Patent Grant
7664165
The present invention relates to a correlation apparatus based on symmetry of a correlation coefficient and a method thereof; and, more particularly, to a correlation apparatus that can reduce complexity of hardware by using symmetry of a correlation coefficient and reducing the number of adders and multipliers, and a method thereof.
Recently, high-speed data communication using a Wireless Local Area Network (WLAN) is increasing since it can reduce costs by using a WLAN having characteristics such as flexible network formation, easy connection and mobility that can not be obtained from conventional wired communication.
Now the WLAN is developed and used based on the standards of the Institute of Electrical and Electronics Engineers (IEEE) 802.11.
The standards are divided into 802.11b, 802.11g and 802.11a according to a frequency band and a data rate. The 802.11b and the 802.11g are standards for the frequency band of 2.4 GHz, and the 802.11a is a standard for the frequency band of 5 GHz with a reference of related frequency band.
The 802.11b provides data rates of 1, 2, 5.5 and 11 Mbps, and uses spread spectrum as a modulation scheme.
The 802.11g supports one data rate among 6, 9, 12, 18, 24, 36, 48 and 54 Mbps by adding Orthogonal Frequency Division Multiplexing (OFDM) to supplement the 802.11b having a maximum data rate of 11 Mbps to thereby provide a maximum data rate of 54 Mbps.
The 802.11a supports one data rate among 6, 9, 12, 18, 24, 36, 48 and 54 Mbps by using the OFDM method and is determined to use a frequency band of 5 GHz.
The OFDM communication method used in the 802.11g and 802.11a of the standards follows the standard defined in “HIGH SPEED PHYSICAL LAYER IN THE 5 GHz BAND” of “WIRELESS LAN MEDIUM ACCESS CONTROL (MAC) AND PHYSICAL LAYER (PHY) SPECIFICATIONS” which is laid open in PART 11 of IEEE 802.
Various modulation methods are provided to support various data rates in the WLAN using the OFDM. Binary phase shift keying (BPSK) for 6.9 Mbps, quadrature phase shift keying (QPSK) for 12 and 18 Mbps, 16 quadrature amplitude modulation (QAM) for 24 and 36 Mbps, and 64 QAM for 48 and 56 Mbps are used.
As shown in
The SP section includes 10 short preambles for a signal sensing, automatic gain control, synchronization acquisition and frequency variation control. The signal field has information such as data rate and data length of a transmitted frame, and the data field has actual data information.
When the frame shown in
A method for finding a correlation value between the received signal and a known data sequence is widely used to detect synchronization. Herein, a preamble which is made to stand interference caused by the multi-path is used as the known data sequence. The correlation is a procedure comparing the received signal with the known data sequence. For example, when the signal which is well known to a transmitting part, i.e., a signal that can be recognized even though it is not restored in a receiving part, such as a preamble signal, are loaded in a first part of a transmitting signal and transmitted, the receiving part compares the receiving signal with a signal of the known pattern in order to know a starting point of a received signal, and detects the synchronization of the received frame by using a part matched maximally. The correlation procedure can be shown as equations.
Herein, Cj represents a jth correlation value; Si represents a known sequence used to obtain synchronization, r represents a receiving signal and L represents the entire length of the sequence for synchronization detection. An SP signal functioning as the known sequence in the WLAN using the OFDM is a signal obtained by performing Inverse Fast Fourier Transform (IFFT) on a complex signal of {0, 0, 1+j, 0, 0, 0, −1−j, 0, 0, 0, 1+j, 0, 0, 0, −1−j, 0, 0, 0, −1−j, 0, 0, 0, 1+j, 0, 0, 0, 0, 0, 0, 0, −1−j, 0, 0, 0, −1−j, 0, 0, 0, 1+j, 0, 0, 0, 1+j, 0, 0, 0, 1+j, 0, 0, 0, 1+j, 0, 0}. Herein, the SP signal includes 16 sample sequences in a time domain, wherein sample time is 1/20 MHz.
The SP signal is used to detect synchronization of reception input. Therefore, the correlation coefficient for detecting synchronization in WLAN using the OFDM is 16 SP sequences having a complex value.
The receiving part detects synchronization from the SP signal transmitted through a wireless channel by using a correlator or a matched filter. Herein, a correlator or a matched filter for detecting synchronization has a structure of a tapped delay line or a finite impulse response filter which has 16 SP signals as correlation coefficients.
As shown in
A complex correlation apparatus shown in
If the synchronization sequence is small, i.e., if L has a small value, the calculated value does not have a great amount of calculation. Otherwise, there is a problem that the amount of calculation increases remarkably.
Also, when realized as hardware, the conventional correlation apparatus includes multipliers and adders/subtracters as many as aforementioned, occupying 10 to 20% of the entire receiver, thereby increasing complexity of the receiver. In particular, since the multipliers require a great amount of logic elements, the complexity of the hardware increases remarkably in case many bits are inputted.
It is, therefore, an object of the present invention to provide a correlation apparatus that can reduce complexity based on symmetry of a correlation coefficient. That is, when values of a real number part and an imaginary number part are exchanged with respect to a middle point of a correlation coefficient sequence and divided into two parts of left and right by the middle point of the correlation coefficient sequence, the values of the real number part and the imaginary number part are even-symmetrical with respect to the middle point of the divided two parts.
Other objects and advantages of the invention will be understood by the following description and become more apparent from the embodiments in accordance with the present invention, which are set forth hereinafter. It will be also apparent that objects and advantages of the invention can be embodied easily by the means defined in claims and combinations thereof.
In accordance with an aspect of the present invention, there is provided a correlation apparatus for correlating a complex correlation coefficient sequence which is symmetrical with respect to a received complex signal sequence, including: a delaying unit for delaying the received complex signal sequence; a first adding unit for adding the complex signal sequence delayed in the delaying unit; a second adding unit for adding each output signal of the first adding unit; a correlation coefficient multiplying unit for multiplying each output signal of the second adding unit by a complex correlation coefficient of the complex correlation coefficient sequence; and a final output adding unit for adding each output signal of the correlation coefficient multiplying unit.
In accordance with another aspect of the present invention, there is provided a correlation method based on symmetry of the complex correlation coefficient sequence, including the steps of: a) delaying the received complex signal sequence; b) adding the complex signal sequence delayed in the step a); c) adding the output signals to be multiplied by a common correlation coefficient among the signals added and outputted in the step b); d) multiplying the signals obtained from the addition in the step c) by the complex correlation coefficient of the complex correlation coefficient sequence; and e) adding the signal obtained from the multiplication in the step d) multiplied by the complex correlation coefficient.
The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:
The objects and advantages of the present invention will become apparent from the following description of the embodiments with reference to the accompanying drawings. Therefore, those skilled in the art that the present invention is included can embody the technological concept and scope of the invention easily. In addition, if it is considered that detailed description on the prior art may blur the point of the present invention, the detailed description will not be provided herein. The preferred embodiments of the present invention will be described in detail hereinafter with reference to the attached drawings.
In the following detailed description, the a short preamble (SP) sequence of Orthogonal Frequency Division Multiplexing (OFDM) method will be described as a complex correlation coefficient sequence, which is a reference sequence for synchronization detection, for an easy explanation. However, it is apparent that various reference sequences can be used.
As shown in
Each value of real number/imaginary number is divided largely into two parts of {circle around (a)} and {circle around (b)}, and each {circle around (a)} and {circle around (b)} part is divided into two parts of {circle around (1)} and {circle around (2)}, and two parts of {circle around (3)} and {circle around (4)}. The {circle around (a)} and the {circle around (b)} have symmetry that the values of the real number and the imaginary number are exchanged with each other with respect to a solid line 310. That is, if the {circle around (a)} part is x+jy, the {circle around (b)} part is y+jx.
Meanwhile, the {circle around (1)} and {circle around (2)} parts of the {circle around (a)} are even-symmetry with respect to a dotted line 320, and the {circle around (3)} and the {circle around (4)} of the {circle around (b)} are even-symmetry with respect to a dotted line 330.
As shown in
The above symmetrical relationship should be applied to an equation of a general correlator to use symmetry of the SP. The symmetrical relationship of the SP can be expressed as equation 2.
Herein, the C(n)=x(n)+jy(n) is a complex coefficient. The C(n) is what the real number part and the imaginary number part of C(n) are exchanged, i.e., a complex coefficient of C(n+L/2). It expresses a length of the correlator.
The (1) of the equation 2 represents a relationship between the {circle around (a)} and the {circle around (b)} in
An operation of the general correlator is as shown in equation 3.
Herein, r(n) represents a value of a complex reception input and r(n)* represents a conjugate value of the complex reception input.
When the relationship between the (2) and the (3) of equation 2 is applied to the equation 3, the {circle around (a)} and the {circle around (b)} parts of
am=C12·rm-2*+C8·rm-7*+C13·(rm-2*+rm-4*)+C14·(rm-1*+rm-5*)+C15·(rm-0*+rm-6*)
bm=C4·(rm-11*+rm-15*)+C5·(rm-10*+rm-12*)+C6·(rm-9*+rm-13*)+C7·(rm-8*+rm-14*) Eq. 4
Herein, the rm-n represents r(m-n), and am and bm represent the {circle around (a)} and {circle around (b)} parts of
When the relationship of the (1) in equation 2 is applied to the equation 4, it is expressed as equation 5.
Herein, Rij represents rm-1+rm-j, i and j are values marking integer numbers between 0 and 15 in two-digit numbers. That is, ‘02’ is a value representing 2, and ‘04’ is a value representing 4 in R0204.
When the wm is divided into the real number part and the imaginary part by using the relationship of equation 6, it is expressed as equation 7.
Real number part=C13R(R0204R+R1012I)+C13I(R0204I+R1012R)+C11R(R1015R+R0913I)+C14I(R0105I+R0913R)+C15R(R0006R+R0814I)+C15I(R0006I+R0814R)+C12R(R03R+R11I)+C12I(R03I+R11R)+|C8|(R07R+R15R+R07I+R15I) (1)
Imaginary number part=C13R(R1012R−R0204I)+C13I(R0204R−R1012I)+C14R(R0903R−R0105I)+C14I(R0105R−R0913I)+C15R(R0814R−R0006I)+C15I(R0006R−R0814I)+C12R(R11R−R03I)+C12I(R03R−R11I)+|C8|(R07R+R15R−R07I−R15I) (2) Eq. 7
Herein, CnR and RnR represent the real number part of Cn and Rn, and CnI and RnI represent the imaginary number part of Cn and Rn. Also, Rnr and RnI represent summation of terms multiplied by a common complex coefficient in the tapped delay line. The Rnr and the RnI appear in common in the real number part and the imaginary number part. Therefore, terms including the Rnr and the RnI can use the tapped delay line of the correlation apparatus in common.
Herein, the real number part and the imaginary number part of the equation 7 have a difference in an adder/subtrator of a polynomial equation including R, and a coefficient multiplied by a polynomial equation including R has a difference in the complex coefficient. That is, if the real number part of the complex coefficient is multiplied to the real number part of the equation 7, the imaginary number part of the same complex coefficient is multiplied to the imaginary number part of the equation 7.
In case of applying the equation 2 showing the symmetrical relationship of the SP, just as equation 7, each output signal of the real number and the imaginary number of the correlation apparatus is expressed as a multiplication of 9 multipliers and a coefficient, and the correlation apparatus is realized through a total of 18 multipliers, which can reduce the multipliers about 70% in comparison with the conventional correlation apparatus requiring 64 multipliers.
As shown in
The real number input 700 of the receiving signal is delayed as much as the sample time by 16 tapped delay lines (TDLs) 701 to 715. The imaginary input 761 of the receiving signal is also delayed as much as the sample time by 16 TDLs 716 to 730.
Each adder/subtracter and multiplier of the correlation apparatus shown in
Referring to table 1, adders 731, 740 and 737 represent (R000GR+R08141) of the equation 7 (1). That is, the adder 731 adds a 0th tap signal with respect to the real number input and a 6th tap signal. The adder 740 adds an 8th tap signal and a 14th tap signal with respect to the imaginary number input. The adder 737 adds output of two adders 731 and 740. The method as described above can be applied to remaining terms. Meanwhile, since C8 has a value of the real number, i.e., A+j0, |C8| in table 1 does not require an additional hardware for finding an absolute value.
As shown in
Also, an Rn term multiplied by the correlation coefficient can be made when the term having an imaginary number value is changed into a negative number. For example, in the imaginary number part of the correlation apparatus of the present invention, C121(R03R−R111) term can be made when C12R(R03R+R111) term is changed as described above. Therefore, the imaginary number part is not different from the real number part except that some adders are changed into subtracters. Table 2 is a corresponding relationship of each adder/subtracter and multiplier of the correlation apparatus shown in
As described above, the part adding the output of the related tap of the TDL, i.e., 2nd and 4th taps in the R0204, can be applied in the real number part and the imaginary number part of the correlation apparatus of the present invention in common, just as shown in
As shown in
y9 + y13
y8 + y14
X8 + X14
X7 + X15
Y7 + y15
Subsequently, the output signal calculated through the AA is inputted in the second adder arrays (AA2) 905 and 906. The AA2s 905 and 906 add AA output signals multiplied by the same correlation coefficient in correlation coefficient multiplier arrays 905 and 906 described as follows. Herein, AA2I 905 shown in
As shown in table 4, the AA2I 905 and the AA2Q 906 include 9 2-input adders and 9 2-input subtracters. Therefore, the AA2905 and the AA2906 include a total of 18 2-input adders/subtracters.
The signal going through the AA2s 905 and 906 is multiplied by the correlation coefficient in the correlation coefficient multiplier arrays (MAs) 907 and 908. Herein, the MAI 907 shown in
The output signals of the MAI 907 and the MAQ 908 are generated by the equation defined in table 5. The values of the real number and the imaginary number of the complex correlation coefficient multiplied by each output signal of the AA2s 905 and 906 in the MAI 907 and the MAQ 908 are exchanged with each other based on symmetry.
Each of the MAI 907 and MAQ 908 includes 9 2-input multipliers, just as shown in the table 5. Also, final output adder arrays 910 and 911 generate a final output signal of the real number and the imaginary number by adding the output signal of the MAs 907 and 908. Herein, the final output adder arrays 910 and 911 require 8 2-input adders to generate a final correlation output of the real number and the imaginary number.
Therefore, the number of the adder required for forming the correlation apparatus of the present invention shown in
Meanwhile, a difference between the real number part and the imaginary number part of the correlation apparatus of the present invention is that the real number part includes the adder and the imaginary number part includes the subtracter in the AA2, and that the real number part and the imaginary number part of the multiplied correlation coefficient are exchanged with each other in the correlation coefficient MA. Herein, if the operating speed of the correlation apparatus is increased twice as fast as, the constitutional element can be reduced by half. That is, in case that the operating speed of the correlation apparatus is twice as fast as the sample speed of the input signal, if a half of the operating time of the correlation apparatus is controlled to calculate the real number part and the other half is controlled to calculate the imaginary number part, it is possible to reduce the number of the adders used in the AA2 of the correlation apparatus by half, the number of the multiplier used in the MA of the correlation apparatus by half, and the number of the adders used in the final output AA by half, thereby reducing the total number of the adders to 31 and the total number of the multipliers to 9. That is, the correlation apparatus of the present invention can reduce the adders 50% and the multipliers 86% in comparison with the conventional correlation apparatus.
As shown in
The AA21005 uniting the calculation of the real number part and the imaginary number part adds up to outputs of a first adder array (AA) 1004 calculated in a delay tap 1002 of a real number input 1000 in the real number part calculation. When the imaginary number part is calculated, it performs subtraction on each output of the AA 1004 calculated in a delay tap 1003 of an imaginary number input 1001.
When the complex correlation coefficient is multiplied by the real number part and the imaginary number part of the output signal from the AA21005, the correlation coefficient MA 1006 crossly multiplies the real number part and the imaginary number part.
As shown in
When the real number part is calculated, output signals AA01100, AA11102, AA21101 and AA31103, which are generated from the AA 1004, should be added individually. The output signals AA01100 and AA11102 are not changed in calculation of the real number part and the imaginary number part, but AA21101 and AA31103, which are output values of a first adder array (AA) 1104 adding a tapped delay value, are changed in the real number part and the imaginary number part. That is, when the real number part is calculated, the input value is added, and when the imaginary number part is calculated, the input value is subtracted. Therefore, the switches or multiplexers 1110 and 1111 are required to select the output values AA21101 and AA31103, or a negative number.
Switches 1110 and 1111 shown in
In case of the multiplier, the real number part and the imaginary number part of the correlation coefficient are changed with each other and multiplied according to the controlling signal. For the operation, the real number value and the imaginary number value of the correlation coefficient are outputted according to the controlling signal, or a 2×2 switch 1106 is required to change the locations of the real number value and the imaginary number value and output them.
Therefore, in the real number part calculation of the correlation apparatus, the correlation coefficient of the real number is multiplied by the first multiplier 1107 and the correlation coefficient of the imaginary number is multiplied by a second multiplier 1108. In calculation of the imaginary number part, the correlation coefficient of the imaginary number is multiplied by a first multiplier 1107 and the correlation coefficient of the real number is multiplied by a second multiplier 1108. The multiplied values are added in a final output adder array (AA) 1009. The method described above is applied when the remaining correlation coefficients are multiplied. Since one multiplier is used to multiply the coefficient of C8, an additional switch is not required. The output of the calculated correlation coefficient MA 1006 passes through the final output AA 1009, and becomes the output of the final correlation apparatus passing through a switch 1010 for keeping the signal as an original sample speed value of the reception input.
In
As shown in the diagrams 1122 and 1123 of
As shown in
At step S1220, the delayed complex signal sequence is added, just as an equation of the table 3.
At step S1230, among the added and outputted signals, those to be multiplied by a common correlation coefficient are added as shown in the equations of the table 4. That is, when a real number part is calculated in the step S1230, among the outputted signals of the step S1220, those to be multiplied by a common correlation coefficient are added. When an imaginary number block is calculated, among outputted signals of the step S1220, those to be multiplied by a common correlation coefficient are subtracted from each other.
At step S1240, the signal added in the step S1230 is multiplied by a complex correlation coefficient of a complex correlation coefficient sequence, which is a reference sequence for synchronization detection, as shown in table 5. Herein, when the real number part and the imaginary number part are calculated, the real number and the imaginary number parts of the complex correlation coefficient are changed with each other and multiplied when the real number part is calculated, and when the imaginary number part is calculated.
At step S1250, a final correlation signal is outputted by adding a signal multiplying a complex correlation coefficient.
In case of using symmetry just as equation 2 of the SP used to secure wireless synchronization, the complexity of the hardware can be reduced, which is shown in table 6. That is, in case of using symmetry and having the same sample speed, the multiplier and the adder can be reduced by 70% and 20%, respectively. In case that the sample speed is twice as fast, the multipliers and the adders can be reduced by 86% and 50% respectively.
As described above, the present invention can be embodied as a program and stored in a computer-readable recording medium, such as CD-ROM, RAM, ROM, a floppy disk, a hard disk and a magneto-optical disk. Since the process can be easily implemented by those skilled in the art, further description will not be provided herein.
The present invention can reduce the multipliers and the adder by 70% and 20% respectively, in comparison with the conventional correlation apparatus, by using symmetry of the correlation efficient.
Also, in case where the operating speed is twice as fast as sample speed of a complex input signal, the present invention can reduce the multipliers and the adders by 86% and 50% respectively, thereby reducing the complexity of the hardware remarkably.
The present application contains subject matter related to Korean patent application No. 2004-0104797, filed with the Korean Intellectual Property Office on Dec. 13, 2004, the entire contents of which is incorporated herein by reference.
While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.
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