Auction framework for resource allocation in AF-OFDMA systems

Deployment of relay nodes (RNs) in cellular orthogonal frequency division multiple access (OFDMA) systems provides an effective solution to increase high data rate coverage and improve cell throughput. However, a challenging issue is that additional interferences caused by RNs may substantially compromise the performance gain if no measure is taken. In this study, the authors address the problem of interference coordination in relay-aided cellular OFDMA systems, aiming at exploiting the benefits of RNs while minimising the negative effects of interferences introduced. The authors first analyse the possible interference scenarios in multi-cell systems. Based on the insights into their analysis, the authors propose resource allocation with interference coordination (RAIC) scheme for cellular OFDMA systems. RAIC selectively perform one of three resource allocation algorithms according to the offered traffic load in the system, to mitigate interferences and thus enhance system throughput. The authors conduct intensive simulation experiments based on the model with realistic broadband channel propagation conditions. Numerical results demonstrate that their proposed RAIC can effectively improve system throughput compared with the resource allocation schemes without appropriate interference coordination.

A low complexity algorithm is proposed for joint allocation of power profiles at the source and relay nodes and subcarrier assignment for single user amplify and forward (AF) cooperative communication using orthogonal frequency division multiplexing (OFDM) system. The relay uses AF cooperative relaying to transmit messages on a set of available subcarriers with diversity. The remaining subcarriers are used for direct transmission without diversity. The objective is to allocate the resources to maximize the sum rate subject to individual power constraint on each node. We formulate such a problem as subcarrier based resource allocation that seeks joint optimization of subcarrier assignment and power profiles at the source and relay nodes. The algorithm is based on an ordering of the channel gain's ratio and splitting them into two partitions, then searching for the partition that maximizes the sum rate. Simulation results demonstrate the merit of the proposed algorithm.

Informing users about new resource assignments has to be broadcast, thus generating a substantial amount of the mapping overhead that influences the system throughput. In particular, the performance of voice-over-Internet protocol (VoIP) services is seriously affected by the mapping overhead because the VoIP packet size is small. In order to reduce the mapping overhead, a semi-fixed mapping scheme based on the periodicity of VoIP traffic was introduced. However, up to now, the detailed operation and the analysis of the semi-fixed mapping scheme have not been studied. This paper develops analytical and simulation models and evaluates the performance of a semi-fixed mapping scheme for VoIP services in wireless orthogonal frequency division multiple access systems.

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.

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.

Orthogonal frequency division multiple access (OFDMA) systems exploit multiuser diversity and frequency-selectivity to achieve high spectral efficiencies. However, they require considerable feedback for scheduling and rate adaptation, and are sensitive to feedback delays. We develop a comprehensive analysis of the OFDMA system throughput as a function of the feedback scheme, frequency-domain scheduler, and discrete rate adaptation rule in the presence of feedback delays. We analyze the popular best-n and threshold-based feedback schemes. We show that for both the greedy and round-robin schedulers, the throughput degradation, given a feedback delay, depends primarily on the fraction of feedback reduced by the feedback scheme and not the feedback scheme itself. Even small feedback delays at low vehicular speeds are shown to significantly degrade the throughput. We also show that optimizing the link adaptation thresholds as a function of the feedback delay can effectively counteract the detrimental effect of delays.

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.

In this paper, we present an analytical approach to design the inner region size for the fractional frequency reused (FFR) time division duplex (TDD) orthogonal frequency division multiple access (OFDMA) systems when supporting asymmetrical traffic services. In TDD system, supporting asymmetrical traffic can be achieved by adjusting the ratio of downlink and uplink transmission period. Nevertheless, the intercell interference may be deteriorated by the cross-slot interference resulting from the different downlink and uplink ratios among neighboring cells. Although the FFR technique can overcome the inter-cell interference, the impact of the cross-slot interference of TDD systems due to various downlink to uplink traffic ratios in different cells on the inner region size of a FFR-based OFDMA system is an open issue to our best knowledge. Intuitively, the larger the inner region of a FFR system, the higher the system capacity. Thus, this paper can provide a systematic method to determine the size of the inner region of FFR-based OFDMA system for different ratios of the downlink to uplink traffic among two neighbor cells.

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.

The relay-assisted cooperative technique is a promising solution for guaranteeing quality of service and improvement in channel capacity. This paper proposes a hierarchical modulation based cooperative relaying method via a fixed relay station (FRS) to improve the performance of cell edge users for orthogonal frequency division multiple access (OFDMA) systems over a multi-cell environment. The grafting of both FRS and hierarchical modulation onto an OFDMA based cooperative system provides opportunities to reduce the interferences, i.e. inter-cell and inter-relay interferences, and to achieve cooperative diversity in a multi-cell environment, simultaneously. Under conditions of severe inter cell interference caused by high carrier collisions, the proposed scheme leads to an improvement in both channel capacity and bit error rate for cell boundary users.

One of the major drawbacks of the orthogonal frequency division multiple access (OFDMA) system is the multi-user interference (MUI) induced by the carrier frequency offsets (CFOs). In sub-band based OFDMA systems, users occupy consecutive and non-overlapping frequency sub-bands. The pilots are usually placed on the edges of a sub-band for channel estimation. However, the channel estimation performance is seriously degraded by the MUI. Traditionally, the MUI is alleviated by inserting a guard sub-carrier between adjacent users. In this paper, a novel pilot architecture is proposed, where three pilots are placed on each edge of a sub-band and pilots of adjacent users are overlapped. The proposed architecture has the same bandwidth efficiency as that of the conventional guard sub-carrier insertion scheme and provides better channel estimation performance and MUI reduction.

In interleaved orthogonal frequency division multiple access (OFDMA) systems uplink, multiple access interference (MAI) occurs due to different carrier frequency offsets (CFOs) from different users. In this paper, a new low complexity scheme is proposed to compensate CFO at the OFDMA receiver. The proposed scheme maximizes signal to interference ratio (SIR). Simulation results show considerable improvement in comparison to the existing methods in the literature.

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

In uplink orthogonal frequency division multiple access (OFDMA) systems, multiuser interference (MUI) occurs due to different carrier frequency offsets (CFO) of different users at the receiver. In this paper, we present a minimum mean square error (MMSE) based approach to MUI cancellation in uplink OFDMA. We derive a recursion to approach the MMSE solution. We present a structure-wise and performance-wise comparison of this recursive MMSE solution with a linear PIC receiver as well as other detectors recently proposed in the literature. We show that the proposed recursive MMSE solution encompasses several known detectors in the literature as special cases.

In recent years, large usage of wireless networks puts forward challenge to the utilization of spectrum resources, and it is significant to improve the spectrum utilization and the system sum data rates in the premise of fairness. However, the existing algorithms have drawbacks in efficiency to maximize the sum data rates of orthogonal frequency division multiple access (OFDMA) systems in the premise of fairness threshold. To address the issue, a novel artificial bee colony algorithm with update quantities of nectar sources is proposed for OFDMA resource allocation in this paper. Firstly, the population of nectar sources is divided into several groups, and a different update quantity of nectar sources is set for each group. Secondly, based on the update quantities of nectar sources set for these groups, nectar sources are initialized by a greedy subcarrier allocation method. Thirdly, neighborhood searches and updates are performed on dimensions of nectar sources corresponding to the preset update quantities. The proposed algorithm can not only make the initialized nectar sources maintain high levels of fairness through the greedy subcarrier allocation but also use the preset update quantities to reduce dimensions of the nectar sources to be optimized by the artificial bee colony algorithm, thereby making full use of both the local optimization of the greedy method and the global optimization of the artificial bee colony algorithm. The simulation results show that, just in the equal‐power subcarrier allocation stage, the proposed algorithm can achieve the required fairness threshold and effectively improve the system sum data rates.