FDD LTE Networks vs TDD LTE Networks

LTE (3GPP Long Term Evolution) seems to be the next generation in mobile phone technology as many providers are beginning to augment their networks with LTE. As we know, mobile phone traffic is divided into two parts: an uplink and a downlink. In this regard, LTE supports two duplexing modes: FDD (Frequency Division Duplexing) and TDD (Time Division Duplexing). The main difference between FDD and TDD is in how they divide the single channel to provide paths for both uploading and downloading. FDD does this by dividing the frequency band allotted into two discrete smaller channels. On the other hand, TDD uses the entire channel but alternates between uploading and downloading.

Because of how FDD operates, it is classified as a full duplex system. This means that both the upload and download are always available. TDD is just half duplex as either upload or download can use the channel but not at the same time. However, because the time divisions are very small, this is not noticeable in applications like voice calls that need full duplex operation.

FDD and TDD LTE have their own strengths and weaknesses. FDD is generally better suited for applications like voice calls that have symmetric traffic. This is because traffic in both directions is always constant and TDD would be wasting bandwidth in constantly switching from one to the other. TDD shines in applications that have asymmetric traffic, an example of which is online browsing. When browsing the web, it is typical that download is much higher than upload; but when you are uploading videos, for example, the reverse is true. TDD can allocate more time for the part that requires more bandwidth, thereby balancing the load. With FDD, the bandwidth cannot be dynamically reallocated and the unused bandwidth is wasted.

Another advantage of FDD LTE appears when planning sites for base stations. Because FDD base stations use different frequencies for receiving and transmitting, they effectively do not hear each other and no special planning is needed. With TDD, special considerations need to be taken in order to prevent neighboring base stations from interfering with each other.

Summary:

1. FDD LTE uses frequency division, while TDD LTE uses time division
2. FDD LTE is full duplex, while TDD LTE is half duplex
3. FDD LTE is better for symmetric traffic, while TDD is better for asymmetric traffic
4. TDD LTE is better at reallocating traffic than FDD LTE
5. FDD LTE allows for easier planning than TDD LTE

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