Amin Azari

Lifetime-Aware Scheduling and Power Control for M2M Communications in LTE Networks

In this paper the scheduling and transmit power control are investigated to minimize the energy consumption for battery-driven devices deployed in LTE networks. To enable efficient scheduling for a massive number of machine-type subscribers, a novel distributed scheme is proposed to let machine nodes form local clusters and communicate with the base-station through the cluster-heads. Then, uplink scheduling and power control in LTE networks are introduced and lifetime-aware solutions are investigated to be used for the communication between cluster-heads and the base-station. Beside the exact solutions, low-complexity suboptimal solutions are presented in this work which can achieve near optimal performance with much lower computational complexity. The performance evaluation shows that the network lifetime is significantly extended using the proposed protocols.

Performance analysis of ad-hoc routing in heterogeneous clustered multi-hop wireless networks

This paper analyzes the performance of clustered decode-and-forward multi-hop relaying (CDFMR) wireless Rayleigh fading networks, and sheds light on their design principles for energy and spectral efficiency. The focus is on a general performance analysis (over all SNR range) of heterogeneous wireless networks with possibly different numbers of relays in clusters of various separations. For clustered multi-hop relaying systems, hop-by-hop routing is known as an efficient decentralized routing algorithm which selects the best relay node in each hop using local channel state information. In this article, we combine hop-by-hop routing and cooperative diversity in CDFMR systems, and we derive (i) a closed-form expression for the probability distribution of the end-to-end SNR at the destination node; (ii) the system symbol error rate (SER) performance for a wide class of modulation schemes; and (iii) exact analytical expressions for the system ergodic capacity, the outage probability and the achievable probability of the SNR (power) gain. We also provide simple analytical asymptotic expressions for SER and the outage probability in high SNR regime. Numerical results are provided to validate the correctness of the presented analyses.

A New Method for Timing Synchronization in OFDM Systems Based on Polyphase Sequences

This paper proposes a synchronization method with a preamble for IEEE 802.16 and other systems that use Orthogonal Frequency Division Multiplexing (OFDM). The preamble for synchronization is composed of two identical periods, which are polyphase codes, and have an autocorrelation function with one main peak and very small sub peaks. Using this signal repetition and autocorrelation, the correlation for symbol timing detection is calculated with a new metric. The proposed metric uses a filtering structure to find the accurate start point. Proposed method drastically improves the performance of timing synchronization, even with a very low SNR, in both AWGN and multipath fading Rayleigh channels.

Novel frame synchronization for WiMAX OFDM systems

Frame synchronization is a critical factor for effective operation of Orthogonal Frequency Division Multiplexing (OFDM) schemes. This paper studies the frame synchronization of OFDM based wireless systems and proposes a new method for IEEE 802.16 (WiMAX) to improve its performance. The preamble, which is used in this method, is consists of two identical halves, and our method uses the correlation between these two parts in a new efficient form. Our metric calculates the start point within two levels. It finds some possible points as start point in the first level and removes the irrelevant candidates at the second level. The performance of proposed metric and existing ones is compared in terms of mean square error (MSE) and probability of correct detection in AWGN and multipath fading channels. Simulation results show that the proposed method has better performances than famous methods, which were proposed by Schmidl, Minn, Park, Kim, Meng, and in both AWGN and multipath fading Rayleigh channels. Also, compared to new methods with more accurate performance, proposed method has egual performance with less complexity.

Power allocation in multi-hop OFDM transmission systems with amplify-and-forward relaying

In this paper, a unified approach for power allocation (PA) in multi-hop orthogonal frequency division multiplexing (OFDM) amplify-and-forward (AF) relaying systems is presented. In the proposed approach, we consider short and long term individual and total power constraints at the source and relays, and devise low complexity PA algorithms when wireless links are subject to channel path-loss and small-scale Rayleigh fading. To manage the complexity, in the proposed formulations, we adopt a two-stage iterative approach consisting of a power distribution phase among distinct subcarriers, and a power allocation phase among different relays. In particular, aiming at improving the instantaneous rate of multi-hop transmission systems with AF relaying, we develop (i) a near-optimal iterative PA algorithm based on the exact analysis of the received SNR at the destination; (ii) a low complexity suboptimal iterative PA algorithm based on an approximate expression of the received SNR at high-SNR regime; and (iii) a low complexity non-iterative PA scheme with limited performance loss. Simulation results show the superior performance of the proposed power allocation algorithms.

RACH Dimensioning for Reliable MTC over Cellular Networks

Successful implementation of massive machine-type communications (MTC) service over cellular networks is an important enabler of Internet of things. As the existing cellular infrastructure has been designed and optimized for moderate traffic, the introduction of MTC in cellular networks results in several key challenges, among them, temporal starvation of initial access resources is of paramount importance. Here, we propose a new traffic model for cellular networks serving machine-type subscribers. This model is subsequently used to derive closed-form expressions for the access rate performance of the system. This closed-form expression are subsequently used for RACH resources planning in the time and frequency domains. Given a target access rate requirement, numerical analysis indicates how and when the required RACH resources in the code/frequency domain, i.e. number of preambles, can be traded with the occurrence frequency of RACH slots in the time domain.