Cdma2000 access
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cdma2000 Access. Telecommunications Industry Association TR 45.5.3.1 RsMA Ad Hoc December 10, 1998. Existing IS-95 A/B Access. IS-95 A/B access scheme is based on a slotted aloha protocol access channel slots are non-overlapping collisions avoided using very narrow demodulation window

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Cdma2000 access

cdma2000 Access

Telecommunications Industry Association

TR 45.5.3.1 RsMA Ad Hoc

December 10, 1998


Existing is 95 a b access

Existing IS-95 A/B Access

  • IS-95 A/B access scheme is based on a slotted aloha protocol

    • access channel slots are non-overlapping

      • collisions avoided using very narrow demodulation window

  • Accessing mobiles send probes on R-ACH:

    • probes consist of:

      • preamble portion (typically 80 ms)

      • message portion (typically 120 ms)

  • Acknowledgements are transmitted on the paging channel

    • acknowledgement time-out (typically 320 ms)

  • If no acknowledgement is received, mobile increases power and tries again (i.e. power ramping)

    • Access slotting is typically 200 ms

    • back-off delays (multiple of 200 ms)

    • persistence delay (multiple of 200 ms)


Is 95a b access procedure

IS-95A/B Access Procedure


Limitations of is 95 a b access scheme

Limitations of IS-95 A/B Access Scheme

  • Detection and acquisition:

    • Energy required to detect is actually ~ 2% of what is typically transmitted

  • Message error rate performance:

    • in order to get message through error free, mobile must transmit at high power (> 6 to 8 dB over operating Eb/No)

    • if message error, retransmission at higher power and increased latency

  • Latency performance:

    • long preamble typically used (base station constraint)

    • 4.8 Kbps data rate is low, so message duration is long

    • protocol delays are large:

      • typical access times ~ 620 ms.

      • typical worst case access times ~ 1340 ms.

  • Impact on data services:

    • reduced system capacity

    • low throughput and large delays

    • no connectionless packet data service capability


Requirements for improved access

Requirements for Improved Access

  • Increase System Capacity

    • Minimize power required to service transactions

      • reduce power on preamble for detection

      • reduce power on message portion

      • minimize message retransmission probability

    • Facilitate better flow control and admissions policies

  • Increase Throughput & Reduce Delay

    • Minimize service transaction times

      • increased data rates (9.6, 19.2 and 38.4 kbps)

      • shortened preamble

      • reduce message error probability

      • reduce protocol latency (i.e. slot duration, ack. timeout, etc.)

  • Increased call setup reliability


Improved access methods

Improved Access Methods

  • Improve probe acquisition performance

    • shorter preamble duration with time diversity/power ramping

    • defer or early abort of message portion to save power

  • Employ overlapped slotting

    • make long code a function of slot time to prevent hard collisions

  • Improve message error rate performance

    • closed loop power control

    • increase preamble duration to allow loop to settle

    • employ adjustable step sizes

  • Protocol Optimization:

    • reduce slot intervals, timeout parameters, etc.

    • for very short messages, closed loop power control provides little gain

    • longer messages can be moved to reserved channels, closed loop power controlled

    • soft handoff can be used to improve access performance


Overview of proposed approach

Overview of Proposed Approach

  • Reservation Multiple Access (RsMA) is composed of three distinct access protocols:

    • Pure Aloha Mode (PA):

      • best for very short messages (e.g. < 20 ms.)

      • open loop power adjustment

      • no soft handoff

    • Power Controlled Aloha Mode (PCA):

      • best for latency sensitive applications

      • closed loop power control on RL

      • no soft handoff

    • Reservation Mode (RsMA):

      • best for longer messages

      • closed loop power control on RL

      • soft handoff facilitated


Access channels

Access Channels

  • Forward Link:

    • Power Control Channel (F-PCCH)

    • Channel Assignment Channel (F-CACH)

  • Reverse Link:

    • Reservation Access Channel (R-RACH)

    • Common Control Channel (R-RCCH)


  • Reverse reservation access channel

    Reverse Reservation Access Channel

    • Reverse Reservation Access Channel (R-RACH)

      • Slotted Aloha random access channels

      • overlapped slots

      • R-RACH is operated in 3 primary modes:

        PA Mode: Short messages sent typically but not restricted

        PCA Mode: Messages sent with closed loop PC

        RsMA Mode: Only reservation requests sent

      • mixed mode operation possible (i.e. both PCA and RsMA)

    • Data rates supported:

      • 9.6 kbps (20 ms frame),19.2 kbps (10, 20 ms frames), 38.4 kbps (5, 10, 20 ms frames)

    • R-RACH Probe Structure:

      • PA Mode: alohaaccess probe (AAP) = initial preamble + message

      • PCA Mode: message access probe (MAP) = initial preamble + mode request frame + message

      • RsMA Mode: reservation access probe (RAP) = initial preamble + mode requestframe


    Reverse common control channel

    Reverse Common Control Channel

    • Reverse Common Control Channel (R-CCCH)

      • A reserved access channels for RsMA

      • Multiple R-CCCH’s may be supported

    • Data rates supported :

      • 9.6 kbps (20 ms frame),19.2 kbps (10, 20 ms frames), 38.4 kbps (5, 10, 20 ms frames)

    • R-CCCH Packet Structure:

      • packet = channel estimation preamble + message

    • Soft Handoff :

      • 2-way soft handoff can be accommodated on the R-CCCH

        • demodulators at 2 separate BTS’s

        • Power controlled independently from 2 BTS’s


    Forward common assignment channel

    Forward Common Assignment Channel

    • Forward Common Assignment Channel (F-CACH)

      • Single Walsh code common control channel serving multiple users

        • Fast Ack in PCA mode

        • Ack/R-CCCH Address in RsMA mode

      • multiple F-CACH’s supported per sector

    • Modulation format:

      • single 128-chip Walsh code channel

      • DTX, QPSK

      • fixed 9.6 kbps; K=9, rate 1/2 FEC

      • fixed 5 ms message duration with CRC and Tail bit

    • Messages:

      • BTS-level channel assignments/acknowledgements

      • load & flow control (wait message)

      • Soft handoff assistance


    Forward power control code channel

    Forward Power Control Code Channel

    • Forward Power Control Channel (F-PCCH)

      • single Walsh code channel, divided into power control sub-channels(PWC-S/C)

      • Each PWC-S/C supports a single R-RACH (PCA mode) or R-CCCH (RsMA mode)

      • Multiple F-PCCH are supported

    • 24 PWC-S/C per F-PCCH, each at 800 bps update rate

    • Modulation format:

      • single 128-chip Walsh code channel

      • DTX, uncoded QPSK

      • fixed 9.6 kbps bit rates at I and Q phase branches

    • Step Sizes

      • Access channel specific up & down steps.


    R rach waveform description

    R-RACH Waveform Description

    • Probe Preamble (sent in all modes):

      • integer number 1.25 ms segments of unmodulated pilot

      • preamble may operate gated with on/off segments multiple of 1.25 ms

    • Mode Request Frame (not sent in PA mode)

      • 5 ms frame, rate =1/2 FEC coded message

      • Message Fields:

        • mode indicator (1 bit): indicates PCA versus RsMA

        • Hash ID (16 bits):random or managed temporary mobile ID

        • rate word (3 bits): indicates data rate and frame length of message

        • neighbor PN (9 bits): PN offset of neighbor

        • soft handoff ID(1 bit): Soft handoff requested

        • CRC (8 bits) and Tail bits (8 bits)

        • reserved (2 bits)

      • pilot aided

    • Message Portion (not sent in RsMA mode)

      • max. message duration is system parameter

      • rate must be consistent with rate word in Mode Request Frame

      • pilot aided


    R rccch waveform description

    R-RCCCH Waveform Description

    • Channel Estimation Preamble:

      • integer number 1.25 ms. segments of unmodulated pilot

      • preamble can be divided into multiple ‘on’ and ‘off’ pieces

    • Long Code

      • common long code mask

      • designated mode: user specific long code mask

    • Message portion:

      • message is an integer number of frames

      • max. duration is system parameter

      • data rate must be consistent with resource grant

      • CRC’s per frame

      • Pilot used to aid in coherent detection


    F cach waveform description

    F-CACH Waveform Description

    • M|D|1 Queue

      • fixed messages duration (5 ms/slot) --> fixed slot rate (200 slots/sec)

      • Single 128-chip Walsh Code channel,

      • QPSK modulation with r=1/2, K=9 FEC Coding

      • Channel is DTX

        • no message --> no power

    • Message types (3 bits)

      • Channel assignment message field

      • Wait message (admissions/flow control) field

      • 6 reserved message types( Use TBD such as HCAM on p-26)


    F cach messages

    F-CACH Messages

    • Overhead Bits (16 bits):

      • Encoder Tail (8 bits)

      • CRC (8 bits)

    • Channel Assignment Message (32 bits):

      • Message Type (3 bits)

      • Mobile Hash ID (16 bits)

      • R-CCCH/F-PCCH Channel Address (6 bits)

      • Rate Assignment (3 bits)

      • Reserved/TBD (4 bits)

    • Wait Message (32 bits):

      • Message Type (3 bits)

      • Mobile class mark threshold (4 bits)

      • Max data rate for mobiles with class marks over the threshold (2 bits)

      • Max data rate for mobiles with class marks under the threshold (2 bits)

      • Minimum delay to retransmission for all reservation mode mobiles (10 bits)

      • Reserved (12 bits)


    F pcch waveform description

    F-PCCH Waveform Description

    • PC rate determines the number of PWC-S/C supported:

      • 24 @ 800 bps, 48 @ 400 bps, 96 @ 200 bps.

    • In PCA Mode, PC subchannel assignment is implicitly given by:

      • SUBCH_OFFSET + (SLOT_OFFSET modulo SUPERSLOT_SIZE)

        • SUBCH_OFFSET is the index of first F-PCCH subchannel

        • SLOT_OFFSET is the slot index selected for transmission

        • SUPERSLOT_SIZE is the number of slots per superslot on the R_RACH

    • In RsMA Mode, PC subchannel given explicitly in F-CACH channel assignment message.

      • SUBCH_OFFSET = CHAN_ASSN modulo PC_CHAN_PER_FPCCH

        • CHAN_ASSN is the address in the F-CACH Channel Assignment Message

        • PC_CHAN_PER_FPCCH is the number of power control channels per F-PCCH.

    • Mixed mode operation possible using separate PWC-S/Cs

      • e.g. @ 800 bps PC rate, SUBCH_OFFSET = 12:

        • subchannels 0-11 --> I-phase --> RsMA

        • subchannels 12-23 --> Q-phase --> PCA


    Admission flow control

    Admission/Flow Control

    • Admission/flow control:

      • Slow Response Time (~ 200 ms, typical):

        • access parameters conveyed on F-BCCH give current persistence parameters and delays

        • these parameters control flow on the R-RACH(s)

        • sent periodically with dynamic control possible

      • Moderate Response Time ( 5 ms):

        • “wait message” is used to affect mobiles already accessing

        • sent when “overload” or “all busy” condition is near or prevailing

        • parameters affect:

          • flow on both the R-RACH and R-CCCH for reservation mode traffic

          • system loading

        • Inhibit Sense mode can be invoked:

          • mobiles required to examine F-CACH prior to transmitting

          • behavior is ISMA-like


    Channel organization

    Channel Organization


    Pure aloha procedures

    Pure Aloha Procedures

    • mobile “randomly” selects from the corresponding R-RACH set and transmits a Aloha Access Probe (AAP)

    • mobile uses persistence parameters to regulate access attempts

    • After AAP transmitted on R-RACH, mobile monitors F-CCCH for acknowledgement:

      • If no ACK within time out, retry at higher power


    Pure aloha mode

    Pure Aloha Mode


    Pca procedures

    PCA Procedures

    • Mobile “randomly” selects a R-RACH and transmits a Message Access Probe (MAP) conditioned on:

      • observed Ec/Io > T_rqst dB

      • “current” persistence parameters

    • Mobile uses persistence parameters to regulate access attempts

    • After initial MAP, mobile monitors both F-PCCH and F-CACH:

      • Closed loop power control begins after parameterized delay value

      • Mobile looks for Channel Assignment Message (CAM) containing its hash ID as confirmation of acquisition

    • Conditions:

      • If no CAM received within time-out, mobile ceases transmission of current MAP and retransmits MAP at higher power some time later

      • If wait message sent, cease and retransmit MAP later

      • Stop transmission if either:

        • Ec/Io falls below T_fade for T1 seconds

        • Ec/Io exceeds T_good and Ec/Io of PC bits is below T_bad for L PC bits

    • If Inhibit Mode active (system parameter) monitor F-CACH for wait msg before transmission of MAP


    Pc aloha mode

    PC Aloha Mode


    Rsma procedure no sho

    RsMA Procedure (no SHO)

    • Mobile “randomly” selects a R-RACH and transmits a Reservation Access Probe (RAP) conditioned on:

      • observed Ec/Io > T_rqst dB

      • “current” persistence parameters

    • Mobile uses persistence parameters to regulate access attempts

    • After initial RAP, mobile monitors corresponding F-CACH for:

      • Channel Assignment Message or Wait Message

    • Conditions:

      • If no message within time-out, retransmit RAP at higher power

      • If wait message sent, retransmit RAP later

      • If channel assignment rcvd., transmit message on assigned R-CCCH at next access slot and begin closed loop power control.

      • Stop transmission if either:

        • Ec/Io falls below T_fade for T1 seconds

        • Ec/Io exceeds T_good and Ec/Io of PC bits is below T_bad for L PC bits

    • If Inhibit Mode active (system parameter) monitor F-CACH for wait msg before transmission of MAP


    Rsma mode no sho

    RsMA Mode (no SHO)


    Rsma procedure sho

    RsMA Procedure (SHO)

    • Mobile “randomly” selects a R-RACH and transmits a Reservation Access Probe (RAP) conditioned on:

      • observed Ec/Io > T_rqst dB

      • “current” persistence parameters

    • Mobile uses persistence parameters to regulate access attempts

    • After initial RAP, mobile monitors corresponding F-CCCH for:

      • Handoff Channel Assignment Message (HCAM)

    • Conditions:

      • If no HCAM message within time-out, retransmit RAP at higher power

      • If HCAM rcvd., transmit message on assigned R-CCCH at next access slot and begin closed loop power control using F-PCCH subchannels indicated in HCAM.

      • Stop transmission if either:

        • Ec/Io falls below T_fade for T1 seconds

        • Ec/Io exceeds T_good and Ec/Io of both PC bit streams falls below T_bad for L PC bits

    • If Inhibit Mode active (system parameter) monitor F-CACH for wait msg before transmission of MAP


    Rsma mode w sho

    RsMA Mode (w/SHO)


    Base station system procedures

    Base Station System Procedures

    • System defines access parameters and admission control using F-BCCH/ F-CCCH

    • System monitors R-RACH’s for messages & requests on R-RACH slot boundaries

      • search windows set to accommodate PN randomization (if not 0) + prop. delay + multipath spread

    • Pure Aloha Mode:

      • If AAP detected on R-RACH, system:

        • demodulates and decodes message

        • send ACK back on F-CCCH

    • PCA Mode:

      • If MAP detected on R-RACH, system:

        • begins closed loop power control,

        • queue’s channel assignment message,

        • transmits the message in the assigned F-CACH slot(s).


    System procedures cont

    System Procedures (cont.)

    • Reservation Mode:

      • If RAP detected on R-RACH, system:

        • queue’s channel assignment/access control message,

        • transmits the message in the assigned F-CACH slot(s).

      • If no SHO request-->CAM:

        • system monitors the assigned R-CCCH for channel estimation preamble

        • If preamble detected system demodulates and power controls message portion

        • Else if preamble not detected system releases R-CCCH for subsequent requests and ceases sending PC bits on F-PCCH after timeout

      • If SHO request -->HCAM

        • system exchanges data with neighbor cell

        • HCAM sent on F-CCCH (in soft handoff) with F-PCCH info.

        • If any base stations detect preamble, start transmitting closed loop PC bits on assigned F-PCCH subchannel

        • Else if preamble not detected, continue to send power up commands


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