Antenna Combining for the MIMO Downlink Channel

A multiple antenna downlink channel where limited channel feedback is available to the transmitter is considered. In a vector downlink channel (single antenna at each receiver), the transmit antenna array can be used to transmit separate data streams to multiple receivers only if the transmitter has very accurate channel knowledge, i.e., if there is high-rate channel feedback from each receiver. In this work it is shown that channel feedback requirements can be significantly reduced if each receiver has a small number of antennas and appropriately combines its antenna outputs. A combining method that minimizes channel quantization error at each receiver, and thereby minimizes multi-user interference, is proposed and analyzed. This technique is shown to outperform traditional techniques such as maximum-ratio combining because minimization of interference power is more critical than maximization of signal power in the multiple antenna downlink. Analysis is provided to quantify the feedback savings, and the technique is seen to work well with user selection and is also robust to receiver estimation error.Comment: Submitted to IEEE Trans. Wireless Communications April 2007. Revised August 200

Process Matters: Specialization in Federal Appellate Review of Noncapital Section 2254 Cases

This Note assesses the need for specialized review in the federal circuit courts of noncapital habeas cases brought by state prisoners under 28 U.S.C. § 2254. It first argues that the complexity of federal habeas law, the substantial disuniformity between circuits, the conflicting visions proffered by the Warren Court’s habeas jurisprudence and Congress’s recent statutory enactments—together with the greatest stakes possible at issue, liberty—are all factors warranting the creation of a national court of appeals that would hear only habeas cases. Recognizing, however, that creating such a court is a low priority for Congress at best and simply unfeasible at worst, this Note also makes another recommendation for injecting specialized review into appellate adjudication. Specifically, the circuit courts’ use of line staff attorneys to screen petitions can be much improved by creating a career staff attorney position dedicated solely to review of noncapital § 2254 cases. A formal position will attract better candidates, have lower rates of turnover, and concentrate experience and expertise to the benefit of judges and litigants

Exploring demand for forestry in Lake Victoria Basin (Western Kenya): An econometric approach

This paper determines the demand for a forestry program amongst rural households in western Kenya. It is based on a field survey with 277 households, using a stratified random sampling approach. The study follows attribute based method to elicit farmers’ preferences. Demand is measured in terms of additional number of trees that a household is willing to plant under different price schedules, including direct economic incentive to plant new seedlings. The mean willingness to plant new trees per household increases from 44 trees when farmers have to pay 10ksh/seedling, to 244 trees when farmers receive a payment of 10ksh/seedling. The paper uses fixed effects, random effects and random effect tobit models to estimate relevant parameters. Hausman specification test is returned insignificant, while implies that random effects specification is not incorrect. Price of seedlings (negative effect), availability of timber species (positive effect), gender of the respondent (men likely to plant more trees than women), and availability of agricultural labor at the household (positive) were all found to be significant. Increase in price of a seedling by 1Ksh reduced demand by nine seedlings, while addition of an adult who works full-time on the family farm will raise the demand for seedlings by 18. Furthermore, farmers in Yala River basin were likely to plant more trees than those in the Nyando River basin.Kenya, Lake Victoria, demand, tree seedlings, attribute based method, Demand and Price Analysis, Resource /Energy Economics and Policy, C23, Q23, Q57,

Networked Computing in Wireless Sensor Networks for Structural Health Monitoring

This paper studies the problem of distributed computation over a network of wireless sensors. While this problem applies to many emerging applications, to keep our discussion concrete we will focus on sensor networks used for structural health monitoring. Within this context, the heaviest computation is to determine the singular value decomposition (SVD) to extract mode shapes (eigenvectors) of a structure. Compared to collecting raw vibration data and performing SVD at a central location, computing SVD within the network can result in significantly lower energy consumption and delay. Using recent results on decomposing SVD, a well-known centralized operation, into components, we seek to determine a near-optimal communication structure that enables the distribution of this computation and the reassembly of the final results, with the objective of minimizing energy consumption subject to a computational delay constraint. We show that this reduces to a generalized clustering problem; a cluster forms a unit on which a component of the overall computation is performed. We establish that this problem is NP-hard. By relaxing the delay constraint, we derive a lower bound to this problem. We then propose an integer linear program (ILP) to solve the constrained problem exactly as well as an approximate algorithm with a proven approximation ratio. We further present a distributed version of the approximate algorithm. We present both simulation and experimentation results to demonstrate the effectiveness of these algorithms

Opportunistic Routing in Ad Hoc Networks: How many relays should there be? What rate should nodes use?

Opportunistic routing is a multi-hop routing scheme which allows for selection of the best immediately available relay. In blind opportunistic routing protocols, where transmitters blindly broadcast without knowledge of the surrounding nodes, two fundamental design parameters are the node transmission probability and the transmission spectral efficiency. In this paper these parameters are selected to maximize end-to-end performance, characterized by the product of transmitter density, hop distance and rate. Due to the intractability of the problem as stated, an approximation function is examined which proves reasonably accurate. Our results show how the above design parameters should be selected based on inherent system parameters such as the path loss exponent and the noise level.Comment: 5 pages, 8 figures, Submitted to IEEE GLOBECOM 201