Average channel capacity for generalized-selection combining RAKE receivers

RAKE reception has been considered as an effective way to anticipate multipath signal fading in direct sequence code division multiple access (DS-CDMA) communications systems. Common diversity techniques used in conventional fingered RAKE receivers are maximal-ratio combining (MRC) and equal-gain combining (EGC). Conventional fingered RAKE receivers offer increased complexity, since the number of taps is fixed and independent of the number of multipath signals. The complexity of MRC and EGC diversity receivers depends on the number of resolvable paths available, which can be quite high for wideband spread spectrum signals, while SC receivers utilize only one path out of L available and thus, do not fully exploit the amount of diversity offered by the channel. Generalized-selection combining (GSC) has been proposed to bridge the gap between the two extreme cases MRC/EGC and SC. While MRC RAKE receivers provide optimum performance and high complexity, the GSC RAKE receivers offer less complexity, but with comparable performance. In GSC(L, Lc), the strongest Lc resolvable paths among the L paths available are adaptively combined [1]. The GSC reception is equivalent to MRC reception, if all L branches are being combined (Lc 1⁄4 L), while it is equivalent to SC reception, if one of the L branches is being used Lc 1⁄4 1. In this letter, we derive a closed-form expression for the achievable average Shannon’s channel capacity per user, of a noncooperative DS-CDMA system operating in Rayleigh fading. We essentially extend the results described in References [2, 3], using an efficient GSC RAKE receiver. Numerical examples are presented to show that the GSC RAKE receiver offer similar capacity with optimum MRC RAKE receiver.