Towards A Practical Multicarrier Modem for Underwater Telemetry and Distributed Networks

Transcription

1 Towards A Practical Multicarrier Modem for Underwater Telemetry and Distributed Networks Dr. Shengli Zhou Underwater Sensor Network Laboratory, University of Connecticut August 16, 2012 The success of multicarrier modulation in the form of orthogonal-frequency-division-modulation (OFDM) in radio channels illuminates a clear path one could take towards high-rate underwater acoustic communications. However, earlier work on the application of OFDM in underwater has only had limited success. We aim to make OFDM work for underwater acoustic channels and build a practical multicarrier modem prototype. We have worked on four different aspects of this problem. Modulation: Make OFDM work underwater. Channel coding: Drastically improve the system performance. Detection and synchronization: Pave the way towards online receivers. Prototype development: Put our algorithms into practice. Our progress is summarized as follows. 1 Modulation 1.1 SIMO-OFDM For an OFDM system with a single transmitter, the goal is to improve the error performance, especially the robustness against fast channel variations. The main challenge is to deal with the intercarrier interference (ICI) due to the channel Doppler effects. The following journal papers document different receivers that we have developed. ICI-ignorant receiver [1]. The performance can be improved by noise whitening [2]. ICI-aware receiver [3]. Frequency-domain oversampling can further improve the performance [4]. A better channel parameterization can also improve the performance [5]. ICI-progressive receiver [6]. It can self-adapt to changing channel conditions without a prior information. The progressive receiver can be initiated by the channel estimate from the previous block [7]. A block-to-block adaptive receiver which models channel variations in a cluster-by-cluster fashion [8]. We have contributed an overview paper on the application of compressive sensing for sparse channel estimation in the IEEE Communications Magazine, Nov [9]. The results on SIMO-OFDM have been presented in various conferences [10 18, 18 21]. 1

2 1.2 MIMO-OFDM The use of MIMO is to increase the data rate through parallel transmissions. We have developed the following receivers. Non-iterative ICI-ignorant receiver [22]. Iterative ICI-ignorant receiver using the Turbo principle [23]. ICI-aware/progressive MIMO-OFDM receiver [24]. The results on MIMO-OFDM have been presented in various conferences [25, 25 28]. 1.3 OFDM for deep water acoustic channels Deep water horizontal acoustic channels have extremely long delay spreads but tend to have a clustered multipath structure. For such a type of channels, we have developed a multiuser based receiver [29] and a factor-graph based receiver [30, 31], where the interblock interference (IBI) and the intercarrier interference (ICI) are jointly mitigated. 1.4 OFDM in the presence of external interference An OFDM receiver in the presence of Sonar interference [32, 33]. 1.5 Multiuser OFDM A receiver for asynchronous multiuser OFDM [34]. 2 Channel Coding Gallager s low-density-parity-check (LDPC) codes achieve Shannon capacity in additive-white-gaussian-noise (AWGN) channels. We have constructed nonbinary LDPC codes for underwater OFDM systems [35], [36]. Further, we have constructed quasi-cyclic (QC) nonbinary LDPC codes with various code lengths [37 39]. Codes with multiple rates and multiple lengths will facilitate future work on adaptive modulation and coding (AMC). Our experience with real data is that whenever the uncoded BER is below 0.1, normally no decoding errors will occur for the rate 1/2 nonbinary LDPC codes used. Hence, the goal of OFDM demodulation is to achieve an uncoded BER within the range of 0.1 and Nonbinary LDPC coding will then boost the overall system performance. 3 Detection and Synchronization Existing synchronization used in underwater telemetry are almost exclusively based on linearly frequency modulated (LFM) signals, also known as Chirp signals. This approach suffers from the following two deficiencies: first, the noise level at the receiver has to be constantly estimated to achieve a constant false alarm rate (CFAR), usually accomplished using order statistics; second, its performance will degrade in the presence of dense and unknown multipath channels. 2

3 We develop a novel method that utilizes multicarrier waveforms for detection, synchronization and Doppler scale estimation [40, 41]. Compared with the LFM-preamble based approach, the proposed method has the following advantages: (1) the detection threshold is between 0 and 1, and doesn t depend on the channel or operating SNR; (2) it has a very good detection performance, which is based on the signal energy from all paths rather than only a single path; (3) it leads to accurate Doppler scale estimation; (4) after coarse timing and resampling, it allows the use of fine timing algorithms developed for radio channels; (5) the algorithm can be implemented with very low complexity, as done in [42]. The proposed method can start decoding when each OFDM block comes in (no need to buffer a data packet of multiple OFDM blocks). This paves the way towards online receiver operation for multicarrier underwater acoustic communication. In a recent work [43], we have compared different synchronization approaches for both single-user and multiuser OFDM systems. 4 Prototype Development 1. PC-based implementation as reported in [44]. See Fig. 1. This implementation is based on Matlab programming on two laptops. Two laptops can communicate with each other via two-way acoustic links. Link A to B Link B to A Figure 1: The PC-based prototype with two-way communication 2. DSP-based implementation as reported in [42, 45, 46]. See Fig. 2. This implementation is based on a TMS320C6713 DSP board. For an OFDM block duration of 230 ms, the demodulation-plus-decoding time at the receiver is about 200 ms, and hence a real-time one-way communication is accomplished. The bandwidth is 5.5 khz, and the overall data rate is 3.1 kbps after rate 1/2 convolutional coding. Figure 2: The DSP-based prototype for real-time one-way communication 3

4 These two prototypes were demonstrated at WUWNet, Montreal, Sept A three-node relay network as reported in [47]. See Fig. 3 Figure 3: The three-node testbed using the water tank Building upon the point-to-point data transmission, we have designed and experimented a three-node underwater relay network. We considered two scenarios for generating messages. In the first scenario, a message input from the graphic user interface can be transmitted to any specified destination in the network. In the second scenario, a motion sensor is attached to one node for continuous motion monitoring. Once an event is detected, an alert message is generated and broadcast to the whole network. We have tested the three-node network in a water tank and in a lake. 4. PC-based and DSP-based (2 2) MIMO-OFDM acoustic modem prototypes are demonstrated in WUWNet, San Francisco, CA, Sept. 15, 2008; See Fig. 4. Using two transmitters, the data rate is 6.2 kb/s, with QPSK modulation, rate 1/2 coding, and a bandwidth of 5.5 khz. Figure 4: The MIMO-OFDM prototypes (left) PC based and (right) DSP based implementation These two prototypes were demonstrated at WUWNet, San Francisco, CA, Sept and won the first-prize in demo category, as voted by workshop participants. 5. A stand-alone OFDM modem, termed as Aqua-fModems, was demonstrated at WUWNET, Berkeley, Nov. 2, 2009, and at WUWNET, Woods Hole, Sept. 30, 2010; See Fig. 5 for the stand-alone modem. 6. The application of the Aqua-fModems developed in [45, 46] can be found in [48 50], where five Aqua-fModems have been used to test a localization algorithm. 7. MAC protocols have been running on Aqua-fModems [51]. The demos of networked OFDM Modems have been done in MobiCom 2011, and WUWNET 2011, as shown Fig. 7. 4

5 Figure 5: The Aqua-fModem prototype Figure 6: The Aqua-fModem demonstration setup 8. The article DSP based receiver implementation for OFDM acoustic modems [46] is featured online on Advances In Engineering, August Commercialization Three patents based on the results in [1], [41], [35], respectively, have been exclusively licensed to Aquatic Sensor Network Technologies (AquaSeNT), LLC. 6 List of Experiments The publications in this document have used real data collected from the following experiments. WHOI06 AUVFest07 RACE08 GLINT08 5

6 Figure 7: The networking demo with four Aqua-fModems SPACE08 AUTEC08 WHOI09 MACE10 ACOMM10 AUTEC10 7 Acknowledgements Our research is supported by Office of Naval Research and National Science Foundation. We are grateful to our co-authors for fruitful research collaborations and to the engineering teams who carry out various experiments. References [1] B. Li, S. Zhou, M. Stojanovic, L. Freitag, and P. Willett, Multicarrier communication over underwater acoustic channels with nonuniform Doppler shifts, IEEE Journal of Oceanic Engineering, vol. 33, no. 2, pp , Apr [2] C. R. Berger, W. Chen, S. Zhou, and J. Huang, A simple and effective noise whitening method for underwater acoustic orthogonal frequency division multiplexing, Journal of Acoustical Society of America, vol. 127, no. 4, pp , Apr [3] C. R. Berger, S. Zhou, J. Preisig, and P. Willett, Sparse channel estimation for multicarrier underwater acoustic communication: From subspace methods to compressed sensing, IEEE Transactions on Signal Processing, vol. 58, no. 3, pp , Mar

7 [4] Z.-H. Wang, S. Zhou, G. B. Giannakis, C. R. Berger, and J. Huang, Frequency-domain oversampling for zeropadded OFDM in underwater acoustic communications, IEEE Journal of Oceanic Engineering, vol. 37, no. 1, pp , Jan [5] X. Xu, Z.-H. Wang, S. Zhou, and L. Wan, Parameterizing both path amplitude and delay variations of underwater acoustic channels for block decoding of orthogonal frequency division multiplexing, The Journal of the Acoustical Society of America, vol. 131, pp , June [6] J.-Z. Huang, S. Zhou, J. Huang, C. Berger, and P. Willett, Progressive inter-carrier interference equalization for OFDM transmission over time-varying underwater acoustic channels, IEEE J. Select. Topics Signal Proc., vol. 5, no. 8, pp , Dec [7] J.-Z. Huang, S. Zhou, and Z.-H. Wang, Robust initialization with reduced pilot overhead for progressive underwater acoustic OFDM receivers, in Proc. of MILCOM Conference, Baltimore, Maryland, Nov. 7-10, [8] Z.-H. Wang, S. Zhou, J. Preisig, K. R. Pattipati, and P. Willett, Clustered adaptation for estimation of time-varying underwater acoustic channels, IEEE Transactions on Signal Processing, vol. 60, no. 6, pp , June [9] C. R. Berger, Z.-H. Wang, J.-Z. Huang, and S. Zhou, Application of compressive sensing to sparse channel estimation, IEEE Communications Magazine, vol. 48, no. 11, pp , Nov [10] B. Li, S. Zhou, M. Stojanovic, and L. Freitag, Pilot-tone based ZP-OFDM demodulation for an underwater acoustic channel, in Proc. of MTS/IEEE OCEANS Conference, Boston, MA, Sept , [11] B. Li, S. Zhou, M. Stojanovic, L. Freitag, and P. Willett, Non-uniform Doppler compensation for zero-padded OFDM over fast-varying underwater acoustic channels, in Proc. of MTS/IEEE OCEANS Conference, Aberdeen, Scotland, June 18-21, [12] B. Li, S. Zhou, J. Huang, and P. Willett, Scalable OFDM design for underwater acoustic communications, in Proc. of Intl. Conf. on ASSP, Las Vegas, NV, Mar. 30 Apr. 4, [13] S. Mason, C. Berger, S. Zhou, K. Ball, L. Freitag, and P. Willett, An OFDM design for underwater acoustic channels with Doppler spread, in Proc. of the 13th DSP Workshop, Marco Island, FL, January 4-7, [14] C. R. Berger, S. Zhou, J. Preisig, and P. Willett, Sparse channel estimation for multicarrier underwater acoustic communication: From subspace methods to compressed sensing, in Proc. of MTS/IEEE OCEANS Conference, Bremen, Germany, May 11-14, [15] S. Mason, C. Berger, S. Zhou, K. Ball, L. Freitag, and P. Willett, Receiver comparisons on an OFDM design for Doppler spread channels, in Proc. of MTS/IEEE OCEANS Conference, Bremen, Germany, May 11-14, [16] C. R. Berger, S. Zhou, W. Chen, and J. Huang, A simple and effective noise whitening method for underwater acoustic OFDM, in Proc. of MTS/IEEE OCEANS Conference, Biloxi, Mississippi, USA, Oct , [17] J.-Z. Huang, C. R. Berger, S. Zhou, and J. Huang, Comparison of basis pursuit algorithms for sparse channel estimation in underwater acoustic OFDM, in Proc. of MTS/IEEE OCEANS Conference, Sydney, Australia, May 24 27, [18] Z.-H. Wang, S. Zhou, G. B. Giannakis, C. R. Berger, and J. Huang, Frequency-domain oversampling for zeropadded OFDM in underwater acoustic communications, in Proc. of Global Telecommunications Conference, Miami, Florida, USA,, Dec

8 [19] J.-Z. Huang, S. Zhou, J. Huang, C. R. Berger, and P. Willett, Progressive inter-carrier interference equalization for OFDM transmission over time-varying underwater acoustic channels, in Proc. of MTS/IEEE OCEANS Conference, Sydney, Australia, May 24 27, [20] W. Zhou, Z.-H. Wang, J. Huang, and S. Zhou, Blind CFO estimation for zero-padded OFDM over underwater acoustic channels, in Proc. of MTS/IEEE OCEANS Conference, KONA, Hawaii, September 19-22, [21] Z.-H. Wang, S. Zhou, J. Preisig, K. Pattipati, and P. Willett, Per-cluster-prediction based sparse channel estimation for multicarrier underwater acoustic communications, in Proc. of IEEE International Conference on Signal Processing, Communications and Computing, Xi an, China, September 14-16, [22] B. Li, J. Huang, S. Zhou, K. Ball, M. Stojanovic, L. Freitag, and P. Willett, MIMO-OFDM for high rate underwater acoustic communications, IEEE Journal of Oceanic Engineering, vol. 34, no. 4, pp , Oct [23] J. Huang, J.-Z. Huang, C. R. Berger, S. Zhou, and P. Willett, Iterative sparse channel estimation and decoding for underwater MIMO-OFDM, EURASIP Journal on Advances in Signal Processing, vol. 2010, Article ID , 11 pages, doi: /2010/ [24] J.-Z. Huang, S. Zhou, J. Huang, J. Preisig, L. Freitag,, and P. Willett, Progressive intercarrier and co-channel interference mitigation for underwater acoustic MIMO-OFDM, Wireless Communications and Mobile Computing, Feb. 2012, doi: /wcm [25] J.-Z. Huang, S. Zhou, J. Huang, J. Preisig, L. Freitag, and P. Willett, Progressive MIMO-OFDM reception over time-varying underwater acoustic channels, in Proc. of 44th Asilomar Conf. Signals, Systems, and Computers, Pacific Grove, CA, Nov [26] B. Li, S. Zhou, M. Stojanovic, L. Freitag, J. Huang, and P. Willett, MIMO-OFDM over an underwater acoustic channel, in Proc. of MTS/IEEE OCEANS Conference, Vancouver, BC, Canada, Sept Oct. 4, [27] B. Li, J. Huang, S. Zhou, K. Ball, M. Stojanovic, L. Freitag, and P. Willett, Further results on high-rate MIMO- OFDM underwater acoustic communications, in Proc. of MTS/IEEE OCEANS Conference, Quebec City, Canada, Sept , [28] J. Huang, J.-Z. Huang, C. R. Berger, S. Zhou, and P. Willett, Iterative sparse channel estimation and decoding for underwater MIMO-OFDM, in Proc. of MTS/IEEE OCEANS Conference, Biloxi, Mississippi, USA, Oct , [29] Z.-H. Wang, S. Zhou, J. Catipovic, and J. Huang, OFDM in deep water acoustic channels with extremely long delay spread, in Proc. of the ACM International Workshop on UnderWater Networks (WUWNet), Woods Hole, MA, Sept Oct. 1, [30], Factor-Graph based joint IBI/ICI mitigation for OFDM in underwater acoustic multipath channels with longseparated clusters, IEEE Journal of Oceanic Engineering, 2012 (to appear). [31], A factor-graph based ZP-OFDM receiver for deep water acoustic channels, in Proc. of MTS/IEEE OCEANS Conference, Seattle, Washington, September 20-23, [32] Z.-H. Wang, S. Zhou, J. Catipovic, and P. Willett, Parameterized cancellation of partial-band partial-block-duration interference for underwater acoustic OFDM, IEEE Transactions on Signal Processing, vol. 60, no. 4, pp , Apr

9 [33], Parameterized cancellation of partial-band partial-block-duration interference for underwater acoustic OFDM, in Proc. of the ACM International Workshop on UnderWater Networks (WUWNet), Seattle, Washington, USA, Dec. 1-2, [34], Asynchronous multiuser reception for OFDM in underwater acoustic communications, in Proc. of IEEE/MTS OCEANS conference, May [35] J. Huang, S. Zhou, and P. Willett, Nonbinary LDPC coding for multicarrier underwater acoustic communication, IEEE Journal on Selected Areas in Communications, vol. 26, no. 9, pp , Dec [36], Nonbinary LDPC coding for multicarrier underwater acoustic communication, in Proc. of MTS/IEEE OCEANS Conference, Kobe, Japan, April 8-11, [37] J. Huang, L. Liu, W. Zhou, and S. Zhou, Large-girth nonbinary QC-LDPC codes of various lengths, IEEE Transactions on Communications, vol. 58, no. 12, pp , Dec [38] J. Huang, W. Zhou, and S. Zhou, Structured nonbinary rate-compatible low-density parity-check codes, IEEE Communications Letters, vol. 15, no. 9, pp , Sept [39] L. Liu, W. Zhou, and S. Zhou, Nonbinary multiple rate QC-LDPC codes with fixed information or block bit length, Journal of Communications and Networks, vol. 14, no. 4, pp , Aug [40] S. Mason, C. R. Berger, S. Zhou, and P. Willett, Detection, synchronization, and Doppler scale estimation with multicarrier waveforms in underwater acoustic communication, in Proc. of MTS/IEEE OCEANS Conference, Kobe, Japan, April 8-11, [41], Detection, synchronization, and Doppler scale estimation with multicarrier waveforms in underwater acoustic communication, IEEE Journal on Selected Areas in Communications, vol. 26, no. 9, pp , Dec [42] H. Yan, S. Zhou, Z. Shi, and B. Li, A DSP implementation of OFDM acoustic modem, in Proc. of the ACM International Workshop on UnderWater Networks (WUWNet), Montréal, Québec, Canada, September 14, [43] L. Wan, Z.-H. Wang, S. Zhou, T. Yang, and Z. Shi, Performance comparison of doppler scale estimation methods for underwater acoustic OFDM, Journal of Electrical and Computer Engineering, Special Issue on Underwater Communications and Networks, 2012, doi: /2012/ [44] S. Mason, R. Anstett, N. Anicette, and S. Zhou, A broadband underwater acoustic modem implementation using coherent OFDM, in Proc. of National Conference for Undergraduate Research (NCUR), San Rafael, California, April [45] H. Yan, S. Zhou, Z. Shi, J.-H. Cui, L. Wan, J. Huang, and H. Zhou, DSP implementation of SISO and MIMO OFDM acoustic modems, in Proc. of MTS/IEEE OCEANS Conference, Sydney, Australia, May 24 27, [46] H. Yan, L. Wan, S. Zhou, Z. Shi, J.-H. Cui, J. Huang, and H. Zhou, DSP based receiver implementation for OFDM acoustic modems, Elsevier Journal on Physical Communication, 2011; doi: /j.phycom [47] K. Jusufi, R. Behymer, M. Hoyer, and S. Zhou, Designing a three-node underwater acoustic relay network, in Proceedings of The National Conference On Undergraduate Research (NCUR), April [48] P. Carroll, S. Zhou, H. Zhou, J.-H. Cui, and P. Willett, Underwater localization based on multicarrier waveforms, in Proc. of MTS/IEEE OCEANS Conference, Seattle, Washington, September 20-23, [49], Localization and tracking of underwater physical systems, in Proc. of CHINACOM, Harbin, China, August 17-19,

10 [50] P. Carroll, S. Zhou, H. Zhou, X. Xu, J.-H. Cui, and P. Willett, Underwater localization and tracking of physical systems, Journal of Electrical and Computer Engineering, Special Issue on Underwater Communications and Networks, 2012, doi: /2012/ [51] Z. Peng, H. Mo, J. Liu, Z. Wang, H. Zhou, X. Xu, S. Le, Y. Zhu, J.-H. Cui, Z. Shi, and S. Zhou, NAMS: A networked acoustic modem system for underwater applications, in Proc. of MTS/IEEE OCEANS Conference, KONA, Hawaii,, September 19-22, [52] J. Liu, Z.-H. Wang, Z. Peng, M. Zuba, J.-H. Cui, and S. Zhou, TSMU: A time synchronization scheme for mobile underwater sensor networks, in Proc. of GLOBECOM, Houston, TX, Dec. 5-9,