modules/remote_bitrate_estimator/test/estimators/nada.cc - src/webrtc - Git at Google

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  *
  */

 //  Implementation of Network-Assisted Dynamic Adaptation's (NADA's) proposal.
 //  Version according to Draft Document (mentioned in references)
 //  http://tools.ietf.org/html/draft-zhu-rmcat-nada-06
 //  From March 26, 2015.

 #include <math.h>
 #include <algorithm>
 #include <vector>

 #include "webrtc/modules/remote_bitrate_estimator/test/bwe_test_logging.h"
 #include "webrtc/modules/remote_bitrate_estimator/test/estimators/nada.h"
 #include "webrtc/modules/rtp_rtcp/include/receive_statistics.h"
 #include "webrtc/rtc_base/arraysize.h"

 namespace webrtc {
 namespace testing {
 namespace bwe {

 namespace {
 // Used as an upper bound for calling AcceleratedRampDown.
 const float kMaxCongestionSignalMs =
     40.0f + NadaBweSender::kMinNadaBitrateKbps / 15;
 }  // namespace

 const int NadaBweSender::kMinNadaBitrateKbps = 50;
 const int64_t NadaBweReceiver::kReceivingRateTimeWindowMs = 500;

 NadaBweReceiver::NadaBweReceiver(int flow_id)
     : BweReceiver(flow_id, kReceivingRateTimeWindowMs),
       clock_(0),
       last_feedback_ms_(0),
       recv_stats_(ReceiveStatistics::Create(&clock_)),
       baseline_delay_ms_(10000),  // Initialized as an upper bound.
       delay_signal_ms_(0),
       last_congestion_signal_ms_(0),
       last_delays_index_(0),
       exp_smoothed_delay_ms_(-1),
       est_queuing_delay_signal_ms_(0) {
 }

 NadaBweReceiver::~NadaBweReceiver() {
 }

 void NadaBweReceiver::ReceivePacket(int64_t arrival_time_ms,
                                     const MediaPacket& media_packet) {
   const float kAlpha = 0.1f;                 // Used for exponential smoothing.
   const int64_t kDelayLowThresholdMs = 50;   // Referred as d_th.
   const int64_t kDelayMaxThresholdMs = 400;  // Referred as d_max.

   clock_.AdvanceTimeMilliseconds(arrival_time_ms - clock_.TimeInMilliseconds());
   recv_stats_->IncomingPacket(media_packet.header(),
                               media_packet.payload_size(), false);
   // Refered as x_n.
   int64_t delay_ms = arrival_time_ms - media_packet.sender_timestamp_ms();

   // The min should be updated within the first 10 minutes.
   if (clock_.TimeInMilliseconds() < 10 * 60 * 1000) {
     baseline_delay_ms_ = std::min(baseline_delay_ms_, delay_ms);
   }

   delay_signal_ms_ = delay_ms - baseline_delay_ms_;  // Refered as d_n.
   const int kMedian = arraysize(last_delays_ms_);
   last_delays_ms_[(last_delays_index_++) % kMedian] = delay_signal_ms_;
   int size = std::min(last_delays_index_, kMedian);

   int64_t median_filtered_delay_ms_ = MedianFilter(last_delays_ms_, size);
   exp_smoothed_delay_ms_ = ExponentialSmoothingFilter(
       median_filtered_delay_ms_, exp_smoothed_delay_ms_, kAlpha);

   if (exp_smoothed_delay_ms_ < kDelayLowThresholdMs) {
     est_queuing_delay_signal_ms_ = exp_smoothed_delay_ms_;
   } else if (exp_smoothed_delay_ms_ < kDelayMaxThresholdMs) {
     est_queuing_delay_signal_ms_ = static_cast<int64_t>(
         pow((static_cast<double>(kDelayMaxThresholdMs -
                                  exp_smoothed_delay_ms_)) /
                 (kDelayMaxThresholdMs - kDelayLowThresholdMs),
             4.0) *
         kDelayLowThresholdMs);
   } else {
     est_queuing_delay_signal_ms_ = 0;
   }

   // Log received packet information.
   BweReceiver::ReceivePacket(arrival_time_ms, media_packet);
 }

 FeedbackPacket* NadaBweReceiver::GetFeedback(int64_t now_ms) {
   const int64_t kPacketLossPenaltyMs = 1000;  // Referred as d_L.

   if (now_ms - last_feedback_ms_ < 100) {
     return NULL;
   }

   float loss_fraction = RecentPacketLossRatio();

   int64_t loss_signal_ms =
       static_cast<int64_t>(loss_fraction * kPacketLossPenaltyMs + 0.5f);
   int64_t congestion_signal_ms = est_queuing_delay_signal_ms_ + loss_signal_ms;

   float derivative = 0.0f;
   if (last_feedback_ms_ > 0) {
     derivative = (congestion_signal_ms - last_congestion_signal_ms_) /
                  static_cast<float>(now_ms - last_feedback_ms_);
   }
   last_feedback_ms_ = now_ms;
   last_congestion_signal_ms_ = congestion_signal_ms;

   int64_t corrected_send_time_ms = 0L;

   if (!received_packets_.empty()) {
     PacketIdentifierNode* latest = *(received_packets_.begin());
     corrected_send_time_ms =
         latest->send_time_ms + now_ms - latest->arrival_time_ms;
   }

   // Sends a tuple containing latest values of <d_hat_n, d_tilde_n, x_n, x'_n,
   // R_r> and additional information.
   return new NadaFeedback(flow_id_, now_ms * 1000, exp_smoothed_delay_ms_,
                           est_queuing_delay_signal_ms_, congestion_signal_ms,
                           derivative, RecentKbps(), corrected_send_time_ms);
 }

 // If size is even, the median is the average of the two middlemost numbers.
 int64_t NadaBweReceiver::MedianFilter(int64_t* last_delays_ms, int size) {
   std::vector<int64_t> array_copy(last_delays_ms, last_delays_ms + size);
   std::nth_element(array_copy.begin(), array_copy.begin() + size / 2,
                    array_copy.end());
   if (size % 2 == 1) {
     // Typically, size = 5. For odd size values, right and left are equal.
     return array_copy.at(size / 2);
   }
   int64_t right = array_copy.at(size / 2);
   std::nth_element(array_copy.begin(), array_copy.begin() + (size - 1) / 2,
                    array_copy.end());
   int64_t left = array_copy.at((size - 1) / 2);
   return (left + right + 1) / 2;
 }

 int64_t NadaBweReceiver::ExponentialSmoothingFilter(int64_t new_value,
                                                     int64_t last_smoothed_value,
                                                     float alpha) {
   if (last_smoothed_value < 0) {
     return new_value;  // Handling initial case.
   }
   return static_cast<int64_t>(alpha * new_value +
                               (1.0f - alpha) * last_smoothed_value + 0.5f);
 }

 // Implementation according to Cisco's proposal by default.
 NadaBweSender::NadaBweSender(int kbps, BitrateObserver* observer, Clock* clock)
     : BweSender(kbps),  // Referred as "Reference Rate" = R_n.,
       clock_(clock),
       observer_(observer),
       original_operating_mode_(true) {
 }

 NadaBweSender::NadaBweSender(BitrateObserver* observer, Clock* clock)
     : BweSender(kMinNadaBitrateKbps),  // Referred as "Reference Rate" = R_n.
       clock_(clock),
       observer_(observer),
       original_operating_mode_(true) {}

 NadaBweSender::~NadaBweSender() {
 }

 int NadaBweSender::GetFeedbackIntervalMs() const {
   return 100;
 }

 void NadaBweSender::GiveFeedback(const FeedbackPacket& feedback) {
   const NadaFeedback& fb = static_cast<const NadaFeedback&>(feedback);

   // Following parameters might be optimized.
   const int64_t kQueuingDelayUpperBoundMs = 10;
   const float kDerivativeUpperBound =
       10.0f / std::max<int64_t>(1, min_feedback_delay_ms_);
   // In the modified version, a higher kMinUpperBound allows a higher d_hat
   // upper bound for calling AcceleratedRampUp.
   const float kProportionalityDelayBits = 20.0f;

   int64_t now_ms = clock_->TimeInMilliseconds();
   float delta_s = now_ms - last_feedback_ms_;
   last_feedback_ms_ = now_ms;
   // Update delta_0.
   min_feedback_delay_ms_ =
       std::min(min_feedback_delay_ms_, static_cast<int64_t>(delta_s));

   // Update RTT_0.
   int64_t rtt_ms = now_ms - fb.latest_send_time_ms();
   min_round_trip_time_ms_ = std::min(min_round_trip_time_ms_, rtt_ms);

   // Independent limits for AcceleratedRampUp conditions variables:
   // x_n, d_tilde and x'_n in the original implementation, plus
   // d_hat and receiving_rate in the modified one.
   // There should be no packet losses/marking, hence x_n == d_tilde.
   if (original_operating_mode_) {
     // Original if conditions and rate update.
     if (fb.congestion_signal() == fb.est_queuing_delay_signal_ms() &&
         fb.est_queuing_delay_signal_ms() < kQueuingDelayUpperBoundMs &&
         fb.derivative() < kDerivativeUpperBound) {
       AcceleratedRampUp(fb);
     } else {
       GradualRateUpdate(fb, delta_s, 1.0);
     }
   } else {
     // Modified if conditions and rate update; new ramp down mode.
     if (fb.congestion_signal() == fb.est_queuing_delay_signal_ms() &&
         fb.est_queuing_delay_signal_ms() < kQueuingDelayUpperBoundMs &&
         fb.exp_smoothed_delay_ms() <
             kMinNadaBitrateKbps / kProportionalityDelayBits &&
         fb.derivative() < kDerivativeUpperBound &&
         fb.receiving_rate() > kMinNadaBitrateKbps) {
       AcceleratedRampUp(fb);
     } else if (fb.congestion_signal() > kMaxCongestionSignalMs ||
                fb.exp_smoothed_delay_ms() > kMaxCongestionSignalMs) {
       AcceleratedRampDown(fb);
     } else {
       double bitrate_reference =
           (2.0 * bitrate_kbps_) / (kMaxBitrateKbps + kMinNadaBitrateKbps);
       double smoothing_factor = pow(bitrate_reference, 0.75);
       GradualRateUpdate(fb, delta_s, smoothing_factor);
     }
   }

   bitrate_kbps_ = std::min(bitrate_kbps_, kMaxBitrateKbps);
   bitrate_kbps_ = std::max(bitrate_kbps_, kMinNadaBitrateKbps);

   observer_->OnNetworkChanged(1000 * bitrate_kbps_, 0, rtt_ms);
 }

 int64_t NadaBweSender::TimeUntilNextProcess() {
   return 100;
 }

 void NadaBweSender::Process() {
 }

 void NadaBweSender::AcceleratedRampUp(const NadaFeedback& fb) {
   const int kMaxRampUpQueuingDelayMs = 50;  // Referred as T_th.
   const float kGamma0 = 0.5f;               // Referred as gamma_0.

   float gamma =
       std::min(kGamma0, static_cast<float>(kMaxRampUpQueuingDelayMs) /
                             (min_round_trip_time_ms_ + min_feedback_delay_ms_));

   bitrate_kbps_ = static_cast<int>((1.0f + gamma) * fb.receiving_rate() + 0.5f);
 }

 void NadaBweSender::AcceleratedRampDown(const NadaFeedback& fb) {
   const float kGamma0 = 0.9f;
   float gamma = 3.0f * kMaxCongestionSignalMs /
                 (fb.congestion_signal() + fb.exp_smoothed_delay_ms());
   gamma = std::min(gamma, kGamma0);
   bitrate_kbps_ = gamma * fb.receiving_rate() + 0.5f;
 }

 void NadaBweSender::GradualRateUpdate(const NadaFeedback& fb,
                                       float delta_s,
                                       double smoothing_factor) {
   const float kTauOMs = 500.0f;           // Referred as tau_o.
   const float kEta = 2.0f;                // Referred as eta.
   const float kKappa = 1.0f;              // Referred as kappa.
   const float kReferenceDelayMs = 10.0f;  // Referred as x_ref.
   const float kPriorityWeight = 1.0f;     // Referred as w.

   float x_hat = fb.congestion_signal() + kEta * kTauOMs * fb.derivative();

   float kTheta = kPriorityWeight * (kMaxBitrateKbps - kMinNadaBitrateKbps) *
                  kReferenceDelayMs;

   int original_increase = static_cast<int>(
       (kKappa * delta_s *
        (kTheta - (bitrate_kbps_ - kMinNadaBitrateKbps) * x_hat)) /
           (kTauOMs * kTauOMs) +
       0.5f);

   bitrate_kbps_ = bitrate_kbps_ + smoothing_factor * original_increase;
 }

 }  // namespace bwe
 }  // namespace testing
 }  // namespace webrtc
	/*
	* Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
	*
	* Use of this source code is governed by a BSD-style license
	* that can be found in the LICENSE file in the root of the source
	* tree. An additional intellectual property rights grant can be found
	* in the file PATENTS. All contributing project authors may
	* be found in the AUTHORS file in the root of the source tree.
	*
	*/

	// Implementation of Network-Assisted Dynamic Adaptation's (NADA's) proposal.
	// Version according to Draft Document (mentioned in references)
	// http://tools.ietf.org/html/draft-zhu-rmcat-nada-06
	// From March 26, 2015.

	#include <math.h>
	#include <algorithm>
	#include <vector>

	#include "webrtc/modules/remote_bitrate_estimator/test/bwe_test_logging.h"
	#include "webrtc/modules/remote_bitrate_estimator/test/estimators/nada.h"
	#include "webrtc/modules/rtp_rtcp/include/receive_statistics.h"
	#include "webrtc/rtc_base/arraysize.h"

	namespace webrtc {
	namespace testing {
	namespace bwe {

	namespace {
	// Used as an upper bound for calling AcceleratedRampDown.
	const float kMaxCongestionSignalMs =
	40.0f + NadaBweSender::kMinNadaBitrateKbps / 15;
	} // namespace

	const int NadaBweSender::kMinNadaBitrateKbps = 50;
	const int64_t NadaBweReceiver::kReceivingRateTimeWindowMs = 500;

	NadaBweReceiver::NadaBweReceiver(int flow_id)
	: BweReceiver(flow_id, kReceivingRateTimeWindowMs),
	clock_(0),
	last_feedback_ms_(0),
	recv_stats_(ReceiveStatistics::Create(&clock_)),
	baseline_delay_ms_(10000), // Initialized as an upper bound.
	delay_signal_ms_(0),
	last_congestion_signal_ms_(0),
	last_delays_index_(0),
	exp_smoothed_delay_ms_(-1),
	est_queuing_delay_signal_ms_(0) {
	}

	NadaBweReceiver::~NadaBweReceiver() {
	}

	void NadaBweReceiver::ReceivePacket(int64_t arrival_time_ms,
	const MediaPacket& media_packet) {
	const float kAlpha = 0.1f; // Used for exponential smoothing.
	const int64_t kDelayLowThresholdMs = 50; // Referred as d_th.
	const int64_t kDelayMaxThresholdMs = 400; // Referred as d_max.

	clock_.AdvanceTimeMilliseconds(arrival_time_ms - clock_.TimeInMilliseconds());
	recv_stats_->IncomingPacket(media_packet.header(),
	media_packet.payload_size(), false);
	// Refered as x_n.
	int64_t delay_ms = arrival_time_ms - media_packet.sender_timestamp_ms();

	// The min should be updated within the first 10 minutes.
	if (clock_.TimeInMilliseconds() < 10 * 60 * 1000) {
	baseline_delay_ms_ = std::min(baseline_delay_ms_, delay_ms);
	}

	delay_signal_ms_ = delay_ms - baseline_delay_ms_; // Refered as d_n.
	const int kMedian = arraysize(last_delays_ms_);
	last_delays_ms_[(last_delays_index_++) % kMedian] = delay_signal_ms_;
	int size = std::min(last_delays_index_, kMedian);

	int64_t median_filtered_delay_ms_ = MedianFilter(last_delays_ms_, size);
	exp_smoothed_delay_ms_ = ExponentialSmoothingFilter(
	median_filtered_delay_ms_, exp_smoothed_delay_ms_, kAlpha);

	if (exp_smoothed_delay_ms_ < kDelayLowThresholdMs) {
	est_queuing_delay_signal_ms_ = exp_smoothed_delay_ms_;
	} else if (exp_smoothed_delay_ms_ < kDelayMaxThresholdMs) {
	est_queuing_delay_signal_ms_ = static_cast<int64_t>(
	pow((static_cast<double>(kDelayMaxThresholdMs -
	exp_smoothed_delay_ms_)) /
	(kDelayMaxThresholdMs - kDelayLowThresholdMs),
	4.0) *
	kDelayLowThresholdMs);
	} else {
	est_queuing_delay_signal_ms_ = 0;
	}

	// Log received packet information.
	BweReceiver::ReceivePacket(arrival_time_ms, media_packet);
	}

	FeedbackPacket* NadaBweReceiver::GetFeedback(int64_t now_ms) {
	const int64_t kPacketLossPenaltyMs = 1000; // Referred as d_L.

	if (now_ms - last_feedback_ms_ < 100) {
	return NULL;
	}

	float loss_fraction = RecentPacketLossRatio();

	int64_t loss_signal_ms =
	static_cast<int64_t>(loss_fraction * kPacketLossPenaltyMs + 0.5f);
	int64_t congestion_signal_ms = est_queuing_delay_signal_ms_ + loss_signal_ms;

	float derivative = 0.0f;
	if (last_feedback_ms_ > 0) {
	derivative = (congestion_signal_ms - last_congestion_signal_ms_) /
	static_cast<float>(now_ms - last_feedback_ms_);
	}
	last_feedback_ms_ = now_ms;
	last_congestion_signal_ms_ = congestion_signal_ms;

	int64_t corrected_send_time_ms = 0L;

	if (!received_packets_.empty()) {
	PacketIdentifierNode* latest = *(received_packets_.begin());
	corrected_send_time_ms =
	latest->send_time_ms + now_ms - latest->arrival_time_ms;
	}

	// Sends a tuple containing latest values of <d_hat_n, d_tilde_n, x_n, x'_n,
	// R_r> and additional information.
	return new NadaFeedback(flow_id_, now_ms * 1000, exp_smoothed_delay_ms_,
	est_queuing_delay_signal_ms_, congestion_signal_ms,
	derivative, RecentKbps(), corrected_send_time_ms);
	}

	// If size is even, the median is the average of the two middlemost numbers.
	int64_t NadaBweReceiver::MedianFilter(int64_t* last_delays_ms, int size) {
	std::vector<int64_t> array_copy(last_delays_ms, last_delays_ms + size);
	std::nth_element(array_copy.begin(), array_copy.begin() + size / 2,
	array_copy.end());
	if (size % 2 == 1) {
	// Typically, size = 5. For odd size values, right and left are equal.
	return array_copy.at(size / 2);
	}
	int64_t right = array_copy.at(size / 2);
	std::nth_element(array_copy.begin(), array_copy.begin() + (size - 1) / 2,
	array_copy.end());
	int64_t left = array_copy.at((size - 1) / 2);
	return (left + right + 1) / 2;
	}

	int64_t NadaBweReceiver::ExponentialSmoothingFilter(int64_t new_value,
	int64_t last_smoothed_value,
	float alpha) {
	if (last_smoothed_value < 0) {
	return new_value; // Handling initial case.
	}
	return static_cast<int64_t>(alpha * new_value +
	(1.0f - alpha) * last_smoothed_value + 0.5f);
	}

	// Implementation according to Cisco's proposal by default.
	NadaBweSender::NadaBweSender(int kbps, BitrateObserver* observer, Clock* clock)
	: BweSender(kbps), // Referred as "Reference Rate" = R_n.,
	clock_(clock),
	observer_(observer),
	original_operating_mode_(true) {
	}

	NadaBweSender::NadaBweSender(BitrateObserver* observer, Clock* clock)
	: BweSender(kMinNadaBitrateKbps), // Referred as "Reference Rate" = R_n.
	clock_(clock),
	observer_(observer),
	original_operating_mode_(true) {}

	NadaBweSender::~NadaBweSender() {
	}

	int NadaBweSender::GetFeedbackIntervalMs() const {
	return 100;
	}

	void NadaBweSender::GiveFeedback(const FeedbackPacket& feedback) {
	const NadaFeedback& fb = static_cast<const NadaFeedback&>(feedback);

	// Following parameters might be optimized.
	const int64_t kQueuingDelayUpperBoundMs = 10;
	const float kDerivativeUpperBound =
	10.0f / std::max<int64_t>(1, min_feedback_delay_ms_);
	// In the modified version, a higher kMinUpperBound allows a higher d_hat
	// upper bound for calling AcceleratedRampUp.
	const float kProportionalityDelayBits = 20.0f;

	int64_t now_ms = clock_->TimeInMilliseconds();
	float delta_s = now_ms - last_feedback_ms_;
	last_feedback_ms_ = now_ms;
	// Update delta_0.
	min_feedback_delay_ms_ =
	std::min(min_feedback_delay_ms_, static_cast<int64_t>(delta_s));

	// Update RTT_0.
	int64_t rtt_ms = now_ms - fb.latest_send_time_ms();
	min_round_trip_time_ms_ = std::min(min_round_trip_time_ms_, rtt_ms);

	// Independent limits for AcceleratedRampUp conditions variables:
	// x_n, d_tilde and x'_n in the original implementation, plus
	// d_hat and receiving_rate in the modified one.
	// There should be no packet losses/marking, hence x_n == d_tilde.
	if (original_operating_mode_) {
	// Original if conditions and rate update.
	if (fb.congestion_signal() == fb.est_queuing_delay_signal_ms() &&
	fb.est_queuing_delay_signal_ms() < kQueuingDelayUpperBoundMs &&
	fb.derivative() < kDerivativeUpperBound) {
	AcceleratedRampUp(fb);
	} else {
	GradualRateUpdate(fb, delta_s, 1.0);
	}
	} else {
	// Modified if conditions and rate update; new ramp down mode.
	if (fb.congestion_signal() == fb.est_queuing_delay_signal_ms() &&
	fb.est_queuing_delay_signal_ms() < kQueuingDelayUpperBoundMs &&
	fb.exp_smoothed_delay_ms() <
	kMinNadaBitrateKbps / kProportionalityDelayBits &&
	fb.derivative() < kDerivativeUpperBound &&
	fb.receiving_rate() > kMinNadaBitrateKbps) {
	AcceleratedRampUp(fb);
	} else if (fb.congestion_signal() > kMaxCongestionSignalMs \|\|
	fb.exp_smoothed_delay_ms() > kMaxCongestionSignalMs) {
	AcceleratedRampDown(fb);
	} else {
	double bitrate_reference =
	(2.0 * bitrate_kbps_) / (kMaxBitrateKbps + kMinNadaBitrateKbps);
	double smoothing_factor = pow(bitrate_reference, 0.75);
	GradualRateUpdate(fb, delta_s, smoothing_factor);
	}
	}

	bitrate_kbps_ = std::min(bitrate_kbps_, kMaxBitrateKbps);
	bitrate_kbps_ = std::max(bitrate_kbps_, kMinNadaBitrateKbps);

	observer_->OnNetworkChanged(1000 * bitrate_kbps_, 0, rtt_ms);
	}

	int64_t NadaBweSender::TimeUntilNextProcess() {
	return 100;
	}

	void NadaBweSender::Process() {
	}

	void NadaBweSender::AcceleratedRampUp(const NadaFeedback& fb) {
	const int kMaxRampUpQueuingDelayMs = 50; // Referred as T_th.
	const float kGamma0 = 0.5f; // Referred as gamma_0.

	float gamma =
	std::min(kGamma0, static_cast<float>(kMaxRampUpQueuingDelayMs) /
	(min_round_trip_time_ms_ + min_feedback_delay_ms_));

	bitrate_kbps_ = static_cast<int>((1.0f + gamma) * fb.receiving_rate() + 0.5f);
	}

	void NadaBweSender::AcceleratedRampDown(const NadaFeedback& fb) {
	const float kGamma0 = 0.9f;
	float gamma = 3.0f * kMaxCongestionSignalMs /
	(fb.congestion_signal() + fb.exp_smoothed_delay_ms());
	gamma = std::min(gamma, kGamma0);
	bitrate_kbps_ = gamma * fb.receiving_rate() + 0.5f;
	}

	void NadaBweSender::GradualRateUpdate(const NadaFeedback& fb,
	float delta_s,
	double smoothing_factor) {
	const float kTauOMs = 500.0f; // Referred as tau_o.
	const float kEta = 2.0f; // Referred as eta.
	const float kKappa = 1.0f; // Referred as kappa.
	const float kReferenceDelayMs = 10.0f; // Referred as x_ref.
	const float kPriorityWeight = 1.0f; // Referred as w.

	float x_hat = fb.congestion_signal() + kEta * kTauOMs * fb.derivative();

	float kTheta = kPriorityWeight * (kMaxBitrateKbps - kMinNadaBitrateKbps) *
	kReferenceDelayMs;

	int original_increase = static_cast<int>(
	(kKappa * delta_s *
	(kTheta - (bitrate_kbps_ - kMinNadaBitrateKbps) * x_hat)) /
	(kTauOMs * kTauOMs) +
	0.5f);

	bitrate_kbps_ = bitrate_kbps_ + smoothing_factor * original_increase;
	}

	} // namespace bwe
	} // namespace testing
	} // namespace webrtc