|Numéro de publication||USRE41691 E1|
|Type de publication||Octroi|
|Numéro de demande||US 11/805,865|
|Date de publication||14 sept. 2010|
|Date de priorité||13 avr. 2001|
|État de paiement des frais||Payé|
|Autre référence de publication||US6947498, US20020150177|
|Numéro de publication||11805865, 805865, US RE41691 E1, US RE41691E1, US-E1-RE41691, USRE41691 E1, USRE41691E1|
|Inventeurs||Charles Reed, Jr.|
|Cessionnaire d'origine||Reed Jr Charles|
|Exporter la citation||BiBTeX, EndNote, RefMan|
|Citations de brevets (8), Citations hors brevets (5), Classifications (28), Événements juridiques (4)|
|Liens externes: USPTO, Cession USPTO, Espacenet|
This application is a reissue application for U.S. Pat. No. 6,947,498 issued on Sep. 20, 2005.
The invention relates to data synchronization techniques and, more particularly, the invention relates to a method and apparatus for performing joint timing recovery in a digital receiver using multiple received signals.
Data signals transmitted through a communication network are subject to various distortions caused by the transmission medium or channel. Distortions such as noise, channel fading and multipath may cause errors in decoding a received digital signal. For example, multipath may severely distort or fade a received signal. To mitigate multipath induced distortion, the receiver may utilize receiver diversity, i.e., use multiple antennas to receive multiple versions of a transmitted signal.
The receiver demodulates and decodes the multiple received signals and combines the signals into a suitable format for an appliance such as a television, computer, and the like. To accurately perform such demodulation and decoding, the receiver must provide proper timing recovery of the received signals. However, such timing recovery of multiple signals is difficult in the presence of multipath and channel fading.
Therefore, there is a need in the art to provide a method and apparatus for performing joint timing recovery in a digital receiver using multiple input signals.
The present invention provides a method and apparatus for performing joint timing recovery in a digital receiver using multiple input signals. The apparatus comprises a plurality of phase detectors, a summer, a level shifter, a loop filter and a numerically controlled oscillator NCO. Each of the phase detectors produces a phase signal by comparing a timing signal produced by the NCO with each of the input signals. The phase signals are then summed and the level shifter adjusts the summed value to compensate for the number of signals used to form the sum, i.e., the summed value is adjusted to be within the input range of the NCO.
The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.
Illustratively, the front end comprises automatic gain control (AGC) circuits 102 and 104, a joint timing recovery circuit 200, matched filters 106 and 108, feed forward equalizers (FFE) 110 and 112, a summer 114, a carrier recovery circuit 116 and a decision feedback equalizer (DFE) 118.
Inputs from the antennas 101A and 101B are stabilized at the respective AGC circuits 102 and 104. The output of the AGC circuits 102 and 104 are coupled to the joint timing recovery circuit 200 described with reference to
One embodiment of a diversity equalizer is disclosed in U.S. patent application Ser. No. 09/776,078, filed Feb. 2, 1001, which is herein incorporated by reference.
In one embodiment, the joint timing recovery circuit 200 comprises two phase detectors 202 and 204, a summer 206, signal detectors 208 and 210, a decision circuit 212, a level shifter 214, a loop filter 216 and a numerically controlled oscillator (NCO) 218. The phase detector 202 receives input signal A and the output of the NCO 218, compares the phases of these input signals, and generates a phase difference signal between input signal A and the NCO output. Similarly, the phase detector 204 receives input signal B and the output of the NCO 218, compares the phases of these input signals, and generates a signal (referred to herein as a phase signal) representing the difference in phase between input signal B and the NCO output.
The summer 206 adds the phase signals from the phase detectors 202 and 204. The sum of the phase signals is coupled to the decision circuit 212. The signal detectors 208 and 210 determine whether each of the respective inputs A and B are detectable. For example, the signal detectors 208 and 210 may determine whether the amplitude of each input signal A or B is greater than a threshold value. The status of the received signal, e.g., whether the signal was properly received, is coupled to the decision circuit 212.
The decision circuit 212 receives signals from the signal detectors 208 and 210 to determine the total number of input signals that were properly received in the joint timing recovery circuit 200. Thus, the decision circuit 212 may ignore a particularly weak input signal, i.e., an input signal having a low amplitude or signal level. In one embodiment, the decision circuit 212 comprises an n-bit priority encoder that outputs how many of up to 2n−1 inputs were received with a signal level that will facilitate accurate demodulation. For example, if the decision circuit 112 comprises a 2-bit priority encoder, the number of inputs may be 0, 1, 2 or 3.
The level shifter 214 uses the output of the decision circuit 212 to adjust the sum from the summer 206. Namely, the level shifter 214 adjusts the sum of the detected phases in response to the number of input signals that were detected as receivable by the signal detectors 208 and 210. The level shifter 214 adjusts the sum to be within the input range of the NCO 218. Otherwise, if the sum of the detected phases is outside the input range of the NCO 218, i.e., the sum is either too large or too small for the NCO 218, the NCO 218 cannot generate a signal with a correct phase estimate of any of the detected signals.
The level shifter 214 may use different approaches to adjust the sum of the detected phases. In one embodiment, the level shifter 214 divides the sum by the number of detected inputs. In another embodiment, the level shifter 214 either adds or subtracts an offset value to the sum of the phase detectors 202 and 204. For example, if the sum of detected phases is greater than the input range of the NCO 218, the level shifter 212 214 would subtract the offset from the sum. Similarly, if the sum of the detected phases is less than the input range of the NCO 218, the level shifter 212 214 would add the offset to the sum. The value of the offset is configured such that the adjusted sum is within the input range of the NCO 218.
The loop filter 216 filters the adjusted sum from the level shifter 214 to the NCO 218. The loop filter 216 typically comprises an integrator circuit that operates as a low pass filter. The NCO 218 receives the filtered sum and generates a phase estimate of the adjusted sum of detected phases. The generated phase estimate is coupled to the phase detectors 202 and 204. As such, only one NCO 218 is used to generate a common phase estimate for all the inputs, e.g., A and B, in the joint timing recovery system 200.
The phase estimate from the NCO is coupled to the phase detectors 202 and 204. The phase detectors 202 and 204 use the phase estimate and the input signals A and B to derive phase difference signals. Iteration of the phase difference signals in the joint timing recovery system 200 will stabilize the phase estimate from the NCO 218. The output of the NCO 218 is used as a timing signal, e.g., a timing recovery signal within the receiver.
By adjusting the sum of the detected phases within the input range of a single numerically controlled oscillator (NCO), the present invention generates a single timing signal for a receiver that receives multiple input signals. One such application of the joint timing recovery circuit 200 is a receiver having diverse antennas.
Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.
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|US20020136342 *||29 août 2001||26 sept. 2002||Gct Semiconductor, Inc.||Sample and hold type fractional-N frequency synthesezer|
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|1||Gutnik et al., "Clock Distribution Circuits and Methods of Operating Same That Use Multiple Clock Circuits Connected By Phase Detector Circuits To Generate and Synchronize Local Clock Signals".|
|2||Lee et al., "Sample and Hold Type Fractional-N Frequency Synthesizer".|
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|Classification aux États-Unis||375/326, 455/439, 327/150, 375/376, 375/355, 714/700, 375/344, 455/522, 327/159|
|Classification internationale||H04L25/06, H04L1/06, H04L7/033, H04L7/00, H04L27/14|
|Classification coopérative||H04L7/0083, H04L25/062, H03L7/0807, H03L7/093, H04L7/0054, H04L25/063, H03L7/087, H04L7/0331|
|Classification européenne||H04L7/00D, H03L7/08E, H03L7/087, H03L7/093, H04L25/06A3, H04L25/06A1|
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