1,720,970 research outputs found
QoS-Constrained Traffic Engineering for Interference-affected Wireless Mesh Networks with Network Coding
No full textThis thesis focuses on the QoS-constrained Traffic Engineering (TE) of Wireless Mesh Networks (WMNs) affected by Multiple Access Interference (MAI). The goal is to develop a tool for the optimization of network/physical resource allocation that enable to design WMNs supporting multicast multimedia sessions with different Quality of Service (QoS) requirements when intra-session Network Coding (NC), besides routing, can be performed at the network nodes.
A wide-applicability integrated framework is proposed, that allows to jointly optimize session utilities, flow control, QoS differentiation, intra-session network coding, Media Access Control (MAC) design and power control. To cope with the nonconvex nature of the resulting cross-layer optimization problem, this thesis proposes a two-level decomposition that provides the means to attain the optimal solution through suitably designed convex subproblems. Sufficient conditions for the feasibility of the primary (nonconvex) problem and for the equivalence to its related (convex) version are derived. Furthermore, a general procedure to devise simple polyhedral outer-bounds of the capacity region, which will be shown to have a key role in the decomposition, has been developed.
Algorithmic implementation of the two-level decomposition is discussed in both centralized and distributed approaches. Moreover, the asynchronous, iterative Distributed Resource Allocation Algorithm (DRAA), that quickly self-adapts to network time-evolutions (e.g., node failures and/or fading fluctuations), is developed. Numerical results that delve into the potential of both the proposed solution and the resource allocation algorithm, are provided. In detail, the two-level decomposition will be tested in unicast, multicast and multisource scenarios so as to show the performance gain achievable by the joint optimization with respect to the conventional solutions
Interference Management for Multiple Multicasts with Joint Distributed Source/Channel/Network Coding
No full textThis paper focuses on the QoS-constrained jointly optimal adaptive distributed source coding, channel coding, network coding and power control for Co-Channel Interference (CCI)-limited wireless multiple class multicast networks, such as, for example, Wireless Sensor Networks (WSNs). The goal is to allocate the available system-wide resources by jointly performing Loss-Less Distributed Source Coding (LLDSC) and Intra-Session Network Coding (ISNC), while leveraging channel coding and power control for CCI-mitigation. Due to the presence of CCI, the resulting cross-layer optimization problem is inherently nonconvex. Hence, we develop a distributed, iterative and asynchronous algorithm for the optimal adaptive QoS management of the available bandwidth/power/flow resources. Actual performance and adaptive capability of the proposed resource management algorithm in the presence of: i) abrupt changes of the statistics of the source flows; ii) failures of the interior network nodes; and, iii) fast fading, are numerically tested
UltraWide Band Cognitive Pulse Shaping under Physical-Layer QoS Constraints
No full textUltra Wide Band (UWB) communication systems operate in the frequency range between 0 and 10.6 GHz so they induce the Scientific Community to solve the problem of coexistence with concurrent telecommunication services. This is the leading reason why both the Federal Communications Commission (FCC) and the European Telecommunications Standards Institute (ETSI) gave strict indications about the spectral limits to be respected and require the transmitter and receiver to be compliant with these spectral masks. To this end, it is mandatory to carefully shape the UWB pulse, for this can be accurately designed so as to avoid severe performance reduction while guarding inter-systems coexistence. The UWB technology and, more, the pulse shaping allow to apply the cognitive paradigm where the transmitter and receiver are the actors of this functionality since the performance are tied to channel features and interference presence. The widespread choice of Gaussian-like pulses has proven, however, largely suboptimal from a power emission point of view since they fail to optimize performance. Goal of this contribution is to show how to achieve a good compromise between spectral emission, rate and synchronization errors robustness, via a modified version of the Parks-McClellan method, considering channel impairments due to its frequency-selective nature and to the inter-pulse interference
Optimal Cross-Layer flow-control for wireless Maximum-Throughput delivery of VBR media contents
No full textEmerging media overlay networks for wireless applications aim at delivering Variable-Bit-Rate (VBR) encoded media contents to nomadic end-users by exploiting the (fading-impaired and time-varying) access capacity offered by the "last-hop" wireless channel. In this application scenario, a still open question concerns the design of control policies maximizing the average throughput over the wireless last-hop, under constraints on the maximum connection bandwidth allowed at the Application (APP) layer, the queue-capacity available at the data-link (DL) layer, and the average and peak transmit energies sustained by the Physical (PHY) layer. The main feature of the approach we follow relies on the maximization (on a per-slot basis) of the throughput averaged over the fading statistics and conditioned on the queue-state. The resulting optimal controller is rate-based and operates in a cross-layer fashion that involves the APP, DL and PHY layers of the underlying protocol stack. This means that the proposed controller dynamically allocates connection bandwidth at the APP Layer, throughput at the DL layer and transmit energy at the PHY layer by basing on both current queue and channel states. The carried out numerical tests give insights about the connection bandwidth-vs.-queue delay tradeoff attained by optimal controller. ©2009 IEEE
A Secrecy Constrained Power Allocation for MIMO Wire-Tap Channels
No full textSince a wireless transmission requires to access to a shared medium, the communication is susceptible to adversarial eavesdropping. This paper describes how eavesdropping can potentially be limited by resorting to waterfilling-like algorithms with additional constraints. A Gaussian wiretap channel (WTC) is considered in which a transmitter sends confidential messages to its reference receiver in the presence of a passive eavesdropper. We approach the problem from two different perspectives, focusing either on the rate of the main link or the secrecy level. Through numerical analysis, we show how the information-secrecy regions can be the means to evaluate the quality of the main link and the secrecy level, resulting from our algorithms application. Finally we analyze the case of interfering signals (induced by users sharing the same transmission resource) to show their effects on both information rate and secrecy, even in the case of an eavesdropper able to mitigate the interference
QoS traffic engineering for self-adaptive resource allocation in MAI-affected wireless networks
No full textTraffic Engineering application to the cross-layer design of Multiple Access Interference (MAI)-affected powerlimited wireless networks, when Quality of Service constraints are also present, leads to deal with nonconvex resource allocation problems. Although several manageable-complexity solutions have been proposed, they are based on specific capacity functions and, generally, fail to provide reliable results in low-SINR (Signal to Interference plus Noise Ratio) scenarios. We develop a two-level decomposition that is able to find the optimal solution of a wide nonconvex cross-layer problem, which combines user utility, flow control, QoS multipath routing,Medium Access Control (MAC) design and power control, by means of a suitable relaxed convex version of its comprising flow control and power-allocation sub-problems. Sufficient conditions for the equivalence of the primary (nonconvex) problem and its related (convex) version are provided. Moreover, we develop a distributed, iterative, asynchronous algorithm for computing the solution of the overall nonconvex resource allocation problem, that is able to (quickly) self-adapt to possible network time evolutions (as, for example, node failure events) and, most importantly, that may be implemented on top of connectionless networking platforms. Actual performance of the overall proposed solution and its robustness against node-failure events are numerically tested and compared with the corresponding ones of Destination Sequenced Distance Vector-based single-path routing algorithms. © 2011 IEEE
Physical-Layer Goodput Maximization for Power Line Communications
No full textIn this paper, we present a new solution to the well-known integer bit loading problem for Power Line Communication systems, that is able to jointly consider transmission rate and bit error rate (BER) as performance parameters. This goal is achieved by means of a Trellis Coded Modulation (TCM), by taking advantage of its appealing property to combine modulation and coding, so as to state the power allocation problem as an optimization in which both BER and rate are tied to the TCM optimal design. The need to compare such a scheme with others known in the Literature in terms of performances, led us to give a brief insight into the two standard approaches: Maximum Rate (MR) and Minimum BER (MB), which consider as objective functions only rate or BER, respectively. Numerical results are presented to stress how our solution improve system performances, both in ideal condition and with additional impairments such as crosstalk and impulsive noise. ©2009 IEEE
SDMA with Secrecy Constraints
No full textWireless transmission requires the access to a shared medium, so the communication may be susceptible to adversarial eavesdropping. This paper describes how eavesdropping can potentially be limited by resorting to waterfilling-like algorithms by introducing additional constraints. A Gaussian Wire-Tap Channel (WTC) has been considered as the channel in which a transmitter sends confidential messages to its reference receiver in the presence of a passive eavesdropper. In the more general context of an ad-hoc network, we propose two different Space Division Multiple Access (SDMA) techniques by paying attention to the rate of the main link and to secrecy level. Through numerical analysis, we show the information-secrecy regions to evaluate the quality of main link and secrecy level that the algorithms can allow when constrained SDMA is considered. Finally, we evaluate the effect of interference (induced by users sharing the same transmission resource) to evaluate the effect of disturbing signals on information rate and secrecy
Collision erasure and generalized access in MIMO Cognitive ad-hoc networks
No full textMain goal of this work is to give insight on the possible performance improvement arising in the wireless local ad-hoc access from the synergic cooperation of two emerging paradigms, Multi-Antenna and Cognitive radios. The target is the competitive maximization of each access rate in presence of Multiple-Access Interference (MAI) induced by the other accessing terminals. Being the radios cognitive, they are capable to autonomously learn the ambient-context and, then, self-configure their access strategy via suitable power-allocation, that is, timefrequency-code-space signal-shaping. Furthermore, a generalized approach is developed to allow the node to access with a (possibly hybrid) scheme to the medium by combining different x-DMA strategies under QoS-guaranteed access policy. © 2008 IEEE
- …
