EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS Euro. Trans. Telecomms. 2004; 15:497–500 (DOI: 10.1002/ett.1002) Letter Signal Processing Average channel capacity for generalized-selection combining RAKE receivers Nikos C. Sagias 1 , Panagiotis Varzakas 1 , George S. Tombras 1 * and George K. Karagiannidis 2 1 Laboratory of Electronics, Department of Physics, University of Athens, Panepistimiopolis, 15784 Athens, Greece 2 Electrical and Computer Engineering Department, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece SUMMARY A novel closed-form expression for the achievable average channel capacity of a generalized-selection combining RAKE receiver in Rayleigh fading, is derived. Performance comparison for the capacity achieved with maximal-ratio combining and RAKE receivers is also presented. The expression derived, fully conforms to the upper bound of the Shannon–Hartley theorem. Copyright # 2004 AEI. 1. INTRODUCTION RAKE reception has been considered as an effective way to anticipate multipath signal fading in direct sequence code division multiple access (DS-CDMA) communica- tions systems. Common diversity techniques used in con- ventional 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 indepen- dent 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 uti- lize 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 pro- posed 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 compar- able performance. In GSC(L, L c ), the strongest L c resolvable paths among the L paths available are adap- tively combined [1]. The GSC reception is equivalent to MRC reception, if all L branches are being combined (L c ¼ L), while it is equivalent to SC reception, if one of the L branches is being used L c ¼ 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 recei- ver offer similar capacity with optimum MRC RAKE receiver. 2. SYSTEM MODEL For a user transmitting signal with bandwidth W and power P over an additive white Gaussian noise (AWGN) channel, the received signal-to-noise ratio (SNR) is Received 8 September 2003 Revised 23 October 2003 Copyright # 2004 AEI Accepted 15 December 2003 *Correspondence to: George S. Tombras, Laboratory of Electronics, Department of Physics, University of Athens, Panepistimiopolis, 15784 Athens, Hellas, Greece. E-mail: gtombras@cc.uoa.gr