Experimental demonstration of multiuser communication in deep water using time reversal

Abstract

Multiuser communication is demonstrated using experimental data (450-550 Hz) collected in deep water, south of Japan. The multiple users are spatially distributed either in depth or range while a 114-m long, 20-element vertical array (i.e., base station) is deployed to around the sound channel axis (~1000 m). First, signals received separately from ranges of 150 km and 180 km at various depths are combined asynchronously to generate multiuser communication sequences for subsequent processing, achieving an aggregate data rate of 300 bits/s for up to three users. Adaptive time reversal is employed to separate collided packets at the base station, followed by a single channel decision feedback equalizer. Then it is demonstrated that two users separated by 3 km in range at ~1000 m depth can transmit information simultaneously to the base station at ~500 km range with an aggregate data rate of 200 bits/s.

Equivalence of adaptive time reversal and least squares for cross talk mitigation

“…5 in Ref. 6, Thus the ATR subsequently is followed by a DFE to suppress the residual ISI (ATR-DFE). In contrast, multi-carrier MIMO-OFDM assumes that the channel frequency responses H i (f) are flat over the bandwidth of each subcarrier (i.e., no ISI) and an additional equalizer is not required.…”

“…6,11 In this letter, the ATR weight vector in the frequency domain is further analyzed and shown essentially equivalent to the least squares (LS) solution to an overdetermined system with a matrix consisting of channel transfer function vectors from each user or transmitter as the columns.…”

“…As a result, adaptive time reversal (ATR) combining followed by a DFE (ATR-DFE) has been developed to suppress the CCI, offering significant performance improvement over the CTR counterpart (CTR-DFE). 6,11 Subsequently, two similar approaches have been proposed to provide an additional CCI mitigation: Successive interference cancellation (SIC) 12 and parallel interference cancellation (PIC). 3 Note that both approaches are applied to a single-channel time series after CTR multichannel combining [i.e., q(t)] to remove the CCI, but prior to the DFE, such that CTR-SIC-DFE and CTR-PIC-DFE, respectively.…”

Introduction of measurement techniques in ultrasonic electronics: Basic principles and recent trends

“…[500][501][502][503][504][505][506][507][508][509][510][511][512] A combination of signal processing and physics (using a sensor array) is also utilized for communication as a time-reversal approach. [513][514][515][516][517][518][519][520][521][522] Underwater positioning is a technique to determine the positions of vehicles underwater by measuring distances and directions, and experimental results and the improvement of accuracy by utilizing signal processing techniques (e.g., the use of reflected signals) have been reported. 501,[523][524][525][526][527][528] To support these applications, underwater acoustic transducers are necessary.…”

Experimental demonstration of single carrier underwater acoustic communication using a vector sensor

“…So a vertical array with multiple sensors is always used in single carrier communications. Song et al [12][13][14] studied time reversal DFE which is proved to have a similar performance with multichannel DFE [15,16]. Both methods exploit spatial diversity achieved by a vertical array to get nearly ideal results.…”