382 research outputs found
Capacity Results for Block-Stationary Gaussian Fading Channels with a Peak Power Constraint
We consider a peak-power-limited single-antenna block-stationary Gaussian
fading channel where neither the transmitter nor the receiver knows the channel
state information, but both know the channel statistics. This model subsumes
most previously studied Gaussian fading models. We first compute the asymptotic
channel capacity in the high SNR regime and show that the behavior of channel
capacity depends critically on the channel model. For the special case where
the fading process is symbol-by-symbol stationary, we also reveal a fundamental
interplay between the codeword length, communication rate, and decoding error
probability. Specifically, we show that the codeword length must scale with SNR
in order to guarantee that the communication rate can grow logarithmically with
SNR with bounded decoding error probability, and we find a necessary condition
for the growth rate of the codeword length. We also derive an expression for
the capacity per unit energy. Furthermore, we show that the capacity per unit
energy is achievable using temporal ON-OFF signaling with optimally allocated
ON symbols, where the optimal ON-symbol allocation scheme may depend on the
peak power constraint.Comment: Submitted to the IEEE Transactions on Information Theor
Capacity per Unit Energy of Fading Channels with a Peak Constraint
A discrete-time single-user scalar channel with temporally correlated
Rayleigh fading is analyzed. There is no side information at the transmitter or
the receiver. A simple expression is given for the capacity per unit energy, in
the presence of a peak constraint. The simple formula of Verdu for capacity per
unit cost is adapted to a channel with memory, and is used in the proof. In
addition to bounding the capacity of a channel with correlated fading, the
result gives some insight into the relationship between the correlation in the
fading process and the channel capacity. The results are extended to a channel
with side information, showing that the capacity per unit energy is one nat per
Joule, independently of the peak power constraint.
A continuous-time version of the model is also considered. The capacity per
unit energy subject to a peak constraint (but no bandwidth constraint) is given
by an expression similar to that for discrete time, and is evaluated for
Gauss-Markov and Clarke fading channels.Comment: Journal version of paper presented in ISIT 2003 - now accepted for
publication in IEEE Transactions on Information Theor
A Two-Phase Maximum-Likelihood Sequence Estimation for Receivers with Partial CSI
The optimality of the conventional maximum likelihood sequence estimation
(MLSE), also known as the Viterbi Algorithm (VA), relies on the assumption that
the receiver has perfect knowledge of the channel coefficients or channel state
information (CSI). However, in practical situations that fail the assumption,
the MLSE method becomes suboptimal and then exhaustive checking is the only way
to obtain the ML sequence. At this background, considering directly the ML
criterion for partial CSI, we propose a two-phase low-complexity MLSE
algorithm, in which the first phase performs the conventional MLSE algorithm in
order to retain necessary information for the backward VA performed in the
second phase. Simulations show that when the training sequence is moderately
long in comparison with the entire data block such as 1/3 of the block, the
proposed two-phase MLSE can approach the performance of the optimal exhaustive
checking. In a normal case, where the training sequence consumes only 0.14 of
the bandwidth, our proposed method still outperforms evidently the conventional
MLSE.Comment: 5 pages and 4 figure
A Simple Recursively Computable Lower Bound on the Noncoherent Capacity of Highly Underspread Fading Channels
Real-world wireless communication channels are typically highly underspread: their coherence time is much greater than their delay spread. In such situations it is common to assume that, with sufficiently high bandwidth, the capacity without Channel State Information (CSI) at the receiver (termed the noncoherent channel capacity) is approximately equal to the capacity with perfect CSI at the receiver (termed the coherent channel capacity). In this paper, we propose a lower bound on the noncoherent capacity of highly underspread fading channels, which assumes only that the delay spread and coherence time are known. Furthermore our lower bound can be calculated recursively, with each increment corresponding to a step increase in bandwidth. These properties, we contend, make our lower bound an excellent candidate as a simple method to verify that the noncoherent capacity is indeed approximately equal to the coherent capacity for typical wireless communication applications. We precede the derivation of the aforementioned lower bound on the information capacity with a rigorous justification of the mathematical representation of the channel. Furthermore, we also provide a numerical example for an actual wireless communication channel and demonstrate that our lower bound does indeed approximately equal the coherent channel capacity.The work of T. H. Loh was supported by the 2013 - 2017 Electromagnetics and Time Metrology Programme of the National Measurement Office, an Executive Agency of the U.K. Department for Business, Innovation and Skills, under Projects EMT13018This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/TWC.2016.253167
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A Simple Recursively Computable Lower Bound on the Noncoherent Capacity of Highly Underspread Fading Channels
Real-world wireless communication channels are typically highly underspread: their coherence time is much greater than their delay spread. In such situations it is common to assume that, with sufficiently high bandwidth, the capacity without Channel State Information (CSI) at the receiver (termed the noncoherent channel capacity) is approximately equal to the capacity with perfect CSI at the receiver (termed the coherent channel capacity). In this paper, we propose a lower bound on the noncoherent capacity of highly underspread fading channels, which assumes only that the delay spread and coherence time are known. Furthermore our lower bound can be calculated recursively, with each increment corresponding to a step increase in bandwidth. These properties, we contend, make our lower bound an excellent candidate as a simple method to verify that the noncoherent capacity is indeed approximately equal to the coherent capacity for typical wireless communication applications. We precede the derivation of the aforementioned lower bound on the information capacity with a rigorous justification of the mathematical representation of the channel. Furthermore, we also provide a numerical example for an actual wireless communication channel and demonstrate that our lower bound does indeed approximately equal the coherent channel capacity.The work of T. H. Loh was supported by the 2013 - 2017 Electromagnetics and Time Metrology Programme of the National Measurement Office, an Executive Agency of the U.K. Department for Business, Innovation and Skills, under Projects EMT13018This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/TWC.2016.253167
Quantized vs. Analog Feedback for the MIMO Downlink: A Comparison between Zero-Forcing Based Achievable Rates
We consider a MIMO fading broadcast channel and compare the achievable
ergodic rates when the channel state information at the transmitter is provided
by analog noisy feedback or by quantized (digital) feedback. The superiority of
digital feedback is shown, with perfect or imperfect CSIR, whenever the number
of feedback channel uses per channel coefficient is larger than 1. Also, we
show that by proper design of the digital feedback link, errors in the feedback
have a minor effect even by using very simple uncoded modulation. Finally, we
show that analog feedback achieves a fraction 1 - 2F of the optimal
multiplexing gain even in the presence of a feedback delay, when the fading
belongs to the class of Doppler processes with normalized maximum Doppler
frequency shift 0 <= F <= 1/2.Comment: Submitted to ISIT, January 2007. 5 page
Upper and Lower Bounds to the Information Rate Transferred Through First-Order Markov Channels With Free-Running Continuous State
partially_open4noStarting from the definition of mutual information, one promptly realizes that the probabilities inferred by Bayesian tracking can be used to compute the Shannon information between the state and the measurement of a dynamic system. In the Gaussian and linear case, the information rate can be evaluated from the probabilities computed by the Kalman filter. When the probability distributions inferred by Bayesian tracking are nontractable, one is forced to resort to approximated inference, which gives only an approximation to the wanted probabilities. We propose upper and lower bounds to the information rate between the hidden state and the measurement based on approximated inference. Application of these bounds to multiplicative communication channels is discussed, and experimental results for the discrete-time phase noise channel and for the Gauss-Markov fading channel are presented.openBarletta, L.; Magarini, M.; Pecorino, S.; Spalvieri, A.Barletta, Luca; Magarini, Maurizio; Pecorino, Simone; Spalvieri, Arnald
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