Showing papers on "Multi-user MIMO published in 2001"

Channel capacity of MIMO architecture using the exponential correlation matrix

Abstract: Multiple-input multiple output (MIMO) communication architecture has recently emerged as a new paradigm for wireless communications in rich multipath environment, which has spectral efficiencies far beyond those offered by conventional techniques. The channel capacity of the MIMO architecture in independent Rayleigh channels scales linearly as the number of antennas. However, the correlation of a real-world wireless channel may result in a substantial degradation of the MIMO architecture performance. In this letter, we investigate the MIMO channel capacity in correlated channels using the exponential correlation matrix model. We prove that, for this model, an increase in correlation is equivalent to a decrease in signal-to-noise ratio (SNR). For example, r=0.7 is the same as 3-dB decrease in SNR.

Multiuser diversity for MIMO wireless systems with linear receivers

Abstract: MIMO communication links, i.e. those with multiple transmit and receive antennas, offer significant advantages in terms of rate and reliability. In cellular systems, however, gains may be limited due to fading and interference. One potential solution is known as multiuser diversity, in which a packet scheduler improves throughput by exploiting the independence of the fading and interference statistics of different users. In this paper, we consider the problem of exploiting multiuser diversity in MIMO systems, especially those with zero forcing linear receivers. We propose a number of different scheduling disciplines and compare them in terms of average throughput as a function of the number of users and number of antennas.

MIMO wireless communication system

Abstract: Previous MIMO systems have used spatially diverse antenna elements in order not to reduce the number of orthogonal channels that can be realised. The present invention recognises that this leads to large antenna sizes, as compared to multiple beam antenna systems which use closely spaced antenna elements. In order to provide a compact antenna unit, whilst still allowing a MIMO system to be exploited, the present invention recognises that polarisation diversity only can be used in a MIMO system without the need for spatially diverse antenna elements. Closely spaced antenna elements are used and this enables a compact MIMO antenna unit to be provided. In addition, such MIMO systems with polarisation diversity but no spatial diversity can advantageously be used in line of sight situations and also combined with multi-beam antenna systems to further increase capacity.

MIMO vector channel sounder measurement for smart antenna system evaluation

Abstract: For the simulation and design of smart antenna transmission principles in mobile radio, precise knowledge of the time-variant directional multipath structure in various radio environments is required. In this paper, a new real-time multiple-input-multiple-output (MIMO) vector radio channel sounder is described, which uses multiple antennas at the transmitter as well as at the receiver position. The proposed MIMO measurement principle can be effectively exploited to estimate the propagation direction at both ends of the wireless link simultaneously, and thus, dramatically enhance overall resolution of the multiple path parameters. Applying a proper antenna architecture and the multidimensional unitary ESPRIT algorithm, joint superresolution estimation of the direction of departure (DOD), time- delay of arrival (TDOA), Doppler shift, and direction of arrival (DOA) of the propagating waves becomes possible. The measured results can also be used directly for the simulation of combined transmit-receive diversity (MIMO) transmission principles and space-time (ST) adaptive receivers in a multi-user scenario. Results based on measurements in different locations are referenced, including a complicated indoor environment as is typical for industrial WLAN applications.

Preamble design for multiple-antenna OFDM-based WLANs with null subcarriers

Abstract: The so-called orthogonal frequency division multiplexing (OFDM) technique has received considerable interest, especially in the area of wireless local area networks (WLANs). One way of meeting the demands for increased data rates in WLANs is to provide the transmitter and receiver with multiple antennas. In this letter, we consider the estimation of the channel and the design of optimal preambles (training sequences) for an OFDM system with two transmit and multiple receive antennas.

Space-Time Coding and Signal Processing for High Data Rate Wireless Communications

Abstract: The information capacity of wireless communication systems can be increased dramatically by employingmultiple transmit and receive antennas [?, ?]. An effective approach to increasing data rate over wireless channels is to employ coding techniques appropriate to multiple transmit antennas, that is space-time coding. Space-time codes introduce temporal and spatial correlation into signals transmitted from different antennas, in order to provide diversity at the receiver, and coding gain over an uncoded system. The spatial-temporal structure of these codes can be exploited to further increase the capacity of wireless systems with a relatively simple receiver structure. This chapter provides an overview of space-time coding techniques and the associated signal processing framework.

Water filling capacity of Rayleigh MIMO channels

Abstract: MIMO channels can attain high capacities provided that the propagation medium contains enough scatterers. The capacity of MIMO channels can further be increased by performing optimal power distribution over transmit antennas. This, in turn, necessitates knowledge of the channel at the transmitter. It is shown in this paper that for low signal-to-noise ratios (SNR) and small number of antennas, this increase in capacity can be of interest. Rayleigh fading conditions are considered.

Measured characteristics of the MIMO wireless channel

Abstract: This paper presents results from an experimental platform designed to measure the transfer matrix for indoor and outdoor multiple-input multiple-output (MIMO) channels with up to 16 transmit and receive antenna elements. Key aspects of the hardware system and data post-processing techniques are provided. A variety of measurements have been taken with the platform at 2.45 GHz in a typical indoor environment. The collected data have been processed to highlight a variety of channel features, including the statistical distributions of the channel matrix elements and the inherent capacity of the wireless MIMO channel for different numbers of antenna elements, polarizations, and element directivities.

Linear precoding and decoding for multiple input multiple output (MIMO) wireless channels

Abstract: Space-time coding and spatial multiplexing are prime candidates for achieving high data rates and link quality in multiple-input multiple-output (MIMO) wireless links. However, both the schemes assume no channel knowledge at the transmitter. In a number of applications, channel knowledge can be made available at the transmitter. A natural question to ask is how to use these channel estimates to further optimize the transmitter. There can be several ways to linearly or non-linearly optimize the transmitter and receiver depending on channel knowledge. In this thesis, we consider linear optimization schemes at the transmitter (precoding) and receiver (decoding) to improve performance of MIMO systems. We consider a number of designs depending on the performance criteria and degree of channel knowledge at the transmitter. First, assuming perfect channel knowledge at the transmitter and receiver, and a flat-fading channel, we propose a generalized linear block precoding and decoding scheme based on the weighted mean square error criteria, assuming a total power constraint at the transmitter. The optimum design forces transmission only on the

Spatial multiuser access with MIMO smart antennas for OFDM systems

Abstract: Indoor wireless communication systems have grown rapidly because of their clear advantages such as mobility, flexibility, and inexpensive network reconfiguration. In order to offer higher data rates approaching those provided by wired LANs, a combined OFDM/SDMA-based approach is an effective solution for increasing the system capacity and spectral efficiency. However, in multi-user environments, the system performance is limited by co-channel interference. Multi-input-multi-output (MIMO) smart antennas with prior knowledge of the channel at the transmitter is another promising technique for providing significant increase in system capacity and performance in wireless communication systems. We investigate the use of smart antennas at both the base and mobile stations, operating jointly, to maximize the SINR of each user before multiuser detection. By doing so, the performance of multi-user detection is significantly improved.

Correlation properties of MIMO radio channels for indoor scenarios

Abstract: Multiple input- multiple output (MIMO) systems have the potential to achieve very high capacities, depending on the propagation environment. Capacity increases as signal correlation decreases. We present the measurements of a MIMO system under strong and weak line-of-sight conditions. The system capacity decreases as the separation from the transmitter increases; indeed the transmitter correlation increases as the separation increases. The receiver correlation is lower than the transmitter correlation under both propagation conditions. Also, there lies a benefit in using vertically polarized, vertically separated antennas.

Experimental characterization of the MIMO wireless channel

Abstract: We report the development of an experimental platform designed to measure the transfer matrix for indoor and outdoor multiple input multiple output (MIMO) channels. The key aspects of the hardware system are presented, including a discussion of measurement issues and data processing approaches. Representative data obtained with the instrument in several indoor environments we presented. These results reveal the large increase in capacity that can be achieved using MIMO architectures coupled with space-time coding implementations.

A MIMO WLAN based on linear channel inversion

Abstract: Multiple-input multiple-output (MIMO) techniques may increase the capacity of wireless local area networks (WLAN) since they profit from rich scattering of radio waves in indoor environments. On the other hand, much signal processing must be performed in a very short time to reach practical data rates. This paper reports on elementary steps towards MIMO transmission when the channel is known to the transmitter. In most cases, channel information can be obtained at the transmitter by means of reciprocity. Linear channel inversion (LCI) may then be employed allowing simple processing suitable for real-time applications. In contrast to signal processing at the receiver, LCI offers isotropic noise gain which simplifies coding. On the other hand, power distribution at the transmitter depends on the statistical properties of the MIMO channel. Results in the case of Rayleigh fading indicate that at least one additional antenna is needed at the transmitter for reliable operation. A simple formula for the mean transmitter power is reported and confirmed by simulation. Performance can now be expressed in terms of transmitter power and a fair comparison with transmission based on signal processing at the receiver is possible. (6 pages)

MIMO communication capacity using infinite dimension random matrix eigenvalue distributions

Abstract: Wireless communication using multiple-input multiple-output (MIMO) systems enables increased spectral efficiency for a given total transmit power. MIMO capacity is a strong function of the singular value distribution of the channel matrix, the receive antenna to transmit antenna transfer matrix. In this paper the capacity is calculated using an asymptotic large random matrix approach. Bounds on the maximum spectral efficiency of MIMO systems in which both transmitter and receiver know the channel (channel estimate feedback), are compared with MIMO systems in which only the receiver knows the channel. In addition, MIMO performance in the presence of cooperative and uncooperative interfering MIMO systems is presented.

Experimental measurements of capacity for MIMO indoor wireless channels

Abstract: This paper presents the results of experiments obtained with a narrowband, multiple-input multiple-output (MIMO) channel probe in an indoor office/laboratory environment. The system employs ten transmit and ten receive antennas, and computes the 10/spl times/10 narrowband channel matrix at 2.4 GHz every 80 milliseconds. We use the data to study the distribution of the channel coefficients, their temporal variability, and the resulting effects on channel capacity. We also compare the empirical results with those predicted by WiSE, a state-of-the-art channel simulator based on ray-tracing from Lucent Technologies.

MIMO measurement for double-directional channel modelling

Abstract: In this paper a parametric modelling approach for double-directional radio channels is introduced that is based on measured data. The MIMO (multiple-input multiple-output) measurement principle using multiple antennas at both the transmitter and receiver site can be effectively exploited to estimate the propagation direction, delay and Doppler shift of any significant path at both ends of the wireless link simultaneously. From the estimated parameter sets a precise reconstruction of the multidimensional wave field in the aperture domains of time, frequency and space is possible. Since this way the measurement antenna properties are excluded from the channel, the influence of a variety of other array architectures can be investigated with the reconstructed wave field. This builds the basis for manifold analyses and simulations of MIMO transmission links in a very realistic way.

Temporal variation of multiple-input multiple-output (MIMO) channels in indoor environments

Abstract: The measurement and characterisation of multiple-input multiple-output (MIMO) channels has gained increasing attention. Previous analysis of MIMO measurements has generally focused on the evaluation of the capacity of such systems in differing locations and configurations. We present measurements made in an indoor environment at 5.2 GHz, specifically to investigate temporal channel variation. It is shown that the performance of the overall MIMO channel varies at a slower rate than the individual channels between the transmit and receive elements.

Virginia Tech Space-Time Advanced Radio (VT-STAR)

Abstract: With the integration of the Internet and multimedia applications in next generation wireless communications, the demand for reliable high data rate services is rapidly growing. Traditional wireless communications systems use a single input single output (SISO) channel, meaning one antenna at each side of the link. Information theory research has shown an enormous potential growth in the capacity of wireless systems by using multiple element array (MEA) technology at both ends of the link. Space-time coding exploits the spatialtemporal diversity provided by the multiple input multiple output (MIMO) channel, significantly increasing both the system capacity and the reliability of the wireless link. The Virginia Tech Space-Time Advanced Radio (VT-STAR) system presents a visual demonstration of the capabilities of space-time coding techniques. The VT-STAR system has integrated an MPEG-2 video stream to show a representation of the effect of the wireless channel on a video transmission in real-time. Core algorithms are implemented on Texas Instruments TMS320C67 Evaluation Modules (EVM). Data conversion between the digital and analog domains is performed by TI THS5661 EVM and TI THS1206 EVM for the transmitter and receiver, respectively. The radio frequency subsystem is composed of multi-channel transmitter and receiver chains implemented in hardware. The capabilities of the MIMO channel are demonstrated in a non-line of sight (NLOS) indoor environment. Real-time monitoring of physical layer parameters, such as the bit error rate and diversity advantage, as well as a video display are presented on an attached personal computer.

On MIMO decoding algorithms for UMTS

Abstract: With the understanding of the channel capacity in wireless systems that allows much higher data rates in high scattering environments, transmission over multiple antenna systems has become an attractive option. In this paper we present candidate algorithms for decoding multiple-input-multiple-output (MIMO) systems and study their behavior and implementation for a 4-by-4 antenna system in a UMTS environment.

Experimental Investigation of the Joint Spatial and Polarisation Diversity for MIMO Radio Channel

Abstract: This paper presents analysis of MIMO radio channel measurements. A description of both the measurement set-up and the picocell environment is given. The correlation properties of the MIMO radio channel are investigated considering different diversity techniques such as spatial, polarisation and joint spatial and polarisation diversity techniques. It is shown that a combination of space and polarisation diversity is an attractive solution for achieving compact MIMO implementation especially when a large number of antenna ports is considered. The issue of unbalanced Branch Power Ratio (BPR) is addressed and its influence on the power gain of the potential subchannel generated by the MIMO concept is analysed.

MIMO-a solution for advanced wireless access?

Abstract: The application of smart antenna technology to wireless communication systems has attracted considerable attention over the last decade or so, as a means of capacity enhancement. Here, the application of space-time processing using a single antenna array at the base-station has been considered in order to obtain interference reduction (both co-channel and multipath) as well as range extension. The application of dual antenna array architectures to create multiple-input multiple-output (MIMO) configurations, has attracted considerable interest both within academia and industry as a means of providing significant capacity gains over conventional array-based enhancement methods. This paper provides an introduction to these MIMO communication systems and explains how such capacity gains can be achieved using this technology.

MIMO channel capacity for fixed wireless: measurements and models

Abstract: Recent breakthroughs in the application of information theory have shown great capacity increase by deploying multiple transmitting and multiple receiving antennas as compared to conventional single antenna systems. This work presents an experimental verification of the theoretical capacity prediction and a summary of measurement results for 16 fixed wireless locations in suburban New Jersey.

Performance of 60 GHz Virtual Cellular Networks using Multiple Receiving Antennas Invited paper selected from WPMC01

Abstract: During the past years, research covering propagation, channel characterization and wireless systems performance have yield a substantial knowledge of the 60 GHz channel. The unlicensed 60 GHz frequency band presents many attractive properties for wireless communications. The environments in which the 60 GHz infrastructure are to be designed are typically propagation- and coverage-limited. This paper describes the important factors that must be taken into account when designing a WLAN architecture operating in this frequency band. Therefore, we motivate the reasons of using distributed transmitting antennas and multiple receiving antennas (MRA) in order to mitigate the poor Direction of Arrival (DoA) diversity and to exploit the spatial diversity at the receiver. Such a system can be considered as a MIMO system. We investigate the advantages of combining a Virtual Cellular Network (VCN) (using single frequency network and distributed antennas) and MRA for the downlink. Several ways to combine the signals with different levels of complexity are presented. In the most complex case using Singular Value Decomposition (SVD), it is possible to add coherently the contribution of each antenna in a virtual cell while retaining the path diversity inherent to the VCN infrastructure. The schemes yield several advantages: symbol diversity is improved, path diversity is still present, antenna gain using multiple beamformers is increased and the multipath can be reduced. The concept is applicable to most types of single frequency networks but it is especially well appropriate for the 60 GHz VCN/WLAN using OFDM. Simulations give a realistic performance for QPSK, 8-PSK, and 16-QAM baseband modulations with a 256-subcarrier OFDM using a rate 1/2-convolutional code for a N × N VCN system. Results show a Eb/N0 improvement of up to 7.4 dB using the singular value decomposition method with 16-QAM compared to the SISO coded reference.

Wireless base station and transmission method

Abstract: PROBLEM TO BE SOLVED: To reduce transmission power of a wireless base station when the base station transmits common information to one wireless communication terminal or more. SOLUTION: When the number m of wireless communication terminals being transmission objects of the common information is greater than a preset threshold value M0, the base station transmits the common information through a common wireless channel to the one wireless communication terminal or more. When the number m of the wireless communication terminals is smaller than the preset threshold value M0, the base station transmits the common information through an individual wireless channel assigned to each wireless communication terminal. COPYRIGHT: (C)2003,JPO

Measurement-based simulation of mobile radio channels with multiple antennas using a directional parametric data model

Abstract: A parametric modeling approach for multiple input multiple output (MIMO) radio channels is introduced that is based on measured data. The MIMO measurement principle can be effectively exploited to estimate the propagation direction of any significant path at both ends of the wireless link simultaneously. From the estimated parameter sets a precise reconstruction of the multidimensional wave field in the aperture domains of time, frequency and space is possible. This enables various analyses and simulations of MIMO transmission links in a very realistic way.

Theory of MIMO biorthogonal partners and their application in channel equalization

Abstract: Channel equalization is an important step in most applications of digital communications. In this paper we consider the equalization of multiple input multiple output (MIMO) channels. To that end we derive the theory of MIMO biorthogonal partners, a concept that has already been introduced (only in the scalar case) by the authors. We develop conditions for the existence of an FIR MIMO biorthogonal partners and describe their application in the MIMO channel equalization. We also show that it is possible to exploit the non-uniqueness of FIR MIMO biorthogonal partners in order to design flexible fractionally spaced MIMO equalizers that will be more robust to the channel noise.

A New Approach to Multiple Antenna Systems

Abstract: Using an isomorphism between the mul- tiuser detection problem and transmission of informa- tion over MIMO channels coupled to recent results on optimal signature waveform construction, we provide a new approach to information transfer in multiple antenna systems. The approach is based on a multi- carrier modulation scheme at each transmit antenna with sinusoids as carriers, which leads to a matrix model of the MIMO channel. A set of bits is transmit- ted over the MIMO channel in parallel by assigning dieren t codewords to each bit in the set similar to the way codewords are assigned to dieren t users in a CDMA system. Optimal codewords can be obtained by application of interference avoidance methods, and the corresponding optimal linear receiver structure is a set of matched lters. An analysis of the MIMO channel is performed using singular value decomposi- tion and the dimensionality of the problem is reduced only to those dimensions of the signal space that ac- tually carry information.

Performance evaluation of a space-time turbo equalizer in frequency selective MIMO channels using field measurement data

Abstract: Evaluating in-field performances of our proposed MIMO turbo equalizer, soft canceller (SC) followed by MMSE (SC/MMSE) space-time (S/T) MIMO turbo equalizer, is the primary objective of this paper. The SC/MMSE S/T MIMO turbo MIMO turbo equalizer discussed in this paper performs joint MIMO channel estimation, SC/MMSE MIMO signal detection, and decoding of the channel code used, all in an iterative manner. Full diversity gain can be achieved with practical computational complexity in the presence of rich scattering in space and time domains in MIMO communication environments. A series of field measurement campaigns took place in an urban area of Tokyo using a channel sounder system, and sets of collected channel impulse response data were used in off-line simulations to evaluate in-field performance of the MIMO turbo equalizer. In 2-user 2-receive antenna MIMO uplink environments, bit error rate performance was evaluated for the two simultaneous users. Results of the simulations are presented in this paper. (5 pages)