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2 © 2006 Nokia
Contents
Radio network evolutionHSPA conceptOFDM adopted in 3.9GScheduling techniques
3 © 2006 Nokia
3G long-term evolution – Roadmap
Radio Network EvolutionHSDPA conceptScheduling techniques
Starting point:
ExistingGSM/EDGE &
WCDMA/HSDPAinfrastructure
4 © 2006 Nokia
3G long-term evolution – Key requirements
High data rates / user througput
Improved spectrum efficiency
Significantly redused delay / latency
Packet – domain services only
(including e.g. VoIP)
Spectrum flexibility
5 © 2006 Nokia
3G LTE - Complementary radio technologiesM
obili
ty a
nd c
over
age
Vehicular
Pedestrian
Stationary
0.1 1 10 100 1000
WCDM
A Rel 4
3G Future
Evolution
Cdm
a2000 1X, EDG
E
Evolved 3G 4Gresearch target
1xEV-DO
WLAN802.11a,g
WLAN802.11b
WLAN802.11n
802.16(WiMax)
Flarion
UMTS-TDD(IP Wireless)
HSDPA
1xEV-DVData Rate (Mbps)
6 © 2006 Nokia
3G LTE – data rates
WCDMA384kbps DL384kbps ULRTT ~150msCS/PS
HSDPA14.4Mbps peak
RTT ~100msPS
HSUPA
5.7Mbps peakRTT ~50msPS
Towards 4G
2009/102007/82005/62003/4
UTRA evolution : WCDMA: 5MHz UTRA Long term evolution: Up 20 MHz BW
Approx. year of roll-out
New radio access technique
EUTRA100Mbps peak DL50Mbbps peak ULRTT ~10msPS only
3GPP Rel.99/4 Release 5 Release 6 Release 7-8 ?
2011/12
Latency improvementsCapacity enhancements
7 © 2006 Nokia
3G LTE – spectrum flexibility
• Operation in all cellular bands
- 2600 MHz, 2100 MHz, 1900 MHz, 1700 MHz, 900 MHz, 800 MHz, 450 MHz, etc
. . . as well as other frequency bands
• Efficient operation in differently-sized spectrum allocations
- Up to 20 MHz to enable very high data rates
- 5 MHz (or less) to enable migration of e.g. 2G spectrum
8 © 2006 Nokia
3G LTE – WCDMA Evolving to HSPA
What is HSPA ???HSPA – High Speed Packed AccessHSPA = HSDPA + HSUPA
9 © 2006 Nokia
3G LTE - HSDPA
Peak data rates increased to significantly higher than 2 Mbps; Theoretically exceeding 10 Mbps
Packet data throughput increased 50-100% compared to 3GPP release 4
Reduced delay from retransmissions.
Solutions• Adaptive modulation and coding - QPSK and 16-QAM
• Layer1 hybrid ARQ
• Short frame 2ms
Schedule in 3GPP• Part of Release 5
• Firstspecificationsversion completed 03/02
HSDPA
AMC
MIMO ?
Short Frame Size(TTI=2 ms)
Fast Packet Scheduling
H-ARQ
Potential features in Rel’6
Agreed features in Rel’5
10 © 2006 Nokia
3G LTE - HSDPA
• Shown code rates are examples since real values are given by transport block size as well as transmission and rate matching parameters.
• 16QAM with 15 multi-codes supports >10Mbit/s throughput. QPSK alone can support up to 5.3 Mbit/s (up to 7.2 Mbit/s by disabling coding).
• Theoretically up to 14.4 Mbit/s can be sustained but 3GPP hardware specifications do not support it (+ interference problems from e.g. synchronization channel).
QPSK
1/4
Modulation EffectiveCode rate
2/4
3/4
16
SF
16
16
16QAM2/4
3/4
16
16
1.2 Mbit/s
Data rate(10 codes)
2.4 Mbit/s
3.6 Mbit/s
4.8 Mbit/s
7.2 Mbit/s
1.8 Mbit/s
Data rate(15 codes)
3.6 Mbit/s
5.3 Mbit/s
7.2 Mbit/s
10.7 Mbit/s
600 kbit/s
Data rate(5 codes)
1.2 Mbit/s
1.8 Mbit/s
2.4 Mbit/s
3.6 Mbit/s
4/416 4.8 Mbit/s 7.2 Mbit/s2.4 Mbit/s
SF – spreading factor
11 © 2006 Nokia
3G LTE - HSUPA
Peak data rates increased to significantly higher than 2 Mbps; Theoretically exceeding 5.8 Mbps
Packet data throughput increased, through not quite high numbers expected as with HSDPA
Reduced delay from retransmissions.
Solutions• Layer1 hybrid ARQ
• Node B based scheduling for uplink
• Frame sizes 2 ms & 10 ms
Schedule in 3GPP• Part of Release 6
• Firstspecificationsversion completed 12/04
12 © 2006 Nokia
3G LTE - HSUPA
• Shown code rates are examples since real values are given by transport block size as well as transmission and rate matching parameters.
• Theoretically up to 5.76 Mbit/s can be sustained
BPSK
1/4
Modulation EffectiveCode rate
3/4
4/4
960 kbit/s
Data rate(2 codes)
1.44 Mbit/s
1.92 Mbit/s
1.92 Mbit/s
Data rate(4 codes)
2.88 Mbit/s
3.84 Mbit/s
480 kbit/s
Data rate(1 code)
720 kbit/s
950 kbit/s
2.88 Mbit/s
Data rate(6 codes)
4.32 Mbit/s
5.76 Mbit/s
13 © 2006 Nokia
Evolution to 3.9G and 4G
• The first discussions about the UTRAN (UMTS Radio Access Network) LTE -November 2004. Release 8 expected ???
• Raise the performance of WCDMA
• System performance requirements for 3.9G• Peak Data Rate up to 100 Mbps DL; 50 Mbps UL
• User Throughput• DL: 2 to 3 times to rel-6 HSDPA
• UL: 2 to 3 times to rel-6 HSUPA
• Spectrum Efficiency• DL: 3 to 4 times to rel-6 HSDPA (MIMO included)
• UL: 2 to 3 times to rel-6 HSUPA
• Mobility: Optimized up to 15 km/h, 120 km/h with high performance, cellular NW mobility supported up to 350 km/h.
14 © 2006 Nokia
OFDM for 3.9G ?
• The problems in high bit rate transmissin• Multi-path interference• Affected by impulse noise• ...
• OFDM can solve many problems that will appear in high-bitrate transmission system
• Multi-path ImmunityAchieved using cyclic-prefix > channel delay-spread
• Bandwidth (spectral) EfficiencyAchieved using sub-carrier orthogonality
• Narrowband interferenceAchieved using large number of subcarrier
• Inpulse NoiseAchieving using FFT demultiplaxing
• OFDM is adopted in 3.9G!
15 © 2006 Nokia
What is OFDM?
• OFDM – Orthogonal Frequency Division Multiplaxing• N sub-channel signals generated jointly to make sure they are orthogonal each other• In traditional FDM, signals are generated separately for each sub-carrier• So in case of frequency resource allocation, OFDM is very similar to conventional
FDM
OFDM can achieve large delay spread tolernce at high bit rate by:• Converting single bit stream into N paralel bit streams
• Symbol duration is increased, so relative delay spread decreases• Each parallel bit stream is modulated on one of N sub-carriers
• Adding a guard time to each OFDM symbol• Inter symbol interference (ISI) is avoided• Guard loss is made small (<1 dB) by choosing N large enough
16 © 2006 Nokia
OFDM cont
Total channel bandwidth
Transmitted frequency spectrum:
S/P IFFT CPM-QAM
Transmitter structure Receiver structure
S/P FFTCPRe-
moval
1 TapEqua-lizer
M-QAM
Pros• Flexible and efficient spectrum usage.• Well suited for both unicast and multicast• Robustness against narrowband interference• Excellent robustness in multipath environments
using Cyclic Prefix• Simple frequency domain equalizer based on FFT• Superior performance in MIMO applications (due to
narrow carriers)• Frequency diversity and scheduling can be easily
utilized
Cons• Severe High PAPR• Non-linear amplification destroys orthogonality
between sub-carriers• Sensitive to phase noise for low carrier
spacing• Sensitive to frequency, clock an phase offset• Requires overhead to Cyclic Prefix
17 © 2006 Nokia
OFDM cont.
• Guard time and cyclic prefix• Guard time
The guard time is chosen larger than the expected delay spread, such that multi-path components from one symbol can not interfere with the next symbol. The guard time could consist of no signal at all. However, in that case the problem of inter carrier interference (ICI) would arise. ICI is cross-talk between different sub-carriers, which mean that they are not orthogonal.
• Cyclic prefix (CP)
CP helps the signal to be protected against both ISI and ICI
CP ensures that delayed replicas of the OFDM symbol always have an integer number of cycles within the FFT interva. In this way, the orthogonality is preserved and no ICI is present in the received signal.
18 © 2006 Nokia
OFDM cont.Flexible and efficient communications systems - by applying OFDM in combination with multiple access schemes such as CDMA, TDMA or FDMA.
• In OFDM-CDMA each user is assigned with a subset of orthogonal codes, so the information symbols can be spread in either the time or frequency domain.
• In OFDM-TDMA each user occupies whole bandwidth, but differentiated by different time slots.
• OFDM-FDMA (OFDMA) scheme allocates to each user a unique group of sub-carriers, which is part of system bandwidth.
19 © 2006 Nokia
3G LTE – 4G ?
Next step after 3.9G is 4G
Research stage
Part of All – IP network
Data rates > 1 Gbps
Price/performance
20 © 2006 Nokia
Packet schedulerWhat is the task of Packet Scheduler ?
• The task of Packet Scheduler (PS) is to select a most suitable user to access the channel in order to optimise throughput, fairness, and delayperformances.
• Fast packet scheduler is the mechanism determining which user to transmit to in a given transmission time interval (TTI)
• It is a key element in the design of packet-data system as it to a large extent determines the overall behavior of the system.
21 © 2006 Nokia
Scheduling principle - HSDPA
• Fast scheduling is done directly in Node-B based on feedback information from UE and knowledge of current traffic state.
UE2
Channel quality(CQI, Ack/Nack, TPC)
Channel quality(CQI, Ack/Nack, TPC)
Data
Data
Users may be time and/or code multiplexed
New base station functions• HARQ retransmissions• Modulation/coding selection• Packet data scheduling (short TTI)
New base station functions• HARQ retransmissions• Modulation/coding selection• Packet data scheduling (short TTI)
UE1
0 20 40 60 80 100 120 140 160-202468
10121416
Time [number of TTIs]
QPSK1/4
QPSK2/4
QPSK3/4
16QAM2/4
16QAM3/4
Inst
anta
neou
s EsN
o [d
B]
22 © 2006 Nokia
UE2
Channel quality(CSI, Ack/Nack)
Channel quality(CSI, Ack/Nack)
Data
Data
UE1
Multi-user selection diversity(give shared channel to “best” users)
USER 1 Es/N0USER 2 Es/N0
Scheduled user
Packet scheduling can utilize information on the instantaneous channel
conditions for each user.
Scheduling
freqtime
23 © 2006 Nokia
HARQ
What is HARQ ?
• HARQ is a transmission scheme that combines an error detection/correction with a retransmission mechanism of the erroneous packet
• HARQ is based on Stop-And-Wait (SAW) protocol • Four types of HARQ schemes.
• Conventional ARQ • HARQ with Chase Combining• HARQ with full IR• HARQ with Partial IR
26 © 2006 Nokia
Adaptive Modulation and Coding
AMC - adjusts modulation and coding rate according to the current radio channel conditions
Modulation schemes – QPSK, 16QAM, 64 QAM …• HSDPA – higher order modulation is 16 QAM• 3.9 G - higher order modulation is 64 QAM
Link Adaptation is performed my AMC• UEs is needed to conduct LA• CQI information
27 © 2006 Nokia
Blind Scheduling Methods• Round RobinThe priority is defined as:
i=1,..,Nwhere,
is the priority of user i at time instant t is the queuing time of user i since the last channel access.
• Average C/IThe priority is defined as:
i=1,..,Nwhere,
is the average channel quality of user i at time instant t
( ) ( )tQtP ii =
( )tPi
( )tQi
( ) ( )tCtP ii =
( )tCi
Scheduling techniques
28 © 2006 Nokia
Scheduling techniques (cont.)
• Fair ThroughputThe priority is defined as:
i=1,..,N
where,represents the average offered data rate for user i at time instant t
Intelligent Scheduling Methods• Maximum C/IThe priority is defined as:
i=1,..,Nwhere,
is the channel quality of user i at time instant t
( )( )tT
tPi
i1
=
( )tTi
( ) ( )tCtP ii =
( )tCi
29 © 2006 Nokia
Scheduling techniques (cont.)
• Proportional FairThe priority is defined as:
i=1,..,N
where,is the supportable data rate for user i at time instant t
• Fast Fair ThroughputThe priority is defined as:
i=1,..,N
where,is the average supportable data rate of user i
is the max. of the average supportable data rates taken over all users j
( )( )tTtRtP
i
ii
)(=
( )tRi
( )( )
{ }⎥⎥⎦
⎤
⎢⎢⎣
⎡=
)()(max)(
tRtR
tTtRtP
i
jj
i
ii
{ })(max tRjj
)(tRi
ii
ioldi
i Rt
Tt
T 111 , +⎟⎟⎠
⎞⎜⎜⎝
⎛−= 1/ ti is called the forgetting factor
30 © 2006 Nokia
Benefit of Node-B Based Scheduling
Enables to allow more high bit rate users with faster data rate control
31 © 2006 Nokia
Frequency Domain Scheduling
New scheduling schemes for beyond 3G
• Possible only with OFDMA
• Performed for a sub-band instead of a time slot
• Could be combined with TD scheduling schemes• De-coupled time - frequency domain schedulers
• Coupled time - frequency domain schedulers
33 © 2006 Nokia
Performance comparison of PS (cont.)
Packet scheduling performance
With different forgetting factors the Proportional Fair scheduler can perform as most of the other scheduling schemes !
34 © 2006 Nokia
Performance comparison of PS (cont.)
Scheduler Scheduling rate Serve order Radio resource fairness
Round Robin Slow Sequential order Same amount of average radio resources to all UEs
Fair Throughput Slow User with lowest average offered data
rate
Fair throughput among all users
Proportional Fair Fast User with highest relative
instantaneous channel quality
Same amount of average radio resources under certain assumptions
Fast-Fair Throughput Fast User with highest equalized relative
instantaneous channel quality
Fair throughput among all users under certain assumptions