Half Duplex
Half Duplex Definition
Half duplex is a communication mode where devices can send and receive signals, but only in one direction at a time. This means a device can either transmit or accept a message at any given moment; it can’t do both simultaneously.
How Half-Duplex Systems Work
When one device sends data, the other has to wait until the channel is free before it can respond. This back-and-forth communication helps prevent signals from interfering with each other. Each side can get a clear message, one at a time.
Walkie-talkies are a great example of half-duplex communication. One person holds down a talk button, which activates the transmitter to convert voice into a radio signal and send it over the air. The other walkie-talkie picks up the signal and plays the audio. The first person releases the talk button, and their walkie-talkie returns to listening mode. The second person can now press their button and speak.
Real-World Half-Duplex Examples
- CB (Citizen Band) radio: A short-range communication system often used by truckers to share traffic updates and hobbyists like off-roaders or campers.
- Wi-Fi networks: Devices on the same Wi-Fi communicate over the same radio frequency channel and take turns sending or receiving data.
- Bluetooth: Classic Bluetooth uses a method called time-division duplexing, a form of half duplex that takes turns sending and receiving data very quickly.
- Early Ethernet networks: Early Ethernet used a half-duplex model called CSMA/CD. Devices would check if the Ethernet cable was free before sending data. If two devices sent data at the same time, a collision would occur. Both would stop, wait for a random time, and try again.
Advantages of Half Duplex
- Simpler hardware: The system setup makes the hardware less complex, so it’s easier to build and maintain.
- Lower cost: Half-duplex devices are cheaper due to simpler designs and fewer components.
- Reduced interference: Devices take turns to transmit, which means less chance of overlapping signals. This helps in crowded radio environments where lots of devices might be using the same frequency.
- Preserved bandwidth: One device transmits at a time, which helps manage limited bandwidth, especially in older or slower networks.
- Reduced power consumption: Half-duplex devices often use less power, making them a good fit for battery-powered or low-energy systems.
Half Duplex vs Full Duplex and Simplex
| Simplex | Half Duplex | Full Duplex | |
| Data direction | One-way only | Two-way, one at a time | Two-way, both at the same time |
| Example devices | TV broadcast | Walkie-talkie, Wi-Fi | Phone calls |
| Communication flow | Sender to receiver | Alternates between sender/receiver | Simultaneous send and receive |
| Complexity | Very simple | Moderate | More complex |
Read More
- What Is a Communications System?
- What Are Real-Time Communications?
- What Is Telecommunications Equipment?
FAQ
Most Wi-Fi works in half-duplex mode. This means devices take turns sending and receiving data on the same radio frequency channel. Even with newer versions like Wi-Fi 6 and 7, only one device can talk on a channel at a time. These versions are faster and more efficient, but they still don’t support true full-duplex communication, where data flows both ways at the same time.
Half duplex can be slower because only one device can send data at a time. This can cause minor delays, especially when lots of devices are using one network. It’s not the best choice for activities like video calls or online games, which need quick two-way communication.
Walkie-talkies are half duplex because they use one channel for both talking and listening, but not at the same time. Unlike full-duplex devices, which can send and receive transmissions simultaneously, walkie-talkies are limited to one action at a time. This saves battery, avoids signal problems, and works well for short, back-and-forth messages.
Full duplex lets two devices send and receive data simultaneously, like a phone call. Half duplex means they take turns, so only one can send while the other waits, like a walkie-talkie. Full duplex is faster and more efficient, while half duplex is simpler, cheaper, and uses less power.
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