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LTE-Advanced (Long Term Evolution-Advanced) is used on fourth generation (4G) in mobile phone technology as many providers are beginning to augment their networks with LTE. As known, mobile phone traffic is divided into two parts: an uplink and a downlink. This paper presents the LTE two duplexing modes: LTE-TDD (Time Division Duplexing) and LTE-FDD (Frequency Division Duplexing). Where LTE-TDD favored by a majority of implementations because of flexibility in choosing uplink to downlink data rate ratios, ability to exploit channel reciprocity, ability to implement in non-paired spectrum and less complex transceiver design. In the case of FDD operation there are two carrier frequencies, one for uplink transmission (f U L) and one for downlink transmission (f DL). During each frame, there are thus ten uplink subframes and ten downlink subframes, so uplink and downlink transmission can occur simultaneously within a cell. LTE-FDD implies that downlink and uplink transmission take place in different, sufficiently separated, frequency bands, while TDD implies that downlink and uplink transmission take place in different, non overlapping time slots. Thus, TDD can operate in unpaired spectrum, whereas FDD requires paired spectrum. Also the required flexibility and resulting requirements to support LTE operation in different paired and unpaired frequency arrangements are discussed in this Paper. This paper focuses on the main difference between LTE-FDD and LTE-TDD in how they divide the single channel to provide paths for both uploading (mobile transmit) and downloading (base-station transmit). FDD does this by dividing the frequency band allotted into two discrete smaller channels. TDD uses the entire channel but alternates between uploading and downloading and in the case of TDD uplink and downlink communication taking place in the same frequency band but in separate non-overlapping time slots; there is typically a high fading correlation between the downlink and uplink.
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