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FDD-LTE vs TD-LTE

FDD-LTE and TD-LTE versions of LTE almost the same they are different only in the physical layer and, as a result, the version implemented is transparent to the higher layers. This means that UE will be able to support both TD-LTE and FDD-LTE with one chipset with only minor modifications required. UE based on those chipsets are (or will soon be) available from Sony Ericsson, Huawei, Samsung, Nokia, and others.

These features are unique to TD-LTE:
1. Frame structure – 3GPP has specified a special subframe that allows switching between downlink and uplink transmission.

2. Random access – Several additional random access formats exist
in certain subframes. Also, several random access channels exist in
every subframe.

3. Scheduling – The scheduling for the uplink is multi-frame.

4. HARQ – The number of HARQ processes depends on the uplink/downlink resource allocation.

5. ACK/NACK – Multiple acknowledgements and negative acknowledgements are combined on the uplink control channels.This ultimately leads to increased control signaling and lower spectrum/resource utilization.

6. Guard periods – These are used in the center of special subframes. They allow for the advance of the uplink transmission timing.

Another difference between FDD-LTE and TD-LTE is that in FDD-LTE every downlink subframe can be associated with an uplink subframe. In TD-LTE the number of downlink and uplink subframes is different and such association is not possible.

In terms of spectrum efficiency, the performances of TD-LTE and FDD-LTE are similar for non-delay sensitive traffic. The lower performance of TD-LTE is due to the guard periods mentioned above.

Finally, TD-LTE and TD-SCDMA work together with minimum interference issues, even if both technologies are deployed in the same frequency band (assuming that the TD-LTE UL:DL configurations are chosen correctly and both systems are synchronized to the same time source).

LTE Overview

LTE (Long Term Evolution) or the E-UTRAN (Evolved Universal Terrestrial Access Network), introduced in 3GPP R8, is the access part of the Evolved Packet System (EPS). The main requirements for the new access network are high spectral efficiency, high peak data rates, short round trip time as well as flexibility in frequency and bandwidth.

GSM was developed to carry real time services, in a circuit switched manner (blue in figure 1), with data services only possible over a circuit switched modem connection, with very low data rates. The first step towards an IP based packet switched (green in figure 1) solution was taken with the evolution of GSM to GPRS, using the same air interface and access method, TDMA (Time Division Multiple Access).

To reach higher data rates in UMTS (Universal Mobile Terrestrial System) a new access technology WCDMA (Wideband Code Division Multiple Access) was developed. The access network in UMTS emulates a circuit switched connection for real time services and a packet switched connection for datacom services (black in figure 1). In UMTS the IP address is allocated to the UE when a datacom service is established and released when the service is released. Incoming datacom services are therefore still relying upon the circuit switched core for paging.

The Evolved Packet System (EPS) is purely IP based. Both real time services and datacom services will be carried by the IP protocol. The IP address is allocated when the mobile is switched on and released when switched off.
The new access solution, LTE, is based on OFDMA (Orthogonal Frequency Division Multiple Access) and in combination with higher order modulation (up to 64QAM), large bandwidths (up to 20 MHz) and spatial multiplexing in the downlink (up to 4x4) high data rates can be achieved. The highest theoretical peak data rate on the transport channel is 75 Mbpsin the uplink, and in the downlink, using spatial multiplexing, the rate can be as high as 300 Mbps.

The LTE access network is simply a network of base stations, evolved NodeB (eNB), generating a flat architecture (figure 2). There is no centralized intelligent controller, and the eNBs are normally inter-connected viathe X2-interface and towards the core network by the S1-interface (figure 2). The reason for distributing the intelligence amongst the base-stations in LTE is to speed up the connection set-up and reduce the time required for a handover. For an end-user the connection set-up time for a real time data session is in many cases crucial, especially in on-line gaming. The time for a handover is essential for real-time services where end-users tend to end calls if the handover takes too long.

source http://www.3gpp.org/technologies/keywords-acronyms/98-lte

Motivation for LTE

LTE (both radio and core network evolution) is now available on the market. Release 8 was frozen in December 2008 and this has been the basis for the first wave of LTE equipment. LTE specifications are very stable, with the added benefit of enhancements having been introduced in all subsequent 3GPP Releases.

The motivation for LTE

•     Need to ensure the continuity of competitiveness of the 3G system for the future
•     User demand for higher data rates and quality of service
•     Packet Switch optimised system
•     Continued demand for cost reduction (CAPEX and OPEX)
•     Low complexity
•     Avoid unnecessary fragmentation of technologies for paired and unpaired band operation

What is 4G LTE?

It stands for Long Term Evolution, commonly called as 4G LTE. It is a wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies. It has increase the capacity and speed using a different radio interface together with core network improvements.

4G LTE is has speed up to 10x faster than 3G.2, that gives you clear, crisp video streaming and it's faster than ever before. You can also download music, apps, and games in an instant.

4G LTE was first introduced in public by TeliaSonera in Stockholm and Oslo on December 14, 2009.

Carriers are now upgrading their networks to LTE with both GSM/UMTS networks and CDMA2000 networks like Verizon Wireless. Verizon Wireless launched the first large-scale LTE network in North America in 2010, and au by KDDI in Japan have announced they will migrate to LTE.
In India Airtel offered the LTE services in April 2012. LTE is believe to become the first truly global mobile phone standard, although the different LTE frequencies and bands used in different countries will mean that only multi-band phones will be able to use LTE in all countries where it is supported.

Companies market LTE as 4G wireless service, LTE (as documented in the 3GPP Release 8 and 9 document series) does not satisfy the technical requirements the 3GPP consortium has adopted for its new standard generation, and which were originally set forth by the ITU-R organization in its IMT-Advanced specification. However, due to marketing pressures and the significant advancements that WIMAX, HSPA+ and LTE bring to the original 3G technologies, ITU later decided that LTE together with the aforementioned technologies can be called 4G technologies. The LTE Advanced standard formally satisfies the ITU-R requirements to be considered IMT-Advanced.And to differentiate LTE Advanced and WiMAX-Advanced from current 4G technologies, ITU has defined them as "True 4G".

LTE in the USA:

AT&T 4G LTE claim that they covers about 280 million people. And with their other network technologies they cover over 300 million which means a Nationwide coverage that is dependable. you can count on.

View AT&T coverage map Here AT&T
T-Mobile 4G LTE network covers over 200 million people.
View T-mobile Markets here
Verizon superfast 4G LTE network map
U.S. Cellular 4G LTE network
Virgin Mobile 4G LTE (powered by the Sprint)
Sprint Coverage Map
XFINITY Comcast 4G LTE Map Finder