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Frequency sharing hotspot communication under uplink multi-carrier CDMA cellular system

In multi-carrier CDMA cellular systems, hotspot communication can be established to support the high-traffic areas by using the same frequency band of the original cellular systems. However, interference from the hotspots deteriorates the communication performance of the original cellular system. In this paper, in order to decrease the interference, we set up the access point (AP) of hotspots with the adaptive array antenna and code assignment method between the cellular and the hotspot communication is considered. In the proposed system, OFDM hotspot communication is overlapped to the uplink of MC-DS-CDMA cellular system in the same frequency band and the beam-forming method is applied to eliminate inter-system interference. Moreover, by allocating orthogonal variable spreading factors (OVSF) code to the both hotspot users and cellular users in the hotspot uplink period, the orthogonality of each user is kept. As a result, we can embed many hotspots into the cellular system with very small interference toward the uplink communication of the cellular system and we can improve the throughput of total system. The performance of the proposed system is evaluated by computer simulation under additive white Gaussian noise (AWGN) and Rayleigh fading environment. Copyright © 2007 John Wiley & Sons, Ltd.