title page
Contents
ABSTRACT 8
I. INTRODUCTION 10
II. SYNCHRONIZATION AND CHANNEL ESTIMATION IN OFDMA SYSTEMS 13
2.1. OFDMA system description 13
2.2. Synchronization in OFDMA systems 17
2.2.1. Timing synchronization 17
2.2.2. Carrier frequency offset synchronization 18
2.3. Channel estimation in OFDMA downlink systems 18
2.3.1. MMSE estimators 20
2.3.2. LS estimators 21
III. A ROBUST OFDMA CHANNEL ESTIMATION AGAINST IMPERFECT SYNCHRONIZATION 23
3.1. System Model 23
3.2. Effect of synchronization errors in other synchronization and channel estimation 26
3.2.1. Effect of Timing Offset 26
3.2.2. Effect of Carrier Frequency Offset 28
3.3. The proposed robust channel estimation 31
IV. COMPUTER SIMULATION 39
V. CONCLUSION 52
VI./VII. REFERENCES 53
Table 1. System parameters 39
Table 2. Channel Model 40
Figure 2.1. Baseband OFDM transceiver system 16
Figure 2.2. The structure of an 802.16a OFDM packet[내용없음;p.9] 18
Figure 2.3. Pilot arrangement in 2-D grid 19
Figure 3.1. Channel estimation with timing offset 28
Figure 3.2. ICI arised in case of a carrier synchronization error 29
Figure 3.3. Phase rotation due to carrier offset 31
Figure 3.4. Proposed scheme for synchronization and channel estimation 32
Figure 3.5. The illustration of timing advancement 33
Figure 4.1. BER performance comparison with perfect time synchronization and imperfect… 42
Figure 4.2. Mean Square Error of frequency offset estimate in perfect time… 43
Figure 4.3. BER performance of channel estimation comparison with perfect… 44
Figure 4.4. BER performance comparison with conventional channel estimation and… 46
Figure 4.5. BER performance comparison with conventional channel estimation and… 47
Figure 4.6. BER performance comparison with conventional channel estimation and… 48
Figure 4.7. BER performance comparison with conventional channel estimation and… 50
Figure 4.8. Mean Square Error comparison conventional channel estimation and proposed channel estimation 51