Title of Invention  A SOFT DECISION METHOD AND APPARATUS FOR DEMODULATING A RECEIVED SIGNAL 

Abstract  The present invention relates to a demodulation method using soft decision for QAM (Quadrature Amplitude Modulation). In a soft decision method for demodulation of a received signal of square QAM comprised of the same phase signal component and a orthogonal phase signal component, the demodulation method using soft decision has a characteristic wherein the processing speed is improved, and the manufacturing expense is reduced by gaining a condition probability vector value, which is each soft decision value, corresponding to a beat position of hard decision using a function which includes a condition judgement operation from a orthogonal phase component value of a received signal and the same phase component value. 
Full Text  A DEMODULATION METHOD USING SOFT DECISION FOR QUADRATURE AMPLITUDE MODULATION AND APPARATUS THEREOF Technical Field The present invention relates to a soft decision demodulation of an Quadrature Amplitude Modulation (hereinafter, referred to as QAM) signal, and more particularly, to a soft decision demodulation method capable of enhancing a process speed of soft decision using predetermined function and pattern upon demodulating a received signal. Background Art QAM scheme is capable of transmitting loading two or more bits to a given waveform symbol, whose waveform can be mathematically expressed in two real numbers and imaginary numbers that do not interfere each other. That is, in a complex number imaginary number a + {3 i, a change of value a does not affect a value 3 . Due to that reason, an quadrature signal component can correspond to a , and inphase signal component can correspond to J3 . Generally, the quadrature signal component is referred to as Qchannel, and the inphase component signal is referred to as Ichannel. A constellation diagram of QAM is to connect amplitudes of such two waves with each other so as to make a number of combinations, position the combinations on a complex number plane to have an equal conditional probability, and promise such a position. Fig. 2 is a diagram showing an example of such constellation diagram, whose size is 16 combinations. Also, each of points shown in Fig. 2 is referred to as a constellation point. Also, combinations of binary numbers written under each constellation diagram is symbols set to each point, that is, a bundle of bits. Generally, a QAM demodulator serves to convert signals incoming to an I channel and Q channel, that is, a received signal given as a + {3 i into the original bit bundle according to the promised position mentioned above, that is, the combination constellation diagram. At this time, however, the received signals are not positioned on places assigned previously in most cases due to the effect of noise interference, and accordingly the demodulator has to restore the signals converted due to the noise to the original signals. However, since there is often some excessivenesses to guarantee a reliability of communication in that the demodulator takes a charge of the role of noise cancellation, it is possible to embody more effective and reliable communication system by rendering the role to the next step of a channel decoder. However, since there is an information loss in a bit quantization process performed by a binary bit detector as in a hard decision by making a demodulation signal having a continuous value to correspond to discrete signals of 2 levels in order to perform such a process, a similarity measure with respect to a distance between a received signal and the promised constellation point is changed from a Hamming distance to an Euclidean distance without using the binary bit detector, so that an additional gain can be obtained. As shown in Fig. 1, in order to modulate and transmit a signal encoded by a channel encoder and demodulate the signal in a channel demodulator through a hard decision coding process, the demodulator has to have a scheme for generating the hard decision values corresponding to each of the output bits of a channel encoder from a receiving signal consisted of an inphase signal component and a quadrature phase signal component. Such scheme generally includes two procedures, that is, a simple metric procedure proposed by Nokia company and a dual minimum metric procedure proposed by Motorola, both procedures calculating LLR (Log Likelihood Radio) with respect to each of the output bits and using it as an input soft decision value of the channel demodulator. The simple metric procedure is an event algorithm that transforms a complicated LLR calculation equation to a simple form of approximation equation, which has a degradation of performance due to an LLR distortion caused by using the approximation equation even though it makes the LLR calculation simple. On the other hand, the dual minimum metric procedure is an event algorithm that uses the LLR calculated using more precise approximation equation as an input of the channel demodulator, which has a merit of considerably improving the degradation of performance caused in the case of using the simple metric procedure, but it has an expected problem that more calculations are needed compared with the simple metric procedure and an its complication is considerably increased upon embodying hard ware. Disclosure of the Invention Therefore, an object of the present invention is to solve the problems involved in the prior art, and to provide a soft decision scheme for demodulating a Quadrature Amplitude Modulation (QAM) receiving signal consisted of an inphase signal component and an quadrature phase signal component, where a conditional probability vector value being each of a soft decision value corresponding to a bit position of a hard decision can be obtained using a function including a conditional determination calculation from an quadrature phase component value and an inphase component value of the received signal, and so it is expected that process rate can be improved and a real manufacturing cost of hard ware can be reduced. In order to perform such a procedure, first, a known form of a combinational constellation diagram of QAM and its characteristic demodulation scheme will be described as follows. The combinational constellation diagram of QAM may be generally divided into 3 forms according to an arrangement of bit bundle set in the constellation point. The First of it is a form constellated as shown in Figs. 2 to 4, the second is a form constellated as shown in Figs. 5 to 7, and the third is a form not included in this application. A characteristic of the form shown in Fig. 2 can be summarized as follows. In the case that the magnitude of the QAM is 2 n, the number of bits set in each point becomes 2n, where conditional probability vector values corresponding to the first half of the number, that is, the first to nth bits are demodulated by one of the received signals a and p and the conditional probability vector values corresponding to the second half of the number, that is, the (n+l)th to the 2nth bits are demodulated by the remaining one receiving signal. Also, an equation that is applied to both demodulations has the same procedure in the first half and second half demodulations. That is, when the value of receiving signal corresponding to the second half is substituted in the first half demodulation method, the result of the second half can be obtained. (Hereinafter, such form is referred to as 'the first form') The characteristic of the form shown in Fig. 5 can be summarized as follows. In the case that the magnitude of the QAM is 2 , the number of the bits set in each of the points becomes 2n, and the demodulation method of the conditional probability vector corresponding to oddordered bit is the same as the calculation method of the conditional probability vector corresponding to the next evenordered bit. However, the receiving signal value used to calculate the conditional probability vector corresponding to the oddordered bit uses one of a and 3 according to a given combination constellation diagram and the receiving signal value for the evenordered bit is used for the remaining one. In other word, in the cases of the first and second conditional probability vector calculations, they use the same demodulation method but the values of the receiving signals are different. (Hereinafter, such form is referred to as 'the second form'). Brief Description of the Drawings The above objects, other features and advantages of the present invention will become more apparent by describing the preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1 is a block diagram for explaining a general digital communication system; Fig. 2 is a view showing a combination constellation point for explaining a soft decision demodulation method in accordance with a first embodiment of the present invention; Figs. 3 and 4 are views for explaining a bit constellation in the combination constellation diagram shown in Fig. 2; Fig. 5 is a view showing a combination constellation diagram for explaining a soft decision demodulation method in accordance with a second embodiment of the present invention; Figs. 6 and 7 are views for explaining a bit constellation in the combination constellation diagram shown in Fig. 5; Fig. 8 is a view showing a conditional probability vector decision procedure in accordance with the present invention as a functional block; Fig. 9 is an output diagram with respect to each conditional probability vector of a first formofl024QAM; Fig. 10 is an output diagram with respect to each conditional probability vector of a second form of 1024QAM; Fig. 11 is a view showing a function applied to a first probability vector of a third embodiment of the present invention; Fig. 12 is a view showing a function applied to a second probability vector of the third embodiment of the present invention; Fig. 13 is a view showing a function applied to a first probability vector of the fourth embodiment of the present invention; Fig. 14 is a view showing a function applied to a second probability vector of the fourth embodiment of the present invention; and Fig. 15 is a view showing a hard ware configuration for a soft decision of a first form of 64QAM in accordance with the present invention. Best Mode for Carrying Out the Invention Reference will now be made in detail to a preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings. The present invention remarkably improves process speed by applying a conditional probability vector equation instead of a log likelihood ratio method being a soft decision demodulation method of a square QAM signal that is generally used in the industry. A newly developed demodulation method of a square QAM signal is divided into 2 forms, and a first and a third embodiments are used for the first form and a second and a fourth embodiments are used for the second form. Also, an output of the final conditional probability vector value covers an area between a real number "a" and another real number "a". First, explaining several basic prerequisites before entering into the description, the magnitude of the QAM can be characterized by the mathematical expression 1 and accordingly the number of bits set in each point of the constellation diagram can be characterized by the mathematical expression 2. [mathematical expression 1 ] 22n  QAM. n  2, 3, 4 [mathematical expression 21 the number of bits set in each point = 2n Accordingly, the number of the conditional probability vector values being the final output values also becomes 2n. Now, a first one among the method for demodulating the square QAM signals of the present invention will be explained. First, a soft decision method of receiving signal of the square QAM signal corresponding to the first form will be explained. In the case of the first form, although it was mentioned that one of values of the quadrature phase component (real number part or a ) or the inphase signal component (imaginary number part or {3 ) is used to calculate the conditional probability vector corresponding to the first half bit combination when explaining the characteristic of the first form, the first half and the second half demodulate using the value {3 and value a respectively, for the convenience of understanding and an output area according to the demodulation is set as a value between 1 and 1 for the convenience' sake in the following description. Also, k is used as a parameter indicating an order of each bit. A method for calculating a conditional probability vector corresponding to the case that the first bit, that is, k is 1 in the first form can be expressed as a mathematical expression 3, and Fig. 5 is a visualization of it. [mathematical expression 3] In the case of the first conditional probability vector (k =1), output value is determined as 2 However, the value of n is determined by the magnitude of QAM using the mathematical expression 1. A method for calculating the conditional probability vector corresponding to the second bit (k = 2) in the first form can be expressed by a mathematical expression 4, and Fig. 6 is a visualization of it. [mathematical expression 4] In the case of the second conditional probability vector (k = 2), the output value unconditionally determined as 2" Here, n is a magnitude parameter of the QAM in the mathematical expression 1, and c is a constant. A method for calculating a conditional probability vector corresponding to a third bit to nth bit (k =3, 4, •*•■, n1, n) in the first form can be expressed as a mathematical expression 5. Here, as can be seen from Fig. 9, since the conditional probability vector corresponding to the third or later bit indicates a determined iteration (v shape) form, it is noted that an expression be repeatedly used using such property, [mathematical expression 5] First, dividing the output diagram with a basic vshaped form, the conditional probability vector corresponding to each bit is divided into (2k~3 + 1) areas. d , , (2) A basic expression according to the basic form is determined as 2""+ (E) If finding a belonging area as the given {3 and substituting a value of  {3  m that is subtracted a middle value m of each area (for example, since the repeated area is one when k = 4, the area becomes 2n~2 the output value can be determined. ® Finally, in the left and right outer areas among the divided areas, that is, (2k_2 l)2n_k+2 Here, d is a constant that is changed according to a value of k. A method for calculating the conditional probability vector corresponding to the second half bits of the first form, that is, bit number n+1 to 2n can be obtained by substituting the {3 into a in the method for obtaining the conditional probability vector of the first half according to the characteristic of the first form. In other word, the condition that all of {3 in the mathematical expression 3 are substituted with a becomes a calculation expression of the first conditional probability vector of the second half, that is, a conditional probability vector corresponding to (n+1) bit. The conditional probability vector corresponding to the (n + 2) bit of the second conditional probability vector of the second half can be determined by substituting 3 with a in the mathematical expression 4 that is the condition to calculate the second conditional probability vector of the first half, and the conditional probability vector corresponding to the bit number n+3 to 2n being the next case can be determined by transforming the mathematical expression to the above description. Next, a method for performing a soft decision of the receiving signal of a square QAM corresponding to the second form will be explained. For convenience of understanding, demodulation is performed to determine the conditional probability vector corresponding to oddordered bits using the value of a and to determine the conditional probability vector corresponding to evenordered bits using the value of ]3 and accordingly the output scope is determined between 1 and 1 as is in the first form for convenience' sake. In the second form, a method for calculating the conditional probability vector corresponding to the first bit (k=l) can be expressed as a mathematical expression 6 and Fig. 6 is a visualization of it. [mathematical expression 6 J l —j a ® In the case of the first bit (k=l), the output value is determined as 2 However, the value of n is determined by the mathematical expression 1 according to the magnitude of the QAM. In the second form, the conditional probability vector corresponding to the second bit (k=2) can be obtained by substituting the a with {3 in the mathematical expression 6 for calculating the first conditional probability vector according to the characteristic of the second form. In the second form, a method for calculating the conditional probability vector corresponding to the third bit (k=3) can be expressed as a mathematical expression 7. [mathematical expression 7] If a p > 0, c i i (a) In the case of the third bit (k=3), the output value is determined as 2 If a {3 0. Here, n is a magnitude parameter of the QAM in the mathematical expression 1 and c is a constant. As such, it can be another characteristic of the second form QAM that the conditional probability vector is obtained in the cases of a *{3 >0 and a {3 An expression to obtain the conditional probability vector corresponding to the fourth bit (k=4) of the second form can be obtained by substituting a with j3 and 3 with a in the mathematical expression 7 used to obtain the third conditional probability vector according to the second form. The expression used to obtain the conditional probability vector corresponding to the fifth bit (k=5) of the second form can be obtained by applying the mathematical expression 8. Here, as can be seen from Fig. 10, since the conditional probability vector corresponding to the fifth or later bit indicates a determined an iteration (v shape) form, it is noted that an expression be repeatedly used using such property. However, when the conditional probability vector corresponding to the fifth or later bit is calculated, the evenordered determination value uses the expression that was used to calculate just before oddordered determination value according to the property of the second form, which is applied when the magnitude of the QAM is less than 64 only. And, when the magnitude is over 256, the remaining part can be divided into two parts and the calculation can be performed in the first half part and then in the second half part as is in the first form. [mathematical expression 8l If a {3 >0, ® First, on dividing the output diagram into a basic Vshaped form, the conditional probability vector corresponding to each bit can be divided into (2k~5 + 1) areas. ® A basic expression according to a basic form is determined as 2' © If finding a belonging area as the given a and substituting a value of I a I m that is subtracted a middle value m of each area (for example, since the repeated area is one when k = 6, the area becomes 2n~ ^  a  @ Finally, in the left and right outer areas among the divided areas, that is, (2k~2 l)2n"k+2 In the case of a 3 The calculation of the conditional probability vector corresponding to the sixth bit of the second form can be obtained by substituting a with £ and ]3 with a in the mathematical expression 8 used to obtain the fifth conditional probability vector by the property of the second form in the case that the magnitude of the QAM is 64QAM. However, in the case that the magnitude of the QAM is more than 256QAM, the first half is obtained by dividing total remaining vectors into 2 and the second half is obtained by substituting the received value (a or {3 )) into the expression of first half. At this time, changed value in the expression of first half is the received value only, and the bit number value (k) is not changed but substituted with that of first half. Consequently, in the case that the magnitude of the QAM is more than 256, the calculation of the conditional probability vector corresponding to the fifth to (n+2)th bit of the second half is determined by the mathematical expression 8. The calculation of the conditional probability vector corresponding to the (n+3)th to the last, 2nth bit of the second form is determined by substituting the parameter a with {3 in the mathematical expression as mentioned above. The soft decision demodulation of the square QAM can be performed using the received signal, that is, a + {3 i through the procedure described above. However, it is noted that although the method described above arbitrarily determined an order in selecting the received signal and substituting it into a determination expression for convenience of understanding, the method is applied in more general in real application so that the character a or P expressed in the mathematical expressions can be fireely exchanged each other according to the combination constellation form of the QAM and the scope of the output values may be nonsymmetrical such as values between a and b, as well as values between a and a. It can be said that such fact enlarges the generality of the present invention, so that it increases its significance. Also, although the mathematical expressions described above seems to be very complicated, they are generalized for general applications so that it is realized that they are very simple viewing them through really applied embodiments. First Embodiment The first embodiment of the present invention is a case corresponding to the first form and is applied the property of the first form. The first embodiment includes an example of 1024QAM where the magnitude of QAM is 1024. The order selection of the received signal is intended to apply a in the first half and {3 in the second half. Basically, QAM in two embodiments of the present invention can be determined as following expression. A mathematical expression 1 determines the magnitude of QAM and a mathematical expression 2 shows the number of bits set in each point of a combination constellation diagram according to the magnitude of QAM. [mathematical expression 1] 22nQAM,n = 2,3,4 •■•• [mathematical expression 2] the number of bits set in each point = 2n Basically, the magnitude of QAM in the first embodiment of the present invention is determined as the following expression, and accordingly the conditional probability vector value of the final output value becomes 2n. A case where 22*5  QAM equals to 1024  QAM according to the mathematical expression 1 and the number of bits set in each constellation point equals to 2 x 5 = 10 bits according to the mathematical expression 2 will be explained using such mathematical expressions 1 and 2. First, prior to entering into calculation expression applications, it is noted that if a calculation expression for 5 bits of the first half among 10 bits are known by the property of the first form, a calculation expression for remaining 5 bits of the second half is also known directly. First, the first conditional probability vector expression is a case of k=l, and has its output value determined as 2 unconditionally. Next, the second (that is, k=2) conditional probability vector has its output value A case where n equals to 5, that is, 2  QAM equals to 1024  QAM according to the mathematical expression 1 and the number of bits set in each constellation point equals to 2 x 5 = 10 bits according to the mathematical expression 2 will be explained when n is 5 using such mathematical expressions 1 and 2. First, the first conditional probability vector calculation is a case of k=l, where the l output value is determined as 2 unconditionally. Next, the second (k2) conditional probability vector calculation expression is a case where the first calculation expression is substituted, where the output value is determined as l Next, for the third (k=3) conditional probability vector calculation expression, when a £J ^ 0, the following will be given, where the output value is determined as C l ! cyrM 1 unconditionally. However, c is a constant. When a 3 Next, for the fourth (k=4) conditional probability vector calculation, (1) when a 3 > 0, the following will be given, where the output value is determined as 2 unconditionally. (2) When a 3 the expression used for the method for determining the output of the fourth conditional probability vector explained just above (a 3 > 0). Next, for the fifth (that is, k=5) conditional probability vector calculation expression, when a J3 > 0, the following will be given, where a basic expression according to the basic form is determined as 2 Here, the expression is divided into 2 areas, where if a  — atf — a32tf determined as 2 , and the output value is determined as 2 for other cases. (2) When a J3 0). Next, for the sixth conditional probability vector (that is, k=6), when Qp^O, a basic expression according to the basic form is determined as d l i w —j\a\d 2 , and here, the expression is divided into 3 areas, where if a  determined as 2 , the output value is determined as 2 , and the output value is 4a32 determined as 2 for other cases. When a 3 0). Next, for the calculation expression of the seventh (k=7) conditional probability vector, when a {3 > 0, a basic expression according to the basic form is determined as this calculation expression is obtained by substituting a with {3 in the expression used for the method for determining the output of the seventh conditional probability vector explained just above (a 3 ^ 0). A method for obtaining the eighth to tenth conditional probability vectors is obtained by substituting a with ]3 and {3 with a in the expression to obtain the fifth to seventh conditional probability vectors. Next, the second one of the method for demodulating square QAM signal will be explained. First, a soft decision method of the square QAM corresponding to the first form will be explained. In the case of the first form, while anyone of the real number part and the imaginary number part among the received signal is used in order to calculate the conditional probability vector corresponding to the first half bit combination, the first half is demodulated expression 13 is substituted with a becomes the first conditional probability vector of the second half, that is, the conditional probability vector calculation expression corresponding to the (n+l)th bit. Also, the conditional probability vector corresponding to the (n+2)th bit, that is, the second conditional probability vector of the second half can be determined by substituting {3 with a in the mathematical expression 14 that is the condition where the second conditional probability vector of the first half is calculated, and the conditional probability vector corresponding to the bit number n+3 to 2n, that is, the following cases, can be determined by transforming the mathematical expressions 15 and 16 as described above. Next, a soft decision method of the received signal of a square QAM corresponding to the second form will be explained. Also, for convenience of understanding, the value a is used to determine the conditional probability vector corresponding to the oddordered bit and the value {3 is used to determine the evenordered bit. In the second form, the method for calculating the conditional probability vector corresponding the first bit can be expressed as the mathematical expression 17 and Fig. 13is a visualization of it. [mathematical expression 17] as sigt In the second form, a method for calculating the conditional probability vector corresponding to the second bit can be obtained by substituting all of a with £5 in the mathematical expression 17 used to calculate the first conditional probability vector according to the property of the second form. In the second form, the method for calculating the conditional probability vector corresponding to the third bit can be expressed as the mathematical expression 18. [mathematical expression 18] If a x p 0. As such, the method for obtaining the conditional probability vector in each cases of ax p^O and ax p The expression for obtaining the conditional probability vector corresponding to the fourth bit of the second form is obtained by substituting a with {3 and {3 with a in the mathematical expression 18 used to obtain the third conditional probability vector by the property of the second form in the case that the magnitude of the QAM is less than 64QAM. However, the case where the magnitude of QAM is more than 256QAM is expressed as the mathematical expression 19. according to the property of the second form in the case that the magnitude of QAM is 64QAM. However, a case where the magnitude of QAM is more than 256QAM is expressed as the mathematical expression 19. A calculation of the conditional probability vector corresponding to the seventh to n bit of the second form is determined as the mathematical expression 19. A calculation of the conditional probability vector corresponding to the (n+l)th bit of the second form is expressed as the mathematical expression 21 and this is a specific case of the mathematical expression 19. [mathematical exoression 211 A calculation of the conditional probability vector corresponding to the (n+2)th bit of the second form is obtained by substituting a with {3 and £ with a in the mathematical expression 18. A calculation of the conditional probability vector corresponding to the (n+3)th to (2nl)th bit of the second form is obtained by substituting a with {3 in the mathematical expression 19. However, the bit number of the value k that is used at this time is 4 to n, which is sequentially substituted instead of n+3 to 2nl. A soft decision demodulation of the square QAM can be implemented using the received signal, that is, the value of a +]3 i through such process. However, although the method described above arbitrarily decided the order in selecting the received signal and substituting that into the determination expression for the convenience of understanding, it is noted that it is applied in more general in its real application so that the character a or p expressed in the expression can be freely exchanged according to the combination constellation form of the QAM and the scope of the output value can be asymmetrical such as a value between "a" and "b" as well as a value of "a" or "a". That enlarges the generality of the present invention and increases its significance. Also, although the mathematical expressions described above seems to be very complicated, they are generalized for general applications so that it is realized that they are very simple viewing them through really applied embodiments. Third Embodiment The third embodiment of the present invention is a case corresponding to the first form and is applied the property of the first form. The third embodiment includes an example of 1024QAM where the magnitude of QAM is 1024. The order selection of the received signal is intended to apply a in the first half and {3 in the second half, (referring to Figs. 11 and 12). Basically, QAM in two embodiments of the present invention can be determined as following expression. A mathematical expression 1 determines the magnitude of QAM and a mathematical expression 2 shows the number of bits set in each point of a combination constellation diagram according to the magnitude of QAM. [mathematicalexpression 2 J the number of bits set in each point  2n Basically, the magnitude of QAM in the third embodiment of the present invention is determined as the following expression, and accordingly the number of the conditional probability vector value of the final output value becomes 2n. A case where 22*5  QAM equals to 1024  QAM according to the mathematical expression 1 and the number of bits set in each constellation point equals to 2 x 5 = 10 bits according to the mathematical expression 2 will be explained when n is 5 using such mathematical expressions 1 and 2. First, prior to entering into calculation expression applications, it is noted that if a calculation expression for 5 bits of the first half among 10 bits are known by the property of the first form, a calculation expression for remaining 5 bits of the second half is also known directly. ] Also, if 25 Also, if 29 Next, the calculation expressions of the sixth to tenth conditional probability vectors can be obtained by substituting 3 with a in the first to fifth conditional probability vector according to the property of the first form. Fourth Embodiment The fourth embodiment of the present invention is a case corresponding to the second form and is applied the property of the second form. The fourth embodiment includes an example of 1024QAM where the magnitude of QAM is 1024. The order selection of the received signal is intended to apply a at first. A mathematical expression 1 determines the magnitude of QAM and a mathematical expression 2 shows the number of bits set in each point of a combination constellation diagram according to the magnitude of QAM, as is in the third embodiment, [mathematical expression 1J 22nQAM,n = 2,3,4 •■■• [mathematical expression 2 J the number of bits set in each point = 2n Basically, the magnitude of QAM in the fourth embodiment of the present invention is determined as the above expression, and accordingly the number of the conditional probability vector value of the final output value becomes 2n. A case where 2  QAM equals to 1024  QAM according to the mathematical expression 1 and the number of bits set in each constellation point equals to 2 x 5 = 10 bits 0.0625 5 , , n . —rr"t2 Ha]i Also, if 7*22'Ka ^ 2M, the output is determined as 2 ~2 When a (3 in this case, the calculation expression is obtained by substituting a with J3 in the ©,®,© expressions of the method for determining the fifth conditional probability vector (a J3 Next, for the sixth conditional probability vector (that is, k=6, m^O, 1, 2, ... 7, 8, « 1,2,3,...7,8), (l)when a {3 > 0, ® ifm*22Ka  At this time, the output is obtained by applying m=0, 1, 2, .. .7, 8. That is, ifl Also, if 2 l Also, if 3*22Ka ^ 3*22+l, the output is determined as 1. Also, if 7*22Ka  Also, if 25l Also, ® if (2£ 1)*2Ka  the output is determined by substituting k =1, 2, 3,.. .7,8 in the (l)e +1{0.9375a 0.9375(2£ 1)*2}, here, if Ka  Also, if5 Also, if 9 Also, if 25 Also, if 29 (2) When a 0 in this case, the calculation expression is obtained by substituting a with {3 in the 0, ® expressions of the method for determining the output of the fifth conditional probability vector (a {3 > 0) described just above. Next, the calculation expressions of the seventh to tenth conditional probability vector are obtained by substituting a with {3 and {3 with a in the calculation expressions of the third to sixth conditional probability vector. Fig. 11 is a view showing a functional block for a conditional probability vector decision process in accordance with the present invention. Fig. 12 is a view showing an example of hard ware configuration for a conditional probability vector of a first form of 64QAM in accordance with the present invention. A person skilled in the art can configure the hard ware by making a modification within the scope of the present invention. While the present invention has been described in conjunction with preferred embodiments thereof, it is not limited by the foregoing description, but embraces alterations, modifications and variations in accordance with the spirit and scope of the appended claims. Industrial Applicability In accordance with the present invention, it is expected to enhance the process speed remarkably and to save a manufacturing cost upon embodying hard ware by applying a linear conditional probability vector equation instead of a log likelihood ratio method being soft decision demodulation method of a square QAM signal that is generally used in the industrial field. PCT/KR2004/000032 RO/KR 23 8 2004 Claims 1. A soft decision method for demodulating a received signal of a square Quadrature Amplitude Modulation (QAM) consisted of an inphase signal component and a quadrature phase signal component, wherein a conditional probability vector value being each soft decision value corresponding to a bit position of a hard decision is obtained using a function including a conditional determination operation from the quadrature phase component and the inphase component of the received signal. 2. The method according to claim 1, wherein the conditional probability vector decision method for a first half of total bits is the same as the decision method for the remaining half of bits, which is determined by substituting the quadrature phase component value and the inphase component value each other. 3. The method according to claim 2, wherein the conditional probability vector values corresponding to a first to nth bit are demodulated by one of the received signal a and {3 , and the conditional probability vector values corresponding to the (n+1) to 2n bits of the second half are demodulated by the remaining received signal, and equation applied for the two demodulations has the same method in the first half and the second half. 4. The method according to claim 2, wherein the demodulation method of the conditional probability vector corresponding to an oddordered bit is the same as a calculation method of the conditional probability vector corresponding to the next evenordered bit, where the received signal value used to calculate the conditional probability vector corresponding to the oddordered bit uses one of the a and {3 according to a given combination constellation PCT/KR2004/000032 RO/KR23.08.2004 diagram and the received signal value for the evenordered bit uses the remaining one. 5. The method according to claim 3, wherein the first conditional probability vector is determined by selecting one of the received values a with P according to the combination constellation diagram and applying a following mathematical expression 22, where in the mathematical expression 22, a — Q 0 an output value is unconditionally determined as 2 [here, Q, is a selected and received value which is one of a and {3 , and a is an arbitrary real number set according to a desired output scope]. 6. The method according to claim 3, wherein the second conditional probability vector is determined by the received value selected when determining the first conditional probability vector and a following mathematical expression 23, where, in the mathematical expression 23, the output value is unconditionally determined as [here, Qis a selected and received value, n is a magnitude of the QAM, that is, a parameter used to determine 22n, a is an arbitrary real number set according to a desired output scope, and c is an arbitrary constant]. 7. The method according to claim 3, wherein the third to n conditional probability vectors are determined by a received value set when determining the first conditional probability vector and a following mathematical 24, where in the mathematical expression 24, PCT/KR2004/000032 RO/KR23.08.2004 first, dividing an output diagram in a shape of a basic V form, the conditional probability vector corresponding to each bit is divided into (2 ~ +1) areas, the basic expression according to the basic form is determined as l 3) the output is determined by finding an involved area using the given ffi and substituting a value of (Q m) that a middle value is subtracted from each area into the basic expression as a new Q, , (4) rendering the middle value as m~2n and substituting the value of (\Q m) into the basic expression as a new Q in an area that is in the most outer left and right sides among the divided areas, that is, (2K~Z l)2n"K+/ 8. The method according to claim 3, wherein the (n+1) to 2n conditional probability vectors are sequentially obtained using the received value that is not selected when the first conditional probability vector is determined and the mathematical expressions described above (however, the number k of the conditional probability vector included in the mathematical expression 24 sequentially substitutes 3 to n with n+1 to 2n). 9. The method according to claim 4, the first conditional probability vector is determined by selecting any one of the received values a and {3 according to a form of the combination constellation diagram and then according to a mathematical expression 25, where in the mathematical expression 25, PCT/KR2004/000032 RO/KR23.08. 2004 form in the cases of a [3 > 0 and a P 13. The method according to claim 4, wherein the fifth conditional probability vector selects one of the received values a and {3 according to the form of the combination constellation diagram, uses a following mathematical expression 27 in the case of a {3 > 0, and determines by substituting the received value selected in the mathematical expression 27 with the received value that is not selected in the expression in the case of a P the mathematical expression 27, ® first, dividing an output diagram in a shape of a basic V form, the conditional probability vector corresponding to each bit is divided into 2 areas, (2) the basic expression according to the basic form is determined i (3) the output is determined by finding an involved area ushig mw gi»wi ooonu substituting a value of (Q m) that a middle value is subtracted from each area into the basic expression as a new Q,, ® rendering the middle value as m=2n and substituting the value of \Q> m into the basic expression as a new Q in an area that is in the most outer left and right sides among the divided areas, that is, 7*2n~3 14. The method according to claim 4, wherein when the magnitude of QAM is 64QAM, the sixth conditional probability vector is calculated by substituting each of received values used with each of the received values that are not used in the method for obtaining the fifth conditional probability vector of the second form in the cases of a j3 > 0 and a {3 PCT/KR2004/000032 RO/KR 23.08. 2004 15. The method according to claim 4, wherein when the magnitude of QAM is more than 256QAM, the fifth to (n *2)th conditional probability vector select one of the received values a and £5 according to the form of the combination constellation diagram, is determined by a following mathematical expression 28 in the case of a £> > 0, and determines by substituting the received value selected in the mathematical expression 28 with the received value that is not selected in the expression in the case of a {3 expression 28, ® first, dividing an output diagram in a shape of a basic V form, the conditional probability vector corresponding to each bit is divided into (2k"5+l) areas, (2) the basic expression according to the basic form is determined; (3) the output is determined by finding an involved area using the given Q> and substituting a value of \Q, m that a middle value m (for example, in the case of k=6, since repeated area is 1, this area is 2n 2 ^ \Q  ® rendering the middle value as m^2n and substituting the value of ffi m into the basic expression as a new ffl in an area that is in the most outer left and right sides among the divided areas, that is, (2k_2 l)2n_k+2 16. The method according to claim 4, wherein when the magnitude of QAM is more than 256QAM, the (n+3)th to (2n)th conditional probability vectors is selected by the PCT/KR2004/000032 RO/KR 23.08,2004 mathematical expression 28 using the received value that is not selected when determining the fifth to (n t2)n conditional probability vector of the second form in the case of a [3 > 0, and is obtained by substituting the received value selected in the mathematical expression 28 with the received value that is not selected in the expression in the case of a ]3 17. The method according to claim 3, wherein the first conditional probability Vector of the first form is determined by selecting any one of the received values a and 3 according to a form of the combination constellation diagram and then according to a mathematical expression 29, where in the mathematical expression 29, [here, Q, is anyone of the received values a and £5 , csign(Q )'indicates the sign of the selected and received value, V is an arbitrary real number set according to a desired output scope, a is a received value of I (real number) channel, and {3 is a received value of Q(imaginary number) channel]. 18. The method according to claim 3, wherein the second conditional probability vector of the first form is determined by the received value selected when determining the first conditional probability vector and the mathematical expression 30, where in the mathematical expression 30 ® if 2n2n(2'm) PCT/KR2004/000032 . 2004 [here, Q is a selected and received value, n is the magnitude of QAM, that is, a parameter used to determine 22n, ca' is an arbitrary real number set according to a desired output scope, and m=l,2]. 19. The method according to claim 3, wherein the third to (nl)th conditional probability vectors of the first form are determined by the received value selected when determining the first conditional probability vector and the mathematical expression 31, where in the mathematical expression 30, [nere, J> PCT/KR2004/000032 RO/KR 23. 08. 2004 f  the first form is determined by the received value selected when determining the first conditional probability vector and the mathematical expression 32, where in the mathematical expression 32, 21. The method according to claim 3, wherein the (n+l)th to 2nth conditional probability vectors of the first form are sequentially obtained using the received value that is not selected when determining the first conditional probability vector and the mathematical expressions 30 to 32, respectively [however, the conditional probability vector number k included in the mathematical expression 31 is sequentially used as 3 to n1 instead of n+3 to 2nl]. 22. The method according to claim 4, wherein the first conditional probability Vector of the second form is determined by selecting any one of the received values a and £5 according to a form of the combination constellation diagram and then according to a mathematical expression 33, where in the mathematical expression 33, CD if Q ^ 2nl, the output is determined as a*sign(Q ), also, (2) \Q> ^ 1, the output is determined as a*0.9375*sign(Q ), also, CD \ ^ 2nl, the output is determined as "a*[5/g/i(n)^^l(Ql)+0/9275] 22 [here, Q, is the selected and received value, 'sign(ffl Vindicates the sign of the selected and received value, a is an arbitrary real number set according to a desired output scope, a is a PCT/KR2004/000032 RO/KR23.08. 2004 received value of I (real number) channel, and {3 is a received value of Q(imaginary number) channel]. 23. The method according to claim 4, wherein the second conditional probability vector of the second form is calculated by substituting the received value selected in the method for obtaining the first conditional probability vector of the second form with the received value that is not selected in the method. 24. The method according to claim 4, wherein the third conditional probability vector of the second form selects anyone of the received values a and £> according to the combination constellation diagram, and determines using the following mathematical expression 34 in the case of a *{3 > 0, and substituting the selected and received value in the mathematical expression 34 with the received value that is not selected in the mathematical expression 34 in the case of a *{3 [here, Q, is a selected and received value, V is an arbitrary real number set according to a desired output scope, a is a received value of I (real number) channel, P is a received value of Q(imaginary number), and m=l,2]. 25. The method according to claim 4, wherein when the magnitude of QAM of the second form is less than 64QAM, the fourth conditional probability vector is calculated by PCT/KR2004/000032 RO/KR 23 08.2004 substituting each of received values used with each of the received values that are not used in the method for obtaining the third conditional probability vector of the second form in the cases of a *P >0and a *P 26. The method according to claim 4, wherein when the magnitude of QAM of the second form is 64QAM, the fifth conditional probability vector select one of the received values a and {3 according to the form of the combination constellation diagram, and determines using the following mathematical expression 35 in the case of a *{3 > 0, and substituting the received value selected in the mathematical expression 35 with the received value that is not selected in the expression in the case of a *J3 expression 35, the output is determined as a*(l)e +1{0.9375P 0.9375(2£ l)*2n_1}, [here, Q, is a selected and received value, 'a' is an arbitrary real number set according to a desired output scope, a is a received value of I (real number) channel, {3 is a received value of Q(imaginary number) channel, m=0, 1,2, and I =T, 2]. 27. The method according to claim 4, wherein when the magnitude of QAM of the second form is 64QAM, the sixth conditional probability vector is calculated by substituting each of received values used with each of the received values that are not used in the method for obtaining the fifth conditional probability vector of the second form in the cases of a *{3 > 0 and a *{3 28. The method according to claim 4, wherein when the magnitude of QAM of the PCT/KR2004/000032 RO/KR23.08. 2004 second form is more than 256QAM, the fourth to nth conditional probability vectors select one of the received values a and J3 according to the form of the combination constellation diagram, is determined by a following mathematical expression 36 in the case of a *£> > 0, and determines by substituting the received value selected in the mathematical expression 36 with the received value that is not selected in the expression in the case of a *{3 [here, k is conditional probability vector numbers (4, 5,..., n), & is a selected and received value, 'a' is an arbitrary real number set according to a desired output scope, a is a received value of I (real number) channel, {3 is a received value of Q (imaginary number) channel, m= 0, l,..2k"3, H is 1, 2,...3k~3, andp=l5 2..., 2k~2]. 29. The method according to claim 4, wherein when the magnitude of QAM of the second form is more than 256QAM, the (n+l)th conditional probability vectors is a received value selected when determining the fourth to nth conditional probability vector of the second form, is determined using the mathematical expression 37 in the case of a *J3 > 0, and is PCT/KR2004/000032 RO/KR23.08.2004 obtained by substituting the received value selected in the mathematical expression 37 with the received value that is not selected in the expression in the case of a *]3 ® ifm*22l also, ® if(2« l)*2]\ the output is determined as a*(l)* +I {0.9375{(Q 0.9375(2« ~1)*21), [here, Q, is a selected and received value, 'a' is an arbitrary real number set according to a desired output scope, a is a received value of I (real number) channel, {3 is a received 1 "i i 1 value of Q (imaginary number) channel, m= 0, 1, ..2 " , and I is 1, 2,.. .3 " ]. 30. The method according to claim 4, wherein when the magnitude of QAM of the second form is more than 256QAM, the method for obtaining the (n+2)1 conditional probability vector is the same as the method for obtaining the fourth conditional probability vector in the case that the magnitude of QAM of the second form is less than 256QAM. 31. The method according to claim 4, wherein when the magnitude of QAM of the second form is more than 256QAM, the (n+3)tb to (2nl)th conditional probability vectors are calculated by substituting each of received values used with each of the received values that are not used when determining the fourth to nth conditional probability vectors in the cases of a *j3 > 0 and a *]3 32. The method according to claim 4, wherein when the magnitude of QAM of the second form is more than 256QAM, the 2nth conditional probability vector is calculated by substituting each of received values used with each of the received values that are not used PCT/KR2004/000032 RO/KR23.08.2004 when determining the fourth to the (nH)lh conditional probability vector in the cases of a *[3 ^0 and a *{3 33. An apparatus for demodulating an QAM receiving signal consisted of an inphase signal component and an quadrature phase signal component, wherein the apparatus comprises a conditional probability vector determination unit for obtaining a conditional probability vector value being each soft decision value corresponding to a bit position of a hard decision is obtained using a function including a conditional determination operation from the quadrature phase component and the inphase component of the received signal. 34. The apparatus according to claim 33, wherein in the conditional probability vector determination unit, an operation for determining the conditional probability vector for a first half of total bits is the same as an operation for determining the conditional probability vector for the remaining half bits, and is determined by substituting the quadrature phase component value with the inphase component value, respectively. 35. The apparatus according to claim 33 or 34, wherein in the conditional probability vector operation unit, the conditional probability vector values corresponding to the first to xi bits are demodulated by anyone of the received signals a and {3 , and the conditional probability vector values corresponding to the (n+1) to the 2n bits of the second half are demodulated by the received signal of the remaining one, and first half and second half equations applied to the two demodulations are same. 36. The apparatus according to claim 33 or 34, wherein in the conditional probability PCT/KR2004/000032 RO/KR23.08.2004 Vector operation unit, the demodulation operation of the conditional probability vector corresponding to an oddordered bit is identical to the operation of the conditional probability vector corresponding to the next evenordered bit, and the received signal value to calculate the conditional probability vector corresponding to the oddordered bit uses anyone of a and 3 5 according to a given combination constellation diagram, and the received signal value for the evenordered bit uses the remaining one. 37. A soft decision method for demodulating a received signal of a square Quadrature Amplitude Modulation (QAM) substantially as herein described with reference to the accompanying drawings. 38. An apparatus for demodulating an QAM receiving signal substantially as herein described with reference to the accompanying drawings. Abstract: The present invention relates to a demodulation method using soft decision for QAM (Quadrature Amplitude Modulation). In a soft decision method for demodulation of a received signal of square QAM comprised of the same phase signal component and a orthogonal phase signal component, the demodulation method using soft decision has a characteristic wherein the processing speed is improved, and the manufacturing expense is reduced by gaining a condition probability vector value, which is each soft decision value, corresponding to a beat position of hard decision using a function which includes a condition judgement operation from a orthogonal phase component value of a received signal and the same phase component value. 

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Patent Number  237678  

Indian Patent Application Number  1050/CHENP/2005  
PG Journal Number  2/2010  
Publication Date  08Jan2010  
Grant Date  04Jan2010  
Date of Filing  27Mar2005  
Name of Patentee  SEO, HongSeok  
Applicant Address  403605 Maehwamaeuljugong Apt., 211 Yatapdong, Bundanggu, 463070 SeongnaM  
Inventors:


PCT International Classification Number  H04L 27/26  
PCT International Application Number  PCT/KR2004/000032  
PCT International Filing date  20040110  
PCT Conventions:
