4 research outputs found
From Multi-Keyholes to Measure of Correlation and Power Imbalance in MIMO Channels: Outage Capacity Analysis
An information-theoretic analysis of a multi-keyhole channel, which includes
a number of statistically independent keyholes with possibly different
correlation matrices, is given. When the number of keyholes or/and the number
of Tx/Rx antennas is large, there is an equivalent Rayleigh-fading channel such
that the outage capacities of both channels are asymptotically equal. In the
case of a large number of antennas and for a broad class of fading
distributions, the instantaneous capacity is shown to be asymptotically
Gaussian in distribution, and compact, closed-form expressions for the mean and
variance are given. Motivated by the asymptotic analysis, a simple,
full-ordering scalar measure of spatial correlation and power imbalance in MIMO
channels is introduced, which quantifies the negative impact of these two
factors on the outage capacity in a simple and well-tractable way. It does not
require the eigenvalue decomposition, and has the full-ordering property. The
size-asymptotic results are used to prove Telatar's conjecture for
semi-correlated multi-keyhole and Rayleigh channels. Since the keyhole channel
model approximates well the relay channel in the amplify-and-forward mode in
certain scenarios, these results also apply to the latterComment: accepted by IEEE IT Trans., 201
Antenna selection and performance analysis of MIMO spatial multiplexing systems
Multiple-input multiple-output spatial multiplexing (MIMO-SM) systems offer an essential benefit referred to as spatial multiplexing gain. Two important signal reception techniques for MIMO-SM systems are the zero-forcing (ZF) and ordered successive interference cancellation (OSIC) as, for example, in the case of the decision-feedback detector (DFD). This thesis studies the communication and signal processing aspects of MIMO-SM. We first investigate the bit error rate (BER) performance of the ZF receiver over transmit correlated Ricean flat-fading channels. In particular, for a MIMO channel with M transmit and N receive antennas, we derive an approximation for the average BER of each sub-stream. A closed-form expression for the optimal transmit correlation coefficient, which achieves the maximum capacity (i.e., uncorrelated case) of two-input two-output spatial multiplexing (TITO-SM) systems, is presented. We further propose an antenna selection (AS) approach for the DFD over independent Rayleigh flat-fading channels. The selected transmit antennas are those that maximize both the post-processing signal-to-noise ratio (SNR) at the receiver end, and the system capacity. An upper bound on the outage probability for the AS approach is derived. It is shown that the AS approach achieves a performance comparable to optimal capacity-based selection based on exhaustive search, but at a lower complexity. Finally, we investigate a cross-layer transmit AS approach for the DFD over spatially correlated Ricean flat-fading channels. The selected transmit antennas are those that maximize the link layer throughput of correlated MIMO channels. A closed-form expression for the system throughput with perfect channel estimation is first derived. We further analyze the system performance with pilot-aided channel estimation. In that, we derive a closed-form expression for the post-detection signal-to-noise-plus-interference ratio (SNIR) of each transmitted substream, conditioned on the estimated channels. The derived SNIR is then used to evaluate the overall system throughput. It is observed that the cross-layer AS approach always assigns the transmission to the antenna combination which sees better channel conditions, resulting in a substantial improvement over the optimal capacity-based AS approach. Considering a training-based channel estimation technique, we compare the performance of the proposed cross-layer AS with that of optimal capacity-based AS when employed with a training-based channel estimation. Our results show that the latter is more robust to imperfect channel estimation. However, in all cases, the cross-layer AS delivers higher throughput gains than the capacity-based A
Antenna Selection in Keyhole Channels
Abstract—This letter presents two results for antenna selection under keyhole condition. First, we analyze the capacity of the antenna-selection keyhole channel. We show that in an w 2 x system a small number of selected antennas can match the capacity of a baseline full-antenna system (baseline system has no feedback). Second, we formally prove the intuitive result, until now unproven, that antenna selection in the keyhole multiple-input multiple-output channel preserves the available diversity of the channel. Index Terms—Antenna selection, capacity, diversity order, keyhole channel. I