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LTE TDD vs LTE FDD; Time-Division Long-Term Evolution

Time-division Long-Term Evolution (TD-LTE), also referred to as Long-Term Evolution Time-Division Duplex (LTE TDD), is a 4G telecommunications technology and standard co-developed by an international coalition of companies, including China Mobile, Datang Telecom, Huawei, Nokia Solutions and Networks, Qualcomm, Samsung, and ST-Ericsson. It is one of two variants of the Long Term Evolution (LTE) technology standard, the other being Frequency-Division Long-Term Evolution (LTE FDD).

LTE-TDD gamit ng ULTERA hindi yung common na LTE-FDD na gamit ng Globe at Smart.

The TDD mode is preferred for the following reasons:

1- It enables dynamic allocation of DL and UL resources to efficiently support asymmetric DL/UL traffic (adaptation of DL:UL ratio to DL/UL traffic).
2- It ensures channel reciprocity for better support of link adaptation; MIMO and other closed-loop advanced antenna techniques such as transmit beam-forming.
3- Unlike FDD, which requires a pair of channels, TDD only requires a single channel for both downlink and uplink providing greater flexibility for adaptation to varied global spectrum allocations.
4- Transceiver designs for TDD implementations are less complex and therefore less expensive (restrictions in the number of DL/UL switching points).

5-The TDD spectrum is less expensive while both offer similar performance/spectral efficiency. Therefore, more operators are heading to TDD for LTE.

There are two major differences between TD-LTE and LTE FDD: how data is uploaded and downloaded, and what frequency spectra the networks are deployed in.

While LTE FDD uses paired frequencies to upload and download data, TD-LTE uses a single frequency, alternating between uploading and downloading data through time.

The ratio between uploads and downloads on a TD-LTE network can be changed dynamically, depending on whether more data needs to be sent or received.TD-LTE and LTE FDD also operate on different frequency bands,with TD-LTE working better at higher frequencies, and LTE FDD working better at lower frequencies.Frequencies used for TD-LTE range from 1850 MHz to 3800 MHz, with several different bands being used. The TD-LTE spectrum is generally cheaper to access, and has less traffic.Further, the bands for TD-LTE overlap with those used for WiMAX, which can easily be upgraded to support TD-LTE.

Despite the differences in how the two types of LTE handle data transmission, TD-LTE and LTE FDD share 90 percent of their core technology, making it possible for the same chipsets and networks to use both versions of LTE. A number of companies produce dual-mode chips or mobile devices, including Samsung and Qualcomm, while operators China Mobile Hong Kong Company Limited and Hi3G Access have developed dual-mode networks in China and Sweden, respectively.

As of January 2014, there were 28 commercial TD-LTE networks operating in 21 countries worldwide, with an additional 45 networks planned or in deployment.TD-LTE deployments are especially popular in Asia and the Pacific, with 47 percent of TD-LTE contracts awarded to vendors from this region. In second place is the Middle East, with 18 percent of contracts.According to a report conducted by research firm Ovum Ltd. in June of 2012, TD-LTE connections are expected to make up 25 percent of all LTE connections worldwide by 2016, with operators in Japan, Australia, Saudi Arabia, Sweden, and Denmark having implemented the technology, or planning to in the future.

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