HIPERLAN channel assignment strategies

Introduction: HIPERLAN (high performance radio local area network) is a wireless LAN standard recently adopted by the European Telecommunications Standards Institute (ETSI) [1]. HIPERLAN (type 1) operates in 150MHz of spectrum in the 5.15–5.30GHz band, with five TDD channels capable of data transmission at speeds of up to 23.5Mbit/s. HIPERLAN uses a (31, 26) BCH code to encode data to be transmitted into 31 bit segments, and Gaussian minimum shift keying (GMSK) with BT = 0.3 to modulate these encoded bits for transmission over the air at a high bit rate (23.5Mbit/s). Each HIPERLAN cell site or hub may transmit on any HIPERLAN channel, however the hub and all terminals within the cell operate on only one RF channel at any given time. Only one terminal in each HIPERLAN cell may transmit a packet at a time. The hub RF channel may be chosen dynamically in accordance with the HIPERLAN clear channel assessment (CCA) scheme [1]. The CCA scheme flags a channel as being ‘free’ if < –75dBm of RF energy (RSSI or received signal strength indication) is detected in that channel. HIPERLAN includes the provision for the CCA threshold (CCAT) to be increased to above –75dBm, but not lowered. This Letter examines the impact of lowering the CCAT below – 75dBm.