Downlink Interference Alignment In LTE System

Interference is universal in wireless network. In cellular systems, different base stations often share same resources such as frequency, time slots and signal spaces, to achieve multiplexing gain. Therefore inter cell interference is caused to each channel in this network when communication links transmit symbols using the same frequency carrier or time slot. Especially at the edge of every cell, users suffer greater interference from neighboring cells. Interference alignment (IA) is recently raised to suppress interference, which has been proved to be a promising technique to maximize the system capacity by mitigating interference. This paper focuses on the work of IA.Since the multi-cell multiple-input-multiple-output (MIMO) interfering broadcast channel (IBC) models the scenarios of actual wireless network where a base station (BS) servers multiple users, we will talk about IA for MIMO IBC in this paper. The work contains the introduction of IA, the traditional algorithms to achieve IA, the degrees of freedom gained by IA, and the impact of imperfect channel state information (CSI) on IA. However, though it could theoretically improve the performance of MIMO network, IA encounters several challenges when put into practice. First of all, IA is implemented by encoding signals, which often needs the knowledge of extensive CSI and cooperation of users to design the transmitting beamformer and receiving filter. Secondly, IA needs multiple dimensions to align interfering signals and depart them from desired signals. In addition, the complexity of IA algorithm is another challenge for application. Taking these problems into consideration, we proposed a new IA algorithm in this paper-Interference Alignment Based on Time Pulse on-off Strategy.The proposed IA scheme will align and eliminate the inter-cell interference (ICI) by a time pulse on-off strategy, and remove the inter-user interference (IUI) by a precoding method with low feedback quantity. In addition to achieving a considerable system sum rate in cellular network, more remarkable is that the proposed IA scheme needs only a proper number of antennas and local information feedback within the corresponding cell. The numerical analysis and simulation results demonstrate that the proposed IA scheme is more practical in contrast to previous approaches.