In underwater acoustic communications the time variation in the channel is a huge chal- lenge. The estimation of the impulse response at the receiver is crucial for the decoding of the signal to become accurate. One way is to transmit a superimposed pilot sequence along the unknown message, and by the knowledge of the sequence have the possibility to continuously track the variation in the channel over time. This thesis investigates if it is possible by the aid of superimposed pilot sequences to separate the taps in the channel impulse response and using a parametric method to describe the taps as polynomial phase signals. The method used for separation of the taps was a moving least squares estimator. Thereafter each tap was optimised to a polynomial phase signal (PPS) using a weighted non-linear least squares estimator. The non-linear parameters of the model was then determined with the Levenberg-Marquardt method. The performance of the method was evaluated both for simulated data as well as for data from eld tests. The performance was determined by calculating the mean squared error (MSE) of the model over dierent frame lengths, signal to noise ratio (SNR), weights for the superimposed pilots, rapidness of time variation and impulse response lengths. The method was not sensitive to the properties of the channel. Even though the model had high performance, the complexity of the computations generated long compilation times. Hence, the method needs further work before a real time implementation could be possible.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-74460 |
| Date | January 2019 |
| Creators | Trulsson, Felix |
| Publisher | Luleå tekniska universitet, Institutionen för system- och rymdteknik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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