Wireless data communication and telemetry during drilling deep oil and gas wells are important enablers for safe and timely drilling operations. The transmission of information through drill strings and pipes using sound waves is a useful and practical approach. However, given the limited available bandwidth, transmission rates are typically smaller than what is needed. In this paper, a new method and system are proposed to increase the transmission rate over the same bandwidth, by deploying more than one actuator. Upon using multiple actuators, several data streams can be transmitted simultaneously. This increases the data rate without the need for additional bandwidth. The experimental results of a testbed with two actuators are presented, where the transmission rate is doubled with no bandwidth increase. A strain sensor receiver and accelerometer receivers are used to separate and demodulate the two data streams. It is demonstrated that it is possible to recover the data in the new faster system benefiting from two actuators, while having about the same bit error probability performance as a one-actuator system. Various combinations of strain and acceleration sensors are considered at the receive side. Due to some properties of strain channels (e.g., smaller delay spreads and their less-frequency-selective behavior) presented in this paper, it appears that a strain sensor receiver and an accelerometer receiver together can offer a good performance when separating and demodulating the two actuators’ data in the testbed. Overall, the experimental results from the proposed system suggest that upon using more than one actuator, it is feasible to increase the data rate over the limited bandwidth of pipes and drill strings.
Chirp signals, also known as linear frequency modulated signals, are widely used for synchronization, signal acquisition, and frame detection in underwater communication systems. This is due to the peak at the output of the chirp matched filter at the receive side. In low signal-to-noise ratio (SNR) scenarios, however, this peak can be buried in noise, which results in major synchronization errors and system performance loss. While a scalar array of spatially separated hydrophones can increase SNR to improve synchronization, the size of the array may not be suitable for small platforms. Acoustic vector sensors, on the other hand, are small-size devices that can serve as multichannel communication receivers. In this paper, performance of a vector sensor receiver for synchronization using a chirp signal is studied. Our experimental results indicate that a compact vector sensor receiver can significantly enhance the output of the filter matched to the chirp signal. This is because the proposed vector matched filter significantly suppresses the noise and provides a sharp peak at the output. This is particularly important for synchronization and signal acquisition in underwater communication systems operating in low SNR environments. [This work was supported in part by the National Science Foundation (NSF), Grant IIP-1500123.]
Vector sensors and transducers are compact multichannel devices that can be used for underwater communication via acoustic particle velocity channels (A. Abdi and H. Guo, “A new compact multichannel receiver for underwater wireless communication networks,” IEEE Transactions on Wireless Communications, vol. 8, pp. 3326-3329, 2009). In this paper, a multiple-input multiple-output (MIMO) underwater acoustic communication system is presented using orthogonal frequency division multiplexing (OFDM) modulation. Upon transmitting multiple independent data streams simultaneously over several channels, this MIMO system can increase the transmission rate, whereas the OFDM modulation mitigates the highly frequency selective underwater channels. Various components of the system including vector transducers and algorithms for synchronization, channel estimation, MIMO detection, channel coding, etc., are designed and implemented. Using this system, experiments are conducted to measure and study acoustic particle velocity channels in the MIMO setup. Additionally, system performance parameters such as bit error rate and spectral efficiency are measured and discussed for various conditions and configurations, to understand the performance of the developed vector MIMO-OFDM system. [The work was supported in part by the National Science Foundation (NSF), Grant IIP-1500123.]
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