We investigate modulation-based parallel delta-sigma (ΔΣ) converters for wideband A/D conversion applications. A code division parallel ΔΣ conversion method is proposed, where each path consisting of a ΔΣ modulator operates on an input signal modulated with different binary code. In contrast to standard Hadamard based modulation schemes, the design provides flexibility in choosing the number of parallel paths and the type of binary modulation sequences. We exploit the information-theoretical approach to design an iterative probabilistic decoding procedure for optimal decoding of the ΔΣ modulator outputs. To demonstrate the decoding method, a maximum a posteriori probability decoder for the first order ΔΣ modulator is developed. Simulation results verify the iterative decoding procedure, demonstrate the use of arbitrary number of paths, and show that the A/D converter based on pseudo-random sequences achieves improved spurious-free dynamic range.

We consider optimal power allocation for wireless video sensors (WVSs), including the image sensor subsystem in the system analysis. By assigning a power-rate-distortion (P-R-D) characteristic for the image sensor, we build a comprehensive P-R-D optimization framework for WVSs. For a WVS node operating under a power budget, we propose power allocation among the image sensor, compression, and transmission modules, in order to minimize the distortion of the video reconstructed at the receiver. To demonstrate the proposed optimization method, we establish a P-R-D model for an image sensor based upon a pixel level sigma-delta (Σ∆) image sensor design that allows investigation of the tradeoff between the bit depth of the captured images and spatio-temporal characteristics of the video sequence under the power constraint. The optimization results obtained in this setting confirm that including the image sensor in the system optimization procedure can improve the overall video quality under power constraint and prolong the lifetime of the WVSs. In particular, when the available power budget for a WVS node falls below a threshold, adaptive sensing becomes necessary to ensure that the node communicates useful information about the video content while meeting its power budget.