tailieunhanh - CDMA: Access and Switching P8

Tham khảo tài liệu 'cdma: access and switching p8', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CDMA Access and Switching For Terrestrial and Satellite Networks Diakoumis Gerakoulis Evaggelos Geraniotis Copyright 2001 John Wiley Sons Ltd ISBNs 0-471-49184-5 Hardback 0-470-84169-9 Electronic 8 Carrier Recovery for Sub-Coherent CDMA Overview In this chapter we examine possible methods of carrier recovery for the SECDMA presented in Chapter 6. In particular we propose evaluate and compare two techniques namely Symbol-Aided Demodulation SAD and the Pilot-Aided Demodulation PAD . The performance analysis of each scheme SAD and PAD includes both Rician and Rayleigh multipath fading channels and thus are also useful in addition to the satellite in terrestrial mobile applications. Both schemes are promising alternatives to diilorftitiallv mliontil for c cnaririos characterized with uncertainties in the carrier phase that make coherent demodulation unfeasible. The frequency selective fading multipath the Doppler pliohoinonon diie to user mobility and or to satellite drift motion and the temperature variation and ventilation conditions at the sites of the various local oscillators that generate the transmitted signals cause the carrier phase uncertainty. Coherent demodulation requires the extraction of a reliable perfect phase reference from the received signal. A traditional alternative is the differentially coherent demodulation that uses the phase of the previous bit symbol as a reference but requires almost 3dB for M-ary PSK modulation in AWGN channels it is less than that for BDPSK of additional signal-to-noise Eb N0 in order to achieve the same bit error rate as coherent demodulation. This problem is more severe in DS CDMA systems which are limited by other-user interference the additional cost in dBs of differentially coherent over coherent demodulation increases linearly with the number of users in the system so as to render the fully-loaded multi-user system impractical 1 . Recently SAD 2 and PAD 3 have been considered a form of .