OFDM for Wireless Communications Systems
In this practical resource, established and new technologies are explained clearly and comprehensively, from OFDM basics to a detailed account of a new technique, hybrid OFDM CDMA slow frequency hopping.
TABLE OF CONTENTS OFDM for Wireless Communications Systems
7.3: Comparison to MC-CDMA
7.3 Comparison to MC-CDMA
In this section, a comparison is made between the hybrid approach and the MC-CDMA system as proposed by Yee and Linnartz [8] and Fazel and Papke [9]. It shows that the proposed system is simpler to implement and, without SFH, performs similarly to MC-CDMA systems. It shows that the hybrid system has greater flexibility in terms of the size of the OFDM modulators and number of users and lends itself easily to FH with much higher data rates as compared to MC-CDMA systems.
7.3.1 Background
MC-CDMA was first proposed by Linnartz and Fettweis [17] in PIMRC '93. Their proposal as envisaged in [17] involved transmitting each data symbol over N narrowband SCs, where each SC is encoded with a 0 or ? phase offset. If the number of and spacing between SCs is appropriately chosen, it is unlikely that all of the SCs will be in deep fade; consequently, frequency diversity is achieved. As an MC-CDMA signal is composed of N narrowband SC signals, each with a symbol duration T b much larger than the delay spread T d,, an MC-CDMA signal will not experience significant ISI. Multiple access is achieved with different users transmitting at the same set of SCs, but with spreading codes that are orthogonal to the codes of other users. A paper by Fazel and Papke [9] on OFDM/CDMA improves considerably on the MC-CDMA proposal, although in mathematical terms it is similar to MC-CDMA, but more elegant...
Copyright Ramjee Prasad 2004 under license agreement with Books24x7
