Luciano Sarperi

Blind OFDM Receiver Based on Independent Component Analysis for Multiple-Input Multiple-Output Systems

We propose a novel blind orthogonal frequency division multiplexing (OFDM) receiver structure for multiple- input multiple-output (MIMO) systems based on independent component analysis (ICA), which increases the spectral efficiency effectively compared to training based systems, and provides considerable performance enhancement over previous ICA based methods. To further improve the performance, we also incorporate ICA with iterative layered space-time equalization (LSTE), which provides performance close to the case with perfect channel state information (CSI). The reduced-complexity versions of the two proposed structures, which use channel interpolation, result in similar performance at a substantially lower computational cost. Our receiver structures also have significantly better performance and lower complexity than a previously proposed subspace method when a large number of subcarriers are employed.

Multiuser Detection and Channel Estimation in MIMO OFDM Systems via Blind Source Separation

This paper proposes a blind multiuser detection and channel estimation method for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems based on blind source separation (BSS). Using multiple antennas for transmission and reception the multiuser detection problem can be cast as a BSS problem of linear instantaneous mixtures. The proposed method uses BSS in each subcarrier to detect the user signals. The source order and scaling indeterminacies inherent to BSS methods are overcome by exploiting the cross correlation between the subcarriers introduced by convolutional encoding. Additionally, the method provides an estimate of the channels. It is shown that this method provides significant performance enhancement over previous work.

Semi-Blind Layered Space-Frequency Equalization for Single-Carrier MIMO Systems with Block Transmission

This letter proposes a novel semi-blind layered space-frequency equalization (LSFE) receiver for single- carrier cyclic-prefix (SC-CP) multiple-input multiple-output (MIMO) systems with block transmission, based on independent component analysis (ICA). Simulation results show that semi- blind LSFE with various Doppler shifts can provide performance close to the case with perfect channel state information (CSI), using a training overhead of only 0.05%. It also significantly outperforms its orthogonal frequency division multiplexing (OFDM) counterpart with perfect CSI and semi-blind linear SC frequency domain equalization (SC-FDE) over a wide range of signal to noise ratios (SNRs).

Low-complexity ICA based blind multiple-input multiple-output OFDM receivers

This paper proposes two novel blind receivers for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless communication systems using independent component analysis (ICA). They increase the spectral efficiency compared to conventional systems, without any training/pilot data required. The first proposed receiver, termed ICA-MMSE, uses ICA in one subcarrier of OFDM and a linear minimum mean squared error (MMSE) approach to unmix the remaining subcarriers. The second proposed receiver, termed ICA-MMSE+SIC, uses ICA-MMSE as a first stage and iterative successive interference cancellation (SIC) as a second stage to improve the performance. Simulations show that ICA-MMSE+SIC can obtain performance close to the case with perfect channel knowledge at the receiver and both methods outperform a previously proposed ICA based method considerably.

An inter-cell co-operative interference cancellation scheme for 4G MIMO networks

This paper discusses MIMO pre-coding based interference cancellation schemes for 4G networks, which are currently being considered in LTE-A and WiMAX IEEE 802.16m standardization processes. A novel user selection algorithm for inter-cell coordination of MIMO pre-coding is proposed. This is shown to provide a net capacity benefit in the downlink, through simulations based on measured MIMO channel data.

Reduced Complexity Blind Layered Space-Time Equalization for MIMO OFDM Systems

This paper proposes a reduced complexity blind layered space-time equalization (LSTE) for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM). Blind source separation (BSS) combined with a vertical Bell Laboratories layered space-time (V-BLAST) scheme is used in a small portion of subcarriers to perform blind signal detection and channel estimation iteratively. In the remaining subcarriers the channel state information (CSI) is obtained by interpolation using the previously acquired CSI, and signal detection is subsequently carried out with a V-BLAST scheme. Compared to previous work where BSS is used in each subcarrier, the proposed system obtains similar performance while significantly reducing the computational complexity and improving the robustness to the propagation of permutation errors. Also, the performance of the blind LSTE can approach the ideal case with perfect CSI, by using a moderate number of iterations

On sub-stream ordering for OSIC detection in 4G distributed MIMO schemes

This paper analyses the problem of optimal sub-stream ordering when OSIC detection is utilized for distributed MIMO schemes. We present a novel heuristic metric for user ordering, which linearly combines the pre-detection SNR and the SNR gap from a performance threshold. We demonstrate through a theoretical model and simulation results the performance improvement from the ordering metric.

Advanced Techniques for Improving the QoS of the WiMAX Cell Edge User

This paper discusses two of the advanced techniques, fractional frequency reuse (FFR) and multi-hop relay (MR), available to the WiMAX network operator for improving the quality of service (QoS) for the cell edge user. The benefits of FFR are shown as reductions of the interference levels, while the benefits of MR are shown as improvements in coverage and signal quality. The corresponding results have been obtained through analytical studies and network planning exercises and are supported by system level simulations.

An efficient feed-forward method for lattice reduction MIMO schemes

This paper presents a novel, efficient feed-forward method for lattice reduction MIMO schemes, which allows the receiver to be simple and power efficient, yet obtain significantly improved detection performance. The proposed method is based on decomposing the uni-modular lattice reduction matrix into a series of totally uni-modular matrices and using a codebook to feed this information forward to the receiver. We develop the codebooks for different orders of MIMO channels and compare the performance of the proposed scheme with a default feed-forward option.

Uplink Post-Coding for Inter-Cell Interference Cancellation in 4G Mobile Broadband Systems

This paper proposes an uplink MIMO post-coding scheme for inter-cell interference cancellation. The cost of using some of the MIMO spatial modes for interference cancellation is minimized by proposing to incorporate rank deficient MIMO channels in this scheme. Another novelty is that it can exploit the same vectors as in a previously proposed downlink MIMO pre-coding method. This duality avoids additional signaling overhead in a time division duplex (TDD) system. Simulation results show that the proposed scheme obtains an overall system capacity gain, while improving the SINR for the targeted in-cell or cell edge users.