Department of Computer Science Institute for System Architecture, Chair for Computer Networks

Transcription

1 Department of Computer Science Institute for System Architecture, Chair for Computer Networks LTE, WiMAX and 4G Mobile Communication and Mobile Computing Prof. Dr. Alexander Schill

2 LTE: Characteristics LTE is the European implementation of IMT (International Mobile Telecommunications) by ETSI (European Telecommunication Standards Institute) high data rates: up to 100 Mbit/s in local area (even up to 300 Mbit/s with advanced antenna technology [MIMO] and Modulation via OFDMA for down link and SC-FDMA for up link) flexible channel bandwidth (1.4, 3, 5, 10, 15 or 20 MHz) small latency of 5ms between mobile phone and conventional telephone network optimized for travelling speeds of up to 15 km/h (up to 500km/h possible) up to 200 participants per cell (at 5MHz channel bandwidth) only packet oriented propagation (VoIP) Handover/Roaming also between LTE, UMTS, GSM/GPRS and satellite networks configurable as Single-frequency network (Broadcast and Multicast efficiency like DVB-T/-H) 2

3 LTE: Modulation basics OFDM LTE Modulation techniques are based on OFDM (Orthogonal frequencydivision multiplexing) in OFDM data is distributed over a large number of closely spaced orthogonal subcarriers (two subcarriers are orthogonal if the maximum amplitude of one subcarrier is reached while the other subcarriers amplitude is zero) Subcarriers modulated with conventional modulation scheme (QAM) Pro: robust against interference because interference on subcarrier does not influence the whole frequency band, Improved spectrum efficiency and lower bandwidth demand W with OFDM Con: expense for coding and decoding and therefore the power consumption increases with the number of subcarriers OFDM with 3 subcarriers FDM with 3 subcarriers f f 3

4 LTE: Modulation techniques LTEs modulation techniques used for Downlink and Uplink are based on OFDM with a special focus on simultaneous access of multiple users *OFDMA (Orthogonal frequency-division multiple access) for Down Link subsets of subcarriers are assigned to individual users > simultaneous (low data rate) transmission for several users *SC-FDMA (Single Carrier FDMA) for Up Link multiple access realized by insertion of coefficients on the transmitter side before Fourier transformation, and removing on the receiver side. Different users are assigned to different coefficients (subcarriers). More energy-efficient for battery-driven mobile devices. 4

5 LTE: User Equipment Categories Category Peak data rate Mbit/s DL UL Capability of physical functionalities RF bandwidth Modulation Multi-antenna QPSK, 16QAM 20 MHz QPSK, 16QAM, 64QAM 2 Rx diversity Assumed in performance requirements 2x2 MIMO Not supported Mandatory 4x4 MIMO Not supported Mandatory 5

6 LTE: German frequency bands frequency spectrum of the digital dividend: better building penetration & propagation features > higher range 790 MHz 862 MHz (72 Mhz) 5 MHz frequency block Duplex gap* 12 MHz 820 MHz 832 MHz * The Duplex gap is meant as a fallback position for wireless production technology. frequency spectrum of the IMT extension band: Enough blocks for 20 MHz bandwidth > Higher data rate 2500 MHz (190 Mhz) 2690 MHz 5 MHz frequency block 2570 MHz 10 x 5 MHz blocks uncoupled 2620 MHz 6

7 LTE Licenses in Germany source: 7

8 LTE: TDD and FDD subframe = 1 millisecond Uplink (UL) Downlink (DL) FDD Special Frame UpPTS Uplink (UL) Downlink (DL) TDD DwPTS Guard Period two versions of LTE provide solutions for coupled/uncoupled frequency blocks transmitted signals divided into subframes (time units of 1 ms) FDD (Frequency division duplex) -separated frequency blocks for UL/DL TDD (Time division duplex) one frequency block alternately used for UL/DL: - Downlink subframes, Uplink subframes and Special Frames Special Frame = one subframe for each switching from down to up link; contains DwPTS (Downlink Pilot Timeslot), GP (Guard Period avoids overlay of sent and received messages) and UpPTS (Uplink Pilot Timeslot) 8

9 WiMAX / IEEE WiMAX: Worldwide Interoperability for Microwave Access, standardized by IEEE and WiMAX-Forum (more than 230 members, including AOL, Deutsche Telekom, Intel, Microsoft, Nokia) IEEE FBWA (Fixed Broadband Wireless Access) is an alternative for broadband cable services like DSL; frequency range: initially GHz, in assumption of LOS (line of sight) Enhancement IEEE a; frequency band: 2-11 GHz, NLOS (non line of sight) Enhancement IEEE e for MBWA (Mobile Broadband Wireless Access); frequency band: 2-6 GHz, NLOS 9

10 WiMAX/IEEE : overview Standard a e Spectrum, GHz LOS-condition LOS NLOS NLOS Bit rate, MBit/s <75 (extensions up to 365) Range, km max. 50 (cellular) 15 (with further extensions) 2-5 Channel bandwith, MHz 20, 25 and 28 Variable: 1,5 20 1,5-20 Modulation QPSK, 16QAM, 64QAM OFDM, QPSK, 16QAM, 64QAM OFDM, QPSK, 16QAM, 64QAM approved (N)LOS (Non) Line-of-Sight 10

11 WiMAX: Frequencies worldwide For Germany especially: 3,41-3,452 GHz and 3,51-3,552 GHz 11

12 Physical Layer Specification Frequency band Channel bandwidth Duplex method Modulatio n Line-of- Sight WirelessMAN-SC WirelessMAN- SCa WirelessMAN- OFDM WirelessMAN- OFDMA WirelessHUMAN GHz Licensed bandwidth 2-11 GHz Licensed bandwidth 2-11 GHz Licensed bandwidth 2-11 GHz Licensed bandwidth 2-11 GHz Licensefree 20, 25, 28 MHz 3,5, 7, 10, 20 MHz variable 1,25-20 MHz variable 1,25-28 MHz TDD, FDD TDD, FDD Single carrier Single carrier LOS NLOS TDD, FDD OFDM NLOS TDD, FDD OFDMA ( multiple access ) 10, 20 MHz TDD OFDM, OFDMA NLOS NLOS 12

13 WiMAX: Modulation WiMAX: strong dependency of effective channel capacity, spectrum efficiency, range, signalnoise-ratio etc. on used modulation method: BPSK Binary Phase Shift Keying QPSK Quadrature Phase Shift Keying 16QAM Quadrature Amplitude Modulation 64QAM Quadrature Amplitude Modulation (typical example distribution (percentage) of users in different coverage areas) 13

14 Medium Access TDMA (Time Division Multiple Access) Each communication channel gets fixed slot for data transmission DAMA (Demand Assigned Multiple Access) 2 Phases: Reservation: every station tries to acquire slot for each transmission phase (collision possible) Data transmission: within reserved slot guaranteed collision free transmission Duplex connection FDD (Frequency Division Duplex): simultaneous use of different frequencies TDD (Time Division Duplex): Switching between upand downlink on the same frequency 14

15 Protocol Stack Two lowest (PHY, MAC) layers specified according to the ISO/OSI-model OSI-layer application representation session transport network security bittransfer Service-Specific Convergence Sublayer (SSCS) Common Part Sublayer (CPS) Security Sublayer PHYsublayers MAC 15

16 MAC - SSCS Service-Specific Convergence Sublayer (SSCS) Receive PDUs of higher layers and classify depending on classification processing and forwarding to the CPS (Common Part Sublayer) Packet Convergence logic interface to Packet-based protocol e.g. IP, Point-to-Point-Protocols, Ethernet 16

17 MAC Security Sublayer Security layer directly in MAC Encryption with DES or AES; digital certificates based on X.509 with public-key-method RSA PKM (Privacy Key Management) Protocol authentication Subscriber Station sends digital certificates, consisting of MAC-Address and Public Key to Base Station, which verifies If valid, an authorization key (AK) with Public Key of the Subscriber Station is encrypted and sent back Subscriber Station decrypts with private key and can log on at the Base Station with AK 17

18 WiMAX: Cellular backbone Network e.g Gigabit Ethernet PHY OFDM- PHY UMTS cell WiMAX cell Point to Point Backbone Point to Multipoint 18

19 Network topologies (1&2) 1) Last Mile or 2) Point to Multipoint (PMP) network (see bellow) Base Station (BS) is the central point for the Mobile Stations (MS) Sending in Downlink-direction: Broad-, Multi-, Unicast Connection of a MS to BS is characterized via Channel ID (CID), Channel id gives the possibility for the BS to receive multicast messages Network MS/BS BS MS MS/BS MS MS MS 19

20 Network topologies (3) 3) Mesh network MS can communicate directly Mesh BS: connected with a network outside the mesh other differentiation neighbor: direct connection to a node neighborhood: all other neighbors extended neighborhood: remote neighborhoods Network Mesh MS Mesh MS Mesh MS Mesh BS Mesh MS Mesh MS Mesh MS 20

21 MBWA (Mobile Broadband Wireless Access); (1) Working Group originated from goal: Specification of PHY and MAC for Packet-based MBWA- System Should close the gap between WLAN and slower but highly mobile networks (UMTS) features variable cell size Handover- and Roaming-mechanism Velocity up to 250 km/h Transport of IP-data traffic QoS on transport layer Licensed bands below 3,5 GHz, variable bandwidth NLOS, for in- and outdoor TDD, FDD, Half-Duplex FDD More than 100 simultaneous sessions per cell End to End Security, AES 21

22 (2) Goals characteristic User data rate Downlink User data rate Uplink Data rate Downlink per cell Data rate Uplink per cell Cell size goal > 1 MBit/s > 300 KBit/s > 4 MBit/s > 800 KBit/s Correspond. to all modern MANs, with ability to use the existing infrastructure Peak data rates Data rates 1.25 MHz 5 MHz Downlink Uplink Downlink Uplink Peak data rate per user 4.5 MBit/s 2.25 MBit/s 18 MBit/s 9 MBit/s 22

23 Technology comparison pre-4g UMTS/HSPA/HSPA+ WiMAX MBWA LTE Mobility Handover, Roaming Handover, Roaming, Mobile IP --- Max Speed 300 km/h 120 km/h 250 km/h 500 km/h Switching type circuit and packet Packet switching Peak data rates Down Link 2/14,4/28 Mbit/s (5MHz channel) Cell sizes pico(1) -, micro (2) -, macro (3) -cells QoS End-to-end QoS Different classes 365 Mbit/s (2x 20MHz channel, variations) variable End-to-end QoS Different classes pico (1) -, micro (2) -, macro (3) -cells End-to-end QoS Mbit/s ( MHz channel) pico (1) -, micro (2) -, macro (3) -cells End-to-end QoS Different classes Scalability variable data rate ~ Multiple users per BS Air Interface CDMA adaptive Modulation MIMO OFDM(A), adaptive Modulation MIMO OFDM Adaptive Modulation OFDM, SC-FDMA adaptive Modulation MIMO Security AES AES, X.509 AES SNOW 3G (1) <100m, (2) ~500m, (3) >1km 23

24 4G requirements high mobility Handover, Roaming, velocity up to 300 km/h switching technique pure packet switching integrated multi-media-services VoIP, TVoIP, VoD, Streaming high data rate (1Gbit/s) even at high mobility should be like DSL Size of cell variable and scalable QoS prioritization of specific data packages scalability available and reliable with many users air interface OFDM (better spectrum efficiency) security up to date standards (e.g. AES) Extension / integration of UMTS and WLAN approaches 24

25 Technology comparison 3G to 4G LTE (3G) LTE Advanced (4G) Peak data rate Down Link (DL) Peak data rate Up Link (UL) Transmission bandwidth DL Transmission bandwidth UL Coverage Scalable bandwidths Scalability Capacity 300 Mbit/s 1 Gbit/s 75 Mbit/s 500 Mbit/s 20 Mhz (max.) 100 Mhz 20 Mhz (max.) 40 Mhz (requirements as defined by ITU) Full performance up to 5km 1.4, 3, 5, 10 and 20 MHz MHz variable data rate Multiple users per BS 200 active participants per cell at 5 MHz Same as LTE requirement. Should be optimized or deployed in local areas/micro cell environments. variable data rate Multiple users per BS 3 times higher than that in LTE 25

26 Data rate and mobility High-speed /Wide-area Mobility Medium-speed /Urban area Walking /Local area 2G Standing /Indoors Source: Bitrate, MBit/s 26

27 Some further readings 3GPP long term evolution: en.wikipedia.org/wiki/3gpp_long_term_evolution WiMAX technology: IEEE web sites for and : grouper.ieee.org/groups/802/16/ and /802/20 LTE: