Spread Spectrum Communication: Techniques And Anti-Jamming Broadcast Communication

System Models

Spread spectrum is considered to be a form of wireless communication technology, in this way of communication the frequency of transmitted signals is keep varied. Due to this the bandwidth of transmission signals can be increased. Generally the frequency of conventional wireless signal is in between the range of megahertz and gigahertz and it never change with time (Woerner). Spread spectrum communication is the most popular and firing topic in the field of research and development nowadays. The research on this topic was firstly reviewed in the era of 1989 and then it became the significant topic for research. In this research paper we will discuss the spread spectrum techniques which can be beneficial in anti-jamming broadcast communication (Rouse). We then elaborate the proposed system and about the implementation of proposed system in later sections. How the performance of this technique can be evaluated will be discussed in upcoming section of research paper.

If we talk about spread spectrum communication principle, then we can see that digital transmission which is considered better performers having adequate bit rate for satisfactory performance can be categorized in two ways:

The applications which are based on satellite communication, in these type of applications the spread spectrum communication provide optimum usage of power available.

The second type of applications which are based on spread spectrum communication are mobile wireless applications which have the capability to give better performance on limited bandwidth (Nigam). These types of applications are in huge demand right now.

Both of the above applications are prone to jamming and radio interference. Spread spectrum communication can provide the great protection against these attacks because it can exchange the bandwidth at the time of jamming. The changes in bandwidth in spread spectrum communication are acquired through coding process. This coding is not dependent on the message which are to be sent or on modulation which are being used in transmission process.

In spread spectrum communication, the transmission signals are produced on much higher bandwidth which is actually required in communication. There are many ways to generate this type of transmission signals, some of them are as follows:

• Direct sequence
• Frequency hop
• Time hop
• Multicarrier

The combination of above techniques can also be used.

Under the threats of attacker efforts and many a trials to jam critical wireless transmissions, Spread Spectrum Techniques represents the mutual way to attain the anti-jamming communications. The anti-jamming communications are generally used in the commercial and military related connections and applications related to security, between paired devices of sender to multiple devices that are going to receive the signals or messages (Yu Zhang). This SS technique mainly uses the data independently, random sequences to release a narrowband of information signals over a wide band of frequencies.

Anti-jamming broadcast communication techniques

Just by analyzing and finding out the flow of information among the devices doesn’t solve the problems related to anti-jamming and its broadcast as the key analyzing and pre-distribution is not that feasible when the receivers are unknown or unidentified or the case may be related to the serious scalability issues or errors. A right infrastructure of public key doesn’t solve this problem just because of the reason that the SS techniques require the specific keys to share the secret information or messages, and the devices still need to communicate as they need to agree to receive the messages as a secret information.

On the other hand the USS Technique which is also called as Uncoordinated Spread Spectrum is beneficial in enabling the jamming-resistant transmission of information without the sharing of secrets keys. 

The concept is more closely related to Spread Spectrum techniques as they also release the information signals over a frequency band which tends to be much larger than the band required for flow of information. In USS the person who is sending the information doesn’t apply any kind of pre-agreed releasing sequence but uses a number of pairs of communicating channels that are within the available or appropriate frequency band, and these pairs are known to all the receivers. It can also be understood as the sender selects the communication set channel for the transmission of each and every message or flow of information from a random pair and keeps it the choice of secret for the transmission (Popper, Strasser and Capkun). On the other hand the receivers try to take a random guess on the selection of the sender so as to receive the message. They also overcome the lack of knowledge of the operation releasing through the sender by accepting a delay in the receiving of the information and by the time, they try to guess the choice of sender repeatedly one after the other (Stuber). 

This is closely related to frequency hopping and is majorly based on the thinking that the attacker can’t jam all frequency channels on which the nodes are communicating on the same instant of time (An Liu). How so ever, this has been opposed to the coordinated frequency hopping, with UFH the receiver and the sender don’t agree on a secret channel or set pair sequence before-hand, and they choose the set pair over which there would be an ease in flowing of information randomly from a predefined set of frequency channels. Communication becomes possible just because at the same instant of time, the sender as well as the receiver send, listen and transmit the information over the same frequency channel.
 

Basic concepts of USS Techniques

This concept is based on the principle of DSSS in accordance with releasing of the data using the spreading sequences. In contrast to anti jamming DSSS, the releasing sequence is a kind of secret and is shared only by the communicating partners in the following UDSSS, a public set pair is being used by the sender and the receivers (Capkun). Each time a message is to be transmitted the sender repeatedly selects a new random spread sequence for a set pair and releases the whole information along with the sequence.

The implementation of proposed spread spectrum communication model which is based on uncoordinated spread spectrum based techniques, can be elaborated and implemented using Universal software radio peripherals technique (Smith). This technique is based in an A/D or D/A type of converter which works on input and output signals of 64 Mbps or 128 Mbps. The resolution of input and output signal can be 12 or 14 bits. In the proposed system explained in the above section, the connections were done using 480 Mb/s USB 2.0 link. It was connected to Intel core 2 Duo CPU having processing speed of 2.20GHz. This system may have LINUX operating system and GnuRadio. To analyze the performance of transmission signals the coding is done in C++ programming language to implement the application which is supported by Python language. For the synchronization of transmission signals with USRP and the actual signal, the USRP drivers are to be adapted. This system model can be represented using following schematic diagram:

If we consider a case in which a sender tends to transmit a message M to a group having G number of receivers. By the theory that has been evolved through various studies, it can be easily said that more than three receivers were obtained by combining various multiple transmission runs for the specific parameter. This guidance is to be provided rarely in the randomness of the reception processes (Bhosle).

Once after having the complete evaluation, the result shows that the best output is acquired if either a pure UFH or UDSSS is brought in for consideration and being implemented. Noting that the following evaluation considered reveals that the attacker’s strength is only determined by the achieved processing gains and thus it remains constant. Spreading the Uncoordinated Frequency Hopping signal with a code through a small set pair of codes might be helpful and tends to be much more advisable as it has the impact over the attacker to make the use of more advanced transmission signal detection techniques than a simpler narrow band signal strength indicator (prabhakaran). Somehow, we get to observe that the time for the transmission of the messages or information increases in a linear manner along with the size of the message but only logarithmically in the case where it is considered with respect to the number of receivers. With USRP-based prototype implementations, the net average time to disseminate a message of around 2000bits to approximately 100 receivers is about 5 seconds, only if the processing gain of around 23dB is sufficient for the jamming (Pravin Waghmare). For those 5 seconds the attacker still has the option for jamming 20% of the pairs. Hence, it can be clearly stated that purpose-built FH transceivers or the broadband receivers helps significantly to decrease the time of transmission. Disseminating a particular message to a large group of receivers with UFH or UDSSS thus scales very well and in a more efficient manner. The UFH implementations in cases or theories perform in a much better way as compared to the UDSSS only for the systems that are based on USRP’s and GNU Radio, and can’t be generalized for different hardware.

Uncoordinated Frequency Hopping (UFH)

The main purpose of this whole example is to have a perfect demonstration of the feasibility of the proposed uncoordinated spread spectrum schemes (Takeshi Nishida). Thus it shows a great example that the achieved transmission times should not be stated as a final benchmark for the performance (Ismail, Qiao and Zhou). Purpose-built frequency hopping transceivers also provides the timing of frequency switching in order of time span of one microsecond along with the bit-rates of several of Mbps, the decoding of a bit is basically of a single-step on hardware-based DSSS receivers. Realistic message transmission time of purpose-built UFH or UDSSS transceivers are more likely to be 10-100 times lower than the terms achieved with the presented implementations.

The spread spectrum communication is primarily used in many fields such as industrial, scientific, avionics and military. Following are some of the examples for which this communication technique can be used:

Communication system to control the jamming.

Code division multiple access radios: This can be used in situations where multiple access during communication is required over a single shared channel. A unique frequency is allocated to every user which allows him to communicate over the channel uninterruptedly. By using this concept the chances of interference can be minimized.

High resolution range: This spread spectrum technique is used in high resolution range. To find out the location of any object with best accuracy is possible using this technique. It is also used in GPS for the same reason.

WLAN is one more common example where spread spectrum communication can be used. For the same IEEE 802.11 is a universal standard which supports this mobile communication.

In Cordless phone many manufacturer are using this technique which provides security, more clear sound and wide range for better communication.

Conclusion

In this technical report, we have discussed the various techniques used to resolve the problems of anti-jamming broadcast communication among various entities which are not capable to share their keys. In report we have represented the proposed solutions which will handle the transmission signals or alert signals to suspicious receivers. This proposed system is based on uncoordinated spread spectrum communication model which is anti-jamming technique. The model is represented by USRP/GNU type of radio based implementation model. In this proposed system the average time to transmit a message which is of 2000 bits in size to 100 receivers is measured about 5s. This timing is feasible for this transmission which has the purpose of a hardware and such type of broadband receivers which can significantly decreases the timings in transmitting signals. 

References 

An Liu, Peng Ning, Huaiyu Dai, Yao Liu. USD-FH: Jamming-resistant Wireless Communication using Frequency Hopping. 19 January 2012. https://pdfs.semanticscholar.org/1126/c5fbfcdfd0a98622accd2385edd8c79f20be.pdf.

Bhosle, Sanjay Deshmukh and Udhav. "Performance Evaluation of Spread Spectrum System Using different modulation schemes." Science Direct (2016): 7. https://ac.els-cdn.com/S1877050916305555/1-s2.0-S1877050916305555-main.pdf?_tid=2c7a64ae-d46a-11e7-bc7e-00000aacb35e&acdnat=1511893994_4001967d2255059742e6a66da6318c68.

Capkun, Srdjan. Uncoordinated Direct Sequence Spread Spectrum. 10 April 2015. https://link.springer.com/referenceworkentry/10.1007%2F978-1-4419-5906-5_64.

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Pravin Waghmare, Prof Rahul Nawkhare. Performance Evaluation of DSSS and FHSS. Nagpur, 23 October 2015. https://www.rroij.com/open-access/performance-evaluation-of-dsss-and-fhss-using-modulation-technique-IJIRCCE-2015-%200310006.pdf.

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Smith, Jenny. spread spectrum. Malaysia, 20 October 2016. https://www.ccs.neu.edu/home/rraj/Courses/6710/S10/Lectures/SpreadSpectrum.pdf.

Stuber, G. L. "Understanding Spread Spectrum for Communications." National Instruments (2014). https://www.ni.com/white-paper/4450/en/.

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