Question

a) What is the meaning of UMTS and LTE?

B) Briefly describe the purpose of the four UMTS/LTE layers.

Answer 1

a) Meaning of UMTS and LTE:

UMTS: UMTS means Universal Mobile Telecommunications System. It is a Third Generation (3G) standard for cellular systems. In other words it is a mobile communication system based on GSM (Global System for Mobile communications) technology and supports WCDMA. UMTS was develped under 3GPP (3rd Generation Partnership Project). The main competitor of UMTS is CDMA2000 and it was develped under 3GPP2 (3rd Generation Partnership Project 2).

UMTS Broadband transmits data in a packet-based manner with rates of transmission upto 2 Mbps (Megabits per second). If Evolved HSPA (HSPA+) is used in the network then UMTS can have a data transfer rate of upto 42 Mbps. However, this value is theoritical and practically realised rates are lesser than this.

UMTS offers higher bandwidth than its predecessors and can support services like Video Conferencing or IPTV (Internet Protocol Television) which require high handwidth and data transmission speed.

LTE: It is the successor of UMTS and an advanced technology. It means Long-Term Evolution and it too has been developed by 3GPP just like UMTS. But tt is faster than UMTS. It can provide download speed of 300 Mbps and upload speed of 75 Mbps. It can support multi-cast and broadcast streams. It also supports MBSFN (multicast-broadcast single-frequency network) which is used for services like Mobile TV.

Due to its higher data transfer speeds, t is often termed a 4G (Fouth Generation) System. However, from a techinical point of view it does not fullfil all the criteria of a 4G weireless system set by ITU-R, the Radiocommunications section of International Telecommunication Union (ITU). (ITU is a United Nations organisation responsible for issues concerning information and communication technologies.) Some people like to call LTE as 3.9G or "Beyond 3G" !

It was NTT DoCoMo, a japanese company, that proposed LTE for the first time in 2004. Thereafter it kept evolving.

Besides having data transfer rates higher than UMTS, LTE differs from UMTS mainly in being an all-IP (Internet Protocol) based System. That means besides sending and receiving digital data like multimedia over IP, LTE transfers even the Voice calls over IP. This is known as VoIP (Voice over Internet Protocol). While as in UMTS Voice Core network is seperate from Data Core Network.

b) Purpose of the four UMTS/LTE Layers:

There are four protocol layers in UMTS-LTE Systems.They are called Physical Layer, MAC Layer, RLC Layer and PDCP Layer. Each layer has its own functions and transfers data to the next layer before or after it.

Physical Layer: The purpose of this layer is to convert data from RF Packets to Digital Bits and vice-versa. This happends between the the access point and the device using UMTS LTE Technology.

MAC Layer - MAC means medium access control layer. The purpose of this layer is to coordinate access to the system. It handles the requests asking for access to the system. Practically its role is to handle the movement of data packets from one Network Interface Card (NIC) to another if a shared channel is available between the two.

RLC Layer - It means radio link control layer. Its purpose is to maintain the connection between the mobile device and the base station through the radio link.It also handles error detection and recovery. If error correction feature is available, then that too is handled by this layer. There are three modes for it to transfers data from Upper Layer: Acknowledged Mode (AM), Unacknowledged Mode (UM) and Transparent Mode (TM).

PDCP Layer - It means Packet Data Convergence Protocol Layer. It is the top most layer of this protocol. Its purpose is to ensure that the transfer of all data packets takes place in correct order. It also handles ciphering and integrity protection. It provides service of Header Compression and attaches a PDCP Header before sending the packet forward.