A battery-powered hydroacoustic modem concept has been developed to enable underwater communication. These modems face challenges due to limited computing capacity and battery life. To save power, the modem can go into sleep mode and wake up only when it receives important information, which requires efficient detection algorithms. In the marine environment, interfering factors such as noise, Doppler effects, reflections and signal absorption can affect signal quality and the performance of detection algorithms. The performance of two detection algorithms, one non-coherent and one coherent, was evaluated. For the non-coherent detection algorithm, four different codewords were evaluated and showed that codeword 1 performed best and detected at the lowest SNR. The varying performance between different codewords may be due to the suppression of certain frequencies in different channels. Simulations with different thresholds showed that a threshold of 0 dB gave the best detection performance. The algorithm performed sufficiently in all tested channels and could handle a Doppler velocity of 2 m/s. Its performance decreased at 5 m/s, which was within acceptable limits. For the coherent detection algorithm, a threshold of 0.05 was the best. It met the requirement to handle Doppler velocities of 2 m/s in all channels except one, a channel recorded on Hawaii named KAU2, possibly due to higher time delays in this channel. To reduce the number of replicas in the Doppler bank, an approximately 4 dB higher SNR was required for effective detection, with an increase of 8 dB for Doppler velocities of 5 m/s. A comparison between the two algorithms shows that the choice of the best method depends on the specific conditions and requirements of the particular use case. The coherent detection algorithm is generally preferred because it has high performance in the case of noisy signals, but it fails to detect in some channels due to their conditions. In scenarios where channel conditions vary and it is important to be able to detect in different conditions, even if it means slightly worse noise performance, the non-coherent detection algorithm is more suitable. Also, the coherent detection algorithm may be more suitable for scenarios where faster symbol rate and easier decoding are critical, while the non-coherent detection algorithm may be beneficial in situations where more detailed information from the detection is more important than speed.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-532357 |
| Date | January 2024 |
| Creators | Schönfeldt, Tyra |
| Publisher | Uppsala universitet, FREIA |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | UPTEC F, 1401-5757 ; 24038 |
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