Spreading code assignment for multicarrier CDMA system over frequency-selective fading channels

Takashi Shono, Tomoyuki Yamada, Kiyoshi Kobayashi, Katsuhiko Araki, Iwao Sasase

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

In multicarrier code division multiple access (MC-CDMA) systems, the orthogonality among the spreading codes is destroyed because the channels exhibit frequency-selective fading and the despreading stage performs gain control; that is, inter-code interference (ICI) can significantly degrade system performance. This paper proposes an optimum spreading code assignment method that reflects our analysis of ICI for up and downlink MC-CDMA cellular systems over correlated frequency-selective Rayleigh fading channels. At first, we derive theoretical expressions for the desired-to-undesired signal power ratio (DUR) as a quantitative representation of ICI; computer simulation results demonstrate the validity of the analytical results. Next, based on the ICI imbalance among code pairs, we assign specific spreading codes to users to minimize ICI (in short, to maximize the multiplexing performance); our proposed method considers the quality of service (QoS) policy of users or operators. We show that the proposed method yields better performance, in terms of DUR, than the conventional methods. The proposed method can maximize the multiplexing performance of a MC-CDMA cellular system once the channel model, spreading sequence, and combining strategy have been set. Three combining strategies are examined at the despreading stage for the uplink, equal gain combining (EGC), orthogonality restoring combining (ORC), and maximum ratio combining (MRC), while two are considered for the downlink, EGC and MRC.

Original languageEnglish
Pages (from-to)3734-3746
Number of pages13
JournalIEICE Transactions on Communications
VolumeE87-B
Issue number12
Publication statusPublished - 2004 Dec

Keywords

  • Broadband mobile communications
  • Equal gain combining (EGC)
  • Inter-code interference (ICI)
  • Maximum ratio combining (MRC)
  • Multicarrier code division multiple access (MC-CDMA)
  • Orthogonality restoring combining (ORC)
  • Spreading code assignment

ASJC Scopus subject areas

  • Software
  • Computer Networks and Communications
  • Electrical and Electronic Engineering

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