1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
|
/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*
* [Sample Rate Estimator]
* This module periodically estimates the mean sampling rate of a uniformly
* sampled signal. Note, this estimator uses a floating point accumulator for
* the timing intervals. This trades-off some accumulation of finite precision
* error to enhance the range of estimated sampling rates and prevent overflow
* when an equivalent 32bit integer accumulator is used. In typical use cases
* (sample rates: 5Hz - 2kHz, num_intervals_to_collect 10 - 100), the sample
* rate accuracy is typically much better than 0.1Hz.
*
* FUNCTIONALITY:
* sampleRateEstimatorInit -- Initializes the estimator. Sets the number of time
* intervals require to compute the sample rate mean, and the upper limit for
* the acceptable time interval.
*
* new_sampling_rate_estimate_ready -- Check this boolean flag if polling for
* new estimates is desired.
*
* sampleRateEstimatorGetHz -- Returns the latest sample rate estimate and
* resets the polling flag.
*
* sampleRateEstimatorUpdate -- Processes new timestamp data and computes new
* sample rate estimates.
*/
#ifndef LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_SAMPLE_RATE_ESTIMATOR_SAMPLE_RATE_ESTIMATOR_H_
#define LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_SAMPLE_RATE_ESTIMATOR_SAMPLE_RATE_ESTIMATOR_H_
#include <stdbool.h>
#include <stdint.h>
#include <sys/types.h>
#ifdef __cplusplus
extern "C" {
#endif
// Designates the value used to indicate an invalid sample rate estimate.
#define SAMPLE_RATE_ESTIMATOR_INVALID_SAMPLE_RATE_HZ (-1.0f)
// Sample rate estimator data structure.
struct SampleRateEstimator {
// Used to compute sample intervals to estimate the sampling rate.
uint64_t last_timestamp_nanos;
// Accumulator used for computing the mean sampling interval.
float interval_accumulator_nanos;
// The upper limit on the acceptance of valid time intervals (in nanoseconds).
// Larger time deltas result in a reset of the interval accumulator.
float max_interval_nanos;
// The most recent mean sampling rate estimate.
float mean_sampling_rate_estimate_hz;
/*
* The targeted number of time intervals required for a new sample rate mean
* calculation.
*
* NOTE: Assuming that the time interval noise is independent and identically
* distributed and drawn from a zero-mean normal distribution with variance
* 'Sigma^2'. The expected noise reduction is related to the choice of
* 'num_intervals_to_collect' as:
*
* Output RMS Noise = Sigma / sqrt(num_intervals_to_collect).
*
* Example, a value of 100 for a 100Hz signal would provide updates once every
* second and provide a 90% reduction (i.e., [1 - 1/sqrt(100)] * 100%) in time
* interval noise.
*/
size_t num_intervals_to_collect;
// The number of time intervals currently collected.
size_t num_intervals_collected;
// Polling flag used to signal that a new estimate is ready. This flag is
// reset when 'sampleRateEstimatorGetHz' is called.
bool new_sampling_rate_estimate_ready;
};
// Initializes the sample rate estimator, sets the number of time intervals
// for the mean sample rate calculation, and defines the tolerable gap in timing
// data (in seconds).
void sampleRateEstimatorInit(struct SampleRateEstimator* sample_rate_estimator,
size_t num_intervals_to_collect,
float max_interval_sec);
// Rather than using a function to poll for new sample rate estimates, which
// would incur an additional function call, simply check
// 'new_sampling_rate_estimate_ready' directly.
// Returns the most recent sampling rate estimate, and resets the
// 'new_sampling_rate_estimate_ready' polling flag. Note, if polling is not
// used, one may access the sample rate estimate directly from the struct and
// avoid this function call.
float sampleRateEstimatorGetHz(
struct SampleRateEstimator* sample_rate_estimator);
// Takes in a new timestamp and updates the sampling rate estimator.
void sampleRateEstimatorUpdate(
struct SampleRateEstimator* sample_rate_estimator,
uint64_t timestamp_nanos);
#ifdef __cplusplus
}
#endif
#endif // LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_SAMPLE_RATE_ESTIMATOR_SAMPLE_RATE_ESTIMATOR_H_
|
