1,721,069 research outputs found
Congestion Control Mechanisms in IEEE 802.11p and Sidelink C-V2X
No full textConnected vehicles are expected to play a major role in the next future to improve safety and traffic efficiency on the road and short-range technologies have been defined to enable the direct exchange of information. To this aim, two solutions are currently the subject of a debate that goes beyond the technician, i.e., IEEE 802.11p and sidelink cellular-vehicle-to-anything (C-V2X). Tested and mature for deployment the first, possibly more efficient the second. In both cases, one of the main aspects is the management of channel congestions, which can cause serious packet losses and have a critical impact on the reliability of applications. Congestions can be managed through different approaches, including the control of transmission power, packet generation frequency, and the adopted modulation and coding scheme. Congestion management has been well studied in IEEE 802.11p, with consolidated algorithms included in the standards, whereas it appears somehow as a new topic looking at C-V2X. In this work, a review of the main congestion control mechanisms and a discussion of their applicability and efficiency in the two technologies is provided. This topic is addressed without focusing on specific algorithms and with the aim to provide general guidelines as a starting point for new proposals
A softer vertical handover algorithm for heterogeneous wireless access networks
No full textFuture wireless access will involve a variety of integrated and interworking technologies. Depending on the conditions (e.g., the specific application, the quality of service requirements, the user mobility) each session will be served through the most suited access network; following some event, there will be a variation of the access technology, which is called vertical handover. Although the use of one technology at a time is mostly envisioned, the use of multiple wireless links at the same time, hereafter called parallel transmission, is also envisioned for higher throughput. On the basis of parallel transmission, in this paper the original definition of softer vertical handover is given and an algorithm for softer vertical handover in heterogeneous wireless access networks is proposed; the achievable improvement is shown in two reference scenarios
On uncoordinated multi user multi RAT combining
No full textNowadays, wireless systems allow us to have connectivity almost everywhere. Different radio access technologies are integrated in the same device and they can be used following the specific service requirements, the actual received signal levels, and the costs related to their use. Presently, technologies are always seen as alternatives, but it is envisioned that different wireless connections may be used cooperatively in order to enhance the throughput perceived by the end user. In this paper we discuss this opportunity trying to understand what would be the impact of a multi technology combining in a multi user scenario with no coordination among access networks. © 2011 IEEE
WLAN hot spots to increase UMTS capacity
No full textThe seamless integration of heterogeneous wireless access networks is currently one of the issues of major interest in the field of telecommunication systems. In an early future technologies like UMTS, WLAN and WiMAX will give broadband access to users that perform their voice/video calls or data sessions without knowledge of the specific technology their terminals are using, following the paradigm of always best connected. In this scenario, UMTS and WLAN integration has a primary role, due to the coverage of cellular systems and the low cost of the latter technology. This work, in particular, focuses on the gain in terms of capacity that the deployment ofWLAN access points allows in an area fully covered by an UMTS network, assuming that the radio resources are not managed by complex multi radio resource management algorithms. For this scope a real scenario is accurately simulated and the end users perception is evaluated taking care of all aspects related to each level of the protocol stack, with particular attention to radio propagation. ©2010 IEEE
Position based routing in crowd sensing vehicular networks
Full text linkUsing vehicles as sensors allows to collect high amount of information on large areas without the need to deploy extensive infrastructures. Although cellular technologies are presently the only solution to upload data from vehicles to control centers, in the next future short range wireless technologies could be used to offload part of this data traffic through vehicle to vehicle and vehicle to roadside communications. In such scenario, the greedy forwarding (GF) position based routing is an interesting algorithm to efficiently route packets from vehicles to the destination. However, GF suffers from the well known problem of local minima, which causes part of the packets to remain blocked in certain areas of the scenario. To deal with this issue, we propose two novel routing algorithms, specifically designed for crowd sensing vehicular networks (CSVNs): GF with available relays (GFAVR), fully distributed and independent of the scenario, and GF with virtual roadside units (GFVIR), exploiting a preliminary design phase where local minima are located. Through extensive simulations performed in different realistic urban scenarios, results demonstrate that both algorithms allow to improve data delivery by 10-40%, with negligible overhead and limited increase of complexity
Adaptive cross-layer techniques for cellular systems and WLANs: Simulative results within NEWCom Proj.C
No full textThis work reports some results of a joint activity research pursued within the Project C of NEWCom (European network of excellence in communications). The aim of the activity is to investigate adaptive cross-layer techniques for heterogeneous wireless networks and try to obtain some general rules. In particular the singular or joint adaptation of scheduling and link adaptation algorithms is studied by means of simulation platforms for which proper scenarios and metrics have been defined
Vehicular visible light networks for urban mobile crowd sensing
Full text linkCrowd sensing is a powerful tool to map and predict interests and events. In the future, it could be boosted by an increasing number of connected vehicles sharing information and intentions. This will be made available by on board wireless connected devices able to continuously communicate with other vehicles and with the environment. Among the enabling technologies, visible light communication (VLC) represents a low cost solution in the short term. In spite of the fact that vehicular communications cannot rely on the sole VLC due to the limitation provided by the light which allows communications in visibility only, VLC can however be considered to complement other wireless communication technologies which could be overloaded in dense scenarios. In this paper we evaluate the performance of VLC connected vehicles when urban crowd sensing is addressed and we compare the performance of sole vehicular visible light networks with that of VLC as a complementary technology of IEEE 802.11p. Results, obtained through a realistic simulation tool taking into account both the roadmap constraints and the technologies protocols, help to understand when VLC provides the major improvement in terms of delivered data varying the number and position of RSUs and the FOV of the receiver
Performance analysis of multi-relay SWIPT systems with random placement of nodes
No full textTo facilitate the demand for a higher spectrum and power efficiency, relay-aided cooperative communication is considered as one of the most efficient techniques for achieving high data rate and coverage. In this work, we consider a scenario where the relays are not equipped with fixed batteries but collect the required energy (for processing and transmission purposes) via simultaneous wireless information and power transfer (SWIPT). To investigate the beneficial effect of the presence of many energy harvesting relays, we propose an analytical evaluation of the overall amount of power that can be received by the destination under a large class of propagation and fading models. The results show that, although the power received at the destination by the relays is obviously lower than the amount of the power from the direct source-destination link, this effect can be significantly reduced in dense node scenarios
A survey on the roadmap to mandate on board connectivity and enable V2V-based vehicular sensor networks
Full text linkVehicles will soon be connected and will be interacting directly with each other and with the road infrastructure, bringing substantial benefits in terms of safety and traffic efficiency. The past decade has seen the development of different wireless access technologies for vehicle-to-everything (V2X) communications and an extensive set of related use cases have been drafted, each with its own requirements. In this paper, focusing on short-range communications, we analyze the technical and economic motivations that are driving the development of new road users’ connectivity, discussing the international intentions to mandate on board devices for V2X communication. We also go in depth with the enabling wireless access technologies, from IEEE 802.11p to short-range Cellular-V2X and other complementary technologies, such as visible light communication (VLC) and millimeterWaves, up to hybrid communication and 5G. We conclude our survey with some performance comparison in urban realistic scenarios, underlying that the choice of the future enabling technology is not so easy to predict and mostly depends on mandatory laws at the international level
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