Elettra Venosa

Non-Maximally Decimated Analysis/Synthesis Filter Banks: Applications in Wideband Digital Filtering

We present a new class of highly effective and low complexity digital filters for processing very wideband signals. Digital filtering for wideband signals is often limited by the number of arithmetic operations that has to be performed per input sampling interval. We will show the new architecture permits filtering to be performed on partitioned spectral segments of the input signal at significantly reduced sample rate. The digital filtering will be shown to include various tasks such as linear/non-linear phase finite impulse response (FIR) filtering, fractional delay filter among others. The proposed technique utilizes the framework of non-maximally decimated filter banks (NMDFBs) with perfect reconstruction (PR) property, which makes the filter bank design simpler and more flexible. Compact representation for the generalized DFT based NMDFBs as well as its efficient polyphase implementation will be provided. The digital filtering is made possible by incorporating the desired intermediate processing elements in between the analysis and synthesis filter banks. We will show this embedded intermediate processing elements can achieve spectral shaping/signal manipulation task, which is a generalization of the concept of manipulating a digital filter in the frequency domain. We also analyze both analytically and experimentally, the spectral shaping accuracy based on different design strategies.

Two channel TI-ADC for communication signals

Time-interleaved analog-to-digital converters (TI-ADCs) offer a significant increase in the available sample rate of ADCs. Their performance is degraded by timing and gain mismatches. Most of the literature on mismatch estimation and correction in TI-ADCs is concentrated on low-pass converting baseband signals. This paper provides a semi-blind solution, for both timing and gain mismatches correction, in the digital data section of a two-channel TI-ADC for band-pass input signals. This is a realistic communications system scenario. Modern system designs lean towards having the ADC interface with intermediate frequency (IF) signal in the analog section of a digital receiver rather than the DC centered, analog down converted, in-phase and quadrature pair.

Interleaving different bandwidth narrowband channels in perfect reconstruction cascade polyphase filter banks for efficient flexible variable bandwidth filters in wideband digital transceivers

Cascade perfect reconstruction (PR) non-maximally decimated analysis and synthesis filter banks (NMDFBs have been applied to the task of performing filtering of extremely wide bandwidth digital signals collected at multiple GHz sample rates; rates comparable to the clock speeds of the DSP processing engines. An M-path analysis channelizer efficiently partitions a wide bandwidth input signal with sample rate fS into M baseband time signals with bandwidths fS/M operating at reduced sample rate of 2·fS/M. A binary mask delivers a selected subset of the channelized time series to the synthesis channelizer which up-samples and up-converts the selected multiple streams to synthesize a reduced bandwidth output time series. The binary mask connecting the analysis and synthesis filter banks can synthesize filters with bandwidths k·fS/M. Additional processing of the low-bandwidth signal components between the filter banks is required to synthesize filter bandwidths that differ from integer multiples of channel width. In this paper we interleave two or more variable bandwidth channel banks to permit the synthesis of a more flexible range of output filter bandwidths.

Multi-resolution PR NMDFBs for programmable variable bandwidth filter in wideband digital transceivers

This paper describes a novel application of perfect reconstruction (PR) non-maximally decimated filter banks (NMDFBs). PR non-maximally decimated analysis/synthesis chains are used for performing resampling, channelization and filtering in very wideband software defined radios. Digital wideband filtering is currently limited by the hardware clock speed which constrains the maximum signal bandwidth that can be processed digitally. Polyphase channelizers decrease the sample rate of the input signals and parallelize the wideband filtering process at cost of a single filter. In this paper we show how to assemble multiple-tier PR analysis/synthesis channelizer chains for implementing, in a very efficient way, variable bandwidth digital filters and multi-resolution systems operating on very wideband signals. When an internal tier analysis channelizer is applied to a single output channel of a first external tier analysis channelizer it decomposes this channel in multiple narrower subchannels and, by applying appropriate complex processing elements to those sub-channels we can modify the designed filter bandwidth as desired.

QAM Receiver with Band-Pass Sampling and blind synchronization

In this paper we propose a methodology for designing a fully-digital reconfigurable receiver for QAM signals. Band-Pass Sampling (BPS) is used as a first stage with a unique Analog-to-Digital Converter (ADC) positioned immediately after the receiver antenna. The band-pass sampling is analyzed with reference to noise aliasing deriving from band-pass filter and the results in the numerical frequency domain are presented. The inescapable frequency, symbol and phase synchronization problem in our model of receiver is approached and solved blindly with an information-theoretic criterion: joint entropy maximization is utilized for frequency and symbol synchronization while mutual information minimization is utilized for phase recovery. The innovative contribution of this paper consists in matching band-pass sampling and blind synchronization with a design of a synchronized reconfigurable receiver for QAM signals.

Efficient implementation of multicarrier frequency hopping receiver via polyphase channelizer

The authors present an efficient signal processing algorithm for implementing a full digital multicarrier frequency hopping (MCFH) receiver. FH radios were, at the beginning, developed for military applications because of their characteristic of being highly jamming resistant. The proposed receiver architecture is based on non-maximally decimated filter bank (NMDFB) also known as polyphase channelizer which enables the functionality of simultaneously de-hopping multiple frequency-hopped spread spectrum (FHSS) signals at reduced sample rate. This feature greatly reduces the implementation cost as well as power consumption of a traditional analog based de-hopping circuit. Furthermore, the NMDFB based de-hopping circuit supports fast acquisition by means of conducting parallel search, which gives a much shortened synchronization time. After de-hopping, second tier NMDFBs are used as a bank of band pass filters (BPFs) to perform non coherent demodulation of the underlying M-ary frequency shift keying (MFSK) signal.

Multirate Signal Processing for Software Radio Architectures

Abstract This chapter is about multirate signal processing and the potential that it brings to modern (software) radios. Optimizing the sample rate while processing signals provides many advantages to digital systems. Costs and computational complexity reduction, improved performance and reduced chip size are just some of them. Digital filters, up converters, and down converters are the basic elements for designing multirate architectures and their introduction in this chapter is necessary for a deeper understanding of perfect reconstruction polyphase channelizers, which are the key modules of the modern digital radios. This chapter follows a very practical approach. We decided to keep the mathematical formulation to a minimum to allow more space for concepts and figures. References are given at the end of the chapter for the interested readers.

A novel and efficient multi-resolution channelizer for software defined radio

There are number of software defined radio applications in which a radio receiver must access multiple simultaneous channels with different channel bandwidths. This paper presents the architecture of a novel and extremely efficient implementation of such a channelizer. The receiver described here simultaneously forms ten 5-MHz wide channels and one hundred 0.5 MHz wide channels spanning a 50 MHz input bandwidth. Multirate signal processing techniques are used throughout the processing chain to obtain extremely low processing computational workload.

Proportional bandwidth spectrum analysis in a synthetic instrument

Spectrum analyzers used in communication systems are traditionally modeled by a bank of filters with equally spaced frequency centers and bandwidths. This type of spectrum analyzer decomposes the input signal into basis functions that share common features such as time extent and bandwidth. Another important class of spectrum analyzers is the proportional bandwidth spectrum analyzer modeled by a bank of filters where the spacing between spectral centers and bandwidths increase as a function of the frequency of interest. The filter spacing and bandwidth are seen to have equally spaced centers and equal bandwidths on a logarithmic scale. This type of spectrum analyzer decomposes the input signal into basis functions that share a scaled range of features such as varied time duration and varied bandwidths. Analysis of mechanical systems such as vibrating beams, acoustic resonators, cochlear of the human ear, whale and dolphin sounds, harmonic-rich FM waveforms, and image features are best performed by proportional bandwidth analyzers. This paper presents and analyzes the performance of an extremely efficient implementation of a proportional bandwidth filter bank.

Polyphase up converter channelizers enable fully digital multi-carrier frequency hopping modulators

Frequency hopping (FH) is a spread spectrum transmission technique that achieves frequency diversity gain over frequency selective fading channels and also has a low probability of interception. This technique has been widely used in military applications, for its recognized anti-jamming performance, and in some wireless standards such as GSM and Bluetooth, for its interference resistance. Modern FH systems employ partial digital technology and their performance depends on the hopping bandwidth. The wider is the hopping bandwidth the greater is the performance. The width of the hopping bandwidth is one of the factors that limits the usage of fully digital technology for FH systems. In [7] we proposed a fully digital FH architecture based on polyphase channelizers. In this paper, we extend the proposed transmitting architecture to a multi-carrier frequency hopping (MCFH) system. The proposed structure is composed of a cascade of two polyphase up converter channelizers. The first one performs the M-FSK (or BFSK) modulation while the second one accomplishes the task of hopping the modulated spectra independently over L subcarriers under the control of pseudorandom sequence generators. In this paper, both theoretical aspects and simulation results, demonstrating the effectiveness of the proposed fully digital structure, are provided.