To deal with the congestion problem in a broadcast environment like V2V communication, we believe that receiving nodes should take a role in guiding transmitting nodes to set their transmission parameters e.g., Tx rate and power. This is important because only receiving nodes can evaluate whether or not safety applications requirements have been fulfilled. While most congestion control protocols rely on network-level metrics to optimize their transmission parameters, our proposed method uses a combination of application and network level performance metrics to assign transmission parameters. In the proposed method, nodes calculate the max tolerable time between periodic messages as well as the channel load, and share it with others. The shared data is used to guide neighboring nodes in regulating their messaging rate and Tx power. Receiving nodes adapt their rate or/and power based on their locations w.r.t to the node with degraded safety applications performance. The evaluation shows that our method maintains low inter packet reception time.

Providing vehicles with different services is an important challenge for the Roadside Units (RSUs) to support future Intelligent Transportations Systems applications. In rush hours, tens of vehicles might request different services from a shared RSU. When the RSU becomes close to overloaded situations, the Admission Control (AC) and the resource allocation algorithms play very important role of determining whether accepting new arrivals affects the in-session tasks. Admitting more tasks means pushing their task finish time to their deadlines (RSU range leaving time), which increases the risk of the vehicles, thus, increasing the probability of task failure. In this paper, we propose an admission control and resource allocation algorithm that helps the RSU keep the number of admitted tasks higher, and at the same time reducing the risk of the tasks as the vehicles progress and move toward the edges of the RSU's transmission range. The algorithm calculates the physical expected task finish time for those vehicles, but allocates a virtual air-time transmission plan, which includes an extra time called the backup time. This extra time can be used to download the remaining data in case the task could not be finished on time. This time can automatically be transferred to the air-time transmission plan of the next vehicle closer to leave the RSU region in case it was not used. Simulation results show that our algorithm maintains higher number of admitted tasks and at the same time reduces the failure rate of those tasks.

Updating software in vehicle Electronic Control Units (ECUs) will become a mandatory requirement for a variety of reasons, for examples, to update functionality of an existing system, add new functionality, remove software bugs and to cope up with ITS infrastructure. Since multicasting is the most efficient method of group communication, updating software in an ECU of a large number of vehicles could benefit from it. In a previous work, we proposed an infrastructure-based mobile multicasting for remote software upload (RSU) in vehicle ECUs where an ECU receives the software from a remote software distribution center using the road side Base Stations (BSs) as gateways. Consequently, we proposed two multicast session establishment techniques based on the degree of trust on the BSs named Fully-trusted (FT) and Semi-trusted (ST) systems. In this paper, we conduct extensive simulation studies to evaluate the performance of these two techniques by finding the average latency to authenticate a vehicle and provide it with the multicast session key by the software provider during multicast session initialization. Simulation results show that the link establishment latency per vehicle of our proposed schemes is in the range of few seconds and the ST system requires two to three times higher time than the FT system.

Clustering in Vehicular Ad-hoc Networks (VANET) is one of the control schemes used to organize media access and make VANET global topology less dynamic. Most VANET clustering algorithms are derived from Mobile Ad-hoc Networks (MANET). But, these algorithms model clustering schemes considering only position and direction of vehicles located in a geographic proximity regardless of the degree of the speed difference among them. Since the existence of VANET nodes in the same geographic location doesn't mean that they exhibit similar mobility pattern, we believe that VANET clustering models need to be redefined such that, their characterization is identified by considering the full status elements; speed, location, and direction instead of considering location and direction only. In this paper, we propose a new approach for grouping vehicles, showing similar mobility patterns, in a cluster and at the same time try to minimize the total number of created clusters. A new multi-metric Cluster Head (CH) election technique has also been developed. This technique can be used by vehicles to determine their suitability on the fly to lead the cluster. The simulation is conducted to evaluate the proposed technique and compare it with the most common methods. The simulation results show that our technique increases the cluster stability by about 50% compared to that of the most commonly used techniques.

The new generation vehicles will have many sophisticated systems such as drive-by-wire, navigation, traffic congestion control, road guidance, and advance crash warning. Already, dozens of onboard computers control complex vehicle functions. From time to time, an onboard computer needs reprogramming. Currently, dealers manually reprogram software in onboard computers via a wire based electrical connection. Updating software wirelessly is a preferred alternative to the manual method because the vehicle need not be physically present at a repair facility to perform the update. Wireless software reprogramming will save customers' and technicians' time and money. In this paper, we present a wireless download algorithm for reprogramming of vehicles' electronic control units, using current wireless technologies. Our algorithm proposes a hybrid infrastructure that combines wireless unicasting and multicasting data delivery.

In this paper, we propose a broadcast protocol to preserve drivers' anonymity in vehicle-to-vehicle (V2V) communications network using the keyed-hash message authentication code (HMAC). Future vehicle safety applications will allow vehicles to broadcast their safety-critical information to alert neighboring vehicles of possible collisions. Such safety applications has a very low bandwidth and low communication latencies. We propose to use the keyed-hash message authentication code (HMAC) to provide anonymity, authentication and message integrity. The advantages of HMAC over asymmetric cryptographic algorithms are faster processing speed and a shorter message length which makes it suitable for V2V communications. We show that the additional number of bytes to a broadcasted message in our proposed protocol is 49 bytes. The recipients of the broadcasted message can authenticate the sender and verify the integrity of the message without identifying the source. In case of a dispute, only a Trusted Authority can identify the source of broadcasted messages.

In this preliminary paper we propose new intersection collision avoidance architecture. This system allows vehicles to establish secure links with roadside unit installed at the intersection before entering the furthest point where vehicles start to share their current state with the roadside unit. Early link establishment is chosen to maximize the opportunity of advanced notification for collision warnings.

In Vehicular ad hoc networks, vehicles use periodic messages to inform all nearby vehicles about their current state. Roadside hazardous information can be sent to the vehicles to prevent accidents. Hazardous roadside information can be sent either by using separate messages or by embedding the information into the regular periodic messages. This paper investigates the effectiveness of using only the periodic messages for disseminating warning information. Results show that the dissemination of warning information, by only using periodic messages, will be as effective as using two different types of messages: periodic messages and separate warning messages.

We propose a hybrid media access technique for cluster-based vehicular networks. This technique integrates the centralization approach of cluster management and the universal way of forwarding data, where the farthest vehicle forwards data in an effort to maximize the opportunity of advanced notification. This method leverages contention-free and contention-based MAC, to support the different requirements of safety and non-safety messages. Inter-cluster interference avoidance is also supported. The analysis and simulation show that using this scheme, for inter-cluster communications, provides an early notification compared to other existing clustering methods.

Vehicle-to-vehicle (V2V) communications network is a subclass of mobile ad hoc networks (MANET). With the new dedicated short range communications (DSRC) at 5.9 GHz, vehicles equipped with DSRC devices will communicate and collaborate to broadcast their safety-critical information to each other. DSRC is to be used in a wide range of advanced vehicle safety applications such as intersection collision avoidance system. The DSRC specification is based on the physical (PHY) and medium access control (MAC) layers of the IEEE 802.11a. The MAC mechanism for the IEEE 802.11a is the distributed coordination function (DCF), which is based on carrier sense multiple access with collision avoidance (CSMA/CA). Mobile nodes contend for the channel using a DCF random backoff timer. A random backoff algorithm chooses a Contention Window (CW) value between aCWmin and aCWmax. The random number, CW, is the number of time slots the mobile node has to sense the channel idle before it may transmit. In this paper, we developed an intersection traffic simulator to evaluate the settings of IEEE 802.11a DCF aCWmax on the available bandwidth per vehicle and on the required communication range. Our simulation results show that it is sufficient to set the aCWmax to 200 and the communication range to 200m for the intersection collision avoidance system enabled by DSRC.

The privacy of future drivers will dispute with the evolvement of vehicle-to-vehicle (V2V) communication networks. V2V networks are a subclass of mobile ad hoc networks (MANET). Future vehicles will collaborate for safe and efficient driving using wireless communications. Vehicles will exchange safety-critical information without a control from a centralized basestation or infrastructure. However, a centralized infrastructure, presented as a management entity or a certificate authority (CA), is necessary to establish and provide trust and secure communication protocols among drivers. This can be achieved using the public key infrastructure (PKI) and digital certificates. The CA provides a unique certificate for each driver. The disadvantage of unique certificates is that the identity of drivers can be revealed to other drivers, and the movements and locations the drivers visit can also be traced by other drivers. In this paper, we present an approach to provide privacy among drivers in V2V communication networks. Our approach is based on the concept of group signatures. Drivers, who are members of V2V networks, are organized into groups. Each group has a public key. Members of a group share their group's public key. In addition, each member has its own private key provided by the CA. In our proposed solution, we achieve privacy by allowing members to generate and change their own set of public keys frequently using the Digital Signature Standard (DSS). In our approach the CA is not required to authenticate the frequently generated public keys, and hence vehicles exchange the safety- critical information without requiring a control from the CA. When a group member changes its own public keys, it is hard to trace the movements and locations that member visits. A group member signs messages using the shared group public key, its own private key, and its own frequently-changed public keys. The recipients of a signed message can verify the correctness of the signature without identifying the signer. In case of a dispute and malicious activities, the identity of the member who signed the disputed message can be revealed only by the CA.

We propose an intersection warning channel access priority (IWCAP) protocol to warn drivers of a possible collision when approaching an intersection. Our protocol operates via inter-vehicle communication (IVC) networks with one omni directional antenna per vehicle and one dedicated short range communication (DSRC) channel. The advantage of our protocol is that it can be used as an optional add-on medium access mechanism to the IEEE 802.11a MAC protocol. We describe in details the operation of our protocol and show the performance analysis in terms of latency, bandwidth, the required communication range and the required distance to an intersection to avoid a collision.

A number of errors have been discovered in the paper "Synthetic traces for trace-driven simulation of cache memories" by D. Thjebaut, J.L. Wolf and H.S. Stone (ibid., vol. 41, pp. 388-410, Apr. 1992). The authors of that paper have corrected some of these errors and presented them in a corrigendum (ibid., vol. 42, pp. 635-636, May 1993). The remaining errors are corrected and presented in this correspondence.>

A multiple bus system provides more bandwidth and a high degree of fault tolerance than a single bus system. But such a system becomes very expensive for a large number of processors and memory modules, due to the requirement of too many connections (switches). Lang (1983) proposed a different bus-based system, known as the partial multiple bus system, which requires a lower number of connections than a multiple bus system, but with a slight degradation in system performance. This paper presents a new type of bus-based system, called the multilevel bus system. Such a bus architecture can be used to design hierarchical multiprocessors. This bus-based system requires significantly less connections than multiple and partial multiple bus systems. This system is very cost-effective, as compared to multiple and partial multiple bus systems, when there exists some locality in the computations. Analytical and simulation models have been developed to determine the performance of both synchronous and asynchronous multilevel bus systems. The results obtained from the analysis show that a multilevel bus system performs fairly close to other bus-based systems for the hierarchical reference (HR) model. In the HR model, a processor accesses its nearest memory modules more frequently than other memory modules.>

For memory bandwidth analysis, researchers generally discard requests that are not accepted during a memory cycle. This assumption simplifies the analysis and produces negligible discrepancies with actual results for a system with a non-hierarchical interconnection network. However, the assumption, "the requests that are not occupied during a memory cycle are discarded," cannot be used for a multiprocessor system with a hierarchical interconnection network (HIN), because the error introduced assumption can be several orders of magnitude higher than the actual bandwidth. An improved analytical model to determine the bandwidth of a HIN-based system is presented.>