What is 4G LTE? – FD LTE vs TD LTE

Pretty much every new phone launched internationally now mentions “LTE support”. We don’t seem to hear that term much in India though, that’s because we still don’t have an LTE network for mobile phones, only dongles. But what is 4G LTE? LTE stands for Long Term Evolution, it is the next standard in mobile communications. An evolution of the HSPA or 3G networks, although LTE is branded as “4G” it isn’t considered “true 4G” by the International Telecommunications governing body. That name is reserved for LTE Advanced, which is a complete new technology unlike the evolution that LTE is, and is capable of data transfer rates of upto 5 Gb/s! Read on to find out more about LTE, how fast it is and why LTE phones from one country might not work in another.

What is 4G LTE? – An overview:

Just like 3G improved upon the speeds of 2G in previous mobile generations, LTE increases the data capacities of networks, their data transfer speeds as well as reduce latencies. This is mainly achieved by using digital signal processing and modulation techniques. Even though it improves upon the previous network speeds, the official governing body for telecommunications worldwide, ITU-R doesn’t classify it as a new generation. First proposed by NTT DoCoMo of Japan, LTE was first commercially available in 2008 in a few cities of Sweden. It was introduced by Airtel in India in 2012, only usable by 4G USB dongles as of now.

LTE networks are capable of peak download rates of upto 300 Mb/s and peak upload rates of 75 Mb/s. It is very flexible and operates in many frequency bands and even with different DSP techniques. Support for LTE requires a different LTE chip and radio in mobile devices. That’s the reason some smartphones have different versions since not all SoC’s come with LTE radios. For example, the international Samsung Galaxy S3 sold in India has a quad core SoC which doesn’t have an LTE radio. The Samsung Galaxy S3 sold in the USA has a dual core SoC which comes with an LTE radio.

What is 4G LTE? – Types of LTE networks:

There are different types of LTE networks as well, they are classified based on network spectrums. The two types are FD LTE and TD LTE, FD LTE stands for Frequency Division Long Term Evolution and TD LTE stands for Time Division Long Term Evolution. Even though data rates are the same, differences are found between the type of duplexing used. In other words, download and upload data streams are arranged differently.

Most of the countries around the world use the FD LTE standard while China, India, Hong Kong and a few other countries use the TD LTE standard. This means that if you buy a FD LTE compatible mobile phone in an FD LTE network using region, you won’t be able to use the same phone on a TD LTE network. Even though both FD LTE and TD LTE networks have internal frequency “bands”, as long as you’ve got a phone that can run on either standard, you won’t have to worry about the frequency bands. Ever notice the numbers next to a network on your mobile phone specifications? Those are the frequency bands it supports, and this is applicable even for current 2G/3G networks.

What is 4G LTE? – FD LTE and TD LTE differences:

FD LTE and TD LTE differ in the fundamental way that FD LTE download and upload streams are on different frequencies and it is a paired spectrum, while TD LTE is an unpaired spectrum in which download and upload streams share the same frequency, but the streams are alternatively arranged and divided based on time, as the name suggests. It is basically the same concept used in frequency and time division multiplexing for multiple communication streams on a single channel. The picture below clearly illustrates the differences between FD LTE and TD LTE:

(Picture courtesy DifferenceBetween)

Here are some other differences between FD LTE and TD LTE:

FD LTE	TD LTE
Uses a paired spectrum and requires a guard band.	Does not require a guard band since all communication is on one channel, but requires a guard period.
Expensive since it requires a diplexer to segregate between download and upload streams.	Cheaper since it doesn’t require a diplexer.
More viable for countries where network operators get multiple unpaired frequencies.	More viable for countries where network operators get only a single unpaired frequency.
Download and upload streams cannot be changed since frequency is fixed.	Download and upload streams can be changed by changing time division ratios.
No interference between data streams.	Data interference is possible due to improper guard periods.

I hope that answers your questions about what is 4G LTE and the differences between FD LTE and TD LTE. Please let us know if you have any queries or if you have any suggestions.