论文摘要
Mobile communication systems need to meet users’demands for various wireless services including voice, video and data. Therefore it is necessary to devise a method of increasing bandwidth efficiency in order to provide high-speed multi-media communication services with CDMA systems under limited radio bandwidth resources. Combining CDMA technology with MC modulation, high-rate data transmissions are easily implemented without increasing complexities in a transmitter and a receiver. MC-CDMA （Multi-carrier-CDMA） systems have been chosen for RTT （Radio Transmission technology） of IMT-2000/UMTS by the proposal“CDMA 2000”. The multi-carrier approach is motivated by a spectrum overlay with an existing IS-95 carrier, and is a strong candidate for RTT due to low complexities in a transmitter and a receiver. This paper highlights the limitations of ECPC （Each Carrier Power Control） concept - originally proposed for OFDM and DS-CDMA - when extended to MC-CDMA （Multi-Carrier Code Division Multiple Access） systems: first, its impractical signaling overhead of 80%, secondly, its inability to be used as an uplink power control mechanism. Then we propose BBPC （Band Based Power Control） as a practical alternative to ECPC for MC-CDMA systems. Unlike, ECPC that controls power on each carrier basis, BBPC assigns same power level to a band of carriers （lying within coherence bandwidth of channel）. It has been shown that with a nominal performance loss, BBPC reduces the signaling overheads to 2.5% and by employing the control index estimator after de-spreading; it can be used as an uplink power control mechanism for MC-CDMA. We have used SIR （Signal to Interference Ratio） as a power control index, BER and standard deviation of power control error as performance metric. And, more we propose a new idea to improve the performance of BBPC .