Showing papers on "Multi-user MIMO published in 2007"

A Leakage-Based Precoding Scheme for Downlink Multi-User MIMO Channels

Abstract: In multiuser MIMO downlink communications, it is necessary to design precoding schemes that are able to suppress co-channel interference. This paper proposes designing precoders by maximizing the so-called signal-to-leakage-and-noise ratio (SLNR) for all users simultaneously. The presentation considers communications with both single- and multi-stream cases, as well as MIMO systems that employ Alamouti coding. The effect of channel estimation errors on system performance is also studied. Compared with zero-forcing solutions, the proposed method does not impose a condition on the relation between the number of transmit and receive antennas, and it also avoids noise enhancement. Simulations illustrate the performance of the scheme

MIMO Wireless Communications

Abstract: Multiple-input multiple-output (MIMO) technology constitutes a breakthrough in the design of wireless communications systems, and is already at the core of several wireless standards. Exploiting multipath scattering, MIMO techniques deliver significant performance enhancements in terms of data transmission rate and interference reduction. This book is a detailed introduction to the analysis and design of MIMO wireless systems. Beginning with an overview of MIMO technology, the authors then examine the fundamental capacity limits of MIMO systems. Transmitter design, including precoding and space-time coding, is then treated in depth, and the book closes with two chapters devoted to receiver design. Written by a team of leading experts, the book blends theoretical analysis with physical insights, and highlights a range of key design challenges. It can be used as a textbook for advanced courses on wireless communications, and will also appeal to researchers and practitioners working on MIMO wireless systems.

Channel estimation for wireless ofdm systems

Abstract: Techniques are described for efficiently estimating and compensating for the effects of a communication channel in a multi-carrier wireless communication system. The techniques exploit the fact that the transmitted symbols are drawn from a finite-alphabet to efficiently estimate the propagation channel for multi-carrier communication systems, such systems using OFDM modulation. A transmitter transmits data through a communication channel according to the modulation format. A receiver includes a demodulator to demodulate the data and an estimator to estimate the channel based on the demodulated data. The channel estimator applies a power-law operation to the demodulated data to identify the channel. The techniques can be used in both blind and semi-blind modes of channel estimation.

Survey of channel and radio propagation models for wireless MIMO systems

Abstract: This paper provides an overview of the state-of-the-art radio propagation and channel models for wireless multiple-input multiple-output (MIMO) systems. We distinguish between physical models and analytical models and discuss popular examples from both model types. Physical models focus on the double-directional propagation mechanisms between the location of transmitter and receiver without taking the antenna configuration into account. Analytical models capture physical wave propagation and antenna configuration simultaneously by describing the impulse response (equivalently, the transfer function) between the antenna arrays at both link ends. We also review some MIMO models that are included in current standardization activities for the purpose of reproducible and comparable MIMO system evaluations. Finally, we describe a couple of key features of channels and radio propagation which are not sufficiently included in current MIMO models.

Overcoming interference in spatial multiplexing MIMO cellular networks

Abstract: Multi-antenna transmission and reception (known as MIMO) is widely touted as the key technology for enabling wireless broadband services, whose widespread success will require 10 times higher spectral efficiency than current cellular systems, at 10 times lower cost per bit. Spectrally efficient, inexpensive cellular systems are by definition densely populated and interference-limited. But spatial multiplexing MIMO systems- whose principal merit is a supposed dramatic increase in spectral efficiency- lose much of their effectiveness in high levels of interference. This article overviews several approaches to handling interference in multicell MIMO systems. The discussion is applicable to any multi-antenna cellular network, including 802.16e/WiMAX, 3GPP (HSDPA and 3GPP LTE), and 3GPP2 (lxEVDO). We argue that many of the traditional interference management techniques have limited usefulness (or are even counterproductive) when viewed in concert with MIMO. The problem of interference in MIMO systems is too large in scope to be handled with a single technique: in practice a combination of complementary countermeasures will be needed. We overview emerging system-level interference-reducing strategies based on cooperation, which will be important for overcoming interference in future spatial multiplexing cellular systems.

Multiuser MIMO-OFDM for Next-Generation Wireless Systems

Abstract: This overview portrays the evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station's or radio port's coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment in multiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems.

On the Performance of the MIMO Zero-Forcing Receiver in the Presence of Channel Estimation Error

Abstract: By employing spatial multiplexing, multiple-input multiple-output (MIMO) wireless antenna systems provide increases in capacity without the need for additional spectrum or power. Zero-forcing (ZF) detection is a simple and effective technique for retrieving multiple transmitted data streams at the receiver. However the detection requires knowledge of the channel state information (CSI) and in practice accurate CSI may not be available. In this letter, we investigate the effect of channel estimation error on the performance of MIMO ZF receivers in uncorrelated Rayleigh flat fading channels. By modeling the estimation error as independent complex Gaussian random variables, tight approximations for both the post-processing SNR distribution and bit error rate (BER) for MIMO ZF receivers with M-QAM and M-PSK modulated signals are derived in closed-form. Numerical results demonstrate the tightness of our analysis

MIMO Wireless Communications: From Real-World Propagation to Space-Time Code Design

Abstract: 1. Introduction to multi-antenna communications 2. Physical MIMO channel modelling 3. Analytical MIMO channel representations for system design 4. Mutual information and capacity of real-world random MIMO channels 5. Space-time coding over I.I.D. Rayleigh flat fading channels 6. Error probability in real-world MIMO channels 7.Space-time coding over real-world MIMo channles with no transmit channel knowledge 8. Space-time coding with partial transmit channel knowledge 9.Space-time coding for frequency selective channels Appendices.

Closed-loop mimo systems and methods

Abstract: Systems and methods for closed loop MIMO (multiple input and multiple output) wireless communication are provided. Various transmit formats including spatial multiplexing and STTD are defined in which vector or matrix weighting is employed using information fed back from receivers. The feedback information may include channel matrix or SVD-based feedback.

Network MIMO: Overcoming Intercell Interference in Indoor Wireless Systems

Abstract: Network MIMO is a family of techniques whereby each user in a wireless system is served through all the access points within its range of influence By tightly coordinating the transmission and reception of signals at multiple access points, network MIMO transcends the limits on spectral efficiency due to intercell interference Taking prior information- theoretic analyses of Network MIMO to the next level, this paper quantifies the spectral efficiency gains obtainable under realistic propagation and operational conditions Our study relies on detailed simulations and, for specificity, is conducted within the framework of the IEEE 80216e Mobile WiMAX system All the relevant physical-layer functionalities of Mobile WiMAX are accurately replicated Furthermore, to facilitate the coordination between access points, we postulate an indoor deployment organized around a gigabit-ethernet backhaul The results confirm that Network MIMO stands to provide a multiple-fold increase in spectral efficiency under such conditions

Coding for MIMO Communication Systems

Abstract: Coding for MIMO Communication Systems is a comprehensive introduction and overview to the various emerging coding techniques developed for MIMO communication systems. The basics of wireless communications and fundamental issues of MIMO channel capacity are introduced and the space-time block and trellis coding techniques are covered in detail. Other signaling schemes for MIMO channels are also considered, including spatial multiplexing, concatenated coding and iterative decoding for MIMO systems, and space-time coding for non-coherent MIMO channels. Practical issues including channel correlation, channel estimation and antenna selection are also explored, with problems at the end of each chapter to clarify many important topics. A comprehensive book on coding for MIMO techniques covering main strategies Theories and practical issues on MIMO communications are examined in detail Easy to follow and accessible for both beginners and experienced practitioners in the field References at the end of each chapter for further reading Can be used with ease as a research book, or a textbook on a graduate or advanced undergraduate level course This book is aimed at advanced undergraduate and postgraduate students, researchers and practitioners in industry, as well as individuals working for government, military, science and technology institutions who would like to learn more about coding for MIMO communication systems.

Space-Time/Frequency Coding for MIMO-OFDM in Next Generation Broadband Wireless Systems

Abstract: With the advent of next generation (4G) broadband wireless communications, the combination of multiple-input multiple-output (MIMO) wireless technology with orthogonal frequency division multiplexing (OFDM) has been recognized as one of the most promising techniques to support high data rate and high performance. In particular, coding over the space, time, and frequency domains provided by MIMO-OFDM will enable a much more reliable and robust transmission over the harsh wireless environment. In this article we provide an overview of space-time (ST) coding, space-frequency (SF) coding, and space-time-frequency (STF) coding for MIMO-OFDM systems. Performance results show that STF coding can achieve the maximum diversity gain in an end- to-end MIMO-OFDM system over broadband wireless channels. Furthermore, for orthogonal frequency division multiple access (OFDMA), we propose a multiuser SF coding scheme that can achieve the maximum diversity for each user while minimizing the interference introduced from all the other users.

Multi-user MIMO-SDMA for finite rate feedback systems

Abstract: A multi-user MIMO downlink beamforming system with limited feedback ( 200 ) is provided to enable precoding for multi-stream transmission, where a channel codeword (u i ) and one or more channel quality indicator values (CQI A , CQI B ) are computed at the user equipment ( 201. i ) on the basis of maximizing a predetermined SINR performance metric (ρ i ) which estimates the receive signal-to-noise-ratio (SINR) at the user equipment ( 201. i ). The computed codeword (u i ) and CQI values (or differential values related thereto) are quantized and fed back to help the base station ( 210 ) which applies a correction to the appropriate CQI value in the course of designing the transmit beamforming vectors w and determining the appropriate modulation and coding level to be used for downlink data transmission.

Method and apparatus for providing efficient precoding feedback in a mimo wireless communication system

Abstract: Precoding feedback scheme based on Jacobi rotations to generate the feedback in the uplink. For a wireless communication system including a transmitter and a receiver. The system may use either a single codeword (SOW) or a double codeword (DCW). The precoding scheme is based on transmit beamforming (TxBF). Differential feedback is considered, with periodic non-differential feedback to avoid error accumulation or propagation due to differential processing. Precoding feedback scheme based on Jacobi rotations to generate the feedback in the uplink. For a wireless communication system including a transmitter and a receiver. The system may use either a single codeword (SOW) or a double codeword (DCW). The precoding scheme is based on transmit beamforming (TxBF). Differential feedback is considered, with periodic non-dif f erential feedback to avoid error accumulation or propagation due to differential processing.

Efficient training schemes for MIMO based wireless networks

Abstract: Schemes are disclosed for efficiently training MIMO channels in wireless networks. In at least one embodiment, multiple STAs in a network may share a single channel sounding packet to develop corresponding beamforming matrices or CSI.

Optimum Power Allocation for Single-User MIMO and Multi-User MIMO-MAC with Partial CSI

Abstract: We consider both the single-user and the multi-user power allocation problems in MIMO systems, where the receiver side has the perfect channel state information (CSI), and the transmitter side has partial CSI, which is in the form of covariance feedback. In a single-user MIMO system, we consider an iterative algorithm that solves for the eigenvalues of the optimum transmit covariance matrix that maximizes the rate. The algorithm is based on enforcing the Karush-Kuhn-Tucker (KKT) optimality conditions of the optimization problem at each iteration. We prove that this algorithm converges to the unique global optimum power allocation when initiated at an arbitrary point. We, then, consider the multi-user generalization of the problem, which is to find the eigenvalues of the optimum transmit covariance matrices of all users that maximize the sum rate of the MIMO multiple access channel (MIMO-MAC). For this problem, we propose an algorithm that finds the unique optimum power allocation policies of all users. At a given iteration, the multi-user algorithm updates the power allocation of one user, given the power allocations of the rest of the users, and iterates over all users in a round-robin fashion. Finally, we make several suggestions that significantly improve the convergence rate of the proposed algorithms.

Resource allocation to support single-user and multi-user mimo transmissions

Abstract: Techniques for supporting MIMO transmission are described. Users are classified into a first group of users to be scheduled individually for MIMO transmission and a second group of users that can be scheduled together for MIMO transmission. Transmission resources are allocated to the first and second groups, e.g., based upon various criteria such as the number of users in each group, data requirements of the users, total loading for each group, etc. The transmission resources may be hybrid automatic retransmission (HARQ) interlaces, frequency channels, time frequency resources, etc. The resource allocation may be semi-static. The transmission resources allocated to each group are used for data transmission on the downlink and/or uplink for the users in the group. HARQ with blanking may be used for data transmission for the users in the first group. HARQ without blanking may be used for data transmission for the users in the second group.

Unified design and centralized scheduling for dynamic simo, su-mimo and mu-mimo operation for rl transmissions

Abstract: Systems and methods facilitate pilot signal design, power control, data rate determination, and channel assignment in the reverse link of a wireless communication system for dynamic scheduling and joint operation in SIMO, SU-MIMO, and MU-MIMO. Pilot signal is based on periodic transmissions of multiple sounding reference sequences for channel estimation. Power control is based on a reference signal at a predetermined power spectral density (PSD) level, and on an offset PSD determined and signaled based on an antenna that transmits the reference signal, other cell interference, and power amplifier headroom. PSD levels for SIMO/MIMO data transmissions are determined based on channel estimates and the predetermined PSD and offset PSD. Such data PSD levels are employed to generate data rates, and to dynamically schedule data streams for communication. Communication resources are conveyed through a channel assignment with an overhead that depends on the maximum multiplexing order of the estimated channel.

Approach to a unified SU-MIMO/MU-MIMO operation

Abstract: An apparatus and method to dynamically schedule user devices in a wireless communication system in single-user multiple-input multiple-output (SU-MIMO) or multiple-user multiple-input multiple-output (MU-MIMO) modes of operation. The dynamic scheduling employs an efficient differential reporting of channel state information that reduces uplink feedback overhead, whereby a base layer value of a channel quality indicator (CQI) is reported in conjunction with a CQI offset value. Antenna subset selection is also reported. The offset value reflects gains by detection with successive interference cancellation if multiple antennas are reported (rank>1), while it reflects the actual offset between single-layer SU-MIMO CQI and MU-MIMO CQI if a single antenna is reported. Scheduled SU-MIMO mode of operation is optimized for a user reporting either a single antenna or multiple antennas, whereas MU-MIMO operation is optimized for a user reporting a single antenna.

Throughput Optimization of Wireless Mesh Networks with MIMO Links

Abstract: Multiple input multiple output (MIMO) antennas use sophisticated physical layer techniques to provide significant benefits over conventional antenna technology. Multiple independent data streams can be sent over the MIMO antenna elements. MIMO link can also suppress interference from neighboring links as long as the total useful streams and interfering streams are no greater than the number of receiving antenna elements. For these reasons MIMO antennas are increasingly being considered for use in interference limited wireless mesh networks and have been adopted by WLAN and WIMAX standards. However, the benefits of the MIMO technology in improving network performance are limited unless the higher layer protocols also exploit these capabilities. In this paper we are interested in characterizing the benefits of cross-layer optimizations in interference limited wireless mesh networks with MIMO links. We formulate a framework where data routing at the protocol layer, link scheduling at the MAC layer and stream control at the physical layer can be jointly optimized for throughput maximization in the presence of interference. We then develop an efficient algorithm to solve the resulting throughput optimization problem subject to fairness constraints.

Fundamentals and challenges of optical multiple-input multiple-output multimode fiber links [Topics in Optical Communications]

Abstract: In this article we discuss the application of MIMO processing to multimode fiber links. MIMO processing is shown to increase the information capacity of communication links linearly as the minimum number of transmitters/receivers increases. The fundamentals of optical MIMO fiber links are presented, and the promises and challenges of such systems are elaborated

Characterization and analysis of multi-hop wireless MIMO network throughput

Abstract: Use of multiple antennas or MIMO has great potential for enhancing the throughput of multi-hop wireless networks via spatial reuse and/or spatial division multiplexing. In this paper, we characterize and analyze the maximum achievable throughput in multi-hop wireless MIMO networks under three MIMO protocols, spatial reuse only (SRP), spatial multiplexing only (SMP), and spatial reuse & multiplexing (SRMP), each of which enhances throughput via a different way of exploiting the MIMO's potential. We show via extensive simulation that as the number of antennas increases, the maximum achievable throughput first rises and then flattens out asymptotically under SRP, while it increases "almost" linearly under SMP or SRMP. We evaluate the effects of several network parameters on this achievable throughput. We also demonstrate how these results can be used by designers to determine the optimal parameters of multi-hop wireless MIMO networks.

Mimo precoding in the presence of co-channel interference

Abstract: Methods and systems for communicating in a wireless network include mitigating co-channel interference (CCI) for precoded multiple-input multiple-output (MIMO) systems and incorporating the effect of CCI mitigation on channel characteristics in the design of channel state information (CSI) feedback mechanisms. Various embodiments and variants are also disclosed.

Cooperative MIMO Schemes Optimal Selection for Wireless Sensor Networks

Abstract: A cooperative MIMO scheme selection is proposed for wireless sensor networks where energy consumption is the most important design criterion. Space-time block codes are designed to achieve maximum diversity for a given number of transmit and receive antennas with very simple decoding algorithm. In radio fading channel, STBC require less transmission energy than SISO technique for the same bit error rate and can be employed practically in wireless sensor networks by using the cooperative MIMO scheme. Considering Alamouti and Tarokh space-time block codes, the number of antennas at both the transmission and the reception sides are selected with respect to the transmission distance. By using cooperative MIMO transmission instead of SISO, it is shown that the distance between nodes can be increased and a large amount of the total energy can be saved for middle and long distance transmission. The energy efficiency of cooperative MIMO over SISO and multihop SISO is proved by simulations, and a multi-hop technique for cooperative MIMO is also proposed for good energy-efficiency and limited number of available cooperative nodes

Generalized reference signaling scheme for mu-mimo using arbitrarily precoded reference signals

Abstract: A multi-user MIMO downlink beamforming system (200) is provided to enable transmit beamforming vectors to be efficiently provided to a subset of user equipment devices (201.i), where spatial separation or zero-forcing transmit beamformers (wi) are computed at the base station (210) and used to generate precoded reference signals (216). The precoded reference signals (216) are fed forward to the user equipment devices (201.i) which apply one or more hypothesis tests (207.i, 208.i) to the precoded reference signals to extract the precoding matrix (W), including the specific transmit beamforming vector (wUE) designed for the user equipment, and this extracted information is used to generate receive beamformers (vi).

Reference signaling scheme using compressed feedforward codebooks for MU-MIMO systems

Abstract: A multi-user MIMO downlink beamforming system with limited feed forward ( 200 ) is provided to enable preceding matrix information to be efficiently provided to a subset of user equipment devices ( 201. i ), where zero-forcing transmit beamformers (w i ) are computed at the base station ( 210 ) and assembled into a precoding matrix (W). The precoding matrix is encoded using a compact reference signal codebook ( 225, 207. i ) for forward link signaling, either by sending bits indicating the index of the transmission matrix used, or by transmitting one or more precoded pilots or reference signals wherein the pilot signals are precoded using vectors uniquely representative of the transmission matrix used which includes candidate reference signal matrices which meet a predetermined condition number requirement, such as a condition number threshold. The preceding matrix information ( 227 ) is extracted at the user equipment devices ( 201. i ) using the compact reference signal codebook ( 207. i ) and used by the MMSE receiver ( 209. i ) to generate receive beamformers (v i ).

Iterative Joint Channel Estimation and Multi-User Detection for Multiple-Antenna Aided OFDM Systems

Abstract: Multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems have recently attracted substantial research interest. However, compared to single-input-single-output (SISO) systems, channel estimation in the MIMO scenario becomes more challenging, owing to the increased number of independent transmitter-receiver links to be estimated. In the context of the Bell layered space-time architecture (BLAST) or space division multiple access (SDMA) multi-user MIMO OFDM systems, none of the known channel estimation techniques allows the number of users to be higher than the number of receiver antennas, which is often referred to as a "rank-deficient" scenario, owing to the constraint imposed by the rank of the MIMO channel matrix. Against this background, in this paper we propose a new genetic algorithm (GA) assisted iterative joint channel estimation and multi-user detection (GA-JCEMUD) approach for multi-user MIMO SDMA-OFDM systems, which provides an effective solution to the multi-user MIMO channel estimation problem in the above-mentioned rank-deficient scenario. Furthermore, the GAs invoked in the data detection literature can only provide a hard-decision output for the forward error correction (FEC) or channel decoder, which inevitably limits the system's achievable performance. By contrast, our proposed GA is capable of providing "soft" outputs and hence it becomes capable of achieving an improved performance with the aid of FEC decoders. A range of simulation results are provided to demonstrate the superiority of the proposed scheme.

Adaptive multi-user mimo non-cooperative threshold-based wireless communication system using limited channel feedback

Abstract: A system and methodology for efficient multi-user transmission in a wireless communication with limited feedback are provided. A non-cooperative feedback-based multi-user transmission scheme is described, wherein users in a wireless communication system may independently communicate selected channel information feedback to the base station. The base station may then choose suitable precoding weights based on the received channel information feedback. An adaptive threshold-based feedback approach is also described for multi-user transmission, wherein the quality of feedback for each user can be quantified by a special threshold by the system prior to engaging in multi-user communication.

Characterization of Line-of-Sight MIMO Channel for Fixed Wireless Communications

Abstract: In this letter, we proposed an approach to construct multiple-input-multiple-output (MIMO) channel in line-of-sight (LOS) environment. It could be a potential technique for high-speed data transmission in fixed broadband wireless access (BWA). Based on Ricean fading channel model, our research is focused on the characteristics of the channel matrix such as the condition number. The initial discussion starts from a 4 times 4 MIMO scheme that the four antennas formed a square array on each side. A design constraint for antenna arrangement as a function of frequency and distance is derived for the LOS MIMO communication. Since rigorous constraint is difficult to achieve in practice, simulation results of the acceptable deviation from optimal design in different cases are presented. Smart geometrical arrangement and multipolarization may also weaken this constraint

Capacity Scaling for MIMO Two-Way Relaying

Abstract: This paper considers capacity scaling in the recently proposed two-way MIMO (multiple input multiple output) relay channel. In the two-way relay channel, two nodes use a relay for exchanging data with each other. Under the assumption that each node has perfect receive channel state information and all nodes work only in half duplex mode, this paper shows that the sum capacity scales linearly with the number of transmit antennas and logarithmically with the number of relays, as the number of relays grows large. This result shows that with two- way relay channels it is possible to asymptotically (in the number of relays) obtain full-duplex performance while using only half-duplex nodes.