Non-orthogonal multiple access is a promising technology for the fifth generation systems which exploits the power domain to achieve higher spectral efficiency. The performance of NOMA techniques are usually investigated under an ideal setup with perfect successive interference cancellation. However, the limitations of NOMA techniques under a setup with imperfect successive interference cancellation are not well understood. Contrary to the approaches in the literature, we examine the performance of NOMA under a non-ideal setup and propose two power allocation algorithms. The first algorithm is designed for the max-min problem whereas the second algorithm considers the heterogeneous rate requirements of users and provides solutions based on a novel rate measure. The performance of the algorithms is investigated both theoretically and numerically under a non- ideal setup with channel estimation errors. The theoretical analyses reveal that the algorithms achieve the optimum power allocation for the rate max-min problems. The numerical analyses are not only in agreement with the theoretical analyses, but also show the superiority of the proposed algorithms compared to both the conventional multiple access techniques as well as other NOMA approaches.

The authors study the design of heterogeneous two-tier wireless sensor networks (WSNs), where one tier of nodes is more robust and computationally intensive than the other tier. The authors find the ratios of densities of nodes in each tier to maximise coverage and network lifetime. By employing coverage processes and optimisation theory, the authors show that any topology of WSN derived from random deployments can result in maximum coverage for the given node density and power constraints by satisfying a set of conditions. The authors show that network design in heterogeneous WSNs plays a key role in determining key network performance parameters such as network lifetime. The authors discover a functional relationship between the redundancy, density of nodes in each tier for active coverage and the network lifetime. This relationship is much less pronounced in the absence of heterogeneity. The results of this work can be applied to network design of multi-tier networks and for studying the optimal duty cycles for power saving states for nodes in each tier.

This article studies clustered wireless sensor networks (WSNs), a realistic topology resulting from common deployment methods. We study coverage in naturally clustered networks of wireless sensor nodes, as opposed to WSNs where clustering is facilitated by selection. We show that along with increasing the vacancy in random placement of nodes in a WSN, it also alters the connectivity properties in the network. We analyze varying levels of redundancy to determine the probability of coverage in the network. The phenomenon of clustering in networks of wireless sensor nodes raises interesting questions for future research and development. The article provides a foundation for the design to optimize network performance with the constraint of sensing coverage.

A primary constraint in wireless sensor networks (WSNs) is obtaining reliable and prolonged network operation with power-limited sensor nodes. Most of the approaches to the energy constraint problem focus mainly on the WSN and its architecture without analyzing the underlying process for the depletion of battery levels of individual nodes and consequent reduction in network lifetime: the variation of sensing environment in the deployment region. We study the energy model of a WSN as interdependence between the environmental variation and its impact on the energy consumption at individual nodes. This paper motivates the need for modeling energy variation in WSNs along with the environment in the deployment region. Defining network energy as the sum of residual battery energy at nodes, we provide an analytical framework for the dependence of node energy and sensitivity of network energy as a function of environmental variation and reliability parameters. Using a neural network based approach, we perform adaptive density control and show how reliability requirements and environment variation influences the rate of change of network energy.

An important objective of wireless sensor networks (WSNs) is to reliably sense data about the environment in which they are deployed. Reliability in WSNs has been widely studied in terms of providing reliable routing protocols for message dissemination and reliability of communication from sink to sensors. In this work, we define a reliability metric by the amount of information sensed by the network. In order to satisfy this reliability constraint, we propose a diffusion-based approach for a deployment pattern for the sensor nodes. We show that this deployment pattern while maintaining reliable network operation for the entire duration of deployment satisfies coverage and connectivity constraints for the network. In addition, we show that this diffusion-based deployment pattern requires lesser number of sensors and provides higher degree of reliability of sensing operation than popular regular deployment patterns.

In cellular networks, the implementation of various resource management processes, such as bandwidth reservation and location updates, has been based on the one-to-one resource management information exchange paradigm, between the mobile nodes and the base stations. In this paper, we design and demonstrate the use of a distributed cooperative scheme that can be applied in the future wireless networks to improve the energy consumption for the routine management processes of mobile terminals, by adopting the peer-to-peer communication concept of wireless ad hoc networks. In our approach, the network is subdivided into one-hop ad hoc clusters where the members of each cluster cooperate to perform the required management functions, and conventional individual direct report transmissions of the mobile terminals to the base stations are replaced by two-hop transmissions. The performance evaluation and the corresponding numerical results presented in this paper confirm that our proposed scheme reduces significantly the overall system energy consumption when compared with the conventional one-to-one direct information management exchange approach. Furthermore the issue of fairness in dynamically selecting the various cluster heads in successive operational cycles of the proposed scheme is analyzed, and an enhanced algorithm is proposed and evaluated, which improves significantly the cluster head selection fairness, in order to balance the energy consumption among the various mobile terminals. Copyright © 2005 John Wiley & Sons, Ltd.

We propose the cellular ad hoc augmented networks architecture where each mobile terminal can communicate with either the base station or to a peer mobile located within the ad hoc communication range. We introduce a set of schemes, which are designed towards enabling energy-efficient communications for all entities within the network. Furthermore, the solutions proposed distribute the load across all mobile units. We measure performance through simulations where the results suggest considerable reduction in the average overall power consumption in the network achieved by using CAHAN as opposed to conventional cellular operation. The savings applies to both the uplink and the downlink directions. It is also noted that transmit power reduction is particularly notable in case of large network density. Also, the mobile battery life is increased as a result of energy-efficient communications.

Wireless communications is moving from cellular networks towards a more distributed, self-configuring ad hoc oriented networks. Until a complete metamorphosis occurs, the emerging techniques that allow communication by using no infrastructure at all can be enjoyed at the presence of the vast infrastructure of cellular systems. Alternatively, this situation can be viewed as the cellular systems of today benefiting from the flexible new techniques of ad hoc communications in order to improve current levels of performance. In this paper, we propose ad hoc routing techniques that allows improved packet delivery performance in the next generation of a UMTS system. Our results show that a hybrid network, where each mobile terminal is capable of communicating to a base station and to other mobile terminals in the network, and delivers packets much more successfully than the conventional UMTS network. Furthermore, the number of nodes that can be supported by such a system is much higher than the case of a pure cellular network. We construct 2 alternative routing schemes that exploit the hybrid architecture and show that performance is superior as compared to UMTS.

We propose ad hoc routing strategies that improve throughput performance in the next generation of a UMTS system. We show that a hybrid network, where mobile terminals can communicate both with a BS and with each other, delivers packets more successfully than the conventional UMTS network. The number of nodes that can be supported by such a system is higher than pure UMTS.

An adaptive location registration scheme is proposed for wireless cellular networks. A high speed mobile on a highly directed path does not need to update its location as long as the mobile maintains its speed and direction since the network can predict the location of the mobile using the mobile's speed and direction information. On the other hand, for a mobile doing a random walk, the location prediction using the speed and direction information is inefficient in terms of the signaling cost and prediction accuracy. With this observation, we dynamically classify mobiles based on the predictability of their trajectory. A mobile with predictable trajectory is prescribed a predictive distance-based location update scheme and a mobile with random trajectory is prescribed a (non-predictive) distance-based location update scheme. The performance of the adaptive scheme is compared with the predictive and non-predictive schemes.

Investigations of high-resolution Ethernet local area network (LAN) traces and VBR video traffic has demonstrated that these traffic types exhibit self-similarity. In this paper, we study two commonly used methods in estimating traffic self-similarity level, and compare them in terms of their applicability in providing real-time feedback to resource management algorithms. These methods are variance-time plot and wavelet-analysis. The constraints for selection of a method, wavelet filter types and lengths, number of scales and length of traffic data to be stored and analyzed are given.

We propose a new computationally efficient multiuser detection scheme, based on the multiuser detection of a subset of pre-selected users, and conventional detection of the rest of the users. This approach, called selective multiuser detection (SMD), allows for full exploitation of available processing power at the receiver by use of multiuser detection, and provides the remedy for computational complexity of multiuser detection schemes when the number of active users increases beyond the processing capability. We analyze the SMD scheme using a decorrelator as the multiuser detector, and derive the capacity for the single-cell and the multi-cell CDMA cellular system. We propose and examine three different criteria for selection of users to be processed by the multiuser detector. The capacity improvement with respect to the conventional CDMA detector combines the gain from multiuser detection and reduction of other-cell interference. We analyze the two effects and evaluate them numerically. The results indicate that the SMD is a promising alternative for multiuser detection-oriented CDMA systems with large number of active users.

Location tracking in wireless networks is essential for ubiquitous communication service. Since a user may move freely, the network has to keep track of the location of the mobile terminal to deliver messages or calls. There has been significant effort to address the problem of user mobility; however, most of the mobility models introduced in the previous work do not take the movement direction into account - the parameter called CMR (call to mobility ratio) which is commonly used in the literature is the ratio between the call arrival rate and the cell boundary crossing rate of the mobile. In this paper, we introduce Brownian motion with drift as our mobility model and discuss the effect of movement direction and call arrivals on the performance of the distance-based location update scheme in the predictive and the non predictive mode.

Traffic measurements are key in the development of robust resource management and scheduling algorithms. Bandwidth allocation methods are either static or they adaptively change the bandwidth assigned to applications. Adaptive algorithms predict the near future behavior of traffic based on average queue size and utilization information to update the allocated bandwidth. This work introduces a novel feedback mechanism that uses wavelets and measures the energy of a byte counting process at the output of each dyadic subband filter. The output is then used to predict short and long term fluctuations in the incoming traffic pattern and to readjust the bandwidth allocation accordingly.

We propose a table driven routing algorithm for ad hoc networks using geolocation information of mobiles. Assuming that each mobile is aware of its mobility status (i.e., position, speed and direction of movement), mobiles may exchange this information for the purpose of routing. A high speed mobile on a highly directed path does not need to update its mobility status as long as it maintains its speed and direction. Each mobile can accurately estimate the geolocation of others using the speed and direction information. On the other hand, a slow-moving mobile doing random walk doesn't need to update its geolocation as long as it stays in a small local area. Based on this observation, we classify mobiles into local and global, and let the mobile choose the geolocation update scheme that minimizes the frequency of update for the corresponding mobility class. Each mobile may estimate the network topology using the geolocation information of other mobiles, but the geolocation information alone cannot provide an accurate view of the network because two adjacent mobiles may not be able to establish communication due to the radio communication impairment such as fading, jamming or interference from other radio sources. The proposed routing algorithm dynamically adapts to the physical layer impairment and provide loop-free minimum hop route.

We investigate the performance bounds for interference adaptive dynamic channel assignment (IA-DCA) in wireless networks. IA-DCA has been shown to be a promising radio resource allocation strategy in reuse systems such as FDMA and TDMA. Our previous work has presented the upper performance bound for IA-DCA algorithms by assuming an idealized dynamic channel allocation scheme with instant interference adaptation and maximal packing (IAMP) which not only provided guaranteed quality of received signal but also minimum co-channel reuse distance. The two sets of performance bounds previously obtained are results of exact analysis of the asymptotic case where the number of channels is assumed to be infinite, and an approximate analysis corresponding to the practical case where the number of channels is finite. In this paper, we study the practical case and verify the bounds by means of computer analysis. The idealized IAMP method is modified such that it reaches reasonable accuracy within finite simulation time.

After a novel paper by W.E. Leland et al. published in 1994, self-similar properties of multimedia network traffic became a well known fact. More precisely, aggregate packet level network traffic exhibits fractal-like behavior over time scales on the order of a few hundreds of milliseconds and larger as long as the individual data streams that generate the aggregate traffic have a heavy tailed distribution. This finding has provided new insights into how self-similarity can have an impact on network performance and in what way the quality of service (QoS) parameters can be kept at an optimal level under self-similar traffic. The level of self-similarity is directly related to the degradation of the network performance and this level changes over time depending on the load on the network. In our previous study, we had investigated the methods to detect Hurst parameter (H), a measure of self-similarity, in terms of their reliability and complexity to be implemented on real time applications. Now, this paper is focused on the multiresolution decomposition technique. The optimum number of scales and the optimum number of the taps of a basis filter were addressed and the results have proved that different H is returned for different scale depth and the length of the filters deployed. Also, we, in this study, have demonstrated that H itself is not a good representative of the burstiness of traffic traces. It is shown that, in addition to H, also peak, mean, peak/mean ratio and the burst length should be considered to be able to characterize the subjected traffic.

We evaluate the performance of the copy network under three scenarios: (1) non-buffer non-splitting copy network (NBNS), (2) shared-input buffer-non-splitting copy network (SIBNS), and (3) shared-input-buffer-splitting copy network (SIBS). For NBNS, we derived the exact overflow and cell loss probabilities instead of the Chernoff bound. Furthermore, we propose a general Markov model, a novel theoretical approach, for the performance analysis of the shared-input-buffer copy networks. This analysis method can be applied for both SIBNS and SIBS. In our work, theoretical and simulation results are presented for every scenario. The comparison shows that improved performance of lower cell loss and higher throughput can be achieved by shared-input-buffer (SIBNS and SIBS). However the tradeoff is the long cell delay. With the splitting algorithm, SIBS can provide better performance than the NBNS and SIBNS.

Interference adaptive dynamic channel allocation (IA-DCA) schemes are promising channel assignment strategies in TDMA/FDMA systems. The performance analysis of an IA-DCA scheme focuses on three factors: co-channel interference, traffic distribution, and the processing power of the DCA algorithm. In our previous work the impact of co-channel interference was studied. This paper investigates the impact of the traffic load distribution. As far as the processing power is concerned, an idealized interference adaptive maximum packing scheme is assumed such that it is able to deal with the traffic fluctuation among cells. This scheme gives the best performance for all IA-DCA algorithms under some assumptions. The combined effect of all three factors are considered in deriving an upper performance bound for IA-DCA algorithms in TDMA/FDMA systems.

A method of improving the quality of service in mobile cellular systems based on prioritization of handover requests is presented. The objective is to improve perceived quality of cellular service by minimizing both the probability of forced termination of ongoing calls due to handover failures and the degradation in spectrum utilization. A model based on a multiple-priority nonpreemptive queuing discipline is developed. New calls are blocked if all channels are occupied. Handover requests are queued such that as soon as a channel is available, it is offered to the mobile subscriber with the measurement results closest to the minimum acceptable power level for communication. Service rate is given by channel occupancy time distribution and is assumed to be exponential. The performance of a cellular system employing the proposed handover policy is evaluated analytically and by simulation, and results are compared to those obtained when the cellular system employs nonprioritized call handling and first-in/first-out queuing discipline. This provides lower probability of forced termination and less call blocking, less reduction in traffic, and less delay.>