3G Evolution HSPA and LTE for Mobile Broadband Part II Dr Stefan Parkvall Principal Researcher Ericsson Research stefan.parkvall@ericsson.com
Outline Series of three seminars I. Basic principles Channel and traffic behavior Link adapation, scheduling, hybrid-arq Evolving 3G, inclusion of basic principles in WCDMA II. LTE First step into 4G Path towards IMT-Advanced III. Standardization How are HSPA and LTE created? 3GPP, ITU,...
Recap from First session Radio channel quality is time varying Traffic pattern is time varying Adapt to and exploit variations in the radio channel quality variations in the traffic pattern instead of combating them!
Recap from First session Shared channel transmission Channel-dependent scheduling Rate control Hybrid-ARQ with soft combining
Recap from First session Shared channel transmission Channel-dependent scheduling Hybrid ARQ HSPA ( Turbo-3G ) Packet-data add-on to WCDMA First version ~2002, still evolving Using principles from first session Rate control 5 MHz 5 MHz 10 MHz f Multi-carrier transmission Multi-antenna support
LTE Long-Term Evolution WCDMA HSDPA HSPA HSPA+ LTE
HSPA and LTE = Mobile Broadband HSPA High-Speed Packet Access ( Turbo-3G ) Gradually improved performance at a low additional cost LTE Long-Term Evolution ( 4G ) Significantly higher performance in a wide range of spectrum allocations Downlink up to 300 Mbit/s Uplink up to 75 Mbit/s Reduced latency 10 ms RTT Packet-switched services only WCDMA HSDPA HSPA HSPA evolution 2002 2004 2005 2006 2007 2008 LTE Stefan Parkvall Requirements Studies Spec s
LTE 4G Mobile Broadband From early studies Testbed 2007, 20 MHz, 2x2 MIMO 154 123 97 74 54 37 23 LTE Testbed 2007 via trials 12 700 m to commercial operation! http://www.teliasonera.com/4g/index.htm http://www.ericsson.com/thecompany/press/releases/2009/12/1360881
Spectrum Flexibility Operation in differently-sized spectrum allocations Core specifications support any bandwidth from 1.4 to 20 MHz Radio requirements defined for a limited set of spectrum allocations 1.4 MHz 3 MHz 5 MHz 6 RB ( 1.4 MHz) 10 MHz 15 MHz 20 MHz 100 RB ( 20 MHz) Support for paired and unpaired spectrum allocations with a single radio-access technology economy-of-scale Uplink Downlink frequency frequency frequency FDD time Half-duplex FDD (terminal-side only) time TDD time
Transmission Scheme Downlink OFDM Parallel transmission on large number of narrowband subcarriers Uplink DFTS-OFDM DFT-precoded OFDM DFT precoder OFDM modulator IFFT Cyclic-prefix insertion DFT IFFT Cyclic-prefix insertion Benefits: Avoid own-cell interference Robust to time dispersion Main drawback Power-amplifier efficiency Tx signal has single-carrier properties Improved power-amplifier efficiency Improved battery life Reduced PA cost Critical for uplink Equalizer needed Rx Complexity Not critical for uplink
Time Dispersion and OFDM Time dispersion inter-symbol interference Requires receiver-side processing (equalization) OFDM transmission uses multiple narrowband subcarriers Including of cyclic prefix completely mitigates time dispersion (up to CP) at the cost of additional overhead simple receiver Single carrier Detect symbol n OFDM Detect symbol n Path 1 n-2 n-1 n n+1 Path 2 n-2 n-1 n n+1 (delayed copy)
Downlink OFDM Δf 0 Block of M symbols Size-N IFFT M subcarriers CP insertion 0 T u = 1/Δf T CP T u T CP-E T u Parallel transmission using a large number of narrowband sub-carriers Multi-carrier transmission Typically implemented with FFT Insertion of cyclic prefix prior to transmission Improved robustness in time-dispersive channels requires CP > delay spread Spectral efficiency loss Configuration, Δf CP length Symbols per slot Normal 15 khz 4.7 μs 7 Extended 15 khz 16.7 μs 6 7.5 khz 33.3 μs 3
Uplink DFT-spread OFDM ( SC-FDMA ) Single-carrier uplink transmission efficient power-amplifier operation improved coverage OFDM requires larger back-off than single-carrier DFT-spread OFDM OFDM with DFT precoder to reduce PAR Uplink numerology aligned with downlink numerology Terminal A DFT (M 1 ) 0 IFFT CP insertion M 1 > M 2 Terminal B DFT (M 2 ) 0 IFFT CP insertion
Time-domain Structure FDD Uplink and downlink separated in frequency domain One subframe, T subframe = 1 ms One radio frame, T frame = 10 ms UL DL f U L fd L Subframe #0 #1 #2 #3 #4 #5 #6 #7 #8 #9 TDD Uplink and downlink separated in time domain special subframe Same numerology etc as FDD economy of scale (special subframe) (special subframe) UL DL f DL/UL DwPTS GP UpPTS
Physical Resources One frame (10 ms) One subframe (1 ms) One resource element 12 sub-carriers One slot (0.5 ms) T CP T u
Protocol Architecture User #i User #j SAE bearers MAC MAC scheduler Payload selection Priority handling, payload selection Retransmission control Modulation scheme Antenna and resource assignment PDCP RLC MAC PHY Header Compr. Ciphering Segmentation, ARQ MAC multiplexing Hybrid ARQ Hybrid ARQ Coding + RM Coding Data modulation Modulation Antenna and resrouce Antenna and resource mapping mapping PDCP PDCP Packet Data Header Compr. Convergence Protocol Radio Bearers RLC Radio RLC Link Control Logical Channels MAC MAC demultiplexing MAC Medium Access Control Transport Channel Hybrid Hybrid ARQ ARQ Multiplexing of radio bearers PHY Coding + RM Decoding Data modulation Coding, Modulation Demodulation Redundancy version Packet Data Convergence Protocol Header compression to reduce overhead Ciphering for security Header compression to reduce overhead Deciphering Ciphering for security Segmentation/concatenation Reassembly, ARQ RLC retransmissions In-sequence delivery Hybrid-ARQ retransmissions PHY Physical Layer Multi-antenna Antenna and resrouce Antenna and processing resource mapping demapping Resource mapping Radio Link Control Segmentation/concatenation RLC retransmissions In-sequence delivery Medium Access Control Multiplexing of radio bearers Hybrid-ARQ retransmissions Physical Layer Coding, Modulation Multi-antenna processing Resource mapping
Data Flow in LTE SAE bearer 1 SAE bearer 1 SAE bearer 2 header Payload header Payload header Payload PDCP hdr Payload hdr Payload hdr Payload PDCP header PDCP header PDCP header RLC RLC SDU RLC SDU RLC SDU RLC header RLC header RLC header MAC MAC header MAC SDU MAC header MAC SDU PHY Transport Block CRC Transport Block CRC
Architecture Core network evolved in parallel to LTE EPC Evolved Packet Core Flat architecture, single RAN node, the enodeb Compare HSPA, which has an RNC Internet PSTN Internet Core Network Core Network RNC RNC to other Node Bs to other Node Bs Dedicated channels enodeb UE NodeB UE LTE HSPA
Channel-dependent Scheduling LTE channel-dependent scheduling in time and frequency domain HSPA adaptation in time-domain only Time-frequency fading, user #1 data1 data2 data3 data4 Time-frequency fading, user #2 User #1 scheduled User #2 scheduled 1 ms Time Frequency 180 khz
Uplink Scheduling Base station mandates data rate of terminal Unlike HSPA where terminal selects data rate [limited by scheduler] Motivated by orthgonal LTE uplink vs non-orthgonal HSPA uplink enodeb enodeb RLC buffer RLC buffer Scheduler MAC multiplexing Scheduler Uplink channel quality Modulation, coding Channelstatus Buffer Status TF selection UE UE Modulation, coding Downlink channel quality Priority handling MAC multiplexing RLC buffer RLC buffer Downlink Uplink
Hybrid-ARQ with Soft Combining Parallel stop-and-wait processes 8 processes 8 ms roundtrip time To RLC for in-sequence delivery Block 2 Block 3 Block 4 Block 5 Block 1 Hybrid-ARQ protocol Process #7 Process #1 Process #0 Process #2 Process transport block 3 Process transport block 5 Process transport block 2 Process transport block 4 Process transport block 1 Process transport block 1 Process transport block 1 1 2 3 1 4 5 1
Interaction with RLC Why two transmission mechanisms, RLC and hybrid-arq? Retransmission protocols need feedback Hybrid ARQ [with soft combining] Fast retransmission, feedback every 1 ms interval Frequent feedback need low overhead, single bit Single, uncoded bit errors in feedback (~10-3 ) RLC Reliable feedback (sent in same manner as data) Multi-bit feedback less frequent Hybrid-ARQ and RLC complement each other
Multi-antenna transmission techniques Diversity for improved system peformance Beam-forming for improved coverage (less cells to cover a given area) SDMA for improved capacity (more users per cell) Multi-layer transmisson ( MIMO ) for higher data rates in a given bandwidth The multi-antenna technique to use depends on what to achieve
Scheduling and Interference Handling Scheduling strategy strongly influences system behavior Trade-off between capacity and uniform service provisioning Can take inter-cell interference into account Improve cell-edge data rates...at the cost of system throughput Autonomous handling complemented by exchange of coordination messages between base stations Cell A Cell B
data1 data2 data3 data4 LTE Continuous Evolution OFDM transmission Multi-antenna support ICIC Dual-layer beamforming Multi-antenna extensions N W E S Channel-dependent scheduling Hybrid ARQ Positioning Relaying Bandwidth flexibility FDD and TDD support MBMS Carrier Aggregation Rel-8 Rel-9 Rel-10 2008 2009 2010 Basic LTE functionality Enhancements & extensions Further extensions IMT-Advanced compliant
MBSFN Operation Rel-9 Multicast-Broadcast Single Frequency Network Synchronized transmission from multiple cells Seen as multipath propagation by terminal combining gain for free MBSFN for content known to have many viewers News, sport events, On demand Personalized content Big events Known in advance to have many users
Carrier Aggregation Rel-10 Multiple component carriers operating in parallel Rel-8 one component carrier Rel-10 up to five component carriers Rel-8 Rel-10 Use cases Bandwidths beyond 20 MHz higher data rates Exploitation of fragmented spectrum Straight-forward baseband challenging RF implementation Intra-band aggregation, contiguous component carriers Frequency band A Frequency band B Intra-band aggregation, non-contiguous component carriers Frequency band A Frequency band B Inter-band aggregation Frequency band A Frequency band B
backhaul link access link Relaying Rel-10 Repeater Possible already in Rel-8, simply amplifies and retransmits received signal Relaying (added in Rel-10) Relay = small base station connected to RAN using LTE radio resources Interesting if fiber/microwave is more expensive than using LTE spectrum Donor cell Relay cell
Non-uniform Deployments Improved Support in Rel-10 What? Low power nodes placed throughout a macro-cell layout Hierarchical Cell Structures an old idea revisited Why? High data rates dense infrastructure...but non-uniform user distribution Macro for coverage, pico for high data rates How? Conventional Independent pico cells Relay Independent relay cells Relay connected to macro RRU Remote pico antenna, processing in macro No new pico cells
Beyond Rel-10 CoMP CoMP Coordinated Multi-point transmission/reception Tx/Rx from single point at a time Scheduling coordination to avoid severe interference situations Tx/Rx from multiple points at a time Joint transmission to improve SINR Coordination Coordinated precoding/beamforming Requires spatial information about channels to non-serving cells Coherent or non-coherent transmission Coherent requires accurate tracking of relative phases between points CoMP emerging technology, studied in 3GPP not part of Rel-10
LTE Rel-8 - Summary FDD and TDD support IFFT Bandwidth flexibility Fundamental principle: adapt to and exploit variations in Transmission scheme DL OFDM, UL DFTS-OFDM data1 data2 data3 data4 radio channel quality traffic pattern Channel-dependent scheduling ICIC Multi-antenna support Hybrid ARQ
data1 data2 data3 data4 LTE Rel-9 - Refinements LTE Rel-9 N MBSFN LTE Rel-8 W E S Positioning Dual-stream Beamforming
data1 data2 data3 data4 LTE Rel-10 IMT-Advanced LTE Rel-10 Carrier Aggregation LTE Rel-9 N W E MIMO extensions Up to 4x4 UL and 8x8 DL LTE Rel-8 S Enhanced HetNet support Relaying
For Further information Open the 3GPP specifications......or read The Book! Available in English, Chinese, Korean and Japanese.