Presentation Transcript

1. Framework Proposal for 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 (e.g. 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 in a typical terrestrial HPRD cell
6. Design Goals And Considerations Main services targeted Low rate voice service: VOIP Support 2 kbps vocoder Low rate mobile data service Medium data rates for “big” terminals Broadcast Maximize reverse link margin Minimize changes to the HRPD Initially, will not consider active handoff between different extended cells
7. Physical Layer
8. Design Keys Focus the changes on reverse link to maximize link margin Add 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 Re-examine the MAC channels Overhead reduction Adaptation to the longer path delay and lower SINR environment
9. New Narrowband Reverse Link Why narrowband RL ? Power limited communication environment Majority of terminals do not have enough link margin to take advantage of wider bandwidth Orthogonal channels Remove intra-cell interference Maximize link budget Implementation advantages Dramatically reduced time search space Less stringent requirement on the power and rate control subsystem
10. 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
11. 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
12. 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)
13. Reverse Link Frame Numerology The durations of pilot, MAC and data portion in time are the same for 1 and 2 FDM channel assignment cases
14. Pilot Channel and Symbols Pilot symbols: Known symbol sequence in each frame Two orthogonal pilot sequence patterns Normal pilot All 0’s Marked pilot Alternating 0’s and 1’s Pilot pattern is used to identify the data rate set information
15. 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, 38.4 kbps 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
16. RL Data Rate Determination Rate Set 0 (640 and 1280 bps) is designed for extremely low SINR condition RRI and pilot pattern detection are not reliable in low SINR environment The usage of this data rate set is negotiated during call setup, based on terminal type and system information For Rate Set 1 and 2 1 bit from pilot pattern used to differentiate the rate set 2-bit RRI used to indicate the data rate within a rate set Some blind detections may be needed when the SINR of RRI is low for reliable detection
17. RRI Channel And Symbols 2-bit RRI inserted in every 20-ms frame For multiple frame packet, the same RRI bits are repeated for each frame within the packet
18. Channel Quality Indicator (CQI) CQI replaces the DRC in HRPD Like the Data Rate Control (DRC) channel, CQI indicates the terminal’s highest capable forward link data rate Unlike DRC, CQI does NOT carry the selected serving sector information No hand-off supported initially Two challenges for CQI channel operation Low SINR Long path delay and large delay variation
19. Solving the Low SINR Issue for CQI Channel Sending less CQI bits for those “small” terminals Define 2 types of CQI formats. Negotiated during call setup based on terminal type and system link budget 4-bit CQI format ( one-to-one mapping of 4-bit DRC) Can support all HRPD FL data rates. 2-bit CQI format (corresponding to DRC value 1 to 4) For small terminals in certain systems, only a subset of FL data rates (38.4 kbps, 76.8 kbps, 153.6 kbps, 307.2 kbps ) are realistically possible. Repeat the same CQI content over a longer duration Reduce FL data rate changes
20. CQIPeriod and CQIDelay rlCQIPeriod: Terminal transmits constant CQI value on RL during this period of time CQI value only changed at the boundary of rlCQIPeriod Allow coherent combining of weak CQI symbols at the access network flCQIPeriod: Terminal FL receive data rate to be constant during this period of time Duration of rlCQIPeriod is the same as flCQIPeriod (Denoted by CQIPeriod) A flCQIPeriod is lagging behind its corresponding rlCQIPeriod by the amount of CQIDelay CQIDelay=CQIPeriod + MaxPathDelay where MaxPathDelay>= maximum round trip path delay plus processing delay
21. Synchronized CQI Operation Not drawn to scale
22. 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
23. 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
24. 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
25. Narrowband RL Channel Structure (1)
26. Narrowband RL Channel Structure (2)
27. Access Channel Why 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 Only support one data rate for now: 2.4kbps
28. 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
29. 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
30. 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 xHRPD system since no soft handoff is supported ARQ Channel Hybrid ARQ not feasible due to long round trip path delay
31. RL Power and Frequency Control Channels Modified RL Power Control (RPC) channel RL power control rate can be slow 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
32. Interpretation of MAC Indices Color red highlights the changes from HRPD
33. MAC and Signaling Layers
34. 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 Subtype for the new Narrowband Physical Layer ACMAC Changes
35. Reverse Link Voice-Dedicated Packet Encapsulation
36. Header Reconstruction for Voice Packets When Voice-Dedicated packet passes CRC, the protocol header is reconstructed as follows:
37. Reverse Link Data-Only Packet Encapsulation (same as HRPD)
38. Reverse Link Packet Concurrent Voice and Data Encapsulation
39. EMPA – Zero-Header Compression Protocol Either Flow Protocol or Route Protocol of EMPA can be configured as zero-header compression protocol similar to RoHC
40. xHRPD RLP timers Changes The following timers need to be adjusted to account for long path delay MaxAbort Timer Abort Timer
41. xHRPD Session Configuration New xHRPD Protocol Subtypes Physical Layer RTCMAC
42. 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
43. Reverse Channel Format
44. xHRPD Connection Layer Changes Connection Request Message (Default 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
45. xHRPD RTCMAC new Subtype Supports narrowband physical layer subtype Supports multiflowQoS 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
46. 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
47. xHRPD FTCMAC Protocol Based on HRPD FTCMAC Subtype 1 Hybrid ARQ (H-ARQ) feature has been disabled on the xHRPD protocol to account for the long path delays