Stable Throughput and Delay Analysis of a Random Access Network With Queue-Aware Transmission

In this work we consider a two-user and a three-user slotted ALOHA network with multi-packet reception (MPR) capabilities. The nodes can adapt their transmission probabilities and their transmission parameters based on the status of the other nodes. Each user has external bursty arrivals that are stored in their infinite capacity queues. For the two- and the three-user cases we obtain the stability region of the system. For the two-user case we provide the conditions where the stability region is a convex set. We perform a detailed mathematical analysis in order to study the queueing delay by formulating two boundary value problems (a Dirichlet and a Riemann-Hilbert boundary value problem), the solution of which provides the generating function of the joint stationary probability distribution of the queue size at user nodes. Furthermore, for the two-user symmetric case with MPR we obtain a lower and an upper bound for the average delay without explicitly computing the generating function for the stationary joint queue length distribution. The bounds as it is seen in the numerical results appear to be tight. Explicit expressions for the average delay are obtained for the symmetrical model with capture effect which is a subclass of MPR models. We also provide the optimal transmission probability in closed form expression that minimizes the average delay in the symmetric capture case. Finally, we evaluate numerically the presented theoretical results.Comment: Submitted for journal publicatio

Adaptive authentication and key agreement mechanism for future cellular systems

Since the radio medium can be accessed by anyone, authentication of users is a very important element of a mobile network. Nowadays, in GSM/GPRS a challenge response protocol is used to authenticate the user to the mobile network. Similarly, in third generation mobile systems [3] a challenge response protocol was chosen in such a way as to achieve maximum compatibility with the current GSM security architecture. Both authentication mechanisms use symmetric key cryptography because of the limited processing power of the mobile devices. However, recent research [6] has shown that asymmetric, or public, key cryptography can be enabled successfully in future mobile terminals. In this paper, we propose a new adaptive authentication and key agreement protocol (AAKA) for future mobile communication systems. The novelty of AAKA and its main advantage over other challenge response protocols is that can be adaptive to the mobile environment and use symmetric and/or public key cryptography for user and network authentication

Social media: a guide for researchers

This guide has been produced by the International Centre for Guidance Studies, and aims to provide the information needed to make an informed decision about using social media and select from the vast range of tools that are available. One of the most important things that researchers do is to find, use and disseminate information, and social media offers a range of tools which can facilitate this. The guide discusses the use of social media for research and academic purposes and will not be examining the many other uses that social media is put to across society. Social media can change the way in which you undertake research, and can also open up new forms of communication and dissemination. It has the power to enable researchers to engage in a wide range of dissemination in a highly efficient way.Research Information Networ

Investigation of genetics and genomics in asthma

Asthma is the most common disease of childhood in the westernised world, affecting one child in seven in the United Kingdom alone. It is a complex disease involving both genetic and environmental factors. The financial burden for sufferers approximates £1 billion per annum in the UK and 80% of the sum is attributable to the patients with the severe, “difficult/therapy-resistant” form of the disease. Previously, a Genome Wide Association Study (GWAS) for childhood asthma identified a number of loci significantly associated to the disease. The top ten SNP hits with the highest association (0.0001>P>0.00001) were chosen for an investigation of their importance in cases of severe asthma, both childhood and adult. The 10 SNPs were genotyped in 397 adults and 94 children using TaqMan® SNP Genotyping Assays. Genotyping data was analysed for genetic associations to the severe asthma phenotype using chi-squared tests. Control data was obtained from data generated in the original GWAS for the British controls. SNP rs6585018 located in the PDCD4 gene predicted promoter was found to be significantly associated to childhood asthma (P=3.4x10-7). Additional markers on the PDCD4 gene area were chosen to be typed in 116 severe asthmatic children and 145 healthy children from the UK. SNPs rs6585018 (P=0.005), rs1322997 (P=0.005) in the predicted promoter area and rs34104444 (P=0.01) in exon 5 were associated to severe asthma. The three SNPs were also correlated with PDCD4 transcript levels. PDCD4 genomic area was analysed in silico and ElectroMobility Shift Assay (EMSA) experiments were designed for the rs6548018 alleles to examine how they alter transcription factor binding sites. SNP rs6585018 was found to alter the binding site of the Myb transcription factor possibly altering the expression of PDCD4 gene. This study has provided insights into the genetic factors that are involved in disease aetiology of severe asthma

Multi-Party Trust Computation in Decentralized Environments

In this paper, we describe a decentralized privacy-preserving protocol for securely casting trust ratings in distributed reputation systems. Our protocol allows n participants to cast their votes in a way that preserves the privacy of individual values against both internal and external attacks. The protocol is coupled with an extensive theoretical analysis in which we formally prove that our protocol is resistant to collusion against as many as n-1 corrupted nodes in the semi-honest model. The behavior of our protocol is tested in a real P2P network by measuring its communication delay and processing overhead. The experimental results uncover the advantages of our protocol over previous works in the area; without sacrificing security, our decentralized protocol is shown to be almost one order of magnitude faster than the previous best protocol for providing anonymous feedback