cdma2000 Radio Access Network

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
Mobile Station States
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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.
Assignment Complete
Service Conn Cmplt
Rev Traffic Ch.
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CDMA Evolution (1/3)

• IS-95A (2G)
• First CDMA protocol, published in May99
• 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

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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
Multiple Access Methods
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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

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A Code Channel Example
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

• Forward Traffic Channel Generation

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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
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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

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Near Far Problem

• a user near the base station would jam the user
  far from the base station

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Power Control Motivation

• Overcomes near-far problem
• CDMA wouldnt 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

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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

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Handoff Parameters (2/2)
Pilot Strength
Cell A
Cell B
T_ADD
T_DROP
T_TDROP
Time
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Soft Handoff
BlackMountain
Both cells have the same frequency
PDSN
MSC
BSC
Ericsson
UCSD
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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

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

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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

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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