Safe Distributed Control of Wireless Power Transfer Networks

Distributed Control of Wireless Power Transfer Subject to Safety Constraints

This paper proposes a novel channel estimation method and a cluster-based opportunistic scheduling policy, for a wireless energy transfer (WET) system consisting of multiple low-complex energy receivers (ERs) with limited processing capabilities. Firstly, in the training stage, the energy transmitter (ET) obtains a set of Received Signal Strength Indicator (RSSI) feedback values from all ERs, and these values are used to estimate the channels between the ET and all ERs. Next, based on the channel estimates, the ERs are grouped into clusters, and the cluster that has its members closest to its centroid in phase is selected for dedicated WET. The beamformer that maximizes the minimum harvested energy among all ERs in the selected cluster is found by solving a convex optimization problem. All ERs have the same chance of being selected regardless of their distances from the ET, and hence, this scheduling policy can be considered to be opportunistic as well as fair. It is shown that the proposed method achieves significant performance gains over benchmark schemes.

Deep learning driven physical layer security for a simultaneously wireless information and power transfer network

Power control in wireless networks is useful for minimizing channel congestion (hence increasing network capacity). In this work, we show how the distributed power control algorithm with active link protection (DCP-ALP) can be used as a channel probing tool that allows a new link trying to access a channel to quickly and autonomously determine whether it can be admitted to it (i.e. whether there is a feasible power configuration for the transmitters such that the link quality requirements on all links are met), which significantly improves the capacity and access time of the network.

Wireless energy transfer (WET) is potentially a promising solution to provide convenient and reliable energy supplies for energy-constrained networks, and has drawn growing interests recently. To overcome the significant propagation loss over distance, employing multi-antennas at the energy transmitter (ET) to more efficiently direct wireless energy to desired energy receivers (ERs), termed energy beamforming, is an essential technique for WET. However, the achievable gain of energy beamforming crucially depends on the available channel state information (CSI) at the ET, which needs to be acquired practically. In this paper, we study the optimal design of one efficient channel-acquisition method for a point-to-point multiple-input multiple-output (MIMO) WET system, by exploiting the channel reciprocity based on which the ET estimates the CSI via dedicated reverse-link training from the ER. Considering the limited energy availability at the ER, the training strategy should be carefully designed so that the channel can be estimated with sufficient accuracy, and yet without consuming excessive energy at the ER. To this end, we propose to maximize the net energy at the ER, which is the total energy harvested offset by that used for channel training. The optimal training design, including the number of receive antennas to be trained, as well as the training time and power allocated, is derived. Our result shows that training helps only when the following conditions are satisfied: (i) the channel coherence time is sufficiently large; (ii) the number of antennas at the ET is large enough; and (iii) the effective signal-to-noise ratio (ESNR) is sufficiently high; otherwise, no training should be applied and isotropic energy transmission is optimal.

In this paper, a few schemes are presented to improve the performance of aggressive packet combining scheme (APC). To combat error in computer / data communication networks, ARQ (Automatic Repeat Request) techniques are used. Several modifications to improve performance of ARQ are suggested by recent research and are found in literature. The important modifications are majority packet combining scheme (MjPC proposed by Wicker), packet combining scheme (PC proposed by Sindhu & Chakraborty), modified packet combining scheme(MPC proposed by Bhunia), and packet reversed packet combining(PRPC proposed by Bhunia) scheme. These modifications are appropriate for improving throughput of conventional ARQ protocols. Leung proposed an idea of APC for error control in wireless networks with basic objective of error control in uplink wireless data network. We suggest a few modifications of APC to improve its performance in terms of higher throughput, lower delay and higher error correction capability.

In this paper, we study cross-layer design for rate control in multihop wireless networks. In our previous work, we have developed an optimal cross-layered rate control scheme that jointly computes both the rate allocation and the stabilizing schedule that controls the resources at the underlying layers. However, the scheduling component in this optimal cross-layered rate control scheme has to solve a complex global optimization problem at each time, and hence is too computationally expensive for online implementation. In this paper, we study how the performance of cross-layer rate control can be impacted if the network can only use an imperfect (and potentially distributed) scheduling component that is easier to implement. We study both the case when the number of users in the system is fixed and the case with dynamic arrivals and departures of the users, and we establish desirable results on the performance bounds of cross-layered rate control with imperfect scheduling. Compared with a layered approach that does not design rate control and scheduling together, our cross-layered approach has provably better performance bounds, and substantially outperforms the layered approach. The insights drawn from our analyses also enable us to design a fully distributed cross-layered rate control and scheduling algorithm for a restrictive interference model.

Energy beamforming (EB) is a key technique for achieving efficient radio-frequency (RF) transmission enabled wireless energy transfer (WET). By optimally designing the waveforms from multiple energy transmitters (ETs) over the wireless channels, they are constructively combined at the energy receiver (ER) to achieve an EB gain that scales with the number of ETs. However, the optimal design of transmit waveforms requires accurate channel state information (CSI) at the ETs, which is challenging to obtain in practical WET systems. In this paper, we propose a new channel training scheme to achieve optimal EB gain in a distributed WET system, where multiple separated ETs adjust their transmit phases to collaboratively send power to a single ER in an iterative manner, based on one-bit feedback from the ER per training interval which indicates the increase/decrease of the received power level from one particular ET over two preassigned transmit phases. The proposed EB algorithm can be efficiently implemented in practical WET systems even with a large number of distributed ETs, and is analytically shown to converge quickly to the optimal EB design as the number of feedback intervals per ET increases. Numerical results are provided to evaluate the performance of the proposed algorithm as compared to other distributed EB designs.

The performance of two wireless power transfer scheduling schemes, time sharing (TS) and spatial multiplexing (SM), in terms of provisioning fairness among energy receivers (ERs) is studied and compared while taking into account the nonlinearity of the energy harvesters circuits. In the network, the multiple-antenna energy transmitter (ET) attempts to maximize the harvested energy by the ER which has accumulated the minimum amount of energy among all single-antenna ERs during the wireless power transfer block T-hence the max-min fairness criterion. Two network scenarios are studied: homogeneous, where the channels power coefficients are assumed to be the same for all the well-apart ERs, and heterogeneous, where the said coefficients can take arbitrary values. It is proven analytically that in the homogeneous scenario, the optimal scheduling policy is to allocate each ER the full transmit power P with uniform distribution of charging times among ERs, rather than to allocate the full power transfer block T with uniform distribution of the power among ERs. Generalization of the network to the heterogeneous scenario aims to find the optimal beamforming vector for the SM scheme and the optimal time sharing vector for the TS scheme. It is shown through extensive Monte Carlo simulations that again TS outperforms SM in terms of max-min fairness as a result of taking into account the inherent non-linear characteristics of the harvesting devices.

The convenience and flexibility of wireless networks to allow clients (user nodes) to be connected to the network at any place and any time have resulted in the growth and increased popularity of wireless networks. Access control in wireless networks is very important to prevent unauthorized users from accessing the network. Besides this, client anonymity and resistance to Denial-of-Service (DoS) attacks are also important and should be provided by access control protocols for wireless networks. Password-based authentication provide good solutions for access control protocols, however they usually do not provide client identity confidentiality and DoS resistance. In this paper, we review a DoS-resistant anonymous access control (AAC) protocol and point out that the protocol does not provide protection against three different DoS attacks. We then propose a new DoS-resistant AAC protocol that avoids the flaws of the previous protocol. Our proposed protocol also provides client anonymity and protection against DoS attacks. A security and complexity analysis shows that our proposed protocol is secure and efficient for access control in wireless networks.

In this paper, we provide a holistic overview of the aspect of electromagnetic radiation (EMR) and its efficient control in wireless communication networks. Especially, we focus on the emerging technology of wireless power transfer (WPT). Our global perspective is to suggest methods for the effective control of EMR while keeping at high levels the QoS experienced by users as well as the charging efficiency of WPT. First, we provide formal definitions of EMR in wireless communications and propose related performance metrics and EMR evaluations in wireless communication networks. Then, we focus on EMR control in efficient wireless power transfer, under different WPT models. For the well-known scalar model, we assume finite energy reserves and batteries, and introduce the low radiation efficient charging problem. For this problem, we identify its computational complexity and provide efficient algorithms and heuristics. A vectorial model of WPT is then employed, allowing a more precise management of radiation, via directly exploiting interesting super-additive and cancellative phenomena of received power; we provide algorithms which achieve satisfactory tradeoffs of charging efficiency and radiation. Then, we present a more futuristic model and the method of peer-to-peer wireless power transfer where no strong, central charger stations are used, thus keeping radiation at almost zero levels. Another method of controlling EMR in the case of mobile nodes is adapting the charger change in a dynamic, on-line way so as to avoid unnecessarily large fixed changing ranges. Finally, we discuss some future challenges and related research directions, toward efficiently combining high WPT provisioning and low EMR. Such directions include the effective management of mobility in the network, the use of diverse WPT signal phase-configuration as well as efficient chargers’ scheduling strategies.

The use of power control in wireless networks can lead to two conflicting effects. An increase in the transmission power on a link may (i) improve the quality and thus the throughput on that link but, (ii) increase the levels of interference on other links. A decrease in the transmission power can have the opposite effects. Our primary goal in this work is to understand the implications of power control on interference and contention. We conduct experiments on an indoor mesh network. Based on analysis of our experimental data, we identify three interference scenarios: a) the overlapping case, where the aggregate throughput achievable with two overlapping links cannot be improved via power control; b) the hidden terminal case, where proper power control can primarily improve fairness and, c) the potentially disjoint case, where proper power control can enable simultaneous transmissions and thus improve throughput dramatically. We find that power control can significantly improve overall throughput as well as fairness. However, to our surprise, we note that using virtual carrier sensing in conjunction with power control generally degrades performance, often to a large degree.

On distributed power control in full duplex wireless networks

The rapid deployment of wireless mesh networks across universities and enterprises, and the pervasiveness of mobile devices equipped with Wi-Fi connectivity, has resulted in a scenario wherein end users have the option to choose from a multitude of access points at any given location. Moreover, with the increasing availability of rich online content, there has been a steady increase in mobile Internet traffic. Since the choice of access point that a user associates with will directly impact his performance, it is imperative that there exist an efficient association control mechanism, in order to enhance the end user's experience. As part of this work, we propose Seeker, a novel framework for association control in wireless networks that utilizes "available bandwidth" as the design metric. The goal of Seeker is to assist the mesh network in making an intelligent decision regarding which access point a client should associate with. As part of our scheme, we implement and evaluate a passive tool to estimate available bandwidth in wireless networks. We then describe how we use this tool to implement our association control scheme, and evaluate it via extensive experiments on an outdoor testbed. Seeker takes into consideration the performance of the mesh backhaul, in addition to the client-to-AP link quality, thereby achieving significant advantages over traditional association control schemes for wireless-LANs.

In wireless communications networks with multiple service classes (SCs) of calls, call admission control (CAC) schemes is an essential radio resource management (RRM) function for networks consistency. Apart from the calculation of the call blocking probability (CBP) appropriate criteria and metrics should be considered to evaluate the efficiency of various schemes. Fairness among different services is an important efficiency criterion for CAC in wireless networks with multimedia services while throughput is an efficiency criterion of general validity. In the present paper, four CAC schemes based on guard channel algorithms are proposed for multiclass services, offering priority to real time service class calls while ensuring a certain level of quality of service (QoS). The proposed schemes investigate the CAC problem in terms of ongoing users and occupied channels. Fairness among calls of different classes is evaluated and the network performance is compared with respect to input load.