MIMO Technology Research Articles

A High Throughput Configurable SDR Detector for Multi-user MIMO Wireless Systems

Spatial division multiplexing (SDM) in MIMO technology significantly increases the spectral efficiency, and hence capacity, of a wireless communication system: it is a core component of the next generation wireless systems, e.g. WiMAX, 3GPP LTE and other OFDM-based communication schemes. Moreover, spatial division multiple access (SDMA) is one of the widely used techniques for sharing the wireless medium between different mobile devices. Sphere detection is a prominent method of simplifying the detection complexity in both SDM and SDMA systems while maintaining BER performance comparable with the optimum maximum-likelihood (ML) detection. On the other hand, with different standards supporting different system parameters, it is crucial for both base station and handset devices to be configurable and seamlessly switch between different modes without the need for separate dedicated hardware units. This challenge emphasizes the need for SDR designs that target the handset devices. In this paper, we propose the architecture and FPGA realization of a configurable sort-free sphere detector, Flex-Sphere, that supports 4, 16, 64-QAM modulations as well as a combination of 2, 3 and 4 antenna/user configuration for handsets. The detector provides a data rate of up to 857.1 Mbps that fits well within the requirements of any of the next generation wireless standards. The algorithmic optimizations employed to produce an FPGA friendly realization are discussed.

Transmit Diversity Schemes for BCH Transmission in IEEE 802.16m

IEEE802.16m standard is based on the MIMO-OFDM technology to provide high speed packet data service both in downlink and uplink. For the downlink broadcasting of control information, in order to extend the coverage of a cell, the nominal operating point should be set for the user at the edge of a cell, and no feedback should be used. For broadcasting that information, the MIMO technology should take a transmit diversity form targeted for low SNR. Several transmit diversity schemes are presented and preferable modes of operations for the broadcasting channel are proposed with numerical analysis.

Optimization of the spectral efficiency in MIMO cellular wireless communications

Expressions are derived that make it possible to calculate and optimize the spectral efficiency (SE) of multiple-input-multiple-output (MIMO) cellular wireless communication systems (WCSs) with allowance for the interaction of radiators in the receiving and transmitting antennas of the MIMO systems, the properties of the deterministic radio channel, and the presence of directionally concentrated interference. The effect of the interaction of radiators on the SE of the MIMO systems is studied, and the efficiency of the MIMO technology is analyzed on the basis of the model example of two receiving and two transmitting antennas with a conducting screen placed in between them. It is demonstrated that, in comparison to single-channel-transmission technology, MIMO technology allows an increase the WCS SE only at relatively high values of the signal-to-interference-plus-noise ratio at the receiver input and in the case of nearly equal channel gains. It is shown that the relative positions of the transmitter and receiver at which the MIMO-WCS SE can be significantly increased are dependent on the channel energy and are substantially limited at real powers transmitted under urban conditions.

BER analysis of MPSK space-time code with differential detection over correlated block-fading Rayleigh channel

MIMO technology proposed in recent years can effectively combat the multipath fading of wireless channel and can considerably enlarge the channel capacity, which has been investigated widely by researchers. However, its performance analysis over correlated block-fading Rayleigh channel is still an open and challenging objective. In this article, an analytic expression of bit error rate (BER) is presented for multiple phase shift keying (MPSK) space-time code, with differential detection over correlated block-fading Rayleigh channel. Through theoretical analysis of BER, it can be found that the differential space-time scheme without the need for channel state information (CSI) at receiver achieves distinct performance gain compared with the traditional nonspace-time system. And then, the system simulation is complimented to verify the above result, showing that the diversity system based on the differential space-time block coding (DSTBC) outperforms the traditional nonspace- time system with diversity gain in terms of BER. Furthermore, the numerical results also demonstrate that the error floor of the differential space-time system is much lower than that of the differential nonspace-time system.

Mobile WiMax: The Next Wireless Battle Ground

One of the newest technologies to join the fray is mobile WiMax, a version of traditional WiMax (worldwide interoperability for microwave access), which enables high-speed fixed wireless communications. Mobile WiMax proponents hope their approach will compete with cellular, Wi-Fi, and last-mile Internet-access technologies such as DSL and cable. The IEEE plans to adopt mobile WiMax 2.0, formally called IEEE 802.16m later this year. The technology would offer data rates of 100 Mbps for mobile uses and 1 Gbps for fixed applications via enhanced MIMO technology. If adopted on schedule, industry observers expect mobile WiMax 2.0 to appear in products by 2012.

Enhanced MIMO wireless video communication using multiple-description coding

Significant enhancements in spectral efficiency and error-resilience must be obtained from emerging wireless video systems if high-quality multimedia transmission is to become cost-effective. MIMO (multiple-input-multiple-output) technology promises to deliver the sustainable high transmission quality required for such applications. MIMO is a generic technology which, depending on the actual architecture deployed and the channel conditions encountered, produces variable error conditions. In particular, the way these errors interact with the transmitted data will depend on both the data source and the coding mechanism employed. In this context, this paper focuses on the interactions when MIMO systems are used to transmit compressed video. In terms of multimedia transmission, spatial multiplexing (SM) has often been proposed as the most suitable MIMO technique. Most SM-based video transport schemes focus on the advantages of multiplexing gain, which are achieved at the expense of relatively high SNR values. This paper proposes the use of multiple-description video coding (MDC) as a means of emulating the spatial diversity lacking in SM systems, to provide a new class of wireless video transmission algorithm. Singular value decomposition (SVD) is employed to create orthogonal sub-channels which provide an efficient means of mapping video content to the wireless channels. Extensive simulations demonstrate the effectiveness of MDC as a video decomposition which couples well with the underpinning SVD architecture. In addition, resource allocation in MIMO-SVD systems is examined in the context of transmitted video quality, and further enhancements have been achieved for low SNR values. Results indicate improvements in average PSNR of the decoded test sequences of around 5–7 dB, compared to standard, single-description video transmission. This is further enhanced by an additional 2–3 dB in the case of channels with low SNR values through the use of unequal power allocation. This approach is particularly well suited to MDC. The results presented are supported by significant enhancements in subjective quality and form the basis of a strong case in favour of MDC-based MIMO systems.

An overview of MIMO-oriented channel access in wireless networks

The integration of MIMO technology in WLANs has recently been the locus of extensive research. The main objectives of this technology are to improve channel reuse and or reduce energy consumption. In this article, we give an overview of MIMO systems and their use in WLANs. We highlight the different types of gains that MIMO offers and then discuss some of the work that has been done on MAC design. We conclude by outlining several open issues thai must be addressed for MIMO-based systems.

High Efficient Mobile WiMAX with MIMO and Miltihop Relay

MIMO and relay technology is currently being promoted within the IEEE to enhance performance of broadband wireless standards such as WiMAX. However, due to licensed spectrum, it is necessary to implement highly efficient radio resource management. For optimal system design, it is beneficial to achieve higher system data throughput with fewer radio resources employed. This paper presents a comprehensive study of MIMO mobile WiMAX with multihop relay technology for high efficient multiuser transmission. A directional distributed relaying architecture is introduced in order to leverage link-level and system-level capacity. Practical applications are also demonstrated for an example urban environment.

Advances in smart antennas - Industrial embrace of smart antennas and MIMO

In this article we provide a practical standardization related viewpoint on beamforming and MIMO technologies. In particular, we address the status in different industry-driven standardization for a (3GPP and IEEE 802) and discuss the rationale for possible adoption or use of such technologies in current or future wireless systems. We draw attention to some practical system-level and implementation aspects that need to be resolved before a successful application of beamforming or MIMO in real systems

Low complexity detection of high-order modulations in multiple antenna systems

Mobile receiver complexity persists as one of the key areas of concern in the adoption of MIMO technologies for systems such as high-speed downlink packet access in UMTS. This is particularly the case for high-order modulation schemes such as 16- and 64-QAM, where optimum a posteriori probability detection becomes too complex, and sub-optimal detection based on serial or parallel interference cancellation performs poorly. The above issues are successfully tackled by introducing a judicious layered encoding process at the transmitter which, once appropriately exploited at the receiver, allows considerable reductions in computational complexity in addition to improvements in performance. Also, the applicability of high-order modulations with layered encoding is investigated using system-level simulations for a 2-cell and a 7-cell urban scenario. It is shown that high-order modulations can be used in a substantial area of the cell for both investigated scenarios.

A MIMO-OFDM prototype for next-generation wireless WANs

Coupled with a robust and efficient OFDM air interface, MIMO technologies lead to a very compelling high-speed data downlink solution for future wireless systems. This article presents Nortel Networks' MIMO-OFDM concept prototype and measured performance results. This prototype has been developed in the framework of a Nortel Networks system concept for 3G evolution systems and next-generation wide area wireless networks. The prototype is based on a shared access MIMO-OFDM physical layer in the downlink, supporting adaptive modulation and coding, with peak rates up to 37 Mb/s. The uplink is based on an enhanced UMTS WCDMA physical layer. Performance for the high-speed downlink has been measured under various emulated fading conditions. The measured performance illustrates the robustness of OFDM in frequency-selective channels and high-speed mobility channels, supporting speeds as high as 200 km/h. The prototype can also be used for over-the-air assessment of the technology.