1. Full-Duplex vs Half-Duplex
| Term | Meaning |
|---|---|
| Half-Duplex (HD) | The same antenna is used for TX and RX, but not at the same time. TX and RX take turns. Example: walkie-talkies, some Wi-Fi modes. |
| Full-Duplex (FD) | The same antenna transmits and receives simultaneously. Harder to implement because the transmitted signal can overwhelm the receiver. |
2. How Single-Antenna Duplex Works
a) Half-Duplex (Simple)
- Use time-division duplexing (TDD):
- TX for time slot 1
- RX for time slot 2
- Switch the antenna using a duplexer or RF switch
- No interference issue, simple hardware
b) Full-Duplex (Advanced)
- Transmit and receive simultaneously on the same frequency
- Main challenge: self-interference (your transmitted signal is much stronger than the received signal)
- Solutions:
- Analog cancellation: subtract transmitted signal at RF before the RX chain
- Digital cancellation: subtract transmitted signal digitally after ADC
- Isolation techniques: circulators, directional couplers, or antennas with high isolation
- Practical in lab/advanced Wi-Fi/cellular prototypes, but expensive and tricky
- Single TX/RX antenna is fine for half-duplex → widely used, simple
- Full-duplex with one antenna → possible but requires complex self-interference cancellation
- Many real systems use separate TX/RX antennas for full-duplex to reduce interference
Summary
- Half-duplex: Single antenna works easily
- Full-duplex: Possible with one antenna, needs advanced interference cancellation