Description:TECHNICAL FIELD
[0001] The present disclosure relates to the field of signal modulation technique. More particularly, the present disclosure relates to a method and system for peak to average power ratio (PAPR) of the multicarrier modulated waveforms in wireless communication systems.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Multicarrier modulation is one of the suitable techniques for high speed wireless communication systems because of its bandwidth efficiency and ability in dealing with multipath fading. Due to presence of large number of independently modulated subcarriers, the peak power of the signal can be very high as compared to the average power of the signal. The high Peak-to-Average power ratio (PAPR) of a multicarrier modulated signal is a major drawback in dealing with Power Amplifiers (PA) at the transmitter. High peaks of a signal cause Power Amplifier (PA) Non-linear effects, leading to signal distortion, producing interference between subcarriers and corrupting the signal spectrum. Because of signal distortion, the bit error rate (BER) of the communication link increases which degrades the quality of service (QOS) and also increases the adjacent channel power ratio (ACPR) which causes interference to adjacent channels. Therefore, it is preferable to reduce the PAPR of the Multicarrier OFDM transmitter signal. There are many solutions to the problem of high PAPR in multicarrier modulation.
[0004] There are solutions which targets the design of Power amplifier such that high PAPR of multicarrier modulation does not degrade the signal quality. One such solution is to use a linear PA with large dynamic range. This solution increases the cost as well as degrades the power efficiency of the PA. Other approach is to reduce the average power of the multicarrier modulated signal to avoid the PA to enter into the saturation region. However, reducing the average power level will bring down the Signal to Noise (SNR) which degrades the Bit Error Rate (BER) performance which in turn affects the quality of service.
[0005] There are other approaches which use signal coding techniques. By coding with different sequence sets multiple modulated transmitter signals are generated. By transmitting one of them with minimum PAPR, the probability of incurring high PAPR can be reduced. These solutions are complex and introduce extra redundant information in the form of codes which reduces the data rate of the system.
[0006] An existing Patent US20050089116A1 describes a method which generates a multicarrier modulation signal and compares its PAPR value against the required PAPR value, if PAPR is greater than the required value, the data is scrambled and modulated again iteratively till the required PAPR value is obtained. This method is complex in terms of resources for real time implementation and it adds more delay to the system to generate a multicarrier signal with required PAPR.
[0007] There are other solutions which reduce the PAPR by distorting the multicarrier modulated signal in the baseband before being converted into analog signal with the help of distortion based techniques. However, Distortion based techniques are non linear processes and may cause significant distortion, which degrades the performance of the system. These methods are less complex and can be implemented in real time applications with fewer resources. In patent EP2429141B1, a method is proposed to reduce the peak to average power ratio of multicarrier modulation signal which monitors the PAPR of the signal; according to peak power level it reduces the PAPR by clipping the signal amplitude using parabolic elementary transfer function. This method uses less resources and less complexity to implement in the real time multicarrier modulation systems.
[0008] The present disclosure relates to the field of signal modulation technique. More particularly, the present disclosure relates to a method and system for peak to average power ratio of the multicarrier modulated waveforms in wireless communication systems.
OBJECTS OF THE PRESENT DISCLOSURE
[0009] Some of the objects of the present disclosure, which at least one embodiment herein satisfies are as listed herein below.
[0010] Present invention provides a method and system for peak to average power ratio (PAPR) of the multicarrier modulated waveforms in wireless communication systems.
[0011] It is an object of the present disclosure to provide improved spectral efficiency where a lower PAPR allows for better use of the available spectrum.
[0012] It is an object of the present disclosure to increase transmission range, where a lower PAPR can transmit signals over a greater distance with the same power, since a lower peak power reduces the distortion and attenuation that signals experience during transmission.
[0013] It is an object of the present disclosure to reduced interference, where a lower PAPR reduces the likelihood of interference with other signals in the same frequency band, since a lower peak power means that the signal is less likely to cause interference with other signals.
[0014] It is an object of the present disclosure to improve power efficiency, where a lower PAPR requires less power to transmit the same information, which can reduce operating costs and increase battery life for mobile devices.

SUMMARY
[0015] The present disclosure relates to the field of signal modulation technique. More particularly, the present disclosure relates to a method and system for peak to average power ratio (PAPR) of the multicarrier modulated waveforms in wireless communication systems.
[0016] An aspect of the present disclosure pertains to a method for peak to average power ratio of the multicarrier modulated waveforms in wireless communication systems. The method comprising the steps of: estimating, by a soft core processor along with a memory interface controller and a bus controller dynamic threshold, the buffered and exported modulated multicarrier transmitted symbols after handshaking with Multicarrier transmitter circuit in real time dynamically. The method comprising the steps of limiting the PAPR value of digital multicarrier transmitted signal within the required PAPR. The method comprising the steps of: preserving the phase of the amplitude limited signal by using the in-phase and quadrature phase components of the original transmitted signal. The method comprising the steps of: filtering, by a programmable filtering circuit which filters, the PAPR limited transmitted signal to remove adjacent channel leakage or spectral re-growth and perform hand-shaking with RF transceiver circuit to convert PAPR limited multicarrier modulated digital signal to analog and further up-convert the signal to radio frequency.
[0017] In an aspect, limiting the PAPR value of digital multicarrier transmitted signal, wherein in-phase and quadrature phase component values of the original signal samples are used to maintain the phase continuity.
[0018] In an aspect, initiate, in-phase and quadrature phase component values of the incoming signal samples are computed with the help of low complex CORDIC.
[0019] In an aspect, an average power of the incoming data is computed in real time.
[0020] In an aspect, the average power of the incoming data is compared with computed dynamic threshold to decide the possibility of clipping in real time.
[0021] In an aspect, complex multiplication is employed in real time to perform phase preserved clipping by avoiding division operation.
[0022] In an aspect, PAPR reduction threshold is estimated and updated dynamically in real time.
[0023] In an aspect, a 2:1 multiplexing unit can be configured to select at least one of a amplitude limited phase preserved signal, and a direct input signal based on the decision of a limiter unit.
[0024] An aspect of the present disclosure pertains to a system for peak to average power ratio of the multicarrier modulated waveforms in wireless communication systems. The system is configured to receive one or more information bits by a multicarrier transmitter block, and transform the one or more information bits into time domain and generate digital multicarrier transmitter signal. The system is configured to enable an embedded design with a soft core processor along with a memory interface controller and a bus controller which buffer and export the digital transmitter samples from multicarrier transmitter circuit. The system is configured to calculate the amplitude threshold value by a threshold calculator circuit from the buffered and exported transmitter samples to limit the peak power of the transmitted signal. The system is configured to generate PAPR limited digital transmitter signal by one or more reprogrammable logic blocks including a CORDIC, complex multiplier, limiter, multiplexer and filtering circuit. The system is configured to compute the phase of incoming samples a Low complexity CORDIC unit and translates it into corresponding in-phase and quadrature phase component values. The system is configured to monitor the amplitude of input signal a threshold limiter circuit, and compare with dynamic threshold value and limits its amplitude value if the value is greater than the calculated threshold value. The system is configured to select by a 2:1 multiplexing unit at least one of a amplitude limited phase preserved signal, and a direct input signal based on the decision of a limiter unit. The system is configured to filter by a programmable filtering circuit the digital transmitter signal to remove the leakage in adjacent channels and confines the signal information within the allowed bandwidth. The system is configured to enable, by an RF transceiver unit, to examine PAPR limited digital samples, and initiate digital to analog conversion, and up-converts the analog PAPR limited multicarrier modulated signal to transmitter radio frequency.

BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0026] The diagrams are for illustration only, which thus is not a limitation of the present disclosure, and wherein:
[0027] FIG. 1 illustrates block diagram of the transmitter path of multicarrier wireless communication system, in accordance with an exemplary embodiment of the present disclosure.
[0028] FIG. 2 illustrates block diagram of the functional modules of PAPR unit in the transmitter path of multicarrier wireless communication system, in accordance with an exemplary embodiment of the present disclosure.
[0029] FIG. 3 illustrates the proposed method for peak to average power ratio reduction in a multicarrier transmitter system, in accordance with an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION
[0030] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0031] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0032] In some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0033] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0034] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0035] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
[0036] The present disclosure relates to the field of signal modulation technique. More particularly, the present disclosure relates to a system and method for synchronization for medium data rate communication in high multipath fading environment.
[0037] FIG. 1 illustrates block diagram of the transmitter path of multicarrier wireless communication system, in accordance with an exemplary embodiment of the present disclosure.
[0038] In an embodiment, FIG.1 depicts the transmitter path of multicarrier wireless communication system which includes a multicarrier transmitter 102, a peak to average power ratio (PAPR) module 104, a Radio Frequency (RF) transceiver 106, and Power Amplifiers (PA) 108. A multicarrier transmitter signal is the sum of N independent baseband I-Q symbols modulated onto sub-carriers of equal bandwidth with frequency separation of 1/T between adjacent subcarriers. “T” is the time duration of the multicarrier modulated signal. A set of information bits as shown in Figure 1 is mapped onto I-Q symbols to create complex-valued symbol vector = T, which is transformed into a discrete-time signal T via an IFFT operation; i.e.,
---- Equation (1)
where W(n) is a discrete-time rectangular window with amplitude 1 over the interval [0,N-1].
[0039] In an embodiment, the root cause of the PAPR problem is the result of weighted sum of random variables (frequency domain I-Q samples) causing the time domain samples x[n] to have a Gaussian-like distribution for large no of sub-carriers (N). To transmit the large peaks at the tails of the distribution, the power amplifier (PA) 108 at the transmitter must support a very large dynamic range. Mathematically, the Peak to Average Power Ratio (PAPR) of a given block of digital transmitter samples can be written as
---- Equation (2)
where x(n) is a baseband multicarrier transmitter sample.
[0040] In an embodiment, to operate the Power Amplifiers 108 with this multicarrier modulated waveform with high PAPR value, a significant amount of input signal power level back-off is required to avoid spectral re-growth and distortions in the transmitted signal. Hence, it is preferable to reduce the peak power of the multicarrier modulated signal.
[0041] In an embodiment,, a scheme is proposed to reduce the peak to average power ratio of multicarrier modulated signal using clipping and filtering based PAPR module 104 as shown in Figure 2. PAPR module 101 as illustrated in figure 1 takes I/Q samples of the multicarrier transmitter unit 100 and provides I`/Q` samples as outputs with targeted low PAPR value.
[0042] FIG. 2 illustrates block diagram of the functional modules of PAPR unit in the transmitter path of multicarrier wireless communication system, in accordance with an exemplary embodiment of the present disclosure.
[0043] In an embodiment, Figure 2 illustrates the functional details of PAPR module 104. The threshold value for the PAPR reduction module is calculated within the embedded processor unit 208 comprising a threshold calculator 206 with the help of stored buffer 202 samples. Different threshold values are calculated for different PAPR values of the transmitter waveform having multiple sub-carriers. The PAPR reduced I`/Q` digital samples of the transmitter waveform are sent to RF transceiver 104 for RF conversion.
[0044] In an embodiment, inside PAPR module 101, the Clipping technique is employed. In this method, it calculates the phase of input I/Q samples to preserve the phase of the incoming signal even after clipping. The phase is measured with the help of CORDIC unit 212. Once the phase is calculated, the in-phase (sin (Ɵ)) and quadrature-phase (cos (Ɵ)) components are calculated with the help of low complexity CORDIC unit 212. Calculated in-phase and quadrature phase components are multiplied with clipping level threshold value in the complex multiplier reconfigurable unit 212 to generate the Clipped I`/Q` components. While generating clipped I`/Q` samples, the power calculation is also done in parallel using the input I/Q samples. Once Clipped I`/Q` samples are ready, depending on the power level of the original I/Q samples, decisions are taken to send out original I/Q samples or clipped I`/Q` samples with the help of 2:1 multiplexer 212. If the power of the original signal samples is greater than the threshold, then clipped I`/Q` samples are sent out, else the original I/Q samples are sent to RF transceiver 104 for RF conversion. Due to hard clipping/limiting, out-of-band radiation, which causes out-of-band interference to adjacent channel, is observed. To overcome this drawback, programmable filtering module 212 which acts as a smoothing filter, is employed to reduce the out-of-band radiation. An RF transceiver unit 104 which takes PAPR limited digital samples and does digital to analog conversion and up-converts the analog signal to transmitter radio frequency. Further, power amplifier unit 106 amplifies the PAPR limited multicarrier modulated signal.
[0045] FIG. 3 illustrates the proposed method for peak to average power ratio reduction in a multicarrier transmitter system, in accordance with an exemplary embodiment of the present disclosure.
[0046] In an embodiment, I/Q samples are received and buffered at step 302 with the help of buffer and memory interface controller. Peak and average power of each symbol of the transmitter at step 304 is calculated as shown in equation 2. Amplitude threshold value is determined from the average power and the target PAPR at step 306. Peak powers of each modulated symbol are compared at step 308 with the dynamic threshold values of corresponding symbols received from the embedded unit 202. If peak power of the symbol is well within the threshold value, original I/Q samples are sent to RF transceiver 102 for RF conversion at step 316. The in-phase (sin (Ɵ)) and quadrature-phase (cos (Ɵ)) components are calculated at step 310 using the phase (Ɵ) of the original I/Q samples with the help of low complexity CORDIC unit 212. Calculated in-phase and quadrature phase components are multiplied with dynamic threshold value at step 312 in the complex multiplier reconfigurable unit 212 to generate the Clipped I`/Q` components. A RF transceiver unit 102 which takes filtered and PAPR limited digital samples, does digital to analog conversion and up-converts the analog signal to transmitter radio frequency at step 314. Further, Power Amplifier unit 103 amplifies the PAPR limited multicarrier modulated signal.
[0047] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGS OF THE INVENTION
[0048] The proposed invention a method and system for peak to average power ratio (PAPR) of the multicarrier modulated waveforms in wireless communication systems.
[0049] The proposed invention provides improved spectral efficiency where a lower PAPR allows for better use of the available spectrum.
[0050] The proposed invention increases transmission range, where a lower PAPR can transmit signals over a greater distance with the same power, since a lower peak power reduces the distortion and attenuation that signals experience during transmission.
[0051] The proposed invention reduces interference, where a lower PAPR reduces the likelihood of interference with other signals in the same frequency band, since a lower peak power means that the signal is less likely to cause interference with other signals.
[0052] The proposed invention improves power efficiency, where a lower PAPR requires less power to transmit the same information, which can reduce operating costs and increase battery life for mobile devices.
, Claims:1. A method for peak to average power ratio of the multicarrier modulated waveforms in wireless communication systems, the method comprising the steps of:
estimating, by a soft core processor (208) along with a memory interface controller (204) and a bus controller (214) dynamic threshold (216), the buffered and exported modulated multicarrier transmitted symbols after handshaking with a multicarrier transmitter circuit (102) in real time dynamically;
limiting the PAPR value of digital multicarrier transmitted signal within the required PAPR module (104);
preserving the phase of the amplitude limited signal by using the in-phase and quadrature phase components of the original transmitted signal; and
filtering, by a programmable filtering circuit (212) which filters, the PAPR limited transmitted signal to remove adjacent channel leakage or spectral re-growth and perform hand-shaking with RF transceiver circuit (106) to convert PAPR limited multicarrier modulated digital signal to analog and further up-convert the signal to radio frequency.

2. The method as claimed in claim 1, wherein limiting the PAPR value of digital multicarrier transmitted signal, wherein in-phase and quadrature phase component values of the original signal samples are used to maintain the phase continuity.

3. The method as claimed in claim 1, wherein an in-phase and quadrature phase component values of the incoming signal samples are computed with the help of low complex CORDIC unit (212).

4. The method as claimed in claim 1, wherein an average power of the incoming data is computed in real time.

5. The method as claimed in claim 1, wherein the average power of the incoming data is compared with computed dynamic threshold (216) to decide the possibility of clipping in real time.

6. The method as claimed in claim 1, wherein complex multiplication is employed in real time to perform phase preserved clipping by avoiding division operation.

7. The method as claimed in claim 1, wherein PAPR reduction threshold is estimated and updated dynamically in real time.

8. The method as claimed in claim 1, wherein a 2:1 multiplexing unit (102) is configured to select at least one of a amplitude limited phase preserved signal, and a direct input signal based on the decision of a limiter unit.

9. A system (100) for peak to average power ratio of the multicarrier modulated waveforms in wireless communication systems as claimed in claim 1, the system is configured to:
receive one or more information bits by a multicarrier transmitter block (102), and transform the one or more information bits into time domain and generate digital multicarrier transmitter signal;
enable an embedded design with a soft core processor (208) along with a memory interface controller (204) and a bus controller (214) which buffer and export the digital transmitter samples from multicarrier transmitter circuit (102);
calculate the amplitude threshold value by a threshold calculator circuit (206) from the buffered and exported transmitter samples to limit the peak power of the transmitted signal;
generate PAPR limited digital transmitter signal by one or more reprogrammable logic blocks including a CORDIC, complex multiplier, limiter, multiplexer and filtering circuit (212);
compute the phase of incoming samples a Low complexity CORDIC unit (212) and translates it into corresponding in-phase and quadrature phase component values;
monitor the amplitude of input signal a threshold limiter circuit, and compare with dynamic threshold value and limits its amplitude value if the value is greater than the calculated threshold value;
select by a 2:1 multiplexing unit (102) at least one of a amplitude limited phase preserved signal, and a direct input signal based on the decision of a limiter unit;
filter by a programmable filtering circuit (212) the digital transmitter signal to remove the leakage in adjacent channels and confines the signal information within the allowed bandwidth; and
enable, by a RF transceiver unit (106), for examining PAPR limited digital samples and initiate digital to analog conversion, and up-converts the analog PAPR limited multicarrier modulated signal to transmitter radio frequency.