Study On Equalization Method Of High-speed Broadband Mobile Communication System

This thesis discusses the technologies of suppressing interferences in multicarrier system over the mobile communications. Multicarrier systems consist of orthogonal frequency-division multiplexing (OFDM) system, multicarrier code-division multiple-access (CDMA) system and generalized multicarrier (GMC)-CDMA system. In order to resist against variety of interference, multicarrier modulation, orthogonal coding and widely linear zero-forcing (WL-ZF) equalization are adopted. A novel algorithm of subspace-based blind channel identification using the widely linear (WL) algorithm is presented for blind channel identification.The development of mobile communication systems is firstly introduced. And in the second chapter, the basic characteristics of wireless communication channels and the impact of multipath fading are given. In the third chapter, the technique of OFDM and CDMA is described. OFDM is a multicarrier modulation technology, which can compensate for frequency selective fading. Furthermore, due to the fact that CDMA possesses the characteristic of suppressing interferences for spreading spectrum, the combination of OFDM and CDMA (i.e., multicarrier CDMA system) would be a sensible selection, which can take full advantages of them. And GMC-CDMA system satisfies the need of high speed multimedia communications.When the mobile communication system in the presence of narrowband interference (NBI), the conventional zero-forcing (ZF) linear receivers usually perform poorly since they are not capable of suppressing satisfactorily the NBI. To synthesize interference-resistant detection algorithms, we resort to widely linear (WL) filtering, which allows one to exploit the noncircularity property of the desired signal constellation by jointly processing the received signal and its complex-conjugate version. In particular, we synthesize new WL-ZF receivers for multicarrier systems, which mitigate, in the minimum output-energy (MOE) sense, the NBI contribution at the receiver output, without requiring knowledge of the NBI statistics. By exploiting the noncircularity property, we also propose a new subspace-based blind channel identification algorithm and derive the channel identifiability condition. Blind identification can be performed satisfactorily also in the presence of NBI, requiring only an approximate rank determination of the NBI autocorrelation matrix. The performance analysis shows that the proposed WL-ZF receiver assures a substantial improvement over the conventional linear ZF one.