On Amplify-and-Forward Relaying Over Hyper-Rayleigh Fading Channels

Relayed transmission holds promise for the next generation of wireless communication systems due to the performance gains it can provide over non-cooperative systems. Recently hyper-Rayleigh fading, which represents fading conditions more severe than Rayleigh fading, has received attention in the context of many practical communication scenarios. Though power allocation for Amplify-and-Forward (AF) relaying networks has been studied in the literature, a theoretical analysis of the power allocation problem for hyper-Rayleigh fading channels is a novel contribution of this work. We develop an optimal power allocation (OPA) strategy for a dual-hop AF relaying network in which the relay-destination link experiences hyper-Rayleigh fading. A new closed-form expression for the average signal-to-noise ratio (SNR) at destination is derived and it is shown to provide a new upper-bound on the average SNR at destination, which outperforms a previously proposed upper-bound based on the well-known harmonic-geometric mean inequality. An OPA across the source and relay nodes, subject to a sum-power constraint, is proposed and it is shown to provide measurable performance gains in average SNR and SNR outage at the destination relative to the case of equal power allocation

Ali Wyne on Understanding Poverty Edited by Abhijit Vinayak Banerjee, Roland Bénabou, and Dilip Mookherjee. Oxford: Oxford University Press, 2006. 496pp.

A review of: Understanding Poverty Edited by Abhijit Vinayak Banerjee, Roland Bénabou, and Dilip Mookherjee. Oxford: Oxford University Press, 2006. 496pp

Countering Chinese Influence in Sudan

It is difficult to imagine a more poisonous symbiosis than that between China and Sudan. The former requires a continuous flow of low-cost oil imports to satisfy its soaring oil demand, and the latter requires sufficient economic support to immunize itself against international interventions and preempt potential internal uprisings. Sudan supplies 64 percent of its oil to China (meeting seven percent of the economic power’s demand in 2006), and China, for its part, has invested heavily in Paloich, one of the country’s central oil-producing areas

Examining the Declining Utility of Military Force

A review of: The New American Militarism: How Americans Are Seduced by War by Andrew J. Bacevich. Oxford: Oxford University Press, 2005. 270pp

AIPAC\u27s Good Intentions Undermine Israel\u27s Interests

While the American Israel Public Affairs Committee (AIPAC) is nominally pro-Israel, its advice undermines Israel’s interests. It does not encourage Israel to make concessions, but rather recommends that Israel ignore the reformists within and outside of it. The folly of such counsel becomes apparent when one recognizes that Israel’s current strategy cannot be sustained

Characterization of Single- and Multi-antenna Wireless Channels

The wireless propagation channel significantly influences the received signal, so that it needs to be modeled effectively. Extensive measurements and analysis are required for investigating the validity of theoretical models and postulating new models based on measurements. Such measurements, analysis, and modeling are the topic of this thesis. The focus of the included contributions are Multiple-Input Multiple-Output (MIMO) propagation channels and radio channels for sensor network applications. Paper I presents results from one of the first MIMO measurements for a double-directional characterization of the outdoor-to-indoor wireless propagation channel. Such channels are of interest for both cellular and wireless LAN applications. We discuss physical aspects of building penetration, and also provide statistics of angle and delay spreads in the channel. The paper also investigates the coupling between DOD and DOA and the two spectra are found to have non-negligible dependence. We test the applicability of three analytical channel models that make different assumptions on the coupling between DODs and DOAs. Our results indicate that analytical models, that impose fewer restrictions on the DOD to DOA coupling, should be used preferrably over models such as the Kronecker model that have more restrictive assumptions. Paper II presents a cluster-based analysis of the outdoor-to-indoor MIMO measurements analyzed in Paper I. A subset of parameters of the COST 273 channel model, a generic model for MIMO propagation channels, are characterized for the outdoor-to-indoor scenario. MPC parameters are extracted at each measured location using a high-resolution algorithm and clusters of MPCs are identified with an automated clustering approach. In particular, the adopted clustering approach requires that all MPC parameters must be similar in order for the MPCs to form a cluster. A statistical analysis of the identified clusters is performed for both the intra- and inter-cluster properties. Paper III analyzes the spatial fading distribution for a range of canonical sensor deployment scenarios. The presented results are relevant to communicating within, and between, clusters of nodes. Contrary to the widely accepted assumption in published literature that the channel is AWGN at a small-enough distance, our measurements indicate that values of the Rice factor do not, in general, increase monotonically as the Tx-Rx distance is reduced. A probability mixture model is presented, with distance dependent parameters, to account for the distance dependent variations of the Rice factor. A simulation model that includes small- and large-scale fading effects is presented. According to the modeling approach, a sensor node placed anywhere within the spatial extent of a small-scale region will experience the channel statistics applicable to that region. Paper IV presents results characterizing a radio channel for outdoor short-range sensor networks. A number of antennas are placed on the ground in an open area and time-variation of the channel is induced by a person moving in the vicinity of the nodes. The channel statistics of both the LOS path and the overall narrowband signal are non-stationary. We investigate the stationarity interval length to be used for small-scale analysis. Our analysis of the various measured links shows that the Rx signal strength is significantly influenced by a moving person only when the person blocks the LOS path. We present a generic approach for modeling the LOS blockage, and also model the time-variant Doppler spectrum of the channel's scattered components

Ali Wyne on The Economic Life of Refugees by Karen Jacobsen. Bloomfield, CT: Kumarian Press, 2005. 131pp.

A review of: The Economic Life of Refugees by Karen Jacobsen. Bloomfield, CT: Kumarian Press, 2005. 131pp