Non-sample Spaced Effect in 802.16a STC System

System

The non-sample spaced effect also exists in 802.16a STC system while transform domain interpolation techniques are considered. We test linear, cubic-spline, DFT-based, and DCT-based estimators in the simulations. The grouping scheme is scheme 2 in 5.3.1. In this simulation, Model 3 described in Chapter 4 is used here. In order to evaluate the performance under non-sample spaced channel, the taps of continuously channel model are located at 0, 3.5402, 8.1082, 12.448, 19.757, 28.664 samples.

0 5 10 15 20 25 30 10^-5

10^-4 10^-3 10^-2 10^-1 10⁰

SNR in dB

BER in logarithm scale

DFT-based channel estimation DCT-based channel estimation Linear channel estimation SPINE channel estimation

Figure 5.28 BER versus SNR plot of different estimators under non-sample spaced channel

In Figure 5.28, DCT-based estimator is better than DFT-based estimator.

Compared to Figure 5.6 (a) and (b), the improvement is more significant in 802.16a STC system. This is because the number of multipaths and the total power in Model 3 is larger than Model 1 and Model 2. As shown, DCT, linear, and cubic-spline estimators have almost equal performance.

Chapter 6 Conclusion

In this thesis, several kinds of channel estimation schemes for MIMO OFDM are considered. Before we start to discuss these approaches, the conventional Jakes’

fading model is reviewed and the feature of spatial correlation is added to the conventional simulator. The simulation shows that the simulator can achieve the properties of MIMO channels. After that, a comparative investigation on these schemes is presented and analyzed in terms of bit error rate curves. Both 802.16a with STC and 802.11n-like systems are considered in our studies. In 802.11n-like systems with scattered preamble, the results show that the equi-spaced pilots are suitable for transform-domain interpolation skills. Under non-sample spaced channel, the results show that the DCT-based estimator improves the performance degeneration of DFT-based estimator. Among all interpolation skills, piecewise linear interpolation outperforms other interpolation skills in this scenario.

In the studies of STBC coded preamble MIMO OFDM system, a decision-direct channel tracking skill with smoothing process is applied to this system. The simulation results in 5.2.1 show that the tracking skill improves the performance of channel estimator in this system under time-varying channels. While we focus on all-pilot preamble MIMO OFDM systems, a LS-based estimator is applied to detect all-pilot MIMO preambles from interference of other antennas. For large matrix

inversion in this approach, a modification is also applied. In our simulations, different parameters ( ) are tried to evaluate their corresponding performances. Both BER curves and MSE are presented. According to our simulations, the system has best performance while is set approximately to the maximum delay spread of the channel. The proposed decision algorithm for channel length is good for cases of two and three antennas, but not suitable for case of four antennas.

K0

K0

As for 802.16a system with STC, we consider different schemes to combine multiple OFDM symbols to improve estimation accuracy. Consider the accuracy and the latency. We discuss combination flow based on piecewise linear extrapolation with a sliding window. The simulations show that it performs well in this system.

This thesis focuses on existing MIMO OFDM channel estimation skills, and some advanced issues should be explored in the future. All the channel conditions in this thesis are assumed to be static in a single OFDM symbol. However, the ICI introduced by fast-fading channel should be studied and compensated. The method to detect channel length in Chapter 4 is not very robust for present studies. The improvement is another future work. The implementation of integrated IEEE 802.11n systems with data detection and synchronization is the next goal of our research. For this integrated work, more MIMO channel characteristics need to be added to present channel simulator.

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Autobiography

詹偉廷，1981 年 1 月 5 日出生於台南市。2003 年自國立交通大 學電機工程系畢業，隨即進入國立交通大學電子工程研究所攻讀碩士 學位，致力於訊號處理與通訊系統研究。論文題目是多輸入多輸出之 正交分頻多工通信系統通道估測設計