minstrel-wifi-manager.h

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/*
 * Copyright (c) 2009 Duy Nguyen
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Authors: Duy Nguyen <duy@soe.ucsc.edu>
 *          Matías Richart <mrichart@fing.edu.uy>
 */
 
#ifndef MINSTREL_WIFI_MANAGER_H
#define MINSTREL_WIFI_MANAGER_H
 
#include "ns3/traced-value.h"
#include "ns3/wifi-remote-station-manager.h"
 
#include <fstream>
#include <map>
 
namespace ns3
{
 
class UniformRandomVariable;
 
/**
 * A struct to contain all information related to a data rate
 */
struct RateInfo
{
    /**
     * Perfect transmission time calculation, or frame calculation
     * Given a bit rate and a packet length n bytes
     */
    Time perfectTxTime;
 
    uint32_t retryCount;         ///< retry limit
    uint32_t adjustedRetryCount; ///< adjust the retry limit for this rate
    uint32_t numRateAttempt;     ///< how many number of attempts so far
    uint32_t numRateSuccess;     ///< number of successful packets
    uint32_t prob;               ///< (# packets success)/(# total packets)
    /**
     * EWMA calculation
     * ewma_prob =[prob *(100 - ewma_level) + (ewma_prob_old * ewma_level)]/100
     */
    uint32_t ewmaProb;
    uint32_t throughput; ///< throughput of a rate in bps
 
    uint32_t prevNumRateAttempt; //!< Number of transmission attempts with previous rate.
    uint32_t prevNumRateSuccess; //!< Number of successful frames transmitted with previous rate.
    uint64_t successHist;        //!< Aggregate of all transmission successes.
    uint64_t attemptHist;        //!< Aggregate of all transmission attempts.
 
    uint8_t numSamplesSkipped; //!< number of samples skipped
    int sampleLimit;           //!< sample limit
};
 
/**
 * Data structure for a Minstrel Rate table
 * A vector of a struct RateInfo
 */
typedef std::vector<RateInfo> MinstrelRate;
/**
 * Data structure for a Sample Rate table
 * A vector of a vector uint8_t
 */
typedef std::vector<std::vector<uint8_t>> SampleRate;
 
/**
 * \brief hold per-remote-station state for Minstrel Wifi manager.
 *
 * This struct extends from WifiRemoteStation struct to hold additional
 * information required by the Minstrel Wifi manager
 */
struct MinstrelWifiRemoteStation : public WifiRemoteStation
{
    Time m_nextStatsUpdate; ///< 10 times every second
 
    /**
     * To keep track of the current position in the our random sample table
     * going row by row from 1st column until the 10th column(Minstrel defines 10)
     * then we wrap back to the row 1 column 1.
     * note: there are many other ways to do this.
     */
    uint8_t m_col;                ///< column index
    uint8_t m_index;              ///< vector index
    uint16_t m_maxTpRate;         ///< the current throughput rate in bps
    uint16_t m_maxTpRate2;        ///< second highest throughput rate in bps
    uint16_t m_maxProbRate;       ///< rate with highest probability of success in bps
    uint8_t m_nModes;             ///< number of modes supported
    int m_totalPacketsCount;      ///< total number of packets as of now
    int m_samplePacketsCount;     ///< how many packets we have sample so far
    int m_numSamplesDeferred;     ///< number samples deferred
    bool m_isSampling;            ///< a flag to indicate we are currently sampling
    uint16_t m_sampleRate;        ///< current sample rate in bps
    bool m_sampleDeferred;        ///< a flag to indicate sample rate is on the second stage
    uint32_t m_shortRetry;        ///< short retries such as control packets
    uint32_t m_longRetry;         ///< long retries such as data packets
    uint32_t m_retry;             ///< total retries short + long
    uint16_t m_txrate;            ///< current transmit rate in bps
    bool m_initialized;           ///< for initializing tables
    MinstrelRate m_minstrelTable; ///< minstrel table
    SampleRate m_sampleTable;     ///< sample table
    std::ofstream m_statsFile;    ///< stats file
};
 
/**
 * \brief Implementation of Minstrel Rate Control Algorithm
 * \ingroup wifi
 *
 * Minstrel is a rate control algorithm implemented in MadWifi and Linux.
 * The basic principle is to probe the environment and adapt the rate
 * based on statistics collected on the probability of successful
 * transmission.  The algorithm adapts the rate to the highest rate
 * that it considers successful, and spends a fraction of its time
 * doing 'look around' by trying other rates.
 *
 * Minstrel is appropriate for non-HT configurations; for HT (i.e. 802.11n
 * or higher), users should use MinstrelHtWifiManager instead.
 * Minstrel will error exit if the user tries to configure it with a
 * Wi-Fi MAC that supports 802.11n or higher.
 *
 * Some notes on this implementation follow.  The implementation has
 * been adapted to bring it closer to the Linux implementation.
 * For each rate, a new parameter samplesSkipped is added. This parameter
 * is intended to solve an issue regarding the sampling of low rates when
 * a high rate is working well, which leads to outdated statistics.
 * This change makes throughput a bit lower in simple, stable scenarios,
 * but may help in dynamic scenarios to react faster and more accurately
 * to changes.
 *
 * Related to the previous, the logic for deciding when to sample random
 * rates is as follows.  When a sample rate is deferred to the second MRR
 * chain stage, a new parameter (numSamplesDeferred) is increased. This
 * parameters is used (jointly with sampleCount) to compare current
 * sample count with the lookaround rate.
 *
 * Also related with sampling, another parameter sampleLimit is added.
 * This parameter limits the number of times a very low or very high
 * probability rate is sampled, avoiding to try a poorly working sample
 * rate too often.
 *
 * When updating the EWMA probability of a rate for the first time, it does
 * not apply EWMA but instead assigns the entire probability.
 * Since the EWMA probability is initialized to zero, this generates
 * a more accurate EWMA.
 */
class MinstrelWifiManager : public WifiRemoteStationManager
{
  public:
    /**
     * \brief Get the type ID.
     * \return the object TypeId
     */
    static TypeId GetTypeId();
    MinstrelWifiManager();
    ~MinstrelWifiManager() override;
 
    void SetupPhy(const Ptr<WifiPhy> phy) override;
    void SetupMac(const Ptr<WifiMac> mac) override;
    int64_t AssignStreams(int64_t stream) override;
 
    /**
     * Update the rate.
     *
     * \param station the station object
     */
    void UpdateRate(MinstrelWifiRemoteStation* station);
 
    /**
     * Update the Minstrel Table.
     *
     * \param station the station object
     */
    void UpdateStats(MinstrelWifiRemoteStation* station);
 
    /**
     * Find a rate to use from Minstrel Table.
     *
     * \param station the station object
     * \returns the rate in bps
     */
    uint16_t FindRate(MinstrelWifiRemoteStation* station);
 
    /**
     * Get data transmit vector.
     *
     * \param station the station object
     * \returns WifiTxVector
     */
    WifiTxVector GetDataTxVector(MinstrelWifiRemoteStation* station);
 
    /**
     * Get RTS transmit vector.
     *
     * \param station the station object
     * \returns WifiTxVector
     */
    WifiTxVector GetRtsTxVector(MinstrelWifiRemoteStation* station);
 
    /**
     * Get the number of retries.
     *
     * \param station the station object
     * \returns the number of retries
     */
    uint32_t CountRetries(MinstrelWifiRemoteStation* station);
 
    /**
     * Update packet counters.
     *
     * \param station the station object
     */
    void UpdatePacketCounters(MinstrelWifiRemoteStation* station);
 
    /**
     * Update the number of retries and reset accordingly.
     *
     * \param station the station object
     */
    void UpdateRetry(MinstrelWifiRemoteStation* station);
 
    /**
     * Check for initializations.
     *
     * \param station the station object
     */
    void CheckInit(MinstrelWifiRemoteStation* station);
 
    /**
     * Initialize Sample Table.
     *
     * \param station the station object
     */
    void InitSampleTable(MinstrelWifiRemoteStation* station);
 
  private:
    void DoInitialize() override;
    WifiRemoteStation* DoCreateStation() const override;
    void DoReportRxOk(WifiRemoteStation* station, double rxSnr, WifiMode txMode) override;
    void DoReportRtsFailed(WifiRemoteStation* station) override;
    void DoReportDataFailed(WifiRemoteStation* station) override;
    void DoReportRtsOk(WifiRemoteStation* station,
                       double ctsSnr,
                       WifiMode ctsMode,
                       double rtsSnr) override;
    void DoReportDataOk(WifiRemoteStation* station,
                        double ackSnr,
                        WifiMode ackMode,
                        double dataSnr,
                        uint16_t dataChannelWidth,
                        uint8_t dataNss) override;
    void DoReportFinalRtsFailed(WifiRemoteStation* station) override;
    void DoReportFinalDataFailed(WifiRemoteStation* station) override;
    WifiTxVector DoGetDataTxVector(WifiRemoteStation* station, uint16_t allowedWidth) override;
    WifiTxVector DoGetRtsTxVector(WifiRemoteStation* station) override;
 
    bool DoNeedRetransmission(WifiRemoteStation* st,
                              Ptr<const Packet> packet,
                              bool normally) override;
 
    /**
     * Estimate the TxTime of a packet with a given mode.
     *
     * \param mode Wi-Fi mode
     * \returns the transmission time
     */
    Time GetCalcTxTime(WifiMode mode) const;
    /**
     * Add transmission time for the given mode to an internal list.
     *
     * \param mode Wi-Fi mode
     * \param t transmission time
     */
    void AddCalcTxTime(WifiMode mode, Time t);
 
    /**
     * Initialize Minstrel Table.
     *
     * \param station the station object
     */
    void RateInit(MinstrelWifiRemoteStation* station);
 
    /**
     * Get the next sample from Sample Table.
     *
     * \param station the station object
     * \returns the next sample
     */
    uint16_t GetNextSample(MinstrelWifiRemoteStation* station);
 
    /**
     * Estimate the time to transmit the given packet with the given number of retries.
     * This function is "roughly" the function "calc_usecs_unicast_packet" in minstrel.c
     * in the madwifi implementation.
     *
     * The basic idea is that, we try to estimate the "average" time used to transmit the
     * packet for the given number of retries while also accounting for the 802.11 congestion
     * window change. The original code in the madwifi seems to estimate the number of backoff
     * slots as the half of the current CW size.
     *
     * There are four main parts:
     *  - wait for DIFS (sense idle channel)
     *  - Ack timeouts
     *  - Data transmission
     *  - backoffs according to CW
     *
     * \param dataTransmissionTime the data transmission time
     * \param shortRetries short retries
     * \param longRetries long retries
     * \returns the unicast packet time
     */
    Time CalculateTimeUnicastPacket(Time dataTransmissionTime,
                                    uint32_t shortRetries,
                                    uint32_t longRetries);
 
    /**
     * Print Sample Table.
     *
     * \param station the station object
     */
    void PrintSampleTable(MinstrelWifiRemoteStation* station) const;
 
    /**
     * Print Minstrel Table.
     *
     * \param station the station object
     */
    void PrintTable(MinstrelWifiRemoteStation* station);
 
    /**
     * typedef for a vector of a pair of Time, WifiMode.
     * Essentially a map from WifiMode to its corresponding transmission time
     * to transmit a reference packet.
     */
    typedef std::map<WifiMode, Time> TxTime;
 
    TxTime m_calcTxTime;      ///< to hold all the calculated TxTime for all modes
    Time m_updateStats;       ///< how frequent do we calculate the stats
    uint8_t m_lookAroundRate; ///< the % to try other rates than our current rate
    uint8_t m_ewmaLevel;      ///< exponential weighted moving average
    uint8_t m_sampleCol;      ///< number of sample columns
    uint32_t m_pktLen;        ///< packet length used to calculate mode TxTime
    bool m_printStats;        ///< whether statistics table should be printed.
    bool m_printSamples;      ///< whether samples table should be printed.
 
    /// Provides uniform random variables.
    Ptr<UniformRandomVariable> m_uniformRandomVariable;
 
    TracedValue<uint64_t> m_currentRate; //!< Trace rate changes
};
 
} // namespace ns3
 
#endif /* MINSTREL_WIFI_MANAGER_H */