Method and apparatus for performing DC-offset compensation in a radio receiver

• US 6,370,205 B1
• Filed: 07/02/1999
• Issued: 04/09/2002
• Est. Priority Date: 07/02/1999
• Status: Expired due to Fees

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Kullendorf, Nils, Lindoff, Bengt, Stenström, Sven Erik Niklas
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): TRAN, KHANH C
• Application Number:
  US09/347,020
• Time in Patent Office: 1,012 Days
• Field of Search: 375/319, 375/317, 375/340, 375/341, 375/342, 375/346, 375/350, 375/231, 375/232, 375/260, 375/262, 370/314, 370/336, 370/337, 370/345, 370/347, 370/350, 370/442, 370/529, 370/527, 370/498, 455/304, 455/305, 455/310, 455/311, 455/296, 329/320, 329/349, 329/353
• US Class Current: 375/319
• CPC Class Codes: H04L 25/0212 of impulse response
• CPC Class Codes: H04L 25/0242 using matrix methods
• CPC Class Codes: H04L 25/062 Setting decision thresholds using feedforward techniques only

Abstract

In order to increase accuracy of DC-offset compensation within radio receivers and to ensure that such compensation does not erode the dynamics of the decoders located within the receivers, the present invention separately performs mean value estimation and channel estimation. Additionally, a bias DC offset value caused by the use of a training sequence to perform mean value estimation can be corrected for in the channel estimator and equalizer.

Claims

1. A method for compensating for DC-offset in a receiver comprising the steps of:

receiving a transmitted signal burst at said receiver;

downconverting said signal burst into a set of baseband component values;

finding a known training sequence in the set of baseband component values;

estimating a DC-offset value using said known training sequence;

subtracting said DC-offset value from said from said set of baseband component values to obtain a second set of baseband component values;

performing channel estimation using said set of second baseband component values and outputting a channel model and a bias DC offset value, and

performing equalization of said second set of baseband component values using said second set of baseband signals, said estimated channel model and said bias DC offset value.

2. The method of claim 1, wherein said first set of baseband component values are digitized signals.

3. The method of claim 1, wherein said set of baseband component values are in-phase and quadrature components of said received signal.

4. The method of claim 1, wherein said known training sequence comprises L+N pilot values, and said DC offset value estimation is performed according to the following equation:

$\hat{m}=\frac{1}{N}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\tilde{y}}_{j;<br><br>\mathrm{TS}}$

where, {tilde over (y)}<sub>j;

TS</sub> is a j;

th vector of L+1 of the pilot symbols.

5. The method of claim 1, wherein said bias DC offset value is determined according to the following equation:

$R_{D<br><br>\text{\hspace{1em}<br><br>}<br><br>C}=\frac{1}{N}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>H^T<br><br>U_{j;<br><br>\mathrm{TS}}=H^T<br><br>{\stackrel{\_}{U}}_{\mathrm{TS}}$

where H is a channel model and U is a reference training sequence.

6. The method of claim 1, after said finding step, further comprising the step of:

determining the location of at least one DC step value within said received baseband signal.

7. The method of claim 6, wherein said determining step further comprises:

differentiating said baseband component values; and

determining whether said differentiated baseband component values exceed a predetermined threshold value.

8. The method of claim 6, wherein said subtracting step further comprises:

controlling the subtraction of said DC offset estimates from said received signal to ensure data synchronism between the estimated DC offset values and said set of baseband components.

9. The method of claim 6, wherein if said DC step occurs within a training sequence of said transmitted sequence, the estimating step is performed independently over a part of the received message affected by said DC step and over a part of the message not affected by the DC step.

10. The method of claim 6, wherein if said DC step does not occur over a training sequence of said received burst, said DC offset value estimation over the DC step is performed according to the following equation:

${\hat{m}}_2=\frac{1}{B-i_0+1}<br><br>\underset{k=i_0}{\overset{B}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\tilde{y}}_k$

where B is the amount of data and i₀ is the time of determined DC step.

11. An apparatus for compensating for DC-offset in a receiver comprising:

means for receiving a transmitted signal burst at said receiver;

means for downconverting said signal burst into a set of baseband component values;

means for locating a known training sequence in the set of baseband component values;

means for estimating a DC-offset value using said known training sequence;

means for subtracting said DC-offset value from said from said set of baseband component values to obtain a second set of baseband component values;

means for performing channel estimation using said set of second baseband component values and outputting a channel model and a bias DC offset value, and

means for performing equalization of said second set of baseband component values using said second set of baseband signals, said estimated channel model and said bias DC offset value.

12. The apparatus of claim 11, wherein said first set of baseband signal components are digital signals.

13. The apparatus of claim 11, wherein said set of baseband component values are in-phase and quadrature components of said received signal.

14. The apparatus of claim 11, wherein said known training sequence comprises L+N pilot values, and DC offset value estimation is performed according to the following equation:

$\hat{m}=\frac{1}{N}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\tilde{y}}_{j;<br><br>\mathrm{TS}}$

where, {tilde over (y)}<sub>j;

TS</sub> is a j;

th vector of L+1 of the pilot symbols.

15. The apparatus of claim 11, wherein said bias DC offset value is determined according to the following equation:

$R_{D<br><br>\text{\hspace{1em}<br><br>}<br><br>C}=\frac{1}{N}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>H^T<br><br>U_{j;<br><br>\mathrm{TS}}=H^T<br><br>{\stackrel{\_}{U}}_{\mathrm{TS}}$

where H is a channel model and U is a reference training sequence.

16. The apparatus of claim 11, further comprising:

means for determining the location of at least one DC step value within said received baseband signal.

17. The apparatus of claim 16, wherein said means for determining further comprises:

means for differentiating said baseband component values; and

means for determining whether said differentiated baseband component values exceed a predetermined threshold value.

18. The apparatus of claim 16, further comprising:

means for controlling the subtraction of said DC offset estimates from said received signal to ensure data synchronism between the estimated DC offset values and said set of baseband components.

19. The apparatus of claim 16, wherein if said DC step occurs within a training sequence of said transmitted sequence, the estimating step is performed independently over a part of the received message affected by DC step and over a part of the message not affected by the DC step.

20. The apparatus of claim 16, wherein if said DC step does not occur over a training sequence of said received burst, said DC offset value estimation over the DC step is performed according to the following equation:

${\hat{m}}_2=\frac{1}{B-i_0+1}<br><br>\underset{k=i_0}{\overset{B}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\tilde{y}}_k$

where B is the amount of data and i₀ is the time of determined DC step.