Multiple Antenna Techniques Research Articles

Antenna Selection in Interference-Constrained Underlay Cognitive Radios: SEP-Optimal Rule and Performance Benchmarking

In the underlay mode of cognitive radio, secondary users are allowed to transmit when the primary is transmitting, but under tight interference constraints that protect the primary. However, these constraints limit the secondary system performance. Antenna selection (AS)-based multiple antenna techniques, which exploit spatial diversity with less hardware, help improve secondary system performance. We develop a novel and optimal transmit AS rule that minimizes the symbol error probability (SEP) of an average interference-constrained multiple-input-single-output secondary system that operates in the underlay mode. We show that the optimal rule is a non-linear function of the power gain of the channel from the secondary transmit antenna to the primary receiver and from the secondary transmit antenna to the secondary receive antenna. We also propose a simpler, tractable variant of the optimal rule that performs as well as the optimal rule. We then analyze its SEP with \tL transmit antennas, and extensively benchmark it with several heuristic selection rules proposed in the literature. We also enhance these rules in order to provide a fair comparison, and derive new expressions for their SEPs. The results bring out new inter-relationships between the various rules, and show that the optimal rule can significantly reduce the SEP.

Cognitive beamforming based smart metering for coexistence with wireless local area networks

The ZigBee network has been considered to monitor electricity usage of home appliances in the smart grid network. Zig-Bee, however, may suffer from a coexistence problem with wireless local area network (WLAN). In this paper, to resolve the coexistence problem between ZigBee network and WLAN, we propose a new protocol constructing a cognitive smart grid network for supporting monitoring of home appliances. In the proposed protocol, home appliances first estimates the transmission timing and channel information of WLAN by reading request to send/clear to send (RTS/CTS) frames of WLAN. Next, based on the estimated information, home appliances transmit a data at the same time as WLAN transmission. To manage the interference between WLAN and smart grid network, we propose a cognitive beamforming algorithm. The beamforming algorithm is designed to guaranteeing zero interference to WLAN while satisfying a required rate for smart metering. We also propose an energy efficient rate adaptation algorithm. By slowing down the transmission rate while satisfying an imperceptible impact of quality of service (QoS) of the receiver, the home appliance can significantly save transmit power. Numerical results show that the proposed multiple antenna technique provides reliable communications for smart metering with reduced power comparing to the simple transmission technique.

Video streaming exploiting multiple-antenna techniques of wirelessMAN-advanced systems

In this paper, a novel video streaming technique is proposed for the recently standardized IEEE802.16m system also known as the Wireless MAN-Advanced or WIMAX2 system. The antenna mode considered is single user spatially multiplexed (SUSM) transmission suitable for video streaming. In previous works, the linear signal detection method was used in order to achieve unequal error protection (UEP). In this paper, it is shown that a joint signal detection method can also be used to achieve UEP. Computer simulations demonstrate improved performance using the proposed method. In the simulations, H.264/AVC compressed video is used, and the PHY layer procedures such as resource unit allocation, convolutional turbo code (CTC), pilot tone insertion, and pre-coding are implemented in strict accordance with the IEEE 802.16m standard.

Superanalysis of Optimum Combining with Application to Femtocell Networks

A femtocell technology-towards the deployment of small-cell networks-is a key enabler for improving indoor coverage and throughput per network area at a low cost in future wireless networks. However, these small-cell networking inevitably increases cochannel interference due to aggressive (even uncontrolled) reuse of spectral resources. One of the attractive approaches to alleviating the cochannel interference is a multiple-antenna technique for which accurately characterizing the effects of interference is crucial but challenging. To elucidate this important problem, we analyze the performance of interference rejection diversity combining, often called the optimum combining, in an uplink two-tier femtocell network. Specifically, we consider that a single-antenna femtocell user (transmitter) communicates with a closed femtocell access point (receiver) with multiple antennas in the presence of single-antenna cochannel interferers from co-tier (femtocells) and cross-tier (macrocell) networks. We introduce a new mathematical methodology to analyze the average symbol error probability of optimum combining diversity systems in Rayleigh fading, accounting for multiple unequal-power interferers, each is spatially correlated across receiving antennas. The analysis resorts to the so-called Berezin's supermathematics that treats both commuting and Grassmann anticommuting variables on an equal footing. This powerful supermathematical framework enables us to quantify the cross- and co-tier interference effects in terms of interference power heterogeneity and spatial correlation.

Multiple-antenna techniques in LTE-advanced

In this article we discuss the different multiple antenna techniques introduced in LTE-Advanced. Rather than describing the technical details of the adopted solutions, we approach the problem starting from the design targets and the antenna deployments prioritized by the operators. Then we present the main enabling solutions introduced for downlink and uplink transmissions, and subsequently assess the performance of these solutions in different scenarios. Finally, we discuss some possible future developments.

Downlink SNR to CQI Mapping for Different MultipleAntenna Techniques in LTE

Long Term Evolution (LTE) is a step towards the 4th generation (4G) of radio technologies designed to increase the capacity and speed of mobile wireless access. In Release 8, LTE was standardized by 3GPP as the successor of the Universal Mobile Telecommunication System (UMTS).Before full commercial deployment of LTE, downlink SNR to CQI mapping for different multiple antenna techniques can be of enormous significance for the operators. Such vital RF parameters should be tuned before full-fledged commercial launch. In LTE, Adaptive Modulation and Coding (AMC) has to ensure a BLER value smaller than 10%. The SNR-to-CQI mapping is required to achieve this goal. In this paper, Downlink SNR to CQI Mapping for LTE has been performed for Flat Rayleigh channel in fast fading in different transmission modes considering HARQ.

A Universal Space-Time Architecture for Multiple-Antenna Aided Systems

In this tutorial, we first review the family of conventional multiple-antenna techniques, and then we provide a general overview of the recent concept of the powerful Multiple-Input Multiple-Output (MIMO) family based on a universal Space-Time Shift Keying (STSK) philosophy. When appropriately configured, the proposed STSK scheme has the potential of outperforming conventional MIMO arrangements.

Environmental Analysis of MIMO Channel Capacity Under Variable

كانت الاتصالات الرقمية باستخدام MIMO واحدة من أكثر مجالات البحث الواعدة في مجال الاتصالات اللاسلكية في الوقت الحاضر لأنها تقدم الكثير من الوعود للاتصالات اللاسلكية المستقبلية. يبدو أن MIMO هي التقنية الوحيدة التي تعمل على تطوير الصناعة اللاسلكية من أنظمة 3G إلى 4G. تمت دراسة نظام MIMO بتفصيل كبير ومحاكاة لحالات مختلفة وتم التركيز على أداء طاقته في ظل ظروف بيئية عديدة. يوفر نظام MIMO مكاسب كبيرة في الأداء مقارنة بأنظمة الاتصالات اللاسلكية التقليدية. يزيد تعدد الإرسال المكاني من إنتاجية النظام دون استهلاك طيف التردد والتنوع المكاني مما يجعل الارتباط أكثر قوة. تم وصف نظام MIMO وعرض نتائج المحاكاة ومناقشتها. تعد تقنيات الهوائيات المتعددة مفتاحًا لتعزيز أداء الأنظمة اللاسلكية الحديثة.الكلمات المفتاحية: MIMO ، تعدد الإرسال المكاني ، السعة ، التنوع ، نسبة الإشارة إلى الضوضاء (SNR)

Energy efficient radio resource management strategies for green radio

Mobile communication industries are increasingly contributing to the worldwide energy consumption and CO2 emission. This study addresses a number of key radio resource management (RRM) strategies across PHY and MAC layers for reducing base station energy consumption, as measured by a ‘Joules per bit’ metric. These strategies including power efficient link adaptation, exploitation of multi-user diversity and trading bandwidth for energy efficiency. By collectively taking advantage of those RRM strategies, a multi-user adaptive power and resource allocation algorithm is proposed to ease the power requirements of a base station, while maintaining the same levels of service to the user. The scheduling algorithm is applied to an LTE downlink simulator and its performance is evaluated for various traffic load conditions. The results show that the proposed algorithm achieves a significant energy saving (up to 86%) over a conventional non-energy aware resource allocation scheme. Furthermore, the energy efficiency performance of various multiple antenna techniques is evaluated along with the impact of control signalling overhead. These multiple antenna schemes are then incorporated into the proposed scheduling algorithm and the additional achievable energy savings are quantified.

Performance of Optimal Beamforming with Partial Channel Knowledge

Multiple antenna techniques are used to enhance wireless links and therefore have been studied extensively. Many practical systems that differ from ideal schemes have been discussed in the literature. One example is a system that lacks precise channel information at the transmitter. We evaluate analytically the performance of a multiple input multiple output (MIMO) technique that uses partial channel knowledge. Specifically, we analyze a scheme with M transmit antennas and N receive antennas, employing eigenbeamforming at the transmitter and MRC at the receiver. We assume that only partial channel matrix is known to the transmitter, specifically only P out of N rows of the channel matrix are known. We derive the optimal beamformer for a single stream transmission case and show that it is the singular vector of the known channel submatrix. We show that the diversity order of a transmission scheme where such a precoder is used is MP+N-P and further show that increasing the value of P by one increases the diversity order by M-1. We also derive the array gain for this scheme. All the results are supported by simulations.

Spatial modulation for multiple-antenna wireless systems: a survey

Multiple-antenna techniques constitute a key technology for modern wireless communications, which trade-off superior error performance and higher data rates for increased system complexity and cost. Among the many transmission principles that exploit multiple-antenna at either the transmitter, the receiver, or both, Spatial Modulation (SM) is a novel and recently proposed multiple-antenna transmission technique that can offer, with a very low system complexity, improved data rates compared to Single-Input- Single-Output (SISO) systems, and robust error performance even in correlated channel environments. SM is an entirely new modulation concept that exploits the uniqueness and randomness properties of the wireless channel for communication. This is achieved by adopting a simple but effective coding mechanism that establishes a one-to-one mapping between blocks of information bits to be transmitted and the spatial positions of the transmit-antenna in the antenna-array. In this article, we summarize the latest research achievements and outline some relevant open research issues of this recently proposed transmission technique.

On the error exponent of MIMO-ARQ system over the fast fading channels

In this paper, the random coding exponent for fast fading multi-input multi-output channel equipped with automatic repeat request (ARQ) protocol is derived. This exponent can be used to express the probability of error as a function of the data rate and codeword length. This measure provides an intuition into a fundamental trade-off between communication reliability, information rate and delay. This paper shows that using multiple antenna and ARQ techniques are promising tools for communication over fast fading channels. Copyright © 2011 John Wiley & Sons, Ltd.

A survey of next generation mobile communications research in China

With the rapid development of wireless communication networks, the fourth generation (4G) has emerged to move beyond the limitations of the third generation (3G), with increased bandwidth, enhanced quality of services, and reduced costs of resources. In this paper, we discuss the key technologies of 4G and focus on surveying the ongoing research in 4G communications in China. The 4G technologies under investigation include multicarrier transmission, multiple antenna techniques, carrier aggregation, relays, cognitive radio, distributed antenna systems, network convergence, and network self-optimization. These technologies are the building blocks of 4G and contribute largely to the requirements of International Mobile Telecommunications Advanced (IMT-Advanced). For each technology, its benefits, research topics, and some existing approaches are examined. Finally, we briefly discuss the challenges and future research issues in 4G systems.

Multihop relaying and multiple antenna techniques: performance trade-offs in cellular systems

Two very important and active areas of wireless research are multihop relaying and multiple antenna techniques. Wireless multihop relaying can increase the aggregate network data capacity and improve coverage of cellular systems by reducing path loss, mitigating shadowing, and enabling spatial reuse. In particular, multihop relaying can improve the throughput for mobiles suffering from poor signal to interference and noise ratio at the edge of a cell and reduce cell size to increase spectral efficiency. On the other hand, multiple antenna techniques can take advantage of scattering in the wireless channel to achieve higher capacity on individual links. Multiple antennas can provide impressive capacity gains, but the greatest gains occur in high scattering environments with high signal to interference and noise ratio, which are not typical characteristics of cellular systems. Emerging standards for fourth generation cellular systems include both multihop relaying and multiple antenna techniques, so it is necessary to study how these two work jointly in a realistic cellular system. In this paper, we look at the joint application of these two techniques in a cellular system and analyze the fundamental tradeoff between them. In order to obtain meaningful results, system performance is evaluated using realistic propagation models.

Waveform Design and Signal Processing Aspects for Fusion of Wireless Communications and Radar Sensing

Since traditional radar signals are “unintelligent,” regarding the amount of information they convey on the bandwidth they occupy, a joint radar and wireless communication system would constitute a unique platform for future intelligent transportation networks effecting the essential tasks of environmental sensing and the allocation of ad-hoc communication links, in terms of both spectrum efficiency and cost-effectiveness. In this paper, approaches to the design of intelligent waveforms, that are suitable for simultaneously performing both data transmission and radar sensing, are proposed. The approach is based on classical phase-coded waveforms utilized in wireless communications. In particular, requirements that allow for employing such signals for radar measurements with high dynamic range are investigated. Also, a variety of possible radar processing algorithms are discussed. Moreover, the applicability of multiple antenna techniques for direction-of-arrival estimation is considered. In addition to theoretical considerations, the paper presents system simulations and measurement results of complete “RadCom” systems, demonstrating the practical feasibility of integrated communications and radar applications.

The Effects of Spatial Correlation on Multiple Antenna Techniques with Multiuser Scheduling

This letter investigates the effects of spatial correlation on several multiple antenna schemes in multiuser environments. Using an order statistics upper bound on achievable capacity, we quantify the interaction among spatial correlation, spatial diversity, spatial multiplexing and multiuser diversity. Also, it is verified that the upper bound is tighter than asymptotic capacity when the number of users is relatively small.

MIMO Network Coding-Based PHY/MAC Protocol for Replacement of CSMA/CA in Efficient Two-Way Multihop Relay Networks

Backbone wireless mesh networks have attracted much of attention due to their wide-range applications. The use of CSMA/CA basedMAC protocols in mesh networks, however, leads to an inefficient resource utilization, and to high latency. Several alternative protocols including directional MAC, multichannel MAC only provide marginal improvement. Recently, a cross-layer design employing multiple antenna techniques and network coding called MIMO network coding was proposed. Owing to multiple access interference cancellation ability of MIMO, bi-directional flow multiplexing capability of network coding in combination with an efficient channel access scheme of TDMA/TDD, MIMO two-way relay provides significantly high end-to-end capacity. In this paper, MIMO network coding is considered as an alternative PHY/MAC protocol of CSMA/CA. This paper provides details of the protocol and develops network simulators for performance evaluation. Furthermore, an efficient retransmission scheme for transmission system employing network coding is proposed. The paper shows that MIMO network coding achieves significant network performance improvement with respect to CSMA/CA mesh networks. The proposed retransmission scheme is also shown to be effective in terms of resource usage as well as QoS guarantee.

Diversity multiplexing trade-off in shadowed fading SIMO/MISO channels

The diversity-multiplexing trade-off (DMT) in shadowed fading channels is evaluated while the multiple antenna technique is used at the transmit or receive sides. It is shown that, at infinite signal-to-noise ratio (SNR), the asymptotic DMT is not affected by lognormal shadowing. However, the shadowing phenomenon can dramatically reduce the finite SNR DMT.

Multiple antenna spectrum sensing in cognitive radios

In this paper, we consider the problem of spectrum sensing by using multiple antenna in cognitive radios when the noise and the primary user signal are assumed as independent complex zero-mean Gaussian random signals. The optimal multiple antenna spectrum sensing detector needs to know the channel gains, noise variance, and primary user signal variance. In practice some or all of these parameters may be unknown, so we derive the generalized likelihood ratio (GLR) detectors under these circumstances. The proposed GLR detector, in which all the parameters are unknown, is a blind and invariant detector with a low computational complexity. We also analytically compute the missed detection and false alarm probabilities for the proposed GLR detectors. The simulation results provide the available traded-off in using multiple antenna techniques for spectrum sensing and illustrates the robustness of the proposed GLR detectors compared to the traditional energy detector when there is some uncertainty in the given noise variance.

802.11 with multiple antennas for dummies

The use of multiple antennas and MIMO techniques based on them is the key feature of 802.11n equipment that sets it apart from earlier 802.11a/g equipment. It is responsible for superior performance, reliability and range. In this tutorial, we provide a brief introduction to multiple antenna techniques. We describe the two main classes of those techniques, spatial diversity and spatial multiplexing. To ground our discussion, we explain how they work in 802.11n NICs in practice.