Device and method for synchronizing and channel estimation in a TDMA radio communication system

• US 5,373,507 A
• Filed: 01/12/1993
• Issued: 12/13/1994
• Est. Priority Date: 01/13/1992
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Skold, Johan
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US08/003,474
• Time in Patent Office: 700 Days
• Field of Search: 370/95.3, 370/105.1, 370/104.1, 370/105.4, 375/94, 375/95, 375/96, 375/114, 375/116
• US Class Current: 370/350
• CPC Class Codes: H04L 7/005 Correction by an elastic buffer
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15
• CPC Class Codes: H04L 7/08 the synchronisation signals recurring cyclically
• CPC Class Codes: H04W 56/0085 detecting a given structure in the signal

Abstract

A method of synchronizing a received signal frame in a TDMA radio system with a locally generated (TR) training sequence and of determining a channel estimate based on the comparison the received signal frame and the locally generated training sequence. A center of energy value is calculated for a first vector having M correlation values. A second vector having N consecutive correlation values distributed around the center of energy is chosen to form the channel estimate. The center of energy in the second vector can be chosen as synchronizing position.

Claims

1. A method of channel estimation in a TDMA radio communication system comprising the steps of:

calculating a center of energy value w of a first vector having M correlation values between a synchronization sequence and M parts of a signal frame, which are partially overlapping and mutually displaced one sampling interval, substantially in accordance with the formula ##EQU5## where c(k) designates a correlation value in position k in said first vector and M is an integer;

rounding the value w to a nearest integer to form a preliminary window center position m_w in said first vector; and

choosing N consecutive correlation values distributed around said preliminary window center position m_w to form a second vector of N correlation values for channel estimation where N is an integer.

2. The method of claim 1, wherein said first vector comprises 11 correlation values, that is M=11.

3. The method of claim 1, wherein said second vector comprises 5 correlation values, that is N=5.

4. The method of claim 1 wherein said calculating step further comprises the steps of:

receiving a radio signal and converting said radio signal into a complex input signal; and

correlating said complex input signal with a training sequence to generate correlation values.

5. The method of claim 4 wherein said correlation values are generated by a correlator and said training sequence is generated by a training sequence generator local to said correlator.

6. A method for channel estimation in a TDMA radio communication system comprising the steps of:

calculating a center of energy value w of a first vector having M correlation values between a synchronization sequence and M parts of a signal frame, which are partially overlapping and mutually displaced one sampling interval, substantially in accordance with the formula ##EQU6## where c(k) designates a correlation value in position k in said first vector and M is an integer;

rounding the value w to a nearest integer to form a preliminary window center position m_w in said first vector;

choosing 2L+1 partially overlapping vectors which are mutually time displaced one sampling interval, each comprising N consecutive correlation values distributed around said preliminary window center position m_w, where N=2K+1 and K, L, and N are integers; and

choosing a vector from the 2L+1 chosen vectors that has a largest energy content E_n, that is that vector that maximizes the expression ##EQU7## as a second vector of N correlation values for channel estimation where |c(j+m_w +n)|² designates a correlation value magnitude.

7. The method of claim 6, further comprising the step of choosing L in dependence of the current time dispersion.

8. The method of claim 7, further comprising the step of choosing L proportional to the delay spread s defined substantially in accordance with ##EQU8##

9. The method of claim 6, further comprising the step of providing a center position of said second vector in said first vector as a final synchronization position m.

10. The method of claim 6, further comprising the steps of:

calculating a center of energy x within said second vector substantially in accordance with the formula ##EQU9## where m_w +1 designates a center position of said second vector in said first vector;

adding the value of x to the center position m_w +1 of said second vector to produce a position value; and

providing the position value obtained in the previous step as a final synchronization position m.

11. The method of claim 6, wherein said first vector comprises 11 correlation values, that is M=11.

12. The method of claim 6, wherein said second vector comprises 5 correlation values, that is N=5.

13. A method for channel estimation in a TDMA radio communication system comprising the steps of:

calculating a center of energy value w of a first vector having M correlation values between a synchronization sequence and M parts of a signal frame, which are partially overlapping and mutually displaced one sampling interval, substantially in accordance with the formula ##EQU10## where c(k) designates a correlation value in position k in said first vector and M is an integer;

rounding the value w to a nearest integer to form a preliminary window center position m_w in said first vector;

choosing two partially overlapping vectors which are mutually time displaced one sampling interval, each comprising N consecutive correlation values surrounding said preliminary window center position m_w, where N=2K+1 and K and N are integers; and

choosing a vector from the two chosen vectors that has a largest energy content E_n, that is that vector that maximizes the expression ##EQU11## as a second vector of N correlation values for channel estimation where |c(j+m_w +n)|² designates a correlation value magnitude.

14. The method of claim 13, further comprising the step of providing a center position of said second vector in said first vector as a final synchronization position m.

15. The method of claim 13, further comprising the steps of:

calculating a center of energy x within said chosen second vector substantially in accordance with the formula ##EQU12## where m_w +1 designates a center position of said second vector in said first vector;

adding the value of x to the center position m_w +1 of said second vector to produce a position value; and

providing the position value obtained in the previous step as a final synchronization position m.

16. The method of claim 13, wherein said first vector comprises 11 correlation values, that is M=11.

17. The method of claim 13, wherein said second vector comprises 5 correlation values, that is N=5.

18. A method of determining a synchronization position m of a signal frame in a vector in a TDMA radio communication system, said vector comprising M correlation values between a synchronization sequence and M parts of said signal frame, which parts are partially overlapping and mutually time displaced one sampling interval, comprising the steps of:

calculating a center of energy w substantially in accordance with the formula ##EQU13## where c(k) designates a correlation value in position k in said vector and m is an integer, said calculated center of energy value w forming said synchronization position m.

19. A device in a TDMA radio communicating system for allowing determination of a synchronization position comprising:

means for correlating a training sequence with a complex input signal to provide correlation values and correlation value magnitudes;

a calculator having an input to receive said correlation value magnitudes and an output to provide a weighted average of said correlation value magnitudes;

a first summation unit having an input to receive said correlation value magnitudes and an output to provide a sum of the correlation value magnitudes;

a divider having a first input connected to receive said calculator output as a dividend and a second input connected to receive said first summation unit output as a divisor and an output to provide a quotient, said quotient being a center of energy value w;

means for rounding having an input connected to receive said divider output and an output to provide a value m_w, said value m_w being the center of energy value w rounded to a nearest integer;

a second summation unit having a first input connected to receive said correlation value magnitudes and a second input connected to receive said rounding means output and an output to provide an energy value for each of a plurality of windows distributed about position m_w and mutually displaced one sampling step;

means for detecting a maximum value having an input connected to receive said second summation unit output and an output to provide a window selected from said plurality of windows having a maximum energy value, said selected window having a center position m allowing for determination of said synchronization position.

20. The device of claim 19 wherein said center position m is said synchronization position.

21. The device of claim 19 further comprising means for selecting a subset of said correlation values that are substantially centered about said center position m to determine a channel estimate.

22. The device of claim 19 wherein the synchronization position is the center position m.

23. The device of claim 19 wherein the synchronization position is a center of energy position of said window selected from said plurality of windows.