Abolfazl Mehbodniya

Least mean square/fourth algorithm for adaptive sparse channel estimation

Broadband signal transmission over frequency-selective fading channel often requires accurate channel state information at receiver. One of the most attracting adaptive channel estimation (ACE) methods is least mean square (LMS) algorithm. However, its performance is often degraded by random scaling of input training signal. To overcome this degradation, in this paper we consider the use of standard least mean square/fourth (LMS/F) algorithm. Since the broadband channel is often described by sparse channel model, such sparsity could be exploited as prior information. First, we propose an adaptive sparse channel estimation (ASCE) method with zero-attracting LMS/F (ZA-LMS/F) algorithm by introducing an ℓ1-norm sparse constraint into the cost function. Then, to exploit the sparsity more effectively, an improved ASCE with reweighted zero-attracting LMS/F (RZA-LMS/F) algorithm is proposed. For different channel sparsity, we propose a Monte Carlo method for a regularization parameter selection in RA-LMS/F and RZA-LMS/F to achieve better steady-state estimation performance. Simulation results show that the proposed ASCE methods achieve better estimation performance than the conventional one.

Sparse signal recovery with OMP algorithm using sensing measurement matrix

Orthogonal matching pursuit (OMP) algorithm with random measurement matrix (RMM), often selects an incorrect variable due to the induced coherent interference between the columns of RMM. In this paper, we propose a sensing measurement matrix (SMM)-OMP which mitigates the coherent interference and thus improves the successful recovery probability of signal. It is shown that the SMM-OMP selects all the significant variables of the sparse signal before selecting the incorrect ones. We present a mutual incoherent property (MIP) based theoretical analysis to verify that the proposed method has a better performance than RMM-OMP. Various simulation results confirm our proposed method efficiency.

Decentralized Energy Allocation for Wireless Networks With Renewable Energy Powered Base Stations

In this paper, a green wireless communication system in which base stations are powered by renewable energy sources is considered. This system consists of a capacity-constrained renewable power supplier (RPS) and a base station (BS) that faces a predictable random connection demand from mobile user equipments (UEs). In this model, the BS, which is powered via a combination of a renewable power source and the conventional electric grid, seeks to specify the renewable power inventory policy, i.e., the power storage level. On the other hand, the RPS must strategically choose the energy amount that is supplied to the BS. An M/M/1 make-to-stock queuing model is proposed to investigate the decentralized decisions when the two parties optimize their individual costs in a noncooperative manner. The problem is formulated as a noncooperative game whose Nash equilibrium (NE) strategies are characterized to identify the causes of inefficiency in the decentralized operation. A set of simple linear contracts are introduced to coordinate the system so as to achieve an optimal system performance. The proposed approach is then extended to a setting with one monopolistic RPS and N BSs that are privately informed of their optimal energy inventory levels. In this scenario, we show that the widely used proportional allocation mechanism is no longer socially optimal. To make the BSs truthfully report their energy demand, an incentive compatible (IC) mechanism is proposed for our model. Simulation results show that using the green energy can present significant traditional energy savings for the BS when the connection demand is not heavy. Moreover, the proposed scheme provides valuable energy cost savings by allowing the BSs to smartly use a combination of renewable and traditional energy, even when the BS has a heavy traffic of connections. Also, the results show that performance of the proposed IC mechanism will be close to the social optimal when the green energy production capacity increases.

A fuzzy extension of VIKOR for target network selection in heterogeneous wireless environments

Abstract In a highly integrated ubiquitous wireless environment, the selection of a network that can fulfill end-users’ service requests while keeping their overall satisfaction at a high level, is vital. The wrong selection can lead to undesirable conditions such as unsatisfied users, weak Quality of Service (QoS), network congestions, dropped and/or blocked calls, and wastage of valuable network resources. The selection of these networks is performed during the handoff process when a Mobile Station (MS) switches its current Point of Attachment (PoA) to a different network due to the degradation or complete loss of signal and/or deterioration of the provided QoS. Traditional schemes perform the handoff necessity estimation and trigger the network selection process based on a single metric such as Received Signal Strength (RSS). These schemes are not efficient enough, as they do not take into consideration the traffic characteristics, user preferences, network conditions and other important system metrics. This paper presents a novel multi-attribute vertical handoff algorithm for heterogeneous wireless networks which achieves seamless mobility while maximizing end-users’ satisfaction. Two modules are designed to estimated the necessity of handoff and to select the target network. These modules utilize parallel Fuzzy Logic Controllers (FLCs) with reduced rule-set in combination with a network ranking algorithm developed based on Fuzzy VIKOR (FVIKOR). Simulation results are provided and compared with a benchmark.

Coexistence Between DS-UWB and MB-OFDM: Analysis and Interference Mitigation

Ultra wideband (UWB) technology is one of the promising solutions for future short-range communication which has recently been receiving increasing attention by many researchers. So far, two standards have been proposed to the IEEE 802.15.3a task group (TG3a) as high-speed physical technologies for next-generation wireless personal area networks (WPAN). These standards are based on multiband orthogonal frequency division multiplexing (MB-OFDM) UWB or direct-sequence (DS) UWB, two different technologies that will have to coexist in the near future. In this paper, we provide a performance analysis of MB-OFDM UWB communication in the presence of binarv phase-shift keying time-hopping (BPSK-TH) UWB or BPSK-DS UWB interfering transmissions. In the bit error rate (BER) analysis, it is considered that there are multiple UWB interferers affecting the MB-OFDM signal. A Gaussian approximation is considered for the DS-UWB and TH-UWB interferers under consideration and used in the analysis of the BER performance of a MB-OFDM UWB system. Furthermore, a waveforming technique is suggested for mitigating the effect of interference and its efficiency is illustrated in terms of BER improvement. Numerical and simulation results are provided and compared for different coexistence scenarios.

Ultra wideband technologies coexistence in Nakagami-m fading channels

The wide spectrum of ultra wideband (UWB) communications makes it inevitable to consider strategies for avoiding and mitigating interference from narrowband wireless systems such as GPS, UMTS, and WLAN, or other UWB wireless technologies. In this paper, we provide a performance analysis of multiband orthogonal frequency division multiplexing (MB-OFDM) UWB in the presence of binary phase-shift keying time-hopping (BPSK-TH) UWB or BPSK-DS UWB interfering transmissions under Nakagami-m fading. In the bit-error rate (BER) analysis, several UWB interferers are considered to affect the MB-OFDM signal. A Gaussian approximation is considered for the UWB interferers and used in the analysis of the BER performance of the MB-OFDM UWB system. The Nakagami-m distribution is applied to characterise the amplitude of the fading channels for both the reference signal and the interference signals. Furthermore, a waveforming technique is considered for mitigating the effect of interference and its efficiency is illustrated in terms of BER improvement. Numerical and simulation results are provided and compared for different coexistence scenarios.

Effects of MB-OFDM System Interference on the Performance of DS-UWB

So far, two ultrawideband (UWB) standards have been proposed as high-speed physical technologies for next-generation wireless personal area networks (WPANs). These standards are based on multiband orthogonal frequency-division-multiplexing (MB-OFDM) UWB or direct-sequence UWB (DS-UWB). However, because of the withdrawal of the plan for a unique standardization process by the IEEE 802.15.3a task group (TG3a), these two technologies will coexist in the future. In this context, this correspondence provides a performance analysis of DS-UWB communication in the presence of MB-OFDM interfering transmissions, where the channel is modeled through the IEEE 802.15.3a standard model, and the network topology for the MB-OFDM interferers is based on a clustered structure as per the IEEE 802.15.3 descriptions for medium access control (MAC) and physical layer specifications for high-rate WPANs. The DS-UWB system performance is assessed in terms of bit error rate (BER). Specifically, an analytical expression for the average BER is derived, conditioned on the channel impulse response using a pulse collision model. Numerical and simulation results are provided and compared for different coexistence scenarios.

A fuzzy MADM ranking approach for vertical mobility in next generation hybrid networks

The wireless technologies in a heterogeneous wireless network usually differ in terms of, but not limited to, their offered bandwidths, operating frequencies and costs, coverage areas, and latencies. Currently, no single wireless technology claims to provide cost-effective services, which offers high bandwidths and low latencies to all mobile users in a large coverage area. This is where the need for well-organized vertical handoffs (VHOs) between heterogeneous wireless technologies become evident. This paper presents a new VHO algorithm which takes into account a complete set of system attributes to fulfill two tasks. The first task is to perform the VHO Necessity Estimation (VHONE) utilizing several parallel Fuzzy Logic Controllers (FLCs) with reduced rule sets to estimate the VHO necessity. The second task is the selection of the best network as the target for VHO, where a ranking algorithm is developed based on TOPSIS. Priority Weights for the different system attributes are calculated based on a Fuzzy Analytical Hierarchy Process (FAHP). Later, simulations based on four traffic classes (conversational, streaming, background, and interactive) in the presence of three wireless networks (WLAN, WMAN, and WWAN), are carried out using a comprehensive wireless simulation test-bed that contains all the necessary Radio Resource Management (RRM) modules.

Outage and BER Analysis for Ultrawideband-Based WPAN in Nakagami-

This paper presents a performance analysis of multiband orthogonal frequency-division multiplexing (MB-OFDM) in ultra wideband (UWB)-based personal area networks (UPANs). A UPAN consists of devices with different UWB technologies at the physical layer. Approximate expressions for the outage probability and average bit error rate (BER) are derived in closed form for the MB-OFDM target receiver, taking into account multi-user interference (MUI), as well as external interference in the form of time-hopping (TH) and direct-sequence (DS) UWB signals.

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Broadband wireless communication often requires accurate channel state information (CSI) at the receiver side due to the fact that broadband channel is described well by sparse channel model. To exploit the channel sparsity, invariable step-size zero-attracting normalized least mean square (ISS-ZA-NLMS) algorithm was applied in adaptive sparse channel estimation (ASCE). However, ISS-ZA-NLMS cannot trade off the algorithm convergence rate, estimation performance and computational cost. In this paper, we propose a variable step-size ZA-NLMS (VSS-ZA-NLMS) algorithm to improve the adaptive sparse channel estimation in terms of bit error rate (BER) and mean square error (MSE) metrics. First, we derive the proposed algorithm and explain the difference between VSS-ZA-NLMS and ISS-ZA-NLMS algorithms. Later, to verify the effectiveness of the proposed algorithm, several selected computer simulation results are shown.