| IEEE 802.11 WLAN is very important in wireless computing.Nowadays,multimedia applications develop rapidly.However,multimedia applications need the support of QoS,such as the guarantee of delay,bandwidth,error rate and jitter.MAC is very important for the guarantee of QoS,because of sending data with shared channel in WLAN.It is a great challenge to support QoS in 802.11 WLAN,because of the multiple route hop and various condition of PHY for the noise interference.Therefore,it is very meaningful to research and improve the IEEE 802.11 MAC protocol and make it support the QoS requirement.The basic mode of IEEE 802.11 is DCF.Besides,another mode of IEEE 802.11 is PCF,which is polling-based.However,IEEE 802.11 does not support QoS.To enhance QoS,IEEE 802.11 e is proposed,which prioritizes the applications according to their categories.There are two modes in IEEE 802.11e: EDCA and HCCA.However,802.11 e has the following disadvantages,restricted type,bad expansibility,inadaptability for multiple hop and the hunger of low priority traffic.This paper mainly proposes a new MAC protocol called MAC based on per-hop latest departure time in PCF(PLDT-PCF).It is different from traditional end-to-end latest departure time.PLDT-PCF evaluates the degree of urgency of packets with their per-hop latest departure time.To send several most urgent frames continuously,this paper proposes two algorithms,which are based on ordered queue or min-heap.Besides,cumulative acknowledgement is employed to reduce ACK.The NS-2 simulation results show that the throughput and delay of PLDT-PCF are better than 802.11 DCF,802.11 PCF and 802.11 e EDCA. |
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