Packet access using DS-CDMA with frequency-domain equalization

• Published in: IEEE journal on selected areas in communications Vol. 24; no. 1; pp. 161 - 170
• Main Authors: Garg, D., Adachi, F.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-01-2006; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Adaptive modulation coding (AMC); Adaptive systems; Automatic repeat request; Channels; Computer simulation; Data transmission; Direct-sequence code-division multiple access; direct-sequence code-division multiple access (DS-CDMA); Downlink; Equalization; equalizers; error correction coding; Frequency; High speed; high-speed downlink packet access (HSDPA); hybrid automatic repeat request (HARQ); Information systems; minimum mean-square error frequency-domain equalization (MMSE-FDE); Mobile communication; Modulation; Modulation coding; Multiaccess communication; multicode; Rakes; Receiving; Redundancy; Throughput; Wideband; Wireless communications
• ISSN: 0733-8716; 1558-0008
• DOI: 10.1109/JSAC.2005.858899

The next-generation mobile communications system is anticipated to support very high-speed data rates exceeding several tens megabits per second. In this paper, we consider high-speed downlink packet access for direct-sequence code-division multiple access (DS-CDMA) as in third-generation wideband code-division multiple-access systems. Adaptive modulation and coding (AMC), multicode operation and hybrid automatic repeat request (HARQ) will be the enabling technologies. With such high-speed data transmissions, however, multicode operation severely suffers from the loss of orthogonality among the spreading codes since the wireless channel becomes severely frequency-selective. In this paper, we apply frequency-domain equalization (FDE) based on minimum mean-square error (MMSE) criterion instead of conventional rake combining for receiving the packet. A new MMSE-FDE weight is derived for packet combining. The throughput in a frequency-selective Rayleigh-fading channel is evaluated by computer simulation for Chase combining and incremental redundancy (IR) packet combining. It is shown that the use of MMSE-FDE for the reception of multicode DS-CDMA packet gives an improved throughput irrespective of the channel's frequency-selectivity.