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

324 Additional Techniques for Capacity and Flexibility Enhancementdifferent ways. The SPC vector c n for the two states is defined as [16]{(1, 1) T State Ac n =(1,e −jπ ) T State B . (6.23)The property of SPC is that the receiver evaluates the received signal and decides if theSPC should remain in the actual state or should perform a state change. The receiverdoes not need to know the actual state of the spatial phase pre-coder. It is sufficient toevaluate a predefined flipping criterion and based on this to indicate to the transmittervia a feedback channel that it needs to flip the phase on one antenna compared to theprevious transmission, i.e. to perform a state change, or to remain in the actual state. Thecriterion for a state change is define as follows [16]:{no state change |H n |≥F =state change |H n | < , (6.24)where F is the feedback information from the receiver to the transmitter indicating if astate change is necessary or not. The principle of SPC is shown in Figure 6-27. Figure6-27(a) shows H n (1) and H n(2) with a relative angle α n such that |α n |