src/core/utils/channel_monitor.hpp

/*
 *  Copyright (c) 2018, The OpenThread Authors.
 *  All rights reserved.
 *
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 *  modification, are permitted provided that the following conditions are met:
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *  3. Neither the name of the copyright holder nor the
 *     names of its contributors may be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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 */

/**
 * @file
 *   This file includes definitions for channel monitoring module.
 */

#ifndef CHANNEL_MONITOR_HPP_
#define CHANNEL_MONITOR_HPP_

#include "openthread-core-config.h"

#if OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE

#include <openthread/platform/radio.h>

#include "common/locator.hpp"
#include "common/non_copyable.hpp"
#include "common/timer.hpp"
#include "mac/mac.hpp"
#include "radio/radio.hpp"

namespace ot {
namespace Utils {

/**
 * @addtogroup utils-channel-monitor
 *
 * @brief
 *   This module includes definitions monitoring quality of channels.
 *
 * @{
 */

/**
 * This class implements the channel monitoring logic.
 *
 * Channel Monitoring will periodically monitor all channels to help determine the cleaner channels (channels
 * with less interference).
 *
 * When Channel Monitoring is active, every `kSampleInterval`, a zero-duration Energy Scan is performed on every
 * channel collecting a single RSSI  sample per channel. The RSSI samples are compared with a pre-specified RSSI
 * threshold `kRssiThreshold`. As an indicator of channel quality, the `ChannelMonitor` maintains and provides the
 * average rate/percentage of RSSI samples that are above the threshold within (approximately) a specified sample
 * window (referred to as "channel occupancy").
 *
 */
class ChannelMonitor : public InstanceLocator, private NonCopyable
{
public:
    /**
     * The channel RSSI sample interval in milliseconds.
     *
     */
    static constexpr uint32_t kSampleInterval = OPENTHREAD_CONFIG_CHANNEL_MONITOR_SAMPLE_INTERVAL;

    /**
     * The RSSI threshold in dBm.
     *
     * It is recommended that this value is set to same value as the CCA threshold used by radio.
     *
     */
    static constexpr int8_t kRssiThreshold = OPENTHREAD_CONFIG_CHANNEL_MONITOR_RSSI_THRESHOLD;

    /**
     * The averaging sample window length (in units of sample interval).
     *
     */
    static constexpr uint32_t kSampleWindow = OPENTHREAD_CONFIG_CHANNEL_MONITOR_SAMPLE_WINDOW;

    /**
     * This constructor initializes the object.
     *
     * @param[in]  aInstance     A reference to the OpenThread instance.
     *
     */
    explicit ChannelMonitor(Instance &aInstance);

    /**
     * This method starts the Channel Monitoring operation.
     *
     * Once started, any previously collected data is cleared.
     *
     * @retval kErrorNone      Channel Monitoring started successfully.
     * @retval kErrorAlready   Channel Monitoring has already been started.
     *
     */
    Error Start(void);

    /**
     * This method stops the Channel Monitoring operation.
     *
     * @note After `Stop()`, the previous data is still valid and can be read.
     *
     * @retval kErrorNone      Channel Monitoring stopped successfully.
     * @retval kErrorAlready   Channel Monitoring has already been stopped.
     *
     */
    Error Stop(void);

    /**
     * This method indicates whether the Channel Monitoring operation is started and running.
     *
     * @returns TRUE if the Channel Monitoring operation is running, FALSE otherwise.
     *
     */
    bool IsRunning(void) const { return mTimer.IsRunning(); }

    /**
     * This method clears all currently stored data.
     *
     */
    void Clear(void);

    /**
     * This method returns the total number of RSSI samples (per channel) taken so far (since call to `Start()`).
     *
     * @returns total number of RSSI sample taken since last call to `Start()`.
     *
     */
    uint32_t GetSampleCount(void) const { return mSampleCount; }

    /**
     * This method returns the current channel occupancy for a given channel.
     *
     * The channel occupancy represents the average rate/percentage of RSSI samples that were above RSSI threshold
     * `kRssiThreshold` ("bad" RSSI samples).
     *
     * For the first `kSampleWindow` samples, the average is maintained as the actual percentage (i.e., ratio of number
     * of "bad" samples by total number of samples). After `kSampleWindow` samples, the averager uses an exponentially
     * weighted moving average logic with weight coefficient `1/kSampleWindow` for new values. Practically, this means
     * the occupancy is representative of up to `3 * kSampleWindow` last samples with highest weight given to the
     * latest `kSampleWindow` samples.
     *
     * Max value of `0xffff` indicates all RSSI samples were above RSSI threshold (i.e. 100% of samples were "bad").
     *
     * @param[in]  aChannel     The channel for which to get the link occupancy.
     *
     * @returns the current channel occupancy for the given channel.
     *
     */
    uint16_t GetChannelOccupancy(uint8_t aChannel) const;

    /**
     * This method finds the best channel(s) (with least occupancy rate) in a given channel mask.
     *
     * The channels are compared based on their occupancy rate from `GetChannelOccupancy()` and lower occupancy rate
     * is considered better.
     *
     * @param[in]  aMask         A channel mask (the search is limited to channels in @p aMask).
     * @param[out] aOccupancy    A reference to `uint16` to return the occupancy rate associated with best channel(s).
     *
     * @returns    A channel mask containing the best channels. A mask is returned in case there are more than one
     *             channel with the same occupancy rate value.
     *
     */
    Mac::ChannelMask FindBestChannels(const Mac::ChannelMask &aMask, uint16_t &aOccupancy) const;

private:
#if (OPENTHREAD_CONFIG_RADIO_2P4GHZ_OQPSK_SUPPORT && OPENTHREAD_CONFIG_RADIO_915MHZ_OQPSK_SUPPORT)
    static constexpr uint8_t kNumChannelMasks = 8;
#else
    static constexpr uint8_t kNumChannelMasks = 4;
#endif
    static constexpr uint8_t  kNumChannels       = (Radio::kChannelMax - Radio::kChannelMin + 1);
    static constexpr uint32_t kTimerInterval     = (kSampleInterval / kNumChannelMasks);
    static constexpr uint16_t kMaxJitterInterval = 4096;
    static constexpr uint32_t kMaxOccupancy      = 0xffff;

    static void HandleTimer(Timer &aTimer);
    void        HandleTimer(void);
    static void HandleEnergyScanResult(Mac::EnergyScanResult *aResult, void *aContext);
    void        HandleEnergyScanResult(Mac::EnergyScanResult *aResult);
    void        LogResults(void);

    static const uint32_t mScanChannelMasks[kNumChannelMasks];

    uint8_t    mChannelMaskIndex : 3;
    uint32_t   mSampleCount : 29;
    uint16_t   mChannelOccupancy[kNumChannels];
    TimerMilli mTimer;
};

/**
 * @}
 *
 */

} // namespace Utils
} // namespace ot

#endif // OPENTHREAD_CONFIG_CHANNEL_MONITOR_ENABLE

#endif // CHANNEL_MONITOR_HPP_