Effect of non-reciprocity on infrared wireless local-area networks

An infrared (IR) wireless network standard called Advanced Infrared (AIr) was proposed to the Infrared Data Association in April 1997. AIr provides a dynamic trade-off between bit rate and transmission range by employing four-slot pulse-position modulation (PPM) with variable-rate repetition coding (RC). At the media-access control (MAC) layer carrier-sensing multiple access/collision avoidance (CSMA/CA) is utilized. To prevent collisions in case of hidden terminals, request-to-send and clear-to-send (RTS/CTS) packets are exchanged to reserve the channel. To insure that RTS/CTS exchange works reliably, it is necessary to maintain reciprocity, which means that the signal-to-noise ratio is symmetric between each pair of transceivers. In practice, however, reciprocity can be violated due to poor transceiver design, manufacturing tolerances, or ambient light noise. We use a layered simulation approach to investigate the impact of non-reciprocity on the performance of IR wireless LANs. Studying the example of AIr in detail we show that non-reciprocity can substantially reduce throughput and increase unfairness.