Читать книгу Spatial Multidimensional Cooperative Transmission Theories And Key Technologies - Lin Bai - Страница 47

The technique of obtaining space diversity by combining or space–time coding described above belongs to the direct transmit diversity technique. By using well-known SISO techniques, converting space diversity to time or frequency diversity can also be realized.

Assuming M_T = 2, the phase shift is achieved by delaying the signal on the second transmit branch by one symbol period or by selecting the appropriate frequency shift. If the channels h₁ and h₂ are independent and identically distributed Rayleigh channels, the space diversity (using two antennas) is converted to frequency and time diversity, respectively. Indeed, the receiver has a frequency or time fading problem for an effective two-branch summed SISO channel, which can be overcome by conventional diversity techniques, such as forward error correction or interleaving for frequency diversity.