Tatiana Patriarca

Stochastic traffic engineering for real-time applications over wireless networks

In this work, we focus on the Stochastic Traffic Engineering (STE) problem arising from the support of QoS-demanding real-time media-streaming applications over fading and congestion affected TCP-friendly/IP multiantenna wireless pipes. First, after recasting the tackled STE problem in the form of a suitable cross-layer nonlinear stochastic optimization problem, we develop a traffic analysis of the overall underlying multiple-input multiple-output (MIMO) wireless pipe that points out the relative effects of both fading-induced errors and congestion-induced packet losses on the goodput offered by the resulting end-to-end connection. Second, we develop an optimal cross-layer resource management policy that allows a joint scheduling of the media encoding rate (i.e., playin rate), transmit energy and delivery rate (i.e., playout rate) of each end-to-end connection active over the considered access network. Salient features of the presented joint scheduling policy are that: (i) it is self-adaptive; (ii) it is able to provide hard (i.e., deterministic) QoS guarantees, in terms of hard limited playout delay and playout rate-jitter; and (iii) it explicitly accounts for the performance interaction of the protocols implemented at all layers of the considered stack.

QoS Stochastic Traffic Engineering for the wireless support of real-time streaming applications

In this work, the Stochastic Traffic Engineering (STE) problem arising from the support of QoS-demanding real-time (e.g., delay and delay-jitter sensitive) media-streaming applications over unreliable IP-over-wireless pipes is addressed. Two main contributions are presented. First, we develop an optimal resource-management policy that allows a joint scheduling of the source rate, transmit energy and playout rate. Salient features of the proposed scheduling policy are that: (i) it is self-adaptive; and, (ii) it is able to provide hard (i.e., deterministic) QoS guarantees, in terms of hard limited playout delay, playout rate-jitter and pre-roll delay. Second, by referring to power and bandwidth limited access scenarios, we develop a traffic analysis of the underlying IP-over-wireless pipes that allows us to analyze the effects of both fading-induced errors and congestion-induced packets losses on the end-to-end performance of the proposed scheduler.

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

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.

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.

Stochastic traffic engineering for live audio/video delivering over energy-limited wireless access networks

We study the Stochastic Traffic Engineering (STE) problem arising from the support of QoS-demanding live (e.g., real time) audio/video applications over unreliable IP-over-wireless access pipes. First, we recast the problem to be tackled in the form of a suitable nonlinear stochastic optimization problem, and then we develop a goodput analysis for the resulting IP-over-wireless pipe that points out the relative effects of fading-induced errors and congestion-induced packets losses. Second, we present an optimal resource-management policy that allows a joint scheduling of playin, transmit and playout rates. Salient features of the developed joint scheduling policy are that: i) it is self-adaptive; and, ii) it is able to implement reliable Constant Bit Rate (CBR) connections on the top of unreliable energy-limited wireless pipes.

Optimized joint bandwidth and playout control for streaming-traffic over wireless-channels

Media-streaming applications over time-varying faded wireless channels present mul- tiple still open challenges, mainly arising from the energy-limited nature of the wireless connections, as well as the delay and delay-jitter sensitive features of the conveyed media traffic. In this paper, we recast the challenges to be tackled in the form of a suitable non- linear constrained optimization problem involving finite-capacity G/G/1 queues at both transmit and receive nodes of the considered connection. Afterwards, we develop an opti- mized scheduling policy that seeks to improve media-streaming performance by building up adaptive joint control of the media source rate (e.g., the connection bandwidth), chan- nel rate (e.g., transmit rate) and delivery rate (e.g., playout rate). Formally speaking, the objective that we consider is the maximization of the average transmit rate, when con- straints on the: i) allowed average and peak energies; ii) maximum connection bandwidth (e.g., maximum source rate); and: iii) buffer’ capacities are simultaneously present. Fur- thermore, to properly cope with the jitter-sensitive feature of media-streaming, we also require that the joint controller to be developed is able to guarantee jitter values below any desired target limit. The joint controller we derive as solution of the described opti- mization problem works in an adaptive (e.g., time-varying) and Cross-Layer (CL) way, and requires synergic cooperation of the Application (APP), Data Link (DL) and Phys- ical (PHY) layers of the underlying protocol stack. The presented numerical results give insight about the attained optimized tradeoff among transmit rate, delay and delay-jitter.

Joint control of bandwidth and playout-delay for streaming traffic over faded links

In this paper we develop an optimized control strategy for the connection bandwidth maximization over a time varying wireless channel, by jointly controlling the adaptive source rate and the client/playout buffering policy with constraints on the maximum connection bandwidth allowed at the Application (APP) layer, the queue-capacities available at the DataLink (DL) layer and the average and peak transmit energies sustained by the Physical (PHY) layer. The main feature of the approach we follow lies in the fact that the maximization of the throughput is performed with respect to the channel state information as well as the occupancies of the transmitter and receiver buffers, taking into account also for the need to optimize the playout buffer service so to reduce the stream-jitter provided to the final user. The resulting optimal controllers operate in a Cross-Layer (CL) fashion that involves the APP, DL and PHY layers of the underlying protocol stack. Via a parameter-depending optimization we are able to handle the jitter of the stream provided to the final user without significant impact on the bandwidth performances. The carried out numerical tests give insight into the tradeoff among average throughput, delay and jitter attained by the optimized controllers.