3G long-term evolution by Stanislav Nonchev e-mail : stanislav.nonchev@tut.fi 1 2006 Nokia
Contents Radio network evolution HSPA concept OFDM adopted in 3.9G Scheduling techniques 2 2006 Nokia
3G long-term evolution Roadmap Radio Network Evolution HSDPA concept Scheduling techniques Starting point: Existing GSM/EDGE & WCDMA/HSDPA infrastructure 3 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 4 2006 Nokia
3G LTE - Complementary radio technologies Vehicular Flarion Evolved 3G 4G research target Mobility and coverage Pedestrian Cdma2000 1X, EDGE WCDMA Rel 4 1xEV-DV 1xEV-DO HSDPA 3G Future Evolution 802.16 (WiMax) Stationary UMTS-TDD (IP Wireless) WLAN WLAN 802.11b802.11a,g WLAN 802.11 n 0.1 1 10 100 1000 Data Rate (Mbps) 5 2006 Nokia
3G LTE data rates WCDMA 384kbps DL 384kbps UL RTT ~150ms CS/PS HSDPA 14.4Mbps peak RTT ~100ms PS HSUPA 5.7Mbps peak RTT ~50ms PS EUTRA 100Mbps peak DL 50Mbbps peak UL RTT ~10ms PS only New radio access technique Towards 4G UTRA evolution : WCDMA: 5MHz UTRA Long term evolution: Up 20 MHz BW 3GPP Rel.99/4 Release 5 Release 6 Release 7-8? 2003/4 2005/6 2007/8 Approx. year of roll-out Latency improvements Capacity enhancements 2009/10 2011/12 6 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 7 2006 Nokia
3G LTE WCDMA Evolving to HSPA What is HSPA??? HSPA High Speed Packed Access HSPA = HSDPA + HSUPA 8 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 H-ARQ AMC Layer1 hybrid ARQ Short frame 2ms Fast Packet Scheduling Agreed features in Rel 5 Schedule in 3GPP Part of Release 5 Short Frame Size (TTI=2 ms) HSDPA Potential features in Rel 6 Firstspecificationsversion completed 03/02 MIMO? 9 2006 Nokia
3G LTE - HSDPA Modulation SF Effective Code rate Data rate (5 codes) Data rate (10 codes) Data rate (15 codes) 16 1/4 600 kbit/s 1.2 Mbit/s 1.8 Mbit/s QPSK 16 16 2/4 3/4 1.2 Mbit/s 1.8 Mbit/s 2.4 Mbit/s 3.6 Mbit/s 3.6 Mbit/s 5.3 Mbit/s 16 4/4 2.4 Mbit/s 4.8 Mbit/s 7.2 Mbit/s 16QAM 16 16 2/4 3/4 2.4 Mbit/s 3.6 Mbit/s 4.8 Mbit/s 7.2 Mbit/s 7.2 Mbit/s 10.7 Mbit/s 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). 10 2006 Nokia SF spreading factor
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 11 2006 Nokia
3G LTE - HSUPA Modulation Effective Code rate Data rate (1 code) Data rate (2 codes) Data rate (4 codes) Data rate (6 codes) 1/4 480 kbit/s 960 kbit/s 1.92 Mbit/s 2.88 Mbit/s BPSK 3/4 720 kbit/s 1.44 Mbit/s 2.88 Mbit/s 4.32 Mbit/s 4/4 950 kbit/s 1.92 Mbit/s 3.84 Mbit/s 5.76 Mbit/s 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 12 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. 13 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 Immunity Achieved using cyclic-prefix > channel delay-spread Bandwidth (spectral) Efficiency Achieved using sub-carrier orthogonality Narrowband interference Achieved using large number of subcarrier Inpulse Noise Achieving using FFT demultiplaxing OFDM is adopted in 3.9G! 14 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 15 2006 Nokia
OFDM cont Transmitted frequency spectrum: Total channel bandwidth M- QAM S/P IFFT CP CP Removal S/P FFT 1 Tap Equa -lizer M- QAM Pros Transmitter structure 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 Receiver structure 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 16 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. 17 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 subcarriers, which is part of system bandwidth. 18 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 19 2006 Nokia
Packet scheduler What 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 delay performances. 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. 20 2006 Nokia
Scheduling principle - HSDPA Channel quality (CQI, Ack/Nack, TPC) UE1 Channel quality (CQI, Ack/Nack, TPC) UE2 Data Data 16 14 12 10 8 6 4 2 0-2 0 20 40 60 80 100 120 140 160 Time [ number of TTIs] 16QAM3/4 Instantaneous EsNo [db] 16QAM2/4 QPSK3/4 QPSK2/4 QPSK1/4 New New base base station station functions HARQ HARQ retransmissions Modulation/coding selection Packet Packet data data scheduling (short (short TTI) TTI) Users may be time and/or code multiplexed Fast scheduling is done directly in Node-B based on feedback information from UE and knowledge of current traffic state. 21 2006 Nokia
Scheduling Channel quality (CSI, Ack/Nack) Packet scheduling can utilize information on the instantaneous channel conditions for each user. UE1 Data Multi-user selection diversity (give shared channel to best users) Channel quality (CSI, Ack/Nack) Data Scheduled user UE2 USER 2 Es/N0 time USER 1 Es/N0 freq 22 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 23 2006 Nokia
24 2006 Nokia HARQ : Chase Combining
25 2006 Nokia HARQ: Incremental Redundancy
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 26 2006 Nokia
Scheduling techniques Blind Scheduling Methods Round Robin The priority is defined as: P () t Q ( t) where, P i () t () t Qi i = i i=1,..,n is the priority of user i at time instant t is the queuing time of user i since the last channel access. Ci Average C/I The priority is defined as: P () t C i ( t) i = where, () t i=1,..,n is the average channel quality of user i at time instant t 27 2006 Nokia
Scheduling techniques (cont.) Fair Throughput The priority is defined as: 1 P() t i=1,..,n i = T i where, Ti () t () t represents the average offered data rate for user i at time instant t Intelligent Scheduling Methods Maximum C/I The priority is defined as: P() t C ( t) i=1,..,n C i i = where, () t i is the channel quality of user i at time instant t 28 2006 Nokia
Scheduling techniques (cont.) Proportional Fair The priority is defined as: Ri ( t) P() t i=1,..,n i = T i where, R i () t () t 1 1 Ti = 1 Told, i + Ri t 1/ ti is called the forgetting factor i ti is the supportable data rate for user i at time instant t Fast Fair Throughput The priority is defined as: R ( ) max R ( t) i t j j Pi () t = T i () t Ri ( t) where, R i max (t { } i=1,..,n is the average supportable data rate of user i { ( t) } j )R j is the max. of the average supportable data rates taken over all users j 29 2006 Nokia
Benefit of Node-B Based Scheduling Enables to allow more high bit rate users with faster data rate control 30 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 31 2006 Nokia
Performance comparison of PS Packet scheduling performance 32 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! 33 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 Proportional Fair Fast User with highest relative instantaneous channel quality Fast-Fair Throughput Fast User with highest equalized relative instantaneous channel quality Fair throughput among all users Same amount of average radio resources under certain assumptions Fair throughput among all users under certain assumptions 34 2006 Nokia
For Further Information WCDMA for UMTS : Radio Access for Third Generation Mobile Communications by Harry Holma, Antti Toskala www.3gpp.org 35 2006 Nokia