The Common Wireless Protocols and What Each Is Good For
Wireless protocol selection fixes physical range, payload boundaries, power draw profiles, regulatory approvals, and landed hardware costs across target markets.
Pure ALOHA
Meaning
A simple channel access protocol where a station transmits a data packet immediately whenever it has information to send, without checking if the medium is clear. This pure aloha method was the first random access protocol developed for radio networks and serves as the foundation for more advanced contention systems. Because there is no coordination between the different stations, collisions occur whenever two or more devices transmit at the same time.
When a collision happens, the data is lost and the stations must retransmit the packets after a random delay. The protocol is easy to implement as it requires no carrier sensing or complex timing synchronization between the nodes. It is primarily used in systems with very low traffic density where the risk of overlap is minimal.
Collision Probability
The performance of this protocol is limited by the high likelihood of data interference as the network load increases. In a pure aloha system, the vulnerable period for a packet is twice its transmission time because any other packet starting within this window will cause a collision. This lack of sensing means that even a partial overlap between two signals results in the total loss of both packets.
As the number of active stations grows, the probability of a successful transmission drops rapidly, leading to a state of network congestion. The maximum throughput of the system is mathematically limited to approximately eighteen percent of the total channel capacity. This boundary makes the protocol unsuitable for modern high speed networks but it remains an important theoretical model for understanding random access behavior.
Retransmission Strategy
To handle the inevitable data loss, the protocol relies on a simple acknowledgment and retransmission mechanism. After a station sends a packet, it waits for a confirmation from the receiver within a specific time window. If no acknowledgment is received, the station assumes that its transmission was lost in a collision.
It then waits for a random interval before attempting to send the same packet again. This random delay is vital to prevent the same two stations from colliding repeatedly on their subsequent attempts. The length of this backoff period can be adjusted based on the observed collision rate to improve the stability of the network.
This process continues until the data is successfully delivered or a maximum number of retries is reached.
Modern Applications
While replaced by more efficient protocols in most systems, the principles of this method are still found in certain low power satellite and sensor networks. In these applications, the simplicity of the pure aloha approach reduces the power consumption of the terminal because it does not need to keep the receiver active to sense the channel. It is also used in the initial access phase of some cellular systems where a device sends a short request to the base station.
The low complexity makes it a cost effective choice for simple devices that transmit only a few bytes of data. Testing the effectiveness of this protocol involves monitoring the collision rate and the total packet latency under different traffic loads.