On the Structure of the Capacity Region of Asynchronous Memoryless Multiple-Access Channels

The asynchronous capacity region of memoryless multiple-access channels is the union of certain polytopes. It is well-known that vertices of such polytopes may be approached via a technique called successive decoding. It is also known that an extension of successive decoding applies to the dominant face of such polytopes. The extension consists of forming groups of users in such a way that users within a group are decoded jointly whereas groups are decoded successively. This paper goes one step further. It is shown that successive decoding extends to every face of the above mentioned polytopes. The group composition as well as the decoding order for all rates on a face of interest are obtained from a label assigned to that face. From the label one can extract a number of structural properties, such as the dimension of the corresponding face and whether or not two faces intersect. Expressions for the the number of faces of any given dimension are also derived from the labels.Comment: 21 pages, 5 figures and 1 table. Submitted to IEEE Transactions on Information Theor

Improving the Secrecy of Distributed Storage Systems using Interference Alignment

Regenerating codes based on the approach of interference alignment for wireless interference channel achieve the cut-set bound for distributed storage systems. These codes provide data reliability, and perform efficient exact node repair when some node fails. Interference alignment as a concept is especially important to improve the repair efficiency of a failed node in a minimum storage regenerating (MSR) code. In addition it can improve the stored data security in presence of passive intruders. In this paper we construct a new code resilient against a threat model where a passive eavesdropper can access the data stored on a subset of nodes and the downloaded data during the repair process of a subset of failed nodes. We achieve an optimal secrecy capacity for the new explicit construction of MSR interference alignment code. Hence, we show that the eavesdropper obtains zero information from the original message stored across the distributed storage, and that we achieve a perfect secrecy.Comment: 20 pages, 3 figure

Rayleigh Fading Multiple Access Channel without Channel State Information

In this paper we determine bounds of the capacity region of a two-user multiple-access channel with Rayleigh fading when neither the transmitters nor the receiver has channel state information (CSI). We assume that the fading coefficients as well as the additive noise are zero-mean complex Gaussian and there is an average power constraint at the channel input for both senders. Results that we get show that the lower (inner) and the upper (outer) bound of the capacity region are quite close for low and high signal-to-noise ratio (SNR). Surprisingly, the boundary of the capacity region is achieved by time sharing among users, which is not the case for fading channels with perfect CSI at the receiver. As an additional result we derive a closed form expression for the mutual information if the input is on-off binary. Index Terms− Multiple-access channel, capacity region, Rayleigh fading, channel state information, volume of the capacity region

Blockchain-Based Application for Certification Management

Blockchain technology will bring a disruption in plenty of industries and businesses. Recently it proved the robustness, immutability, auditability, in many crucial practical applications. The blockchain structure offers traceability of actions, alterations, alerts, which is an important property of a system needed for development of sustainable technologies. A crucial part of the blockchain technology regarding the optimization of the processes is the smart contract. It is a self-executable computer code, open and transparent, encoding the terms of a regular contract. It is able to automate the processes, thus decreasing the human-factor mistakes or counterfeits. In this paper, we are presenting the feasibility of the blockchain technology in the certification processes, with an application developed for university diploma certification. The example is easily transferable in other areas and business models such as logistics, supply chain management, or other segments where certification is essential

Improved Wireless Secrecy Capacity using Distributed Auction Theory

International audiencePhysical layer security is an emerging security area that explores possibilities of achieving perfect secrecy data transmission between the intended network nodes, while possible malicious nodes that eavesdrop the communication obtain zero information. The so-called secrecy capacity can be improved using friendly jammers that introduce extra interference to the eavesdroppers. Here, we investigate the interaction between the multiple source-destination links and a friendly jammer who assists by “masking” the eavesdropper. In order to obtain a distributed solution, one possibility is to introduce a distributed auction theoretic approach. The auction is defined such that the source-destination links provide bids for the jammer to interfere the eavesdropper, therefore increasing their secrecy capacities. We propose a distributed auction using the share auction and iteratively updating the bids. To compare with the performances, we construct a centralized solution and a VCG auction, which cannot be implemented in practice. Our analysis and simulation results show the effectiveness of friendly jamming and convergence of the proposed scheme. The distributed game solution is shown to have similar performances to those of the centralized ones

Physical Layer Security Game: How to Date a Girl with Her Boyfriend on the Same Table

International audiencePhysical layer security is an emerging security technology that achieves perfect secrecy data transmission between the intended network nodes, while the eavesdrop- ping malicious nodes obtain zero information. The so-called secrecy capacity can be improved using friendly jammers that introduce extra interference to the eavesdropping ma- licious nodes while the interference to the intended desti- nation is limited. In this paper, we investigate the interac- tion between the source that transmits the desired data and friendly jammers who assist the source by \disguising" the eavesdropper. In order to obtain a distributed solution, we introduce a game theoretic approach. The game is de¯ned in such a way that the source pays the friendly jammers to interfere the eavesdropper, therefore increasing its secrecy capacit; and the friendly jammers charge the source with a certain price for the jamming. There is a tradeo® for the price: If the price is too low, the pro¯t of the jammers is low; and if the price is too high, the source would not buy the \service" (jamming power) or would buy it from other jammers. To analyze the game outcome, we de¯ne and in- vestigate a Stackelburg game and construct a distributed algorithm. Our analysis and simulation results show the ef- fectiveness of friendly jamming and the tradeo® for setting the price. The fancy title comes from the fact that it is similar to a scenario where the main character, namely the \source" tries to send a dating message to a lady (the in- tended destination), whose poor boyfriend plays the role of the eavesdropper that may hear the message. Friends of the source, the so called \friendly jammers," try to distract the boyfriend, so that the dating message can be secretly trans- mitted. The game is de¯ned in order to derive what is the optimal price that the friends can charge for this \friendly" action

Trading Application Based on Blockchain Technology

Blockchain is a growing distributed list of records that are linked using cryptographic hashes. Its robustness, simplicity, immutability and trust are basis for development of interesting innovative business solutions. Considering some use-case scenarios within the financial sector, we developed a Blockchain based trading application placed on the Cosmos network. Cosmos is a decentralized network of independent, scalable, and interoperable Blockchains, creating the foundation for new economy. Our work describes the application functionalities for buying, selling and renting goods. It shows the easiness of trading, while eliminating the third parties and demonstrates the disruptive potential of the Blockchain technologies