Design of Power and Area Efficient Digital Down-converters for Broadband Communications Systems

This paper shows that when a digital receiver is designed utilizing two clock scopes, the digital down-converter can be designed to be efficient in terms of area and power consumption. The main design parameter that contributes to make the design efficient is the relationship between the transition band of the designed filter and its sampling frequency.

Design of Variable Two-Dimensional FIR Digital Filters by McClellan Transformation

In this paper, the technique of McClellan transformation is applied to design variable 2-D FIR digital filters. Compared with the conventional transformation, the 2-D transformation subfilter and the 1-D prototype filter are designed such that their frequency characteristics are adjustable. Moreover, they are tunable by the same variable parameter, so the variable characteristics of 1-D prototype filters are coincident with those of 2-D subfilters. Several examples, including variable fan filters, variable circularly symmetric filters, and variable elliptically symmetric filters with arbitrary orientation, are presented to demonstrate the effectiveness and the flexibility of the presented method.      

Oscillation Test Scheme of SC Biquad Filters Based on Internal Reconfiguration

In this paper, we explore general conditions for the oscillation based test of switched-capacitor biquad filter stages. Expressions describing the characteristics of a filter stage put into oscillation are derived and conditions for achieving oscillation by internal transformation of the filter stage are explored. Reconfiguration scheme based on the transformation of the biquad filter stage to a quadratic oscillator is studied. Theoretically the circuit can be put into oscillation by de-activating a single capacitor. Simulations, however, show that in practice a carefully designed low feed-back loop is required to achieve acceptable oscillation test mode.

Forward and Reverse Converters and Moduli Set Selection in Signed-Digit?Residue?Number?Systems

This paper presents an investigation into using a combination of two alternative digital number representations; the residue number system (RNS) and the signed-digit (SD) number representation in digital arithmetic circuits. The combined number system is called RNS/SD for short. Since the performance of RNS/SD arithmetic circuits depends on the choice of the moduli set (a set of pairwise prime numbers), the purpose of this work is to compare RNS/SD number systems based on different sets. Five specific moduli sets of different lengths are selected. Moduli-set-specific forward and reverse RNS/SD converters are introduced for each of these sets. A generic conversion technique for moduli sets consisting of any number of elements is also presented. Finite impulse response (FIR) filters are used as reference designs in order to evaluate the performance of RNS/SD processing. The designs are evaluated with respect to delay and circuit area in a commercial 0.13 μm CMOS process. For the case of FIR filters it is shown that generic moduli sets with five or six moduli results in designs with the best area × delay products.

Hardware Implementation of Skeletonization Algorithm for Parallel Asynchronous Image Processing

This paper presents an FPGA realisation of an application-specific cellular processor array designed for asynchronous skeletonization of binary images. The skeletonization algorithm is based on iterative thinning utilizing a ‘grassfire’ transformation approach. The purpose of this work was to test the performance of a fully parallel asynchronous processor array and to evaluate the inhomogeneity of wave propagation velocity. A proof-of-concept design has been implemented and evaluated, the results are presented and discussed.

Adaptive Beamforming and DOA Estimation Using Uniform Concentric Spherical Arrays with Frequency Invariant Characteristics

This paper proposes a new digital beamformer for uniform concentric spherical array (UCSA) having nearly frequency invariant (FI) characteristics. The basic principle is to transform the received signals to the phase mode and remove the frequency dependency of the individual phase mode through the use of a digital beamforming network. It is shown that the far field pattern of the array is determined by a set of weights and it is approximately invariant over a wide range of frequencies. FI UCSAs are electronic steerable in both the azimuth and elevation angles, unlike their concentric circular array counterpart. The frequency invariant characteristic of the FI UCSA also makes it possible to design separately the compensation network and beamformer weighting coefficients. The design of the compensation network is formulated as a second order cone programming (SOCP) problem and is solved optimally for minimax criterion. Thanks to the frequency invariant characteristic, traditional narrow band adaptive beamforming algorithms such as minimum variance beamforming (MVB) can be applied to the FI UCSA. Also, traditional narrow band 2-D direction of arrival (DOA) estimation algorithms such as unitary ESPRIT can be extended to broadband DOA estimation using FI UCSA. Simulation results show that the proposed adaptive beamformer using FI UCSA can obtain a higher output signal to inference plus noise ratio over the conventional tapped-delay line approach. Simulation results also show that FI UCSA has uniform beampattern and resolution around 360° in both azimuth and elevation angles, unlike FI uniform concentric circular array. The usefulness of the proposed UCSA-FIB in broadband 2-D DOA estimation is also verified by computer simulation.

MPOE Based Prefiltering and MRT Beamforming with Matched Filter Receiver for DS-CDMA Systems

In order to reduce the complexity of the mobile receiver, we develop two prefilter models using a linear FIR prefilter for minimizing the probability of error in multi-user transmission scenario. We consider downlink transmission. In the first system model, we have a single common prefilter for all users at the base station transmitter and in the second system model, we consider an individual prefilter for each and every user. We assume complete knowledge of the channel at the base station. In order to fully utilize the knowledge available at the transmitter, the filter weights are computed, conditioned on the transmitted bit vector sequence. This also makes the computation of the prefilter coefficients linear in the number of users as opposed to the exponential complexity otherwise. Coefficients of FIR prefilter are computed by minimizing the conditional probability of error and the mean square error. To further improve the performance of the proposed models, we consider Maximum Ratio Transmission (MRT) beamforming at the base station for both the models. Simulation results illustrate the performance of the proposed system models.

Adaptive Particle Filter for Data Fusion of Multiple Cameras

Occlusion is a difficult problem for visual tracking and we use multiple wide baseline cameras to deal with occlusion. We propose a data fusion approach for visual tracking using multiple cameras with overlapping fields of view. First, we present a spatial and temporal recursive Bayesian filter to fuse information from multiple cameras. An adaptive particle filter is formulated to realize the spatial and temporal recursive Bayesian filter. Our algorithm is able to recover the target’s position even under complete occlusion in a camera.

An Enhanced Memory Address Mapping Scheme for Improved Memory Access Performance of 2-D DWT Processing Systems

The implementation of the memory for storing image and transform coefficients in 2-D DWT processing systems using the more cost-effective external memory module such as DDR DRAM is shown to suffer from effective memory bandwidth which is significantly lower than the memory system peak bandwidth if the conventional direct logical-to-physical memory address mapping is adopted. The low effective memory bandwidth is caused by the high level of memory overhead cycle occurrence which is in turn is closely related to the logical memory access patterns of 2-D DWT processes. The problem becomes even more severe for the 2-D DWT processing of video. An analysis on the logical memory access patterns of multi-level 2-D DWT is carried out and an enhanced logical-to-physical memory mapping scheme which minimizes the occurrence of memory overhead cycles is proposed. The proposed scheme is simulated and its performance in terms of effective memory access bandwidth is evaluated and compared with the conventional direct mapping scheme.

Maintaining Optimal Communication Chains in Robotic Sensor Networks using Mobility Control

This paper presents a decentralized mobility control algorithm for the formation and maintenance of an optimal cascaded communication chain between a lead sensor-equipped robot and a control station, using a team of robotic vehicles acting as communication relays in an unknown and dynamic RF environment. The gradient-based controller presented uses measurements of the signal-to-noise ratio (SNR) field of neighbor communication links, as opposed to relative position between nodes, as input into a localized performance function. By using the SNR field as input into the control system, the controller is reactive to unexpected and unpredictable changes in the RF environment that is not possible with range-based controllers. Since the operating environment is not known a priori to deployment of a robotic sensor network, an adaptive model-free extremum seeking (ES) algorithm, that uses the motion of the relays to estimate the performance function gradient, is presented to control the motion of 2D nonholonomic vehicles acting as communication relays using the gradient-based controller. Even without specific knowledge of the SNR field, simulations show that the ES decentralized chaining controller using measurements of the SNR field, will drive a team of robotic vehicles to locations that achieve the global objective of maximizing capacity of a cascaded communication chain, even in the presence of an active jamming source.

A High-Performance Doubly-Balanced Mixer in 0.35-μm CMOS for Mode-1 MB-OFDM UWB Receivers

A new design of CMOS doubly-balanced down-conversion mixer intended for Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) receiver of UWB group#1 bands and optimized for 0.35-μm technology is presented. The proposed mixer uses the current-bleeding technique in both the driver and switching stages with wideband impedance matching, consisting of a bandpass filter embedding the RF stage. The mixer performances are optimized for the AMS 0.35 μm CMOS process parameters. Over 3.1–4.8 GHz, the circuit drawing 6 mA from 3-V supply, shows a conversion gain of 14.0±1.0 dB, IIP3 of 0±2 dBm, doubly-sideband noise figure of 4.5–4.8 dB, and port-to-port isolation above 61.0 dB.

On Low-Delay Frequency-Response Masking FIR Filters

This paper offers two main contributions to the theory of low-delay frequency-response masking (FRM) finite impulse response (FIR) filters. First, a thorough investigation of the low-delay FRM FIR filters and their subfilters or three different structures, referred to as narrow-, wide-, and middle-band filter structures, is given. The investigation includes discussions on delay distribution over the subfilters as well as estimation of the optimal periodicity of the periodic model filter. Second, systematic design procedures are given, with explicit formulas for distribution of the ripples and the delay to the subfilters. For each of the three structures, two design procedures are given that include joint optimization of the subfilters. The first proposal uses partly linear-phase FIR subfilters and partly low-delay FIR subfilters. Thus, it has a lower arithmetic complexity compared to the second proposal, which has exclusively low-delay FIR subfilters. The second proposal is instead more flexible and can handle a broader range of specifications. The design procedures result in low-delay FIR filters with a lower arithmetic complexity compared to previous results, for specifications with low delay and narrow transition band.     

Power-Aware Design of An 8-Bit Pipelining ANT-Based CLA Using Data Transition Detection

A high speed and low-power 8-bit carry-lookahead adder (CLA) using two-phase all-N-transistor (ANT) blocks which are arranged in a PLA design style with power-aware pipelining is presented. The pull-up charging and pull-down discharging of the transistor arrays of the PLA are accelerated by inserting two feedback MOS transistors between the evaluation NMOS blocks and the outputs. The analysis of the area (transistor count) tradeoff is also provided in this work. The output of the addition of two 8-bit binary numbers is done in two cycles. The proposed power-aware pipelining design methodology using a simple data transition detection circuit takes advantage of shutting down the processing stages with identical inputs in two consecutive cycles. The data transition detection circuit is used to monitor the state switching of input data. Not only is it proved to be also suitable for long adders, the power consumption is drastically reduced by at most 50% at every process corner.

Modified Guard Band Power Detection for Coarse Carrier Frequency Offset Recovery in OFDM System

Conventional guard band power detection (GPD) method for orthogonal frequency division multiplexing (OFDM) coarse carrier frequency offset (CFO) estimation has to be operated after the fine CFO recovery due to its sensitivity to the inter-channel interference (ICI). In the paper, modified GPD methods are presented for OFDM system to obtain more accurate estimation of CFO. The accuracy of GPD estimation can be first improved with a simple operation of power average. Then, extending the idea of Reference symbol Power Adjustment (RPA), two general patterns of sub-carrier power adjustment to improve the estimation performance under nonzero fine CFO are presented. According to complete simulations under the COST 207 multi-path fading channel, estimation performance with the presented modified GPD methods can be significantly improved and therefore can be concurrently operated with the fine carrier offset adjustment.

Adaptive Multiuser Channel Estimation using Reduced Kalman/LMS Algorithm

This paper presents an adaptive multiuser channel estimator using the reduced-Kalman least-mean-square (RK-LMS) algorithm. The frequency-selective fading channel is modeled as a tapped-delay-line filter with smoothly time-varying Rayleigh distributed tap coefficients. The multiuser channel estimator based on minimum-mean-square-error (MMSE) criterion is used to predict the filter coefficients. We also present its convergence characteristics and tracking performance using the RK-LMS algorithm. Unlike the previously available Kalman filtering algorithm based approach (Chen, Chen IEEE Trans Signal Process 49(7): 1523–1532, 2001) the incorporation of RK-LMS algorithm reduces the computational complexity of multiuser channel estimator used in the code division multiple access wireless systems. The computer simulation results are presented to demonstrate the substantial improvement in its tracking performance under the smoothly time-varying environment.

MGFs for Rayleigh Random Variables

Expressions are given for the moment generating functions of the Rayleigh and generalized Rayleigh distributions.

Capacity and SER Analysis of MIMO MRC Systems in an Interference-Limited Environment

The effect of co-channel interference (CCI) is considered in multiple-input multiple-output (MIMO) systems employing maximal ratio combining (MRC) under independent and identically distributed Rayleigh fading. Closed-form capacity and symbol error rate expressions are presented to evaluate the performance without any numerical integrations or statistical simulations. The analytical results are compared with Monte Carlo simulations and the good agreement is obtained.

Improved Fractional Fourier Transform Based Receiver for Spatial Multiplexed MIMO Antenna Systems

In this work the performance of a Fractional Fourier transform (FrFT) based Minimum Mean Squared Error receiver for MIMO systems with space time processing over Rayleigh faded channels is presented. The proposed receiver called Optimum FrFT based MIMO receiver (OFMR) shows improved performance outperforming the simple MMSE receiver in Rayleigh faded channel.

Delay-dependent H ∞ control for 2-D discrete state delay systems in the second FM model

This paper is concerned with the problem of delay-dependent H _∞ control for two-dimensional (2-D) discrete state delay systems described by the second Fornasini and Marchesini (FM) state-space model. Based on a summation inequality, a sufficient condition to have a delay-dependent H _∞ noise attenuation for this 2-D system is given in terms of linear matrix inequalities (LMIs). A delay-dependent optimal state feedback H _∞ controller is obtained by solving an LMI optimization problem. Finally, a simulation example of thermal processes is given to illustrate the effectiveness of the proposed result.

Sub-Carrier and Band Hopped Orthogonal Frequency Division Multiple Access (OFDMA) Systems

This article proposes a novel way of grouping users in an orthogonal frequency division multiplexing (OFDM) communication link based on predefined criteria. The total available spectrum is divided into a number of bands equal to the number of groups. For efficient time-frequency resource allocation, sub-carrier and band hopping are used simultaneously. Under some constraints, sub-carriers can also be assigned to different users based on known channel characteristics using dynamic sub-carrier allocation. Sub-carrier and band hopping are used for mitigating the frequency selectivity of the wireless channel and for minimizing and avoiding interference in the system. The proposed scheme is equally applicable to both downlink and uplink.