Burst Transmissions Technology And Characteristics

“Strategy is the art of making use of time and space. I am less concerned about the latter than the former. Space we can recover, lost time never”

– Napolean Benoparte

BURST TRANSMISSIONS TECHNOLOGY

1. Having understood the surveillance network requirements, carried out an analysis of our present surveillance network and identified burst transmission as an alternative means to pass the information to surveillance centres, the aim of this part is to analyse the effectiveness of burst transmission technology for the networking of surveillance resources in desert terrain for offensive operations.

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BURST TRANSMISSIONS TECHNOLOGY AND CHARACTERISTICS

2. Electromagnetic waves, like all other waves are characterized by their frequency and intensity. The electromagnetic spectrum consists of electromagnetic waves of all possible frequencies. This spectrum extends from the VHF ranges to mill metric waves in military [1] . The electromagnetic waves do not follow the man made rules/ international boundaries. They can be easily intercepted and analysed to get intelligence about the enemy [2] . Today we are using VHF radio as the primary means of passing our surveillance information to our surveillance centres.

3. Working Of Burst Transmission. The term burst transmission involves compressing the data, high data signaling rate and transmitting in short bursts which are not easily detectable by the enemy. Burst transmission basically compresses the same data and sends it in bursts. This technology is very popular among the spies and military personals due to its advantages [3] .

4. A radio packet is a short transmission in burst form of data that occurs on a radio channel. The burst data may have different types of radio characteristics i.e the modulation type, error coding, preamble length and transmission guard time periods. It contains reference sequences in form of a preamble and possible a midamble, control information and payload of data. The combination of all the above mentioned characteristics is called the burst profile [4] . A burst set is a single burst transmission packet and it has the preamble along with one or more bursts of data. The bursts of information will contain packets having different modulation and coding. A burst frame contains the complete set of information for a burst transmission. The bursts within a burst set are sequenced according to their modulation complexity. With the bursts having lower complexity modulation beginning located at the beginning of the radio packet. Subsequent bursts can use modulation types with higher complexity (e.g. QPSK, QAM). This allows subscriber stations to receive and decode all the bursts up to the burst with the highest modulation type it can receive [5] .

5. To enable the receiving device to lock on, the radio bursts start with a sequence of bits i.e a preamble that the receiving device can recognize and lock onto. On locking onto the preamble, it knows the location of the rest of the packets. For longer radio bursts, midamble sequences may be inserted which helps the receivers in the decoding of bursts. A midamble is defined as a sequence of bits which the receiving device can recognize and lock onto to assist in decoding the bits surrounding it. Sending preambles and midambles frequently give the user an increased mobility. Data packets may be inserted within the payload of a single radio burst. They may be located at one place or divided or fragmented over several radio packet bursts or multiple small packets and packed into the burst payload. The figure below depicts an example of a radio packet which is made of a preamble and a set of bursts [6] .

http://1.bp.blogspot.com/_tuOGu0JuGOE/SsgZscaJj2I/AAAAAAAAC0I/cC-iCmchLxM/s400/1.jpg

Figure Radio Packet Containing Preamble And Data

6. Characteristics Of Burst Transmission Technology.

It is a relatively high bandwidth transmission over short period of time [7] .

Very high data signaling rate with very short transmission time [8] .

Data is stored for a given time are sent at 10 to more than 100 times the normal rates, recorded when received and then slowed down to normal rate for use by the receiver [9] .

It has Low Probability of Intercept and Low Probability of Detection [10] . The actual transmission time is very less which make it difficult to detect.

The download time might use 2Mbit/s on a average while having peaks bursting up to 2.4 Mbits/s [11] .

Data transmission is interrupted at intervals [12] .

Data is digitally encrypted [13] .

7. Limitation Of Burst Transmission Technology.

The system is dependent on the radio interface for transmission of data. Line of sight is still a major consideration for VHF transmission. HF transmission is recommended to obviate the problem [14] .

The error in data during transmission / reception can lead to error at the receiving end.

8. The burst transmission is a suitable means to transmit data over a long range in secure mode due to the following reasons:-

The transmission takes place for a short period i.e only when data has to be passed, thus it has a Low Probability of Intercept and Low Probability of Detection.

It is difficult for enemy Direction Finding systems to locate the radio as it transmits for a short duration that is only when required.

MODELS IN USE

9. The burst transmission technology is one of the technologies being used in the armed forces of other countries for networking. The Harris RF- 3700, Falcon II AN/PRC – 150 (c), GRA -71 all of USA, GRC -6400 400W HF Radio System, Tadiiran HF -6000 Radio System of Israel and HF – 7000 of Germany are examples of use of burst transmission in military communication. Similar equipments using burst transmission have been designed and developed in India by Bharat Electronic Limited.

10. Harris RF – 3700 Harris Universal Transmission Software (HUITS). It is a Microsoft-Windows 2000/XP compatible software being used by United States forces for fast and reliable transmission of high resolution digital imagery, motion video clips and other data difficult tactical communication channels. It has a data transfer rate of 64 kbps and uses burst transmission to transmit data. Data/ images are transferred using HF/VHF/ UHF/ landline media on a click of a button once acquired [15] .

11. Falcon II AN/PRC – 150 (c). It is a software defined HF radio system being used by United States forces for tactical communication including data transfer. It uses burst transmission and has high speed modem for data transfer. It can be interfaced with US Tactical Internet without any additional boxes [16] .

12. GRC -6400 400W HF Radio System. It is a 400W HF radio system being used by Israel for tactical communication including data transfer. It uses burst transmission and has an adaptive high rate modem up to 4.8 Mbit/s for data transfer [17] .

13. Tadiiran HF – 6000. It is a HF radio system being manufactured by Elbit Systems, Israel for tactical communication including data transfer. It can also use burst transmission for data transfer. It is available in fixed station, ship, vehicle, man pack and high power versions [18] .

14. HF – 7000. It is a HF radio system being used in Germany for tactical communication including data transfer. It uses burst transmission for fast data transfer. It is available in fixed, semi mobile base, vehicle and man pack versions [19] .

EQUIPMENT AVAILABLE FROM BHARAT ELECTRONIC LIMITED

15. There are similar equipments being made in India by Bharat Electronic Limited. However they have not been exploited for surveillance network till today. The equipments available from Bharat Electronic Limited are discussed in succeeding paras.

16. Spurt Message Alphanumeric Radio Terminal (SMART). It is a message processing and transmission equipment based on a microprocessor for field use. It provides reliable burst transmission capability and reduces radio channel occupancy time with in reduction in probability of interference and jamming. It has a facility to prepare messages ‘off air’ with the alphanumeric keyboard and display unit of the equipment. It supports both free and formatted text messages and has built-in encryption for text message. Voice Links on HF Radio can be done using the built-in modem. It can operate in poor channel conditions. A hard copy of messages can be taken by connecting a printer to a serial port ASCII printer. The terminal can also be optimized for a particular application. Interface with PC is also available as an optional S/W module to handle messages having relatively longer length, thus giving an user friendly edit capability. It is being used by the Mobile Observation flights of Indian Air Force [20] .

17. Hand Held Radio Terminal (HART). It is a small size, light weight and low power consuming terminal used for preparation and transmission of alphanumeric messages digitally. Its ideal for field use. The terminal reduces the chances of interference and jamming by providing reliable burst transmission capability and reduce radio channel occupancy time. Messages are prepared “off-air” with the alphanumeric keyboard. Messages reception is automatic [21] .

18. HF Trans receiver. It is an advanced lightweight 20W HF portable radio set. It meets all the requirements of short-range communication to operate in crowded HF band. It provides voice, data, telegraphy and flash (burst) message communication. Communication reliability is improved by means of automatic link establishment, which enable real-time selection of optimum channel frequency [22] .

19. Stand Alone Communication Unit (SACU). It is a high speed, secure data communication equipment using burst communication technique with built in encryption method and modems contained in a rugged compact unit. It has the facility for communication over three independent channels simultaneously. The advantage provides are short ‘on-air’ time and high network capacity. It has capability to edit, address, transmit, receive, acknowledge, store and print the messages [23] .

20. Burst Error Control System for Teleprinter (BEST Mk II). It is a microprocessor based forward error control equipment for reliable burst transmission of alphanumeric messages. It can be easily connected with conventional teleprinters and personal computers to prepare messages “off-air” from the terminal and transmit synchronously in a burst mode. It has additional features like automatic reception, message numbering, date and time, multiple copy print out, auto print mode, auto repeat facility, etc [24] .

21. There are a number of VHF radio sets using burst transmission for data communication; however they are not being discussed further since VHF radio has limited bandwidth and limited range being a line of sight communications. It is thus unsuitable for offensive operation in deserts [25] .

22. Deductions. The burst transmission is being used by tactical radio manufactures in USA, Germany, Israel and many other countries due to its advantages like high data transfer, digital encryption, low probability of Intercept and detection. Software Defined Radio and software like Harris RF-3700 Harris Universal Transmission Software not only enable the easy transfer of images/ data but also give the facility to connect to tactical internet network without any additional connections. Thus real time fast and reliable transmission of high resolution digital imagery, motion video clips and other data which is difficult over VHF radio based tactical communication networks can be achieved through burst transmission. The United States is using this technology in their Joint Tactical System Program [26] .