Parallel Wireless is Hiring

Tuesday, 14 October 2014

'Real' Full Duplex (or No Division Duplex - NDD?)

We all know about the two type of transmission schemes which are FDD and TDD. Normally, this FDD and TDD schemes are known as full duplex schemes. Some people will argue that TDD is actually half-duplex but what TDD does is that it emulates a full duplex communication over a half duplex communication link. There is also a half-duplex FDD, which is a very interesting technology and defined for LTE, but not used. See here for details.

One of the technologies being proposed for 5G is referred to as Full Duplex. Here, the transmitter and the receiver both transmit and receive at the same frequency. Due to some very clever signal processing, the interference can be cancelled out. An interesting presentation from Kumu networks is embedded below:

The biggest challenge is self-interference cancellation because the transmitter and receiver are using the same spectrum and will cause interference to each other. There have been major advances in the self-interference cancellation techniques which could be seen in the Interdigital presentation embedded below:


Jakub Bluszcz (via 3GPP 5G Standards Linkedin group) said...

This solution brings back memories of the old analogue fixed subscriber line, with both directions on a single circuit, hybrids, anti-local system, echo canceller, etc…

Behzad Mohebbi (via 3GPP 5G Standards Linkedin group) said...

Looks very interesting for a single link, as you can cancel your own transmissions. However, I am not sure if it can cancel the transmissions from another nearby handset. I must say, in-device IC is a big and interesting subject.

blue ridge mountain said...

Even you can cancel your own signal, but how can you cancel the noise in your own transmission signal? The Tx SNR is limited to ~35dB. Tx noise compare to Rx signal is huge. Once signal passes through mixer, you can't reproduce noise.