Transcript Yeni

cdma2000
Radio Access Network
Salih Ergut
7/7/2003
1
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
2
Network Architecture
Packet
Network
PSTN
Black
Mountain
PDSN
MSC
BSC
Ericsson
UCSD
3
Call Processing - Pilot
First MS monitors Pilot channel for
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Initial acquisition
Channel estimation
Detection of multipaths for rake receiver
Handoffs
Pilot Ch
4
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
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Protocol Revision (P-REV)
Network Identifier (NID)
Pilot PN offset
Long-code state
Paging channel
data rate
Sync Ch
5
Call Processing - Paging
MS decodes the Paging Channel with the
information received from the Sync
Channel. Paging channel provides
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Overhead messages: systems parameter,
access parameter, neighborlist, channel list
Mobile directed messages: page request,
SMS
Paging Ch
6
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
7
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
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Mobile Station States
Power Up
Call origination
or page response
Synchronization
Initialization
State
Paging Loss
Idle
State
Access
State
Traffic
State
Page response completed
End of call
9
Mobile Originated Voice Call Flow
MSC
BSC
Overhead Info
MS
Paging Ch.
Access Ch. Origination Msg
Paging Ch.
BS Ack Order
CM Service Request
Null Frames
Fwd Traffic Ch.
SCCP Connection Cfm
Paging Ch.
Rev Traffic Ch.
Fwd Traffic Ch.
Rev Traffic Ch.
Fwd Traffic Ch.
Rev Traffic Ch.
Channel Assign Msg
Preamble
BS Ack Order
MS Ack Order
Assignment Request
Service Connect
Service Conn Cmplt
10
Assignment Complete
CDMA Evolution (1/3)
 IS-95A (2G)
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First CDMA protocol, published in May’99
14.4/9.6 kbps circuit/packet data
 IS-95B (2.5G)
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Most analog information is removed
Some technical corrections
New Capabilities, such as higher data rate
64 kbps packet data
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CDMA Evolution (2/3)
 CDMA2000 1X
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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
12
CDMA Evolution (3/3)
 1X EV-DO (1xRTT Evolution for high-speed
integrated Data Only)
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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)
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Voice and High Speed Data mixed on one carrier
Backward-compatible with CDMA2000 1X
3.1 Mbps packet data
13
Multiple Access Methods
Dedicated band during entire call
Each user transmits at the same time,
at the same frequency with a unique
code
Certain frequency, time-slotted
14
Frequency Re-use Patterns
B
G
C
A
F
A
B
A
A
A
G
D
E
A
E
A
A
FDMA and TDMA
vs.
A
A
A
F
A
A
A
CDMA
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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
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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
1001
11
1010
1100
1111
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A Code Channel Example
Power Control bit
Block
Interleaver
19.2 ksps
MUX
Encoder and
Repetition
1.2288 Mcps
Wt
1.2288 Mcps
Long Code
PN Generator
Decimator
800 Hz
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
Wt
cos wot
Baseband
Filter
Baseband
Filter
Q-PN
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sin wot
Use of Multipath in CDMA Systems
 FDMA/TDMA (narrow-band)
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multipath hurts
equalizers are used to cancel multipath
 CDMA (wide-band)
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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 wouldn’t work without it
 Copes with path loss and fading
22
Power Control – Algorithm
 Capacity is maximized
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By having each user transmitting just sufficient
SNR to maintain a target FER
 Open Loop Estimate
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Initial transmit power level for the mobile is
determined by the received pilot strength
 Closed Loop Power Control
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Base station controls the power level on the
mobile by the received quality information.
23
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
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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:
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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
Black
Mountain
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
30
Hard Handoff
 Break-before-make
 Handoff between different
frequencies, nonsynchronized or disjoint
cells which are controlled
by different BSCs
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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
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Registration Types
 Autonomous Registration: power-up, power-
down, timer-based, distance-based, zonebased 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:
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Home state (not roaming)
Network roaming
System roaming
Network 2
Network 1
System
Network 3
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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
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Summary (1/2)
 cdma2000 supports both voice and data
services in the same carrier
 provides enhanced voice capacity
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Forward link
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Fast power control in forward/reverse links
Lower code rates
New code channels
Reverse Link
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Coherent detection
36
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
37