Method and apparatus for improving the performance of pilot symbol assisted receivers in the presence of narrowband interference
A method for reducing interference from at least one narrowband interferer in a pilot symbol assisted receiver ( 10 ) includes the steps of; receiving a stream of received data, passing the stream of received data through an adaptive filter that reduces interference from any narrowband interferer, passing the filtered data through a correlator ( 7, 8 ) arranged to detect pilot symbols, when a pilot symbol is detected passing the stream of received data to a receiving apparatus without first passing the received data through the adaptive filter ( 3 ), and wherein the pilot symbol includes one or more repetitions of known data or pseudo noise.
1. A method for reducing interference from at least one narrow band interferer in a pilot symbol assisted receiver comprising the steps of;
receiving a stream of received data,
passing the stream of received data through an adaptive filter that reduces interference from any narrowband interferer,
passing the filtered data through a correlator arranged to detect pilot symbols,
when a pilot symbol is detected passing the stream of received data to a receiving apparatus without first passing the received data through the adaptive filter,
and wherein the pilot symbol has a length and includes one or more repetitions of known data or pseudo noise.
2. A method for reducing interference from at least one narrow band interferer in a pilot symbol assisted receiver as claimed in claim 1 wherein the adaptive filter has a number of taps and the number of taps in the adaptive filter is greater than a maximum number of interferers to be cancelled.
3. A method for reducing interference from at least one narrow band interferer in a pilot symbol assisted receiver as claimed in claim 1 wherein the adaptive filter uses a stream of the received data delayed by a known length as a reference signal.
4. A method for reducing interference from at least one narrow band interferer in a pilot symbol assisted receiver as claimed in claim 3 wherein the length of the delay in the delayed stream of received data is longer than the length of the pilot symbol.
5. A method for reducing interference from at least one narrow band interferer in a pilot symbol assisted receiver as claimed in claim 1 wherein the step of detecting the pilot symbol in the correlator comprises the steps of;
detecting a peak in a sliding window correlator and,
when the peak is detected in the sliding window correlator operating a pilot symbol detector to detect the pilot symbol.
6. A method for reducing interference from at least one narrow band interferer in a pilot symbol assisted receiver as claimed in claim 5 wherein the step of detecting a pilot symbol further comprises a step of timing out if the pilot symbol is not detected in the pilot symbol detector within a predetermined number of operations.
7. A method for reducing interference from at least one narrow band interferer in a pilot symbol assisted receiver as claimed in claim 6 wherein when the timeout occurs continuing to search for a peak with the sliding window correlator and when a peak is detected in the sliding window correlator operating the pilot symbol detector to detect the pilot symbol.
8. A method for detecting a pilot symbol in the presence of narrowband interference in a receiver comprising the steps of;
receiving a stream of received data,
passing the stream of received data through an adaptive filter to reduce interference from any narrowband interferers,
passing the output of the adaptive filter to a correlator,
when the correlator produces a peak over a threshold value triggering a pilot symbol detector to search for a pilot symbol in the filtered data,
triggering a timeout during which the pilot symbol detector will not operate if the pilot symbol detector does not detect a pilot symbol in the filtered data within a predetermined number of operations, and
sending a signal that triggers removal of the adaptive filter from a receiver path if the pilot symbol detector detects a pilot symbol in the filtered data within a predetermined number of second correlator operations,
and wherein the pilot symbol includes one or more repetitions of known data or pseudo noise sequence.
9. A method for detecting a pilot symbol in the presence of narrowband interference in a receiver as claimed in claim 8 wherein the pilot symbol detector is a matched filter correlator.
10. A method for detecting a pilot symbol in the presence of narrowband interference in a receiver as claimed in claim 8 wherein a number of taps in the adaptive filter is greater than a maximum number of interferers to be cancelled.
11. A method for detecting a pilot symbol in the presence of narrowband interference in a receiver as claimed in claim 8 wherein the adaptive filter uses a delayed stream of the received data as a reference signal.
12. A narrowband interference reducing system for a receiver comprising;
a front end arranged to receive data,
an adaptive filter arranged to filter narrowband interference from the received data and provide filtered data,
a correlator arranged to detect pilot symbols in the filtered data, and
a logic system arranged to reroute the received data to a receiving apparatus without passing the received data through the adaptive filter when a pilot symbol has been detected, and wherein
the pilot symbol has a length and includes one or more repetitions of known data or pseudo noise sequence.
13. A narrowband interference reducing system for a receiver as claimed in claim 12 wherein a number of taps in the adaptive filter is greater than a maximum number of interferers to be cancelled.
14. A narrowband interference reducing system for a receiver as claimed in claim 12 wherein the adaptive filter uses a delayed stream of the received data delayed by a known length as a reference signal.
15. A narrowband interference reducing system for a receiver as claimed in claim 14 wherein the length of the delay in the delayed stream of received data is longer than the length of the pilot symbol.
16. A narrowband interference reducing system for a receiver as claimed in claim 12 further comprising a matched filter correlator.
17. A narrowband interference reducing system for a receiver as claimed in claim 16 wherein when a peak is detected in a sliding window correlator operating the matched filter correlator to detect the pilot symbol.
18. A narrowband interference reducing system for a receiver as claimed in claim 17 wherein the logic system is arranged to produce a timeout if the pilot symbol is not detected in the matched filter correlator within a predetermined number of matched filter correlator operations.
19. A narrowband interference reducing system for a receiver as claimed in claim 18 wherein when a timeout occurs the sliding window correlator continues operating and when a peak is detected in the sliding window correlator the matched filter correlator begins operating.
20. A narrowband interference reducing system for a receiver as claimed in claim 19 wherein the logic system is arranged to bypass the adaptive filter by rerouting the receive data when the matched filter correlator detects a pilot symbol.