The IEEE 802.11 WLAN standards adopt CSMA/CA protocol with a backoff algorithm as medium access control technique. When the number of stations which attempt to access a network increases, the throughput efficiency of the standard goes down. In this paper, we propose a modified backoff algorithm which adaptively selects the Contention Window (CW) size according to the variation of the number of contending stations and present the results of simulation analysis.

Wireless communications technology continues to change and yield new standards for satisfying the user demands. As a result, multiple standards coexist and wireless communications systems supporting different air interfaces cannot interact with one another. Software-defined radio is regarded as the most promising solution to cope with this problem. In this paper, we discuss the design considerations of SDR systems from a base station point of view and propose new architecture which meets the inherent requirements of SDR platform. We then introduce hardware/software of SDR platform we accomplished on the basis of the new architecture. In addition, the results of basic transmission and receiving performance are presented to prove the feasibility of the proposed platform as a base station.