Mobile Network Evolution Part 2 From UMTS to LTE or How to Further Increase Network Capacity and QoS Andreas Mitschele-Thiel Advanced Mobile Communication Networks 1
Outline Evolution from Circuit Switching to Packet Switching LTE Architecture Packet handling Resource management and QoS Features and requirements Architecture Packet handling and resource management References Advanced Mobile Communication Networks 2
Review: From GSM to UMTS Base station Base station PSTN Base station +EDGE GSM RAN Base station controller MSC GSM Core (Circuit switched) GMSC HLR AuC EIR node B node B +HSPA node B UTRAN Radio network controller SGSN GPRS Core (Packet Switched) IMS GGSN Internet Advanced Mobile Communication Networks 3
Circuit vs. Packet Switched Communication Connection (e.g. voice, CS data) => principle for GSM & UTRAN design clearly defined start and end times no burstiness => dedicated channels connection setup connection release Packet session => supported by GPRS core, IMS, SAE, HSPA, LTE packet arrival times are typically unknown to the system traffic is highly bursty => shared channels & packet scheduling minutes hours seconds Advanced Mobile Communication Networks 4
Resource Management in UMTS (radio link) When to free resources? After short or long breaks? latency idle setup delay T 3 T 2 transient resource usage resource consumption T 1 cell_dch radio resources channel codes HW resources Advanced Mobile Communication Networks 5
End-to-End Resource Management in UMTS (contr. plane) A sophisticated QoS architecture TE Local Service Control Transl. MT UMTS BS Adm./Cap. Control UTRAN Adm./Cap. Control RAB Adm./Cap. Control CN EDGE UMTS BS Subscr. Control Gateway Adm./Cap. Control UMTS BS Transl. Ext. Netw. Ext. Service Control Local BS Radio BS Radio BS Iu BS Adm. Iu BS Contr CN BS CN BS Ext. BS UTRA ph. BS M UTRA ph. BS M Iu NS Iu NS BB NS BB NS service primitive interface protocol interface For details see 3GPP TS 23.207 Advanced Mobile Communication Networks 6
End-to-End Resource Management in UMTS (user plane) TE MT UTRAN CN EDGE Gateway Ext. Netw. Class if Class if Cond. Cond. Cond. Mapper Mapper Mapper Local BS Resource Resource Resource Resource Resource Resource External BS UTRA phys. BS Iu network service BB network service data flow with indication of direction Advanced Mobile Communication Networks 7
Evolution from GSM to UMTS and LTE GSM: voice-dominated, dedicated channels, heavy states GPRS: add support for packet data on shared channels; add IP-based core network EDGE: increased packet data capacity of GSM system UMTS: separate voice and packet data support; focus on dedicated channels and heavy states, complicated RAN architecture and protocols due to macro diversity and QoS requirements HSPA: improved support for packet data; emphasis on shared channels and fast radio resource management IMS: support for IP-based services, e.g. voice (VoIP) LTE: strong packet data support (latency, throughput, control overhead), limited state; simplified protocols; PS only, i.e. no CS core network Transition from circuit switching to packet switching from slow, explicit setup and release of resources to fast channelcondition- and demand-specific resource management Advanced Mobile Communication Networks 8
Evolution towards LTE Architecture LTE radio system is a packet-only network - there is no support for circuit-switched services (no MSC) LTE starts on a clean state - everything is up for discussion including the system architecture and the split of functionality between Radio Access Network (RAN) and Core Network (CN) 3GPP (3 rd Generation Partnership Program) study items 3G Long-term Evolution (LTE) for new Radio Access and System Architecture Evolution (SAE) for Evolved Network Advanced Mobile Communication Networks 9
Evolution towards LTE Architecture Base station Base station PSTN Base station GSM RAN Base station controller MSC GSM Core (Circuit switched) GMSC HLR AuC EIR e- e- node B node B e- node B S-GW SGSN Radio network controller E- UTRAN EPC GPRS Core (Packet Switched) P-GW IMS GGSN Internet Advanced Mobile Communication Networks 10
LTE: Evolved Packet System (EPS) Architecture 2 instead of 4 user plane entities MME/S-GW MME/S-GW Key changes enb: merging of base station and RNC functionality s-gw: merger of SGSN and GGSN functionality enb S1 S1 S1 S1 X2 S1 S1 enb EPC E-UTRAN X2 enb X2 EPC = Evolved Packet Core Advanced Mobile Communication Networks 11
LTE: Requirements and Performance Targets Advanced Mobile Communication Networks 12
LTE Key Features (Release 8) Support for both FDD and TDD Adaptive modulation and coding DL modulations: QPSK, 16QAM, and 64QAM UL modulations: QPSK and 16QAM Hybrid ARQ in addition to ARQ Multi-antenna solutions (2 or 4) x (2 or 4) downlink and uplink supported Multi-layer transmission with up to four streams Multi-user MIMO also supported Implicit support for interference coordination Advanced Mobile Communication Networks 13
Multi-antenna Solutions Advanced Mobile Communication Networks 14
Scheduling and Resource Allocation Fast scheduling Scheduled, shared channel on both uplink and downlink all transmissions in UL and DL must be explicitly scheduled Support for "semi-persistent" (periodical) allocation of resources, e.g. for VoIP Advanced Mobile Communication Networks 15
Interference Coordination Advanced Mobile Communication Networks 16
Self-Organization in LTE Goal: minimize OPEX by automation of planning, optimization and repair Use Cases Physical cell-id automatic configuration (PCI) Automatic Neighbor Relation (ANR) Coverage and capacity optimization (CCO) Inter-cell interference coordination (ICIC) Random Access Channel (RACH) optimization Mobility load balancing optimization (MLB) Mobility robust optimization (MRO) Energy saving (power on/off) Advanced Mobile Communication Networks 17
Example: RACH Optimization Delay to access to RACH depends on current network parameters Transmission power, handover threshold, etc. changing networks parameters requires optimizing the RACH Approach enb measures derived random access delay, random access success rate, random access load, etc. RACH parameters are optimized based on measurements RACH physical resources, RACH persistence level and backoff control, RACH transmission power control, etc. Advanced Mobile Communication Networks 18
Mobility Robustness Optimization (MRO) Filtered RSRP [db] Optimize HO performance amidst mobility Hence Mobility Robustness Optimization Hys Goal: minimize link failures due to early HO link failures due to late HO HO to wrong cell ping-pong handovers Parameters Hysteresis (Hys) Time to Trigger (TTT) Optimal settings depend on user mobility other cell paramaters Advanced Mobile Communication Networks 19
MRO Late HOs: UE leaves coverage cell before HO is complete RLF Early HOs: island coverage of cell B inside cell A s coverage or UE handed over before cell B is steadily better than cell A HO Triggering RLF HO to wrong cell: improper settings between cells A and B UE handed to cell C when should have been handed to cell B E.g. due to PCI confusion HO Triggering RLF Advanced Mobile Communication Networks 20
Load Balancing Overloaded Cells Advanced Mobile Communication Networks 21
Mobility Load Balancing (RSRP t +CIO t ) (RSRP s +CIO s ) > Hys RSRP CIO S Source Cell s CIO t Target Cell t RSRP: Reference Signal Received Power Hys: Hysteresis CIO: Cell Individual Offset TTT: Time to Trigger P: Preparation time Hys Start of TTT HO Decision P HO Command Time Advanced Mobile Communication Networks 22
SON Coordination Problem Use Cases (UCs) conflict within and across cells MRO CC O CELL 1A. MLB ICIC MRO Base Station 1 MLB MRO CC O MLB CELL 2C. ICIC Base Station 2 CC O CELL 1B. ICIC MLB: Mobility Load balancing (MLB) MRO: Mobility Robustness (Handover) Optimization CCO: Coverage and Capacity Optimization ICIC: Inter Cell Interference Coordination Possible Conflicts / dependencies Intra-cell Inter cell, intrabs - same UC Inter cell, intrabs - different UCs NB: Inter BS == inter cell Advanced Mobile Communication Networks 23
LTE vs. WiMax vs. 3GPP2 WiMAX IMS 3GPP/LTE PCRF IMS 3GPP2/UMB PCRF IMS AAA HA HSS PDN GW AAA HA Authenticator Paging Controller Page buffering Handover Control Radio Resource Management ARQ/MAC/PHY L2 Ciphering Classification/ ROHC CAP-C FA/Router Access Point Local mobility Session setup Bearer mapping Authenticator Paging Controller Session setup MME Handover Control Radio Resource Management ARQ/MAC/PHY L2 Ciphering ROHC E-Node B Bearer mapping Serv GW Local mobility Page buffering Authenticator Paging Controller SRNC Handover Control Radio Resource Management ARQ/MAC/PHY L2 Ciphering ROHC ebts Access GW Local mobility Session setup Bearer mapping IETF-centric architecture IETF-friendly, but still some flavor of UMTS/GPRS GTP, etc IETF-centric architecture Advanced Mobile Communication Networks 24
References LTE/SAE A. Toskala et al, UTRAN Long-Term Evolution, Chapter 16 in Holma/ Toskala: WCDMA for UMTS, Wiley 2007 E. Dahlman et al, 3G Evolution, HSPA and LTE for Mobile Broadband, Elsevier Journal, 2007 Special Issue on LTE/ WIMAX, Nachrichtentechnische Zeitung, pp. 12 24, 1/2007 3rd Generation Partnership Project Long Term Evolution (LTE), official website: http://www.3gpp.org/highlights/lte/lte.htm Technical Paper, UTRA-UTRAN Long Term Evolution (LTE) and 3GPP System Architecture Evolution (SAE), last update October 2006, available at: ftp://ftp.3gpp.org/inbox/2008_web_files/lta_paper.pdf Standards TS 36.xxx series, RAN Aspects TS 36.300, E-UTRAN; Overall description; Stage 2 TR 25.912, Feasibility study for evolved Universal Terrestrial Radio Access (UTRA) and Universal Terrestrial Radio Access Network (UTRAN) TR 25.814, Physical layer aspect for evolved UTRA TR 23.882, 3GPP System Architecture Evolution: Report on Technical Options and Conclusions Self-organizing networks and LTE Self-organizing networks and LTE, http://www.lightreading.com/document.asp?doc_id=158441 NGMN Recommendation on SON and O&M Requirements, Dec. 5, 2008, NGMN, http://www.ngmn.org/uploads/media/ngmn_recommendation_on_son_and_o_m_requirements.pdf Advanced Mobile Communication Networks 25