Transcript 809 Introduction to CDMA v2.0
Copyright 2003, ZTE CORPORATION
CDMA KEY TECHNOLOGY
2004.10.3
Objectives Upon completion of this lesson, the student will be able to master: -- Power control in CDMA why power control how to realize -- Handoff in CDMA what is handoff CDMA’s soft handoff soft handoff procedure
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• • • • •
Why Power Control?
All CDMA users occupy the same frequency at the same time! Frequency and time are not used as discriminators.
CDMA operates by using CODES to discriminate between users.
CDMA interference comes mainly from nearby users Each user is a small voice in a roaring crowd -- but with a uniquely recoverable code.
Transmit power on all users must be tightly controlled so their signals reach the base station at the same signal level and at the absolute minimum power level necessary to ensure acceptable service quality Figure of Merit: E c /I o , E b /N o (energy per chip [bit] / interference [noise] spectral density ) CDMA: E c /I o -17 to -2 dB CDMA: E b /N o ~6to7 dB
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Reverse Open Loop Power Control
Reverse Open Loop Power Control BTS Mobile
• The mobile station makes a coarse initial estimation of the required transmit power, based upon the total received power.
• Problems with Reverse Open Loop Power Control: – Assumes same exact path loss in both directions; therefore, cannot account for asymmetrical path loss – Estimates are based on total power received; therefore the power received from other cell sites by mobile station introduces inaccuracies Copyright 2003, ZTE CORPORATION
Estimated Reverse Open Loop Output 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) Copyright 2003, ZTE CORPORATION 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
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)
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Reverse Closed Loop Power Control
Mobile Reverse Closed Loop Power Control BTS
or
Signal Strength Measurement Setpoint
• Compensates for asymmetries between the forward and reverse paths • Consists of power up (0) & power down (1) commands sent to the mobile stations, based upon their signal strength measured at the Base Station and compared to a specified threshold • Each command requests a 1dB increase or decrease of the mobile station transmit power • Transmitted 800 times per second, always at full power • Allows to compensate for the effects of fast fading Copyright 2003, ZTE CORPORATION
Reverse Outer Loop Power Control
Mobile Reverse Closed Loop Power Control BTS
or
Signal Strength Measurement BSC Setpoint Reverse Outer Loop Power Control
FER Copyright 2003, ZTE CORPORATION • Most gradual form of reverse link power control – Setpoint is varied according to the FER on the Reverse Traffic Channel (determined at the Base Station Controller) – Sampled at a rate of 50 frames per second (20 ms / frame) – Setpoint adjusted every 1-2 seconds
Mobile
Forward Traffic Channel Power Control
BSC BTS Adjust Fwd.
power
FER
Forward Link Power Control
• The base station slowly decreases power to each mobile station.
• As the FER (determined at the mobile station) increases, the mobile station requests a Forward Traffic Channel power increase.
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Summary of All Power Control Mechanisms
Mobile
FER
Reverse Open Loop Power Control BTS Reverse Closed Loop Power Control
or
Signal Strength Measurement Setpoint BSC Reverse Outer Loop Power Control
FER
Adjust Fwd.
power Forward Link Power Control
All types of power control work together to minimizes power consumption at the mobile stations, and increases the overall capacity of the system transmit power.
Copyright 2003, ZTE CORPORATION
Handoffs
• Handoff is the process by which a mobile station maintains communications with the Mobile Telephone Switching center(MSC), when traveling from the coverage area of one base station to that of another.
• Handoffs keep the call established during the following conditions: – Subscriber crosses the boundaries of a cell – Subscriber experiences noise or other interference above a specified threshold – A base station component experiences an out-of-service condition during a call Copyright 2003, ZTE CORPORATION
Cell Site B
CDMA Handoffs
CDMA Cell Site B Cell Site A Cell Site A
• CDMA Handoffs – Make-before-break – Directed by the mobile not the base station – Undetectable by user – Improves call quality • Handoffs consist of the following phases: – Initiation (trigger), Target Selection, and Completion (execution) Copyright 2003, ZTE CORPORATION
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CDMA Handoffs (cont.)
While in the Idle State Idle Handoff During a Call Soft Handoff Softer Handoff Inter-System Soft Handoff CDMA-to-CDMA Handoff CDMA-to-Analog Handoff
Cell Site A
Soft Handoff
PSTN MSC Cell Site B B S C
• • Soft Handoff: the mobile station starts communications with a target base station without interrupting communications with the current serving base station.
Can involve up to three cells simultaneously and use all signals – Mobile station combines the frames from each cell Copyright 2003, ZTE CORPORATION
Copyright 2003, ZTE CORPORATION
alpha gamma
Softer Handoff
beta
• Handoff is between sectors of the same cell • Communications are maintained across both sectors until the mobile station transition has completed • May happen frequently • MSC is aware but does not participate • All activities are managed by the cell site • Signals received at both sectors can be combined for improved quality
Inter-System Soft Handoffs (ISSHO)
TIA/EIA-41D MSC MSC SVBS SVBS E1 Links HIRS HIRS A f1 B f1 C f1 D f1 E f1 F f1 U f1 V f1 W f1 X f1 Y f1 Z f1 CDMA Soft Handoff ISSHO CDMA Hard Handoff
• Mobile Station starts communications with a new cell controlled by a different BSC while still communicating with the cell controlled by the source BSC • Soft Handoffs over Hard Handoffs • Fewer border cell Copyright 2003, ZTE CORPORATION
PSTN
CDMA-to-CDMA Hard Handoff
PSTN MSC MSC MSC T1 or E1 Links TIA/EIA-41D BSC BSC BSC A ( ƒ 1 ) B ( ƒ 2 ) A B
• Between cells operating on different frequencies • Between cells that could be on the same frequency, but which are subordinated to different MSC Copyright 2003, ZTE CORPORATION
Receiver RF Section IF, Detector
What
’
s In a Handset?
Digital Rake Receiver
Symbols Chips
Traffic Correlator PN xxx Walsh xx
Symbols
Traffic Correlator PN xxx Walsh xx
S
Viterbi Decoder
AGC
Traffic Correlator PN xxx Walsh xx
Messages
RF Bit Packets Audio
Duplexer Pilot Searcher PN xxx Walsh 0 CPU Vocoder
RF
Transmit Gain Adjust
Audio
Messages
Transmitter RF Section Transmitter Digital Section Long Code Gen.
Bit Packets
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Soft Handoff Key: Understand the searcher’s effect in different state --- MS power up state --- MS idle and calling state
Short PN Code Offsets
Active Set Candidate Set Rake Fingers 1 2 3 Neighbor Set Pilots Above Searched In This Order: A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N R A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N R A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N R
Until all are scanned…then repeat
Remaining Set
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Pilot Sets
Pilot Sets 1. Active 2. Candidate 3. Neighbor 4. Remaining
• Pilot sets: – Active Set: Pilots associated with the forward traffic channels assigned to the mobile station (max 6 pilots) – Candidate Set: by the mobile with sufficient strength to indicate that the corresponding Traffic Channels can be successfully demodulated (max 5 pilots) – Neighbor Set: that are likely handoff candidates (at least 20 pilots) – Remaining Set: Pilots not currently in the Active Set, but received Pilots not currently on the Active or Candidate Sets, All other possible pilots in the current system on the current CDMA frequency assignment • All pilots in a set have the same frequency assignment • These sets can be updated during handoff by the base station Copyright 2003, ZTE CORPORATION
Active
Pilot Set Initialization
(While in the Idle or in an Active Call)
Pilot whose
Paging Channel
is being monitored or associated with the assigned
Forward Traffic Channel Candidate Neighbor Remaining
Empty Pilots specified in the most recently received
Extended Neighbor List Message
(AGE set at NGHBR_MAX_AGE) Any other possible pilot in the system Copyright 2003, ZTE CORPORATION
Active Candidate Neighbor Remaining
Pilot Set Maintenance
(While in an Active Call)
Pilots listed the most recently received
Extended Handoff Direction Msg
Pilots whose strength exceeds
T_ADD
Pilots specified in the most recently received
Neighbor List Update Message
(or whose AGE is still less than NGHBR_MAX_AGE) Any other possible pilot in the system Copyright 2003, ZTE CORPORATION
Pilot Strength Measurement Message (PSMM)
A B Timing C Pilot Channel
• The Pilot Strength Measurement Message is used by the mobile station to direct the base station in the handoff process.
• Mobile station reports the strength of the pilots associated with forward traffic channels currently being demodulated (and whether it would like to continue to receive traffic from them), as well as pilots from the neighbor and remaining list which are being received with sufficient strength so that traffic could be demodulated from them successfully.
Copyright 2003, ZTE CORPORATION
Pilot Search Windows
Search Window for pilots in the Active and Candidate Set: SRCH_WIN_A
Earliest arriving usable multipath component of the pilot
Search Window for pilots in the Neighbor Set: SRCH_WIN_N
pilot PN offset
Search Window for pilots in the Remaining Set: SRCH_WIN_R
pilot PN offset • A search window is a range of PN offsets (in chips) where the mobile station searches for usable multipath components of the pilots in a set –
Usable
means that multipath components can be used for demodulation of an associated traffic channel Copyright 2003, ZTE CORPORATION
Soft Handoff Signaling
PSMM sent (request to add) , Pilot added to Candidate Set
Pilot Strength
Pilot Strength exceeds T_ADD
T_ADD T_DROP N (1) (2) C (3)
EHOD message received, Pilot Added to Active Set, EHOC message sent, NLU message received Pilot strength drops below T_DROP, Drop Timer started Drop Timer expires PSMM Sent (request to remove)
T_TDROP A (4) (5)(6) (7)
EHOD message received, Pilot Dropped into Neighbor Set, EHOC message sent, NLU message received
Time N
• T_ADD: pilot detection threshold
(Typically 26 = -13dB)
• T_DROP: pilot drop threshold
(Typically 30 = -15 dB)
• T_TDROP: drop timer value experiences a fade
(Typically 3 = 4 sec)
– Prevents unnecessary transmissions of PSMM when a mobile station Copyright 2003, ZTE CORPORATION
System Parameters Message (PCH)
Length (bits) Field
MSG_TYPE (‘00000001’) 8 HOME_REG 1 PWR_REP_THRESH 5 PILOT_PN CONFIG_MSG_SEQ SID NID REG_ZONE TOTAL_ZONES ZONE_TIMER MULT_SIDS MULT_NIDS BASE_ID BASE_CLASS PAGE_CHAN MAX_SLOT_CYCLE_INDEX 9 6 15 16 3 1 12 3 1 16 4 3 3 FOR_SID_REG FOR_NID_REG POWER_UP_REG POWER_DOWN_REG PARAMETER_REG REG_PRD BASE_LAT BASE_LONG REG_DIST
SRCH_WIN_A SRCH_WIN_N SRCH_WIN_R NGHBR_MAX_AGE
11
4 4 4 4
1 1 1 1 1 7 22 23 PWR_REP_FRAMES PWR_THRESH_ENABLE PWR_PERIOD_ENABLE PWR_REP_DELAY RESCAN
T_ADD T_DROP T_COMP T_TDROP
EXT_SYS_PARAMETER EXT_NGHBR_LIST GLOBAL_REDIRECT RESERVED
4
1 1 1 1 4 1 1 5 1
6 6 4
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Power Control during Soft Handoff
• During soft handoff, the mobile station receives power control bits from multiple base stations.
• If two or more power control subchannels are identical, their power control bits are diversity combined into one per 1.25 ms time slot.
• If the mobile station receives different power control bits from different power control subchannels, it decreases its mean power output level by 1 dB.
• Only if the power control bits from ALL power control subchannels request a power increase, the mobile station increases its mean power output level by 1 dB .
Copyright 2003, ZTE CORPORATION
Soft Handoff New Parameter in 1X
10log 10 i A PS i Pilot St rength IS-2000princinple P2 P1 Copyright 2003, ZTE CORPORATION T _ADD T _DROP P2 Neighbor Set (1) (2) Candidat e Set (3) Active Set P1 (4) (5) (6) Candidat e Set (7) (8) Neighbor Set T ime
Copyright 2003, ZTE CORPORATION
Handoff Parameters
• • • • • • • • • •
T_ADD T_DROP T_TDROP T_COMP SOFT_SLOPE ADD_INTERCEPT DROP_INTERCEPT SRCH_WIN_A SRCH_WIN_N SRCH_WIN_R
Prefered Parameters Setting
name T_ADD T_DROP T_TDROP T_COMP SRCH_WIN_A SRCH_WIN_N SRCH_WIN_R SOFT_SLOPE ADD_INTERCEPT DROP_INTERCEP T Copyright 2003, ZTE CORPORATION range 0~31 0~31 0~15 0~15 0~15 0~15 0~15 0~63 0~63 0~63 Prefered range 24~28 28~32 2~4 4~6 7~9 9~11 9~11 0~63 0~63 0~63 Qualcomm prefered 28 32 3 5 8 10 10 18 6 2~6
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Search Window Setting
SRCH_WIN_val 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Width, Chips 4
( ± 2)
6
( ± 3)
8
( ± 4)
10
( ± 5)
14
( ± 7)
20
( ± 10)
28
( ± 14)
40
( ± 20)
60
( ± 30)
80
( ± 40)
100
( ± 50)
130
( ± 65)
160
( ± 80)
226
( ± 113)
330
( ± 165)
452
( ± 226)
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