The TDMA-Iridium and the CDMA GlobalStar are two of the main LEO satellite systems. Since the trend is towards CDMA due to its valuable advantages, a version of the TDMA-Iridium namely CDMA-Iridium is proposed. A comparison between GlobalStar and the proposed system is performed concerning the signal-tointerference ratio (SIR), the throughput of the Dense Traffic Satellite (DTS) and Sparse Traffic Satellite (STS) are considered. Adaptive Transmit Permission Control (ATPC) method is used to improve the throughput for both systems.

A new traffic model for Low Earth Orbit (LEO) Satellite system is proposed. Two different cases are considered. The first case represents the situation in which the traffic load follows a bimodal contaminated Gaussian distribution. The second case considers the trimodal distribution. The parameters of this new distribution model are introduced and their effects on the Signal to Interference Ratio (SIR) and the capacity are investigated. KEYWORDS Low Earth Orbit Satellite Communication I. INTRODUCTIONLow earth orbit satellite communication systems are one of the most appropriate systems to offer personal communications (PC) [1][2][3]. They can also provide additional advantages for the global communication networks, e.g., small propagation delay and loss, and high elevation angle in high latitude [4]. One of the most recent candidates for establishing the multiple access in LEO satellite systems is Code Division Multiple Access (COMA). CDMA has higher capacity than TDMA and FDMA if voice activity and frequency reuse by spatial isolation are employed [5]. The non-uniform distribution of the traffic is a normal feature of our globe. However there are only few studies on the effect of this nonuniformity of the traffic on the performance of LEO systems. Performance analysis of