1. CDMA Technology Overview
Lesson 5 – Power Control, Registration, and Handoffs

2. Power Control

3. 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
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

4. Reverse Open Loop Power Control

5. Estimated Reverse Open Loop Output Power
mean output power (dBm) = - mean power input (dBm)
+ K
+ NOM_PWR - 16 x NOM_PWR_EXT
+ INIT_PWR
Power output level for the initial probe during open loop probing on the Access Channel (with closed loop correction inactive):
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 assuming a 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

6. Estimated Reverse Open Loop Output 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)

7. Reverse Closed Loop Power Control

8. Power Output Estimations (Summary)

9. Reverse Outer Loop Power Control

10. Forward Traffic Channel Power Control

11. Summary of All Power Control Mechanisms

12. Registration

13. Roaming
Home
SID/NID List
(2, 3)
(2, 0)
(3, 1)
SID = 2
SID = 4
SID Roaming
NID = 7
NID =3
NID = 0
NID Roaming
Not Roaming
Roaming Status
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)

14. 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

15. 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

16. Forms of CDMA Registration
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
All types of registration can be enabled or disabled by means of the System Parameters Message
Registration Types NOT
Supported by Nortel

17. Power-Up Registration
Access Channel
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

18. Power-Down Registration
OFF
Access Channel
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)

19. Timer-Based Registration
Access Channel
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

20. Distance-Based Registration
BS-1
BS-2
BS-3
REG_DIST
Paging Channel
Access Channel
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

21. Zone-Based Registration1 2 3 4 5
NOTE: These are registration zones, not TMSI zones!
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

22. Parameter-Change Registration
SLOT_CYCLE_INDEX
SLOTTED_MODE
MOB_TERM_HOME
etc.
Access Channel
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

23. Implicit Registration
Origination Message
Access Channel
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

24. Ordered and Traffic Channel Registration
Paging Channel
Access Channel
Forward Traffic Channel
Reverse Traffic Channel
Registration Message
Traffic Channel Registration
Registration Request Order
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

25. Handoffs

26. Ec Io Ec/Io dB What is Ec/Io? 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/Io dB
-25
-15
-10 Ec
Energy of
desired pilot alone Io
Total energy received

27. S What’s In a Handset? Digital Rake Receiver Traffic Correlator
RF Section
IF, Detector
Transmitter
Vocoder
Digital
Rake Receiver
Traffic Correlator
PN xxx
Walsh xx
Pilot Searcher
Walsh 0
Viterbi
Decoder
CPU
Duplexer
Digital Section
Long Code Gen.
Open Loop
Transmit Gain Adjust
Messages
Audio
Bit Packets
Symbols
Chips RF
AGC S

28. CDMA-to-CDMA Hard Handoff CDMA-to-Analog Hard Handoff
CDMA Handoffs
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
While in the
Idle State
Idle Handoff
CDMA-to-CDMA Hard Handoff
Softer Handoff
During
a Call
Soft Handoff
CDMA-to-Analog Hard Handoff

29. CDMA Soft Handoff Mechanics
Handset
Rake Receiver RF
PN Walsh
Searcher
PN W=0 S
Voice,
Data,
Messages
Pilot Ec/Io
BTS
BSC
MTX
Sel.
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

30. Each BTS sector has unique PN offset & pilot
Softer Handoff
Handset
Rake Receiver RF
PN Walsh
Searcher
PN W=0 S
Voice,
Data,
Messages
Pilot Ec/Io
BTS
BSC
MTX
Sel.
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

31. 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

32. CDMA-to-CDMA Hard Handoff
(ƒ1)
MTX
BSC
PSTN B
(ƒ2) A
(D1)
MTX
BSC
PSTN B
(D2)
Between cells operating on different frequencies
Between cells with traffic channels whose frames are staggered differently

33. CDMA-to-CDMA Hard Handoff
MTX
PSTN
BSC B A
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)

34. Pilot Detection Trigger – CELL_PILOT_BEACON sectors
The mobile station has no knowledge
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.
Handoff Trigger
CELL_STANDARD
CELL_PILOT_BEACON
BTS
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

35. Hard Handoff using Beacon Pilot Sectors

36. Boundary Sector Trigger (“CELL_BORDER” Sectors)
The mobile station has no knowledge of the “border sector” concept. As far as the mobile station is concerned, a border sector is just the same as any other standard CDMA sector.
First-stage trigger
Second-stage
trigger
CELL_STANDARD
CELL_BORDER
RTD
BTS
This is a two-stage trigger which indirectly 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_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

37. Hard Handoff Using Border Sectorsƒ1 ƒ2
Border Sector for ƒ1
Border Sector for ƒ2

38. 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

39. 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.

40. 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.