25-06-2012, 06:01 PM
secret communication
[attachment=25510]
The secret communication between transmitter and receiver plays a major role in militaries, radar and wireless communication. The rapid growth of internet has greatly facilitated the unauthorized distribution and hacking of digital media (text, audio, image and video) is easier due to availability of processing platforms. As a result the music industry claims a multibillion dollar annual revenue loss due to piracy. The traditional data protection methods such as scramble or encryption cannot be used since the content must be played back in the original form, at which point it can always be rerecorded and then freely distributed. Hence watermarking provides a promising solution to the problem.
Special domain watermarking modifies the signal by slightly changing the bit values. It is called as temporal domain. In frequency domain, the values of certain frequencies are altered from the signal. It is called transform domain. Hence the watermark is applied to the whole signal so as not to remove. The invisible watermarks are imperceptible under normal conditions. The robust watermarking has property which is infeasible to remove them. with the different classification of watermarking, it is concluded that, frequency domain is good than special domain, because it is faster than special domain. And compare to visible watermarking, the invisible watermarking provides good secure communication and it used to provide the covert communication for the application of militaries, the invisible audio watermarking is used .While compare to fragile, the robust watermarking provides strong embedding of the data. Blind (public) watermarking scheme can detect and extract watermarks without the use of un-watermarked audio signal. Therefore it requires only a half storage capacity and half bandwidth compared with the non-blind (private) watermarking scheme. Hence it is concluded that, for secure communication of the secret messages, the watermarking should be imperceptible, good robustness, high capacity (pay load), and high speed. Hence from the watermarking classification, the frequency working domain yields high speed, good robustness. According to human perception, the invisible watermark yields high security. For strong watermarking process the robust watermark is used and for high speed and low power application, the blind watermarking is used. Finally concluding that, frequency domain and blind watermarking is chosen for the secret communication. There are different techniques used in audio watermarking, they named as, LSB coding, echo hiding, phase coding and spread spectrum watermarking.
The LSB coding audio watermarking is one of the simplest ways to embed the data. It provides high watermark channel bit rate, good imperceptible, since there is no need to transform the host signal, this algorithm has a low complexity It works very well for fragile watermarking scheme, but the simple random changes of the LSB, destroys the coded watermark .Whereas the phase coding provides good robustness but the watermark does not dispersed over the entire data set available and thus it can be easily removed . The robustness of the watermarking can be further increased in echo hiding techniques by embedding the high energy echoes, but embedding the high energy echoes in the signal leads to audio distortion. The noise is increased when the payload is increased . The spread spectrum technique is one of the widely used secure data communication scheme. It conserves available bandwidth to reduce the power. The security is more hence it is used in military communication. Among all these techniques, the spread spectrum audio watermarking techniques provides, high watermark channel bit rate, good robustness, very good imperceptible, high security which enables to provide for convert communication.
TECHNIQUES:
PHASE ENCODING:
This watermarking technique exploits the human auditory system’s lack of sensitivity to absolute phase changes by encoding the watermark data in an artificial phase signal.
Phase encoding works by breaking the audio signal into frames, and performing spectral analysis on each frame. Once the spectrum has been computed, the magnitude and phase of consecutive frames are compared, and an artificial phase signal is created to transmit data (see Figure 11). The artificial phase is modulated in with the phase from each frame, and the new phase frames are combined to form the watermarked signal.
The modified phase frames can also be smoothed to limit the amount of distortion present in the marked signal (Figure 12), but in minimizing distortion, the data rate of the watermark is constrained respectively.
SPREAD SPECTRUM WM:
This watermarking technique relies on direct sequence spread spectrum (DSSS) to spread the watermarked signal over the entire audible frequency spectrum such that it approximates white noise, at a power level as to be inaudible. A pseudorandom sequence (chip) is used to modulate a carrier wave which creates the spread signal watermark code (Figure 13). This code is attenuated to a level roughly equal to 0.5% of the dynamic range of the original audio file, before being mixed with the original.
Spread Spectrum. Figure courtesy of Bender, et al.
The data rate from this technique is much lower than previous methods, and averages around 4 bits per second. The low data rate is compensated by the robustness of this algorithm due to high noise immunity.
Echo Watermarking
The echo data hiding technique relies on distorting an audio signal in a way which is perceptually dismissed by the human auditory system as environmental distortion.
The original audio signal is copied into two segments (kernels), one which leads the original signal in time, and one which lags. Each kernel represents either a zero or a one bit for watermark data transmission. The bit stream of watermark data is used to mix the two kernels together (Figure 14). The signals are mixed with gradually sloped transitions to reduce distortion.
DSSS AND FHSS:
In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated. The name 'spread spectrum' comes from the fact that the carrier signals occur over the full bandwidth (spectrum) of a device's transmitting
1. DSSS phase-modulates a sine wave pseudorandomly with a continuous string of pseudonoise (PN) code symbols called "chips", each of which has a much shorter duration than an information bit. That is, each information bit is modulated by a sequence of much faster chips. Therefore, the chip rate is much higher than the information signal bit rate.
2. DSSS uses a signal structure in which the sequence of chips produced by the transmitter is known a priori by the receiver. The receiver can then use the same PN sequence to counteract the effect of the PN sequence on the received signal in order to reconstruct the information signal.
3. [edit] Transmission method
4. Direct-sequence spread-spectrum transmissions multiply the data being transmitted by a "noise" signal. This noise signal is a pseudorandom sequence of 1 and −1 values, at a frequency much higher than that of the original signal.
5. The resulting signal resembles white noise, like an audio recording of "static"
Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. It is utilized as a multiple access method in the frequency-hopping code division multiple access (FH-CDMA) scheme.
A spread-spectrum transmission offers three main advantages over a fixed-frequency transmission:
1. Spread-spectrum signals are highly resistant to narrowband interference. The process of re-collecting a spread signal spreads out the interfering signal, causing it to recede into the background.
2. Spread-spectrum signals are difficult to intercept. An FHSS signal simply appears as an increase in the background noise to a narrowband receiver. An eavesdropper would only be able to intercept the transmission if the pseudorandom sequence was known.
Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference. The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result, bandwidth can be utilized more efficiently.
Chirp ss:
In digital communications, Chirp spread spectrum (CSS) is a spread spectrum technique that uses wideband linear frequency modulated chirp pulses to encode information.[1] A chirp is a sinusoidal signal whose frequency increases or decreases over a certain amount of time.
As with other spread spectrum methods, Chirp Spread Spectrum uses its entire allocated bandwidth to broadcast a signal, making it robust to channel noise. Further, because the chirps utilize a broad band of the spectrum, Chirp Spread Spectrum is also resistant to multi-path fading even when operating at very low power. However, it is unlike direct-sequence spread spectrum (DSSS) or frequency-hopping spread spectrum (FHSS) in that it does not add any pseudo-random elements to the signal to help distinguish it from noise on the channel, instead relying on the linear nature of the chirp pulse. Additionally, Chirp Spread Spectrum is resistant to the Doppler effect, which is typical in mobile radio applications.[2]
[attachment=25510]
The secret communication between transmitter and receiver plays a major role in militaries, radar and wireless communication. The rapid growth of internet has greatly facilitated the unauthorized distribution and hacking of digital media (text, audio, image and video) is easier due to availability of processing platforms. As a result the music industry claims a multibillion dollar annual revenue loss due to piracy. The traditional data protection methods such as scramble or encryption cannot be used since the content must be played back in the original form, at which point it can always be rerecorded and then freely distributed. Hence watermarking provides a promising solution to the problem.
Special domain watermarking modifies the signal by slightly changing the bit values. It is called as temporal domain. In frequency domain, the values of certain frequencies are altered from the signal. It is called transform domain. Hence the watermark is applied to the whole signal so as not to remove. The invisible watermarks are imperceptible under normal conditions. The robust watermarking has property which is infeasible to remove them. with the different classification of watermarking, it is concluded that, frequency domain is good than special domain, because it is faster than special domain. And compare to visible watermarking, the invisible watermarking provides good secure communication and it used to provide the covert communication for the application of militaries, the invisible audio watermarking is used .While compare to fragile, the robust watermarking provides strong embedding of the data. Blind (public) watermarking scheme can detect and extract watermarks without the use of un-watermarked audio signal. Therefore it requires only a half storage capacity and half bandwidth compared with the non-blind (private) watermarking scheme. Hence it is concluded that, for secure communication of the secret messages, the watermarking should be imperceptible, good robustness, high capacity (pay load), and high speed. Hence from the watermarking classification, the frequency working domain yields high speed, good robustness. According to human perception, the invisible watermark yields high security. For strong watermarking process the robust watermark is used and for high speed and low power application, the blind watermarking is used. Finally concluding that, frequency domain and blind watermarking is chosen for the secret communication. There are different techniques used in audio watermarking, they named as, LSB coding, echo hiding, phase coding and spread spectrum watermarking.
The LSB coding audio watermarking is one of the simplest ways to embed the data. It provides high watermark channel bit rate, good imperceptible, since there is no need to transform the host signal, this algorithm has a low complexity It works very well for fragile watermarking scheme, but the simple random changes of the LSB, destroys the coded watermark .Whereas the phase coding provides good robustness but the watermark does not dispersed over the entire data set available and thus it can be easily removed . The robustness of the watermarking can be further increased in echo hiding techniques by embedding the high energy echoes, but embedding the high energy echoes in the signal leads to audio distortion. The noise is increased when the payload is increased . The spread spectrum technique is one of the widely used secure data communication scheme. It conserves available bandwidth to reduce the power. The security is more hence it is used in military communication. Among all these techniques, the spread spectrum audio watermarking techniques provides, high watermark channel bit rate, good robustness, very good imperceptible, high security which enables to provide for convert communication.
TECHNIQUES:
PHASE ENCODING:
This watermarking technique exploits the human auditory system’s lack of sensitivity to absolute phase changes by encoding the watermark data in an artificial phase signal.
Phase encoding works by breaking the audio signal into frames, and performing spectral analysis on each frame. Once the spectrum has been computed, the magnitude and phase of consecutive frames are compared, and an artificial phase signal is created to transmit data (see Figure 11). The artificial phase is modulated in with the phase from each frame, and the new phase frames are combined to form the watermarked signal.
The modified phase frames can also be smoothed to limit the amount of distortion present in the marked signal (Figure 12), but in minimizing distortion, the data rate of the watermark is constrained respectively.
SPREAD SPECTRUM WM:
This watermarking technique relies on direct sequence spread spectrum (DSSS) to spread the watermarked signal over the entire audible frequency spectrum such that it approximates white noise, at a power level as to be inaudible. A pseudorandom sequence (chip) is used to modulate a carrier wave which creates the spread signal watermark code (Figure 13). This code is attenuated to a level roughly equal to 0.5% of the dynamic range of the original audio file, before being mixed with the original.
Spread Spectrum. Figure courtesy of Bender, et al.
The data rate from this technique is much lower than previous methods, and averages around 4 bits per second. The low data rate is compensated by the robustness of this algorithm due to high noise immunity.
Echo Watermarking
The echo data hiding technique relies on distorting an audio signal in a way which is perceptually dismissed by the human auditory system as environmental distortion.
The original audio signal is copied into two segments (kernels), one which leads the original signal in time, and one which lags. Each kernel represents either a zero or a one bit for watermark data transmission. The bit stream of watermark data is used to mix the two kernels together (Figure 14). The signals are mixed with gradually sloped transitions to reduce distortion.
DSSS AND FHSS:
In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated. The name 'spread spectrum' comes from the fact that the carrier signals occur over the full bandwidth (spectrum) of a device's transmitting
1. DSSS phase-modulates a sine wave pseudorandomly with a continuous string of pseudonoise (PN) code symbols called "chips", each of which has a much shorter duration than an information bit. That is, each information bit is modulated by a sequence of much faster chips. Therefore, the chip rate is much higher than the information signal bit rate.
2. DSSS uses a signal structure in which the sequence of chips produced by the transmitter is known a priori by the receiver. The receiver can then use the same PN sequence to counteract the effect of the PN sequence on the received signal in order to reconstruct the information signal.
3. [edit] Transmission method
4. Direct-sequence spread-spectrum transmissions multiply the data being transmitted by a "noise" signal. This noise signal is a pseudorandom sequence of 1 and −1 values, at a frequency much higher than that of the original signal.
5. The resulting signal resembles white noise, like an audio recording of "static"
Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. It is utilized as a multiple access method in the frequency-hopping code division multiple access (FH-CDMA) scheme.
A spread-spectrum transmission offers three main advantages over a fixed-frequency transmission:
1. Spread-spectrum signals are highly resistant to narrowband interference. The process of re-collecting a spread signal spreads out the interfering signal, causing it to recede into the background.
2. Spread-spectrum signals are difficult to intercept. An FHSS signal simply appears as an increase in the background noise to a narrowband receiver. An eavesdropper would only be able to intercept the transmission if the pseudorandom sequence was known.
Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference. The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result, bandwidth can be utilized more efficiently.
Chirp ss:
In digital communications, Chirp spread spectrum (CSS) is a spread spectrum technique that uses wideband linear frequency modulated chirp pulses to encode information.[1] A chirp is a sinusoidal signal whose frequency increases or decreases over a certain amount of time.
As with other spread spectrum methods, Chirp Spread Spectrum uses its entire allocated bandwidth to broadcast a signal, making it robust to channel noise. Further, because the chirps utilize a broad band of the spectrum, Chirp Spread Spectrum is also resistant to multi-path fading even when operating at very low power. However, it is unlike direct-sequence spread spectrum (DSSS) or frequency-hopping spread spectrum (FHSS) in that it does not add any pseudo-random elements to the signal to help distinguish it from noise on the channel, instead relying on the linear nature of the chirp pulse. Additionally, Chirp Spread Spectrum is resistant to the Doppler effect, which is typical in mobile radio applications.[2]