frequencies used. A solid line 210, which rotates through each frequency in each group from left to right and top to bottom i8 depicted to represent the flow of the scan receiver through each time slot and each frequency. Mathematically, the scan receiver assignment changes from frequency fxy to frequency fx+l,y with X being reinitialized to 1 after the Mth fre~uency. A series of vertical dotted line~ 220, are depicted to illustxata the frequency transition for a hopping radiotelephone in a particular time slot of a group during communication.
From block 310, flow proceeds to block 312 where the frequency of the scan receiver is set to the first frequency of group 1 (fll of Fig. 2).
'7~l - g - CE12r At block 314, a software timer (internal to the microcomputer 144 of Fig. lb) is ~et to begin timing a time interval equal to the time requlred to receive 1 frame of data. This timer is used to limit the length of time that the scan receiver will r~main on any given freguency to receive data in a designated frameO
At block 316, tests are repeatedly perfo~med to determine if either the timer has timed out or if the preestablished preamble has been detected in the received signal. As previously discussed, each radiotelephone transmisslon is preceded by a predetermined data pattern dafining the preamble. However, although a transmission will be expected, there may not be a transmission on every time slot of a given frame.
If the preamble is detected before the timer times out, flow procaeds to block 318. At block 318, because the preamble has been detected, the microcomputer presumes that a valid radiotelephone transmission has been received. The quality of the data following the preamble is tested for signal strength and signal "integrity" (i.e., the data legibility or data bit error ratio) using conventional digital analysis methods. In addition, the microcomputer examines the data to determine the base station's unique identification code (to identify the radiotelephone's site), and determines in which time slot the transmission was made. The particular time slot can be determined from the local base equipment r~ference timing if the system has synchronized base stations.
If the system does not have synchronized base stations, the time slot can be determined by extracting time slot informatlon from the received message. E.g., the radiotelephone's unique identification (ID) code can be extracted from the preamble and passed to the - 10 - CE12r microcomputer which can then identify the time slot using a conventional memory look-up technique with the ID code as the address.
From block 318, flow proceeds to block 320 where the microcomputer's data base ia updated to indicate the presence o~ a radiotelephone transmission in the detected time slot, and the measurements for that transmission are stored accordingly. From block 320, flow returns to block 316 so that a transmission in the next time slot can be detected.
I~ the preamble is not detected before the timer times out, flow proceeds from block 316 to block 322 where a test is performed to determine if the scan receiver has just finished receiving data in tha frame of the last group. In Fig. 2, this test is satisfied after the scan receiver receives data from the eigh~h time slot of the Nth group.
If the scan receiver has not ~inished receiving data from the frame of the last group, flow proceeds from block 322 to block 324 where the scan receiver is assigned to the frequency of the next group. In Fig. 2, this is a horizontal mov~ along the solid line from the left to the right. From block 324, flow returns to block 314 so that the scan receiver can begin receiving data for a new frame.
If the scan receiver has finished receiving data for the frame of the last group, flow proceeds from block 322 to block 328 where a test is performed to determine if the scan receiver has completed receiving data from the frame of the last group. In Fig. 2, this test would comprise a determination as to whether or not the frequency being monitored is f~. If the scan receiver is not monitoring fre~uency fNM at this point, flow proceeds to block 330 where the scan receiver is assigned ~8 1 !
~ CE12r to the next ~requency of tha ~irst group. IP khe frequency is e~ual to ~NM at this point, ~low returns to block 312 where tha entire proce~s i~ reinitiated ~rom tha first ~requency o~ the first group.
As this process continuas, the microcomputer's data base, as indicated at ~lock 320, is continuously updated.
Because the data base i5 be1ng updated with measurements of signal quality and strength for any radiotelephone's trans~ission from an ad;acent ~ell, the switch controller (Fig la) is provided acc2ss with an up-to-date status of a radiotelephone's potential to be handed-o~ to the as~ociated call s$te.
This staku~ information can ba used in a conventional handof~ process such as the ones de~cribed ln U.S. Pat.
Nos. 4,485,486 (Webb et al.), 4,654,867 (Labedz) and 4,696,027 (Bonta et a~ ach assign~d to the same assignee. It should be pointed out, however, that because this information is immediately available to the switch controller, the switch controller does not have to raquest the base ~ite equipment at ad~acent calls to first perform the requisite monitoring ~or each hando~ candidate radiotelephone. The switch controller merely queries the ad~acent cell ~ite eguipment to provide the in~ormation already stored in the database. Alternatively, the ad~acent cell site equipment can continually provide this accumulated signal information to the switch controller to alleviate the extra step of having the switch controller first make the request. Using either implementation, this provides a signi~icant advantage over known system san monitoring techniques because it substantially reduces the time otherwise necessary to detexmine where and when to make a handoff.
Another aspect o~ the present invention involves the $?~
~2~
- 12 - CE12r manner in which con~unication frequencies (channels) are assigned at each of the cell sites. As indicated previously, each time a scan receiver is assigned a new frequency, an inherent delay occurs before the scan receiver can actually receive data on the new frequency.
In a frequency hopping TDMA cellular system, a significant amount of data can be missed by a scan receiver if thi~ delay becomes excessive.
To overcome this problem, the present invention employs a novel radiotelephone time slot/frequency assignment. Referring to Fig. 2, this asRignment involves selecting an open time slot from a group frame such that the group frames are filled one fram~ at a time, and that each group is filled before another group is filled.
For example, presume that at a particular time the base site targetted for a handoff includes two designated groups ~Gl and G2), and ~our corresponding frequencies (F11, F12, F21, F22). Further, at a given point in time presume that in the group frame Fll, radiotelephone calls are active in frames 1, 3, 5, 6, 7 and 8 in the group frame F12 radiotelephone calls are active in frames 1, 2 and 3: and in the group frames F21 and F22, there are no active radiotelephona calls.
According to the present invention, the first open time slot in this given frequency assignmant (for a radiotelephone candidate or for a radiotelephone call initiation? is the second time slot of the group frame designated Fll. Thus, the second time slot of the group frame designated Fl1 will be chosen.
The next radiotelephone call assignment at this site will be (presuming the same active calls as described earlier) the fourth time slot of the group frame designated Fl1. Once the entire frame F11 contains '7~
- 13 - CE12r active calls, time ~lot from frame F12 will ha chosen from left to right, and then time 810t~ ~rom F21 and then F22.
As radiotelephone calls are dropped or handed off to 5 adjacent cell sitas, time slots from the group ~rames (Fll, F12, F21, F22) will become free to enable additional radiotelephone call time slot assignments in a similar manner.
Additionally, tha present invention provides a method 10 O~ minimi~ing the a~ount of data passed between the base ~ites, while, at ths ~ame time, allowing aach bas2 site to ~ore effectively scan the active communication fre~uencies of a particular group. A~ each new group (comprising at least one time partitioned ~rams) i~
15 established for comm~!nlcation use at ~ach ba~ 6ite, a message is passed to the adjacent cell sites to inform them that the new group should be scan monitored. This allows ~he ~ystem to monitor aotivQ call , or those calls about to become active, without rQquiring that all 20 frequencies be scanned and w~thout re~u~ring in~tructions for scan monitoring to the ad~acent cell sites each time a new active call i8 establish~d. Similarly, a5 groups become unused (idle) a single m~esage ~s communicated to the ad-Jacent base ~ite~ to ~top scanning the unused 25 group.
In Fig. 4, a ~low chart illustrates an example of the r switch controller (Fig. la) directing a handoff from site 1 to site 2 (re~erring to Fig. la), according to ~he pxesent invention and con5i5tant with the previous 30 examples. The ~low chart b~gins at block 410 where a test is performed to datermine if there i5 a handoff candidate present at th~ site 1. If there i5 not a handoff candidate present, the procedure ends and similar tests are performed at another site~
. .
- 14 CE12r If a hando~f candidat~ is present a~ site 1, rlow proceeds from block 410 to block 420 where th~ 3witch controller requssts the relevent data base signal measurement lnformation for the radiotelephone ~rom the cell site that i~ ad~acent the host cell site (site 2).
As discussed previously ~with blocks 31~ and 320 of Fig.
3), each adjacenk cell site can instantaneously provide a report to the ~witch controller o~ the radiotelephones communicating in ad~acent cell sites. Thus, the switch controller inform~ site 2 of the frequency and time slot in which the radlotelephone handoff candidate is communicating (or alternatively informs site 2 of the radiotelephone 1 5 identi~ication number depending on site 2's data base methodology).
Using the reports from each of the ad~acent cell sites (~ite 2), at block 430 the switch controller d~termine~ the best cell ~lte in which the radiotelephone handoff candidate should communicate n~xt.
At block 440, the switch controller determines the firs~ open ~ima slot and ~requency at the target ~ite ~or the handof~ a signment. As previou~ly discussed, this entails filllng each group ~rame one frame at a time, one group at a tim~ 80 that tha ~can receiver will not be exceq6ively burdensd with changing ~requenciea to monitor an entir2 group ~ramQ gerving merely one or two active calls.
At block 450, the switch controller in~orms the base site equipment of the assignment to e~fect the handoff at the target cell ~ite.
Alternatively, since all time ~lot and ~requency information is pre~ent at each cell site, the cell ~ite can perform the determination indicated at block 440 and inform the switch controller of the first open time slot and frequency.
~ 15 - CE12r In yet another a~peak of the present invention, u~aqe e~ficiency of the scan receiver can be improved by slightly modifying the ~teps illustrated in ~ig. 3 to delay the scan receiver within each group ~or ~ ~rames be~ore the scan receiver moves to the next group. Figure 5 is illustxatiYe.
In Fig. 5, the flow chart o~ Fi~. 3 is shown in modified form to include ~our additional steps, depicted as blocks 5~3, 517, 519 and 521. Once again, the flow o~
the steps depicted in Fig. 5 will be illustrated using F~g. 2. Once the ~reguency hopping pattern~ ~or all groups have been established (block 310), and the scan receiver is tuned to the ~irst ~requency (Fll) o~ group 1 (block 513), a counting variable "COUNT" is set equal to M, where M is the number o~ frequencies in each group.
From block 513 ~low proceeds to block 314 where the the timer i8 initiated, and the test to determine i~ tha timer has expired or a preamble has been detected ~ollows at block 316.
If the preamble i8 detected, flow proceeds through block 318 and block 320 to update the data base with the corresponding signal measurements.
When the timer expires, ~low proceeds from block 316 to block 417 where COUNT is decremented.
At block 519, a test ls per~ormed to determine if COUNT haq been decremented to zero. If COUNT has not been decremented to zero, ~low proceeds from block 519 to block 521 where the microcomputer reinitilizss the timer so that the scan receiver will continue to receive another eight time slots ~rom the ~rame of the present ~requency. This loop, establlshed at blocks 316, 517, 519 and 521, cycle~ M time~. For example, i~ M equals 3, the scan xeceiver will remain at the same frequency (Fll) until it receives three ~rames.
~;
~9~
- 16 -- CE12r Once the COUNT variable has been decremanted to zero, ~low proceeds from block 519 to block 322 wher~ the scan receiver frequency assignment continues as descrihed with Fig. 3.
Delaying the scan receiver such that it continues to receive a single frequency ~or more than one frame can provide a significant advantage in a frequency hopping TDMA system. Referring to group 1 of Fig~ 2, presuming that M equals 3 and there are aight active calls in Fll, Fl2 and Fl3, then after receiving threa frames at frequency Fll, the scan receiver will hav received transmissions from a total o~ 24 mohiles without having to incur a single delay. This is because its frequency was never changed. In this manner, the scan receiver receives M frames of data at Fll, then M frames of data at F2l, then M frames of data at F3l, and then returns to group 1 to receive M frames of data at Fl2, then M frame9 of data at F22~ ~tc-The scan receiver preferably rotates between frequencies of each group, rather than always monitoringthe same group frequency in the rotation, so that more accurate signal measurements can be made without introducing problems such as fading at a single ~requency. For example, a radiotelephone call which is active in time slot l of group l will have its transmitted signal measured three times in fre~lency ll, then three times in frequency 12 then three times in frequency 13 before the scan receiver returns to frequency 11 for additional measurements.
It should be pointed out that where M i9 large, as the scan receiver moves from one frequency hopping group to another (for example, from group l to group 2), a substantia! number of signal measurements from active calls will be missed. In certain situations, this number ~Z~7~3~
- 17 - CE12r may become unacceptable to overall system operation. For this type of situatlon, a second scan receiver, as illustrated in ~ig. lb, is employed to reduce thi~
problem by a factor of 50%. Tha second scan receiver can be controlled in a manner identical to that depicted in Fig. 5, except that its individual frequency as~ignments follows tha first scan receiver's individual frequency assignments by a time lag equal to one-half o~ the time it takes for a single scan receiver to cycle through each frequency, i.e., to flow from Fll, along the solid line 210 o~ Fig. 2 through FNM. Additional scan receiYer3 can be included to further reduce this problem.
It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope thereof.
What is claimed is:
Using the reports from each of the ad~acent cell sites (~ite 2), at block 430 the switch controller d~termine~ the best cell ~lte in which the radiotelephone handoff candidate should communicate n~xt.
At block 440, the switch controller determines the firs~ open ~ima slot and ~requency at the target ~ite ~or the handof~ a signment. As previou~ly discussed, this entails filllng each group ~rame one frame at a time, one group at a tim~ 80 that tha ~can receiver will not be exceq6ively burdensd with changing ~requenciea to monitor an entir2 group ~ramQ gerving merely one or two active calls.
At block 450, the switch controller in~orms the base site equipment of the assignment to e~fect the handoff at the target cell ~ite.
Alternatively, since all time ~lot and ~requency information is pre~ent at each cell site, the cell ~ite can perform the determination indicated at block 440 and inform the switch controller of the first open time slot and frequency.
~ 15 - CE12r In yet another a~peak of the present invention, u~aqe e~ficiency of the scan receiver can be improved by slightly modifying the ~teps illustrated in ~ig. 3 to delay the scan receiver within each group ~or ~ ~rames be~ore the scan receiver moves to the next group. Figure 5 is illustxatiYe.
In Fig. 5, the flow chart o~ Fi~. 3 is shown in modified form to include ~our additional steps, depicted as blocks 5~3, 517, 519 and 521. Once again, the flow o~
the steps depicted in Fig. 5 will be illustrated using F~g. 2. Once the ~reguency hopping pattern~ ~or all groups have been established (block 310), and the scan receiver is tuned to the ~irst ~requency (Fll) o~ group 1 (block 513), a counting variable "COUNT" is set equal to M, where M is the number o~ frequencies in each group.
From block 513 ~low proceeds to block 314 where the the timer i8 initiated, and the test to determine i~ tha timer has expired or a preamble has been detected ~ollows at block 316.
If the preamble i8 detected, flow proceeds through block 318 and block 320 to update the data base with the corresponding signal measurements.
When the timer expires, ~low proceeds from block 316 to block 417 where COUNT is decremented.
At block 519, a test ls per~ormed to determine if COUNT haq been decremented to zero. If COUNT has not been decremented to zero, ~low proceeds from block 519 to block 521 where the microcomputer reinitilizss the timer so that the scan receiver will continue to receive another eight time slots ~rom the ~rame of the present ~requency. This loop, establlshed at blocks 316, 517, 519 and 521, cycle~ M time~. For example, i~ M equals 3, the scan xeceiver will remain at the same frequency (Fll) until it receives three ~rames.
~;
~9~
- 16 -- CE12r Once the COUNT variable has been decremanted to zero, ~low proceeds from block 519 to block 322 wher~ the scan receiver frequency assignment continues as descrihed with Fig. 3.
Delaying the scan receiver such that it continues to receive a single frequency ~or more than one frame can provide a significant advantage in a frequency hopping TDMA system. Referring to group 1 of Fig~ 2, presuming that M equals 3 and there are aight active calls in Fll, Fl2 and Fl3, then after receiving threa frames at frequency Fll, the scan receiver will hav received transmissions from a total o~ 24 mohiles without having to incur a single delay. This is because its frequency was never changed. In this manner, the scan receiver receives M frames of data at Fll, then M frames of data at F2l, then M frames of data at F3l, and then returns to group 1 to receive M frames of data at Fl2, then M frame9 of data at F22~ ~tc-The scan receiver preferably rotates between frequencies of each group, rather than always monitoringthe same group frequency in the rotation, so that more accurate signal measurements can be made without introducing problems such as fading at a single ~requency. For example, a radiotelephone call which is active in time slot l of group l will have its transmitted signal measured three times in fre~lency ll, then three times in frequency 12 then three times in frequency 13 before the scan receiver returns to frequency 11 for additional measurements.
It should be pointed out that where M i9 large, as the scan receiver moves from one frequency hopping group to another (for example, from group l to group 2), a substantia! number of signal measurements from active calls will be missed. In certain situations, this number ~Z~7~3~
- 17 - CE12r may become unacceptable to overall system operation. For this type of situatlon, a second scan receiver, as illustrated in ~ig. lb, is employed to reduce thi~
problem by a factor of 50%. Tha second scan receiver can be controlled in a manner identical to that depicted in Fig. 5, except that its individual frequency as~ignments follows tha first scan receiver's individual frequency assignments by a time lag equal to one-half o~ the time it takes for a single scan receiver to cycle through each frequency, i.e., to flow from Fll, along the solid line 210 o~ Fig. 2 through FNM. Additional scan receiYer3 can be included to further reduce this problem.
It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope thereof.
What is claimed is:
Claims (21)
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED
AS FOLLOWS:
1. A time-division-multiple-access (TDMA) radiotelephone cellular communication system having base site equipment at at least one site with an associated radiotelephone communication coverage area and having a switch controller for connecting radiotelephone communication, and wherein the base site equipment employs a plurality of frequencies which are used for radiotelephone communication in a time partitioned manner, comprising:
monitoring means coupled with the base site equipment for monitoring a signal quality parameter of at least one radiotelephone call on the system;
processing means for maintaining a record of which frequencies and which time partitions at the base site equipment are being utilized for radiotelephone communication; and assigning means responsive to said processing means and said monitoring means, for assigning radiotelephone calls to time partitions of the base site equipment frequencies based on a frequency prioritization technique that concentrates radiotelephone calls within each frequency.
- 19 - CE12r
monitoring means coupled with the base site equipment for monitoring a signal quality parameter of at least one radiotelephone call on the system;
processing means for maintaining a record of which frequencies and which time partitions at the base site equipment are being utilized for radiotelephone communication; and assigning means responsive to said processing means and said monitoring means, for assigning radiotelephone calls to time partitions of the base site equipment frequencies based on a frequency prioritization technique that concentrates radiotelephone calls within each frequency.
- 19 - CE12r
2. A TDMA radiotelephone cellular communication system, according to claim 1, wherein the monitoring means includes means for monitoring the signal strength of said at least one radiotelephone call on the system.
3. A TDMA radiotelephone cellular communication system, according to claim 1, wherein the monitoring means includes means for monitoring the signal integrity of said at least one radiotelephone call on the system.
4. A TDMA radiotelephone cellular communication system, according to claim 1, wherein the monitoring means includes means for monitoring said at least one radiotelephone call in the base site equipment's coverage area.
5. A time-division-multiple-access (TDMA) radiotelephone cellular communication system having at least first base site equipment and second base site equipment with associated radiotelephone communication coverage areas, wherein each base site equipment employs a plurality of frequencies which are used for radiotelephone communication in time partitioned frames, and wherein the system has identified a radiotelephone handoff candidate within the coverage area of the first base site equipment, comprising:
monitoring means included with the second base site equipment for monitoring frequencies from the first base site equipment to obtain signal quality parameters of radiotelephone calls, including the radiotelephone handoff candidate, active in the first base site equipment's coverage area;
processing means for maintaining a record of which frequencies and which time partitions at the second base site equipment are being utilized for radiotelephone communication; and assigning means, responsive to said processing means and said monitoring means, for effecting a handoff to the coverage area of the second base site equipment by assigning the radiotelephone handoff candidate to a time partition in one of the second base site equipment frequencies based on a frequency prioritization technique that concentrates radiotelephone calls within each frequency.
- 21 - CE12r
monitoring means included with the second base site equipment for monitoring frequencies from the first base site equipment to obtain signal quality parameters of radiotelephone calls, including the radiotelephone handoff candidate, active in the first base site equipment's coverage area;
processing means for maintaining a record of which frequencies and which time partitions at the second base site equipment are being utilized for radiotelephone communication; and assigning means, responsive to said processing means and said monitoring means, for effecting a handoff to the coverage area of the second base site equipment by assigning the radiotelephone handoff candidate to a time partition in one of the second base site equipment frequencies based on a frequency prioritization technique that concentrates radiotelephone calls within each frequency.
- 21 - CE12r
6. A TDMA radiotelephone cellular communication system, according to claim 5, wherein said assigning means includes means for selecting a first group of frequencies which is considered for radiotelephone call assignments before other frequencies are considered for such assignments.
7. A TDMA radiotelephone cellular communication system, according to claim 6, wherein said assigning means further includes means for selecting a second group of frequencies which is considered for radiotelephone call assignments if the first group of frequencies cannot carry another radiotelephone call.
8. A TDMA radiotelephone cellular communication system, according to claim 5, wherein said monitoring means includes means for alternately monitoring a second frequency from the first base site equipment.
9. A TDMA radiotelephone cellular communication system, according to claim 8, wherein said monitoring means further includes means for monitoring each frequency for a plurality of time partitioned frames before monitoring another frequency.
10. A switch controller for use in a time-division-multiple-access (TDMA) radiotelephone cellular communication system having a plurality of cell sites including a first cell site, wherein each cell site has associated base site equipment and corresponding radiotelephone communication coverage areas and each cell site employs a plurality of frequencies which are used for radiotelephone communication in a time partitioned manner, comprising:
a) coupling means for communicating with the base site equipment at each of the cell sites;
b) determination means for determining that there is a radiotelephone handoff candidate present in the first cell site coverage area;
c) means, responsive to said determination means, for selecting a target cell site for the radiotelephone at a cell site which is adjacent to the first cell site;
d) means for selecting a frequency and time slot from the target cell site based on a frequency prioritization technique that concentrates radiotelephone calls within each frequency; and e) means for assigning the selected frequency and time slot to effect the handoff at the target cell site.
- 23 - CE12r
a) coupling means for communicating with the base site equipment at each of the cell sites;
b) determination means for determining that there is a radiotelephone handoff candidate present in the first cell site coverage area;
c) means, responsive to said determination means, for selecting a target cell site for the radiotelephone at a cell site which is adjacent to the first cell site;
d) means for selecting a frequency and time slot from the target cell site based on a frequency prioritization technique that concentrates radiotelephone calls within each frequency; and e) means for assigning the selected frequency and time slot to effect the handoff at the target cell site.
- 23 - CE12r
11. A switch controller, according to claim 10, wherein said selecting means includes means for selecting a first group of frequencies which is considered for radiotelephone call assignments before other frequencies are considered for such assignments.
12. A switch controller, according to claim 11, wherein said selecting means further includes means for selecting a second group of frequencies which is considered for radiotelephone call assignments if the first group of frequencies cannot carry another radiotelephone call.
13. A base site controller for use in a time-division-multiple-access (TDMA) cellular radiotelephone communication system having a plurality of cell sites including a first cell site, wherein each cell site has associated base site equipment and corresponding radiotelephone communication coverage areas and each cell site employs a plurality of frequencies which are used for radiotelephone communication in time partitioned frames, said base site controller at each cell site comprising:
monitoring means coupled with the base site equipment for monitoring frequencies to obtain signal quality parameters of radiotelephone communications active on the system;
processing means for maintaining a record of which frequencies and which time partitions at the base site equipment are being utilized for radiotelephone communication; and means, responsive to said processing means and to said monitoring means, for assigning radiotelephone calls to time partitions of the base site equipment frequencies based on a frequency prioritization technique that concentrates radiotelephone calls within each frequency.
- 25 - CE12r
monitoring means coupled with the base site equipment for monitoring frequencies to obtain signal quality parameters of radiotelephone communications active on the system;
processing means for maintaining a record of which frequencies and which time partitions at the base site equipment are being utilized for radiotelephone communication; and means, responsive to said processing means and to said monitoring means, for assigning radiotelephone calls to time partitions of the base site equipment frequencies based on a frequency prioritization technique that concentrates radiotelephone calls within each frequency.
- 25 - CE12r
14. A base site controller, according to claim 13, wherein said assigning means includes means for selecting a first group of frequencies which is considered for radiotelephone call assignments before other frequencies are considered for such assignments.
15. A base site controller, according to claim 14, wherein said assigning means further includes means for selecting a second group of frequencies which is considered for radiotelephone call assignments if the first group of frequencies cannot carry another radiotelephone call.
16. A base site controller, according to claim 14, further including means for alternately monitoring the frequencies within said first group of frequencies.
17. A base site controller, according to claim 13, wherein said monitoring means further includes means for monitoring each frequency for a plurality of time partitioned frames before monitoring another frequency.
18. A base site controller for use in a radiotelephone frequency-hopping time-division-multiple-access (TDMA) cellular radiotelephone communication system having a plurality of cell sites including a first cell site, wherein each cell site has associated base site equipment and corresponding radiotelephone communication coverage areas and each cell site employs a plurality of frequencies which are used for radiotelephone communication in time partitioned frames, said base site controller at each cell site comprising:
monitoring means coupled with the base site equipment for monitoring a signal quality parameter of radiotelephone communications in adjacent cell sites;
means for storing records of which time partitions and frequencies are carrying radiotelephone communications; and processing means, responsive to said means for storing and coupled with said monitoring means, for programming said monitoring means to monitor selected communication frequencies in adjacent cell sites such that said monitoring means continuously monitors one of said selected frequencies for a plurality of time partitioned frames.
monitoring means coupled with the base site equipment for monitoring a signal quality parameter of radiotelephone communications in adjacent cell sites;
means for storing records of which time partitions and frequencies are carrying radiotelephone communications; and processing means, responsive to said means for storing and coupled with said monitoring means, for programming said monitoring means to monitor selected communication frequencies in adjacent cell sites such that said monitoring means continuously monitors one of said selected frequencies for a plurality of time partitioned frames.
19. A base site controller for use in a radiotelephone frequency-hopping time-division-multiple-access (TDMA) cellular radiotelephone communication system having a plurality of cell sites including a first cell site, wherein each cell site has associated base site equipment and corresponding radiotelephone communication coverage areas and each cell site employs a plurality of frequencies which are used for radiotelephone communication in time partitioned frames, said base site controller at each cell site comprising:
monitoring means coupled with the base site equipment for monitoring a signal quality parameter of radiotelephone calls active on the system;
processing means,coupled with said monitoring means, and including:
means for programming said monitoring means to monitor selected frequencies used for carrying frequency-hopping radiotelephone calls in adjacent cell sites such that said monitoring means continuously measures said selected frequencies for a plurality of time partitioned frames, and means for assigning radiotelephone calls to time partitioned frames of the base site equipment frequencies in a frequency prioritized manner such that radiotelephone calls are concentrated within each frequency.
monitoring means coupled with the base site equipment for monitoring a signal quality parameter of radiotelephone calls active on the system;
processing means,coupled with said monitoring means, and including:
means for programming said monitoring means to monitor selected frequencies used for carrying frequency-hopping radiotelephone calls in adjacent cell sites such that said monitoring means continuously measures said selected frequencies for a plurality of time partitioned frames, and means for assigning radiotelephone calls to time partitioned frames of the base site equipment frequencies in a frequency prioritized manner such that radiotelephone calls are concentrated within each frequency.
20. A time-division-multiple access (TDMA) radiotelephone cellular communication system having base site equipment at at least one site with an associated radiotelephone communication coverage area and having a switch controller for connecting radiotelephone communication, and wherein the base site equipment employs a plurality of frequencies which are used for radiotelephone communication in a time partitioned manner, comprising:
monitoring means coupled with the base site equipment for monitoring a signal quality parameter of at least one radiotelephone call on the system;
processing means for maintaining a record of which frequencies and which time partitions at the base site equipment are being utilized for radiotelephone communication;
means, responsive to said processing means and said monitoring means,for instructing base site equipment to begin monitoring frequencies as they become used for radiotelephone calls.
- 29 - CE12r
monitoring means coupled with the base site equipment for monitoring a signal quality parameter of at least one radiotelephone call on the system;
processing means for maintaining a record of which frequencies and which time partitions at the base site equipment are being utilized for radiotelephone communication;
means, responsive to said processing means and said monitoring means,for instructing base site equipment to begin monitoring frequencies as they become used for radiotelephone calls.
- 29 - CE12r
21. A TDMA radiotelephone cellular communication system, according to claim 20, further including means, responsive to said processing means and said monitoring means, for instructing base site equipment to stop monitoring frequencies as they become idle.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/158,960 US4866710A (en) | 1988-02-22 | 1988-02-22 | Reuse groups for scan monitoring in digital cellular systems |
| US158,960 | 1988-02-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1299781C true CA1299781C (en) | 1992-04-28 |
Family
ID=22570474
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000584960A Expired - Lifetime CA1299781C (en) | 1988-02-22 | 1988-12-05 | Reuse groups for scan monitoring in digital cellular systems |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4866710A (en) |
| EP (1) | EP0329997B1 (en) |
| JP (1) | JP2540074B2 (en) |
| AT (1) | ATE122525T1 (en) |
| CA (1) | CA1299781C (en) |
| DE (1) | DE68922512T2 (en) |
| FI (1) | FI89994C (en) |
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-
1988
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- 1988-12-05 CA CA000584960A patent/CA1299781C/en not_active Expired - Lifetime
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1989
- 1989-02-01 FI FI890472A patent/FI89994C/en not_active IP Right Cessation
- 1989-02-03 DE DE68922512T patent/DE68922512T2/en not_active Expired - Fee Related
- 1989-02-03 AT AT89101892T patent/ATE122525T1/en not_active IP Right Cessation
- 1989-02-03 EP EP89101892A patent/EP0329997B1/en not_active Expired - Lifetime
- 1989-02-22 JP JP1042890A patent/JP2540074B2/en not_active Expired - Fee Related
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| FI890472A (en) | 1989-08-23 |
| DE68922512T2 (en) | 1996-01-11 |
| DE68922512D1 (en) | 1995-06-14 |
| FI890472A0 (en) | 1989-02-01 |
| US4866710A (en) | 1989-09-12 |
| JP2540074B2 (en) | 1996-10-02 |
| EP0329997B1 (en) | 1995-05-10 |
| JPH01251929A (en) | 1989-10-06 |
| EP0329997A2 (en) | 1989-08-30 |
| EP0329997A3 (en) | 1990-11-22 |
| FI89994B (en) | 1993-08-31 |
| FI89994C (en) | 1993-12-10 |
| ATE122525T1 (en) | 1995-05-15 |
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