Radio Access Network
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  • Salih Ergut is a full-time employee at Ericsson Wireless Communication Inc. (San Diego, CA) and pursuing his PhD part-time at ECE Department of UCSD. E-mails: [email_address] [email_address]

Radio Access Network Radio Access Network Presentation Transcript

  • cdma2000 Radio Access Network Salih Ergut 7/7/2003
  • 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
  • Network Architecture Ericsson Black Mountain UCSD MSC BSC PSTN Packet Network PDSN
  • Call Processing - Pilot
    • First MS monitors Pilot channel for
      • Initial acquisition
      • Channel estimation
      • Detection of multipaths for rake receiver
      • Handoffs
    Pilot Ch
  • 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 offset Long-code state
      • Paging channel data rate
    Sync Ch
  • 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
  • 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
  • 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
  • Mobile Station States Power Up Initialization State Access State Traffic State Synchronization Paging Loss Call origination or page response Page response completed End of call Idle State
  • Mobile Originated Voice Call Flow MS BSC MSC Paging Ch. Rev Traffic Ch. Paging Ch. Fwd Traffic Ch. Paging Ch. Access Ch. Fwd Traffic Ch. Rev Traffic Ch. Fwd Traffic Ch. Assignment Complete Overhead Info BS Ack Order Origination Msg Null Frames Channel Assign Msg Preamble BS Ack Order MS Ack Order Service Connect CM Service Request SCCP Connection Cfm Assignment Request Service Conn Cmplt Rev Traffic Ch.
  • 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
  • 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
  • CDMA Evolution (3/3)
    • 1X EV-DO ( 1x RTT Ev olution for high-speed integrated D ata O nly)
      • 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 ( 1x RTT Ev olution for high-speed integrated D ata and V oice)
      • Voice and High Speed Data mixed on one carrier
      • Backward-compatible with CDMA2000 1X
      • 3.1 Mbps packet data
  • Multiple Access Methods Dedicated band during entire call Certain frequency, time-slotted Each user transmits at the same time, at the same frequency with a unique code
  • Frequency Re-use Patterns
    • FDMA and TDMA vs. CDMA
    A A A A A A A A A A A A A D C G B E F E G F B A
  • 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
  • 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
    1 10 11 1001 1010 1100 1111
  • A Code Channel Example
    • Forward Traffic Channel Generation
    Encoder and Repetition Block Interleaver Long Code PN Generator Decimator MUX Decimator Power Control bit Wt 1.2288 Mcps 19.2 ksps 800 Hz 1.2288 Mcps
  • 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 Q-PN Wt Baseband Filter Baseband Filter sin wot cos wot
  • 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
  • Near – Far Problem
    • a user near the base station would jam the user far from the base station
  • Power Control – Motivation
    • Overcomes near-far problem
    • CDMA wouldn’t work without it
    • Copes with path loss and fading
  • 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.
  • 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
  • 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
  • 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
  • Handoff Parameters (2/2) T_DROP T_ADD Pilot Strength Time T_TDROP Cell B Cell A
  • Soft Handoff Ericsson Black Mountain UCSD MSC BSC PDSN Both cells have the same frequency
  • 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
  • Soft Handoff Gain Power (dBm) Distance Cell A Cell B Total at MS
  • Hard Handoff
    • Break-before-make
    • Handoff between different frequencies, non-synchronized or disjoint cells which are controlled by different BSCs
  • 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
  • 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
  • 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 1 Network 2 Network 3 System
  • 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
  • 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
  • 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