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CDMA Technology Overview. Lesson 5 – Power Control, Registration, and Handoffs. Power Control. CDMA Power Control. CDMA is an interference-limited system based on the number of users Unlike AMPS/TDMA, CDMA has a soft capacity limit Each user is a noise source on the shared channel

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Cdma technology overview

CDMA Technology Overview

Lesson 5 – Power Control, Registration, and Handoffs



Cdma power control
CDMA Power Control

  • CDMA is an interference-limited system based on the number of users

  • Unlike AMPS/TDMA, CDMA has a softcapacity limit

    • Each user is a noise source on the shared channel

    • The noise contributed by users is cumulative

    • This creates a practical limit to how many users a system will sustain

  • Precise power control of the mobile stations is critical if we want to

    • Maximize system capacity

    • Increase battery life of the mobile stations

  • The goal is to keep each mobile station at the absolute minimum power level necessary to ensure acceptable service quality

    • Ideally the power received at the base station from each mobile station should be the same (minimum signal to interference)

    • Mobile stations which transmit excessive power increase interference to other mobile stations



Estimated reverse open loop output power
Estimated Reverse Open LoopOutput Power

Power output level for the initial probe during open loop probing on the Access Channel (with closed loop correction inactive):

mean output power (dBm) = - mean power input (dBm)

+ K

+ NOM_PWR - 16 x NOM_PWR_EXT

+ INIT_PWR

Subsequent probes in the sequence are sent at increased power levels

(each probe is incremented by a value equal to the parameter PWR_STEP)

The “turn around constant” K is calculated assuminga nominal cell Effective Radiation Power (ERP) of 5 W

and a nominal cell loading of 50%.

Its value is -73 for cellular systems and -76 for PCS systems


Estimated reverse open loop output power1
Estimated Reverse Open LoopOutput Power

Power output level for the initial transmission on the Reverse Traffic Channel:

mean output power (dBm) = - mean power input (dBm)

+ K

+ NOM_PWR - 16 x NOM_PWR_EXT

+ INIT_PWR

+ the sum of all access probe corrections (dB)








Roaming
Roaming

SID = 4

SID = 2

Home

SID/NID List

NID = 0

NID = 7

NID =3

(2, 3)

(2, 0)

(3, 1)

Roaming Status

SID Roaming

NID Roaming

Not Roaming

  • A mobile station may be in any of the following roaming states:

    • Home: mobile station is at its home location (not roaming)

    • NID roaming: mobile station is within a foreign NID but in the home SID

    • SID roaming: mobile station is within a foreign SID

  • A mobile station maintains a list of one or more “home pairs”

    • These are SID/NID combinations defining the mobile station’s home location

    • They are stored in semi-permanent memory

  • The identity of current SID/NID is contained in the System Parameters Message (sent on the Paging Channel)


Hlr vlr
HLR & VLR

Contains permanent subscriber data

provisioning information

service information

features available to the subscriber

Contains dynamic information

mobile station’s current location

Supports call routing

Queried by the MTX when subscriber information is needed, regardless of the mobile station’s current location

Stores a subset of the HLR information pertaining to the mobile stations currently registered in the VLR’s service area

HLR

VLR


Cdma registration
CDMA Registration

  • Registration is the means by which a mobile station notifies the cellular system of its location, status, identification, and other characteristics

  • Balance is required between paging and registration

    • Infrequent registration results in a high rate of paging

    • Frequent registration places a high load on access channels

  • Proper system design allows a base station to efficiently page the mobile station when establishing a mobile-terminated call

  • Registration also provides

    • The mobile station’s SLOT_CYCLE_INDEX and SLOTTED_MODE

    • The mobile station class mark and protocol revision number so that the base station will know the mobile station’s capabilities

  • Two types of mobile registration

    • Non-Autonomous: explicitly requested by the base station, or implied based on other types of messages received by the mobile station

    • Autonomous: triggered by some event other than the reception of an explicit or implicit request from the base station


Forms of cdma registration
Forms of CDMA Registration

All types of registration can be enabled or disabled by means of the System Parameters Message

  • Power-up registration

  • Power-down registration

  • Timer-based registration

  • Zone-based registration

  • Distance-based registration

  • Parameter-change registration

  • Implicit registration

  • Ordered registration

  • Traffic channel registration

Autonomous

Registration

Non-Autonomous

Registration

Registration Types NOT

Supported by Nortel


Power up registration
Power-Up Registration

ON

  • Mobile station registers when

    • Directed to power-on by the user

    • Switched to an alternate serving system

    • Switched from using an analog system

  • Delays 20 seconds

    • Preventing multiple registrations whenever power is quickly turned on and off

  • Access Channel


Power down registration
Power-Down Registration

OFF

  • Mobile station registers when directed to power-down by the user

  • Mobile station will not power down until attempt is completed

  • Mobile station will not do power down registration if

    • Not registered in the current system

  • Prevents unnecessary attempts to reach a user

    • Can be unreliable (v.gr., user powers down in garage)

  • Access Channel


Timer based registration
Timer-Based Registration

  • Mobile station registers when a timer expires

  • Registration period is determined by the base station

  • Allows system to de-register mobile stations that fail to register on power-down

  • Access Channel


Distance based registration
Distance-Based Registration

  • Paging Channel

  • Access Channel

REG_DIST

BS-1

BS-2

a

b

Idle Handoff

BS-3

c

d

Idle Handoff

  • Mobile Station MS registers whenever it does an “Idle Handoff” (handoff when not in a call) into a cell which lays outside a circle with REG_DIST radius and centered at the base station where MS last registered

    • At position “a” MS registers with Base Station BS-1. BS-1 transmits its latitude and longitude, and the REG_DIST parameter on its paging channel

    • At position “b” MS does an idle handoff into BS-2 and reads the latitude and longitude of this base station. MS then calculates the distance between BS-2 and BS-1, and if the result is less than REG_DIST it does not have to re-register

    • At position “c” MS is still listening to BS-2 (no need to re-register yet)

    • At position “d” MS does an idle handoff into BS-3. MS reads the latitude and longitude of BS-3 and calculates the distance between BS-3 and BS-1. As this distance exceeds REG_DIST, MS re-registers


Zone based registration
Zone-Based Registration

2

1

3

5

4

  • The mobile station registers when it enters a new zone

  • A zone is a subset of the base stations within a network

  • The mobile station keeps a list of the zones where it has registered, up to a maximum determined by the base station

  • Each zone is uniquely identified by the registration zone number parameter (REG_ZONE) plus the SID and the NID to which it belongs

  • The mobile station activates a timer for every zone where it has registered, except the active one, and de-registers when the timer expires

  • The mobile station will not re-register if it enters a zone which is already in its list

NOTE: These are registration zones, not TMSI zones!


Parameter change registration
Parameter-Change Registration

  • The mobile station registers after it modifies any of the following parameters (stored in the mobile station):

    • the preferred slot cycle index

    • the slotted mode indicator

    • the call termination enabled indicators

  • or the following capabilities supported by the mobile station:

    • the band classes

    • the power classes

    • the rates

    • the operating modes

SLOT_CYCLE_INDEX

SLOTTED_MODE

MOB_TERM_HOME

etc.

  • Access Channel


Implicit registration
Implicit Registration

  • Occurs when the mobile station and base station exchange messages not directly related to registration

    • Messaging conveys sufficient information to identify mobile station and its location

  • Considered successful whenever mobile station sends an Origination Message or Page Response Message

  • Compatible with AMPS and IS-54 methods

  • Effectiveness considered adequate to preclude use of ordered registration

Origination Message

  • Access Channel


Ordered and traffic channel registration
Ordered and Traffic Channel Registration

Registration Request Order

Registration Message

Registration Request Order

Traffic Channel Registration

  • Paging Channel

  • Access Channel

  • Forward Traffic Channel

  • Reverse Traffic Channel

  • Ordered Registration

    • Allows the base station to order a mobile station to register

      • mobile station can be idle or in an active call

  • Traffic Channel Registration

    • Allows the base station to obtain registration information about a mobile station that has been assigned to a Traffic Channel

    • Information exchange occurs on the Traffic Channel

    • Suggested use is on inter-system handoffs

  • Neither one is supported by Nortel’s CDMA system



What is ec io
What is Ec/Io?

-25

-15

-10

0

Ec/Io dB

  • Ec/Io

    • Measures the “strength” of the pilot

    • Foretells the readability of the associated traffic channels

    • Guides soft handoff decisions

    • Is digitally derived as the ratio of good to total energy seen by the search correlator at the desired PN offset

    • Never appears higher than Pilot’s percentage of serving cell’s transmitted energy

    • Can be degraded by strong RF from other cells, sectors

    • Can be degraded by noise

Ec

Energy of

desired pilot alone

Io

Total energy received


What s in a handset
What’s In a Handset?

Digital

Rake Receiver

Symbols

Chips

Traffic Correlator

S

PN xxx

Walsh xx

Symbols

Receiver

RF Section

IF, Detector

Traffic Correlator

Viterbi

Decoder

PN xxx

Walsh xx

Bit Packets

Traffic Correlator

AGC

Messages

PN xxx

Walsh xx

Audio

RF

Vocoder

CPU

Pilot Searcher

Duplexer

Open Loop

PN xxx

Walsh 0

RF

Transmit Gain Adjust

Audio

Messages

Transmitter

RF Section

Transmitter

Digital Section

Long Code Gen.

Bit Packets


Cdma handoffs
CDMA Handoffs

While in the

Idle State

Idle Handoff

Soft Handoff

During

Softer Handoff

a Call

CDMA-to-CDMA Hard Handoff

CDMA-to-Analog Hard Handoff

Handoff is the process by which a mobile station maintains communications with the Mobile Services Switching Center (MSC/BSC), when traveling from the coverage area of one base station to that of another


Cdma soft handoff mechanics
CDMA Soft Handoff Mechanics

MTX

BSC

Handset

Rake Receiver

PNWalsh

S

Voice,

Data,

Messages

Sel.

RF

PNWalsh

PNWalsh

BTS

BTS

Searcher

PNW=0

Pilot Ec/Io

  • CDMA soft handoff is driven by the handset

    • Handset continuously checks available pilots

    • Handset tells system pilots it currently sees

    • System assigns sectors (up to 6 max.), tells handset

    • Handset assigns its fingers accordingly

    • All messages sent by dim-and-burst, no muting!

  • Each end of the link chooses what works best, on a frame-by-frame basis!

    • Users are totally unaware of handoff


Softer handoff
Softer Handoff

Handset

Rake Receiver

MTX

BSC

PNWalsh

S

Voice,

Data,

Messages

RF

PNWalsh

Sel.

BTS

PNWalsh

Searcher

PNW=0

Pilot Ec/Io

  • Each BTS sector has unique PN offset & pilot

  • Handset will ask for whatever pilots it wants

  • If multiple sectors of one BTS simultaneously serve a handset, this is called Softer Handoff

  • Handset is unaware, but softer handoff occurs in BTS in a single channel element

  • Handset can even use combination soft-softer handoff on multiple BTS & sectors


Overall handoff perspective
Overall Handoff Perspective

  • Soft & Softer Handoffs are the best

    • but a handset can receive BTS/sectors simultaneously only on one frequency

    • all involved BTS/sectors must connect to a single BSC (the BSC must choose packets each frame)

    • must be same on all BTS/sectors

  • If above not possible, handoff still can occur but will be “hard” like AMPS/TDMA/GSM

    • intersystem handoff: hard

    • change-of-frequency handoff: hard

    • CDMA-to-AMPS handoff: hard, no handback

      • auxiliary trigger mechanisms available


Cdma to cdma hard handoff
CDMA-to-CDMA Hard Handoff

Between cells operating on different frequencies

Between cells with traffic channels whose frames are staggered differently

MTX

PSTN

PSTN

MTX

BSC

BSC

A

(ƒ1)

B

(ƒ2)

A

(D1)

B

(D2)


Cdma to cdma hard handoff1
CDMA-to-CDMA Hard Handoff

PSTN

MTX

MTX

BSC

BSC

A

B

  • Between cells that could be on the same frequency and have the same frame alignment, but which are subordinated to different BSCs which are not interconnected.

    • This type of hard handoff would become a soft handoff if the frames received at both cells could be delivered quickly to the same BSC for comparison, by interconnecting both BSCs with a high-speed link (see Inter BSC Soft Handoff / Inter System Soft Handoff)


Pilot detection trigger cell pilot beacon sectors
Pilot Detection Trigger – CELL_PILOT_BEACON sectors

Handoff Trigger

The mobile station has no knowledge

BTS

BTS

of the “beacon sector” concept. As

far as the mobile station is concerned,

a beacon sector is just the same as

any other standard CDMA sector.

CELL_STANDARD

CELL_PILOT_BEACON

  • This trigger utilizes the existing soft handoff algorithm in the mobile station to facilitate the hard handoff.

  • Certain pilots in the region where hard handoff is desired are identified as CELL_PILOT_BEACON in the Pilot Database of the SBS Controller

  • The cell on the left serves the mobile station on frequency f1

  • The cell on the right operates in frequency f2 and has a Pilot Beacon Unit that generates a pilot on frequency f1 (or this pilot is generated by a standard CDMA cell of an adjacent system/market)

  • As the mobile station travels into the region in which hard handoff is desired, soft handoff processing is initiated when the mobile station reports to the network that the signal of the beacon cell is received with sufficient strength

  • SBS software determines that the reported pilot corresponds to a beacon cell, and hard handoff processing commences



Boundary sector trigger cell border sectors
Boundary Sector Trigger(“CELL_BORDER” Sectors)

First-stage trigger

The mobile station has no knowledge of the “border sector” concept. Asfar as the mobile station is concerned, a border sector is just the same asany other standard CDMA sector.

BTS

RTD

Second-stage

trigger

CELL_STANDARD

CELL_BORDER

  • This is a two-stage trigger which indirectlyutilizes the existing soft handoff algorithm in the mobile station to facilitate the hard handoff

    • certain pilots in the region where hard handoff is desired are identified as “CELL_BORDER” in the Pilot Database of the SBS Controller

    • as the mobile station travels from left to right, it enters into handoff with both sectors and eventually ceases communication with the sector on the left (“CELL_STANDARD”)

    • when the active set contains only sectors datafilled as “CELL_BORDER,” the first-stage trigger is met and the second-stage trigger is enabled

    • the SBS starts monitoring the Round Trip Delay (RTD) of the signals between the mobile station and the base station from which it derives its time reference

    • when the RTD exceeds a certain threshold, the second-stage trigger is met and handoff processing continues with the target selection activity


Hard handoff using border sectors
Hard Handoff Using Border Sectors

Border Sector for ƒ1

ƒ1

ƒ1

ƒ2

ƒ2

Border Sector for ƒ2

ƒ1

ƒ1

ƒ2

ƒ2


Cdma to analog handoff
CDMA-to-Analog Handoff

  • The mobile station is directed from a forward traffic channel to an analog voice channel

  • Radio link continuity is not maintained

  • Two types of handoff:

    • Inter-system - occurs while the mobile station is traveling into another system that has no CDMA service

      • Messaging will tell the mobile station to select AMPS

      • Currently, the mobile station cannot handoff back from AMPS to CDMA (until the end of the call, when the mobile station reacquires the system) because the necessary signaling messages not supported)

    • Intra-system - occurs while the mobile station is traveling within the system

      • Load balancing

      • Improve voice quality

      • No CDMA service


Lesson review
Lesson Review

  • What is the purpose of power control?

    To maximize system capacity by minimizing noise/interference, and to increase battery life in the mobile stations.

  • What is the ideal situation at the base station regarding power level of the received mobile station signals?

    To receive exactly the same (minimum) power level from every mobile station.

  • Define CDMA registration and explain its purpose

    CDMA registration is the means in which a mobile station notifies the cellular system of its location, status, identification and other characteristics. The purpose of CDMA registration is to allow the system to efficiently page the mobile station when establishing a mobile terminated call.


Lesson review1
Lesson Review

  • Name the forms of registration, indicating whether they are autonomous or not.

    Autonomous:

    Power-up registration,

    Power-down registration,

    Timer-based registration,

    Distance-based registration, and

    Zone-based registration.

    Non-autonomous:

    Parameter-change registration, Implicit registration,

    Ordered registration and Traffic Channel registration.

  • Identify the cases of CDMA handoff that can occur when the mobile station is in the Traffic Channel State.

    Soft handoff, Softer handoff, CDMA-to-CDMA Hard Handoff, and CDMA-to-Analog Hard Handoff.

  • Identify the message sent by the mobile station to report the strength of the pilots it measures

    Pilot Strength The Measurement Message.


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