Spreading sequences for uplink and downlink MC‐CDMA systems: PAPR and MAI minimization

Abstract

Abstract. This paper deals with spreading sequences selection for downlink and uplink Multi-Carrier Code Division Multiple Access (MC-CDMA) systems with the aim of minimizing the dynamic nnge of the tcansrnitted rnulticamer signal envelope and the multiple access interference. The crest factor of orthogonal and non-orthogonal sequences are compared analytically and by simulation for downlink and uplink phase shift keying MC-CDMA transmissions. Then, in order to minimize the multiple access interference produced by frequency selective channels, an optimized spreading sequence allocation procedure is presented. Finally, a selection of the spreading codes which jointly reduces the multiple access interference and the crest factor is proposed for downlink MC-CDMA systems.

New quasi‐orthogonal BCH‐derived sequences for CDMA applications

“…The numerical results we obtained confirmed that the new family of even BCH-derived sequences contains a high number of (quasi-orthogonal) sequences with low correlation levels, better than those presented by the even sequences of the recent UMTS system [16,17] and higher PGs, even when compared with the LS sequences [19,25] of the LAS-CDMA system. These characteristics can make the even BCH-derived sequences very attractive in fading dispersive channels, either in synchronous or quasi-synchronous channels.…”

“…For instance, the well-known orthogonal binary Walsh-Hadamard sequences are used to eliminate the MAI in synchronous channels (in-phase channels), like the downlink transmission in mobile communication systems. However, these sequences have the worst values of cross-correlation when compared with other (orthogonal and non-orthogonal) PN sequences usually used in asynchronous (or quasi-synchronous) CDMA systems [14][15][16][17].…”

An Improved Downlink MC-CDMA System for Efficient Image Transmission

“…In the downlink system, the spread data of all active users are added synchronously and mapped on to the L c sub-carriers [7]. The sequence, B (k) i is applied to a serial-to-parallel converter and multiplied by the k with the user specific spreading code of Walsh C (k) i of length L [5], [7], In [31], [7] confirmed that the WalshHadamard codes are the best choice for the downlink, also for the minimization of multiple access interference.…”

Performance Evaluations of Multi-Carrier CDMA System with Cyclic Shifted Scramble Code in Multi-path Fading Channel

“…Nobilet et al, Garía-Armada et al, and Saito el al. evaluated the PAPR properties of MC-CDMA both uplink and downlink for various channelization codes [7]- [9]. On the other hand, we have analyzed the effect of a scramble code on the PAPR performance, and concluded that a scramble code eliminates the differences amongst the PAPR properties of channelization codes [10].…”