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22
Vehicular Opportunistic Communication Under the Microscope
- In ACM MobiSys
, 2007
"... We consider the problem of providing vehicular Internet access using roadside 802.11 access points. We build on previous work in this area [18, 8, 5, 11] with an extensive experimental analysis of protocol operation at a level of detail not previously explored. We report on data gathered with four c ..."
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We consider the problem of providing vehicular Internet access using roadside 802.11 access points. We build on previous work in this area [18, 8, 5, 11] with an extensive experimental analysis of protocol operation at a level of detail not previously explored. We report on data gathered with four capture devices from nearly 50 experimental runs conducted with vehicles on a rural highway. Our three primary contributions are: (1) We experimentally demonstrate that, on average, current protocols only achieve 50 % of the overall throughput possible in this scenario. In particular, even with a streamlined connection setup procedure that does not use DHCP, high packet losses early in a vehicular connection are responsible for the loss of nearly 25 % of overall throughput, 15 % of the time. (2) We quantify the effects of ten problems caused by the mechanics of existing protocols that are responsible for this throughput loss; and (3) We recommend best practices for using vehicular opportunistic connections. Moreover, we show that overall throughput could be significantly improved if environmental information was made available to the 802.11 MAC and to TCP. The central message in this paper is that wireless conditions in the vicinity of a roadside access point are predictable, and by exploiting this information, vehicular opportunistic access can be greatly improved.
CARS: Context Aware Rate Selection for Vehicular Networks
- In ICNP
, 2008
"... Abstract—Traffic querying, road sensing and mobile content delivery are emerging application domains for vehicular networks whose performance depends on the throughput these networks can sustain. Rate adaptation is one of the key mechanisms at the link layer that determine this performance. Rate ada ..."
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Abstract—Traffic querying, road sensing and mobile content delivery are emerging application domains for vehicular networks whose performance depends on the throughput these networks can sustain. Rate adaptation is one of the key mechanisms at the link layer that determine this performance. Rate adaptation in vehicular networks faces the following key challenges: (1) due to the rapid variations of the link quality caused by fading and mobility at vehicular speeds, the transmission rate must adapt fast in order to be effective, (2) during infrequent and bursty transmission, the rate adaptation scheme must be able to estimate the link quality with few or no packets transmitted in the estimation window, (3) the rate adaptation scheme must distinguish losses due to environment from those due to hiddenstation induced collision. Our extensive outdoor experiments show that the existing rate adaptation schemes for 802.11 wireless networks underutilize the link capacity in vehicular environments. In this paper, we design, implement and evaluate CARS, a novel Context-Aware Rate Selection algorithm that makes use of context information (e.g. vehicle speed and distance from neighbor) to systematically address the above challenges, while maximizing the link throughput. Our experimental evaluation in real outdoor vehicular environments with different mobility scenarios shows that CARS adapts to changing link conditions at high vehicular speeds faster than existing rate-adaptation algorithms. Our scheme achieves significantly higher throughput, up to 79%, in all the tested scenarios, and is robust to packet loss due to collisions, improving the throughput by up to 256% in the presence of hidden stations. I.
MAC in Motion: Impact of Mobility on the MAC of Drive-Thru Internet
"... Abstract—The pervasive adoption of IEEE 802.11 radios in the past decade has made possible for the easy Internet access from a vehicle, notably drive-thru Internet. Originally designed for the static indoor applications, the throughput performance of IEEE 802.11 in the outdoor vehicular environment ..."
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Abstract—The pervasive adoption of IEEE 802.11 radios in the past decade has made possible for the easy Internet access from a vehicle, notably drive-thru Internet. Originally designed for the static indoor applications, the throughput performance of IEEE 802.11 in the outdoor vehicular environment is, however, still unclear especially when a large number of fast-moving users transmitting simultaneously. In this paper, we investigate the performance of IEEE 802.11 DCF in the highly mobile vehicular networks. We first propose a simple yet accurate analytical model to evaluate the throughput of DCF in the large scale drive-thru Internet scenario. Our model incorporates the high node mobility with the modeling of DCF and unveils the impacts of mobility (characterized by node velocity and moving directions) on the resultant throughput. Based on the model, we show that the throughput of DCF will be reduced with increasing node velocity due to the mismatch between the MAC and the transient high-throughput connectivity of vehicles. We then propose several enhancement schemes to adaptively adjust the MAC in tune with the node mobility. Extensive simulations are carried out to validate the accuracy of the developed analytical model and the effectiveness of the proposed enhancement schemes. Index Terms—Vehicular Networks, mobility, distributed coordinated function (DCF), embedded Markov chain. 1
Sparse WiFi Deployment for Vehicular Internet Access with Bounded Interconnection Gap
"... Vehicular Internet access via open WLAN access points (AP) has been demonstrated to be a feasible solution to provide opportunistic data service to moving vehicles. Using an in situ deployment, however, such a solution does not provide worstcase performance guarantees due to unpredictable intermitt ..."
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Vehicular Internet access via open WLAN access points (AP) has been demonstrated to be a feasible solution to provide opportunistic data service to moving vehicles. Using an in situ deployment, however, such a solution does not provide worstcase performance guarantees due to unpredictable intermittent connectivity. On the other hand, a solution that tries to cover every point in an entire road network with APs (a full coverage) is not very practical due to prohibitive deployment and operational costs. In this paper, we introduce a new notion of intermittent coverage for mobile users, called α-coverage, which provides worst-case guarantees on the interconnection gap while using significantly fewer APs than needed for full coverage. We propose efficient algorithms to verify whether a given deployment provides α-coverage and approximation algorithms for determining an economic deployment of APs that will provide α-coverage. Our algorithms can also be used to supplement open WLAN APs in a region with appropriate number of additional APs that will provide worst-case guarantees on interconnection gap. We compare α-coverage with opportunistic access of open WLAN APs (modeled as a random deployment) via simulations over real-world road networks and show that using the same number of APs as in case of random deployment, α-coverage limits the interconnection gap to a much smaller distance.
Dynamic Optimal Random Access for Vehicle-to-Roadside Communications
"... Abstract—In a drive-thru scenario where vehicles drive by a roadside access point (AP) to obtain temporary Internet access, it is important to design efficient resource allocation schemes to fully utilize the limited communication opportunities. In this paper, we study the random access problem in d ..."
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Abstract—In a drive-thru scenario where vehicles drive by a roadside access point (AP) to obtain temporary Internet access, it is important to design efficient resource allocation schemes to fully utilize the limited communication opportunities. In this paper, we study the random access problem in drivethru communications in a dynamic environment, where both the channel contention level and channel capacity vary over time. We assume that a vehicle has a file to upload when it is within the coverage range of the AP. The vehicle will pay a fixed amount each time it tries to access the AP, and will incur a penalty if it cannot finish the file uploading when leaving the AP. We first formulate the optimal transmission problem as a finite-horizon sequential decision problem. Then we solve the problem using dynamic programming, and design a dynamic optimal random access algorithm. Simulation results based on a realistic vehicular traffic model show that our algorithm achieves the minimal total cost, the highest probability of completing file upload, and the highest upload ratio as compared with two other heuristic schemes. I.
Enabling Location Specific Real-time Mobile Applications
"... As cellular networks open up and foster the deployment of richer user-centric mobile services, we envision the evolution of a new class of services that involve significant mobile user collaboration for making the services realizable and rapidly deployable. Our position is grounded on the intuition ..."
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As cellular networks open up and foster the deployment of richer user-centric mobile services, we envision the evolution of a new class of services that involve significant mobile user collaboration for making the services realizable and rapidly deployable. Our position is grounded on the intuition that mobile devices that users carry can act as “powerful ” sensors for diverse information about a specific location, and can aid in providing real-time updates to other interested users that are not present at the location. Realizing such services is, however, challenging due to the need for several mechanisms such as (a) incentives for participation from users and network providers, (b) locationspecific data collection and delivery and (c) determining trust in users providing updates. These mechanisms become significantly more complex to realize with user mobility. Unifying these mechanisms, in this paper, we propose a framework FLORA that enables rapid evolution of location-specific real-time services.
An Open Onboard Internet System Model for the MCommerce on Train
- in International Conference on Management and Service Science. MASS ‘09
, 2009
"... Abstract—An open onboard Internet system model based on the centralized access mode is designed for the M-Commerce on train which is easy to merge the oncoming broadband wireless access and network technologies.The functionalities and entities in each layer are investigated and the hot issues are di ..."
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Abstract—An open onboard Internet system model based on the centralized access mode is designed for the M-Commerce on train which is easy to merge the oncoming broadband wireless access and network technologies.The functionalities and entities in each layer are investigated and the hot issues are discussed according to this model. It is shown that the onboard Internet applications including the M-Commerce on train are feasiable based on this open model.
Design Principles for Robust Opportunistic Communication
"... Abstract—A mobile device can simultaneously increase its throughput and dramatically reduce energy and bandwidth usage costs by exploiting transient communication opportunities. We argue that this opportunistic communication mode will play a significant role in future mobile communication systems. W ..."
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Abstract—A mobile device can simultaneously increase its throughput and dramatically reduce energy and bandwidth usage costs by exploiting transient communication opportunities. We argue that this opportunistic communication mode will play a significant role in future mobile communication systems. We present some non-trivial applications that exploit opportunistic communication and their corresponding communication requirements. We outline the Opportunistic Communication Management Protocol, developed over the last four years at the University of Waterloo, that meets most of these requirements. We then focus on some design principles for robust opportunistic communication drawing from our experiences in developing and deploying several practical systems. We conclude with a sketch of some areas for future research. I.
Measurement-based Design of Roadside Content Delivery Systems
"... Abstract—With today’s ubiquity of thin computing devices, mobile users are accustomed to having rich location-aware information at their fingertips, such as restaurant menus, shopping mall maps, movie showtimes and trailers. However, delivering rich content is challenging, particularly for highly mo ..."
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Abstract—With today’s ubiquity of thin computing devices, mobile users are accustomed to having rich location-aware information at their fingertips, such as restaurant menus, shopping mall maps, movie showtimes and trailers. However, delivering rich content is challenging, particularly for highly mobile users in vehicles. Technologies such as cellular-3G provide limited bandwidth at significant costs. In contrast, providers can cheaply and easily deploy a small number of WiFi infostations that quickly deliver large content to vehicles passing by for future offline browsing. While several projects have proposed systems for disseminating content via roadside infostations, most use simplified models and simulations to guide their design for scalability. Many suspect that scalability with increasing vehicle density is the major challenge for infostations, but few if any have studied the performance of these systems via real measurements. Intuitively, per-vehicle throughput for unicast infostations degrades with the number of vehicles near the infostation, while broadcast infostations are unreliable, and lack rate adaptation. In this work, we collect over 200 hours of detailed highway measurements with a fleet of WiFi-enabled vehicles. We use analysis of these results to explore the design space of WiFi infostations, in order to determine whether unicast or broadcast should be used to build high-throughput infostations that scale with device density. Our measurement results demonstrate the limitations of both approaches. Our insights lead to Starfish, a high-bandwidth and scalable infostation system that incorporates device-to-device data scavenging, where nearby vehicles share data received from the infostation. Data scavenging increases dissemination throughput by a factor of 2–6, allowing both broadcast and unicast throughput to scale with device density.
DORA: Dynamic Optimal Random Access for Vehicle-to-Roadside Communications
"... Abstract-In this paper, we study random access in a drivethru scenario, where roadside access points (APs) are installed on a highway to provide temporary Internet access for vehicles. We consider vehicle-to-roadside (V2R) communications for a vehicle that aims to upload a file when it is within th ..."
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Abstract-In this paper, we study random access in a drivethru scenario, where roadside access points (APs) are installed on a highway to provide temporary Internet access for vehicles. We consider vehicle-to-roadside (V2R) communications for a vehicle that aims to upload a file when it is within the APs' coverage ranges, where both the channel contention level and transmission data rate vary over time. The vehicle will pay a fixed amount each time it tries to access the APs, and will incur a penalty if it cannot finish the file uploading when leaving the APs. First, we consider the problem of finding the optimal transmission policy with a single AP and random vehicular traffic arrivals. We formulate it as a finite-horizon sequential decision problem, solve it using dynamic programming (DP), and design a general dynamic optimal random access (DORA) algorithm. We derive the conditions under which the optimal transmission policy has a threshold structure, and propose a monotone DORA algorithm with a lower computational complexity for this special case. Next, we consider the problem of finding the optimal transmission policy with multiple APs and deterministic vehicular traffic arrivals thanks to perfect traffic estimation. We again obtain the optimal transmission policy using DP and propose a joint DORA algorithm. Simulation results based on a realistic vehicular traffic model show that our proposed algorithms achieve the minimal total cost and the highest upload ratio as compared with some other heuristic schemes. In particular, we show that the joint DORA scheme achieves an upload ratio 130% and 207% better than the heuristic schemes at low and high traffic densities, respectively. Index Terms-Random access, medium access control, vehicular ad hoc networks, dynamic programming, Markov decision processes, threshold policy.
