Overview of UMTS Radio Access Network Technology

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Overview of UMTS Radio Access Network Technology [Copy link]

Based on a brief introduction to the UTRAN network structure of 3GPP Release 99 , the overall functions of UTRAN are introduced , and the functions of each interface of UTRAN are briefly summarized. Finally, it is explained that the all- IP network solution is the direction of future UMTS network development . Keywords UMTS UTILAN WCDMA I. Introduction After the first generation analog system and the second generation cellular digital mobile system, mobile communications are developing towards the third generation mobile communication system ( 3G ) with WCDMA as the technical core . UMTS is the third generation mobile communication system standard formulated by 3GPP , and its principle is to clearly separate the radio access network and the core network. The core network is developed on the basis of the existing GSM / GPRS . It has good inheritance of GSM and will provide more powerful network carrying capacity and rich service functions, such as real-time multimedia services, broadband data services, etc. UTRAN ( UMTS Terrestrial Access Network ) is the application of WCDMA technology to the nine-line local loop system. The excellent characteristics of WCDMA depend on the implementation of the UTRAN interface function. The Release 99 UTRAN interface is based on ATM packet technology. The efficient ATM packet switching will greatly improve the transmission efficiency and network capacity, and provide rich options for the on-demand configuration of link bandwidth between UTRAN and between UTRAN and UMTS core network. Since the UMTS network is based on packet switching technology and considering the characteristics of WCDMA , the entire system capacity will be larger and the cost performance will be higher. This article will give a brief overview of Release 99 UTRAN . 2. UTRAN network structure Release 99 UMTS network consists of two parts: one is UTRAN . The other part is the core network CN . The two parts are connected through the Iu interface. The core network can be logically divided into the circuit switching domain ( CS ) and the packet switching domain ( PS ). The CS domain is the circuit switching core network of UMTS , which is used to support circuit data services. The PS domain is the packet service core network of UMTS , which is used to support packet data services ( GPRS ) and some multimedia services. According to the different logical domains of UTKAN connected to the core network, Iu can be divided into Iu - CS and Iu - PS , where In - CS is the interface between UTRAN and CS domain, and Iu - PS is the interface between UTRAN and PS domain . UTRAN includes multiple radio network subsystems RNS . The radio network subsystem NS includes a radio network controller RNC and one or more base stations NodeB . NodeB and RNC are interconnected through the Iub interface. In UTRAN , different RNS are interconnected through the Iur interface. Iur can be connected through direct physical connection RNCs or through a transmission network. NodeB is equivalent to the base transceiver station (BTS) in the GSM network.























BTS ), which can work in FDD, TDD mode
or dual mode . Each NodeB serves a wireless cell and provides access to wireless resources. RNC is equivalent to the base station controller ( BSC ) in the GSM
network , providing wireless resource control functions.
III. UTRAN Function Overview
UTRAN 's capabilities include radio access bearer capabilities and radio access bearer control, supporting the establishment, renegotiation and release of wireless resource connections with individual services and performance
characteristics . The renegotiation of QoS attributes and bearer attributes may be caused by a layer request
or wireless conditions (handover, change of cellular load, etc.), or may be initiated by the mobile station or the network. UTRAN will allow a
mobile terminal to handle multiple radio access bearer services at the same time. Each radio access bearer service may have its own rate and performance
requirements , but the number of radio access bearer services handled at the same time will be limited by the terminal and network capabilities. UTRAN
will also support radio access bearers for broadcast and multicast applications.
UTRAN has the following traffic management mechanisms: application of admission control ( CAC ) during connection establishment and renegotiation ; application of usage parameter control ( UPC
) after the connection is established .
For a UMTS network consisting of UTRANs with different UTILA modes , the cell selection and paging process should allow the service
area to be covered by cells supporting a specific mode or by cells supporting multiple modes. The network of the UMTS network operator should
support bidirectional handover of mobile terminals that can handle one or more radio access bearer services, which is carried out between
two UTRAN cells with different UTKA modes . In addition, the handover between cells using two different UTILA modes should be similar to the handover between the same
modes . UTILAN will also support seamless handover of the radio access bearer service of a mobile terminal between cells of UTKA Nr
. UTILAN should make it easier to determine the location of UMTS mobile terminals, and various methods can be used to complete the positioning function, such as mobile positioning , network-based positioning or hybrid positioning structure. In various wireless environments, the minimum positioning accuracy is about 50m . UTILAN should support the concept of local service area ( LSA ), which will make it easier to select radio resources based on local service areas and users . IV. UTRAN interface 1 . UTRAN radio interface ( 1 ) Radio transmission technology 3GPP has determined that UMTS terrestrial radio access ( UTRA ) includes two modes: time division duplex ( TDD ) in asymmetric frequency bands , using TDCDMA , and frequency division duplex ( FDD ) in symmetric frequency bands , using WCDMA . WCDMA mainly works in areas and provides medium and low-speed services, while TD - CDMA mainly focuses on areas with busy services and can provide services with speeds up to 2Mbit/s . Only WCDMA is discussed here. Basic parameters of WCDMA : ① WCDMA operating frequency band: ETSI stipulates that the 1920 ~ 1980MHZ frequency band is allocated to the FDD uplink, the 2110 ~ 2170MHz frequency band is allocated to the FDD downlink, and the asymmetric 1900 ~ 1920MHz frequency band is allocated to the TDD duplex mode. ② The basic working bandwidth is 5MHz , but its actual value can be increased in steps of 200kHz , and can be between 4.4 and 5.2MHz as needed.














The basic bandwidth can be expanded to 10 / 20MHz .
③ The basic spread spectrum code rate is 4.096Mcps , which can be expanded to 8.192 / 16.384Mcps .
④ The frame length is 10ms , each frame contains 16 time slots, each time slot is 0.625ms , representing an industrial control cycle.
⑤ The uplink channel adopts QPSK modulation, and the downlink channel adopts BPSK modulation.
⑥ Power control adopts open-loop + closed-loop adaptation.
In the field of nine-line transmission technology, China has independently researched and proposed TDSCDMA , which integrates the current international leading technology intelligent large line.
Synchronous C17MA and software radio, etc., with high spectrum utilization, low cost and greater flexibility, and is very
competitive.
( 2 ) Wireless interface protocol
The wireless Um interface is divided into three protocol layers: physical layer, data link layer and high layer. The physical layer is the radio frequency interface part, and the data
link layer is responsible for providing various logical channels of the air interface. The data link is further divided into the network access control layer ( MAC ) and the radio
link control layer ( RLC ). The main function of MAC is to define and allocate various logical channels of the air interface so that these channels can be shared by
different mobile terminals. RLC is a radio link protocol based on HDLC . Its main function is to add
RLC addresses and frame addresses to high-level data units to generate complete KLC frames. In addition, RLC can also realize point-to-multipoint addressing and data frame retransmission control.
The logical channels of the wireless interface are divided into two categories: public channels and dedicated channels.
① Public channels are used for multiple users to work together to transmit user information or control information between the network and the mobile terminal. Public channels
are further divided into broadcast control channels ( BCCH ), forward access channels ( FACH ), paging channels ( PCH ), and random access channels
( RACH ). BCCH is a common channel used in the downlink to transmit special control information of the broadcast system and the cell; FACH
is a common channel used in the downlink to carry control information and user short messages in the cell, which requires the system to know
the cell location of the mobile terminal; PCH is a common channel in the downlink, which carries control information to the
mobile ; RACH is an uplink transmission channel used to carry control information from the mobile terminal, and it can also carry short user
packet data.
② Dedicated channel ( DCH ), used to transfer user information or control information between the network and the mobile terminal allocated to a designated user.
Dedicated channels can be divided into dedicated service channels ( DSCH ), bypass dedicated control channels ( SD - CCH ) and auxiliary dedicated
control channels ( ACCH ).
2. In interface Release99 The In interface of
UTRAN connected to the circuit switching part of the core network is called Iu - CS , and the Iu interface connected to the packet
switching is called Iu - PS . These two interfaces have different signaling and user data connections.
( 1 ) The Iu interface protocol is divided into two planes:
① User plane protocol, which implements wireless access services, that is, transmits user data through the access plane.
② Control plane protocol, which is used to control the wireless access bearer and connection between the UE
and the network, including the requested services, control of different transmission resources, switching and traffic, etc., and also includes the transparent transmission of NAS messages. The wireless network signaling of the Iu
interface is composed of the radio access network application part RANAP . The RANAP protocol constitutes the mechanism for handling all procedures between the CN and UTRAN
. It can also transparently transmit messages between the CN and UE without the need forUTILAN interpretation and processing.
( 2 ) The characteristics of the Iu interface are as follows:
① The signaling bearer uses SCCP
to transmit signaling messages between CN and RNC . RANAP is the user function module of SCCP and uses the connectionless
and connection-oriented services of SCCP
. ② User data bearer
AAL2 is used as the user data bearer to CS . The AAL2 protocol is used to dynamically establish the AAL - 2 connection from the Iu interface to CS . GTP - U
is used as the user data bearer to PS. RANAP signaling is used to establish, modify and release the GTP - U channel to PS .
( 3 ) Main functions of the Iu interface: ① Management of
radio access bearer ( RAB ), including establishment, modification and release of RAB , RAB feature mapping and RAB queuing,
pre-clearing and priority functions.
② Radio resource management functions, including radio resource access control and broadcast information management functions.
③ Iu link management functions, including In signaling management, ATM virtual connection management, AAL2 and AAL5 connection establishment and release management,
and GTP - U tunnel management functions.
④ Mobility management functions, including mobile terminal location information update function, inter- RNC switching, service RNS relocation,
and UMTS - GSM inter-system switching function.
⑤ Security functions, including wireless interface encryption. Encryption key management and user identification confidentiality functions. ⑥ Service and network access
functions, including core network signaling data transmission speed change function, data volume report, mobile terminal tracking and
location report. Paging coordination function.
3. Iub interface ( 1 ) The information transmitted by the Iub interface includes: signaling related to wireless applications, such as information on wireless resource RNC and NodeB , information on controlling broadcast channels and paging channels, data streams of wireless frames, including wireless data streams such as DCH data streams, RACH data streams, FACH data streams, PCH data streams, etc.; quality assessment and synchronization data of uplink frames. ( 3 ) Main functions of the Iub interface: ① NodeB operation and maintenance and system information update. System information is sent by KNC to NodeB . ② Traffic management of public wireless channels and dedicated wireless channels. ③ Macro-diversity merging/splitting of radio frame data blocks and topology control of macro-diversity merging/splitting. ④ Soft handover decision. ⑤ NodeB hardware resource processing. ⑥ Power control and access control of uplink and downlink channels. 4 Iur interface ( 1 ) RNS is usually divided into service RNS ( ServeRNS ) and drift RNS ( Drift RNS ). DRNS supports SKNS by providing radio resources . ( 2 ) Main functions of Iur interface: ① Merging and splitting of data streams. For DRNS














DRNS performs the merging and separation of data streams within its management cell, while SRNS performs the merging and separation of Iur interface data streams from or to DKNS and the merging and separation of data streams within the cell managed by SRNS
. ② Merging and separation topology control function. ③ Processing of DRNS hardware resources ④ Allocation of physical channels, which is implemented by DRNS ⑤ Uplink / downlink power control function ⑥ Access control function, which is implemented by DRNS V. Development trend of UMTS Unified processing and unified transmission of voice and data ( IP ) is the development trend of communication technology. At present, ITU is formulating a Release 2000UMTS network solution based on all-IP, which will enable UTRAN to better integrate with fixed packet data networks, which is consistent with the trend of PSTN being integrated with IP backbone networks. The traditional mobile network will be limited to the wireless access side, while the UMTS core network will eventually merge with the IP network to form a unified IP network. This unified IP network will provide voice services in VOIP mode while providing broadband packet data services . IP will serve as a unified carrier for voice, data, and signaling. Traditional network entity functions will be separated by level. On the IP network, logically independent signaling processing servers and business application servers will be built to process control signaling and services, thereby realizing the so-called logical separation of " service / control / exchange " .