Physical layer simulations of the IEEE 802.11b wireless LAN-standard

The purpose of this report is to investigate the coexisting possibilities between Wireless Local Area Networks (W-LAN), defined by IEEE 802.11b, and BlueTooth at the unlicenced ISM band. The ISM band is situated at 2.4000- 2.4835 GHz and there are several applications, for example BlueTooth, using this spectrum.

A physical layer simulator of the W-LAN (defined by IEEE 802.11b) has been constructed in Matlab in order to simulate the radio interface. Both the 5.5 Mbps and the 11 Mbps modes have been implemented, but the slower basic and enhanced access rates, i.e. 1 Mbps and 2 Mbps, are not implemented. According to the IEEE specification the W-LAN should transmit the data in frames, but the preamble and the header are not implemented. Only the part which contains the data to be transmitted is implemented. So, the synchronisation issue and other issues, like redundancy check, are not studied in this report.

The performance of the W-LAN when it is interfered by another W-LAN (also IEEE 802.11b) at adjacent channels is investigated. An existing BlueTooth physical layer simulator has been used to evaluate the W-LAN’s performance in terms of bit error rate when interfered by a BlueTooth unit. The performance degradation of the BlueTooth system when interfered of a W-LAN is also simulated.

The simulations show that both wireless systems can coexist with each other in the ISM band, but they both experience performance degradation. At a bit error rate of $10^{-5}$ (corresponding to the W-LAN sensitivty level) for the W-LAN the Carrier-to-Interferer (C/I) ratio is 4 dB with BlueTooth as interferer. At a bit error rate of $10^{-3}$ (corresponding to the BlueTooth sensitivity level) for the BlueTooth system the C/I ratio is 4 dB with a W-LAN as interferer. So, both systems seem to require the same C/I ratio to obtain a bit-error rate corrresponding to their respective sensitivity levels.

Author: Lindgren, Magnus

Source: LuleƄ University of Technology

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