Demonstration of Wireless Multi-Path Communication to Improve Reliability

Understanding Packet Delivery Performance In Dense Wireless Sensor Networks ∗ Computer Science Department University of Southern California Los Angeles, CA 90089-0781 Jerry Zhao Computer Science Department University of Southern California Los Angeles, CA 90089-0781 Ramesh Govindan zhaoy@usc.edu ABSTRACT Wireless sensor networks promise fine-grain monitoring in a wide variety of environments. Many of these environ- ments (e.g., indoor environments or habitats) can be harsh for wireless communication. From a networking perspec- tive, the most basic aspect of wireless communication is the packet delivery performance: the spatio-temporal charac- teristics of packet loss, and its environmental dependence. These factors will deeply impact the performance of data acquisition from these networks. In this paper, we report on a systematic medium-scale (up to sixty nodes) measurement of packet delivery in three different environments: an indoor office building, a habitat with moderate foliage, and an open parking lot. Our findings have interesting implications for the design and evaluation of routing and medium-access protocols for sensor networks. ramesh@usc.edu spectrum under use, the particular modulation schemes un- der use, and possibly on the communicating devices them- selves. Communication quality can vary dramatically over time, and has been reputed to change with slight spatial displacements. All of these are true to a greater degree for ad-hoc (or infrastructure-less) communication than for wire- less communication to a base station. Given this, and the paucity of large-scale deployments, it is perhaps not surpris- ing that there have been no medium to large-scale measure- ments of ad-hoc wireless systems; one expects measurement studies to reveal high variability in performance, and one suspects that such studies will be non-representative. Wireless sensor networks [5, 7] are predicted on ad-hoc wireless communications. Perhaps more than other ad-hoc wireless systems, these networks can expect highly variable wireless communication. They will be deployed in harsh, inaccessible, environments which, almost by definition will exhibit significant multi-path communication. Many of the current sensor platforms use low-power radios which do not have enough frequency diversity to reject multi-path prop- agation. Finally, these networks will be fairly densely de- ployed (on the order of tens of nodes within communica- tion range). Given the potential impact of these networks, and despite the anecdotal evidence of variability in wireless communication, we argue that it is imperative that we get a quantitative understanding of wireless communication in sensor networks, however imperfect. Our paper is a first attempt at this. Using up to 60 Mica motes, we systematically evaluate the most basic aspect of wireless communication in a sensor network: packet delivery. Particularly for energy-constrained networks, packet de- livery performance is important, since that translates to net- work lifetime. Sensor networks are predicated using low- power RF transceivers in a multi-hop fashion. Multiple short hops can be more energy-efficient than one single hop over a long range link. Poor cumulative packet delivery per- formance across multiple hops may degrade performance of data transport and expend significant energy. Depending on the kind of application, it might significantly undermine application-level performance. Finally, understanding the dynamic range of packet delivery performance (and the ex- tent, and time-varying nature of this performance) is impor- tant for evaluating almost all sensor network communication protocols. We study packet delivery performance at two layers of the communication stack (Section 3). At the physical-layer and in the absence of interfering transmissions, packet de- Categories and Subject Descriptors C.2.1 [Network Architecture and Design]: Wireless communication; C.4 [Performance of Systems]: Perfor- mance attributes, Measurement techniques General Terms Measurement, Experimentation Keywords Low power radio, Packet loss, Performance measurement 1. INTRODUCTION Wireless communication has the reputation of being no- toriously unpredictable. The quality of wireless communica- tion depends on the environment, the part of the frequency ∗ This work is supported in part by NSF grant CCR-0121778 for the Center for Embedded Systems. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. SenSys’03, November 5–7, 2003, Los Angeles, California, USA. Copyright 2003 ACM 1-58113-707-9/03/0011 ... $ 5.00.

An orthogonal frequency division multiplexing (OFDM) is one of the effective techniques used in wireless communications. In OFDM systems, channel impairments due to multipath dispersive wireless channels can cause deep fades in wireless channels. The OFDM receiver also requires an accurate and computationally efficient channel state information when coherent detection is involved. Therefore, it needs a good robust estimation method of the channel in wireless communication for OFDM systems. And one of these channel estimation methods is minimum mean square error (MMSE) channel estimation. MMSE channel estimation one most used method in OFDM systems. In this work we enhanced robustness of MMSE channel estimation by using it in base of quasi-cyclic low density parity check (QC-LDPC) coded OFDM system.

In the urban utility tunnel, wireless communication severe serious multi-path effect, which causes significant fast fading and results in uniformity of the coverage. An antenna array which consists of five antenna elements with very simple structure is proposed in this paper for the purification of the multi-path communication channel in urban utility tunnel. The proposed antenna array is capable of operating at three frequency bands which can well satisfy the requirements of collaborative deployment of multiple communication systems in urban utility tunnel. Moreover, the sector radiation pattern of the antenna array has narrow HPBW on cross section of the tunnel and very wide HPBW on vertical plane along the tunnel, which conforms to the physical structure of the tunnel. Therefore, it can greatly reduce the reflection in the tunnel, purify the multi-path environment in the tunnel, and effectively improve the uniformity of wireless coverage in the tunnel.KeywordsChannel modelingUrban utility tunnelChannel fading effectSector patternAntenna array

With the emergence of the adaptive bit rate (ABR) streaming technology, the video/content streaming technology is shifting toward a file-based content distribution. That is, video content is encoded into a set of smaller media files containing video of 2–10 seconds before transmission. This file-based content distribution, coupled with increasingly rapid adoption of smartphones, requires an efficient file-based distribution algorithm to satisfy the QoS demand in wireless networks. In this paper, we study the transmission of a finite-sized file over wireless networks using multipath routing, with the objective to minimize file transmission delay instead of average packet delay. The file transmission delay is defined as the time interval from the instant that a file is first transmitted to the time at which the file can be reconstructed in the destination node. We observe that file transmission delay depends not only on the mean of the packet delay but also on its distribution, especially the tail. This observation leads to a better understanding of the file transfer delay in wireless networks and a minimum delay file transmission strategy. In a wireless multipath communication scenario, we propose to use packet level erasure code (e.g., digital fountain code) to transmit data file with redundancy. Given that a file with k packets is encoded into n packets for transmission, the use of digital fountain code allows the file to be received when only k out of n packets are received. By adding redundant packets, the destination node does not have to wait for the packet to arrive late, hence reducing the delay of the file transmission. We characterize the tradeoff between the code rate (i.e., the ratio of the number of transmitted packets to the number of the original packets) and the file delay reduction. As a rule of thumb, we provide practical guidelines in determining an appropriate code rate for a fixed file to achieve a reasonable transmission delay. We show that only a few redundant packets are needed to achieve a significant reduction in file transmission delay.

In digital wireless communications, blind equalization without training sequence or any priori knowledge of the channel dynamics has become a topic problem, and one of its most important performance criterions is the convergence speed. Traditional constant modulus algorithm (CMA) with many advantages is a popular blind equalization approach, but its slower convergence rate is unsuitable for the compensation of the multipath fading wireless channels. In this paper, a novel blind channel equalization algorithm is presented by introducing a decorrelation factor into the equalization process. The improvement in convergence rate as well as residual MSE of the proposed algorithm is confirmed by computer simulation results.

A hybrid access scheme called time code division multiple access (TCDMA) is proposed for indoor wireless communications. The indoor radio channel is modeled in terms of channel impulse response by taking into account various indoor measurement results. Various simulation methods are used to reduce the computational complexity and to ensure the result accuracy. The simulation results of system performance reveal the capability and the capacity of TCDMA in a typical indoor cell such as in an office building of medium size.

Wireless Multimedia Sensor Networks (WMSNs) are a special type of Wireless Sensor Network (WSN) where large amounts of multimedia data are transmitted over networks composed of low power devices. Hierarchical routing protocols typically used in WSNs for multi-path communication tend to overload nodes located within radio communication range of the data collection unit or data sink. The battery life of these nodes is therefore reduced considerably, requiring frequent battery replacement work to extend the operational life of the WSN system. In a wireless sensor network with mesh topology, any node may act as a forwarder node, thereby enabling multiple routing paths toward any other node or collection unit. In addition, mesh topologies have proven advantages, such as data transmission reliability, network robustness against node failures, and potential reduction in energy consumption. This work studies the feasibility of implementing WMSNs in mesh topologies and their limitations by means of exhaustive computer simulation experiments. To this end, a module developed for the Synchronous Energy Saving (SES) mode of the IEEE 802.15.5 mesh standard has been integrated with multimedia tools to thoroughly test video sequences encoded using H.264 in mesh networks.

In this thesis, we describe a method for uniquely identifying a specific radio among nominally similar devices using a combination of software defined radio (SDR) sensing capability and machine learning (ML) techniques. Our approach of radio fingerprinting applies ML over raw I/Q samples without specifically selecting features of interest. It distinguishes devices using only the transmitter hardware-induced signal modifications that serve as a unique signature for a particular device. No higher level decoding, feature engineering, or protocol knowledge is needed, further mitigating challenges of ID spoofing and coexistence of multiple protocols in a shared spectrum. Advances in SDR technology allows unprecedented control on the entire processing chain, allowing modification of each functional block as well as sampling the changes in the input waveform. We first demonstrate RF impairments by modifying the operational blocks in a typical wireless communications processing chain in a simulation study. We then generate over-the-air dataset compiled from an experimental testbed of SDRs such as B210 and X310 and train the data using an optimized deep convolutional neural network (CNN) architecture that gives good classification accuracy. We describe the parallel processing needs and choice of several hyper parameters to enable efficient training of the CNN model. We then compare the performance quantitatively with alternate techniques such as support vector machines and logistic regression. Overall our results show that we can achieve up to 90-99% experimental accuracy at transmitter-receiver distances varying between 2-50 feet over a noisy, multi-path wireless channel--Author's abstract

In this paper, we describe how we can finely adjust the electromagnetic losses inside a mode-stirred reverberation chamber (MSRC) using a device containing a variable quantity of conductive liquid. This device can be used for several applications such as decreasing the lowest usable frequency in MSRCs for ElectroMagnetic Compatibility (EMC) tests or, controlling the RMS Delay Spread inside a configured MSRC to reproduce the wireless multipath channel of different ElectroMagnetic (EM) environments such as those inside vehicles. In this work, we will focus on wireless environment simulation applications. The RMS Delay Spread is determined inside a cavity provided with apertures and loaded with a conductive liquid. It is compared to the one obtained inside an automotive vehicle for different positions of a couple of wireless communication antennas. The comparisons show that, in our case, the static wireless multipath channel of a complex EM environment of a vehicle may be simulated inside such a cavity.