Wireless Networks: An Introduction

Master Universitario en Ingenierıa de Telecomunicacion

I. Santamarıa

Universidad de Cantabria

Introduction Cellular Networks WLAN WPAN Conclusions

Contents

Introduction

Cellular Networks

WLAN

WPAN

Conclusions

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Basic model

Data in

Channel

ChannelEncoder

I/Q Symbol Mapper

Basebandfilters

Interleaver Up-Conv.RF TX

NoiseFading

Interference

RF RXDown Conv.

I/Q demod

De-interleaver

ChannelDecoder

Symbol,Bit recovery Data out

Frequency, phase, symbol & timing recovery

I System resources: frequency, time, space (MIMO), codes(CDMA), power,...

I Figures of merit: BER, SER, FER, PER, SNR, SINR, QoS,...

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Fundamental Limits (AWGN)

5 10 15 20 25 30SNR dB

0

2

4

6

8

10

Cap

acity

(bp

s/H

z)64-QAM

16-QAM

4-QAM (QPSK)

Gaussian inputs log(1+SNR)

Shaping gain (1.53 dB)

Pe (symbol) = 10-6 (uncoded)

I Nowadays, the use of power channel encoders (e.g. LDPC orturbo codes) allows us to operate close to capacity in AWGNchannels

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Wireless Technologies

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1 Mbps

10 Mbps

100 Mbps

1 Gbps

1 m 10 m 100 m km

Communication range

Bluetooth/Zigbee

c802.11b

802.11a/g

802.11n

UWB

802.16WiMax

c3G (UMTS)

2.5 G2G (GSM)

4G (LTE, LTE-A)

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Cellular Networks

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Evolution1

HUAWEI TECHNOLOGIES CO., LTD. Huawei Proprietary - Restricted Distribution Page 2

1Reprinted from Huawei TechnologiesWireless Networks: An Introduction 6/16

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Radio Access TechnologiesI 2G-GSM

I Two frequency bands of 25 MHz each (890-915 MHz uplink,935-960 MHz downlink)

I Channel spacing 200 kHz, 124 channels per frequency bandI Modulation format: Gaussian Minimun Shift Keying (GMSK)I Multiple Access Technique: Time Division Multiple Access

(TDMA)

I 3G-UMTSI Frequency band: 1.8-2.4 GHzI Bandwidth: 1.25, 5 or 20 MHzI Modulation format: Spread Spectrum, chip rate: 3.84

Mchips/s, orthogonal variable spreading factor codes (OVSF),spreading factor 4-256

I Multiple Access Technique: Code Division Multiple Access(DS-CDMA),

I Duplexing (uplink/downlink): Frequency Division Duplex(FDD), Time Division Duplex (TDD)

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I 4G-LTEI Frequency band: 2-8 GHzI Bandwidth: up to 100 MHz via carrier aggregationI Modulation format: OFDMI Multiple Access Technique: Orthogonal Frequency Division

Multiple Access (OFDMA)

I 5G: technologies under discussionI New Waveforms (filtered OFDM, FBMC, GFDM, ...)I New spectrum sharing (NOMA or Non-Orthogonal Multiple

Access Techniques)I New radio frame design (e.g., Short TTI)I New L1/L2 control signaling design (Low latency HARQ,

decouple data TTI with control channel, fully dynamicresource assignment,...)

I Full Duplex TransceiversI Massive MIMO data transmission

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LTE Frame Structure

I Generic frame used in FDD for both Downlink and Uplink

I LTE frame are 10 ms in duration

I They are divided in 10 subframes (Transmission Time Interval:shortest decodable transmission)

I Each subframe is further divided in two slots

I Slots consist of either 6 or 7 OFDM symbols

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Available Downlink Bandwidth is Divided into Physical Resource Blocks

LTE Reference Signals are Interspersed Among Resource Elements

[source: 3GPP TR 25.814]

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LTE

I OFDM modulation parameters (BW = 20 MHz)

Total Subcarriers (NFFT ) 2048

Payload subcarriers 1200

Subcarrier spacing ∆f 15 kHz

Sampling frequency (fs) 30.72 MHz (∆f ∗ NFFT )

OFDM Symbol duration Ts 66.7 µs

Normal cyclic prefix (TGn) 4.7 µs

Extended cyclic prefix (TGe) 16.7 µs

Occupied Bandwidth 18 MHz

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WiFi Networks

I IEEE 802.11 denotes a set of WLAN standards developed bythe Working Group 11 of the IEEE LAN/MAN Committee

Parameter 802.11a/g 802.11n 802.11acAir rate 54 Mbps 200+ Mbps 500+ MbpsRange 30 m 50 m 50 m

Frequency 5 GHz 2.4/5 GHz 5 GHzBandwidth 20 MHz 20/40 MHz 80/160 MHzModulation OFDM OFDM+MIMO OFDM+MIMO

Spatial streams 1 1,2,3,4 up to 8

I WiGig: Multi-Gigabit per second transmissions over theunlicensed 60 GHz band (also OFDM based)

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802.11a

I OFDM modulation parameters

Total Subcarriers (NFFT ) 64

Payload subcarriers 48

Subcarrier spacing ∆f 312.5 kHz

Sampling frequency (fs) 20 MHz (∆f ∗ NFFT )

Pilot subcarriers 4

OFDM Symbol duration Ts 4 µs

Cyclic prefix (TG ) 800 ns

Occupied Bandwidth 16.56 MHz

GI Signal

0.8+3.2=4μs

GI Data 1

0.8+3.2=4μs

GI Data n

0.8+3.2=4μs

GI2 LT1 LT2

2x0.8+2x3.2=8μs

t1 t2 t3 t4 t5 t6 t7 t8 t9 t0

10x0.8=8μs

Short Training Symbols:Frame detect, AGC,

Time and coarse Freq. Sync.

Long Training Symbols:Channel Estimation

Frequency offset correction

DATA Field:SERVICE + PSDU + TAIL + PAD

Signal Field:rate + length

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Modulation and Coding Scheme (MCS)

I 802.11a provides 8 PHY layer modes with differentmodulation schemes and different convolutional coding rates

Mode Modulation Channel Coding Data rate1 BPSK 1/2 6 Mbps2 BPSK 3/4 9 Mbps3 QPSK 1/2 12 Mbps4 QPSK 3/4 18 Mbps5 16-QAM 1/2 24 Mbps6 16-QAM 3/4 36 Mbps7 64-QAM 2/3 48 Mbps8 64-QAM 3/4 54 Mbps

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Wireless Personal Area Networks

I IEEE 802.15 wireless personal area standarsI Bluetooth (802.15.1)

I Communications between multiple electronic devices within10m each other

I 2.4 GHz frequency bandI Frequency Hopping- Spread Spectrum (FHSS)I Rate: 1 - 3 MbpsI Nodes/Master 7

I ZigBee(802.15.4)I Range 70-300 mI Intended for Wireless Sensor Networks (thousands of devices)I Low cost/low power consumptionI 868 MHz band/ 915 MHz bandI Rate: 250 kbps, 40 kbps, 20 kpbsI Modulation format: Offset quadrature phase-shift

keying(OQPSK)and DSSS (Direct Sequence Spread Spectrum)

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Conclusions

I Range, coverage and mobility are key aspects defining thevarious types of wireless networks

I Cellular Networks: 2G (GSM), 3G (UMTS, GPRS, EDGE,HSDPA,...), 4G (LTE, LTE-A), and 5G soon

I WLAN networks: 802.11 standards

I WPAN networks: Bluetooth, ZigBee

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