Performance Analysis of Spatially Block Coded OFDM Systems
Date Issued
2006
Date
2006
Author(s)
Chiang, Ping-Hung
DOI
en-US
Abstract
Recently, the demand for high performance fourth-generation (4G) broadband wireless mobile communication systems has increased remarkably and hence using multiple antennas at both base station and subscriber ends becomes a must. Multiantenna technologies can provide high transmission capacities required by Internet and multimedia services and also dramatically increase the range and reliability of wireless transmission. In a fading environment, a multiple-input- multiple-output (MIMO) system having multiple antennas at the transmitter and receiver can provide diversity. By employing multiple antennas, multiple spatial channels are created and it is unlikely all channels will fade simultaneously.
With its natural resistance to multipath fading and its ability to support extremely high data rates, orthogonal frequency division multiplexing (OFDM) has been adopted in several wireless standards such as digital audio broadcasting (DAB), terrestrial digital video broadcasting (DVB-T), IEEE 802.11a wireless local area network (WLAN), and IEEE 802.16 wireless metropolitan area networks (WMAN). Rather than a single carrier solution, OFDM is chosen as a result that its equalizer dealing with the problem of high channel delay spread has lower complexity. It reduces the effect of frequency-selective fading by dividing the transmission bandwidth into many narrowband subcarriers, each of which exhibits approximately flat fading. By combining OFDM with MIMO techniques, the channel response becomes a matrix. Since each subcarrier can be equalized independently, the complexity of space-time equalizers is avoided. Thereupon, MIMO OFDM, a combination of MIMO and OFDM, is adopted as one of the 4G air interfaces.
To gain more insights of MIMO OFDM, the most promising 4G air interface, we study its coherent and noncoherent system structures in multipath time-varying Rayleigh fading channels. Based on the Alamouti scheme, we analyze, discuss, and compare two-input-multiple-output (2IMO) OFDM systems with coherent and noncoherent detections. The extensions to MIMO OFDM systems with three and more transmit antennas are also provided. By comparing coherent and noncoherent system structures based on implementation issues and bit-error-rate (BER) performances, we obtain and summarize some important points which are useful for system design.
The major contributions of this dissertation are summarized as follows. In Chapter 3, for Alamouti diversity systems, we generalize the zero-forcing (ZF), decision-feedback (DF), and joint ML (JML) detectors, proposed by Vielmon et al., to their 2IMO versions and derive the corresponding BER expressions. For the ZF detector, we prove explicitly that, in extremely varying channels, the diversity advantage from transmit diversity vanishes. For the DF detector, we derive its BER expression which takes the effect of error propagation into account. In Chapter 4, we interpret the NSD and its special cases hierarchically and apply them to noncoherent SIMO and 2IMO OFDM systems. For the noncoherent 2IMO OFDM systems, we propose three novel system structures. We also give some remarks on differential encoding directions, which are crucial in designing noncoherent OFDM systems.
Subjects
天線分集
最大可能性偵測
多輸入多輸出
非同調最大可能性序列偵測
正交分頻多工
效能分析
塊狀時空碼。
Antenna diversity
maximum-likelihood (ML) detection
multiple-input-multiple-output (MIMO)
noncoherent ML sequence detection (NSD)
orthogonal frequency division multiplexing (OFDM)
performance analysis
space-time block coding (STBC).
Type
thesis
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