Pilot Optimization and Power Allocation for OFDM-Based Full-Duplex Relay Networks With IQ-Imbalances

In orthogonal frequency division multiplexing relay networks with in-phase and quadrature imbalances and full-duplex relay station (RS), how to optimize pilot pattern and power allocation using the criterion of minimizing the sum of mean square errors (Sum-MSE) for the frequency-domain least-squares channel estimator has a heavy impact on self-interference (SI) cancellation. First, the design problem of pilot pattern is casted as a convex optimization. From the Karush-Kuhn-Tucker conditions, the optimal analytical expression is derived when source and RS powers are given or fixed. Second, under the total transmit power sum constraint of source node and RS, an optimal power allocation (OPA) strategy is proposed to further alleviate the effect of Sum-MSE. Simulation results show that the proposed OPA performs better than equal power allocation (EPA) in terms of Sum-MSE, and the Sum-MSE performance gain increases with deviating ρ from the value of ρ
^o
minimizing the Sum-MSE, where ρ is defined as the average ratio of the residual SI channel gain at RS to the intended channel gain from source to RS. For example, the OPA achieves approximately 5-dB signal-to-noise ratio gain over EPA by shrinking or stretching ρ with a factor 4. More importantly, the more ρ decreases or increases, the more the performance gain becomes significant.