Different Number Of Antennas Research Articles

Error Performance of Physical-Layer Network Coding in Multiple-Antenna TWRC

In this paper, the error performance of physical-layer network coding (PNC) is studied in multiple-antenna two-way relay channels (TWRCs), where two users exchange their messages with the help of a relay. We assume that the TWRC system uses binary phase-shift keying (BPSK) modulation and that all channels are Rayleigh faded. In particular, we consider a general system model where two users may have different numbers of antennas and different average signal-to-noise ratios (SNRs) to the relay. Considering a TWRC with multiple antennas at both users and the relay [referred to as multiple-input multiple-output (MIMO)-TWRC], we derive the upper and lower bounds on the uplink error probability of PNC based on maximum-likelihood (ML) detection. In this scheme, a transmit antenna selection (TAS) strategy is applied at two users, where each user selects the strongest transmit antenna for transmission. Furthermore, we also present the upper and lower bounds for two special cases, namely, the single-input multiple-output (SIMO)-TWRC with single-antenna users and the multiple-antenna relay and the multiple-input single-output (MISO) TWRC with multiple-antenna users and the single-antenna relay. Then, the diversity order is investigated for the schemes. We show that the PNC with TAS outperforms the PNC with space-time block codes (STBCs) significantly. The numerical results also demonstrate that our bounds are very tight to the Monte Carlo simulation.

Adaptive Scheduling in MIMO-Based Heterogeneous Ad Hoc Networks

The demands for data rate and transmission reliability constantly increase with the explosive use of wireless devices and the advancement of mobile computing techniques. Multiple-input and multiple-output (MIMO) technique is considered as one of the most promising wireless technologies that can significantly improve transmission capacity and reliability. Many emerging mobile wireless applications require peer-to-peer transmissions over an ad hoc network, where the nodes often have a different number of antennas, and the channel condition and network topology vary over time. It is important and challenging to develop efficient schemes to coordinate transmission resource sharing among a heterogeneous group of nodes over an infrastructure-free mobile ad hoc network. In this work, we propose a holistic scheduling algorithm that can adaptively select different transmission strategies based on the node types and channel conditions to effectively relieve the bottleneck effect caused by nodes with smaller antenna arrays, and avoid the transmission failure due to the violation of lower degree of freedom constraint resulted from the channel dependency. The algorithm also takes advantage of channel information to opportunistically schedule cooperative spatial multiplexed transmissions between nodes and provide special transmission support for higher priority nodes with weak channels, so that the data rate of the network can be maximized while user transmission quality requirement is supported. The performance of our algorithm is studied through extensive simulations and the results demonstrate that our algorithm is very effective in handling node heterogeneity and channel constraint, and can significantly increase the throughput while reducing the transmission delay.

GNSS antenna array-aided CORS ambiguity resolution

Array-aided precise point positioning is a measurement concept that uses GNSS data, from multiple antennas in an array of known geometry, to realize improved GNSS parameter estimation proposed by Teunissen (IEEE Trans Signal Process 60:2870–2881, 2012). In this contribution, the benefits of array-aided CORS ambiguity resolution are explored. The mathematical model is formulated to show how the platform-array data can be reduced and how the variance matrix of the between-platform ambiguities can profit from the increased precision of the reduced platform data. The ambiguity resolution performance will be demonstrated for varying scenarios using simulation. We consider single-, dual- and triple-frequency scenarios of geometry-based and geometry-free models for different number of antennas and different standard deviations of the ionosphere-weighted constraints. The performances of both full and partial ambiguity resolution (PAR) are presented for these different scenarios. As the study shows, when full advantage is taken of the array antennas, both full and partial ambiguity resolution can be significantly improved, in some important cases even enabling instantaneous ambiguity resolution. PAR widelaning and its suboptimal character are hereby also illustrated.

Wireless Network Coding for MIMO Two-Way Relaying

The design of modulation schemes for the physical layer network-coded two-way MIMO relaying scenario is considered, with the denoise-and-forward protocol which employs two phases: Multiple Access phase and Broadcast phase. It is shown that for MIMO two-way relaying, the minimum distance of the effective constellation at the relay becomes zero when all the rows of the channel fade coefficient matrix belong to a finite number of vector subspaces referred to as the singular fade subspaces. The singular fade subspaces can be classified into two kinds based on whether their harmful effects can be removed or not: (i) the removable and (ii) the non-removable singular fade subspaces. It is shown that network coding maps obtained by the completion of appropriate partially filled Latin Rectangles can remove the harmful effects of all the removable singular fade subspaces. For 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</sup> -PSK signal set, the removable and non-removable singular fade subspaces are characterized and, it is shown that the number of non-removable singular fade subspaces is a small fraction of the total number of singular fade subspaces and this fraction tends to zero as the constellation size tends to infinity. The Latin Rectangles for the case when the end nodes use different number of antennas are shown to be obtainable from the Latin Squares for the case when they use the same number of antennas. Also, the network coding maps which remove all the removable singular singular fade subspaces are shown to be obtainable from a small set of Latin Squares. The removal of all the singular fade subspaces by properly choosing the network coding map, provides a gain of 5.5 dB over the conventional Exclusive-OR network coding, in a Rayleigh fading scenario with 2 antennas at the end nodes and one antenna at the relay node, for 4-PSK signal set.

Performance analysis of CSMA/CA protocols with multi-packet transmission

Wireless objects equipped with multiple antennas are able to simultaneously transmit multiple packets by exploiting the channel’s spatial dimensions. In this paper, we study the benefits of such Multiple Packet Transmission (MPT) approach, when it is used in combination with a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol for fully interconnected networks, addressing the interactions between the two mechanisms and showing the performance gains that can be achieved. To this end, a very simple Media Access Control (MAC) protocol that captures the fundamental properties and tradeoffs of a CSMA/CA channel access protocol supporting MPT is introduced. Using this protocol as a reference, a new analytical model is presented for the case of non-saturated traffic sources with finite buffer space. Simulation results show that the analytical model is able to accurately characterize the steady-state behavior of the reference protocol for different number of antennas and different traffic loads, providing a useful tool for understanding the performance gains achieved by MAC protocols supporting MPT.

Bit Allocation Between Per-Cell Codebook and Phase Ambiguity Quantization for Limited Feedback Coordinated Multi-Point Transmission Systems

Coordinated multi-point (CoMP) transmission is a promising technique for improving spectral efficiency of full frequency reuse cellular systems. However, its performance will be severely degraded if the feedback strategies are not carefully designed for providing channel information through limited uplink resources to the coherently cooperated base stations. In this paper, we study per-cell codebook based limited feedback scheme, which is highly desirable for CoMP systems due to its scalability and flexibility. Specifically, we investigate the issues related to phase ambiguity (PA), which comes from the per-cell codebook structure. We first analyze how many bits are required for the PA feedback to ensure an allowed performance loss. We then propose an adaptive bit allocation algorithm to divide a given amount of feedback bits between the per-cell codebooks for single-cell channel direction quantization and a codebook for PA quantization, aiming at minimizing the average global channel direction quantization error. Finally we provide a scaling law of the number of feedback bits per-user when the bit allocation algorithm is used. Simulation results show that the proposed bit allocation algorithm significantly improves the throughput of coherent CoMP systems either with equal number or different number of antennas at each base station.

Comparative Performance Analysis of Multi-Antenna Regenerative Cooperative Relay in Nakagami-m Fading Channel

Performance of cooperative relay schemes employing infrastructure based fixed relays having multiple antennas, has been investigated. Closed form expressions of outage probability, bit error rate and throughput for such system have been derived for Nakagami-m fading channels, with integer values of m. Here, relay and destination may perform either maximum ratio combining or selection combining of the signals. Comparative performance analysis of all four possible combinations has been analyzed for various relay locations, different number of antennas on the relay, various transmission rate and different fading conditions.

Performances of Amplify-and-Forward Cooperative Relay Networks with Different Topologies

When the sizes of terminals are limited, cooperative relay networks are recommended as promising virtual MIMO systems to improve the performances of wireless communication systems in literature. Accordingly, some comparisons on the performances of different systems are useful to guide the selection and deployment of cooperative relay systems in field applications. In this paper, we compare the outage probabilities of cooperative relay networks of different topologies (different numbers of antennas used at a transmitter and relays used in a system), as well as the outage probabilities of the MISO systems. We propose an aggregated channel mode, which combines the power gain obtained from the reduction of path loss through the deployment of relays, and the flat fading caused by multi-path propagation. During the evaluation of the performances of different systems, we apply information theory in the calculation of ergodic capacities and consider the requirement on wireless resources in the estimation of outage probabilities. Numerical simulation shows that (1) cooperative networks with multiple relays outperform those with multiple antennas; (2) only when the power gain is included, the performances of cooperative relay networks are comparable with their counterparts in direct transmission; (3) the performances are significantly affected by the locations of relays.

Optimized Power Allocation for Layered-Steered Space-Time Codes

Layered Steered Space-Time Codes (LSSTC) is a recently proposed multiple-input multiple-output system that combines the benefits of vertical Bell Labs space-time (VBLAST) scheme, space-time block codes and beamforming. We suggest a new downlink scheme employing LSSTC with asymmetric power allocation, by assuming that the user feeds the BS with the average signal-to-noise ratio per VBLAST layer through the uplink feedback channel. The motivation behind proposing such a system is to enhance the error performance by assigning power to the layers in an optimal manner. We refer to the system proposed as the optimal power allocation LSSTC (OPA-LSSTC). Our analysis is general such that it includes asymmetric layered systems in which each layer may have different number of antennas and also the power can be assigned to layers asymmetrically.

Microwave Energy as a Precoagulative Device to Assist in Hepatic Resection

Microwave energy is another energy source than can be used to precoagulate hepatic tissue during hepatic resection. The aim of this study was to develop an optimal microwave precoagulation technique in a porcine model and then validate the technique during hepatic resection in patients. Institutional Animal Care and Use and Institutional Review Board (IRB)-approved protocols were utilized for hepatic resection in a porcine model and validation in patients using microwave energy for precoagulation. Different numbers of antennas (one, two or three; spaced 5 mm apart) and ablation times (20, 30, 40, and 60 s) were evaluated to identify an optimal technique that effectively provided precoagulation. Animal studies: Two antennas for 30 s provided the optimal ablation time, ablation width, mean size of largest vessel coagulated, and minimal bleeding when compared with other techniques. However, given that this is not an optimal technique for laparoscopic precoagulation, one antenna for 60 s was found to provide similar precoagulation success. Patient validation: To validate these techniques, three patients underwent open hepatectomy using two antennas with 5 mm spacing for 30 s, demonstrating successful precoagulation up to inflow/outflow vessels of 10 mm size or greater, which were controlled with a vascular stapler. In addition three patients underwent laparoscopic hepatectomy using one antenna for 60 s and demonstrated successful precoagulation up to inflow/outflow vessels of 8 mm or greater, which were controlled with a vascular stapler. Microwave energy is a safe and effective precoagulation device to achieve good hemostasis during hepatic resection with both open and laparoscopic technique.

Euclidean Geometry LDPC-VBLAST System Design and Performance Evaluation

Among popular multi-transmit and multi-receive antennas techniques, the VBLAST (Vertical Bell Laboratories Layered Space-Time) architecture has been shown to be a good solution for wireless communications applications that require the transmission of data at high rates. Recently, the application of efficient error correction coding schemes such as low density parity-check (LDPC) codes to systems with multi-transmit and multi-receive antennas has shown to significantly improve bit error rate performance. Although irregular LDPC codes with non-structure are quite popular due to the ease of constructing the parity check matrices and their very good error rate performance, the complexity of the encoder is high. Simple implementation of both encoder and decoder can be an asset in wireless communications applications. In this paper, we study the application of Euclidean geometry LDPC codes to the VBLAST system. We assess system performance using different code parameters and different numbers of antennas via Monte-Carlo simulation and show that the combination of Euclidean geometry LDPC codes and VBLAST can significantly improve bit error rate performance. We also show that interleaving data is necessary to improve performance of LDPC codes when a higher number of antennas is, used in order to mitigate the effect of error propagation. The simplicity of the implementation of both encoder and decoder makes Euclidean geometry LDPC codes with VBLAST system attractive and suitable for practical applications.

Reconfigurable architecture for MIMO systems based on CORDIC operators

The MIMO system is an attractive technology for wireless 3G/4G systems. In this article we propose the realization on FPGA of a MIMO ‘V-BLAST Square Root’ algorithm based on a variable number of CORDIC operators. The CORDIC operator is highly suitable for this implementation as it only relies on simple techniques of addition and vector offsets. This square root algorithm architecture is reconfigurable in order to adapt itself to different numbers of antennas and different data rates. The proposed architecture can achieve a data rate of 600 Mbit/s in a Virtex-II FPGA circuit from Xilinx for the MIMO system with QPSK modulation. To cite this article: H. Wang et al., C. R. Physique 7 (2006).

Cooperative Space–Time Coding for Wireless Networks

We consider a cooperative transmission scheme in which the collaborating nodes may have multiple antennas. We present the performance analysis and design of space-time codes that are capable of achieving the full diversity provided by user cooperation. Our codes use the principle of overlays in time and space, and ensure that cooperation takes place as often as possible. We show how cooperation among nodes with different numbers of antennas can be accomplished, and how the quality of the interuser link affects the cooperative performance. We illustrate that space-time cooperation can greatly reduce the error rates of all the nodes involved, even for poor interuser channel quality.

Performance Analysis and Design Optimization of LDPC-Coded MIMO OFDM Systems

We consider the performance analysis and design optimization of low-density parity check (LDPC) coded multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems for high data rate wireless transmission. The tools of density evolution with mixture Gaussian approximations are used to optimize irregular LDPC codes and to compute minimum operational signal-to-noise ratios (SNRs) for ergodic MIMO OFDM channels. In particular, the optimization is done for various MIMO OFDM system configurations, which include a different number of antennas, different channel models, and different demodulation schemes; the optimized performance is compared with the corresponding channel capacity. It is shown that along with the optimized irregular LDPC codes, a turbo iterative receiver that consists of a soft maximum a posteriori (MAP) demodulator and a belief-propagation LDPC decoder can perform within 1 dB from the ergodic capacity of the MIMO OFDM systems under consideration. It is also shown that compared with the optimal MAP demodulator-based receivers, the receivers employing a low-complexity linear minimum mean-square-error soft-interference-cancellation (LMMSE-SIC) demodulator have a small performance loss (< 1dB) in spatially uncorrelated MIMO channels but suffer extra performance loss in MIMO channels with spatial correlation. Finally, from the LDPC profiles that already are optimized for ergodic channels, we heuristically construct small block-size irregular LDPC codes for outage MIMO OFDM channels; as shown from simulation results, the irregular LDPC codes constructed here are helpful in expediting the convergence of the iterative receivers.

Robust progressive image transmission over OFDM systems using space-time block code

A joint source-channel coding (JSCC) scheme for robust progressive image transmission over broadband wireless channels using orthogonal frequency division multiplexing (OFDM) systems with spatial diversity is proposed for the application environments where no feedback channel is available such as broadcasting services. Most of current research about JSCC focuses on either binary symmetric channels (BSC) or additive white Gaussian noise (AWGN) channels. To deal with fading channels in most previous methods, the fading channel is modeled as two state Gilbert-Elliott channel model and the JSCC is normally aimed at the BER of bad channel status, which is not optimal when the channel is at good status. By using diversity techniques and OFDM, the frequency selective fading effects in broadband wireless channels can be significantly decreased and we show that subchannels in OFDM systems approach Gaussian noisy channels when the diversity gain gets large; as a result, the system performance can be improved in terms of throughput and channel coding efficiency. After analyzing the channel property of OFDM systems with spatial diversity, a practical JSCC scheme for OFDM systems is proposed. Simulation results are presented for transmit diversity with different numbers of antennas and different multipath delay and Doppler spread. It is observed from simulations that the performance can be improved more than 4 dB in terms of peak signal-to-noise ratio (PSNR) of the received image Lena and the performance is not very sensitive to different multipath spread and Doppler frequency.