UMTS TDD vs UMTS FDD: Differences Explained

This page compares UMTS TDD vs UMTS FDD and mentions the difference between UMTS TDD and UMTS FDD topologies. It also describes UMTS TDD and FDD frame structures.

Introduction:

As we know, TDD stands for Time Division Duplex, and FDD stands for Frequency Division Duplex. In TDD topology, the same frequency is used for both uplink and downlink directions, but they use different time slots for transmissions. In FDD topology, different frequencies are used for both uplink and downlink directions, but they both use the same time slots for transmissions.

Figure 1: TDD vs FDD

The figure above depicts simple TDD and FDD configurations pictorially. Refer to the advantages and disadvantages of TDD and FDD.

UMTS FDD

Figure 2: UMTS FDD frame structure

• Figure 2 depicts the UMTS FDD frame structure.
• In UMTS FDD, both uplink and downlink use separate frequency bands with a duplex distance of 190 MHz between them.
• As shown, 1920 to 1980 MHz is used for uplink, whereas 2110 to 2170 MHz is used for downlink.
• The total BW (Bandwidth) of 60 MHz is divided into 12 divisions, each having 5 MHz BW for each channel.

UMTS TDD

Figure 3: UMTS TDD frame structure

• Figure 3 depicts the UMTS TDD frame structure.
• In UMTS TDD, both uplink and downlink share the same frequency band at the same time period.
• The equipment requires switching between transmission and reception. Hence, there is a guard period between transmission and reception to avoid interference.
• UMTS uses either 1900 to 1920 MHz or 2010 to 2025 MHz for both uplink/downlink directions.