The invention in particular relates to radar based positioning system.
BACKGROUND OF THE INVENTION:
Accuracy and precision are crucial assets of good measurement techniques. The same applies to measurement of distance where contact measurement practices have always carried negligible error. However, with advances in technology and new demands in growing industries, efforts and implementation of next generation of distance measurement and positioning techniques are needed using non-contact methods. Distance measurement and positioning in the industrial arena provides a new dimension for the advancement of the relevant technologies. Global Positioning System (GPS) is one such example in this realm, which uses a constellation of satellites to determine an object's position on the earth.
Over the last few decades, wireless technology is the biggest contribution given to the mankind. This technology has conquered the heights and limits beyond our sight. Each region of this technology plays an important part in our lives, and in the business. While measuring distances without any mesh of wires or cables can be extremely useful in many applications, but it do has its own challenges. Gaining the equivalent accuracy and precision as that of the contact methods of distance measurement is the utmost task in this wireless domain. Once achieved, this precision and accuracy will continue even when the object is moving.

The wireless measurement can be carried through the transmission of waves. Waves are of two types longitudinal and transverse. The former is the example of sound/mechanical waves. Although, these waves are highly energetic and can be transmitted over distances, their measurement suffer from temperature and pressure deviations. The latter includes the electromagnetic waves, further classified as visible and the non-visible range. Electromagnetic radiations are transverse waves and travel at the speed of light. The visible spectrum includes the LASER devices. Measurements done by LASER are very precise but they suffer enormously in dusty environment. Also LASER measurements are error prone when the alignment is not Proper.
On the other hand, the non-visible spectrum of electromagnetic waves consists of the microwaves, whose frequency ranges from several megahertz to few gigahertz. These waves are used in the RADAR systems to detect and measure distance of various objects. Primarily, the distance is measured by using Time of Flight (TOF) principle. This method tends to have some drawbacks/challenges like clock synchronization. Even a nanosecond offset in the clocks can generate error of several meters in the measured distance. To overcome this proposed invention uses Return Time of Flight (RTOF) method where measurement is carried out using single clock. RTOF measurement using passive reflectors in presence of other scattering objects, suffers additional delay due to multipath propagation. This affects the measurement statistics greatly and needs to be rejected. Hence, a novel measuring instrument with active return with frequency shift has been developed which measures distance with very high precision and accuracy using RTOF.

OBJECTS OF THE INVENTION:
An object of the invention is to measure distance of two objects.
Another object of the invention is to provide a slave station with active return and frequency shift.
A still further object of the invention is to provide a device to measure distance with very high precision and accuracy using return time of flight (RTOF) method.
BREIF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
Fig 1 shows a schematic diagram of the trans-receiver station in
accordance to the invention.
Fig 2 shows a block diagram of the master station in accordance to the
invention.

Fig 3 shows a block diagram of the master slave station in accordance to the invention.
The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
Figure 1 illustrates a schematic diagram of the trans-receiver station in accordance to the invention. The invention uses two active trans-receiving stations to measure distance between two points using RTOF (Return Time of Flight). These two trans-receiving stations can be termed as Master and Slave. They are separated by distance (d) which has to be measured. The signal sent by Master at time (t1) is received by the Slave at time (t1+At), where At is the time of flight between the stations. The value of At increases with increase in the distance between the Master and Slave, i.e. At is directly proportional to the distance ‘d’. The Slave provides synchronization by providing a delay of time (td), such that during the transmission sequence by the Slave, the Master is toggled to the receiving mode. Hence, the Master receives the signal at (tl+2At+td) time. The Return Trip Time (RTT) is calculated by the difference of the reception time (t1+2At+td) and the transmission time (t1) at the master. While calculating the RTT the fixed processing delay from the slave (td) has been subtracted. Thus the distance between the stations (d) is calculated as half the product of the Speed of light (c) and RTT.

Figure 2 illustrates a block diagram of the master station (11) in accordance to the invention. The master station (11) uses a pulsed clock (24) source to start transmission. The ON time of the clock denotes transmission time where as the off time corresponds to reception time. The same clock source is used to generated a modulated ASK (Amplitude shift keying) signal from the oscillator (22) operating at frequency (f1). A RF switch has been used to share the same antenna between transmitter and the receiver. The RTOF measurement is done by TMC (25) (Time measurement circuitry) and the clock source is used to provide the START time. The echo signal is then received back and amplified using LNA (low noise amplifier) which is fed amplifier envelope detector (27) to the envelope detector (27) for retrieving the clock signal. The output of the envelope detector (27) is converted to TTL (26) logic and this received clock signal is fed to the TMC (25) as STOP signal and thus the delay is measured. This delay is directly proportional to the distance between the stations whose distance has to be measured. A BSF (Band STOP filter) has been used in the receiver section to improve the system performance. It has the dual purpose of filtering out the leakage from the transmitter part through the switch. Also it rejects the unwanted reflections from the scattering objects in the field of view of the antenna with frequency (f1). Only the return from the slave is considered in the receiver which has a different frequency (f2). The AGC (Automatic gain control) unit in the receiver improves the dynamic range of the receiver by taking care of the varying received signal power level for different distances.
Figure 3 illustrates a block diagram of the master slave station (12) in accordance to the invention. The primary purpose of the slave station

(12) is to echo the signal back to the base station. Additionally, it synchronizes and amplifies the received signal from the master station
(11) initially the base station is in receiving mode; it receives the signal
from master station (11) and amplifies it using a LNA (Low noise
amplifier) which is fed to the envelope detector (36) followed by TTL (35)
conversion for retrieving the clock pulse from the master. The delay
circuit (34) provides a known delay (td) to synchronize the master and
slave station (12). This ensures that the master is in receiving mode
when the transmission sequence of slave station (12) starts. The
transmission frequency of the slave station (12) is (f2). The slave station
(12) similarly uses a BSF in its receiver section to reject unwanted echo
from the scatter and the transmitter leakage signal.

WE CLAIM:
1. A radar based positioning system to measure distance between two objects, the system comprising:
- a first and a second trans-receiving station selectively operable as master station (11) and slave station (12); wherein the master station (11) and slave station (12) includes a transmission section and receiving section;
- wherein the said master station (11) generates a clock pulse by a pulsed clock (24) source, wherein the said pulsed clock (24) source generates a modulated and amplitude shift keying (ASK) signal from an oscillator (22) at frequency (f1) to initiate the transmission station;

- wherein the said master station (11) operable as a receiver for receiving an echo signal from amplified and then inputed in an envelope detector (27) to be converted to TTL (26) logic, further configured to be inputed in a TMC (25) (time measured circuitry);
- wherein the slave station (12) comprises a transmission section and receiving section; wherein the receiving section synchronizes and amplifies the signal received from the master station (11) and inputs to an envelope detector (36) followed by a TTL (35) conversion, wherein a delay circuit (34) generates a delay time (td) to synchronize the master station (11) and the slave station (12); wherein the time difference is compared to compute the distance between the said objects.

2. The radar based positioning system as claimed in claim 1, wherein a band stop filter (BSF) filters the signal in the master station (11) and slave station (12).
3. The radar based positioning system as claimed in claim 1, wherein the ON state of master station (11) denotes transmission and OFF state of master station (11) denotes reception.
4. A method to measure distance between a first object and second object comprising a first and a second trans-receiving station, the method comprising steps of:

- transmitting a signal at a time (t1) from the first trans-receiving station;
- receiving the signal at a time interval (t1+Δt) at the second trans-receiving station;
- generating a delay time (td) by the second trans-receiving station;
- transmitting an echo signal to the first trans-receiving station;
wherein the delay time (td) synchronizes the first trans-receiver station and second trans-receiver station;
wherein the comparison of the time transmittal from first trans-receiver and echo signal received by the first trans-receiver determines the distance between the first object and second object.

5. The method to measure distance as claimed in claim 1, wherein the first trans-receiver station is the master station and second trans-receiver station is the slave station.
6. The method to measure distance as claimed in claim 1, wherein as illustrated in the accompanying drawings.