Aliazam Abbasfar

Design and VLSI implementation for a WCDMA multipath searcher

The third generation (3G) of cellular communications standards is based on wideband CDMA. The wideband signal experiences frequency selective fading due to multipath propagation. To mitigate this effect, a RAKE receiver is typically used to coherently combine the signal energy received on different multipaths. An effective multipath searcher is, therefore, required to identify the delayed versions of the transmitted signal with low probability of false alarm and misdetection. This paper presents an efficient and novel WCDMA multipath searcher design and VLSI architecture that provides a good compromise between complexity, performance, and power consumption. Novel multipath searcher algorithms such as time domain interleaving and peak detection are also presented. The proposed searcher was implemented in 0.18 /spl mu/m CMOS technology and requires only 150 k gates for a total area of 1.5 mm/sup 2/ consuming 6.6 mw at 100 MHz. The functionality and performance of the searcher was verified under realistic conditions using a channel emulator.

Peak Power Reduction of OFDM Systems Through Tone Injection via Parametric Minimum Cross-Entropy Method

It is well known that the major drawback of orthogonal frequency-division multiplexing (OFDM) is its high peak-to-mean envelope power ratio (PMEPR). One of the promising schemes proposed for alleviating the high PMEPR of OFDM signals is tone injection (TI). In this paper, we propose a novel low-complexity algorithm for PMEPR reduction using TI. This algorithm first formulates the TI scheme as a combinatorial optimization problem and then finds a near-optimal solution to this problem via parametric minimum cross-entropy (PMCE) method. We also demonstrate that by effectively exploiting TI schemes in conjunction with cross constellations, it is possible to reduce the peak power of the system by more than 2 dB compared with sign selection schemes over conventional quadrature-amplitude modulation (QAM) constellations. Simulation results show that our algorithm outperforms similar existing algorithms, including the cross-entropy (CE) TI algorithm, the greedy sign selection algorithm, and the derandomization sign selection algorithm, in terms of PMEPR. We also present a threshold-based PMCE algorithm for TI that results in significant complexity reduction. Numerical results show that to achieve a prescribed PMEPR threshold, this threshold-based PMCE algorithm requires less computational complexity than the CE TI algorithm.

Optimal power and rate allocation in the degraded Gaussian relay channel with energy harvesting nodes

Energy Harvesting (EH) is a novel technique to prolong the lifetime of the wireless networks such as wireless sensor networks or Ad-Hoc networks, by providing an unlimited source of energy for their nodes. In this sense, it has emerged as a promising technique for Green Communications, recently. On the other hand, cooperative communication with the help of relay nodes improves the performance of wireless communication networks by increasing the system throughput or the reliability as well as the range and efficient energy utilization. In order to investigate the cooperation in EH nodes, in this paper, we consider the problem of optimal power and rate allocation in the degraded full-duplex Gaussian relay channel in which source and relay can harvest energy from their environments. We consider the general stochastic energy arrivals at the source and the relay with known EH times and amounts at the transmitters before the start of transmission. This problem has a min-max optimization form that along with the constraints is not easy to solve. We propose a method based on a mathematical theorem proposed by Terkelsen [1] to transform it to a solvable convex optimization form. Also, we consider some special cases for the harvesting profile of the source and the relay nodes and find their solutions efficiently.

Algorithm and FPGA implementation of interpolation-based soft output mmse mimo detector for 3GPP LTE

The number of orthogonal frequency division multiplexing (OFDM) sub-carriers in modern wireless communication systems such as Third Generation Partnership Project (3GPP) long term evolution (LTE) can be as high as 2048. Channel matrix of data sub-carriers in conventional multiple-input-multiple-output (MIMO) receivers is derived by interpolating channel matrix of pilot sub-carriers and MIMO detection is performed on each interpolated channel matrix. Symbol detection on sub-carrier by sub-carrier basis demands a very high computational power. This study presents the first very-large scale integration implementation of a novel 4 × 4 interpolation-based soft output minimum-mean-squared error (MMSE) MIMO detector which combines channel estimation and MIMO detection. The detector computes MMSE matrix on pilot sub-carriers using proposed division-free matrix inversion algorithm and obtains MMSE matrix of data sub-carriers by interpolation, reducing computational complexity by more than 66%. The throughput of the implemented detector on Virtex-7 field programmable gate array (FPGA) exceeds 1 Gbps with 2.1 μs latency.

Efficient two-dimensional compressive sensing in MIMO radar

Compressive sensing (CS) has been a way to lower sampling rate leading to data reduction for processing in multiple-input multiple-output (MIMO) radar systems. In this paper, we further reduce the computational complexity of a pulse-Doppler collocated MIMO radar by introducing a two-dimensional (2D) compressive sensing. To do so, we first introduce a new 2D formulation for the compressed received signals and then we propose a new measurement matrix design for our 2D compressive sensing model that is based on minimizing the coherence of sensing matrix using gradient descent algorithm. The simulation results show that our proposed 2D measurement matrix design using gradient decent algorithm (2D-MMDGD) has much lower computational complexity compared to one-dimensional (1D) methods while having better performance in comparison with conventional methods such as Gaussian random measurement matrix.

A watermarking method for digital speech self-recovery

Authentication and tampering detection of the digital signals is one of the main applications of the digital watermarking. Recently, watermarking algorithms for digital images are developed to not only detect the image tampering, but also to recover the lost content to some extent. In this paper, a new watermarking scheme is introduced to generate digital self-embedding speech signals enjoying the self-recovery feature. For this purpose, the compressed version of the speech signal generated by a speech codec and protected against the tampering by the proper channel coding is embedded into the original speech signal. Experimental results show that the self-embedding speech signal is recoverable with proper speech quality for high tampering rates, without significant loss in the quality of the original speech signal.

Coding techniques to mitigate out-of-band radiation in high data rate OFDM-based cognitive radios

User coexistence in physical layer of OFDM-based cognitive radio is provided by employing out-of-band (OOB) power suppression methods at the cost of large computational complexity which is prohibitive in physical layers with mega bits per second data rate. This paper proposes three new coding techniques to mitigate the OOB radiation of an OFDM system with high order modulation schemes, without introducing much complexity or transmission of side information, at the cost of small system throughput degradation compared to other existing methods. In these methods, a few subcarriers at the edge of the signal spectrum that have main contribution in OOB radiation are coded such that either modulate with minimum signal magnitude of the constellation or cancel out the OOB radiation of their adjacent subcarrier. With these methods, up to 11.5dB OOB suppression is achieved at the maximum costs of 40% system throughput reduction, and 1.2dB peak to average power ratio (PAPR) augmentation, when coding is applied to the 40% of total subcarriers at each edge of the signal spectrum.

Qos-aware discrete bit loading for OFDMA networks

Performance optimization of practical communication networks should be performed by considering some practical constraints such as limitation of maximum transmitted power, discrete bit allocation to carriers and users, and quality of service (QoS) requirements for different users. In this paper, we provide the optimum resource allocation solution for an OFDMA downlink in which subcarriers are loaded with discrete number of bits. Using minimum data rate with a certain BER as the criterion for the QoS, the optimization makes sure that the QoS of all users are satisfied. We analyze the complexity of this solution and propose a sub-optimum solution with much less complexity. These solutions are compared with existing methods using simulation results.

Power allocation in the energy harvesting full‐duplex Gaussian relay channels

In this paper, we propose a general model to study the full-duplex non-coherent decode-and-forward Gaussian relay channel with energy harvesting (EH) nodes, called NC-EH-

Performance analysis for energy harvesting communication protocols with fixed rate transmission

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