1,105 research outputs found
Hard-input-hard-output capacity analysis of UWB BPSK systems with timing errors
The hard-input-hard-output capacity of a binary phase-shift keying (BPSK) ultrawideband system is analyzed for both additive white Gaussian noise and multipath fading channels with timing errors. Unlike previous works that calculate the capacity with perfect synchronization and/or multiple-access interference only, our analysis considers timing errors with different distributions, as well as the interpath (IPI), interchip (ICI), and intersymbol (ISI) interferences, as in practical systems. The sensitivity of the channel capacity to the timing error is examined. The effects of pulse shape, the multiple-access technique, the number of users, and the number of chips are studied. It is found that time hopping is less sensitive to the pulse shape and that the timing error has higher capacity than direct sequence due to its low duty of cycle. Using these results, one can choose appropriate system parameters for different applications
A Statistical Analysis of Multipath Interference for Impulse Radio UWB Systems
In this paper, we develop a statistical characterization of the multipath
interference in an Impulse Radio (IR)-UWB system, considering the standardized
IEEE 802.15.4a channel model. In such systems, the chip length has to be
carefully tuned as all the propagation paths located beyond this limit can
cause interframe/intersymbol interferences (IFI/ISI). Our approach aims at
computing the probability density function (PDF) of the power of all multipath
components with delays larger than the chip time, so as to prevent such
interferences. Exact analytical expressions are derived first for the
probability that the chip length falls into a particular cluster of the
multipath propagation model and for the statistics of the number of paths
spread over several contiguous clusters. A power delay profile (PDP)
approximation is then used to evaluate the total interference power as the
problem appears to be mathematically intractable. Using the proposed
closed-form expressions, and assuming minimal prior information on the channel
state, a rapid update of the chip time value is enabled so as to control the
signal to interference plus noise ratio.Comment: 17 pages, 9 figures; submitted to the Journal of the Franklin
Institute on Sept. 24, 201
Effect of Jitter on the Settling Time of Mesochronous Clock Retiming Circuits
It is well known that timing jitter can degrade the bit error rate (BER) of
receivers that recover the clock from input data. However, timing jitter can
also result in an indefinite increase in the settling time of clock recovery
circuits, particularly in low swing mesochronous systems. Mesochronous clock
retiming circuits are required in repeaterless low swing on-chip interconnects.
We first discuss how timing jitter can result in a large increase in the
settling time of the clock recovery circuit. Next, the circuit is modelled as a
Markov chain with absorbing states. The mean time to absorption of the Markov
chain, which represents the mean settling time of the circuit, is determined.
The model is validated through behavioural simulations of the circuit, the
results of which match well with the model predictions. We consider circuits
with (i) data dependent jitter, (ii) random jitter, and (iii) combination of
both of them. We show that a mismatch between the strengths of up and down
corrections of the retiming can reduce the settling time. In particular, a 10%
mismatch can reduce the mean settling time by up to 40%. We leverage this fact
toward improving the settling time performance, and propose useful techniques
based on biased training sequences and mismatched charge pumps. We also present
a coarse+fine clock retiming circuit, which can operate in coarse first mode,
to reduce the settling time substantially. These fast settling retiming
circuits are verified with circuit simulations.Comment: 23 pages, 40 figure
NASA 60 GHz intersatellite communication link definition study. Addendum A: Mixed baseband and IF signals
As part of a definition study for a 60 GHz intersatellite communications link system (ICLS), baseline design concepts for a channelized crosslink were identified. The crosslink would allow communications between geostationary satellites of the planned Tracking and Data Acquisition System (TDAS) and would accommodate a mixture of frequency translation coherent links (bent pipe links) and baseband-in/baseband-out links (mod/demod links). A 60 GHz communication system was developed for sizing and analyzing the crosslink. For the coherent links this system translates incoming signals directly up to the 60 GHz band; trunks the signals across from one satellite to a second satellite at 60 GHz then down converts to the proper frequency for re-transmission from the second satellite without converting to any intermediate frequencies. For the baseband-in/baseband-out links the baseband data is modulated on to the 60 GHz carrier at the transmitting satellite and demodulated at the receiving satellite. The frequency plan, equipment diagrams, and link calculations are presented along with results from sizing and reliability analyses
Accurate Jitter Decomposition in High-Speed Links
In a high-speed digital communication system, jitter performance plays a crucial role in Bit-Error Rate (BER). It is important to accurately derive each type of jitter as well as total jitter (TJ) and to identify the root causes of jitter by jitter decomposition.
In this work, we propose new jitter decomposition techniques in high-speed links testing. The background of jitter decomposition is described in chapter 1. In chapter 2, duty cycle distortion jitter amplification is introduced. As channel loss results in both ISI and jitter amplification, DCD amplification is a big concern in high-speed links. The derivation of a formula of DCD amplification for data channels is included and the calculation result matches the time-domain simulation in the system.
Chapter 3 provides an accurate jitter decomposition algorithm using Least Squares (LS) which simultaneously separates ISI, RJ, and PJ. A new time domain ISI model is proposed, which is faster and more accurate than the conventional ISI model. This algorithm obtains the estimated individual jitter component value with fine accuracy by using less samples of total jitter data compared with conventional methods. The simulation and measurement show the accuracy and efficiency of this algorithm with less data samples.
In chapter 4, a low-cost comparator-based jitter decomposition algorithm is proposed. Instead of using TIE jitter sequence to decompose, it uses a low cost and simple comparator network to identify the deviation of current sampling positions from the ideal sampling positions to represent the TIE. It simultaneously separates ISI, DCD, and PJ and can achieve similar accuracy compared to the instrument test. Both the simulation and measurement show the decomposition algorithm with great accuracy and efficiency.
In chapter 5, a low cost and simple dithering method to improve the test of linearity of analog-to-digital converter (ADC) is proposed. This method exhibits an improvement and enhancement for the ultra-fast segmented model identification of linearity error (uSMILE) algorithm which reduces 99% of the test time compared to the conventional method. In this study, we proposed three types of distribution dithering methods adding to the ramp input signal to reduce the estimation error when uSMILE was applied in low resolution ADCs. The fix pattern distribution was proved as the most efficient and cost-effective method by comparing with the Gaussian, uniform, and fix-pattern distributions. Both the simulation results and hardware measurement indicate that the estimation error can be significantly reduced in 12-bit SAR ADC with effective dithering
MOL-Eye: A New Metric for the Performance Evaluation of a Molecular Signal
Inspired by the eye diagram in classical radio frequency (RF) based
communications, the MOL-Eye diagram is proposed for the performance evaluation
of a molecular signal within the context of molecular communication. Utilizing
various features of this diagram, three new metrics for the performance
evaluation of a molecular signal, namely the maximum eye height, standard
deviation of received molecules, and counting SNR (CSNR) are introduced. The
applicability of these performance metrics in this domain is verified by
comparing the performance of binary concentration shift keying (BCSK) and BCSK
with consecutive power adjustment (BCSK-CPA) modulation techniques in a
vessel-like environment with laminar flow. The results show that, in addition
to classical performance metrics such as bit-error rate and channel capacity,
these performance metrics can also be used to show the advantage of an
efficient modulation technique over a simpler one
Communication Subsystems for Emerging Wireless Technologies
The paper describes a multi-disciplinary design of modern communication systems. The design starts with the analysis of a system in order to define requirements on its individual components. The design exploits proper models of communication channels to adapt the systems to expected transmission conditions. Input filtering of signals both in the frequency domain and in the spatial domain is ensured by a properly designed antenna. Further signal processing (amplification and further filtering) is done by electronics circuits. Finally, signal processing techniques are applied to yield information about current properties of frequency spectrum and to distribute the transmission over free subcarrier channels
Energy-Efficient Communication over the Unsynchronized Gaussian Diamond Network
Communication networks are often designed and analyzed assuming tight
synchronization among nodes. However, in applications that require
communication in the energy-efficient regime of low signal-to-noise ratios,
establishing tight synchronization among nodes in the network can result in a
significant energy overhead. Motivated by a recent result showing that
near-optimal energy efficiency can be achieved over the AWGN channel without
requiring tight synchronization, we consider the question of whether the
potential gains of cooperative communication can be achieved in the absence of
synchronization. We focus on the symmetric Gaussian diamond network and
establish that cooperative-communication gains are indeed feasible even with
unsynchronized nodes. More precisely, we show that the capacity per unit energy
of the unsynchronized symmetric Gaussian diamond network is within a constant
factor of the capacity per unit energy of the corresponding synchronized
network. To this end, we propose a distributed relaying scheme that does not
require tight synchronization but nevertheless achieves most of the energy
gains of coherent combining.Comment: 20 pages, 4 figures, submitted to IEEE Transactions on Information
Theory, presented at IEEE ISIT 201
Maximum-Likelihood Sequence Detector for Dynamic Mode High Density Probe Storage
There is an increasing need for high density data storage devices driven by
the increased demand of consumer electronics. In this work, we consider a data
storage system that operates by encoding information as topographic profiles on
a polymer medium. A cantilever probe with a sharp tip (few nm radius) is used
to create and sense the presence of topographic profiles, resulting in a
density of few Tb per in.2. The prevalent mode of using the cantilever probe is
the static mode that is harsh on the probe and the media. In this article, the
high quality factor dynamic mode operation, that is less harsh on the media and
the probe, is analyzed. The read operation is modeled as a communication
channel which incorporates system memory due to inter-symbol interference and
the cantilever state. We demonstrate an appropriate level of abstraction of
this complex nanoscale system that obviates the need for an involved physical
model. Next, a solution to the maximum likelihood sequence detection problem
based on the Viterbi algorithm is devised. Experimental and simulation results
demonstrate that the performance of this detector is several orders of
magnitude better than the performance of other existing schemes.Comment: This paper is published in IEEE Trans. on communicatio
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