Wireless Networks: An Introduction

Transcription

1 Wireless Networks: An Introduction Master Universitario en Ingeniería de Telecomunicación I. Santamaría Universidad de Cantabria

2 Contents Introduction Cellular Networks WLAN WPAN Conclusions Wireless Networks: An Introduction 0/16

3 Basic model Data in Channel Encoder Interleaver I/Q Symbol Mapper Baseband filters Up-Conv. RF TX Channel Noise Fading Interference Frequency, phase, symbol & timing recovery RF RX Down Conv. I/Q demod Symbol, Bit recovery Deinterleaver Channel Decoder Data out System resources: frequency, time, space (MIMO), codes (CDMA), power,... Figures of merit: BER, SER, FER, PER, SNR, SINR, QoS,... Wireless Networks: An Introduction 1/16

4 Capacity (bps/hz) Fundamental Limits (AWGN) 10 Shaping gain (1.53 db) 8 6 Gaussian inputs log(1+snr) 64-QAM 4 16-QAM 2 4-QAM (QPSK) 0 Pe (symbol) = 10-6 (uncoded) SNR db Nowadays, the use of power channel encoders (e.g. LDPC or turbo codes) allows us to operate close to capacity in AWGN channels Wireless Networks: An Introduction 2/16

5 Wireless Technologies Wireless Networks: An Introduction 3/16

6 1 Gbps UWB 100 Mbps n WiMax a/g 10 Mbps 4G (LTE, LTE-A) 1 Mbps Bluetooth/Zigbee b c 3G (UMTS) c 2.5 G 2G (GSM) 1 m 10 m 100 m km Communication range Wireless Networks: An Introduction 4/16

7 Cellular Networks Wireless Networks: An Introduction 5/16

8 Evolution 1 1 Reprinted from Huawei Technologies Wireless Networks: An Introduction 6/16

9 Radio Access Technologies 2G-GSM Two frequency bands of 25 MHz each ( MHz uplink, MHz downlink) Channel spacing 200 khz, 124 channels per frequency band Modulation format: Gaussian Minimun Shift Keying (GMSK) Multiple Access Technique: Time Division Multiple Access (TDMA) 3G-UMTS Frequency band: GHz Bandwidth: 1.25, 5 or 20 MHz Modulation format: Spread Spectrum, chip rate: 3.84 Mchips/s, orthogonal variable spreading factor codes (OVSF), spreading factor Multiple Access Technique: Code Division Multiple Access (DS-CDMA), Duplexing (uplink/downlink): Frequency Division Duplex (FDD), Time Division Duplex (TDD) Wireless Networks: An Introduction 7/16

10 4G-LTE Frequency band: 2-8 GHz Bandwidth: up to 100 MHz via carrier aggregation Modulation format: OFDM Multiple Access Technique: Orthogonal Frequency Division Multiple Access (OFDMA) 5G: technologies under discussion New Waveforms (filtered OFDM, FBMC, GFDM,...) New spectrum sharing (NOMA or Non-Orthogonal Multiple Access Techniques) New radio frame design (e.g., Short TTI) New L1/L2 control signaling design (Low latency HARQ, decouple data TTI with control channel, fully dynamic resource assignment,...) Full Duplex Transceivers Massive MIMO data transmission Wireless Networks: An Introduction 8/16

11 LTE Frame Structure Generic frame used in FDD for both Downlink and Uplink LTE frame are 10 ms in duration They are divided in 10 subframes (Transmission Time Interval: shortest decodable transmission) Each subframe is further divided in two slots Slots consist of either 6 or 7 OFDM symbols Wireless Networks: An Introduction 9/16

12 Available Downlink Bandwidth is Divided into Physical Resource Blocks LTE Reference Signals are Interspersed Among Resource Elements [source: 3GPP TR ] Wireless Networks: An Introduction 10/16

13 LTE OFDM modulation parameters (BW = 20 MHz) Total Subcarriers (N FFT ) 2048 Payload subcarriers 1200 Subcarrier spacing f 15 khz Sampling frequency (f s ) MHz ( f N FFT ) OFDM Symbol duration T s 66.7 µs Normal cyclic prefix (T Gn ) 4.7 µs Extended cyclic prefix (T Ge ) 16.7 µs Occupied Bandwidth 18 MHz Wireless Networks: An Introduction 11/16

14 WiFi Networks IEEE denotes a set of WLAN standards developed by the Working Group 11 of the IEEE LAN/MAN Committee Parameter a/g n ac Air rate 54 Mbps 200+ Mbps 500+ Mbps Range 30 m 50 m 50 m Frequency 5 GHz 2.4/5 GHz 5 GHz Bandwidth 20 MHz 20/40 MHz 80/160 MHz Modulation OFDM OFDM+MIMO OFDM+MIMO Spatial streams 1 1,2,3,4 up to 8 WiGig: Multi-Gigabit per second transmissions over the unlicensed 60 GHz band (also OFDM based) Wireless Networks: An Introduction 12/16

15 802.11a OFDM modulation parameters Total Subcarriers (N FFT ) 64 Payload subcarriers 48 Subcarrier spacing f khz Sampling frequency (f s ) 20 MHz ( f N FFT ) Pilot subcarriers 4 OFDM Symbol duration T s 4 µs Cyclic prefix (T G ) 800 ns Occupied Bandwidth MHz 10x0.8=8μs 2x0.8+2x3.2=8μs =4μs =4μs =4μs t1 t2 t3 t4 t5 t6 t7 t8 t9 t0 GI2 LT1 LT2 GI Signal GI Data 1 GI Data n Short Training Symbols: Frame detect, AGC, Time and coarse Freq. Sync. Long Training Symbols: Channel Estimation Frequency offset correction Signal Field: rate + length DATA Field: SERVICE + PSDU + TAIL + PAD Wireless Networks: An Introduction 13/16

16 Modulation and Coding Scheme (MCS) a provides 8 PHY layer modes with different modulation schemes and different convolutional coding rates Mode Modulation Channel Coding Data rate 1 BPSK 1/2 6 Mbps 2 BPSK 3/4 9 Mbps 3 QPSK 1/2 12 Mbps 4 QPSK 3/4 18 Mbps 5 16-QAM 1/2 24 Mbps 6 16-QAM 3/4 36 Mbps 7 64-QAM 2/3 48 Mbps 8 64-QAM 3/4 54 Mbps Wireless Networks: An Introduction 14/16

17 Wireless Personal Area Networks IEEE wireless personal area standars Bluetooth ( ) Communications between multiple electronic devices within 10m each other 2.4 GHz frequency band Frequency Hopping- Spread Spectrum (FHSS) Rate: 1-3 Mbps Nodes/Master 7 ZigBee( ) Range m Intended for Wireless Sensor Networks (thousands of devices) Low cost/low power consumption 868 MHz band/ 915 MHz band Rate: 250 kbps, 40 kbps, 20 kpbs Modulation format: Offset quadrature phase-shift keying(oqpsk)and DSSS (Direct Sequence Spread Spectrum) Wireless Networks: An Introduction 15/16

18 Conclusions Range, coverage and mobility are key aspects defining the various types of wireless networks Cellular Networks: 2G (GSM), 3G (UMTS, GPRS, EDGE, HSDPA,...), 4G (LTE, LTE-A), and 5G soon WLAN networks: standards WPAN networks: Bluetooth, ZigBee Wireless Networks: An Introduction 16/16