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Improved spectrum efficiency for transform domain communication systems

As an overlay cognitive radio system, transform domain communication system (TDCS) has been proposed to support multiuser communication with low spectral density by using spectrum bin nulling and frequency domain spreading. It has been shown that TDCS has a low spectrum efficiency compared to other wireless communication systems. To solve this problem, this paper presents a cluster-based TDCS scheme to improve spectrum efficiency. Different from the utility of clusters in OFDM systems, the entire unoccupied spectrum bins are divided into L clusters, where each one is used for transmitting the data stream independently, to obtain L times spectrum efficiency of the traditional scheme. Simulation results demonstrate that the proposed TDCS using random allocation scheme is shown to provide the capability of improving spectrum efficiency without seriously degrading power efficiency.