Hybrid Smart Antenna Research Articles

Low Complexity Hybrid Smart Antenna with Directional Elements over Frequency Selective Fading Channel

In this paper, a low complexity hybrid smart antenna system with directional elements and reduced-size digital beamformer is proposed to combat the inter-symbol interference (ISI) problem over frequency-selective fading channels. The conventional smart antenna systems with omni-directional elements utilize the full-size digital beamformer to suppress interference and obtain the optimum performance. However, the proposed hybrid smart antenna system with directional elements can split the linear receive array into two subarrays. One subarray contains the elements with no ISI, which can be processed with a simple maximum ratio combiner (MRC). The second subarray includes the elements with the ISI interference, which require the use of a reduced-size optimum beamformer for interference suppression. Finally, the outputs of the two subarrays are combined for optimal detection of the transmitted signals. Simulation results confirm that the proposed low complexity hybrid smart antenna system can provide robust performance under the multipath fading channel with ISI, and outperform the conventional smart antenna systems due to the use of directional antennas and utilization of multipath diversity gain.

Experimental Verification of the Hybrid Smart Antenna Algorithm With Modulated Waveforms

The hybrid smart antenna approach utilizes a subset of array elements selected according to the receive signal strengths to perform beamforming, thus improving the computational efficiency, and reducing the hardware implementation cost. The previous implementations and published experimental results of this algorithm have been based on continuous-wave (CW) transmit signals, and without modulation. In order to verify the operation of the hybrid smart antenna algorithm with modulated waveforms, the developed 2.4- and 60-GHz testbeds are modified to generate and receive data modulated waveforms. The modifications also include the use of preamble bits at the beginning of each data frame transmitted, and implementation of a sliding window correlator at the receiver to synchronize with the data frames. Binary phase shift keying (BPSK) modulation is used with a 1 megabit per second (Mb/s) data rate for information transfer. The obtained beam patterns agree well with the theoretical results thus verifying the developed hybrid smart antenna algorithm.

Implementation and Experimental Verification of a Smart Antenna System Operating at 60 GHz Band

With the introduction of the unlicensed spectrum at the 60 GHz range, the development of communication systems with data rates in Gb/s range has become feasible. However, there are quite significant challenges at this frequency range such as high propagation loss, oxygen absorption, antenna alignment and unavailability of high-gain, high power circuit elements. In this paper we present a novel 2-channel hybrid smart-antenna system operating at 60 GHz band which can be used with an antenna switching system to improve the signal power performance and to serve as an automated alignment system. The critical system parameters for a smart-antenna system at this frequency are the transmitter to receiver distance, element spacing, and antenna beamwidth. As the widely known beamforming assumptions may not hold for some configurations, a more general beamforming formulation is given in the paper to serve as a guideline for system designers. The twist angle of array elements is introduced as a new array design parameter. By selecting the optimal twist angle to help overlap radiation patterns, the fine alignment of the transmit and receive beams is established electronically using beamforming, thus reducing the cost of deployment and maintenance of the 60 GHz indoor communication systems.

Eigenspace-based blind pattern optimisations of steerable antenna array for interference cancellation

A novel adaptive algorithm for an array using directional elements called a hybrid smart antenna system is proposed. The algorithm controls the element patterns on the basis of an objective function composed of eigenvalues of a covariance matrix. A high and stable array output signal-to-interference-plus-noise ratio is achieved by improving both the received powers and the spatial correlation coefficient between incident waves, without prior knowledge such as directions-of-arrival, channel state information or training signals. The characteristics of the proposed algorithm are theoretically and numerically clarified for a simple case involving two incident waves. Convergence with least mean squares algorithm is found to be as fast as that with recursive least squares algorithm in this system. Also, simulation for statistical performance evaluation is carried out in comparison with a conventional system. Furthermore, a method to implement the proposed eigenspace control algorithm without having to solve the eigenvalue problem is shown.

Genetic-Algorithm-Based Antenna Array Design for a 60-GHz Hybrid Smart Antenna System

The previously described hybrid smart-antenna system solves the transmitter receiver alignment problem of 60-GHz wireless systems when high gain antennas are used. Utilizing multiple highly directional array elements and coherently combining the outputs of a few elements adaptively, the hybrid smart antenna achieves the desired performance and results in significant hardware cost and computational complexity savings. For optimal alignment, however, the output power of the hybrid smart antenna should stay constant over the scanning range. This minimizes the so-called scalloping effects and necessitates a careful selection of the array elements being used in beamforming. In this letter, a genetic-algorithm solution to optimally adjust the beam pattern overlaps the array elements to minimize the output-power fluctuations in a given scan range. It is shown that while the hybrid algorithm may perform satisfactorily with less than one-third of the total number of the array elements (e.g., two or three elements in an array of ten antennas), there is an optimal number of elements for a given array that provides minimal power fluctuation in a specified scan range. A tradeoff between the acceptable level of power fluctuation and the total received power is identified.

A novel super-resolution beamforming algorithm

A novel simply-structured hybrid smart antenna system suitable to be used in ad-hoc network terminals is proposed in this letter. The super-resolution beamforming algorithm is also presented based on the system using DOA estimation results. The algorithm can switch the beamforming to the direction of the expected signal and get the best transmitting performance after the pre-beamforming of the Butler matrix. The shifting value formulas are presented to obtain the best SNR when there is no interfering signal and to acquire the highest Signal to Interference Ratio (SIR) as there is one interfering signal. When there are more than one interfering signals, the pre-beamforming feature of the Butler matrix can also suppress the interfering signals. Simulation results verified the algorithm.

Implementation and Experimental Verification of Hybrid Smart-Antenna Beamforming Algorithm

In the literature (Zhang et al., and Rezk et al.), a hybrid beamforming algorithm utilizing a subset of array elements according to receive signal strength is proposed. The algorithm utilizes a smart switch which selects a subset of antennas that receive the signals with higher strength and a beamforming algorithm is performed to calculate the weights for the selected antennas. Since earlier results were based on simulations by Zhang et al., and Rezk et al., in this letter we present experimental results of testing a smart-antenna prototype with an eight-element array. This array is designed and implemented by the authors to verify the accuracy and performance of the proposed hybrid-beamforming algorithm. In general, the experimental results confirmed the simulation data. Specifically, it is shown that the proposed hybrid algorithm using a subset of the array has nearly the same performance as the adaptive system with the full array. Tradeoffs regarding beamwidth and the sidelobe levels are confirmed and additional experimental results illustrating the angle resolution of the developed system are presented

Performance comparison of a novel hybrid smart antenna system versus the fully adaptive and switched beam antenna arrays

In this letter, we investigate and compare the performance of a newly proposed hybrid smart antenna system with the fully adaptive and switched beam smart antenna arrays. Simulation results show that the adaptive and the proposed hybrid systems have nearly the same performance accuracy, with the hybrid system offering faster tracking time, improved computational efficiency, and a possible reduction in the implementation cost. The comparative study also included measured radiation pattern from a recently developed coplanar waveguide continuous transverse stub (CPW-CTS) antenna.

Hybrid smart antenna system using directional elements - Performance analysis in flat Rayleigh fading

Smart antenna and associated technologies are expected to play a significant role in enabling broadband wireless communication systems. Smart antennas exploit space diversity to help provide high data rates, increased channel capacity, and improved quality of service at an affordable cost. In this paper we present a new procedure for implementing smart antenna algorithms. It is a hybrid approach that integrates the features of the switched beam method and the adaptive beam forming approach. Specifically it is shown that by using high gain antenna elements and combining the switched beam process with the adaptive beam forming procedure on a limited number of elements (as low as two in an eight-element array), a performance close to that of a more complex eight-element adaptive array may be achieved. The proposed hybrid method, therefore, is fast, is computationally efficient, and provides a cost effective approach for exploiting space diversity. Even with the inclusion of interference signals, the proposed hybrid approach out-performed the switched beam method, and provided performance similar to that of an adaptive array with less number of elements (three in an eight-element array). Implementation of an adaptive array also includes estimations; hence, reducing the number of elements in an array may lead to improved accuracy, in addition to fast convergence and reduced complexity.