Cross-layer optimization for DS-CDMA visual sensor networks and video transmission over DS-CDMA hardware channels
Pynadath, Elizabeth Serena
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In the first part of this work, we propose an approach for cross-layer optimization that works across the physical layer, the link layer and the application layer in a Direct Sequence Code Division Multiple Access (DS-CDMA) visual sensor network where nodes monitor scenes with varying levels of motion. Cross-layer algorithms have taken center stage because of the inherent differences between the wired networks that layered architecture was developed for and the wireless networks that are receiving an ever-increasing amount of attention. Our technique simultaneously assigns a source coding rate, a channel coding rate, and a power level to all nodes in the network based on two criteria that maximize the quality of video of the entire network as a whole, subject to a constraint on the total chip rate. One criterion results in the minimal average end-to-end distortion amongst all nodes, while the other criterion minimizes the maximum distortion of the network. To reduce the computational complexity of the solution, Universal Rate Distortion Characteristics (URDCs) are obtained experimentally to relate bit error probabilities to the distortion of corrupted video. The URDCs are used in conjunction with channel characteristic plots obtained by using Rate Compatible Punctured Convolutional (RCPC) codes for channel coding. In the second part of this work, we use a hardware testbed to demonstrate the interference mitigation capabilities of the auxiliary vector (AV) receiver for video transmission over DS-CDMA systems. The proposed receiver design is compared to the conventional RAKE matched-filter (RAKE-MF) and sample matrix inversion minimum variance distortionless response (SMI-MVDR) receivers. The DS-CDMA video stream is transmitted over an RF channel under realistic Rayleigh-faded multipath channel conditions, emulating open and/or urban battlefield environments. The state-of-the-art Agilent E4438C RF Arbitrary Waveform Generator and the N115A Baseband Studio fader hardware/software package is used to provide a configurable "real-time" RF channel. In this work, the "foreman" video sequence is source encoded using an MPEG-4 compatible video codec and channel encoded using RCPC codes. After spreading and modulating, the resultant bitstream is transmitted over a user-defined wireless channel environment created by Agilent equipment. Upon chip-matched filtering and sampling at the chip-rate on a hardware testbed, the received data is despread and demodulated using the AV, RAKE-MF and SMI-MVDR receivers. The resulting data is then channel and source decoded to recover the original transmitted video sequence. The results from this work show that the AV receiver outperforms the RAKE-MF and SMI-MVDR receiver counterparts over a wide range of rates and channel conditions.