Short Packets over Block-Memoryless Fading Channels: Pilot-Assisted or Noncoherent Transmission?

We present nonasymptotic upper and lower bounds on the maximum coding rate achievable when transmitting short packets over a Rician memoryless block-fading channel for a given requirement on the packet error probability. We focus on the practically relevant scenario in which there is no \emph{a priori} channel state information available at the transmitter and at the receiver. An upper bound built upon the min-max converse is compared to two lower bounds: the first one relies on a noncoherent transmission strategy in which the fading channel is not estimated explicitly at the receiver; the second one employs pilot-assisted transmission (PAT) followed by maximum-likelihood channel estimation and scaled mismatched nearest-neighbor decoding at the receiver. Our bounds are tight enough to unveil the optimum number of diversity branches that a packet should span so that the energy per bit required to achieve a target packet error probability is minimized, for a given constraint on the code rate and the packet size. Furthermore, the bounds reveal that noncoherent transmission is more energy efficient than PAT, even when the number of pilot symbols and their power is optimized. For example, for the case when a coded packet of $168$ symbols is transmitted using a channel code of rate $0.48$ bits/channel use, over a block-fading channel with block size equal to $8$ symbols, PAT requires an additional $1.2$ dB of energy per information bit to achieve a packet error probability of $10^{-3}$ compared to a suitably designed noncoherent transmission scheme. Finally, we devise a PAT scheme based on punctured tail-biting quasi-cyclic codes and ordered statistics decoding, whose performance are close ($1$ dB gap at $10^{-3}$ packet error probability) to the ones predicted by our PAT lower bound. This shows that the PAT lower bound provides useful guidelines on the design of actual PAT schemes.Comment: 30 pages, 5 figures, journa

Low-latency Ultra Reliable 5G Communications: Finite-Blocklength Bounds and Coding Schemes

Future autonomous systems require wireless connectivity able to support extremely stringent requirements on both latency and reliability. In this paper, we leverage recent developments in the field of finite-blocklength information theory to illustrate how to optimally design wireless systems in the presence of such stringent constraints. Focusing on a multi-antenna Rayleigh block-fading channel, we obtain bounds on the maximum number of bits that can be transmitted within given bandwidth, latency, and reliability constraints, using an orthogonal frequency-division multiplexing system similar to LTE. These bounds unveil the fundamental interplay between latency, bandwidth, rate, and reliability. Furthermore, they suggest how to optimally use the available spatial and frequency diversity. Finally, we use our bounds to benchmark the performance of an actual coding scheme involving the transmission of short packets

Identification-detection group testing protocols for COVID-19 at high prevalence

Group testing allows saving chemical reagents, analysis time, and costs, by testing pools of samples instead of individual samples. We introduce a class of group testing protocols with small dilution, suited to operate even at high prevalence (5–10%), and maximizing the fraction of samples classified positive/negative within the first round of tests. Precisely, if the tested group has exactly one positive sample then the protocols identify it without further individual tests. The protocols also detect the presence of two or more positives in the group, in which case a second round could be applied to identify the positive individuals. With a prevalence of 5 % and maximum dilution 6, with 100 tests we classify 242 individuals, 92 % of them in one round and 8 % requiring a second individual test. In comparison, the Dorfman’s scheme can test 229 individuals with 100 tests, with a second round for 18.5 % of the individuals

Performance versus overhead for fountain codes over Fq

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Random access on graphs: A survey and new results

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Generalized IRA erasure correcting codes for hybrid iterative/maximum likelihood decoding

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Pivoting algorithms for maximum likelihood decoding of LDPC codes over erasure channels

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Increasing the competitiveness of e-vehicles in Europe

Introduction This paper is concerned with incentives for the take-up and use of e-vehicles that are in place in different European countries. Especially, it analyses Norway and Austria, in order to establish and understand factors influencing the competitiveness of e-vehicles and potential market penetration. Norway currently enjoys the world’s largest take-up of electric cars per capita, achieved through an extensive package of incentives. Austria has used the concept of Model Regions with government support to stimulate market introduction. So far, this has been a less effective approach. Methods The paper brings in and combine analyses of national travel survey data and web surveys to e-vehicle owners and non-e-vehicle owners. It considers socio-economic factors including convenience and time savings due to e-vehicle policies. Results Analysing national travel surveys, we find a considerable potential for e-vehicles based on people’s everyday travel. Social networks play a crucial role in spreading knowledge about this relatively new technology. The take-up of battery electric vehicles correlates relatively closely with the user value of e-vehicle incentives. The fiscal effects of e-vehicle incentives are non-trivial – especially in the longer run. The cost of lifting a new technology into the market by means of government incentives is significant. We point to the importance of a strategy for the gradual phasing out of e-vehicle policies in countries with large incentives when the cost of vehicles goes down and the technology improves. Conclusions Successful market uptake and expansion of electric vehicles requires massive, expensive and combined policies. Central government backing, long term commitment and market-oriented incentives help reduce the perceived risk for market players like car importers and allow the e-vehicle market to thrive. For countries with low e-vehicle market shares the potential is promising. Battery electric vehicles are already a real option for the majority of peoples’ everyday trips and trip chains. However, their relative disadvantages must be compensated by means of incentives – at least in the initial market launch phase. Diffusion mechanisms play a sizeable role. The lack of knowledge in the population at large must be addressed

On the performance of moderate-length non-binary LDPC codes for space communications

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