Enhanced Backoff Scheme in CSMA/CA for IEEE

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Presentation transcript:

Enhanced Backoff Scheme in CSMA/CA for IEEE 802.11 Actor: Hsien-pang Tsai 2019/6/28

Outline Introduction Proposed Backoff Scheme Analysis Conclusion Reference

DCF & PCF DCF is defined for asynchronous data transmissions DCF shares access to the medium based on the CSMA/CA protocol. PCF is used to support time-bounded data transfer.

CSMA/CA Station is unable to detect the channel and transmit data simultaneously. Listen before talk. The receiving station sends the acknowledgment packet after a SIFS.

CSMA/CA (1)

Carrier-sense Mechanism Physical and virtual carrier-sense functions are used to determine the state of the medium. A virtual carrier-sense mechanism is referred to as the network allocation vector (NAV).

RTS & CTS To incorporate the virtual carrier sensing mechanism. Exchange of short RTS/CTS frames before data transmission is to avoid long collisions and reduce the amount of bandwidth wasted in collisions.

RTS & CTS (1)

Backoff Procedure The backoff delay is an integer uniformly chosen in the range [0, W-1]. The initial backoff window size is set to W=CWmin + 1. If collisions occur, the backoff window size is doubled until it reaches the maximum value, W=CWmax + 1. W will be reset to CWmin after every successful transmission.

Backoff Procedure (1)

Proposed Backoff Scheme Search the optimal value of CW To optimize the performance of the CSMA/CA protocol. Propose a dynamic CW resetting scheme to let the backoff counter oscillate around the optimal value.

Proposed Backoff Scheme (1) Transmission successes, w is set to the value max[w/2, CWmin +1]. Transmission fails, w is set to the value min[2w, CWmax +1].

The Markov chain of the proposed scheme {s(t), b(t)}, is a discrete-time Markov chain. b(t), the random backoff window value at slot time t. s(t), the backoff stage i for the same station at time t. p for transmitted packets to collide. pb for the channel to be in a busy status.

The Markov chain of the proposed scheme (2) Collision Proposed Reseting to CMin

Analysis Parameters

Analysis Basic access mode (m=3) Throughput

Analysis (1) RTS-CTS access mode (m=3) Throughput

Analysis (2) Basic access mode (m=3) Delay

Analysis (3) RTS-CTS access mode (m=3) Delay

Analysis (4) Basic access mode (w=16) Throughput

Analysis (5) RTS-CTS access mode (w=16) Throughput

Analysis (6) Basic access mode (w=16) Delay

Analysis (7) RTS-CTS access mode (w=16) Delay

Conclusion CSMA/CA. Proposed Backoff Scheme. Analysis Result.

Reference IEEE standard for Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, ISO/IEC 8802-11:1999(E), Aug. 1999. Wen-Kuang Kuo and C.-C. Jay Kuo,” Enhanced Backoff Scheme in CSMA/CA for IEEE 802.11”.