On Interference Immunity of Direct Sequence Spread Spectrum Communication Systems with Moderate Bandwidth Efficiency

摘要

This article presents interference immunity analysis of Direct Sequence Spread Spectrum systems (DS-SS) recommended for the high rate extension of IEEE 802.11b New High-Rate Wireless LAN standards. The IEEE802.11b adopted complementary code keying (CCK) as the basis for the high-rate extension to deliver data rate up to 11 Mb/s. CCK modulation was chosen especially for its relatively easy interoperability with the existing networks by maintaining the same RF bandwidth. The definition of DS-SS systems is related to notions of Processing Gain (PG). Widely used definition of SS communications refers to expansion of the bandwidth well beyond what is required to transmit data. USA FCC defines PG through the measurement of communication system performance in the presence of Constant Waveform (CW) interference. Therefore interference immunity of two modulation schemes of comparable Bandwidth Efficiency (BE) is examined The first scheme is based on the CCK modulation, the second one on the concept of DS-SS communication namely DS-SS 16QAM. Different types of interference (AWGN, CW, multipath, co-channel) are considered using Matlab/Simulink environment Based on simulation results it is shown that CW jammer margin is higher for CCK compared to DS-SS 16QAM for the most positions of CW jammer.