Apparatus and method for detecting ranging signal in an orthogonal frequency division multiple access mobile communication system

• US 20060098749A1
• Filed: 10/12/2005
• Published: 05/11/2006
• Est. Priority Date: 10/12/2004
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Sung, Sang-Hoon, Hwang, In-Seok, Yoon, Soon-Young, Cho, Jae-Hee, Chang, Chung-Ryul, Huh, Hoon
• Granted Patent: US 7,564,909 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

An apparatus and method for receiving a ranging signal in an OFDMA mobile communication system are provided. The ranging signal receiving apparatus including, a ranging subchannel extractor for extracting subcarrier values with a ranging signal from a (FFT) signal; a plurality of multipliers for code-demodulating the sub-carrier values by multiplying them by a plurality of ranging codes; each of a plurality of correlators for calculating a plurality of differential correlations in a code-demodulated signal received from a corresponding multiplier; each of a plurality of inverse fast Fourier transform (IFFT) processors for IFFT-processing differential correlations received from a corresponding correlator by mapping the differential correlations to predetermined subcarriers and each of a plurality of maximum value detectors for detecting a maximum value in an IFFT signal received from a corresponding IFFT processor and calculating a timing offset using an IFFT output index having the maximum value.

Claims

1. A base station apparatus in a broadband mobile communication system, comprising:

a ranging subchannel extractor for extracting subcarrier values with a ranging signal from a fast Fourier transform (FFT) signal;

a plurality of multipliers for code-demodulating the subcarrier values by multiplying the subcarrier values by a plurality of ranging codes;

a plurality of correlators, each for calculating a plurality of differential correlations in a code-demodulated signal received from a corresponding multiplier;

a plurality of inverse fast Fourier transform (IFFT) processors, each for IFFT-processing differential correlations received from a corresponding correlator by mapping the differential correlations to predetermined subcarriers; and

a plurality of maximum value detectors, each for detecting a maximum value in an IFFT signal received from a corresponding IFFT processor and calculating a timing offset using an IFFT output index having the maximum value.

2. The base station apparatus of claim 1, wherein each of the correlators groups a code-demodulated signal received from a corresponding multiplier according to predetermined subbands, calculates differential correlations between two subcarriers spaced apart by k (where k is an index defined by 1≦

k≦

k_max) over all cases, produces k^th-order differential correlations by summing the differential correlations across the ranging bands, complex-conjugates the k^th-order differential correlations and outputs 2×

k_max correlations to a corresponding IFFT processor.

3. The base station apparatus of claim 1, further comprising a plurality of peak-to-average power ratio (PAPR) comparators, each for verifying a timing offset calculated by a corresponding maximum value detector by calculating the PAPR of an IFFT signal received from a corresponding IFFT processor and comparing the PAPR with a predetermined threshold.

4. The base station apparatus of claim 1, wherein each of the correlators calculate 2×

k_max differential correlations (Z_k) by

$Z_k=\{\begin{array}{cc}\underset{l=0}{\overset{5}{\sum <br><br>}}<br><br>\underset{n=0}{\overset{23-k}{\sum <br><br>}}<br><br>\left(Y_{l,n}<br><br>C_{l,n}\right)<br><br>{\left(Y_{l,m+k}<br><br>C_{l,n+k}\right)}^{*},& l\le <br><br>k\le <br><br>k_{\max }\\ Z_{J-k}^{*},& J-k_{\max }\le <br><br>k<<br><br>J\end{array}<br><br><br><br>\mathrm{where},<br><br>Z_k<br><br>\text{;<br><br>}<br><br>J<br><br>\text{-}<br><br>\mathrm{point}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{IFFT}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{complex}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{input}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{value}<br><br><br><br>k<br><br>\text{;<br><br>}<br><br>J<br><br>\text{-}<br><br>\mathrm{point}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{IFFT}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{input}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{index},0\le <br><br>k<<br><br>J<br><br>\text{-}<br><br>\mathrm{point}$

and wherein k is an input index of a J-point IFFT processor, L+1 is a number of subbands, N+1 is a number of subcarriers per subband, Y_1,n is a received signal response of an n^th subcarrier in an 1^th subband, C_1,n is a ranging code bit allocated to the n^th subcarrier in the 1^th subband, and k_max=N.

5. The base station apparatus of claim 1, wherein zeroes are padded at IFFT processor inputs to which the differential correlations are not mapped.

6. The base station apparatus of claim 1, wherein the maximum value detectors calculate the timing offset (Δ

t_offset) by

$n={\mathrm{argmax}}_{0\le <br><br>n\le <br><br>J-1}<br><br>\left\{{<br><br>z_n<br><br>}^2\right\}$ $\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t_{\mathrm{offset}}=\{\begin{array}{cc}\mathrm{DR}\times <br><br>n,& \mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>n\le <br><br>\frac{j}{2}\\ \mathrm{DR}\times <br><br>n-N_{\mathrm{FFT}},& \mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>n><br><br>\frac{j}{2}\end{array}$

wherein z_n is an IFFT signal and DR (Decimation Ratio) is equal to N_FFT/J (where J is an input index and N_FFT is an FFT size), each of

7. The base station apparatus of claim 1, wherein the IFFT signals output from the IFFT processors are defined by a sin c function.

8. A receiving method in a base station in a broadband mobile communication system, comprising the steps of:

extracting subcarrier values with a ranging signal from a fast Fourier transform (FFT) signal;

code-demodulating the sub-carrier values by multiplying the subcarrier values by a plurality of ranging codes and forming code-demodulated signals;

calculating a plurality of differential correlations in each of the code-demodulated signals;

inverse fast Fourier transform (IFFT)-processing the differential correlations for each of the plurality of ranging codes by mapping the differential correlations to predetermined subcarriers and outputting IFFT signals; and

detecting a maximum value in each of the IFFT signals and calculating a timing offset using an IFFT output index having the maximum value.

9. The receiving method of claim 8, wherein the differential correlation calculation step comprises:

grouping each of the code-demodulated signals according to predetermined subbands, calculating differential correlations between two subcarriers spaced apart by k (where 1≦

k≦

k_max) over all cases, forming k^th-order differential correlations by summing the differential correlations across the ranging bands,

and obtaining 2×

k_max correlations by complex-conjugating the k^th-order differential correlations.

10. The receiving method of claim 8, further comprising verifying the reliability of each timing offset by calculating a peak-to-average power ratio (PAPR) of each of the IFFT signals and comparing the PAPR with a predetermined threshold.

11. The receiving method of claim 8, wherein 2×

k_max differential correlations (Z_k) are calculated by

$Z_k=\{\begin{array}{cc}\underset{l=0}{\overset{L}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\underset{n=0}{\overset{N-k}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(Y_{l,n}<br><br>C_{l,n}\right)<br><br>{\left(Y_{l,m+k}<br><br>C_{l,n+k}\right)}^{*},& 1\le <br><br>k\le <br><br>k_{\max }\\ Z_{J-k}^{*},& J-k_{\max }\le <br><br>k<<br><br>J\end{array}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{where},<br><br>Z_k<br><br>\text{;<br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>J<br><br>\text{-}<br><br>\mathrm{point}<br><br>\text{ <br><br> <br><br>}<br><br>\mathrm{IFFT}<br><br>\text{\hspace{1em}<br><br>}<br><br>\text{complex <br><br> <br><br>input <br><br> <br><br>value}<br><br><br><br>k<br><br>\text{;<br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>J<br><br>\text{-}<br><br>\mathrm{point}<br><br>\text{ <br><br> <br><br>}<br><br>\mathrm{IFFT}<br><br>\text{\hspace{1em}<br><br>}<br><br>\text{input <br><br> <br><br>index},0\le <br><br>k<<br><br>J<br><br>\text{-}<br><br>\mathrm{point}$

and wherein k is an input index of a J-point IFFT, L+1 is a number of subbands, N+1 is a number of subcarriers per subband, Y_1,n is a received signal response of an n^th subcarrier in an 1^th subband, C_1,n is a ranging code bit allocated to the n^th subcarrier in the 1^th subband and k_max=N,

12. The receiving method of claim 8, further comprising the step of padding zeroes at IFFT inputs to which the differential correlations are not mapped.

13. The receiving method of claim 8, wherein the timing offset (Δ

t_offset) is calculated by

$n=\arg <br><br>\text{\hspace{1em}<br><br>}<br><br>{\max }_{0\le <br><br>n\le <br><br>J-1}<br><br>\left\{{<br><br>z_n<br><br>}^2\right\}$ $\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t_{\mathrm{offset}}=\{\begin{array}{c}\mathrm{DR}\times <br><br>n,\mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>n\le <br><br>\frac{j}{2}\\ \mathrm{DR}\times <br><br>n-N_{\mathrm{FFT}},\mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br>n><br><br>\frac{j}{2}\end{array}$

wherein z_n is an IFFT signal and DR (Decimation Ratio) is equal to N_FFT/J (where J is an input index and N_FFT is an FFT size).

14. The receiving method of claim 8, wherein the IFFT signals are a sin c function.

15. An apparatus for estimating a timing offset in a broadband mobile communication system, comprising:

a channel extractor for extracting subcarrier values of a predetermined channel from a fast Fourier transform (FFT) signal;

a correlator for calculating a plurality of differential correlations from the subcarrier values;

an inverse fast Fourier transform (IFFT) processor for IFFT-processing the differential correlations by mapping the differential subcarriers to predetermined subcarriers and outputting an IFFT signal; and

a maximum value detector for detecting a maximum value from the IFFT signal and estimating a timing offset using an IFFT output index having the maximum value.

16. The apparatus of claim 15, wherein the predetermined channel is a ranging channel.

17. The apparatus of claim 15, wherein for the input of the subcarrier values, the correlator calculates differential correlations between two subcarriers spaced by k (where k≧

1) over all cases, produces k^th-order differential correlations by summing the differential correlations, complex-conjugates the k^th-order differential correlations and outputs the k^th-order differential correlations and the complex conjugates.

18. The apparatus of claim 15, further comprising a peak-to-average power ratio (PAPR) comparator for verifying the reliability of the timing offset by calculating the PAPR of the IFFT signal and comparing the PAPR with a predetermined threshold.

19. The apparatus of claim 15, wherein zeroes are padded at subcarriers to which the differential correlations are not mapped.

20. A method of estimating a timing offset in a broadband mobile communication system, comprising the steps of:

extracting subcarrier values of a predetermined channel from a fast Fourier transform (FFT) signal;

calculating a plurality of differential correlations from the subcarrier values;

inverse fast Fourier transform (IFFT)-processing the differential correlations by mapping differential subcarriers to predetermined subcarriers and outputting an IFFT signal; and

detecting a maximum value from the IFFT signal and estimating a timing offset using an IFFT output index having the maximum value.

21. The method of claim 20, wherein the predetermined channel is a ranging channel.

22. The method of claim 20, wherein the differential correlation calculation step comprises calculating differential correlations between two subcarriers spaced by k (where k≧

1) over all cases, and producing k^th-order differential correlations by summing the differential correlations.

23. The method of claim 20, further comprising the step of verifying the reliability of the timing offset by calculating a peak-to-average power ratio (PAPR) for IFFT signal and comparing the PAPR with a predetermined threshold.

24. The method of claim 20, further comprising the step of padding zeroes at subcarriers to which the differential correlations are not mapped.