Timing recovery for use in an ultra-wideband communication system
In an ultra-wideband (“UWB”) receiver, a received UWB signal is periodically digitized as a series of ternary samples. During a carrier acquisition mode, the samples are continuously correlated with a predetermined preamble sequence to develop a correlation value. When the value exceeds a predetermined threshold, indicating that the preamble sequence is being received, estimates of the channel impulse response (“CIR”) are developed. When a start-of-frame delimiter (“SFD”) is detected, the best CIR estimate is provided to a channel matched filter (“CMF”). During a data recovery mode, the CMF filters channel-injected noise from the sample stream. Both carrier phase errors and data timing errors are continuously detected and corrected during both the carrier acquisition and data recovery modes of operation.
1. A method for use in an ultra-wideband (UWB) communication system in which a modulated carrier signal is transmitted via a transmission channel having an impulse response, the method comprising the steps of:
1.0. developing a plurality of complex estimates of said impulse response;
2.0. in a carrier acquisition mode of operation:
2.1. performing carrier recovery, comprising the steps of:
2.1.1. developing a first accumulated estimate of said impulse response as a function of a first set of said complex estimates comprising selected first and second ones of said plurality of complex estimates;
2.1.2. developing a complex product vector by correlating the accumulated estimate with a third complex estimate;
2.1.3. developing a carrier error angle as a function of said complex product vector;
2.1.4. accumulating said third complex estimate with said first accumulated estimate; and
2.1.6. repeating steps 2.1.2 through 2.1.4; and
2.2. performing timing recovery, comprising the steps of:
2.2.1. developing a second accumulated estimate of said impulse response as a function of a second set of said complex estimates;
2.2.2. correlating with said second accumulated estimate a third set of said complex estimates;
2.2.3. developing an estimated peak of said correlation, said peak corresponding to a selected on-time estimate in said third set of complex estimates; and
2.2.4. developing a timing phase error as a function of said on-time estimate, a selected early estimate in said third set of complex estimates preceding said on-time estimate, and a selected late estimate in said third set of complex estimates following said on-time estimate; and
3.0. in a data recovery mode of operation:
3.1. performing carrier recovery, comprising the steps of:
3.1.1. filtering the carrier signal as a function of said second accumulated estimate to develop a filtered carrier signal;
3.1.2. despreading the filtered carrier signal to develop a carrier error angle;
3.1.3. rotating the filtered carrier signal as a function of the carrier error angle; and
3.1.4. repeating steps 3.1.2 through 3.1.3; and
3.2. performing timing recovery, comprising the steps of:
3.2.1. developing a third accumulated estimate of said impulse response as a function of a selected fourth set of said complex estimates;
3.2.2. filtering the carrier signal as a function of said third accumulated estimate to develop a filtered carrier signal;
3.2.3. despreading the filtered carrier signal to develop a set of timing error metrics comprising an early metric, an on-time metric and a late metric; and
3.2.4. developing said timing phase error as a function of at least a selected one of said metrics.
2. The method according to claim 1 wherein step 2.1.2 is further characterized as:
2.1.2. developing a complex product vector by performing a selected one of:
2.1.2.1. developing a first complex conjugate of a selected third one of said plurality of complex estimates; and
2.1.2.2. developing said complex product vector by multiplying said first accumulated estimate by said first complex conjugate;
and:
2.1.2.3. developing a second complex conjugate of said first accumulated estimate; and
2.1.2.4. developing said complex product vector by multiplying said third complex estimate by said second complex conjugate.
3. A method for use in an ultra-wideband (UWB) communication system in which a modulated carrier signal is transmitted via a transmission channel having an impulse response, the method comprising the steps of:
1.0. developing a plurality of complex estimates of said impulse response;
2.0. performing carrier recovery, comprising the steps of:
2.1. developing a first accumulated estimate of said impulse response as a function of a first set of said complex estimates comprising selected first and second ones of said plurality of complex estimates;
2.2. developing a complex product vector by correlating the first accumulated estimate with a third complex estimate;
2.3. developing a carrier error angle as a function of said complex product vector;
2.4. accumulating said third estimate with said first accumulated estimate; and
2.5. repeating steps 2.2 through 2.4; and
3.0. performing timing recovery, comprising the steps of:
3.1. developing a second accumulated estimate of said impulse response as a function of a second set of said complex estimates;
3.2. correlating with said second accumulated estimate a third set of said complex estimates;
3.3. developing an estimated peak of said correlation, said peak corresponding to a selected on-time estimate in said third set of estimates; and
3.4. developing a timing phase error as a function of said on-time estimate, a selected early estimate in said third set of estimates preceding said on-time estimate, and a selected late estimate in said third set of estimates following said on-time estimate.
4. The method according to claim 3 wherein step 2.2 is further characterized as:
2.2. developing a complex product vector by performing a selected one of:
2.2.1. developing a first complex conjugate of a selected third one of said plurality of complex estimates; and
2.2.2. developing said complex product vector by multiplying said first accumulated estimate by said first complex conjugate;
and:
2.2.3. developing a second complex conjugate of said first accumulated estimate; and
2.2.4. developing said complex product vector by multiplying said third complex estimate by said second complex conjugate.
5. The method of claim 3 wherein step 2.3 is further defined as comprising the steps of:
2.3.1. developing a carrier error angle as a function of said product vector;
2.3.2. filtering the carrier error angle as a function of a selected carrier loop filter proportional gain and a selected carrier loop filter integral gain to develop a filtered carrier error angle; and
2.3.3. rotating the filtered carrier signal as a function of the filtered carrier error angle.
6. The method of claim 3 wherein step 3.4 is further defined as comprising the steps of:
3.4.1. developing a timing phase error as a function of said on-time estimate, a selected early estimate in said second set of estimates preceding said on-time estimate, and a selected late estimate in said second set of estimates following said on-time estimate;
3.4.2. filtering the timing phase error as a function of a selected timing loop filter proportional gain and a selected timing loop filter integral gain to develop a filtered timing phase error; and
3.4.3. resampling the filtered carrier signal as a function of the filtered timing phase error.
7. The method of claim 6 wherein, in step 3.4.2, the timing loop filter proportional and integral gains are selected from a plurality of predetermined gains as a function of a predetermined timing loop filter gear-shifting algorithm.
8. The method according to claim 1 or claim 3 wherein the early estimate comprises the estimate in said second set immediately preceding said on-time estimate.
9. The method according to claim 1 or claim 3 wherein the late estimate comprises the estimate in said second set immediately following said on-time estimate.