Multipath streaming: fundamental limits and efficient algorithms

We investigate streaming over multiple links. A file is split into small units called chunks that may be requested on the various links according to some policy, and received after some random delay. After a start-up time called pre-buffering time, received chunks are played at a fixed speed. There is starvation if the chunk to be played has not yet arrived. We provide lower bounds (fundamental limits) on the starvation probability of any policy. We further propose simple, order-optimal policies that require no feedback. For general delay distributions, we provide tractable upper bounds for the starvation probability of the proposed policies, allowing to select the pre-buffering time appropriately. We specialize our results to: (i) links that employ CSMA or opportunistic scheduling at the packet level, (ii) links shared with a primary user (iii) links that use fair rate sharing at the flow level. We consider a generic model so that our results give insight into the design and performance of media streaming over (a) wired networks with several paths between the source and destination, (b) wireless networks featuring spectrum aggregation and (c) multi-homed wireless networks.Comment: 24 page

Hybrid Spectrum Sharing in mmWave Cellular Networks

While spectrum at millimeter wave (mmWave) frequencies is less scarce than at traditional frequencies below 6 GHz, still it is not unlimited, in particular if we consider the requirements from other services using the same band and the need to license mmWave bands to multiple mobile operators. Therefore, an efficient spectrum access scheme is critical to harvest the maximum benefit from emerging mmWave technologies. In this paper, we introduce a new hybrid spectrum access scheme for mmWave networks, where data is aggregated through two mmWave carriers with different characteristics. In particular, we consider the case of a hybrid spectrum scheme between a mmWave band with exclusive access and a mmWave band where spectrum is pooled between multiple operators. To the best of our knowledge, this is the first study proposing hybrid spectrum access for mmWave networks and providing a quantitative assessment of its benefits. Our results show that this approach provides major advantages with respect to traditional fully licensed or fully unlicensed spectrum access schemes, though further work is needed to achieve a more complete understanding of both technical and non technical implications

Sharing the Burden of Collective Security in the European Union. Research Note

This article compares European Union (EU) burden-sharing in security governance distinguishing between assurance, prevention, protection, and compellence policies. We employ joint-product models and examine the variation in the level of publicness, the asymmetry of the distribution of costs and benefits, and aggregation technologies in each policy domain. Joint-product models predict equal burden sharing for protection and assurance because of their respective weakest-link and summation aggregation technologies with symmetric costs. Prevention is also characterized by the technology of summation, but asymmetry of costs implies uneven burden-sharing. Uneven burden-sharing is predicted for compellence because it has the largest asymmetry of costs and a best-shot aggregation technology. Evaluating burden-sharing relative to a country?s ability to contribute, Kendall tau-tests examine the rank-correlation between security burden and the capacity of EU member states. These tests show that the smaller EU members disproportionately shoulder the costs of assurance and protection; wealthier EU members carry a somewhat disproportionate burden in the provision of prevention, and larger EU members in the provision of compellence. When analyzing contributions relative to expected benefits, asymmetric marginal costs can largely explain uneven burden-sharing. The main conclusion is that the aggregated burden of collective security governance in the EU is shared quite evenly

Feeling the squeeze? Tabbies or tigers: the case of social enterprises contracting in the fields of recycling and work integration

Current UK policy is encouraging the identification, emergence, transmutation or invention of third sector organisations that will have a social enterprise orientation with a particular focus on them as vehicles for the delivery of public services (Audit Commission 2005). This can be seen as part of the new governance agenda (Taylor, Wilkinson and Craig 2001, Kendal 2003, Stoker 2004) the form of which is still emergent. One view of governance refers to a 'hollowing out' of state powers (Rhodes, 1997) and a shift from state control to co-ordination using mechanisms such as networks and partnerships to bring together the public, private and third sector as well as community actors and citizens in reforming services. Local Authority white paper (2006) promised further decentralisation moving functions downwards to special purpose bodies and outwards to agencies and communities. The new Local Government White Paper emphasises the role of community engagement, partnership arrangements and devolved budgets with voluntary organisations at the local level (NCVO 2006: 2-3). Such processes are aimed both at both private and third sector providers. In this new distributed system of governance partnership and collaboration plays an important role in the implementation of social goods although these processes are never unproblematic (Huxham & Vangen 2000; Taylor Taylor, Wilkinson and Craig 2001). Nevertheless the contracting out processes continue to gather speed: with recycling and waste, care, leisure services, work advice, health services, prison and probation at various stages in the continuum of change. Against this background the role and form of social enterprise organisations appears at times to be assumed to be 'heterogeneous' and 'good' with all organisations tending towards similar development trajectories with uniform support needs. What is often not distinguished so clearly are the differing types of social enterprise; the different sub-sectors of the economy they are operating in; the variety of markets and funding regimes they are involved in; the different partnership regimes they are embedded within; and their different cultures and connection to local communities. All of these factors have implications for what types of organisations (large/small social enterprise; local/national organisations, and even social enterprise or private organisation) are favoured in the contracting processes and how such processes may affect their wider mission and ethos. Social enterprises are sometimes treated by policy makers, and at times by leaders, practitioners and researchers within the sector as if they were one thing. Crudely we might say they are treated as if they are all cats when in reality some are tigers and some are tabbys – with every breed in between. Nevertheless, despite the heterogeneity of the social enterprise scene we are seeing evidence of a convergence of form in contracting processes which, we argue, tends to favour the tigers and squeeze the tabbys. This paper reports on recent empirical research and analysis in 2 sub fields of social enterprise activity: (a) the delivery of waste and recycling services (Slater 2006) and (b) the delivery of work integration and advice activities for the disadvantaged (Aiken 2006, 2007)