First, by perfect provision of the guard interval, the maximum delay spread is not greater than the guard interval length, i.e., (t_{q,N_{mathrm {P}}~-~1}~-~t_{q,0}~leq ~t_{g}thrm {g}}), where t g is the guard interval length.
Assume denote the length of guard interval, then the maximum length of nonzero is, and for.
Perfect synchronisation and a guard interval longer than the maximum channel delay are assumed.
The modified synchronization algorithm needs only a maximum margin of 16 points into the guard interval to insure the position in the cyclic prefix.
We recall that for the multicarrier transmission system with CP as guard interval, the use of Vandermonde codes allows the maximum diversity gain when multi-user maximum likelihood detection is employed.
To prevent IFI, the frame length is set to Tf = 2D + Tg, where the guard interval Tg equals to D/2, the maximum synchronization error used in this article.
To prevent IFI, the frame length is set to T f =2D+T g, where the guard interval T g equals to D/2, the maximum synchronization error used in this paper.
The guard interval is assumed to be equal to the maximum delay spread in the sense that the multipath effects is perfectly removed for the conventional OFDM systems.
The simulation scenarios are generated by using different combinations of parameters given in Table 2. Table 2 The transmitted DVB-T primary user signal parameters Bandwidth 8 MHz Mode 2K Guard interval 1/4 Channel models Rayleigh/Rician (K = 1) Maximum Doppler shift 100 Hz Frequency-flat Single path Sensing time 1.25 ms Location variability 10 dB.
Assume that the maximum channel delay spread is less than or equal to the guard interval L, and w(n) is zero-mean, complex additive white Gaussian noise with variance σ w 2. The k th subcarrier output from the FFT can be expressed as[26] Y k = 1 N ∑ n = 0 N − 1 y ( n ) e − j 2 Π nk / N = d k H k + I k + W k (3).
