Corruption of C-band microwave brightness observations by radio-frequency interference (RFI) has been reported in recent data from orbiting radiometers; methods for mitigating these effects are of ...great importance for the design of future spaceborne microwave radiometers. One approach that has been suggested involves the use of multiple subchannels at C-band as opposed to a single channel; the use of multiple subchannels allows RFI to be detected and mitigated by analyzing relationships among subchannel brightnesses. While this approach has been utilized in previous airborne measurements, demonstrations of the RFI mitigation performance achieved have been difficult to obtain. To address this issue, an enhanced airborne system for observing radio-frequency interference effects on C-band microwave radiometers was developed, and is described in this paper. The system includes a traditional microwave radiometer with four C-band subchannels, so that RFI removal is possible using a subchannel mitigation algorithm. In addition, the system includes a digital receiver with the capability of providing high temporal and spectral resolution observations of interference. This high-resolution data allows improved understanding of RFI sources to be obtained, and also allows analysis of subchannel mitigation algorithm performance. Observations using the system in a test flight near Wallops Island, VA are described. Results show the four subchannel approach generally to be effective in mitigating the observed RFI sources, although examples are also illustrated using the digital receiver data to demonstrate failure of this approach. While studies of the digital receiver data alone could be performed to demonstrate further improvements in RFI mitigation, issues with this initial dataset limit the extent of such studies. Nevertheless, the results obtained still demonstrate qualitatively the improved RFI mitigation that can be achieved in brightness observations through the use of digital receivers
We study the performance of multiple-antenna systems under finite-rate feedback of some function of the current channel realization from a channel-aware receiver to the transmitter. Our analysis is ...based on a novel geometric paradigm whereby the feedback information is modeled as a source distributed over a Riemannian manifold. While the right singular vectors of the channel matrix and the subspace spanned by them are located on the traditional Stiefel and Grassmann surfaces, the optimal input covariance matrix is located on a new manifold of positive semi-definite matrices - specified by rank and trace constraints - called the Pn manifold. The geometry of these three manifolds is studied in detail; in particular, the precise series expansion for the volume of geodesic balls over the Grassmann and Stiefel manifolds is obtained. Using these geometric results, the distortion incurred in quantizing sources using either a sphere-packing or a random code over an arbitrary manifold is quantified. Perturbative expansions are used to evaluate the susceptibility of the ergodic information rate to the quality of feedback information, and thereby to obtain the tradeoff of the achievable rate with the number of feedback bits employed. For a given system strategy, the gap between the achievable rates in the infinite and finite-rate feedback cases is shown to be O(special characters omitted) for Grassmann feedback and O(special characters omitted) for other cases, where N is the dimension of the manifold used for quantization and Nf is the number of bits used by the receiver per block for feedback. The geometric framework developed enables the results to hold for arbitrary distributions of the channel matrix and extends to all covariance computation strategies including, waterfilling in the short-term/long-term power constraint case, antenna selection and other rank-limited scenarios that could not be analyzed using previous probabilistic approaches.
The Multi-Ring Network (MRN) is proposed as a new topology which is free from the disadvantages of the hypercube and the star graph. The MRN possesses most of the features which have led to the ...popularity of non-trivial topologies like the hypercube and cube connected cycles. It is symmetric, has a small diameter, requires few communication ports per processor and can be used to connect a large number of processors using relatively few links. It is proven that the MRN has a smaller diameter than most other networks. A simple, shortest path routing algorithm for the MRN is presented. The MRN is compared with several existing networks and it is shown that the MRN is a better alternative.
A "usable speech" extraction system was proposed (Yanatorno, 1998) to separate co-channel speech into "usable" frames that are minimally corrupted by interfering speech. Studies indicate that a ...significant amount of cochannel speech can be considered "usable" for speaker identification (SID). Therefore, it is necessary to establish criteria for usable speech frames for SID. Voiced speech, of which usable speech is entirely comprised, is shown to be information rich for SID. In addition, SID accuracy increases as the frame-based target to interferer ratio (TIR) increases when evaluated independently of the amount of available segments. Krishnamachari et al. (2000) developed a frame-based spectral autocorrelation ratio (SAR) technique for determining usable frames within co-channel speech. The ability of the SAR method to determine usable frames at various thresholds is examined. This paper investigates the effectiveness of a frame-based usable speech extraction technique for speaker identification.
An airborne system for observing radio frequency interference at C-band is described. The digital receiver included has the capability of providing high temporal and spectral resolution of ...interference, as well as implementing simple mitigation strategies. Plans for observations with the system are discussed.
We study the finite-rate feedback of optimal input covariance matrices from the channel-aware receiver to the transmitter in a multi-antenna single-user setup. Under a block fading model for the ...channel matrix, the receiver computes the covariance matrix corresponding to the current channel realization and feeds back information about it using a finite, say N f , number of bits per block. Our finite-rate feedback analysis is based on a novel geometric paradigm whereby the feedback information is modeled as a source distributed over a new Riemannian surface called the Pn manifold. For a given system strategy, the gap between the achievable rates in the infinite and finite-rate feedback cases is shown to be O(2 - N f /N ), where N is the dimension of the Pn manifold used for quantization.
Optimal design of an electric hybrid powertrain system using a decomposition-based approach is presented. In this approach, a general system design problem is first formulated without specifying ...objectives. The mathematical model is analyzed using partitioning techniques, and an optimal design problem that can be readily decomposed and solved using an appropriate coordination strategy is derived. Basic concepts for hybrid powertrains in automotive applications and a mathematical design model are introduced. Different ways of synthesizing a hierarchically decomposed optimization problem statement are described, and one such problem is solved using a sensitivity-based coordination strategy.
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