A Complete Simulation of Target Detection
and Estimation Using 77 GHz Radar
Arun Kumar Singh, Samerendra Nath Sur, Amit Agarwal, Rabindranath Bera
Department of Electronics and Communication Engineering.
Sikkim Manipal Institute Of Technology,Majhitar
Rangpo,Sikkim,India
{arunsingh.smit, samar.sur, amiteng2007, rbera50}@gmail.com
ABSTRACT
In this paper the modeling/simulation of 77 GHz Radar having a bandwidth of 1.2 GHz has been discussed that gives the information about target distance and the velocity. This kind of Radar can be useful in the field of car-to-car communication. They have the capability to detect the multiple targets even when they are closely spaced to each other. Since the bandwidth of the Radar is 1.2 GHz therefore it can be termed as ultra wide band (UWB) Radar and hence it has another property that it can even detect minute movement like heartbeat of a person and thus it can be very useful in situation where there are some person buried under the building or underground as a consequence of earthquake or landslides etc.
Keywords: Ultra-wide band Radar(UWB), Automatic cruise control (ACC), Collision avoidance and warning
systems (CAWAS), infinite impulse response (IIR) and finite impulse response (FIR) .
1. INTRODUCTION
Ultra Wide Band RADAR, as the name suggests is the radar which is having a larger bandwidth. The bandwidth is in the range of GHz. The kind of radar can be used practically in all cases where we need highly precise remote observation of moving objects at short distances. The radar shown in this paper is operating at 77 GHz and hence it has a property of millimeter wave radar and thus this type of Radar is very much popular in the field of vehicle communication where it can be used to control vehicle from collisions while driving and parking, in the field of under wall imaging. This type of radars can be applied in a rescue service to detect people buried under building obstructions or snow slips by their movement; if a person is motionless, the detection can be performed using person’s heart and thorax beats. It will be very useful for combating terrorism as we often come across the news like some group of ill-social elements are hiding inside the building, at that time through these kind of radar (through wall imaging ) can be used to detect their position.
The potential advantage of UWB waveforms for radar include better spatial resolution, detectable materials penetration, easier target information recovery from reflected signals, and lower probability of intercept signals than with narrowband signals. Most narrowband systems carry information also called the baseband signal, as a modulation of much higher carrier frequency signal. The important distinction is that the UWB waveform combines the carrier and baseband signal. Baseband or impulse radar are other names for UWB radar and radio signals. The UWB signals generally occur as either short duration impulse signals and as non- sinusoidal (e.g square, triangular, chirped, pulsed) waveforms.
2. APPLICATION AREA OF 77 GHz RADAR
The use of 77 GHz Radar is very much effective when dealing in terms of vehicular communication. Effectively 77 GHz Radar is millimeter wave radar. Compared with other types of sensors, millimeter-wave radar has the advantage of providing stable detection of targets even under inclement weather conditions such as rain or snow. Recent remarkable advances in RF technology have facilitated production of highly functional and efficient radar sensors. Thus, millimetre- wave radar has been marketed as, a vehicular collision warning sensor. This radar can be used for Automatic cruise control (ACC), Collision avoidance and warning systems (CAWAS).
3. PROBLEM DEFINITION
Objective of this work is to design and simulate a radar which can detect target and gives information regarding the target distance and velocity. The other task was to enhance the range resolution. Therefore for this the bandwidth of the radar is taken to be 1.2 GHz. To do this following steps are taken:
a) Generation of signal which is having the desired bandwidth.
b) Design of filter (up conversion) so as to produce the desired center frequency.
c) Design of filter for down conversion
d) Target detection and estimation of velocity and range.
3.1 Generation of Signal
The input given to system is having a wider bandwidth of 1.2 GHz. The main advantage of using wider bandwidth is to improve the range resolution.
Range= C/2B……….. (i)
Therefore if the bandwidth is 1 GHz, the range resolution will be 15 cm. In this radar the input signal has a bandwidth of 1.2 GHz and then the range resolution will be 12.5 cm. Fig 2 shows the frequency spectrum of the input signal.
Fig.2 Input signal spectrum.
In the generation of ultra-wide band signal there is generally a pulse signal which is treated with a barker code of 13 bit length as shown in fig.3. The duty cycle for this case is 25%. Duty cycle can be calculated from
Ton = % duty Cycle……….(ii)
Ton + Toff
3.2 Filter Design
Filter design is the most critical part of any system. To design a filter , the designer should be very much clear with the system requirements and its operation. In this particular transmission prior to transmission a band-pass filter is needed to be designed. The basic bandpass filter is given as:
Fig.4. (a) Circuit for LC bandpass filter Fig.4(b) response of bandpass filter.
Fig.4(a)and (b) shows the basic circuit and response of bandpass filter. A filter is characterized by its transfer function, or equivalently, its difference equation. As such, designing a filter consists of developing specifications appropriate to the problem (for example, a second-order low pass filter with a specific cut-off frequency), and then producing a transfer function which meets the specifications. The transfer function for a linear, time-invariant, digital filter can be expressed as a transfer function in the Z-domain; if it is causal, then it has the form:
…….(iii)
where the order of the filter is the greater of N or M. This is the form for a recursive filter with both the inputs (Numerator) and outputs (Denominator), which typically leads to an IIR (infinite impulse response) behavior, but if the denominator is made equal to unity i.e. no feedback, then this becomes an FIR or finite impulse response filter. The impulse response is a characterization of the filter's behavior. Digital filters are typically considered in two categories: infinite impulse response (IIR) and finite impulse response (FIR). In the case of linear time-invariant FIR filters, the impulse response is exactly equal to the sequence of filter coefficients:
…...(iv)
IIR filters on the other hand are recursive, with the output depending on both current and previous inputs as well as previous outputs. The general form of the IIR filter is thus:
………(v)
Difference Equation: In discrete-time systems, the digital filter is often implemented by converting the transfer
function to a linear constant-coefficient difference equation (LCCD) via the Z-transform. The discrete frequency-domain transfer function is written as the ratio of two polynomials. For example:
……….(vi)
………(vii)
and divided by the highest order of z:
………….(viii)
The coefficients of the denominator, ak, are the 'feed-backward' coefficients and the coefficients of the
numerator are the 'feed-forward' coefficients, bk. The resultant linear difference equation is:
……….(ix)
or, for the example above:
………..(x)
rearranging terms:
………(xi)
then by taking the inverse z-transform:
….…(xii)
and finally, by solving for y[n]:
…..(xiii)
This equation shows how to compute the next output sample, y[n], in terms of the past outputs, y[n − p], the present input, x[n], and the past inputs, x[n − p]. Applying the filter to an input in this form is equivalent to a Direct Form I or II realization, depending on the exact order of evaluation.
3.3 Receiver Correlation
Correlation is basically the relation between two variables. In context of this paper correlation is done between two signals so as calculate the target distance. It is calculated from the time taken by the reflected wave to reach to the receiving antennas. It is given as:
R = C. Td /2 ……….(xiv)
where R is the distance, C is the speed of light[4] and Td is the traveling time to the target and back and is calculated by the correlation between the received barker code and the reference barker code.
……….(xv)
Autocorrelation figure for Barker code is given as:
Fig.5. Autocorrelation figure for 13 bit Barker Code
4. Modeling/Simulation description
For the modeling and simulation of the ultra-wide band radar operating in millimeter wave range of 77 GHz is done using Matlab . For the detection of target a point scatterer has been used. The detection is shown as below:
Time Time
Fig. 6 (a). Detection of single target Fig. 6(b). Detection of two target
The above figure shows the detection of targets. In fig. 6(a) and (b) there are two pulses. the upper one in each of the detection is the transmitted pulse and the lower one in both the cases are the target detection. The targets were detected as shown above and are plotted respectively. The single target is detected as shown in fig.4. in the time scope of fig.4, the upper one is the transmitted pulse and the lower one is the detected pulse. There we can see a delay between the two. The calculated delay and the observed were same.
4.1 Range estimation
The target detection is worthless unless and until the distance of the target is known. For this distance estimation delay is needed to be calculated. The delay is the delay between a signal and a delayed, and possibly distorted version of itself.
Fig.7 Range estimator
Fig.7 shows the range estimator block. In this block based on the delay between the output and the reference signal, the range is estimated(in meters). The display shows the numeric value which is the target distance from the processing station.
4.2 Velocity Estimation
When the radar is operating in a vehicle as a sensor to detect other vehicle and hence to avoid collision between them, velocity estimation is very much important to know that with what speed another vehicle is coming towards the objective vehicle.
Therefore doppler processing is must for the velocity estimation. Unlike with communication signals, the reflected radar signal of an object moving with a relative velocity of Vrel will experience twice the amount of Doppler shift according to
……….(xvi)
where = c0/fc, with c0 being the speed of light and fc, the carrier frequency.
The simulation model shown in fig 8 calculates the velocity.
Fig.8 Velocity estimator.
Algorithm: If the symbols occurring during the observation interval are x(1), x(2), x(3),..., x(L), then the resulting carrier phase estimate is:
………(xvii)
where the arg function returns values between -180 degrees and 180 degrees.
This is how phase is recovered from the target report signal. After some further processing the velocity is calculated from that phase information.
5. Explanation of Simulation model
Velocity and range estimation are the principle requirement for collision avoidance sensor based on radar principle. With this in mind the model was prepared and simulated. First the signal of desired bandwidth in ultra wide band range was generated. Now after the designing of filter (shown in section3.2), the desired carrier frequency (77GHz) was obtained. Operating at this frequency the targets were detected and the range and velocity information was extracted out of the system. A complete simulation model is shown in Fig. 9.
Fig.9. Complete Simulation model Of UWB Radar for single target detection operating at 77 GHz.
6. Conclusion
Our literature survey reveals that radar operating at 77 GHz is most effective in collision avoidance system and having a bandwidth of 1.2 GHz improves the range resolution. Thus, the authors have tried to present the best possible radar which can be most effective in this field. However further work can be done in field of communication link with other vehicle, therefore to have a complete integrated radar and communication simulation model.
7. References
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