Providing end-to-end reliability for data transmission is a major challenge for energy-constrained and bandwidth-limited wireless sensor networks. To meet this challenge, attempts have been made using a multi-path transmission mechanism that encodes an information bitstream using forward error correction (FEC), and sends the obtained packets over a number of paths to the destination. Algorithms that, given the paths statistics (e.g., failure probability and energy cost of data transmission over the paths), find the number of channel packets and their transmission paths that optimize the reliability-energy cost tradeoff have been proposed. Once a transmission strategy is obtained, all packets are transmitted regardless of the actual state of the wireless links, which may result in energy and bandwidth losses due to unnecessary transmissions. This can be more severe when arbitrary transmission strategies have to be used due, for example, to the unavailability of paths statistics at the source node, which is the case in many practical applications. In this paper, we propose a hybrid FEC-feedback mechanism. The feedback scheme is used to send ACK packets from the sink to the source node when the information bitstream is actually recovered. We then derive a measure of the expected energy cost of data transmission for the hybrid mechanism. Simulation results show that, on average, the hybrid mechanism consumes up to about 44% less energy than the FEC-based mechanism for the transmission of a bitstream with the same reliability constraint. The energy savings of the hybrid mechanism are even higher when arbitrary transmission strategies have to be used.

In wireless sensor networks, the power of energy- constrained sensor nodes is largely drained by data communication tasks. Designing energy-efficient data communication mechanisms is, therefore, a major key to maximizing the life-time of wireless sensor networks. This challenge is magnified for visual sensor networks, where the collected and transmitted data is often very large and composed of multiple signals (Infrared signals, audio, video, ...) which have different and varying quality of service requirements (QoS). Motivated by this challenge, we investigate a forward error correction recovery mechanism for multi-path data transmission in wireless sensor networks. Based on this mechanism, we propose a fast algorithm for the trade-off between the end-to-end energy cost and reliability requirement of multi-path data transmission. Under the practical considerations of a fixed transmission power and a realistic modulation scheme, we derive the reliability and expected energy cost metrics of transmission paths. We then demonstrate the efficiency of our algorithm through simulations and discuss future work.

Many unequal error protection algorithms used in image communication systems need the operational distortion-rate (D/R) curve of the source coder whose computation is time-consuming. We study the use of parametric models instead of the true D/R curves for wavelet-based embedded image and video coders. We propose a Weibull model and show its superiority to the previous models for real-time applications. For unequal error protection over binary symmetric and packet erasure channels, the Weibull model yielded performance similar to the one obtained with the true D/R curve while satisfying the real-time constraint.

For optimal progressive transmission of an embedded image code over a noisy channel, we consider an unequal error protection strategy that minimizes the average of the expected distortion over a set of intermediate rates. In contrast to previous work, we find a near-optimal solution in real-time. For a binary symmetric channel, two state-of-the-art source coders (SPIHT and JPEG200), and a rate-compatible punctured turbo coder as a channel coder, we compare our solution to the strategy that optimizes the end-to-end performance.

We consider unequal error protection strategies for the efficient progressive transmission of embedded image codes over noisy channels. In progressive transmission, the reconstruction quality is important not only at the target transmission rate but also at the intermediate rates. An adequate error protection strategy may, thus, consist of optimizing the average performance over the set of intermediate rates. The performance can be the expected number of correctly decoded source bits or the expected distortion. For the rate-based performance, we prove some interesting properties of an optimal solution and give an optimal linear-time algorithm to compute it. For the distortion-based performance, we propose an efficient linear-time local search algorithm. For a binary symmetric channel, two state-of-the-art source coders (SPIHT and JPEG2000), we compare the progressive ability of our proposed solutions to that of the strategies that optimize the end-to-end performance of the system. Experimental results showed that the proposed solutions had a slightly worse performance at the target transmission rate and a better performance at most of the intermediate rates, especially at the lowest ones.