Subcarrier selection with variable spreading factor for reverse link of TDD multi-carrier/DS-CDMA system

This paper proposes subcarrier selection in conjunction with variable spreading factor to be applied in the reverse link of TDD multi-carrier/DS-CDMA system, to improve the system performance, against multiple access interference (MAI), in frequency selective fading channel, without reducing the throughput of the system. In frequency selective fading channel, MC/DS-CDMA subcarrier suffers from different attenuation, and when some subcarriers are severely faded, it may cause significant effect of MAI, and thus degrade the system performance. To avoid this, we apply subcarrier selection method that selects the subcarriers that are in good channel condition for transmission, thus the transmission will use a part of available subcarriers. In order to avoid throughput degradation due to this method, we employ variable spreading factor that adjust the spreading factor of each user depends on the number of subcarriers used for the transmission. Moreover, the proposed method is very easy to be realized in TDD system using the reciprocity of forward and reverse link. The performance of proposed method is evaluated using computer simulation.