1 OFDM, Mobile Software Development Framework 9/27/2012 Y. Richard Yang.

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OFDM, Mobile Software Development Framework

9/27/2012

Y. Richard Yang

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Admin.

Homework 2 to be posted by Friday

Start to think about project

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Recap

Inter-Symbol Interference (ISI) Handle band limit ISI Handle multipath ISI

• Viterbi– problems: Its complexity

grows exponentially with D (the number of multipaths taps relative to the symbol time)

– Q: how to reduce D?

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OFDM: Basic Idea

Uses multiple carriers modulation (MCM) each carrier (called a subcarrier) uses a low

symbol rate• for N parallel subcarriers, the symbol time can be N

times longer spread symbols across multiple subcarriers

• also gains frequency diversity

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Benefit of Symbol Rate on ISI

1 2 3 4

1 2 3 4

1 2

1 2

Multiple Carrier Modulation

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Multiple Carrier Modulation (MCM): Problem

Despite wave shaping, there can be leak from one subcarrier to another subcarrier

Conventional design: guard bands to avoid interference among subcarriers

Guard band wastes spectrum

i j

Objective: Avoid subcarrier interference Interference of subcarrier i on subcarrier j

Assume no pulse wave shaping, matched filter

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i j

Condition for the interference to be always 0?

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Objective: Avoid subcarrier interference

if integer number of cycles in [0, T]

# cycles in T is T * f => T * f = integer

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OFDM Key Idea: Orthogonal Subcarriers Each subcarrier frequency is chosen so

that an integral number of cycles in a symbol period, i.e., subcarrier freq = k 1/T

They do not need to have the same phase, so long integral number of cycles in symbol time T !

OFDM Modulation

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Orthogonal Frequency Division Multiplexing

http://www1.linksys.com/products/images/ofdm.gif

OFDM allows overlapping subcarriers frequencies

802.11a

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OFDM Implementation

Take N symbols and place one symbol on each subcarrier (freq.)

Q: complexity of the implementation strategy?

Freq0

FreqN-1

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OFDM: Implementation Issue

Hardware implementation can be expensive if we use one oscillator for each subcarrier

Software implementation requires N multiplications per time output => N2 multi. per N outputs

Freq0

FreqN-1

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OFDM: Key Idea 2

Consider data as coefficients in the frequency domain, use inverse Fourier transform to generate time-domain sequence

Assume N outputs per symbol time T, fsc=1/T

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OFDM Implementation: FFT

channel

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OFDM Implementation

Parallel data streams are used as inputs to an IFFT

IFFT does multiplexing and modulation in one step !

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Guard Interval: Removing ISI

Orthogonal subcarriers remove inter-carrier interference

Slow symbol rate reduces inter-symbol interference, but may still have ISI

Basic idea of GI: skip the first part “damaged” signal

1 2

1 2

More details: Chap. 13.1.4 Gast

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OFDM Guard Interval

http://www.dsplog.com/2008/02/17/cylcic-prefix-in-orthogonal-frequency-division-multiplexing/

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OFDM Implementation

http://proquest.safaribooksonline.com/0596100523?tocview=true

OFDM in 802.11a

Subcarrier frequency spacing 312.5KHz 1/312.5KHz = 3.2us 64 samples FFT 16 samples

Guard Interval

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http://standards.ieee.org/getieee802/download/802.11a-

1999.pdf

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Other Multipath Techniques

There are other techniques to handle multipath such as Rake Receiver

See backup slides for somedetails

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Summary of PHY

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Wireless PHY

http://setemagali.com/2009/10/12/climbing-the-mountain-everyday/

PHY

Big Picture

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Foundational Services: Communications, Location, Service Discovery,

UI/Media, Power Management, Security

Wireless/Mobile Application Development Framework

Applications

Overview

Mobile/Wireless software development framework for mobile wireless applications is a quite large topic

We have already seen Gnuradio as an example framework

We will cover more examples TinyOS, J2ME, Android, IOS

Approach for designing/evaluating each software development framework: Focus on the key concepts introduced by each

framework26

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Outline

Admin and recap Mobile/wireless development framework

GNURadio

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GNURadio: Design Objective

A software development toolkit that provides signal processing blocks to implement software-defined radio systems.

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Outline

Admin and recap Mobile/wireless development framework

GNURadio• Hardware setting

GNURadio Hardware Arch

Hardware Frontend Host Computer

RF Frontend(Daugtherboar

d)

ADC/DAC andDigital Frontend

(USRP)

http://mobiledevices.kom.aau.dk/fileadmin/mobiledevices/teaching/software_testing/Gnu_radio_lecture.pdf

GNU RadioSoftware

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Outline

Admin and recap Mobile/wireless development framework

GNURadio• Hardware setting• Software concepts

Basic Software Concepts Block

Flow graph

Basic Software Concepts http://gnuradio.org/doc/doxygen/

classgr__block.html

gr_basic_block (name, in/out signature, msg queue) gr_block (Leaf block; key functions

forecast/general_work) Example:

http://www.gnu.org/software/gnuradio/doc/howto-write-a-block.html

gr_hier_block2 (container block; key functions: connect/disconnect/lock/unlock) gr_top_block (flow graph; start/stop/wait)

Software/Execution Model

Python

Application developmentFlow graph construction

C++

Signal processing blocks

Software model Python

Application management (e.g., GUI)

Flow graph construction Non-streaming code (e.g.,

MAC-layer)

C++ Signal processing blocks Certain routines also coded

in assembly

Execution model Python thread for each

top_block

Discussion: benefits/issues of the hybrid software structure?

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Summary: GNURadio

Interesting/key software design techniques you learned from GNURadio?

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Outline

Admin and recap Mobile/wireless development framework

GNURadio• Hardware setting• Software concepts

TinyOS

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Design Goal

A free and open source component based operating system and platform targeting wireless sensor networks (WSNs)

Example app Environment monitoring, e.g.,

• measure temperature, lighting values/events• periodically transmit measurements/events to a base

station• forward data for other nodes that are out of range of

the base station

…http://www.tinyos.net/tinyos-1.x/doc/tutorial/

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Hardware

Assembled from off-the-shelf components

4Mhz, 8bit MCU (ATMEL) 512 bytes RAM, 8KB ROM

Devices serial Port temperature sensor & light

sensor 900Mhz Radio (RF monolithics)

• 10-100 ft. range LED outputs

1.5” x 1.5”

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Schematic Diagram of a Mote

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Outline

Admin and recap Mobile/wireless development framework

GNURadio• Hardware setting• Software concepts

TinyOS• Hardware setting• Software concepts

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Requirements on Software Dev. Framework

Flexible configuration of attached devices

Small foot print devices have limited

memory and power resources

TinyOS: Software Concept

TinyOS: Generate customized OS + application for each given scenario support one application at a time but flexible

reprogramming

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Schematic Diagram

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TinyOS: Software Concepts

A TinyOS consists of one or more components linked together software components motivated by hardware

component

Each component specifies that it provides some interfaces

• allows other components to control it also uses some interfaces

• control other components

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Interface

An interface declares a set of

functions called commands that provider must implement

another set of functions called events that the interface user must implement

A uses interfaces I1 and I2

B provides I1 C provides I2

commands events commands eventsI1 I2

C provides I3

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Interface: Examples

StdControl.nc

interface StdControl {  command result_t init();  command result_t start();  command result_t stop();}

Timer.nc

interface Timer {

command result_t start(

char type,

uint32_t interval); 

command result_t stop(); 

event result_t fired();

}

ADC.nc

interface ADC {

async command result_t getdata(); 

async command result_t getContinuousData(); 

event result_t dataReady(uint 16_t data);

}

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TinyOS Component: Implementation

Component contains: commands and event

handlers• can invoke lower level

commands, but cannot block

frame (storage)• statically allocated, fixed

size to know memory requirement and avoid overhead of dynamic allocation

Component

Internal StateInternal Tasks

Commands Events

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Linking Components

Two types of components:

modules: individual components

configurations : assemble components together, connecting interfaces (objects) used by components to interfaces (objects) provided by others

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Example Application

A simple TinyOS application which periodically reads in the light intensity value, computes a moving average, displays it on the LEDSee SenseTaskM.nc

SenseTask.nc

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Running tinyOS Program make mica ncc -o main.exe -target=mica SenseTask.nc avr-objcopy --output-target=srec main.exe

main.srec Use uisp to install

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TinyOS Execution Model

Concurrency model: only two threads long running tasks that can be interrupted by hardware

event handlers

Tasks perform the primary computation work commands and event handlers post tasks call lower level commands signal higher level events schedule other tasks within a component

Each task is atomic with respect to other tasks run to completion, but can be preempted by events the task scheduler is a simple FIFO scheduler

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A More Complete Sample Application Sensor network

monitoring monitor temperature and

light conditions periodically transmit

measurements to a base station

sensors can forward data for other sensors that are out of range of the base station

dynamically determine the correct routing topology for the network

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Internal Component Graph

RFM

Radio byte

Radio Packet

UART

UART Packet

I2C

Temp

Light

Active Messages

Clocksbit

byte

packet

Ad hoc Routing Applicationapplication

HW

SW

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Message Send Transition

Total propagation delay up the 5 layer radio communication stack is about 80 instructions

Timing diagram of event propagation

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Evaluation: Storage

Component Name Code Size (bytes)

Data Size (bytes)

RoutingAM_dispatchAM_temperatureAM_lightAMRADIO_packetRADIO_byteRFMLightTempUARTUART_packetI2C

884078

1463563348103108464

196314198

00

328

4040

81111

408

Processor_initTinyOS schedulerC runtime

17217882

3016

0

Total 3450 226

Scheduler only occupies 178 bytes

Complete application only requires 3 KB of instruction memory and 226 bytes of data (less than 50% of the 512 bytes available)

Only processor_init, TinyOS scheduler, and C runtime are required

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Evaluation: Timing

Operations Cost (cycles)

Time (µs)

Normalized to byte copy

Byte copy 8 2 1

Post an Event

Call a Command

Post a task to scheduler

Context switch overhead

10104651

2.52.5

11.512.7

5

1.251.25

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Interrupt (hardware cost) 9 2.25 1

Interrupt (software cost) 71 17.75

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Summary: TinyOS Components

provide commands andrequire callback hooks for event-driven programming

Configurations Link components

TinyOS an app (configuration)

at a time, linkingonly necessary components

Two threads exec one for event one for task

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ADC.nc

interface ADC {

async command result_t getdata(); 

async command result_t getContinuousData(); 

event result_t dataReady(uint 16_t data);

} configuration SenseTask { // this module does not provide any interfaces}implementation{ components Main, SenseTaskM, LedsC, TimerC, DemoSensorC as Sensor;

Main.StdControl -> TimerC; Main.StdControl -> Sensor; Main.StdControl -> SenseTaskM;

SenseTaskM.Timer -> TimerC.Timer[unique("Timer")]; SenseTaskM.ADC -> Sensor; SenseTaskM.Leds -> LedsC;}

Discussion: Compare TinyOS/GNURadio

What are some similar software concepts?

What are some differences?

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Discussion

Can we use GNURadio/TinyOS for writing mobile applications for mobile phones, or in other words, what are missing?

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Java2 Micro Edition (J2ME)

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Outline

Admin and recap Mobile/wireless development framework

GNURadio TinyOS J2ME

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Java Platforms

Java2 is divided into three platforms J2EE (Java2 Enterprise Edition)

• business applications

J2SE (Java2 Standard Edition)• general applications

J2ME (Java2 Micro Edition)• small devices such as mobile phone, PDA, car navigation

Oracle’s claims on Java on mobile devices http://www.java.com/en/about/

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J2ME Basic Concepts: Versioning To accommodate heterogeneous mobile

devices, define configurations and profiles

http://developers.sun.com/techtopics/mobility/getstart/articles/survey/

-A configuration provides fundamental services for a broad category of devices (e.g., lang, io, util)

- A profile supports higher-level services common to a more specific class of devices or market (e.g., life cycle, GUI)

-An optional package adds specialized services that are useful on devices of many kinds, but not necessary on all of them

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J2ME

128-512K mem16-32 bit proc

Upto 2M mem32 bit proc

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Example J2ME Configurations

Connected Limited Device Configuration (CLDC) 160 KB to 512 KB of total memory available 16-bit or 32-bit processor low power consumption and often operating with battery

power connectivity with limited bandwidth examples: cell phones, certain PDAs

Connected Device Configuration (CDC) 2 MB or more memory for Java platform 32-bit processor high bandwidth network connection, most often using

TCP/IP examples: set-top boxes, certain PDAs

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CLDC Available Packages

java.lang java.util java.io javax.microedition.io

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CLDC Classes Boolean Byte Character Class Integer Long Math Object Runnable Runtime Short String StringBuffer System Thread Throwable

Calendar Date Enumeration Hashtable Random Stack TimeZone Vector

ByteArrayOutputStream ByteArrayInputStream DataOuput DataInput DataInputStream DataOutputStream InputStream InputStreamReader OutputStream OutputStreamWriter PrintStream Reader Writer

java.lang java.util java.io

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Example J2ME Profiles

Mobile Information Device Profile (MIDP) GUI, multimedia and game functionality,

end-to-end security, and greater networked connectivity

mobile phones and entry level PDAs

Foundation Profile set of Java APIs that support resource-constrained devices

without a standards-based GUI system

Personal Profile Full set of AWT APIs, including support for applets and Xlets CDC + Foundation Profile + Personal Profile for high-end PDA

…

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Mobile Phone Framework

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MIDP Hardware

Memory (added to CLDC memory) 128 KB non-volatile for MIDP components 8 KB non-volatile for application persistent

data 32 KB volatile for KVM

Display screen 96x54 display depth 1-bit pixel shape (aspect ratio) 1:1

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MIDP Hardware

Input (one or more)one-handed keyboard (ITU-T phone

keypad)two-handed keyboard (QWERTY keyboard)or touch screen

Networking two-way wireless possibly intermittent limited bandwidth

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MIDP Packages

java.io java.lang java.util javax.microedition.io javax.microedition.lcdui javax.microedition.rms javax.microedition.midlet

javax.microedition.lcdui.game javax.microedition.media javax.microedition.media.contr

ol javax.microedition.pki

addition in version 2.0version 1.0

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MIDP Technology Stack

Mobile Information

Device Profile

KVMCLDC = KVM + J2ME Core

APIs in this

example DSP chip(e.g., ARM)

J2ME core APIs

YourMIDlet

Yellow Pages, train schedules and ticketing, games…

UI, HTTP networking...

Threads, no Floats…

32-bit RISC, 256K ROM, 256K Flash, 64K RAM

MIDlet

GUI based

Each MIDP has one instance of Display• Display.getDisplay(this) to get the manager• At any instance of time at most one Displayable

object can be shown on the display device and interact with user– display.setCurrent(<Displayable object>)

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MIDlet

An MIDP application is called a MIDlet similar to the J2SE applet

A MIDlet moves from state to state in the lifecycle, as indicated

start – acquire resources and start executing

pause – release resources and become quiescent (wait)

destroy – release all resources, destroy threads, and end all activity

Pause

Active

Destroyed

startApp

destroyApp

pauseApp

destroyApp

MIDP Visual Display

Each MIDP has one instance of Display

Display.getDisplay(this) to get the manager

At any instance of time at most one Displayable object can be shown on the display device and interact with user• display.setCurrent(<Displayable object>)

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MIDP Visual Display

Displayable Canvas

• GameCanvas

Screen• Alert, List, TextBox, Form

Form can contain multiple form items for organization Labels, Image Items, String Items, Text Fields, Date

Fields, Gauges, Choice Groups

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MIDP: User Interaction

Displayable objects can declare commands and declare a command listener: addCommand(Command cmd) addCommandListener()

Command(<label>, <type>, <priority>) Type: BACK, CANCEL, EXIT, HELP, ITEM, OK, SCREEN, and STOP

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HelloWorldMIDlet.javaimport javax.microedition.midlet.*;import javax.microedition.lcdui.*;

public class HelloWorldMIDlet extends MIDletimplements CommandListener {

private Command exitCommand;private Display display;private TextBox t;

public HelloWorldMIDlet() { display = Display.getDisplay(this);exitCommand = new Command("Exit", Command.EXIT, 2);t = new TextBox(“CS434", "Hello World!", 256, 0);t.addCommand(exitCommand);t.setCommandListener(this);

}public void startApp() { display.setCurrent(t); }public void pauseApp() { }public void destroyApp(boolean unconditional) { }public void commandAction(Command c, Displayable s) {

if (c == exitCommand) {destroyApp(false);notifyDestroyed();

}}

}

MIDP: Persistent State

Record store defined in javax.microedition.rms

Record store identified by name: static String[] listRecordStores();

recordStore = RecordStore.openRecordStore("scores", true);

recordId = addRecord(byte[] data, int offset, int numBytes);

getRecord(int recordId);

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Summary : J2ME

Scale down a popular programming environment to ease learning

Use virtual machines to mask device heterogeneity

Use configuration/profiling to handle device heterogeneity and avoid using lowest common denominator

MIDLet to manage app life cycle Displayable to visual display, commands and

provides command listener Introduce persistent record store

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Windows .NET Compact Framework Similar to J2ME Scales down a popular programming environment to ease

learning the .NET CF is a subset of the full .NET framework with some additions designed for resource constrained devices 1,400 classes for .NET CF vs. 8,000 for full 27 UI controls for .NET CF vs. 52 for full 1.5 MB for .NET CF vs. 30 MB for full

Uses versioning to avoid using lowest common denominator pocket PC pocket PC phone version smart phone version

Uses virtual machines to mask device heterogeneity programming languages compile to MSIL

• MSIL is JIT compiled on the device• MSIL code is smaller than native executables• MSIL allows your code to be processor independent

Andriod

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http://developer.android.com/index.html

Android Features

Linux kernel as foundation Java based framework (J2SE not J2ME)

Dalvik Virtual machine Nice features

Touch screen, accelerometer, compass, microphone, camera, GPS,

GSM, EDGE, and 3G networks, WiFi, Bluetooth, Near field communications

Media, SQLite, WebKit, SSL Location-based service, map (Google API)

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Andriod

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Activity

A single, focused thing that the user can do.

Interaction with users: creating a window to place UI views

full-screen windows, floating windows, embedded inside of another activity

Android Activity Life cycle

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View

A view component is a building block for user interface components.

Widget Toolbox TextView, EditText, Button, Form,

TimePicker… ListView Layout

• Positions of controls• LinearLayout, Relativelayout

http://developer.android.com/guide/tutorials/views/index.htm

Rake Receiver

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Multipath Diversity: Rake Receiver

Instead of considering delay spread as an issue, use multipath signals to recover the original signal

Used in IS-95 CDMA, 3G CDMA, and 802.11

Invented by Price and Green in 1958 R. Price and P. E. Green, "A

communication technique for multipath channels," Proc. of the IRE, pp. 555--570, 1958

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Multipath Diversity: Rake Receiver

Use several "sub-receivers" each delayed slightly to tune in to the individual multipath components

Each component is decoded independently, but at a later stage combined this could very well result in

higher SNR in a multipath environment than in a "clean" environment

LOS pulsemultipathpulses

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Rake Receiver Blocks

Correlator

Finger 1

Finger 2

Finger 3

Combiner

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Rake Receiver: Matched Filter

Impulse response measurement Tracks and monitors peaks with a

measurement rate depending on speeds of mobile station and on propagation environment

Allocate fingers: largest peaks to RAKE fingers

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Rake Receiver: Combiner

The weighting coefficients are based on the power or the SNR from each correlator output

If the power or SNR is small out of a particular finger, it will be assigned a smaller weight:

M

ii

mm

Z

Z

1

2

2

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Discussion

What are major considerations in designing a software environment for mobile wireless applications for mobile devices?

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Mobile Programming Requirements

Handle heterogeneous devices/configurations Be extremely efficiency on using resources

(memory, battery, …) Easy programming for event-driven

programming …

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Comparison [PAH95]

MCM is OFDM