Juuso Alhava

Complex modulated critically sampled filter banks based on cosine and sine modulation

This paper explores subband processing of complex (I/Q) signals which finds various important applications especially in communications signal processing. Instead of using traditional DFT based systems, the filter bank based systems are very interesting choices when high selectivity in the subchannels is required. We present a novel efficient complex modulated critically sampled filter bank structure which is based on a combination of cosine and sine modulated filter banks. We show that in case of critically sampled analysis-synthesis filter bank system with complex input signal and highly selective channel filters, perfect reconstruction can be achieved only if the low-rate subchannel signals are real.

Efficient Implementation of Complex Modulated Filter Banks Using Cosine and Sine Modulated Filter Banks

The recently introduced exponentially modulated filter bank (EMFB) is a-channel uniform, orthogonal, critically sampled, and frequency-selective complex modulated filter bank that satisfies the perfect reconstruction (PR) property if the prototype filter of an-channel PR cosine modulated filter bank (CMFB) is used. The purpose of this paper is to present various implementation structures for the EMFBs in a unified framework. The key idea is to use cosine and sine modulated filter banks as building blocks and, therefore, polyphase, lattice, and extended lapped transform (ELT) type of implementation solutions are studied. The ELT-based EMFBs are observed to be very competitive with the existing modified discrete Fourier transform filter banks (MDFT-FBs) when comparing the number of multiplications/additions and the structural simplicity. In addition, EMFB provides an alternative channel stacking arrangement that could be more natural in certain subband processing applications and data transmission systems.

Implementation of parallel cosine and sine modulated filter banks for equalized transmultiplexer systems

Filter bank-based transmultiplexer systems have certain advantages compared with existing DFT-based multicarrier systems and they are promising candidates for data transmission in frequency-selective channels. We have recently proposed a novel and efficient channel equalization idea to be used with critically decimated perfect reconstruction cosine modulated transmultiplexer systems. The equalizer utilizes parallel cosine and sine modulated filter banks in the receiver end. This paper explores efficient realization structures for the needed parallel filter bank system, which finds applications also in other areas.

Efficient implementation of complex exponentially-modulated filter banks

In an Exponentially-Modulated Filter Bank (EMFB) the complex subfilters are generated from a real-valued prototype filter by multiplying the filter impulse response with complex exponential sequences. This allows the possibility of using block transforms with computationally fast algorithms. Our definition for the EMFB is based on the Extended Lapped Transform (ELT). Then we apply Fast ELT based algorithms for cosine-modulated and sine-modulated filter banks (CMFB, SMFB) as basic building blocks in the implementation of this complex filter bank. Alternatively, a modified polyphase structure with 2 branches can be used. The latter structure can be employed with non-perfect reconstruction filter bank designs that allow some additional degrees of freedom in the optimization. In this paper, we explore these alternative realization structures for CMFBs and SMFBs.

Efficient Implementation of 2

This paper studies 2times oversampled exponentially modulated filter banks because they can be a useful solution for various communications signal processing problems. At first, the perfect reconstruction (PR) property of this kind of 2M-channel complex modulated filter bank is proven by using the results of M-channel PR cosine-/sine-modulated filter banks (CMFBs/SMFBs). Then, two efficient implementation structures are developed. The computational complexities of CMFB/SMFB-based and discrete Fourier transform (DFT)-based realizations are practically the same when comparing the required number of multiplications and additions. However, the DFT-based structures can be further simplified by using an intuitive spectral interpretation. This results in the modified filter bank part that requires less arithmetic operations than the original one

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A complex filter bank divides the spectrum of a complex (I/Q) signal into several low-rate subbands (analysis bank) or combines the low-rate signals into a single high-rate signal (synthesis bank). These operations are often cascaded to form analysis-synthesis (AS) or transmultiplexer (TMUX) configurations. Such systems find applications in many areas, especially in communications signal processing. In this paper we develop further the lapped transform theory to cover also the cases of complex, exponentially modulated filter banks. Using the shift-orthogonality of lapped transforms, we show how to design complex critically sampled AS and TMUX systems such that the perfect-reconstruction condition is satisfied.

Oversampled Exponentially Modulated Filter Banks

We consider filter bank based multicarrier systems which have been considered for fast digital subscriber line applications and possibly could be interesting also for broadband wireless LAN applications. In addition to being resistant to narrowband interference, these systems provide better spectral shaping than DFT-based OFDM and DMT systems for the subchannels, as well as for the overall signal. Furthermore, they provide better efficiency because the time-domain guard interval is not needed and the guard-band in frequency domain can be reduced. The channel equalization for such systems has been an open problem, but the paper demonstrates that it can be solved, at least in principle, even though effective adaptive equalization algorithms are still under development. Another open question is the performance when nonlinearities are included in the chain, especially in the transmitter power amplifier. In the paper, it is demonstrated that the performance of filter bank based systems with nonlinear power amplifiers is only slightly worse than in the corresponding OFDM/DMT systems. When the number of channels is the same, no more than 1 dB higher input backoff is required.

Exponentially-modulated filter bank-based transmultiplexer

This paper investigates the use of effective and flexible fast-convolution (FC) implementation for two main types of filter bank multicarrier (FBMC) waveforms, FBMC/OQAM and filtered multitone (FMT). The generated waveforms are spectrally well-contained, with very small power leakage to adjacent frequencies, and are thus good candidates for opportunistic and heterogeneous spectrum use scenarios. On the receiver side, the FC filter bank (FC-FB) approach can be used for simultaneously processing multiple channels with individually tunable bandwidths, center frequencies, and timing offsets, supporting asynchronous multi-user operation. FC-FB implementations are compared with traditional polyphase designs in terms of spectral characteristics and computational complexity.

On the performance of filter bank based multicarrier systems in xDSL and WLAN applications

In this paper we consider filter bank based multicarrier systems, which provide better spectral shaping than DFT-based orthogonal frequency division multiplexing (OFDM) or discrete multitone (DMT) systems for the subchannels, as well as for the overall signal. Due to their better performance in case of narrowband interference, such techniques have received attention especially in the context of very high-speed digital subscriber line (VDSL) system development. However, the channel equalization for such systems is still an open problem. In this paper, it is demonstrated that filter bank based multicarrier systems are very sensitive to the nonlinear phase response of the channel. Alternative ways to perform the channel equalization are discussed. Also measurement results from real subscriber lines are presented and, based on these results, a two-step equalization approach is proposed.

Fast-convolution implementation of filter bank multicarrier waveform processing

In this paper we formulate the prototype filter design problem for arbitrary delay exponentially-modulated filter banks. Further on, we set a constraint for the two lowpass analysis subfilters to capture the constant component of the complex-valued input signal. This is the polyphase normalization property for odd-stacked exponential modulation. The perfect reconstruction conditions are given in a programming language friendly form. A generalization of the design problem is presented to provide arbitrary delay and arbitrary length prototypes for modulated filter banks.