Showing papers on "Multi-user MIMO published in 2011"

The Secrecy Capacity of the MIMO Wiretap Channel

Abstract: We consider the MIMO wiretap channel, that is a MIMO broadcast channel where the transmitter sends some confidential information to one user which is a legitimate receiver, while the other user is an eavesdropper. Perfect secrecy is achieved when the transmitter and the legitimate receiver can communicate at some positive rate, while insuring that the eavesdropper gets zero bits of information. In this paper, we compute the perfect secrecy capacity of the multiple antenna MIMO broadcast channel, where the number of antennas is arbitrary for both the transmitter and the two receivers. Our technique involves a careful study of a Sato-like upper bound via the solution of a certain algebraic Riccati equation.

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 a few 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 also show through simulations that our technique provides respectable gain under a more realistic scenario: it gives approximately 28% gain for a 19 hexagonal wrap-around-cell layout. Furthermore, we show that our scheme has the potential to provide substantial gain for macro-pico cellular networks where pico-users can be significantly interfered with by the nearby macro-BS.

Gigabit wireless LANs: an overview of IEEE 802.11ac and 802.11ad

Abstract: This paper gives an overview of the upcoming IEEE Gigabit Wireless LAN amendments, i.e. IEEE 802.11ac and 802.11ad. Both standard amendments advance wireless networking throughput beyond gigabit rates. 802.11ac adds multi-user access techniques in the form of downlink multi-user (DL MU) multiple input multiple output (MIMO)and 80 and 160 MHz channels in the 5 GHz band for applications such as multiple simultaneous video streams throughout the home. 802.11ad takes advantage of the large swath of available spectrum in the 60 GHz band and defines protocols to enable throughput intensive applications such as wireless I/O or uncompressed video. New waveforms for 60 GHz include single carrier and orthogonal frequency division multiplex (OFDM). Enhancements beyond the new 60 GHz PHY include Personal Basic Service Set (PBSS) operation, directional medium access, and beamforming. We describe 802.11ac channelization, PHY design, MAC modifications, and DL MU MIMO. For 802.11ad, the new PHY layer, MAC enhancements, and beamforming are presented.

System and method for channel state related feedback in multi-user multiple-input-multiple-output systems

Abstract: System and method for dimension reduction and for channel and interference condition feedback in a Multi-User Multiple-Input-Multiple-Output (MU MIMO) wireless communication systems. The method for dimension reduction includes determining a number of virtual antennas,ν?K#191, for beamformees pertaining to a multi user (MU) transmission group, reducing the dimension of said matrix by selecting a sub-set of antennas or by Eigen mode selection and sending a reduced dimension candidate transmit beamforming matrix or an effective channel matrix to a beamformer. The method for channel and interference condition feedback Interference condition includes sending to a beamformee metric indicative of the interference level from other streams.

Analysis of the pilot contamination effect in very large multicell multiuser MIMO systems for physical channel models

Abstract: We consider multicell multiuser MIMO systems with a very large number of antennas at the base station. We assume that the channel is estimated by using uplink training sequences, and we consider a physical channel model where the angular domain is separated into a finite number of directions. We analyze the so-called pilot contamination effect discovered in previous work, and show that this effect persists under the finite-dimensional channel model that we consider. We further derive closed-form bounds on the achievable rate of uplink data transmission with maximum-ratio combining, for a finite and an infinite number of base station antennas.

MIMO Broadcasting for Simultaneous Wireless Information and Power Transfer

Abstract: This paper studies the performance limits of multi-antenna wireless broadcasting systems for simultaneous information and power (energy) transfer. For the purpose of exposition, a three-node network is investigated, in which one receiver harvests energy and another receiver decodes information separately from the signals broadcast by a common transmitter. Two scenarios are examined, where the information receiver and energy receiver are separated and see different channels from the transmitter, or co-located and see the same channel from the transmitter. For the case of separated receivers, we derive the optimal transmission strategies to achieve different tradeoffs for maximal information rate versus energy transfer, which are characterized by the boundary of a so-called rate-energy (R-E) region. For the case of co-located receivers, we show an outer bound for the achievable R-E region, due to the potential limitation that practical circuits for harvesting energy from radio signals are not yet able to decode the carried information at the same time. Under this constraint, we propose two practical receiver designs for the co-located receivers, namely, time switching and power splitting, and characterize their achievable R-E regions in comparison with the outer bound.

Correlation Rotation Linear Precoding for MIMO Broadcast Communications

Abstract: A simple linear precoding technique is proposed for multiple input multiple output (MIMO) broadcast systems using phase shift keying (PSK) modulation. The proposed technique is based on the fact that, on an instantaneous basis, the interference between spatial links in a MIMO system can be constructive and can contribute to the power of the useful signal to improve the performance of signal detection. In MIMO downlinks this co-channel interference (CCI) can be predicted and characterised prior to transmission. Contrary to common practice where knowledge of the interference is used to eliminate it, the main idea proposed here is to use this knowledge to influence the interference and benefit from it, thus gaining advantage from energy already existing in the communication system that is left unexploited otherwise. The proposed precoding aims at adaptively rotating, rather than zeroing, the correlation between the MIMO substreams depending on the transmitted data, so that the signal of interfering transmissions is aligned to the signal of interest at each receive antenna. By doing so, the CCI is always kept constructive and the received signal to interference-plus-noise ratio (SINR) delivered to the mobile units (MUs) is enhanced without the need to invest additional signal power per transmitted symbol at the MIMO base station (BS). It is shown by means of theoretical analysis and simulations that the proposed MIMO precoding technique offers significant performance and throughput gains compared to its conventional counterparts.

Clearing the RF smog: making 802.11n robust to cross-technology interference

Abstract: Recent studies show that high-power cross-technology interference is becoming a major problem in today's 802.11 networks. Devices like baby monitors and cordless phones can cause a wireless LAN to lose connectivity. The existing approach for dealing with such high-power interferers makes the 802.11 network switch to a different channel; yet the ISM band is becoming increasingly crowded with diverse technologies, and hence many 802.11 access points may not find an interference-free channel.This paper presents TIMO, a MIMO design that enables 802.11n to communicate in the presence of high-power cross-technology interference. Unlike existing MIMO designs, however, which require all concurrent transmissions to belong to the same technology, TIMO can exploit MIMO capabilities to decode in the presence of a signal from a different technology, hence enabling diverse technologies to share the same frequency band. We implement a prototype of TIMO in GNURadio-USRP2 and show that it enables 802.11n to communicate in the presence of interference from baby monitors, cordless phones, and microwave ovens, transforming scenarios with a complete loss of connectivity to operational networks.

An analysis of pilot contamination on multi-user MIMO cellular systems with many antennas

Abstract: This paper considers a two-cell cellular system with multiple antennas at the base station (BS) and single antenna user terminals. In such a scenario, the presence of channel state information (CSI) at the BS is essential for efficient system performance. In reciprocal TDD systems, CSI can be obtained via uplink training. Since only finite time-frequency resources are available, such uplink training generally must be performed using non-orthogonal resources (for different users), leading to pilot contamination between users who train simultaneously. In particular, we analyze the rate of convergence of SINR (in presence of pilot contamination) as the number of antennas (M) at the BS increases to an infinite limit. The effect of SNR and the fading coefficients of the user channels on this rate of convergence is also determined.

On the degrees of freedom of MIMO X channel with delayed CSIT

Abstract: The multiple-input multiple-output (MIMO) Gaussian X channel in i.i.d. fading environment and with delayed channel state information at transmitters (delayed CSIT) is considered. It is assumed that each transmitter has M antennas and each receiver has N antennas. New achievable results on the sum degrees of freedom (DoF) of this channel are provided and shown to be tight for all possible values of M and N except for 1/2 < N/M < 4/3. It is noteworthy that for certain values of M and N, the channel DoF coincides with the DoF of the broadcast channel obtained by assuming perfect transmitter cooperation.

Order Statistics in Wireless Communications: Diversity, Adaptation, and Scheduling in MIMO and OFDM Systems

Abstract: Covering fundamental principles through to practical applications, this self-contained guide describes indispensable mathematical tools for the analysis and design of advanced wireless transmission and reception techniques in MIMO and OFDM systems. The analysis-oriented approach develops a thorough understanding of core concepts and discussion of various example schemes shows how to apply these concepts in practice. The book focuses on techniques for advanced diversity combining, channel adaptive transmission and multiuser scheduling, the foundations of future wireless systems for the delivery of highly spectrum-efficient wireless multimedia services. Bringing together conventional and novel results from a wide variety of sources, it will teach you to accurately quantify trade-offs between performance and complexity for different design options so that you can determine the most suitable design choice based on your specific practical implementation constraints.

Preamble and header bit allocation for power savings within multiple user, multiple access, and/or MIMO wireless communications

Abstract: Preamble and header bit allocation for power savings within multiple user, multiple access, and/or MIMO wireless communications. Within a multi-user packet, information (e.g., partial address information) related to a recipient group of wireless communication devices (e.g., as few as one wireless communication device or any subset of a number of wireless communication devices, sometimes including all of the wireless communication devices) is emplaced within a PHY (e.g., physical layer) header of such a multi-user packet to be communicated within a multi-user (MU) environment. Such recipient indicating information can be encoded with relatively higher robustness (e.g., lower coding rates, lower ordered modulation, cyclic redundancy check (CRC), etc.) that remaining portions of the multi-user packet. Various portions of the remainder of the multi-user packet may respectively correspond to different wireless communication devices (e.g., a first field for a first wireless communication device, a second field for a second wireless communication device, etc.).

MU-MIMO in LTE Systems

Abstract: A relatively recent idea of extending the benefits of MIMO systems to multiuser scenarios seems promising in the context of achieving high data rates envisioned for future cellular standards after 3G (3rd Generation). Although substantial research has been done on the theoretical front, recent focus is on making Multiuser Multiple-Input Multiple-Output (MUMIMO) practically realizable. This paper presents an overview of the different MU-MIMO schemes included/being studied in 3GPP standardization from LTE (long-term evolution) to LTE Advanced. MU-MIMO system concepts and implementation aspects have been studied here. Various low-complexity receiver architectures are investigated, and their performance assessed through link-level simulations. Appealing performance offered by low-complexity interference aware (IA) receivers is notably emphasized. Furthermore, system level simulations for LTE Release 8 are provided. Interestingly, it is shown that MU-MIMO only offers marginal performance gains with respect to single-user MIMO. This arises from the limited MU-MIMO features included in Release 8 and calls for improved schemes for the upcoming releases.

MIMO Communication for Cellular Networks

Abstract: As the theoretical foundations of multiple-antenna techniques evolve and as these multiple-input multiple-output (MIMO) techniques become essential for providing high data rates in wireless systems, there is a growing need to understand the performance limits of MIMO in practical networks. To address this need, MIMO Communication for Cellular Networks presents a systematic description of MIMO technology classes and a framework for MIMO system design that takes into account the essential physical-layer features of practical cellular networks. In contrast to works that focus on the theoretical performance of abstract MIMO channels, MIMO Communication for Cellular Networks emphasizes the practical performance of realistic MIMO systems. A unified set of system simulation results highlights relative performance gains of different MIMO techniques and provides insights into how best to use multiple antennas in cellular networks under various conditions. MIMO Communication for Cellular Networks describes single-user, multiuser, network MIMO technologies and system-level aspects of cellular networks, including channel modeling, resource scheduling, interference mitigation, and simulation methodologies. The key concepts are presented with sufficient generality to be applied to a wide range of wireless systems, including those based on cellular standards such as LTE, LTE-Advanced, WiMAX, and WiMAX2. The book is intended for use by graduate students, researchers, and practicing engineers interested in the physical-layer design of state-of-the-art wireless systems.

Threshold Receiver Model for Throughput of Wireless Devices With MIMO and Frequency Diversity Measured in Reverberation Chamber

Abstract: We present a simple theoretical model for the throughput data rate of a wireless LTE device including the improvements of data rate due to diversity in frequency (OFDM) and spatial domains (MIMO) under frequency selective fading. The model is based on defining an ideal threshold receiver for the line-of-sight (LOS) case, corresponding to reception with advanced error-correcting codes. The theoretical throughput model is in agreement with measurements in a reverberation chamber of a commercial LTE device for the 1 × 2 SIMO case, both regarding diversity and MIMO array gains, and it can therefore be used to complement measured results in evaluation of performance of LTE devices.

Exploiting MIMO antennas in cooperative cognitive radio networks

Abstract: Recently, a new paradigm for cognitive radio networks has been advocated, where primary users (PUs) recruit some secondary users (SUs) to cooperatively relay the primary traffic. However, all existing work on such cooperative cognitive radio networks (CCRNs) operate in the temporal domain. The PU needs to give out a dedicated portion of channel access time to the SUs for transmitting the secondary data in exchange for the SUs' cooperation, which limits the performance of both PUs and SUs. On the other hand, Multiple Input Multiple Output (MIMO) enables transmission of multiple independent data streams and suppression of interference via beam-forming in the spatial domain over MIMO antenna elements to provide significant performance gains. Researches have not yet explored how to take advantage of the MIMO technique in CCRNs. In this paper, we propose a novel MIMO-CCRN framework, which enables the SUs to utilize the capability provided by the MIMO to cooperatively relay the traffic for the PUs while concurrently accessing the same channel to transmit their own traffic. We design the MIMO-CCRN architecture by considering both the temporal and spatial domains to improve spectrum efficiency. Further we provide theoretical analysis for the primary and secondary transmission rate under MIMO cooperation and then formulate an optimization model based on a Stackelberg game to maximize the utilities of PUs and SUs. Evaluation results show that both primary and secondary users achieve higher utility by leveraging MIMO spatial cooperation in MIMO-CCRN than with conventional schemes.

Breaking the Gigabit-per-second barrier with 802.11AC

Abstract: Summary form only given. The 802.11ac standard will push wireless LAN throughputs over the gigabit-per-second barrier in the coming years. Rather than only improving single link throughput by using more bandwidth and 256 QAM, 802.11ac also improves network throughput by adding MU MIMO capability. MU-MIMO makes it possible to achieve large throughputs cost effectively by having relatively simple client devices with just one or two antennas that can be simultaneously transmitted to by an access point that may have up to eight antennas.

System and method for selecting a transmission channel in a wireless communication system that includes an adaptive array

Abstract: A method for establishing wireless communication between a transmitter and a receiver in a wireless communication system is disclosed. The receiver includes an adaptive array that has at least two antennas. Each antenna receives a signal and produces a received signal. The transmitter includes at least two transmission channels for communicating the signal from the transmitter to the receiver. The wireless communication system suppresses interference at the receiver by applying an interference suppression technique when combining the received signals. The selection of a channel at the transmitter is based on the channel performance at the receiver for each transmission channel. The channel performance is based on a combining technique different from the interference suppression technique.

3-Cell Network MIMO Architectures with Sectorization and Fractional Frequency Reuse

Abstract: In this paper, we present a 3-cell network multiple-input multiple-output (MIMO) architecture with fractional frequency frequency (FFR) and a novel tri-sector frequency partition scheme. One fundamental question to apply the network MIMO technique in such a high interference environment is: how many base stations should be coordinated together to provide sufficient performance? We will demonstrate that the FFR-based 3-cell network MIMO architecture with the proposed tri-sector frequency partition can not only effectively overcome the inter-group interference, but can avoid executing the complex multi-base-station joint processing for a huge number of cluster of cells at all locations. It will be shown that the proposed 3-cell network MIMO with the rearranged tri-sector frequency partition strategy can outperform the 7-cell network MIMO with omni-directional antennas. Various sector antenna architectures and the method for determining the inner region of the FFR cell planning are also discussed and analyzed on top of the network MIMO system. We hope that this study can provide important insights into the design of the network MIMO systems from the perspectives of architecture and deployment.

Evolution of uplink MIMO for LTE-advanced

Abstract: The evolution of LTE uplink transmission toward MIMO has recently been agreed in 3GPP, including the support of up to four-layer transmission using precoded spatial multiplexing as well as transmit diversity techniques. In this article, an overview of these uplink MIMO schemes is presented, along with their impact on reference signals and DL control signaling. Receivers suitable for uplink MIMO are presented, and their link performances are compared.

Max-Min Fairness Linear Transceiver Design for a Multi-User MIMO Interference Channel

Abstract: Consider the max-min fairness linear transceiver design for a multi-user MIMO interference channel. Assuming perfect channel knowledge, this problem can be formulated as the maximization of minimum SINR utility, subject to individual power constraints at each transmitter. In this paper, it is shown that when the number of antennas at each transmitter (receiver) is at least two and at each receiver (transmitter) is at least three, the problem of checking whether the given target SINR is feasible is strongly NP-hard. A cyclic coordinate ascent algorithm is also proposed for this design problem. Monotonicity and global convergence to KKT solution of the proposed algorithm are proved.

Wireless lan device and controlling method thereof

Abstract: A wireless LAN device for wirelessly communicating using a specific frequency channel shared by a radar and a wireless LAN system. The wireless LAN device includes a plurality of antennas; a wireless communication unit including a plurality of transceiver circuits respectively provided for each of the plurality of antennas; and a controller that controls the wireless communication unit. The wireless communication unit wirelessly communicates in accordance with a multiple input multiple output (MIMO) scheme by the plurality of transceiver circuits, and the controller controls the wireless communication unit to execute radar wave monitoring on a frequency channel different from a frequency channel in use for wireless communication using one of the plurality of transceiver circuits when the frequency channel in use for the wireless communication is the specific frequency channel.

PSMP-Based Downlink Multi-User MIMO Communications

Abstract: A scheduling-based down-link MU-MIMO mechanism is proposed in a wireless communication system. An access point transmits a first scheduling message to a plurality of stations. The first scheduling message reserves a first transmission burst for channel sounding. The AP then transmits a sounding signal and in response receives channel state information (CSI) from the plurality of stations. Based on the CSI, the AP performs MU-MIMO encoding and applies transmit beamforming (precoding). The AP transmits a second scheduling message that reserves a second transmission burst for MU-MIMO transmission. The AP then transmits downlink data streams to multiple stations simultaneously. Finally, the AP receives uplink acknowledgements from the stations. In one embodiment, the scheduling-based MU-MIMO is implemented using PSMP scheduling technique. PSMP-based downlink MU-MIMO allows both 802.11n and 802.11ac stations to process multiple spatial streams with reduced complexity, enhanced performance, and significant power saving.

Codebook adaptation in MIMO communication systems using multilevel codebooks

Abstract: A method includes holding in a receiver a definition of a codebook including precoding matrices, and a definition of multiple sub-codebooks including different respective subsets of the precoding matrices in the codebook. A sub-codebook is selected in coordination with a transmitter, for use in a given time interval or frequency range. A Multiple-Input Multiple-Output (MIMO) signal that is transmitted from the transmitter is received. Feedback is generated in the receiver based on the received MIMO signal. The feedback is indicative of one or more preferred precoding matrices, which are chosen from the selected sub-codebook and which are to be used in precoding subsequent MIMO signals in respective partitions of the given time interval or frequency range. The feedback is transmitted from the receiver to the transmitter.

The Degrees of Freedom Regions of Two-User and Certain Three-User MIMO Broadcast Channels with Delayed CSIT

Abstract: The degrees of freedom (DoF) region of the fast-fading MIMO (multiple-input multiple-output) Gaussian broadcast channel (BC) is studied when there is delayed channel state information at the transmitter (CSIT). In this setting, the channel matrices are assumed to vary independently across time and the transmitter is assumed to know the channel matrices with some arbitrary finite delay. An outerbound to the DoF region of the general K-user MIMO BC (with an arbitrary number of antennas at each terminal) is derived. This outer-bound is then shown to be tight for two classes of MIMO BCs, namely, (a) the two-user MIMO BC with arbitrary number of antennas at all terminals, and (b) for certain three-user MIMO BCs where all three receivers have an equal number of antennas and the transmitter has no more than twice the number of antennas present at each receivers. The achievability results are obtained by developing an interference alignment scheme that optimally accounts for multiple, and possibly distinct, number of antennas at the receivers.

Systems and methods for uplink multi-user multiple input multiple output (mu mimo) medium access and error recovery

Abstract: Embodiments of systems and methods for uplink multi-user multiple input multiple output (MU MIMO) medium access and error recovery are generally described herein. Other embodiments may be described and claimed.

MIMO for Inhome Power Line Communications

Abstract: Inhome Power Line Communications (PLC) enables new and highly convenient networking functions without any additional cables to mains-powered devices Throughput measurements have shown that current PLC technology does not provide sufficient bandwidth for all typical inhome applications in a reliable way This paper clarifies if Multiple Input Multiple Output (MIMO) methods, being well-known from the wireless world, can significantly increase the PLC channel throughput and the link reliability After proving the theoretical capacity increase on measured PLC channels, different MIMO schemes are compared regarding their suitability for the PLC channel

Evaluation of a New Wideband Slot Array for MIMO Performance Enhancement in Indoor WLANs

Abstract: A new wideband compact slot antenna array for indoor WLAN access points (AP) is described, covering several wireless communication services from 2.4 to 4.8 GHz, that is especially designed to enhance MIMO system capacity. The array topology provides both spatial and polarization diversity. Despite very close packing of the array elements, these exhibit very low mutual coupling and low cross-polarization, greatly favoring MIMO diversity gain. A detailed MIMO performance comparison is conducted against a common array of patches in indoor environment, based both on simulation and indoor measurements: the new antenna shows a clear improvement in terms of channel capacity.

Characterizing multiplexing and diversity in visual MIMO

Abstract: Mobile optical wireless has so far been limited to very short ranges for high data rate systems. It may be feasible to overcome the data rate limitations over large transmission range in optical wireless through camera receivers and light emitting transmitter arrays through a concept what we call “visual MIMO”. In this concept multiple transmit elements of a light emitting array (LEA) are used as transmitters to communicate to the individual pixel elements of the camera which act as multiple receive elements to create the visual MIMO channel. Multiplexing information over parallel data channels albeit be very similar to RF MIMO in concept, the visual MIMO approach dramatically differs in its characterization. In visual MIMO since the received signal is essentially the image of the transmitting element, the perspective distortions in the visual channel dominate over some of the important properties of a RF wireless channel such as distance based attenuation and multipath fading. Some of the prominent perspective distortions include the reduction in the size of the image with distance and skew/rotation in the image due to angular view. Further lens blur (typically due to focus imperfection or jerks while capturing the image) can also significantly depreciate the image quality. In this paper we will detail how MIMO techniques such as multiplexing and diversity are characterized based on the effect of perspective distortions. Based our visual MIMO channel model we will derive the analytical channel capacity of the visual MIMO channel and using the same we illustrate the significance of parameters such as distance, viewing angle and blur in characterizing multiplexing and diversity in visual MIMO.