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

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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 tabu- lated 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 dis- patch 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. 2 3 EP 1 168 873 B1 4 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.
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