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

Interaction Channel for DVB-T: DVB-RCT 287is adapted to each terminal station link condition individually. Results in Reference [20]show that compared to a single PHY mode, the area spectral efficiency can be at leastdoubled if adaptive PHY modes are employed.5.5.4.2 Link BudgetThe transmit power, depending on the coverage distance, is given byP Tx = Pathloss + P Noise − G Antenna + FadeMargin + Rx loss + C N , (5.5)where( 4πfc d η/2 ) 2Pathloss = 10 log 10 (5.6)cis the propagation path loss, d represents the distance between the transmitter and thereceiver, f c is the carrier frequency, and c is the speed of light. In the case of WLANs,η can be estimated to be in the order of 3 to 5.P Noise = FN Thermal = FKTB (5.7)is the noise power at the receiver input, where F is the receiver noise factor (about 6 dB),K is the Boltzman constant (K = 1.38 × 10 −23 J/K), T is the temperature in K, and B istotal occupied Nyquist bandwidth. The noise power is expressed in dBm.G Antenna is the sum of the transmit and receive antenna gains, expressed in dBi. InWLANs, the terminal station antenna can be omni-directional with 0 dBi gain, but thebase station antenna may have a gain of about 14 dBi. The fade margin is the marginneeded to counteract the fading and is about 5 to 10 dB. Rx loss is the margin for allimplementation losses and all additional uncertainties such as interference. This margincan be about 5 dB. C/N is the carrier-to-noise power ratio (equivalent to E s /N 0 ) forBER = 10 −6 . By considering a transmission power of about 23 dBm and following theabove parameters, the maximum coverage for the robust PHY mode at 2.4 GHz carrierfrequency can be estimated to be about 300 m for an omni-directional antenna.The minimum receiver sensitivity thresholds for IEEE 802.11a, depending on the PHYmode, i.e. the data rate for a BER of 10 −6 , are given in Table 5-49. The receiver sensitivitythreshold Rx th is defined byRx th = P Noise + C N + Rx loss. (5.8)5.6 Interaction Channel for DVB-T: DVB-RCTThe VHF and the UHF frequency bands (typically from 120 to 860 MHz) are reservedespecially for broadcast TV services and similarly to convey uplink information fromthe subscriber premises, i.e. terminal stations, to the base station for interactive services.In addition to the uplink channel, interactive services also require a downlink channel