LTE and next generation mobile networks

Transcription

1 LTE and next generation mobile networks Luca Reggiani Dipartimento di Elettronica, Informazione e Bioingegneria Politecnico di Milano

2 Outline 1. The evolution of cellular networks 2. LTE Standard status Enabling technologies Network architecture System architecture Physical layer Radio planning 3. LTE-Advanced 4. Next generation networks

3 The evolution of cellular networks 1/5 Mobile traffic forecast Combined annual growth rate [Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, ]

4 The evolution of cellular networks 2/5 Mobile traffic forecast [Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, ]

5 The evolution of cellular networks 3/5 The mobile technology generations 2G 3G 4G 5G GSM FDMA / TDMA GPRS EDGE UMTS CDMA HSPA HSPA+ LTE OFDMA LTE-A OFDMA? Macro-cells R = 1-20 km Micro-cells in dense urban areas Macro-cells R = 1 20 km Increased use of micro-cells and DAS Macro-cells R = 1 20 km Hetnets Data rate kbit/s Data rate 1 10 Mbit/s Data rate Mbit/s

6 The evolution of cellular networks 4/5 The mobile technology generations ITU key features of IMT (International Mobile Telecommunications) Advanced (4G) - a high degree of commonality of functionality worldwide while retaining the flexibility to support a wide range of services and applications in a cost efficient manner - compatibility of services within IMT and with fixed networks - capability of interworking with other radio access systems - high quality mobile services - user equipment suitable for worldwide use - user-friendly applications, services and equipment - worldwide roaming capability - enhanced peak data rates to support advanced services and applications (100 Mbit/s for high and 1 Gbit/s for low mobility). [

7 The evolution of cellular networks 5/5 The mobile technology generations 5G (2020?) No official definition for what comes beyond 4G is available yet. Let us guess - Further increase in network capacity, spectral efficiency, energy efficiency - pervasive user connectivity - high service quality - User personalization - High context awareness

8 LTE Standard status 1/3 Long Term Evolution Enhancements including CoMP, HetNets LTE-Advanced 1 Gbps with 40 MHz, 8x8 Small enhancements including VoIP, femto handovers, LTE 150 Mbps with 20 MHz, 2x2 Rel see Work Plan for Features in each Release Spec version number (see note 4) [ Functional freeze date, indicative only (see note 3) Rel x.y Stage 1 freeze March 2013 Stage 2 freeze December 2013 Stage 3 freeze June 2014 (RAN protocols: September 2014) Rel x.y Stage 1 freeze September 2011 Stage 2 freeze March 2012 Stage 3 freeze September 2012 (core network protocols stable December 2012, radio access protocols stable March though performance parts of RAN work items may not be complete before June 2013) Rel x.y Stage 1 freeze March 2010 Stage 2 freeze September 2010 Stage 3 freeze March 2011 (protocols stable three months later) Rel-9 9.x.y Stage 1 freeze December 2008 Stage 2 freeze June 2009 Stage 3 freeze December 2009 Rel-8 8.x.y Stage 1 freeze March 2008 Stage 2 freeze June 2008 Stage 3 freeze December 2008

9 LTE Standard status 2/3 "Stage 1" refers to the service description from a service-user s point of view. "Stage 2" is a logical analysis, breaking the problem down into functional elements and the information flows amongst them across reference points between functional entities. "Stage 3" is the concrete implementation of the protocols appearing at physical interfaces between physical elements onto which the functional elements have been mapped. ITU-T (originally CCITT) method for categorizing specifications (Recommendation I.130). [

10 LTE Standard status LTE-A 3/3 Long Term Evolution - Advanced Release 10 Higher capacity for fulfilling ITU 4G requirements - Increased peak data rate, DL 3 Gbps, UL 1.5 Gbps - Higher spectral efficiency, from a maximum of 16 bps/hz in R8 to 30 bps/hz in R10 - Increased number of simultaneously active subscribers - Improved performance at cell edges (e.g. for DL 2x2 MIMO at least 2.40 bps/hz/cell) Main new functionalities introduced in LTE-Advanced - Carrier Aggregation (CA) - Enhanced use of multi-antenna techniques (MIMO) - Support for Relay Nodes (RN). [

11 Enabling technologies 1/1 Network architecture More functionality in the base station (enodeb) Packet switched domain System architecture Channel dependant scheduling Physical layer OFDMA in downlink SC-FDMA in uplink MIMO (multiple antenna technologies) Radio Planning Frequency Reuse 1 (No frequency planning) Fractional frequency reuse (FFR)

12 LTE network architecture 1/2 MME / S-GW EPC MME / S-GW E-UTRAN: enbs providing the user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol for the UEs. enbs are interconnected each other by means of X2 interface. enb #1 enbs are connected by means of the S1 interface to the core network EPC (Evolved Packet Core). MME = Mobility Management Entity S-GW = Serving Gateway. enb #1 enb #2 UE enbs : radio resources management, handover, scheduling UL/DL, phy layer functions (coding, decoding, modulation, demodulation, interleaving, de-interleaving, ), H-ARQ UE

13 LTE network architecture 2/2 Evolution w.r.t. GSM/UMTS The Evolved Packet System (EPS) is purely IP based Real time and datacom services will be carried by the IP protocol GGSN CN E-UTRAN LTE radio access network SGSN Flat network of evolved NodeB (enb base stations) RNC UTRAN Improve MAC efficiency and velocity (UE <-> enb) Improve scheduling efficiency speed up connection set-up reduce handover time Increase BS organization and cooperation capabilities UE NB #1 NB #2 Universal Terrestrial Radio Access Network SGSN = Serving GPRS Support Node (HLR) GGSN = Gateway GPRS Support Node

14 LTE system architecture 1/2 Protocol stack PDCP = Packet Data Convergence Protocol RLC = Radio Link Control MAC = Medium Access Control RRC = Radio Resource Control RBC = Radio Bearer Control RAC = Radio Admission Control CMC = Connection Mobility Control enb Inter cell RRM RBC CMC MME Mobility mngt Idle state handling RAC Measurements SAE BC UE PDCP RLC MAC PHY Scheduler RRC PDCP RLC MAC PHY Layer 3 Layer 2 Layer 1 S-GW Mobility anchor. PDN-GW UE IP address allocation Packet filtering

15 LTE system architecture 2/2 Scheduler The scheduler is a key component for fast and efficient radio resource utilization OFDM + fast update rate allow advanced scheduling Periodically (each TTI = 1ms) the enb scheduler adapt the UE Modulation and Coding scheme (AMC) according to UE radio quality (CQI report). AMC is completed by HARQ (Hybrid Automatic Repeat Request) with soft-combining. The scheduler address UE QoS requirements (especially delay sensitive services or high data peak rates). The enb transmits information on allocated resources to UEs (either downlink or uplink). Channel quality information: CQI (Channel Quality Indicators), PMI (Precoding Matrix Indicators), RI (Rank Indicators). Aperiodic / Periodic, Wideband / Sub-band.

16 Physical layer 1/16 Basic parameters FDD: Timeframe structure 1 TDD: Timeframe structure 2 Frequency flexibility and bandwidth scalability Carriers for FDD and TDD: Peak data rates: Reduced latency: Bandwidths: 1.4, 3, 5, 10, 15, 20 MHz MHz, 1.4 GHz, GHz, GHz 75 (UL) / 300 (DL) Mbps < 10 ms Downlink resource allocation: Uplink resource allocation: OFDMA x frame SC-OFDM x frame The downlink and uplink (time, frequency) grids are composed by resource blocks of 12 sub-carriers (frequency spacing = 15 khz) x 0.5 ms ( = 1 timeslot).

17 Physical layer 2/16 Italy Bandwidth assignments in Sept. 2011: MHz: 2 blocks (1 block = 5 MHz FDD) to Vodafone Italia, Telecom Italia, Wind Telecomunicazioni MHz: 1 block (1 block = 5 MHz FDD) to Vodafone Italia, Telecom Italia, 3 Italia MHz: no offers MHz: 4 blocks (1 block = 5 MHz FDD) to 3 Italia and Wind Telecomunicazioni, 3 blocks to Telecom Italia and Vodafone Italia.

18 Physical layer 3/16 Time organization Frame structure [10 TTI] TTI = 1 ms 2 time-slots TTI frame slot sym 6/7 OFDM symbols Sub carrier spacing = 15 khz CP length = s / 16.7 s Modulation (DL) QPSK, 16-QAM, 64-QAM (UL) QPSK, 16-QAM, (64-QAM)

19 Physical layer Downlink OFDMA 4/16 OFDMA: Orthogonal Frequency Division Multiple Access The signal is based on OFDM, i.e. a superposition of N orthogonal channels, each one associated to a sub-carrier. A resource block (RB) occupies 12 adjacent sub-carriers. Sub-carriers are separated by a fixed frequency spacing f = 15 khz Symbol duration T = 1/ f = s Each symbol is completed by the cyclic prefix (CP), for a duration = T + T CP = s Normal cyclic prefix T CP = 5.2 s, 4.7 s Extended cyclic prefix T CP = 16.7 s Bandwidth [MHz] N (RB) 72 (6) 180 (15) 300 (25) 600 (50) 900 (75) 1200 (100) DL band [MHz] UL band [MHz] Sampling rate [Mbaud] 0.5 x x x x x x 3.84 FFT size

20 Physical layer Review on OFDM OFDM basics: signal in the frequency domain S(f) f*t

21 Physical layer Review on OFDM OFDM basics: signal in the time domain High PAPR (Peak to average power ratio) 4 s(t) t/t

22 Physical layer Review on OFDM OFDM basics: discrete implementation DFT / IDFT correspondence between time and frequency samples

23 Physical layer Review on OFDM OFDM basics: cyclic prefix 8 6 Cyclic prefix Symbol 4 real(s(t)) Interference of symbol t/t CP 0 Symbol 0 CP 1 Symbol 1 CP 2 Symbol 2

24 Physical layer Review on OFDM OFDM basics: advantages drawbacks - High spectral efficiency. - Digital implementation by means of IFFT/FFT blocks. - Simple channel equalization - Flexibility - Linear power amplifiers. - Cyclic prefix causes a rate and energy efficiency loss. - Sensitivity to phase noise - Adequate frequency, time symbol and sampling frequency synchronization

25 Physical layer Uplink SC-FDMA 5/16 SC-FDMA Single Carrier FDMA OFDM has a high PAPR (Peak Average Power Ratio) This requires highly nonlinear power amplifiers, i.e. energy consuming and expensive at UE side Reduced PAPR means lower RF hardware requirements. SC-FDMA combines the PAPR of single-carrier system with the multipath resistance and flexible subcarrier frequency allocation of OFDM. While OFDMA transmits data in parallel across multiple subcarriers, SC-FDMA transmits data in series employing multiple subcarriers

26 Physical layer Uplink SC-FDMA 6/16 OFDMA : parallel transmission of multiple symbols TX S / P IFFT P/S R (sym/s) a n s k + CP D/A RF up conv. f C SC- FDMA : modulation symbols go through another FFT block before IFFT TX R (sym/s) FFT (n) IFFT P/S + CP D/A RF up conv. a n s k f C This process reduces PAPR considerably.

27 Physical layer Downlink / Uplink Frame - FDD 7/16 Radio frame 1 = 10 ms Subframe (TTI) Slot number KHz resource block (RB) 12 sc.. N subcarriers.. resource element = 1 sub-carrier x 1 OFDMA symbol time 1 RB = 12 sc x 7 OFDMA symbols (normal CP) 12 sc x 6 OFDMA symbols (extended CP) A user is assigned a set of resource blocks.

28 Resource Element Physical layer Resource block 8/16 Each RB has 84 or 72 resource elements. 12 subcarriers = 180 khz Normal CP Extended CP 7 symbols = 0.5 ms 6 symbols = 0.5 ms Each resource element is loaded by 2, 4 or 6 bits (QPSK, 16-QAM, 64-QAM). The assignment for an UE of an RB corresponds to 144 ksps or 168 ksps or kbit/s

29 Physical layer Downlink / Uplink Frame - FDD 9/16 Coding: Turbo parallel code, R = 1/3 Tailbiting convolutional code, R = 1/3 Rates: 0.35, 0.45,, 0.95 associated to QPSK, 16-QAM, 64-QAM Control channels, reference symbols. PSCH = Primary Synchronization Channel SSCH = Secondary Synchronization Channel PBCH = Physical Broadcast Channel RS = cell-specific Reference Signal (for each Tx antenna) PCFICH = Physical Control Format Indicator Channel PHICH = Physical Hybrid ARQ Indicator Channel PDCCH = Physical Downlink Control Channel [see

30 Physical layer Downlink / Uplink Frame - TDD 10/16 Subframe Radio frame 2 = 2 half-frames = 2 x 5 ms Slot number 0 1 resource block (RB) resource element = 1 sub-carrier x 1 SC-OFDM symbol time Several uplink/downlink divisions of subframes N subcarriers Subframe number 0 DwPTS, GP, UpPTS 4 9 DwPTS, GP, UpPTS.. DwPTS = Downlink Pilot Time Slot GP = Guard Period UpPTS = Uplink Pilot Time Slot

31 Physical layer TX architecture 11/16 Main operations for downlink signal generation Encoding Scrambling Modulation Element mapper OFDM modulator.. Layer mapper Precoder.. Encoding Scrambling Modulation Element mapper OFDM modulator x multiple antennas

32 Physical layer 12/16 Multiple antennas Transmit diversity [Open loop] 2 ant. SFBC (Space Frequency Block Code) 4. ant. SFBC+FSTD (Frequency Shift Transmit Diversity) Each layer corresponds to an antenna Layer mapper L1 Precoder 1/ 2 -Im L2 -Re 1/ 2

33 Physical layer Multiple antennas 13/16 Encoding strategy from space time code 2 x 2 Antenna 1 Antenna 2 Time (or frequency) 1 x 1 x 2 Time (or frequency) 2 -x * 2 x * 1 [Alamouti s scheme]

34 Physical layer Review on multiple antennas Diversity principle

35 Physical layer Review on multiple antennas Alamouti s scheme: diversity at the transmitter

36 Physical layer Review on multiple antennas MIMO systems and capacity multiplication

37 Physical layer 14/16 Multiple antennas Spatial mutiplexing SU-MIMO [DL] Open loop [from UE: RI + CQI] 2 x 2 [Capacity x2 during a subframe] 4 x 4 [Capacity x2, x3, x4] Closed loop [from UE: RI + CQI + PMI] 2 x 2 [Capacity x1 or x2] 4 x 4 [Capacity x1, x2, x3, x4] N. layers <= N. antennas

38 Physical layer Multiple antennas 15/16 Spatial mutiplexing MU-MIMO [typically 2 users] MU-MIMO is transparent to the UEs. Each layer is addressed to one UE More users share the same RB! Precoding provides a beamforming effect MU-MIMO increases cell capacity SU-MIMO increases peak UE data rate

39 Physical layer 16/16 Performance Rel. 8 LTE Performance Verification [T. Nakamura (3GPP TSG RAN Chairman), «3GPP LTE Radio Access Network», GSMA Americas Conf., June 2010]

40 Network planning principles 1/2 Frequency reuse N = Radio planning 1 tier R M A B C D E F D N = 7 D/R = 3N

41 Radio planning 2/2 Network planning principles Channel model attenuation Channel model: multipath fading Link performance S/I) MIN Statistical distribution of S/I R, N Modulation Encoding Diversity... Link quality: BER Linkk quality: P OUT In LTE N is supposed to be 1 FFR static and dynamic fractional frequency reuse Dynamic: resource allocation in terms of power and bandwidth are coordinated between neighboring cells. F 1 F 0 F 3 F1 F0 F 3 F 2 F 2

42 LTE-Advanced 1/2 Main objectives - Peak data rate: DL 3 Gbps UL 1.5 Gbps 1 Gbps data rate will be achieved by 4-by-4 MIMO and transmission bandwidth wider than approximately 70 MHz - Peak spectrum efficiency: 30 bps/hz in Rel. 10 DL: Rel. 8 LTE satisfies IMT-Advanced requirement (15 bps/hz) UL: Need to double from Release 8 to satisfy IMT-Advanced requirement (3.75 bps/hz vs 6.75) - Increased number of simultaneously active subscribers - Improved performance at cell edges

43 LTE-Advanced 2/2 Main features - Improved MIMO: improved codebook/feedback for MU-MIMO (up to 50% spectral efficiency gain), added 8x8 DL and 4x4 UL [Rel. 10] - CA: Carrier aggregation to achieve wider bandwidth. Support of spectrum aggregation for peak data rate and spectrum flexibility. - Relay Nodes (RN) - Coordinated multipoint transmission and reception (CoMP) for cell-edge user throughput, coverage, deployment flexibility [Rel. 11]

44 Next generation networks 1/8 Key factors Cooperation CoMP: Coordinated multipoint transmission and reception Multiple transmit and receive antennas from multiple sites Enhance the received signal quality and decrease the received interference 3GPP CoMP techniques classification - Coordinated scheduling and coordinated beamforming (CS/CB) Multiple coordinated TPs share only CSI for multiple UEs, while data packets are available only at one TP. - Joint transmission (JT) The same data transmission from multiple coordinated TPs with appropriate beamforming weights. - Transmission Point selection (TPS) Transmission of beamformed data for a given UE is performed at a single TP at each time instance, while the data is available at multiple coordinated TPs.

45 Next generation networks Key factors 2/8 Broadcast MIMO Network MIMO UE UE enb 1 UE enb UE UE UE enb 2 enb 3

46 Next generation networks Key factors 3/8 Heterogeneous networks Small cells complement macro cells for improving throughput and coverage. Macrocell [N. users > 256] The approach can include the use of micro-cells, pico-cells, low-power remote radio units (RRH, DAS) and other technologies (e.g. Wi-Fi). Microcells [N. users > 100] Picocells [N. users = ] Femtocells [N. users < 10-30]

47 Next generation networks Key factors 4/8 Relay nodes (RN) RN improve the possibility for efficient heterogeneous network planning. RN is connected to the Donor Macro Base Station (DeNB in LTE) via a radio interface (Un in LTE-A). In the Donor cell, radio resources are shared among UEs served directly by the Donor BS and the Relay Nodes. In general RNs work in a frequency or time division scheme managed by the donor BS. Macrocell DeNB UE1 UE2 RN2 RN1

48 Next generation networks Key factors 5/8 SON - Self Organizing Networks SON is a set of solutions and technologies for making planning (e.g. frequency reuse), configuration ("plug-and-play" paradigm), management (e.g. a SON establishes neighbor relations automatically), optimization (e.g. BS parameters), healing (e.g. in case of a BS failure) of mobile radio access networks easier, more efficient and less expensive.

49 Next generation networks Key factors 6/8 Centralized processing The trend for next generation networks is to separate RF function in the remote radio heads (RRH) from baseband processing, performed in central units (CU). RF signals are down converted, digitalized and transmitted to the CU for demodulation. BBU B1 RRH A1 RRH A2 RRH A3 RRH B1 RRH B2 RRH B3 MUX / DEMUX BBU B2 BBU B3 BBU A1 BBU A2 BBU A3 Baseband central processing The existing solutions are CPRI (Common Public Radio interface) or OBSAI (Open Base Station Architecture Initiative).

50 Next generation networks Key factors 7/8 DAS Distributed antenna systems They are an evolution of RRHs since they represent the implementation of a more integrated, at the physical layer, system with multiphe RRHs that share baseband processing. Transport networks In this context, front-hauling, as the last mile of radio access networks, is a crucial issue for next generation networks. RRH Fronthaul network CU Backhaul network Internet

51 Next generation networks Key factors 8/8 HW Dense networks with smaller cells More spatial dimensions (antennas) More connections SW More cooperation Automatic and adaptive configurations according to the radio environment (channels, traffic, ) More Smartness

52 References [1] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; General description". [2] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation " [3] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding" [4] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures" [5] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Services provided by the physical layer" [6] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio access capabilities" [7] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Acces Control (MAC) protocol specification" [8] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control (RLC) protocol specification" [9] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data Convergence Protocol (PDCP) specification" [10] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC) protocol specification". Books [*] E. Dahlman, S. Parkvall, J.Sköld,P. Beming, «3G Evolution: HSPA and LTE for Mobile Broadband», Academic Press, [*] H. Holma, A. Toskala, «LTE for UMTS: Evolution to LTE-Advanced», Wiley, [*] C. Johnson, «Long Term Evolution in Bullets», CreateSpace Independent Publishing Platform, 2012.