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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. 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

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  1. cdma2000 Access Telecommunications Industry Association TR 45.5.3.1 RsMA Ad Hoc December 10, 1998

  2. 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)

  3. IS-95A/B Access Procedure

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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)

  9. 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

  10. 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

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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)

  16. 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)

  17. 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

  18. 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

  19. Channel Organization

  20. 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

  21. Pure Aloha Mode

  22. 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

  23. PC Aloha Mode

  24. 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

  25. RsMA Mode (no SHO)

  26. 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

  27. RsMA Mode (w/SHO)

  28. 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).

  29. 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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