1:00, ITT-L1.1
ENERGY EFFICIENT SYSTEM PARTITIONING FOR DISTRIBUTED WIRELESS SENSOR NETWORKS
A. WANG, A. CHANDRAKASAN
In this paper a scheme for efficient system partitioning of computation in wireless sensor networks is presented. Local computation of the sensor data in wireless networks can be highly energy-efficient, because redundant communication costs can be reduced. It is important to develop energy-efficient signal processing algorithms to be run at the sensor nodes. This paper presents a technique to optimize system energy by parallelizing computation through the network and by exploiting underlying hooks for power management. By parallelizing computation, the voltage supply level and clock frequency of the nodes can be lowered, which reduces energy dissipation. A 60% energy reduction for a sensor application of source localization is demonstrated. The results are generalized for finding optimal voltage and frequency operating points that lead to minimum system energy dissipation.

1:20, ITT-L1.2
DECISION FEEDBACK EQUALIZATION FOR BLUETOOTH SYSTEMS
M. NAFIE, A. GATHERER, A. DABAK
Gaussian Frequency Shift Keying modulation has been chosen as the modulation technique for the physical layer of Bluetooth. Bluetooth is a standard for low cost and low power wireless communications between various mobile devices. The optimal demodulation of a GFSK signal involves an extremely complex Viterbi decoder. Therefore designers have opted for the noncoherent detection of GFSK which uses a frequency discriminator, followed by symbol by symbol detection. Here, we describe a decision feedback equalizer to be added after the discriminator. The DFE receiver gives gains in excess of 2 dBs. We also describe how to increase the current data rate of a Bluetooth system by increasing the symbol rate and not the alphabet size.

1:40, ITT-L1.3
A DSP-BASED DS/CDMA MODEM FOR MULTIMEDIA APPLICATIONS OVER GEO-STATIONARY SATELLITE NETWORKS
C. SACCHI, L. RONGA
Multimedia services over satellite networks require a large amount of bandwidth for the delivery of variable-bit-rate video and audio signal with adequate quality of service. Hence, the bandwidth allocation has to be efficiently managed. In such sense, CDMA is a flexible multiple access technique since it allows a dynamic configuration of the resources allotted to the users of the system. This paper aims at describing a DSP-based DS/CDMA satellite multimedia system for multimedia applications, working in geo-stationary (GEO) satellite networks. The DSP implementation of the satellite modem is described in detail, both for what concerns the hardware section and the signal processing algorithmic section. The developed prototype, whose test is expected during year 2001, should be considered as a basic platform for developing flexible software radio-based architectures for satellite communications.

2:00, ITT-L1.4
NONLINEAR ECHO CANCELLATION USING DECOUPLED A-B NET STRUCTURE
G. SENTONI, J. COUSSEAU, P. DINIZ
This paper proposes a general nonlinear digital filter structure for echo cancellation applications. Although echo cancelers employing linear digital filter structures are more widely used, there are many applications where nonlinear filters must be used. In this paper, we propose using the DABNet (Decoupled A-B Net) filter, which is composed of a decoupled linear dynamic system followed by a nonlinear static map, for echo cancellation. The linear dynamic system is initially spanned by a set of discrete Laguerre systems, and then cascaded with a single hidden layer Perceptron. A model reduction technique can be performed not only to identify the main time constants, but also to reduce the dimensionality of the Perceptron input. The DABNet structure is able to approximate any nonlinear, causal, discrete time invariant, multiple-input single-output system with fading memory. Comparisons between echo cancelers implemented with the DABnet and nonlinear FIR filters are presented.

2:20, ITT-L1.5
A STABLE AND EFFICIENT DSP IMPLEMENTATION OF A LSL ALGORITHM FOR ACOUSTIC ECHO CANCELLING
A. CAREZIA, P. BURT, M. GERKEN, M. MIRANDA, M. DA SILVA
In this paper we present an optimized DSP implementation of a modified error-feedback lattice least-square (EF-LSL) adaptive filtering algorithm. Simple measures that provide numerical stability for poor persistent excitation are also proposed. As a result of the optimization and the stability measures, an efficient and stable implementation of a fast algorithm of the RLS family was attained. We present the results of an acoustic echo cancelling experiment performed with the implemented algorithm. With a 40 MIPS Sharc DSP, up to 290 adaptive filter coefficients can be used. This represents an effective alternative to algorithms of the LMS family, while still retaining the good convergence properties of the RLS family.

2:40, ITT-L1.6
FREQUENCY ESTIMATION FOR SENSORLESS CONTROL OF INDUCTION MOTORS
M. HILAIRET, F. AUGER
In the motor control industry, DSP systems offer major improvements over analog designs, enabling notably to replace speed or position sensors by the implementation of sensorless control algorithms. In this paper, we propose a new viable method which estimates the rotor velocity from the ``rotor slot harmonics'' included in the stator current signals. This approach is based on both an adjustable digital filter, which is fitted to this particular application, and an extended Kalman filter whose computational burden has been reduced thanks to an additionnal virtual state.