[show abstract][hide abstract] ABSTRACT: We consider a simple closed-loop spatial multiplexing architecture which can be incorporated into an outer system with off-the-shelf single-input single-output encoders/decoders. Instead of relying on transmitter-side channel state information for matching the layers of the multidimensional signal to the eigenmodes of the multiple-input multiple-output channel through a precoding, the eigenmodes with high attenuation are identified in the receiver and a retransmission of the affected signal parts requested through a feedback channel. The requested backup facilitates a linear array signal reconstruction subject to limited noise amplification. Since the backup is always embedded in a subsequent signal frame, the multiplexing becomes a recursive procedure. We propose appropriate transmit antenna selection policies for limiting the number of recursions and thereby the memory requirement and incurred delay. Optimal policies are obtained using the theory of Markov decision processes. Moreover, the use of a simple unsupervised learning method lets the system adapt to unknown channel conditions while always guaranteeing a target signal-to-noise ratio at the decoder input.
Communications (ICC), 2011 IEEE International Conference on; 07/2011
[show abstract][hide abstract] ABSTRACT: We investigate the performance of a closed-loop multiple-input multiple-output (MIMO) architecture featuring recursive spatial multiplexing (RSM) in the presence of co-channel interference. RSM is effective even when the MIMO channel varies arbitrarily from frame to frame transmission. The RSM scheme evades the noise enhancement inherent in zero forcing (ZF) and minimum mean squared error (MMSE) based receivers and also avoids the increasing complexity that arises in V-BLAST receivers. Using Monte-Carlo simulations, it turns out that RSM outperforms the conventional ZF and MMSE receivers and is an interesting approach in the presence of co-channel interference.
Communications and Vehicular Technology in the Benelux (SCVT), 2010 17th IEEE Symposium on; 12/2010
[show abstract][hide abstract] ABSTRACT: We propose a closed-loop multiple-input multiple-output (MIMO) architecture which incorporates unitary precoding and recursive spatial multiplexing. Both techniques take advantage of a feedback channel in a similar way for the transmission of data at high rates with limited signal processing complexity. Unitary precoding is effective in situations with accurate channel state information (CSI) at the transmitter end. In situations with outdated CSI due to time-variant channels, a linear signal reconstruction at the receiver end may result in severe noise amplification. Recursive multiplexing mitigates the noise enhancement by means of retransmissions of signal parts in critical subspaces. This significantly increases the ergodic capacity achieved by precoding based on outdated CSI, as shown for the cases of time-variant (4x4) and (8x8) MIMO channels.
[show abstract][hide abstract] ABSTRACT: We investigate a closed-loop spatial multiplexing architecture with linear array signal processing, which can be combined with off-the-shelf single-input single-output encoders/decoders. Rather than resorting to sophisticated interference cancellation schemes, excessive noise amplification due to ill-conditioned multiple-input multiple-output (MIMO) channels is evaded by retransmission of signal parts in critical subspaces, facilitated by a low-rate feedback channel. This lets the great capacities of MIMO channels be capitalized on with low system complexity, without requiring channel state information at the transmitter end. The closed-loop architecture involves a reverse propagation of the noise power, which we study using the theory of Markov chains. Conditions are defined under which stationarity is attained, considering both infinite and finite-rate feedback, and the constrained ergodic capacity of the system is expressed. It turns out that in the case of an (8 times 8) MIMO channel with uncorrelated Rayleigh fading, the constrained capacity comes as close as 4 dB to the unconstrained ergodic MIMO capacity.
Information Theory and Its Applications, 2008. ISITA 2008. International Symposium on; 01/2009
[show abstract][hide abstract] ABSTRACT: We study a novel spatial multiplexing scheme for a multiple-input/multiple-output (MIMO) architecture with vertical coding and a feedback channel. Rather than for sending back channel state information (CSI), the feedback channel is used to request the retransmission of signal parts in critical signal subspaces. This enables the receiver to perform linear reconstruction of the layered signals without the destructive noise enhancement in ill-conditioned channel matrices that is experienced with conventional linear processors. Moreover, a given target signal-to-noise ratio at the decoder input can be ensured. A comparison against standard MIMO architectures in terms of achievable throughput lets us conclude that the proposed multiplexing facilitates an advantageous closed-loop MIMO system which does not rely on accurate transmitter-side CSI.
Information, Communications & Signal Processing, 2007 6th International Conference on; 01/2008