tailieunhanh - Enhanced Radio Access Technologies for Next Generation Mobile Communication phần 4

Các đặc điểm kỹ thuật Bluetooth lần đầu tiên được phát triển bởi Ericsson (hiện nay là Sony Ericsson), và sau đó đã được chính thức hoá do Tập đoàn Bluetooth Special Interest (SIG). SIG chính thức công bố vào ngày 20 tháng năm năm 1999. | 86 CHAPTER 3 Time-domain spreading SC-CDMA signal a Transmitter b Power spectrum c Rake receiver Figure 5. Transmitter receiver structure for SC-CDMA with rake combining spread signal resulting in the MC-CDMA signal. MC-CDMA with SF 1 is OFDM. The GI insertion is necessary to avoid the orthogonality destruction among Nc subcarriers due to the presence of multipaths with different time delays. The GI length needs to be larger than the maximum time delay difference among multipaths. At the receiver after removing the GI the received signal is decomposed by Nc-point FFT into Nc subcarrier components. The distortion of the signal spectrum due to frequency-selective fading is compensated by using one-tap FDE. The equalized subcarrier components are parallel-to-serial P S converted into the time-domain spread signal followed by despreading as in SC-CDMA receiver. FDE can be jointly used with antenna diversity reception for further performance improvement in MC-CDMA. Among various FDE weights it was shown that the use of minimum mean square error MMSE weight provides the best bit error rate BER performance. This is because the MMSE weight can provide the best compromise between the noise enhancement and suppression of frequencyselectivity. MC-CDMA with MMSE-FDE provides much better BER performance than SC-CDMA with coherent rake combining. Because of this until recently research attention was shifted from SC techniques to MC techniques such as MC-CDMA and OFDM SF 1 . But as will be shown in this chapter FDE can FUNDAMENTALS OF SINGLE-CARRIER CDMA TECHNOLOGIES 87 Carrier frequency Frequency b Power spectrum Frequency-domain equalization c Receiver Figure 6. Transmitter receiver structure for MC-CDMA also be applied to SC-CDMA with much improved performance compared to rake combining. SC-CDMA is considered again as a promising access technique similar to mc-cDma. 4. FREQUENCY-DOMAIN EQUALIZATION The application of MMSE-FDE to SC-CDMA can replace the coherent rake .