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Overview of Extended Cell High Rate Packet Data (xHRPD)

Overview of Extended Cell High Rate Packet Data (xHRPD). Outline. Overview of xHRPD Physical Layer MAC and Signaling Layers. Overview of xHRPD. Background of xHRPD. Extended Cell HRPD (xHRPD) is an HRPD system adapted to the limited link budget environment

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Overview of Extended Cell High Rate Packet Data (xHRPD)

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  1. Overview of Extended Cell High Rate Packet Data (xHRPD)

  2. Outline • Overview of xHRPD • Physical Layer • MAC and Signaling Layers

  3. Overview of xHRPD

  4. Background of xHRPD • Extended Cell HRPD (xHRPD) is an HRPD system adapted to the limited link budget environment • xHRPD can enable many new services/applications • Satellite terrestrial hybrid networks: MSS/ATC Allow a handset with the same form factor as existing cellular phones to operate in both mobile satellite system (MSS) and ancillary terrestrial component (ATC) • Machine to Machine (M2M) Relax PA requirements Allow higher in-building losses Reach distant telemetry devices

  5. Operation Environment of xHRPD • Limited link budget For example, geostationary satellite path loss is approximately 190 dB • Long round trip path delay (satellite link) • Around 500 ms or longer for GEO satellite • Large cell • For satellite system, the beam (cell) diameter can be as large as 1000 km Large signal delay variation exists within a cell • Likely to have highly overlapped cell coverage • May need to support more terminals in an extended cell than a typical terrestrial HPRD cell

  6. Main Features of xHRPD • Supported services • Low rate voice service: VOIP Support fixed rate 2kbps vocoder • Low rate mobile data service • Medium data rates for “big” terminals • Broadcast • New reverse link to maximize reverse link margin • Minimum changes to the HRPD forward link and upper layers • No support for active handoff between different extended cells

  7. Physical Layer

  8. Main Features • Narrowband reverse link to maximize link margin • New lower data rates RL lowest data rates HRPD : 9.6 kbps for Access and 4.8 kbps for Traffic xHRPD : 2.4 kbps for Access and 640 bps for Traffic • Improve link efficiency for small packets • Better coding • Reduce overheads(CRC, tail bits, header, etc.) • Forward link changes mostly in the MAC channel • MAC channels • Adaptation to the longer path delay and lower SINR environment

  9. Reverse Link Narrowband Channelization • Divide the 1.25 MHz CDMA spectrum into 192 narrowband FDM (frequency division multiplexing) channels • Each channel bandwidth is 6.4 kHz 192 x 6.4 kHz = 1.2288 MHz • Flexible bandwidth assignment depending on terminal type and system load • A terminal can be assigned one or two FDM channels 1 channel: 6.4 kHz bandwidth, 5.6k symbol rate 2 channels: 12.8 kHz bandwidth, 11.2k symbol rate • Always single carrier transmission Contiguous allocation required for 2 channel assignment

  10. Reverse Link Channel Structure Differences from HRPD: • Removed channels: Auxiliary Pilot, ACK, Data Source Control (DSC) • Data Rate Control (DRC) channel replaced by (FL) Channel Quality Indicator (CQI) channel which is used for sending DRC-like information but without DRC cover

  11. Reverse Link Frame Structure • Basic RL transmission time unit: 20 ms frame To accommodate vocoder frame duration. Different from the current 26.67 ms HRPD frame duration • Data, pilot and MAC (RRI and CQI) symbols are time division multiplexed (TDM) into one frame 1 FDM channel assignment case. (BW=6.4 k, sym rate =5.6 k) 2 FDM channel assignment case. (BW=12.8 k, sym rate =11.2 k)

  12. RL Data Rate Sets • Narrowband RL supports 9 data rates, separated into 3 Rate Sets • Rate Set 0: 640 bps, 1280 bps Used for 1 FDM channel assignment • Rate Set I: 2.4, 4.8, 9.6 kbps Used for both 1 and 2 FDM channel assignments • Rate Set 2: 12.8, 19.2, 25.6, 38.4kbps Used for 2 FDM channel assignment • VOIP traffic needs at least 2.4 kbps, thus can only be sent using Rate Set 1 or 2

  13. Two Types of RL Physical Layer Packet • Voice dedicated packet • Optimized for vocoder payload 2 kbps vocoder generates 40 bits every 20 ms Plus 8-bits CRC, it can fit nicely into the 2.4 kbps channel • Always single frame packet • ZERO protocol header/trailer from MAC and layers above The header/trailer is reconstructed at the receiver end • Can tolerate higher packet error decision rate so protected by weaker CRC 8-bit CRC for 48 bits voice packet • Data packet: normal HRPD physical layer packet • Used for sending data and signaling • Can last multiple frames • Has regular protocol header/trailer • Shall be protected by 16-bit CRC • Packet type is blindly determined at the receiver by testing different CRCs

  14. Encoding, Modulation, Interleaving & Puncturing • Two encoding methods • Convolutional encoding • Basic code: ¼ rate maximum hamming distance code with constraint length of 11 • Tailbiting convolutional code for small size (48 and 96 bits) data block No tail bits overhead! • Regular convolutional code with 10 bits tail for 192 bit data block • Turbo encoding for larger size packet (>192 bits) Same turbo encoder as in HRPD • Modulation BPSK, QPSK, 8PSK, 16-QAM and 64-QAM • Interleaver and puncturing methods similar to those in HRPD • Interleaver based code rate puncturing

  15. PN Covering and Baseband Filtering • PN quadrature covering • Benefits from PN covering Scrambling, interference averaging • PN sequences generation Common short PNs covered by masks • Baseband filtering • Square-root raised-cosine pulse shaping filter with 14% excess bandwidth

  16. Access Channel • Narrowband Access Channel • Dramatically reduced PN search space A 1000km diameter cell has around 6ms round trip delay variation => more than 7000 CDMA chips PN search space => only 34 narrowband symbols • Link budget advantage • Collision is a severe issue for narrowband access channel • Operation: Slotted Aloha • Many access channel operation parameters need to be updated • Currently the standard supports only one data rate: 2.4kbps

  17. Summary of RL Physical Layer Changes • Narrowband reverse traffic and access channel • New 6.4 kHz narrowband reverse channel design tailored for limited link budget environment to maximize link margin • Flexible assignment of narrowband frequency channels One or two adjacent channels can be assigned, depending on terminal type and system load • New data rates and transmission formats • Normal data rates: 2.4 kbps to 38.4 kbps • Also supports two low data rates 640 bps and 1.28 kbps for low rate data service • New voice dedicated physical layer packet format • Tail-biting convolution code for small size packet • MAC channel adaptation to long delay and low SINR environment

  18. Forward Link Physical Layer of xHRPD • Essentially the same as HRPD Rev A. Forward Link • All changes are in the MAC channel Disabled in xHRPD Modified for xHRPD New addition in xHRPD

  19. Disabled FL MAC Channels • Reverse Activity Channel • Reverse Activity Bit (RAB) is used for reverse link load control in HRPD • Not needed for narrowband RL • DRCLock Channel • Transmits a RL quality indication used by the AT for Forward link serving sector selection • Not needed for the GMSA system since no soft handoff is supported • ARQ Channel • Hybrid ARQ not feasible due to long round trip path delay

  20. RL Power and Frequency Control Channels • Modified RL Power Control (RPC) channel • RL power control rate can be slowed down significantly due to the presence of long path delay HRPD: 150 bps power control rate xHRPD: 50bps (1 power control bit per 20 ms RL frame received) • New RL Frequency Control (RFC) channel • May cause significant inter-channel interference if narrowband RL signal has large frequency offset • Open loop frequency error correction is recommended but may not be enough • Closed loop RL frequency error control is needed Very slow frequency correction rate is needed. The control signal rate can be set to 50 bps

  21. MAC and Signaling Layers

  22. xHRPD MAC/Signaling Layer • xHRPD preserves HRPD protocol stack • Maintains EMPA for multi-flow differentiated QoS • However, changes in the following vs. HRPD – • Reverse Link Physical Layer Packet Encapsulation • EMPA – Zero-Header Compression Protocol • RLP timers Changes • Session Configuration Changes • Connection Layer Signaling Changes • New RTCMAC for the new Narrowband Physical Layer • ACMAC Changes

  23. Reverse Link Voice-Dedicated Packet Encapsulation

  24. Reverse Link Data-Only Packet Encapsulation (same as HRPD)

  25. Reverse Link Packet Concurrent Voice and Data Encapsulation

  26. EMPA – Zero-Header Compression Protocol Either Flow Protocol or Route Protocol of EMPA can be configured as zero-header compression protocol similar to RoHC

  27. xHRPD RLP timers Changes • The following timers need to be adjusted to account for long path delay • MaxAbort Timer • Abort Timer

  28. xHRPD Session Configuration • New xHRPD Protocol Subtypes • Physical Layer • RTCMAC • ACMAC • FTCMAC • Idle State • Route Update

  29. xHRPD Connection Layer Changes • For Reverse Link, a new Channel Record format is introduced for xHRPD to define reverse narrowband channel • The existing HRPD Channel Record format is applicable for Forward Link Channel

  30. xHRPD Connection Layer Changes • Connection Request Message (Idle State Protocol) • New field added to indicate narrowband channel bandwidth requested by AT • Traffic Channel Assignment Message • HRPD channel record indicates only the forward link channel number • New reverse channel record to indicate the reverse link narrowband channel assigned to the AT • RouteUpdate Message • Channel record contains only forward link channel number • Initial CQI

  31. xHRPD RTCMAC • Supports narrowband physical layer subtype • Supports multiflow QoS • Optimized for voice packet flow by adding no RLP/MAC header overhead and tightly-fit voice packet emanating out of the vocoder into voice-dedicated physical layer packet

  32. xHRPD ACMAC Protocol • Physical Layer Format Used • 192-bit physical layer packet for transmitting over 2.4 kbps channel • Access Parameter Message Changes • AccessChannelCount: Indicates the number of narrowband access channels available in a sector • NarrowbandChannels: Specifies narrow band access channels • AccessChannelOffset: Indicates access offset for each access channel • Access Probe Timers • Adjusted for long path delay

  33. xHRPD FTCMAC Protocol • Based on HRPD FTCMAC • Hybrid ARQ (H-ARQ) feature has been disabled on the xHRPD protocol to account for the long path delays • Fixed rate state removed

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