Interference-based cancellation techniques for TDD

The objective of this chapter is to consider techniques that remove multiuser detection algorithms from the mobile terminal while maintaining satisfactory performance. The motivation for this is the significantly reduced complexity of the receiver required in the mobile terminal. The chapter will initially discuss the motivation for this and the special conditions that make this idea realistic in a W-CDMA-TDD system. Section 10.3 presents the precoding concept and provides an analytical framework for the calculation of its bit error rate performance. Section 10.4 then classifies precoding techniques into two categories and some power issues are introduced in section 10.5. Motivation: The linearity of a conventional CDMA system, presented simplified in Figure 10.1, suggests that it might be possible to circumvent the complexity implications of using a multiuser detection technique. The aims therefore are to transfer the complexity and computational load to the transmitter (BS) where weight and size are of less concern and resources (such as power and space for hardware) are readily available while maintaining at least the same performance that receiver-based MUD techniques would provide. The MS is restricted to the knowledge of its own signature waveform. Therefore, the k-subscriber's receiver shall consist of a simple correlator or a filter matched to the spreading sequence, ck, which is ideal for a single-user in an additive white Gaussian noise (AWGN) channel where no channel estimation, adaptive equalisation or feedback from the BS is required.