System and method for recovering system time in direct sequence spread spectrum communications
First Claim
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1. In direct sequence spread spectrum (DSSS) communications, a method for recovering system timing, the method comprising:
- disabling a reference clock during a sleep interval;
following the sleep interval, enabling the reference clock; and
modifying the system timing by a ratio, where the ratio is the reference clock frequency divided by a sleep clock frequency wherein the ratio is adjusted for frequency drift;
measuring a reacquisition error;
wherein calculating the ratio includes calculating the ratio in response to the reacquisition error; and
wherein the ratio is further adjusted by an average of a number of rising and falling edges of the reference clock.
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Abstract
A sleep control system and method are provided that permit a reference clock and the direct sequence spread spectrum (DSSS) modem in a mobile station receiver to be turned off and turned back on at arbitrary points in time while still maintaining accurate base station system time. Accurate timing is made possible through a number of techniques including precise initial calibration using a rising edge/falling edge averaging system, determining the sleep clock and reference clock frequencies, and the determination of the frequency drift of the sleep clock that occurred during the previous sleep interval.
22 Citations
42 Claims
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1. In direct sequence spread spectrum (DSSS) communications, a method for recovering system timing, the method comprising:
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disabling a reference clock during a sleep interval; following the sleep interval, enabling the reference clock; and modifying the system timing by a ratio, where the ratio is the reference clock frequency divided by a sleep clock frequency wherein the ratio is adjusted for frequency drift; measuring a reacquisition error; wherein calculating the ratio includes calculating the ratio in response to the reacquisition error; and wherein the ratio is further adjusted by an average of a number of rising and falling edges of the reference clock.
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2. In direct sequence spread spectrum (DSSS) communications, a method for recovering system timing, the method comprising:
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disabling a reference clock during a sleep interval; following the sleep interval, enabling the reference clock; advancing the system timing by a ratio, where the ratio is a nominal reference clock frequency divided by a nominal sleep clock frequency; calculating the ratio in response to frequency drift of the sleep clock; measuring a reacquisition error wherein calculating the ratio includes calculating the ratio in response to the reacquisition error; determining the frequency drift of the sleep clock; determining the number of sleep clock periods using the ratio in the sleep interval prior to disabling the reference clock wherein disabling the reference clock during the sleep interval includes disabling the reference clock for the determined number of sleep clock periods; and wherein determining the number of sleep clock periods in the sleep interval includes multiplying the sleep interval, times the nominal reference clock frequency, times the inverse of the ratio as follows;
Nsleep— clk=Tsleep×
fref×
(1/R)=Tsleep×
fref×
(fsleep′
/fref′
). - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. In direct sequence spread spectrum (DSSS) communications, a method for recovering system timing, the method comprising:
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measuring sleep clock frequency using an initial ratio;
disabling a reference clock during a sleep interval;
following the sleep interval, enabling the reference clock;
advancing the system timing in response to the ratio;measuring the reference clock frequency and the sleep clock frequency to supply a current ratio; determining a ratio in response to a previous ratio and the current ratio; measuring the reacquisition error; and wherein determining the ratio in response to the previous ratio and the current ratio includes weighting the importance of the current ratio and previous ratio in response to the reacquisition error. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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21. In direct sequence spread spectrum (DSSS) communications, a method for recovering system timing, the method comprising:
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measuring sleep clock frequency using an initial ratio;
disabling a reference clock during a sleep interval;
following the sleep interval, enabling the reference clock;
advancing the system timing in response to the ratiomeasuring the reference clock frequency and the sleep clock frequency to supply a current ratio; determining a ratio in response to a previous ratio and the current ratio; and wherein determining the ratio includes determining the ratio in response to a plurality of previous ratios and the current ratio.
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22. In direct sequence spread spectrum (DSSS) communications network, a receiver system for recovering system timing, the receiver system comprising:
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a clock system having a first output to provide a reference clock signal with a reference clock frequency and a second output to supply a PN code sequence, the clock system having a first input to accept commands to enable and disable the reference clock and a second input to accept system timing advancement commands; a sleep clock having an output to provide a sleep clock signal with a sleep clock frequency, less than the reference clock frequency; and a controller having a first input connected to the clock system first output, a second input connected to the sleep clock output, and a third input to receive reacquisition errors, the controller having a first output connected to the first input of the clock system to disable the reference clock during a sleep interval and to enable the reference clock after the sleep interval, the controller having a second output connected to the second input of the clock system to advance the system timing in response to determining the ratio of reference clock frequency and sleep clock frequency. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39)
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40. In direct sequence spread spectrum (DSSS) communications, a method for recovering system timing, the method comprising:
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disabling a reference clock during a sleep interval; following the sleep interval, enabling the reference clock; and modifying the system timing by a ratio, where the ratio is the reference clock frequency divided by a sleep clock frequency wherein the ratio is adjusted for frequency drift; measuring a reacquisition error; wherein calculating the ratio includes calculating the ratio in response to the reacquisition error; and
wherein the ratio is further adjusted for quantization error.
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41. In direct sequence spread spectrum (DSSS) communications, a method for recovering system timing, the method comprising:
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disabling a reference clock during a sleep interval; following the sleep interval, enabling the reference clock; and modifying the system timing by a ratio, where the ratio is the reference clock frequency divided by a sleep clock frequency wherein the ratio is adjusted for frequency drift; and applying an IIR filter to a current and a previous value of the ratio, whereby an error in the ratio is smoothed out; and wherein the ratio is further adjusted for quantization error.
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42. In direct sequence spread spectrum (DSSS) communications, a method for recovering system timing, the method comprising:
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measuring sleep clock frequency using an initial ratio; disabling a reference clock during a sleep interval; following the sleep interval, enabling the reference clock; advancing the system timing in response to the initial ratio; measuring the reference clock frequency and the sleep clock frequency, as adjusted for frequency drift, to supply a current ratio; determining a ratio in response to a previous ratio and the current ratio; and reducing a quantization error in the initial ratio by averaging both edges of the reference clock.
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Specification