The comparison of TDD LTE and FDD LTE

Paired spectrum

TDD

Does not require paired spectrum as both transmit and receive occur on the same channel

FDD

Requires paired spectrum with sufficient frequency separation to allow simultaneous transmission and reception

Hardware cost

 

TDD

Lower cost as no diplexer is needed to isolate the transmitter and receiver. As cost of the UEs is of major importance because of the vast numbers that are produced, this is a key aspect.

FDD

Diplexer is needed and cost is higher.

Channel reciprocity

TDD

Channel propagation is the same in both directions which enables transmit and receive to use on set of parameters

FDD

Channel characteristics different in both directions as a result of the use of different frequencies

UL / DL asymmetry 

TDD

It is possible to dynamically change the UL and DL capacity ratio to match demand

FDD

UL / DL capacity determined by frequency allocation set out by the regulatory authorities. It is therefore not possible to make dynamic changes to match capacity. Regulatory changes would normally be required and capacity is normally allocated so that it is the same in either direction.

Guard period / guard band

TDD

Guard period required to ensure uplink and downlink transmissions do not clash. Large guard period will limit capacity. Larger guard period normally required if distances are increased to accommodate larger propagation times.

FDD

Guard band required to provide sufficient isolation between uplink and downlink. Large guard band does not impact capacity.

Discontinuous transmission

TDD

Discontinuous transmission is required to allow both uplink and downlink transmissions. This can degrade the performance of the RF power amplifier in the transmitter.

FDD

Continuous transmission is required.

Cross slot interference 

TDD

Base stations need to be synchronised with respect to the uplink and downlink transmission times. If neighbouring base stations use different uplink and downlink assignments and share the same channel, then interference may occur between cells

FDD

Not applicable

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: