In this paper, the performance of in-band full- duplex OFDM relaying systems with energy- harvesting and self-interference cancellation in the polarization domain is analyzed. Specifically, we use the time switching-based relaying protocol to implement energy harvesting. The harvested energy is used by the relay to forward the transmitted information from the source. To cancel the self-interference, the polarization-enabled digital self-interference cancellation scheme is deployed at the relay. Our simulation results show that the full-duplex OFDM energy harvesting relaying system almost doubles the throughput, while maintaining the same bit error performance by a modest increase in the signal-to-noise ratio compared to the half-duplex OFDM energy harvesting relaying system. It is also revealed that the optimal time splitting factor should be less than 0.3 to maximize the full-duplex system throughput.

The CORNER propagation model, first proposed in 2010, has been previously validated and found to be a reasonably accurate representation of propagation scenarios in urban Vehicular Ad Hoc Networks (VANETs). This paper considers the impact of the propagation environment on routing performance and reveals a pressing need to consider more accurate propagation models when designing urban VANET routing protocols. A greedy routing protocol, which uses CORNER's propagation estimates for neighbour selection, is then presented. The new protocol, named Corner Propagation Stateless Routing (CPSR) is compared to GPSR, a benchmark protocol for VANETs, showing between 87% and 300% improvement in packet delivery ratio at higher network loads.

In Wireless Body Area Networks (WBANs), on-body channels undergo temporal variations predominantly because of the body motion and shadowing of tissue. This paper focuses on a common human activity, walking, to explore the characteristics of the dynamic on-body propagation channel. A customized portable wireless sounder is built and utilized to collect the original on-body channel data both for the indoor and outdoor environments. We focus on exploring the second-order statistics of the on-channel data during walking, including the temporal autocorrelation, the cross- correlation and the path loss discrepancy between the two correlated links. This channel characterization facilitates more efficient designs and evaluations of WBAN systems, including more efficient network resource allocation and more efficient deployment of cooperative communication.

Stereo matching algorithms attempt to estimate depth from the images obtained by two cameras. In most cases, the arrangement of cameras (their locations and orientations with respect to the scene) is determined based on human experience. In this paper, it is shown that the camera arrangement can be optimized using the concept of correspondence field (CF) for better acquisition of depth. Specifically, this paper demonstrates the relationship between the CF of a pair of cameras and depth estimation accuracy and presents a method to optimize their arrangement based on the gradient of the CF. The experimental results show that a pair of cameras optimized by the proposed method can improve the accuracy of depth estimation by as much as 30% compared with the conventional camera arrangements.

This paper proposes the concept of perceptual pruning to improve the scalability of immersive video conferencing (IVC) systems. The aim of perceptual pruning is to enable servers to dynamically reduce the bit rate of videos on-the-fly in response to changes in virtual distance and orientation of videos with respect to the receiving client. It is shown that the video of each participant will have to undergo varying degrees of texture to pixel mapping before it is rendered by the client. By reducing the resolution of the video at the scale of each transform block in response to nuances of this mapping, the video bit rate could be reduced without any noticeable degradation of quality. This paper presents the results of experimental tests and also real-world scalability tests to quantify the impact of perceptual pruning. It is concluded that perceptual pruning will be of significant benefit, especially in those situations when the number of videos in the client's viewpoint is large.

In Wireless Body Area Networks (WBANs), the tradeoff between network throughput and energy efficiency remains a key challenge. Most current transmission schemes try to cope with the challenge from the perspective of general Wireless Sensor Networks (WSNs), which may not take the peculiarities of WBAN channels into account. In this paper, we take advantage of the correlation of on-body channels in walking scenarios to achieve a better tradeoff between throughput and energy consumption. We first analyze the characteristics of on-body channels based on realistic channel gain datasets, which are collected by our customized wireless transceivers in walking scenarios. The analytical results confirm the rationale of our newly proposed transmission scheme A3NC, which explores the combination of the aggregative allocation (AA) mechanism in MAC layer and the Analog Network Coding (ANC) technique in PHY layer. Both theoretical analyses and simulation results show that the A3NC scheme achieves significant improvement in upload throughput and energy efficiency, compared to the conventional approaches.

Wireless Body Area Network (WBAN) has been considered as a revolutionary technology to address current healthcare needs. However, before the extensive deployment of WBAN, one main challenge to be met is how to balance the trade-off between data transmission rate and energy efficiency. In this paper, we utilize WBAN's spatial correlation characteristics during movement and propose an efficient cross-layer scheme, named A3NC, which combines analog network coding (ANC) and MAC layer channel allocation. Our simulation results show that the A3NC scheme achieves significant improvement in upload throughput and energy efficiency compared to the conventional approaches. Meanwhile, our scheme also maintains a better balance between correlated sensors' upload throughput.

Cooperative retransmission can significantly improve link reliability over lossy and time-varying wireless links. However, comparing retransmission protocols is challenging, and generally requires simplistic assumptions specific to each protocol. In this paper, we develop a general model to evaluate cooperative retransmission protocols with distributed, slot-based contention algorithms. Specifically, we propose to calculate the relay time-out probabilities at a MAC time-slot scale, formulate retransmission outcomes as functions of the time-out probabilities, and derive the probability of a retransmission process for every data frame. We also propose a Markov extension of our model to characterise the dependency between retransmissions of multiple frames. This enables our model to analyse continuous retransmissions of successive frames. Validated by QualNet simulations, our model can analytically predict the probabilities of cooperative retransmissions with an accuracy of ±1%. As a result, direct comparisons between cooperative retransmission protocols become tangible, without implementing the full protocol in a state-based simulator.

Light field (LF) rendering is widely used in free viewpoint video systems (FVV). Different methods have been proposed to employ depth maps to improve the rendering quality. However, estimation of depth is often error-prone. In this paper, a new method based on the concept of effective sampling density (ESD) is proposed for evaluating the depth-based LF rendering algorithms at different levels of errors in the depth estimation. In addition, for a given rendering quality, we provide an estimation of number of rays required in the interpolation algorithm to compensate for the adverse effect caused by errors in depth maps. The proposed method is particularly useful in designing a rendering algorithm with inaccurate knowledge of depth to achieve the required rendering quality. Both the theoretical study and numerical simulations have verified the efficacy of the proposed method.

In this study, the authors investigate energy efficiency in antenna selection multi‐input multi‐output automatic repeat request (MIMO ARQ) wireless systems. The authors first derive an approximate expression for the average frame‐error rate (FER) in antenna selection MIMO systems over quasi‐static Nakagami‐ m fading channels. The FER approximation is then used to obtain an analytical expression of an energy‐efficiency metric that is defined as the total energy required to successfully deliver one information bit. The authors prove that this energy‐efficiency metric is a quasi‐convex function with respect to the average signal‐to‐noise ratio value. Based on this analysis, the authors obtain the optimal value of the average energy per transmitted data symbol such that the total energy consumption in the system is minimised. The results show that the energy efficiency in antenna selection MIMO ARQ systems is improved when the number of equipped antennas is increased. Simulation results are provided to validate the analysis.

In a light field-based free viewpoint video (LF-based FVV) system, effective sampling density (ESD) is defined as the number of rays per unit area of the scene that has been acquired and is selected in the rendering process for reconstructing an unknown ray. This paper extends the concept of ESD and shows that ESD is a tractable metric that quantifies the joint impact of the imperfections of LF acquisition and rendering. By deriving and analyzing ESD for the commonly used LF acquisition and rendering methods, it is shown that ESD is an effective indicator determined by system parameters and can be used to directly estimate output video distortion without access to the ground truth. This claim is verified by extensive numerical simulations and comparison to PSNR. Furthermore, an empirical relationship between the output distortion (in PSNR) and the calculated ESD is established to allow direct assessment of the overall video distortion without an actual implementation of the system. A small scale subjective user study is also conducted which indicates a correlation of 0.91 between ESD and perceived quality.

This paper aims at minimising the video downstream bit rate of immersive video conferencing (IVC) applications by judiciously modifying the video quality based on the relative virtual positions of participants in the virtual environment. The paper reports on the results of a user study to assess the influence of participants' perspectives on the perceptual impact of relevant video parameters, such as resolution and frame rate. A mathematical model for video rate is proposed that expresses the total rate as the product of spatial resolution and frame rate. Results from the user study are combined with the proposed model to predict the rate parameters which will result in perceptually acceptable quality for a given user perspective. The simulation results show that by exploiting the proposed method, the downstream network load for the client can be significantly reduced with little or no impact on the perceived quality.

In this paper, we derive the random coding error exponent of amplify-and-forward (AF) relay networks in presence of arbitrary number of independent and identically distributed (i.i.d.) interferers both at the relay and the destination. Multiuser networks are common examples of interference limited networks. We derive the ergodic capacity of the network and present simulation results on the performance of the network where we compare the capacity and error exponent performance of interference limited networks with noise limited networks. Numerical results show that noise limited networks outperform interference limited networks even when only a very few interferers exist in the network.

This is a simulation study of weight-based and precedence-based clustering paradigms in VANETs under an experimentally-derived channel model. The study reveals that CH election schemes accounting for driver intention form more stable and long-lived clusters. The results also show that ignoring elements of the VANET channel (such as vehicular shadowing) results in an unreliable comparative analysis of protocol performance.

We investigate the network connectivity of Vehicular Ad Hoc Networks (VANETs) for a typical highway at the free flow state. We propose a new approach to model the spatial distribution of vehicles in a given area using the statistical properties of spatial point patterns. We consider the VANET as a homogenous Poisson point process in which the number of vehicles per unit area has a Poisson distribution. The main advantage of such an approach is its ease of translation to a practical system. Our proposed model provides an analytical result for the vehicles' nearest-neighbour distance distribution. We present simulation results to verify the obtained closed form solution of the network connectivity. Our model is verified by comparing it to real data obtained from the Bureau of Transport Statistics (BTS) NSW, Australia. The main advantage of our proposed model is reducing data acquisition in measuring of data, as the network connectivity can be studied dynamically using aerial images taken by aerial traffic monitoring systems. Another advantage is the ease with which arbitrary function for transmission coverage areas (e.g., antenna radiation pattern) can be included in the final closed form solution which shows capability and flexibility of the proposed model.

Cooperative retransmission schemes can significantly improve transmission reliability and performance over high loss and time-varying links. However, analytically comparing performance between retransmission strategies is challenging and generally requires simplistic assumptions. This paper presents a general model for the performance of distributed, slot-based contention algorithms for opportunistic decode and forward retransmission algorithms. The model is independent of specific modulation or coding schemes and may be adapted to suit state-based transmission probability models. The model is validated through QualNet simulations.

Acquisition of a free viewpoint video (FVV) system is theoretically considered as a problem of plenoptic signal sampling. It is typically performed by using a regular camera grid. While a regular acquisition itself results in non-uniform sampling density, this non-uniformity does not match the scene complexity and frequency variations. This paper proposes an irregular acquisition method for optimum non-uniform plenoptic sampling corresponding to the variations of the scene complexity. Specifically, scene complexity is measured through analyzing DCT coefficients of reference images of the scene, describing the frequency behavior of the plenoptic signal over the scene space. An optimization model is formulated to calculate the optimum configurations of the acquisition cameras including positions and orientations. The theoretical analysis and numerical simulations demonstrate that the rendered video quality can be significantly improved (around 40% in mean PSNR) by employing the proposed irregular acquisition compared with the regular camera grid.

In a free viewpoint video system, the scene is captured by a number of cameras and it would be desirable to optimize the configuration of cameras, such as their location or orientation, to improve the rendering quality. This paper introduces a mathematical representation of the multi-camera geometry, called the correspondence field (CF), which can be used to quantify the suitability of a camera configuration for a given arrangement of objects in the scene. The correspondence field describes the spatial topology of the intersecting rays of cameras, arranged as a number of layers or surfaces in the field of view of cameras. The paper derives the topology of CF for certain camera arrangements and analyzes the impact of changes in camera location or orientation on this topology. It demonstrates that CF can be used to find the optimum camera configuration for a given objective. It also presents simulation results of this method using our light field simulator.

Calculation of the number of cameras required to capture the scene is an essential problem in a practical light field based free viewpoint video (FVV) system. Existing methods calculate the Nyquist rate by assuming a band-limited signal and perfect reconstruction of an arbitrary view using linear interpolation, which often results in an impractically high number of cameras. This paper proposes a new method based on the concept of effective sampling density (ESD). It is demonstrated that there is a trade-off between the depth information accuracy, the required number of cameras, and the desired rendering quality, which could be exploited to minimize the number of cameras for a given objective. Theoretical and numerical results show that the resulting number of cameras is significantly lower than what was reported in other studies with only a few percent reduction in the output PSNR. Moreover, it is shown that the methods proposed in those studies are special cases of the one presented in this paper.

In this paper we analyze the outage performance of a multihop cooperative relay network where relays in the system can change positions dynamically and use all possible links to forward the message to the next hop over Rayleigh fading channels. We derive the general closed form expression of outage probability and asymptotic coding gain of the network.

In this paper we analyze the error performance of a cooperative multihop parallel relay network over Nakagami-m fading channels using M-ary Phase-shift keying (MPSK) modulation. We derive the general closed form expression of the symbol error probability (SEP) and present numerical results on the performance of the network.

In harsh and hostile environments, swift relocation of currently deployed nodes in the absence of centralized paradigm is a challenging issue in WSNs. Reducing the burden of centralized relocation paradigms by the distributed movement models comes at the price of unpleasant oscillations and excessive movements due to nodes' local and limited interactions. If the nodes' careless movements in the distributed relocation models are not properly addressed, their power will be exhausted. Therefore, in order to exert proper amount of virtual radial/angular push/pull forces among the nodes, a fuzzy logic relocation model is proposed and by considering linear combination of the presented performance metric(s)(i.e. coverage, uniformity, and average movement), its parameters are locally and globally tuned by particle swarm optimization(PSO). In order to tune fuzzy parameters locally and globally, PSO benefits respectively from nodes' neighbours within different ranges and all the given deployed area. Performance of locally and globally tuned fuzzy relocation models is compared with one another in addition to the distributed self-spreading algorithm (DSSA). It is shown that by applying PSO to the linear combinations of desired metric(s) to obtain tuned fuzzy parameters, the relocation model outperforms and/or is comparable to DSSA in one or more performance metric(s).

CORNER is an urban propagation model which simulates the presence of buildings in city scenarios and models radio propagation as a series of reflections and diffractions around buildings. CORNER was validated in the original publication with a series of packet-delivery-ratio measurements. However, the accuracy of these measurements is limited by interference from nearby networks. This paper independently evaluates the CORNER model using signal strength measurements across three separate sites in Sydney and Wollongong. The measurements are analysed and compared with the predicted analytical estimates. The fading model is also analysed with direct measurements. A new CORNER link classification algorithm is also proposed in this paper.

This paper investigates the performance of the space-time-frequency coded (STFC) multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) system over wireless body area network (WBAN) channels, using the Alamouti code. Different MIMO configurations and different modulations are used for comparison. The effect of body directions is also assessed by simulation in this paper. Simulation results show that the proposed STFC MB-OFDM UWB system provides a significantly better BER performance, compared to the conventional MB-OFDM system, even from a reasonably low Eb/Norange. The simulations also confirm that the body direction affects the system performance significantly due to the availability of line-of-sight (LOS) or partial LOS paths. Overall, the STFC MB-OFDM UWB system can provide an energy efficient and robust, high data rate transmission for WBAN applications.

Accurate modelling of the radio channel is often the most difficult aspect of a Vehicular Ad Hoc Network (VANET) simulation due to the large variability present in vehicular terrain. CORNER is a propagation model that calculates path-loss in an urban terrain with a large concentration of buildings, based on the position of the transmitter and receiver on a street map. This paper proposes additions to the CORNER propagation model to take selective multi-path fading into account and investigates the performance of the GPSR routing protocol under the CORNER propagation model in a realistic city environment.

In this paper, the application of space time trellis codes to multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) systems is investigated. We propose a coding scheme that could fully exploit all the available channel diversity, including space diversity, frequency diversity and inter-subband diversity. Performance of the proposed system is compared with that of the conventional MB-OFDM UWB system in terms of packet error rate (PER). Simulation results show that this system outperforms the conventional one. As an example, an improvement of at least 5 dB at PER=10-2 could be achieved over the IEEE 802.15.3a channel models of CM1 and CM2 in the system equipped with only two transmit antennas and one receive antenna. Moreover, the system performance could be further improved when the number of antennas and/or the number of trellis states is increased.

In this paper we present a generalization of the concept of car-pooling for a public transport system, in which members of the community donate their trips to the 'transport commons'. The proposed system will then match the passengers to vehicles based on a range of criteria, including trip times, personal choices and economic incentives. We develop an analytical model to determine the probability of obtaining a ride from the transport commons in a worst-case scenario. The results of the analysis as well as simulation study demonstrate that the transport commons can provide a practical basis for a dependable public transport service.

A video rate control mechanism based on a modified LMS algorithm is presented. The control mechanism is used within a real-time IP multicast based system. Simulation results show that such a control mechanism allows the system to adapt to the varying network conditions of receiving clients.

Light field rendering (LFR) is an active research area in computer vision and computer graphics. LFR plays a crucial role in free viewpoint video systems (FVV). Although several rendering algorithms have been suggested for LFR but the lack of appropriate datasets with known ground truth has prevented a comparison and evaluation study of LFR algorithms. In most of the LFR papers the method is applied to several test cases for validation and as a result, just a subjective visualized output is given. To overcome this problem, this paper presents a quantitative approach for comparison and evaluation of LFR algorithms. The core of the proposed methodology is a simulation model and a 3D engine. The platform produces the reference images and ground truth data for a given 3D model. Subsequently, data are injected to a comparison engine to compare synthesized images from light field engine with original images from simulation, generating objective results for evaluation. The methodology is highly flexible and efficient to automatically generate LFR datasets and objectively compare and analyze any subset of LFR methods for any given experiment design scheme. Five key rendering algorithms are evaluated with proposed methodology to validate it. Overall, it is shown that the proposed quantitative methodology could be used for LFR objective evaluation and comparison.

Physical damage and/or node power exhaustion may lead to coverage holes in WSNs. Coverage holes can be directly detected by certain proximate nodes known as boundary nodes (B-nodes). Due to the sensor nodes' redundant deployment and autonomous fault detection, holes are surrounded by a margin of B-nodes (MB-nodes). If all B-nodes in the margin take part in the hole recovery processes, either by increasing their transmission power or by relocating towards region of interest (ROI), the probability of collision, interference, disconnection, and isolation may increase affecting the rest of the network's performance and QoS. Thus, distributed boundary node selection algorithms (BNS-Algorithms) are proposed to address these issues. BNS-algorithms allow B-nodes to self-select based on available 1-hop information extracted from nodes' simple geometrical and statistical features. Our results show that the performance of the proposed distributed BNS-algorithms approaches that of their centralized counterparts.

Light field rendering (LFR) is an active research area in computer vision and computer graphics. LFR plays a crucial role in free viewpoint video systems (FVV). Several rendering algorithms have been suggested for LFR. However, comparative evaluation of these methods is often limited to subjective assessment of the output. To overcome this problem, this paper presents a geometric measurement, Effective Sampling Density of the scene, referred to as effective sampling for brevity, for objective comparison and evaluation of LFR algorithms. We have derived the effective sampling for the well-known LFR methods. Both theoretical study and numerical simulation have shown that the proposed effective sampling is an effective indicator of the performance for LFR methods.

Opportunistic cooperation promises to enhance the user experience when streaming media over wireless devices by improving wireless network reliability at the link level. This paper presents DAFMAC, an efficient cooperative diversity partner selection algorithm for IEEE 802.11 devices. Simulation results show DAFMAC provides a significantly higher transmission reliability in poor channel conditions than traditional ARQ techniques without modifying the device hardware. Further analysis shows the low overhead of DAFMAC makes it highly competitive with other proposed cooperative retransmission mechanisms in an ad-hoc network.

In this paper we analyze the outage probability of a cooperative multihop parallel relay network in Nakagami-m fading channels. The general closed form expression of the outage probability is derived both for integer and arbitrary Nakagami parameter m. We present numerical results on the performance of the network. It shows a careful configuration of the network size and power sharing between nodes can ensure optimal outage performance in the network.

In this paper we focus on the subcarrier allocation for the uplink OFDMA based cooperative relay networks. Multiple cells were considered, each composed of a single base station (destination), multiple amplify and forward (AF) relay stations and multiple subscriber stations (sources). The effects of inter-cell interference (ICI) have been considered to optimize the subcarrier allocation with low complexity. The optimization problem aims to maximize the sum rate of all sources and at the same time maintain the fairness among them. Full channel state information (CSI) is assumed to be available at the base station. In the proposed algorithm the subcarrier allocation is performed in three steps; firstly the subcarriers are allocated to the Relay Stations (RSs) by which the received ICI on each RS is minimized. Then, the pre-allocated subcarriers are allocated to subscribers to achieve their individual rate requirements. Finally the remaining subcarriers are allocated to subscribers with the best channel condition to maximize the total sum of their data rates. The results show that the proposed algorithm significantly reduces the complexity with almost the same achievable rate of the optimal allocation in a single cell case. In case of multi-cell, the proposed algorithm outperforms the conventional algorithm in terms of total network achievable data rate and overall network complexity.

This paper evaluates the performance of the IEEE 802.11 broadcast traffic under both saturation and non- saturation conditions. The evaluation highlights some important characteristics of IEEE 802.11 broadcast traffic as compared to corresponding unicast traffic. Moreover, it underlines the inaccuracy of the broadcast saturation model proposed by Ma and Chen due to the absence of backoff counter freeze process when channel is busy. Computer simulations are used to validate the accuracy of the new model and demonstrate the importance of capturing the freezing of backoff counter in the analytical study of IEEE 802.11 broadcast.

Over the years, a considerable research effort has been applied to the design of ad hoc network routing protocols. However, there is still a lack of understanding of the subtle interactions between routing protocols and lower layers in the protocol stack. In this paper, the instability which may arise when reactive routing protocols interact with the IEEE 802.11 MAC protocol is investigated. In particular, several erratic behaviours of the Ad hod On-demand Distance Vector (AODV) routing protocol in a congested IEEE 802.11 ad hoc network are demonstrated. A cross-layer solution is proposed based on an Adaptive Bulk Trigger policy and a Dynamic Window Selection scheme. Simulation studies are presented which show that the proposed solution is effective in alleviating erratic behaviour of AODV and improving the end-to-end path stability.

Massively multiplayer online role playing games feature huge maps that can be partitioned into smaller components called zones to achieve scalability. In peer-to-peer (P2P) systems, those zones can be assigned to peers who are willing to take up the role of zone servers. A seamless map requires inter-zone communications to allow interactions between players across zone boundaries. In assigning zones to peers, it is critical to seek approaches to reduce the inter-zone communication cost in P2P system. In this paper, we formulate the zone assignment problem for P2P system and demonstrate that the problem is NP-hard. We hence propose a low-cost heuristic that partitions the physical network into bins, as well as, aggregating the partitions of the virtual world by clustering neighboring zones in a game map. We then demonstrate that by assigning clustered neighboring zones in the virtual map into peers in common physical network bins, we are able to achieve similar inter-zone communication cost for the zone assignment problem as that can be achieved by the optimization model we formulated, while avoiding the prohibitively high computation cost required by the latter.

In our previous work, we proposed a distributed server architecture to deliver multi-party immersive voice communication service to mobile clients (e.g. Sony PSP) accessing a distributed virtual environment (DVE). We refer to such immersive voice communication service as mobile immersive communication environment (MICE). We also proposed solutions to assign server to create the auditory scene for each avatar. In this work, we ascertain the necessary update period of server reassignment in order to cope with avatar mobility in the virtual world. In our simulations, we measure the percentage differences in delay deviation and bandwidth cost between the case of no server reassignment update since t=l second (the initial time instant) and the case of ideal server reassignment at every second. Our results show that the impact of avatar mobility leads to increases in both delay deviation and bandwidth cost as the time elapse further from t=l second. Such increase in delay deviation and bandwidth cost is more significant at the low avatar densities than at the higher avatar densities. The optimal server assignment algorithm is found to be too computationally intensive to be executed within the required update periods. A much faster greedy heuristic has been devised to perform server assignment within the required update periods.

Fairness and playability in online multiplayer games Playability and fairness are crucial elements of an enjoyable online game experience. The unavoidable propagation time introduced by the geographical distance between participants can deteriorate the game responsiveness and playability. Also, differences in these delays can provide unfair advantages and/or disadvantages to different players. This paper explores the causal relationships between propagation time, inconsistencies, playability and fairness in online multiplayer games. It clearly defines causes of unfairness and introduces a theoretical quantification supported by an experimental technique to evaluate it in simulations. It also demonstrates through simulations the impact of changes in network architecture and topology on playability and fairness.

This paper investigates the minimisation of the computational cost of providing Immersive Voice Communication (IVC) for mobile clients attached to a Distributed Virtual Environment (DVE). When experiencing IVC, each listening avatar in the DVE, receives a mix of the surrounding avatars’ voices, all rendered according to their respective positions in the virtual world. We propose to deliver our mobile IVC service using a type of server-based network architecture to perform voice spatialisation function and mixing for each mobile client. This model will minimise both the access bandwidth and processing power requirements of the mobile devices. We propose a model for computation reduction in servers that re-uses the result of audio spatialisation for several clients by allowing certain level of voice localisation error. Using Linear Programming (LP), we have developed two optimisation formulations to examine different scenarios of applying the computation reduction scheme, with different avatar densities and under varying rendering accuracy constraints. The insights gained from our analytical results should benefit future IVC service providers for mobile DVE.

Multicasting of real-time streams (voice, video, etc.) for interactive communication in networked virtual environments (V.E.) is becoming an increasingly important service. Here as an example characteristics of interactive voice scenes for participants in a V.E. are presented. Proxy based overlay multicasting of real-time streams is a candidate architecture for this type of service. Here we propose a scheme for angular clustering of destination proxies in multi dimensional network geometric spaces as the core algorithm for construction of efficient overlay multicast trees. We show that using the proposed angular clustering scheme it is possible to construct source rooted overlay trees with acceptable delay and overhead traffic performances.

In this work, we propose a peer-to-peer (P2P) voice delivery architecture for the support of an immersive communication environment (ICE). An ICE service allows multiple users in a distributed virtual environment (DVE) to exchange live voices which are rendered with the directional and distance cues corresponding to the users' positions in the DVE. Our architecture addresses the scalability issue in peer access bandwidth consumption encountered by the "brute force" full- mesh P2P architecture. On the other hand, our P2P architecture seeks a good balance between access bandwidth scalability and the voice quality delivered. The three key aspects of voice quality considered are voice transmission delay, directional voice rendering accuracy and voice attenuation accuracy. Our P2P architecture achieves access bandwidth reduction by organising all the pair-wise close peers into non-overlapping clusters and by mixing the voice streams within the same cluster so as to reduce the number of direct peer to peer voice exchanges. Different sets of experiments were conducted to compare the performances of our P2P architecture against the benchmark of the full-mesh P2P architecture.

In this paper a scheme for peer-to-peer (p2p) multiparty voice communication is proposed. The paper considers realistic constraints on the upstream and downstream bandwidth of peers and their processing capacity. We propose a novel mechanism for distributed mixing of the audio streams that can improve the scalability of this service while meeting the capacity constraints. The paper also proposes an algorithm to form a multipoint-to-multipoint spanning tree (MMST) among the peers within a communication zone. The simulation results show that the performance of algorithm in terms of delay stretch and its impact on bandwidth reduction in comparison to multiple source rooted overlay multicast trees is quite acceptable.

In this paper we propose a system design for delivery of immersive communications to mobile wireless devices based on a distributed proxy model. It is demonstrated that this architecture addresses key technical challenges for the delivery of these services, that is, constraints on link capacity and power consumption in mobile devices. However, additional complexity is introduced with respect to mobility management. The paper proposes three possible methods for updating proxy assignments in response to mobility and compares the performance of these methods

Delivery of immersive communications to mobile devices presents several technical challenges. These include the limitations of wireless link bandwidth and scarcity of computational resources in mobile devices. We propose a system design to overcome these bottlenecks based on a distributed proxy model where bandwidth management tasks and low level functions associated with service mobility are implemented in proxies within the fixed network infrastructure. However, additional complexity is introduced with respect to mobility management. This is associated with both mobility of avatars in the virtual world and movement of users in the physical world. This paper proposes an efficient method to enable adaptation of the communication flows between the distributed proxies in response to both virtual and physical movements.

This paper develops a scalable system design for the creation, and delivery over the Internet, of a realistic voice communication service for crowded virtual spaces. Examples of crowded spaces include virtual market places or battlefields in online games. A realistic crowded audio scene including spatial rendering of the voices of surrounding avatars is impractical to deliver over the Internet in a peer-to-peer manner due to access bandwidth limitations and cost. A brute force server model, on the other hand, will face significant computational costs and scalability issues. This paper presents a novel server-based architecture for this service that performs simple operations in the servers (including weighted mixing of audio streams) to cope with access bandwidth restrictions of clients, and uses spatial audio rendering capabilities of the clients to reduce the computational load on the servers. This paper then examines the performance of two components of this architecture: angular clustering and grid summarization. The impact of two factors, namely a high density of avatars and realistic access bandwidth limitations, on the quality and accuracy of the audio scene is then evaluated using simulation results.

A growing area of technical importance is that of distributed virtual environments for work and play. For the audio component of such environments to be useful, great emphasis must be placed on the delivery of high quality audio scenes in which participants may change their relative positions. In this paper we describe and analyze an algorithm focused on maintaining relative synchronization between multiple users of such an environment and examine the subjective quality of service achieved.

Service and application requirements on network resilience have increased over the past few years. New on-line services such as e-commerce and connection-oriented interactive real-time services require higher network resilience than the more traditional off-line services. Programmable virtual networks promise fast and easy provisioning of new services but no consideration to meet the diverse resilience requirements has been made. This paper discusses issues related to resilience-differentiation in programmable virtual networks. A set of general guidelines is presented that apply to resilience-differentiation in programmable virtual network architectures. A case study is used to illustrate how the proposed guidelines can be met by extending an existing programmable virtual network architecture.

This paper discusses issues in providing immersive audio communication to massively multi-player online games (MMOG). We focus on network and server architectures for creating immersive audio scenes for game clients. We examine advantages and limitations of several architectures, including central server, distributed servers, and peer-to-peer architectures. We focus on a dynamic centralized server architecture which is suitable for the current MMOG in terms of sealability at end users and resource efficiency. We propose algorithms to optimize the performance of a centralized server. Finally, a simulation study is carried out to evaluate the performance of our proposed centralized server architecture and provide some comparisons with others in term of delays and network resource usage.

This paper examines appropriate network and server infrastructures for the provision of a realistic audio scene from the perspective of avatars in large-scale virtual environments. The audio scene of each avatar combines the voices and other sources of sound in the vicinity of the avatar, spatially placed, attenuated according to distance from the listener, and addition of sound effects to reflect the acoustic characteristics of the environment. We examine a range of delivery options including central-server, peer-to-peer with and without multicast, distributed proxies, distributed locale servers, and a hybrid model. We provide numerical results on the effect of different virtual world characteristics such as avatar density, hearing range, and correlation between the positions in the virtual and physical worlds. We compare delivery architectures based on a set of delay metrics aimed at measuring the interactive delay between avatars as well as accuracy of the scene. We make several recommendations on scalable implementation of such applications.

Optical burst switches (OBSes) have been proposed to improve the utilization of a network of optical cross connect (OXCs). Current studies on OBS assume a network consisting of OBSes alone. While this is a reasonable assumption for evaluating a new technology, the question of how a network of OXCs can be evolved to a network of OBSes has not been studied. In this paper, we propose a hybrid architecture consisting of OBSes at the network edge and OXCs in the network core. This architecture allows carriers to gradually migrate from an OXC-based network to an OBS-based network with an improved network utilization. In addition, we use queueing analysis to study the performance of this new architecture.

Active and programmable networks allow innovative new services to be deployed rapidly. However, in a carrier grade network, it is imperative to maintain a scalable fast path mechanism so that the delay and throughput requirements are met. This is particularly important since, in many cases, network-level processing is only needed for a subset of packets and the remainder of traffic must be forwarded on the fast path. It is a challenge to design a cost effective node architecture that can satisfy this requirement. Current models are often 'revolutionary' and may not scale to the required performance levels of a carrier grade network. We develop an evolutionary architecture that uses MPLS label stacks to enable efficient and scalable extraction of active packets from the fast path without penalising the rest of the traffic. Our model can be used to extend the reach of programmable networks over a legacy infrastructure and provide a migratory path for existing carriers towards a programmable infrastructure.

This paper proposes to use a programmable network to offer a new type of wholesale product. By augmenting the wholesale of carriage with the wholesale of network-based computation, the need for server overlay deployment to support retail service providers is reduced or eliminated. The paper develops an efficient algorithm for allocation and management of processing and transport resources. This algorithm is designed to optimize a large network supporting many retail service providers. The algorithm is based on the Lagrangian relaxation method and provides error bounds so that the accuracy of the solution can be ascertained. Numerical results are presented and the benefit of the optimization for a simple multiservice scenario is assessed.

This paper explores the potential benefits of programmable networks for telecommunication carriers. It particularly focuses on using a programmable network to offer a new type of wholesale product by adding value to the wholesale of pure carriage. By augmenting the wholesale of carriage with the wholesale of network-based computation, the need for server overlay deployment to support retail service providers is reduced or eliminated. The paper develops an efficient algorithm for allocation and management of computation and transport resources within the network infrastructure. This algorithm is designed to optimize a large network supporting many retail service providers and can be used by the wholesaler for the optimal management of scarce computational and transport resources. The algorithm is based on the Lagrangian relaxation method and provides error bounds so that the accuracy of the solution can be ascertained. Numerical results are presented and the benefit of the optimization for a simple multi-service scenario is assessed.

This paper deals with the problem of dynamic allocation of bandwidth in a hierarchical transport platform. By hierarchical we mean that the crossconnect platform is comprised of both broadband and wideband crossconnects which react to fluctuations of traffic on different time scales. The model developed in this paper takes advantage of both the multi-service and multi-hour character of traffic profiles. Obtaining a minimum-cost network for multi-hour traffic profile for multi-service is a large scale optimisation problem. We formulate the problem of capacity variation for a long term time scale as mixed integer programming and for a short term time scale as linear programming problems and examine the problem complexity in terms of the number of variables and constraints.

This paper deals with the ring network architectures for provision of switched broadband services. After a cost comparison of several architectures based on SDH and ATM self-healing rings, the paper proposes the self-healing wheel topology and protocol. The self-healing wheel leads to simpler peripheral nodes, allows the possibility of using existing SDH add/drop multiplexer nodes and achieves bandwidth utilisation superior to an ATM ring. It also provides the opportunity of offering non-protected services up to the level of an equivalent star topology. It is shown that in high growth environments, the self-healing wheel will outperform all the other architectures in terms of cost and efficiency.

This paper introduces a new cost based network planning approach where the main concern of the planner is decreasing the product unit cost rather than increasing the resource utilisation. The paper identifies inherent trade-offs in the network architecture that take advantage of the disparity between the cost of carriage components. Considering previous trends in the cost of hardware, software, and labour, the paper proposes a flat network architecture in accordance with the prevailing trend. It identifies the limitations of the current concept of ATM virtual paths in decoupling between the switching and transport utilisation. Consequently, it proposes a new approach to the operation of virtual paths called discordant virtual paths that enables maximum switching layer utilisation while maintaining an under-utilised transport platform. The discordant virtual path approach allows the network operator to adapt to variations in the cost of components.