3gpp Based LTE Network Architecture for Broad band Wireless Communication

Transcription

1 Volume 118 No ISSN: (on-line version) url: 3gpp Based LTE Network Architecture for Broad band Wireless Communication T.Vasu deva Reddy 1, M.Obula Reddy 2, B.Naresh kumar 3,P.Kavitha Reddy 4 1 ECE Dept B V Raju Institute Of Technology, Narsapur, Medak(Dt), 2 Associate professor, M.V.S T, Hyderabad 3,4 Dept of ECE,Associate professor, B V Raju Institute Of Technology, Narsapur, Medak(Dt), 1 vasu.tatiparthi@bvrit.ac.in, 2 moreddy2003@gmail.com, 3 nareshkumar.b@bvrit.ac.in, 4 kavithareddy.p@bvrit.ac.in April 18, 2018 Abstract Long Term Evaluation (LTE) Network is designed with a aim of providing higher data rates of uplink (Encode b to User E) & down link (UE to E node) speed of 100Mbps & data rates 50Mbs. It also supports for various bandwidths ranging from 1.25MHZ to 20MHZ. In1991, 2G GSM Networks are designed & deployed for the voice centric services based on circuit switched telephone network. Later on GSM networks are improved for the packet based services with name of 2.5 GPRS. This network offers higher data rates approximately 170 kbps. In 1999, 3G Universal Mobile Telecommunications System (UMTS) is designed to offer higher data rates with 2Mbps for the pedestrian environment. Later on it has improved to higher data rates of High Speed Packet Access (HSPA) around 14mbps with 1

2 back word compatibility. LTE network is designed and optimized for internet protocol (IP) based networks. LTE networks are targeted to provide various real time services like voice, video telephony, etc and non real time services of file down load, ,sms, mms streaming, gaming, broad cast, multicast services and so on. This research paper describes the overview of LTE network architecture for broad band wireless communication Key Words:LTE/3GPP, UMTS, UE, MM, E-Node B, SGW, PGW 1 INTRODUCTION In 1991, 2G GSM network is designed for voice based service on circuit switch network principle & supports less data rates of 9.6 kbps for data communication services. It also enhanced for the SMS, Supplementary services, value added services like a ring back caller tunes. Around 1995 packet based services are added on top GSM network with name of 2G GPRS services. In 1999 first 3G UMTS network designed and deployed in various parts of the world. 3G UMTS network offers global roaming, improving voice quality, network capacity and data communication services. In 3G UMTS, WCDMAradio access technology with carrier bandwidth of 5MHZ is applied. Later on 3G UMTS networks are improved with data rates around 14 to15mbps with the help of advanced modulation like MIMO techniques. In 2008, first LTE network specifications are released for the global community. Basically LTE Fig 1: 3G UMTS High level Network components 2

3 network is designed with all IP core network, excluding the circuit switched network. LTE network supports circuit switched services with the help of IP multimedia subsystem service platform.[1]. In LTE Network, No Separate Radio Network Controller, all RNC functions are shifted to Encoder for reducing latency. Fig 2: LTE Network, network nodes 2 Description of LTE network Nodes and Device Basically LTE network consists of UE, ENODEB, MME, SGW, PDNGW, and HSS. 2.1 User Equipment Functions (UE) Contains the Universal Subscriber Identity Module (USIM) which holds authentication information and Operator Specific information. Various services & applications supported by UE are Monitors radios and conveys performance to the Evolved Node B (enb). Channel quality indicator (CQI) Supports LTE uplink and downlink air interface Maps upstream traffic into traffic classes that are defined by upstream traffic flow templates 2.2 Enodeb/E-Utran functions [1] The main features supported by the Endoeb are the following: a) Radio Bearer management: This includes Radio Bearer setup and release and also involves radio resource management features for initial admission control and bearer allocation. This set of functions is under the control of the MME through the S1 interface during session Setup & release and modification phases. 3

4 b) Radio interface transmission and reception: This includes radio channel modulation/demodulation as well as channel coding and decoding[6,7]. c) Uplink and Downlink Dynamic radio resource management and data packet scheduling: This is probably the most critical function which requires the enodeb to cope with many different constraints (like radio-link quality, user priority and requested Quality of Service). So as to be able to multiplex different data flows over the radio interface and make use of available resources in the most efficient way. d) Radio Mobility management: This function relates to terminal mobility handling while the terminal is in an active state. This function implies radio measurement configuration and processing as well as the handover algorithms for mobility decision and target cell determination. Radio Mobility has to be distinguished from Mobility Management in Idle, which is a feature handled by the Packet Core. e) User data IP header compression and encryption: This item is a key to radio interface data transmission. It answers to the requirements to maintain privacy over the radio interface and transmit IP packets in the most efficient way. f) Network signaling security: Because of the sensitivity of signaling messages exchanged between the enodeb itself and the terminal or between the MME and the terminal, all this set of information is protected against eaves dropping and alteration. In addition, the enodeb also supports some additional functions, which are less obvious but Still mandatory to make the overall system work g) Scheduling and transmission of broadcast information: This function is present in most, if not all, of the cellular systems. It refers to system information broadcasting so that idle terminals can learn network characteristics and be able to access and register to it. h)scheduling and transmission of paging messages: This function is essential for the network to be able to set up mobile terminated sessions. In addition, paging is also used for non idle but inactive terminals which the network needs to join. i) Selection of MME at terminal attachment this nonessential feature may be used to increase network resilience to EPC node 4

5 failure, and also helps to cope up with network load management. It is part of the S1 flexibility. 2.3 MME Function [1] The main features supported by the MME are the following: a)nas signaling support: NAS (Non Access Stratum) signaling refers to the signaling layer being used between the Packet Core and the terminal supporting functions such as network attachment and data session setup. b)active session mobility support: This refers to user context transfer in the case of active session mobility, either between 2G and 3G systems (which involves user context transfer over the S3 interface) or between MME nodes (which involves S10 support). c)idle mode terminal Mobility Management: This function is also known as terminal location tracking. It allows the EPC to know where to page terminals in case of user-terminated sessions. d)authentication and Key Agreement (AKA) This refers to user and network-mutual Authentication and session key agreement between terminal and EPC. e)determination of Serving and PDN GW at bearer establishment: This function is the EPC Equivalent of the GGSN selection function which is performed in 2G/GPRS and 3G/UMTS Networks by the SGSN. 2.4 SGW functions [1] The main features supported by the Serving GW are: Packet routing between E-UTRAN and EPC. Mobility anchoring: The Serving GW is actually the User plane anchor point in case of active session mobility between 2G and 3G systems (which involves the S4 interface) or between encoded in E-UTRAN. a) PDNGW functions [1] The main PDN GW features are Packet routing between the EPC and external PDN (Packet Data Network): In this context, PDN is a very generic term which covers any kind of IP network as well as IMS domain. 5

6 b)policy enforcement: Based on the rules provided by the PCRF. Charging support: As being the EPC edge router, the PDN GW is in charge of applying specific data-flow charging rules. c)ip address allocation for terminals: The IP address allocation is performed when the initial bearer is set up during the network attachment procedure. d) HSS functions The HSS (Home Subscriber Server) is the concatenation of the HLR (Home Location Register) and the AuC (Authentication Center) two functions being already present in pre-ims 2G/GSM and 3G/UMTS networks[9]. The HLR part of the HSS is in charge of storing and updating when necessary the database containing all the user subscription information, including (list is non exhaustive): e)user identification and addressing: This corresponds to the IMSI (International Mobile Subscriber Identity) and MSISDN (Mobile Subscriber ISDN Number) or mobile telephone number. f)user profile information: This includes service subscription states and user-subscribed Quality of Service information (such as maximum allowed bit rate or allowed traffic class).the AuC part of the HSS is in charge of generating security information from user identity keys. This security information is provided to the HLR and further communicated to other entities in the network. Security information is mainly used for mutual network-terminal authentication. Radio path ciphering and integrity protection, are used to ensure data and signaling transmitted between the network and the terminal is neither eavesdropped nor altered. 3 Radio Interface Protocols: The E-UTRAN Radio Layered Architecture: a)rrc LAYER: Starting from the top of the picture, the RRC layer (Radio Resource Control) supports all the signaling procedures between the terminal and the enodeb. This includes mobility procedures as well as terminal connection management. The signaling from the EPC Control plane (e.g. for terminal registration or authentication) is transferred to the terminal through the RRC protocol, hence the link between the RRC and upper layers. 6

7 Protocol layered structure in enodeb for downlink channels as shown fig3 Fig 3: Protocol layered structure in enodeb for downlink channels b)pdcp Layer: The PDCP layer (whose main role consists of header compression and implementation of security such as encryption and integrity) is offered to Radio Bearers by E-UTRAN lower layers. Each of these bearers corresponds to a specific information flow such as User plane data (e.g. voice frames, streaming data, IMS signaling) or Control plane signaling (such as RRC or NAS signaling issued by the EPC). Due to their specific purpose and handling, Information flows generated by System Information Broadcast and.paging Functions are transparent to the PDCP layer. c)rlc Layer: The RLC layer provides to the PDCP layer basic OSI-like Layer 2 services such as packet data segmentation and ARQ (Automatic Repeat Request) as an error-correction mechanism. There is oneto-one mapping between each RLC input flow and Logical channels provided by RLC to the MAC layer. d)mac Layer: The MAC layers main task is to map and multiplex the logical channels onto the transport Channels after having performed priority handling on the data flows received from the RLC layer. The flow being multiplexed on a single transport channel may be originated by a single user (e.g. one or more instances of DCCH 7

8 and DTCH) or multiple users (e.g. several DTCH from different users). The MAC also supports HARQ (Hybrid ARQ), which is a fast repetition process. finally, the MAC delivers the transport flows to the PHY layer, which will apply the Channel coding and modulation before transmission over the radio interface[6,7]. e) The Radio Channels: In general, it is critical, especially in the case of radio mobility, that E-UTRAN signaling messages are transmitted as fast as possible, using the best error-protection scheme. On the other hand, voice or data streaming applications can accept a reasonable frame loss due to radio transmission. Interactive connection-oriented applications (such as Web browsing) are also different, as the endto-end retransmission can help to recover from radio propagation issues. In order to be flexible and allow different schemes for data transmission. The E-UTRAN Specifications introduce several types of channels: a) The logical channels what is transmitted. b)the transport channels how it is transmitted. The physical & logical channels correspond to data-transfer services offered by the radio interface protocols to upper layers. Basically, there are only two types of logical channels: the control channels (for the transfer of Control plane information) and the traffic channels (for the transfer of User plane information). Each of the channels of these two categories corresponds to a certain type of information flow[5]. Logical control of E-UTRAN channels: a) The BCCH (Broadcast Control Channel): this channel is a downlink common channel, used by the network to broadcast E- UTRAN system information to the terminals presents in the radio cell. This information is used by the terminal, e.g. to know serving cell network operator, to get information about the configuration of the cell common channels, how to access to the network, etc. b)the PCCH (Paging Control Channel): the PCCH is a downlink common channel which transfers paging information to terminals presents in the cell, e.g. in case of mobile terminated communication session. c)the CCCH (Common Control Channel): The CCCH is a special kind of transport channel, used for communication between the terminal and E-UTRAN when no RRC connection is available. 8

9 Typically, this channel is used in the very early phase of a communication establishment. d)the MCCH (Multicast Control Channel): This channel is used for the transmission of MBMS (Multimedia Broadcast and Multicast Service) information from the network to one or several terminals. e)dcch (Dedicated Control Channel): The DCCH is a pointto-point bi-directional channel supporting control information between a given terminal and the network. In the DCCH context, the control information only includes the RRC and the NAS signaling. The Application-level signaling (such as SIP of RTCP) is not handled by the DCCH. E-UTRAN logical traffic channels: The DTCH (Dedicated Traffic Channel): The DCCH, the DTCH is a point-to-point bidirectional Channel, used between a given terminal and the network. It can support the transmission of user data, which include the data themselves as well as application-level signaling associated to the data flow[3]. The MTCH (Multicast Traffic Channel): A point-to-multipoint data channel for the transmission of traffic data from the network to one or several terminals. As for the MCCH, this channel is associated to the MBMS service[3]. E-UTRAN Transport Channels The transport channels describe how and with what characteristics data are transferred over the radio interface. For example, the transport channels describe how the data are protected against transmission errors, the type of channel coding, CRC protection or interleaving which is being used, the size of data packets sent over the radio interface, etc. All this set of information is known as the Transport Format. As in the specification, the transport channels are classified into two categories:downlink transport channels (from the network to the terminal Uplink transport channels (from the terminal to the network)[3]. E-UTRAN downlink transport channels: BCH (Broadcast Channel), associated to the BCCH logical channel. The BCH has a fixed and predefined Transport Format, and shall cover the whole cellarea. PCH (Paging Channel) associated to the BCCH.The DL-SCH (Downlink Shared Channel), which is used to transport user control or traffic data. 9

10 MCH (Multicast Channel) which is associated to MBMS user control of transport information E-UTRAN uplink transport channels are: The UL-SCH (Uplink Shared Channel), which is the uplink equivalent of the DL-SCH The RACH (Random Access Channel) which is a specific transport channel supporting limited control information, e.g. during the early phases of communication establishment or in case of RRC state change. Physical channels: The physical channels are the actual implementation of the transport channel over the radio interface. They are only known to the physical layer of E-UTRAN and their structures tightly dependent on physical interface OFDM characteristics [5]. Types Of physical channels defined in the downlink Physical Downlink Shared Channel (PDSCH) carries user data and higher-layer Signaling Physical Downlink Control Channel (PDCCH): This channel carries scheduling assignments for the uplink. Physical Multicast Channel (PMCH) bears Multicast/Broadcast information Physical Broadcast Channel (PBCH) holds System Information. Physical Control Format Indicator Channel (PC- FICH) This informs the UE about the Number of OFDM symbols used for the PDCCH. Physical Hybrid ARQ Indicator Channel (PHICH): which carries ACK and NACK, NodeB responses to uplink transmission, relative to the HARQ mechanism [5,6]. The physical channels defined in the uplink Physical Uplink Shared Channel (PUSCH): Carries user data and higher-layer Signaling. Physical Uplink Control Channel (PUCCH) Channel carries uplink control information, Including ACK and NACK responses from the terminal to downlink transmission, relative to the HARQ mechanism Physical Random Access Channel (PRACH) which carries the random access preamble sent by terminals to access to the network[5,6] 10

11 FIG 4:ENODEB CHANNEL MAPPING 4 DIFFERENT NETWORK ARCHI- TECTURE S FOR LTE Basically LTE network consists of access network and packet based core network [1], which is connected to IMS service platform. 3Gpp LTE group specifies various Network architectures like a simple LTE home network, LTE roaming network, Inter operability of 2G/3G UMTS networks, Interoperability with other Non 3Gpp networks of WLAN, WIMAX etc in both trusted and non trusted modes. The following section shows various network architect models [8,9]. Merging the two gateways [4] Fig 5: Merging S1 Control AND User plane 11

12 Fig 6: EPC roaming architecture home-routed traffic Fig 7: EPC roaming architecture local breakout 12

13 Fig 8: Non-3GPP Access Architecture The EPC architecture for trusted WLAN access Fig 9: HSS Interface Architecture: 13

14 Fig 10: Interface of HSS with MME V. Important EPC protocol stack: The following sections shows the various protocol stack for the LTE network & Control plane between UE, enodeb and MME [2] Fig 11: GTP based protocol stack Basically in GTP based protocol stack defined for different intefaces with various parameters according to interface requiremenets. MME MME (S10), MME - SGW(S11), Serving GW PDN GW (S5/S8) 14

15 Fig 12: MMEHSS (S6a) protocol stack User Plane Protcol Stack UE enodeb Serving GW PDN GW (GTP-U) Fig13: interfacing of UE with PDN GW 5 Typical Signaling flows The following sections shows various signaling flows a) Subscriber registration 15

16 Fig 14: Subscriber registration b). Subscriber Deregistration Fig 15: Subscriber Deregistration 16

17 Fig 16: Service Request Architecture 6 Conclusion In this paper addressesd overview of LTE network Acrchitecture, Scheduling and transmission, Types Of physical channels, logical control data rates,protocol tacks,some of the improtant signaling flows. A. Abbreviations and Acronyms 3GPP : Third Generation Partnership Project3 3GPP2 : 3rd Generation Partnership Project 2 ARQ : (Automatic Repeat Request). CQI : Channel Quality Indicator. enodeb : evolved NodeB. EPC : Evolved Packet Core EPS : Evolved Packet System HLR : Home Location Register HSS : Home Subscriber Server References [1] Pierre Lescuyer and Thierry Lucidarme, Evolved Packet Systems (EPS), John Wiley & Sons Ltd,

18 [2] Magnus Olsson, Stefan Rommer, Catherine Mulligan, Shabnam Sultana, Lars Frid, SAE and the Evolved Packet Core: Driving the Mobile Broadband Revolution, Academic Press; 1 edition (1 August 2009) [3] TS (rel 8), GPRS Enhancements for E-UTRAN Access [4] TS23.402, Architecture Enhancements for Non-3GPP Accesses [5] TS3GPP , LTE Physical Layer: General Description [6] TS ,Physical Channels and Modulation [7] TS , Multiplexing and Channel Coding [8] Erik Dahlman, Stefan Parkvall, Johan Skold, 4G: LTE/LTE- Advanced for Mobile Broadband Academic Press, 21-Mar Technology & Engineering. [9] Harri Holma, Antti Toskala, LTE for UMTS: Evolution to LTE-Advanced, Wiley; 2 editions, (April 25, 2011) 18