Outage Capacity and Optimal Transmission for Dying Channels

In wireless networks, communication links may be subject to random fatal impacts: for example, sensor networks under sudden power losses or cognitive radio networks with unpredictable primary user spectrum occupancy. Under such circumstances, it is critical to quantify how fast and reliably the information can be collected over attacked links. For a single point-to-point channel subject to a random attack, named as a \emph{dying channel}, we model it as a block-fading (BF) channel with a finite and random delay constraint. First, we define the outage capacity as the performance measure, followed by studying the optimal coding length $K$ such that the outage probability is minimized when uniform power allocation is assumed. For a given rate target and a coding length $K$, we then minimize the outage probability over the power allocation vector \mv{P}_{K}, and show that this optimization problem can be cast into a convex optimization problem under some conditions. The optimal solutions for several special cases are discussed. Furthermore, we extend the single point-to-point dying channel result to the parallel multi-channel case where each sub-channel is a dying channel, and investigate the corresponding asymptotic behavior of the overall outage probability with two different attack models: the independent-attack case and the $m$-dependent-attack case. It can be shown that the overall outage probability diminishes to zero for both cases as the number of sub-channels increases if the \emph{rate per unit cost} is less than a certain threshold. The outage exponents are also studied to reveal how fast the outage probability improves over the number of sub-channels.Comment: 31 pages, 9 figures, submitted to IEEE Transactions on Information Theor

On Design of Collaborative Beamforming for Two-Way Relay Networks

We consider a two-way relay network, where two source nodes, S1 and S2, exchange information through a cluster of relay nodes. The relay nodes receive the sum signal from S1 and S2 in the first time slot. In the second time slot, each relay node multiplies its received signal by a complex coefficient and retransmits the signal to the two source nodes, which leads to a collaborative two-way beamforming system. By applying the principle of analog network coding, each receiver at S1 and S2 cancels the "self-interference" in the received signal from the relay cluster and decodes the message. This paper studies the 2-dimensional achievable rate region for such a two-way relay network with collaborative beamforming. With different assumptions of channel reciprocity between the source-relay and relay-source channels, the achievable rate region is characterized under two setups. First, with reciprocal channels, we investigate the achievable rate regions when the relay cluster is subject to a sum-power constraint or individual-power constraints. We show that the optimal beamforming vectors obtained from solving the weighted sum inverse-SNR minimization (WSISMin) problems are sufficient to characterize the corresponding achievable rate region. Furthermore, we derive the closed form solutions for those optimal beamforming vectors and consequently propose the partially distributed algorithms to implement the optimal beamforming, where each relay node only needs the local channel information and one global parameter. Second, with the non-reciprocal channels, the achievable rate regions are also characterized for both the sum-power constraint case and the individual-power constraint case. Although no closed-form solutions are available under this setup, we present efficient numerical algorithms.Comment: new version of the previously posted, single column double spacing, 24 page

Bottom partner B' and Zb production at the LHC

Some new physics models, such as "beautiful mirrors" scenario, predict the existence of the bottom partner $B'$. Considering the constraints from the data for the $Z\rightarrow b\bar{b}$ branching ratio $R_{b}$ and the $FB$ asymmetry $A_{FB}^{b}$ on the relevant free parameters, we calculate the contributions of $B'$ to the cross section $\sigma(Zb)$ and the $Z$ polarization asymmetry $A_{Z}$ for $Zb$ production at the $LHC$. We find that the bottom partner $B'$ can generate significant corrections to $\sigma(Zb)$ and $A_{Z}$, which might be detected in near future.Comment: 15 pages, 5 figures. Version published in Phys. Lett.

The Shaping Process of Urban Form Under a Socialist System: Townscape Diversity and its Formation in Sanlitun, Beijing

[EN] The difference between socio-economic systems is an important factor in the diversity of urban form. M. R. G. Conzen (1960) established a framework for urban morphology in the context of a British social system and culture. It was suggested that this did not necessarily apply to cities affected by revolutionary planning measures. China, which is markedly different in social system and culture from Britain by most standards qualifies as revolutionary, at least in the post-war period. Sanlitun in Beijing, China, is an interesting case for comparison with British cities. It was a site containing few buildings during the initial stage of new China, but subsequently became the ‘Second Embassy District’ where many embassies gathered. Now it has become a commercial core district and cultural meeting place of Westerners and Chinese. The townscape of Sanlitun, which has experienced a number of socialist construction periods reveals the process of changing urban form under a socialist system. Identifying morphological periods, the changing process of townscape development in Sanlitun is articulated. Morphological units are delimited. They clarify the variations in Sanlitun’s landscapes and their formation. Based on these, this paper reflects on the shaping process of townscape under different socio-cultural systems, and further considers the universality, applicability and particularities of Conzenian theory.Meng, Y.; Zeng, M.; Song, F. (2018). The Shaping Process of Urban Form Under a Socialist System: Townscape Diversity and its Formation in Sanlitun, Beijing. En 24th ISUF International Conference. Book of Papers. Editorial Universitat Politècnica de València. 273-284. https://doi.org/10.4995/ISUF2017.2017.5690OCS27328