Adaptive Channel Access Method Adaptives Kanalzugriffverfahren Méthode D’Accès À Des Canaux De Façon Adaptative

(19) &

(11) EP 1 168 873 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.: of the grant of the patent: H04W 4/00 (2009.01) H04B 7/26 (2006.01) 18.03.2009 Bulletin 2009/12

(21) Application number: 01114561.2

(22) Date of filing: 18.06.2001

(54) Adaptive channel access method Adaptives Kanalzugriffverfahren Méthode d’accès à des canaux de façon adaptative

(84) Designated Contracting States: • O’Dea, Robert J. AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU Fort Lauderdale, MC NL PT SE TR Florida 33305 (US) • Palacios, Juan C. (30) Priority: 19.06.2000 US 596442 Plantation, Florida 33324 (US) (43) Date of publication of application: • Chen, Priscilla L. 02.01.2002 Bulletin 2002/01 Sunrise, Florida 33351 (US) (73) Proprietor: MOTOROLA, INC. Schaumburg, IL 60196 (US) (74) Representative: Cross, Rupert Edward Blount et al Boult Wade Tennant (72) Inventors: Verulam Gardens • Perkins, Matthew R. 70 Gray’s Inn Road Sunrise, London WC1X 8BT (GB) Florida 33351 (US) • Allen, Vernon A. (56) References cited: Sunrise, FR-A- 2 780 593 GB-A- 2 319 436 Florida 33323 (US) US-A- 4 870 408 US-A- 5 369 783

Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 1 168 873 B1

Printed by Jouve, 75001 PARIS (FR) 1 EP 1 168 873 B1 2

Description defining the features of the invention that are regarded as novel, it is believed that the invention will be better [0001] This invention relates in general to radio com- understood from a consideration of the following descrip- munication systems, and more particularly, to a method tion in conjunction with the drawing figures, in which like for providing an adaptive channel access scheme in a 5 reference numerals are carried forward. radio communication system. [0005] The present invention utilizes communication statistics to minimize collision occurrence during channel BACKGROUND access. This requires that connection statistics be tabulated and recorded, either by each device (radios) or a [0002] In shared-channel environments that incorpo- 10 master device (central radio communication resource), rate channel-access devices, two or more devices may for the purpose of reducing simultaneous channel ac- transmit data simultaneously, causing collisions. Most cess. The results of these tabulations are used to group communication protocols use a form of random back- off radio users into subgroups according to the desired com- protocol to resolve these collisions, which ultimately re- munication statistic. The radios within a subgroup then sults in a communication delay. FR2780593 describes 15 share a communication channel, separated by time or the gathering of statistical values associated with com- frequency from the communication channels allocated munication channels to ensure that a determined fraction to other subgroups, to access the communication system of the values are above the statistical value. This inven- in an organized fashion such that channel-access colli- tion seeks to minimize the number of collisions that occur sions are minimized. The recorded connection statistics during simultaneous channel access requests, and im- 20 could be based on, but are not limited to, average channel prove throughput and delay for any given channel that usage, number of channel accesses per unit time, device may experience contention. US 4870,408 describes a priority, average on time of the devices, peak usage pe- method for dynamically allocating data channels on a riods, or averaged receive signal strength. trunked communication system where an offset seed pa- [0006] Referring now to FIG. 1, there is shown a sim- rameter is added to statistically redistribute device25 plified diagram of a wireless communication system such groups across available data channels. as a trunked radio system that can be used with the present invention’s adaptive channel access scheme. BRIEF DESCRIPTION OF THE DRAWINGS The communication system includes a system or dispatch controller 102, at least one base site 104, and a [0003] The features of the present invention, which are 30 plurality of communication units 1-9. Base site 104 pro- believed to be novel, are set forth with particularity in the vides communication service to a corresponding service appended claims. The invention, together with further ob- coverage area 120. The base site 104 could as one spe- jects and advantages thereof, may best be understood cific example comprise an "iDEN" Enhanced Base Trans- by reference to the following description, taken in con- ceiver Site and the system controller 102 could comprise junction with the accompanying drawings, in the several 35 an ’iDEN’ Dispatch Application Processor both manufac- figures of which like reference numerals identify like el- tured by Motorola Inc. The present invention can be im- ements, and in which: plemented using many different types of communication systems. In the preferred embodiment, the base site 104 FIG. 1 illustrates a simplified communication system preferably supports one or more trunking communication diagram in accordance with the present invention. 40 platforms (modes), such as FDMA (frequency division FIG. 2 shows subgroup time slots embedded in a multiple access), TDMA (time division multiple access), control string in accordance with the present inven- CDMA (code division multiple access), etc. In the pre- tion. ferred embodiment, the communication system compris- FIG. 3 illustrates the talk time and average talk time es a synchronized radio communication system such as information that is stored in the table shown in FIG. 45 a TDMA mode system. 4 in accordance with the invention. [0007] In a typical trunked system, requests for a re- FIG. 4 shows a scenario and possible contention al- source such as a channel (or time slot in TDMA, etc.) are gorithm table in accordance with the invention. made by the communication devices or radios 1-9 to the FIG. 5 shows a subgroup cumulative score table in system controller 102 via a control channel or by sending accordance with the invention. 50 control signals over one or more of the working channels. FIG. 6 illustrates the subgroup location of the differ- The system controller 102 then assigns available com- ent radio users in different intervals of time in accord- munication resources from the system (a channel, time ance with the invention. slots, etc.) to the requesting radio. [0008] When a particular radio, such as radio 1 wants DETAILED DESCRIPTION OF THE PREFERRED EM- 55 to initiate a call with one or more other radios, the user BODIMENT of radio 1 presses and holds his push-to-talk (PTT) switch. The system controller 102 then allocates an in- [0004] While the specification concludes with claims bound resource such as channel (IB1) 112 to radio 1.

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System controller 102 also allocates an outbound re- to reduce the likelihood of a subgroup timeslot collision. source, channel (OB) 118, for transmitting audio or other If, after separation, one subgroup has a cumulative talk- information to all radios affiliated with the call. time score that is much higher than that of another sub- [0009] To illustrate how the contention algorithm of the group, lower talk-time scoring users may be assigned to present invention works, an example of a channel access 5 different subgroups in order to minimize the cumulative in a Public Mobile Radio (PMR) system, such as system talk-time of every subgroup. This, in turn, gives every 100, in which there are nine users attempting to gain user the best probability of accessing a control channel access to the control channel will be discussed. In this time slot without contention. example, the control channel or control string has been [0015] In the particular example shown in FIG. 4, call divided in time to accommodate three groups of users 10 initiation is established at t=0. As previously stated, the as shown in FIG. 2. The three slots include User Group nine radio users are immediately subdivided into three I (UGI) 202, User Group II (UGII) 204 and User Group III subgroups as shown in FIG. 4 into UGI 402, UGII 404 (UGIII) 206. and UGIII 406 (shown using different crosshatch pat- [0010] In this example, a particular statistic, average terns). At time t=1, radio users 1, 3, 5 and 8 accumulate channel usage, translates to a user’s average talk-time 15 talk-time statistics. Since radio users 1 and 3 are in the and is used as the table metric for the preferred embod- same talkgroup and accumulated two of the highest talk iment, although other statistics can be used. Upon sys- time scores, the contention algorithm will attempt to sep- tem initiation, the nine radios are divided into three sub- arate them. In this case, user 1 is moved out of UGI 402 groups that each contains three radios. The initial group- to UGIII 406 and radio 7 is moved to the open spot in ing can either be random or predetermined depending 20 UGI 402. At time t=2, more radio users accumulate talk- on the particular system design. These initial groupings time statistics which results in more subgroup realloca- can and will be modified over time depending on the sta- tion as noted. During this time interval, users 6 and 7 tistics gathered over time. These initial subgroups are switch groups. The above reallocation procedure will UGI 202, UGII 204 and UGIII 206 and comprise radios: continue as long as the system is active. However, in radios 1-3, radios 4-6, and radios 7-9, respectively. As 25 other system designs the reallocation and statistic gath- explained earlier, these radios are only permitted to ac- ering can be performed only during predetermined peri- cess the control channel during their respective subgroup ods of time (e.g., peak system usage times, etc.). The timeslot (UGI, UGII or UGIII) and they may not use a reallocation and statistics gathered can also be reset dur- timeslot that is dedicated for another subgroup. ing periodically either at predetermined times, or by a [0011] After the system is initialized, the contention al- 30 central system device, such as system controller 102. gorithm periodically tabulatesthe averagetalktime or oth- [0016] In FIG. 5, there are shown cumulative talktime er statistic in use for each user and for each subgroup, scores for each of the time intervals for UGI 502, UGII and determines whether the subgroups should be reor- 504 and UGIII 506. In this example, it can be seen that ganized based on the results. As mentioned before, this the cumulative talk time scores are more nearly equal at tabulation can be performed by a central resource, such 35 t=9 than they would have been if the groups were not as system controller 102 or by each of the individual ra- reorganized. In FIG. 6, there is shown the radio user dios 1-9 in the system. System controller 102 and/or ra- grouping into UGI 602, UGII 604 and GUIII 606 over each dios 1-9 can perform the tabulation by monitoring the of the noted time intervals. system activity in order to collect the particular statistic [0017] While the preferred embodiments of the inven- that is key to the channel access scheme. 40 tion have been illustrated and described, it will be clear [0012] FIG. 4 illustrates an example of tabulated talk- that the invention is not so limited. Numerous modifica- time statistics for a group of radio users. Radios 1-9 are tions, changes, variations, substitutions and equivalents represented by the table rows 408 and the table columns will occur to those skilled in the art. By maintaining com- represent the results of the algorithm calculations at dif- munication statistics on the radio users of a shared radio ferent periods of time. 45 communication system, channel access collisions can [0013] As shown in FIG. 3, the upper triangle 302 of be minimized. In the preferred embodiment, by grouping each table entry in FIG. 4 contains a number that repre- the radios 1-9 in the system 100 into different subgroups sents each user’s instantaneous talk-time score (higher based on their collected statistical information, channel talk-time scores correspond to longer talk times) which access contentions are minimized. The radios 1-9 are is used to calculate each users average talk-time score 50 preferably sub-grouped so that the chances of two ran- shown in the lower triangle 304 of each table entry in domly selected members of a particular subgroup ac- FIG. 4. The three highest average talk-time scores of cessing the system 100 at the same time are minimized each algorithm tabulation are printed in bold face for each based on the collected statistics. of the time periods. Equal talk time scores can result in more than three users having the three highest average 55 talk time scores, as illustrated in time period 1. Claims [0014] The users that have the highest talk- time scores at a given tabulation interval are separated by subgroups 1. A method for accessing a radio communication sys-

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tem having a plurality of radio devices (1-9), com- periods of time. prising the steps of: 6. A method as defined in claim 5 wherein the radio (a) separating the plurality of radio devices (1-9) communication system comprises a time division into two or more groups (202, 204, 206), wherein 5 multiple access radio communication system. the radio devices (1-9) within a group (202, 204, 205) share a communication channel that is dif- 7. A method as defined in claim 1 or 5, wherein steps ferent to the communication channel allocated (b) and (c) are repeated periodically. to the other group or communication channels allocated to the other groups of radio devices 10 8. A method as defined in claim 1 or 5, wherein the (b) gathering a communication connection sta- communication connection statistic in step (b) is tistic on the plurality of radio devices (1-9) char- gathered by a central radio communication system acterised by resource. (c) determine whether the two or more groups should be reconfigured based on the gathered 15 9. A method as defined in claim 1 or 5, wherein the communication statistics and communication connection statistic in step (b) is (d) when a determination is made that the two gathered by each of the plurality of radio devices or more groups should be reconfigured, recon- (1-9). figuring the grouping of radio devices (1-9) based on the communication connection statis- 20 10. A method as defined in claim 1 or 5, wherein steps tic gathered in step b, wherein the communica- (b) and (c) are performed at predetermined periods tion connection statistics are used to determine of time. the reconfigured radio device groupings and wherein the radio device within a reconfigured group share a communication channel that is 25 Patentansprüche different to the communication channel allocated to the other group or communication chan- 1. Verfahren zum Zugriff auf ein Funkkommunikations- nels allocated to the other groups of radio de- system, welches eine Vielzahl von Funkvorrichtun- vices. gen (1-9) aufweist, wobei das Verfahren die folgen- 30 den Schritte umfasst: 2. A methodas defined in claim1, further compromising the step of: (a) Trennen der Vielzahl von Funkvorrichtungen (1-9) in zwei oder mehr Gruppen (202, 204, (d) allowing access to the radio communication 206), wobei sich die Funkvorrichtungen (1-9) in- system based on the grouping of the radio de- 35 nerhalb einer Gruppe (202, 204, 205) einen vices (1-9). Kommunikationskanal teilen, welcher sich von dem der anderen Gruppe zugeordneten Kom- 3. A method as defined in claim 1, wherein the com- munikationskanal oder den den anderen Grup- munication connection statistic gathered in step (b) pen von Funkvorrichtungen zugeordneten Kom- comprises one of the following: the average channel 40 munikationskanälen unterscheidet; usage by each of the plurality of radio devices (1-9), (b) Erstellung einer Kommunikationsverbin- the number of channel accesses per unit time by dungsstatistik über die Vielzahl von Funkvor- each of the plurality of radio devices (1-9), the priority richtungen (1-9), gekennzeichnet durch: of each of the plurality of radio devices (1-9) or the (c) Bestimmung, ob die zwei oder mehr Gruppen average received signal strength of each of the plu- 45 basierend auf der erstellten Kommunikations- rality of radio devices (1-9). statistik neu konfiguriert werden sollten; und (d) sobald eine Entscheidung getroffen worden 4. A method as defined in claim 1, wherein the two or ist, dass die zwei oder mehr Gruppen neu kon- more groups of radio devices (1-9) established in figuriert werden sollten, Neukonfiguration der step (a) can access the radio communication system 50 Einstufung in Gruppen bzw. Gruppierung von at specified times which are different for each of the Funkvorrichtungen (1-9) basierend auf der in two or more groups. Schritt b erstellten Kommunikationsverbin- dungsstatistik, wobei die Kommunikationsver- 5. A method as defined in claim 1; further comprising: bindungsstatistik zur Bestimmung der neu kon- 55 figurierten Funkvorrichtungsgruppierungen ver- (d) allowing access to the radio communication wendet wird und wobei sich die Funkvorrichtun- system by each of the two or more groups of gen innerhalb einer neu konfigurierten Gruppe radio devices (1-9) at different predetermined einen Kommunikationskanal teilen, welcher

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sich von dem der anderen Gruppe zugeordne- dadurch gekennzeichnet, dass die Kommunikati- ten Kommunikationskanal oder den den ande- onsverbindungsstatistik in Schritt (b) mit Hilfe einer ren Gruppen von Funkvorrichtungen zugeord- jeden aus der Vielzahl von Funkvorrichtungen (1-9) neten Kommunikationskanälen unterscheidet. erstellt wird. 5 2. Verfahren gemäß Definition in Anspruch 1, welches 10. Verfahren gemäß Definition in Anspruch 1 oder 5, des Weiteren den folgenden Schritt aufweist: dadurch gekennzeichnet, dass die Schritte (b) und (c) in vorher festgelegten Zeitperioden durchge- (d) Genehmigen eines Zugriffs auf das Funk- führt werden. kommunikationssystem basierend auf der Ein- 10 stufung in Gruppen bzw. Gruppierung der Funk- vorrichtungen (1-9). Revendications

3. Verfahren gemäß Definition in Anspruch 1, dadurch 1. Méthode d’accès à un système de communication gekennzeichnet, dass die in Schritt (b) erstellte 15 radio ayant une pluralité de dispositifs radio (1-9), Kommunikationsverbindungsstatistik Folgendes comprenant les étapes de: aufweist: die durchschnittliche Kanalbenutzung durch jede aus der Vielzahl von Funkvorrichtungen (a) séparer la puralité de dispositifs radio (1-9) (1-9), oder die Anzahl von Kanalzugriffen pro Zeit je en deux ou plusieurs groupes (202, 204, 206), Einheit durch jede aus der Vielzahl von Funkvorrich- 20 où les dispositifs radio (1-9) dans un groupe tungen (1-9), oder die Priorität einer jeden aus der (202, 204, 205) partagent un canal de commu- Vielzahl von Funkvorrichtungen (1-9) oder die durch- nication qui est différent du canal de communi- schnittliche empfangene Signalstärke einer jeden cation attribué à l’autre groupe ou bien des ca- aus der Vielzahl von Funkvorrichtungen (1-9). naux de communication attribués aux autres 25 groupes de dispositifs radio, 4. Verfahren gemäß Definition in Anspruch 1, dadurch (b) établir des statistiques de connection de gekennzeichnet, dass die zwei oder mehr Gruppen communication se rapportant à la pluralité des von Funkvorrichtungen (1-9), welche in Schritt (a) dispositifs radio (1-9), caractérisée par gebildet bzw. festgelegt wurden, auf das Funkkom- (c) déterminer si les deux ou plusieurs groupes munikationssystem zu bestimmten Zeiten, welche 30 devraient être reconfigurés sur la base des sta- sich für jede der zwei oder mehrGruppen unterschei- tistiques de communication réunies et den, zugreifen können. (d) lorsqu’il est établi que les deux ou plusieurs groupes devraient être reconfigurés, reconfigu- 5. Verfahren gemäß Definition in Anspruch 1, welches rer le groupement de dispositif radio (1-9) sur la des Weiteren den folgenden Schritt aufweist: 35 base des statistiques de connection de communication réunies à l’étape b, où les statistiques (d) Genehmigen eines Zugriffs auf das Funk- de connection de communication sont utilisées kommunikationssystem durch jede der zwei pour déterminer les groupements de dispositifs oder mehr Gruppen von Funkvorrichtungen radio reconfigurés, et où les dispositifs radio (1-9) zu unterschiedlichen voher festgelegten 40 dans un groupe reconfiguré partagent un canal Zeitperioden. de communication qui est différent du canal de communication attribué à l’autre groupe ou des 6. Verfahren gemäß Definition in Anspruch 5, dadurch canaux de communication attribués aux autres gekennzeichnet, dass das Funkkommunikations- groupes de dispositifs radio. system ein Zeitvielfachzugriffs- bzw. TDMA-Funk- 45 kommunikationssystem aufweist. 2. Méthode selon la revendication 1, comprenant en outre l’étape de: 7. Verfahren gemäß Definition in Anspruch 1 oder 5, dadurch gekennzeichnet, dass die Schritte (b) (d) permettre l’accès au système de communi- und (c) periodisch wiederholt werden. 50 cation radio sur la base du groupement des dispositifs radio (1-9). 8. Verfahren gemäß Definition in Anspruch 1 oder 5, dadurch gekennzeichnet, dass die Kommunikati- 3. Méthode selon la revendication 1, où les statistiques onsverbindungsstatistik in Schritt (b) mit Hilfe einer de connection de communication réunies à l’étape zentralen Funkkommunikationssystem-Hilfsquelle 55 (b) comprennent un des suivants: l’usage moyen du erstellt wird. canal par chacun de la pluralité de dispositifs radio (1-9), le nombre d’accès à des canaux par temps 9. Verfahren gemäß Definition in Anspruch 1 oder 5, unitaire par chacun de la pluralité des dispositifs ra-

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dio (1-9), la priorité de chacun de la pluralité des dispositifs radio (1-9) ou la force de signal moyenne reçue de chacun de la pluralité de dispositifs radio (1-9). 5 4. Méthode selon la revendication 1, où les deux ou plusieurs groupes de dispositifs radio (1-9) établis à l’étape (a) peuvent accéder au système de communication radio à des temps spécifiés qui sont diffé- rents pour chacun des deux ou plusieurs groupes. 10

5. Méthode selon la revendication 1, comprenant en outre:

(d) permettre l’accès au système de communi- 15 cation radio par chacun des deux ou plusieurs groupes de dispositifs radio (1-9) à différentes périodes de temps prédéterminées.

6. Méthode selon la revendication 5, où le système de 20 communication radio comprend un système de communication radio à accès multiple, à division de temps.

7. Méthode selon la revendication 1 ou 5, où les étapes 25 (b) et (c) sont répétées périodiquement.

8. Méthode selon la revendication 1 ou 5, où les statistiques de connection de communication dans l’étape (b) sont réunies par une ressource centrale 30 du système de communication radio.

9. Méthode selon la revendication 1 ou 5, où les statistiques de connection de communication dans l’étape (b) sont réunies par chacun de la pluralité de 35 dispositifs radio (1-9).

10. Méthode selon la revendication 1 ou 5, où les étapes (b) et (c) sont exécutées à des périodes de temps prédéterminées. 40

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• FR 2780593 [0002] • US 4870408 A [0002]