MU-MIMO with Localized Downlink Base Station Cooperation and Downtilted Antennas

Abstract

Abstract-Multi-cellular radio systems are often limited due to the presence of cochannel interference. Proposed physical layer concepts, e.g. coordinated joint transmission and interference rejection combining, try to strengthen the signal while combating the interference. It is well known that base station cooperation yields great capacity improvement for downlink multi-antenna cellular networks. However, the proposed solutions assume a central processing unit, coordinating the information exchange and thus determining the optimal resource allocation of the overall cellular network. Recently multi-user eigenmode transmission was proposed to relax the constraint of channel state information at the transmitter. It requires the terminals to feed back their dominant eigenmodes only. To reduce the computational costs and the information exchange further, we consider limited localized base station cooperation. We demonstrate potential capacity gains in a cellular orthogonal frequency division multiplexing system using real 3D measured antenna patterns and the scaling with the number of cooperating antenna arrays. Additionally, we use minimum mean square error equalization at the terminal side to combat residual cochannel interference.

Field trials using coordinated multi-point transmission in the downlink

“…We have put all intra-and inter-site locations of MT1 into separate statistics. Obviously, the geometry of the intra- site scenario is too optimistic, with higher SINR compared to typical cellular deployments, while the inter-site scenario contains a fairly realistic interference distribution similar to multicell simulations [24]. According to the geometry, in the intra-site trials there are several locations where a relatively high data rate is assigned already in the interference-limited case because the scheduler is aware of the SINR which includes both, the channels to the own BS and to the interfering BS (see Fig.…”

“…Simulations have been done according to [24] with 10 • tilted antennas. Bottom: Throughput compared to isolated cell.…”

Partial Joint Processing for Frequency Selective Channels

“…However, this implies that the subclusters of BSs for the user may change in each RB for a given time slot and that the benefit of the PJP scheme, i.e., the decreased amount of interbase information exchange, is no longer possible, since all the user data needs to be available in each BS. In recent approaches involving clustering of sectors or BSs in frequency selective channels, this problem is solved by performing user grouping in a first step [6], and then allocating each group of users to a given RB. However, we are interested in the case where all the users are allocated to all the available RBs in each time slot, so that it is possible to take advantage of the frequency selectivity of the channel.…”

Integrating energy efficiency analysis of massive MIMO-based C-RAN

“…In EE study, the energy harvesting (EH) technology is proposed and widely studied recently [3,4], for the EE optimization [3], simultaneous wireless information and power transfer (SWIPT) [4] and other issues. In addition, the authors of [5] propose one cellular zooming scheme, to divide the cellular coverage area into different ring sections with respect to the distance from the base station (BS) to the user terminal and to select the needed area(s) for zooming in (with users) or out (without users) while cooperating with the cooperative multi-point (CoMP) technology [6]. To step further, a cooperative transmission with BS and antenna selecting/sleeping is investigated in [7,8], and the authors in [9] introduce this selecting/sleeping method into RF chain study.…”