An easy approach to understand tech specs
4G LTE wireless access technologies in FDD and TDD modes of Transmit and Receive
LTE supports both FDD and TDD access technologies. FDD is the mode preferred in USA whereas TDD is gaining traction in China.
FDD stands for Frequency Division Duplex.
Separate frequency channel is used for transmit and receive.
TDD stands for Time Division Duplex.
Single frequency channel is shared among transmit & receive slots.
The coding technologies used in LTE are OFDMA and SC-FDMA. Discussed on this page.
Refer this link to find LTE technological differences in FDD and TDD modes of operation.
General (non technical) Discussion on FDD vs. TDD. Access technical here
Traffic flow -
FDD is best suited for high throughput symmetric traffic which requires large bandwidth in each direction.
TDD is best suited for asymmetric traffic. Like on Internet we request a link then the server returns the link and all data associated with the website.
LTE Technologies used for Uplink or transmit
SC-FDMA - Single Carrier Frequency Division Multiple Access
SC-FDMA is still a multiple access scheme like OFMDA but avoids multiple carriers in transmission. With only one carrier at transmitter the signal has comparatively low peak-to-average power ratio (PAPR).
Peak-to-Average Power Ratio (PAPR) -
Its a ratio of the peak amplitude of the waveform divided by the Root Mean Square Value (RMS) of the waveform.
With low PAPR the mobile terminal can increase transmit power efficiency.
Spectrum efficiency -
FDD systems requires large spectrum to provide independent channels with guard bands. This approach is not possible for areas with huge demand/cost for spectrum.
TDD utilizes the spectrum more efficiently than FDD.
Hardware cost -
FDD is costly system. Independent resources like antennas are required to physically isolate the transmit and receive paths.
TDD optimizes hardware costs by sharing the resources. The transmitter and receiver operates on same frequency but at different times.
LTE Technology used for Downlink or receive.
OFDMA - Orthogonal Frequency Division Multiple Access
Its a modulation scheme which transmits data over a large number of channels know as sub carriers. The most important property of OFDM is the orthogonal relationships of the sub-carriers.