EETS 8316 Wireless Networks Fall 2013

Transcription

1 EETS 8316 Wireless Networks Fall 2013 Lecture: Cellular Overview: 3G and 4G Dr. Shantanu Kangude

2 Third Generation Systems High-speed wireless communications to support multimedia, data, and video in addition to voice 3G capabilities: voice quality comparable to PSTN 144 kbps available to users over large areas 384 kbps available to pedestrians over small areas support for Mbps for office use symmetrical and asymmetrical data rates packet-switched and circuit-switched services adaptive interface to Internet more efficient use of available spectrum support for variety of mobile equipment allow introduction of new services and technologies 2

3 Driving Forces Trend toward universal personal telecommunications Universal communications access GSM cellular telephony with subscriber identity module, is step towards goals Personal communications services (PCSs) and personal communication networks (PCNs) also form objectives for third-generation wireless Technology is digital using time division multiple access or code-division multiple access PCS handsets low power, small and light 3

4 IMT-2000 Terrestrial Radio Alternative Interfaces 4

5 CDMA Design Considerations Bandwidth and Chip Rate Dominant technology for 3G systems is CDMA 3 CDMA schemes, share some design issues Bandwidth (limit channel to 5 MHz) 5 MHz reasonable upper limit on what can be allocated for 3G 5 MHz is enough for data rates of 144 and 384 khz Chip rate given bandwidth, chip rate depends on desired data rate, need for error control, and bandwidth limitations chip rate of 3 Mbps or more reasonable 5

6 CDMA Design Considerations Multirate Provision of multiple fixed-data-rate channels to user Different data rates provided on different logical channels Logical channel traffic can be switched independently through wireless fixed networks to different destinations Flexibly support multiple simultaneous applications Efficiently use available capacity by only providing the capacity required for each service Two methods Use TDMA within single CDMA channel or use multiple CDMA codes 6

7 CDMA Multirate Time and Code Multiplexing 7

8 UMTS Architecture & Domains UTRAN UMTS Terrestrial Radio Access Network User Equipment (UE) = Mobile Node B = Base Station Radio Network Controller = RNC like BSC Core Network (Reuse GSM CN) Circuit Switched Domain MSC, GMSC Packet Switched Domain SGSN, GGSN

9 GSM and UMTS High level Original Src: gsm.htm

10 UMTS Release 4 UTRAN is same as release 99 Core Network Modified only in the CS domain MSC = 2 entities Media Gateway(MGW) for user plane MSC server for the control plane

11 Release 4 Architecture + IMS Src:

12 UMTS Release 5 Core: New platform IMS( IP Multimedia Subsystem) RAN: HSDPA(High Speed Downlink Packet Access) technology allows 14.4 Mbps peak data rate in DL data rate achievable by software updates in nodeb to support new modulations and coding schemes assign up to 15 codes for one user.

13 UMTS Release 6 RAN HSUPA allows upto 5.5 Mbps in UL Core IMS v2

14 Long Term Evolution (LTE) or 4G wireless cellular networks from 3GPP Evolved UMTS Terrestrial Radio Access Network Release 8+

15 Terms and Definitions UE: User Equipment (Mobile) enb: Evolved Node B (Base station) S-GW: Serving Gateway (Cellular network edge router or MTSO) E-UTRA/N: Evolved UMTS Terrestrial Radio Access/Network (Official name of LTE) EPS: Evolved Packet System (MTSO network) MME: Mobility Management Entity (also at MTSO) 15

16 X2 X2 Network Architecture S1: Logical Interface between edge router and enb May involve multiple hops X2: Control interface between 2 enbs Only exists between enbs that may need to communicate MME (control plane) Tracks the location of mobile in the network S-GW (user plane) Routes packets to appropriate enb Radio Network Core Network 16

17 Radio Network Functions Forwarding of core network control information Paging (from network to UE) Tracking area update (from UE to network) Other IDLE mode mobility/tracking procedures Data forwarding in both directions while connected Satisfy QoS for flows through scheduling Radio resource management Manage Radio connection (participation in the radio network) Manage mobility during connection Measurements, configurations, and other control 17

18 Core Network Functions Control Protocol between UE and MME (MTSO) Track the location of UE in idle mode Track the state (active or idle) of the UE Page UE to request it to be active Data Forwarding in both directions QoS control between S-GW (MTSO) and enb Active mode UE mobility (Control information between MME (MTSO) and enb) Track UE in active mode / Handoff 18

19 Core Network: Tracking Areas and Paging Tracking Area A subset of enbs represented as a single unit Multiple overlapping tracking areas possible Multiple hierarchical tracking areas possible Benefits of tracking areas Lower resolution of tracking of Idle UEs by MME less frequent tracking updates in MME as UE moves in IDLE Paging Request by core network to join the radio network Performed over a tracking area when traffic pending for a UE All cells in a tracking area PAGE a UE Importance of tracking areas and paging Critical for the UE and the core to maintain correct tracking area Paging reliability is important UE joins a radio network after receiving a valid page Data communications only possible after joining the radio network 19

20 RRC Connection and Radio Network Radio Resource Control (RRC): Manages radio network participation of UEs Two states: RRC_IDLE (UE is not part of the radio network) No UE state in the enb UE may perform tracking area updates for core network (mobility) UE may receive PAGE from the core network RRC_CONNECTED (UE becomes part of radio network) UE state exists in the enb Data flows with their characteristics Any measurement or capability reports A UE address called C-RNTI (Cell-Radio Network Temporary ID) UE may be scheduled in the UL and DL enb is responsible for mobility (Handoff) 20

21 Core network states and RRC states Inactivity - Release C-RNTI - Allocate DRX for PCH Perform Registration - Allocate C-RNTI, TA-ID, IP addr - Perform Authentication - Establish security relation Power-Up LTE_IDLE RRC: RRC_IDLE Context in network: - Includes information to enable fast transition to LTE_ACTIVE (e.g. security key information) Allocated UE-Id(s): - IMSI - ID unique in Tracking Area (TA-ID) - 1 or more IP addresses UE position: - Known by network at Tracking Area (TA) level Mobility: - Cell reselection DL activity: - UE is configured with DRX period LTE_ACTIVE RRC: RRC_CONNECTED RRC Context in network: - Includes all information necessary for communication Allocated UE-Id(s): - IMSI - ID unique in Tracking Area (TA-ID) - ID unique in cell (C-RNTI) - 1 or more IP addresses UE position: - Known by network at cell level Mobility: - Handover DL/UL activity: - UE may be configured with DRX/DTX periods LTE_DETACHED RRC: NULL RRC Context in network: - Does not exist Allocated UE-Id(s): - IMSI UE position: - Not known by network Mobility - PLMN/Cell selection DL/UL activity: - None New traffic - Allocate C-RNTI Change of PLMN/deregistration - Deallocate C-RNTI, TA-ID, IP address 21 Timeout of periodic TA-update - Deallocate TA-ID, IP address

22 FDD Frames and Sub-Frames Frame System level quantum of repetition 10 ms Sub-frame Smallest quantum for scheduling in time-domain Comprises of 2 slots (significance for PHY only) 1 ms 10 sub-frames per frame 22

23 FDD DL Frame Composition OFDM frequency carriers One Resource Block (RB) = 12 subcarriers 1 sub-frame = 14 OFDM symbols OFDM symbols are MIN quantum of time in OFDM systems for any data carriage 10 Sub-frames per frame Time Resource Block = Minimum Quantum for Scheduling in DL or UL 23 L1-L2 Control Channel: Maximum 3 out of 14 symbols

24 Overhead in DL frames Broadcast System information interspersed in the DL (e.g. Network name etc.) L1-L2 Control channel: Allocation of transmission grants For DL transmissions (like DL-MAP in WiMax) For UL transmissions (like UL-MAP in WiMax) Unicast control PDUs to UEs Random Access (as Ranging in WiMax) Responses 24

25 FDD UL Frame Composition Control channel on the edges 1 Resource Block (RB) = 12 subcarriers 10 Sub-frames per frame Data in UL- SCH Random Access Channel (RACH) Slot for Ranging 25

26 UL Overhead Control Channel on the edges for HARQ ACK-NACKs, Scheduling Requests etc. RACH channel or Ranging Slots as in WiMax In band unicast control packets in the UL 26

27 Random Access/Ranging Used by a UE in UL when No dedicated resources for TX available No UL synchronization Utilizes Preamble transmission in enb configured RACH slots enb responds with the Timing Advance value A RACH access is the only way the possible existence of UE s transmission is not preknown to the enb; All other transmissions are pre-scheduled by the enb 27

28 Handover (Handoff) Mobility of the UE => The UE-eNB association changes Idle mode mobility (cell-reselection) Camping (ready to connect) on best cells desired Tracking area updates to core network if any change No urgency as no calls/flows on going Connected mode mobility (Handover) Current enb manages the transition based on measurement reports from UE Preparations as in RRC connection establishment required at target enb before UE can transition Low break latency desired as calls/flows ongoing 28

29 Handover Procedure 29

30 LTE: Operators and Vendors Interest Operators backing LTE All former GSM and UMTS operators AT&T, Docomo, Vodafone, T-Mobile, Orange, Telecom Italia etc. Some former CDMA-2000 supporters Verizon and Sprint (?) Convergence to LTE Vodafone CEO seeks Wimax as a standard under LTE umbrella Some analysts forecast 80% LTE and 20% Wimax for next generation market share 30

31 Summary 3G Cellular Systems Overview LTE: 4G Wireless Systems Overview 31