In order to meet future communication system requirements channel estimation over fast fading and frequency selective channels is crucial. In this paper Space Alternated Generalized Expectation Maximization Maximum a Posteriori (SAGE-MAP) based channel estimation algorithm is proposed for Orthogonal Frequency Division Multiplexing (OFDM) systems for Autoregressive (AR) modeled time-varying sparse channels. Also an initialization algorithm has been developed from the widely used sparse approximation ...

In this paper a new transmit diversity technique is proposed for wireless communications over frequency selective fading channels. The proposed technique utilises orthogonal frequency division multiplexing (OFDM) to transform a frequency selective fading channel into multiple flat fading subchannels on which first space-frequency coding and then additional space-time coding are applied resulting in a space-time-frequency OFDM (STF-OFDM) scheme. This scheme provides a quasi-orthogonal 4 x 4 ...

In general commercially available software tools are preferred to design broadband matching networks for wireless communication systems. But they need a properly selected matching network topology with good initial element values. Therefore in this paper a new real frequency technique is presented to generate broadband single matching networks with suitable initial element values. In the proposed method load impedance is written in terms of ABCD-parameters of the desired matching network and the ...

Underwater acoustic communication is a rapidly growing field of applied research and is a technique of sending and receiving message below water. There are several ways of doing such communication but the most common one is realized by using transducers. In underwater acoustic communication one of the most important problems is driving the transducers with matched network. In this study design of impedance matching network for B&K 8104 hydrophone that can be used for underwater communication was ...

A new method is introduced to design mixed lumped and distributed element network

To design broadband matching networks for microwave communication systems commercially available computer aided design (CAD) tools are always preferred. But these tools need proper matching network topology and element values. Therefore in this paper a practical method is proposed to generate distributed-element matching networks with good initial element values. Then the gain performance of the designed matching network can be optimized employing these tools. The utilization of the proposed method ...

Computer-aided design (CAD) tools are always preferred for designing broadband matching networks. However these tools give excellent results when the suitable matching network topology and initial element values are provided. Therefore in this brief a new initialization algorithm is proposed to get suitable network topology and element values for CAD tools. Then the power transfer capability of the matching network can be improved by using any CAD tool. It is clear from the example studied that ...

In literature there exist some tables containing normalized element values to design low-pass lumped-element prototype filters with several different responses like maximally flat or equal-ripple. In this work an algorithm is presented to form such tables for stepped impedance prototype filters. By using the proposed algorithm a table for 0.5 dB equal-ripple stepped impedance prototype filter is formed. Then a design example is given to show the utilization of the formed table.

Cognitive radios (CRs) may be sharing multiple frequency bands with primary systems if the CR is a wideband or an ultra wideband (UWB) system. In that case the CR should ensure all the coexisting primary systems in these bands are detected before it can start data transmission. In this work we study the primary system detection performance of a wideband CR assuming that there are multiple coexisting primary systems and that these primary systems may be jointly active. Accordingly we consider the ...

Underlay ultra wideband (UWB) systems have to be able to detect the presence of primary systems operating in the same band for detect-and-avoid (DAA) operation. In this paper the performances of joint and independent detection of multiple primary systems are investigated assuming that the primary systems are potentially dependent (e.g. frequency division duplex uplink-downlink communications). Joint detection is performed based on generating the maximum a posteriori (MAP) decision variables at the ...