Inter-Cell Interference in Noncooperative TDD Large Scale Antenna Systems

Abstract

Abstract-In this paper we study the performance of cellular networks when its base stations have an unlimited number of antennas. In previous work, the asymptotic behavior of the signal to interference plus nose ratio (SINR) was obtained. We revisit these results by deriving the rigorous expression for the SINR of both downlink and uplink in the scenario of infinite number of antennas.We show that the contamination of the channel estimates happens whenever a pilot sequence is received at a base station simultaneously with non-orthogonal signals coming from other users. We propose a method to avoid such simultaneous transmissions from adjacent cells, thus significantly decreasing interference. We also investigate the effects of power allocation in this interference-limited scenario, and show that it results in gains of over 15dB in the signal to interference ratio for the scenario simulated here. The combination of these two techniques results in rate gains of about 18 times in our simulations.

Pilot contamination reduction in massive MIMO systems based on pilot scheduling

“…Currently, pilot contamination reduction schemes in massive MIMO systems can be classified into three groups: channel estimation [6][7][8][9][10][11], precoding [12], and pilot scheduling [13][14][15][16][17][18][19][20]. In [6], pilot contamination was tackled by a multi-cell precoding method based on the minimum mean square error channel estimation.…”

“…Under the assumption of spatially correlated channels, it has been found that the pilot contamination would disappear by exploiting the covariance information of user channels and using a coordinated pilot assignment strategy among cells [7]. Alternatively, the concept of time-shifted pilots was proposed to avoid the inter-cell interference via rearranging the order of uplink pilot transmission in different cells [8]. However, this asynchronous transmission scheme may result in strong interference when two closely located users in neighboring cells are transmitting or receiving simultaneously [9].…”

Successive Pilot Contamination Elimination in Multiantenna Multicell Networks

“…Consider practical constraints in which the number of BS antennas is usually limited, the authors in [5] proposed a time-shifted structure to alleviate the effect of pilot contamination by assigning orthogonal pilot transmissions across different cells. Base on this structure, the authors in [6] proposed time staggered pilots scheme which can asymptotically remove pilot contamination whenever pilot intervals at different cells do not overlap. However, to ensure the orthogonality among pilot transmissions across different cells, it requires a central controller to manage the staggering of pilot training in all cells, which obviously becomes challenging with large number of users and cells.…”

Adaptive Pilot Allocation Algorithm for Pilot Contamination Mitigation in TDD Massive MIMO Systems

“…Therefore, the channel estimate of the kth user at the lth BS becomes a linear combination of the channels to the kth users in all the other cells, causing what is known in literature as pilot contamination. It has been extensively shown in the literature, for example [3], [9], and [1], that with pilot contamination and when the number of BS antennas is very large (M → ∞), the uplink signal-tointerference-plus-noise ratio SINR of the kth user in the lth cell approaches the following limit…”

“…Thus, several methods have been proposed to mitigate or reduce the effect of pilot contamination. In [3], [4] and [5], a scheme based on a time-shifted (asynchronous) pilot transmission protocol is proposed to reduce the effect of pilot contamination. The proposed scheme partitions cells into several groups A 1 , A 2 , .…”