A Novel OSSMIC Receiver for Downlink MIMO MC-CDMA Systems Antonis Phasouliotis and Daniel K.C. So School of Electrical & Electronic Engineering The University of Manchester Manchester, UK email: antonis.phasouliotis@postgrad.manchester.ac.uk, d.so@manchester.ac.uk Abstract — In this paper, a chip level ordered successive spatial and multiuser interference cancellation (OSSMIC) receiver architecture is presented for downlink multiple-input multiple- output multi-carrier code division multiple access (MIMO MC- CDMA) systems. The proposed receiver performs ordered layer space-time detection. Unlike the existing ordered successive interference cancellation (OSIC) receiver, the proposed receiver cancels both spatial & multiuser interference in the SIC process. This allows detection in multiuser scenario, which is not possible in conventional chip level OSIC receiver. Simulation results show that the proposed receiver significantly outperforms both the existing chip level OSIC detector and the chip level linear receiver. As the proposed receiver only requires the knowledge of the desired user’s spreading sequence, it is a viable solution for downlink MIMO MC-CDMA communications. I. INTRODUCTION The introduction of new wireless communication services including mobile internet, video telephony, and high quality multimedia streaming increases the demand for more bandwidth efficient wireless communication systems that can achieve higher user capacities and faster data rates from already existing technologies. The research towards a new wireless platform, called fourth generation (4G), has been initiated worldwide. One of the possible solutions for 4G is the multiple input multiple output multi-carrier code division multiple access (MIMO MC-CDMA) system [1]. This refers to the combination of MIMO techniques [2] with MC-CDMA system [3], the latter being the combined scheme of orthogonal frequency division multiplexing (OFDM) with code division multiple access (CDMA). OFDM is a multicarrier modulation technique employed for high data rate wireless applications and is suitable for combating inter-symbol interference (ISI) that arises in frequency selective channels. CDMA is a multiplexing technique which permits multiple users to access the wireless channel simultaneously by modulating and spreading their input data signals with different spreading sequences. In addition, MIMO system, a scheme based on multiple transmitting and multiple receiving antennas can achieve very high data rates in rich multipath scattering environment without increasing the transmission bandwidth or the total transmitted power of the system. The vertical Bell labs layered space-time (V-BLAST) architecture (or ordered successive interference cancellation (OSIC)) [4] is a MIMO system that has recently gained major research attention because it can realize very high data transfer rates by using spatial multiplexing to exploit the multiple spatial channels. For MIMO MC-CDMA system, a chip level OSIC receiver has been proposed and demonstrated good performance for single user case [5]. However, its performance is severely degraded in multiuser cases and has a high error floor appearing in medium SNR range due to multiple access interference (MAI) and error propagation. Therefore, it performs even worse than the linear zero forcing (ZF) or minimum mean square error (MMSE) receivers. In [6], chip level and symbol level MMSE linear receivers are presented. Although the symbol level detector has better performance over the chip level detector, it needs high computational complexity and also requires the knowledge of all other users’ spreading sequence. A partial MMSE-OSIC receiver based on multiuser detection [7] achieves similar performance to the symbol level MMSE-OSIC, but also requires all other users’ spreading sequence. Without a practical receiver architecture, downlink MIMO MC-CDMA system is not as favourable as other simpler transceiver schemes such as MIMO OFDMA. In this paper, a more practical receiver namely the chip level ordered successive spatial and multiuser interference cancellation (OSSMIC) receiver is proposed for downlink MIMO MC-CDMA systems. This receiver performs layered space-time processing with both spatial and multiuser interference cancellation. It outperforms linear receivers [6] and unlike [5], it is capable for multiuser scenarios. Moreover, the receiver does not require the knowledge of other users’ spreading sequences and is suitable for downlink communications. It should also be noted that the proposed scheme invalidates the perception that linear MMSE detector performs better than iterative detectors for MIMO MC-CDMA systems [7, 8, 9]. The rest of this paper is organized as follows. Section II introduces the system model by presenting both the transmitted and the received signal. In Section III, the novel chip level OSSMIC receiver design for the downlink MIMO MC-CDMA is proposed. In Section IV, the performance of the proposed architecture is evaluated through simulations and is compared with the performance of the linear detectors and the chip level OSIC detector. Finally, section V concludes and summarizes the paper. 978-1-4244-1645-5/08/$25.00 ©2008 IEEE 1271