Method and apparatus for estimation of phase offset between communication channels

• US 7,149,258 B2
• Filed: 11/28/2001
• Issued: 12/12/2006
• Est. Priority Date: 11/28/2001
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Nilsson, Johan, Eriksson, Håkan
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US09/997,344
• Publication Number:
  US 20030099216A1
• Time in Patent Office: 1,840 Days
• Field of Search: 375/147, 375/316, 375/130, 375/148, 375/144, 370/335, 370/342, 370/441
• US Class Current: 375/316
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0212 of impulse response
• CPC Class Codes: H04L 25/0224 using sounding signals

Abstract

Methods and apparatus are described for estimating a phase offset between two channels in a communication system to allow the use of both in determining a complex channel estimate. The phase offset arises from the system'"'"'s rotation of only one of the two signaling channels prior to its transmission on one of the two antennas in transmission diversity mode. The phase offset is calculated in a receiver, such as a mobile station. For example, in a 3GPP system, the DPCH, which is rotated, and the CPICH, which is not, may be used in channel estimation.

Claims

1. A method of determining a phase offset between signaling channels in a communication system, comprising the steps of:

deriving a first set of channel estimates from symbols received through a first signaling channel;

deriving a second set of channel estimates from symbols received through a second signaling channel;

deriving first and second antenna phase estimates from the first and second sets of channel estimates, respectively; and

determining an estimate of the phase offset based on the set of first and second antenna phase estimates without using the first and second sets of channel estimates.

2. The method of claim 1, wherein the first and second signaling channels are pilot channels.

3. The method of claim 1, wherein the first and second signaling channels are a common pilot channel (CPICH) and a dedicated physical channel (DPCH), respectively.

4. A method of determining a set of complex channel estimates for a transmission channel in a communication system, comprising the steps of:

deriving a first set of channel estimates from symbols received through a first signaling channel;

deriving a second set of channel estimates from symbols received through a second signaling channel;

determining a phase offset value, φ

, between signaling channels in the communication system based on a set of first and second antenna phase estimates derived from the first and second sets of channel estimates, respectively; and

determining the set of complex channel estimates by compensating the first set of channel estimates based on the phase offset value.

5. The method of claim 4, wherein the phase offset value φ

is determined by choosing φ

among a set of predetermined feasible choices of φ

that minimizes the following expression;

$\mathrm{\phi <br><br>\epsilon <br><br>}<br><br>\left\{\begin{array}{c}\min \\ \mathrm{\pi <br><br>}/4,3<br><br>\mathrm{\pi <br><br>}/4,5<br><br>\mathrm{\pi <br><br>}/4,7<br><br>\mathrm{\pi <br><br>}/4\end{array}\right\}<br><br>\underset{i=1}{\stackrel{n}{\sum <br><br>}}<br><br>\frac{{\left({\widehat{\mathrm{\alpha <br><br>}}}_i-{\widehat{\mathrm{\beta <br><br>}}}_i+\mathrm{\phi <br><br>}\right)}^2}{{\mathrm{\sigma <br><br>}}_{\mathrm{ei}}^2}$

where;

i∈

[1, n] is a rake finger number of the receiver, and

{circumflex over (α

)}_i and {circumflex over (β

)}_i are the respective antenna phase estimates derived for rake finger i from the first and second sets of channel estimates, and

σ

_ei² is related to the power of interference.

6. The method of claim 5, wherein the complex channel estimate is determined by performing a linear combination of the first and second set of channel estimates.

7. The method of claim 4, wherein the first and second signaling channels are a common pilot channel (CPICH) and a dedicated physical channel (DPCH), respectively.

8. A channel estimator adapted to operate with a receiver in a communication system and to determine a set of complex channel estimates for a transmission channel of the communication system, the channel estimator comprising:

means that derive a first set of channel estimates from symbols received through a first signaling channel;

means that derive a second set of channel estimates from symbols received through a second signaling channel;

means that determine a phase offset value, φ

, between signaling channels in the communication system based on a set of first and second antenna phase estimates derived from the first and second sets of channel estimates, respectively; and

means that determine the set of complex channel estimates by compensating the first set of channel estimates based on the phase offset value.

9. The channel estimator of claim 8, wherein the means that determine a phase offset value comprise:

means that de-rotate the symbols received through the first and second signaling channels;

means that filter the de-rotated symbols;

means that convert the filtered de-rotated symbols to polar representations;

means that calculate the phase offset value according to the polar representations.

10. The channel estimator of claim 9, wherein the phase offset value φ

is calculated by choosing φ

among a set of predetermined feasible choices of φ

that minimizes the following expression;

$\mathrm{\phi <br><br>\epsilon <br><br>}<br><br>\left\{\begin{array}{c}\min \\ \mathrm{\pi <br><br>}/4,3<br><br>\mathrm{\pi <br><br>}/4,5<br><br>\mathrm{\pi <br><br>}/4,7<br><br>\mathrm{\pi <br><br>}/4\end{array}\right\}<br><br>\underset{i=1}{\stackrel{n}{\sum <br><br>}}<br><br>\frac{{\left({\widehat{\mathrm{\alpha <br><br>}}}_i-{\widehat{\mathrm{\beta <br><br>}}}_i+\mathrm{\phi <br><br>}\right)}^2}{{\mathrm{\sigma <br><br>}}_{\mathrm{ei}}^2}$

where;

i∈

[1, n] is a rake finger number of the receiver, and

{circumflex over (α

)}_i and {circumflex over (β

)}_i are the respective first and second antenna phase estimates derived for rake finger i from the first and second sets of channel estimates, and

σ

_ei² is related to the power of interference.

11. The channel estimator of claim 8, wherein the set of complex channel estimates is determined by performing a linear combination of the first and second set of channel estimates.

12. The channel estimator of claim 8, wherein the receiver is a RAKE receiver.

13. The channel estimator of claim 8, wherein the receiver operates in a cellular communication system.

14. The channel estimator of claim 8, wherein the first and second signaling channels are received by the receiver after transmission using transmit diversity.

15. The channel estimator of claim 8, wherein the first and second signaling channels are a common pilot channel (CPICH) and a dedicated physical channel (DPCH), respectively.

16. User equipment for a communication system, the user equipment adapted to determine a set of complex channel estimates for a transmission channel of the communication system, the user equipment comprising:

means that derive a first set of channel estimates from symbols received through a first signaling channel;

means that derive a second set of channel estimates from symbols received through a second signaling channel;

means that determine a phase offset value, φ

, between signaling channels in the communication system based on a set of first and second antenna phase estimates derived from the first and second sets of channel estimates, respectively; and

means that determine the set of complex channel estimates by compensating the first set of channel estimates based on the phase offset value.

17. The user equipment of claim 16, wherein the means that determine a phase offset value comprise:

means that de-rotate the symbols received through the first and second signaling channels;

means that filter the de-rotated symbols;

means that convert the filtered de-rotated symbols to polar representations;

means that calculate the phase offset value according to the polar representations.

18. The user equipment of claim 16, wherein the phase offset value φ

is calculated by choosing φ

among a set of predetermined feasible choices of φ

that minimizes the following expression;

$\mathrm{\phi <br><br>\epsilon <br><br>}<br><br>\left\{\begin{array}{c}\min \\ \mathrm{\pi <br><br>}/4,3<br><br>\mathrm{\pi <br><br>}/4,5<br><br>\mathrm{\pi <br><br>}/4,7<br><br>\mathrm{\pi <br><br>}/4\end{array}\right\}<br><br>\underset{i=1}{\stackrel{n}{\sum <br><br>}}<br><br>\frac{{\left({\widehat{\mathrm{\alpha <br><br>}}}_i-{\widehat{\mathrm{\beta <br><br>}}}_i+\mathrm{\phi <br><br>}\right)}^2}{{\mathrm{\sigma <br><br>}}_{\mathrm{ei}}^2}$

where;

i∈

[1, n] is a rake finger number of the receiver, and

{circumflex over (α

)}_i and {circumflex over (β

)}_i are the respective first and second antenna phase estimates derived for rake finger i from the first and second sets of channel estimates, and

σ

_ei² is related to the power of interference.

19. The user equipment of claim 16, wherein the set of complex channel estimates is determined by performing a linear combination of the first and second set of channel estimates.

20. The user equipment of claim 16, wherein the first and second signaling channels are a common pilot channel (CPICH) and a dedicated physical channel (DPCH), respectively.

21. A method of determining a phase offset between signaling channels in a communication system, comprising the steps of:

deriving a first set of channel estimates from symbols received through a first signaling channel;

deriving a second set of channel estimates from symbols received through a second signaling channel; and

determining an estimate of the phase offset based on a set of first and second antenna phase estimates derived from the first and second sets of channel estimates, respectively,

wherein the estimate of the phase offset is determined by choosing a phase offset value, φ

, among a set of predetermined feasible choices of φ

that minimizes the following expression;

$\mathrm{\phi <br><br>\epsilon <br><br>}<br><br>\left\{\begin{array}{c}\min \\ \mathrm{\pi <br><br>}/4,3<br><br>\mathrm{\pi <br><br>}/4,5<br><br>\mathrm{\pi <br><br>}/4,7<br><br>\mathrm{\pi <br><br>}/4\end{array}\right\}<br><br>\underset{i=1}{\stackrel{n}{\sum <br><br>}}<br><br>\frac{{\left({\widehat{\mathrm{\alpha <br><br>}}}_i-{\widehat{\mathrm{\beta <br><br>}}}_i+\mathrm{\phi <br><br>}\right)}^2}{{\mathrm{\sigma <br><br>}}_{\mathrm{ei}}^2}$

where;

i∈

[1, n] is a rake finger number of the receiver, and

{circumflex over (α

)}hd i and {circumflex over (β

)}_i are the respective first and second antenna phase estimates derived for rake finger i from the first and second sets of channel estimates, and

σ

_ei² is related to the power of interference.