Cellular receiver and reception method
The invention relates to a reception method and a receiver in a system comprising in each cell a base station communicating with terminals located in its area. A received signal comprises a sum signal of signals originating from several transmitters. The receiver comprises means for performing interference elimination and a simultaneous multi-user detection to the signal and means for searching signal parameters. In order to reduce the required computational capacity, the receiver further comprises means for removing the effect of the signals of the known users from the receives sum signal, and means for estimating the parameters of the unknown signals from a narrowband residual signal.
1. A reception method in a cellular radio system including in each cell, at least one base station communicating with terminals located in its area and in which system Code Division Multiple Access is employed, wherein a received signal includes a sum signal of signals originating from several transmitters, the method comprising:
performing interference elimination and a simultaneous multi-user detection to said received signal, including
generating an estimate for the received signal, wherein the estimate includes one or more estimates of a received user signal, and the effect of the symbols estimated on the symbol level is subtracted from the received sum signal, whereby a narrowband, symbol-level residual signal is obtained,
correlating the received signal by a particular spreading code, whereby a first symbol-level signal is obtained,
correlating the computed estimate by the same spreading code, whereby a second symbol-level signal is obtained, and
subtracting the second symbol-level signal from the first symbol level signal, whereby a narrowband, symbol-level residual signal is obtained.
2. A method as claimed in claim 1 further comprising estimating parameters of unknown signal from the narrow-band residual signal.
3. A method as claimed in claim 2 , further comprising detecting by means of the estimated parameters the found signals using the simultaneous multi-user detection.
4. A method as claimed in claim 1 , further comprising first conveying the sum signal to a number of matched filters in which parameters of known signals are estimated, and said known signals are conveyed to a detector in which the simultaneous multi-user detection is performed.
5. A method as claimed in claim 4 , wherein the parameters comprise the signals' phase, amplitude and spreading code used.
6. A method as claimed in claim 4 , wherein the signal parameters are estimated in parallel.
7. A method as claimed in claim 4 , wherein the signal parameters are estimated sequentially.
8. A method as claimed in claim 4 , further comprising, when some parameters of the unknown signals are known, these data are utilized when other parameters are searched.
9. A method as claimed in claim 1 , wherein the residual signal comprises user symbols and the method further comprises combining the symbols incoherently.
10. A method as claimed in claim 1 , wherein the residual signal comprises user symbols and the method further comprises combining that the symbols are combined coherently.
11. A method as claimed in claim 1 , further comprising estimating parameters in several stages in such a manner that preliminary estimates are searched first, whereupon a more accurate, final estimate is estimated from among found, preliminary estimates.
12. A receiver in a cellular radio system including, in each cell, at least one base station communicating with terminals located in its area, in which system Code Division Multiple Access is employed, wherein a received signal includes a sum signal of signals originating from several transmitters, said receiver comprising:
means for performing interference elimination and a simultaneous, multi-user detection to the received signal, means performing interference elimination and a simultaneous multi-user detection to said received signal, including
means for generating an estimate for the received signal, wherein the estimate includes one or more estimates of a received user signal, and the effect of the symbols estimated on the symbol level is subtracted from the received sum signal, whereby a narrowband, symbol-level residual signal is obtained,
means for correlating the received signal by a particular spreading code, whereby a first symbol-level signal is obtained,
means for correlating the computed estimate by the same spreading code, whereby a second symbol-level signal is obtained, and
means for subtracting the second symbol-level signal from the first symbol level signal, whereby a narrowband, symbol-level residual signal is obtained.