Method and arrangement for channel estimation in a wireless communication system
View Patent ↗A method and arrangement ( 100 ) for PRACH burst channel detection in a UTRA TDD wireless communication system in which training sequences are constructed from a single periodic base code. Unwanted cross-correlation peaks, having magnitude less than correlation peaks, are removed ( 440 ) from the correlator outputs, maintaining optimal signal-to-noise ratio of the channel estimates, providing a low probability of false detection, and extending the cell size of a CDMA network to that determined by the guard period duration. The cell size can be extended further by ensuring that no transmissions are scheduled for the timeslot subsequent to that in which the channel estimation bursts are scheduled.
1. A method for channel estimation in a receiver for receiving transmissions comprising channel information, the transmission from a plurality of wireless units, the method comprising:
estimating correlations between received channel information and a plurality of midamble sequences, each midamble sequence derived from a single periodic base code;
producing estimate signals for the correlations;
identifying peaks in the correlation estimate signals; and
removing identified peaks in the correlation estimate signals that correspond to cross-correlations for transmissions from wireless units other than a selected wireless unit.
2. The method of claim 1 wherein identifying includes identifying a cross-correlation peak by identifying a correlation peak with a smaller magnitude than another identified correlation peak.
3. The method of either claim 1 or claim 2 , wherein the wireless communication system is a UMTS system.
4. The method of claim 3 wherein the UMTS system is a UTRA TDD system.
5. The method of claim 4 wherein the transmissions comprise random access PRACH bursts.
6. The method of any one of claims 1 or 2 wherein the step of removing cross-correlation peaks comprises repeatedly removing cross-correlation peaks by identifying a next largest correlation peak remaining after removing of a previously identified correlation peak determined to be smaller than an another identified correlation peak.
7. The method of claim 6 wherein repeatedly removing is performed a predetermined number of times.
8. The method of claim wherein 6 repeatedly removing is performed until an identified next largest peak has a magnitude less than a predetermined value.
9. The method of any one of claims 1 - 2 further comprising ensuring that no transmission occurs in a timeslot immediately following a times lot for which the correlation estimates were obtained.
10. A receiver for receiving from a plurality of wireless communication units signals representative of channel information, the channel information comprising midamble sequences constructed from a single periodic base code, the receiver comprising:
a channel correlation estimator operable to receive the channel information and produce therefrom correlation channel estimate signals by correlating the channel information with midamble sequences constructed from a single periodic base code, each midamble sequence associated with a different one of the plurality of wireless communication units;
a correlation peak identifier coupled to the correlation channel estimator, and operable to identify correlation peaks from the correlation channel estimate signals; and
a cross-correlation peak remover coupled to the correlation channel estimator and the correlation peak identifier, and operable to remove from the correlation channel estimate signals identified cross-correlation peaks corresponding to midamble sequences of wireless communication units other than a desired wireless unit.
11. The receiver of claim 10 wherein the correlation peak identifier comprises cross-correlation peak identification means for identifying a cross-correlation peak as having a smaller magnitude than a correlation peak.
12. The receiver of claim 11 wherein the wireless communication system is a UMTS system.
13. The receiver of claim 12 wherein the UMTS system is a UTRA TDD system.
14. The receiver of claim 13 wherein the input signals comprise random access PRACH bursts.
15. An integrated circuit comprising the receiver of claim 10 .
16. A receiver according to claim 10 wherein the receiver is provided in a base station of a wireless communication system.
17. A computer readable medium comprising instructions for implementing a method in a receiver, the receiver for receiving, frow a plurality of wireless units, transmissions comprising channel information, the method comprising;
estimating correlations between received channel information and each of a plurality of midamble sequences, each midamble sequence derived from a single periodic base code;
identifying peaks in the correlations;
identifying one of the peaks as corresponding to a transmission from a selected wireless unit; and
removing an identified peak in correlations that corresponds to a correlation of the received channel information and a midamble sequence associated with another of the plurality of wireless units.