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

208 Implementation Issues10 0BER10 −110 −2Q = 0, simulQ = 0, analyQ = 16, simulQ = 16, analyQ = 32, simulQ = 32, analyQ = 8, no correc10 −310 −42.0 4.0 6.0 8.0 10.0 12.0 14.0E b /N 0 in dBFigure 4-66Performance of narrowband interference rejection with MC-CDMAThese results show that the combination of spread spectrum with OFDM in the presenceof multi-tone narrowband interference in a frequency- and time-selective fading channelis a promising approach.4.7.4 Link Budget EvaluationIn order to estimate the transmit power for a given coverage area a link budget analysis isalways necessary, especially for a cellular mobile communications system. This analysisallows one to estimate the minimum transmit power that a terminal station should select toguarantee a given link availability. Especially for mobile terminal stations, it is importantto save power in order to enable a longer battery life cycle. For any link budget evaluation,especially for the base station, the transmit power must be checked to find out whether itis compliant with the maximum allowed transmission power specified by the regulatorybodies.The transmit power P TX can be calculated as follows:P TX = Path loss + P Noise − G Antenna + Offset + Rx loss + C/N, (4.100)where( 4πfc d η/2 ) 2Path loss = 10 log 10 (4.101)cis the propagation loss in dB. In the case of mobile communications η can be estimatedto be in the order of 3 to 5 (see Section 1.1.1). The variable d represents the distancebetween the transmitter and the receiver, f c is the carrier frequency, and c is the speedof light. In the presence of line of sight (LOS), as in case of free space, η = 2andthe