Device and method for cancelling code interference in a CDMA communication system

• US 6,459,693 B1
• Filed: 07/07/1999
• Issued: 10/01/2002
• Est. Priority Date: 07/07/1998
• Status: Expired due to Term

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Young-Ky, Ahn, Jae-Min, Park, Su-Won
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): Vuong, Quochien B.
• Application Number:
  US09/348,701
• Time in Patent Office: 1,182 Days
• Field of Search: 370/206, 370/208, 370/209, 370/320, 370/335, 370/342, 370/441, 375/142, 375/144, 375/148, 375/150, 455/67.1, 455/67.3, 455/226.1
• US Class Current: 370/342
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04J 13/004 Orthogonal
• CPC Class Codes: H04L 25/03178 Arrangements involving sequence estimation techniques
• CPC Class Codes: H04L 25/0328 with interference cancellation circuitry adaptations for interference cancellation within a sequence estimator H04L25/03305; interference related aspects of direct sequence spread spectrum H04B1/7097; interference related aspects of frequency hopping spread spectrum H04B1/715; see also H04B1/10
• CPC Class Codes: H04L 5/026 using code division
• CPC Class Codes: H04M 3/00 Automatic or semi-automatic exchanges

Abstract

A device and method for cancelling code interference in a receiver of a CDMA (Code Division Multiple Access) communication system simultaneously using orthogonal codes and quasi-orthogonal codes are provided. In a receiver according to an embodiment of the present invention, a channel estimator produces a channel estimation value of a pilot channel signal spread by an orthogonal code through despeading. A quasi-orthogonal channel receiver receives a channel signal spread by a quasi-orthogonal code, despreads the channel signal, demodulates the despread channel signal by use of the channel estimation value, and provides an output. An interference estimator estimates an interference value of the pilot channel signal with the channel signal spread by the quasi-orthogonal code by obtaining a correlation value between the orthogonal code corresponding to a pilot channel and the quasi-orthogonal code corresponding to a quasi-orthogonal channel. An interference canceller cancels the estimated interference from the output of the quasi-orthogonal channel receiver.

Claims

1. A receiver which simultaneously uses orthogonal codes and quasi-orthogonal codes in a CDMA (Code Division Multiple Access) communication system, said receiver comprising:

a channel estimator for producing a channel estimation value of a pilot channel signal spread by an orthogonal code through despeading;

a quasi-orthogonal channel receiver for receiving a channel signal spread by a quasi-orthogonal code, despreading the channel signal, demodulating the despread channel signal by use of the channel estimation value, and providing an output;

an interference estimator for estimating an interference value of the pilot channel signal with the channel signal spread by the quasi-orthogonal code by obtaining a correlation value between the orthogonal code corresponding to a pilot channel and the quasi-orthogonal code corresponding to a quasi-orthogonal channel; and

an interference canceller for cancelling the estimated interference from the output of the quasi-orthogonal channel receiver.

2. The receiver of claim 1, wherein the interference canceller comprises:

a complex conjugator for calculating a complex conjugate of an output of the channel estimator;

a first multiplier for multiplying the output of the channel estimator by the complex conjugate; and

a second multiplier for estimating the interference value of the pilot channel with the quasi-orthogonal channel by multiplying the correlation value by an output of the first multiplier.

3. The receiver of claim 1, wherein the interference canceller comprises:

a squarer for squaring an output of the channel estimator; and

a multiplier for estimating the interference value of the pilot channel with the quasi-orthogonal channel by multiplying the correlation value by an output of the squarer.

4. The receiver of claim 1, wherein the correlation value is calculated as follows:

$C_{i,j}^m=\underset{k=0}{\overset{L-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(W_{i,k}·<br><br>Q_{j,k}^m\right)=\underset{k=0}{\overset{L-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left[W_{i,k}·<br><br>\left(M_k^{m·<br><br>W_{j,k}}\right)\right]$

where i is a Walsh code used for the pilot channel, j is a basic orthogonal code used to generate a quasi-orthogonal code, m is a quasi-orthogonal code mask, and L is the length of the orthogonal code.

5. A receiver which simultaneously uses orthogonal codes and quasi-orthogonal codes in a CDMA (Code Division Multiple Access) communication system, said receiver comprising:

a PN (Pseudo Noise) despreader for PN-despreading a received signal;

a quasi-orthogonal channel receiver for despreading the PN-despread signal by a quasi-orthogonal code;

an interference estimator for estimating an interference value of an orthogonal code used to generate the quasi-orthogonal code with a quasi-orthogonal channel from the PN-despread signal; and

an interference canceller for cancelling the estimated interference value from an output of the quasi-orthogonal channel receiver.

6. The receiver of claim 5, wherein the interference estimator comprises:

a fast Hadamard transformer for detecting orthogonal code symbols which are not used and orthogonal code symbols which are used;

a decider for comparing an output of the fast Hadamard transformer with a predetermined value and removing the orthogonal code symbols which are not used; and

an operator for multiplying a vector of an output of the decider by a vector of a correlation value between the quasi-orthogonal code of the quasi-orthogonal channel and a corresponding orthogonal code to generate the estimated interference value of the orthogonal code with the quasi-orthogonal channel.

7. The receiver of claim 6, wherein the fast Hadamard transformer detects the orthogonal code symbols which are not used by the following equation:

$\left(d_0,d_1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},d_{L-1}\right)=\left({\mathrm{\gamma <br><br>}}_0,{\mathrm{\gamma <br><br>}}_1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\gamma <br><br>}}_{L-1}\right)<br><br>\text{\hspace{1em}<br><br>}\left[\begin{array}{cccc}{W}_{0,0}& W_{1,0}& \mathrm{\dots <br><br>}& W_{L-1,0}\\ W_{0,1}& W_{1,1}& \mathrm{\dots <br><br>}& W_{L-1,1}\\ \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}\\ W_{0,L-1}& W_{1,L-1}& \mathrm{\dots <br><br>}& W_{L-1,L-1}\end{array}\right]$

and the operator estimates the interference value by the following equation;

$\left(d_0,d_1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},d_{L-1}\right)<br><br>\text{\hspace{1em}<br><br>}\left[\begin{array}{c}-C_{0,a}^m\\ -C_{1,a}^m\\ \mathrm{⋮<br><br>}\\ -C_{L-1,a}^m\end{array}\right]=-\underset{i=0}{\overset{L-1}{\sum <br><br>}}<br><br>d<br><br>\text{\hspace{1em}<br><br>}<br><br>i·<br><br>C_{i,a}^m$

where m is a quasi-orthogonal code mask number, α

is a basic orthogonal code used to generate a quasi-orthogonal code, and L is the length of an orthogonal code.

8. The receiver of claim 6, wherein the interference canceller comprises:

a multiplier for multiplying an output of the operator by a complex conjugate of a pilot channel estimation value; and

an adder for removing an output of the multiplier from the quasi-orthogonal channel receiver.

9. A receiver which simultaneously uses orthogonal codes and quasi-orthogonal codes in a CDMA (Code Division Multiple Access) communication system, said receiver comprising:

a PN despreader for PN-despreading a received signal;

an orthogonal channel receiver for despreading the PN-despread signal by an orthogonal code;

an interference estimator for estimating an interference value of the quasi-orthogonal code with a basic orthogonal code used to generate the quasi-orthogonal code from the PN-despread signal; and

an interference canceller for cancelling the estimated interference value from an output of the orthogonal channel receiver.

10. The receiver of claim 9, wherein the interference estimator comprises:

a fast Hadamard transformer for distinguishing orthogonal code symbols which are not used and orthogonal code symbols which are used by operating on quasi-orthogonal code symbols of the PN-despread signal;

a decider for comparing an output of the fast Hadamard transformer with a predetermined value and removing the orthogonal code symbols which are not used; and

an operator for multiplying a vector of an output of the decider by a vector of a correlation value between the orthogonal code of the orthogonal channel and a corresponding quasi-orthogonal code to generate the estimated interference value of the quasi-orthogonal code.

11. The receiver of claim 10, wherein the fast Hadamard transformer detects the orthogonal code symbols which are not used by the following equation:

$\left(d_0^m,d_1^m,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},d_{L-1}^m\right)=\left({\mathrm{\gamma <br><br>}}_0,{\mathrm{\gamma <br><br>}}_1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\gamma <br><br>}}_{L-1}\right)<br><br>\text{\hspace{1em}<br><br>}\left[\begin{array}{cccc}{W}_{0,0}^m& W_{1,0}^m& \mathrm{\dots <br><br>}& W_{L-1,0}^m\\ W_{0,1}^m& W_{1,1}^m& \mathrm{\dots <br><br>}& W_{L-1,1}^m\\ \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}\\ W_{0,L-1}^m& W_{1,L-1}^m& \mathrm{\dots <br><br>}& W_{L-1,L-1}^m\end{array}\right]$

and the operator estimates the interference value by the following equation;

$\left(d_0^m,d_1^m,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},d_{L-1}^m\right)<br><br>\text{\hspace{1em}<br><br>}\left[\begin{array}{c}-C_{A,0}^m\\ -C_{A,1}^m\\ \mathrm{⋮<br><br>}\\ -C_{A,L-1}^m\end{array}\right]=-\underset{i=0}{\overset{L-1}{\sum <br><br>}}<br><br>d_i^m·<br><br>C_{A,i}^m$

where m is a quasi-orthogonal code mask number, A is an orthogonal code used in the orthogonal channel receiver, and L is the length of the orthogonal code.

12. The receiver of claim 10, wherein the interference canceller comprises:

a multiplier for multiplying an output of the operator by a complex conjugate of a pilot channel estimation value; and

an adder for removing an output of the multiplier from the orthogonal channel receiver.

13. A method of cancelling interference between codes in a receiver which simultaneously uses orthogonal codes and quasi-orthogonal codes in a CDMA communication system, comprising the steps of:

producing a channel estimation value of a pilot channel signal spread by an orthogonal code through despeading

receiving a channel signal spread by a quasi-orthogonal code, despreading the channel signal, and demodulating the despread channel signal by use of the channel estimation value;

estimating an interference value of the pilot channel signal with the channel signal spread by the quasi-orthogonal code by obtaining a correlation value between the orthogonal code corresponding to a pilot channel and the quasi-orthogonal code corresponding to a quasi-orthogonal channel; and

cancelling the estimated interference value from the demodulated quasi-orthogonal despread channel signal.

14. A method of cancelling interference between codes in a receiver which simultaneously uses orthogonal codes and quasi-orthogonal codes and receives a channel signal spread by a quasi-orthogonal code in a CDMA communication system, said method comprising the steps of:

distinguishing orthogonal code symbols which are not used and orthogonal code symbols which are used by means for fast-Hadamard-transforming orthogonal code symbols of a PN-despread signal;

comparing an output of the means for fast-Hadamard-transforming orthogonal code symbols with a predetermined value and removing the orthogonal code symbols which are not used;

multiplying a vector of a signal free of the orthogonal code symbols which are not used by a vector of a correlation value between a quasi-orthogonal code of a quasi-orthogonal channel signal and a corresponding orthogonal code and generating an estimated interference value of an orthogonal code with the quasi-orthogonal channel signal; and

removing the estimated interference value from the quasi-orthogonal channel signal.

15. A method of cancelling interference between codes in a receiver which simultaneously uses orthogonal codes and quasi-orthogonal codes and receives a channel signal spread by an orthogonal code in a CDMA communication system, said method comprising the steps of:

distinguishing orthogonal code symbols which are not used and orthogonal code symbols which are used by means for fast-Hadamard-transforming quasi-orthogonal code symbols of a PN-despread signal;

comparing an output of means for fast-Hadamard-transforming with a predetermined value and removing the orthogonal code symbols which are not used;

multiplying a vector of a signal free of the orthogonal code symbols which are not used by a vector of a correlation value between a orthogonal code of an orthogonal channel signal and a corresponding quasi-orthogonal code and generating an estimated interference value of a quasi-orthogonal code with the orthogonal channel signal; and

removing the estimated interference value from the orthogonal channel signal.