Contention Based Protocol

FCC ID: PIDASMAX36

Operational Description

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FCCID_910490

March 6, 2008 Federal Communication Commission Office of Engineering and Technology USA Form 731 Confirmation Number EA553449 Correspondence Reference Number: 34949 Subject: FCC ID:PIDASMAX36 The FCC mentions the WiMAX technology as an example of restricted contention protocol: "34. Under the Commission’s rules, contention-based protocols can be broadly categorized as either “unrestricted” or “restricted.” … restricted contention protocols can prevent interference only with other devices incorporating the same protocol. WiMAX, with its scheduling protocol, currently stands as the main example of a restricted contention technology. In its present format, WiMAX technology effectively prevents interference among multiple transmitters on a single WiMAX system. Different WiMAX systems can be coordinated to avoid interfering with each other, thus providing each WiMAX device a “reasonable opportunity to operate.” (FCC 07-99). WiMAX Protocol Brief WiMAX MAC protocol is a centralized protocol in which the base station controls access to the air interface. In the downlink, all decisions related to the allocation of bandwidth to various MSs are made by the BS, which does not require the involvement of the MS. As packets arrive for each terminal, the BS schedules them for the PHY resources, based on their QoS requirements. Once dedicated PHY resources have been allocated for the transmission of the MAC PDU, the BS indicates this allocation to the MS, using the specific MAC messages. In general, WiMAX terminal is a slave to the BS. In the uplink, the MS requests resources by using a contention bases protocol. WiMAX uses a truncated binary exponential backoff algorithm for contention-resolution during polling of user terminals. When it needs to send a bandwidth request the MS first enters a contention resolution phase, if selecting a uniformly distributed random number between 0 and BACKOFF WINDOW. This random value indicates the number of transmission opportunities—allocated resources for multicast/broadcast poll—the MS will wait before sending its bandwidth request. BACKOFF WINDOW is the maximum number of transmission opportunities an MS can wait before sending the pending bandwidth request. If it does not receive a bandwidth allocation based on the UL MAP message within a time window specified by a timer, the MS assumes that its bandwidth request message was lost, owing to collision with another MS, in which case MS increases is backoff window and repeats the process. If bandwidth is still not allocated after a maximum number of retries, the MAC PDU is discarded. Sincerely yours Zion Levi compliance & testing engineer Airspan Networks (Israel) Ltd. Airspan Networks (Israel) Ltd. Unitronics Bldg., 1 Harava street, P.O.B. 199, Airport City, 70100, Israel tel. +972 3977 7444 FAX: +972 3977 7400 www.airspan.com


Document Created: 2008-03-06 16:15:04
Document Modified: 2008-03-06 16:15:04
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