Description:TECHNICAL FIELD
[0001] The present disclosure relates, in general, to wireless communication systems and more specifically, relates to a system and method for generating soft-decision demodulated bits from M-amplitude and phase shifting keying (APSK) modulations.

BACKGROUND
[0002] A digital wireless communication system consists of modulation, inter-leaver, scrambler and channel encoding. The channel encoding is used to encode the transmitted information bits by adding redundant bits, so that at the receiver side bit errors (resulting due to channel noise) can be corrected by decoding the received bits. There exist numerous channel encoding techniques, out of which turbo, viterbi and Low-Density Parity Check (LDPC) code are quite popular in digital wireless communication. These encoding techniques perform better when using soft-decision bits for decoding as compared to hard-decision bits. In order to provide soft-decision bits to the channel decoder, the receiver signal needs to be processed during demodulation.
[0003] A patent document CN113965438B titled “Method for solving soft information in 16APSK high-order modulation mode” describes a solving of soft information for 16APSK modulation. In the described method, a 16APSK constellation diagram is divided into 16 different areas uniformly according to the position characteristics of a received signal in a constellation diagram and then carrying out the mean value estimation according to the 16APSK signal. Demodulation is done using a threshold value of an inner circle and an outer circle in the 16APSK constellation diagram.
[0004] Another patent document US 8718205 B1 titled “Hard and soft bit demapping QAM non-square constellations” discloses the demapping of QAM signal with grey coded and non-square constellation. The patent document relates to a method for demapping of non-square, gray coded 64-QAM by using a general partitioning approach. In the method, equalized symbols are first converted into preliminary soft-bits or hard-bits via the application of bit decision rules. According to the bit decision rules, a constellation diagram is divided into defined regions where the each bit in the 64-QAM modulating sequence (6 bits) is either 1 or 0 in the particular region. These preliminary soft-bits are multiplied with a factor (factor depends on signal to noise ratio of received signal) to get the final soft-bits.
[0005] Another patent document EP3039788A1 titled “Soft decision decoding method and system thereof” describes a method of soft decision decoding by receiving information bits through a communication network. In the disclosed method, a signal frame carrying a message is received through the communication network and a bit information of data structure is obtained. By using the frame structure information soft decoding is carryout. This patent document is related to soft decision decoding and not for soft bits generation.
[0006] Further, a patent document US 2011/0222618A1 titled “Method and apparatus for efficient soft modulation for gray mapped QAM symbols” provides a method to generate soft value of gray mapped QAM signal. A real part and an imaginary part of received symbol is processed separately and a lookup table is used to generate a soft value. Pre-computed bits are stored in the lookup table which is used to generate complex soft symbol value. Soft demodulation process is performed separately for the real and imaginary parts of each symbol of interest (gray mapped) to decompose each of the real and imaginary parts into binary soft modulations for each bit, and then using a computationally-efficient lookup table to calculate the binary soft modulation.
[0007] Furthermore, the patent document US 7761777B2 (20-07-2010) titled “Soft decision demapping method suitable for higher-order modulation for iterative decoder and error correction apparatus using the same” describes a soft decision demapping method. The method includes generating a soft decision using distances between the received symbol and constellation point coordination. Further the difference between the maximum value of distance values when particular bit is 0 and maximum value among distance values when particular bit is 1, calculated for soft decision demapping for particular bit. For example difference between a maximum value of distance values when a first bit is 0 and a maximum value of distance values when the first bit is 1 during a soft decision of the first bit of N-bit received signal symbol.
[0008] However, the aforementioned patent documents do not disclose any general solution to generate soft decision bits for all APSK modulations which improve error-correcting capabilities of the channel decoder of the wireless communication system.
[0009] Therefore, there is a need in the art to provide a system and method for generating soft-decision demodulated bits from M-amplitude and phase-shifting keying (APSK) modulations to enhance error correcting capabilities of the channel decoder.

OBJECTS OF THE PRESENT DISCLOSURE
[0010] An object of the present disclosure relates to wireless communication systems, in general, a system and method for estimating soft-decision demodulated bits for M- amplitude and phase-shifting keying (APSK) modulations.
[0011] Another object of the present disclosure is to provide an improved and effective system and method for estimating soft-decision demodulated bits for M-order APSK modulations for enhancing error correcting capabilities of the channel decoder.
[0012] Yet another object of the present disclosure is to provide a less complex method which utilises simple operators instead of exponential and log functions, thereby allowing easy implementation on hardware without over burdening processing hardware.

SUMMARY
[0013] The present disclosure relates, in general, to wireless communication systems and more specifically, relates to a system and method for generating soft-decision demodulated bits from M-amplitude and phase-shifting keying (APSK) modulations.
[0014] An aspect of the present disclosure pertains to a system for generation of soft-decision demodulated bits for M-Amplitude and Phase-Shifting keying (APSK) modulations. The system comprises a receiver synchronization device that receives a plurality of In-phase (I) and Quadrature phase (Q) data from an analog-to-digital converter (ADC) and applies receiver synchronization to correct timing offset, carrier or frequency offset, and channel distortion in the received I, Q data. The system comprises a soft decision demodulation unit to process the synchronized I, Q data for soft decision demodulation to estimate the strength of a received symbol for high-order APSK modulation. Further, the soft decision demodulation unit is configured to convert, by an absolute value calculation unit, the synchronized I, Q data of the received symbol into absolute values. Furthermore, the soft decision demodulation unit is configured to calculate, by a distance measurement unit, distance between the absolute values of the I, Q data and stored I, Q data of constellation point in positive quadrant. Moreover, the soft decision demodulation unit is configured to determine, by a comparator, minimum distance among the calculated distance to identify most probable symbol. Also, the soft decision demodulation unit is configured to estimate, by a strength calculation unit, soft strength values of the received symbol using concentric boundaries drawn around the probable constellation points and the calculated minimum distance, where the soft strength value indicates proximity of the received symbol from the most probable symbol. The soft decision demodulation unit is further configured to demap, by a demapping unit, the received symbol to generate hard decision bits and append, by a soft decision value unit, the estimated soft strength value to the each demapped hard decision bits to form demodulated soft decision bits.
[0015] In an aspect, the soft decision unit may pass the demodulated soft decision bits to a channel decoder for bit error correction.
[0016] In an aspect, the absolute value calculation unit may be configured to deduce the absolute value of the I, Q data based on monitoring of most significant bits (MBS).
[0017] In an aspect, the absolute value calculation unit may include a monitoring unit configured to observe the MSB of received I and Q data, where if the MSB value is '0', the received values of the I and Q data are transmitted to the distance measurement unit without any alteration and if the MSB value is '1', the received values of the I and Q data are flipped, and one is added before transmitting to the distance measurement unit.
[0018] In an aspect, the most probable symbol may be determined by calculating the distance measured between the absolute values of the received I, Q data and stored I, Q data of the constellation points in positive quadrant including positive axes.
[0019] In an aspect, the distance measurement unit may calculate the distance by difference between I component of the received symbol and I component of the constellation point is added with difference between Q component of the received symbol and Q component of the constellation point to obtain distance value.
[0020] In an aspect, the soft strength value may be assigned strongest if the absolute value of the received symbol is located within inner most boundary and the soft strength value assigned weakest if the absolute value of the received symbol is located outside an outermost boundary.
[0021] In an aspect, a number of concentric boundaries and a number of different levels of strength may depend on number of binary bits to represent the soft strength value, wherein the number of concentric boundaries may depend on the number of binary bits assigned.
[0022] In an aspect, the concentric boundaries around the most probable symbol may be determined by a largest concentric circle radius (RL), where the largest concentric circle radius (RL) is equal to half of difference between two consecutive constellation circle’s radius in which the most probable symbol falls. The concentric boundaries may be placed between largest concentric circle and the most probable symbol by dividing radius in such a fashion that width of the concentric boundaries segment formed is monotonically increasing from farthest to closest.
[0023] In another aspect, the present disclosure relates to a method for generation of soft-decision demodulated bits for M- Amplitude and Phase-Shifting keying (APSK) modulations. The method includes receiving a plurality of In-phase (I) and Quadrature phase (Q) data from an analog-to-digital converter (ADC) device and applying receiver synchronization, via a receiver synchronization device, to correct timing offset, carrier or frequency offset, and channel distortion in the received I, Q data. The method includes processing, by a soft decision demodulation unit, the synchronized I, Q data for soft decision demodulation to estimate strength of a received symbol for high-order modulation. The method includes converting, by an absolute value calculation unit, the synchronized I, Q data of the received symbol into absolute values. The method also include calculating, by a distance measurement unit, distance between the absolute values of the I, Q data and stored I, Q data of constellation point in positive quadrant. The method further includes determining, by a comparator, minimum distance among the calculated distance to identify most probable symbol. Further, the method includes estimating, by a strength calculation unit, soft strength values of the received symbol using concentric boundaries drawn around the probable constellation points and the calculated minimum distance, wherein the soft strength value indicates proximity of the received symbol from the most probable symbol. Furthermore, the method includes demapping, by a demapping unit, the received symbol to generate hard decision bits. Moreover, the method includes appending, by a soft decision value unit, the estimated soft strength value to the each demapped hard decision bits to form demodulated soft decision bits.
[0024] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0026] FIG. 1 illustrates a schematic block diagram of a digital wireless communication system, in accordance with an embodiment of the present disclosure.
[0027] FIG. 2 illustrates an exemplary system for for generating soft-decision demodulated bits for M order APSK modulations, in accordance with an embodiment of the present disclosure.
[0028] FIG. 3 illustrates an exemplary 32APSK constellation diagram and concentric boundary diagram for a particular constellation point, in accordance with an embodiment of the present disclosure.
[0029] FIG. 4 illustrates an exemplary 16APSK constellation diagram and concentric boundaries diagram for a particular constellation point, in accordance with an embodiment of the present disclosure.
[0030] FIG. 5 illustrates an exemplary 8PSK constellation diagram and concentric boundaries diagram for a particular constellation point, in accordance with an embodiment of the present disclosure.
[0031] FIG. 6 illustrates a diagram for concentric boundaries in accordance with the present embodiment of invention, in accordance with an embodiment of the present disclosure.
[0032] FIG. 7 illustrates a flowchart of the method for generating soft decision demodulated bits for high-order APSK modulation, in accordance with an embodiment of the present disclosure.
[0033] FIG. 8 illustrates a block diagram of method for generating soft-decision demodulated bits for M high-order APSK modulations, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION
[0034] 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. If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0035] 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.
[0036] The present disclosure relates, in general, to wireless communication systems and more specifically, relates to a system and method for generating soft-decision demodulated bits from M-amplitude and phase-shifting keying (APSK) modulations.
[0037] The present disclosure relates to a soft-decision estimation using concentric circular boundaries around a most probable constellation point. Based on the concentric circular boundaries, the soft strength values of received signals is are estimated which leads to the formation of the soft- decision by using demapped hard bits as most significant bit (MBS). Further, the disclosed method is effective and less-complex as compared to the existing devices. The proposed method utilises register, comparator, addition/ subtraction operators instead of exponential and log functions, thereby allowing easy implementation on hardware without over burdening processing hardware. Additionally, the proposed device requires a logic device and memories for storing data.
[0038] The present disclosure elaborates upon a digital wireless communication system. The digital wireless communication system having a transmission side and a receiver side. The transmission side includes a channel encoding unit and a high-order modulation unit. The receiver side includes a receiver synchronization device, a soft demodulation unit and a channel decoding unit. The channel encoding unit encodes information bits by adding redundant bits. Even though adding the redundant bits can increase overheads but helps in correcting bit errors at the receiver unit caused due to a wireless channel. To increase the effectiveness of the channel decoder, soft decision bits are utilized. The present disclosure addressing the problem of soft decision bits estimation for high order modulations (APSK) without using complex logarithmic and exponential functions.
The present disclosure can be described in enabling detail in the following examples, which may represent more than one embodiment of the present disclosure.
[0039] FIG. 1 illustrates a schematic block diagram of a digital wireless communication system, in accordance with an embodiment of the present disclosure.
[0040] Referring to FIG 1, a schematic block diagram of a wireless communication system is shown in accordance with an embodiment of the present invention. The wireless communication system 100 having a transmission side and a receiver side communicable connected to the transmission side through a wireless channel 108. The transmission side includes a channel encoding unit 104 and a high-order modulation unit 106. The receiver side includes a receiver synchronization device 110, a soft decision demodulation unit 112 and a channel decoding unit 114. The channel encoding unit 104 is configured to encode information bits by adding redundant bits. The high-order modulation unit 106 is configured to modulate the encoded information bits. The receiver side receives a plurality of In-Phase (I) data and a plurality of Quadrature-Phase (Q) data from an Analog-to-Digital Convertor (ADC) device 102. The received plurality of In-Phase (I) data and the plurality of Quadrature-Phase (Q) data are transmitted to the receiver synchronization device 110 to correct timing offset, carrier or frequency offset and distortion due to channel. The synchronized plurality of In-Phase (I) data and the plurality of Quadrature-Phase (Q) data are de-mapped by the soft decision demodulation unit 112.
[0041] The present disclosure relates to a method of soft decision demodulation which is suitable for high-order APSK signals in digital wireless communication. Soft decision demodulation is helpful in enhancing error correcting capability of the channel decoding unit 114. In the proposed method, soft decision is estimated with the help of concentric circular boundaries around the most probable symbol (Sp) in positive quadrant. The most probable symbol is estimated by calculating shortest distance between the absolute values of received data i.e., synchronized and channel distortion corrected data and all constellation point in positive quadrant. Demodulated soft bits are generated by using the concentric boundaries on input data with the help of a comparator 206. The method can be implemented in logic device which consist of flip-flop, counter, comparator, adder/subtraction, registers and memories.
[0042] The present disclosure relates to a method and a system 200 for estimation of soft-decision bits while demodulating the higher-order APSK modulation in order to improve the error correcting capability of channel decoders. In particular, the patent describes an effective and implementable method (in FPGA based hardware) of estimation of soft decision bits based on the circular threshold boundaries around the closest symbol in the positive I, Q coordinate system (In-phase and Quadrature phase). These threshold boundaries are estimated around the intended symbol by dividing the space in non-uniform concentric circles. Received I, Q samples are compared with the threshold boundaries to estimate the strength of the received symbol. Strength being considered stronger if received symbol is nearer to the intended symbol and weaker if it is farther.
[0043] Referring now to FIG. 2, a schematic diagram of a system 200 for generating soft-decision demodulated bits for M- Amplitude and Phase-Shifting keying (APSK) modulations is shown, in accordance with an embodiment of the present disclosure.
[0044] The system 200 includes a receiver synchronization device 110 that receives a plurality of In-phase (I) and Quadrature phase (Q) data from the analog-to-digital converter (ADC) device 102 and applies receiver synchronization to correct timing offset, carrier or frequency offset, and channel distortion in the received I, Q data.
[0045] The system 200 includes a soft decision demodulation unit 112 configured to process the synchronized I, Q data for soft decision demodulation to estimate strength of a received symbol for high-order modulation. The soft decision demodulation unit 112 includes an absolute value calculation unit 202, a distance measurement unit 204, a comparator 206, a strength calculation unit 208, a soft decision value unit 210 and a demapping unit 212. The synchronized plurality of In-Phase (I) component data and the plurality of Quadrature-Phase (Q) data are transmitted from the receiver synchronization device 110 to the absolute value calculation unit 202 to convert the received the synchronized I, Q data of the received symbol into absolute values. The absolute value calculation unit 202 may include a monitoring unit to monitor a most significant bits (MBS) of received data. In case, the MBS is ‘0’, then without changing the input sample is assigned to output sample and in case, the MBS is ‘1’ then all bits of input sample are flipped and one is added before assigning it to the output sample. The soft decision demodulation unit 112 is configured with the distance measurement unit 204 to calculate a distance between the absolute value of the plurality of In-Phase (I) data and the plurality of Quadrature-Phase (Q) data, and stored plurality of In-Phase (I) and Quadrature-Phase (Q) data of positive quadrant constellation point in positive quadrant.
[0046] Further, to determine the distance, the difference between the plurality of In-Phase (I) data of input samples and the In-Phase (I) of constellation point is added with a difference between the plurality of Quadrature-Phase (Q) data of input samples and the Quadrature-Phase (Q) of constellation point. The positive quadrant is the quadrant between positive in-phase (I) axis and positive quadrature (Q) axis. Number of distance measure is equal to the number of constellation point in positive quadrant including positive axes. These distances (d1, d2 …dn, where n is the number of constellation point in positive quadrant) are passed to the comparator 206 for finding minimum value (dsh) among the calculated distances. The comparator operator is used in multiple stages. The number of stages depend on the number of calculated distances (d1, d2…dn). Concentric circular boundaries are generated around the probable constellation point based on type of modulation and space between consecutive constellation circles by a concentric boundaries unit 214. Based on the concentric circular boundaries and the minimum value (dsh) among the calculated distances, soft strength values are calculated by the strength calculation unit 208. The soft strength values indicate closeness of the received signal from most probable symbol. The most probable symbol is the symbol in positive quadrant which is nearest to the received signal among symbols in the positive quadrant. Hard decision bits are generated by demodulation and demapping the received symbol. The received signal is passed to the demapping unit 212 for demapping the received symbol and generating the hard decision bits. An actual symbol can be using the information calculated for positive quadrant. This reduces complexity nearly one fourth. The most probable symbol is estimated in positive quadrant by determining minimum distance by the comparator 206. Sign information of the received plurality of in-phase signal and plurality of quadrature signal give the indication of quadrant, which in turn helps in selecting the actual symbol (Sa). The actual symbol (Sa) provides the hard bits by demapping using a look-up table (LUT). The soft decision demodulation unit 112 is configured with the soft decision value unit 210 to append the estimated soft strength value to the demapped hard decision bits to form demodulated soft decision bits. The soft decision value is further transmitted to the channel decoder unit 114 for correcting errors more efficiently.
[0047] FIG. 3 illustrates an exemplary 32APSK constellation diagram and concentric boundary diagram 300 for a particular constellation point, in accordance with an embodiment of the present disclosure.
[0048] As shown in FIG. 3, s1, s2, s3, s4, s5, s17, s18, s19 and s29 are positive quadrant points. A largest concentric circle radius (RL) is half of distance between two consecutive constellation circles. For symbols s1, s2, s3, s4 and s5, the largest concentric circle radius (RL1) is half of difference between r3 and r2. For symbols s17, s18 and s19, the largest concentric circle radius (RL2) is minima of (r3-r2)/2 and (r2-r1)/2. For symbol s29 largest concentric circle radius (RL3) is minima of (r2-r1)/2 and r1. Different RL can be stored for different constellation circle points. Further, all RL can be stored same as minima of ((r3-r2)/2, (r2-r1)/2, r1). The RL is used to decide the concentric boundaries around the most probable point. In FIG. 3, s18 is selected as the most probable point (Sp) to show the pictorial diagram of the concentric boundaries around the most probable point.
[0049] FIG. 4 illustrates an exemplary 16APSK modulation constellation diagram and concentric boundaries diagram 400 for a particular constellation point, in accordance with an embodiment of the present disclosure.
[0050] Referring to FIG. 4, in the 16APSK modulation constellation, the constellation points are places in two circles. Symbols s1, s2, s3 and s13 are in positive quadrant. Here, s13 is assumed as the most probable point (Sp). The largest concentric boundary radius (RL) is minima (r1, (r2-r1)/2). The actual symbol (Sa) can be any symbol selected from any one of s16, s15, s14 and s13.
[0051] FIG. 5 illustrates an exemplary 8PSK constellation diagram and concentric boundaries diagram 500 for a particular constellation point, in accordance with an embodiment of the present disclosure.
[0052] Referring to FIG. 5, symbols s1, s2 and s13 are in positive quadrant. The most probable point (Sp) is assumed to be s1, which is on an axis. In case, when the most probable point (Sp) is on the axis, then a positive side of the concentric boundaries are considered due to utilization of the absolute value of the received sample which lie in the positive quadrant only. For the 8PSK, RL can be taken as half of the distance between two neighboring constellation points. However, there is exception in case, when the most probable point lie on the axis, then the most probable point can be demapped to two possible points i.e. s1 or s5 and cannot be s3 and s7.
[0053] Thus, the proposed method is effective for all APSK modulations (even for 64, 128 and 256 APSK) and any kind of symbol bit mapping (i.e. with or without gray mapping).
[0054] FIG. 6 illustrates a diagram for concentric boundaries 600 in accordance with an embodiment of the present disclosure. The concentric circular boundaries 600 around the most probable (Sp) is shown in FIG. 6. The number of concentric boundaries depend on a number of binary bits (K) assign to represent a strength value (Sth). K bits can represent 2k values, then the number of concentric boundary are 2k-1. In an exemplary embodiment, three bits are assumed for representation of the strength value (K=3). Hence, the number of concentric boundaries required are 23-1 i.e. 7. Here, Sth= ‘111’ represents strongest or nearest point to the most probable symbol Sp. When Sth= ‘000’ represents weakest or farthest to the most probable symbol Sp. In an exemplary embodiment, the seven concentric boundaries can be placed by dividing distance between RL and Sp uniformly or non-uniformly. It is observed that non-uniform division gives better result, where the division near the Sp assigned more space and gradually space decreases between the consecutive circles toward outer most circles.
[0055] As shown in FIG. 6, the radius of the concentric boundaries 600 are shown as L1, L2….L7. One of the probable example for non-uniform division of space for 7 level is (d, 2*d, 3*d, 4*d, 5*d, 6*d, 7*d and 8*d) as arithmetic propagation such that (RL = d+2*d+3*d+4*d+5*d+6*d+7*d+8*d) therefore d=RL/36 and L1=8*d, L2=15*d, L3=21*d, L4=26*d, L5=30*d, L6=33*d, L7=35*d. The estimated shortest distance ‘dsh’ by the comparator 206 is compared with the levels (L1, L2….L7) to assign the strength value using a look up table (LUT). If dsh is shorter than L1, then the strength Sth value assigned to strongest i.e. ‘111’ and if dsh is greater than L7, then the strength value Sth is assigned as weakest i.e. ‘000’ accordingly all different level or bits are assigned to Sth depending on dsh position. Further, if dsh lies between L3 and L4, the dsh is greater than L3 but lesser than L4, then ‘100’ is assigned to Sth. The strength Sth bits are appended behind each bit of demapped hard bits to form demapped soft decision bits for the channel decoder.
[0056] FIG. 7 illustrates a flowchart of the method 700 for generating soft decision demodulated bits for high-order APSK modulation, in accordance with an embodiment of the present disclosure.
[0057] Referring to FIG. 7, a plurality of In-Phase (I) data and a plurality of Quadrature-Phase (Q) data received from an Analog-to-Digital Convertor (ADC) device 102 are pre-processed before giving the soft decision demodulation.
[0058] At step 702, the received (I, Q) data are synchronized and equalized to remove frequency offset, timing offset and channel distortions.
[0059] At step 704, absolute values of the plurality of In-Phase (I) data and the plurality of Quadrature-Phase (Q) data of samples calculated. The purpose of calculating absolute values is to bring received symbol in positive quadrant.
[0060] At step 706, distance from each constellation point of positive quadrant is calculated 706. The distance is calculated by adding the plurality of In-Phase (I) and the plurality of Quadrature-Phase (Q) of difference as it is complex value i.e. d1=abs(IR-IC) + abs(QR-QC) where d1 is the distance between received symbol and one of the constellation point in positive quadrant, IR and QR are the In-phase and Quadrature-phase component of received symbol mapped in positive quadrant, IC and QC are the In-phase and Quadrature-phase component of one of the constellation point of positive quadrant. Likewise all the distances d1, d2….dn are calculated where ‘n’ is the number of constellation point present in positive quadrant. For 8PSK n=3, 16APSK n=4, 32APSK n=9, 64APSK n=16 and 128APSK n=32 etc.
[0061] At step 708, a minimum distance among ‘n’ distances are calculated using the comparator 206. The minimum distance is stored as ‘dsh’ and minimum distance corresponding constellation point is named as ‘Sp’. For generation of soft-decision bits strength of received signal and hard-decision bits are required.
[0062] At step 710, hard-decision bits are the de-mapped bits of symbol ‘Sa’ where ‘Sa’ is the symbol estimated as actual transmitted symbol. The quadrant of received symbol (QRS) is found by the plurality of In-Phase (I) and the plurality of Quadrature-Phase (Q) component sign information. By changing sign of I and Q component as QRS quadrant of Sp symbol (no change in amplitude) Sa is obtained. For example in figure 3 if ‘s2’ is ‘Sp’ and QRS is QII then s16 will be Sa.
[0063] At step 712, concentric boundaries are calculated and stored. Number of concentric boundaries depends on the number of bits used to represent strength value Sth. These concentric boundary radiuses are pre-calculated in accordance with modulation type and stored in memory or registers.
[0064] At step 714, a shortest distance dsh is compared with the stored concentric boundaries radius to get strength value Sth using look-up table (LUT).
[0065] At step 716, the Sth is appended behind each demodulated hard bits to get soft-decision demapped bits.
[0066] FIG. 8 illustrates a block diagram of method 800 for generating soft-decision demodulated bits for M order APSK modulations, in accordance with an embodiment of the present disclosure.
[0067] At block 802, the method 800 may include receiving a plurality of In-phase (I) and Quadrature phase (Q) data from an analog-to-digital converter (ADC) device 102 and applying receiver synchronization to correct timing offset, carrier or frequency offset, and channel distortion in the received I, Q data.
[0068] At block 804, the method 800 may include processing the synchronized I, Q data for soft decision demodulation to estimate strength of a received symbol for high-order modulation.
[0069] At block 806, the method 800 may include converting the synchronized I, Q data of the received symbol into absolute values.
[0070] At block 808, the method 800 may include calculating distance between the absolute values of the I, Q data and stored I, Q data of constellation point in positive quadrant.
[0071] At block 810, the method 800 may include determining minimum distance among the calculated distance to identify most probable symbol.
[0072] At block 812, the method 800 may include estimating soft strength values of the received symbol using concentric boundaries drawn around the constellation points and the calculated minimum distance, wherein the soft strength value indicates proximity of the received symbol from the most probable symbol.
[0073] At block 814, the method 800 may include demapping the received symbol to generate hard decision bits.
[0074] At block 816, the method 800 may include appending the estimated soft strength value to the demapped hard decision bits to form demodulated soft decision bits.
[0075] In an embodiment, the method may include correcting bit error by passes the demodulated soft decision bits to the channel decoder 114.
[0076] In an embodiment, the soft strength value is assigned strongest if the absolute value of the received symbol is located within inner most boundary and the soft strength value assigned weakest if the absolute value of the received symbol is located outside an outermost boundary.
[0077] In an embodiment, a number of concentric boundaries and a number of different levels of strength depends on a number of binary bits to represent the soft strength value, wherein the number of concentric boundaries depends on the number of binary bits assigned.
[0078] In an embodiment, the concentric boundaries around the most probable symbol is determined by a largest concentric circle radius (RL), wherein the largest concentric circle radius (RL) is equal to half of distance between two consecutive constellation circles in which the most probable symbol falls, and wherein the concentric boundaries are placed between largest concentric circle and the most probable symbol by dividing radius in such a fashion that width of the concentric boundaries segment formed is monotonically increasing from farthest to closest.
[0079] It will be apparent to those skilled in the art that the system of the disclosure may be provided using some or all of the mentioned features and components without departing from the scope of the present disclosure. While various embodiments of the present disclosure have been illustrated and described herein, it will be clear that the disclosure is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the scope of the disclosure, as described in the claims.

ADVANTAGES OF THE PRESENT DISCLOSURE
[0080] The present disclosure provides a system for estimating soft-decision demodulated bits for M order APSK modulations.
[0081] The present disclosure provides an improved and effective system to estimate soft-decision demodulated bits for higher-order APSK modulations to enhance error correcting capabilities of the channel decoder.
[0082] The present disclosure provides a less complex method which utilises simple operators instead of exponential and log functions, thereby allowing easy implementation on hardware without over burdening processing hardware.
, Claims:1. A system (200) for generation of soft-decision demodulated bits for M-Amplitude and Phase-Shifting keying (APSK) modulations, the system comprising:
a receiver synchronization device (110) that receives a plurality of In-phase (I) and Quadrature phase (Q) data from an analog-to-digital converter (ADC) device (102) and applies receiver synchronization to correct timing offset, carrier or frequency offset, and channel distortion in the received I, Q data; and
a soft decision demodulation unit (112) process the synchronized I, Q data for soft decision demodulation to estimate strength of a received symbol for high-order M-APSK modulation, the soft decision demodulation unit (112) is configured to:
convert, by an absolute value calculation unit (202), the synchronized I, Q data of the received symbol into absolute values;
calculate, by a distance measurement unit (204), distance between the absolute values of the I, Q data and stored I, Q data of constellation point in positive quadrant;
determine, by a comparator (206), minimum distance among the calculated distance to identify a most probable symbol;
estimate, by a strength calculation unit (208), soft strength values of the received symbol estimated using concentric boundaries drawn around the probable constellation point and the calculated minimum distance, wherein the soft strength value indicates proximity of the received symbol from the most probable symbol;
demap, by a demapping unit (212), the received symbol to generate hard decision bits; and
append, by a soft decision value unit (210), the estimated soft strength value to the each demapped hard decision bits to form demodulated soft decision bits.
2. The system (200) as claimed in claim 1, wherein the soft decision value unit (210) passes the demodulated soft decision bits to a channel decoder (114) for bit error correction.
3. The system (200) as claimed in claim 1, wherein the absolute value calculation unit (202) configured to deduce the absolute value of the I and Q data based on monitoring of most significant bits (MBS).
4. The system (200) as claimed in claim 3, wherein the absolute value calculation unit (202) comprises a monitoring unit configured to observe the MSB of received I and Q data, wherein if the MSB value is '0', the received values of the I and Q data are transmitted to the distance measurement unit (204) without any alteration and if the MSB value is '1', the received values of the I and Q data are flipped, and one is added before transmitting to the distance measurement unit (204).
5. The system (200) as claimed in claim 1, wherein the most probable symbol is determined by calculating the distance measured between the absolute values of the received I, Q data and stored I, Q data of the constellation points in positive quadrant including positive axes.
6. The system (200) as claimed in claim 1, wherein the distance measurement unit (204) calculate the distance by difference between I component of the received symbol and I component of the constellation point is added with difference between Q component of the received symbol and Q component of the constellation point to obtain distance value.
7. The system (200) as claimed in claim 1, wherein the soft strength value is assigned strongest if the absolute value of the received symbol is located within innermost boundary and the soft strength value is assigned weakest if the absolute value of the received symbol is located outside an outermost boundary.
8. The system (200) as claimed in claim 1, wherein a number of concentric boundaries and a number of different levels of strength depends on a number of binary bits to represent the soft strength value, wherein the number of concentric boundaries depends on the number of binary bits assigned.
9. The system (200) as claimed in claim 1, wherein the concentric boundaries around the most probable symbol are determined by a largest concentric circle radius (RL), wherein the largest concentric circle radius (RL) is equal to half of difference between two consecutive constellation circle’s radius in which the most probable symbol falls, and wherein the concentric boundaries are placed between largest concentric circle and the most probable symbol by dividing radius in such a fashion that width of the concentric boundaries segment formed is monotonically increasing from farthest to closest.
10. A method (800) for generation of soft-decision demodulated bits for M- Amplitude and Phase-Shifting keying (APSK) modulations, the method (800) comprising:
receiving (802) a plurality of In-phase (I) and Quadrature phase (Q) data from an analog-to-digital converter (ADC) device (102) and applying receiver synchronization, via a receiver synchronization device (110), to correct timing offset, carrier or frequency offset, and channel distortion in the received I, Q data;
processing (804), by a soft decision demodulation unit (112), the synchronized I, Q data for soft decision demodulation to estimate strength of a received symbol for high-order modulation;
converting (806), by an absolute value calculation unit (202), the synchronized I, Q data of the received symbol into absolute values;
calculating (808), by a distance measurement unit (204), distance between the absolute values of the I, Q data and stored I, Q data of constellation point in positive quadrant;
determining (810), by a comparator (206), minimum distance among the calculated distance to identify most probable symbol;
estimating (812), by a strength calculation unit (208), soft strength values of the received symbol estimated using concentric boundaries (214) drawn around the probable constellation point and the calculated minimum distance, wherein the soft strength value indicates proximity of the received symbol from the most probable symbol;
demapping (814), by a demapping unit (212), the received symbol to generate hard decision bits; and
appending (816), by a soft decision value unit (210), the estimated soft strength value to the each demapped hard decision bits to form demodulated soft decision bits.