Method and system for rapid initial control signal detection in a wireless communications system
First Claim
1. A method for control channel acquisition by a receiver in a wireless communication system wherein a known reference signal is periodically sent, the method comprising the steps of:
- (a) producing a sampled sequence z n! of complex valued digital samples from a baseband radio frequency signal that may include the known reference sequence, the baseband radio frequency signal determined from a received signal received at the receiver;
(b) differential sample encoding said sampled sequence z n! to produce a differential sample encoded sample sequence u n!;
(c) differential sample encoding a version x n! of said reference signal to produce a differential sample encoded reference sequence y n!; and
(d) correlating the differential sample encoded sample sequence u n! with the differential sample encoded reference sequence y n! to produce a correlator output signal v n! which has an amplitude peak when the known reference signal exists in the baseband radio frequency signal,wherein the differential sample encoding of steps (b) and (c) are chosen to reduce the sensitivity of any amplitude peak in the correlator output signal v n! to variations in frequency offset in the baseband radio frequency signal, and wherein the differential encoding of steps (b) and (c) determine
space="preserve" listing-type="equation">u n!=z n!*z'"'"' n-M.sub.O !,and
space="preserve" listing-type="equation">y n!=x n!*x'"'"' n-M.sub.O !,respectively, where '"'"' denotes the complex conjugate operation, * denotes multiplication, and MO is a non-negative integer which determines a differential encoding period Td.
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Abstract
A wireless communication subscriber unit comprises a radio frequency downconversion stage that produces in-phase and quadrature phase digital samples. A digital signal processor is connected to receive the samples and process them to produce a control channel correlation output and a carrier frequency offset estimate. The acquisition of the control channel is made substantially immune from initial carrier frequency offsets by differential sample encoding the samples. These are input to a correlator whose coefficients are a pre-stored differential sample encoded, decimated and rate expanded version of the known reference sequence. When the the reference sequence is present, the correlator produces a peak output that can be used to detect the presence of the reference sequence. The time position of the peak can be used for time alignment, for signal quality estimation, and to directly obtain a frequency offset estimate.
116 Citations
29 Claims
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1. A method for control channel acquisition by a receiver in a wireless communication system wherein a known reference signal is periodically sent, the method comprising the steps of:
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(a) producing a sampled sequence z n! of complex valued digital samples from a baseband radio frequency signal that may include the known reference sequence, the baseband radio frequency signal determined from a received signal received at the receiver; (b) differential sample encoding said sampled sequence z n! to produce a differential sample encoded sample sequence u n!; (c) differential sample encoding a version x n! of said reference signal to produce a differential sample encoded reference sequence y n!; and (d) correlating the differential sample encoded sample sequence u n! with the differential sample encoded reference sequence y n! to produce a correlator output signal v n! which has an amplitude peak when the known reference signal exists in the baseband radio frequency signal, wherein the differential sample encoding of steps (b) and (c) are chosen to reduce the sensitivity of any amplitude peak in the correlator output signal v n! to variations in frequency offset in the baseband radio frequency signal, and wherein the differential encoding of steps (b) and (c) determine
space="preserve" listing-type="equation">u n!=z n!*z'"'"' n-M.sub.O !,and
space="preserve" listing-type="equation">y n!=x n!*x'"'"' n-M.sub.O !,respectively, where '"'"' denotes the complex conjugate operation, * denotes multiplication, and MO is a non-negative integer which determines a differential encoding period Td. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for determining the presence of a known reference signal in a baseband radio frequency signal from a sampled sequence z n! of complex valued digital samples of the baseband radio frequency signal, the method comprising the steps of:
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(a) differential sample encoding said sampled sequence z n! to produce a differential sample encoded sample sequence u n!; and (b) correlating the differential sample encoded sample sequence u n! with a set of correlator coefficients, the correlator coefficients including a differential sample encoded reference sequence y n! determined by sampling and differential sample encoding a version x n! of said reference signal, the correlating producing a correlator output signal v n! which has an amplitude peak when the known reference signal exists in the baseband radio frequency signal, the differential sample encoding in u n! and y n! being the same type and chosen to reduce the sensitivity of any amplitude peak in the correlator output signal v n! to variations in frequency offset in the baseband radio frequency signal, and the differential encoding in u n! and v n! determining
space="preserve" listing-type="equation">u n!=z n!*z'"'"' n-M.sub.O !,and
space="preserve" listing-type="equation">y n!=x n!*x'"'"' n-M.sub.O !,respectively, where '"'"' denotes the complex conjugate operation, * denotes multiplication, and MO is a non-negative integer which determines a differential encoding period Td.
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22. A wireless communication system, comprising:
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(a) a radio receiver, the radio receiver including an antenna for receiving a received signal, a front end, coupled to the antenna and producing a sequence of complex valued digital samples of a baseband radio frequency signal from the received signal; (b) a digital signal processor for differential sample encoding said samples to produce a differential sample encoded sample sequence; (c) a correlator, including a correlator coefficient memory for storing correlator coefficients, the correlator coupled to the digital signal processor and correlating the differential sample encoded sample sequence with the correlator coefficients, the correlator having an output comprising a correlator output signal; (d) means for differential sample encoding a sampled version x n! of the known reference signal to produce a differential sample encoded reference sequence y n!; and (e) means for loading the differential sample encoded reference sequence into the correlator coefficient memory, wherein the differential encoding of steps (b) and (d) determine
space="preserve" listing-type="equation">u n!=z n!*z'"'"' n-M.sub.O !,and
space="preserve" listing-type="equation">y n!=x n!*x'"'"' n-M.sub.O !,receptively, where '"'"' denotes the complex conjugate operation, * denotes multiplication, and MO is a non-negative integer which determines a differential encoding period Td. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29)
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Specification