Xianbo Chen

Performance and reliability of DSRC vehicular safety communication: a formal analysis

IEEE- and ASTM-adopted dedicated short range communications (DSRC) standard toward 802.11p is a key enabling technology for the next generation of vehicular safety communication. Broadcasting of safety messages is one of the fundamental services in DSRC. There have been numerous publications addressing design and analysis of such broadcast ad hoc system based on the simulations. For the first time, an analytical model is proposed in this paper to evaluate performance and reliability of IEEE 802.11a-based vehicle-to-vehicle (V2V) safety-related broadcast services in DSRC system on highway. The proposed model takes two safety services with different priorities, nonsaturated message arrival, hidden terminal problem, fading transmission channel, transmission range, IEEE 802.11 backoff counter process, and highly mobile vehicles on highway into account. Based on the solutions to the proposed analytic model, closed-form expressions of channel throughput, transmission delay, and packet reception rates are derived. From the obtained numerical results under various offered traffic and network parameters, new insights and enhancement suggestions are given.

Unsaturated Performance of IEEE 802.11 Broadcast Service in Vehicle-to-Vehicle Networks

In this paper, we propose an analytic model for performance evaluation of IEEE 802.11 ad hoc broadcast networks without the assumption of saturation condition that is not true in safety related vehicle-to-vehicle (v2v) communication. We use a discrete time M/G/l queue to model occasional occurrences of safety related message in each vehicle. By means of probability generating function (PGF) and a recursive algorithm, we obtain solution to the analytic model. Based on the solution, we derive several important performance indices for IEEE 802.11 broadcast service, such as packet delay, throughput, packet delivery ratio, and service time distribution. The proposed analytic model is validated by extensive simulations. Numerical results also reveal characteristics of the broadcast service in a typical v2v wireless network.

A Quantitative Approach to Evaluate DSRC Highway Inter-Vehicle Safety Communication

Inter-vehicle safety applications on highways rely considerably on the real-time and reliable communication in the vehicular ad hoc network. For engineers and researchers, it is greatly necessary and important to evaluate the provisions of the communication systems before they start designing them for such applications. This paper presents a quantitative approach to evaluate the quality of service that the inter-vehicle communication (using IEEE- and ASTM-adopted dedicated short range communication (DSRC)) can provide to the inter-vehicle safety application in the context of highway scenarios. Based on the proposed model, we analyze performance indices such as delay and packet delivery ratio (PDR). Outputs of the model are validated by computer simulations. On one hand, our quantitative model provides not only a convenient framework to conduct fast evaluation for the communication of the inter-vehicle safety applications but also a means to analyze the suitability of 802.11a- based DSRC for highway safety applications. On the other hand, it reveals the requirements for further improvement of the performance.

Saturation Performance of IEEE 802.11 Broadcast Scheme in Ad Hoc Wireless LANs

Broadcast communication is important in inter- vehicle communication. Vehicles broadcast safety related messages to pre-warn the vicinity vehicles. The new IEEE 802.11p is being developed based on IEEE 802.11a to address the need for vehicle-to-vehicle and vehicle-to-roadside-unit communication. In this paper, we study the saturation performance of IEEE 802.11 broadcast by developing an analytic model as well as by conducting simulation. Having investigated the literature and studied the features of the broadcast, we point out that the analytic models for IEEE 802.11 unicast cannot be simply applied for broadcast. We construct our model to characterize the operation of the backoff counter in broadcast. Based on solutions to the model, closed form expressions of performance indices including throughput, packet delay, and packet deliver ratio are derived. Numerical results reveal several characteristics of the broadcast service. Our research work provides a new means to approach analysis and enhancement of IEEE 802.11 broadcast performance and reliability in wireless ad hoc networks.

On the Broadcast Packet Reception Rates in One-Dimensional MANETs

In this paper, we investigate saturation performance of broadcast service in IEEE 802.11 based one-dimensional mobile ad hoc networks (MANETs) under multi-hop environment. Having analyzed the features of the multi-hop broadcast MANETs, for the first time we derive a closed form expression of broadcast packet reception rates, which is one of the important reliability metrics for broadcast communications. The analytic model takes IEEE 802.11 backoff counter process and hidden terminal problem into account. The proposed analytic model is validated by extensive simulations. From the obtained numerical results under various network parameters, new observations and potential enhancement suggestions are given.

An on-demand scatternet formation and multi-hop routing protocol for BLE-based wireless sensor networks

As new features are introduced into the Bluetooth core specification, the ability to use Bluetooth Low Energy (BLE) technology to construct a mobile ad-hoc network (MANET) becomes a reality. Key features included in Bluetooth Specification version 4.1 are the ability for a single node to be part of multiple piconets, and the ability for a node to act dual mode, as both a piconet master and slave. These features allow the possibility of multi-hop routing spanning multiple connected piconets. Although multi-hop routing is theoretically possible with version 4.1, no multi-hop routing algorithm has never been presented which exploits this possibility. In this paper we propose an approach to scatternet formation and multi-hop routing for networks using BLE version 4.1. We define procedures for device discovery, communication between piconets and forming multi-hop scatternet. Our approach has the following properties, 1) it can be used with existing Bluetooth hardware, 2) the protocol is fully distributed, so global connectivity information is not required for formation and routing, and 3) it supports ad-hoc network formation. We have implemented our approach using real Bluetooth SoCs including the Broadcom BCM434x chipset which is used in the iPhone 6. Our experiments demonstrate the routing delay and throughput using networks containing different numbers of nodes in order to demonstrate the impact of network size on performance. As the network size increases, our protocol does not incur a large delay and achieves better resource utilization.

SDMA: On The Suitability for VANET

Medium access control (MAC) is critical for vehicular ad hoc networks (VANET). A real commercial VANET system has not come into the market. Different MAC schemes have been proposed to attempt to achieve the expected performance, such as bounded delay, high packet reception rate, security, etc. Space Division Multiple Access (SDMA) is one of the VANET MAC proposals and has been theoretically investigated. However, it has not been studied whether SDMA is realistically feasible in VANET. In this paper, the suitability of SDMA for VANET is studied. The core mechanisms of the proposed SDMA and of the possible SDMA functions for VANET are analyzed and evaluated. Concerns upon practical implementation issues and theoretical limits are presented, based on which the conclusion of the unsuitability of SDMA for VANET is drawn.

Broadcasting Performance Comparison Among IVC MAC Protocol Candidates

Inter-vehicle communication (IVC) is essential for any intelligent transportation system implementation. In North America, dedicated short range communication (DSRC) protocol based on carrier sense multiple access with collision avoidance (CSMA/CA) was proposed. At the same time, in Europe, IVC implementation is based on R-ALOHA medium access protocol. In this paper we conduct a performance comparison between CSMA/CA and R-ALOHA protocols in a mobile environment while vehicles broadcast their messages. Computer simulation is used to obtain performance parameters such as delay, throughput, and packet delivery ratio. The results reveal that while the delay performance of both protocols is acceptable, the system throughput of CSMA/CA performs worse when being compared to R-ALOHA. Packet delivery ratio characteristics are also shown through simulation.

Fighting against access collision and hidden node problem in broadcast scheme of wireless ad hoc networks

Broadcast service is an integral part of wireless networks, through which important control and signaling information are typically exchanged. However, its multi-receiver nature determines that broadcast suffers more from access collision and hidden node problem. In wireless ad hoc networks, the phenomenon becomes even worse due to the absence of a central coordinator. Existing media access control (MAC) protocols in wireless ad hoc networks were primarily designed for unicast service and the potential broadcast support is not satisfying. In this paper, we introduce a MAC layer protocol, namely Parallel Signaling and Persistently Synchronous MAC (PS2MAC) that can significantly alleviate both access collision and hidden node problem. A novel relay technique is deployed in PS2MAC so that a superior broadcast performance, such as throughput and packet delivery ratio, is achieved. The conclusion is supported with simulation analysis.

Transient Analysis of Sliding Frame R-ALOHA for Real-Time Ad Hoc Wireless Networks with Capture Effect

In this paper, performance of sliding frame R-ALOHA protocol for real-time mobile ad hoc wireless networks is investigated analytically and by simulation. A discrete Markov chain and Monte Carlo modeling are constructed to evaluate dynamic behavior of the protocol in transient state, which includes distribution and mean of the system stabilization time (SST), and the average number of successful terminals. Capture effects on the R-ALOHA in the presence of multipath and shadowing are also addressed by the Markov chain analysis. The results reveal dynamic characteristics of the R-ALOHA system, and also show effectiveness and correctness of the models we developed.