Linkquest: Direct Sequence Spread Spectrum

(DSSS)

Introduction

History

•  In 1941, Hollywood actress Hedy Lamarr and pianist George Antheil described a secure radio link to control torpedoes and received U.S. patent #2.292.387.

•  In 1981, U.S. Army started using this technology and has become increasingly popular for applications that involve radio links in hostile environments.

Process

Security Concern

•  Since Pseudo Code is known by the transmitter and the receiver. It raises a question about privacy of the network.

•  This is what our project is going to be!!!.....

Benefits

•  Resistance to intended or unintended jamming

•  Sharing of a single channel among multiple

•  Reduced signal noise level

Uses

•  GPS (Navigation Systems)

•  DS-CDMA (Verizon, Sprint)

•  IEEE 802.11 (Wi-Fi)

•  Radio-Controlled model Vehicles

Note from the pres

•  UWM2000H (model to research)

References

•  AN1890, AN 1890, APP1890, Appnote1890, Appnote 1890

•  Wikipedia

AquaSeNT OFDM

Underwater Acoustic Communication

Multiplexing: FDM

•  “Multiplexing can serve two purposes: First, it enables several users to share a channel resource. Second, with the appropriate redundancy using frequency, code, time, or spatial diversity, we can improve the reliability of a message reaching its destination. ” (Carlson, 297).

•  Frequency-division Multiplexing uses sideband modulation and has the practical problem of crosstalk.

•  Crosstalk arises from nonlinearities in the system that causes one carrier to appear as modulation on another. This is overcome with negative feedback control.

[1] A. Bruce Carlson, Communications Systems; An Introduction to Signals and Noise in Electrical Communication, 5th ed. , New York, NY: McGraw-Hill, 2010.

Multiplexing: FDM

(a)

(b)

fc1

fc2

fc3

fc1 fc1 + W1 fc2

+ W2 fc3 + W3 fc2 fc3

!

X1( f )

x1(t)

x2(t)

xc2(t)

xc1(t)

xc3(t)

xb(t) xc(t)

x3(t)

W1 f

Xb( f )

f

LPF SSB

LPF SSB

Guard band

LPF

Carriermod

SSB

X2( f )

W2 f

X3( f )

W3 f

Figure 7.2–1 Typical FDM transmitter: (a) input spectra and block diagram; (b) basebandFDM spectrum.

298 CHAPTER 7 • Analog Communication Systems

Assuming that the subcarrier frequencies are properly chosen, the multiplexingoperation has assigned a slot in the frequency domain for each of the individual mes-sages in modulated form, hence the name frequency-division multiplexing. Thebaseband signal may then be transmitted directly or used to modulate a transmittedcarrier of frequency fc. We are not particularly concerned here with the nature of thefinal carrier modulation, since the baseband spectrum tells the story.

Message recovery or demodulation of FDM is accomplished in three steps por-trayed by Fig. 7.2–2. First, the carrier demodulator reproduces the baseband signalxb(t). Then the modulated subcarriers are separated by a bank of bandpass filters inparallel, following which the messages are individually detected.

The major practical problem of FDM is crosstalk, the unwanted coupling ofone message into another. Intelligible crosstalk (cross-modulation) arises primarilybecause of nonlinearities in the system which cause one message signal to appear as

car80407_ch07_287-344.qxd 12/16/08 6:10 PM Page 298

[1] A. Bruce Carlson, Communications Systems; An Introduction to Signals and Noise in Electrical Communication, 5th ed. , New York, NY: McGraw-Hill, 2010.

QAM: Quadrature-Carrier Modulation •  This method uses phase shifting to allow

two double side-band signals to occupy the same frequency

Sync

Channel±90° ±90°

!

!

x2(t) x2(t)

x1(t)x1(t)

!

!

+

LPF

LPF

7.2 Multiplexing System 303

Show how the QAM scheme of Fig. 7.2–6 enables x1(t) or x2(t) to be transmitted overthe same channel without interference.

Time-Division MultiplexingA sampled waveform is “off” most of the time, leaving the time between samplesavailable for other purposes. In particular, sample values from several different sig-nals can be interleaved into a single waveform. This is the principle of time-divisionmultiplexing (TDM) discussed here.

The simplified system in Fig. 7.2–7 demonstrates the essential features of time-division multiplexing. Several input signals are prefiltered by the bank of input LPFsand sampled sequentially. The rotating sampling switch or commutator at the trans-mitter extracts one sample from each input per revolution. Hence, its output is aPAM waveform that contains the individual samples periodically interleaved in time.A similar rotary switch at the receiver, called a decommutator or distributor, sepa-rates the samples and distributes them to another bank of LPFs for reconstruction ofthe individual messages.

If all inputs have the same message bandwidth W, the commutator should rotateat the rate fs ! 2W so that successive samples from any one input are spaced byTs " 1/fs # 1/2W. The time interval Ts containing one sample from each input iscalled a frame. If there are M input channels, the pulse-to-pulse spacing within aframe is Ts/M " 1/Mfs. Thus, the total number of pulses per second will be

(2)

which represents the pulse rate or signaling rate of the TDM signal.Our primitive example system shows mechanical switching to generate multi-

plexed PAM, but almost all practical TDM systems employ electronic switching.Furthermore, other types of pulse modulation can be used instead of PAM. There-fore, a more generalized commutator might have the structure diagrammed inFig. 7.2–8, where pulse-modulation gates process the individual inputs to form the

r " Mfs ! 2MW

Figure 7.2–6 Quadrature-carrier multiplexing.

EXERCISE 7.2–2

car80407_ch07_287-344.qxd 12/11/08 11:03 PM Page 303

[1] A. Bruce Carlson, Communications Systems; An Introduction to Signals and Noise in Electrical Communication, 5th ed. , New York, NY: McGraw-Hill, 2010.

PSK: Phase Shift Keying

10CCU

Wireless Access Tech. Lab.

2.3.1 Mapping - Phase Shift Keying

)M-ary phase shift keyingA Consider M-ary phase-shift keying (M-PSK) for which the signal set is

where is the signal energy per symbol, is the symbol duration, and is the carrier frequency.

A This phase of the carrier takes on one of the M possible values, namely, , where .

� � � �2 12cos 2 0 , 1,2,...,s

i c ss

iEs t f t t T i MT M

SS

�§ · � d d ¨ ¸

© ¹

� �2 1i i MT S � 1, 2,...,i M

sE sTcf

1/2

11CCU

Wireless Access Tech. Lab.

2.3.1 Mapping - Phase Shift Keying

)An example of signal-space diagram for 8-PSK .

sE�

2m

3m

4m

5m

6m

7m

8m

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2I

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sE�

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d

d

MSMS 1m

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1IsE

2/2

•  PSK work by shifting the phase of the carrier

•  The Equation above represents a PSK signal set for an m-ary.

•  The diagram represents the decision regions for an 8-PSK system.

[2] CCU, Wireless Access Lab

Multiplexing: OFDM •  Uses signals that are orthogonal to each other,

and therefore includes both phase and frequency multiplexing.

[1] A. Bruce Carlson, Communications Systems; An Introduction to Signals and Noise in Electrical Communication, 5th ed. , New York, NY: McGraw-Hill, 2010.

Multiplexing: OFDM

•  OFDM may use either PSK or QAM modulation

•  An example of a parallel transmission system. •  Each sub carrier only occupies a small portion of

total bandwidth

•  Has the advantage of reducing frequency selective channel fading by employing frequency diversity.

•  OFDM suffers less from cross talk than an FDM system would

•  OFDM requires strict signal synchronization.

Multiplexing: OFDM

•  Intersymbol interference (ISI) is defined as the crosstalk between signals within the same sub-channel of consecutive FFT frames, which are separated in time by the signaling interval T.

•  Inter-carrier interference (ICI) is the crosstalk between adjacent subchannels or frequency bands of the same FFT frame.

[2] CCU, Wireless Access Lab

OMFD: Advantages

•  3x to 10x greater data transmission rates; possibly higher over short ranges

•  Insensitive to “multipath:” echoes, reflected signals that arrive with a delay time

•  Benefits to the user

•  More robust communication link: fewer errors or severed links

•  3x – 10x increase in quantity of data in an application

•  Multi-node networks are now possible: •  Assets over an area of the sea floor can be wirelessly

networked together •  Signal hopping networks can transmit data over long

ranges

OFDM: Current Uses •  IEEE 802.11a, g, n and HIPERLAN/2.

•  The wireless personal area network (PAN) ultra-wideband (UWB) IEEE 802.15.3a implementation

•  Used in several 4G and pre-4G cellular networks and mobile broadband standards:

•  The mobility mode of the wireless MAN/broadband wireless access (BWA) standard IEEE 802.16e (or Mobile-WiMAX).

•  The mobile broadband wireless access (MBWA) standard IEEE 802.20.

•  the downlink of the 3GPP Long Term Evolution (LTE) fourth generation mobile broadband standard. The radio interface was formerly named High Speed OFDM Packet Access (HSOPA), now named Evolved UMTS Terrestrial Radio Access (E-UTRA).

•  Underwater Acoustic Communications

AquaSeNT Background

•  Aquatic Sensor Network Technology (AquaSeNT) has pioneered orthogonal frequency division multiplexing (OFDM) technology for subsea communication.

•  AquaSeNT’s OFDM technology has the capacity to deliver more information using a narrower bandwidth than competing technologies.

•  Founders: •  Dr. Jun-Hong Cui - networking theory •  Dr. Shengli Zhou- digital signal processing •  Dr. Jerry Shi - low power, embedded system

design

AquaSeNT Company Overview

•  Founded in 2007

•  3 founders from the University of Connecticut School of Engineering

•  Part of UConn’s Technology Incubation Program

•  Located in Storrs and Groton Connecticut, USA

•  3 full time employees, 9 P/T

•  Leverage over $10 million in research funding by NSF & Office of Naval Research

•  Phase 1 and Phase 2 SBIR grantee

•  Today: early stage of commercialization; seeking development opportunities

AquaSeNT Technology & Product Development Status •  8 years of technology / concept development (academic &

commercial research)

•  Core technology is patented; 2 additional patents pending

•  Thousands of hours of lab and lake tests

•  Prototype testing, Fall, 2011 •  -  Validated 3100 bps / 5 km range / horizontal communication

channel •  -  High “multipath” environment where other systems fail

•  6 months continuous service, Chesapeake Bay NOAA application

•  Commercial launch: October 2012

•  AquaSeNT technology: adapted OFDM modulation techniques from WIFI and the telecommunications industry to underwater communication; data is transmitted in parallel, not in series, delivering significant benefits to the user

AquaSeNT: Applications

•  Research in underwater communications and underwater sensor networks

•  Underwater infrastructure monitoring

•  Environmental monitoring

•  Marine mammal / fisheries monitoring

•  Harbor and port security

•  Tsunami warning

•  Marine resource exploration

•  National security and defense

AquaSeNT Modem Specs

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Rec

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Transm

it

OFDM 3.2kbps 14 to 20kHz

<4km <200m

Dry: 7.6kg Wet: -1.3kg Dry: 16.7lb Wet: -2.8lb

Dia: 168mm Len: 570mm Dia: 6.625” Len: 22.5”

RS-232 Serial

12 to 24V 2A max

<0.12W <0.7W 5 to 20W

Jamming and Anti-jamming

•  Goals for the project:

•  Determine effective network attack techniques for acoustic networks in an aquatic environment

•  Based on those techniques determine solid defenses in an effort to make to network more robust

[1] A. Bruce Carlson, Communications Systems; An Introduction to Signals and Noise in Electrical Communication, 5th ed. , New York, NY: McGraw-Hill, 2010. [2] Aquatic Sensor Network Technology, Products Tab, http://www.aquasent.com/products , Storrs, CT: AquaSeNT, 2013.

Benthos Frequency-Shift Keying (FSK)

Underwater Acoustic Communication

Frequency-Shift Keying

•  One of the basic methods for digital frequency modulation

•  x(t) is a digital signal that controls a switch which selects the modulated frequency from a set of M oscillators

•  The modulated signal is discontinuous at every switching instant t = kD

Frequency-shift keying represented conceptually (Carlson, 619-620)

Sidelobes •  “Unless the amplitude, frequency, and phase

of each oscillator has been carefully adjusted, the resultant output spectrum will contain relatively large sidelobes which don't carry any additional information and thus waste bandwidth.” (Carlson, 619)

Challenges

•  The speed of sound in water •  Approx. 1500 meters/s

•  Signal fading due to •  Sound absorption •  Destructive interference •  Sea surface, sea floor and other object reflections

Benthos Background

•  Founded: 1962 by Samuel O. Raymond in North Falmouth, Mass.

•  During the first thirty years: focused on supplying underwater equipment to military and government markets esp. the scientific community

•  2006: Acquired by Teledyne Technologies Incorporated (Now known as Teledyne Benthos)

History Highlights

•  1985 Benthos imaging and acoustic equipment used by Woods Hole Oceanographic Institution team to discover the remains of the Titanic

•  1989 Benthos deep sea cameras were used by a team led by Dr. Robert Ballard to capture images of the German WWII battleship Bismarck

•  2000 First e-mail sent from a submarine traveling at speed and depth was sent to the surface using Benthos modems Bismarck Wreckage

http://www.wrecksite.eu/docbrowser.aspx?87

Teledyne Benthos Underwater Acoustic Modems

•  These acoustic modems are used around the world to transmit data wirelessly in underwater applications.

•  Benefits include: •  Significant cost saving over expensive underwater

cabling •  Option of extending the reach of cabled networks (by

using a set of sensor nodes that can transfer data back to the cabled networks)

•  Variety of modems available rated for different depths and operation in both shallow or deep water

910 Series ATM-915

•  500 meter depth rated

•  Dimensions: 4.0 inches (diameter) × 32.2 inches (length)

•  Weight: 24 lbs (in air), 8 lbs (in water)

•  Power: 378 W×Hr internal batteries (can also be powered by external source)

•  Frequency Options: Low Freq. (LF): 9-14 kHz Mid Freq. (MF): 16-21 kHz Band C Freq.: 22-27 kHz

910 Series ATM-915 Specifications (cont.)

•  Transducer: Omni directional (180° beam), Directional (60° beam)

•  Connection: MCBH16M connector, wired for dual serial port option

•  Baud Rate: 140-15,360 bps

•  Bit Error Rate: Better than 10-7 with high SNR

•  Data Storage: 6144 kByte Datalogger standard

•  Processing: Data redundancy, ½ rate convolutional coding multipath guard period selection MFSK and PSK modulation scheme

•  Distances/Ranges: 2-6 km common, greater distances possible 20 km+ available using repeater functionality

960 Series ATM-966

•  6,000 meter depth rated

•  Dimensions: 5.0 inches (diameter) × 14.5 inches (length)

•  Weight: 15 lbs (in air), 5 lbs (in water)

•  Power: No internal batteries (12-36 VDC external power required)

•  Frequency Options: Low Freq. (LF): 9-14 kHz Mid Freq. (MF): 16-21 kHz Band C Freq.: 22-27 kHz

910 Series ATM-915 Specifications (cont.)

•  Transducer: Omni directional (180° beam), Directional (60° beam)

•  Connection: MCBH16M connector, wired for dual serial port option

•  Baud Rate: 140-15,360 bps

•  Bit Error Rate: Better than 10-7 with high SNR

•  Data Storage: 6144 kByte Datalogger standard

•  Processing: Data redundancy, ½ rate convolutional coding multipath guard period selection MFSK and PSK modulation scheme

•  Distances/Ranges: 2-6 km common, greater distances possible 20 km+ available using repeater functionality

Resources "910 Series ATM-915." Teledyne Benthos. N.p., n.d. Web. 9 Sept. 2013.

<http://www.benthos.com/index.php/product/acoustic_modems/910-series-atm-915>. "960 Series ATM-966." Teledyne Benthos. N.p., n.d. Web. 9 Sept. 2013.

<http://www.benthos.com/index.php/product/acoustic_modems/960-series-atm-966>. "Acoustic Modems." Dashboard. Teledyne Benthos, n.d. Web. 09 Sept. 2013.

<http://www.benthos.com/index.php/product_dashboard/acoustic_modems>. Carlson, A. Bruce, Paul B. Crilly, and Janet C. Rutledge. Communication Systems:

An Introduction to Signals and Noise in Electrical Communication. Boston: McGraw-Hill, 2002. Print.

Green/ Teledyne Benthos, Inc., Dale. Underwater Acoustic Communications

And Networks. Tech. Wuxi, China: Sixth International Symposium on Underwater

Technology, 2009. Print.

Evologics - S2C Sweep Spread Carrier Technology

Background

•  Evologics is a German company founded in 2000 by leading international scientists

•  They work to develop innovative key technologies for the aerospace, maritime, and offshore industries through engineering and life sciences

•  Improving engineering by learning from nature

Sweep Spread Carrier Technology

Behind the Technology

•  S2C = Sweep Spread Carrier Technology

•  Hydro-acoustics communications mimic dolphin’s sound pattern •  dolphins chirp and sing across broad frequency

bandwidths

•  This technology spreads the signal energy over a wide range of frequencies and adapt the signal structure so that multipath components don’t interfere with each other

Behind the Technology

•  At the receiver end, advanced signal processing collects the energy and converts the signals into narrow band signals •  This achieves significant depression of

disturbances and substantial system gain •  Enables successful decoding of signals in crucial

environments even when the environments are heavily masked by noise

R-Series Underwater Acoustic Modems

Configuration Options

•  Housing: Derlin (high-grade plastic), aluminum-magnesium alloy, stainless steel

•  Interface: RS-232 (RS-485 optional) and/or Ethernet

•  Wake Up Module to save battery power •  Wakes up device only when needed

•  External power supply or internal rechargeable battery pack

References

•  http://www.evologics.de/