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

Multi-Carrier Modulation and Demodulation 133g(t) =[ πtsinT s′](1 − α)[πtT ′ s+ kαtT s′[ πtcosT s′](1 + α)( ) ]kαt2, (4.7)1 −T ′ swhere T ′s = (1 + α)T s and k is the maximum number of samples that the pulse shall notexceed. The spectral efficiency of the system is equal to 1/(1 + (1 + α)/N c ).ForlargeN c , it approaches the optimum normalized value of 1 bit/s/Hz.4.1.1 Pulse Shaping in OFDMOFDM employs a time-limited rectangular pulse shaping which leads to a simple digitalimplementation. OFDM without guard time is an optimum system, where for large numbersof sub-carriers its efficiency approaches the optimum normalized value of 1 bit/s/Hz.The impulse response of the receiver filter ish(t) ={1 if− Ts