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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