Code acquisition device and method using two-step search process in DS-CDMA UWB modem

• US 20060093021A1
• Filed: 02/24/2005
• Published: 05/04/2006
• Est. Priority Date: 11/03/2004
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Park, Kwang Roh, Choi, Sangsung, Kang, Kyu Min, Kang, Bub Joo
• Granted Patent: US 7,382,822 B2
• Time in Patent Office: Days
• US Class Current: 375/149
• CPC Class Codes: H04B 1/70735 Code identification H04B1/7083 takes precedence
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 1/7183 Synchronisation

Abstract

There is provided a code acquisition device and method using a two-step search process in a DS-CDMA UWB modem. The device includes: an I/Q channel symbol generating unit for, generating a plurality (i) of n_th I/Q channel symbols in a first search process and generating a plurality of n_th I/Q channel symbols in a second search process; a spread code selecting unit for receiving the plurality of n_th I/Q channel symbols in the first search process; an N_NC2N_S tap I/Q channel symbol matched filter unit for, in the second search process, receiving the plurality (i) of n_th I/Q channel symbols; a switching unit for changing to a closed state of the second search process; and a super frame and symbol boundary time deciding unit for deciding a super frame time and a symbol boundary time.

Claims

1. A code acquisition device using a two-step search process in a Direct Sequence-Code Division Multiple Access (DS-CDMA) Ultra Wide Band (UWB) modem, the device comprising:

an I/Q channel symbol generating unit for, in a first search process, generating a plurality (i) of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) consistent with a plurality (i) of code phases for a multi-path reception signal (r(t)) by using six spread code sequences, and in a second search process, generating a plurality of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) consistent with a plurality (i) of code phases for the multi-path reception signal (r(t)) by using a spread code having a maximal value among six spread codes acquired in the first search process;

a spread code selecting unit for, in the first search process, receiving the plurality of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) from the I/Q channel symbol generating unit to respectively combine the received channel symbols (Y_I,_n(i), Y_Q,_n(i)) at N_NC1 times, and summing the combined result value (Z_i) at each of the six spread codes to generate six symbol energies (E_m, m=1,2, . . . ,

     6) consistent with the six spread codes, and deciding the spread code having the maximal value among the six symbol energies (E_m, m=1,2, . . . ,

     6), as a spread code of a piconet coordinator;

an N_NC2N_S tap I/Q channel symbol matched filter unit having an N_s-length tap and for, in the second search process, receiving the plurality (i) of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) from the I/Q channel symbol generating unit to generate a result value (S_n,_k(i)) through a predetermined arithmetic operation, and performing a noncoherent combining to the result value (S_n,_k(i)) at N_NC2 times to output an arbitrary result value (X_n(i));

a switching unit disposed between the I/Q channel symbol generating unit and the N_NC2N_S tap I/Q channel symbol matched filter unit, for changing an opened state of the first search process to a closed state of the second search process to connect the I/Q channel symbol generating unit with the N_NC2N_S tap I/Q channel symbol matched filter unit; and

a super frame and symbol boundary time deciding unit for deciding a super frame time (packet synchronization) and a symbol boundary time (firstly received path) by using the output values (Xn(i)) of the plurality of N_NC2N_S tap I/Q channel symbol matched filters in the second search process.

2. The device of claim 1, wherein the I/Q channel symbol generating unit comprises:

a plurality (i) of multipliers for respectively multiplying the multi-path reception signal (r(t)), which is sequentially delayed by one PN chip period (T_c), by the six spread code sequences in the first search process; and

a plurality (i) of I/Q channel coherent correlators for, in the first search process, respectively generating the plurality of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) consistent with the plurality (i) of code phases on the basis of result values of the plurality (i) of multipliers, and in the second search process respectively generating the plurality of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) consistent with the plurality (i) of code phases for the multi-path reception signal (r(t)) by using the spread code acquired through the spread code selecting unit in the first search process.

3. The device of claim 2, wherein the multi-path reception signal (r(t)) and the code phases, which are consistent with the plurality (i) of I/Q channel coherent correlators, have a relation where the code phases are allocated to from remaining second I/Q channel coherent correlator to the last (i) I/Q channel coherent correlator in a form of being sequentially delayed by one PN chip period (T_c), on the basis of the code phase of a path firstly received at the first I/Q channel coherent correlator.

4. The device of claim 2, wherein the plurality (i) of I/Q channel coherent correlators have a parallel structure.

5. The device of claim 1, wherein the spread code selecting unit comprises:

a plurality (i) of symbol energy generators for, in the first search process, respectively receiving the plurality (i) of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) from the I/Q channel symbol generating unit to combine the received channel symbols (Y_I,_n(i), Y_Q,_n(i)) at N_NC1 times and respectively output the combined result value (Z_i); and

a maximum-value spread code deciding unit for summing the result value (Z_i) of the plurality (i) of symbol energy generators at each of the six spread codes to generate the symbol energies (E_m, m=1,2, . . . ,

     6) consistent with the six spread codes, and deciding the spread code having the maximal value among the six symbol energies (E_m, m=1,2, . . . ,

     6), as the spread code of the piconet coordinator.

6. The device of claim 5, wherein the result value (Z_i) of the plurality (i) of symbol energy generators can be calculated in the following Equation:

$\underset{n=1}{\overset{N_{\mathrm{nc1}}}{\sum <br><br>}}<br><br>\left[Y_{I,n}^2<br><br>\left(i\right)+Y_{Q,n}^2<br><br>\left(i\right)\right]$ $\left(i=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},24\right)$

7. The device of claim 5, wherein the symbol energies (E_m, m=1,2, . . . , 6) consistent with the six spread codes generated through the maximum-value spread code deciding unit can be calculated in the following Equation:

$E_m=\underset{i=1}{\overset{24}{\sum <br><br>}}<br><br>Z_i<br><br>\left(m=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},6\right)$

8. The device of claim 1, wherein the N_NC2N_S tap I/Q channel symbol matched filter unit is comprised of a plurality (i) of N_NC2N_S tap I/Q channel symbol matched filters having the N_s-length tap and for receiving the plurality of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) from the I/Q channel symbol generating unit to respectively generate the result value (S_n,_k(i)) through a coherent summation(combining) of N_s number of symbols, and respectively performing the noncoherent combining to the result value (S_n,_k (i)) at N_NC2 times to generate an arbitrary result value (Xn(i)).

9. The device of claim 8, wherein the plurality (i) of N_NC2N_S tap I/Q channel symbol matched filters respectively comprises:

a reception symbol forming unit for receiving the n_th I/Q channel symbol (Y_I,_n(i), Y_Q,_n(i)), and eliminating a sign component stored in the N_s number of the taps by using a preamble symbol designated to the N_s-length tap, thereby forming the N_s number of reception symbols; and

an arithmetic processing unit for obtaining the coherent summation(combining) of the N_s number of reception symbols of the reception symbol forming unit, and multiplying the obtained coherent summation(combining) by an I/Q channel component and summing the multiplied result to output the result value (S_n,_k(i)), thereby eliminating an effect of a phase component.

10. The device of claim 9, wherein since the N_NC1, N_s, N_NC2 values are lengths of coherent summation(combining), they is selected as optimal values by performing a performance simulation depending on a channel environment in consideration of a frequency error, a probability of signal detection and a code acquisition time.

11. The device of claim 9, wherein the result value (S_n,_k(i)) of the arithmetic processing unit can be calculated in the following Equation:

$S_{n,k}<br><br>\left(i\right)={\left(\underset{m=1}{\overset{N_S}{\sum <br><br>}}<br><br>Y_{I,n-\mathrm{mk}}<br><br>\left(i\right)\right)}^2+{\left(\underset{m=1}{\overset{N_s}{\sum <br><br>}}<br><br>Y_{Q,n-\mathrm{mk}}<br><br>\left(i\right)\right)}^2,i=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>24,k=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},N_{\mathrm{NC2}}$

12. The device of claim 8, wherein each result value (X_n(i)) of the plurality of N_NC2N_S tap I/Q channel symbol matched filters can be calculated in the following Equation:

$X_n<br><br>\left(i\right)=\underset{k=1}{\overset{N_{\mathrm{NC2}}}{\sum <br><br>}}<br><br>\left[{\left(\underset{m=1}{\overset{N_S}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{I,n-\mathrm{mk}}<br><br>\left(i\right)\right)}^2+{\left(\underset{m=1}{\overset{N_s}{\sum <br><br>}}<br><br>Y_{Q,n-\mathrm{mk}}<br><br>\left(i\right)\right)}^2\right],i=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},24$

13. The device of claim 1, wherein the super frame and symbol boundary time deciding unit decides the super frame time (packet synchronization) in such a manner that a summation (Q_n) of the output values (X_n(i)) of the N_NC2N_S tap I/Q channel symbol matched filter unit is compared with and a threshold value (θ

_s) at an arbitrary n_th symbol time position so that if it is determined that the summation (Q_n) of the output values (X_n(i)) of the N_NC2N_S tap I/Q channel symbol matched filter unit exceeds the threshold value (θ

_s), it is determined that the super frame time (packet synchronization) is successfully acquired, to decide the n_th symbol time position as the super frame time (packet synchronization).

14. The device of claim 13, wherein the summation (Qn) of the output values (Xn(i)) of the N_NC2N_S tap I/Q channel symbol matched filter unit can be calculated at the arbitrarily n_th symbol time position in the following Equation:

$Q_n=\underset{i=1}{\overset{24}{\sum <br><br>}}<br><br>X_n<br><br>\left(i\right),n=0,1,2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\dots <br><br>}$

15. The device of claim 1, wherein the super frame and symbol boundary time deciding unit decides a symbol boundary time (firstly received path) in such a manner that the code phase consistent with a maximal one of the output values (X_n(i)) of the N_NC2N_S tap I/Q channel symbol matched filter unit is decided as the symbol boundary time (firstly received path).

16. A code acquisition method using a two-step search process in a Direct Sequence-Code Division Multiple Access (DS-CDMA) Ultra Wide Band (UWB) modem, the method comprising:

a step 10 of generating a plurality (i) of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) consistent with a plurality (i) of code phases for a multi-path reception signal (r(t)) by using six spread code sequences;

a step 20 of respectively combining the plurality of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) at N_NC1 times, and summing the combined result value (Z_i) at each of six spread codes to generate six symbol energies (E_m, m=1,2, . . . ,

     6) consistent with the six spread codes, and deciding the spread code having a maximal value among the six symbol energies (E_m, m=1,2, . . . ,

     6), as a spread code of a piconet coordinator;

a step 30 of generating a plurality (i) of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) consistent with a plurality (i) of code phases for the multi-path reception signal (r(t)) by using the spread code having the maximal value among the six spread codes;

a step 40 of respectively performing an arithmetic operation for the plurality of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) to generate the result value (S_n,_k(i)), and respectively performing the noncoherent combining to the result value (S_n,_k(i)) at N_NC2 times to generate an arbitrary result value (Xn(i)); and

a step 50 of deciding a super frame time (packet synchronization) and a symbol boundary time (firstly received path) by using the generated result value (Xn(i)) obtained through the step 40.

17. The method of claim 16, wherein in the step 20, the result value (Z_i) obtained by respectively combining the plurality of n_th I/Q channel symbols (Y_I,_n(i), Y_Q,_n(i)) at N_NC1 times can be calculated in the following Equation:

$\underset{n=1}{\overset{N_{\mathrm{nc1}}}{\sum <br><br>}}<br><br>\left[Y_{I,n}^2<br><br>\left(i\right)+Y_{Q,n}^2<br><br>\left(i\right)\right]$ $\left(i=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},24\right)$

18. The method of claim 16, wherein in the step 20, the symbol energies (E_m, m=1,2, . . . , 6) consistent with the six spread codes can be calculated in the following Equation:

$E_m=\underset{i=1}{\overset{24}{\sum <br><br>}}<br><br>Z_i<br><br>\left(m=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},6\right)$

19. The method of claim 16, wherein in the step 40, the result value (S_n,_k(i)) of the arithmetic operation can be calculated in the following Equation:

$S_{n,k}<br><br>\left(i\right)={\left(\underset{m=1}{\overset{N_S}{\sum <br><br>}}<br><br>Y_{I,n-\mathrm{mk}}<br><br>\left(i\right)\right)}^2+{\left(\underset{m=1}{\overset{N_s}{\sum <br><br>}}<br><br>Y_{Q,n-\mathrm{mk}}<br><br>\left(i\right)\right)}^2,i=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>24,k=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},N_{\mathrm{NC2}}$

20. The method of claim 16, wherein in the step 40, the result value (X_n(i)) of the noncoherent combining can be calculated in the following Equation:

$X_n<br><br>\left(i\right)=\underset{k=1}{\overset{N_{\mathrm{NC2}}}{\sum <br><br>}}<br><br>\left[{\left(\underset{m=1}{\overset{N_S}{\sum <br><br>}}<br><br>Y_{I,n-\mathrm{mk}}<br><br>\left(i\right)\right)}^2+{\left(\underset{m=1}{\overset{N_s}{\sum <br><br>}}<br><br>Y_{Q,n-\mathrm{mk}}<br><br>\left(i\right)\right)}^2\right],i=1,2,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},24$

21. The method of claim 16, wherein the step 50 comprises:

a step 51 of calculating a summation (Q_n) of the result values (X_n(i)) obtained through the step 40 at an arbitrary n_th symbol time position;

a step 52 of determining whether or not the summation (Q_n) of the result values (X_n(i)) exceeds a threshold value (θ

_s);

a step 53 of if it is determined in the step 52 that the summation (Q_n) of the result values (X_n(i)) exceeds the threshold value (θ

_s), it is determined that the super frame time (packet synchronization) is successfully acquired, to decide the n_th symbol time position as the super frame time (packet synchronization); and

a step 54 of deciding the code phase consistent with a maximal one of the output values (X_n(i)) at the symbol time position at which the super frame time is decided, as the symbol boundary time (firstly received path).

22. The method of claim 21, further comprising a step 55 of calculating a summation (Q_n) of the result values (X_n(i)) at a next symbol time position and returning to the step 52 if it is determined in the step 51 that the summation (Q_n) of the output values (X_n(i)) at the n_th symbol time position does not exceed the threshold value (θ

_s).

23. The method of claim 21, wherein the summation (Q_n) of the output values (X_n(i)) can be calculated at the n_th symbol time position in the following Equation:

$Q_n=\underset{i=1}{\overset{24}{\sum <br><br>}}<br><br>X_n<br><br>\left(i\right),n=0,1,2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\dots <br><br>}$