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3G Evolution 3G Evolution 3G Evolution 3G Evolution Chapter: 9 9 9 9 Chapter: Chapter: Chapter: High-Speed Downlink High-Speed Downlink Packet Access Deepak Dasalukunte Department of Electrical and Information Technology 16-Apr-2009

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3G Evolution 3G Evolution 3G Evolution 3G Evolution

Chapter: Chapter: Chapter: Chapter: 9

9 9 9

High-Speed Downlink

Deepak Dasalukunte Department of Electrical and Information Technology

High-Speed Downlink Packet Access

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 1

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Outline Outline Outline Outline

  • Overview

– Shared channel transmission – Channel dependent scheduling – Rate control – Hybrid ARQ and soft combining

  • Details/Finer details of HSPA

– Channels – downlink/uplink, data/control... – Channels – downlink/uplink, data/control... – MAC-hs and physical layer processing

  • Scheduling
  • Rate control
  • Hybrid ARQ with soft combining
  • In-sequence delivery to higher layers from MAC
  • CQI/ downlink quality
  • Uplink and Downlink control signalling

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 2

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Part I : Overview Part I : Overview Part I : Overview Part I : Overview

  • Major extension of WCDMA radio interface
  • Enhancing WCDMA packet data performance and capabilities

– Higher peak data rates – Reduced latency – Increased capacity

  • Achieved through

– Channel dependent scheduling

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 3

– Channel dependent scheduling – Higher order modulation – Rate conrol – Hybrid ARQ and soft combining

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Shared channel transmission Shared channel transmission Shared channel transmission Shared channel transmission

  • Resources in a cell are common to user and shared dynamically

– Downlink radio resources – Channelization codes

  • Configurable: 1-15
  • Remaining: control and other purposes

– Transmit power

  • Allocation depending on requirement.

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 4

  • Allocation depending on requirement.
  • Power remaining after serving other

channels is allocated to HS-DSCH

  • 2ms TTI (transmit time interval):

– reduces overall latency – also exploited by rate control – and channel dependent scheduling

  • More SCHs and CCHs later

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al

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Recap from chapter 7 Recap from chapter 7 Recap from chapter 7 Recap from chapter 7

  • Channel dependent scheduling

– Scheduler decides which user at a given time instance gets the resource – effective channel variations as seen by NodeB is better. – Larger gains with larger channel variations and larger number of users

  • Rate control and higher order modulation

– QPSK, 16QAM – Higher bandwidth utilization in better channels – Data rate varies every TTI (2ms)

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 5

– Data rate varies every TTI (2ms)

  • Hybrid ARQ and soft combining

– Incremental redundancy – Chase combining

  • Discussed in this chapter:

– Parameters to be used

  • Channelization codes, modulation schemes, coding rates, transport block sizes etc.

– when and what to use in a particular situation – Implementation details: specifications, actual numbers and examples

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al

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SLIDE 6

Architecture Architecture Architecture Architecture

  • HSDPA techniques: adaptation to variations in radio conditions

– Should be placed close to the radio interface ￫ NodeB

  • Minimize architectural changes

– Simplifies HSPA introduction in already deployed networks – Cells not upgraded to HSPA can co-exist

  • A new MAC sub layer in NodeB: MAC-hs
  • A new MAC sub layer in NodeB: MAC-hs
  • At network side HSDPA introduction implies

– Enhancements to RNC – MAC-hs layer in NodeB

  • UE can move out of the cell supporting HSDPA and vice versa.

– Uninterrupted service to user (lower data rate) – Switch user to deidcated channel in non-HSDPA cell – To enter HSDPA cell: UE should be HSDPA-capable

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 6

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al

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Part II: Details/Finer details of HSDPA Part II: Details/Finer details of HSDPA Part II: Details/Finer details of HSDPA Part II: Details/Finer details of HSDPA

  • Channels – downlink/uplink, data/control...
  • MAC-hs and physical layer processing
  • Scheduling, rate control
  • Hybrid ARQ with soft combining

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 7

  • Finer details:

– In-sequence delivery to higher layers – CQI/ downlink quality – Uplink and Downlink control signaling

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Channels: Shared/Dedicated, Channels: Shared/Dedicated, Channels: Shared/Dedicated, Channels: Shared/Dedicated, Uplink/Downlink, … Uplink/Downlink, … Uplink/Downlink, … Uplink/Downlink, …

  • HS-DSCH: transport channel, supports
  • Shared channel transmission
  • Channel dependent scheduling
  • Rate control
  • Hybrid-ARQ with soft combining
  • Other channels
  • Control signaling
  • Circuit switched services

NodeB UE

  • Circuit switched services
  • Resource sharing mainly in time domain
  • Exploit channel dependent scheduling advantages
  • Code domain also possible with channelization codes
  • Constant Tx power with HS-DSCH
  • 2ms TTI result of tradeoff between
  • Obtaining small end user delay
  • Reduce control signaling overhead

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 8

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al

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SLIDE 9

Channels: Shared/Dedicated, Channels: Shared/Dedicated, Channels: Shared/Dedicated, Channels: Shared/Dedicated, Uplink/Downlink, … (2) Uplink/Downlink, … (2) Uplink/Downlink, … (2) Uplink/Downlink, … (2)

  • HS-SCCH(Shared Control CH): control signaling for DSCH

– Notifies

  • code tree used
  • Modulation scheme
  • Block size

– All users receive this, to find out if they have been scheduled or not.

  • HS-DPDCH: uplink user data.
  • HS-DPDCH: uplink user data.
  • HS-DPCCH (Dedicated Physical Control CH): Uplink control signaling

– ACK/NAK – CQI: Downlink channel conditions fed back to NodeB

  • for channel dependent scheduling and rate control
  • DPCH (Dedicated Physical CH): power control commands (NodeB￫UE)

– Can also be used for user data – f-DPCH (fractional): reduce consumption of downlink channelization codes.

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 9

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MAC MAC MAC MAC-

  • hs and PHY layer processing

hs and PHY layer processing hs and PHY layer processing hs and PHY layer processing

  • Changes in MAC-hs, reflects some changes in PHY layer
  • MAC-hs
  • Scheduling
  • Priority handling
  • Transport-format selection (block size)
  • Hybrid-ARQ mechanism
  • PHY layer

PHY MAC

  • PHY layer
  • Rate 1/3 turbo coding
  • Rate matching (RM) – to obtain code rate selected by

rate control mechanism

– Puncturing/repetition

  • RM as a part of hybrid-ARQ

– Generate different redundancy versions -IR

  • Constellation rearrangement if 16-QAM is used.

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 10

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al

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MAC MAC MAC MAC-

  • hs: Scheduling

hs: Scheduling hs: Scheduling hs: Scheduling

  • Implementation is not specified
  • Information required for scheduling

– Instantaneous channel conditions at UE – Buffer status and priorities of data flow

  • Channel Quality Indicator(CQI) – 5 bits of information fed back to

nodeBs (HS-DPCCH)

– Calculated at UE using the received pilot symbols – Calculated at UE using the received pilot symbols – Converted to transport block size, also accounting Rx performance

  • For same channel, a more advanced UE receiver reports higher CQI
  • Important signals are put on higher priority level in the scheduler

– Radio resource control signaling information about change of cell. – Streaming services also can tolerate only a marginal delay

  • For this a priority queue is included which the scheduler makes use of.

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 11

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MAC MAC MAC MAC-

  • hs: Rate control

hs: Rate control hs: Rate control hs: Rate control

  • Adjusting data rate to match channel conditions
  • Modulation
  • Channel coding rate
  • MAC-hs sets transport format independently
  • Transport block:

– 254 different possibilities – 63 values per channelization code – 63 values per channelization code and modulation scheme – 13 – 27952 bits – coding rate: 1/3 to 1

  • The block size also depends on the traffic situation

– Better channel conditions implies larger block size – Relatively smaller block size enough at low traffic conditions

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 12

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al

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Hybrid Hybrid Hybrid Hybrid-

  • ARQ with soft combining

ARQ with soft combining ARQ with soft combining ARQ with soft combining

  • Faster compared to RLC based retransmissions
  • No signaling between nodeB and RNC
  • RLC (higher layer within MAC) configured with infrequent status reports
  • 1 transport block per TTI and entire block re-transmitted

– Lesser uplink signalling

  • Short TTI ensures static channel during transmission of one transport

block block

  • Incremental redundancy during re-transmissions is achieved through

the rate matching block in PHY

  • Soft combining happens through new data indicator for the same

transmitted block

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 13

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Hybrid Hybrid Hybrid Hybrid-

  • ARQ with soft combining (2)

ARQ with soft combining (2) ARQ with soft combining (2) ARQ with soft combining (2)

  • One hybrid-ARQ entity with multiple hybrid-ARQ processes

– To allow continuous transmission – No. of processes is configurable – Configured according to roundtrip time b/w nodeB and UE – Up to 8 processes configurable, typical is 6 as it provides 2.8ms of processing time for nodeB – Each process has its own soft buffer in UE

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 14

– Each process has its own soft buffer in UE – Soft buffer in UE configured by nodeB by downlink signaling – Transport blocks out of sequence:

  • reordering before passing it to RLC

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al

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Changes in PHY layer due to MAC Changes in PHY layer due to MAC Changes in PHY layer due to MAC Changes in PHY layer due to MAC-

  • hs

hs hs hs

  • MAC-hs
  • Scheduling
  • Rate control – modulation scheme selection
  • Transport-format selection – block size using no. of channelization codes and

modulation scheme

  • Hybrid-ARQ mechanism – multiple Hybrid-ARQ processes
  • PHY layer
  • Rate matching (RM) – to obtain code rate selected by

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 15

  • Rate matching (RM) – to obtain code rate selected by

rate control mechanism

– Puncturing/repetition

  • RM as a part of hybrid-ARQ

– Generate different redundancy versions -IR

  • Constellation rearrangement if 16-QAM is used.
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Hybrid Hybrid Hybrid Hybrid-

  • ARQ : PHY layer processing

ARQ : PHY layer processing ARQ : PHY layer processing ARQ : PHY layer processing

  • Rate matching:
  • Corresponds rate control and hybrid-ARQ in MAC
  • Rate chosen by MAC-hs layer independently
  • Output bits from Turbo coder different
  • RM works in 2 stages

– 1st stage: limits to match soft buffer in UE – 2nd stage: to match physical channel block size

Rate matching block

– 2nd stage: to match physical channel block size

  • Depends on modulation and channelization code
  • Help in generating different sets of coded bits (r,s)

– s: systematic bits, r: retransmission

  • Example:
  • MAC-hs configures block size = 3840 (QPSK, 4

channelization codes)

  • Transport block to be transmitter = 2404
  • UE soft buffer size for one hybrid-ARQ process is

7000

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 16

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et . al

(size=7000) (size=3840)

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Hybrid Hybrid Hybrid Hybrid-

  • ARQ : PHY layer processing (2)

ARQ : PHY layer processing (2) ARQ : PHY layer processing (2) ARQ : PHY layer processing (2)

  • Constraints on r and s in 2nd stage of RM – more details

– Initial transmission: s=1 and code rate<1 for good performance – s=1 and r=0 for all re-transmission attempts – Same set of bits in re-transmission: chase combining chase combining chase combining chase combining – s=1 and r=0 initial Tx; s=0 and r>0 in re-Tx: incremental redundancy incremental redundancy incremental redundancy incremental redundancy – More possibilities using s s s s and r r r r

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 17

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Interleaving and constellation Interleaving and constellation Interleaving and constellation Interleaving and constellation rearrangement rearrangement rearrangement rearrangement

  • Systematic bits more important than parity bits in Turbo decoding
  • While using 16QAM

– Systematic bits mapped to more reliable positions in 16 QAM symbol – Two interleaver scheme

  • QPSK

– Single interleaver

  • 16QAM with hybrid-ARQ with chase combining

– Performance gain with constellation rearrangement + re-transmissions – Gains not significant with incremental redundancy

  • Constellation rearrangement:

– bit manipulations/reordering – Essentially selecting one out of 4 constellations for 16QAM – ?? Which is which is not evident (supposedly color coded)

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 18

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al

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Mobility Mobility Mobility Mobility

  • Change of serving cell
  • RRC signaling
  • Measurements from UE reported to RNC
  • RNC reassigns the UE to corresponding NodeBs
  • Several measurement mechanisms
  • Measurement event 1D is one such
  • Common pilot strength from neighboring cell
  • Common pilot strength from neighboring cell

is reported to be stronger than current cell

  • Reconfiguration of UE

– Synchronous

  • Pre-defined activation time, all nodes involved switch at this time
  • Packet losses during handover, taken care of by RLC protocol

– Asynchronous

  • Involved nodes reconfigure as soon as they receive the message
  • Can result in data loss, due to delays in one of the nodes not updating quickly

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 19

Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al

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Downlink control signaling: Downlink control signaling: Downlink control signaling: Downlink control signaling: HS HS HS HS-

  • SCCH; F

SCCH; F SCCH; F SCCH; F-

  • DPCH

DPCH DPCH DPCH

  • UE to properly despread, demodulate, and decode HS-DSCH data
  • Every HS-DSCH TTI, one HS-SCCH carries PHY layer signaling
  • Several SCCHs in parallel can exist
  • UE should be able to decode 4 HS-SCCHs in parallel
  • HS-SCCH carries
  • Transport format

– Channelization code – Channelization code – Modulation scheme – Transport block size info

  • Hybrid ARQ

– Hybrid ARQ process # – Redundancy version – New data indicator

  • UE ID that identifies which UE the HS-SCCH is intended
  • Power control commands for UE
  • Adjust uplink transmission power
  • When UE is moving towards/away from the NodeB

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 20

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Uplink control signaling: HS Uplink control signaling: HS Uplink control signaling: HS Uplink control signaling: HS-

  • DPCCH

DPCCH DPCCH DPCCH

  • Hybrid-ARQ protocol
  • For NodeB to get instantaenous channel conditions
  • Separate physical channel using channelization code
  • One bit for ACK/NAK

− Repetition coded to 10 bits to fit first slot of HS-DPCCH sub-frame − Possibility to repeat ACK/NAK in 10 subsequent ACK/NAK slots

  • Cannot receive HS-DSCH in those consecutive TTIs

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  • Cannot receive HS-DSCH in those consecutive TTIs
  • But can be helpful in soft handover situations / very large cells
  • Much more protocol specific information related to control signaling
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Other topics Other topics Other topics Other topics

  • In-sequence delivery

– Multiple hybrid-ARQ processes does not ensure delivery of packets in sequence. – Reordering required as the upper layer assumes in-sequence delivery. – Reordering queue: store all data blocks until all data blocks with lower sequence number have been delivered. – Timer based mechanism to determine lost data blocks. – Timer based mechanism to determine lost data blocks.

  • Resource control for HS-DSCH

– Parts of Radio resource management handled by NodeB – RNC can set max Tx power for NodeB to use for HSDPA related transmissions – Admission control: allowing a new user enter the cell (Tx power availability)

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 22

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Others topics (2) Others topics (2) Others topics (2) Others topics (2)

  • UE categories

– used by network to select a configuration – Soft buffer memory (14 400-172 800 soft bits) – Capability to de-spread physical channels (5,10,15)

  • Data flow

– Flow of user data in different layers – Flow of user data in different layers

  • MAC-hs header

– Reordering of higher layer (MAC-d) PDUs

  • CQI and other means to assess the downlink quality

– Tables showing what each UE category supports and so on

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 23

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SLIDE 24

Chapter summary Chapter summary Chapter summary Chapter summary

  • Channels: data/control, uplink/downlink... for signaling and data
  • New MAC-hs sub layer introduced in NodeB

– Scheduling – Rate control:

  • modulation schemes
  • block size choice through CQI feed back

– Hybrid-ARQ with soft combining – Hybrid-ARQ with soft combining – Control signaling

  • PHY layer

– Rate control from MAC-hs resulted in rate matching

  • Puncturing/repetition to match UE soft buffer, transmit block size

– Hybrid-ARQ: rate matching also used here for incremental redundancy and chase combining

  • Reordering due to multiple hybrid-ARQ processes
  • Mobility: handover

16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 24

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Questions? Questions?

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