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⛄ 内容介绍
多通道时隙ALOHA是一种多址随机访问协议，用于在无线传感器网络等多用户环境中实现异步通信。它将时间划分为一系列时隙，并使用多个通道来进行并行传输。
以下是多通道时隙ALOHA的基本原理：
- 时隙划分：时间被划分为一系列固定长度的时隙，每个时隙用于传输一个数据包。
- 多通道分配：系统拥有多个可以同时工作的通道。这些通道可以是不同的频率或代码资源。用户可以从可用的通道集合中选择一个通道用于传输。
- 数据传输：用户在每个时隙中决定是否要发送数据。如果用户决定发送数据，则它会选择一个空闲的通道，并将数据包传输到该通道。
- 冲突检测与解决：由于多用户同时尝试传输数据，可能会发生冲突。这时需要进行冲突检测和解决。常见的方法是通过在接收端检测冲突并向发送方发送冲突通知，发送方则在下一个时隙重新发送。
- 重传机制：如果数据包发生冲突，发送方会根据反馈信息在后续的时隙中选择重新发送。
- 数据接收：接收方在每个时隙中监听所有通道上的传输，并接收到正确的数据包。
⛄ 部分代码
% Multichannel slotted ALOHA
% Bariq Firmansyah, 2020
clear all; close all; clc;
k=1;
for NumberofChannel=[5, 10]
i=1;
for NumberofUser=[10, 50]
j=1;
for lambda=[0:0.2:15]
simulationTime=1e5;
userStatus = zeros(1,NumberofUser);
% 0: idle source
% 1: active
attemptUser = zeros(1, NumberofChannel);
pcktTransmissionAttempts = 0;
ackdPacketCount = 0;
pcktCollisionCount = 0;
currentSlot = 0;
pr=lambda/NumberofUser;
while currentSlot < simulationTime
currentSlot = currentSlot + 1;
transmissionAttemptsEachSlot = zeros(1, NumberofChannel);
for user = 1:NumberofUser
if rand(1) <= pr
channelChoosen=randi(NumberofChannel,1);
transmissionAttemptsEachSlot(channelChoosen) = transmissionAttemptsEachSlot(channelChoosen)+1;
pcktTransmissionAttempts = pcktTransmissionAttempts+1;
attemptUser(channelChoosen) = user;
end
end
for channel=1:NumberofChannel
if transmissionAttemptsEachSlot(channel) == 1
ackdPacketCount = ackdPacketCount + 1;
userStatus(attemptUser(channel)) = 0;
elseif transmissionAttemptsEachSlot(channel)>1
pcktCollisionCount = pcktCollisionCount+1;
end
end
end
trafficOffered(i,j,k) = pcktTransmissionAttempts / currentSlot;
throughput(i,j,k) = ackdPacketCount / (currentSlot);
pcktCollisionProb(i,j,k) = pcktCollisionCount / (currentSlot);
j=j+1;
end
i=i+1
end
k=k+1
end
%% plot
figure(1)
plot(trafficOffered(1,:,1),throughput(1,:,1), '-x')
title('Average Throughput of Finite-Station Multichannel Slotted ALOHA')
xlabel('G (Offered Traffic)')
ylabel('Average Throughput')
hold on;
G=[0:0.2:15];
S=G.*(1-G/(10*5)).^(10-1);
plot(G,S);
hold on;
plot(trafficOffered(2,:,1),throughput(2,:,1), '-o')
hold on;
S=G.*(1-G/(50*5)).^(50-1);
plot(G,S);
hold on;
plot(trafficOffered(1,:,2),throughput(1,:,2), '-d')
hold on;
S=G.*(1-G/(10*10)).^(10-1);
plot(G,S);
hold on;
plot(trafficOffered(2,:,2),throughput(2,:,2), '-*')
hold on;
S=G.*(1-G/(50*10)).^(50-1);
plot(G,S);
legend('simulation, M=10 N=5', 'analytical, M=10 N=5','simulation, M=50 N=5', 'analytical, M=50 N=5', 'simulation, M=10 N=10', 'analytical, M=10 N=10', 'simulation, M=50 N=10', 'analytical, M=50 N=10');
grid on
figure(2)
plot(trafficOffered(1,:,1),pcktCollisionProb(1,:,1)/5, '-x')
title('Collision Probability of Finite-Station Slotted ALOHA')
xlabel('G (Offered Traffic)')
ylabel('Collision Prob')
hold on;
S=1-(1-G/(10*5)).^(10)-(G/5).*(1-G/(10*5)).^(10-1);
plot(G,S);
hold on;
plot(trafficOffered(2,:,1),pcktCollisionProb(2,:,1)/5, '-o')
hold on;
S=1-(1-G/(50*5)).^(50)-(G/5).*(1-G/(50*5)).^(50-1);
plot(G,S);
hold on;
plot(trafficOffered(1,:,2),pcktCollisionProb(1,:,2)/10, '-d')
hold on;
S=1-(1-G/(10*10)).^(10)-(G/10).*(1-G/(10*10)).^(10-1);
plot(G,S);
hold on;
plot(trafficOffered(2,:,2),pcktCollisionProb(2,:,2)/10, '-*')
hold on;
S=1-(1-G/(50*10)).^(50)-(G/10).*(1-G/(50*10)).^(50-1);
plot(G,S);
legend('simulation, M=10 N=5', 'analytical, M=10 N=5','simulation, M=50 N=5', 'analytical, M=50 N=5', 'simulation, M=10 N=10', 'analytical, M=10 N=10', 'simulation, M=50 N=10', 'analytical, M=50 N=10');
grid on
⛄ 运行结果
⛄ 参考文献
[1] 方飞,蒋猛.时隙ALOHA在MATLAB中的仿真[J].内江师范学院学报, 2012, 27(8):5.DOI:10.3969/j.issn.1671-1785.2012.08.006.
[2] 冯媛,蔡增玉,谭前进,等.帧时隙ALOHA防碰撞算法仿真与研究[J].中原工学院学报, 2012, 23(6):4.DOI:10.3969/j.issn.1671-6906.2012.06.002.
