Wireless Communications Lab

transcript

Wireless Networking and Communications GroupDepartment of Electrical and Computer Engineering

The University of Texas at Austin, Austin TX USAENS 435

http://www.profheath.orgrheath@utexas.edu

Robert W. Heath Jr. Ph.D, P.E.KE5NCG

Wednesday, September 4, 13

OutlineReview of the syllabus

Introduction to wireless communication

A DSP approach to wireless

Connection to the lab

How the course works

Syllabus ReviewInstructor: Robert W. Heath Jr.

TA: Yingzhe Li

EE 471C Prerequisites: EE 345S or EE 351M or EE 360K

Reading Materials Based on course reader already posted to Blackboard

Occasional updates to reader will be made

All previous homework and exam problems in reader

Undergrad: Tech area fulfillmentCommunications / Networking and Signal Processing

Graduate: Counts as a CommNetS course

Class will be video recorded but please come to class

Wireless is Everywhere

cellular networks local area networks

personal area networks emerging applications

The Cellular Concept

Base stations serve multiple subscribers

Frequencies are geographically reused in cells

Handoff provides seamless connection

Base Station (BS)

Co-ChannelInterference

Mobile Station (MS)or

User Equipment (UE)The same frequency is

reused in multiple clusters

Handoff

Cluster

Evolution of Cellular Systems

First generation systems - known after the fact as 1G

Conceived in the 1960’s

Deployed in the late 1970’s / early 1980’s

Built around analog technology, FM modulation

Limited data, little security

Expensive due to analog technology

Little roaming

Examples AMPS, NTT, NMT-450, etc.

Most of you in have never used 1G

Second generation systems - known as 2G

Deployed in the 1990’s

Digital Voice

More subscribers per bandwidth, some data

Enabled roaming in Europe (GSM), not in US (IS-95, IS-136)

Examples GSM, IS-95, IS-136, PDC, EDGE (2.5G)

Most of you have a 2G compatible

Third generation systems - known as 3G

Deployed in the 2000’s

Digital voice plus data

Video telephony

Higher capacity

CDMA (code division multiple access)

Examples: 3GPP WCDMA, HSDPA, etc.

3GPP2 cdma2000, 1xEV, 1xEV-DO, 1xEV-DV, etc.

Most of you use 3G on a daily basis

After 3G, cellular systems began fine-grained development3GPP updates were made in stages e.g. R7, R8, R9, R10, R11, etc

Transition to 4G happened at Release 10 known as 3GPP LTE Advanced

Fourth generation systems - known as 4G

IP based backbone, supports VoIP

OFDMA allows efficient resource allocation

MIMO (multiple antennas 8 @ base station, 4 at handset)

Higher data rates

3GPP Long Term Evolution Advanced

4G devices are now being sold

Have one?

Fifth generation systems - known as 5G

3GPP after Release 14 will likely be considered 5G

Development is ongoing

Possible technologies that could make 5GMassive MIMO - hundreds of antennas at the base station

Millimeter wave - use millimeter wave spectrum to obtain larger bandwidth

New concepts supported by 5GDevice-to-device

Machine-to-machine

Vehicle-to-vehicle

Active area of research, good area of senior design and PhD dissertations

The Wireless LAN Concept

Wireless LANs provide wireless Internet access (and LAN)

Access Points (APs) serve multiple clients

Uses unlicensed frequency bands

Little to no coordination between adjacent APs

IEEE 802.11 Wireless LANIEEE is the Institute of Electrical and Electronics Engineers

Main professional society for electrical engineers

Everyone should become a student member of the IEEE

You might also want to join COMSOC (communications society), SPSOC (signal processing society), and ITSOC (information theory society)

IEEE 802 is a group that develop local area network and metropolitan area network standards, focusing on the PHY, MAC, and LINK layers

IEEE 802.11 is WLAN working group (members develop standards + vote)

digression

IEEE 802.11 Subgroups

802.11: 1/2Mbps in 2.4GHz band, FHSS or DSSS

802.11a: extend to 5GHz ban, 54Mbps, OFDM

802.11b: (WiFi) DSSS with 11Mbps in 2.4GHz band

802.11g: similar to 802.11a but for 2.4GHz

802.11n: MIMO enhancement, 100-200Mbps

802.11ac: Very high throughput < 6GHz carrierMore bandwidth aggregation, more MIMO, multiuser MIMO

802.11ad: Very high throughput > 6GHz carrierExploits 60GHz unlicensed bands, lots of antennas, beamforming

11 11b 11g 11n 11ac 11ad

many more subgroups, some successful and some not

Discussion has started on beyond 11ac/adWednesday, September 4, 13

Personal Area Networks (PAN)

Lower range connectivity compared to WLANCable replacement is one of the primary applications

Has an ad hoc network architecture (usually called a piconet)

IEEE 802.15 is the main standardExamples are Bluetooth used for keyboards and handsfree headsets

Upcoming 802.15.3c uses 60GHz for HDMI cable replacement

Set-top Box

10 Gbps

6 Gbps

5 Gbps

PAN / LAN boundaries are blurring

Emerging Applications

body area networks

car area networks

mobile ad hoc networks

powerline communication

vehicular area networks

underwater communication

The Network Stack

Physical Layer

LogicalLink

Control

Network Layer

Transport Layer

Session Layer

Presentation Layer

Data LinkLayer

Application Layer

OSI Network Model

Antennas & Circuits

Signal Processing Algorithms

Focus of this class

Typical Digital Communication Sys.

SourceChannelCoding

Modulation Analog Processing

Sink ChannelDecoding

Demodulation Analog Processing

transmitter

receiver

Propagation Medium

SourceCoding

SourceDecoding real

channel

digital analog

DSP Approach to Wireless

Use systems approach for communication

Inputs System Outputs

0110110 h[n]

0110110

Wireless Communications Lab @ UTPremises of the course

Analog communication is no longer required

Wireless communication can be learned by all EEs

Wireless communication can be taught without a communication background

You can implement what you learn while you learn it

Key ideasLearn digital communication from a digital signal processing perspective

Incorporate modulation, channel estimation, equalization, synchronization

Use algorithmic design examples, not comprehensive theory

Leverage flexible software defined radio prototyping

Exploit LabVIEW & USRP

Developed and tested over 7 years

EE 471C / EE 381V

Technical Concepts in the CourseDSP Models for communication

Sampling, up/down conversion, baseband vs. passband, complex baseband

Power spectrum, bandwidth, pulse-shaping

Basics of digital communicationQAM modulation, ML detection

Dealing with impairmentsChannel estimation

Frame/sample/carrier frequency offset synchronization

Equalization, single carrier frequency domain equalization

Standards: GSM, IEEE 802.11a, IEEE 802.11n

Channel models: large scale, small scale, coherence

Multiple antennas: receive, transmit, MIMO

Content of the CourseDigital comm overviewSignals, stochastic processesTransforms, sampling theormFrequency response, power spectrum, bandwidthUpconversion, downconversion, complex basebandQuadrature pulse amplitude modulationOptimal pulse shapesMaximum likelihood detection in AWGNSample timing offset, sample timing algorithmsFrequency selective channels, least squares channel estimationFrequency offset estimation and correction, frequency domain equalizationSingle carrier frequency domain equalization, OFDM, the cyclic prefixIEEE 802.11a, GSM standardIntroduction to propagation, large-scale fading, link budgets, path-lossSmall-scale fading, coherence time, coherence bandwidthProbability of error in fading channelsSources of diversity, Alalmouti space-time code, maximum ratio combiningIntroduction to MIMO communication, spatial multiplexingIntroduction to MIMO-OFDM, highlights of the IEEE 802.11n standard

Mathematical preliminaries

Basic digital comm

Channel impairments

StandardsFading

The Lab

Located in ENS 113

Lab has ten workstations for transmit / receiveWork in teams of 2, same team the whole semester

Use your windows laptop to connect (need GigEthernet)

NI USRP 2921

ethernet cable

MIMOcable

antennas

How this Fits with the Lab

Source ChannelCoding

Modulation D/A RF Upconversion

Sink ChannelDecoding

Demodulation A/D RF Downconversion

channel

transmitter

receiver

Laptop with LabVIEW NI USRP 2921Real world

(all digital signal processing)

Content of the CourseDigital comm overviewSignals, stochastic processesTransforms, sampling theormFrequency response, power spectrum, bandwidthUpconversion, downconversion, complex basebandQuadrature pulse amplitude modulationOptimal pulse shapesMaximum likelihood detection in AWGNSample timing offset, sample timing algorithmsFrequency selective channels, least squares channel estimationFrequency offset estimation and correction, frequency domain equalizationSingle carrier frequency domain equalization, OFDM, the cyclic prefixIEEE 802.11a, GSM standardIntroduction to propagation, large-scale fading, link budgets, path-lossSmall-scale fading, coherence time, coherence bandwidthProbability of error in fading channelsSources of diversity, Alalmouti space-time code, maximum ratio combiningIntroduction to MIMO communication, spatial multiplexingIntroduction to MIMO-OFDM, highlights of the IEEE 802.11n standard

Donein the Lab

Lab MaterialLaboratory manual

DIGITAL COMMUNICATIONS: Physical Layer Exploration Using the NI USRP

141 pages

8 Laboratory experiments

Lab experimentsBackground information

Include prelab to be completed prior to lab

Laboratory experiments

Postlab

Complete software framework

Dr. Robert W. Heath, University of Texas at Austin

DIGITAL COMMUNICATIONS

PHYSICAL LAYER EXPLORATION LAB USING THE NI USRP™ PLATFORM

front.pdf 1 9/12/11 4:46 PM

Included with the Digital Communications Teaching Bundlehttp://sine.ni.com/nips/cds/view/p/lang/en/nid/210385

free!!

Outline of Lab Manual

“book” — 2011/9/29 — 15:18 — page v — #5 !!

Contents

Preface vii

About the Author xi

Lab 1: Part 1 Introduction to NI LabVIEW 1

Lab 1: Part 2 Introduction to NI RF Hardware 10

Lab 2: Part 1 Modulation and Detection 22

Lab 2: Part 2 Pulse Shaping and Matched Filtering 35

Lab 3: Synchronization 51

Lab 4: Channel Estimation & Equalization 63

Lab 5: Frame Detection & Frequency Offset Correction 82

Lab 6: OFDM Modulation & Frequency Domain Equalization 99

Lab 7: Synchronization in OFDM Systems 115

Lab 8: Channel Coding in OFDM Systems 130

Appendix A: Reference for Common LabVIEW VIs 139

Bibliography 141

Sample Pages

“book” — 2011/9/29 — 15:18 — page 51 — #63 !!

Lab 3: Synchronization:Symbol Timing Recovery in Narrowband

Channels

Summary

In this lab you will consider the problem of symbol timing recovery alsoknown as symbol synchronization. Timing recovery is one of several syn-chronization tasks; others will be considered in future labs.

The wireless communication channel is not well modeled by simple ad-ditive white Gaussian noise. A more realistic channel model also includesattenuation, phase shifts, and propagation delays. Perhaps the simplest chan-nel model is known as the frequency flat channel. The frequency flat channelcreates the received signal

z(t) = !ej"x(t ! #d) + v(t), (1)

where ! is an attenuation, " is a phase shift, and #d is the delay.The objective of this lab is to correct for the delay caused by #d in discrete-

time. The approach will be to determine an amount of delay k̂ and then todelay the filtered received signal by k̂ prior to downsampling. This willmodified the receiver processing as illustrated in Figure 1.

Two algorithms will be implemented for symbol synchronization in thislab: the maximum energy method and the Early Late gate algorithm. Themaximum energy method attempts to find the sample point that maximizesthe average received energy. The early–late gate algorithm implements adiscrete-time version of a continuous-time optimization to maximize a certain

SymbolSync

( )z t [ ]RXg n

Figure 1: Receiver with symbol synchronization after the digital matched filtering.

“book” — 2011/9/29 — 15:18 — page 43 — #55 !!

Lab 2: Part 2 Pulse Shaping and Matched Filtering 43

Figure 3: Hierarchy of code framework for new simulator.

top rx.vi and provides each with the appropriate inputs. The parts of thesimulator you will be modifying are located in transmitter.vi and receiver.vishown in Figures 4 and 5 respectively.

You will be putting your VIs into transmitter.vi and receiver.vi, replacingthe locked versions that are already there. After doing this, you will thenopen up simulator.vi, that you will use to confirm your VIs operate correctlybefore implementing them on the NI-USRP.

Notice that pulse shaping.vi and matched filtering.vi do not take any pa-rameters as inputs. All of the pulse shaping and oversampling parameters youneed to use for these VIs can be accessed from the modulation parameters incluster. After building these VIs, replace the existing code in the simulatorwith your code. Replace a subVI in the transmitter or receiver with your code

Figure 4: Block diagram of transmitter.vi.

Overall Course StructureLectures

Lecturing on document camera or white board

Focus on DSP approach to communication

Laboratory sessionsLabs performed in groups of 2 (same all semester)

Implement pre-lab ahead of lab in simulation

Experiments performed during the session

AssignmentsPre-labs prepare for lab, turned in prior to lab, performed in groups

Homework due every week, supplement the theory portions of the lab

Lab reports summarize lab findings, due week after completion of a lab

except first lab, you have to learn LabVIEW

there is a lot of stuff here but you can do it!

Grad versus UndergradLectures, assignments, homeworks all the same

Graduate course requires a final projectLiterature review, or

Implementation, or

Research paper

Final grading of undergrad and grad sections is independent Please note the grading is not dependent

Seriously, the grades are computed differently

This doesn’t mean, however, that you should slack off in either case

Is this just a rip-off of EE 445S?In short, no…

EE 345S deals with real-time DSP

Emphasis is on DSP background and real-time implementation issues

Digital modem used as significant design example

EE 471C differs in the following waysBasics of DSP assumed already known(thus the prereq)

Emphasis is on wireless communication using your existing DSP toolset

Build a real wireless modem that operates over the air

Programming is in LabVIEW, less concern for real-time implementation

Discuss many new topics including symbol/frame/frequency synchronization, standards, fading, bit error rate analysis, and wireless cellular systems

What about 360K?Again not really

EE 360K deals with digital communication

Emphasis is on mathematical theory

Note: Grad digital comm is even more theory :-(

EE 371C differs in the following waysEmphasis is on wireless digital communication

Examine complete physical layer system

Cover many topics to build intuition

Implement every topic in the lab

Discuss features of current standards & why certain design choices were made

Build a real wireless modem that operates over the air

Why Should I Take EE 381V?If you are a grad student, you may wonder why you should take this course?

Many topics not found in other graduate course at UT AustinFrame / frequency offset synchronization

Channel estimation

Software defined radio

GSM and IEEE 802.11a system design issues

Single carrier frequency domain equalization

OFDM with channel estimation and synchronization

You have the opportunity to conduct a research projectCan leverage your ongoing research

Can help you find a research advisor

Preparation for Next WeekReading

Chapter 1 and 2 of course notes (posted shortly)

LectureIntroduction to digital communication

LabNo lab next week but there will be a LabVIEW tutorial given by the TA

Lab 1.1 will be posted next week

Primarily involves learning LabVIEW - start early!

HomeworkHomework #1 will be posted shortly, due next week

Questions?

Wireless Communications Lab

Documents