In a cognitive radio system, the goal is to make better use of the radio electric spectrum, allowing non-licensed users access to those currently unused electromagnetic bands assigned to licensed users (LUs). This can be achieved using OFDM, where the non-licensed users must select the temporarily available subcarriers and turn off those subcarriers used by LUs in order to avoid interference. Hence, only a subset of the subcarriers can be used for data or pilot tone transmission. To this end, some pilot allocation algorithms have been proposed for this dynamic scenario, but they are designed in such away that an equispaced pilot placement is respected (as much as possible) while minimizing the mean squared error of the channel estimate. Nevertheless, this equispaced placement can lead to the use of an increased number of pilots in order to achieve a good channel estimation. In this work, a new pilot allocation algorithm based on wavelet transform is presented. The proposed algorithm uses the discrete wavelet transform to analyze the previous channel state information, taking the knowledge of the available subcarriers into account to provide a suboptimal solution for the pilot positions. This solution leads to a non-equispaced pilot placement, which improves the channel estimation and consequently, the system performance. Likewise, the introduced algorithm allows a reduction of the number of necessary pilots, which aids in increasing the data rate. Finally, simulation results corroborate the effectiveness of the algorithm in dynamic channel scenarios.

https://link.springer.com/content/pdf/10.1007%2Fs11235-017-0386-0.pdf

Dynamic wavelet-based pilot allocation algorithm for OFDM-based cognitive radio systems

The emerging wireless applications are facing new challenges in combating frequency congestion problems. As a result, the opportunistic utilization of available frequency spectrum and channel bonding is becoming increasingly common in new wireless standards. In these systems, the transmit waveforms are required to have nulls in specific frequency bands to avoid interference with primary users. However, these nulls can significantly affect the performance of channel estimation algorithms. This work proposes a novel Iterative Multiband (MB) Spectrally Constrained Time-Domain (SCTD) technique to developed to reduce the residual error of correlation due to spectrally constrained waveforms. The performance of the newly developed technique is evaluated through extensive numerical experiments, where the Mean Squared Error (MSE) and Bit Error Rate (BER) are computed for various scenarios. The accuracy of the proposed technique is compared with known channel state information and with conventional techniques. The simulation results show that the proposed Time-Domain Iterative Method, SCTD, performs better than conventional techniques for various Rayleigh channel conditions with Additive White Gaussian Noise (AWGN). It was found that after ten iterations, the proposed technique outperforms the conventional technique for both stationary and mobile frequency-selective channels. Furthermore, it was observed that the proposed SCTD technique requires fewer pilot signals to achieve a similar performance. The results show that the proposed SCTD method supersedes the conventional techniques for stationary and mobile frequency selective channel scenarios within ten iterations. Subsequently, it is observed that the proposed SCTD method requires 50% fewer pilots to provide similar performance compared to conventional methods. It is also observed that the proposed SCTD method provides an average of 6 dB mean squared error (MSE) advantage for low signal-to-noise ratio per bit ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Eb / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N 0 ) regime cases. It can be concluded that the proposed technique is highly suitable, particularly for low <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Eb / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N 0 regimes and can be used for various communication systems.

Advancing Multiband OFDM Channel Sounding: An Iterative Time Domain Estimation for Spectrally Constrained Systems

In this paper we consider OFDM systems with non-contiguous subcarriers where distributed spectrum fragments are applicable for transmission. A new model is proposed for pilot optimization with respect to location and power. The least-square approach is applied for channel estimation at the receiver and the optimization objective is to minimize the mean square error of the channel estimation. This optimization problem is then formulated as minimizing the spread of the eigenvalues of a positive semidefinite matrix, which is a typical semidefinite programming problem, and hence it can be solved with conventional interior-point method. Simulation results show the efficiency of the proposed algorithm.

Optimal pilot design for OFDM systems with non-contiguous subcarriers based on semi-definite programming

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of {limit} columns in the table. Remove at least 1 column to add or create another one.

Ting Chen

Author Tools

Chat about Author

Papers

Optimal pilot design for OFDM systems with non-contiguous subcarriers based on semi-definite programming