UTRAN ARCHITECTURE an OVERVIEW

UTRAN is a collective term for the network and equipment that connects mobile handsets to the public telephone network or the internet. This communication network commonly referred to as 3G ( for 3rd Generation Wireless Mobile Communication Technology), can carry many traffic types from Real time Circuited Switched (CS) to IP based Packet Switched (PS). The UTRAN allows connectivity between the UE and the core network. Compared to the GSM network architecture, the Radio Access Network of UMTS, called the UTRAN ( Universal Terrestrial Radio Access Network) constitutes the main innovation, and allows data and signaling traffic exchange between User Equipment (UE) and Core Network (CN). It handles the allocation and withdrawal of radio bearers required for the traffic support on the radio interface and controls some functions related to UE mobility and network access. It contains the base stations, which are called Node B’s and Radio Network controllers (RNCs) which make up the UMTS Radio Access Network. The UTRAN is the link between the UE and the CN domains respectively through the “Uu” and “Iu” interfaces. In cellular telephone communications, the air interface is the radio-frequency portion of the circuit between the cellular phone set or wireless modem (usually portable or mobile) and the active base station. The logical connections between the network elements are known as interfaces. The UTRAN architecture can be divided into three main elements. User Equipment (UE) Radio Network Subsystem (RNS) Core Network (CN) The interface between the RNC and the Circuit Switched Core Network (CS-CN) is called Iu-CS and between the RNC and the Packet Switched Core Network is called Iu-PS. Other interfaces include Iub (between the RNC and the Node B) and Iur (between RNCs in the same network). Iu interfaces carry user traffic (such as voice or data) as well as control information. In UTRAN, user equipment (UE) is any device used directly by an end-user to communicate. It can be a hand-held telephone, a laptop computer equipped with a mobile broadband adapter or any other device. The radio interface between the UE and the node B is called “UU” functionality of user equipment: User equipment can handle the following tasks towards the core network: Mobility Management Call Control Session Management Identity Management The RNS also known as UMTS radio access network, UTRAN is the equivalent of the previous base station subsystem or BSS in GSM. It provides and manages the air interface for the overall network. A RNS is in its turn composed of one Radio Network controller (RNC) and one or several node Bs controlled via “Iub” interface The RNS has two main logical elements: Node B and an RNC. The RNS is responsible for the radio resources and transmission / reception in a set of cells. A cell (sector) is one coverage area served by a broadcast channel. A RNC is responsible for the use and allocation of all the radio resources of the RNS to which it belongs. It can also handles the user voice and packet data traffic. It can perform the necessary action to access the radio bearers on the user data streams. Intra UTRAN handover Frame synchronization Radio resource management Macro diversity combining/ splitting of “Iub” data streams Outer loop power control “IU” interface user plane setup Radio resource allocation Frame selection/ distribution functions necessary for soft handover UMTS radio link control (RLC) sublayers function execution Termination of MAC, RLC and RRC protocols for transport channels Iub’s user plane protocols termination Node B is the exchange node between the UTRAN and all the UEs located in the cell or sectors covered by node B. It mainly assures physical layer functions such as interleaving, channel coding and decoding, rate matching, spreading QPSK modulation etc. A node B is responsible for radio transmission and reception in one or more cells to/ from the user equipment (UE) Radio transmission and reception handling Transmission of “Iub” interface from RNC Involved in the mobility management Termination of MAC protocol for transport channels Inner and open power control Radio channel coding/decoding Macro diversity combining/ splitting of data streams from its cells Termination of “Uu” interface from User Equipment (UE) Frequency and time synchronization Power weighting and combining of physical channels Multiplexing of transport channels and demultiplexing of coded composite transport channels. Error detection on transport channels and indication to higher layers.