Asynchronous amplify‐and‐forward relay communications for underwater acoustic networks

Abstract

Underwater acoustic communications (UAC) feature frequency-dependent signal attenuation, long propagation delay and doubly-selective fading. Thus the design of reliable UAC protocols is challenging. On the other hand, cooperative relay communications, which have been extensively studied in terrestrial environments, are promising paradigms for reliable communications. However, their application to UAC has not been thoroughly explored. In this study, the authors will design an asynchronous relaying protocol to achieve reliable underwater communications. This new scheme accounts for and takes advantage of the unique characteristics of UAC channels. To avoid time synchronisation difficulty in UAC, and facilitate energy-efficient relay processing, asynchronous amplify-and-forward relaying is adopted in the protocol. In addition, precoded orthogonal frequency division multiplexing is chosen to address the frequency selectivity issue in UAC, while collecting ample multipath diversity provided by the channel and enabled by the asynchronous relaying design. To demonstrate the performance of the protocol, the end-to-end signalto-noise ratio is derived, the average pair-wise error probability is evaluated and the maximum collectable diversity is also proven. Simulations and comparisons are presented to corroborate the analyses and design.

Time Reversal Aided Bidirectional OFDM Underwater Cooperative Communication Algorithm with the Same Frequency Transmission

“…The structure of the self-interference suppressed time reversal cooperative transmission system is shown in Figure 1. Assume the distance between these two sensor nodes is quite far; then because of the severe attenuation over long range underwater acoustic channel, the base station is required for relaying to enable the bidirectional transmission [10]. In Figure 1, taking into account the fact that the size of the sensor nodes is often limited, it supposes only one transmitter and receiver elements are available at each node.…”

“…Figure 6. From Figure 6, it can be seen that the same frequency bidirectional amplify-and-forward underwater cooperative method applied in [10] has poor performance. It requires 25 dB to keep the bit error ratio below 10 −3 .…”

“…Sparsity of underwater acoustic channel is often large in deep sea and calm sea state, while it may be weaker in coastal waters or rough sea state. To this end, a more complex channel Bit error ratio Reference [10] Reference [9] Reference [8] Reference [6] The proposed method Figure 6: Bit error ratio over sparse channel with respect to different signal to noise ratio. is adopted to validate the performance of the proposed timereverse-and-forward underwater acoustic cooperative communication method.…”

“…Comparison of the transmission rate of the proposed time-reverse-and-forward underwater acoustic cooperative communication method to that of the existing cooperative method is shown in Table 1. In Table 1, it can be seen that when the signal to noise ratio is over 15 dB, the transmission rate of the proposed Bit error ratio Reference [10] Reference [9] Reference [8] Reference [6] The proposed method Figure 7: Bit error ratio over complex channel with respect to different signal to noise ratio.…”

Joint Adaptive Combining and Variable Tap-Length Multiuser Detector for Underwater Acoustic Cooperative Communication

“…Therefore, the combining technique would partly influence the system performance. Most of existing studies in underwater acoustic cooperative communication(UACC) system adopt equal gain combining (EGC) [5][6][7][8][9][10][11] or maximum ratio combining (MRC) [5,[12][13][14][15][16]. The MRC approach can achieve better performance.…”