This paper investigates the use of WiFi and mobile device-to-device networks, with vehicular ad hoc networks being a typical example, as a complementary means to offload and reduce the traffic load of cellular networks. A novel cooperative content dissemination strategy is proposed for a heterogeneous network consisting of different types of devices with different levels of mobility, ranging from static WiFi access points to mobile devices such as vehicles. The proposed strategy offloads a significant proportion of data traffic from cellular networks to WiFi or device-to-device networks. Detailed analysis is provided for the content dissemination process in heterogeneous networks adopting the strategy. On that basis, the optimal parameter settings for the content dissemination strategy are discussed. Simulation and numerical studies show that the proposed strategy effectively reduces data traffic for cellular networks while guaranteeing successful content delivery.
With the fast development in ad hoc wireless communications and vehicular technology, it is foreseeable that, in the near future, traffic information will be collected and disseminated in real-time by mobile sensors instead of fixed sensors used in the current infrastructure-based traffic information systems. A distributed network of vehicles such as a vehicular ad hoc network (VANET) can easily turn into an infrastructure-less self-organizing traffic information system, where any vehicle can participate in collecting and reporting useful traffic information such as section travel time, flow rate, and density. Disseminating traffic information relies on broadcasting protocols. Recently, there have been a significant number of broadcasting protocols for VANETs reported in the literature. In this paper, we classify and provide an in-depth review of these protocols. A major problem in wireless sensor network localization is erroneous local geometric realizations in some parts of the network due to the sensitivity to certain distance measurement errors, which may in turn affect the reliability of the localization of the whole or a major portion of the sensor network. This phenomenon is well-described using the notion of "flip ambiguity" in rigid graph theory. In a recent study by the coauthors, an initial formal geometric analysis of flip ambiguity problems has been provided. The ultimate aim of that study was to quantify the likelihood of flip ambiguities in arbitrary sensor neighborhood geometries. In this paper we propose a more general robustness criterion to detect flip ambiguities in arbitrary sensor neighborhood geometries in planar sensor networks. This criterion enhances the recent study by the coauthors by removing the assumptions of accurately knowing some inter- sensor distances. The established robustness criterion is found to be useful in two aspects: (a) Analyzing the effects of flip ambiguity and (b) Enhancing the reliability of the location estimates of the prevailing localization algorithms by incorporating this robustness criterion to eliminate neighborhoods with flip ambiguity from being included in the localization process. Wireless access through vehicle-to-roadside (V2R) communications can be used in public transportation vehicles for streaming applications, e.g., video and interactive advertisements. Efficient wireless access schemes are required to minimize the cost of wireless connectivity for downloading data and to minimize the probability of buffer outage (or underrun) during playout of the streaming data. In this paper, a hierarchical optimization framework is presented to obtain both short- and long-term optimal decisions on wireless access for streaming applications in a public transportation system. This framework considers the application requirements, the cost of wireless connectivity for transit service provider, and the revenue of the wireless network service provider. The onboard unit in a vehicle makes a short-term decision on whether to download streaming data while it is in the coverage area of a roadside unit (RSU). The objective of this decision is to minimize the cost of wireless connectivity while satisfying the application quality-of-service (QoS) requirement in terms of the maximum buffer underrun probability. The transit service provider makes a long-term decision on whether to reserve wireless access or to access wireless service in an on-demand basis in a service area of an RSU. The network service provider makes a long-term decision on pricing on-demand wireless access for V2R communications so that the highest revenue is achieved.