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Multihop TDD-CDMA cellular system becomes a promising candidate for fourth generation (4G) cellular systems because it provides wider coverage and higher throughput. In this paper, we analyze the uplink system capacity of a multihop TDD-CDMA cellular system. We first analyze a one-hop TDDCDMA cellular system with different base station's (BS's) direct coverage area. We find that the system capacity can be improved if a BS only covers a center small area of the cell. Besides, the high downlink transmission power of the surrounding BSs can degrade the capacity severely. Thus, we propose a multihop TDD-CDMA cellular system to overcome the high downlink inter-cell interference. In our system, a cell area is divided into two regions: inner-region and outer-region. The mobile users in the inner- and outer- region of the cell communicate with BS and relay station (RS), respectively. Based on this model, the uplink system capacity in both regions with the assumption that the inter-cell and intra-cell interference follow the Gaussian distribution is obtained. A comparison equation to provide a fair comparison with conventional one-hop TDD-CDMA cellular system is presented. From the results, we conclude that multihop TDD-CDMA cellular system can improve capacity significantly.
Date of Publication: February 2009