Ari Viholainen

Pilot-Based synchronization and equalization in filter bank multicarrier communications

This paper presents a detailed analysis of synchronization methods based on scattered pilots for filter bank based multicarrier (FBMC) communications, taking into account the interplay of the synchronization, channel estimation, and equalization methods. We show that by applying pilots designed specifically for filter banks, the carrier frequency offset (CFO), fractional time delay (FTD), and channel response can be accurately estimated. Further, a novel joint FTD and channel estimation scheme, based on iterative interference cancelation, permits extending the FTD estimation range well beyond the limit imposed by the pilot separation. The channel parameter estimation and compensation are successfully performed totally in the frequency domain, in a subchannel-wise fashion, which is appealing in spectrally agile and cognitive radio scenarios. The performance evaluation is done in a hypothetical WiMAX scenario in which an FBMC system would substitute OFDM maintaining as much physical layer compatibility as possible.

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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In this contribution we evaluate pilot-based carrier frequency offset (CFO) estimation and its correction in a filter bank based multicarrier (FBMC) system. We show that by applying certain pilots designed specifically for filter banks, the CFO can be accurately estimated. The performance evaluation is done in a hypothetical WiMAX scenario in which an FBMC system would substitute OFDM maintaining as much physical layer compatibility as possible.

Oversampled Exponentially Modulated Filter Banks

Recently, multirate filter banks have been recognized as high performance signal processing tools that could significantly enhance the efficiency and flexibility of future wireless communications. Filter bank-based multicarrier (FBMC) modulation allows increasing the spectral efficiency of high data rate transmission, both through the lack of time domain guard periods and the reduced frequency domain guard bands. Further, the inherent frequency selectivity is regarded as a vital characteristic, which enables high quality radio scene analysis, necessary for successful deployment of dynamic spectrum access in the context of cognitive radio technology. When applied to multicarrier communications, the filter banks are operated in the so-called transmultiplexer configuration where typically equal-size synthesis and analysis filter banks are utilized at the transmitter and receiver, respectively. This paper presents a new approach to generate an FBMC signal waveform. We focus on contiguous narrowband subcarrier allocation, which is often encountered in uplink transmission. Instead of using a full-size M-subchannel synthesis filter bank, the proposed scheme relies on a cascade of a P-subchannel synthesis bank (P ≪ M), time domain interpolation, and a user-specific frequency shift. This method allows constructing a transmitter-receiver pair using synthesis and analysis filter banks of different sizes. The presented approach is shown to provide notable computational complexity savings over a wide range of practical user bandwidth allocations, when compared to the conventional implementation consisting of equally sized filter banks. Therefore, this novel scheme provides flexible and low-complexity synthesis of spectrally well-localized FBMC uplink waveforms, which show strong potential for future broadband mobile communications.

CFO estimation and correction in a WiMAX-like FBMC system

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.

Generation of Filter Bank-Based Multicarrier Waveform Using Partial Synthesis and Time Domain Interpolation

Recently, spectrum agile radios have been proposed for resolving the challenge of spectrum shortage in future wireless communications. These smart radios would monitor and sense their radio environment in order to identify spectral resources temporarily and/or spatially unused by their primary (licensed) users. This would enable opportunistic spectrum access for the secondary (unlicensed) users in case their transmissions cause no harmful interference to the primary systems. In this paper, the trade-off between the level of interference caused by secondary transmission to primary user and the spectral efficiency of secondary user is discussed in the context of cognitive radio. In particular, we analyze the influence of the choice of pulseshape used for the multicarrier modulation based overlay secondary transmission. It is shown that, with a proper choice of multicarrier scheme, spectrally efficient secondary multiplexing is possible while simultaneously minimizing the interference caused to the primary system.