Method for cell initial search in a CDMA mobile communication system

• US 6,778,588 B2
• Filed: 09/25/2002
• Issued: 08/17/2004
• Est. Priority Date: 03/27/2000
• Status: Expired due to Term

• Current Assignee: Datang Mobile Communications Equipment Company Limited (China Information Communication Technology Group Co. Ltd.)
• Original Assignee: China Academy of Telecom Technology (China Information Communication Technology Group Co. Ltd.)
• Inventors: Xu, Tiezhu, Li, Feng, He, Yusong, Ran, Xiaolong
• Primary Examiner(s): Tran, Khai
• Application Number:
  US10/255,334
• Publication Number:
  US 20030031238A1
• Time in Patent Office: 692 Days
• Field of Search: 375/130, 375/142, 375/145, 375/147, 375/149, 375/150, 375/326, 455/422, 455/456, 455/12.1, 455/67.4, 370/342, 370/331, 370/320, 370/335
• US Class Current: 375/130
• CPC Class Codes: H04B 1/70758 Multimode search, i.e. using multiple search strategies
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 1/7083 Cell search, e.g. using a three-step approach
• CPC Class Codes: H04W 52/32 TPC of broadcast or control channels
• CPC Class Codes: H04W 52/50 at the moment of starting communication in a multiple access environment
• CPC Class Codes: H04W 56/00 Synchronisation arrangements

Abstract

The invention relates to a cell initial search method for user equipment (UE) in a CDMA digital cellular mobile communication system. The method includes: a UE after selecting a working frequency point, obtains downlink synchronization with the base station; and corrects carrier deviation between the UE and the base station. The downlink synchronization includes: deciding a range of downlink training sequence timeslot (DwPTS) based on training sequence power characteristic window value method; solving correlation of received data and training sequence in the range to obtain accurate receiving position of a UE. The correction of carrier deviation between a UE and the base station includes: estimating carrier deviation between a UE and the base station by software, recovering carrier frequency difference by using decision and feedback method to adjust hardware and carrier deviation correction method based on joint detection to correct carrier deviation.

Claims

1. A cell initial search method for a CDMA digital mobile communication system so that user equipment correctly receives information sent by a base station, comprising:

selecting a working frequency point by the user equipment; and

obtaining downlink synchronization with the base station at the working frequency point by;

(a) deciding a range of downlink training sequence timeslots by using a power characteristic window value method based on a training sequence; and

(b) obtaining accurate receiving position for the user equipment by calculating a correlation of received data and training sequences in the range.

2. The method according to claim 1, wherein the power characteristic window value method based on a training sequence comprises:

(a) increasing transmitting power of synchronization symbols in a downlink pilot sequence timeslot (DwPTS) of a base station data frame and making no transmitting power on protected symbols located before and after the synchronization symbols in the DwPTS; and

(b) searching power characteristic window values of the DwPTS first by user equipment, during receiving, to discover a position range of the synchronization symbols and after having discovered the position range of the synchronization symbols, making the correlation calculation only near the position.

3. The method according to claim 2, wherein searching power characteristic window values of the DwPTS to discover a position range of the synchronization symbols comprises:

locking in a working frequency point by the user equipment first, and receiving a data frame;

calculating each synchronization symbol power in the DwPTS;

calculating power characteristic window values at each synchronization symbol position;

calculating an average power characteristic window value over the complete data frame;

searching for a minimum value for the power characteristic window values at all synchronization symbols'"'"' position of the receiving data frame;

comparing a ratio of average power characteristic window value to the minimum power characteristic window value to a threshold value;

if the ratio of average power characteristic window value to the minimum power characteristic window value is greater than a threshold value, then the position of the minimum power characteristic window value becomes a beginning position for the DwPTS; and

solving the correlation calculation near the beginning position to obtain an accurate receiving beginning point and ending downlink synchronization.

4. The method according to claim 3, wherein calculating each synchronization symbol'"'"'s power comprises:

selecting as a beginning point the beginning of a synchronization symbol as received at the receiving moment, adding powers of all chips belonging to the synchronization symbol, and getting the power of the synchronization symbol.

5. The method according to claim 3, wherein calculating power characteristic window values at each synchronization symbol position comprises:

sliding with a symbol level on the receiving data frame, and calculating each position power characteristic window value R(i) at each position with the following formula;

$R_i=\left(\underset{k=i}{\overset{i+N-1}{\sum <br><br>}}<br><br>P<br><br>\left(k\right)+\underset{k=i+N+M}{\overset{i+2<br><br>N+M-1}{\sum <br><br>}}<br><br>P<br><br>\left(k\right)\right)/\underset{k=i+N}{\overset{i+N+M-1}{\sum <br><br>}}<br><br>P<br><br>\left(k\right),$

wherein i represents a real receiving position, P(k) represents power value of each synchronization symbol, N and M are characteristic window parameters.

6. The method according to claim 3, wherein calculating power characteristic window values at each synchronization symbol position comprises:

sliding with a chip level based on each chip'"'"'s power, and calculating the power characteristic window value at each position.

7. A cell initial search method for a CDMA digital mobile communication system so that user equipment correctly receives information sent by a base station, comprising:

tracing carrier deviation between the user equipment and the base station by the user equipment; and

correcting the carrier deviation in a digital demodulator of the user equipment by;

(a) estimating the carrier deviation by software, and adjusting the digital demodulator'"'"'s hardware by using a decision and feedback method; and

(b) suppressing multipath and multiple access interference and correcting the carrier deviation to a range required by baseband demodulation by using a carrier deviation correction method based on joint detection.

8. The method according to claim 7, further comprising:

estimating the carrier deviation of each data frame by software;

calculating an adjustment value for the digital demodulator'"'"'s hardware; and

adjusting automatic frequency control (AFC) hardware in the digital demodulator with the calculated adjustment value.

9. The method according to claim 8, wherein the carrier deviation of each data frame is estimated by a formula comprising:

$A<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{<br><br>}}^{-j<br><br>\text{\hspace{1em}<br><br>}<br><br>k<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}}<br><br>\frac{1}{L}<br><br>\underset{L}{\sum <br><br>}<br><br>{{\left[I<br><br>\left(i\right)+j<br><br>\text{\hspace{1em}<br><br>}<br><br>Q<br><br>\left(i\right)\right]}^{*}<br><br>\left[I<br><br>\left(i+K\right)+j<br><br>\text{\hspace{1em}<br><br>}<br><br>Q<br><br>\left(i+K\right)\right]}^{*},$

wherein α

represents the estimated frequency deviation, I and Q are orthogonal demodulation signals, and L is a statistic length.

10. The method according to claim 8, wherein an adjustment value for the automatic frequency control hardware is calculated by a formula comprising:

11. The method according to claim 7, wherein suppressing multipath and multiple access interference and correcting the carrier deviation to a range required by baseband demodulation by using a carrier deviation correction method based on joint detection further comprises:

inserting a training sequence midamble of data burst into each data frame for estimating real channel response;

suppressing multipath and multiple access interference with joint detection technology by the user equipment, and demodulating symbols near the training sequence midamble; and

adjusting automatic frequency control hardware with the carrier deviation information included in these symbols.

12. The method according to claim 11, wherein suppressing multipath and multiple access interference with joint detection technology and demodulating symbols near the training sequence midamble comprises:

demodulating receiving data with joint detection technology, and getting P characters before and after the training sequence midamble, and recorded as X(1) . . . X(P) and Y(1) . . . Y(P), respectively;

calculating Xi(n)=X(n)/Xj(n) , Yi(n)=Y(n)/Yj(n) , respectively, wherein Xj(n)=Yj(n)=±

π

/4 or ±

3π

/4;

getting carrier deviation direction by the formula;

$Z=\underset{n=1}{\overset{P}{\sum <br><br>}}<br><br>Y<br><br>\text{\hspace{1em}<br><br>}<br><br>i<br><br>\left(n\right)/X<br><br>\text{\hspace{1em}<br><br>}<br><br>i<br><br>\left(n\right);<br><br>$

setting an adjustment step length of automatic frequency control hardware based on the calculated carrier frequency deviation direction; and

adjusting automatic frequency control hardware with the adjustment step length according to the carrier frequency deviation direction.

13. A cell initial search method for a CDMA digital mobile communication system, comprising:

selecting a working frequency point by an user equipment and obtaining downlink synchronization with a base station at the working frequency point; and

tracing carrier deviation between the user equipment and the base station by the user equipment, and correcting the carrier deviation in a digital demodulator;

wherein obtaining downlink synchronization with a base station comprises;

(a) deciding a range of downlink training sequence timeslot first by using a power characteristic window value method based on a training sequence;

(b) obtaining an accurate receiving position of the user equipment by calculating correlation of data received and the training sequence in the range; and

(c) correcting the carrier deviation in a digital demodulator by;

(i) estimating the carrier deviation by software, and adjusting the digital demodulator'"'"'s hardware by using a decision and feedback method; and

(ii) suppressing multipath and multiple access interference by using a carrier deviation correction method based on joint detection, and correcting the carrier deviation to a range required by baseband demodulation.

14. A cell initial search method for a CDMA digital mobile communication systems comprising:

searching a rough position range of DwPTS by using a power characteristic window value method and defining a working frequency point;

searching accurate receiving position by solving a correlation calculation method in the position range defined and obtaining downlink synchronization; and

recovering carrier deviation by using a carrier deviation correction method based on joint detection.

15. The method according to claim 14, wherein searching a rough position range of DwPTS by using a power characteristic window value method comprises:

locking in a working frequency point first by a user equipment and receiving a complete data frame;

calculating each symbol power P;

calculating power characteristic window values at each symbol position;

calculating average power characteristic window value;

searching for a minimum value of all power characteristic window values;

calculating a ratio of average power characteristic window value and minimum power characteristic window value; and

deciding whether the ratio is greater than a threshold value and, if it is, then the position of the minimum power characteristic window value being the starting position of DwPTS.

16. The method according to claim 15, wherein calculating each symbol power P further comprises:

assuming the receiving moment is a symbol beginning point, and then adding the power of all chips belonging to the symbol, resulting in the power of the symbol.

17. The method according to claim 14, wherein recovering carrier deviation by using a carrier deviation correction method based on joint detection comprises:

(a) setting a frame number n=0, receiving a data frame;

(b) estimating carrier frequency deviation of the data frame by software;

(c) calculating an adjustment value of carrier frequency deviation, i.e. calculating a hardware adjustment value;

(d) adjusting automatic frequency control hardware according to the calculated hardware adjustment value, incrementing the frame number n=n+1, deciding whether n is greater than a preset number of adjustment frames Q, if n is greater than Q then ending, otherwise receiving the next data frame, estimating the carrier frequency deviation of the data frame by software, and adjusting the automatic frequency control hardware according to the calculated hardware adjustment value and incrementing the frame number n=n+1 until n is greater than Q.

18. The method according to claim 17, wherein recovering carrier deviation by using a carrier deviation correction method based on joint detection further comprises the steps of:

(e) receiving m data frames;

(f) demodulating the m data frames received with joint detection technology, i.e. demodulating data symbols near a training sequence midamble and getting P symbols before and after the training sequence midamble, respectively;

(g) calculating carrier frequency deviation direction on the P symbols before and after the training sequence midamble of m data frames, respectively;

(h) setting an adjustment step length for automatic frequency control hardware, according to the calculated carrier frequency deviation direction; and

(i) adjusting automatic frequency control hardware with the adjustment step length, according to the frequency carrier deviation direction obtained.

19. The method according to claim 18, further comprising repeating steps (e) to (i).