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

Multi-Carrier FDMA 117T s ′= QTTd 0d 1 d 2d Q −1Q T cd 0 d 1... d Q −1 d 0 d 1... d Q −1 d 0 d 1... d Q −1 d 0 d 1... d Q −1 d 0 d 1... d Q −1L g Q T cL Q T cFigure 3-7IFDMA signal design with guard intervalThe IFDMA signal design is illustrated in Figure 3-7. A block of Q data symbolsd (k) = (d (k)0 ,d(k) 1 ,...,d(k) Q−1 )T (3.14)assigned to user k is used for the construction of one IFDMA symbol. The duration of adata symbol is T and the duration of an IFDMA symbol isT s ′ = QT . (3.15)In order to limit the effect of ISI to one IFDMA symbol, a guard interval consisting of acyclic extension of the symbol is included between adjacent IFDMA symbols, comparableto the guard interval in multi-carrier systems. Each IFDMA symbol of duration T s ′ includesthe guard interval of durationT g = L g QT c . (3.16)An IFDMA symbol is obtained by compressing each of the Q symbols from symbolduration T to chip duration T c ,i.e.T c =TL g + L , (3.17)and repeating the resulting compressed block (L g + L) times. Thus, the transmissionbandwidth is spread by the factorThe compressed vector of user k can be written asP G = L g + L. (3.18)⎛⎞Ts (k) 1 ⎜= ⎝d (k)T , d (k)T ,...,d (k)T ⎟L g + L } {{ }⎠(L g +L)copies. (3.19)