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Title: Overview of Extended Cell High Rate Packet Data
Abstract: This contribution provides an overview of Extended Cell High Rate Packet Data (xHRPD) system
Source: Rhys W. Robinson ([email protected]).
TerreStar Networks
Sourabh Gupta ([email protected])
DBSD North America (ICO)
Eric Jacks ([email protected])
LightSquared Communications
Alok Gupta ([email protected])Qualcomm Incorporated
Date: September 14, 2011
Recommendation: FYINotice
LightSquared Communications, DBSD North America (ICO), TerreStar Networks, and QUALCOMM Incorporated grant a free, irrevocable license to 3GPP2 and its Organizational Partners to incorporate text or other copyrightable material contained in the contribution and any modifications thereof in the creation of 3GPP2 publications; to copyright and sell in Organizational Partner’s name any Organizational Partner’s standards publication even though it may include all or portions of this contribution; and at the Organizational Partner’s sole discretion to permit others to reproduce in whole or in part such contribution or the resulting Organizational Partner’s standards publication. LightSquared Communications, DBSD North America (ICO), TerreStar Networks, and QUALCOMM Incorporated are also willing to grant licenses under such contributor copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing an Organizational Partner’s standard which incorporates this contribution.
This document has been prepared by LightSquared Communications, DBSD North America (ICO), TerreStar Networks, and QUALCOMM Incorporated to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on LightSquared Communications, DBSD North America (ICO), or QUALCOMM Incorporated. LightSquared Communications, DBSD North America (ICO), TerreStar Networks, and QUALCOMM Incorporated specifically reserve the right to amend or modify the material contained herein and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of LightSquared Communications, DBSD North America (ICO), TerreStar Networks, or QUALCOMM Incorporated other than provided in the copyright statement above.
Overview of Extended Cell High Rate Packet Data (xHRPD)
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Outline
• Overview of xHRPD • Physical Layer • MAC and Signaling Layers
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Overview of xHRPD
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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 requirementsAllow higher in-building losses Reach distant telemetry devices
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Operation Environment of xHRPD
• Limited link budgetFor 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 kmLarge 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
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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
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Physical Layer
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Main Features
• Narrowband reverse link to maximize link margin New lower data rates
RL lowest data ratesHRPD : 9.6 kbps for Access and 4.8 kbps for TrafficxHRPD : 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
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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
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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
Traffic
Reverse
Medium Access Control
Data
ReverseRate
Indicator
ChannelQuality
Indicator
Access
Data PilotPilot
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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)
2RRI
2Data
1Pilot
7Data
1Pilot
7Data
1Pilot
7Data
1Pilot
7Data
2CQI
1Data
1Pilot
1Pilot
7Data
4RRI
1Pilot
7Data
3CQI
1Pilot
1Pilot
7Data
1Pilot
7Data
1Pilot
7Data
1Pilot
6Data
1CQI
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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
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Two Types of RL Physical Layer Packet • Voice dedicated packet
Optimized for vocoder payload 2 kbps vocoder generates 40 bits every 20 msPlus 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
CRC8-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
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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
• ModulationBPSK, QPSK, 8PSK, 16-QAM and 64-QAM
• Interleaver and puncturing methods similar to those in HRPD Interleaver based code rate puncturing
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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
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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
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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
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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
MediumAccessControl
Pilot Traffic
ReverseActivity ARQ
Forward
Control
DRCLock Reverse Power
Control
Reverse Frequency
Control
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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
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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 delayHRPD: 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
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MAC and Signaling Layers
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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
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Reverse Link Voice-Dedicated Packet Encapsulation
Decapsulation of 48-bit Voice-Dedicated Physical Layer Frame
RLP payload (40 bits)
MAC payload (40 bits) CRC (8 bits)
VoIP payload (40 bits)RTP/IP/UDP header(20 bytes)
VoIP payload (40 bits)
Zero-Header Compression: RTP/UDP/IP header removed
RLP Packet
48-bit Voice-Dedicated Physical Layer Frame Transmitted
VoIP RTP packet – 200 bits
Quarter Rate Vocoder Frame Encapsulation over 48-bit Voice-Dedicated Physical Layer Frame
Voice Data (40 bits)
MAC payload (40 bits)
RTCMAC layer
RL Demod interface reconstructs MAC/Stream/RLP header (formatA connection packet is assumed)
48-bit Voice-Dedicated Physical Layer Frame Received
Coneection/Stream Layer
CRC (8 bits)
Voice Data (40 bits)
RLP header(14 bits)
MAC trailer(8 bits)
stream header(2 bits)
RLP header(14 bits)
Stream header(2 bits)
Voice data (40 bits)RLP header
(14 bits)
EMPA/Header Decompressor reconstructsRTP/UDP/IP headers
RLP Layerdata (40 bits)
data (40 bits)RTP/UDP/IP header
Stream/Connection Layer bypassed
No RLP header
xHRPD Airlink
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Reverse Link Data-Only Packet Encapsulation (same as HRPD)
Payload 232 bits
MAC payload (232 bits)MAC Trailer
(2 bits)
Signaling data (HDR, SIP, PPP)
Payload 230 bits Stream Layer
Connection Layer Format A
Physical Layer Data FrameFCS+Tail
(16+6 bits)
2bits
6bits Payload 224 bits
Signaling data is divided into multiple RLP packets
RLP Layer
Payload 224 bits
MAC payload (232 bits)MAC Trailer
(2 bits)
Signaling data (HDR, SIP, PPP)
Payload 222 bits Stream Layer
Connection Layer Format B
Physical Layer Data Frame
FCS + Tail(16+6 bits)
Header8bits
2bits
6bits Payload 216 bits
Signaling data is divided into multiple RLP packets
RLP Layer
256-bit frame format Connection layer format B
256-bit frame format Connection layer format A
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Reverse Link Packet Concurrent Voice and Data Encapsulation
Connection layer payload
Stream layer payload
VoIP data
RLP payload
Voice data (40 bits)RTP/UDP/IP header
RLP header(14 bits)
Stream header(2 bits)
Connection Header (8 bits)
Connection layer payload
Stream layer payload
RLP payload
Non-VoIP data
RLP header(14 bits)
Stream header(2 bits)
Connection layerHeader (8 bits)
MAC payload 160 bits
Connection layer padding. . .
MAC trailer (8 bits)
Non-VoIP data
VoIP header removed before passing to RLP
MAC payload 168 bits 16-bit CRC
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EMPA – Zero-Header Compression Protocol
AT
UDP/IP/
PPP
Route protocol
VoIP Client Application
SIP
SIP
RLP
RTP
RTP
RLP
AN
ROHCU-mode
Compressor
Flow protocol Flow protocol
Route protocol
ROHCU-mode
Decompressor
Either Flow Protocol or Route Protocol of EMPA can be configured as zero-header compression protocol similar to RoHC
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xHRPD RLP timers Changes
• The following timers need to be adjusted to account for long path delay MaxAbort Timer Abort Timer
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xHRPD Session Configuration
• New xHRPD Protocol Subtypes Physical Layer RTCMAC ACMAC FTCMAC Idle State Route Update
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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
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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
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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
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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
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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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