Packet scheduling for OFDMA based relay networks

The combination of relay networks with orthogonal frequency division multiple access （OFDMA） has been proposed as a promising solution for the next generation wireless system. Considering different traffic classes and user quality of service （QoS）, three efficient scheduling algorithms are introduced in such networks. The round-robin （RR） algorithm in relay networks serves as a performance benchmark. Numerical results show that the proposed algorithms achieve significant improvement on system throughput and decrease system packet loss rate, compared with the RR and absence of relaying system （traditional network）. Furthermore, comparisons have been carried out among the three proposed algorithms.     

Quantized feedback MIMO scheduling for heterogeneous broadcast networks

One-bit quantization of signal-to-interference-plus-noise ratio is discussed in literature for user scheduling in homogeneous network where users are assumed to have equal signal-to-noise ratio (SNR). It is mentioned in literature that 1-bit quantization with fixed quantization threshold does not achieve multiuser diversity. Moreover, the system sum-rate achieved by this lags significantly behind that of full feedback scheme. Two multi-bit quantized feedback scheduling schemes are proposed for broadcast network with heterogeneous users experiencing different channel statistics. It is presented that these two schemes with fixed optimum quantization thresholds profit from the diversity provided by independent and identically distributed channels. Moreover, proposed optimistic multi-bit quantized scheduling scheme achieves higher system sum-rate than the proposed multi-bit quantized scheme by addressing the limitations of the later one. The optimum quantization thresholds depend on the number of transmit antennas and system SNR. Moreover, these multi-bit quantized feedback scheduling schemes also ensure user fairness. Simulation results are presented to support the numerical analysis.     

Delay sensitive scheduling schemes for heterogeneous QoS over wireless networks

Future wireless networks will support the growing demands of heterogeneous and delay sensitive applications. In this paper, a users' satisfaction factor (USF) is defined to quantify quality of service (QoS) for different types of services such as voice, data, and multimedia, as well as for different delay constraints. This USF not only predicts the final delivered QoS during transmission, but also take advantages of the fact that different packets can be decoded at different time in the receivers. Based on this USF, four types of scheduling schemes considering tradeoffs between system performance and individual fairness are proposed. These schemes explore the time, channel, and multi-user diversity to guarantee quality of service and enhance the network performance. From the simulation results, the proposed scheduling schemes achieve different tradeoffs between individual fairness and high system performance for the heterogeneous and delay sensitive applications, compared with the weighted round-robin and the modified proportional fairness scheduling schemes     

Cross-layer quality-driven adaptation for scheduling heterogeneous multimedia over 3G satellite networks

Wireless networks are experiencing a paradigm shift from focusing on the traditional data transfer to accommodating the rapidly increasing multimedia traffic. Hence, their scheduling algorithms have to concern not only network-oriented quality-of-service (QoS) profiles, but also application-oriented QoS targets. This is particularly challenging for satellite multimedia networks that lack fast closed-loop power control and reliable feedbacks. In this paper, we present a cross-layer packet scheduling scheme, namely Hybrid Queuing and Reception Adaptation (HQRA), which performs joint adaptations by considering the traffic information and QoS targets from the applications, the queuing dynamics induced from the network, as well as the end-to-end performance and channel variations from respective users. By jointly optimizing multiple performance criteria at different layers, the scheme enjoys quality-driven, channel-dependant, and network-aware features. HQRA can well accommodate return link diversity and the imperfect feedbacks, whilst ensuring robustness in highly heterogeneous and dynamic satellite environments. We evaluate its performance over diverse network and media configurations in comparison with the state-of-the-art solutions. We observe noticeable performance gains on application-oriented QoS, bandwidth utilization, and objective video quality, together with favorable fairness and scalability measures.     

Utility driven cooperative spectrum sensing scheduling for heterogeneous multi-channel cognitive radio networks

Owing to the spectrum scarcity and energy constrained devices in wireless networks arises the demand for an efficient spectrum sensing technique which improves both sensing performance and energy efficiency for cognitive radio networks. This paper proposes a cooperative spectrum sensing scheduling (CSSS) scheme for heterogeneous multi-channel cognitive radio networks with the objective of finding an efficient sensing schedule to enhance network utility while keeping the energy depletion at a lower level. We start with formulating the CSSS problem as an optimization problem, which captures both the energy-performance and performance opportunity trade-offs. We prove that the formulated CSSS problem is non-deterministic polynomial hard (NP-hard). To tackle the higher computational complexity of the formulated problem, we propose a greedy-based heuristic solution, which produces a sub-optimal result in polynomial time. To reduce energy consumption during spectrum sensing, we make secondary users to adaptively decide on the sensing duration based on the received signal-to-noise ratio (SNR), where higher SNR leads to lower sensing duration and vice-versa. For enhancing network throughput, SUs sense multiple channels in the order of their suitability for data transmission to explore as many numbers of channels as possible within the permitted maximum sensing time. We consider erroneous nature of reporting channel to make the cooperative decision robust against errors during reporting. Simulation based results show the effectiveness of the proposed scheme in terms of utility, energy overhead, and the number of channels explored compared to similar schemes from literature.

     

Profit-oriented resource allocation using online scheduling in flexible heterogeneous networks

In this paper, we discuss a generalized measurement-based adaptive scheduling framework for dynamic resource allocation in flexible heterogeneous networks, in order to ensure efficient service level performance under inherently variable traffic conditions. We formulate our generalized optimization model based on the notion of a “profit center” with an arbitrary number of service classes, nonlinear revenue and cost functions and general performance constraints. Subsequently, and under the assumption of a linear pricing model and average queue delay requirements, we develop a fast, low complexity algorithm for online dynamic resource allocation, and examine its properties. Finally, the proposed scheme is validated through an extensive simulation study. Portions of this paper have been presented at the 39th Conference on Information Sciences and Systems, CISS 2005, and at the Third IFIP Workshop on Next Generation Networks: Architectures, Protocols, Performance, 2005.     

One-dimensional dual-polarization beamforming networks based on coupled metal waveguides

One-dimensional dual-polarization beamforming networks on the basis of an array of identical coupled square metal waveguides with phase shifters are considered. An electrodynamic model of the structure, which enables determination of the field distribution at the network output and the radiation pattern is proposed. It is shown that linear coupling coefficients for waves with different polarizations have different signs. The realizability of two systems of identical almost flat-topped patterns for waves with two orthogonal polarizations is demonstrated.     

Decentralized beamforming design and power allocation for limited coordinated multi-cell network

Multi-cell processing （MCP） is capable of providing significant performance gain, but this improvement is accompanied by dramatic signaling overhead between cooperative base stations. Therefore, balancing the performance gain and overhead growth is crucial for a practical multi-base cooperation scheme. In this paper, we propose a decentralized algorithm to jointly optimize the power allocation and beamforming vector with the goal of maximizing the system performance under the constraint of limited overhead signal and backhaul link capacity. In particular, combined with calculating the transmission beamforming vector according to the local channel state information, an adaptive power allocation is presented based on the result of sum capacity estimation. Furthermore, by utilizing the concept of cell clustering, the proposed framework can be implemented in a practical cellular system without major modification of network architecture. Simulation results demonstrate that the proposed scheme improves the system performance in terms of the sum capacity and cell-edge capacity.     

Efficient scheduling algorithms for mixed services in wireless OFDMA system

Orthogonal Frequency Division Multiple Access (OFDMA) is an attracting system for combating the frequency selective fading. It’s widely considered as a promising candidate modulation and access scheme for next generation mobile communication systems. However, the explosive growth of multimedia applications raises higher performance requirements for Radio Resource Management (RRM) in OFDMA system. In particular, limited bandwidth and fierce resource competition impose a challenging issue on the design of packet scheduler. In this paper, we propose two scheduling algorithms applicable to mixed services (i.e., real-time and non-real-time services), that is QoS-oriented Dynamic Threshold Control (DTC) algorithm and fairness-oriented Fairness Aware and QoS Aware (FAQA) algorithm. These two algorithms are both composed of two stages, i.e., initial subcarrier allocation and subcarrier reallocation. For the DTC algorithm, in the stage of initial subcarrier allocation, based on the different metrics to weigh QoS between both services, we design a unique scheduling strategy for each type of service. A dynamic threshold is adopted to help users quickly recover from starvation, so that any one user in system can escape from severely degraded QoS. In the stage of subcarrier reallocation, we will reallocate the surplus subcarriers from the buffer-empty users to the buffer-nonempty users so as to increase spectrum efficiency. For FAQA algorithm, in the stage of initial subcarrier allocation, for the purpose of achieving Proportional Fairness (PF) with lower complexity, we deduce a simple scheduling strategy satisfying PF criterion by means of Greedy algorithm. In the stage of subcarrier reallocation, in order to increase the number of users satisfying QoS requirements, we’ll reallocate the surplus subcarriers from the QoS-satisfied users to the QoS-unsatisfied users. Simulation results demonstrate that, on one hand, the DTC algorithm not only guarantees the quality of both services, but also increases the spectrum efficiency; on the other hand, the FAQA algorithm well maintains the fairness among users, and increases the QoS satisfaction degree at the same time.     

Pseudo-handover based subchannel and power adaptation scheme for interference mitigation in OFDMA two-tier femtocell networks

In the two-tier femtocell network,a central macrocell is underlaid with a large number of shorter range femtocell hotspots,which is preferably in the universal frequency reuse mode.This kind of new network architecture brings about urgent challenges to the schemes of interference management and the radio resource allocation.Motivated by these challenges,three contributions are made in this paper:1) A novel joint subchannel and power allocation problem for orthogonal frequency division multiple access (OFDMA) downlink based femtocells is formulated on the premise ofminimizing radiated interference of every Femto base station.2) The pseudo-handover based scheduling information exchange method is proposed to exchange the co-tier and cross-tier information,and thus avoid the collision interference.3) An iterative scheme of power control and subchannel is proposed to solve the formulated problem in contribution 1),which is an NP-complete problem.Through simulations and comparisons with four other schemes,better performance in reducing interference and improving the spectrum efficiency is achieved by the proposed scheme.     

Low Complexity Carrier Frequency Offset and Channel Estimation for Multiuser OFDMA Networks

Wireless Personal Communications - Multiple carrier frequency offsets exist in the orthogonal frequency-division multiple access (OFDMA) uplink receivers, and consequently induce inter-carrier...     

Outage and energy efficiency analysis for cognitive based heterogeneous cellular networks

Cognitive radio and small cells are the promising techniques to minimize energy consumption and satisfy the exponentially increasing data rates for the heterogeneous cellular network (HCN). In this paper, a theoretical framework is developed to calculate the outage probability of the HCN based on the opportunistic utilization of the traditional cellular bandwidth and television white space (TVWS) for the cognitive femto base stations. This work investigates overlay, underlay, mixed overlay-underlay based two tiers cognitive HCN. It also investigates the impact of the TVWS in the overlay-TVWS mixed spectrum sharing technique (SST). Tools from stochastic geometry are used to model cognitive HCN. Furthermore, the tier selection probability, average ergodic rate, area spectral efficiency (ASE), and energy efficiency (EE) of the HCN are also calculated for different SSTs. Numerical results show that mixed SST achieves a significant reduction in tier outage probability and total outage probability as compared to underlay and overlay techniques alone. It is also demonstrated that compared to the traditional single tier network, cognitive based HCN can improve the total ASE and EE of the order of \(10^{2}\) and 10, respectively.     

Performance impact of flexible power arrangement in OFDMA based cellular communication networks

In the OFDMA-based downlink of wireless cellular communication networks, the intercell interference would be a key performance-limiting factor, especially for the cell edge users. To enhance the cell edge user performance, several flexible power allocation schemes have been proposed, e.g., the so-called soft frequency reuse scheme and the partial frequency reuse scheme. This paper analyzes those schemes in a very realistic multicell setting, investigates the layer 2 resource allocation algorithms that are associated to the physical layer setting, and finally gives results of the performance evaluation.     

QoS aware adaptive resource allocation techniques for fair scheduling in OFDMA based broadband wireless access systems

A system based on orthogonal frequency division multiple access (OFDMA) has been developed to deliver mobile broadband data service at data rates comparable to those of wired services, such as DSL and cable modems. We consider the resource allocation problem of assigning a set of subcarriers and determining the number of bits to be transmitted for each subcarrier in OFDMA systems. We compare simplicity, fairness and efficiency of our algorithm with the optimal and proposed suboptimal algorithms for varying values of delay spread, number of users and total power constraint. The results show that the performance of our approach is appealing and can be close to optimal. We also consider another resource allocation scheme in which there is no fixed QoS requirements per symbol but capacity is maximized.     

Effect of opportunistic scheduling on the quality of service perceived by the users in OFDMA cellular networks

Our objective is to analyze the impact of fading and opportunistic scheduling on the quality of service perceived by the users in an orthogonal frequency-division multiple access cellular network. To this end, assuming Markovian arrivals and departures of customers that transmit some given data volumes, as well as some temporal channel variability (fading), we study the mean throughput that the network offers to users in the long run of the system. Explicit formulas are obtained in the case of allocation policies, which may or may not take advantage of the fading, called respectively opportunistic and non-opportunistic. The main practical results of the present work are the following: Firstly, we evaluate for the non-opportunistic allocation the degradation due to fading compared to additive white Gaussian noise (AWGN; that is, a decrease of at least 13% of the throughput). Secondly, we evaluate the gain induced by the opportunistic allocation. In particular, when the traffic demand per cell exceeds some value (about 2?Mbits/s in our numerical example), the gain induced by opportunism compensates the degradation induced by fading compared to AWGN.     

Energy minimization resource allocation schemes for relay-enhanced OFDMA networks

This paper studies the problem of joint allocation of subchannel, transmission power, and phase duration in the relay-enhanced bidirectional orthogonal frequency-division multiple access time division duplex systems. The challenges of this resource allocation problem arise from the complication of multiple-phase assignments within a subchannel since the relay station can provide an additional signal path from the base station to the user equipments (UEs). Existing research work does not fully consider all the influential factors to achieve feasible resource allocation for the relay-based networks. Since energy consumption is one of the principal issues, the energy minimization resource allocation (EMRA) schemes are proposed in this paper to design the allocation of subchannel, power, and phase duration for the UEs with the consideration of UE’s quality-of-service (QoS) requirements. Both the four-phase and two-phase bidirectional relaying assignments and the network coding technique are adopted to obtain the suboptimal solutions for the proposed EMRA schemes. Different weights are designed for the UEs to achieve the minimization of weighted system energy for the relay-enhanced networks. Simulation results show that the proposed EMRA schemes can provide comparably better energy conservation and outage performance with QoS support.

     

Proportional-fair energy-efficient radio resource allocation for OFDMA smallcell networks

This paper investigates the energy-efficient radio resource allocation problem of the uplink smallcell networks. Different from the existing literatures which focus on improving the energy efficiency (EE) or providing fairness measured by data rates, this paper aims to provide fairness guarantee in terms of EE and achieve EE-based proportional fairness among all users in smallcell networks. Specifically, EE-based global proportional fairness utility optimization problem is formulated, taking into account each user’s quality of service, and the cross-tier interference limitation to ensure the macrocell transmission. Instead of dealing with the problem in forms of sum of logarithms directly, the problem is transformed into a form of sum of ratios firstly. Then, a two-step scheme which solves the subchannel and power allocation separately is adopted, and the corresponding subchannel allocation algorithm and power allocation algorithm are devised, respectively. The subchannel allocation algorithm is heuristic, but can achieve close-to-optimal performance with much lower complexity. The power allocation scheme is optimal, and is derived based on a novel method which can solve the sum of ratios problems efficiently. Numerical results verify the effectiveness of the proposed algorithms, especially the capability of EE fairness provisioning. Specifically, it is suggested that the proposed algorithms can improve the fairness level among smallcell users by 150–400 % compared to the existing algorithms.     

Flow rank based probabilistic fair scheduling for wireless ad hoc networks

Fair scheduling is an ideal candidate for fair bandwidth sharing and thereby achieving fairness among the contending flows in a network. It is particularly challenging for ad hoc networks due to infrastructure free operation and location dependent contentions. As there is no entity to serve coordination among nodes, we need a mechanism to overcome inherent unreliability of the network to provide reduced collision and thereby higher throughput and adequate fair allocation of the shared medium among different contending flows. This paper proposes a flow rank based probabilistic fair scheduling technique. The main focus is to reduce the collision probability among the contending flows while maintaining the prioritized medium access for those flows, which ensures a weighted medium access control mechanism based on probabilistic round robin scheduling. Each flow maintains a flow-table upon which the rank is calculated and backoff value is assigned according to the rank of the flow, i.e., lower backoff interval to lower ranked flow. However, flow-table instability due to joining of a new flow, partially backlogged flow, hidden terminal and partially overlapped region exhibits a challenging problem that needs to be mitigated for our mechanism to work properly. We take appropriate measures to make the flow-table stabilized under such scenarios. Results show that our mechanism achieves better throughput and fairness compared to IEEE 802.11 MAC and existing ones.