Communication channel

About: Communication channel is a research topic. Over the lifetime, 137411 publications have been published within this topic receiving 1715077 citations. The topic is also known as: communication channel & communications channel.

On Ultra-Wideband MIMO Systems with 1-bit Quantized Outputs: Performance Analysis and Input Optimization

Abstract: We study the performance of multi-input multi-output (MIMO) channels with coarsely quantized outputs in the low signal-to-noise ratio (SNR) regime, where the channel is perfectly known at the receiver. This analysis is of interest in the context of ultra-wideband (UWB) communications from two aspects. First the available power is spread over such a large frequency band, that the power spectral density is extremely low and thus the SNR is low. Second the analog-to-digital converters (ADCs) for such high bandwidth signals should be low-resolution, in order to reduce their cost and power consumption. In this paper we consider the extreme case of only 1-bit ADC for each receive signal component. We compute the mutual information up to second order in the SNR and study the impact of quantization. We show that, up to first order in SNR, the mutual information of the 1-bit quantized system degrades only by a factor of 2/pi compared to the system with infinite resolution independent of the actual MIMO channel realization. With channel state information (CSI) only at receiver, we show that QPSK is, up to the second order, the best among all distributions with independent components. We also elaborate on the ergodic capacity under this scheme in a Rayleigh flat-fading environment.

Method and apparatus for performing service level analysis of communications network performance metrics

Abstract: A data transmission system includes probes (probe A, probe B) connected between end user sites (site A, site B) and a data switching network (12). Each probe is connected to the switching network (12) via an access channel (20, 21, 26 or 27) wherein transmission circuits establish paths between the sites through the access channel (20, 21, 26 or 27) and switching network (12). The probes capture and retransmit data traveling between the sites over respective transmission circuits, and can thereby insert service level anaylsis (SLA) messages into data traffic in order to actively communicate network performance information to other probes. For each transmission circuit, the probes periodically collect measurements related to one or more network performance metrics, including round-trip delay (RTD), data delivery ratio (DDR) and network availability. During each SLA measurement cycle, a sequence of SLA messages is exchanged over each transmission circuit, which messages contain data used to determine RTD and DDR.

Measurement and characterization of link quality metrics in energy constrained wireless sensor networks

Abstract: In wireless sensor networks, a good cost metric encapsulating wireless link quality is essential to an energy-efficient routing topology. For many wireless network scenarios, rapid variation in the channel precludes an efficient mechanism for knowing instantaneous link quality at the time of transmission, thus making it difficult to estimate the instantaneous value of the cost metric. This paper explores what a good cost metric may be and how it can be measured in an energy-efficient way. We present an experimental study of wireless link quality variation over a period of several days in a sensor network placed in two different indoor office environments. The nodes are equipped with low power transceivers operating in the 900 MHz band. Results are documented for several different link configurations, i.e., relative placement of the transmitter and receiver. Based on detailed observations of link quality variation, we form quantitative measures of link quality, and propose a cost metric. We find that reasonably few channel measurements are sufficient to obtain a good estimate of the cost metric, hence even during the initialization phase one can obtain sufficient information about links in order to design an efficient topology. The estimate can be improved further as more measurements are taken during the normal operation of the network.

Large dynamic range cameras

Abstract: A digital camera includes a plurality of channels and a processing component operatively coupled to the plurality of channels. Each channel of the plurality of channels includes an optics component and a sensor that includes an array of photo-detectors. The processing component is configured to separately control an integration time of each channel, where a first integration time of a first channel is less than a second integration time of a second channel. The processing component is also configured to combine data from the plurality of channels to generate an image.