Blind communication schemes for multiantenna CDMA wireless networks

This dissertation aims at presenting and discussing limited-complexity blind multiuser detection strategies for CDMA-based wireless networks, wherein multiple spatially-distributed antennas are employed at the transmitter and/or at the receiver. A number of relevant scenarios are investigated. At first, a conventional smart-antennas system is considered, wherein the array’s elements are physically co-located on the wireless devices. Two different space-time transmission architectures are analyzed. On one hand, assuming that the incoming bit-stream of each user is spatially multiplexed across the t transmit antennas, a linear two-stage detection strategy suitable for overloaded networks is introduced and discussed. At the analysis stage, a closed-form formula for the bit-error-rate (BER) and a lower-bound to the near far-resistance are derived. Also, it is shown that blind separation of the t spatially multiplexed substreams requires assigning a different spreading code to each transmit antenna. Successively, the two-stage detection strategy is extended to the case where differentially space-time Alamouti encoding is adopted at the multiantenna transmitter. In this case, we show that using a single spreading code per user is possible: indeed, the additional signature provided by the Alamouti code itself in the space-time domain can effectively be exploited for antenna separation and data demodulation. In the last part of the thesis, two-user cooperation is used in order to create a virtual transmit antenna array through distributed transmission and signal processing. Focusing on the use of (blind) linear multiuser detection strategies, two cooperative protocols are studied, namely decode-and-forward (DAF) and amplify-and-forward (AAF). Closed-form formulas for the (asymptotic) signal-to-interference-plus-noise ratio and BER are derived, showing that, at least for the AAF scheme, full spatial diversity is achieved, as if each terminal had two co-located transmit antennas. The influence of the partner choice on the average system BER is also investigated and a simple, yet effective, partner allocation strategy is discussed.