| 1. |
- Al-Askary, Omar
(författare)
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Papr reduction of coded OFDM signals based on iterative codeword construction
- 2004
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Ingår i: ISCCSP. - NEW YORK : IEEE. - 0780383796 ; , s. 763-766
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Konferensbidrag (refereegranskat)abstract
- Orthogonal Frequency Division Multiplexing (OFDM) allows transmission of data with high data rates over broad-band radio channels without the need for powerful equalization. However, OFDM is sensitive to non-linearities in the system due to the high Peak to Average Power Ratio (PAPR) in the transmitted signal. In this paper, we propose a simple method for reducing the PAPR in the OFDM signals using the well known BCH codes. The method relies on an iterative procedure to select a codeword that has a low PAPR from a translation of the code to another partition in a larger BCH code. The information about the chosen partition is loaded in the redundancy of the sent codeword and, therefore, no subcarriers are reserved for transmitting this information. The cost payed for this PAPR reduction is reduced error correction capability. Using this method, a reduction of the PAPR of up to 6 dB can be achieved with moderate complexity.
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| 2. |
- Gustafsson, Oscar, et al.
(författare)
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MILP design of frequency-response masking FIR filters with few SPT terms
- 2004
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Ingår i: First International Symposium on Control, Communications and Signal Processing, 2004. - Tunisia : IEEE. - 0780383796 ; , s. 405-408
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Konferensbidrag (refereegranskat)abstract
- In this work we formulate a mixed integer linear programming (MILP) problem that minimizes the number of signed-power-of- two (SPT) terms given a filter specification for linear-phase frequency-response masking (FRM) filters. The proposed method designs the filters in two steps. The model filter and the masking filters are designed separately, but subject to each other. Hence, it is not guaranteed that the global minimum is obtained. However, each solution is optimal given the other filter(s), and iteration may improve the overall solution. The filter design problems are formulated using normalized peak ripple magnitude (NPRM), which for FRM filters introduces some implications, which is also discussed in this work.
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| 3. |
- Ljung, Lennart
(författare)
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Challenges of non-linear identification
- 2004
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Ingår i: FIRST INTERNATIONAL SYMPOSIUM ON CONTROL, COMMUNICATIONS AND SIGNAL PROCESSING. - New York, USA : IEEE conference proceedings. - 0780383796 ; , s. 539-539
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Konferensbidrag (refereegranskat)abstract
- Identification of non-linear systems is an important problem in many applications. The topic is substantially richer than linear system identification. One reason for this is of course that the problem is significantly more difficult, but also that it has engaged several different research communities. With origins in statistical non-linear and non-parametric regression theory, areas like neural networks and learning theory can now be seen as research fields in their own right. In addition to the control field, many areas like artificial intelligence, pattern recognition, signal processing, oceanography, geology, etc, have developed their own approaches to the problem. This has lead to a very substantial literature on the topic. This talk will not attempt to give any survey of all approaches. It will focus on some core features of the problem which represent the basic challenges. The foremost problem is the inherent lack of data support to build complex models. A black box model with n explaining variables (regressors) can be seen as a surface in Rn+1. Even for moderately large n, this is a huge space to fill with observations. The remedy will be to assume or look for sub-structures in the model/data, linearity in certain directions etc. For control applications it is natural to complement the data support with structures based on physical insights, "grey-box models". Interfacing physical modeling tools with identification techniques is thus important. Grey-box models, on other hand, typically lead to minimization problem with many local minima. This is another challenge, which possibly can be dealt with using modem computer algebra and optimization techniques.
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