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The Optimal Transmitter Design for OFDM System with Limited Feedback

Author: WangXin
Tutor: LuoHanWen
School: Shanghai Jiaotong University
Course: Communication and Information System
Keywords: Wideband wireless communication OFDM Adaptive resource allocation Precoder limited feedback MMSE Qos codeword selection
CLC: TN919.3
Type: Master's thesis
Year: 2008
Downloads: 17
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Abstract

With the development of wireless multimedia, wireless network and mobile computing equipment, recently the wideband mobile communication systems become the hot research technique. Several new techniques on wireless communication and wireless access field are brought forward, which absorb many researchers all over the world. During all these wireless techniques, Orthogonal Frequency Division Multiplexing (OFDM) is the most outstanding technique. OFDM technique has big advantage over other techniques both in its high availability of frequency and in its ability for mitigating the effects of delay spread, moreover, OFDM technique also can allocate the system resource dynamically. OFDM has became an effective technique with its outstanding advantages. From WLAN to WiMAX and Flash-OFDM, From LTE to B3G and even to UWB technique, OFDM is the symbol in the new generation of wireless communication.Firstly, the paper introduces the principle and architecture of wideband OFDM mobile systems. Moreover, this paper presents the key techniques which include space-time coding, synchronization, channel estimation and adaptive technique, etc.Considering that optimal design in transmitter is the key technique of wideband OFDM mobile communication systems, this paper does some research on the two aspects in optimal design in transmitter part, one is the optimal resource allocation in transmitter part, the other is the optimal precoder design with limited feedback.The technique of optimal resource allocation in transmitter part belongs to the adaptive techniques in link level. In this technique we can adjust the parameter of resource allocation according to channel state information (CSI) in order to raise the availability of wireless resource in OFDMA system. Adaptive resource allocation adopts the optimization method and improves the system performance compared to the static resource allocation method. An improved sub-carrier and power allocation algorithm for multi-user is introduced in this paper which uses the concept of grouped sub-carrier. After grouping the subcarrier according to the relativity of adjacent OFDM symbols, we do the optimal allocation among grouped sub-carriers and power. Simulation results show the improved algorithm has a lower computational complexity and a higher capacity compared to the previous ones, and meets the constraints of proportionality at the same time.In MIMO spatial multiplexing system, the precoder in transmitter part is very important to system performance. The signal can adapt to the channel state after pretreatment by which can enhance system performance. The design of optimal precoder depends on CSI, however, we could not get the fully exact CSI in practice, this paper focus on the research on the situation of partial CSI at transmitter. We designs the precoder based on limited feedback. This paper firstly introduces the problem module of optimal precoder design in the transmitter part. Then this paper brings forward the method of precoder design with limited feedback. Following that, this paper proposes a joint optimal precoding algorithm for MIMO system with limited feedback. Based on optimize theory, we propose the optimal transmitter structure which combines power control with precoding, and we also bring forward a novel MMSE criteria based codebook construction algorithm. Simulation results show that the proposed structure and codebook design algorithm outperform the precious equal power allocation based codebook. Based on this new algorithm, this paper also proposes a combined precoder design algorithm based on capacity with Qos constrain.Simulation results show that the proposed algorithm improves the system capacity with the same feedback spending and achieves the Qos demand at the same time. In the scheme of optimal precoder design with limited feedback the codebook design and codeword selection parts are the most crucial. Considering different principles in codeword selection step, this paper proposes a Qos based codeword selection scheme in optimal precoder design with limited feedback which selects the best codeword in order to optimize system performance of MSE and BER. The simulation results show that the proposed scheme is more direct and outperform the precious codeword selection method. And the most important thing is that this Qos based scheme is applicable to any codebook and any precoder design method with limited feedback.The paper does deep research about the design of optimal transmitter in wideband OFDM system according to the important techniques in 3GPP LTE conference, and forms some papers and patents. We need do more research about the techniques of mobile communication and application in real life, especially on the technique of precoder design with limited feedback.

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