Multiple‐Access Channels

This chapter focuses on uplink multiple‐access (MA) channels, which can be classified into two cases of flat fading and frequency‐selective fading. It investigates the mutual information of various MA schemes in two cases: AWGN and flat‐fading channels. For illustrating the practical application of MA schemes, the chapter considers IS‐95A CDMA and long term evolution (LTE) systems. In CDMA, a direct consequence of spanning each symbol of a user over its signature sequence is the spreading of its power spectrum. Processing gain associated with spreading spectrum in a CDMA system has an intuitive explanation. The chapter presents commonly used pseudo‐random (PN) sequences include m‐sequences, Walsh sequences, Gold sequences, and constant amplitude zero autocorrelation (CAZAC) sequences. CAZAC sequences have been adopted by third generation partnership project (3GPP) LTE as preamble signatures for the random access channel (RACH) in the uplink.