Resilience against radio jamming is a key feature for the trustworthiness of next-generation mobile radio access networks (RAN) and systems for detecting jamming attacks are required in order to notify operators and effectively deploy mitigation techniques. This paper proposes a novel approach for jamming detection in 5G new radio (NR) that leverages user equipment (UE) as distributed sensors by collecting and analyzing standardized UE measurement reports. We propose a detection method based on the signal-to-interference-and-noise ratio (SINR) measured at the UEs and analytically derive the corresponding error probabilities. Furthermore, we provide a method for positioning the jammer source based on information on the location of the UEs. We validate the effectiveness of the proposed method based on SINR measurements obtained from a static 5G network simulator. Our results show that the method accurately detects the jammer even at low transmit power and provides a coarse indication of the jammer position.

Novel bounds on the left- and right-tail probability of the Binomial distribution are presented. Specifically, bounds on the left-tail probability$\text {P}\!\left [{S_{n}\leqslant an}\right]$with$a\in (0,p)$and the right-tail probability$\text {P}\!\left [{S_{n}\geqslant an}\right]$with$a\in (p,1)$, where$S_{n}$follows the Binomial law with parameters$n\geqslant 1$and$p\in (0,1)$, are derived. The bounds are tighter than the best known closed-form expressions. The presented upper and lower bounds on the right-tail match an asymptotic expansion of$\log \text {P}\!\left [{S_{n}\geqslant na}\right]$up to, and including, the$\log n$term. In particular, the ratio between the upper and lower bounds is$1/(1-c/n)$, where$c$is independent of$n$. Similar results are presented for the left-tail probability. Applications to finite blocklength source and channel coding are presented.

A nonlinear detector derived within a maximum likelihood estimation framework is shown to be effective in retrieving the channel coefficients and data of users on the uplink channel of a noncooperative wireless system without the access point having any prior channel state information (no CSI or noncoherent setup). Rather than relying on pilot-assisted transmissions, it is shown that a maximum likelihood-based detector emerges naturally from an information-theoretic argument. The assumptions under which the detector is designed are as follows: 1) the uplink data from different users are independent and non-Gaussian; 2) the coherence block of the channel is much larger than the number of users (in practice, the square of the number of users); 3) the number of antennas at the access point or base station is equal to the number of users; 4) users continuously transmit within the coherence block; and 5) the transmission occurs at high signal-to-noise ratio. No coordination between the access point and unintended users (interference) is needed. Some coordination with intended users is needed. Finally, the system is assumed to be symbol-synchronous.

This paper investigates the probability that the delay and the peak-age of information exceed a desired threshold in a point-to-point communication system with short information packets. The packets are generated according to a stationary memoryless Bernoulli process, placed in a single-server queue and then transmitted over a wireless channel. A variable-length stop-feedback coding scheme-a general strategy that encompasses simple automatic repetition request (ARQ) and more sophisticated hybrid ARQ techniques as special cases-is used by the transmitter to convey the information packets to the receiver. By leveraging finite-blocklength results, the delay violation and the peak-age violation probabilities are characterized without resorting to approximations based on larg-deviation theory as in previous literature. Numerical results illuminate the dependence of delay and peak-age violation probability on system parameters such as the frame size and the undetected error probability, and on the chosen packet-management policy. The guidelines provided by our analysis are particularly useful for the design of low-latency ultra-reliable communication systems.

This paper investigates the distribution of delay and peak age of information in a communication system where packets, generated according to an independent and identically distributed Bernoulli process, are placed in a single-server queue with first-come first-served discipline and transmitted over an additive white Gaussian noise (AWGN) channel. When a packet is correctly decoded, the sender receives an instantaneous error-free positive acknowledgment, upon which it removes the packet from the buffer. In the case of negative acknowledgment, the packet is retransmitted. By leveraging finite-blocklength results for the AWGN channel, we characterize the delay violation and the peak-age violation probability without resorting to approximations based on large deviation theory as in previous literature. Our analysis reveals that there exists an optimum blocklength that minimizes the delay violation and the peak-age violation probabilities. We also show that one can find two blocklength values that result in very similar average delay but significantly different delay violation probabilities. This highlights the importance of focusing on violation probabilities rather than on averages.

Motivated by recent theoretical challenges for 5G, this study aims to position relevant results in the literature on code‐domain non‐orthogonal multiple access (NOMA) from an information‐theoretic perspective, given that most of the recent intuition of NOMA relies on another domain, that is, the power domain. Theoretical derivations for several code‐domain NOMA schemes are reported and interpreted, adopting a unified framework that focuses on the analysis of the NOMA spreading matrix, in terms of load, sparsity, and regularity features. The comparative analysis shows that it is beneficial to adopt extreme low‐dense code‐domain NOMA in the large system limit, where the number of resource elements and number of users grow unboundedly while their ratio, called load, is kept constant. Particularly, when optimum receivers are used, the adoption of a regular low‐dense spreading matrix is beneficial to the system achievable rates, which are higher than those obtained with either irregular low‐dense or dense formats, for any value of load. For linear receivers, which are more favourable in practice due to lower complexity, the regular low‐dense NOMA still has better performance in the underloaded regime (load ), while the irregular counterpart outperforms all the other schemes in the overloaded scenario (load ).

Capacity of energy harvesting communications with deterministic energy arrival and finite battery size is investigated. An abstraction of the physical layer is considered, where binary sequences are transmitted through a binary symmetric channel, and a cost function is associated with the transmission of each symbol. Upper and lower bounds on the channel capacity are derived for the general case by studying the normalized exponent of the cardinality of the set of feasible input sequences. Several upper bounds on the exponent are proposed by studying supersets of the feasible set. Lower bounds are derived by applying the binary entropy-power inequality and by using specific signaling schemes based on a save-and-transmit strategy. Numerical results are presented for several values of the energy arrival rate and battery size, validating the usefulness of the capacity bounds established for the energy harvesting channels.

Spectral efficiency of low-density spreading non-orthogonal multiple access channels in the presence of fading is derived for linear detection with independent decoding and optimum decoding. The large system limit, where both the number of users and number of signal dimensions grow with fixed ratio, called load, is considered. In the case of optimum decoding, it is found that low-density spreading underperforms dense spreading for all loads. Conversely, linear detection is characterized by different behaviors in the underloaded versus overloaded regimes. In particular, it is shown that spectral efficiency changes smoothly as load increases. However, in the overloaded regime, the spectral efficiency of low-density spreading is higher than that of dense spreading.

Time reversal (TR) is an effective solution in both single user and multiuser communications for moving complexity from the receiver to the transmitter, in comparison to traditional postfiltering based on Rake receivers. Imperfect channel estimation may, however, affect pre‐ versus postfiltering schemes in a different way; this paper analyzes the robustness of time reversal versus All‐Rake (AR) transceivers, in multiple access communications, with respect to channel estimation errors. Two performance indicators are adopted in the analysis: symbol error probability and spectral efficiency. Analytic expressions for both indicators are derived and used as the basis for simulation‐based performance evaluation. Results show that while TR leads to slight performance advantage over AR when channel estimation is accurate, its performance is severely degraded by large channel estimation errors, indicating a clear advantage for AR receivers in this case, in particular when extremely short impulsive waveforms are adopted. Results however also show a stronger non‐Gaussianity of interference in the TR case suggesting that the adoption of a receiver structure adapted to non‐Gaussian interference might tilt the balance towards TR.

With the reuse of identical training sequences by users in different cells, massive MIMO is severely affected by pilot contamination due to residual error in channel estimation. In this paper, we consider the traditional structure of the training phase, where orthogonal pilot sequences are reused, and analyze a recently proposed group- blind detector in the uplink of an interference- limited network. We derive the asymptotic SINR gain achievable by the group-blind detector compared to conventional schemes, and find that it depends on the number of cells and channel gains only. We show that group-blind detection can significantly improve the asymptotic achievable rate. We propose a simple scheme, that we call method of silences, to estimate the aggregate instantaneous out-of-cell channel covariance that is required to implement the group-blind detector. Numerical results confirm our analysis in scenarios of practical interest, and show cases where a scheme as simple as the method of silences allows to achieve a large fraction of the promised SINR gain.

Millimeter wave (mmWave) communications use large transmission bandwidth and experience severe propagation conditions. This forces the communication system to operate in the so-called wideband regime, where signals must be increasingly “peaky” in order to attain a large fraction of the peak unconstrained wideband capacity. This paper investigates the capacity of the noncoherent channels as a function of bandwidth for signals with average and peak power constraints operating in the millimeter spectrum. Upper and lower bounds on capacity are provided, and the impact of features peculiar to mmWave channels is investigated. Numerical results for a scenario based on recent experimental campaigns are provided. It is shown that the rate achievable by a typical user in a mmWave cell with “non-peaky” signaling can be bounded away from the peak unconstrained wideband capacity. This suggests to reconsider the role of signaling “peakedness” in future mmWave communications.

Massive MIMO is, in general, severely affected by pilot contamination. As opposed to traditional detectors, we propose a group-blind detector that takes into account the presence of pilot contamination. While sticking to the traditional structure of the training phase, where orthogonal pilot sequences are reused, we use the excess antennas at each base station to partially remove interference during the uplink data transmission phase. We analytically derive the asymptotic SINR achievable with group-blind detection, and confirm our findings by simulations. We show, in particular, that in an interference-limited scenario with one dominant interfering cell, the SINR can be doubled compared to non-group-blind detection.

Millimeter wave communications will use large bandwidth and experience severe attenuation due to the pathloss. The two above conditions may force the communication system to enter the so-called wideband regime, where transmitted signals must be increasingly “peaky” in order to achieve a large fraction of the wideband capacity. This paper investigates noncoherent capacity of millimeter wave communications with average and peak power constrained inputs as a function of bandwidth. The impact of several parameters, in particular coherence block size and strength of the normalized specular component in line-of-sight propagation, is also studied. Capacity upper and lower bounds are provided and suggest that in practical scenarios the communication system may have to operate in the wideband regime. Paired with non-line-of-sight propagation, dense signaling is shown to limit the maximum achievable rate for typical users in the cell.

A multiple-access channel where point processes are randomly transformed by timing channels and then superposed is considered. An achievable rate region for the K-user channel is established. A single-user achievable rate in the presence of “many” interfering users is proposed. Results are applied to exponential server timing channels.

A queue timing channel with random arrival and service times is investigated. The message is encoded into a sequence of additional delays that packets are subject to before they depart from the queue. We derive upper and lower bounds of the channel capacity for general arrival and service processes, and general load. We establish the channel capacity for the queue with exponential server and no load constraint by keeping the queue stable. We discuss the consequences of this result and describe a possible application where the timing channel is used to send covert information.

Traditionally paired with impulsive communications, time-hopping code-division multiple access (TH-CDMA) is a multiple access technique that separates users in time by coding their transmissions into pulses occupying a subset of Nschips out of the total N included in a symbol period, in contrast with the traditional direct-sequence CDMA (DS-CDMA), where Ns= N. This paper analyzes the TH-CDMA with random spreading, by determining whether peculiar theoretical limits are identifiable, with both optimal and suboptimal receiver structures, in particular in the archetypal case of sparse spreading, that is, Ns= 1. Results indicate that the TH-CDMA has a fundamentally different behavior than DS-CDMA, where the crucial role played by energy concentration, typical of TH, directly relates with its intrinsic uneven use of degrees of freedom.

In this paper we deal with the problem of minimizing the complexity of an IR-UWB system by the introduction of Time-Reversal, under a power constraint and fixing a reachable performance in terms of BER. An approximate trade-off in the choice of the number of taps at the transmitter and the number of fingers at the receiver is proposed.