Key Techniques Of The Next Generation Wireless Communications System

The research of this paper focuses on the transmission technology of the wireless communication systems of the next generation, with emphesis on improving spectral efficiency and reducing transmit power. Specificly this thesis studies channel coding and decoding, multiple antenna frequency domain equalization over frequency selective fading channel and joint iterative detection and decoding over frequency flat fading channel. The main part of this thesis is as follows:From a perspective of simulation of wireless communication systems, Chapter two of this thesis is concerned about characteristics of wireless communication channels. Because of mobolity, complicated and adverse transmission conditions feature the channel. In order to effectively compat the impact of fading effect, anti-fading techniques such as diversity, spread spectrum and error correcting coding should be appllied to these systems. Furthermore, signalling or transmission schemes, including modulation, changes according to different scenarios. Meanwhile, researchers need to design various kinds of digital transmission technology and different signal processing algorithms, it is important to understand in depth the characteristics of mobile wireless channels.In chapter three, the author studies channel coding and decoding techniques, that is Woven codes. On the basis of other researchers'results, the author presents a four-port soft input and soft output module, in order to facilitate iterative decoding process of concatenated codes. This module is not only suit for decoding a concatenated code with non RSCs as its constituent codes, but also it can provide soft information output of both codeword and information bits, so it can be applied to decoding a Turbo code and joint detection and decoding. Taking into consideration serial and parallel concatenated Turbo code, the author proposes a combined code, with 2 outer codes and 2 inner cods as its constituent codes, i.e., 2×2 Woven code. To evaluate the performance of Woven codes, a simple multicode multislot transmission scheme is proposed in addition to the basic AWGN channel. In the multicode and multislot scheme, the system performance of multiple antennas deployed scenarios is investigated and furthermore a simple channel estimation method is presented. Theoretical analysis and simulations shows that the proposed 2×2 Woven code can provide bettertradeoff between complexity and error floor.Chapter 4 presents a comparative study of single carrier systems and multicarrier systems. First, different frequency domain equlization techniques in single antenna systems are investigated. In case of schemes without coding, OFDM is equivelent to converting a frequency selective fading channel to multiple parallel flat fading channels, and has no frequency diversity gain. A scheme with decision feedback single carrier frequency domain equalizations can provide better system performance than OFDM. Second, a Alamouti-like block based space time architecture is proposed to compat the multipath effect over frequency selective fading channels, in which the proposed scheme can provide full diversity gain. And at the same time, the proposed scheme can be implemented with FFT, hence with a low computational complexity. At last the performance of the multiple input and multiple output frequency domain equaliazation system is pressented in case of the ideal channel estimation and ideal signal to noise ratio estimation.Chapter 5 studies joint iterative detection and decoding problems. First a thorough investigation on detection algorithms in layered space time systems is presented, and from a perspective of information theory, the author considers the method of EXtrinsic Information Transfer. Second the author applies joint iterative detection and decoding to multiple antenna scenarios, hence presents a joint iterative detection and decoding system. Simulation results show that this scheme can provide significient capacity improvement than a conventional one.