About this communication paper-presentations : (Frequency hopping)
Communications plays an important role in the upliftment of the standard of living. There has been an explosive growth during past few decades, as phenomenal advances both in research and applications have been made as a result internet services, cellular technology, and many more gave new dimension to communication. These changes are also producing challenges for privacy and communications security. In cases such as military security, this creates an urgent need for advancing the state-of-the-art in communication channel security.
Wireless military communication systems have been developed to account for ever-increasing sophistication in electronic warfare (EW), ECM (Electronic counter measure), and ECCM (Electronic counter counter measure). Military systems have been developed to counteract jamming, spoofing, and detection using antijam, anti-spoofing, and low-probability-of-intercept methods.
TEXT CONTENT
Digital signal processor, one of the most significant breaks through in electronic technologies is the high-speed microprocessors and microcomputers designed specifically to perform computation-intensive Digital Signal Processing algorithms.
In the normal communication any receiver can capture the transmitted signal, because the transmission is only at one frequency. In addition, intentional or unintentional jamming signals, spoofing, or eavesdroppers can easily interfere with the usefulness of these systems. Appropriate countermeasures have to be developed to prevent such a situation. For providing secrecy in communications, we are implementing ECCM module and the DSP starter kit to improve upon a frequency-hopping rate of 8 hops/sec to 40hops/sec respectively with synchronization between the two stations. Latch is an interface between ECCM module and synthesizer module.
For development, DSP technology is used by means of TMS320C5X processor. Because of the many advantages DSP’s are becoming more prevalent in areas of general purpose Digital Signal Processing, Telecommunications, voice/speech/graphics/imaging, control, instrumentation and the military.
Transmitter is designed to operate in amplitude modulation (AM) and frequency modulation (FM) modes using narrow band or wide band transmissions in the VHF/UHF frequency bands .It comprises a transmitter (TX) control module, RF power amplifier (RFPA) assembly and a filter/coupler assembly. The Transmitter control circuits accept the equipment’s data and speech inputs, and provide amplification and control of local/remote, speech/data and FM/AM modes of operation.
Receiver is designed to operate in AM modes in both VHF & UHF frequency bands. The final IF is switched through either a wideband or a narrow band crystal filter depending on which mode is selected. The output is then obtained from audio amplifier.
FUNCTIONAL DESCRIPTION OF DEVELOPMENT DIAGRAM FOR FREQUENCY HOPPING
Development diagram for frequency hopping (40 hops/sec).
The above functional block diagram consists of ECCM module, latch circuit module, DSP starter kit and the synthesizer module. The schematic functional block diagram is shown in the above figure.
ECCM (Electronic Counter Counter Measure) gives a standard 8 hops/sec. we have to develop it to 40 hops/sec using Digital Signal Processing starter kit TM320C5X.
We are using Latch circuit to hold the frequency data coming from ECCM and the DSP kit. ECCM gives different frequency data’s 8 times per sec .The frequency data coming from ECCM and the DSP starter kit to the latch circuit are associated with interrupts .The former one has highest priority. To add in the additional frequency changes, the DSP starter kit takes the ECCM frequency data and calculates the frequency band, and calculates different frequencies and sends it to the latch circuit for every 25msec till next ECCM interrupt comes in. The data hold by latch circuit is then passed to the synthesizer module, which is a RF drive-in synthesizer module, PLL locks the frequency data.
ECCM module:
The ECCM module provides the frequency data and hop pulse to the synthesizer module. ECCM works in the UHF band from 225 to 399.975 MHz .The type of modulation used in ECCM is AM voice (WB). In normal communication any receiver can capture the transmitted signal, because the transmission is only at one frequency. So, to maintain security for the signal the ECCM module is integrated in the transceiver.
LATCH CIRCUIT:
The Latch circuit is the interface between ECCM module and the synthesizer module. The data (frequency information and hop pulse) from ECCM module is given to the Latch circuit. A frequency data from ECCM module is read by the DSP module and Processes for other frequencies and will pass through latch circuit to the synthesizer module.
SYNTHESIZER MODULE:
The synthesizer provides the RF drive signals for the transmitter RF power amplifier stages and local oscillator injection signals for the receiver 1st and 2nd mixers.
DSP STARTER KIT:
DSP starter kit consists of TMS320C50 processor and analog to digital converter interface circuit. The DSP processor through latch board reads the frequency data and hop pulse from the ECCM module; the program developed for 40 hops per sec will generate different frequencies and hop pulse (INT). Whenever hop pulse occurs, the frequency data from DSP module through latch circuit will change the frequency in synthesizer module and transmission takes place in that frequency.
Frequency Hopping: In the Frequency hopping mode, the frequency will change both at the transmitter and receiver ends simultaneously. Both the transmitter and receiver frequencies should be in synchronization, then only the communication exists between the two stations.
TRANSMITTER:
The transmitter is designed to operate in amplitude modulation (AM) and frequency modulation (FM) modes using narrow band or wide band transmissions in the VHF/UHF frequency bands .It comprises a transmitter (TX) control module, RF power amplifier (RFPA) assembly and a filter/coupler assembly.
• The Transmitter control is a plug in module, which is interconnected through the main and front interconnection assemblies at module position. The module contains the transmitter input/output control functions, the audio processing circuits and the BIT/control interfaces for the I2C busses.
• The RFPA assembly is mounted on the right hand heat sink as viewed from the front of the unit. The UHF driver and power amplifier circuits are located at the rear of the assembly with the VHF driver and power amplifier circuits located at the front of the assembly.
• The filter/coupler assembly is mounted on the left hand heat sink, as viewed from front side of the unit. The assembly contains the requisite filters (VHF, UHF or VHF/UHF), directional couplers and the power regulator circuits for the power amplifiers drivers and the directional couplers.
• The transmitter circuitry is contained on the TX control module, RFPA assembly, filter/coupler assembly, synthesizer and the BIT assembly. The modules and assemblies provide the following functions.
a) TX control module: Processes the audio and provides control signals for transmitter operation.
b) RFPA assembly: Provides the AM modulator and the AM/FM power amplification for the UHF and VHF RF carriers.
c) Filter/coupler assembly: The filter coupler assembly contains low pass filters to remove any RF component both 160 MHz and 400 MHz. It also contains a directional coupler, which detects the forward and reflected power levels; and a power regulator assembly that provides the regulated power supplies for the RFPA circuits.
d) Synthesizer module: Produces the carrier frequency for the RFPA assembly. In FM mode, the synthesizer’s carrier frequency is modulated and in AM mode, the carrier amplitude is modulated in the RFPA.
e) BIT assembly: Supervises the PTT (press to talk) signals, which can be activated from either the equipment’s front panel, or a remote control unit. This assembly also provides pre-amplification for the microphone audio.
RECEIVER:
• The receiver is designed to operate in Amplitude modulation (AM) modes with the capability for voice (narrow band) or data (wide band) reception in both the VHF and UHF frequency bands. It comprises a receiver RFmodule and receiver IF and audio module. • Both the receiver RF and receiver IF and audio boards are plug in modules interconnected through the main and front interconnection assemblies at module positions 6&8 respectively. The receiver RF module contains the RF filters, RF converter and BIT/control circuits. The receiver IF and audio module contains the receiver IF, receiver IF and audio, and receiver IF and audio BIT/control circuits.
• The received signal is connected from the appropriate rear panel N type connector through the antenna filter assembly. The RF signal is connected to the receiver RF module where it is routed through the RF filter circuit comprising a series of band pass filters selected by a pin diode-switching matrix and controlled by the software installed in the BIT assembly.
• The output of the appropriate RF filter is connected to the first stage of RF amplification. From the amplifier stage the signal is connected to the 1st mixer and mixed with a drive signal from the Synthesizer module to produce an IF signal. The resulting 1st IF is amplified, filtered and connected through a coaxial interconnecting link to the receiver IF and audio module.
• After filtering the signal is applied to a 2nd mixer and mixed with a drive signal from the synthesizer module routed via a filter/multiplier. The resulting 2nd IF is then switched through either a wide band or a narrow band crystal filter depending on which mode is selected. The audio signals are detected from the IF signal by AM & FM demodulators then routed through the audio circuits to the audio output amplifiers.
RESULTS AND DISCUSSION
As the receiver can trap any message signal if it is tuned to that frequency, Frequency- Hopping is employed in V/UHF transceivers operating in hopping mode in the UHF range to maintain secrecy of the message signal. ECCM provides 8 hops/sec, which provides the confidentional Communication but the search receivers are much faster for acquiring these signals. So by providing a hop rate of 40hops/sec, we are able to provide better secrecy to the communication. 40 hops per sec can be further developed to 100 hops per sec and 200 hops per sec to ensure high efficiency.
APPLICATIONS
It is used to maintain secrecy in defence purposes, this can be maintained by increasing the hop rate and also by changing the transmitter frequency regularly i.e., providing a hop rate of 40 hops per sec. To ensure high efficiency in providing secrecy in communication by further developing hop rate to 100 hops per sec and 200 hops per sec.
CONCLUSION
The spectrum of the atmosphere is of plethora of signals, those contains different frequencies and different modulation types that are being used in domestic and commercial applications, for example like cellular, fax, FM, AM, internet etc. Receiver can trap any signal, if it is tuned to that particular frequency. But when we need confidential communication, which should not be trapped by any unknown receivers, the normal communication fails. ECCM provides 8 hops/sec, which provides the confidentional Communication but the search receivers are much faster for acquiring these signals. If we increase the hop rate, better confidential communication can be ensured.
By changing the transmitter frequency regularly i.e. providing a hop rate of 40hops/sec, we are able to provide better secrecy to the communication. Subsequently, frequency hoping of 40 hops per sec can be further developed to 100 hops per sec and 200 hops per sec to ensure high efficiency in providing the secrecy in communication.
REFERENCES
1. Texas Instruments,
TMS320C5X,
User’s Guide,
1993, DSP Products.
2. TMS320C5X,
DSP Starter Kit,
User’s Guide,
1997, Microprocessor development systems.
3. Digital Signal Processing,
A Computer based approach,
By: Sanjit .K. Mitra.