Sharif Digital Repository

Femtocell has appeared as a solution to increase both the coverage and the capacity of cellular networks. However, interference problem between the macrocell and the femtocell must be solved before any deployment. Since femtocells are deployed by home users in random locations, decentralised interference management schemes remain worth of investigation. In this study, the author deal with the problem of aggregate interference modelling and static resource allocation in orthogonal frequency division multiple access (OFDMA)-based two-tier femtocell networks for both closed and open access femtocells. It is assumed that for macrocell users (MUs), spectrum allocation is accomplished through... 

Interference control is one of the fundamental challenges in resource allocation of femtocell networks that use orthogonal frequency-division multiple access (OFDMA). In this paper, a method is proposed that reduces the interference between femtocells. This method is implemented by the femtocells in a self organizing manner and increases frequency reuse factor. Thus, the network throughput will increase and the fairness between femtocells remains reasonable we also propose a mechanism that can be applied increase the frequency resources assigned to each femtocell. These new frequencies can be used when femtocells require more frequency resources to carry higher traffic loads. Results of... 

A novel orthogonal frequency division multiple access-based cognitive cooperative relaying scheme is proposed in which cognitive users assist primary users (PUs) by relaying their information. Both PUs and cognitive users communicate to a common base station. Based on the received feedback, cognitive users relay data of PUs. Two different schemes of relay assignment and power allocation are considered. Probability of error of PU and outage probabilities of both primary and cognitive users are investigated. Our analyses show substantial improvements in the probability of error and outage probability of PU while the outage probability of the cognitive user does not change significantly. We... 

Achieving higher transmission rate while reducing transmission power and induced interference on neighboring receivers is deemed necessary for the advancement of future generation networks and is particularly challenging, since these directions could be conflicting in nature. This letter adopts a multiobjective optimization (MOOP) approach to settle the tradeoffs between these three conflicting objectives in orthogonal frequency-division multiple access-based cognitive radio networks. Besides, unlike most of the work in the literature that studied the imperfect channel side information (CSI) of the link between the secondary transmitter and the primary receiver to evaluate ergodic capacity,... 

This paper considers a resource allocation problem in device-to-device (D2D) communications sharing the same frequency spectrum. In particular, the cellular users (CUs) utilize non-orthogonal multiple access (NOMA) while D2D users (DUs) adopt the orthogonal frequency division multiple access (OFDMA). A multi-objective optimization problem (MOOP) is formulated, which jointly maximizes the sum rate of DUs and CUs in uplink communications while taking into account the maximum transmit power budget and minimum data rate requirement for DUs and CUs. This MOOP is handled by the weighted Tchebycheff method, which converts it into a single-objective optimization (SOOP). Then, the monotonic... 

Delta-orthogonal multiple access (D-OMA) has been recently investigated as a potential technique to enhance the spectral efficiency in the sixth-generation (6G) networks. D-OMA enables partial overlapping of the adjacent sub-channels that are assigned to different clusters of users served by non-orthogonal multiple access (NOMA), at the expense of additional interference. In this paper, we analyze the performance of D-OMA in the uplink and develop a multi-objective optimization framework to maximize the uplink energy efficiency (EE) in a multi-access point (AP) network enabled by D-OMA. Specifically, we optimize the sub-channel and transmit power allocations of the users as well as the... 

Integral imaging could be considered as one of the prospective methods for recording and displaying 3D images based on its distinct features. Some of the most important challenges with this approach are the field of view and resolution limitation. In this work we investigate using frequency division multiple access (FDMA) idea for solving this problem. Simulation results show an increase of more than ten percent in the performance of the 3D reconstructed images using the proposed method  

In this paper, we study the power allocation problem in multi-cell orthogonal frequency division multiple access (OFDMA) networks. In order to improve system performance in cell-edges, users are separated into two groups with respect to their distance from base-stations (BSs): Central users and cell-edge users. Coordinated multi-point joint transmission (CoMP-JT) technology incorporated with static clustering is used for users near the cell-edges. In addition, our goal is to serve users with different target signal to interference plus noise ratio (SINR) according to their requested quality of services. Consequently, revenue of the service provider is considered as another factor and two... 

This paper introduces a novel low-complexity multiple-input multiple-output (MIMO) detector tailored for single-carrier frequency division-multiple access (SC-FDMA) systems, suitable for efficient hardware implementations. The proposed detector starts with an initial estimate of the transmitted signal based on a minimum mean square error (MMSE) detector. Subsequently, it recognizes less reliable symbols for which more candidates in the constellation are browsed to improve the initial estimate. An efficient high-throughput VLSI architecture is also introduced achieving a superior performance compared to the conventional MMSE detectors with less than 28% added complexity. The performance of... 

In this paper, the resource allocation and scheduling problem for a full-duplex (FD) orthogonal frequency-division multiple-access network is studied where an FD base station simultaneously communicates with multiple pairs of uplink (UL) and downlink (DL) half-duplex (HD) users bidirectionally. In this paper, we aim to maximize the network sum-rate through joint UL and DL user pairing, OFDM subchannel assignment, and power allocation. We formulate the problem as a non-convex optimization problem. The optimal algorithm requires an exhaustive search, which will become prohibitively complicated as the numbers of users and subchannels increase. To tackle this complex problem more efficiently, we... 

This letter is concerned with the optimal power allocation in femtocell networks using a new technique based on multiobjective optimization. In this letter, we consider a cochannel framework for the coexistence of orthogonal frequency division multiple access (OFDMA)-based macrocell and femtocell networks. We jointly maximize the total rate of OFDMA femtocell network and minimize the total transmit power of femtocell base stations while satisfying a target constraint on transmit power when either the cross femtocell interference is included or excluded. Additionally, the results show that the proposed method for power transmission contributes toward improving the energy efficiency of... 

In this paper, we study a resource allocation problem in orthogonal frequency division multiple access (OFDMA)-based Device-to-Device (D2D) communications. To this end, we propose a multi-objective optimization problem (MOOP) framework, which jointly maximizes the sum rate of D2D users (DUs) and cellular users (CUs) in uplink communications and minimizes the total transmit power. The proposed problem formulation takes into account the minimum data-rates and the maximum transmitted power budget for both DUs and CUs. We transform this MOOP into a single-objective optimization problem (SOOP) using the weighted sum method and then propose an approach to solve this SOOP via a monotonic approach... 

Deployment of low-power low-cost small access points such as femtocell access points (FAPs) constitute an attractive solution for improving the existing macrocell access points' (MAPs) capacity, reliability, and coverage. However, FAP deployment faces challenging problems such as interference management and the lack of flexible frameworks for deploying the FAPs by the service providers (SPs). In this paper, we propose a novel solution that jointly associates the user equipment (UE) to the APs, and allocates the FAPs to the SPs such that the the total satisfaction of the UEs in an uplink OFDMA network is maximized. We model the competitive behaviors among the UEs, FAPs, and SPs as a dynamic... 

Femtocell has appeared as a solution to increase both coverage and capacity of cellular networks. However, interference problem between the macrocell and the femtocell must be solved before any deployment. In this paper, we deal with the problem of joint subband, rate, and power allocation in OFDMA based two-tier femtocell networks. It is assumed that for macrocell users, spectrum allocation is accomplished through Fractional Frequency Reuse (FFR). Our objective is to maximize the femtocell user's throughput while maintaining as little as possible reduction in the macrocell users' performance. Our proposed algorithm is decentralized, and needs to be done only when femtocell access point is... 

The trade-off between the aliasing in integral imaging (II) and the level of interference among adjacent elemental images is mathematically studied in this paper. It is then shown that the multiple-access techniques successfully used in communication systems, e.g. frequency-division multiple access (FDMA), canbeinvoked to ease the trade-off. Implementation of spatial FDMA technique in three-dimensional II is discussed together with its nonidealities and limitations. Elemental images of three toy cars and their corresponding three-dimensional image are finally provided to demonstrate the superiority of the here-proposed spatial FDMA technique  

In this paper, we study the resource allocation and scheduling problem for a downlink non- orthogonal multiple access (NOMA) network where the base station (BS) allocates the spectrum resources and power to the set of users. We aim to optimize the sub-channel assignment and power allocation to achieve a balance between the number of scheduled users and total sum-rate maximization. To solve the above problem, we propose a many-to-many two-sided user-subchannel matching algorithm in which the set of users and sub-channels are considered as two sets of players pursuing their own interests. The algorithm converges to a pair-wise stable matching after a limited number of iterations. Simulation... 

In this study, the authors evaluate the performance of asynchronous optical multi-carrier code division multiple access (MC-CDMA) for intensity modulated/direct detection systems to be used in next-generation optical access networks. The proposed system employs Gold sequence in frequency-domain to provide asynchronous resource sharing. In long-reach passive optical networks, fibre impairments degradation to the performance of ordinary optical CDMA can be avoided by frequency-domain digital compensation methods in the proposed MC-CDMA. In comparison with orthogonal frequency division multiple access, peak-to-average power ratio in the proposed MC-CDMA is reduced and asynchronous resource... 

A novel low-complexity detection scheme is proposed for the multiple-input multiple-output (MIMO) single-carrier frequency division-multiple access (SC-FDMA) systems, which is suitable for ASIC implementations. The proposed detection scheme makes an initial estimate of the transmitted signal based on a minimum mean square error (MMSE) frequency domain equalizer (FDE) detector and finds symbols with higher error probability among them and browse more candidates for them in the constellation to improve their initial estimate. Based on this approach, architecture is introduced that achieves superior bit error rate (BER) performance compared to the conventional MMSE FDE. The performance of the... 

In this paper, we propose a distributed rate and power allocation algorithm for real time traffic by using second order statistics of the channel. Our method minimizes the average delay of transmission over the fading channel. We assume that each sub carrier relies on its own buffer, and a constant arrival rate from higher layer application arrives at input buffers of each sub-carrier. This constant rate is optimally distributed through individual sub-rates transmitted over each sub-channel. Optimum power coefficients are also derived to minimize the average delay of transmission. In addition, collision and buffer overflows are taken into account while achieving acceptable throughputs  

In this paper, we use delay-amplify-and-forward relays in the uplink direction of a coordinated multi-point network based on orthogonal frequency division multiplexing. The key novelty is that we assume delay from users to different base stations (BSs), in general, may exceed cyclic prefix (CP) length as might be the case in large cells and cannot be completely compensated by traditional timing advance strategies. Consequently, interchannel interference and intersymbol interference may arise under such assumptions. We first optimize the adjustable delays added at users, relays and BS nodes in order to reduce the effective delay spread at the receive sites, then we optimize relays' weights...