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۱QoS Aware Dynamic Resource Allocation in Multiuser OFDM Systems with Priority for Different Performances
نویسنده(ها): ،
اطلاعات انتشار: چهاردهمین کنفرانس مهندسی برق ایران، سال
تعداد صفحات: ۶
In this paper, we propose an algorithm for dynamic resource allocation in OFDM (orthogonal frequency division multiplexing) or OFDMA (OFD multiple access) based networks. We consider two groups of users consisting of group 1 called constant bit–rate (CBR) users (who are delay–sensitive and datarate sensitive) and group 2 called best effort (BE) users. The proposed algorithm gives higher priority to the first group at the time of resource (transmitted power levels and subchannels) allocation to each user, to meet their CBR requirements. The performance of the proposed algorithm is evaluated through computer simulations, which show that the algorithm performs near optimum with the added superiority of meeting the bit requirements of the first group users.<\div>

۲Effects of Non–Ideal Pre–Distorter High Power Amplifiers in WCDMA Using Multi–User Detectors
نویسنده(ها): ،
اطلاعات انتشار: Iranian Journal of Electrical and Electronic Engineering، ششم،شماره۳، Sep ۲۰۱۰، سال
تعداد صفحات: ۷
Wide band code division multiple access (WCDMA) signals, transmitted by the base station high power amplifiers (HPAs), show high peak to average power ratios (PAPR), which results in nonlinear distortions. In this paper, using computer simulations effect of using a predistorted HPA on the symbol error rate (SER) of multi–user detectors in terms of output back–off (OBO) in the transmit power is analyzed. As well, using polynomials for modeling predistorters to remove nonlinear distortions of traveling wave tube amplifiers (TWTAs) and of solid state power amplifiers (SSPAs), effect of different degrees of polynomials on the SER is investigated. Simulation results show that a polynomial of degree 4 is a sufficient degree polynomial, which fits to the AM\AM characteristic of the predistorter for TWTAs. As well, for solid state power amplifiers (SSPAs) with different p values, different approximations are considered and sufficient degree polynomials are found.

۳Mathematical Analysis of Optimal Tracking Interval Management for Power Efficient Target Tracking Wireless Sensor Networks
نویسنده(ها): ، ،
اطلاعات انتشار: Iranian Journal of Electrical and Electronic Engineering، هشتم،شماره۳، Sep ۲۰۱۲، سال
تعداد صفحات: ۱۱
In this paper, we study the problem of power efficient tracking interval management for distributed target tracking wireless sensor networks (WSNs). We first analyze the performance of a distributed target tracking network with one moving object, using a quantitative mathematical analysis. We show that previously proposed algorithms are efficient only for constant average velocity objects; however, they do not ensure an optimal performance for moving objects with acceleration. Towards an optimal performance, first, we derive a mathematical equation for the estimation of the minimal achievable power consumption by an optimal adaptive tracking interval management algorithm. This can be used as a benchmark for energy efficiency of these adaptive algorithms. Second, we describe our recently proposed energy efficient blind adaptive time interval management algorithm called Adaptive Hill Climbing (AHC) in more detail and explain how it tries to get closer to the derived optimal performance. Finally, we provide a comprehensive performance evaluation for the recent similar adaptive time interval management algorithms using computer simulations. The simulation results show that using the AHC algorithm, the network has a very good performance with the added advantage of getting 9 % closer to the calculated minimal achievable power consumption compared with that of the best previously proposed energy efficient adaptive time interval management algorithm.

۴Performance Analysis of ZF Pre–Coder and Extended Joint Channel Estimation Method in Downlink CDMA with HPA
نویسنده(ها): ،
اطلاعات انتشار: Iranian Journal of Electrical and Electronic Engineering، نهم،شماره۱، Mar ۲۰۱۳، سال
تعداد صفحات: ۱۲
In the down link scenario of code division multiple access (CDMA) systems, multi user detectors (MUDs) such as linear de–correlating detector (LDDs) provide satisfactory symbol error rates (SERs) at the expense of much increased complexity, they require all active users’ spreading sequences, which is impractical from privacy point of view. To overcome this impracticality, a simple matched filter receiver is considered in this paper, which requires no knowledge of co–users’ spreading sequences. However, this simple receiver degrades the SER due to multiple access interference (MAI). To overcome this SER degradation, a zero force (ZF) pre–coder is employed in the transmitter traditionally. Moreover, a composite of CDMA signals has a large peak to average power ratio (PAPR), which causes nonlinear distortion (NLD) at the output of the base station high power amplifier (HPA). This also results in degrading the SER. We analyze the down link scenario of CDMA system to derive an equation for the SER of system with ZF–pre–coder plus HPA in the transmitter and matched filter in the receiver over two cases: additive white Gaussian noise (AWGN) and AWGN plus flat fading channels. Theoretical analysis and numerical results show that the ZF pre–coder increases the total degradation of the link significantly compared with that of the LDD. So, as a solution, rather than using ZF pre–coder, we propose a new method which is called extended joint channel estimation method, it is based on joint estimation of channel gains and LDD operator by the mobile station (MS). In that base station (BS) transmits the row k of LDD operator to the MS k. Simulation results show that the SER of this new proposed method is matched to that of LDD in AWGN channel when the number of pilot symbol repetition is equal to 8. Moreover, this method has the two added advantages of no need for providing the spreading sequences of all co–users and meeting a satisfactory total degradation. Furthermore, our analysis shows that loss in spectral efficiency due to transmitting the pilot symbols in the proposed method is negligible for the practical values of traffic variations.
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