LTE tutorial | Tutorial on LTE Basics
This LTE tutorial covers LTE basics, LTE features, LTE air interface, LTE channels and LTE frame structure. The tutorial on LTE also covers LTE protocol stack, LTE physical layer, LTE network architecture and so on.
LTE standard has been published by 3GPP as an extension of UMTS(based on 3GPP standard) and 1xEV-DO(base on 3GPP2 standard) technologies. LTE is mainly designed for high speed data applications both in the uplink and downlink. LTE network offers about 300Mbps data rate in the downlink and about 75 Mbps in the uplink. There is possibility of supporting voice over LTE(VoLTE) in the future. There are various methods under progress to support VoLTE some of them includes VOIP, legacy fallback to previous existing wireless networks.
LTE Air interface
The Air interface between LTE network and UE supports high data rate owing to OFDM and Multiple antenna techniques employed.
OFDMA is used from network to UE air interface and SC-FDMA is used from UE to network air interface.
Refer following links to know OFDMA basics.
OFDMA Types OFDM versus OFDMA OFDMA Physical layer
The channels in LTE system are mainly categorized into logical, transport and physical channels based on their functions. The downlink channels are PBCH, PDSCH, PDCCH, PMCH, PCH etc. The uplink channels are PRACH, PUSCH and PUCCH.
LTE Frame structure
LTE frame is 10 ms in duration and consists of 10 subframes. Each subframe consists of two slots. The frame structure is different for FDD and TDD topologies. Refer LTE Frame >>.
LTE Protocol Stack
The stack consists of different layers viz. Physical, MAC, RLC, PDCP and RRC as shown in the figure. Refer LTE stack >>.
LTE Physical layer
The figure depicts LTE eNodeB physical layer and LTE UE physical layer transmitter modules.
Refer LTE Physical Layer >> for more information.
LTE System Architecture Evolution
As shown in the figure LTE SAE(System Architecture Evolution) consists UE,eNodeB and EPC(evolved packet core). Various interfaces are designed between these entities which include Uu between UE and eNodeB, X2 between two eNodeB, S1 between EPC and eNodeB. eNodeB has functionalities of both RNC and NodeB as per previous UMTS architecture.LTE is completely IP based network.
The basic architecture contains the following network elements.
1. LTE EUTRAN (Evolved Universal Terrestrial Radio)
2. LTE Evolved Packet Core.
It is a radio access network standard meant to be a replacement of the UMTS, HSDPA and HSUPA . Unlike HSPA, LTE's E-UTRA is an entirely new air interface system. It provides higher data rates, lower latency and is optimized for packet data. EUTRAN (Evolved Universal Terrestrial Radio) consists of eNB (Base station). EUTRAN is responsible for complete radio management in LTE. When UE powered is on, eNB is responsible for Radio Resource Management, i.e. it shall do the radio bearer control, radio admission control, allocation of uplink and downlink to UE etc. When a packet from UE arrives to eNB, eNB shall compress the IP header and encrypt the data stream. It is also responsible for adding a GTP-U header to the payload and sending it to the SGW. Before the data is actually transmitted the control plane has to be established. eNB is responsible for choosing a MME using MME selection function. The QoS is taken care by eNB as the eNB is only entity on radio. Other functionalities include scheduling and transmission of paging messages, broadcast messages, and bearer level rate enforcements also done by eNB.
LTE Evolved Packet Core (EPC)
The LTE EPC consists of MME, SGW, PGW, HSS and PCRF. Refer LTE architecture >> for more information on functions of EPC network elements.
LTE Advanced Architecture
LTE Advanced architecture for E-UTRAN consists of P-GW, S-GW, MME, S1-MME, eNB, HeNB, HeNB-GW, Relay Node etc.
LTE Advanced protocol stack consists of user plane and control plane for AS and NAS.
Refer LTE Advanced Architecture and Stack➤.
This LTE tutorial for beginners is very useful to learn basic knowledge on LTE and LTE advanced technologies.
LTE tutorial related links
This tutorial on LTE system covers following sub topics on LTE technology:
Main page features terminologies Frame TDD FDD Channel types PHY stack throughput VoLTE CA cell search network entry Timers PSS vs SSS Security LTE Bands EARFCN Hotspot router