John S. Thompson

A Fixed-Complexity Soft-MIMO Detector via Parallel Candidate Adding Scheme and its FPGA Implementation

This paper presents a fully parallel candidate adding (PCA) scheme for the soft-output sphere decoder, which can be used in turbo-coded multiple-input multiple-output (MIMO) systems to provide extrinsic soft information to the outer decoder for more robust decoding. The PCA assisted MIMO detector has been implemented and validated on a state-of-the-art Xilinx FPGA device. The results obtained indicate that the proposed scheme is clearly suitable for a highly parallel and fully pipelined hardware implementation which outperforms alternative algorithms with respect to the resource requirements and the decoding latency.

Design and hardware implementation of a low-complexity multiuser vector precoder

In the multiuser MIMO broadcast channel, the use of precoding techniques is required in order to detect the signal at the users terminals without any cooperation between them. This contribution presents the design and hardware implementation of a high-capacity precoder based on vector perturbation. The most challenging part of the vector precoding (VP) scheme, that is, the search for the perturbing signal in an infinite lattice, has been completed by the reduced-complexity albeit high-performance Fixed Sphere Encoder (FSE) algorithm. The most remarkable feature of the FSE is its fixed complexity, which makes it highly suitable for hardware implementation on field-programmable gate arrays (FPGA), where the parallelization and pipelining of resources can be applied to enhance the system throughput. An optimized reduced-complexity implementation is proposed, which achieves high performance with a reduced hardware resource usage.

A Simplified Unbiased MMSE Metric Based QRDM Decoder for MIMO Systems

In contrast to the conventional QR-decomposition M (QRDM) algorithm, the unbiased MMSE metric based QRDM algorithm exploits MMSE metric instead of the maximum likelihood (ML) metric, leading to enhanced performance with less complexity. However, for an efficient hardware implementation, the sorting stages involved at every QRDM detection stage can still be quite time and resource consuming. Hence, we propose a simplified QRDM approach, denoted as S-QRDM, which only performs the full enumeration (FE) on certain number of top search layers, while utilizing the single enumeration (SE) for the remaining search layers. Therefore, the need for the sorting process for those layers is eliminated and the required number of multipliers is reduced simultaneously. The proposed S-QRDM detector has been implemented on a state-of-the-art Xilinx FPGA device and the results indicate that the proposed approach is more efficient in either logic or computational FPGA resources compared to the original algorithm.

Wiener filter-based fixed-complexity vector precoding for the MIMO downlink channel

A fixed-throughput Wiener filter vector precoding (VP) approach specially suitable for hardware implementation in field programable gate array (FPGA) devices is introduced in this paper. The lattice decoding algorithm, which is based on the sphere decoder (SD) lattice search, performs in its first stage a reordering of the matrix to be used for the tree search. Afterwards, the search tree is configured so as to yield an appropriate BER performance, and a fixed-complexity search is carried out. Simulation results show that the BER performance of the proposed algorithm is very close to the ML solution whereas its complexity is significantly smaller than that of the SD algorithm or the exhaustive search method.

FPGA implementation of an efficient high-throughput sphere decoder for MIMO systems based on the smallest singular value threshold

In this paper, we present an efficient high-throughput threshold based sphere decoder (TSD) for multiple-input multiple-output (MIMO) systems. Depending on the instantaneous channel conditions, the proposed TSD compares the smallest singular value of the channel matrix with a predefined threshold on a frame-by-frame basis and switches between full expansion (FE) and partial expansion (PE) for the tree traversal to accelerate the detection procedure. The TSD has been implemented and validated on an FPGA platform and results indicate that the proposed decoder is very suitable for a highly-parallel and fully-pipelined hardware implementation. The proposed algorithm offers considerable throughput improvement over the original fixed-complexity sphere decoder (FSD) with only slightly increased resource use.

Design and Implementation of a Low-Complexity Multiuser Vector Precoder

Precoding techniques are used in the downlink of multiuser multiple-input multiple-output MIMO systems in order to separate the information data streams aimed at scattered user terminals. Vector precoding VP is one of the most promising non-linear precoding schemes, which achieves a performance close to the optimum albeit impractical dirty paper coding DPC with a feasible complexity. This contribution presents a novel design for the hardware implementation of a high-throughput vector precoder based on the Fixed Sphere Encoder FSE algorithm. The proposed fixed-complexity scheme greatly reduces the complexity of the most intricate part of VP, namely the search for the perturbing signal in an infinite lattice. Additionally, an optimized reduced-complexity implementation is presented which considerably reduces the resource usage at the cost of a small performance loss. Provided simulation results show the better performance of the proposed vector precoder in comparison to other fixed-complexity approaches, such as the K-Best precoder, under similar complexity constraints.

An adaptive rate compress-and-forward cooperation for virtual-MIMO systems

A practical virtual multiple-input multiple-output (MIMO) system that implements compress-and-forward (CF) cooperation is proposed in this paper. Bit-interleaved coded modulation (BICM) technique is implemented here to provide forward error correction and improve the system performance. A closed-form union bound for the system error probability is derived, based on which we prove that the smallest singular value of the cooperative channel matrix dominates the system error performance. Accordingly, an adaptive rate CF scheme is proposed, which uses the smallest singular value as the switching criterion. Depending on the instantaneous channel conditions, the relay could therefore choose various quantization rates. It is shown that the adaptive rate CF scheme eliminates unnecessary complexity for the quantization at the relay, and enables the virtual-MIMO system to achieve almost MIMO performance.