Abstract—In the orthogonal frequency-division multiplexing (OFDM) scheme, some subcarriers may be subject to a deep fading. Adaptive techniques can be applied to mitigate this effect if the channel-state information (CSI) is available at the transmitter. In this paper, we study the performance of an OFDM-based communication system whose transmitter has only one bit of CSI per subcarrier, obtained through a low-rate feedback. Three adaptive approaches are considered to exploit such a CSI feedback: adaptive subcarrier selection; adaptive power allocation (APA); and adaptive modulation selection (AMS). Under the conditions of a constant raw data rate and perfect feedback channel, the performance of these approaches are analyzed and compared in terms of raw bit-error rate. It is shown that one-bit CSI feedback can greatly enhance the system performance. Moreover, imperfections of the feedback channel are considered, and their impact on the performance of these techniques is studied. It is shown that by exploiting the knowledge that the feedback channel is imperfect, the performance of the APA and AMS techniques can be substantially improved. Index Terms—Channel-state information (CSI), feedback channel, orthogonal frequency-division multiplexing (OFDM).

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Abstract — In this paper, we analyze the outage probability of a single user system with multiple antennas at the transmitter, single antenna at the receiver, and finite rate feedback power control. The optimum power control is complex and the analysis is not tractable. Hence we propose a sub-optimal power allocation scheme, with very low computational complexity, which is asymptotically optimum. Analyzing the proposed algorithm we show that the diversity order can potentially be increased unboundedly by increasing the feedback rate and without increasing number of transmit or receive antennas. We find a closed form approximation to this diversity-like gain at large SNRs, as a function of number of transmit antennas, number of quantization levels, and average available SNR. Simulation results confirm the validity of the analysis. I.

In this paper, we derive lower bounds on optimal diversity-multiplexing tradeoff in multiple antenna channels when the transmitter has finite bits of channel state information. We show that for each mul-tiplexing gain, the diversity order is higher than the case without feedback. Furthermore, as the number of feedback bits increases, the diversity-multiplexing tradeoff grows unboundedly to approach the case of perfect channel state information at the transmitter. The major reason for diversity order gain is the opportunistic use of channel degrees of freedom, in the form of “location-dependent ” temporal power control, which adapts the power control strategy based on the average signal to noise ratio of the channel.