Hamid Gharavi

Multigate Communication Network for Smart Grid

It is envisioned that one of the most important issues in smart grid will be to design a network architecture that is capable of providing secure and reliable two-way communication from meters to other Smart Grid domains. While networking technologies and systems have been greatly enhanced, in wireless communication environments the smart grid faces new challenges in terms of reliability and efficiency. In this paper we present a multigate mesh network architecture to handle real-time traffic for the last mile communication. The paper consists of three parts; multigate routing, real-time traffic scheduling, and multichannel (MC) aided wireless mesh routing. The multigate routing is based on a flexible mesh network architecture that expands on the hybrid tree routing of the IEEE 802.11s. The network is specifically designed to operate in a multi gateway structure in order to meet the smart grid requirements in terms of reliability, self-healing, and throughput performance. This includes developing a timer-based multiple-path diversity scheme that takes advantage of the multi gateway network structure. With respect to packet scheduling, we introduce a novel and efficient scheme that is capable of balancing the traffic load among multiple gateways. The proposed scheme, which is based on the backpressure concept due to its simplicity, is suitable for practical implementation. We also present an MC aided wireless mesh routing protocol which is specifically designed for multigate smart grid networks. The results indicate that a combination of multipath routing and the backpressure-based packet-scheduling scheme can show a significant improvement in the network reliability, latency, and throughput performance. We also show an improvement in the order of magnitude can be achieved via the proposed multichannel aided routing protocol.

Transmission of subband-coded images via mobile channels

The feasibility of a mobile video handset is investigated for Rayleigh-fading channels, where transmissions must be confined to the channels coherence bandwidth to avoid the deployment of complex high-power-consumption channel equalizers. This necessitates the utilization of a low-bit-rate image codec error-protected by embedded low-complexity BCH codecs and spectrally efficient 16-level quadrature amplitude modulation (16 QAM). Motion-compensated nonuniform seven-band subband coding with subband-specific scanning, adaptive quantization, runlength coding, and adaptive buffering to equalize bit-rate fluctuations offer good objective and subjective image quality at moderate complexity and a bit-rate of 55 kb/s. Using a twin-class embedded-BCH error protection as well as pilot symbol 16 QAM and diversity assisted, the 22 kBd candidate system yields unimpaired image quality for average channel signal-to-noise ratios (SNRs) in excess of about 16-18 dB, when the mobile speed is 4 miles/h. >

A Hybrid Frame Concealment Algorithm for H.264/AVC

In packet-based video transmissions, packets loss due to channel errors may result in the loss of the whole video frame. Recently, many error concealment algorithms have been proposed in order to combat channel errors; however, most of the existing algorithms can only deal with the loss of macroblocks and are not able to conceal the whole missing frame. In order to resolve this problem, in this paper, we have proposed a new hybrid motion vector extrapolation (HMVE) algorithm to recover the whole missing frame, and it is able to provide more accurate estimation for the motion vectors of the missing frame than other conventional methods. Simulation results show that it is highly effective and significantly outperforms other existing frame recovery methods.

Smart Grid: The Electric Energy System of the Future [Scanning the Issue]

Three dominant factors are impacting future electric systems of the world: governmental policies at both federal and state levels, customer efficiency needs, and new intelligent computer software and hardware technologies. In addition, environmental concerns are driving the entire energy system to efficiency, conservation, and renewable sources of electricity. Customers are becoming more proactive and are being empowered to engage in energy consumption decisions affecting their day-to-day lives. At the same time, energy needs are continually expanding. For example, consumer participation will soon include extensive use of electric vehicles (both cars and trucks), remote control of in-home appliances to promote energy conservation, ownership of distributed generation from ever more renewable energy sources, and management of electricity storage to locally match supply to demand. The availability of new technologies such as distributed sensors, two-way secure communication, advanced software for data management, and intelligent and autonomous controllers has opened up new opportunities for changing the energy system. For instance, while networking technologies and systems have been greatly enhanced, the Smart Grid faces challenges in terms of reliability and security in both wired and wireless communication environments. In particular, smart home appliances represent a major part of the Smart Grid vision, which aims at increasing energy efficiency. To achieve this goal, home appliances need to communicate with entities and players in other Smart Grid domains via home area networks. Therefore, the electric system of the future will address all these needs and concerns by using new advanced technologies to create a smarter, more efficient and sustainable grid. Although many different definitions have been proposed for the Smart Grid, in most cases, the users have chosen narrowly focused definitions related to their specific applications and local needs. The main objective of this special issue is to report on some, if not all, of the technical challenges posed by this conversion. While acknowledging its limited coverage, this special issue offers a range of valuable contributions. For the benefit of readers before beginning your excursion, we first provide a description of the current conventional electric energy system. We then identify the key areas that must change in order to provide the intelligence and control necessary to convert to the safe, secure, and efficient Smart Grid of the future.

Multihop sensor network design for wide-band communications

This paper presents a master/slave cellular-based mobile ad hoc network architecture for multihop multimedia communications. The proposed network is based on a new paradigm for solving the problem of cluster-based ad hoc routing when utilizing existing wireless local area network (WLAN) technologies. The network architecture is a mixture of two different types of networks: infrastructure (master-and-slave) and ad hoc. In this architecture, the participating slave nodes (SNs) in each cluster communicate with each other via their respective master nodes (MNs) in an infrastructure network. In contrast to traditional cellular networks where the base stations are fixed (e.g., interconnected via a wired backbone), in this network the MNs (e.g., base stations) are mobile; thus, interconnection is accomplished dynamically and in an ad hoc manner. For network implementation, the IEEE 802.11 WLAN has been deployed. Since there is no stationary node in this network, all the nodes in a cluster may have to move together as a group. However, in order to allow a mobile node to move to another cluster, which requires changing its point of attachment, a handoff process utilizing Mobile IP version 6 (IPv6) has been considered. For ad hoc routing between the master nodes (i.e., MNs), the Ad hoc On-demand Distance Vector (AODV) Routing protocol has been deployed. In assessing the network performance, field test trials have been carried out to measure the proposed network performance. These measurements include packet loss, delays under various test conditions such as a change of ad hoc route, handoffs, etc.

Subband coding algorithms for video applications: videophone to HDTV-conferencing

Various subband coding schemes are developed for high compression video coding applications. These schemes are based on two distinct interframe subband models. Both models are compared and show that they perform equally under certain conditions. The first model, which is relatively less complex but operates at full speed, was considered for video conferencing applications at lower rates. The second model, however, due to its generic structure which operates at a reduced speed, was found to be suitable for high quality video applications. As a result, a CCITT compatible video coding scheme for HDTV conferencing is developed. For the best performance, the higher frequency bands were coded with a combination of interframe differential pulse code modulation (DPCM) and direct PCM. >

Efficient Motion Vector Interpolation for Error Concealment of H.264/AVC

In video communications the compressed video stream is very likely to be corrupted by channel errors. In order to combat these channel errors, many methods have been proposed. In this paper, a new method for motion vectors (MVs) interpolation with the help of MV extrapolation (MVE), is presented to conceal the corrupted frame of H.264/AVC. In our proposed method, the MVs of lost blocks can be obtained after interpolation with the extrapolated MVs. Experimental results show that this method is able to provide better performance than existing algorithms in terms of PSNR.

Multichannel Mobile Ad Hoc Links for Multimedia Communications

This paper is mainly concerned with multichannel transmission of real-time information such as video over multihop ad hoc links. We propose two multichannel routing protocols. The first is based on single-path routing and aims at suppressing the intrapath interference in a carrier sense multiple access/collision avoidance network. This is achieved by developing a link-partitioning scheme where nodes in the neighboring partitions operate at different nonoverlapping frequency bands. For this approach, we present a systematic channel assignment technique that has been specifically developed for the ad hoc on-demand distance vector routing protocol. It is shown that this partitioning scheme can considerably enhance the throughput performance of a multihop link. The second multichannel scheme is developed for transmission of real-time traffic over multiple-path routes. Bear in mind that multiple-path diversity routing has been shown to be very effective in dealing with network congestion in wireline Internet protocol networks. Unfortunately, in mobile ad hoc network environments, particularly for real-time traffic, this approach can suffer greatly from cochannel interference due to the simultaneous transmission of packets via multiple routes. In this respect, we have designed a dual-path routing protocol, which guarantees a different frequency band for each path, thus eliminating any interpath interference. We show that this protocol has an important property, which is reducing the probability of losing both routes at the same time. Based on this important property, we demonstrate that a combination of the routing protocol and dual-description video coding can greatly enhance the ad hoc network performance of video transmission for real-time traffic.

Multi-Path Multi-Channel Routing Protocol

In this paper we present a DSR-based multi-path routing protocol, which has been developed for transmission of multiple description coded (MDC) packets in wireless ad-hoc network environments. The protocol is designed to eliminate co-channel interference between multiple routes from source to destination by assigning a different frequency band to each route. In the route discovery process we use three metrics to select the best multiple routes. These are hop count, power budget, and the number of joint nodes between the different routes. For continuous media communications we show that in order to effectively benefit from the advantages associated with multipath diversity routing, it is important to use a multi-channel protocol such as the one developed here

Dynamic adjustment packet control for video communications over ad-hoc networks

This paper is concerned with transporting video information via multihop mobile ad-hoc channels. The major problem with transmitting real-time video information over these channels is the issue of link reliability. To improve the quality of the video reception we propose a cross layer feedback control mechanism that can allow the application layer to adapt itself to a dynamically changing network topology. We also present packet transmission strategies capable of recovering video signals under long bursts of packet drops, typical of a route change condition. This feedback control scheme has been developed for transmission of RTP/UDP/IP packets using the emerging H.264/AVC video-coding standard.