Title of Invention	METHOD AND SYSTEM FOR CHIRP BASED MULTIPLE ACCESS SYSTEM WITH FRACTIONAL FOURIER TRANSFORM BASED RECEIVER
Abstract	A method and system for Chirp Based Multiple Access. The method utilizes chirp signals with different initial frequency and same slope to modulate and identify a user's data signal. At a receiver, a received signal is the addition of a user's signal from a cluster, an attenuated signal from the neighbouring clusters, and white Gaussian noise. The receiver is a Fractional Fourier Transform (FrFT) based receiver. The FrFT based receiver produces impulses corresponding to each chirp signal. To separate out a particular user's chirp signal, few samples of an impulse corresponding to the user's chirp signal are retained and rest of the samples are discarded, and a resultant signal is obtained. An inverse FrFT of the resultant signal is then carried out. This produces a reconstructed chirp signal corresponding to the user. The use of FrFT based receiver for separating these signals also reduces Multiple Access Interference (MAI) significantly and improves signal to noise ratio (SNR).

Title of Invention

METHOD AND SYSTEM FOR CHIRP BASED MULTIPLE ACCESS SYSTEM WITH FRACTIONAL FOURIER TRANSFORM BASED RECEIVER

Abstract

A method and system for Chirp Based Multiple Access. The method utilizes chirp signals with different initial frequency and same slope to modulate and identify a user's data signal. At a receiver, a received signal is the addition of a user's signal from a cluster, an attenuated signal from the neighbouring clusters, and white Gaussian noise. The receiver is a Fractional Fourier Transform (FrFT) based receiver. The FrFT based receiver produces impulses corresponding to each chirp signal. To separate out a particular user's chirp signal, few samples of an impulse corresponding to the user's chirp signal are retained and rest of the samples are discarded, and a resultant signal is obtained. An inverse FrFT of the resultant signal is then carried out. This produces a reconstructed chirp signal corresponding to the user. The use of FrFT based receiver for separating these signals also reduces Multiple Access Interference (MAI) significantly and improves signal to noise ratio (SNR).

Full Text	FIELD OF THE INVENTION The present invention, in general pertains to multi-user communication system. Particularly, the present invention proposes a method and system for increasing the number of simultaneous users without increasing the bandwidth. More particularly, this invention relates to method and system for Chirp Based Multiple Access system with Fractional Fourier Transform based receiver. DESCRIPTION OF RELATED ART Currently GSM (FDMA/TDMA) and CDMA are the multi-user communication techniques in use. In a publication titled "SAVING THE BANDWIDTH IN THE FRACTIONAL DOMAIN BY GENERALIZED HILBERT TRANSFORM PAIR RELATIONS" it has been discussed about the symmetry of spectrum in the case of signal being real or causal. If the signal is causal then real and the imaginary part of the spectrum forms the Hilbert transform pair and if the signal is real then the spectrum is conjugate symmetric. Due to this symmetry we can save half the bandwidth. The same kind of relationship the authors have developed for Fractional Fourier Transform. They have shown that if the signal is causal then even part and the odd part of the fractional Fourier transformed signal forms a fractional Hilbert transform pair. If the signal is causal or real and if it is multiplied by chirp then half of the bandwidth can be save in FrFT domain. If the signal is both causal and real and if multiplied by chirp then 3/4th bandwidth can be saved in FrFT domain. However this paper does not discuss about chirp signal's application for multiuser communication and FrFT based receiver system. In yet another publication titled "FILTERING OF CHIRPED ULTRASOUND ECHO SIGNALS WITH THE FRACTIONAL FOURIER TRANSFORM" it has been disclosed that the application of FrFT to localize the chirp signals. It describes chirp signal's application for medical imaging. Chirp signal provides high imaging resolution compared to high frequency signals. With the help of experiment it has been shown the output of the FrFT of a signal matches with the matched filter output. Matched filter requires replica of the signal to generate the output while in case of FrFT one can get the opfimal domain depending on the chirp parameters and can localize the signal in Fractional Fourier domain. Then after windowing one can get the original signal back in time domain by applying inverse transform. However this paper also does not discuss about the chirp signal's application for mulfiuser communication and the FrFT based receiver system. SUMMARY OF THE INVENTION The present invention proposes communicafion system wherein chirp signals are used with different initial frequencies as a carrier signal to modulate users data signals. The system uses Fractional Fourier Transform based receiver. The FrFT is very useful in localizing (providing compact support) chirp signals. It can significantly reduce the MAI due to this property. Chirp signals with different initial frequencies, but with the same slope has compact support in a particular Fractional Fourier Domain. The chirp signals can be easily separated out by applying band pass filter in the Fractional Fourier Domain. Accordingly there is provided a method for Chirp Based Multiple Access, the method comprising the steps of (a) Using chirp signals as a carrier to modulate data thereby increasing the number of users without increasing bandwidth (b) Using Fractional Fourier Transform (FrFT) to separate users signal at the receiving end Accordingly there is provided a system for Chirp Based Multiple Access, the system comprising of several clusters comprising of several cells using Chirp signals with different initial frequencies connected through a common transmission channel which in turn is connected to a receiver with additive white Gaussian channel added These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 illustrates Geometrical interpretation of the relation between optimal angle and the chirp slope 2a(Reference 1) Figure 2 illustrates Localization of Chirp signal in Fractional Fourier Domain (a) Chirp (Linear FM) Signal, (b) Its Fractional Fourier Transform at optimal angle, (c) Spectrogram (Magnitude square of STFT) of the chirp signal Figure 3 illustrates Block diagram of the proposed system Figure 4 illustrates (a) Composite signal of 50 users (received signal), (b) Its Fractional Fourier Transform at optimal angle, (c) Spectrogram (Magnitude square of STFT) of the composite signal Figure 5 illustrates the magnified view of figure 4 Figure 6 illustrates recovered signal Figure 7 illustrates the % Normalized error between the input signal and recovered signal Figure 8 illustrates distribution of chirp signals among the different cells of different clusters DETAILED DESCRIPTION OF THE INVENTION The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail. The proposed invention supports more number of simultaneous users in mobile communication without increasing the bandwidth. It uses chirp signals for modulating user's data. The users can be separated at the receiver side using the Fractional Fourier Transform (FrFT) based receiver. The chirp signals have compact support in Fractional Fourier domain because the basis signals for FrFT are chirp signals. This property of FrFT helps in reducing the MAI significantly in multi-access communication which will improve the SNR of received signal and in turn the supported simultaneous users. The Fractional Fourier Transform (FrFT) provides a measure about the angular distribution of signal energy in time-frequency plane. It is the generalization of the conventional Fourier Transform. Chirp (Linear Frequency modulated) signals are the basis for the FrFT so, it can easily localize (can give compact support) the chirp signals. In other words the FrFT of the chirp signal will be an impulse function in the Fractional Fourier domain. There will be one particular optimal Fractional Fourier domain for each chirp signal depending on its slope (rate of change of frequency) and the location of the impulse in this domain is related with its initial frequency. These relations are given by the equations 1, 2. There equation can be derived from fig.1. Here 4) is the optimal angle, 2a is the slope of the chirp signal and Oopt is the optimal parameter, p is the location of impulse signal in Fractional Fourier domain and b is the initial frequency of the chirp signal. Fig. 2 shows one chirp signal and its representation in Fractional Fourier Domain. In the optimal Fractional Fourier domain the chirp signal is an impulsive signal. This property of FrFT we use in our proposed receiver. As shown in the Fig. 3 the user's data signals are modulated using chirp signals (with different initial frequency and the same slope). All users are using the same frequency and the bandwidth. In the present invention additive white Gaussian channel is currently considered. At the receiver the received signal will be addition of all users' signals from the same cluster (group of cells), the attenuated signals from other neighboring clusters and white Gaussian noise as shown in Fig 4(a). As shown in the receiver block diagram in the Fig 3, the received signal is passed through the FrFT block. Output of the FrFT block will be a set of impulses as show in Fig 4(b). All this impulses corresponds to chirp signals with different initial frequencies. To separate out particular user's chirp signal few significant sample of that impulse are retained which corresponds to that particular chirp signal as shown in Fig. 5. After retaining those samples and forcing all others to be zero, the Inverse FrFT of that resultant signal is taken. This will give the reconstructed chirp signal as shown in Fig. 6. As explained above few significant samples of the impulse function is retained in order to separate out the desired chirp signal. In order to find out the optimal number of samples, software simulation was carried out in which 5 to 100 significant samples were chosen (by significant samples is meant the samples around the peak of the impulse function) in the steps of 5 samples. The recovered signal for each cases were generated and computed the percentage normalize error between the recovered signal and the original signal. Fig. 7 shows the plot of the percentage normalized error vs. number of chosen samples. From the plot it can be concluded that taking 20-25 samples the resultant error is less than 3.5%. The number is justified because less number of samples cannot represent the impulse function effectively and more will add interference due to other neighboring impulse functions. Fig.8 describes the scenario of the mobile communication system, which consists of several clusters which in turn comprises several cells. It shows three clusters with seven cells each. In the cells of same clusters the present invention proposes to use chirp signals with different initial frequencies and the users in the same cell will not be assigned the chirp signals with consecutive initial frequencies, moreover the neighboring cells will not be assigned the chirp signals with consecutive initial frequencies. The different clusters will have chirp signals with different slopes. Thus the present invention can reduce the interference due to the users of neighboring cells and clusters. The reason behind this fact is 1) Non-consecutive initial frequency chirp signals are assigned to the users of the same cell which will reduce the MAI at the receiver. 2) Neighbonng cells are not assigned the chirp signals with consecutive initial frequencies which will more attenuate the interference from the non-neighboring cells which are assigned the consecutive initial frequency chirp signals which are potential interferers. 3) The neighboring clusters are assigned chirp signals with different slopes which will reduce MAI due to the interfering users of neighboring clusters because the chirp signals with different slope can not find the compact support at the same FrFT angle. The software implementation of the proposed idea has been carried out in MATLAB software. To distinguish users, the users are assigned the chirp signals with different initial frequencies with the same slope in order to make the bandwidth constant. We considered communication system with BW= 5 MHz, T= 10ms (symbol duration), Fs= 10 MHz. With these parameters the system can support 568 simultaneous users. The separation in initial frequency of consecutive chirp signal is 4.4 KHz. ADVANTAGES • Improved SNR of the received signal at the receiver. • Improves capacity of communication system in terms of more simultaneous users. It will also be obvious to those skilled in the art that other control methods and apparatuses can be derived from the combinations of the various methods and apparatuses of the present invention as taught by the description and the accompanying drawings and these shall also be considered within the scope of the present invention. Further, description of such combinations and variations is therefore omitted above. It should also be noted that the host for storing the applications include but not limited to a microchip, microprocessor, handheld communication device, computer, rendering device or a multi function device. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart there from. GLOSSARY OF TERMS AND DEFINITIONS THEREOF CDMA - Code Division Multiple Access FDMA - Frequency Division Multiple Access FrFT - Fractional Fourier Transform MAI - Multi Access Interference STFT - Short Time Fourier Transform REFERENCE 1. Capus C. and Brown K., "Short-time fractional Fourier methods for the time-frequency representations of chirp signals", J Acoust Soc Am., 113(6), pp. 3253-3263, June 2003. We Claim 1. A method for Chirp Based Multiple Access, the method comprising the steps of (c) Using chirp signals as a carrier to modulate data thereby increasing the number of users without increasing bandwidth (d) Using Fractional Fourier Transform (FrFT) to separate users signal at the receiving end 2. The method as claimed in claim 1 wherein the user's data signals are modulated using chirp signals with different initial frequency and the same slope. 3. The method as claimed in the preceding claims wherein the chirp signals have compact support in Fractional Fourier domain because the basic signals for FrFT are chirp signals. 4. The method as claimed in the claim 3 wherein the Multi Access interference (MAI) is greatly reduced. 5. The method as claimed in the claims 3 and 4 wherein the Signal to Noise Ratio (SNR) of the received signal is greatly improved 6. The method as claimed in the preceding claims wherein the Fractional Fourier Transform (FrFT) provides a measure about the angular distribution of signal energy in time-frequency plane. 7. The method as claimed in the preceding claims wherein the FrFT of the chirp signal will be an impulse function in the Fractional Fourier domain. 8. The method as claimed in the preceding claims wherein there is one particular optimal Fractional Fourier domain for each chirp signal depending on its slope and the location of the impulse in this domain is related with its initial frequency. 9. The method as claimed in the claim 8 wherein the location of the impulse in this domain is related with Its initial frequency. 10. The method as claimed in claims 8 and 9 wherein the relationship between slope and impulse is given by 0 is the optimal angle, 2a is the slope of the chirp signal and Oopt is the optimal parameter. (3 is the location of impulse signal in Fractional Fourier domain and b is the initial frequency of the chirp signal. 11. The method as claimed in claim 2 wherein additive white Gaussian channel is considered. 12. The method as claimed in the preceding claims wherein the chirp signals with different slope cannot be localized at the same angle of FrFT. 13. The method as claimed in the preceding claims wherein at the receiving end the received signal will be addition of all users' signals form the particular cell and the attenuated signals from the group of neighboring cells, the attenuated signals from other neighboring clusters and additive white Gaussian noise 14. The method as claimed in claim 13 wherein the received signal is passed through the FrFT block. 15- The method as claimed in claims 13 and 14 wherein the Output of the FrFT block will be a set of impulses corresponding to chirp signals with different initial frequencies. 16. The method as claimed in claims 13, 14 and 15 wherein to separate out a particular user's chirp signal, few significant samples of that impulse are retained which corresponds to that particular chirp signal. 17. The method as claimed in claims 13, 14, 15 and 16 wherein after retaining those samples and forcing all others to be zero, the inverse FrFT of that resultant signal is taken which will give the reconstructed chirp signal. 18. The method as claimed in claims 13, 14, 15, 16 and 17 wherein the chirp signals can be separated by applying band pass filter in the Fractional Fourier Domain. 19. The method as claimed in the preceding claims wherein more number of simultaneous users in mobile communication can be allowed without increasing the bandwidth by using chirp signals for modulating user's data. 20. The method as claimed in the preceding claims wherein there is reduction in interference due to the users of adjacent clusters. 21. A system for Chirp Based Multiple Access, the system comprising of several clusters comprising of several cells using Chirp signals with different initial frequencies connected through a common transmission channel which in turn is connected to a receiver with additive white Gaussian channel added. 22. The system as claimed in claim 21 wherein users in the same cell do not have chirp signals with consecutive initial frequencies, the neighboring cells also do not have chirp signals with consecutive initial frequencies and the different clusters will have chirp signals with different slopes. 23. The system as claimed in claim 21 wherein to distinguish users, the users are assigned the chirp signals with different initial frequencies with the same slope in order to make the bandwidth constant. 24. The system as claimed in claim 21 wherein the received signal is passed through the FrFT block. 25. The system as claimed in claim 21 wherein the output of the FrFT block corresponds to Chirp signals with different initial frequencies. 26. The system as claimed in claim 21 wherein the separation of a particular users chirp signal is done by retaining a few significant samples of that particular impulse which corresponds to that particular chirp signal. 27. The system as claimed in claim 26 wherein after retaining a few samples, all the others are forced to Zero, the inverse of the FrFT resultant signal being taken which gives the reconstructed chirp signal. 28. The system as claimed in claims 25and 26 wherein in the optimal Fractional Fourier domain the chirp signal is an impulsive signal and this property of FrFT is used in this receiver. 29. A Method for Chirp Based Multiple Access substantially as herein described with respect to the accompanying drawings. 30. A System for Chirp Based Multiple Access substantially as herein described with respect to the accompanying drawings.

Full Text

FIELD OF THE INVENTION
The present invention, in general pertains to multi-user communication system. Particularly, the present invention proposes a method and system for increasing the number of simultaneous users without increasing the bandwidth. More particularly, this invention relates to method and system for Chirp Based Multiple Access system with Fractional Fourier Transform based receiver.
DESCRIPTION OF RELATED ART
Currently GSM (FDMA/TDMA) and CDMA are the multi-user communication techniques in use.
In a publication titled "SAVING THE BANDWIDTH IN THE FRACTIONAL DOMAIN BY GENERALIZED HILBERT TRANSFORM PAIR RELATIONS" it has been discussed about the symmetry of spectrum in the case of signal being real or causal. If the signal is causal then real and the imaginary part of the spectrum forms the Hilbert transform pair and if the signal is real then the spectrum is conjugate symmetric. Due to this symmetry we can save half the bandwidth. The same kind of relationship the authors have developed for Fractional Fourier Transform. They have shown that if the signal is causal then even part and the odd part of the fractional Fourier transformed signal forms a fractional Hilbert transform pair. If the signal is causal or real and if it is multiplied by chirp then half of the bandwidth can be save in FrFT domain. If the signal is both causal and real and if multiplied by chirp then 3/4th bandwidth can be saved in FrFT domain. However this paper does not discuss about chirp signal's application for multiuser communication and FrFT based receiver system.
In yet another publication titled "FILTERING OF CHIRPED ULTRASOUND ECHO SIGNALS WITH THE FRACTIONAL FOURIER TRANSFORM" it has

been disclosed that the application of FrFT to localize the chirp signals. It describes chirp signal's application for medical imaging. Chirp signal provides high imaging resolution compared to high frequency signals. With the help of experiment it has been shown the output of the FrFT of a signal matches with the matched filter output. Matched filter requires replica of the signal to generate the output while in case of FrFT one can get the opfimal domain depending on the chirp parameters and can localize the signal in Fractional Fourier domain. Then after windowing one can get the original signal back in time domain by applying inverse transform. However this paper also does not discuss about the chirp signal's application for mulfiuser communication and the FrFT based receiver system.
SUMMARY OF THE INVENTION
The present invention proposes communicafion system wherein chirp signals are used with different initial frequencies as a carrier signal to modulate users data signals. The system uses Fractional Fourier Transform based receiver. The FrFT is very useful in localizing (providing compact support) chirp signals. It can significantly reduce the MAI due to this property. Chirp signals with different initial frequencies, but with the same slope has compact support in a particular Fractional Fourier Domain. The chirp signals can be easily separated out by applying band pass filter in the Fractional Fourier Domain.
Accordingly there is provided a method for Chirp Based Multiple Access, the method comprising the steps of
(a) Using chirp signals as a carrier to modulate data thereby increasing the number of users without increasing bandwidth
(b) Using Fractional Fourier Transform (FrFT) to separate users signal at the receiving end
Accordingly there is provided a system for Chirp Based Multiple Access, the

system comprising of several clusters comprising of several cells using Chirp signals with different initial frequencies connected through a common transmission channel which in turn is connected to a receiver with additive white Gaussian channel added
These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates Geometrical interpretation of the relation between optimal angle and the chirp slope 2a(Reference 1)
Figure 2 illustrates Localization of Chirp signal in Fractional Fourier Domain
(a) Chirp (Linear FM) Signal,
(b) Its Fractional Fourier Transform at optimal angle,
(c) Spectrogram (Magnitude square of STFT) of the chirp signal
Figure 3 illustrates Block diagram of the proposed system
Figure 4 illustrates
(a) Composite signal of 50 users (received signal),
(b) Its Fractional Fourier Transform at optimal angle,
(c) Spectrogram (Magnitude square of STFT) of the composite signal
Figure 5 illustrates the magnified view of figure 4 Figure 6 illustrates recovered signal

Figure 7 illustrates the % Normalized error between the input signal and recovered signal
Figure 8 illustrates distribution of chirp signals among the different cells of different clusters
DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail.
The proposed invention supports more number of simultaneous users in mobile communication without increasing the bandwidth. It uses chirp signals for modulating user's data. The users can be separated at the receiver side using the Fractional Fourier Transform (FrFT) based receiver. The chirp signals have compact support in Fractional Fourier domain because the basis signals for FrFT are chirp signals. This property of FrFT helps in reducing the MAI significantly in multi-access communication which will improve the SNR of received signal and in turn the supported simultaneous users.
The Fractional Fourier Transform (FrFT) provides a measure about the angular distribution of signal energy in time-frequency plane. It is the generalization of the conventional Fourier Transform. Chirp (Linear Frequency modulated) signals

are the basis for the FrFT so, it can easily localize (can give compact support) the chirp signals. In other words the FrFT of the chirp signal will be an impulse function in the Fractional Fourier domain. There will be one particular optimal Fractional Fourier domain for each chirp signal depending on its slope (rate of change of frequency) and the location of the impulse in this domain is related with its initial frequency. These relations are given by the equations 1, 2. There equation can be derived from fig.1. Here 4) is the optimal angle, 2a is the slope of the chirp signal and Oopt is the optimal parameter, p is the location of impulse signal in Fractional Fourier domain and b is the initial frequency of the chirp signal.
Fig. 2 shows one chirp signal and its representation in Fractional Fourier Domain. In the optimal Fractional Fourier domain the chirp signal is an impulsive signal. This property of FrFT we use in our proposed receiver.
As shown in the Fig. 3 the user's data signals are modulated using chirp signals (with different initial frequency and the same slope). All users are using the same frequency and the bandwidth. In the present invention additive white Gaussian channel is currently considered. At the receiver the received signal will be addition of all users' signals from the same cluster (group of cells), the attenuated signals from other neighboring clusters and white Gaussian noise as shown in Fig 4(a). As shown in the receiver block diagram in the Fig 3, the received signal is passed through the FrFT block. Output of the FrFT block will be a set of impulses as show in Fig 4(b). All this impulses corresponds to chirp signals with different initial frequencies. To separate out particular user's chirp signal few significant sample of that impulse are retained which corresponds to that particular chirp signal as shown in Fig. 5. After retaining those samples and forcing all others to be zero, the Inverse FrFT of that resultant signal is taken. This will give the reconstructed chirp signal as shown in Fig. 6.
As explained above few significant samples of the impulse function is retained in order to separate out the desired chirp signal. In order to find out the optimal

number of samples, software simulation was carried out in which 5 to 100 significant samples were chosen (by significant samples is meant the samples around the peak of the impulse function) in the steps of 5 samples. The recovered signal for each cases were generated and computed the percentage normalize error between the recovered signal and the original signal. Fig. 7 shows the plot of the percentage normalized error vs. number of chosen samples. From the plot it can be concluded that taking 20-25 samples the resultant error is less than 3.5%. The number is justified because less number of samples cannot represent the impulse function effectively and more will add interference due to other neighboring impulse functions.
Fig.8 describes the scenario of the mobile communication system, which consists of several clusters which in turn comprises several cells. It shows three clusters with seven cells each. In the cells of same clusters the present invention proposes to use chirp signals with different initial frequencies and the users in the same cell will not be assigned the chirp signals with consecutive initial frequencies, moreover the neighboring cells will not be assigned the chirp signals with consecutive initial frequencies. The different clusters will have chirp signals with different slopes. Thus the present invention can reduce the interference due to the users of neighboring cells and clusters. The reason behind this fact is 1) Non-consecutive initial frequency chirp signals are assigned to the users of the same cell which will reduce the MAI at the receiver. 2) Neighbonng cells are not assigned the chirp signals with consecutive initial frequencies which will more attenuate the interference from the non-neighboring cells which are assigned the consecutive initial frequency chirp signals which are potential interferers. 3) The neighboring clusters are assigned chirp signals with different slopes which will reduce MAI due to the interfering users of neighboring clusters because the chirp signals with different slope can not find the compact support at the same FrFT angle.
The software implementation of the proposed idea has been carried out in MATLAB software. To distinguish users, the users are assigned the chirp signals

with different initial frequencies with the same slope in order to make the bandwidth constant. We considered communication system with BW= 5 MHz, T= 10ms (symbol duration), Fs= 10 MHz. With these parameters the system can support 568 simultaneous users. The separation in initial frequency of consecutive chirp signal is 4.4 KHz.
ADVANTAGES
• Improved SNR of the received signal at the receiver.
• Improves capacity of communication system in terms of more simultaneous users.
It will also be obvious to those skilled in the art that other control methods and apparatuses can be derived from the combinations of the various methods and apparatuses of the present invention as taught by the description and the accompanying drawings and these shall also be considered within the scope of the present invention. Further, description of such combinations and variations is therefore omitted above. It should also be noted that the host for storing the applications include but not limited to a microchip, microprocessor, handheld communication device, computer, rendering device or a multi function device.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart there from.

GLOSSARY OF TERMS AND DEFINITIONS THEREOF
CDMA - Code Division Multiple Access
FDMA - Frequency Division Multiple Access
FrFT - Fractional Fourier Transform
MAI - Multi Access Interference
STFT - Short Time Fourier Transform
REFERENCE
1. Capus C. and Brown K., "Short-time fractional Fourier methods for the time-frequency representations of chirp signals", J Acoust Soc Am., 113(6), pp. 3253-3263, June 2003.

We Claim
1. A method for Chirp Based Multiple Access, the method comprising the steps
of
(c) Using chirp signals as a carrier to modulate data thereby increasing the number of users without increasing bandwidth
(d) Using Fractional Fourier Transform (FrFT) to separate users signal at the receiving end
2. The method as claimed in claim 1 wherein the user's data signals are
modulated using chirp signals with different initial frequency and the same slope.
3. The method as claimed in the preceding claims wherein the chirp signals have compact support in Fractional Fourier domain because the basic signals for FrFT are chirp signals.
4. The method as claimed in the claim 3 wherein the Multi Access interference (MAI) is greatly reduced.
5. The method as claimed in the claims 3 and 4 wherein the Signal to Noise Ratio (SNR) of the received signal is greatly improved
6. The method as claimed in the preceding claims wherein the Fractional Fourier Transform (FrFT) provides a measure about the angular distribution of signal energy in time-frequency plane.
7. The method as claimed in the preceding claims wherein the FrFT of the chirp signal will be an impulse function in the Fractional Fourier domain.
8. The method as claimed in the preceding claims wherein there is one particular optimal Fractional Fourier domain for each chirp signal depending on its slope and the location of the impulse in this domain is related with its initial frequency.

9. The method as claimed in the claim 8 wherein the location of the impulse in
this domain is related with Its initial frequency.
10. The method as claimed in claims 8 and 9 wherein the relationship between
slope and impulse is given by

0 is the optimal angle, 2a is the slope of the chirp signal and Oopt is the optimal parameter. (3 is the location of impulse signal in Fractional Fourier domain and b is the initial frequency of the chirp signal.
11. The method as claimed in claim 2 wherein additive white Gaussian channel
is considered.
12. The method as claimed in the preceding claims wherein the chirp signals
with different slope cannot be localized at the same angle of FrFT.
13. The method as claimed in the preceding claims wherein at the receiving end
the received signal will be addition of all users' signals form the particular cell
and the attenuated signals from the group of neighboring cells, the attenuated
signals from other neighboring clusters and additive white Gaussian noise
14. The method as claimed in claim 13 wherein the received signal is passed
through the FrFT block.
15- The method as claimed in claims 13 and 14 wherein the Output of the FrFT block will be a set of impulses corresponding to chirp signals with different initial

frequencies.
16. The method as claimed in claims 13, 14 and 15 wherein to separate out a particular user's chirp signal, few significant samples of that impulse are retained which corresponds to that particular chirp signal.
17. The method as claimed in claims 13, 14, 15 and 16 wherein after retaining those samples and forcing all others to be zero, the inverse FrFT of that resultant signal is taken which will give the reconstructed chirp signal.
18. The method as claimed in claims 13, 14, 15, 16 and 17 wherein the chirp signals can be separated by applying band pass filter in the Fractional Fourier Domain.
19. The method as claimed in the preceding claims wherein more number of simultaneous users in mobile communication can be allowed without increasing the bandwidth by using chirp signals for modulating user's data.
20. The method as claimed in the preceding claims wherein there is reduction in interference due to the users of adjacent clusters.
21. A system for Chirp Based Multiple Access, the system comprising of several clusters comprising of several cells using Chirp signals with different initial frequencies connected through a common transmission channel which in turn is connected to a receiver with additive white Gaussian channel added.
22. The system as claimed in claim 21 wherein users in the same cell do not have chirp signals with consecutive initial frequencies, the neighboring cells also do not have chirp signals with consecutive initial frequencies and the different clusters will have chirp signals with different slopes.
23. The system as claimed in claim 21 wherein to distinguish users, the users

are assigned the chirp signals with different initial frequencies with the same slope in order to make the bandwidth constant.
24. The system as claimed in claim 21 wherein the received signal is passed through the FrFT block.
25. The system as claimed in claim 21 wherein the output of the FrFT block corresponds to Chirp signals with different initial frequencies.
26. The system as claimed in claim 21 wherein the separation of a particular users chirp signal is done by retaining a few significant samples of that particular impulse which corresponds to that particular chirp signal.
27. The system as claimed in claim 26 wherein after retaining a few samples, all the others are forced to Zero, the inverse of the FrFT resultant signal being taken which gives the reconstructed chirp signal.
28. The system as claimed in claims 25and 26 wherein in the optimal Fractional Fourier domain the chirp signal is an impulsive signal and this property of FrFT is used in this receiver.
29. A Method for Chirp Based Multiple Access substantially as herein described with respect to the accompanying drawings.
30. A System for Chirp Based Multiple Access substantially as herein described with respect to the accompanying drawings.

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Patent Number

272687

Indian Patent Application Number

1964/CHE/2007

PG Journal Number

17/2016

Publication Date

22-Apr-2016

Grant Date

19-Apr-2016

Date of Filing

03-Sep-2007

Name of Patentee

SAMSUNG R&D INSTITUTE INDIA-BANGALORE PRIVATE LIMITED

Applicant Address

#2870 ORION BUILDING BAGMANE CONSTELLATION BUSINESS PARK OUTER RING ROAD DODDANEKUNDI CIRCLE MARATHAHALLI POST BANGALORE 560037

Inventors:

#	Inventor's Name	Inventor's Address
1	PUJARA CHIRAG	EMPLOYED AT SAMSUNG INDIA SOFTWARE OPERATIONS PRIVATE LIMITED BAGMANE LAKEVIEW BLOCK 'B' NO 66/1 BAGMANE TECH PARK C V RAMAN NAGAR BYRASANDRA BANGALORE 560093

PCT International Classification Number

H04L 1/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA