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Cdma2000 Radio Access Network

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  1. cdma2000 Radio Access Network Salih Ergut 7/7/2003

  2. Outline • cdma2000 network architecture • Call processing states and call flows • CDMA evolution • Essential elements in a CDMA system • Power Control • Mobility management • Handoffs • Registration • Roaming • Radio Admission Control

  3. Network Architecture BlackMountain Packet Network PSTN PDSN MSC BSC Ericsson UCSD

  4. Call Processing - Pilot First MS monitors Pilot channel for • Initial acquisition • Channel estimation • Detection of multipaths for rake receiver • Handoffs Pilot Ch

  5. Call Processing - Sync Pilot channel is transmitted at all times by the base station. MS uses it to lock to Synch Channel to • Synchronize to CDMA system time • Obtain configuration parameters such as • Protocol Revision (P-REV) • Network Identifier (NID) • Pilot PN offsetLong-code state • Paging channel data rate Sync Ch

  6. Call Processing - Paging MS decodes the Paging Channel with the information received from the Sync Channel. Paging channel provides • Overhead messages: systems parameter, access parameter, neighborlist, channel list • Mobile directed messages: page request, SMS Paging Ch

  7. Call Processing – Access MS uses Access channel to originate a call or to respond to a page request. Access Channel is used in a random access fashion. Access Ch

  8. Call Processing - Traffic • Base station assigns a forward and reverse traffic channel to the mobile when it is in conversation • Traffic Channel conveys signaling and traffic information • When MS is on traffic channel it no longer listens to paging channel or uses the access channel

  9. Power Up Call originationor page response Synchronization Initialization State IdleState AccessState Traffic State Paging Loss Page response completed End of call Mobile Station States

  10. Mobile Originated Voice Call Flow MSC BSC MS Overhead Info Paging Ch. Access Ch. Origination Msg BS Ack Order Paging Ch. CM Service Request Null Frames Fwd Traffic Ch. SCCP Connection Cfm Paging Ch. Channel Assign Msg Rev Traffic Ch. Preamble BS Ack Order Fwd Traffic Ch. Assignment Request Rev Traffic Ch. MS Ack Order Service Connect Fwd Traffic Ch. Rev Traffic Ch. Service Conn Cmplt Assignment Complete

  11. CDMA Evolution (1/3) • IS-95A (2G) • First CDMA protocol, published in May’99 • 14.4/9.6 kbps circuit/packet data • IS-95B (2.5G) • Most analog information is removed • Some technical corrections • New Capabilities, such as higher data rate • 64 kbps packet data

  12. CDMA Evolution (2/3) • CDMA2000 1X • High speed data (144 kbps packet data with Mobile IP) • Coding (Turbo) and Modulation (Hybrid QPSK) • New dedicated and common channels • Enhanced Power Control • Reverse link detection • Forward link modulation

  13. CDMA Evolution (3/3) • 1X EV-DO (1xRTT Evolution for high-speed integrated Data Only) • The objective is to provide the largest practical number of users to run high-speed packet data applications • 2.4 Mbps packet data • 1X EV-DV (1xRTT Evolution for high-speed integrated Data and Voice) • Voice and High Speed Data mixed on one carrier • Backward-compatible with CDMA2000 1X • 3.1 Mbps packet data

  14. Dedicated band during entire call Each user transmits at the same time, at the same frequency with a unique code Certain frequency, time-slotted Multiple Access Methods

  15. B E A A G C B A A A A G A A F D A A A A E F A A Frequency Re-use Patterns FDMA and TDMA vs. CDMA

  16. Channelization • Channelization is provided by orthogonal Walsh codes • cdma2000 uses variable length Walsh codes for supplemental channel data services • Walsh codes can be of length 8, 16, 32, 64, and 128

  17. Walsh Codes • Walsh codes are orthogonal to each other • The shorter the code the higher the data rate since the chip rate is kept constant

  18. A Code Channel Example Forward Traffic Channel Generation Power Control bit 1.2288 Mcps MUX Encoder and Repetition Block Interleaver 19.2 ksps Wt 1.2288 Mcps 800 Hz Long Code PN Generator Decimator Decimator

  19. Cell Separation • Walsh code spreading is followed by quadrature spreading using PN chips with time offsets • Adjacent cells have different PN offsets. • This prevents interference since time shifted PN sequences are orthogonal to each other I-PN cos wot Wt BasebandFilter Baseband Filter Q-PN sin wot

  20. Use of Multipath in CDMA Systems • FDMA/TDMA (narrow-band) • multipath hurts • equalizers are used to cancel multipath • CDMA (wide-band) • can discriminate between the multipath arrivals • Rake receivers are used to combine multipath signals to reduce error rate at the receiver

  21. Near – Far Problem a user near the base station would jam the user far from the base station

  22. Power Control – Motivation • Overcomes near-far problem • CDMA wouldn’t work without it • Copes with path loss and fading

  23. Power Control – Algorithm • Capacity is maximized • By having each user transmitting just sufficient SNR to maintain a target FER • Open Loop Estimate • Initial transmit power level for the mobile is determined by the received pilot strength • Closed Loop Power Control • Base station controls the power level on the mobile by the received quality information.

  24. Mobility management A CDMA system provides mobility: • Handoff – continuity of the service across adjacent cells • Registration – locating the mobile user • Roaming – continuity of the service across different service providers

  25. Handoff • Handoffs between cells are supported while the mobile is in traffic or idle • MS continuously keeps searching for new cells as it moves across the network • MS maintains active set, neighbor set, and remaining set as well as candidate set • There are 4 types of handoffs: • Idle Handoff • Access Handoff • Soft/Softer Handoff • Hard Handoff

  26. Handoff Parameters (1/2) • If a pilot strength (P) is greater than T_ADD it will be added into the candidate set • If pilot strength is less than T_DROP for T_TDROP, it will be moved from active set to neighbor set • If the new pilot strength is T_COMP units greater current pilots a Pilot Strength Measurement Message will be send

  27. Handoff Parameters (2/2) Pilot Strength Cell A Cell B T_ADD T_DROP T_TDROP Time

  28. Soft Handoff BlackMountain Both cells have the same frequency PDSN MSC BSC Ericsson UCSD

  29. Soft Handoff • Make-before-break • Both cells are at the same frequency • Reduces number of call drops • Increases the overall capacity • Mobile transmit power is reduced • Voice quality near the cell boundaries are improved • MS reports the SNR of the candidate sets

  30. Soft Handoff Gain Power (dBm) Cell A Cell B Total at MS Distance

  31. Hard Handoff • Break-before-make • Handoff between different frequencies, non-synchronized or disjoint cells which are controlled by different BSCs

  32. Registration • It is sufficient to know the cell or the region that a MS is active for routing purposes • Mobile station identifier, desired paging slot cycle, and registration type is conveyed • Cell/LAC based paging is preferred to flood paging

  33. Registration Types • Autonomous Registration: power-up, power-down, timer-based, distance-based, zone-based registration. • Parameter-change registration • Ordered registration • Implicit registration • Traffic channel registration

  34. Roaming • Users that are outside their home area can receive service from another system by paying some additional charges • Mobile station can be: • Home state (not roaming) • Network roaming • System roaming Network 2 Network 1 Network 3 System

  35. Radio Admission Control • cdma2000 allocates resources dynamically • Admission control is important to ensure quality of service for the existing users when new resources are requested • A new request can be call setup, supplemental channel set-up, handoff, data rate change • Available Walsh codes, residual power in the forward and reverse links are considered before granting a request

  36. Summary (1/2) • cdma2000 supports both voice and data services in the same carrier • provides enhanced voice capacity • Forward link • Fast power control in forward/reverse links • Lower code rates • New code channels • Reverse Link • Coherent detection

  37. Summary 2/2 • Higher data rates: 1x up to 153.6 kbps and 1x EV-DV up to 3.09 Mbps • Battery life is improved • Introduction of Turbo codes provides better link quality for supplemental channels