Research of heterogeneous service providing in the fast-changing topology vehicular communication networks are important because expansion and integration of this intelligent transport systems platform would greatly improve traffic safety and reduce injuries on the road. At the same time, the trips would be more comfortable. In this work, it is investigated data-transfer capabilities for heterogeneous service support, road safety, assessed their integration potentials and prospects in vehicle communication networks with changing topology. It is showed that to provide quality heterogeneous services it is necessary new routing protocols and channel access methods for the large volume fast changing topology networks.
Today, the vehicle is a very important component of human life, so installed intelligence based software and hardware equipment, can improve the level of travel safety and comfort. Currently, one of the most attentions attracting mobile communication technology is vehicular wireless communication networks. They offer the potential to develop and produce safer, more reliable, economic and comfortable vehicles. These networks are gaining more and more commercial relevance, since the adoption of DSRC (Dedicated Short-Range Communication) / IEEE 802.11p (Wireless access in vehicular environments (WAVE)) standards in both the EU and the U.S., given the possibility to reach an entirely new level of service in a vehicle, covering many areas, including road safety, traffic management, comfort applications. Vehicles do not have strict restrictions on power consumption, and therefore, can be easily equipped with powerful computing devices, wireless transmitters, sensors, complex
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systems - GPS, photo / video cameras, vibration, acoustic, chemical sensors and, etc.
[
Practices of vehicular communication network's deployment, research and
scientific projects are developing in two directions: direct vehicle-vehicle (V2V)
communication and vehicle-to-infrastructure (V2I) communication [
This paper explores the evaluation of the data-transfer efficiency in a mobile communication network when the sender and the receiver is moving in opposite directions at high speed. It is organized as follows: in Section 1, we analyze the vehicular communication networks and their architecture, in Section 2, we briefly present related works. Section 3 describes the experiment methodology and simulation model. In Section 4, we provide the simulation results for our model. Section 5 offers our conclusions and prospects for future research.
Vehicular communication networks can be formed spontaneously between the moving
nodes that are equipped with the homogeneous or heterogeneous wireless interfaces
(802.11a/b/g/n/p, WiMax, 3G, LTE and so on.). These networks, also known as the
VANET (Vehicular Ad-Hoc Network) is one of the MANET (mobile ad-hoc network)
applications, allowing communication between the nearby vehicles and vehicles and
stationary equipment (road side units). Vehicular communication application areas can
be divided into three main categories: general information - multimedia services, road
safety and traffic monitoring and management services [
An analysis of the scenarios where the communication is made between the sender
and the recipient moving in the opposite directions was made; it is given in Table 1.
1.1. The Specific Characteristics of the Vehicular Communication Networks
Vehicular communication networks have special characteristics and properties that
distinguish them from other types of mobile communication networks. According to
[
High energy reserve; Huge mass and size of the vehicle;
Moving by the patterns. Vehicles have much greater energy reserves, compared with a conventional mobile device. Energy can be obtained from the rechargeable battery and gasoline, diesel or alternative-fuel motor. The vehicles are many times greater and larger compared to traditional wireless devices, and therefore, can support a much greater and heavier computing, radio and sensor components. Computers can be bigger, faster, and provide very high-capacity memory devices (terabytes of data), and powerful wireless interfaces, capable of high speed communication. The vehicles can move at very high speed (160 km/h or more), making it difficult to maintain a consistent, coherent V2V communication. However, the existing statistical data on vehicle movements, such as the movement together according to certain patterns or peak time can help to maintain a link between the mobile automotive groups. Vehicle at any time may be out of communication coverage (WiFi, cellular, satellite, etc.), so the network protocols must be designed so that it can easily connect to the Internet, in normal mode. Despite the many positive unique features, vehicular network's development is faced with specific challenges, as their primary: • • • • •
Large-scale networks; High level of mobility; Fragmentation of the network; Changing topology;
Complex communication quality assurance.
Unlike the literature described ad-hoc networks, which are quite limited in size, vehicular communication networks, in principle, can extend across the road network and cover a huge amount of network equipment (vehicles). The environment in which networks are operating is extremely dynamic and, in some cases it may be highly different, for example, in highway speeds can reach up to 300 km/h, in the low-density roads car density may be as only about 1-2 cars kilometer. On the other hand, the speed of cars in urban areas is 50-60 km/h and the car density is quite high, particularly during the peak periods. Often vehicular communication networks may be fragmented.
The dynamic nature of traffic can lead to large gaps between cars in sparsely
populated areas; it can also be created a few isolated clusters of network nodes.
Vehicular communication networks' scenarios are highly different from the classic
adhoc networks, since the cars are moving and constantly changing positions, scenarios
are highly dynamic. Furthermore, the network topology changes extremely frequently,
since the very frequent connections and disconnects between network nodes. In fact,
the degree to which the network is combined depends on two factors: the distance
between the wireless nodes and number of connected vehicles [
There is a growing literature on data-transfer capabilities for heterogeneous service support within vehicular networks, some of which have also considered the application of our analyzing problem. We briefly discuss the key the most recent relevant references next, and highlight their difference from our approach.
Analysis of the performance of DSRC-based VANETs in delivering CVSS
(Cooperative vehicle safety systems) messages was made in [
M. Kurmis et al. / Investigation of Data Transfer Capabilities for Heterogeneous Service Support… 157 CVSS tracking application. A study into how controllable parameters such as rate and range of transmission affect this performance measure has revealed interesting properties of IDR. It is shown that robust control of rate or range of transmission based on the relationship between IDR and channel occupancy is possible. Based on these concepts, a robust range control method is analyzed and evaluated.
Another performance evaluation of information propagation in a vehicular ad-hoc
network was made in [
In [
The performance modeling of message dissemination in vehicular ad-hoc networks
with two priority classes of traffic was presented in [
Performance of the 802.11p Physical Layer was estimating in the [
Nevertheless, the growing number in of researches in terms of data-transfer capabilities in vehicular communication networks, none of them investigates a special scenario where the nodes are moving in the opposite direction in a highway. From this point of view, our work is different and novel.
As it was mentioned in the previous section, the services in the vehicular communication networks can be classified into the road safety, information and multimedia services' categories. To support high-quality services it must be taken into account the data rate, packet delivery efficiency and collision rate. The analysis shows systematic data quality requirements for different services for vehicular communication networks (Table 2). To determine the influence of the number of vehicles in connection capacity it was made a number of experiments which goal is to evaluate data-transfer efficiency when providing mobile multimedia services in the communicative network between in the opposite directions moving sender and receiver nodes at high speed.
The experiments were carried out in the simulation environment NCTUns 6.0 [
It was analyzed and structured requirements for the NCTUns simulation model (Table 3). The experiment was carried out when the number of nodes in the network is from 10 to 100 - simulating different traffic congestion to determine the impact of the vehicle's number for the data-transfer efficiency. Senders and receiver's nodes are moving at high speed (130 km/h) in the opposite directions. The remaining vehicles are moving at different speeds from 90 km/h to 150 km/h, and their speed and directions of movement are spread evenly. These parameters are chosen to simulate the realistic movement of cars on highway conditions.
During the experiments, it was evaluated data transmission efficiency – outgoing throughput, download throughput, packet drops and collisions with a different number of vehicles on the network. The data was transmitted using the UDP protocol, and a packet size of 1000 bytes. Simulation was carried out for 60 seconds. The assumption was made that the communication time between the sender and the recipient is directly proportional to the number of cars on the network. Furthermore, with increasing number of nodes it is expected to increase the collision rate and rejected packets.
Analysis of the data collected during the experiments shows the download speed versus time, with a different node's number on the network (Figure 2). The graph shows that the longest communication time is achieved by operating the largest network of vehicles - 100. With the maximum number of vehicles, the network coverage increases, so the data can be transferred for a longer period of time. With 100 vehicles and about 330 KB/s data transfer rate, we have managed to maintain communication for 30 seconds. The speed from 31 s decreased to 50 Kb/s, but from 37 s to 41 s the rate rises to 230 Kb/s, and from 46 s to 48 s - to 130 KB/s. When the vehicles passed each other the connection was lost. The minimum data rate was achieved by the network operating 50 vehicles. Moreover, in this case, the shortest communication time is achieved. With a small number of vehicles (10-30), it is maintained a relatively high data transfer rate, due to the low collision rate. 1 6 11 16 21 26
31 Time, s 36 41 46 51 56 After the experiment, the other important parameter - the average data uplink and downlink throughput was measured (Figure 3). In this case, the highest mean transfer rate achieved by the network operating 20 vehicles, while the meanest - 30. The maximum average data rate of downlink – 100 vehicles, while the meanest – 50.
It was found out collision's dependence on sender and receiver nodes with a different number of vehicles (Figure 4). Collision rate is directly proportional to the number of vehicles. Up to 40 vehicles, collisions rate at the receiver and sender nodes is similar, but from 50 vehicles, collision is greater in sender node because of unsuitable channel access mechanisms. 16000 s14000 n io12000 s il lo10000 c fo 8000 er 6000 b m4000 u N 2000 0
It was performed the experiments in which was investigated communication and datatransfer efficiency between at high speed moving sender and receiver nodes in the opposite directions, in the mobile multimedia services communicative network. The goal was reached, and it was estimated the transmission efficiency and quality of communication. It was found that the longest communication can be maintained at the maximum number of vehicles, but that communication quality is inversely proportional
M. Kurmis et al. / Investigation of Data Transfer Capabilities for Heterogeneous Service Support… 161 with the number of vehicles, as the increasing number of vehicles - increasing data and network flooding occurs in many collisions.
To provide quality heterogeneous services it is necessary new routing protocols and channel access methods for the large volume fast changing topology networks. This investigation is important because it examining problems associated with communication between the sender and the receiver moving in opposite directions in highway, where the network topology varies very rapidly and, which may contain from one to several hundred of the network nodes. Future plans to extend the study to include other proactive, reactive and hybrid (ADV, DSDV, AORP, etc.) routing protocols.
The authors thank the Projects LLII-061 Development of Joint Research and Training Centre in High Technology Area and LLIV-215 JRTC Extension in Area of Development of Distributed Real-Time Signal Processing and Control Systems for the possibility to complete a scientific research.