Scientists and Technologists involved in the development of radar and remote sensing systems all over the world are now trying to involve themselves in saving of manpower in the form of developing a new application of their ideas in Intelligent Transport system(ITS). The world statistics shows that by incorporating such wireless radar system in the car would decrease the world road accident by 8-10% yearly. The wireless technology has to be chosen properly which is capable of tackling the severe interferences present in the open road. A combined digital technology like Spread spectrum along with diversity reception will help a lot in this regard. Accordingly, the choice is for FHSS based space diversity system which will utilize carrier frequency around 5.8 GHz ISM band with available bandwidth of 80 MHz and no license. For efficient design, the radio channel is characterized on which the design is based. Out of two available modes e.g. Communication and Radar modes, the radar mode is providing the conditional measurement of the range of the nearest car after authentication of the received code, thus ensuring the reliability and accuracy of measurement. To make the system operational in simultaneous mode, we have started the Software Defined Radio approach for best speed and flexibility.
Speed limit in the super highways is generally not imposed on the cars moving at their highest possible speeds. As a result, it often results in severe accidents and deaths. A CDMA radar based collision avoidance system can therefore be thought of which is to be fitted in the cars. This paper will highlight the detailed development of such radar for collision avoidance of cars.
CDMA Technology and its several versions are also popular for communication. It can also be exploited for a wide range of applications including range measurement, material penetration and low probability of interception. DS-CDMA, CDMA2000, MC-CDMA and MIMO CDMA [2], [3] are the different versions of same technology. The heart of such CDMA technology is the spread spectrum technology using PN sequence coding. The CDMA based digital radar technology will give rise to several advantages over conventional radars so that it can be used in ITS application successfully.
Additionally, the same technology can also be explored to meet the communication need in ITS application [1].
The above mentioned two applications of CDMA in ITS can be further expanded in an IMCN which is modeled as shown in figure A. There are 4 cells namely cell1, cell2, cell3 and cell4 where each cell is defined as the geographical area of typically 100 meter over which a wireless communication is to be established between a mobile user and a fixed Base station. cell 1 and cell 2 are the two neighboring cells whereas cell3 and cell4 are another two remote neighboring cells. The four base stations will be placed on the rooftop of each building. All the four Base stations have their wireless connectivity with their respective wireless mobile handsets using the carrier frequency near 5.8GHz. The two neighboring base stations are connected by an MSC (Master Switching Center). So to have a total integrity among the four base stations two MSC namely MSC1 and MSC2 are required. As shown in figure A, MSC1 connects cell1 and cell2 whereas MSC2 connects cell3 and cell4. Each MSC is physically separated by a distance of 200 meter or more and is linked with the wireless network using 12 GHz microwave carrier. Thus the total system will provide full duplex communication with higher data rate of 64 Mbits/s approximately. Thus the total IMCN is too complex requiring a knowledge of several technologies for its design and successful implementation. This paper will highlight only the CDMA technology and other relevant technologies used for the communication and radar applications utilized in the car. The authors are encouraged to exploit the latest digital communication and digital radar technology in their design and implementation.
A radio mounted on the car will normally face a lots of problems like:
- Active Interferences comprising both adjacent as well as co-channel interference ( ACI & CCI). 2. Passive Interference coming from multi path .
When the handset and base station are within line of sight, the primary propagation will usually be the line of sight and secondary propagations due to reflections will be less significant [6]. Reflected propagations become more significant if the line of sight is obstructed. Figure 1 illustrates a simplified multi path propagation. Whenever there is more than one significant impinging wave (with different phases) on a mobile receive antenna, the receiver will be subject to varying signal levels as it moves around. This is caused by constructive and destructive addition of the impinging waves due to their different phase offsets. This mechanism is called multi path fading.
The idea of antenna diversity is that if receive antenna A is experiencing a low signal level due to fading, also called a deep fade, Antenna B will probably not suffer from the same deep fade, provided the two antennas are displaced in position or in polarity. A Matlab based simulation is conducted in the Laboratory considering slow fading and the received signal strength variation is illustrated in figure 2.
The option to select the best antenna significantly improves performance in outdoor environments, but does not necessarily increase the maximum line-of-sight range of a product. Figure 3 illustrates the effect of selecting the best antenna. Antenna diversity is implemented by equipping the base station or handset (or both) with two antennas. Various selection schemes can be implemented, depending on the actual antenna setup. Preamble antenna diversity, also known as fast antenna diversity, has proven its use in fast frequency hopping systems. Preamble antenna diversity is implemented by comparing the RSSI value of each antenna in the beginning of each receive burst. Region II: reception at 12.5 GHz is faded by approximately 30 dB while 11.5 GHz reception remains steady.
Region III: reception at 11.5 GHz is faded by approximately 30 dB while 12.5 GHz reception remains steady. The reason for the above interesting observation is that the same path specified by sea
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