nd that the cyclic prefix prefix insertion then implies that the last NCP samples of does not necessarily have to cover the entire length of the the IFFT output block of length N is copied and inserted channel time dispersion. In general, there is a trade-off at the beginning of the block, increasing the block length between the power loss due to the cyclic prefix and the from N to N + NCP. At the receiver side, the corre- signal corruption (inter-symbol and inter-subcarrier in- sponding samples are discarded before OFDM terference) due to residual time dispersion not covered demodulation by means of, for example, DFT/FFT by the cyclic prefix and, at a certain point, further re- processing. duction of the signal corruption due to further increase of Cyclic-prefix insertion is beneficial in the sense that it the cyclic-prefix length will not justify the corresponding makes an OFDM signal insensitive to time dispersion as additional power loss. This also means that, although the long as the span of the time dispersion does not exceed amount of time dispersion typically increases with the the length of the cyclic prefix. The drawback of cyclic- cell size, beyond a certain cell size there is often no reason prefix insertion is that only a fraction T/(T + TCP) of to increase the cyclic prefix further as the corresponding the received signal power is actually utilized by the power loss due to a further increase of the cyclic prefix OFDM demodulator, implying a corresponding power would have a larger negative impact, compared to the loss in the demodulation. In addition to this power loss, signal corruption due to the residual time dispersion not cyclic-prefix insertion also implies a corresponding loss in covered by the cyclic prefix. terms of bandwidth as the OFDM symbol rate is reduced without a corresponding reduction in the overall signal bandwidth. 4.4.5 Frequency-domain model One way to reduce the relative overhead due to of OFDM transmission cyclic-prefix insertion is to reduce the subcarrier spacing Af, with a 