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 3G Evolution - HSPA and LTE for Mobile Broadband 1
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
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 – Channel dependent scheduling – Higher order modulation – Rate conrol – Hybrid ARQ and soft combining 16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 3
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. 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 16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 4
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) 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 16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 5
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 Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al 16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 6
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 • Finer details: – In-sequence delivery to higher layers – CQI/ downlink quality – Uplink and Downlink control signaling 16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 7
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 NodeB • Rate control • Hybrid-ARQ with soft combining UE • Other channels • Control signaling • Circuit switched services • 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 Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al 16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 8
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
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 MAC • Transport-format selection (block size) PHY • Hybrid-ARQ mechanism • • PHY layer 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. Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al 16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 10
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
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 Figure courtesy: 3G evolution: HSPA and LTE for mobile broadband by Erik Dahlman, Stefan Parkvall et. al 16-Apr-2009 3G Evolution - HSPA and LTE for Mobile Broadband 12
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