Sana Sfar

Analysis of MIMO Systems With Receive Antenna Selection in Spatially Correlated Rayleigh Fading Channels

We consider a receive antenna selection multiple-input-multiple-output (MIMO) system, where only one out of N r receive antennas is selected. Spatial channel correlation will be considered at the receiver side only. Our goal is to investigate the capacity performance of this system. In particular, we will derive a closed-form expression for the outage probability and an upper bound for the ergodic (average) capacity. These quantities will be expressed using an infinite series representation. To do so, we will first derive the joint cumulative distribution function and the joint probability density function of the squared row norms of the channel matrix. This is enabled by taking advantage of the statistical properties of multivariate chi-squared random variables. Using the outage expression derived, we demonstrate that the considered antenna selection system achieves a full diversity order that is similar to a MIMO system without antenna selection. Next, we derive the probability density function of the maximum of the squared row norms of the channel matrix and its moments, which is straightly related to the system ergodic capacity. We also analyze the error rate performance of the aforementioned receive antenna selection MIMO system while using orthogonal space-time block codes (OSTBCs) at the transmitter. Our simulation results are shown to validate our analytical findings.

Receive antenna selection for closely-spaced antennas with mutual coupling

We investigate the achievable rate of receive antenna selection MIMO systems in the presence of mutual coupling and spatial correlation. For that, we assume the antenna array to consist of dipole antennas placed side-by-side in a linear pattern and in a very limited physical space. In a first step, we will assume perfect channel state information at the receiver side only and a negligible training overhead compared with the payload. We will demonstrate that in contrast to what might be expected based on results for cases without mutual coupling, MIMO receive antenna selection can achieve higher data rates than the system using all antennas provided that the total number of receive antennas is larger than a critical value that we will further discuss. We then propose an optimal antenna selection processing that ensures rate maximization regardless of the number of antennas used. In a later step, we will address the impact of training overhead on the system achievable rate when the training overhead is considerable. We will show that such a rate is reduced dramatically due to the large amount of training overhead arising from the presence of mutual coupling. To overcome this problem, we will thus propose a novel channel estimation method, which reduces the training overhead greatly and improves the system achievable rate performance.

Antenna selection for MIMO systems with closely spaced antennas

Physical size limitations in user equipment may force multiple antennas to be spaced closely, and this generates a considerable amount of mutual coupling between antenna elements whose effect cannot be neglected. Thus, the design and deployment of antenna selection schemes appropriate for next generation wireless standards such as 3GPP long term evolution (LTE) and LTE advanced needs to take these practical implementation issues into account. In this paper, we consider multiple-input multipleoutput (MIMO) systems where antenna elements are placed side by side in a limited-size linear array, and we examine the performance of some typical antenna selection approaches in such systems and under various scenarios of antenna spacing and mutual coupling. These antenna selection schemes range from the conventional hard selection method where only part of the antennas are active, to some newly proposed methods where all the antennas are used, which are categorized as soft selection. For the cases we consider, our results indicate that, given the presence of mutual coupling, soft selection can always achieve superior performance as compared to hard selection, and the interelement spacing is closely related to the effectiveness of antenna selection. Our work further reveals that, when the effect of mutual coupling is concerned, it is still possible to achieve better spectral efficiency by placing a few more than necessary antenna elements in user equipment and applying an appropriate antenna selection approach than plainly implementing the conventional MIMO system without antenna selection.

A near-optimal joint transmit and receive antenna selection algorithm for MIMO systems

Antenna selection is a low-complexity low-cost alternative for implementing MIMO systems. It was proposed to trade off system hardware cost and system performance by keeping the same number of antennas and using a fewer RF chains. In this paper, we consider the joint transmit and receive antenna selection capacity-maximization problem in MIMO systems. The optimal joint transmit and receive antenna selection could be achieved by exhaustively searching all the transmit and receive antenna subsets. However, its applicability is limited due to the high computational complexity. The existing suboptimal algorithms decouple the selection into transmit antenna selection and receive antenna selection, and exhibit a performance loss compared to the optimal method. We propose JTRAS, a greedy algorithm to jointly select the transmit and receive antennas to maximize the channel capacity. We will demonstrate that JTRAS performs very close to the optimal exhaustive search method and outperforms the existing suboptimal algorithms. We will also investigate the computational complexity of JTRAS and show it is much lower than that of the optimal solution. Capacity performance of our proposed JTRAS algorithm will be provided by simulation.

On the Importance of Modeling the Mutual Coupling for Antenna Selection for Closely-Spaced Arrays

In this paper we consider a system in which multiple dipole antennas are placed side-by-side within a finite space at the receiver to form a uniform linear array, causing the dipole antennas to be closely spaced. We investigate the achievable rate with receive antenna selection and take into account both spatial correlation and mutual coupling effects between the antennas. We assume the full channel state information is available at the receiver but not at the transmitter. Opposite to what might be expected, the system achievable rate with receive antenna selection can outperform the system employing all the antennas, provided the number of antennas used is larger than a critical value. We also describe the optimal processing scheme which enumerates all possible antenna combinations and selects the combination maximizing the instantaneous achievable rate for a given channel realization.

Transactions letters - Layered group detection for multiuser mimo wireless cdma systems

In this paper, we consider a multiuser multiple input multiple output (MIMO) CDMA system where each user is transmitting different streams spread with the same code on a set of multiple antennas. Signals from one user are received as one group and each user is thought of as a virtual group. At the receiver, group ordered successive interference cancellation detection is applied. Optimal and sub-optimal group detection orders that maximizes the system performance are then derived. Various linear group detectors are considered such as the linear decorrelators and a closed form expression of the optimal order is given for the case of each of these group detectors. Numerical results demonstrate significant gains in the system performance as well as the importance of group ordering

Protocols and system capacity of relay-enhanced HSDPA systems

In this paper we examine the impact of using relays on the throughput and coverage of the High-Speed Packet Downlink Access (HSDPA) cellular system.We consider two cooperation schemes that can be incorporated into the existing HSPDA system with relative ease. Using a system-level simulation approach we demonstrate that relaying, when properly designed and deployed, can have a significant positive impact on the throughput and coverage of cellular systems.

Is relayed collaborative communication worth it

We consider a collaborative wireless distributed network, consisting of one source transmitting information to a remote destination in the presence of N relay nodes. We assume that all nodes have similar capabilities, are randomly distributed geographically, immersed in the clutter and close to the ground, each employing a single antenna. Assuming a Decode-and-Forward technique, we propose various collaborative approaches for signaling. Using well-known channel coding techniques, the destination is not able to start decoding its intended message until all nodes have decoded the entire message. Using more sophisticated coding techniques, the destination can start decoding the transmitted message at the start of the communication by the source. Various ways of organizing the relay collaboration are: Generalized Beamforming; Generalized Alamouti; and Simultaneous Casting. We then evaluate the performance of these collaborative approaches by simulations, employing an appropriate fading/path loss channel model. Obtained results will demonstrate the superiority of the sophisticated coding technique used and provide insights on when collaboration in networked multiple antennae systems is useful. Specifically, a gain of the order of 9 dB in the required transmit power is achieved assuming Simultaneous Casting and 0 dB transmit power per node, compared to the case when these sophisticated codes are not used. Finally, we also observe a gain in the system 10th percentile outage rate on the order of 1.4 bit/s/Hz at a 0 dB transmit power and with Generalized Beamforming, compared to the case where relays are not used.

A simulation study of antenna selection for compact MIMO arrays

We consider a compact multiple-input multiple-output (MIMO) system where antenna elements are placed linearly and side by side in a limited size array. Inevitably, both mutual coupling and spatial correlation effects have a strong presence in such system. We then investigate the performance of both hard and soft antenna selection in such conditions using Monte Carlo simulations. Our results indicate that soft selection could always achieve superior performance as compared to the hard selection even given the presence of mutual coupling. Our results will further conclude on the applicability range of antenna selection schemes.

Outage Probability of MIMO Systems with Receive Antenna Selection in Spatially Correlated Rayleigh Fading Channels

We consider a receive antenna selection MIMO system, where only one receive antenna is selected out of Nr antennas. Spatial channel correlation will be considered at the receiver side only. We investigate here the capacity performance of such a system. In particular, we derive a closed-form expression of its outage probability expressed in an infinite series representation. To do so, we derive the joint cumulative distribution function and joint probability density function of the squared row norms of the channel matrix by using the statistical properties of multivariate chi-square random variables. Our simulation results will be shown to validate our analytical findings.