Direction of Arrival Estimation with Compact Array Antennas

This chapter presents direction of arrival (DoA) estimation with a compact array antenna using methods based on reactance switching. The compact array is the single-port electronically steerable parasitic array radiator (Espar) antenna. The antenna beam pattern is controlled though parasitic elements loaded with reactances. DoA estimation using an Espar antenna is proposed with the power pattern cross correlation (PPCC), reactance-domain (RD) multiple signal classification (MUSIC), and, RD estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithms. The three methods exploit the reactance diversity provided by an Espar antenna to correlate different antenna output signals measured at different times and for different reactance values. The authors hope that this chapter allows the researchers to appreciate the issues that may be encountered in the implementation of direction-finding application with a single-port compact array like the Espar antenna.

Omni-, Sector, and Adaptive Modes of Compact Array Antenna

Three working modes, omni-, sector and adaptive modes, for a compact array antenna are introduced. The compact array antenna is an electronically steerable parasitic array radiator (Espar) antenna, which has only a single-port output, and carries out signal combination in space by electromagnetic mutual coupling among array elements. These features of the antenna significantly reduce its cost, size, complexity, and power consumption, and make it applicable to mobile user terminals. Signal processing algorithms are developed for the antenna. An omnipattern is given by an equal-voltage single-source power maximization algorithm. Six sector patterns are formed by a single-source power maximization algorithm. Adaptive patterns are obtained by a trained adaptive control algorithm and a blind adaptive control algorithm, respectively. The experiments verified the omnipattern, these six sector patterns and the adaptive patterns. It is hope that understanding of the antenna’s working modes will help researcher for a better design and control of array antennas for mobile user terminals.

Field Programmable Gate Array Based Testbed for Investigating Multiple Input Multiple Output Signal Transmission in Indoor Environments

This chapter introduces the concept of Multiple Input Multiple Output (MIMO) wireless communication system and the necessity to use a testbed to evaluate its performance. A comprehensive review of different types of testbeds available in the literature is presented. Next, the design and development of a 2×2 MIMO testbed which uses in-house built antennas, commercially available RF chips for an RF front end and a Field Programmable Gate Array (FPGA) for based signal processing is described. The operation of the developed testbed is verified using a Channel Emulator. The testing is done for the case of a simple Alamouti QPSK based encoding and decoding scheme of baseband signals.

Smart Antennas for Automatic Radio Frequency Identification Readers

Various smart antennas developed for automatic radio frequency identification (RFID) readers are presented. The main smart antennas types of RFID readers are switched beam, phased array, adaptive beamfsorming and multiple input multiple output (MIMO) antennas. New development in the millimeter wave frequency band?60 GHz and above? exploits micro-electromechanical system (MEMS) devices and nano-components. Realizing the important of RFID applications in the 900 MHz frequency band, a 3×2-element planar phased array antenna has been designed in a compact package at Monash University. The antenna covers 860-960 GHz frequency band with more than 10 dB input return loss, 12 dBi broadside gain and up to 40° elevation beam scanning with a 4-bit reflection type phase shifter array. Once implemented in the mass market, RFID smart antennas will contribute tremendously in the areas of RFID tag reading rates, collision mitigation, location finding of items and capacity improvement of the RFID system.

Cross-Layer Performance of Scheduling and Power Control Schemes in Space-Time Block Coded Downlink Packet Systems

In this chapter, we consider a cellular downlink packet data system employing the space-time block coded (STBC) multiple- input-multiple-output (MIMO) scheme. Taking the CDMA high data rate (HDR) system for example, we evaluate the cross-layer performance of typical scheduling algorithms and a point-to-point power control scheme over a time division multiplexing (TDM)-based shared MIMO channel. Our evaluation focuses on the role of those schemes in multi-user diversity gain, and their impacts on medium access control (MAC) and physical layer performance metrics for delay-tolerant data services, such as throughput, fairness, and bit or frame error rate. The cross-layer evaluation shows that the multi-user diversity gain, which comes from opportunistic scheduling schemes exploiting independent channel oscillations among multiple users, can increase the aggregate throughput and reduce the transmission error rate. It also shows that STBC/MIMO and one-bit and multi-bit power control can indeed help the physical and MAC layer performance but only at a risk of limiting the multiuser diversity gain or the potential throughput of schedulers for delay-tolerant bursty data services.

Detection Based on Relaxation in MIMO Systems

This chapter takes a closer look at a class of MIMO detention methods, collectively referred to as relaxation detectors. These detectors provide computationally advantageous alternatives to the optimal maximum likelihood detector. Previous analysis of relaxation detectors have mainly focused on the implementation aspects, while resorting to Monte Carlo simulations when it comes to investigating their performance in terms of error probability. The objective of this chapter is to illustrate how the performance of any detector in this class can be readily quantified thought its diversity gain when applied to an i.i.d. Rayleigh fading channel, and to show that the diversity gain is often surprisingly simple to derive based on the geometrical properties of the detector.

Adaptive MIMO Systems with High Spectral Efficiency

This chapter introduces the adaptive modulation and coding (AMC) as a practical means of approaching the high spectral efficiency theoretically promised by multiple-input multiple-output (MIMO) systems. It investigates the AMC MIMO systems in a generic framework and gives a quantitative analysis of the multiplexing gain of these systems. The effects of imperfect channel state information (CSI) on the AMC MIMO systems are pointed out. In the context of imperfect CSI, a design of robust near-capacity AMC MIMO system is proposed and its good performance is verified by simulation results. The proposed adaptive system is compared with the non-adaptive MIMO system, which shows the adaptive system approaches the channel capacity closer.

Fast Beamforming of Compact Array Antenna

In this chapter, we describe a compact array antenna. Beamforming is achieved by tuning the load reactances at parasitic elements surrounding the active central element. The existing beam forming algorithms for this reactively controlled parasitic array antennas require long training time. In comparison with these algorithms, a faster beamforming algorithm, based on simultaneous perturbation stochastic approximation (SPSA) theory with a maximum cross-correlation coefficient (MCCC) criterion, is proposed in this chapter. The simulation results validate the algorithm. In an environment where the signal-to-interference ratio (SIR) is 0 dB, the algorithm converges within 50 iterations and achieves an output SINR of 10 dB. With the fast beamforming ability and its low power consumption attribute, the antenna makes the mass deployment of smart antenna technologies practical. To give a comparison of the beamforming algorithm with one of the standard beamforming algorithms for a digital beamforming (DBF) antenna array, we compare the proposed algorithm with the least mean square (LMS) beamforming algorithm. Since the parasitic array antenna is in nature an analog antenna, it cannot suppress correlated interference. Here, we assume that the interferences are uncorrelated.

Blind Channel Estimation in Space-Time Block Coded Systems

This chapter analyzes the problem of blind channel estimation under Space-Time Block Coded transmissions. In particular, a new blind channel estimation technique for a general class of space-time block codes is proposed. The method is solely based on the second-order statistics of the observations, and its computational complexity reduces to the extraction of the main eigenvector of a generalized eigenvalue problem. Additionally, the identifiability conditions associated to the blind channel estimation problem are analyzed, which is exploited to propose a new transmission technique based on the idea of code diversity or combination of different codes. This technique resolves the ambiguities in most of the practical cases, and it can be reduced to a non-redundant precoding consisting in a single set of rotations or permutations of the transmit antennas. Finally, the performance of the proposed techniques is illustrated by means of several simulation examples.

Space-Time Modulated Codes for MIMO Channels with Memory

Modulated codes (MC) are error correction codes (ECC) defined on the complex field and therefore can be naturally combined with an intersymbol interference (ISI) channel. It has been previously proved that for any finite tap ISI channel there exist MC with coding gain comparing to the uncoded AWGN channel. In this chapter, we first consider space-time MC for memory channels, such as multiple transmit and receive antenna systems with ISI. Similar to MC for single antenna systems, the space-time MC can be also naturally combined with a multiple antenna system with ISI, which provides the convenience of the study. Some lower bounds on the capacities C and the information rates Ii.i.d of the MC coded systems are presented. We also introduce an MC coded zero-forcing decision feedback equalizer (ZF-DFE) where the channel is assumed known at both the transmitter and the receiver. The optimal MC design based on the ZF-DFE are presented.