arXiv subjects

Joyson Sebastian

Publications and source records attributed to Joyson Sebastian.

5 recordsLinked to original sources

arXiv2021

Explicit Calibration of mmWave Phased Arrays with Phase Dependent Errors

We consider an error model for phased array with gain errors and phase errors, with errors dependent on the phase applied and the antenna index. Under this model, we propose an algorithm for measuring the errors by selectively turning on the antennas at specific phases and measuring the transmitted power. In our algorithm, the antennas are turned on individually and then pairwise for the measurements, and rotation of the phased array is not required. We give numerical results to measure the accuracy of the algorithm as a function of the signal-to-noise ratio in the measurement setup. We also compare the performance of our algorithm with the traditional rotating electric vector (REV) method and observe the superiority of our algorithm. Simulations also demonstrate an improvement in the coverage on comparing the cumulative distribution function (CDF) of equivalent isotropically radiated power (EIRP) before and after calibration.

eess.SP↗

arXiv2020

Generalized Degrees of Freedom of Noncoherent Diamond Networks

We study the generalized degrees of freedom (gDoF) of the block-fading noncoherent diamond (parallel relay) wireless network with asymmetric distributions of link strengths, and a coherence time of T symbol duration. We first derive an outer bound for this channel and then derive the optimal signaling structure for this outer bound. Using the optimal signaling structure we solve the outer bound optimization problem in terms of its gDoF. Using insights from our outer bound signaling solution, we devise an achievability strategy based on a novel scheme that we call train-scale quantize-map-forward (TS-QMF). This uses training in the links from the source to the relays, scaling and quantizing at the relays combined with nontraining-based schemes. We show the optimality of this scheme with respect to the outer bound in terms of the gDoF. In noncoherent point-to-point multiple-input-multiple-output (MIMO) channels, where the fading channel is unknown to transmitter and receiver, an important tradeoff between communication and channel learning was revealed by Zheng and Tse, by demonstrating that not all the available antennas might be used, as it is suboptimal to learn all their channel parameters. Our results in this paper for the diamond network demonstrates that in certain regimes the optimal scheme uses a subnetwork, demonstrating a tradeoff between channel learning and communications. In some regimes, it is gDoF optimal to do relay selection, i.e, use a part of the network. In the other regimes, even when it is essential to use the entire network, it is suboptimal to learn the channel states for all the links in the network, i.e, traditional training-based schemes are suboptimal in these regimes.

cs.IT↗

arXiv2019

Generalized Degrees Freedom of Noncoherent MIMO Channels with Asymmetric Link Strengths

We study the generalized degrees of freedom (gDoF) of block-fading noncoherent multiple input multiple output (MIMO) channels with asymmetric distributions of link strengths and a coherence time of T symbol durations. We derive the optimal signaling structure for communication for the asymmetric MIMO channel, which is distinct from that for the MIMO channel with independent and identically distributed (i.i.d.) links. We extend the existing results for the single input multiple output (SIMO) channel with i.i.d. links to the asymmetric case, proving that selecting the statistically best antenna is gDoF-optimal. Using the gDoF result for the SIMO channel, we prove that for T=1, the gDoF is zero for MIMO channels with arbitrary link strengths., extending the result for MIMO with i.i.d. links We show that selecting the statistically best antenna is gDoF-optimal for the multiple input single output (MISO) channel. We also derive the gDoF for the 2X2 MIMO channel with different exponents in the direct and cross links. In this setting, we show that it is always necessary to use both the antennas to achieve the gDoF, in contrast to the results for the 2X2 MIMO channel with i.i.d. links. We show that having weaker crosslinks, gives gDoF gain compared to the case with i.i.d. links. For the noncoherent MIMO channel with i.i.d. links, the traditional method of training each transmit antenna independently is degrees of freedom (DoF) optimal, whereas we observe that for the asymmetric 2X2 MIMO channel, the traditional training is not gDoF-optimal. We extend this observation to a larger MX M MIMO channel by demonstrating a strategy that can achieve larger gDoF than a traditional training-based method.

cs.IT↗

arXiv2018

On the Generalized Degrees of Freedom of Noncoherent Interference Channel

We study the generalized degrees of freedom (gDoF) of the block-fading noncoherent 2-user interference channel (IC) with a coherence time of T symbol durations and symmetric fading statistics. We demonstrate that a natural training-based scheme for the noncoherent IC, is suboptimal in several regimes. We study and analyze several alternate schemes: the first is a new noncoherent scheme using rate-splitting. We also consider a scheme that treats interference-as-noise (TIN) and a time division multiplexing (TDM) scheme. We show that a standard training-based scheme for the noncoherent IC is outperformed by one of these schemes in several regimes: our results demonstrate that in the very weak interference regime, the TIN scheme is the best; in the strong interference regime, the TDM scheme and the noncoherent rate-splitting scheme give better performance; in other cases either of the TIN, TDM or noncoherent rate-splitting scheme could be preferred. We also study the noncoherent IC with feedback and propose another noncoherent rate-splitting scheme. Again for the feedback case, our results demonstrate that a natural training-based scheme can be outperformed by other schemes.

cs.IT↗

arXiv2018

Approximate Capacity of Fast Fading Interference Channels with No Instantaneous CSIT

We develop a characterization of fading models, which assigns a number called logarithmic Jensen's gap to a given fading model. We show that as a consequence of a finite logarithmic Jensen's gap, approximate capacity region can be obtained for fast fading interference channels (FF-IC) for several scenarios. We illustrate three instances where a constant capacity gap can be obtained as a function of the logarithmic Jensen's gap. Firstly for an FF-IC with neither feedback nor instantaneous channel state information at transmitter (CSIT), if the fading distribution has finite logarithmic Jensen's gap, we show that a rate-splitting scheme based on average interference-to-noise ratio (inr) can achieve its approximate capacity. Secondly we show that a similar scheme can achieve the approximate capacity of FF-IC with feedback and delayed CSIT, if the fading distribution has finite logarithmic Jensen's gap. Thirdly, when this condition holds, we show that point-to-point codes can achieve approximate capacity for a class of FF-IC with feedback. We prove that the logarithmic Jensen's gap is finite for common fading models, including Rayleigh and Nakagami fading, thereby obtaining the approximate capacity region of FF-IC with these fading models. For Rayleigh fading the capacity gap is obtained as 1.83 bits per channel use for non-feedback case and 2.83 bits per channel use for feedback case. Our analysis also yields approximate capacity results for fading 2-tap ISI channel and fading interference multiple access channel as corollaries.

cs.IT↗