Bell Labs Layered Space-time Architecture Research Articles

Performance Analysis of a Multi-layered SVD Based STBC System

Multiple-Input Multiple-Output transmission systems using orthogonal frequency-division multiplexing is a key solution in wireless communications. The performance of MIMO-OFDM systems can be improved using coding schemes such as Space–Time Block Coding (STBC), Singular Value Decomposition (SVD) and Vertical Bell Labs Layered Space–Time Architecture (VBLAST). In this paper we present a (4 × 4) cascaded STBC–SVD multi-layered encoder structured in a VBLAST architecture. The STBC output streams are SVD encoded to improve symbol error rate (SER) performance. The introduced system achieves both spatial multiplexing and diversity gains simultaneously and maintains reliable SER performance. We study the effect of ordering the output streams of the STBC before applying the SVD encoding. We show that there is an optimum ordering that guarantees a minimum overall SER. MATLAB® simulations show that the proposed system performs better over other conventional VBLAST systems. Moreover, we show that better performance is not associated with an increase in the computational complexity.

Performance of joint transmit scheme assisted multiple-input multiple-output multi-carrier IDMA system

In this paper, we present the performance of a multiple-input multiple-output multi-carrier interleave division multiple access (MC-IDMA) system assisted by combined vertical Bell Laboratories layered space–time architecture and space–time block code processing over correlated frequency-selective channels for downlink communication. In MC-IDMA system, multi-carrier is realized by orthogonal frequency division multiplexing, which can eliminate the effects of time dispersion. At the mobile station, we employ zero forcing maximum-a-posteriori and minimum mean square error MAP (MMSE/MAP) multi-user detectors (MUD) to mitigate the effects of multi stream interference and iterative chip detection to combat the effects of multiple access interference. The performance of the considered system is compared with double space–time transmit diversity (DSTTD) aided MC-IDMA system. The simulation results show that the considered scheme outperforms DSTTD MC-IDMA and MC-CDMA system with MMSE/MAP MUD in terms of achievable bit error rate.

Asymptotic Performance Analysis of Coded BLAST Architectures with Statistical Rate and Power Allocations

In this paper we first analyze some mathematical properties of ergodic capacity and outage capacity functions of the layers in Bell labs layered space-time (BLAST) architectures employing successive decoding and interference cancellation. We then present statistical rate allocation and power allocation methods that optimize the asymptotic performance of BLAST architectures. Since the methods are developed by using ergodic capacity and outage capacity functions of the layers, the allocated rates and powers depend only on a given channel statistic. Finally, we prove that the rate allocation yields a better asymptotic performance than the power allocation. Numerical results show that BLAST architectures with the rate and power allocation perform better by 4 dB and 3 dB, respectively, than a BLAST architecture with the same rate and power in all layers.

Cross-layer analysis of downlink V-BLAST MIMO transmission exploiting multiuser diversity

We develop a queuing analytic model to study cross-layer effects on quality of service (QoS) performance for downlink transmission in a Vertical Bell Laboratories Layered Space-Time Architecture (V-BLAST) multiple input multiple output (MIMO) wireless system exploiting multiuser diversity. As in multiuser single input single output (SISO) systems, multiuser diversity has been shown to have a great potential in improving system throughput in multiuser MIMO systems as well. In a V-BLAST MIMO system, the transmit antennas can carry parallel streams and multiple users can be scheduled for transmissions at the same time. We consider a multiuser diversity scheme that can effectively exploit this extra dimension in multiuser scheduling. To investigate the cross-layer aspect of the performance improvement, we perform a queuing analysis to derive buffer statistics, queuing delay distribution, packet throughput and loss rate experienced in the data link layer when this multiuser diversity technique is deployed in the system. We also present selected numerical results to show how the queuing model can help us to relate these important QoS measures to relevant physical layer and traffic parameters. Usefulness of the developed analytical model is also demonstrated through example applications.

Prototype Implementation of Real-Time ML Detectors for Spatial Multiplexing Transmission

SUMMARY We developed two types of practical maximum-likelihooddetectors (MLD) for multiple-input multiple-output (MIMO) systems, us-ing a field programmable gate array (FPGA) device. For implementations,we introduced two simplified metrics called a Manhattan metric and a cor-relation metric. Using the Manhattan metric, the detector needs no multi-plication operations, at the cost of a slight performance degradation within1dB. Using the correlation metric, the MIMO-MLD can significantly re-duce the complexity in both multiplications and additions without any per-formance degradation. This paper demonstrates the bit-error-rate perfor-mance of these MLD prototypes at a 1Gbps-order real-time processingspeed, through the use of an all-digital baseband 4 ×4 MIMO testbed inte-grated on the same FPGA chip. key words: multiple-input multiple-output (MIMO), spatial multiplex-ing, maximum-likelihood detection (MLD), field programmable gate array(FPGA), real-time MIMO detector 1. Introduction Recently, wireless communications systems that exploitmultiple transmitting and receiving antennas have receiveda significant amount of attention. These multiple-inputmultiple-output (MIMO) systems are expected to achievea dramatic increase in spectral efficiency because of theantenna diversity in scattering-rich wireless environments.Therefore, the MIMO system has been one of currentlypromising techniques to realizeGbps-class high-speed wire-less transmission for future communications systems [1].Many researchers have extensively investigated severaltechniques for multiple-antenna systems, such as the BellLaboratories layered space-time architecture (BLAST) [2]and space-time coding (STC) schemes [3].In MIMO spatial multiplexing systems, maximum-likelihood detection (MLD) schemes offer excellent perfor-mance [4]. Since the receiver estimates the most-likely sig-nals out of all the possible transmitting signals, the compu-tational complexity of distance metric calculations becomesextremely high in general. Consequently, many researchershave focused on developing more computationally efficientschemes. As a kind of low-complexity detectors, we canuse spatial filters based on the minimum mean-square error

Iterative detection for BLAST systems with an arbitrary number of receive antennas

Turbo-coded Vertical Bell Labs Layered Space-Time Architecture (V-BLAST) is a multiple-antenna system employing turbo codes and bit-interleaving to offer flexible rates and high-speed wireless data communications. The conventional detection techniques based on one-shot demodulation and decoding algorithms may suffer poor performance or simply fail when there are fewer receive antennas than transmit antennas or when the multiple-input-multiple-output (MIMO) channel exhibits strong spatial correlations. We propose employing an iterative demodulation and decoding algorithm that solves these problems and greatly extends the applicability of V-BLAST. Simulations demonstrate that iterative V-BLAST offers the best-known performance in a wide range of settings. Through complexity analysis, we show that (a) the incremental computing complexity is small, although additional memory is required, compared with the conventional one-shot maximum likelihood (ML) decoding method, and (b) an iterative algorithm employing generalized sphere decoding will be a low-complexity, memory-reduced, and high-performance solution. We also give extensions to the technique beyond simple V-BLAST. In addition, when feedback from the receiver to the transmitter is available, we illustrate how to adapt code rate, modulation, and the power distribution to take advantage of the channel knowledge. With a combination of the “best in class” receiver performance and the ability to decode V-BLAST transmissions with fewer receive antennas than transmit antennas, the techniques described here can be viewed as key “technology enablers” for BLAST/MIMO in next-generation systems.

Channel capacity of n-antenna BLAST architecture

The channel capacity of the Bell Labs layered space-time (BLAST) communication architecture is substantially larger than that of traditional systems in certain applications. However, the correlation between individual channels may severely degrade the BLAST performance. An investigation is presented into the BLAST architecture and a simple formula derived for its channel capacity as a function of the correlation coefficient. This gives a simple method of estimating BLAST performance in realistic environments.