Hamid Reza Bahrami

Space Modulation With CSI: Constellation Design and Performance Evaluation

In this paper, we investigate the effect of channel state information at the transmitter (CSIT) on the performance of a class of transmission schemes for multi-input–multi-output (MIMO) systems that can be collectively called space modulation (SMod) schemes. Space shift keying (SSK) is a simple example of SMod. In SMod, multiple antennas at the transmitter are employed to spatially modulate the information. The constellation vectors at the receiver are linear combinations of columns of the channel matrix, and therefore, the symbol error rate (SER) performance of the system highly depends on the Euclidean distance between each pair of these vectors. In this paper, we propose two novel methods to design the transmit vectors using CSIT such that the distance between each pair of constellation vectors at the receiver becomes larger, which, in turn, reduces the SER. Whereas in the first method we do not impose any constraint on the structure of the transmit vectors, in the second method, we confine the transmit vectors to have only one nonzero entry, and as such, it can be looked at as a modified SSK (MSSK) transmission scheme. This is to avoid interantenna synchronization (IAS) as only one transmit antenna is active at a time. Compared to SSK, the first method provides a significant performance improvement at the expense of increased complexity at the transmitter due to IAS. The second method provides an appealing SER improvement while keeping the complexity the same as that of SSK. Therefore, one can look at the second method as a modified version of SSK in which instead of transmitting a fixed symbol from one of the transmit antennas, in our proposed method, different transmit powers and phases are assigned to different transmit antennas. As acquiring full CSIT is difficult in some cases, we also consider the case of imperfect CSIT and derive alternative SMod transmission schemes in this case. By simulation, we show that the proposed SMod transmission schemes provide a significant performance improvement in terms of the SER in the presence of full or imperfect CSIT.

Precoder Design Based on Correlation Matrices for MIMO Systems

This paper presents a general framework for precoder designs for MIMO systems using partial channel knowledge on the transmit and receive correlation matrices at the transmitter. It is shown that the optimal linear precoder for any uncoded and coded MIMO system based on the MMSE or ergodic capacity criterion, or for an orthogonal ST coded MIMO system based on the minimum PEP criterion, is an eigen-beamformer that transmits the signal along eigenvectors of the transmit correlation matrix. Based on the eigen-values of both the transmit and receive correlation matrices, power loading across the eigen-beams is determined by water-pouring policy. Individual effects of the transmit and receive correlation matrices on the system performance are investigated. Simulation results show noticeable performance improvement over MIMO systems without precoder, particularly when the transmit correlation matrix has low rank

On the Performance of Spatial Modulation: Optimal Constellation Breakdown

Spatial modulation (SM) is a new transmission technique for multi-antenna systems in which the transmit antennas are used to modulate the signal. In this paper, the symbol error rate (SER) performance of SM is investigated. In SM, a signal domain modulation (i.e. amplitude-phase modulation) and an antenna domain modulation (i.e. space shift keying) are combined together to achieve a certain transmission rate while exploiting the properties of two independent modulation domains. A key question is the fine balance between the constellation sizes in the two domains when a constant rate is targeted. For a fixed rate, there are many ways to assign constellation vectors to the spatial and signal domains. In this paper, we investigate optimal constellation breakdown between space and signal domains. The analysis is based on the union bound of the error probability of SM with two typical APM schemes, i.e. phase-shift keying (PSK) and square quadrature amplitude modulation (S-QAM). It is shown that, at any transmission rate, there exists an optimal APM dimension in which the SER is minimized. Furthermore, a trade-off between the number of transmit antennas and the transmit power is introduced.

Iterative Condition Monitoring and Fault Diagnosis Scheme of Electric Motor for Harsh Industrial Application

This paper presents a robust diagnosis technique by iteratively analyzing the pattern of multiple fault signatures in a motor current signal. It is mathematically and experimentally proved that the proposed diagnosis algorithm provides highly accurate monitoring performance while minimizing both false detection and miss detection rate under high noise and nonlinear machine operating condition. These results are verified on a digital-signal-processor-based motor drive system where motor control and fault diagnosis are performed in real time.

Compressive Sensing for Feedback Reduction in MIMO Broadcast Channels

In multi-antenna broadcast networks, the base stations (BSs) rely on the channel state information (CSI) of the users to perform user scheduling and downlink transmission. However, in networks with large number of users, obtaining CSI from all users is arduous, if not impossible, in practice. This paper proposes channel feedback reduction techniques based on the theory of compressive sensing (CS), which permits the BS to obtain CSI with acceptable recovery guarantees under substantially reduced feedback overhead. Additionally, assuming noisy CS measurements at the BS, inexpensive ways for improving post-CS detection are explored. The proposed techniques are shown to reduce the feedback overhead, improve CS detection at the BS, and achieve a sum-rate close to that obtained by noiseless dedicated feedback channels.

Precoder design based on correlation matrices for MIMO systems

This paper presents a general framework for precoder designs for MIMO systems using partial channel knowledge on the transmit and receive correlation matrices at the transmitter. It is shown that the optimal linear precoder for any uncoded and coded MIMO system based on the MMSE or ergodic capacity criterion, or for an orthogonal ST coded MIMO system based on the minimum PEP criterion, is an eigen-beamformer that transmits the signal along eigenvectors of the transmit correlation matrix. Based on the eigen-values of both the transmit and receive correlation matrices, power loading across the eigen-beams is determined by water-pouring policy. Individual effects of the transmit and receive correlation matrices on the system performance are investigated. Simulation results show noticeable performance improvement over MIMO systems without precoder, particularly when the transmit correlation matrix has low rank

Accurate and efficient modeling of SOI MOSFET with technology independent neural networks

This paper presents neural network (NN) approaches for modeling the I-V characteristics of silicon-on-insulator MOSFETs. The modeling approach is technology independent, fast, and accurate, which makes it suitable for circuit simulators. In the model, two different NN architectures, namely, multilayer perceptron and generalized radial basis function, are used and compared. To increase the training efficiency of the NN, both modular and region partitioning methods have been proposed and utilized. In addition, two approaches for obtaining the transconductance and output conductance of the device are discussed. The first approach makes use of an NN for the conductances, while the second uses the numerical differentiation of the I-V results. To confirm the accuracy of the model, the drain-current characteristics as well as conductances obtained by the model are compared to the simulation data for the points where the NNs are not trained. The comparison shows excellent agreements with relative errors of around 1% over a wide range of drain and gate voltages as well as channel lengths and widths.

Performance Analysis of Spatial Modulation in Overlay Cognitive Radio Communications

We study the application of spatial modulation (SM) in overlay cognitive radio (CR) networks, in which the primary and secondary networks work concurrently over the same spectrum band. We assume that the direct link between the primary transmitter and receiver is not available, i.e. broken, and that the CR transmitter assists the primary network as a relay to amplify-and-forward the transmitted symbols of the primary. SM is used in the secondary to split the transmission space into two amplitude-phase modulation (APM) and spatial domains. In the proposed scheme, the secondary transmitter retransmits the primary symbols in APM domain, while its own information is transmitted by the index of transmitting antenna, similar to space shift keying, without causing any interference to the primary receiver. We analyze the performance of the optimal detectors at both the primary and secondary receivers for the case of phase shift keying modulation in terms of the average symbol error rate (ASER). We also study the asymptotic behavior of the ASER at both the primary and secondary at high signal-to-noise ratios. Simulation results show that the SM can be effectively used in overlay CR systems.

Opportunistic Relay Selection With Limited Feedback

Relay selection is a simple technique that achieves spatial diversity in cooperative relay networks. Generally, relay selection algorithms require channel state information (CSI) feedback from all cooperating relays to make a selection decision. This requirement poses two important challenges, which are often neglected in the literature. Firstly, the fed back channel information is usually corrupted by additive noise. Secondly, CSI feedback generates a great deal of feedback overhead (air-time) that could result in significant performance hits. In this paper, we propose a compressive sensing (CS) based relay selection algorithm that reduces the feedback overhead of relay networks under the assumption of noisy feedback channels. The proposed algorithm exploits CS to first obtain the identity of a set of relays with favorable channel conditions. Following that, the CSI of the identified relays is estimated using least squares estimation without any additional feedback. Both single and multiple relay selection cases are considered. After deriving closed-form expressions for the asymptotic end-to-end SNR at the destination and the feedback load for different relaying protocols, we show that CS-based selection drastically reduces the feedback load and achieves a rate close to that obtained by selection algorithms with dedicated error-free feedback.

Distributed BLAST with relay selection for multi-antenna AF relaying

By examining the diversity–multiplexing tradeoff (DMT) of an amplify-and-forward (AF) multi-antenna multi-relay network, a procedure to select the optimal number of relays and relay candidates is established. Subsequently, a distributed BLAST transmission scheme in conjunction with successive nulling and cancellation at destination is proposed to achieve the optimal DMT. Illustrative results indicate that the proposed method can significantly enhance the outage probability performance, and for a selected number of relays in use, the performance enhancement can be further improved by increasing the number of available relays in the AF network. Copyright