Performance Enhancements for Asynchronous Random Access Protocols over Satellite

In this paper, a novel enhancement of the well known ALOHA random access mechanism is presented which largely extends the achievable throughput compared to traditional ALOHA and provides significantly lower packet loss rates. The novel mechanism, called Contention Resolution - ALOHA (CRA), is based on transmitting multiple replicas of a packet in an unslotted ALOHA system and applying interference cancellation techniques. In this paper the methodology for this new random access technique is presented, also w.r.t. existing Interference Cancellation (IC) techniques. Moreover numerical results for performance comparison with state of the art random access mechanisms, such as Contention Resolution Diversity Slotted ALOHA (CRDSA) are provided. Finally the benefit of taking strong forward error correcting codes for the performance of CRA is shown

On the Stability of Contention Resolution Diversity Slotted ALOHA

In this paper a Time Division Multiple Access (TDMA) based Random Access (RA) channel with Successive Interference Cancellation (SIC) is considered for a finite user population and reliable retransmission mechanism on the basis of Contention Resolution Diversity Slotted ALOHA (CRDSA). A general mathematical model based on Markov Chains is derived which makes it possible to predict the stability regions of SIC-RA channels, the expected delays in equilibrium and the selection of parameters for a stable channel configuration. Furthermore the model enables the estimation of the average time before reaching instability. The presented model is verified against simulations and numerical results are provided for comparison of the stability of CRDSA versus the stability of traditional Slotted ALOHA (SA). The presented results show that CRDSA has not only a high gain over SA in terms of throughput but also in its stability.Comment: 10 pages, 12 figures This paper is submitted to the IEEE Transactions on Communications for possible publication. The IEEE copyright notice applie

The legal status of NGOs in international governance and its relevance for the legitimacy of international organizations

This working paper introduces the concept of legal personality of non-state actors as an indicator of the democratic legitimacy of international organizations (IOs). Globalization has led to changes in statehood which are reflected in new democratic forms of participation and new expectations and attitudes towards political institutions. This also affects international politics in that international organizations are questioned with regard to their own legitimacy. In this context, normatively and empirically based policy proposals alike tend to suggest an increased role of new actors, mostly civil society organizations (CSOs) or NGOs, in overcoming the legitimacy deficit of IOs. However, if participation of non-state actors in international governance is to be effective, efficient and have a meaningful and lasting effect, it requires institutional rights and duties - and with it legal personality. Thus, legal personality of non-state actors can be taken as a minimum safeguarding clause for surmounting the legitimacy deficit of international organizations (normative approach). It can also be used as a helpful analytical framework for organizing empirical data on the participation of these actors in IOs (empirical approach). This working paper evaluates the legal rights and duties of NGOs in their cooperation with more than 30 international organizations and seeks to assess whether this implies that they have acquired legal personality and which quality this personality takes on. Such a comparative paper is a novelty in both political science and international law. By combining perspectives from two disciplines, this working paper illustrates the intrinsic empirical and theory-building value of (international) positive law in political science. --

Civil society legitimacy and nuclear non-proliferation

During recent years, civil society legitimacy has generated a growing interest in scholarly research. The present article therefore proposes four normative criteria, namely, independence, transparency, participation, and inclusion, in order to start assessing civil society legitimacy empirically. It does so by using the non-proliferation regime as a field of inquiry. In this context, four different advocacy NGOs active during the Nuclear Non-Proliferation Treaty's review processes - MPI, IPPNW, WILPF, and the Friedenswerkstatt - are analysed. The results give a fairly good score for CSO legitimacy, but show that what seems to matter most in this regard is the organizational culture, rather than the organizational structure of an organization. -- In den letzten Jahren hat die Frage zivilgesellschaftlicher Legitimität ein wachsendes Interesse in der Wissenschaft hervorgerufen. Der vorliegende Artikel schlägt daher vier normative Kriterien vor, nämlich Unabhängigkeit, Transparenz, Beteiligung und Inklusion, um zivilgesellschaftliche Legitimität empirisch zu bewerten. Untersuchungsfeld ist das Nichtverbreitungs-Regime. In diesem Zusammenhang werden vier verschiedene, während des Überprüfungsprozesses des Atomwaffensperrvertrages aktive Advocacy-NGOs - MPI, IPPNW, WILPF, und die Friedenswerkstatt - untersucht. Wie das Ergebnis zeigt, schneiden zivilgesellschaftliche Organisationen in ihrer Legitimität relativ gut ab. Allerdings kommt es hierbei mehr auf die Organisationskultur, und weniger auf die Organisationsstruktur einer Organisation an.

Optimum Header Positioning in Successive Interference Cancellation (SIC) based Aloha

Random Access MAC protocols are simple and effective when the nature of the traffic is unpredictable and sporadic. In the following paper, investigations on the new Enhanced Contention Resolution ALOHA (ECRA) are presented, where some new aspects of the protocol are investigated. Mathematical derivation and numerical evaluation of the symbol interference probability after SIC are here provided. Results of the optimum header positioning which is found to be in the beginning and in the end of the packets, are exploited for the evaluation of ECRA throughput and Packet Error Rate (PER) under imperfect knowledge of packets positions. Remarkable gains in the maximum throughput are observed for ECRA w.r.t. Contention Resolution ALOHA (CRA) under this assumption.Comment: Accepted for publication in the IEEE International Conference on Communications (ICC) 201

Civil society participation in international governance: the UN and the WTO compared

Civil society participation has become a buzzword in the debate about the legitimacy and accountability of international governance. Many organizations, prominently among them the World Trade Organization (WTO), have come under considerable pressure to open up their policy-making process towards non-state actors. Although the WTO has become more transparent in recent years, direct stakeholder access to its policy making is still denied. This situation is often contrasted with that at the United Nations (UN), where there is (allegedly) much more formally regulated and more substantial participation of civil society. In this paper, we compare the patterns of participation in these two organizations and seek to identify some common dynamics. We present a general framework for analysis based on a model of the policy cycle that allows us to distinguish 'push' and 'pull' factors that determine cooperation in different phases of policy making. In our empirical study, we find that in the WTO, there are few incentives for the organization itself to pull civil society actors into its policy-making process. Agendasetting is the task of governments; research and analysis is delivered by the Secretariat; compliance control is undertaken jointly by the organization and its members. To push the door to trade policy making open, civil society can only rely on public shaming, that is, threatening to undermine the organization's legitimacy as it violates widely accepted standards of good governance. In the UN system, there is in fact more cooperation, but it remains largely limited to the policy phases of agenda-setting, research and analysis and compliance control. Quite like the WTO, the UN protects an intergovernmental core of policy making in which cooperation with civil society remains at the discretion of state parties. Evidence for this are informal and ad hoc ways of collaboration and a lack of participatory rights for non-state actors in the Security Council and the General Assembly. We conclude that studying civil society participation in international public organizations through the lens of the policy cycle can give us a fine-grained picture of cooperative arrangements and enables us to identify potentials for cooperation as well as exclusion. Yet, we also observed two other factors at work that were not really grasped by the model of the policy cycle. First, the institutional culture of organizations can be more or less amenable to civil society. Second, organizations are susceptible to campaigns for 'good governance' that invoke standards of due process and may open the door to nonstate actors. --

Does opportunistic testing bias cognitive performance in primates? Learning from drop-outs

Dropouts are a common issue in cognitive tests with non-human primates. One main reason for dropouts is that researchers often face a trade-off between obtaining a sufficiently large sample size and logistic restrictions, such as limited access to testing facilities. The commonly-used opportunistic testing approach deals with this trade-off by only testing those individuals who readily participate and complete the cognitive tasks within a given time frame. All other individuals are excluded from further testing and data analysis. However, it is unknown if this approach merely excludes subjects who are not consistently motivated to participate, or if these dropouts systematically differ in cognitive ability. If the latter holds, the selection bias resulting from opportunistic testing would systematically affect performance scores and thus comparisons between individuals and species. We assessed the potential effects of opportunistic testing on cognitive performance in common marmosets (Callithrix jacchus) and squirrel monkeys (Saimiri sciureus) with a test battery consisting of six cognitive tests: two inhibition tasks (Detour Reaching and A-not-B), one cognitive flexibility task (Reversal Learning), one quantity discrimination task, and two memory tasks. Importantly, we used a full testing approach in which subjects were given as much time as they required to complete each task. For each task, we then compared the performance of subjects who completed the task within the expected number of testing days with those subjects who needed more testing time. We found that the two groups did not differ in task performance, and therefore opportunistic testing would have been justified without risking biased results. If our findings generalise to other species, maximising sample sizes by only testing consistently motivated subjects will be a valid alternative whenever full testing is not feasible.</p

How task format affects cognitive performance:a memory test with two species of New World monkeys

In cognitive tests, animals are often given a choice between two options and obtain a reward if they choose correctly. We investigated whether task format affects subjects' performance in a physical cognition test. In experiment 1, a two-choice memory test, 15 marmosets, Callithrix jacchus, had to remember the location of a food reward over time delays of increasing duration. We predicted that their performance would decline with increasing delay, but this was not found. One possible explanation was that the subjects were not sufficiently motivated to choose correctly when presented with only two options because in each trial they had a 50% chance of being rewarded. In experiment 2, we explored this possibility by testing eight naïve marmosets and seven squirrel monkeys, Saimiri sciureus, with both the traditional two-choice and a new nine-choice version of the memory test that increased the cost of a wrong choice. We found that task format affected the monkeys' performance. When choosing between nine options, both species performed better and their performance declined as delays became longer. Our results suggest that the two-choice format compromises the assessment of physical cognition, at least in memory tests with these New World monkeys, whereas providing more options, which decreases the probability of obtaining a reward when making a random guess, improves both performance and measurement validity of memory. Our findings suggest that two-choice tasks should be used with caution in comparisons within and across species because they are prone to motivational biases