Graph‐based resource allocation algorithms for multiuser downlink MIMO‐OFDMA networks

Multiuser multiple‐input multiple‐output orthogonal frequency division multiple access (MIMO‐OFDMA) is considered as the practical method to attain the capacity promised by multiple antennas in the downlink direction. However, the joint calculation of precoding/beamforming and resource allocation required by the optimal algorithms is computationally prohibitive. This paper proposes computationally efficient resource allocation algorithms that can be invoked after the precoding and beamforming operations. To support stringent and diverse quality of service requirements, previous works have shown that the resource allocation algorithm must be able to guarantee a specific data rate to each user. The constraint matrix defined by the resource allocation problem with these data rate constraints provides a special structure that lends to efficient solution of the problem. On the basis of the standard graph theory and the Lagrangian relaxation, we develop an optimal resource allocation algorithm that exploits this structure to reduce the required execution time. Moreover, a lower‐complexity suboptimal algorithm is introduced. Extensive simulations are conducted to evaluate the computational and system‐level performance. It is shown that the proposed resource allocation algorithms attain the optimal solution at a much lower computational overhead compared with general‐purpose optimization algorithms used by previous MIMO‐OFDMA resource allocation approaches. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance analysis of hexagonal cellular networks in fading channels

This paper analyzes the location‐dependent performance metrics of coverage probability and spectral efficiency in hexagonal cellular networks under Rayleigh fading with a general distribution for shadowing and also including two special cases of no shadowing and lognormal shadowing. The effects of system parameters such as frequency reuse factor, transmission probability of base stations, and signal‐to‐interference‐plus‐noise ratio gap from Shannon capacity are accurately characterized. The proposed approach is applied to fractional frequency reuse (FFR) scheme where the impact of FFR on spectral efficiency is evaluated. Numerical results show that (i) in a lognormal‐shadowed Rayleigh fading channel with the shadowing standard deviation of 12 dB, the cell area wide spectral efficiency is degraded by approximately 40% compared with when there is Rayleigh fading without shadowing; (ii) the improvement in spectral efficiency achieved by FFR over the universal frequency reuse increases as the transmission probability increases and the shadowing becomes less severe; and (iii) in Rayleigh fading without shadowing environment where all the base stations are actively transmitting, FFR achieves approximately 20% improvement in spectral efficiency in the cell edge area. Interestingly, this improvement increases to about 30% if a 3‐dB signal‐to‐interference‐plus‐noise ratio gap from Shannon capacity is further accounted. Copyright © 2015 JohnWiley & Sons     

Minimizing Power Cost in QoS Constrained Wireless Sensor Networks

This paper studies the problem of simultaneous support of energy efficiency and quality of service (QoS) in time division multiple access (TDMA) based wireless sensor networks (WSNs), utilizing the concept of cross-layer optimization. We show that by taking slot reuse into account, the problem has combinatorial complexity, which is determined by the TDMA frame length and the number of links. An iterative reuse factor (IRF) approach is proposed to efficiently solve the problem. By skillfully introducing and iteratively adjusting a slot reuse factor, cross-layer optimization and slot reuse are jointly inter-connected to obtain a TDMA schedule with optimal power consumption and desired QoS objectives in polynomial time. Extensive simulations with a random topology WSN show that the proposed IRF approach provides a flexible tradeoff between energy efficiency and QoS objectives. Under the same packet loss rate objective, the IRF approach achieves up to 30 % of power saving compared to the existing approaches in the literature.     

Cross-layer optimization with cooperative communication for minimum power cost in packet error rate constrained wireless sensor networks

This paper addresses the problem of joint design of routing, medium access control (MAC), and physical layer protocols with cooperative communication to achieve minimum power cost in packet error rate (PER) constrained wireless sensor networks (WSNs). The problem is solved in two steps. First, we calculate the minimum power cost with a specified PER objective between any two nodes, assuming either cooperative (with a single relay node) or direct communication between the two nodes. It is shown that the minimum per-hop power cost is found in 2M and log₂ M steps for cooperative and direct communication, respectively, where M is the number of power levels. Second, we formulate the cross-layer design problem as a linear optimization problem to minimize the power cost of the whole network, using the minimum per-hop power cost determined in the first step as input and assuming time division multiple access (TDMA) at the MAC layer. Numerical results show that, at a desired end-to-end PER objective, cross-layer optimization with cooperative communication achieves up to 70% of power savings compared to that without cooperative communication.     

A simulation study of speech traffic capacity in digital cordlesstelecommunications systems

A computer simulation tool for evaluating the speech traffic handling capability of digital cordless telecommunications systems has been developed. The focus of the paper lies on the teletraffic engineering problems posed by time division multiple access (TDMA) systems operating with time division duplex (TDD) on one radio transceiver in radio environments. The impacts of fixed station separation, fixed station capacity, spatial traffic variability, dynamic channel assignment, microdiversity, and propagation model on the system capacity are investigated. The simulator serves as an invaluable tool for conducting sensitivity studies and its outputs provide useful insights on traffic performance of digital cordless systems     

Performance analysis of hierarchical cellular networks with queueing and user retrials

How to efficiently utilize the scarce radio channel resource while maintaining the desired user‐perceived quality level and improved network performance is a major challenge to a wireless network designer. As one solution to meet this challenge in cellular mobile networks, a network architecture with hierarchical layers of cells has been widely considered. In this paper, we study the performance of a hierarchical cellular network that allows the queueing of both overflow slow‐mobility calls (from the lower layer microcells) and macrocell handover fast‐mobility calls that are blocked due to lack of free resources at the macrocell. Further, to accurately represent the wireless user behaviour, the impact of call repeat phenomenon is considered in the analysis of new call blocking probability. Performance analysis of the hierarchical cellular structure with queueing and call repeat phenomenon is performed using both analytical and simulation techniques. Numerical results show that queueing of calls reduces forced call termination probability and increases resource utilization with minimal call queueing delay. It is also shown that ignoring repeat calls leads to optimistic estimates of new call blocking probability especially at high offered traffic. Copyright © 2005 John Wiley & Sons, Ltd.     

Throughput reliability analysis of cloud‐radio access networks

This paper develops a stochastic geometry‐based analytical approach for calculating the throughput reliability of a cloud‐radio access network (C‐RAN) comprising randomly distributed remote radio heads (RRHs) and randomly located users. A tunable distance‐based RRH transmit power control mechanism along with cooperative joint transmissions by the RRHs is employed to achieve power savings and high throughput reliability. The analytical result for the throughput reliability serves as input to analysis of per user achievable average rate and C‐RAN network‐level performance metrics of spectral efficiency and energy efficiency. The analytical results are validated by Monte Carlo simulation results with good agreement, thus confirming the accuracy of the developed analytical approach. The key finding from the analysis is that by carefully tuning the RRH transmit power and cooperation parameter (cluster radius), it is possible to realize a threefold improvement in the energy efficiency along with 108% enhancement in the spectral efficiency of C‐RANs. Copyright © 2016 John Wiley & Sons, Ltd.     

A Viterbi-like algorithm with adaptive clustering for channelassignment in cellular radio networks

A new channel assignment algorithm, called the Viterbi (1967) -like algorithm (VLA), is proposed to solve the channel assignment problem in cellular radio networks. The basic idea of the proposed algorithm is step-by-step (sequential) channel assignment with the objectives of minimum bandwidth required at every step, subject to adjacent channel and cochannel separation constraints. The VLA provides the benefits of minimum required bandwidth, stability of solution, and fast execution time. The performance of the VLA is evaluated by computer simulation, applied first to 19 benchmark problems on channel assignment and then applied to study cellular radio network performance. Results from computer simulation studies show that bandwidth requirements by VLA closely match or are sometimes better than those of the existing channel assignment algorithms. Furthermore, it is found that execution of VLA is approximately two times faster than the local search algorithm-the existing channel assignment algorithm with the least bandwidth requirements. The combined advantages of minimum required bandwidth, stability of solution, and fast execution time make the VLA a useful candidate for cellular radio network planning     

A centralized energy-efficient routing protocol for wireless sensor networks

Wireless sensor networks consist of small battery powered devices with limited energy resources. Once deployed, the small sensor nodes are usually inaccessible to the user, and thus replacement of the energy source is not feasible. Hence, energy efficiency is a key design issue that needs to be enhanced in order to improve the life span of the network. Several network layer protocols have been proposed to improve the effective lifetime of a network with a limited energy supply. In this article we propose a centralized routing protocol called base-station controlled dynamic clustering protocol (BCDCP), which distributes the energy dissipation evenly among all sensor nodes to improve network lifetime and average energy savings. The performance of BCDCP is then compared to clustering-based schemes such as low-energy adaptive clustering hierarchy (LEACH), LEACH-centralized (LEACH-C), and power-efficient gathering in sensor information systems (PEGASIS). Simulation results show that BCDCP reduces overall energy consumption and improves network lifetime over its comparatives.     

Cross-layer radio resource management in integrated WWAN and WLAN networks

This paper proposes a mobility adaptive network selection scheme in the context of wireless wide area network (WWAN) and wireless local area network (WLAN) radio access technologies (RATs) that supports both real-time (RT) and non-real-time (NRT) service classes. Physical layer information based call admission control (CAC) is considered for the two RATs to enforce service specific QoS requirements. The effectiveness of the cross-protocol-layer information for radio resource management (RRM) in integrated WWAN and WLAN networks is assessed analytically for individual service classes in a multi-service environment using the theory of Markov chains. The impact of non-uniform user and mobility distributions due to the existence of hotspot in the macro-cell area and the effect of network selection parameter measurement errors on the RRM performance are also evaluated. Numerical results show that the proposed network selection scheme minimizes the rate of unnecessary vertical handoffs, thereby providing stable communication without degrading the call blocking probability and call outage probability performance metrics.