[PPT] - Underwater Acoustic OFDM: Past, Present, and Future Shengli Zhou PowerPoint Presentation

SLIDE 1

Underwater Acoustic OFDM: Past, Present, and Future

Shengli Zhou

Dept. of Electrical and Computer Engineering

University of Connecticut http://uwsn.engr.uconn.edu

WUWNET’11

Dec. 2, 2011

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 2

Underwater Communications

Cable Acoustic communications (ACOMM) Electromagnetic communications (Wireless Fibre Systems) Optical communications (Blue-Green Laser)

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 3

ACOMM Techniques

Frequency shift keying (FSK)

◮ e.g., Teledyne Benthos, WHOI Micro-modem

Direct sequence spread spectrum (DSSS)

◮ e.g., LinkQuest, DSPCOMM, Tritech

Single carrier phase-shift-keying (PSK) transmissions

◮ e.g., WHOI Micro-modem, Benthos (additional processing card)

Multicarrier modulation (in the form of OFDM)

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 4

OFDM: A Prevalent Choice for Broadband Wireless Systems

DSL Modem WiFi (IEEE 802.11) WiMax (IEEE 802.16) 3GPP-LTE 4G and beyond

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 5

Number of Publications on OFDM

1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2 4 6 8 10 12 14 Year Number of Publications OCEANS Conference Papers IEEE/JASA Journal Papers

1994 - 2005: sporadic effort and little progress 2006 - 2011: sustained effort and great progress

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 6

Outline

OFDM basics: Pros and Cons Algorithm development Prototype development

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 7

Underwater Acoustic Channel Characteristics

The sound propagates too slow!

◮ Long multipath ◮ Fast variation

The SPACE’08 experiment, Martha’s Vineyard, depth 15 m

2 4 6 8 10 12 20 40 60 80 100 delay [ms] amplitude

Fast-varying multipath channel with a large delay spread

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 8

Block Transmission over LTI Channels

Consider a linear time invariant (LTI) multipath channel h(t) =

Np

p=1

Apδ(τ − τp) Time domain waveform distortion; intersymbol interference (ISI) arises; complex channel equalizer needed y(t) = s(t) ∗ h(t) Frequency domain Y (f) = H(f)S(f) If s(t) is carefully constructed with no ISI in frequency domain S(f)|f=fm = s[m] Then no ISI at the receiver side Y (f)|f=fm = H(fm)s[m]

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 9

Basics of Orthogonal Frequency Division Multiplexing

Frequency domain; fm − fk = (m − k) 1

T

S(f) =

k

s[k]sinc

(f − fk)T
,

S(f)|f=fm = s[m]

−5 −4 −3 −2 −1 1 2 3 4 5 −0.2 0.2 0.4 0.6 0.8 1 1.2

Frequency Frequency Fesponse s[k] s[k+1] s[k−1]

Time domain waveform; g(t): rectangular pulse shaper s(t) =

k

s[k]ej2πfktg(t), fk = fc + k T

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 10

Pros and Cons of OFDM

Pros:

◮ Convert a dispersive channel to a set of parallel simple channels

zm = H(fm)s[m] + nm

K/2−1

m=−K/2

◮ Receiver complexity does not depend on the channel delay spread! Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 11

Pros and Cons of OFDM

Pros:

◮ Convert a dispersive channel to a set of parallel simple channels

zm = H(fm)s[m] + nm

K/2−1

m=−K/2

◮ Receiver complexity does not depend on the channel delay spread!

Cons:

◮ Poor performance on faded subchannels. ◮ Sensitive to the Doppler effect ⋆ Doppler shifts destroy the subcarrier orthogonality, and hence leads

to intercarrier interference (ICI)

◮ Large peak-to-average power ratio (PAPR) Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 12

How to Drastically Enhance Performance in Fading Channels?

5 10 15 20 25 10

−6

10

−5

10

−4

10

−3

10

−2

10

−1

10 SNR(dB) average BER fading AWGN

(a) BER vs SNR

−5 5 10 15 20 25 1 2 3 4 5 6 7 8 9 SNR(dB) Capacity fading AWGN

(b) Capacity vs SNR Fading channel drastically affects the uncoded performance Fading channel has the potential for reliable data transmission Solution: coded OFDM with strong codes, e.g., Turbo, LDPC codes that are capacity-achieving

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 13

How to Deal With the Doppler Effect?

ICI is inevitable! Need signal processing algorithms to address ICI explicitly

Signal processing tailored to underwater channels OFDM demodulation

One example: Progressive receiver [JSTSP’2011] There are other alternative approaches

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 14

Progressive Receiver

Adapt the receiver to channel conditions automatically without any a priori information Achieves both low complexity and robust performance over time-varying UWA channels

H0 H1 H2 H3

z

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . = +

n s

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 15

Receiver Structure

No

success or D = Dmax

Yes

Output decisions Nonbinary LDPC decoding ICI equalization Noise variance estimation Channel estimation Increase D; provide soft information Pre-processing; set D = 0

z = HDs + n

1. The system model keeps

being updated Increase the span of ICI in equalization model Increase the maximum possible Doppler spread in channel estimation

2. Soft information from the

channel decoder is utilized

3. No extra pilot-overhead

needed

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 16

Block Success Percentage: SPACE08

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 2 3 4 5 6 7 8 D = 3 D = 2 D = 1 D = 0 Success percentage vs. number of phones

S1 (60 m)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 2 3 4 5 6 7 8 D = 3 D = 2 D = 1 D = 0 Success percentage vs. number of phones

S5 (1000 m) Averaged over Julian dates 295-302 With 4 phones: 90% (D = 0), 95% (D = 1), and up to 98.8% (D = 3)

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 17

How to Alleviate the PAPR Impact?

6 8 10 12 14 16 10

−3

10

−2

10

−1

10 Thresh [dB] Pr(PAPR>Thresh) QPSK 8−QAM 16−QAM Multicarrier without PAPR control

Multicarrier with PAPR control

Single−Carrier

QPSK: The gap between OFDM and single-carrier is about 6dB QAMs: The gap between OFDM and single-carrier is about 4dB Design considerations on power amplifier and transducer:

◮ Peak or average power constrained? Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 18

Summary

OFDM is an elegant scheme It has a clear advantage for short-range long dispersive multipath channels. It is an appealing technique for shallow-water high-data-rate acoustic applications

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 19

WUWNet’07 Demo, Sept. 2007

Link A to B Link B to A

Single-input single-output (SISO) OFDM in-air demonstration The data rate is 3.1 kb/s, with QPSK modulation, rate 1/2 LDPC coding, and bandwidth of 5.5 kHz

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 20

WUWNet’08 Demo, Sept. 2008

Multi-input multi-output (2 × 2) OFDM in-air demonstration The data rate is 6.2 kb/s, with QPSK modulation, rate 1/2 LDPC coding, and bandwidth of 5.5 kHz

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 21

WUWNet’09 and ’10 Demo, Nov. 2009 & Nov. 2010

Aqua-fModem Prototype: With keyboard input and LCD display Floating-point TMS320C6713 DSP board; running @ 225 MHz Fixed-point TMS320C6416 DSP board; running @ 1 GHz

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 22

WUWNET’11 Demo: A Network of Modems

One-hop network, RTS/CTS based MAC protocol

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 23

Current / Future Issues (1)

Multi-input multi-output (MIMO)

◮ Co-located: Increase the data rate via spatial modulation

x1 x2 x Nt . . . y1 y2 y Nr . . . h11 h12 hNtNr

◮ Distributed MIMO, asynchronous MIMO

User 1 User 2 Recivers User 3 v1 v3 = 0 v2

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 24

Current / Future Issues (2)

Interference (Sonar, impulse interference, multiuser interference)

0.5 1 1.5 2 2.5 x 10

6

−600 −400 −200 200 400 600 Timedomain_for_637_phone_10

◮ Interference mitigation / avoidance / alignment / management Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 25

Current / Future Issues (3)

Networking issues

◮ MAC ◮ Routing ◮ Reliable data transfer ◮ Applications

How to efficiently interact with higher layers? Joint optimization (cross-layer design)?

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 26

Thank you!

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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SLIDE 27

Environmental Impact: S1

295 296 297 298 299 300 301 302 303 1 2 3 4 Julian Date in 2008 Wave height (m) 295 296 297 298 299 300 301 302 303 5 10 15 20 Julian Date in 2008 Wind speed (m/s)

295 296 297 298 299 300 301 302 303 1 2 3 4 5 6 7 8 9

All success, Dmax = 0 All success, Dmax = 1 All success, Dmax = 2 All success, Dmax = 3 With errors, Dmax = 3

S1 (60 m) “All success”: all 20 blocks in a file correctly decoded ICI-ignorant receiver (D = 0) works well during calm days ICI-aware receiver (D > 0) is needed when the channel conditions become worse

Shengli Zhou (University of Connecticut) Plenary Talk

Dec. 2, 2011

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