Transmit diversity scheme with sounding-based channel phase feedback in OFDMA systems

Existing feedback schemes of Channel State Information (CSI) in OFDMA systems can be mainly sorted into two categories as follows: 1) sounding channel feedback, and 2) precoder matrix indicator (PMI) feedback. However, both these two categories have some performance drawbacks and limitation of usage. In this paper, two Sounding-based Phase Feedback (SPF) schemes, namely, Type_1 SPF and Type_2 SPF, are proposed as alternatives of CSI feedback methods. With the proposed feedback schemes, the OFDMA transmitters can obtain the information of channel phases and perform an approximate Equal Gain Combining (EGC) transmission. Comparing to the current sounding channel feedback schemes, these two schemes have the flexibility to be employed in both TDD and FDD modes with comparable overhead. Comparing to the PMI feedback scheme, the proposed schemes have lower computation complexity at the receiver sides since the procedures to find the optimal precoder is not needed. Moreover, the fundamental performance limit due to quantizing the channel status also does not exist in the proposed schemes. Theoretically, the proposed schemes could convey near perfect channel phase information if appropriate estimation algorithms are adopted in the transmitter for channel estimation. Numerical analysis is also provided to evaluate the average receive SNR achieved by the two proposed schemes for comparing their performance under nonideal channel estimations. Simulation results show that the performance of the proposed schemes can achieve close performance to that of EGC (within 0.5 dB) which needs perfect channel phase information at the transmitter.