Slotted ALOHA simulator

Demonstrates the slot efficiency of the slotted ALOHA protocol.

Getting started

Overview

Rules

• Nodes transimit new packets according to a Poisson process and retransmit packets after some random time if collision is detected
• Time is slotted, and a packet can only be transmitted at the beginning of the slot
• After transmitting a packet, the node transmits a new packet after a random time offset, regardless of whether the transmission was successful or not
• The random time offset follows the uniform distribution within [0, W)

What to simulate

• Simulates N senders for 100,000 time slots
• The slot efficiency is defined as # of successful slots / # of total slots
  • successful slot means that there is one and only one transmitted packet in the slot
  • No transmission or two or more transmission in a slot is considered not successful
• Implements the slotted ALOHA simulation
• Plots the slot efficiency graph while varying the number of nodes N from 1 to 32, with the window size 8, 16, 32

Program Flow

Each node has a ttl field, to determine its transmission point

Development Environment

Uses venv for python2.7.

$ uname -a
Linux ubuntu 4.15.0-29-generic #31~16.04.1-Ubuntu SMP Wed Jul 18 08:54:04 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

$ python --version
Python 2.7.12

matplotlib==2.2.4

Prerequisites

To successfully build and run the program, make sure you have the right packages.

import random
import matplotlib.pyplot as plt

Install with the following commands.

sudo apt-get install python-matplotlib

Running the program

Build

It's a python script. No building required.

Run

Format

python aloha.py

Acknowledgements

• ALOHAnet
• Difference between the pure and slotted ALOHA

Authors

• James Sung - Initial work - sjkywalker
• Copyright © 2018 James Sung. All rights reserved.