OFDM, Mobile Software Development Framework
-
Upload
merrill-jensen -
Category
Documents
-
view
26 -
download
3
description
Transcript of OFDM, Mobile Software Development Framework
![Page 1: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/1.jpg)
1
OFDM, Mobile Software Development Framework
9/27/2012
Y. Richard Yang
![Page 2: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/2.jpg)
2
Admin.
Homework 2 to be posted by Friday
Start to think about project
![Page 3: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/3.jpg)
3
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?
![Page 4: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/4.jpg)
4
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
![Page 5: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/5.jpg)
5
Benefit of Symbol Rate on ISI
1 2 3 4
1 2 3 4
1 2
1 2
![Page 6: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/6.jpg)
Multiple Carrier Modulation
6
![Page 7: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/7.jpg)
7
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
![Page 8: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/8.jpg)
Objective: Avoid subcarrier interference Interference of subcarrier i on subcarrier j
Assume no pulse wave shaping, matched filter
8
i j
Condition for the interference to be always 0?
![Page 9: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/9.jpg)
9
Objective: Avoid subcarrier interference
if integer number of cycles in [0, T]
# cycles in T is T * f => T * f = integer
![Page 10: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/10.jpg)
10
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 !
![Page 11: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/11.jpg)
OFDM Modulation
11
![Page 12: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/12.jpg)
12
Orthogonal Frequency Division Multiplexing
http://www1.linksys.com/products/images/ofdm.gif
OFDM allows overlapping subcarriers frequencies
802.11a
![Page 13: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/13.jpg)
13
OFDM Implementation
Take N symbols and place one symbol on each subcarrier (freq.)
Q: complexity of the implementation strategy?
Freq0
FreqN-1
![Page 14: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/14.jpg)
14
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
![Page 15: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/15.jpg)
15
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
![Page 16: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/16.jpg)
16
OFDM Implementation: FFT
channel
![Page 17: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/17.jpg)
17
OFDM Implementation
Parallel data streams are used as inputs to an IFFT
IFFT does multiplexing and modulation in one step !
![Page 18: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/18.jpg)
18
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
![Page 19: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/19.jpg)
19
OFDM Guard Interval
http://www.dsplog.com/2008/02/17/cylcic-prefix-in-orthogonal-frequency-division-multiplexing/
![Page 20: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/20.jpg)
20
OFDM Implementation
http://proquest.safaribooksonline.com/0596100523?tocview=true
![Page 21: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/21.jpg)
21
Example: 802.11a Physical Channels
5150 [MHz]5180 53505200
36 44
center frequency = 5000 + 5*channel number [MHz]
channel#40 48 52 56 60 64
149 153 157 161
5220 5240 5260 5280 5300 5320
5725 [MHz]5745 58255765
channel#
5785 5805
![Page 22: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/22.jpg)
OFDM in 802.11a
Use OFDM to divide each physical channel (20 MHz):20M/64=312.5 KHz each
Subcarrier frequency spacing 312.5KHz 1/312.5KHz = 3.2us 64 samples FFT 16 samples
Guard Interval
22
http://standards.ieee.org/getieee802/download/802.11a-
1999.pdf
![Page 23: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/23.jpg)
23
Other Multipath Techniques
There are other techniques to handle multipath such as Rake Receiver
See backup slides for somedetails
![Page 24: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/24.jpg)
24
Summary of PHY
![Page 25: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/25.jpg)
25
Wireless PHY
http://setemagali.com/2009/10/12/climbing-the-mountain-everyday/
PHY
![Page 26: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/26.jpg)
Big Picture
26
Foundational Services: Communications, Location, Service Discovery,
UI/Media, Power Management, Security
Wireless/Mobile Application Development Framework
Applications
![Page 27: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/27.jpg)
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
framework27
![Page 28: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/28.jpg)
28
Outline
Admin and recap Mobile/wireless development framework
GNURadio
![Page 29: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/29.jpg)
29
GNURadio: Design Objective
A software development toolkit that provides signal processing blocks to implement software-defined radio systems.
![Page 30: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/30.jpg)
30
Outline
Admin and recap Mobile/wireless development framework
GNURadio• Hardware setting
![Page 31: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/31.jpg)
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
![Page 32: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/32.jpg)
32
Outline
Admin and recap Mobile/wireless development framework
GNURadio• Hardware setting• Software concepts
![Page 33: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/33.jpg)
Basic Software Concepts Block
Flow graph
![Page 34: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/34.jpg)
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)
![Page 35: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/35.jpg)
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?
![Page 36: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/36.jpg)
36
Summary: GNURadio
Interesting/key software design techniques you learned from GNURadio?
![Page 37: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/37.jpg)
37
Outline
Admin and recap Mobile/wireless development framework
GNURadio• Hardware setting• Software concepts
TinyOS
![Page 38: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/38.jpg)
38
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/
![Page 39: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/39.jpg)
39
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”
![Page 40: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/40.jpg)
40
Schematic Diagram of a Mote
![Page 41: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/41.jpg)
41
Outline
Admin and recap Mobile/wireless development framework
GNURadio• Hardware setting• Software concepts
TinyOS• Hardware setting• Software concepts
![Page 42: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/42.jpg)
42
Requirements on Software Dev. Framework
Flexible configuration of attached devices
Small foot print devices have limited
memory and power resources
![Page 43: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/43.jpg)
TinyOS: Software Concept
TinyOS: Generate customized OS + application for each given scenario support one application at a time but flexible
reprogramming
43
![Page 44: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/44.jpg)
44
Schematic Diagram
![Page 45: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/45.jpg)
45
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
![Page 46: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/46.jpg)
46
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
![Page 47: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/47.jpg)
47
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);
}
![Page 48: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/48.jpg)
Backup Slides
48
![Page 49: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/49.jpg)
Rake Receiver
49
![Page 50: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/50.jpg)
50
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
![Page 51: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/51.jpg)
51
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
![Page 52: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/52.jpg)
52
Rake Receiver Blocks
Correlator
Finger 1
Finger 2
Finger 3
Combiner
![Page 53: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/53.jpg)
53
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
![Page 54: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/54.jpg)
54
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
![Page 55: OFDM, Mobile Software Development Framework](https://reader036.fdocuments.in/reader036/viewer/2022062408/56813336550346895d9a321a/html5/thumbnails/55.jpg)
55
Comparison [PAH95]
MCM is OFDM