8,965 research outputs found
A radio channel emulator for WCDMA, based on the hidden Markov model (HMM)
One of the main development and research subjects within the telecommunications area activity is the 3G mobile systems standardisation. The radio access is, of course, the main trouble in mobile systems, so it is important to investigate its implication. This paper describes a radio channel emulator for the UTRA-FDD made, based on the hidden Markov model (HMM). Since a statistical system behaviour is needed to train the HMM, off-line simulations have been made. The results between simulated and emulated statistics are presented. The use of emulation models implies a loss of accuracy with respect to simulation models, but is adequate to operate in real time. Certainly, the main advantage of using HMM in the emulator is the huge reduction in time, resources and effort with regard to a real simulation of the system. The emulator will allow in future works, for fast testing and comparison of several higher layer protocols and error control schemes.Peer ReviewedPostprint (published version
A Decision Feedback Based Scheme for Slepian-Wolf Coding of sources with Hidden Markov Correlation
We consider the problem of compression of two memoryless binary sources, the
correlation between which is defined by a Hidden Markov Model (HMM). We propose
a Decision Feedback (DF) based scheme which when used with low density parity
check codes results in compression close to the Slepian Wolf limits.Comment: Submitted to IEEE Comm. Letter
On the Performance of Short Block Codes over Finite-State Channels in the Rare-Transition Regime
As the mobile application landscape expands, wireless networks are tasked
with supporting different connection profiles, including real-time traffic and
delay-sensitive communications. Among many ensuing engineering challenges is
the need to better understand the fundamental limits of forward error
correction in non-asymptotic regimes. This article characterizes the
performance of random block codes over finite-state channels and evaluates
their queueing performance under maximum-likelihood decoding. In particular,
classical results from information theory are revisited in the context of
channels with rare transitions, and bounds on the probabilities of decoding
failure are derived for random codes. This creates an analysis framework where
channel dependencies within and across codewords are preserved. Such results
are subsequently integrated into a queueing problem formulation. For instance,
it is shown that, for random coding on the Gilbert-Elliott channel, the
performance analysis based on upper bounds on error probability provides very
good estimates of system performance and optimum code parameters. Overall, this
study offers new insights about the impact of channel correlation on the
performance of delay-aware, point-to-point communication links. It also
provides novel guidelines on how to select code rates and block lengths for
real-time traffic over wireless communication infrastructures
Fast Polarization for Processes with Memory
Fast polarization is crucial for the performance guarantees of polar codes.
In the memoryless setting, the rate of polarization is known to be exponential
in the square root of the block length. A complete characterization of the rate
of polarization for models with memory has been missing. Namely, previous works
have not addressed fast polarization of the high entropy set under memory. We
consider polar codes for processes with memory that are characterized by an
underlying ergodic finite-state Markov chain. We show that the rate of
polarization for these processes is the same as in the memoryless setting, both
for the high and for the low entropy sets.Comment: 17 pages, 3 figures. Submitted to IEEE Transactions on Information
Theor
Tiny Codes for Guaranteeable Delay
Future 5G systems will need to support ultra-reliable low-latency
communications scenarios. From a latency-reliability viewpoint, it is
inefficient to rely on average utility-based system design. Therefore, we
introduce the notion of guaranteeable delay which is the average delay plus
three standard deviations of the mean. We investigate the trade-off between
guaranteeable delay and throughput for point-to-point wireless erasure links
with unreliable and delayed feedback, by bringing together signal flow
techniques to the area of coding. We use tiny codes, i.e. sliding window by
coding with just 2 packets, and design three variations of selective-repeat ARQ
protocols, by building on the baseline scheme, i.e. uncoded ARQ, developed by
Ausavapattanakun and Nosratinia: (i) Hybrid ARQ with soft combining at the
receiver; (ii) cumulative feedback-based ARQ without rate adaptation; and (iii)
Coded ARQ with rate adaptation based on the cumulative feedback. Contrasting
the performance of these protocols with uncoded ARQ, we demonstrate that HARQ
performs only slightly better, cumulative feedback-based ARQ does not provide
significant throughput while it has better average delay, and Coded ARQ can
provide gains up to about 40% in terms of throughput. Coded ARQ also provides
delay guarantees, and is robust to various challenges such as imperfect and
delayed feedback, burst erasures, and round-trip time fluctuations. This
feature may be preferable for meeting the strict end-to-end latency and
reliability requirements of future use cases of ultra-reliable low-latency
communications in 5G, such as mission-critical communications and industrial
control for critical control messaging.Comment: to appear in IEEE JSAC Special Issue on URLLC in Wireless Network
First-Passage Time and Large-Deviation Analysis for Erasure Channels with Memory
This article considers the performance of digital communication systems
transmitting messages over finite-state erasure channels with memory.
Information bits are protected from channel erasures using error-correcting
codes; successful receptions of codewords are acknowledged at the source
through instantaneous feedback. The primary focus of this research is on
delay-sensitive applications, codes with finite block lengths and, necessarily,
non-vanishing probabilities of decoding failure. The contribution of this
article is twofold. A methodology to compute the distribution of the time
required to empty a buffer is introduced. Based on this distribution, the mean
hitting time to an empty queue and delay-violation probabilities for specific
thresholds can be computed explicitly. The proposed techniques apply to
situations where the transmit buffer contains a predetermined number of
information bits at the onset of the data transfer. Furthermore, as additional
performance criteria, large deviation principles are obtained for the empirical
mean service time and the average packet-transmission time associated with the
communication process. This rigorous framework yields a pragmatic methodology
to select code rate and block length for the communication unit as functions of
the service requirements. Examples motivated by practical systems are provided
to further illustrate the applicability of these techniques.Comment: To appear in IEEE Transactions on Information Theor
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