Chapter 12
Multiple-Symbol Differential Sphere Detection for Differentially Modulated Cooperative OFDM Systems
12.1 Introduction1
Multiple-antenna-aided transmit diversity arrangements [594] constitute powerful techniques of mitigating the deleterious effects of fading, hence improving the end-to-end system performance, which is usually achieved by multiple co-located antenna elements at the transmitter and/or receiver, as discussed in Chapter 11. However, in cellular communication systems, it is often impractical for the mobile to employ several antennas for the sake of achieving a diversity gain owing to its limited size. Furthermore, owing to the limited separation of the antenna elements, they rarely experience independent fading, which limits the achievable diversity gain and may be further compromised by the detrimental effects of the shadow fading, imposing further signal correlation among the antennas in their vicinity. Fortunately, as depicted in Figure 12.1, in multi-user wireless systems mobiles may cooperatively share their antennas in order to achieve uplink transmit diversity by forming a Virtual Antenna Array (VAA) in a distributed fashion. Thus, so-called cooperative diversity relying on the cooperation among multiple terminals may be achieved [595, 596].
Figure 12.1: Cooperative diversity exploiting cooperation among multiple terminals.
On the other hand, in order ...
