24 research outputs found
Quasi-Static SIMO Fading Channels at Finite Blocklength
We investigate the maximal achievable rate for a given blocklength and error
probability over quasi-static single-input multiple-output (SIMO) fading
channels. Under mild conditions on the channel gains, it is shown that the
channel dispersion is zero regardless of whether the fading realizations are
available at the transmitter and/or the receiver. The result follows from
computationally and analytically tractable converse and achievability bounds.
Through numerical evaluation, we verify that, in some scenarios, zero
dispersion indeed entails fast convergence to outage capacity as the
blocklength increases. In the example of a particular 1*2 SIMO Rician channel,
the blocklength required to achieve 90% of capacity is about an order of
magnitude smaller compared to the blocklength required for an AWGN channel with
the same capacity.Comment: extended version of a paper submitted to ISIT 201
Green communication via Type-I ARQ: Finite block-length analysis
This paper studies the effect of optimal power allocation on the performance
of communication systems utilizing automatic repeat request (ARQ). Considering
Type-I ARQ, the problem is cast as the minimization of the outage probability
subject to an average power constraint. The analysis is based on some recent
results on the achievable rates of finite-length codes and we investigate the
effect of codewords length on the performance of ARQ-based systems. We show
that the performance of ARQ protocols is (almost) insensitive to the length of
the codewords, for codewords of length channel uses. Also, optimal
power allocation improves the power efficiency of the ARQ-based systems
substantially. For instance, consider a Rayleigh fading channel, codewords of
rate 1 nats-per-channel-use and outage probability Then, with a
maximum of 2 and 3 transmissions, the implementation of power-adaptive ARQ
reduces the average power, compared to the open-loop communication setup, by 17
and 23 dB, respectively, a result which is (almost) independent of the
codewords length. Also, optimal power allocation increases the diversity gain
of the ARQ protocols considerably.Comment: Accepted for publication in GLOBECOM 201
Block-fading channels at finite blocklength
This tutorial paper deals with the problem of characterizing the maximal achievable rate R(n; ϵ )at a given blocklength n and error probability ϵ over block-fading channels. We review recent results that establish tight bounds on R(n; ϵ )and characterize its asymptotic behavior. Comparison between the theoretical results and the data rates achievable with the coding scheme used in LTE-Advanced are reported
Block-Fading Channels with Delayed CSIT at Finite Blocklength
In many wireless systems, the channel state information at the transmitter
(CSIT) can not be learned until after a transmission has taken place and is
thereby outdated. In this paper, we study the benefits of delayed CSIT on a
block-fading channel at finite blocklength. First, the achievable rates of a
family of codes that allows the number of codewords to expand during
transmission, based on delayed CSIT, are characterized. A fixed-length and a
variable-length characterization of the rates are provided using the dependency
testing bound and the variable-length setting introduced by Polyanskiy et al.
Next, a communication protocol based on codes with expandable message space is
put forth, and numerically, it is shown that higher rates are achievable
compared to coding strategies that do not benefit from delayed CSIT.Comment: Extended version of a paper submitted to ISIT'1
Unsourced Random Access with the MIMO Receiver: Projection Decoding Analysis
We consider unsourced random access with MIMO receiver - a crucial
communication scenario for future 5G/6G wireless networks. We perform a
projection-based decoder analysis and derive energy efficiency achievability
bounds when channel state information is unknown at transmitters and the
receiver (no-CSI scenario). The comparison to the maximum-likelihood (ML)
achievability bounds by Gao et al. (2023) is performed. We show that there is a
region where the new bound outperforms the ML bound. The latter fact should not
surprise the reader as both decoding criteria are suboptimal when considering
per-user probability of error (PUPE). Moreover, transition to projection
decoding allows for significant dimensionality reduction, which greatly reduces
the computation time
Finite-Blocklength Channel Coding Rate Under a Long-Term Power Constraint
This paper investigates the maximal channel coding rate achievable at a given blocklength and error probability , when the codewords are subject to a long-term (i.e., averaged-over-all-codeword) power constraint. The second-order term in the large-n expansion of the maximal channel coding rate is characterized both for AWGN channels and for quasi-static fading channels with perfect channel state information at the transmitter and the receiver. It is shown that in both cases the second-order term is proportional to
On dispersion of compound DMCs
Code for a compound discrete memoryless channel (DMC) is required to have small probability of error regardless of which channel in the collection perturbs the codewords. Capacity of the compound DMC has been derived classically: it equals the maximum (over input distributions) of the minimal (over channels in the collection) mutual information. In this paper the expression for the channel dispersion of the compound DMC is derived under certain regularity assumptions on the channel. Interestingly, dispersion is found to depend on a subtle interaction between the channels encoded in the geometric arrangement of the gradients of their mutual informations. It is also shown that the third-order term need not be logarithmic (unlike single-state DMCs). By a natural equivalence with compound DMC, all results (dispersion and bounds) carry over verbatim to a common message broadcast channel.National Science Foundation (U.S.) (CAREER Award CCF-12-53205)National Science Foundation (U.S.). Center for Science of Information (Grant Agreement CCF-0939370
Short-Packet Transmission over a Bidirectional Massive MIMO link
We consider the transmission of short packets over a bidirectional communication link where multiple devices, e.g., sensors and actuators, exchange small-data payloads with a base station equipped with a large antenna array. Using results from finite-blocklength information theory, we characterize the minimum SNR required to achieve a target error probability for a fixed packet length and a fixed payload size. Our nonasymptotic analysis, which applies to the scenario in which the bidirectional communication is device-initiated, and also to the more challenging case when it is base-station initiated, provides guidelines on the design of massive multiple-input multiple-output links that need to support sporadic ultra-reliable low-latency transmissions. Specifically, it allows us to determine the optimal amount of resources that need to be dedicated to the acquisition of channel state information