Frequency Domain Hybrid-ARQ Chase Combining for Broadband MIMO CDMA Systems

In this paper, we consider high-speed wireless packet access using code division multiple access (CDMA) and multiple-input–multiple-output (MIMO). Current wireless standards, such as high speed packet access (HSPA), have adopted multi-code transmission and hybrid–automatic repeat request (ARQ) as major technologies for delivering high data rates. The key technique in hybrid–ARQ, is that erroneous data packets are kept in the receiver to detect/decode retransmitted ones. This strategy is refereed to as packet combining. In CDMA MIMO-based wireless packet access, multi-code transmission suffers from severe performance degradation due to the loss of code orthogonality caused by both interchip interference (ICI) and co-antenna interference (CAI). This limitation results in large transmission delays when an ARQ mechanism is used in the link layer. In this paper, we investigate efficient minimum mean square error (MMSE) frequency domain equalization (FDE)-based iterative (turbo) packet combining for cyclic prefix (CP)-CDMA MIMO with Chase-type ARQ. We introduce two turbo packet combining schemes: i) In the first scheme, namely “chip-level turbo packet combining”, MMSE FDE and packet combining are jointly performed at the chiplevel. ii) In the second scheme, namely “symbol-level turbo packet combining”, chip-level MMSE FDE and despreading are separately carried out for each transmission, then packet combining is performed at the level of the soft demapper. The computational complexity and memory requirements of both techniques are quite insensitive to the ARQ delay, i.e., maximum number of ARQ rounds. The throughput is evaluated for some This work was partly supported by Maroc Telecom under contract 105 10005462.06/PI. This paper was presented in parts at IEEE IWCMC2008, Crete Island, Greece, Aug. 2008, and IEEE PIMRC 2008, Cannes, France, September 2008. H. Chafnaji ([email protected]) and T. Ait-Idir ([email protected]) are with the Communications Systems Department, INPT, Madinat Al-Irfane, Rabat, Morocco. They are also with the Signal and Communications Department, Institut Telecom/Telecom Bretagne, Brest, France. S. Saoudi ([email protected]) is with the Signal and Communications Department, Institut Telecom/Telecom Bretagne, Brest, France. Athanasios V. Vasilakos ([email protected]) is with the University of Western Macedonia, Greece.