Coordinated Multi-Point transmission with imperfect channel knowledge and other-cell interference

Abstract

Coordinated Multi-Point (CoMP) transmission is a promising technique for LTE-Advanced systems, especially due to the enhanced throughput performance of cell edge users. In this paper, we investigate joint transmission (JT) and coordinated beamforming (CBF) with quantized and delayed feedback, and we derive ergodic rate and outage probability expressions assuming large-scale fading (pathloss), small-scale Rayleigh fading, and other-cell interference (OCI). Furthermore, we employ a moment matching technique that approximates the distributions of the received desired and interference signals with Gamma distributions as a means to facilitate analysis and simulation. The performance of CoMP transmission is quantified and compared with non-cooperative transmission, and operating regions in which CoMP gains are more pronounced are provided. The versatility of the proposed approximate framework enables us to identify key system parameters, such as feedback resolution, pathloss, and transmit SNR for which CoMP becomes a judicious choice of transmission strategy.

Joint power and feedback bit allocation for energy- efficient design in limited-feedback coordinated beamforming systems

“…Consequently, we can find that (27) tends to allocate more bits to the cell with larger QoS requirement. By contrast, the bit allocation algorithm for improving SE proposed in [5,6] only exploits the receive powers in the desired and interfering channels but does not consider the different QoS requirements, and thus cannot be applied in this work.…”

“…where ν > 0 should satisfy (27) shows that the allocated number of bits for quantizing the CDI from the th BS to user b k not only increases with the large-scale fading gain α 2 ,b k but also grows with the parameter g s, defined in (23), which is associated with the QoS requirements (i.e., γ k and O k ) for the users served in the th cell.…”

“…The low complexity algorithm is summarized in Algorithm 2, where the power allocation (21) depends on the bit allocation algorithm (27). It will be shown in the simulation section that under high-quantization resolution, the performance of suboptimal algorithm is close to that of optimal algorithm.…”

“…To validate the upper bound and asymptotic analysis, we compare the total transmit power at all coordinated BSs obtained from the iterative algorithm in Algorithm 1, the low complexity algorithm in Algorithm 2, and the asymptotical analysis in Proposition 2 using the bit allocation in (27).…”

“…In limited-feedback systems, the power minimization problems become more challenging, because the impact of imperfect CDI on the system performance should be properly evaluated. The imperfect CDI not only results in many difficulties to analyze the system performances, e.g., outage probability [10,27], but also may make the optimization problems nonlinear even in single-cell systems [28]. In [28], a power allocation algorithm is proposed to minimize the total transmit power for limited-feedback multi-user MIMO systems under individual outage probability constraints.…”