Flexible duplexing vs Traditional duplexing | Difference between flexible duplexing and Traditional duplexing

This page compares flexible duplexing vs Traditional duplexing used in TDD and FDD duplex. It mentions difference between flexible duplexing vs Traditional duplexing used in LTE and 5G. It mentions benefits or advantages of flexible duplexing method.

Traditional duplexing TDD and FDD

As we know FDD and TDD are popular duplexing techniques often used with multiple access schemes such as FDMA and TDMA. FDD dominates since beginning of mobile communication era. In 5G NR (New Radio), FDD is for lower frequency bands where as TDD is used for frequencies above 10 GHz. TDD is used in very dense deployments.

What is FDD | Frequency Division Duplex

LTE FDD topology

The figure-1 describes FDD concept in LTE system. As shown pair of frequencies are allocated for uplink and downlink directions dedicately.

Example of FDD :
LTE band-13
uplink (UEs to eNodeB) frequency (f1) : 777 to 787MHz
downlink (LTE eNodeB to UEs) frequency (f2) : 746 to 756 MHz
Radio frame duration : 10ms
Entire radio frame is used simultaneously over downlink and uplink directions. Both uplink and downlink will have 10MHz bandwidth each on which entire frame will be used.

What is TDD | Time Division Duplex

TDD LTE topology

The figure-1 describes TDD concept in LTE system. As shown same frequency f1 is used for uplink as well as downlink and but at different time slots.

Example of TDD :
LTE band-33 (1900 to 1920MHz)
Entire bandwidth of 20MHz is used for both eNodeB and UEs.
Radio frame time slots 0 to 9 for UL/DL configuration of zero and 5ms DL/UL switch point periodicity. It is D,S,U,U,U,D,S,U,U,U.
Here D stands for downlink and U stands for uplink.
Hence the subframes of the entire radio frame is divided and used for both the uplink and downlink direction.

Leading chipset manufacturers such as Ericsson, Altair semiconductor,Qualcomm support both TDD and FDD versions of LTE on a single chip.

Flexible duplexing in TDD and FDD

TDD and FDD specific interference occurs in very dense deployments with low power nodes (i.e. Base Stations and mobile devices). Flexible duplexing refers to dynamic assignment of transmission resources (i.e. time and frequency). This is very useful in very dense deployments requiring dynamic traffic variations.

Flexible duplexing

Traditional TDD based mobile technologies will have restrictions on downlink/uplink configurations as mentioned in TD-LTE or TDD-LTE above. Flexible duplexing allows very flexible and dynamic assignment of TDD resources.

Benefits or advantages of Flexible duplexing

Following are the main advantages of flexible duplexing over traditional duplexing.
➨It maximizes spectrum utilization.
➨It optimizes user experience.
➨Carrier aggregation across TDD and FDD is possible.

LTE Tutorial related links


RF and Wireless Terminologies