Transmultiplexers Research Articles

Optimized Reconfigurable Fast Convolution-Based Transmultiplexers for Flexible Radio Access

Multirate fast-convolution (FC) processing can be used for realizing low-complexity filter banks (FBs) and transmultiplexers (TMUXs). The main advantage of the FC-based realizations when compared with the polyphase FBs is the increased configurability, that is, the number of subchannels, their bandwidths, and the center frequencies can be adjusted independently. In general, FC-based FBs are linear periodically shift-variant systems. In this brief, novel matrix representations for the FC synthesis and analysis FBs are first derived. These representations give all the shift-variant impulse responses of the FC-based FBs. Then the TMUX optimization criteria are expressed using these representations. Two examples are included to demonstrate the performance of the optimized designs as well as to illustrate the flexibility of the resulting FC-based TMUXs.

Improved Non Uniform Transmultiplexers for Channelization

An improved Transmultiplexers (TMUXs) structure can be used for the interconversion of signals with different sampling rates between FDM and TDM format. Existing designs for channelization provide non linear optimization with large no. of coefficients and high degree of complexity. To achieve efficient frequency band reallocation and low implementation complexity, the prototype filter design is developed which consists of coefficient decimated cosine modulated FIR filter bank in which each analysis and synthesis filter has linear phase characteristics. This structure has the ability to extract multiple channels of different bandwidth which corresponds to the various communication standards with near perfect reconstruction technique.

On Efficient Design of High-Order Filters With Applications to Filter Banks and Transmultiplexers With Large Number of Channels

This paper proposes a method for designing high-order linear-phase finite-length impulse response (FIR) filters which are required as, e.g., the prototype filters in filter banks (FBs) and transmultiplexers (TMUXs) with a large number of channels. The proposed method uses the Farrow structure to express the polyphase components of the desired filter. Thereby, the only unknown parameters, in the filter design, are the coefficients of the Farrow subfilters. The number of these unknown parameters is considerably smaller than that of the direct filter design methods. Besides these unknown parameters, the proposed method needs some predefined multipliers. Although the number of these multipliers is larger than the number of unknown parameters, they are known a priori. The proposed method is generally applicable to any linear-phase FIR filter irrespective of its order being high, low, even, or odd as well as the impulse response being symmetric or antisymmetric. However, it is more efficient for filters with high orders as the conventional design of such filters is more challenging. For example, to design a linear-phase FIR lowpass filter of order 131071 with a stopband attenuation of about 55 dB, which is used as the prototype filter of a cosine modulated filter bank (CMFB) with 8192 channels, our proposed method requires only 16 unknown parameters. The paper gives design examples for individual lowpass filters as well as the prototype filters for fixed and flexible modulated FBs.

A Class of Multimode Transmultiplexers Based on the Farrow Structure

This paper introduces multimode transmultiplexers (TMUXs) in which the Farrow structure realizes the polyphase components of general lowpass interpolation/decimation filters. As various lowpass filters are obtained by one set of common Farrow subfilters, only one offline filter design enables us to cover different integer sampling rate conversion (SRC) ratios. A model of general rational SRC is also constructed where the same fixed subfilters perform rational SRC. These two SRC schemes are then used to construct multimode TMUXs. Efficient implementation structures are introduced and different filter design techniques such as minimax and least-squares (LS) are discussed. By means of simulation results, it is shown that the performance of the transmultiplexer (TMUX) depends on the ripples of the filters. With the error vector magnitude (EVM) as the performance metric, the LS method has a superiority over the minimax approach.

Reconfigurable Nonuniform Transmultiplexers Using Uniform Modulated Filter Banks

This paper introduces reconfigurable nonuniform transmultiplexers (TMUXs) based on fixed uniform modulated filter banks (FBs). The TMUXs use parallel processing where polyphase components, of any user, are processed by a number of synthesis FB and analysis FB branches. One branch represents one granularity band, and any user can occupy integer multiples of a granularity band. The proposed TMUX also requires adjustable commutators so that any user occupies any portion of the frequency spectrum. The location and width of this portion can be modified without additional arithmetic complexity or filter redesign. This paper considers both cosine modulated and modified discrete Fourier transform FBs. It discusses the filter design, TMUX realization, and the parameter selection. It is shown that one can indeed decrease the arithmetic complexity by proper choice of system parameters. For the critically sampled case and if the number of channels is higher than necessary, we can reduce the arithmetic complexity. In case of an oversampled system, the arithmetic complexity can be reduced by proper choice of the number of channels and the roll-off factor of the prototype filter. The proposed TMUX is compared to existing reconfigurable TMUXs, and examples are provided for illustration.

Design of nonuniform cosine-modulated filter-banks with the perfect-reconstruction property and arbitrary filter lengths

Abstract In this paper' a method is proposed to construct recombination nonuniform cosine-modulated filter banks (CMFBs) with a perfect-reconstruction property and with arbitrary filter lengths. In this filter bank (FB) structure, certain channels of an original M-channel uniform FB are merged by a set of transmultiplexers (TMUXs), yielding nonuniform outputs, and the length restrictions on the original CMPB and the recombination TMUKs are avoided, allong them to have arbifrary filter lengths. By imposing certain improved matching conditions on the protote filters, nonuniform FBs with arbitrary filter lengths and with good properties can be obtained. As a result, the flexibility of selecting modulation types and filter lengths is greatly increased in the design of recombination nonuniform CMFBs. Another benefit due to the flexibility is that the system delay can be reduced. *Supported by National Natural Science FoLndation of China (Grant Nos. 60672125 and 60372047)

Design of linear-phase recombination nonuniform filter banks

This correspondence proposes a novel method for designing a class of recombination nonuniform filter banks (RNFBs) with the linear-phase (LP) property. In the structure of the proposed nonuniform filter bank (FB), certain channels of an M-channel uniform FB are merged by synthesis filters of transmultiplexers (TMUXs), yielding nonuniform subbands. By a detailed analysis of the frequency characteristics of the RNFBs, we derive the existence and matching conditions that are necessary for constructing the proposed RNFBs having good frequency responses. With those conditions being satisfied, the design problem becomes that of a set of LP uniform FBs. By using the Parks-McClellan algorithm, we are able to design the near-perfect-reconstruction LP RNFBs in a very simple and efficient way as demonstrated by two examples

Design of perfect-reconstruction nonuniform recombination filter banks with flexible rational sampling factors

This paper studies the design of a class of perfect-reconstruction (PR) nonuniform filter banks (FBs) called recombination nonuniform FBs (RNFBs). They are constructed by merging subbands in a uniform FB with sets of transmultiplexers (TMUXs). It generalizes the RNFBs previously proposed by the authors to allow more general choice of the sampling factors. The spectral inversion and spurious response suppression problems of these new RNFBs using cosine modulation are analyzed, and a simple design method based on a matching condition is proposed. It is also found that the FB and the TMUX in the recombination structure can be designed separately to satisfy the matching condition. In addition, real-time adaptive merging of the channels to provide dynamic nonuniform frequency partitioning is feasible. Another advantage of the RNFBs is that the recombination and processing of the subband signal can be done at the decimated domain of the uniform FB, which greatly reduces its implementation complexity. Design examples show that high quality nonuniform PR FBs with low implementation complexity and variable time-frequency resolution can be obtained by the proposed method.

The Theory and Design of a Class of Recombination Nonuniform Filter Banks with Linear Phase Filters

This paper proposes a new theory and design method for a class of recombination nonuniform filter banks (RNFBs) with linear phase (LP) filters. In a uniform filter bank (FB), consecutive channels are merged by sets of transmultiplexers (TMUXs) to realize a nonuniform FB. RNFBs with LP analysis/synthesis filters are of great interest because the analysis filters for the partially reconstructed signals, through merging, are LP and hence less phase distortions are introduced to the desired signals. We analyze the spectrum supports of the analysis filters of these LP RNFBs. The conditions on the uniform FB and recombination TMUXs of an LP RNFB with good frequency characteristics are determined. These conditions are relatively simple to be satisfied and the uniform FB and recombination TMUXs can be designed separately without much degradation in performance. This allows dynamically recombination of different number of channels in the original uniform FB to give a flexible and time-varying frequency partitioning. Using these results, a method for designing a class of near-perfect-reconstruction (NPR) LP RNFBs with cosine roll-off transition band using the REMEZ algorithm is proposed. A design example is given to show that LP RNFBs with good frequency responses and reasonably low reconstruction errors can be achieved.