This paper studies the mutual information for a general form of orthogonal M-ary frequency-shift keying modulations with non-coherent detection and Doppler frequency uncertainty at the receiver. The signal model includes as particular cases classical MFSK and special MFSK modulations, the later has been used in space communications for reporting spacecraft status and events during critical phases. The optimal code rates that minimize the energy-per-bit to noise power spectral density ratio required for reliable communications are studied. In addition, optimal and suboptimal metrics for soft-decoders are proposed for non-fading channels with or without average signal and noise power estimation and used to evaluate the performance of LDPC codes.

This paper studies the capacity of orthogonal M-ary frequency-shift keying modulations with non-coherent detection and Doppler frequency uncertainty at the receiver. The optimal code rates that minimize the energy-per-bit to noise power spectral density ratio required for reliable communications are studied. In addition, optimal and suboptimal metrics for soft-decoders are proposed for non-fading channels with or without average signal and noise power estimation and used to evaluate the performance of LDPC codes.

Grant-free random access (RA) techniques are suitable for machine-type communication (MTC) networks but they need to be adaptive to the MTC traffic, which is different from the human-type communication. Conventional RA protocols such as exponential backoff (EB) schemes for slotted-ALOHA suffer from a high number of collisions and they are not directly applicable to the MTC traffic models. In this work, we propose to use multi-agent deep Q-network (DQN) with parameter sharing to find a single policy applied to all machine-type devices (MTDs) in the network to resolve collisions. Moreover, we consider binary broadcast feedback common to all devices to reduce signalling overhead. We compare the performance of our proposed DQN-RA scheme with EB schemes for up to 500 MTDs and show that the proposed scheme outperforms EB policies and provides a better balance between throughput, delay and collision rate.

Random access (RA) schemes are a topic of high interest in machine-type communication (MTC). In RA protocols, backoff techniques such as exponential backoff (EB) are used to stabilize the system to avoid low throughput and excessive delays. However, these backoff techniques show varying performance for different underlying assumptions and analytical models. Therefore, finding a better transmission policy for slotted ALOHA RA is still a challenge. In this paper, we show the potential of deep reinforcement learning (DRL) for RA. We learn a transmission policy that balances between throughput and fairness. The proposed algorithm learns transmission probabilities using previous action and binary feedback signal, and it is adaptive to different traffic arrival rates. Moreover, we propose average age of packet (AoP) as a metric to measure fairness among users. Our results show that the proposed policy outperforms the baseline EB transmission schemes in terms of throughput and fairness.

This paper presents an overview of the coding aspects of a GNSS receiver. Coding allows detection and correction of channel-induced errors at the receiver, here the focus is on the mitigation of threats from malicious interferences. Although the effects of interference at different stages of GNSS baseband processing has been deeply analyzed in the literature, little attention was devoted to its impact on the navigation message decoding stage. Theis paper provides an introduction to the various coding schemes employed by current GNSS signals, discussing their performance in the presence of noise in terms of block-error rate. Additionally, the benefits of soft-decoding schemes for navigation message decoding are highlighted when jamming interferences are present. The proposed scheme requires estimating the noise plus interference power, yielding to enhanced decoding performances under severe jamming conditions. Finally, cryptographic schemes as a means of providing anti-spoofing for geosecurity location-based services, and their potential vulnerability are discussed, with particular emphasis on the dependence on the dependence of the scheme on successful navigation message decoding.

In this paper we develop two new approaches for frame synchronization in the binary-input AWGN channel, in which we account for the sign ambiguity of the received symbols and exploit knowledge of an alternating sequence which precedes the synchronization word. We present an approach based on an extended sliding window and the appropriate decision metric. For the common case that the synchronization word is followed by encoded data we present a solution which exploits the error detection capability of the channel decoder and applies a list decoding approach for frame synchronization. The proposed methods are validated through computer simulations in the deep-space communication uplink and show significant performance gains compared to current solutions.

We consider Incremental Redundancy Hybrid Automatic Repeat reQuest (IR-HARQ) in which the code rate and modulation of the initial transmission and all retransmissions are adjusted based on average channel statistics. In the absence of instantaneous channel state information at the transmitter (CSIT), we present a method which computes, prior to transmission, the optimum code rates and modulations and explicitly considers a given maximum number of retransmissions. For the case that additional feedback on CSI of previous transmission attempts is available, we present two heuristic schemes which exploit this knowledge and offer increased throughput at the cost of higher computational complexity. We employ a rate-adaptive non-binary LDPC coding scheme which makes use of non-binary repetitions. While this coding scheme is particularly well-suited for adaptive IR-HARQ, we note that the presented analysis can be applied to any other channel code which employs soft decoding.

This paper presents the architecture of the VITRO system concept developed under the VITRO project for the realization of Virtual Sensor Networks. The aim of the proposed architecture is to enable the realization of scalable, flexible, adaptive, energy-efficient and trust-aware Virtual Sensor Network platforms, focusing on the reduction of deployment complexity and on advanced interoperability mechanisms. The efforts have been put towards specifying a Service Provisioning architecture and mechanisms for advanced sensor and middleware design.

This paper addresses the problem of TOA and DOA estimation in IR-UWB systems. It considers a frequency domain approach for joint high resolution estimation of Time Of Arrival (TOA) and Direction Of Arrival (DOA). The proposed scheme performs timing acquisition following a two step approach: a first stage where coarse symbol timing is achieved by means of chip energy estimation and a minimum distance criterion based on the time-hopping sequence knowledge, followed by a reduced complexity high resolution TOA estimator that provides fine timing acquisition. The proposed algorithm can resolve time synchronization blindly, without the need for channel estimation and can operate on a single symbol basis. DOA estimation is then obtained from TOA estimates at each array element applying a linear estimator. The joint estimation of TOA and DOA provides robustness and potentially allows positioning with a single reference node. Furthermore, the paper derives the Cramer-Rao Lower Bound from a frequency domain signal model for a multipath channel where no assumptions are made with respect to the paths, which results in a compact closed form.

This paper considers a flexible frequency-selective link adaptation scheme for dynamic scheduling systems. Adaptation is performed based on mutual information metrics imposing no constraints on the scheduling and resource allocation. The proposed bit loading algorithm adjusts the codeword length to the available resource units such that codewords may be transmitted over several slots. Simulation results confirm the flexibility of the proposed algorithm which works irrespective of packet and slot lengths and yields a throughput close to the optimum.

We consider the performance of adaptive coding and modulation (ACM) over a fading channel for the case that the transmitter has only partial channel state information (CSI). We evaluate the degradation due to the partial CSI in terms of additionally required SNR by simulations and an analytical approximation. Then, we propose an ACM scheme with fast link-level retransmissions based on cyclic incremental redundancy and compare its performance to an equivalent scheme based on Chase combining. For both HARQ (hybrid automatic repeat request) schemes, we develop an analytical approximation for the throughput and the delay.

This paper addresses the problem of TOA estimation for ranging applications in IR-UWB. It considers a low complexity frequency-domain approach for the estimation of the TOA that allows sub-Nyquist sampling rate receivers. Two diversity schemes are investigated in combination with the TOA estimation algorithm and are evaluated over realistic channel models, yielding accurate ranging estimation.

We present a low-complexity combination of a BLAST-like MIMO system and bit-interleaved coded modulation with iterative decoding (BICM-ID). We present a method to exploit soft information stemming from the outer decoder to mitigate the influence of multistream interference. Furthermore, we introduce an inner code to remove the error floor which is normally present in BICM-ID systems. This code is of rate one and has memory one; it thus adds no redundancy and only very little complexity. Both schemes are evaluated in the EXIT chart and with BER simulations.

We consider the use of puncturing under the scope of space time turbo trellis codes. On one hand we consider the use of puncturing as a simple mechanism to allow varying the transmission rate, investigating the performance improvement/degradation when decreasing/increasing the spectral efficiency of the code. Then, we focus on the application of the EXIT chart technique to analyse the effect of puncturing on the code performance, and propose guidelines for the design of most suitable puncturing schemes.