SIViP (2011) 5:389–397 DOI 10.1007/s11760-010-0162-z ORIGINAL PAPER An optimized transmultiplexer using combinational window functions Ram Kumar Soni · Alok Jain · Rajiv Saxena Received: 15 July 2009 / Revised: 25 March 2010 / Accepted: 5 April 2010 / Published online: 28 April 2010 © Springer-Verlag London Limited 2010 Abstract This paper proposes an efficient approach for the design of M-channel maximally decimated near-perfect reconstruction (NPR) type transmultiplexer. Cosine modu- lation is used to design the synthesis and analysis sections of the transmultiplexer. The prototype filter is designed by using high sidelobe falloff rate (SLFOR) combinational win- dow functions. A bisection-type optimization algorithm has been applied to minimize the interference parameters like inter-channel interference (ICI) and inter-symbol interfer- ence (ISI). The proposed algorithm has certain advantages than earlier reported work. The algorithm is of general- ized nature, independent of the window function used in the design of the prototype filter. Second, it is fast and compu- tationally efficient as only a single parameter is used as a variable which provides almost uniform interference level in all subchannels. Design examples are included for compari- son with earlier reported work. Very small values of ICI and ISI have been obtained by using variable and combinational window functions. R. K. Soni (B ) Department of Electronics and Communication Engineering, Samrat Ashok Technological Institute (Polytechnic), Vidisha, India e-mail: soniram04@rediffmail.com A. Jain Department of Electronics and Instrumentation Engineering, Samrat Ashok Technological Institute, Vidisha, India e-mail: alokjain6@rediffmail.com R. Saxena Department of Electronics and Communication Engineering, Jaypee Institute of Engineering and Technology, Raghogarh, Guna, India e-mail: rajiv.saxena@jiet.com Keywords OFDM · ICI · ISI · CMT · DWMT · Combinational window functions 1 Introduction Orthogonal frequency division multiplexing (OFDM) and discrete multitone transmission (DMT) are the widely used technologies in multicarrier communication [1]. Both tech- nologies employ the inverse discrete Fourier transform (IDFT) and discrete Fourier transform (DFT) for the modula- tion and demodulation of the signals. Due to multipath fading over wireless communication, the consecutive OFDM sym- bols overlap at the receiver and gives rise to ISI [2]. In order to minimize the ISI, the OFDM system makes use of the guard band, which results in loss of spectral efficiency [3]. In addition, since the DFT-based modulation filters have side- lobes of the order of -13 dB, the significant spectral overlap between the sub-carriers causes ICI [4]. Many authors have worked on this issue and suggested filterbank-based multi- carrier transmission systems (FB-MCTs), such as the over- lapped DMT [4], filtered multitone transmission (FMT) [5] and discrete wavelet multitone transmission (DWMT) [6]. These FB-MCTs systems use filters of greater length than the rectangular filters of DMT systems and typically yield results with improvement in sidelobes attenuation, lower lev- els of ICI, ISI and greater robustness to narrowband interfer- ence [7]. Moreover, there are other efficient techniques for the implementation of FB-MCTs such as complex-modu- lated transmultiplexers (CXMTs), cosine-modulated trans- multiplexers (CMTs) and sine-modulated transmultiplexers (SMTs) [8]. In these systems, all the filters are designed in an efficient manner by modulation of a single prototype filter. In the real communication world, where the transmission chan- nel itself introduces considerable distortion, it is better to go 123