DSP Tips & Tricks [DC Blocker Algorithms]

This paper presents a nonlinear-phase, but computationally efficient, dc blocking filter that achieves ideal operation when output data quantization is used. In addition, we described an alternate dc blocking filter that, at the expense of larger data memory, exhibits a linear-phase frequency response.     

Precise Filter Design [DSP Tips & Tricks]

In this article, we describe an obscure but simple and powerful method for designing a digital filter that approximates an arbitrary magnitude and phase response. Called frequency-domain least-squares (FDLS) method, it can create a filter roughly comparable in computational burden and latency to that created by the bilinear transform method, with fidelity approaching that of fast convolution. In addition, the FDLS method can be applied to a wide variety of other system identification tasks     

Efficient Multitone Detection [DSP Tips & Tricks]

This article presents the digital signal processing (DSP) tricks employed to build a computationally efficient multitone detection system, implemented without multiplications and with minimal data memory requirements. More specifically, the article describes the detection of incoming dial tones, validity checking to differentiate valid tones from noise signals, and the efficient implementation of the detection system. While the discussion focuses on dual-tone multifrequency (DTMF) telephone dial tone detection, the processing tricks presented may be employed in other multitone detection systems     

Precise variable-Q filter design [DSP Tips & Tricks]

We have shown how to analyze and design simple variable-Q bandpass filters. The simplest variable-Q filter suffers from two shortcomings. Its center frequency is not exactly the planned-for center frequency, and the amplitude at the center frequency is not exactly the planned-for amplitude of unity. We presented a slightly more complicated filter in (6) that meets all the variable-Q filter's desired specifications quite precisely.     

Turbocharging Interpolated FIR Filters [DSP Tips & Tricks]

Interpolated finite impulse response (IFIR) filters drastically improve the computational efficiency of low-pass finite impulse response (FIR) filters designed using the traditional Parks-McClellan design method. This article presents a trick to further improve the computational efficiency of traditional IFIR filters.     

Ultra Low Phase Noise DSP Oscillator [DSP Tips & Tricks]

This article describes a novel complex oscillator, which is based on an interesting variation of the traditional CORDIC DDS and produces sine and cosine output samples of any specified angle. Our oscillator provides drastically improved phase noise performance (relative to a traditional CORDIC DDS) without the need for additional CORDIC iteration processing. In addition, our oscillator supports real-time output sample-by-sample digital frequency control. In describing our enhanced complex oscillator, we first present the arithmetic processing needed to generate sine and cosine samples. Next we show how that processing is implemented using the CORDIC algorithm. Then we detail the trick used to reduce oscillator phase noise errors. Finally we show how to guarantee a stable oscillator output amplitude and present an example of our oscillator's ultra low phase noise performance.     

Fast, Accurate Frequency Estimators [DSP Tips & Tricks]

This article presents computationally simple algorithms that provide substantial refinement of the frequency estimation of tones based on DFT samples without the need for increasing the DFT size. When estimating the frequency of a tone, the idea is to estimate the frequency of the spectral peak based on three DFT samples is discussed     

Truncation noise in fixed-point SFGs [digital filters]

A new model for predicting truncation error variance in fixed-point filter implementations is introduced. The proposed model is shown to be more accurate than existing models, particularly for some direct hardware implementations. In addition, some comments are made on the applicability of existing error models     

Novel adaptive IIR filter for frequency estimation and tracking [DSP Tips&Tricks]

In many applications, a sinusoidal signal may be subjected to nonlinear effects in which possible harmonic frequency components are generated. In such an environment we may want to estimate (track) the signal's fundamental frequency as well as any harmonic frequencies. Using a second-order notch filter to estimate fundamental and harmonic frequencies is insufficient since it only accommodates one frequency component [1], [2]. On the other hand, applying a higherorder IIR notch filter may not be efficient due to adopting multiple adaptive filter coefficients.     

Fully integrated analog filters using bipolar-JFET technology [active fifth order Chebyshev low-pass realisation]

A new approach for realizing high-order analog filters which can be fully integrated using a compatible bipolar and ion-implanted JFET process is described. This approach is based on the recognition that what is really needed is a long time constant monolithic integrator which can be effectively realized in a small silicon area. These integrators have been designed, fabricated, and used in a `leapfrog' or active ladder configuration to realize a fifth-order 8 kHz Chebyshev low-pass filter with 0.1 dB passband ripple. No external trimming operations and no anti-aliasing prefilter are required.     

一种用于抑制直扩通信中窄带干扰的非线性自适应方法

在分析线性自适应滤波抑制单频干扰、自回归过程窄带干扰和窄带BPSK调制信号干扰的性能的基础上,提出了一种非线性自适应波抑制方法.在对窄带干扰进行预测前,通过对扩谱信号的估计,使得窄带干扰预测的背景噪声由非高斯转变为高斯,并消除扩谱信号对干扰估计的影响,再通过NLMS和RLS自适应算法进行干扰抑制.理论分析和仿真试验结果表明,这种改进方法对于系统性能的改善效果,明显优于常规自适应滤波抑制方法.     

New adaptive complex IIR filters and their application in OFDM systems

In this article, very low sensitivity variable complex filter (VCF) sections are developed. They have two important advantages: extremely low passband sensitivity and independent tuning of the bandwidth and the central frequency over a wide frequency range. The first advantage provides resistance to quantization effects, while the second one gives a better digital signal processing quality and extends the area of possible applications of the developed filters. Based on the proposed VCF sections an adaptive complex system is designed which demonstrates very fast convergence and low computational complexity. This system is applied for narrowband interference cancellation in multiband orthogonal frequency division multiplexing receivers and wideband noise cancellation in OFDM receivers. It is experimentally verified that a better signal-to-noise ratio and signal-to-interference ratio can be achieved using the proposed adaptive complex filtering scheme.     

Performance analysis of nonlinear interpolation filters in DSspread spectrum systems under narrowband interference condition

The performance of nonlinear interpolation filters is analysed in the presence of narrowband interference. An analytical expression for the signal-to-noise ratio improvement factor is derived and performance comparison with nonlinear prediction filters is achieved. Results show that nonlinear interpolation filters outperform nonlinear prediction filters     

Component-based development of radio systems and subsystems: Are we there yet? [Trends in DSP]

The June 2005 "Trends in DSP" column explored the concept of component-based development for radio systems and subsystems. In this model the intermediate frequency (IF) and baseband signal processing associated with each wireless air interface standard on a given radio product are created from encapsulated software, hardware, and firmware intellectual property (IP) that can be reused from product to product.     

Message Passing in Semantic Peer-to-Peer Overlay Networks [Exploratory DSP]

In this column, we discuss exploratory research related to data management in P2P overlay networks. First, we discuss the notions of unstructured and structured P2P overlay networks. Then, we discuss data management in such networks by introducing an additional layer to handle semantic heterogeneity and data integration. Finally, we present a method based on sum-product message passing to detect inconsistent information in this setting.     

Signal processing challenges in cognitive assistive technology [Exploratory DSP]

Technological supports for people with disabilities are usually referred to as assistive technology. There has been significant work in developing technologies to support people with mobility and sensory disabilities. Developing these tools for people with cognitive disabilities has not been as widespread. In this article, we briefly outline causes and consequences of cognitive disabilities and then concentrate on smart home technologies. One such challenge in smart homes is the desire to have inexpensive components easily installed and selfcalibrating. We briefly mention work in brain-computer interfaces (BCIs).     

DSP Education [Effective Communication: Excellence in a Technical Presentation]

DSP Education introduces a cycle on effective communication. This cycle includes articles on technical presentations, technical writing, technical management, and preparation for entrepreneurship.