Voice transmission in an IEEE 802.11 WLAN based access network

IEEE 802.11 contains a mechanism for transmission of data with realtime constraints known as Point Coordination Function. This supplementary medium access protocol resides on top of the basic medium access mechanism Distributed Coordination Function and uses a centralized polling approach. Due to the complexity of a PCF implementation and the predicted inefficiency of the PCF several proposals have been presented for providing QoS support without the need of a centralized scheduler. Those solutions suffer from the fact that they are shifting implementation complexity from the access point to the mobile nodes. In this paper we compare the suitability of the basic DCF and PCF protocols for the transmission of audio data in an interactive scenario. We show that a simple priority mechanism used on the mobiles as well as the access point is suitable for providing improved QoS in terms of band-width and without the need of an extended DCF protocol. In combination with the PCF an adequate delay characteristic for audio flows is achievable as well. To overcome the limitations in channel capacity caused by the PCF we suggest an implicit signaling scheme for improving the channel capacity by avoiding unsuccessful PCF polling attempts.