如何在 OMNet++ 4.5 中实现 CCA

Question

我正在编写代码以使用 OMNeT++ 4.5 模拟无线传感器网络 MAC 协议。但我不知道如何实施 CCA（运营商渠道评估）。你能帮我提供任何示例代码吗？

Answer 1

我建议阅读 INET 中的 BMacLayer.cc 文件

case CCA:
            if (msg->getKind() == BMAC_CCA_TIMEOUT) {
                // channel is clear
                // something waiting in eth queue?
                if (macQueue.size() > 0) {
                    EV_DETAIL << "State CCA, message CCA_TIMEOUT, new state"
                                 " SEND_PREAMBLE" << endl;
                    macState = SEND_PREAMBLE;
                    radio->setRadioMode(IRadio::RADIO_MODE_TRANSMITTER);
                    changeDisplayColor(YELLOW);
                    scheduleAt(simTime() + slotDuration, stop_preambles);
                    return;
                }
                // if not, go back to sleep and wake up after a full period
                else {
                    EV_DETAIL << "State CCA, message CCA_TIMEOUT, new state SLEEP"
                              << endl;
                    scheduleAt(simTime() + slotDuration, wakeup);
                    macState = SLEEP;
                    radio->setRadioMode(IRadio::RADIO_MODE_SLEEP);
                    changeDisplayColor(BLACK);
                    return;
                }
            }
            // during CCA, we received a preamble. Go to state WAIT_DATA and
            // schedule the timeout.
            if (msg->getKind() == BMAC_PREAMBLE) {
                nbRxPreambles++;
                EV_DETAIL << "State CCA, message BMAC_PREAMBLE received, new state"
                             " WAIT_DATA" << endl;
                macState = WAIT_DATA;
                cancelEvent(cca_timeout);
                scheduleAt(simTime() + slotDuration + checkInterval, data_timeout);
                delete msg;
                return;
            }
            // this case is very, very, very improbable, but let's do it.
            // if in CCA and the node receives directly the data packet, switch to
            // state WAIT_DATA and re-send the message
            if (msg->getKind() == BMAC_DATA) {
                nbRxDataPackets++;
                EV_DETAIL << "State CCA, message BMAC_DATA, new state WAIT_DATA"
                          << endl;
                macState = WAIT_DATA;
                cancelEvent(cca_timeout);
                scheduleAt(simTime() + slotDuration + checkInterval, data_timeout);
                scheduleAt(simTime(), msg);
                return;
            }
            //in case we get an ACK, we simply dicard it, because it means the end
            //of another communication
            if (msg->getKind() == BMAC_ACK) {
                EV_DETAIL << "State CCA, message BMAC_ACK, new state CCA" << endl;
                delete msg;
                return;
            }
            break;

有关更多详细信息，您可以参考 在 MiXiM 中实现 WSN 的 B-MAC 协议，作者是 Anna Förster