Abdorreza Heidari

Adaptive modelling and long-range prediction of mobile fading channels

A key element for many fading-compensation techniques is a (long-range) prediction tool for the fading channel. A linear approach, usually used to model the time evolution of the fading process, does not perform well for long-range prediction applications. An adaptive fading channel prediction algorithm using a sum-sinusoidal-based state-space approach is proposed. This algorithm utilises an improved adaptive Kalman estimator, comprising an acquisition mode and a tracking algorithm. Furthermore, for the sake of a lower computational complexity, an enhanced linear predictor for channel fading is proposed, including a multi-step AR predictor and the respective tracking algorithm. Comparing the two methods in our simulations show that the proposed Kalman-based algorithm can significantly outperform the linear method, for both stationary and non-stationary fading processes, and especially for long-range predictions. The performance and the self-recovering structure, as well as the reasonable computational complexity, makes the algorithm appealing for practical applications.

A 2D camera design with a single-pixel detector

A single-pixel camera for THz imaging has been proposed in [1]. In this article, we propose a new design for a single-detector THz imaging system based on Compressive Sampling (CS), which does not need raster scanning of the object in front of the THz beam. We exploit a time-efficient and cost-effective design to acquire the CS measurements. As a result, the image acquisition time in the proposed imaging system is only limited to the speed of the THz detector. The proposed approach is applicable to other types of imaging as well.

Adaptive Long-Range Prediction of Mobile Fading

Long-range prediction of fading in mobile systems is the key element for many fading-compensation techniques. A linear approach, which is usually used to model the time evolution of the fading process, does not perform well for long-range prediction. In this article, we propose an adaptive channel prediction algorithm by using a novel state-space model for the fading process. Our simulations show that this algorithm significantly outperforms the conventional linear method, for both stationary and non-stationary fading processes, especially for long-range predictions

Signal Recovery in Pulsed Terahertz Integrated Circuits

In this article, a time-domain calibration procedure is proposed for pulsed Terahertz Integrated Circuits (TIC) used in on-chip applications, where the conventional calibration methods are not applicable. The proposed post-detection method removes the unwanted linear distortions, such as interfering echoes and frequency dispersion, by using only one single-port measurement. The method employs a wave-transfer model for analysis of the TIC, and the model parameters are obtained by a proposed blind estimation algorithm. A complete implementation of the method is demonstrated for a fabricated TIC, when used in an on-chip sensing application. The features of interest in the measured signal, such as absorption lines, can be masked or weakened by the distortion of the THz signal happening in a TIC. The proposed signal recovery approach improves the detection of those otherwise hidden features, and can significantly enhance the performance of existing TICs. To show the effectiveness of the proposed de-embedding method, numerical results are presented for simulated and measured signals. The method presented in this article is enabling for accurate TIC applications, and can be utilized to optimally design novel TIC structures for specific purposes.

Closed-Loop Transmit Diversity with Imperfect Feedback

In the closed-loop transmit diversity systems, feedback delay and feedback error, as well as the sub-optimum reconstruction of the quantized feedback data, are the usual sources of deficiency. We address the efficient reconstruction of the beamforming weights in the presence of the feedback imperfections, by exploiting the residual redundancies in the feedback stream. We propose two approaches to improve the performance. One is based on using a channel predictor at the receiver to compensate for the delay. Another approach deals with the feedback imperfections in a unified reconstruction algorithm using JSCC techniques. Furthermore, we introduce the concept of Blind Antenna Verification (BAV). The closed-loop Mode 1 of the 3GPP standard is used as a benchmark, and the performance is examined within a Wideband-CDMA simulation framework. It is demonstrated that the proposed algorithms outperform the standard at all mobile speeds, and are suitable for the implementation in practice.

Enhancing Closed-Loop Wireless Systems Through Efficient Feedback Reconstruction

The closed-loop transmit diversity technique is used to improve the performance of the downlink channel in multiple-input multiple-output (MIMO) communication systems. The wideband code-division multiple-access standard endorsed by the Third Generation Partnership Project (3GPP) adopts a downlink closed-loop scheme based on partial channel state information (CSI) known as mode 1. The information is fed back from the mobile unit to the base station through a low-rate uncoded feedback bit stream. In this paper, several reconstruction techniques are introduced to improve the performance of mode 1 of 3GPP in the presence of feedback error by taking advantage of the redundancy available in the bit stream of the CSI. We propose a number of algorithms for the reconstruction of beamforming weights at the base station with the constraint of a constant transmit power. The performance is examined within a simulated 3GPP framework. It is demonstrated that the proposed algorithms have substantial gain over the conventional method for low, moderate, and high mobile speeds. It is also shown that the proposed algorithms can substitute the antenna weight verification process done at the mobile unit in many cases. The proposed approach is applicable to other feedback schemes as well.

Improved reconstruction of channel state information in 3GPP

The closed-loop transmit diversity technique is used to increase the capacity of downlink channel in multiple-input-multiple-output (MIMO) communications systems. The WCDMA standard endorsed by 3GPP adopts two modes of downlink closed-loop schemes based on partial channel information that is fed back from mobile to base station through a low-rate uncoded feedback bit stream. In this article, soft reconstruction techniques are utilized to improve the performance of Mode 1 of 3GPP, by taking advantage of the redundancy available in the channel state information. We propose several algorithms for efficient reconstruction of beamforming weights, which could be used instead of Antenna Weight Verification algorithms in the closed-loop system. The performance is examined within a simulated 3GPP framework in the presence of feedback error at different mobile speeds. It is demonstrated that the proposed algorithms have substantial gain over the conventional approach, for low to high mobile speeds.

Improved Closed-Loop Communication in the Presence of Feedback Delay and Error

The closed-loop transmit diversity technique is used to improve the performance of the downlink channel in MIMO communication systems. The WCDMA standard endorsed by 3GPP adopts two modes of downlink closed-loop schemes based on partial channel state information. The information is fed back from the mobile unit to the base station through a low-rate uncoded feedback bit stream. Previously it was addressed the efficient reconstruction of the beamforming weight in the presence of feedback error, with the constraint of a constant transmit power. In this article, the issue of feedback delay is also considered. Using joint source-channel coding techniques, a reconstruction algorithm is introduced to improve the performance of mode 1 of 3GPP in the presence of feedback error and delay, by taking advantage of the redundancy available in the bitstream of channel state information. We also introduce the novel concept of blind antenna verification. It can substitute the conventional antenna weight verification process without the need to any training data. The performance is examined within a simulated 3GPP framework. It is demonstrated that the proposed algorithms have substantial gain over the conventional method for low, moderate and high mobile speeds. The proposed approaches are applicable to other feedback schemes as well.

Echo cancellation in pulsed terahertz integrated circuits

A signal processing algorithm based on the propagation and reflection mechanisms is proposed for echo cancellation in pulsed terahertz integrated circuits.