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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)
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
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
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
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 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
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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