Removing interference in passive radar reference channel based on digital TV broadcasting signal by ground transmitters with reproduction approach

Master's Thesis in Electrical Engineering-Communication System

Abstract

Removing interference in passive radar reference channel based on digital TV broadcast signal by terrestrial transmitters with reproduction approach

In this thesis, a digital receiver for signal processing in a passive radar reference receiver based on orthogonal frequency division modulation (OFDM) for digital terrestrial broadcasting (DVB-T) is presented. This receiver includes synchronization blocks, frequency offset estimation and channel estimator. After synchronization, we estimate and compensate the frequency offset, both of which are done by detecting the position of the pilot subsymbols. Then using two methods of linear interpolation and least square error (LS) channel estimation is done. After the channel is estimated, we will compare the channel and finally a reproduction version of the sent signal will be made. In order to check the efficiency of the intended receiver, we have drawn the curve of probability of symbol detection error according to the ratio of signal power to noise power for different methods of channel estimation. Also, to check the effectiveness of the proposed algorithms, we have drawn the curve of the attenuation loss of clutter in a passive radar surveillance receiver based on DVB-T signal to determine that if we weaken the clutter in a surveillance receiver by using the signal reproduced in the proposed receiver, this amount of attenuation will be lost compared to the situation when we try to remove the clutter in a surveillance receiver using an ideal version of the transmitted signal.

Vocabulary key: Synchronization, synchronization, reproduction

Introductions to passive radar

The space around us is full of radio waves that are spreading in all directions. Radio waves are magnetic waves that are usually emitted by antennas. The word radar (Radar) [1] is made from the first letters of several English words meaning detection and ranging using radio waves. This word, which is used all over the world today, has become an international term like radio and television. With radar, you can see inside the environment that is impenetrable to the eye, such as darkness, rain, fog, snow, dust, etc. . Radio waves have a long range, they cannot be sensed by humans and it is easy to detect and receive them even when they are weakened. Therefore, radar is a device that can detect the existence of an object and determine its distance by means of radio waves. Conventional radar systems consist of a transmitter and a receiver, which often use an antenna for sending and receiving. The first experiment on the reflection of radio waves was obtained by the German Hertz in 1886. In the years 1920 to 1930, progress was made in the direction of building radar with the capabilities of determining the distance of targets. In 1960, the use of air and space radars was developed and, in addition to military use, for geographic mapping and scientific discoveries. were used. Based on the location of the transmitter and receiver, radars are divided into single-base[2], double-base[3] or multi-base radars. The early radars were all bipods. With the advancement of technology, antennas were made, which were able to switch from transmitting to receiving. In 1936, bipod radars were replaced by monopod radars. The constituent parts of the radar system are transmitter, receiver, antenna and electrical systems for recording and processing information.

One ??of the types of radars are passive radars. Passive radar is known as PCL [4] and PBR [5] [1]. Passive radar is a two-stage radar that can detect targets without being detected by using a variety of magnetic transmitters and measures the time difference between the signal received directly from the transmitter and the signal received as a result of radiation. This allows to determine the target's status and mobility. There are many analog and digital VHF radio and UHF television transmitters available that passive radar can use as transmitters.There are many analog and digital VHF radio and UHF TV transmitters that passive radar can use as magnetic transmitters.

The advantages of PBR radars include the following:

Low maintenance cost due to not having a transmitter, low construction cost, radar stealth due to not having transmitted waves, smaller size compared to Active radars, the ability to track and deal with stealth fighters, undetectable against anti-radiation missiles.

Passive radars that use magnetic transmitters have a two-stage structure as shown in Figure 1-1. In this case, the signal that is exchanged between the magnetic transmitter and the receiver of the two-base radar is called the direct path signal, and the signal that is exchanged between the target and the receiver of the two-base radar is called the target signal. style="direction: rtl;">Interference Cancellation in The Reference Channel of DVB_T Based Passive Radar Using Regeneration

BY

ZOHREH ASADSANGABI

A digital receiver for signal processing in the reference channel of passive radar based on orthogonal frequency division multiplexing (OFDM) digital video broadcasting terrestrial (DVB-T) is presented in this thesis. The proposed receiver consists of synchronization blocks, the estimation of the frequency offset and channel estimator. After the time synchronization, the estimation and compensation of the frequency offset that is conducted by using the specification of the pilot sub-symbols position. Then, channel estimation is performed by using a linear interpolation method and the method of least square error (LS). After the channel was estimated, the equalizing channel is taken into account and eventually, regeneration of transmitting signal is constructed. To evaluate the performance of the proposed receiver, the curve of the probability of symbol detection error has been mapped as a function of signal power to the noise power for different channel estimation methods. For a more accurate evaluation of the performance of the proposed algorithms, the curve of clutter attenuation loss is plotted in the surveillance channel. It is to determine if we weaken the clutter in the surveillance receiver, using the regenerated signal in the proposed receiver, the amount of attenuation compared to the situation in which we try to remove clutter in the surveillance receiver using an ideal version of the transmitting signal will suffer losses.

Finally the simulation results show that the performance of the proposed algorithms for clutter attenuation are close to ideal, and good overall performance is achievable.