**4. Sensing platforms**

70 Urban Development

WiMAX station the higher the speed and the farther the station the lower the speed. Table 2

Vehicular 10-120 km/h Graceful degradation as function of vehicular speed

Mobility Performance

High Speed Vehicular 120 – 350 km/h System should be able to maintain connection

The third-generation (3G) system comprehends a set of standards that aim to support global communication for mobile telecommunication services such as mobile Internet, video calls and mobile TV. These standards are defined in the IMT-2000 vision of the International Telecommunications Union. The most popular implementations of 3G are: UTMS or 3GPP which is widely utilized in Europe, Japan and some parts of Asia and CDMA2000 also referred as 3GPP2 which has been deployed in the United States, South Korea, Belarus, Romania, and some parts of Russia, Japan and China (Etoh, 2005). The IMT-2000 standard aims to provide minimum transmission rates of 2 Mbps for stationary or walking users, and

This technology is built upon the IEEE 802.15.4 standard which defines the physical and MAC layers for low cost and low rate personal area networks. Zigbee has a coverage range of up to 400 meters and a maximum data rate of 250 kbps with network latency between 15 and 30 ms (Backer, 2005). It operates in three different radio bands: 868 Mhz in Europe, 915 Mhz in the USA and Australia, and 2.4 Ghz worldwide. The Zigbee Alliance defines 7 application profiles including building automation, remote control, smart energy, health care, home automation among others. Besides, the research community is also investigating the usage of Zigbee in vehicular applications such as intra-car wireless sensor networks (Tsai et al., 2007), wireless vehicular identification and authentication system (Dissanayake

Bluetooth is a low power consumption and short-range communication system (powerclass-dependent: 1 meter, 10 meters, 100 meters) originally designed to replace cables connecting electronic devices. Bluetooth devices can communicate with up to 7 slave devices forming a piconet network (1 master + 7 slaves), where a piconet is an ad-hoc computer network of interconnected Bluetooth devices. Piconets can communicate with each other forming a scatternet, in which some devices act as bridges to provide communication between piconets. The Bluetooth core system utilizes a protocol stack consisting of a radio protocol, a link control protocol, a link manager protocol and a logical link control and adaptation protocol. It operates in an unlicensed band at 2.4 to 2.485 Ghz. The list of Bluetooth applications includes wireless headsets, printers, keyboards, game controllers (e.g. Nintendo's Wii and Sony's PlayStation), medical equipment, bar code scanners. -

et al., 2008), wireless sensor networks for CO2 monitoring (Hu et al., 2009).

summarizes the mobility performance of WiMAX (Cudak, 2010).

Table 2. WiMAX mobility support.

348 kbps in a moving vehicle (ITU, 2011).

**3.3 Cellular technology (3G)** 

**3.4 Zigbee** 

**3.5 Bluetooth** 

Stationary, Pedestrian 0-10 km/h Optimized

Successful of vehicular networks will depend upon the definition of sensing platforms that allow providing a means of collecting/processing/accessing sensor data. Comprehensive and accurate data are the primary requirement of vehicular networks. Various technologies have been enhanced/developed in recent years to improve this data collection quantity and quality though two main categories can be identified: urban sensing technologies, where field infrastructure is needed and intra vehicular sensors technologies in which a vehicle needs to be equipped. This section describes the most relevant sensing platforms for collecting information about traffic conditions.

### **4.1 Intra vehicular sensors**

Advances in vehicular communications make it possible to implement vehicular sensor networks, i.e., collaborative environments where mobile vehicles that are equipped with sensors of different nature (from toxic detectors to video cameras) interworking to implement monitoring applications. Vehicles continuously collect sensor data from urban streets (e.g., images, accelerometer data, among others), which are then processed to search for information of interest (e.g., recognizing license plates, or inferring trafc patterns). This challenging environment requires novel solutions with respect to those of more-traditional wireless sensor nodes. Additionally, vehicles can be used by the VSN to improve its performance, for example, vehicles have much higher power reserves than a typical mobile computer, power can be drawn from on-board batteries, and recharged as needed from a gasoline or alternative fuel engine, vehicles are orders of magnitude larger in size and weight compared to traditional wireless clients, and can therefore support significantly heavier computing (and sensorial) components.

Some intra vehicular sensors are:


Emerging Technologies for Urban Traffic Management 73

According to research of Lee and Gerla (U. Lee & Gerla, 2010), some technologies for communications in vehicular environments are DSRC/WAVE, cellular networks, WiMAX/802.16e, WiFi/802.11p. These technologies will enable operations related to the improvement of trafc ow, highway safety, and other ITS applications in a variety of

Given the above sensors and communications technologies, it is possible summarizes

Vehicles only equipped with DSRC can operate on infrastructure-free mode (V2V only), infrastructure mode (V2I), and mixed mode (V2V and V2I) as shown in Fig. 2a. Vehicles equipped with other broadband wireless access (i.e., cellular, WiMAX), can operate on scenarios where vehicles can talk to each other via Internet as in Fig. 2b. For instance, people with smartphones and Internet access can conform a P2P overlay network via the Internet. Finally, when vehicles have both DSRC and other broadband wireless access methods, we can have a mixed access scenario (Fig. 2c). Researchers have mostly focused on the rst scenario, yet the second scenario has recently received a lot of attention due to the

In (Hounsell et al., 2009) authors describe other models and technologies that can be used for traffic data collection. For example, inductive loops embedded are used to detect the movement of vehicles over a road surface and is extensively used in traffic responsive traffic signal systems to provide relevant information about traffic conditions such as traffic density, flows and speeds, among others, that can be used to optimize traffic flows. Beaconbased technology detects a vehicle by a 'beacon' positioned at a known location employing various technologies such as microwave, infra-red and dedicated short-range

application environments.

vehicular networking scenarios as shown in figure 2.

Fig. 2. Wireless vehicular networking scenarios.

widespread usage of smartphones and WiBro (Lee & Gerla, 2010).

speech suggestion of CW will be activated and the evaluation degree is also sent to the far-end monitoring center (U. Lee & Gerla, 2010).

