radio access network
TRANSCRIPT
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cdma2000 Radio Access Network
Salih Ergut
7/7/2003
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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
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Network Architecture
Ericsson
BlackMountain
UCSD
MSCBSC
PSTN Packet Network
Packet Network
PDSN
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Call Processing - Pilot
First MS monitors Pilot channel for Initial acquisition Channel estimation Detection of multipaths for rake receiver Handoffs
Pilot Ch
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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
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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
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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
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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
InitializationState
AccessState
TrafficState
Synchronization
Paging Loss
Call originationor page response
Page response completed
End of call
IdleState
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Mobile Originated Voice Call FlowMS 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 CmpltRev Traffic Ch.
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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
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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
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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
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Frequency Re-use Patterns
FDMA and TDMA vs. CDMA
AA
A
A
A
A A
AA
A
A
AA
D
C
G
B
E F
EG
F
B
A
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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 11
1001 1010 1100 1111
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A Code Channel Example
Forward Traffic Channel Generation
Encoder and Repetition
BlockInterleaver
Long CodePN Generator
Decimator
MU
X
Decimator
Power Control bit
Wt1.2288 Mcps
19.2 ksps
800 Hz
1.2288 Mcps
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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 otherI-PN
Q-PN
Wt BasebandFilter
BasebandFilter
sin wot
cos 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 wouldn’t work without it Copes with path loss and fading
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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.
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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: 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)
T_DROP
T_ADD
Pilot Strength
TimeT_TDROP
Cell BCell A
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Soft Handoff
Ericsson
BlackMountain
UCSD
MSCBSC
PDSN
Both cells have the same frequency
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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)
Distance
Cell ACell BTotal at MS
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Hard Handoff
Break-before-make Handoff between different
frequencies, non-synchronized 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, 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 1Network 2
Network 3System
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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 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