Resource allocation with interference coordination for relay-aided cellular orthogonal frequency division multiple access systems

In this study, the authors propose a fine granularity resource allocation algorithm for enhancing overall quality of users’ received video in the orthogonal frequency division multiple access system. Subcarrier's contribution for video transmission is used as the guideline of resource allocation in this algorithm. The subcarrier with the largest contribution is given priority to be allocated on the basis of two‐level paths search in the whole resource allocation tree. Moreover, the authors design the full search implementation scheme and the simplified implementation scheme for the resource allocation algorithm, respectively. The full search implementation scheme can obtain superior performance gain with high complexity. For reducing the complexity, the authors further propose a simplified implementation scheme subject to some minor quality degradation. At last, the authors compare the fine granularity resource allocation algorithm with other existing resource allocation algorithms for video transmission. In the simulation results, it is shown that the proposed algorithm acquires much more superior performance in overall quality of users’ received video.

In orthogonal frequency division multiple access (OFDMA) systems, efficient resource allocation is very important to improve the performance of the OFDMA system. The general principle of resource allocation in an OFDMA system is to assign each subcarrier to the user with the best channel condition for that subcarrier. However, in delay tolerant traffic, current work did not consider that packets on retransmissions may have different allocation criteria from those on their first transmissions. In this paper, the resource allocation scheme is investigated by considering different criterions to packets on first transmissions and on retransmissions. Under a bit error rate (BER) constraint, the objective is to maximize the throughput of packets on first transmissions, meanwhile decreasing the longest packet delay caused by retransmitted packets and guaranteeing all packets on retransmissions to be sent out. A low-complexity suboptimal algorithm that separates allocation for packets on retransmissions and on first transmissions is proposed. Adaptive modulation scheme is adopted to guarantee the BER constraint, except the modulation for each retransmitted packet remains the same. In order to improve retransmission liability, the retransmitted packets are combined with its failed packets in previous transmission.

Similar to the orthogonal frequency division multiple access (OFDMA) system, the single-carrier frequency division multiple access (SC-FDMA) system also suffers from frequency mismatches between the transmitter and the receiver. As a result, in this system, the carrier frequency offsets (CFOs) disrupt the orthogonality between subcarriers and give rise to inter-carrier interference (ICI) and multiple access interference (MAI) among users. The authors present a new minimum mean square error (MMSE) equaliser, which jointly performs equalisation and carrier frequency offsets (CFOs) compensation. The mathematical expression of this equaliser has been derived taking into account the MAI and the channel noise. A low complexity implementation of the proposed equalisation scheme using a banded matrix approximation is presented here. From the obtained simulation results, the proposed equalisation scheme is able to enhance the performance of the SC-FDMA system, even in the presence of estimation errors.

Resource allocation for a downlink orthogonal frequency division multiple access (OFDMA) system ensures that capacity and throughput are maximized. In the literature, either channel coding is not considered or only a fixed code rate is specified. To overcome this problem, an optimized cross-layer resource allocation strategy that distributes the user, bit and power optimally has been proposed for adaptive modulation and coding (AMC) based single-cell downlink OFDMA systems. The proposed strategy, which is referred to as optimized user, bit and power allocation (OUBPA), considers throughput as a new cost function in terms of spectral efficiency and bit-error rate (BER) to allocate the available resources. An optimized approach is presented for solving the throughput maximization problem and simulation results demonstrating that the throughput performance of the OFDMA-AMC system using OUBPA strategy outperforms conventional techniques.

In this paper, subcarrier allocation schemes for cellular orthogonal frequency division multiple access (OFDMA) systems with adaptive modulation and coding (AMC) is considered. An LP formulation with the constraints of quality-of-service (QoS) and limited bandwidth was made to achieve optimal system throughput. We propose an optimal subcarrier allocation scheme which allows cell coordination to assign subcarrier reuse factor and modulation scheme for each subcarrier. Also, to reduce computational complexity, a simplified cell coordination scheme is suggested. The capacity increase can be achieved by properly selecting modulation scheme and reuse factor of the subcarrier, which is validated by simulations.

Traditional handover algorithms are based on received signal strength indicator (RSSI) and traffic load intensity in orthogonal frequency division multiple access (OFDMA) systems, in order to guarantee all UEs' Quality of Service (QoS) and handover success ratio, a transceiver is activated even if there is only one low date rate activated user in its coverage area. In this paper, we propose an energy efficient handover algorithm combined coordinated multiple-points (CoMP) with OFDMA in a cellular systems, energy efficiency is introduced into the handover algorithm as an important parameter. The idea of the design is to enable adjacent cells to shutdown partial transceivers in some timeslots in low traffic conditions by concentrating the activated edge UEs to less cells. All activated UEs are classified into edge users and center users according to their distance to base stations, the analysis indicates that there exist an optimal edge distance corresponding to the maximum energy efficiency under different load for the proposed algorithm. Furthermore, a practical and low-complexity scheme that only considers the edge users is put forward. The edge users are identified by the reference signal received power (RSRP). Simulation results show that it can obtain up to 60% energy reduction at low traffic scenario.

In this paper, we present a study on the spectrum sharing matter in orthogonal frequency division multiple access (OFDMA) systems under heterogeneous constraints leading to a joint time-frequency resource allocation model. To take advantage of the flexibility of the OFDMA-based resource allocation scheme, we analytically study the spectrum sharing matter by deriving an optimization problem that takes into account the heterogeneous time and frequency constraints. The solution of the formulated problem presents an optimal time-frequency allocation scheme based on optimal derivation of a frequency allocation function as well as a time sharing function. This solution can be seen as a cross-layer PHY-MAC solution as it combines frequency aspects (PHY level) that deal with the channel quality, and time aspects (MAC level) that ensure the quality of service (QoS) support. Simulation results demonstrate the efficiency of the proposed scheme in terms of QoS support and channel use optimization.

We develop an auction-based algorithm for joint allocation of resources, namely power profiles at the source and relay nodes and subcarrier assignment profile for multiple users amplify and forward (AF) orthogonal frequency division multiple access (OFDMA) system. The proposed algorithm is based on sequential single item auction, where each user submits a bid based on either the marginal increase or the relative marginal increase of the data rate after using that subcarrier with optimal power profiles at the source and relay nodes. The first bidding strategy maximizes the sum data rate, whereas the second bidding strategy maximizes the fairness index. In both cases, the subcarrier is assigned to the user who submits the highest bid. The algorithm proceeds in a sequential fashion until all subcarriers are assigned. The system throughput and fairness indices are used to evaluate the performance of the proposed algorithm. Numerical results are used to show the merits of the proposed algorithm.

A new concept-traffic diversity is proposed for resource allocation of orthogonal frequency division multiple access system. With traffic diversity, the transmitter designates different bit error rate (BER) level for each kind of traffic. The transmission data rate corresponds to the BER level. At the receiver, this separated traffic, which belong to the same user, will be aggregated. Simulation results show that traffic diversity can increase the throughput by 27%.

We consider the weighted sum-rate maximization problem in downlink Orthogonal Frequency Division Multiple Access (OFDMA) systems. Motivated by the increasing popularity of OFDMA in future wireless technologies, a low complexity suboptimal resource allocation algorithm is obtained for joint optimization of multiuser subcarrier assignment and power allocation. The algorithm is based on an approximated primal decomposition-based method, which is inspired from exact primal decomposition techniques. The original nonconvex optimization problem is divided into two subproblems which can be solved independently. Numerical results are provided to compare the performance of the proposed algorithm to Lagrange relaxation based suboptimal methods as well as to optimal exhaustive search-based method. Despite its reduced computational complexity, the proposed algorithm provides close-to-optimal performance

Orthogonal Frequency-Division Multiple Access (OFDMA) systems have attracted considerable attention through technologies such as 3GPP Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX). OFDMA is a flexible multiple-access technique that can accommodate many users with widely varying applications, data rates, and Quality of Service (QoS) requirements. OFDMA has the advantages of handling lower data rates and bursty traffic at a reduced power compared to single-user OFDM or its Time Division Multiple Access (TDMA) or Carrier Sense Multiple Access (CSMA) counterparts. In our work, we propose a Particle Swarm Optimization based resource allocation and scheduling scheme (PSORAS) with improved quality of service for OFDMA Systems. Simulation results indicate a clear reduction in delay compared to the Frequency Division Multiple Access (FDMA) scheme for resource allocation, at almost the same throughput and fairness. This makes our scheme absolutely suitable for handling real time traffic such real time video-on demand.

In this work a wireless power transfer (WPT) scheme for orthogonal frequency division multiple access (OFDMA) systems is proposed, with the objective of prolonging the battery life of the receiver. A novel receiver that capitalizes on the presence of a redundant portion of the OFDMA signal, i.e, the cyclic prefix (CP), to harvest energy that can be used to reduce the power consumption of the OFDMA digital signal processing at the receiver, is described. The concept of self-sustainability, a condition achieved when the amount of harvested energy from the received signal is sufficient to perform the digital signal processing at the receiver, is introduced. A parametric model to study the feasibility of several levels of self-sustainability, is provided and an analytical condition to ensure their achievability is derived. Numerical findings show that, under certain reasonable conditions, the full self-sustainability can be achieved for CP sizes compliant with the existing telecommunication standards.

Cellular radio systems are often limited due to the presence of cochannel interference. Basically, radio systems may be operated by utilizing asynchronous or synchronous downlink transmission from all base stations in the system, where synchronization between terminals and their serving base station is mandatory in both concepts. We provide a comparison between the theoretical achievable spectral efficiency in an orthogonal frequency division multiple access systems using different linear equalizers and their resulting performance taking estimation errors into account. It is shown, that the choice of the appropriate receiver depends on the degree of synchronization in the system. We demonstrate that a 3G Long Term Evolution radio system may achieve higher spectral efficiency thanks to interference suppression if fully synchronized data transmission from all base stations is introduced.

In the conventional subcarrier and power allocation schemes in multi-input multi-output and orthogonal frequency division multiple access (MIMO-OFDMA) systems, only equal fairness among users has been considered, and no scheme for proportional data rate fairness is considered. In this paper, subcarrier and power allocation criterion is proposed to maximize the total throughput under the constraints of total power and proportional data rate fairness among users. In the proposed scheme, subchannel allocation is firstly performed by using singular value decomposition (SVD) of channel matrix under the constraint of users' data throughput requirements, and then adaptive bit and power loading is applied. Simulation results show that total throughput is increased as well as each throughput is proportionally distributed among users in MIMO-OFDMA systems.

Multiple input multiple output (MIMO) - Orthogonal Frequency Division Multiple Access (OFDMA) systems have great potential for providing high spectral efficiency due to its integrated space-frequency and multi-user diversity. In this work a dynamic resource allocation scheme has been devised for MIMO-OFDMA systems in a downlink scenario. The scheme optimizes the power distribution, guarantees each user its desired quality of service (QoS), and ensures strict level of fairness to users. The available channel state information at the base station (BS) is utilized in order to help these practical schemes improve system performance, as well as satisfy various QoS constraints. The simulation results obtained show that the proposed scheme satisfies proportional data rate constraints in strict sense and achieves high system capacities.