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© Ericsson AB 2008 1
Broadband Wireless Access –HSPA and LTE
Dr Stefan ParkvallSenior Specialist, Adaptive Radio AccessEricsson Research
© Ericsson AB 2008 2
Mobile Broadband
HSPAHSPA
LTELTE
TurboTurbo--3G3G
© Ericsson AB 2008 3
936 HSPA Devices from 120 Suppliers!
Source: GSMA, November 2008
© Ericsson AB 2008 4
HSPA – The Global Broadband Standard
278 Operators in 93 Countries
Source: GSMA, November 2008
So…what is HSPA and LTE?
© Ericsson AB 2008 6
Mobile Broadband is Already Here!
Rapid subscriber growth Rapid traffic growth
4 million new HSPA subscribers per month, 56 million in total
>240 million WCDMA/HSPA subscribers world wide
High speed packet data Packet data Speech
Source: GSMA and NetQB, September 2008
Data is overtaking voice......but previous cellular systems designed primarily for voice
Sept 2006 July 2008
© Ericsson AB 2008 7
HSPA and LTE = Mobile Broadband
HSPA – High-Speed Packet Access– Evolution of 3G/WCDMA – Gradually improved performance at a low additional cost– Data rates up to ~40 Mbit/s in 5 MHz
LTELTE LTELTE--AdvancedAdvanced
R99 Rel4 Rel5 Rel6 Rel7 Rel8
HSPAHSPAWCDMAWCDMA HSPA evolutionHSPA evolutionHSDPAHSDPA
Rel10
LTE – Long-Term Evolution– Significantly improved performance in a wide range of spectrum allocations– Data rates up to ~300 Mbit/s in 20 MHz– First step towards IMT-Advanced (”4G”)
Different systems – but many basic principles are similar!
© Ericsson AB 2008 8
Radio Channels and Packet Data
Radio channel quality varies...– ...distance to base station– ... random variations in the
environment
Traffic pattern varies...– ...user behavior– ...server load
Adapt to and exploit channel and traffic variations!
LTE – An Overview
© Ericsson AB 2008 10
LTE – Spectrum Flexibility
Operation in differently-sized spectrum allocations– From 1.4 MHz to 20 MHz
system bandwidth
Support for paired and unpaired spectrum allocations
UplinkDownlink
frequency
timeFDD
frequency
timeHalf-duplex FDD
(terminal-side only)
frequency
timeTDD
© Ericsson AB 2008 11
LTE – Basic Principles
Downlink – OFDMParallel transmission on large number of narrowband subcarriers
Uplink – DFTS-OFDMDFT-precoded OFDM
Benefits:– Avoid own-cell interference– Robust to time dispersion
Main drawback– Power-amplifier efficiency
Tx signal has single-carrier propertiesImproved power-amplifier efficiency– Improved battery life – Reduced PA cost– Critical for uplink
Equalizer needed Rx Complexity– Not critical for uplink
Cyclic-prefixinsertion
OFDM modulatorDFT precoder
DFT IFFTIFFT Cyclic-prefixinsertion
© Ericsson AB 2008 12
LTE – Basic Principles
Shared-channel transmission– Packet-data only– No CS support
Channel-dependent scheduling– In time and frequency
Hybrid-ARQ with soft combining
data1data2data3data4
© Ericsson AB 2008 13
Multi-antenna support– Integral part of LTE– All terminals support at least 2 Rx antennas
TXTX
MultiMulti--layer transmissionlayer transmission((““MIMOMIMO””))
Reduced Tx powerICIC– Inter-Cell Interference Coordination– To improve cell-edge performance
MBSFN– Multicast-Broadcast Single-Frequency Network
LTE – Basic Principles
© Ericsson AB 2008 14
LTE – Time-domain Structure
Frame structure type 1 for FDD (full and half duplex)
Frame structure type 2 for TDD– Similar to FS1...but with a special subframe for DL-to-UL switch
ULDL
One radio frame, Tframe = 10 ms
One subframe, Tsubframe = 1 ms
fULfDL
Subframe #0 #1 #2 #3 #4 #5 #6 #7 #8 #9
ULDL
DwPTS GP UpPTS
fDL/UL
(special subframe) (special subframe)
© Ericsson AB 2008 15
LTE – Physical Resources
Time domain structure:– 10 ms frame consisting of 10 subframes of length 1 ms– Each subframe consists of 2 slots of length 0.5 ms– Each slot consists of 7 OFDM symbols (6 symbols in case of extended CP)
Resource element (RE)– One subcarier during one OFDM symbol
Resource block (RB)– 12 subcarriers during one slot (180 kHz × 0.5 ms)
One subframe (1 ms)
One slot (0.5 ms)
One frame (10 ms)
One resource element
12 sub-carriers
TCP Tu
© Ericsson AB 2008 16
Segmentation, ARQ
Ciphering
Header Compr.
Hybrid ARQHybrid ARQ
MAC multiplexing
Antenna and resrouce mapping
Coding + RM
Data modulation
Antenna and resource mapping
Coding
ModulationAntenna and resource assignment
Modulationscheme
Sche
dule
r
Retransmission control
Priority handling, payload selection
Payload selection
RLC
PHY
PDCP
User #i User #j
Reassembly, ARQ
Deciphering
Header Compr.
Hybrid ARQHybrid ARQ
MAC demultiplexing
Antenna and resrouce mapping
Coding + RM
Data modulation
Antenna and resource demapping
Decoding
Demodulation
RLC
PHY
PDCP
MAC
Red
unda
ncy
vers
ion
IP packet IP packet
SAE bearers
Radio Bearers
Logical Channels
Transport Channel
MAC
MAC
LTE – Protocol Architecture
Packet Data Convergence Protocol– Header compression to
reduce overhead– Ciphering for security
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
© Ericsson AB 2008 17
SAE – 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
RNC RNC
to other Node Bs to other Node Bs
Dedicated channels
NodeBUE
PSTN Internet
Core Network
LTELTE HSPAHSPA
eNodeBUE
Internet
Core Network
S1 S1
X2
© Ericsson AB 2008 18
Shared-Channel Transmission
Dedicated channel– User resources assigned at ”call
setup”– Independent of instantaneous traffic
situation
Shared channel– Dynamic sharing of common
resource– Adapts to instantaneous traffic
situation
© Ericsson AB 2008 19
Rate Control
Reliable reception requires a certain Eb/N0
How to control Eb?– Eb = P•T
Cha
nnel
Q
ualit
y
TxP
ower
Dat
a R
ate
Power Control
Dat
a R
ate
Cha
nnel
Q
ualit
y
TxP
ower
Rate Control
Rate control more efficient than power control!
Varying instantaneous data rate acceptable for packet-data services– Rapid – tracks fast fading
© Ericsson AB 2008 20
Rate Control
Data rate controlled through...
...different channel coding rates– Advantageous channel conditions high code rate– Code rates from 1/3 to ~1
...different modulation schemes– Advantageous channel conditions higher-order modulation
...different multi-antenna schemes– Number of transmission layers selected to match channel rank
QPSK 16QAM 64QAM
© Ericsson AB 2008 21
Channel-dependent Scheduling
Scheduling determines at each time instant…– …to whom to assign the shared channel– …which data rate to use
Basic idea: transmit at fading peaks– May lead to large variations in data rate between users– Tradeoff: fairness vs cell throughput
Cha
nnel
Qua
lity User #1
User #2
User #3
Time#1 #3 #2 #3 #1
Effective channel variations seen by the base station
© Ericsson AB 2008 22
Channel-dependent Scheduling
Round Robin (RR)– Cyclically assign the channel to users without taking channel
conditions into account– Simple but poor performance
Max C/I– Assign the channel to the user with the best absolute channel
quality– High system throughput but not fair
Proportional Fair (PF)– Assign the channel to the user with the best relative channel
quality– High throughput, fair
Rad
io L
ink
Qua
lity
Time
Rad
io L
ink
Qua
lity
Time
Rad
io L
ink
Qua
lity
Time
© Ericsson AB 2008 23
data1data2data3data4
TimeFrequency
User #1 scheduled
User #2 scheduled
1 ms
180 kHz
Time-frequency fading, user #1
Time-frequency fading, user #2
Channel-dependent Scheduling
HSPA – channel-dependent scheduling in time-domain only
LTE – channel-dependent scheduling in time and frequency domains
© Ericsson AB 2008 24
Hybrid-ARQ with Soft Combining
Retransmsision of erroneously received packets– Fast (8 ms roundtrip time) no disturbance of TCP behavior
Soft combining of multiple transmission attempts– Soft combining improved performance
Hybrid-ARQ retransmissions complemented by RLC retransmissions
Process transport block 3 Process transport block 5
Process #0Process #1
Process #2
1 12 3 5 14
Process transport block 2 Process transport block 4
Process transport block 1 Process transport block 1 Process transport block 1
Hybrid-ARQprotocol
To RLC for in-sequence delivery
Block 2
Process #7
Block 3 Block 4 Block 5 Block 1
© Ericsson AB 2008 25
R=1
redundancy version 1
Initial transmission
Transmitted bits
Bits input to decoder
Resulting code rate
Accumulated energy
Eb
CRC insertion,Turbo coding, rate 1/3
Data
Puncturing to• generate different redundancy versions
• match the number of coded bits to the channel
redundancy version 2
R=1/2
First retransmission
2Eb
redundancy version 3
R=1/3
Second retransmission
3Eb
Hybrid ARQ with Soft Combining
Incremental redundancy
R=1/3
Third retransmission
redundancy version 1
4Eb
© Ericsson AB 2008 26
Interaction with RLC
Why two retransmission mechanisms, RLC and hybrid-ARQ?– Answer: difference in feedback signaling
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, too high for TCP)
RLC– Reliable feedback (sent in same manner as data)– Multi-bit feedback less frequent longer delay
Hybrid-ARQ and RLC complement each other
Segmentation, ARQARQ
Hybrid ARQHybrid ARQ
MAC multiplexing
RLC
MAC
© Ericsson AB 2008 27
Multi-antenna transmission
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
TX
© Ericsson AB 2008 28
Multi-antenna transmission
One, two, or four antenna ports
Multiple antenna ports multiple time-frequency grids
Each antenna port defined by an associated reference signal
Single-antenna transmisson Multi-antenna transmisson
TX
© Ericsson AB 2008 29
Multi-antenna transmission
Spatial Multiplexing – Multiple parallel data streams Higher data rates– One or two code words– Number of layers ≤ Number of antenna ports
Transmit Diversity (”open-loop”)– Transmission of same information from multiple antenna ports Diversity– One code word– Number of layers = Number of antenna ports
Layermapping Precoding
Up to four layers
RE mappingUp to four
antenna ports
RE mapping
One or two code words
Multi-antenna processing
TX
© Ericsson AB 2008 30
LTE – Example of Testbed Results20 MHz, 2x2 MIMO
Throughput– Max 154 Mbit/s– Mean 78 Mbit/s– Min 16 Mbit/s
Terminal speed – Max 45 km/h– Mean 16 km/h– Min 0 km/h
Distance– Max 710 m– Mean 360 m– Min 50 m
12
23
37
54
74
97
123
154
Ericsson Head OfficeEricsson Head Office
LTE Testbed2007
© Ericsson AB 2008 31
Summary
Adapt to and exploit– variations in radio channel quality– variations in the traffic pattern
…instead of combating them!
Traffic pattern is time varying
Radio channel quality is time varying
Shared-channel transmission Channel-dependent scheduling Rate adaptation Hybrid ARQ with soft combining
Basic Tools
TX
Multi-antenna transmission
Work in 3GPP
© Ericsson AB 2008 33
3G Evolution
R99 Rel4 Rel5 Rel6 Rel7 Rel8
LTELTE
HSPAHSPAWCDMAWCDMA HSPA evolutionHSPA evolutionHSDPAHSDPA
HSPA evolution– gradually improved performance at a low additional cost
in 5MHz spectrum allocation
LTE– significantly improved performance in a wide range of spectrum allocations– further evolved into IMT-Advanced
LTE AdvancedLTE Advanced
Rel10
1999 2002 2005 2007 2008
© Ericsson AB 2008 34
3GPP Organization
PCGProject Coordination Group
TSG RAN
RAN WG1Radio L1
RAN WG2L2/L3
RAN WG3NW protocols
RAN WG4Core, Perf req.
RAN WG5MT conf. testing
WCDMA/HSPAand LTE
TSG GERAN
GERAN1Radio
GERAN2Protocol
GERAN3Testing
GSM/GPRS
TSG SA
SA1Services
SA2Architecture
SA3Security
SA4Codec
SA5Telecom Mgmt.
ServicesOverall System
TSG CT
CT1MM/CC/SM
CT3Interworking
External NWs
CT4MAP/GTP/BCH/SS
CT5Open Service Access
CT6Smart Card Apl.
Core Network
© Ericsson AB 2008 35
Standardization – a Flying Circus?
RAN1 meetings held ~8 times a year– Meetings run from Monday to Friday– Held in various countries in Europe, North America, and Asia
Meeting schedule 2007– January 15-19, Sorrento Italy– February 12-16, St Louis USA– March 26-30, St Juliens Malta– April 17-20, Beijing China– May 7-11, Kobe Japan– June 25-29, Orlando USA– August 20-24, Athens Greece– October 8-12, Shanghai China– November 5-9, Seoul Korea
© Ericsson AB 2008 36
Typical RAN1 Meeting
Approx 200 delegates attending and ~550 documents submitted...Number of Contributions per Agenda Item
0
20
40
60
80
100
120
Appr
oval
of t
he a
gend
a
Appr
oval
of t
he m
inut
es fr
om p
revi
ous
mee
tings
Liai
son
stat
emen
t han
dlin
g
Mai
nten
ance
of R
elea
se 9
9 –
Rel
ease
7
Evol
ved
UTR
A an
d U
TRAN
TDD
Fra
me
Stru
ctur
e
Fina
lizat
ion
of T
S 36
.211
Dow
nlin
k re
fere
nce
sign
als
Upl
ink
refe
renc
e si
gnal
s
Dow
nlin
k C
ontro
l Sig
nallin
g
Upl
ink
Con
trol S
igna
lling
Map
ping
of v
irtua
l res
ourc
e bl
ocks
to p
hysi
cal r
esou
rce
bloc
ks
Bit s
cram
blin
g se
quen
ces
for U
L/D
L tra
nsm
issi
ons
RAC
H
Fina
lizat
ion
of T
S 36
.212
Fina
lizat
ion
of T
S 36
.213
Tim
ing
sync
hron
izat
ion
UL/
DL
Pow
er C
ontro
l
Inte
r-ce
ll Int
erfe
renc
e C
oord
inat
ion
RAC
H ti
min
g an
d pr
eam
ble
sequ
ence
sel
ectio
n
UE
Proc
edur
es fo
r dow
nlin
k sh
ared
cha
nnel
UE
Proc
edur
es fo
r upl
ink
shar
ed c
hann
el
Fina
lizat
ion
of T
S 36
.214
Fina
lizat
ion
of T
S 36
.201
UE
Cat
egor
ies
Com
bina
tion
of H
ighe
r Ord
er M
odul
atio
n an
d M
IMO
in H
SDPA
(FD
D)
Enha
nced
Upl
ink
for C
ell_
FAC
H S
tate
in F
DD
Stud
y Ite
m o
n Sy
nchr
oniz
ed E
-DC
H
© Ericsson AB 2008 37
Standardization in Practice
Contribution driven
Decision by consensus– Coffee breaks important part of meetings (off-line)
Good relations important– Social relations across cultural borders– Mutual respect and co-operation
One week meetings Long meeting days
© Ericsson AB 2008 38
For further details...
Thank You for the Attention!