Simulation Platform

MATLAB is chosen as simulation language, due to its ability to mathematics, such as matrix operation, numerous math functions, and easily drawing figures. A MIMO-OFDM system based on IEEE 802.11n Wireless LANs, TGn Sync Proposal Technical Specification, is used as the reference simulation platform. The major parameters are shown in Table 4-1.

Table 4-1 Simulation parameters

Parameter Value

MCS Set 27 / 29

Antenna No. 4*4

Modulation 16 QAM / 64 QAM

Coding Rate 2/3

PSDU Length 1024 Bytes

W

Carrier Frequency 2.4 GHz

Bandwidth 20 MHz

IFFT / FFT Period 3.2 sμ

4.2 Simulation Result

As mention before, the multiphase generator is used to generate 22 phases between one clock cycles. In other word, the phase error 22 means that signal is delay one cycle, and the phase error 0 means that sign is at ideal phase.

With different initial phase errors, after timing synchronization, including coarse and fine timing synchronization, the final phase errors are convergence into 3 phases. As shown in Figure 3-15 and Figure 3-16.

Next we will show the performance under the simulation platform defined in Table 4.1.

First, consider with the 4*4 MIMO-OFDM system with 64 QAM modulation and TGn channel E (RMS=100ns, Tap=15). The performances are shown in Figure 4-1. The legend ideal sample means to get each sample at right phase (phase error 0). This work sample means use the proposed algorithm in section 3.2 with an unknown initial phase errors to get sample. No synchronization sample means without an algorithm to fix the error of an unknown initial phase.

Figure 4-1-(a) shows the required SNR is 19dB, lost about 1 dB when compare with the ideal sampling. Take the SCO effect into consideration, the required SNR with SCO 400 ppm is about 20dB, lost about 2 dB when compare with no SCO effect. Figure 4-1 -(b) shows the proposed algorithm can tolerance SCO effect about 400 ppm.

Then, consider with the 4*4 MIMO-OFDM system in Time Variance channel with 64 QAM modulation and TGn channel E (RMS=100ns, Tap=15). The performances are shown in Figure 4-2 and Figure 4-3. Figure 4-2-(a) shows the required SNR is about 29 dB in Time variance channel with velocity 30km/hr, lost about 1.2 dB when compare with the ideal sampling. Take the SCO effect into consideration, the required SNR with SCO 400 ppm is about 31dB, lost about 3.5 dB when compare with no SCO effect. Figure 4-2-(b) shows the proposed algorithm can tolerance SCO affect about 400 ppm.

Figure 4-3-(a) shows the required SNR is about 31 dB in Time variance channel with velocity 120km/hr, lost about 1.5 dB when compare with the ideal sampling. Take the SCO effect into consideration, the required SNR with SCO 400 ppm is about 32dB, lost about 2 dB when compare with no SCO effect. Figure 4-3-(b) shows the proposed algorithm can tolerance SCO affect about 400 ppm.

(a) PER vs. SNR

(b) PER vs. SCO

(a) PER vs. SNR

(b) PER vs. SCO

Figure 4-2 : The system performance of 4*4 MIMO-OFDM in Time Variance channel 30km/hr with 64 QAM, TGn channel E

(a) PER vs. SNR

(b) PER vs. SCO

Figure 4-3 : The system performance of 4*4 MIMO-OFDM in Time Variance channel 120km/hr with 64 QAM, TGn channel E

Chapter 5

Conclusion and Future work

N this thesis, based on the preamble structure of IEEE 802.11n standard, a synchronization algorithm for IEEE 802.11n WLANs over TGN channels is proposed.

A realistic channel model was employed, which includes the effects of Time variance channel, sampling clock offset, etc. Loss in system performance due to synchronization error was used as a performance criterion.

5.1 Conclusion

We compare other methods with the proposed algorithm in section 3-2. Due to the reason of lack time, we compare two other methods in our system platform. The major improve is in the converge SNR. The comparison is listed in Table 5.1

5.2 Future work

In this thesis, we proposed a method to solve the synchronization problem cause by the multi-path channel. In the time variance channel, it has the same problem like the multi-path channel, but there is still some other problem need to solve. Some other situations can cause synchronization error, like the boundary detection error, Doppler Effect and serious fading by SCO. Otherwise, man-made noise is also a source to affect the accuracy of timing synchronization. Those problems need to be solved in the future.

As to the system, high QAM constellation likes 256-QAM for higher data rate is going to be deployed. Then, more antennas of transmitter and receiver like 8*8 are taken into consideration. Even huge FFT/IFFT (size bigger than 1000) is also a good research topic.

I

[15] [16] This work

Control Factor Phase (32 phases)

Converge Cycle 4 symbols 1 symbols 4 symbols Table 5-1: Comparisons among timing synchronization algorithm

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