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Capacity improvement by code-hopping in S-CDMA systems

Code-hopping, which is an alternative spreading strategy to the static spreading code assignment of CDMA systems, is evaluated as a method to combat multiuser interference in S-CDMA systems. The uplink capacities of conventional and code-hopping S-CDMA are determined and compared by simulations carried out on a typical S-CDMA system for three nondispersive channels: no-fading, Rayleigh fading and Rician fading. The cellular structure is not composed of regular hexagons, but irregularly shaped natural cells where affiliation of the mobile user depends on the paths to the neighboring base stations. Results are presented for two different values of blocking ratio which is defined as the ratio of the number of rejected call attempts to the number of total call attempts, revealing significant uplink capacity increases provided by code-hopping in both fading and no-fading environments. Furthermore, it is observed that the increase in capacity is greater in fading channels than in no-fading ones.