Cluster-based Transform Domain Communication Systems for High Spectrum   Efficiency
  This paper presents a cluster-based transform domain communication system (TDCS) to improve spectrum efficiency. Unlike the utilities of clusters in orthogonal frequency division multiplex (OFDM) systems, the cluster-based TDCS framework divides entire unoccupied spectrum bins into $L$ clusters, where each one represents a data steam independently, to achieve $L$ times of spectrum efficiency compared to that of the traditional one. Among various schemes of spectrum bin spacing and allocation, the TDCS with random allocation scheme appears to be an ideal candidate to significantly improve spectrum efficiency without seriously degrading power efficiency. In multipath fading channel, the coded TDCS with random allocation scheme achieves robust BER performance due to a large degree of frequency diversity. Furthermore, our study shows that the smaller spectrum bin spacing should be configured for the cluster-based TDCS to achieve higher spectrum efficiency and more robust BER performance. 
Su Hu and Yong Liang Guan and Guoan Bi and Shaoqian Li
cs.NI cs.IT math.IT