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2. Distributed Transmit Beamforming using Feedback Control

Author

Mudumbai, R., Hespanha, J., Madhow, U., and Barriac, G.

Subjects
Computer Science - Information Theory, C.2.1
Abstract

A simple feedback control algorithm is presented for distributed beamforming in a wireless network. A network of wireless sensors that seek to cooperatively transmit a common message signal to a Base Station (BS) is considered. In this case, it is well-known that substantial energy efficiencies are possible by using distributed beamforming. The feedback algorithm is shown to achieve the carrier phase coherence required for beamforming in a scalable and distributed manner. In the proposed algorithm, each sensor independently makes a random adjustment to its carrier phase. Assuming that the BS is able to broadcast one bit of feedback each timeslot about the change in received signal to noise ratio (SNR), the sensors are able to keep the favorable phase adjustments and discard the unfavorable ones, asymptotically achieving perfect phase coherence. A novel analytical model is derived that accurately predicts the convergence rate. The analytical model is used to optimize the algorithm for fast convergence and to establish the scalability of the algorithm.

Published
2006

5. On the uniqueness of maximum likelihood estimation of nuclear sources

Author

Haug, J., Anjum, M. F., Anderson, Brian, Dasgupta, Soura, Mudumbai, R., Baidoo-Williams, H. E., Haug, J., Anjum, M. F., Anderson, Brian, Dasgupta, Soura, Mudumbai, R., and Baidoo-Williams, H. E.

Abstract

In an earlier paper, [1], we have considered the Maximum Likelihood (ML) localization of a stationary nuclear source using the time of arrival of particles modeled as a Poisson process. In this paper we consider whether the ML location estimate characterized in [1] is unique. In particular, we show that the question of uniqueness is equivalent to whether or not the root locus of a certain transfer function admits a single pair of nonzero imaginary axis crossing.

Published
2018

6. A Scalable Feedback Mechanism for Distributed Nullforming with Phase-Only Adaptation

Author

Kumar, A., Mudumbai, R., Dasgupta, S., Rahman, Muhammad Mahboob Ur, Brown Iii, D. R., Madhow, U., Bidigare, T. P., Kumar, A., Mudumbai, R., Dasgupta, S., Rahman, Muhammad Mahboob Ur, Brown Iii, D. R., Madhow, U., and Bidigare, T. P.

Abstract

This paper considers a problem of distributed nullforming, in which multiple wireless transmitters steer a null toward a designated receiver by only adjusting their carrier phases. Since each transmitter transmits at full power, the system maximizes 'power pooling' gains for cooperative communication or jamming, while simultaneously protecting a designated receiver. Analysis in a noiseless setting shows that, while the received power at the designated receiver, as a function of the transmitted phases, is nonconvex with multiple critical points, all of its local minima are also global minima. This implies that a null can be formed using a distributed, scalable protocol based on gradient descent: each transmitter adapts its phase based only on aggregate feedback broadcast by the receiver (so that feedback overhead does not increase with the number of transmitters), along with an estimate of its own channel gain (which can be obtained, e.g., via reciprocity). Simulations show that the convergence rate actually improves with the number of transmitters, and that the algorithm is robust to noise, substantial channel estimation errors, and oscillator drift., QC 20200910

Published
2015
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13. Combined exfoliation and pigment dispersion: an overlap syndrome

Author

Mudumbai, R, Liebmann, J M, and Ritch, R

Subjects
Male, food and beverages, Iris, Middle Aged, Exfoliation Syndrome, Prognosis, eye diseases, Risk Factors, Humans, Female, Pigment Epithelium of Eye, Glaucoma, Open-Angle, Intraocular Pressure, Research Article, Retrospective Studies
Abstract

PURPOSE: To describe a series of patients with combined pigment dispersion syndrome (PDS) and exfoliation syndrome (XFS) and to introduce a concept, the overlap syndrome, to aid in assessing multiple risk factors for glaucomatous damage. METHODS: A retrospective review of the records of all patients on our database who carried a diagnosis of both PDS/pigmentary glaucoma (PG) and XFS/exfoliative glaucoma (XFG). RESULTS: We identified 26 patients as having both XFS/XFG and PDS/PG. The average age was 64.3 +/- 9.8 years and 19 of 26 were men. All patients had bilateral PDS/PG. Bilateral XFS/XFG was present in 9 of 26 patients, and of the 17 patients with unilateral involvement, the left eye was affected in 13. CONCLUSION: Both XFS and PDS are common. Middle-aged patients with known PDS/PG should be suspected of having the onset of XFS if 1 eye escapes intraocular pressure control. Patients presenting with unilateral XFG may also have signs of PDS/PG, often remitted. We define an overlap syndrome as the appearance of a new co-morbidity for glaucomatous damage in a patient with a pre-existing risk factor, which then changes the course, and prognosis of the disease. This concept should be particularly useful in dealing with secondary and normal-tension glaucoma.

Published
1999

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