LTE can be deployed in both paired spectrum for Frequency Division Duplex
(FDD) and unpaired spectrum for Time Division Duplex (TDD). Both FDD and TDD
have their own advantages and disadvantages, the decisions on which duplex
scheme to adopt can be taken is depending on the operator’s business
requirements.
Frequency Division
Duplex (FDD) LTE
FDD LTE transmits the downlink and uplink traffic in separate frequency
bands. Thus, paired spectrum with sufficient frequency separation is required
for FDD to allow simultaneous transmission and reception. The paired spectrum
of FDD LTE is suited to support voice as well as symmetric data applications
such as voice call and video conferencing. In addition, when compared to TDD
LTE, FDD LTE offers advantages both in terms of higher coverage and better
compatibility with existing 3G networks, which are mostly based on paired
spectrum. As a result, FDD LTE is expected to be the logical migration path for
most operators who have deployed 3G networks. In fact in most geography the
majority of the spectrum which has been auctioned is FDD.
Time
Division Duplex (TDD/TD) LTE
TDD LTE (or TD LTE) transmits the uplink and downlink traffic within the
same unpaired frequency band but different time slots and it is predominantly a
mobile broadband technology. TDD LTE offers flexible and adaptable (real-time)
uplink and downlink traffic ratio, which makes this technology suitable for
asymmetric data applications such as HD video download and content upload. The
lower spectrum costs and higher spectral flexibility of TDD LTE makes it an
attractive option for operators in both emerging and developed markets to make
a quick transition to TDD LTE mobile broadband. The considerable interest in TDD
LTE is expected to help build the ecosystem support and bridge the gap with FDD
LTE. Although the adoption of LTE FDD will be the more widespread, it is
reasonable to assume that TD-LTE will also witness significant uptake.
FDD Vs TDD
|
Parameter
|
Favorability Legend
|
Remark
|
|
|
FDD LTE
|
TDD LTE
|
||
|
Spectrum Flexibility
|
Medium
|
Very high
|
•The adaptable Downlink to Uplink ratio means that
TDD LTE ensures maximization of available bandwidth
|
|
Spectrum Costs
|
Medium
|
Very high
|
•TDD spectrum is traditionally auctioned for lower
cost/MHz/population
|
|
Hardware and User
Equipment Costs
|
High
|
Medium
|
• Economies of scale in favor of FDD will lead to
lower hardware and user equipment costs
|
|
Coverage
|
High
|
Medium
|
• TDD LTE has poor compared to FDD and requires base station
synchronization to avoid cross slot interference
|
|
Ease of Migration
|
High
|
Medium
|
• Most of the current 3G deployments are based on
paired spectrum thus it is easier to migrate to FDD LTE
|
|
Ecosystem Support
|
High
|
Medium
|
• Though network and device vendors are committed
to support both FDD and TD LTE technology, higher push is towards FDD
|
|
Suitability for Data
Applications
|
Medium
|
High
|
• TDD LTE is more suitable for IP-based data
applications which are mostly asymmetric in nature
|
