erence and the acceptable out-of-band emissions. 3 Except for the subcarrier at the edge of the spectrum. OFDM transmission CHAPTER 4.4 Normalized Doppler spread (fDoppler/Af) Figure 4.4-15 Subcarrier interference as a function of the normalized Doppler spread Doppler/Af. The basic bandwidth of an OFDM signal equals 4.5 MHz. Assuming, for example, a subcarrier spacing of Nc Af, i.e. the number of subcarriers multiplied by the 15 kHz as selected for LTE, this corresponds to approx- subcarrier spacing. However, as can be seen in Figure imately 300 subcarriers in 5 MHz. 4.4-16, the spectrum of a basic OFDM signal falls off very slowly outside the basic OFDM bandwidth and es- pecially much slower than for a WCDMA signal. The 4.4.8.3 Cyclic-prefix length reason for the large out-of-band emission of a basic OFDM signal is the use of rectangular pulse shaping In principle, the cyclic-prefix length TCP should cover (Figure 4.4-1), leading to per-subcarrier side lobes that the maximum length of the time-dispersion expected to fall off relatively slowly. However, in practice, straight- be experienced. However, as already discussed, in- forward filtering or time-domain windowing will be used creasing the length of the cyclic prefix, without to suppress a main part of the OFDM out-of-band a corresponding reduction in the subcarrier spacing Af, emissions. Thus, in practice, typically in the order of 10% implies an additional overhead in terms of power as well guard-band is needed for an OFDM signal implying, as an as bandwidth. Especially the power loss implies that, as example, that in a spectrum allocation of 5 MHz, the the cell size grows and the system performance becomes basic OFDM bandwidth Nc. Af could be in the order of more power limited, there is a trade-off between the -10.0 -20.0 WCDMA -30.0 -40.0 -50.0 Frequency (MHz) Figure 4.4-16 Spectrum of a basic 5 MHz OFDM signal compared with WCDMA spectrum. CHAPTER 4.4 OFDM transmission loss in power due to the cyclic prefix and the signal to the reserved tones can also b