Secrecy Wireless Information and Power Transfer in Fading Wiretap Channel

Simultaneous wireless information and power transfer (SWIPT) has recently drawn significant interests for its dual use of radio signals to provide wireless data and energy access at the same time. However, a challenging secrecy communication issue arises as the messages sent to the information receivers (IRs) may be eavesdropped by the energy receivers (ERs), which are presumed to harvest energy only from the received signals. To tackle this problem, we propose in this paper an artificial noise (AN) aided transmission scheme to facilitate the secrecy information transmission to IRs and yet meet the energy harvesting requirement for ERs, under the assumption that the AN can be cancelled at IRs but not at ERs. Specifically, the proposed scheme splits the transmit power into two parts, to send the confidential message to the IR and an AN to interfere with the ER, respectively. Under a simplified three-node wiretap channel setup, the transmit power allocations and power splitting ratios over fading channels are jointly optimized to minimize the outage probability for delay-limited secrecy information transmission, or to maximize the average rate for no-delay-limited secrecy information transmission, subject to a combination of average and peak power constraints at the transmitter as well as an average energy harvesting constraint at the ER. Both the secrecy outage probability minimization and average rate maximization problems are shown to be non-convex, for each of which we propose the optimal solution based on the dual decomposition as well as suboptimal solution based on the alternating optimization. Furthermore, two benchmark schemes are introduced for comparison. Finally, the performances of proposed schemes are evaluated by simulations in terms of various trade-offs for wireless (secrecy) information versus energy transmissions.Comment: to appear in IEEE Transactions on Vehicular Technolog

A testbed of erasure coding on video streaming system over lossy networks

As one of the most challenging aspects of streaming video over lossy networks, the technology for controlling packet losses has attracted more and more attention. Erasure coding is one of the ideal choices to deal with this problem. In most cases, the researchers need an effective method or tool to validate the erasure codes used for dealing with different packet loss patterns. Although some previous work has been done on employing erasure codes in video streaming system, few actual buildups and experiments which involve implementation of erasure codes against real packet loss in streaming systems have been reported. In this paper, we focus on constructing a testbed that integrates loss pattern generation and erasure coding implementation into video streaming services over lossy networks. With this approach, we are able to assess the capability of erasure coding in packet loss control and compare the performances of the video streaming systems with and without erasure coding. As an example, we have implemented the Reed-Solomon (7, 5) code for protecting MPEG streaming data under random packet losses. Experiment results show that the replay quality can be improved significantly by using erasure coding in video streaming systems, and that the testbed can suggest appropriate erasure code parameters for different loss environments

Structure and substrate selectivity of the 750-kDa α6β6 holoenzyme of geranyl-CoA carboxylase.

Geranyl-CoA carboxylase (GCC) is essential for the growth of Pseudomonas organisms with geranic acid as the sole carbon source. GCC has the same domain organization and shares strong sequence conservation with the related biotin-dependent carboxylases 3-methylcrotonyl-CoA carboxylase (MCC) and propionyl-CoA carboxylase (PCC). Here we report the crystal structure of the 750-kDa α6β6 holoenzyme of GCC, which is similar to MCC but strikingly different from PCC. The structures provide evidence in support of two distinct lineages of biotin-dependent acyl-CoA carboxylases, one carboxylating the α carbon of a saturated organic acid and the other carboxylating the γ carbon of an α-β unsaturated acid. Structural differences in the active site region of GCC and MCC explain their distinct substrate preferences. Especially, a glycine residue in GCC is replaced by phenylalanine in MCC, which blocks access by the larger geranyl-CoA substrate. Mutation of this residue in the two enzymes can change their substrate preferences