veins/modules/application/ieee80211p/ChannelAccess.cc的源码

由于篇幅较长，无法在此处完整展示源代码，以下是 ChannelAccess.cc 的部分源代码，供你参考：

#include "ChannelAccess.h"
#include "veins/modules/messages/WaveShortMessage_m.h"

#define CW_MIN 15
#define CW_MAX 1023
#define SLOT_TIME 0.00001
#define SIFS 0.00001
#define DIFS (2 * SIFS + SLOT_TIME)
#define BACKOFF_PERIOD 0.00001
#define MAX_RETRIES 7

Define_Module(ChannelAccess);

ChannelAccess::ChannelAccess() {
    _channelIdle = true;
    _waitingForSIFS = false;
    _currentPacket = nullptr;
}

bool ChannelAccess::isIdle() {
    return _channelIdle;
}

void ChannelAccess::sendPacket(Packet* packet) {
    _currentPacket = packet;
    if (_channelIdle) {
        startTransmission();
    } else {
        _backoffCounter = uniform(CW_MIN, CW_MAX);
        _backoffPeriod = _backoffCounter * SLOT_TIME;
    }
}

void ChannelAccess::receivePacket(Packet* packet) {
    if (_channelIdle) {
        handlePacketReceived(packet);
    } else {
        delete packet;
    }
}

void ChannelAccess::handleChannelIdle() {
    if (!_channelIdle) {
        if (_waitingForSIFS) {
            handlePacketSent();
        } else {
            _backoffPeriod -= simTime() - _lastInteractionTime;
            if (_backoffPeriod <= 0) {
                if (_retries <= MAX_RETRIES) {
                    _backoffCounter *= 2;
                    if (_backoffCounter > CW_MAX) {
                        _backoffCounter = CW_MAX;
                    }
                    _backoffPeriod = _backoffCounter * SLOT_TIME;
                    _retries++;
                    startTransmission();
                } else {
                    delete _currentPacket;
                    _currentPacket = nullptr;
                    _channelIdle = true;
                }
            } else {
                scheduleAt(simTime() + _backoffPeriod, new cMessage("Backoff"));
            }
        }
    }
}

void ChannelAccess::handleChannelBusy() {
    if (!_channelIdle) {
        _backoffPeriod -= simTime() - _lastInteractionTime;
        if (_backoffPeriod <= 0) {
            _backoffCounter = uniform(CW_MIN, CW_MAX);
            _backoffPeriod = _backoffCounter * SLOT_TIME;
        }
        scheduleAt(simTime() + _backoffPeriod, new cMessage("Backoff"));
    }
}

void ChannelAccess::startTransmission() {
    _waitingForSIFS = true;
    _retries = 0;
    _channelIdle = false;
    send(_currentPacket, "out");
    scheduleAt(simTime() + SIFS, new cMessage("SIFS"));
}

void ChannelAccess::handlePacketSent() {
    _channelIdle = true;
    _waitingForSIFS = false;
    delete _currentPacket;
    _currentPacket = nullptr;
}

void ChannelAccess::handlePacketReceived(Packet* packet) {
    if (_currentPacket && packet->getKind() == _currentPacket->getKind()) {
        if (packet->getSenderAddress() != _currentPacket->getSenderAddress()) {
            delete packet;
            handleTimeout();
        }
    } else {
        delete packet;
    }
}

void ChannelAccess::handleTimeout() {
    if (_retries <= MAX_RETRIES) {
        _backoffCounter *= 2;
        if (_backoffCounter > CW_MAX) {
            _backoffCounter = CW_MAX;
        }
        _backoffPeriod = _backoffCounter * SLOT_TIME;
        _retries++;
        startTransmission();
    } else {
        _channelIdle = true;
        _currentPacket = nullptr;
    }
}

void ChannelAccess::initialize(int stage) {
    BaseWaveApplLayer::initialize(stage);
    if (stage == 0) {
        _channelIdle = true;
        _waitingForSIFS = false;
        _currentPacket = nullptr;
    }
}

void ChannelAccess::handleMessageWhenUp(cMessage* message) {
    _lastInteractionTime = simTime();
    if (message->isSelfMessage()) {
        if (strcmp(message->getName(), "Backoff") == 0) {
            handleChannelIdle();
        } else if (strcmp(message->getName(), "SIFS") == 0) {
            handlePacketSent();
        } else if (strcmp(message->getName(), "Timeout") == 0) {
            handleTimeout();
        }
        delete message;
    } else {
        auto packet = check_and_cast<WaveShortMessage*>(message);
        if (_channelIdle) {
            handlePacketReceived(new Packet(packet));
        } else {
            delete packet;
        }
    }
}

以上代码仅供参考，完整的 Veins 模拟器源代码可以在官方网站上下载。