Monthippa Uthansakul

Fully spatial wide-band beamforming using a rectangular array of planar monopoles

This paper describes a spatial beamformer which by using a rectangular array antenna steers a beam in azimuth over a wide frequency band without frequency filters or tap-delay networks. The weighting coefficients are real numbers which can be realized by attenuators or amplifiers. A prototype including a 4/spl times/4 array of square planar monopoles and a feeding network composed of attenuators, power divider/combiners and a rat-race hybrid is developed to test the validity of this wide-band beamforming concept. The experimental results prove the validity of this wide-band spatial beamformer for small size arrays.

Impact of wideband signals on smart antenna system

As we known, a smart antenna system is a system considered as an effective system to improve the quality and reliability of a wireless communication system. Therefore, the smart antenna system has to be employed in higher data bit rate, as well as higher frequency spectrum, in the foreseen future for the next generation of wireless communication system. Thus, We investigate the impacts of signal bandwidth on a smart antenna system. We also focus on the beam forming ability and signal quality of the antenna. As shown in the simulation results, while the signal bandwidth increases the interference rejection, as well as the ability to form main beam to the desired direction, cannot only be successfully achieved with the existing narrowband weighting scheme but the output signal quality will be degraded as well.

Self-Interference Cancellation-Based Mutual-Coupling Model for Full-Duplex Single-Channel MIMO Systems

The challenge of a full-duplex single-channel system is the method to transmit and receive signals simultaneously at the same time and on the same frequency. Consequently, a critical issue involved in such an operation is the resulting self-interference. Moreover, for MIMO system, the full-duplex single-channel system is subjected to the very strong self-interference signals due to multiple transmitting and receiving antennas. So far in the pieces of literature, there have not been any suitable techniques presented to reduce the self-interference for full-duplex single-channel MIMO systems. This paper initially proposes the method to cancel the self-interference by utilizing the mutual-coupling model for self-interference cancellation. The interference can be eliminated by using a preknown interference, that is, the mutual-coupling signals. The results indicate that the channel capacity performance of the proposed technique can significantly be improved due to the reduction of the self-interference power. The measurement results indicate that the proposed MIMO system can suppress the self-interference and mutual-interference signals with the reduction of 31 dB received power.

An investigation into smart antenna configurations for wideband communication

The challenge of next generation wireless communication systems comes from the fact that they will have to offer data rates in the hundreds of megabits per second. This requirement translates into the demand for wide frequency bands. The problem of overcoming spectrum limitation while delivering high data rate requirement can be achieved using wideband smart antennas. In this paper, three technologies for a smart antenna system operating over a wide band of frequency are investigated. These concern: space-time signal processing, space-frequency signal processing and fully spatial signal processing. The fundamental principles of these three technologies are examined in this paper.

Angular Beamforming Technique for MIMO Beamforming System

The method of MIMO beamforming has gained a lot of attention. The eigen beamforming (EB) technique provides the best performance but requiring full channel information. However, it is impossible to fully acquire the channel in a real fading environment. To overcome the limitations of the EB technique, the quantized beamforming (QB) technique was proposed by using only some feedback bits instead of full channel information to calculate the suitable beamforming vectors. Unfortunalely, the complexity of finding the beamforming vectors is the limitation of the QB technique. In this paper, we propose a new technique named as angular beamforming (AB) to overcome drawbacks of QB technique. The proposed technique offers low computational complexity for finding the suitable beamforming vectors. In this paper, we also present the feasibility implementation of the proposed AB method. The experiments are undertaken mainly to verify the concept of the AB technique by utilizing the Butler matrix as a two-bit AB processor. The experimental implementation and the results demonstrate that the proposed technique is attractive from the point of view of easy implementation without much computational complexity and low cost.

Experiments with a Low-Profile Beamforming MIMO System for WLAN Applications

MIMO technology has become one of the most promising techniques for enhancing the quality of services in many applications. For WLANs, the issue of MIMO technology has been officially addressed by the IEEE 802.11 n standard. In this standard, five MIMO operations - including spatial multiplexing, transmitting beamforming, space-time block coding, low-density parity-check encoding, and antenna selection - were described. Among these operations, the beamforming MIMO has the benefits of a low complexity with the highest improvement in signal-to-noise ratio. However, it is still requires high computational processing for estimating knowledge of the channel and for finding an appropriate steering vector. To reduce such computations, a selection of a fixed number of formed beams is proposed. In this paper, an experimental study of practically switched beamforming for WLAN applications is presented. Two types of antenna configurations, including 4×1 linear and 2×2 planar arrays, were considered. The results indicated the benefit of switched beamforming by improving average signal power strength by 10.25 dB. In addition, to reduce the burden of estimating the channel, the concept of selecting the best steering vector from the received signal strength instead of the channel information is proposed for low-profile beamforming MIMO systems. The prototype was completely constructed and practically tested. The results confirmed the successful improvement of the proposed prototype over using an omnidirectional antenna for WLAN applications.

Wideband beam and null steering using a rectangular array of planar monopoles

This article presents the design of a wideband rectangular array of planar monopoles, which is able to steer its beam and nulls over a wide frequency band using real-valued weights. These weights can be realized in practice by amplifiers or attenuators leading to a low cost development of a wideband array antenna with beam and null steering capability. The weights are determined by applying an inverse discrete Fourier transform to an assumed radiation pattern. This wideband beam and null forming concept is verified by full electromagnetic simulations which take into account mutual coupling effects between the array elements

A wideband spatial beamformer employing a rectangular array of planar monopoles

The paper presents a wideband spatial beamformer which employs a rectangular antenna array with real valued signal weighting coefficients to steer beam in azimuth. A modified IDFT technique is used to obtain the weighting coefficients for an assumed radiation pattern. The operation of this wideband beamformer is demonstrated in an example of a 4times4 array constituted by wideband planar monopoles

Performance of Antenna Selection in MIMO System Using Channel Reciprocity with Measured Data

The channel capacity of MIMO system increases as a function of antenna pairs between transmitter and receiver but it suffers from multiple expensive RF chains. To reduce cost of RF chains, antenna selection (AS) method can offer a good tradeoff between expense and performance. For a transmitting AS system, channel state information (CSI) feedback is required to choose the best subset of available antennas. However, the delay and error in feedback channel are the most dominant factors to degrade performances. In this paper, the concept of AS method using reciprocal CSI instead of feedback channel is proposed. The capacity performance of proposed system is investigated by own developing Testbed. The obtained results indicate that the reciprocity technique offers a capacity close to a system with perfect CSI and gains a higher capacity than a system without AS method. This benefit is from 0.9 to 2.2 bps/Hz at SNR 10 dB.

Investigations into a wideband spatial beamformer employing a rectangular array of planar monopoles

This paper presents a rectangular array antenna with a suitable signal-processing algorithm that is able to steer the beam in azimuth over a wide frequency band. In the previous approach, which was reported in the literature, an inverse discrete Fourier transform technique was proposed for obtaining the signal weighting coefficients. This approach was demonstrated for large arrays in which the physical parameters of the antenna elements were not considered. In this paper, a modified signal-weighting algorithm that works for arbitrary-size arrays is described. Its validity is demonstrated in examples of moderate-size arrays with real antenna elements. It is shown that in some cases, the original beam-forming algorithm fails, while the new algorithm is able to form the desired radiation pattern over a wide frequency band. The performance of the new algorithm is assessed for two cases when the mutual coupling between array elements is both neglected and taken into account.