Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

Multi-Carrier Transmission 35– Loss in spectral efficiency due to the guard interval.– More sensitive to Doppler spreads than single-carrier modulated systems.– Phase noise caused by the imperfections of the transmitter and receiver oscillatorsinfluences the system performance.– Accurate frequency and time synchronization is required.1.2.3 Applications and StandardsThe key parameters of various multi-carrier-based communications standards for broadcasting(DAB and DVB), WLAN, and WLL are summarized in Tables 1-9 to 1-11.Table 1-9Broadcasting standards DAB and DVB-TParameter DAB DVB-TBandwidth 1.5 MHz 8MHzNumber of 192sub-carriers N c (256 FFT)384(512 FFT)1536(2 k FFT)1705(2 k FFT)6817(8 k FFT)Symbol duration 125 µs 250 µs 1ms 224 µs 896 µsT sCarrier spacing F s 8kHz 4kHz 1kHz 4.464 kHz 1.116 kHzGuard time T g 31 µs 62 µs 246 µs T s /32, T s /16, T s /8, T s /4Modulation D-QPSK QPSK, 16-QAM, 64-QAMFEC coding Convolutional with code rate Reed Solomon + convolutional1/3upto3/4 with code rate 1/2 up to 7/8Max. data rate 1.7 Mbit/s 31.7 Mbit/sTable 1-10Wireless local area network (WLAN) standardParameter IEEE 802.11aBandwidth20 MHzNumber of sub-carriers N c 52 (48 data + 4 pilots) (64 FFT)Symbol duration T s 4 µsCarrier spacing F s312.5 kHzGuard time T g 0.8 µsModulationBPSK, QPSK, 16-QAM, and 64-QAMFEC coding Convolutional with code rate 1/2 up to 3/4Max. data rate54 Mbit/s