Showing papers on "Multi-user MIMO published in 2010"

Multi-Cell MIMO Cooperative Networks: A New Look at Interference

Abstract: This paper presents an overview of the theory and currently known techniques for multi-cell MIMO (multiple input multiple output) cooperation in wireless networks. In dense networks where interference emerges as the key capacity-limiting factor, multi-cell cooperation can dramatically improve the system performance. Remarkably, such techniques literally exploit inter-cell interference by allowing the user data to be jointly processed by several interfering base stations, thus mimicking the benefits of a large virtual MIMO array. Multi-cell MIMO cooperation concepts are examined from different perspectives, including an examination of the fundamental information-theoretic limits, a review of the coding and signal processing algorithmic developments, and, going beyond that, consideration of very practical issues related to scalability and system-level integration. A few promising and quite fundamental research avenues are also suggested.

MIMO techniques in WiMAX and LTE: a feature overview

Abstract: IEEE 802.16m and 3GPP LTE-Advanced are the two evolving standards targeting 4G wireless systems. In both standards, multiple-input multiple-output antenna technologies play an essential role in meeting the 4G requirements. The application of MIMO technologies is one of the most crucial distinctions between 3G and 4G. It not only enhances the conventional point-to-point link, but also enables new types of links such as downlink multiuser MIMO. A large family of MIMO techniques has been developed for various links and with various amounts of available channel state information in both IEEE 802.16e/m and 3GPP LTE/LTE-Advanced. In this article we provide a survey of the MIMO techniques in the two standards. The MIMO features of the two are compared, and the engineering considerations are depicted.

Cooperative MIMO channel models: A survey

Abstract: Cooperative multiple-input multiple-output technology allows a wireless network to coordinate among distributed antennas and achieve considerable performance gains similar to those provided by conventional MIMO systems. It promises significant improvements in spectral efficiency and network coverage and is a major candidate technology in various standard proposals for the fourth-generation wireless communication systems. For the design and accurate performance assessment of cooperative MIMO systems, realistic cooperative MIMO channel models are indispensable. This article provides an overview of the state of the art in cooperative MIMO channel modeling. We show that although the existing standardized point-to-point MIMO channel models can be applied to a certain extent to model cooperative MIMO channels, many new challenges remain in cooperative MIMO channel modeling, such as how to model mobile-to-mobile channels, and how to characterize the heterogeneity and correlation of multiple links at the system level appropriately.

Degrees of Freedom of the MIMO Y Channel: Signal Space Alignment for Network Coding

Abstract: In this paper, we study a network information flow problem for a multiple-input-multiple-output (MIMO) Gaussian wireless network with three users each equipped with M antennas and a single intermediate relay equipped with N antennas. In this network, each user intends to convey independent messages for two different users via the intermediate relay while receiving two independent messages from the other two users. This is a generalized version of the two-way relay channel for the three-user case. We will call it a "MIMO Y channel." For this MIMO Y channel, we show that the capacity is 3M log(SNR) + o(log(SNR)) if N ≥ ⌈3M/2⌉ by using two novel signaling techniques, which are signal space alignment for network coding, and network-coding-aware interference nulling beamforming.

Automatic Secret Keys From Reciprocal MIMO Wireless Channels: Measurement and Analysis

Abstract: Information theoretic limits for random key generation in multiple-input multiple-output (MIMO) wireless systems exhibiting a reciprocal channel response are investigated experimentally with a new three-node MIMO measurement campaign. As background, simple expressions are presented for the number of available key bits, as well as the number of bits that are secure from a close eavesdropper. Two methods for generating secret keys are analyzed in the context of MIMO channels and their mismatch rate and efficiency are derived. A new wideband indoor MIMO measurement campaign in the 2.51- to 2.59-GHz band is presented, whose purpose is to study the number of available key bits in both line-of-sight and nonline-of-sight environments. Application of the key generation methods to measured propagation channels indicates key generation rates that can be obtained in practice for four-element arrays.

Relative channel reciprocity calibration in MIMO/TDD systems

Abstract: Channel state information at the transmitter (CSIT) can greatly improve the capacity of a wireless MIMO communication system. In a time division duplex (TDD) system CSIT can be obtained by exploiting the reciprocity of the wireless channel. This however requires calibration of the radio frequency (RF) chains of the receiver and the transmitter, which are in general not reciprocal. In this paper we investigate different methods for relative calibration in the presence of frequency offsets between transmitter and receiver. We show results of theses calibration methods with real two-directional channel measurements, which were performed using the Eure-com MIMO Openair Sounder (EMOS). We demonstrate that in a single-user MIMO channel and for low signal-to-noise (SNR) ratios, the relative calibration method can increase the capacity close to the theoretical limit.

Downlink Interference Alignment

Abstract: We develop an interference alignment (IA) technique for a downlink cellular system. In the uplink, IA schemes need channel-state-information exchange across base-stations of different cells, but our downlink IA technique requires feedback only within a cell. As a result, the proposed scheme can be implemented with minimal changes to an existing cellular system where the feedback mechanism (within a cell) is already being considered for supporting multi-user MIMO. Not only is our proposed scheme implementable with little effort, it can in fact provide substantial gain especially when interference from a dominant interferer is significantly stronger than the remaining interference: it is shown that in the two-isolated cell layout, our scheme provides four-fold gain in throughput performance over a standard multi-user MIMO technique. We show through simulations that our technique provides respectable gain under a more realistic scenario: it gives approximately 20% gain for a 19 hexagonal wrap-around-cell layout.

Design and experimental evaluation of multi-user beamforming in wireless LANs

Abstract: Multi-User MIMO promises to increase the spectral efficiency of next generation wireless systems and is currently being incorporated in future industry standards. Although a significant amount of research has focused on theoretical capacity analysis, little is known about the performance of such systems in practice. In this paper, we present the design and implementation of the first multi-user beamforming system and experimental framework for wireless LANs. Using extensive measurements in an indoor environment, we evaluate the impact of receiver separation distance, outdated channel information due to mobility and environmental variation, and the potential for increasing spatial reuse. For the measured indoor environment, our results reveal that two receivers achieve close to maximum performance with a minimum separation distance of a quarter of a wavelength. We also show that the required channel information update rate is dependent on environmental variation and user mobility as well as a per-link SNR requirement. Assuming that a link can tolerate an SNR decrease of 3 dB, the required channel update rate is equal to 100 and 10 ms for non-mobile receivers and mobile receivers with a pedestrian speed of 3 mph respectively. Our results also show that spatial reuse can be increased by efficiently eliminating interference at any desired location; however, this may come at the expense of a significant drop in the quality of the served users.

MIMO rate adaptation in 802.11n wireless networks

Abstract: This paper studies MIMO based rate adaptation (RA) in 802.11n wireless networks. Our case study shows that existing RA algorithms offer much lower throughput than even a fixed-rate scheme. The fundamental problem is that, all such algorithms are MIMO oblivious; they do not consider the characteristics of diversity-oriented, single-stream mode and the spatial multiplexing driven, double-stream mode. We propose MiRA, a novel MIMO RA scheme that zigzags between intra- and inter-mode rate options. Our experiments show that MiRA consistently outperforms three representative RA algorithms, SampleRate, RRAA and Atheros MIMO RA, in static, mobility and collision settings.

MIMO Networks: The Effects of Interference

Abstract: Multiple-input multiple-output (MIMO) systems are being considered as one of the key enabling technologies for future wireless networks. However, the decrease in capacity due to the presence of interferers in MIMO networks is not well understood. In this paper, we develop an analytical framework to characterize the capacity of MIMO communication systems in the presence of multiple MIMO co-channel interferers and noise. We consider the situation in which transmitters have no channel state information, and all links undergo Rayleigh fading. We first generalize the determinant representation of hypergeometric functions with matrix arguments to the case when the argument matrices have eigenvalues of arbitrary multiplicity. This enables the derivation of the distribution of the eigenvalues of Gaussian quadratic forms and Wishart matrices with arbitrary correlation, with application to both single-user and multiuser MIMO systems. In particular, we derive the ergodic mutual information for MIMO systems in the presence of multiple MIMO interferers. Our analysis is valid for any number of interferers, each with arbitrary number of antennas having possibly unequal power levels. This framework, therefore, accommodates the study of distributed MIMO systems and accounts for different spatial positions of the MIMO interferers.

Method and apparatus for supporting single-user multiple-input multiple-output (su-mimo) and multi-user mimo (mu-mimo)

Abstract: Techniques for supporting data transmission with single-user multiple-input multiple-output (SU-MIMO) and multi-user MIMO (MU-MIMO) are described. A base station may transmit multiple data streams on a given time-frequency resource to a single user equipment (UE) for SU-MIMO or to multiple UEs for MU-MIMO. In an aspect, an antenna port assignment for a UE for MU-MIMO may be conveyed by reusing one or more fields of a downlink control information (DCI) format. In another aspect, a hierarchical two-tier structure may be used to convey an antenna port assignment for a UE for MU-MIMO. In yet another aspect, a UE may be configured via higher layer to report only channel quality indicator (CQI), or both CQI and precoding matrix indicator (PMI), when operating in a transmission mode supporting SU-MIMO and MU-MIMO. In yet another aspect, a UE may report CQI such that SU-MIMO and MU-MIMO can be supported for the UE.

Least Squares Approach to Joint Beam Design for Interference Alignment in Multiuser Multi-Input Multi-Output Interference Channels

Abstract: In this correspondence, the problem of interference alignment for K-user time-invariant multi-input multi-output interference channels is considered. The necessary and sufficient conditions for interference alignment are converted to a system of linear equations that have dummy variables. Based on this linear system, a new algorithm for beam design for interference alignment is proposed by minimizing the overall interference misalignment. The proposed algorithm consists of solving a least squares problem iteratively. The convergence of the proposed algorithm is established, and its complexity is analyzed. The performance of the proposed algorithm is also evaluated numerically. It is shown that the proposed algorithm has faster convergence and lower complexity than the previous method with a comparable sum rate performance in the most practical case of two receive antennas.

Improving Energy Efficiency in a Wireless Sensor Network by Combining Cooperative MIMO With Data Aggregation

Abstract: In wireless sensor networks where nodes are powered by batteries, it is critical to prolong the network lifetime by minimizing the energy consumption of each node. In this paper, the cooperative multiple-input-multiple-output (MIMO) and data-aggregation techniques are jointly adopted to reduce the energy consumption per bit in wireless sensor networks by reducing the amount of data for transmission and better using network resources through cooperative communication. For this purpose, we derive a new energy model that considers the correlation between data generated by nodes and the distance between them for a cluster-based sensor network by employing the combined techniques. Using this model, the effect of the cluster size on the average energy consumption per node can be analyzed. It is shown that the energy efficiency of the network can significantly be enhanced in cooperative MIMO systems with data aggregation, compared with either cooperative MIMO systems without data aggregation or data-aggregation systems without cooperative MIMO, if sensor nodes are properly clusterized. Both centralized and distributed data-aggregation schemes for the cooperating nodes to exchange and compress their data are also proposed and appraised, which lead to diverse impacts of data correlation on the energy performance of the integrated cooperative MIMO and data-aggregation systems.

Wireless Communication Systems: From RF Subsystems to 4G Enabling Technologies

Abstract: This practically-oriented, all-inclusive guide covers all the major enabling techniques for current and next-generation cellular communications and wireless networking systems Technologies covered include CDMA, OFDM, UWB, turbo and LDPC coding, smart antennas, wireless ad hoc and sensor networks, MIMO, and cognitive radios, providing readers with everything they need to master wireless systems design in a single volume Uniquely, a detailed introduction to the properties, design, and selection of RF subsystems and antennas is provided, giving readers a clear overview of the whole wireless system It is also the first textbook to include a complete introduction to speech coders and video coders used in wireless systems Richly illustrated with over 400 figures, and with a unique emphasis on practical and state-of-the-art techniques in system design, rather than on the mathematical foundations, this book is ideal for graduate students and researchers in wireless communications, as well as for wireless and telecom engineers

Adaptive MIMO transmission techniques for broadband wireless communication systems [Topics in Wireless Communications]

Abstract: Link adaptation is a way to increase data rates in wireless systems by adapting transmission parameters such as the modulation and coding rate. While link adaptation in single antenna systems is now mature, its application to multiple-input multiple-output communication links, presented in several emerging wireless standards, has been challenging. The main reason is that the space-time transmission strategy can also be adjusted in MIMO communication links, introducing a new dimension for adaptation. This means that practical MIMO link adaptation algorithms must also provide a dynamic adaptation between diversity and multiplexing modes of operation. This article reviews a recently proposed framework for adaptive MIMO architectures and shows how to use this framework to reduce adaptive control overhead. We also discuss practical implementation issues. Simulations in an IEEE 802.16e (mobile WiMAX) system illustrate the frame-work's potential improvements in data rates.

Method and apparatus for transmitting reference signal for reducing inter-cell interference in multiple input multiple output communication system

Abstract: Disclosed is a method for transmitting a reference signal, in a method for transmitting a Channel State Information-Reference Signal (CSI-RS) for measuring a transmission channel according to each antenna and a data signal in a broadband wireless communication system based on a MIMO scheme through a plurality of antennas.

Method and apparatus for transmitting multi-user mimo reference signal in wireless communication system for supporting relay

Abstract: A method for transmitting a demodulation reference signal (DMRS) for down-link multi-user MIMO transmission according to an embodiment of the present invention comprises the steps of: mapping a DMRS for a first layer on a down-link physical resource block according to a first DMRS pattern; mapping a DMRS for a second layer on the down-link physical resource block according to a second DMRS pattern; and transmitting the down-link physical resource block. In the down-link physical resource block, a resource element corresponding to the second DMRS pattern can be punctured on the first layer and a resource element corresponding to the first DMRS pattern can be punctured on the first layer and a resource element corresponding to the first DMRS pattern can be punctured on the second layer.

Physical Layer Network Coding with Multiple Antennas

Abstract: The two-phase MIMO NC (network coding) scheme can be used to boost the throughput in a two-way relay channel in which nodes are equipped with multiple antennas. The obvious strategy is for the relay node to extract the individual packets from the two end nodes and mix the two packets to form a network-coded packet. In this paper, we propose a new scheme called MIMO PNC (physical network coding), in which the relay extracts the summation and difference of the two end packets and then converts them to the network-coded form. MIMO PNC is a natural combination of the single-antenna PNC scheme and the linear MIMO detection scheme. The advantages of MIMO PNC are many. First, it removes the stringent carrier-phase requirement in single-antenna PNC. Second, it is linear in complexity with respect to the constellation size and the number of simultaneous data streams in MIMO. Simulation shows that MIMO PNC outperforms the straightforward MIMO NC significantly under random Rayleigh fading channel. Based on our analysis, we further conjecture that MIMO PNC outperforms MIMO NC under all possible realizations of the channel.

A New SLNR-Based Linear Precoding for Downlink Multi-User Multi-Stream MIMO Systems

Abstract: Signal-to-leakage-and-noise ratio (SLNR) is a promising criterion for linear precoder design in multi-user (MU) multiple-input multiple-output (MIMO) systems. It decouples the precoder design problem and makes closed-form solution available. In this letter, we present a new linear precoding scheme by slightly relaxing the SLNR maximization for MU-MIMO systems with multiple data streams per user. The precoding matrices are obtained by a general form of simultaneous diagonalization of two Hermitian matrices. The new scheme reduces the gap between the per-stream effective channel gains, an inherent limitation in the original SLNR precoding scheme. Simulation results demonstrate that the proposed precoding achieves considerable gains in error performance over the original one for multi-stream transmission while maintaining almost the same achievable sum-rate.

Methods and apparatus for multi-user mimo transmissions in wireless communication systems

Abstract: A wireless communication system includes a base station capable of communicating with a plurality of subscriber stations. The base station can transmit control information and data to a subscriber stations. The base station also can identify a set of RS patterns to be used to communicate with the subscriber station, assign a subset of antenna port numbers within the set of RS patterns to the subscriber stations. The base station can indicate the assigned states in a Downlink Control Information (DCI) format transmitted in a Physical Downlink Control Channel (PDCCH). The base station transmits the data using a subset of antenna ports corresponding to the subset of antenna port numbers. The base station also can map reference signals corresponding to the subset of antenna ports according to at least one RS pattern within the set of RS patterns.

MIMO Transmission with Rank Adaptation for Multi-Gigabit 60GHz Wireless

Abstract: In this paper, we propose a practical and systematic approach to implement the MIMO transmission with rank adaptation for 60 GHz systems. In the 60 GHz system with multiple antennas, the transmit and receive (Tx-Rx) antenna arrays are grouped into a number of subarrays with a predetermined subarray separation based on the derived geometrical criteria of creating high rank MIMO in LoS environments. We first apply an enhanced blind beamforming technique based on a stochastic gradient algorithm (SGA) for the inner-subarray antennas, which does not require channel state information (CSI) at either the transmitter or the receiver. Secondly, the composite MIMO channel, as a joint effect of Tx-Rx beamforming and the channel impulse response, can be estimated with much reduced complexity. Finally, the MIMO transmission with rank adaptation is performed by adaptively selecting the better scheme out of the high-rank spatial multiplexing and the rank-1 beamforming whichever gives higher system throughput. Simulation results show that high-rank spatial multiplexing and rank-1 beamforming outperform each other at different geometrical placements and transmit power settings. The proposed MIMO transmission with rank adaptation offers significant performance gain especially at high signal-to-noise ratio (SNR) regions.

Cooperative Diversity in Wireless Networks

Abstract: Transmit Diversity is an effective methodology for improving the quality and reliability of a wireless network by reducing the effects of fading. As majority of the wireless devices (i.e. mobile handsets, etc) are limited to only one antenna, especially due to hardware constraints, size and cost factors; cooperative communication can be utilized in order to generate transmit diversity [1]. This enables single antenna wireless devices to share their antennas during transmission in such a manner that creates a virtual MIMO (multiple-input and multiple-output) system [2] [3]. In this paper, we will analyze the recent developments and trends in this promising area of wireless Ad hoc networks. The article will also discuss various main cooperative signaling methods and will also observe their performance.

Multi-rank precoding matrix indicator (pmi) feedback in a multiple-input multiple-output (mimo) system

Abstract: In at least some embodiments, a system includes a multiple-input multiple-output (MIMO) base station and a plurality of MIMO user equipment (UE) devices in communication with the MIMO base station. The MIMO base station is configured to switch between a single-user (SU)-MIMO mode and a multiple-user (MU)-MIMO mode during communications with the plurality of MIMO UE devices based on multi-rank precoding matrix indicator (PMI) feedback received from at least one of the MIMO UE devices.

A Dynamic Dual-Link Wideband MIMO Channel Sounder for 5.3 GHz

Abstract: In this paper, we present and evaluate the performance of a dynamic dual-link wideband multiple-input-multiple-output (MIMO) channel sounder. The channel sounder can simultaneously measure two wideband dual-polarized links, each with a MIMO matrix size of 30 × 30 and 30 × 32. Multilink MIMO systems, including multiuser and cooperative MIMO, are essential parts of future high-throughput wireless local area networks and fourth-generation cellular systems. To fully understand such systems, the dynamic characteristics of multilink MIMO channels have to be measured. In this paper, we present a channel sounder that enables such measurements, including double-directional parameter estimation possibility for both links. The presented dual-link MIMO channel sounder does not suffer from the deficiencies of previous "virtual multiuser"measurement systems. Furthermore, system analysis and sample results from a measurement campaign with this channel sounder at 5.3 GHz in an indoor office environment are presented.

Experimental Evaluation of MIMO Capacity and Correlation for Narrowband Body-Centric Wireless Channels

Abstract: Using multiple antennas at the transmitter and receiver has shown a remarkable scope for capacity increase for indoor wireless mobile and PAN communications and is here extended to on-body channels. The capacity and multiple-input multiple-output (MIMO) channel correlation analysis has been performed at 2.45 GHz frequency using planar inverted-F antennas (PIFA) for three on-body channels. The improvement offered by 2 × 2 MIMO over the conventional single-input single-output link for the on-body channels has been discussed. The variation of capacity with Rician K-factor is shown and the MIMO channel spatial correlation matrices are presented. The effect of correlation on the channel capacity is discussed.

Improved Linear Transmit Processing for Single-User and Multi-User MIMO Communications Systems

Abstract: In this paper, we propose a novel linear transmit precoding strategy for multiple-input, multiple-output (MIMO) systems employing improper signal constellations. In particular, improved zero-forcing (ZF) and minimum mean square error (MMSE) precoders are derived based on modified cost functions, and are shown to achieve a superior performance without loss of spectrum efficiency compared to the conventional linear and nonlinear precoders. The superiority of the proposed precoders over the conventional solutions are verified by both simulation and analytical results. The novel approach to precoding design is also applied to the case of an imperfect channel estimate with a known error covariance as well as to the multi-user scenario where precoding based on the nullspace of channel transmission matrix is employed to decouple multi-user channels. In both cases, the improved precoding schemes yield significant performance gain compared to the conventional counterparts.

Global and Fast Receiver Antenna Selection for MIMO Systems

Abstract: For a multiple-input multiple-output (MIMO) system with more antennas at the receiver than the transmitter, selecting the same number of receiver antennas as the number of transmit antennas captures most of the advantages of MIMO capacity performance and reduces the system hardware and computational cost at the same time. In this paper, a fast and global-search receive antenna selection algorithm is proposed for this MIMO array configuration. Different from many existing fast but `local' antenna selection algorithms which obtain the sub-optimal channel submatrix by adding or removing one row per step, our algorithm acquires the near-optimal channel matrix by {directly} and {rapidly} searching the maximum-volume submatrix of the original channel matrix. Due to its "globally searching" property, our antenna selection algorithm leads to a substantial improvement in the capacity optimality for moderate to high SNRs, and obtains almost the same capacity performance as that of the exhaustive-search-based optimal antenna selection algorithm. Furthermore, the computational load and memory requirement for our antenna selection method are still comparable to those of the existing sub-optimal antenna selection methods. Numerical results are provided to verify the validity of the proposed methods.

Mimo and mu-mimo ofdm preambles

Abstract: Certain aspects of the present disclosure present frame structures to support a plurality of standards, such as the IEEE 802.11 ac in addition to the IEEE 802.11 a/b/n/g. Preamble of the frame structure can be used by a receiver to detect transmission mode of the packet.

Proportional fair scheduling for multi-cell multi-user MIMO systems

Abstract: In this paper, a multi-cell multi-user MIMO scheme with advanced user pairing and scheduling algorithm is proposed to effectively explore multi-user diversity and to combat both intra-cell and inter-cell interference in the downlink of wireless communication systems. The optimality of the proposed user paring and scheduling algorithm is shown under generalized proportional fair metrics. System-level simulations are conducted to verify the performance of the proposed scheme with the agreed LTE-Advanced (LTE-A) system parameters. The results suggest the proposed scheme is a promising candidate for improving both the cell-edge user throughput and average cell throughput, and furthermore for fulfilling the IMT-Advanced (IMT-A) requirements.

Multi-service multi-carrier broadband MIMO distributed antenna systems for in-building optical wireless access

Abstract: A novel broad spectrum band-shifting technique is experimentally demonstrated to simultaneously transmit broadband (500MHz to 3 GHz) multi-service, multi-carrier MIMO signals for in-building radio-over-fiber based wireless distributed antenna systems. The proposed scheme uses fewer local oscillators and does not require any service-specific narrowband band pass filters, thus upgrading of existing non-MIMO services to MIMO services or adding new MIMO services would be easier and cost-effective.