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Shah T.,Tata Institute of Technology | Dabeer O.,Tata Institute of Technology
IEEE Transactions on Communications

Motivated by the need to reduce power consumption in the receiver analog-to-digital converter (ADC) in multi-Gbps communication systems, in this paper, we study subcarrier power allocation based on channel side information (CSI) at the transmitter. We derive a fixed point equation for subcarrier power allocation that minimizes uncoded symbol error rate (SER) when a finite precision ADC is used at the receiver. We study the sensitivity of the optimal power allocation with respect to a parameter that depends on the ADC precision. Based on this, we propose a simple analytical approximation for the optimal power allocation, which performs within 0.5 dB of the exact case over a wide range of signal-to-noise ratio (SNR). The proposed power allocation leads to only a small increase in the peak-to-average power ratio (PAPR) (< 0.3 dB) for channel models suggested in IEEE 802.15.3c. Further, for a 16-QAM input, 7/8 rate low density parity check (LDPC) code and 3-bit precision ADC, it attains a coded bit error rate (BER) of 10-5 at a SNR of 23.5 dB, which compares favorably with the 25 dB required by a traditional system with equal power allocation across the subcarriers and infinite sampling precision. We also show the robustness of the performance gain to channel estimation errors. © 1972-2012 IEEE. Source

Dutta D.,Tata Institute of Technology | Umashankar M.,Tata Institute of Technology | Lewis E.B.,California Institute of Technology | Rodrigues V.,Tata Institute of Technology | And 2 more authors.
Journal of Neurogenetics

The differentiation of myoblasts to form functional muscle fibers is a consequence of interactions between the mesoderm and ectoderm. The authors examine the role of segment identity in directing these interactions by studying the role of Hox genes in patterning adult muscles in Drosophila. Using the 'four-winged fly' to remove Ultrabithorax function in the developing adult, the authors alter the identity of the ectoderm of the third thoracic segment towards the second and show that this is sufficient to inductively alter most properties of the mesoderm - myoblast number, molecular diversity, and migration pattern - to that of the second thoracic segment. Not all aspects of myogenesis are determined by the segment identity of the ectoderm. The autonomous identity of the mesoderm is important for choosing muscle founder cells in the correct segmental pattern. The authors show this by removal of the function of Antennapedia, the Hox gene expressed in the mesoderm of the third thoracic segment. This results in the transformation of founder cells to a second-thoracic pattern. The authors also report a role for the nervous system in later aspects of muscle morphogenesis by specifically altering Ultrabithorax gene expression in motor neurons. Thus, ectoderm and mesoderm segment identities collaborate to direct muscle differentiation by affecting distinct aspects of the process. © 2010 Informa Healthcare USA, Inc. Source

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