Block Diagonalization Based Multiuser MIMO Aided Downlink Relaying

Visiting researcher: Dr Wei Liu (XDU)
Host researcher: Prof. Lajos Hanzo (University of Southampton)
Duration: 3 months
Status: Completed
 

Biography of the visiting researcher

Wei Liu received the BSc in University of Electronic Science and Technology of China, Chengdu, China and MEng in Xidian University, Xi’an, China 1999 and 2003, respectively, and the PhD degree in Wireless Communications Research Group from University of Southampton, Southampton, UK, in 2007. I jointed the State Key Labs of ISN, Xidian University, Xi’an, China, since 2008. My current research interests include wireless channel estimation and prediction, multiuser detection, joint transceiver design and cooperative communications in the fields of MIMO, OFDM and so on. I have already published over 20 papers in refereed journals and conference proceedings.
 

Background and Motivation

In wireless communications high-rate transmissions can be supported by multiple antennas employed both at the base station (BS) and the mobile stations (MS), when using the concept of the multiple input multiple output (MIMO) systems. This is because MIMO systems are capable of substantially increasing the achievable system capacity, despite being low-power ‘green’ techniques, which are of high significance to both HSPA and LTE across the industry.
 
However, the MIMO-aided downlink (DL) spanning from the BS to the MS may be subject to strongshadowing. Hence the employment of relaying may be expected to extend the cellular coverage area by acting as virtual MIMOs, which are capable of avoiding shadowing as a benefit of the geographic separation of the cooperating MSs. This results in independent fading for each MIMO-link, hence allowing us to approach the MIMO capacity of idealized, independent MIMO links. This may be expected to further promote the employment of distributed MIMOs right across the industry, including the standardization bodies, with special emphasis on LTE Advanced.
 
Provided that the source-relay channel is of sufficiently high quality to ensure that the source-data is received near-perfectly, it can be retransmitted from about half the distance and hence a substantially reduced power is required in the context of a decode-and-forward relay. By contrast, AF relaying is more beneficial, when the mobile is far from the source and hence would be prone to relay-induced decoding error propagation. Hence we will investigate the performance of a hybrid AF/DF solution, with AF being of immediate industrial relevance owing to its low complexity.
 
Single-user MIMO-aided relaying has been investigated intensively. Specifically, the system performance may be significantly improved by employing an optimal linear processing matrix at the RS, which may be designed according to different criteria, such as for example, achieving the maximum capacity, or the minimum mean square error (MMSE) assuming that only the RS and the MS have the DL channel state information (CSI), but not the BS. As far as multiuser MIMO aided DL relaying is considered, most research concentrated on the scenario, where only a single receive antenna is used at each MS. 
 

Research Activities

For a MIMO multiuser downlink scenario, we proposed a block diagonalization based multiuser MIMO-aided relaying scheme using linear matrix-multiplication based processing at the RS. The proposed algorithm does not require any CSI at the BS and it has the capability to decompose a multiuser MIMO aided relaying scheme into several single-user ones. Furthermore, based on the proposed algorithm, the linear processing matrix yielding the maximum achievable capacity is derived. 
 

Outcomes

One paper has been submitted to a referred journal.
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