Study On Joint Detection Algorithm In TD-SCDMA System

TD-SCDMA is an interfere-limited system. Here includes multi-path interference, multi-user interference of intra-cell and inter-cell interference. Those destroy the orthogonality of each channel which reduces the utility of frequency-spectrum in TD-SCDMA system . JD takes all interfere users as useful signals which can make full use of the spread code , range , timing and delay of all users . Thus the multi-path and multi-access interference(MAI) are depressed on a large scale. The core idea of this technology is using equilibrium to cancel the inter-symbol interference(ISI) and the MAI at the same time. Based on that, we work over the application of JD in TD-SCDMA.In this paper, we introduce the basic formations of the physical channel first of all. And make a discrete-time model and expression with matrix according to the character of TD-SCDMA system. It promotes the principle of JD algorithm in general, whereas talks about the linear JD algorithm based on the rule of zero-forces(ZF) and MMSE(minimum mean square error) in detail. The aim of JD is to estimate the signal of users, and the sticking point is to find a fast method so as to decrease the complexity of matrix inverse operation. This paper deduces BLOCK-FFT algorithm in particular which is one of the fast matrix inverse methods,First handle system matrix to block right circulation by block extend, then solve the system matrix in frequency, to some extent, reduce calculation scale. and makes simulation on that. Moreover, we put forward another Cyclic Reduction algorithm based on MMSE. It decreases system matrix dimension to minimize matrix by equivalent variable substitute gradually, And counts the matrix directly , then deduces the rest vectors backward .Comparing with other algorithms, this means avoids the approximate error coming from inversing matrix. The simulation results show that measure is able to cancel the MAI and ISI in effect but has less complexity.