Valentina Polli

Optimal self-adaptive QoS resource management in interference-affected multicast wireless networks

In this paper, we focus on the quality-of-service (QoS)-constrained jointly optimal congestion control, network coding, and adaptive distributed power control for connectionless wireless networks affected by multiple access interference (MAI). The goal is to manage the available network resources, so as to support multiple multicast sessions with QoS requirements when intrasession network coding (NC) is allowed. To cope with the nonconvex nature of the resulting cross-layer optimization problem, we propose a two-level decomposition that provides the means to attain the optimal solution through suitable relaxed convex versions of its comprising subproblems. Sufficient conditions for the equivalence of the primary nonconvex problem and its related convex version are derived, occurrence of such conditions investigated, and performance with respect to conventional routing-based layered solutions analyzed. Moreover, we develop a distributed algorithm to compute the actual solution of the resource allocation problem that quickly adapts to network time-evolutions. Performance of this algorithm and its adaptivity are evaluated in the presence of varying network/fading conditions and noisy measurements.

Interference Management for Multiple Multicasts with Joint Distributed Source/Channel/Network Coding

This 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.

Power-Constrained Physical-Layer Goodput Maximization for Broadband Power Line Communication Links

Power Line Communication (PLC) systems are currently envisioned as a possible solution for distributing multimedia contents and allowing Internet access with a capillary (already built) network without demanding further infrastructure. The real challenge for PLCs consists in providing connectivity where Public Switch Telephone Network (PSTN)-based Internet Access and/or Wi-Fi/WiMAX seem to be unable to solve the problem of Digital Divide. In this paper we introduce a new metric, i.e. the goodput, to balance transmission rate and bit error rate (BER) in resource allocation issues for Power Line Communication systems. In detail, we state the well-known integer bit-loading problem as a goodput maximization with constraints on the power consumption and the maximum decoding time. The use of Trellis Coded Modulation (TCM) allows to pursue the goodput maximization weighing error probability and transmission rate which would have otherwise been in trade-off. Numerical results are presented to stress how our solution improves system performances, both in ideal conditions and with additional impairments such as crosstalk and impulsive noise, with respect to the conventional Maximum Rate (MR) and Minimum BER (MB) approaches and to validate the suitability of TCMs in comparison with higher complexity codes.This work proposed a novel optical pickup head with tracking and focusing system in a monolithic device. The device was fabricated by poly-Si trench-refilled technology and used UV polymer droplet as objective lens. In-plane (tracking) and out-of-plane (focusing) motion were decoupled by springs, gimbal structure, and actuators. In results, we successfully demonstrate the proposed device included single tracking system, single focusing, and integrated system. The resonant frequency of tacking and focusing systems are 9.6 kHz and 4.2 kHz respectively

Iterative multiuser resource allocation for inhome Power Line Communications

In a multiuser scenario, the bit-loading, which has proven decisive in resource optimization for Power Line Communications (PLCs), has to be coupled with channel assignment to fully exploit its potential. Unfortunately, finding the most performing combination of channel and power allocation leads to integer (or mixed) programming problems, which are known to be NP-hard. To overcome the complexity of the resulting optimization problem, in this paper we propose an iterative solution that is able to guarantee both fairness and Quality of Service (QoS) to the users when the overall power consumption of the system is bounded and each subchannel emission is limited. This solution embeds a Connection Admission Control (CAC) that allows to leave out badly-connected users that otherwise would negatively affect the comprehensive system performance. Numerical results compare the presented resource allocation with the common greedy-based single user approach.

UltraWide Band Cognitive Pulse Shaping under Physical-Layer QoS Constraints

Ultra 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.

Physical-layer goodput maximization for Power Line Communications

In 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.

Collision erasure and generalized access in MIMO cognitive ad-hoc networks

Main 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, time-frequency-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.

SDMA with secrecy constraints

Wireless 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.

Optimal Cross-Layer Flow-Control for Wireless Maximum-Throughput Delivery of VBR Media Contents

Emerging 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 the optimal controller.

Closed-form scheduling policies for delay-sensitive traffic over fading channels

Next-generation wireless networks for personal communication services should be designed to transfer delay-sensitive (possibly, heavy-tailed distributed) bursty traffic flows over energy-limited buffer-equipped faded connections. In this scenario, a still open question concerns the closed-form design of scheduling policies minimizing the average transfer-delay under constraints on both average and peak energies. The key-point of the novel approach we follow consists in the minimization (on a per step basis) of the queue-length averaged over the fading statistics and conditioned on the queue occupancy at the previous step. We prove that, under the considered energy constraints, the scheduler retains two optimality properties. First, its stability region is the maximal admissible one. Second, the scheduler also minimizes the unconditional average queue-length (over both queue and link state statistics). Finally, we explicitly derive the optimal scheduler expressions and performances for some systems of practical interest.