Patent EA-004419-B1 (EA)
Title: Cancellation of pilot and unwanted traffic signals in a cdma system
Inventor: OZLUTURK FATIH M
IPC: H04B1/7107
Filed: 1999-01-27
Abstract: 1. A cancellation system for removing selected signals from a traffic signal prior to decoding in a receiver that receives communication signals from a transmitter (19) over a CDMA air interface, the system comprising: a system input (147) for receiving the communication signals; said system input (147) inputted as input (103) to a traffic signal cancellation system (101) having an output (O) equal to the desired traffic signal minus the unwanted traffic signals; said signal input (147) also inputted as input (63) to a pilot signal cancellation system (61), the system (61) processing the input (63) to remove a global pilot signal and having an output (Oadd) equal to the desired traffic signal minus the global pilot signal; and whereby the output (Oadd) of the pilot signal cancellation system (61) is subtracted from the output (O) of the traffic signal cancellation system (101) to provide the cancellation system output (151). 2. The cancellation system according to claim 1 wherein the traffic cancellation system (101) comprises a desired traffic signal despreader (91) coupled to a sum and dump processor (97) to produce an output (Osd3) and an unwanted traffic signal canceler (1151-n), the despreader (1151-n) comprising: an unwanted traffic signal despreader (1391-n) having a signal input (103) coupled to said system input (63) and a summed output; the unwanted traffic signal despreader (1391-n) comprising an unwanted traffic signal code generator (1191-n) and a mixer (1171-n) for mixing an output of the generator (1191-n) with the input (103) to produce a unwanted traffic signal canceler output; said unwanted traffic signal despreader summed output coupled to a hard decision processor (1251-n) having a phase output (phi) and a data output (d); said hard decision processor phase output (phi) coupled to a low pass filter (1271-n), said low pass filter having an output (Olpfn); said low pass filter (1271-n) output (Olpfn) coupled to an input of a processor (1291-n) that filters the product of the unwanted traffic signal to desired traffic signal cross-correlation outputting the unwanted traffic signal strength; said processor (1291-n) output multiplied with said hard decision data output (d) with a first multiplier (1311-n) having an output delivered to an adjustable amplifier (1371-n); an unwanted traffic code generator (119) output coupled to an input of a complex conjugate processor (1351-n) having an output; said complex conjugate output mixed with a complex conjugate of the desired traffic signal code by a first mixer (1331-n) having an output; said first mixer (1331-n) output coupled to an input of a first sum and dump processor (1231-n) having an output; said first sum and dump processor (1231-n) coupled to an input of an amplifier (1371-n) having an adjustable gain controlled by said multiplier (1311-n) output; and said output of said amplifier (1371-n) is coupled to an adder (143) which subtracts the output (1411-n) of each variable amplifier (1371-n) from the output (Osd3) of the desired traffic signal despreader (91) to get the output (O) of the traffic signal cancellation system (101). 3. The cancellation system according to claim 1 wherein the pilot signal cancellation system (61) comprises: a global pilot despreader (65) coupled to said input (63) having a summed output (Osd1); a desired traffic signal and global pilot cross-correlation means having an output (Osd2); said global pilot despreader (65) output (Osd1) coupled to a pilot strength determining means, said determining means having an output (Opm); said pilot strength determining means output (Opm) multiplied with said cross-correlation means output (Osd2); and said multiplied product is said output (Oadd). 4. The cancellation system according to claim 3 wherein said cross-correlation means comprises: a global pilot spreading code complex conjugate code generator (69); a desired traffic signal complex conjugate code generator (79); a second mixer (81) for cross-correlating said global pilot signal code and said desired traffic signal complex conjugate code; and a second sum and dump processor (85) for summing over time said cross-correlation product. 5. The cancellation system according to claim 4 wherein said means to derive said global pilot signal strength further comprises: a low-pass filter (75) having an output (Olpf); and a processor (77) coupled to said low-pass filter (75) deriving and outputting the global pilot signal strength. 6. A global pilot signal cancellation system (61) for use in a receiver that receives communication signals from a transmitter over a CDMA air interface that removes the global pilot signal from a desired traffic signal prior to decoding, the system comprising: an input (63) for receiving the communication signals and a system output (Oadd); said input coupled to a global pilot despreader (65) and a desired traffic signal despreader (91) each having a summed output a desired traffic signal and global pilot cross-correlation means; said global pilot despreader (65) output (Osd1) coupled to a pilot strength determining means, said determining means having an output (Opm); said pilot strength determining means output (Opm) multiplied with said cross-correlation means output (Osd2); and said multiplied product subtracted from a summed output (Osd3) of said desired traffic signal despreader (91) output outputting (Oadd) the desired traffic signal free from the global pilot signal. 7. The global pilot signal cancellation system (61) according to claim 6 wherein said means to derive said global pilot signal strength further comprises: a low-pass filter (75) having an output (Olpf); and a processor (77) coupled to said low-pass filter (75) deriving and outputting the global pilot signal strength (Opm). 8. A traffic signal cancellation system (101) for use in a receiver that receives communication signals from transmitter (19) over a CDMA air interface that removes at least one unwanted traffic signal from a desired traffic signal prior to decoding, the system comprising: an input (103) for receiving the communication signals and a system output (O); said input (103) coupled to a desired traffic signal despreader (91) having a first summed output (Osd3); an at least one unwanted traffic signal canceler (1151-n) comprising: an unwanted traffic signal despreader (1391-n) having an input coupled to said first summed output and a second summed output; the unwanted traffic signal despreader (1391-n) comprising an unwanted traffic signal code generator (1191-n) and a mixer (1171-n) for mixing an output of the generator (1191-n) with the input (103) to produce a unwanted traffic signal despreader output; said unwanted traffic signal despreader (1391-n) summed output coupled to a hard decision processor (1251-n) having a phase output (phi) and a data output (d); said hard decision processor (1251-n) phase output (phi) coupled to a low pass filter (1271-n), said low pass filter (1271-n) having an output (Olpfn); said low pass filter (1271-n) output (Olpfn) coupled to an input of a processor (1291-n) that filters the product of the unwanted traffic signal to desired traffic signal cross-correlation outputting the unwanted traffic signal strength; said processor (1291-n) output multiplied with said hard decision data output (d) with a multiplier having an output delivered to an adjustable amplifier (1371-n); an unwanted traffic code generator (1191-n) output coupled to an input of a complex conjugate processor (1351-n) having an output; said complex conjugate output mixed with a complex conjugate of the desired traffic signal code by a mixer (1331-n) having an output; said mixer (1331-n) output coupled to an input of a second sum and dump processor (1231-n) having an output; said second sum and dump processor (1231-n) coupled to an input of an amplifier (1371-n) having an adjustable gain controlled by said multiplier (1311-n) output; and said output of said amplifier (1371-n) is coupled to an adder (143) which subtracts the output (1411-n) of each variable amplifier (1371-n) from the output (Osd3) of the desired traffic signal despreader (91) to get the output (O) of the traffic cancellation system (101). 9. The cancellation system according to claim 6 wherein said cross-correlation means comprises: a global pilot signal code generator (65); a desired traffic signal complex conjugate code generator (79); a second mixer (81) for cross-correlating said global pilot signal code and said desired traffic signal complex conjugate code; and a second sum and dump processor (85) for summing over time said cross-correlation product. 10. The cancellation system according to claim 9 wherein said means to derive said global pilot signal strength further comprises: a low-pass filter (75) having an output; and a processor (77) coupled to said low-pass filter (75) deriving and outputting the global pilot signal strength. 11. A method for cancelling a global pilot signal from a desired traffic signal, comprising: providing an input for receiving communication signals from a transmitter over a CDMA air interface; said input coupled to a global pilot despreader (65) and a desired traffic signal despreader (91) each having a summed output; identifying a desired traffic signal and provides a global pilot cross correlation means; said global pilot despreader (65) output coupled to a pilot strength determining means having an output, said pilot strength determining means output multiplied with said cross-correlation means output where said cross-correlation means comprising; and said multiplied product subtracted from said desired traffic signal despreader output and outputting the desired traffic signal free from the global pilot signal. 12. The method according to claim 11 wherein said means to derive said global pilot signal strength further comprises: a low-pass filter having an output, and a processor coupled to said low-pass filter (75) derivi