3GPP (3rd generation partnership project)is an agreement set up in 1998 to bring together all telecommunications standard bodies to share technical specifications & reports globally on GSM and Radio Access Technologies.Above image shows the specifications for different technologies released by GPP.

LTE/SAE is specified from 3GPP Rel 8 ,where Long Term Evolution targets the RAN (Radio Access Network) called E-UTRAN and System Architecture Evolution(SAE) targets the Core Network Known as EPC

i.e Evolved Packet Core.The E-UTRAN standard based on OFDM (Orthogonal Frequency Devision Multiplexing) and OFDMA(Orthogonal Frequency Devision Multiple Access Technique) downlink operations & SC-FDMA (Single Carrier Frequency devision Multiple Access uplink operation.Each user in DL has its own time & frequency,called Resource Block,which dynamically alloted to different users at different time.TTI(Transmission Time Interval is 1 ms,speeds up the operation all the time,also reduces the interface latency,which is the main concern behind LTE.

SC-FDMA enables the user to be more power efficient and hence manufactured at lower cost.Also the uplink transmission is well seperated within a cell (intra cell Orthogonality).

Another benefit of LTE is that it provide flexible bandwidth i.e LTE supports wide range of easily available bandwidths (1.4Mhz,2 mhz,6mhz… upto 20Mhz).It supports both FDD & TDD modesof operation and targets  both a paired spectrum allocation with UL & DL seperated in frequency ,also unpaired spectrum with UL/DL operating on same frequency.Furthermore E-UTRAN supports use of multiple antennas (MIMO) and both uplink diversity & Downlink diversity.

LTE sometimes referred as 3.9G insteadof 4G.This is because ITU defined IMT Advanced as 4G technology.LTE Rel 10 will probably fulfill the IMT Advanced requirements.

Evolved Packet System (EPS=EPC+E-UTRAN) in 3GPP Rel 8is based on simplified network architecture compared to Rel6.The no.of userplane nodes is reduced from 4 from Rel6(node b,RNC, SGSN, GGSN) to only 2 in Rel 8(e-nodeb,S-GW) .Only a packet switch is defined in LTE .

Note that the peak data rates depends on no.of transmit and receiving antennas (MIMO configuration) at the UE.The targets for DL and UL peak data rates are specified interms of  a rference  UE configuration comprising:

a) Downlink Capablity: 2 recieve antennas at UE

b) Uplink Capablity : 1 tranmit antenna at UE

The performance of LTE as specified in 3GPP Rel 8shall fulfill a no. of requirements regarding throuhput & Latency as mentioned above.This seems to be quite achievable,thanks to,among other improvements,the simplified architecture.Data rats of more than 300Mbps in DL seems to be possible to reach.

4 thoughts on “LTE Fundamentals

  1. nice article.. though didnt understand what OFDM/OFDMA and SC-FDMA were..

    hope to learn more about them..in a simple manner :p

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