python代码实现csma/ca机制并呈现性能曲线

Sure, I can help you with that! CSMA/CA is a protocol used in wireless networks to avoid collisions by listening to the channel before transmitting data. Here's an example Python code that implements the CSMA/CA mechanism using the Network Simulator 3 library:

from ns3 import *
import matplotlib.pyplot as plt

def run_simulation(n_stations, packet_size, data_rate, sim_time):
    # create wireless nodes and set parameters
    wifi = WifiHelper()
    wifi.SetStandard(WIFI_PHY_STANDARD_80211b)
    wifi_channel = YansWifiChannelHelper.Default()
    wifi_phy = YansWifiPhyHelper.Default()
    wifi_phy.SetChannel(wifi_channel.Create())

    # create CSMA/CA helper and set parameters
    csma = CsmaHelper()
    csma.SetChannelAttribute("DataRate", DataRateValue(DataRate(data_rate)))
    csma.SetChannelAttribute("Delay", TimeValue(MicroSeconds(2)))

    # create network devices and connect them to nodes
    devices = csma.Install(wifi_phy, Nodes())

    # create internet stack and assign IP addresses
    internet = InternetStackHelper()
    internet.Install(Nodes())
    address = Ipv4AddressHelper()
    address.SetBase(Ipv4Address("10.1.1.0"), Ipv4Mask("255.255.255.0"))
    interfaces = address.Assign(devices)

    # create traffic and on/off applications
    port = 9
    on_time = ConstantRandomVariable(0.1)
    off_time = ConstantRandomVariable(0.9)
    for i in range(n_stations):
        # create UDP traffic
        udp_helper = UdpEchoClientHelper(interfaces.GetAddress(i), port)
        udp_helper.SetAttribute("MaxPackets", UintegerValue(1))
        udp_helper.SetAttribute("Interval", TimeValue(Seconds(1)))
        udp_helper.SetAttribute("PacketSize", UintegerValue(packet_size))

        # create on/off application
        on_off_helper = OnOffHelper("ns3::UdpSocketFactory", Address())
        on_off_helper.SetAttribute("DataRate", DataRateValue(DataRate(data_rate)))
        on_off_helper.SetAttribute("PacketSize", UintegerValue(packet_size))
        on_off_helper.SetAttribute("OnTime", StringValue(str(on_time.Get())))
        on_off_helper.SetAttribute("OffTime", StringValue(str(off_time.Get())))
        on_off_helper.SetAttribute("Remote", AddressValue(interfaces.GetAddress(i)))

        # install applications on nodes
        udp_app = udp_helper.Install(NodeList.GetNode(i))
        on_off_app = on_off_helper.Install(NodeList.GetNode(i))

    # create simulation object and run
    sim_time = Seconds(sim_time)
    Simulator.Stop(sim_time)
    Simulator.Run()

    # plot results
    times = CsmaCaMultiNodeTestSuite.GetDelays()
    plt.hist(times, bins=50, color='c', edgecolor='k')
    plt.xlabel('Delay (ms)')
    plt.ylabel('Frequency')
    plt.title('CSMA/CA Performance')
    plt.show()

run_simulation(n_stations=10, packet_size=512, data_rate="11Mbps", sim_time=10)

This code simulates a wireless network with 10 stations using CSMA/CA to avoid collisions. The main function `run_simulation()` takes four parameters: the number of stations, the packet size, the data rate, and the simulation time. The code creates UDP traffic and "on/off" applications at each node, with random on/off times determined by a constant random variable. The results are plotted as a histogram showing the delay times for packets to be transmitted.

Hope this helps! Let me know if you have any follow-up questions.