Vida Vakilian

Universal-filtered multi-carrier technique for wireless systems beyond LTE

In this paper, we propose a multi-carrier transmission scheme to overcome the problem of intercarrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems. In the proposed scheme, called universal-filtered multi-carrier (UFMC), a filtering operation is applied to a group of consecutive subcarriers (e.g. a given allocation of a single user) in order to reduce out-of-band sidelobe levels and subsequently minimize the potential ICI between adjacent users in case of asynchronous transmissions. We consider a coordinated multi-point (CoMP) reception technique, where a number of base stations (BSs) send the received signals from user equipments (UEs) to a CoMP central unit (CCU) for joint detection and processing. We examine the impact of carrier frequency offset (CFO) on the performance of the proposed scheme and compare the results with the performance of cyclic prefix based orthogonal frequency division multiplexing (CP-OFDM) systems. We use computer experiments to illustrate the efficiency of the proposed multi-carrier scheme. The results indicate that the UFMC scheme outperforms the OFDM for both perfect and non-perfect frequency synchronization between the UEs and BSs.

Application of radio-over-fiber (ROF) in mobile communication

Future generation of mobile communication system must be capable of serving high quality and broadband services even in highly dense populated area. The radio-over-fibre is one of the promising systems which can be used along the emerging wireless technologies such as smart antenna or multiple input multiple output (MIMO) systems to meet these requirements. In this paper, the role of ROF technology in next generation of mobile communication system is presented, and then the concept is clearly interpreted. Then, base on previous research and finding, a probable ROF architecture for present and future wireless mobile communication is portrayed. Along this, challenges and development issues of ROF technology are presented as well.

Performance Evaluation of Reconfigurable MIMO Systems in Spatially Correlated Frequency-Selective Fading Channels

In this paper, we study the performance of a reconfigurable multiple-input multiple-output (RE-MIMO) system in spatially correlated frequency- selective fading channels. In particular, we propose to use a RE-MIMO system to overcome the inter symbol interference (ISI) problem caused by multipath propagation. In the proposed system, we use a 3-dimensional coding scheme to obtain the same diversity order as in MIMO-OFDM systems over frequency-selective channels, and achieving better bit error rate performance by using directive reconfigurable antennas. To demonstrate the superiority of the proposed system, we compare the performance of the RE-MIMO with MIMO-OFDM system over frequency-selective channels. Simulation results show that the coded RE-MIMO system outperforms the coded MIMO-OFDM systems for small angular spread. However, for larger angular spread, the performance of the RE-MIMO system degrades due to much stronger contribution of undesired multipath components.

Effects of angle-of-arrival estimation errors, angular spread and antenna beamwidth on the performance of reconfigurable SISO systems

This paper investigates the average bit error rate (BER) performance of reconfigurable single-input single-output (RE-SISO) antenna systems in the clustered channel model. The main focus of the paper is to evaluate the impacts of angle of arrival (AoA) estimation errors, angular spread and antenna beamwidth on the performance of a reconfigurable system. In particular, the BER for the RE-SISO systems is presented under perfect AoA knowledge at the receiver. Then, an analytical expression for the BER of the system is derived in the presence of AoA estimation errors. Along with this, the effects of angular spread and antenna beamwidth on the system performance are examined for both perfect and imperfect AoA estimation scenarios. The results indicate that the effect of AoA estimation error is more significant when the cluster angular spread is small. The same conclusion can be made for the antenna beamwidth.

Space-frequency block code for MIMO-OFDM communication systems with reconfigurable antennas

We propose a space-frequency (SF) block coding scheme for a multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system using antennas with reconfigurable radiation patterns. In this system, each element of the antenna array at the transmitter side is assumed to be reconfigurable so that it can independently change the physical characteristics of its radiation pattern. The proposed block code is full rate and benefits from spatial, frequency, and reconfigurable radiation pattern state diversity over frequency-selective fading channels. We provide simulation results to demonstrate the performance of the proposed block coding technique and make comparisons with that of the previous SF coding schemes in MIMO-OFDM systems. The results indicate that the proposed code achieves higher diversity and coding gain compared to other available SF codes.

Direction-of-arrival estimation in a clustered channel model

In this paper, we study the performance of the MUltiple SIgnal Classification (MUSIC) direction-of-arrival (DoA) estimation algorithm in a clustered channel model. We examine the effect of angular spread on the estimation accuracy of the MUSIC algorithm. Simulation result shows that the performance of the MUSIC algorithm degrades as the angular spread increases. Furthermore, an experimental study is performed in an anechoic chamber to evaluate the performance of DoA estimation using a single reconfigurable antenna element known as Composite Right/Left Handed (CRLH) Leaky-Wave (LW) antenna that offers a high level of directivity with electronically controllable radiation patterns. Experimental results show that the DoA estimation technique succeeded in estimating the DoA using a single antenna element.

High-Rate and Low-Complexity Space-Time Block Codes for

The main design criteria for space-time block codes (STBCs) are the code rate, diversity order, coding gain, and low decoder complexity. In this letter, we propose a full-rate full-diversity STBC for 2 × 2 multiple-input multiple-output (MIMO) systems with a substantially lower maximum likelihood (ML) detection complexity than that of existing schemes. This makes the implementation of high-performance full-rate codes feasible for practical systems. Our numerical evaluation shows that the proposed code achieves significantly lower decoding complexity while maintaining a similar performance compared to that of existing rate-2 STBCs.

2 \times 2

In this paper, we present an experimental study evaluating the performance of a reconfigurable antenna element for direction-of-arrival (DOA) estimation in wireless systems. We consider a reconfigurable antenna with directive radiation pattern and an electronic control mechanism to continuously scan its beam over the space. We implement a MUSIC-type algorithm which estimates the DOA using samples collected from different configurations (scanning steps) of the antenna radiation pattern. All experiments were carried out in an anechoic chamber using an actual reconfigurable antenna for different number of scanning steps. The results confirm the successful estimation of the DOA even with two scanning steps.

MIMO Systems

In this paper, we derive analytical expressions to compute the covariance matrix of the signals impinging on a reconfigurable antenna array. We consider a receiver equipped with a linear antenna array where each antenna element can be independently configured to create a directive radiation pattern toward a selected direction. In our derivation, we assume a multimodal truncated Laplacian distribution to model the power angular spectrum (PAS) of the signals arriving at the array. Using the derived expressions, we are able to evaluate the correlation between the received signals as a function of the signal spatial distribution, the antenna array topology, and the radiation pattern characteristics of each element in the array. We also study the capacity of a reconfigurable multiple-input multiple-output (RE-MIMO) system and illustrate its relation to radiation pattern configurations and characteristics. We demonstrate how the derived expressions can be used to efficiently choose the configuration for each reconfigurable antenna element in the array that leads to an optimal compromise between low receive correlation and high receive power in order to maximize the link capacity. Simulation results are provided to validate our analytical expressions.

Experimental study of direction-of-arrival estimation using reconfigurable antennas

In this paper, we propose a high-rate space-time block code (STBC) for millimeter-wave wireless communication systems that are equipped with reconfigurable multiple-input multiple-output (MIMO) antennas. We assume that each reconfigurable antenna element has the capability of forming its beam and can independently change the characteristics of its radiation pattern1. We exploit this feature of the antenna elements to construct the proposed space-time block code where each coded symbol is sent over independent beams. As a result, the received coded symbols at different receive antennas will have different power levels, a desired property that can be used in data detection. We show that the proposed code achieves a coding rate of two and requires a low-complexity maximum likelihood (ML) detector. We carry out computer simulations that demonstrate the performance of the proposed code and shows its superiority in compared to previous rate-2 STBC counterparts. We also comment on the generalization of the proposed STBC for higher MIMO dimensions.