The Physical Random Access Channel (PRACH) is essential for initial access and synchronization in both 5G and future 6G networks; however, its detection is highly sensitive to impairments such as high user density, large carrier frequency offset (CFO), and fast fading. Although prior studies have examined PRACH detection, they are often restricted to specific scenarios or lack a comprehensive analytical characterization of performance. We introduce a unified analytical framework that characterizes the statistical distribution of the received power delay profile (PDP) under flat Rayleigh fading and supports both coherent combining (CC) and power combining (PC) repetition strategies. For each strategy, we derive optimal threshold expressions and closed-form detection probabilities. Furthermore, we analyze two key cases depending on the coherence time: identical and independent channel realizations per repetition. Secondly, we exploit the correlation induced by CFO across cyclic shifts to design a novel low-complexity detector that exploits PDP dependencies. Numerical results indicate that PC outperforms CC when repetitions experience independent channels, while CC can be preferable under identical realizations in limited settings. On the other hand, the proposed CFO-aware detector delivers improved robustness under severe CFO conditions.

This paper investigates the theoretical basis for using ground relaying in multi-antenna satellites exposed to blocking situations. Inactive and unobstructed User Equipments (UEs) located on the ground are the relaying nodes of UEs that are not in the satellite’s field of view. Exact closed-form relationships of the Signal-to-Noise Ratio (SNR) and the outage probability are obtained for the case where each user is connected to two transmitting antennas at the satellite. The channel between the satellite and ground is modeled as a shadowed-Rician (SR), whereas a Fluctuating Two-Ray (FTR) fading model is used for the mmWaves ground link between relay and UE, as well as cases with perfect and imperfect Channel State Information (CSI). The simulation results showed that if perfect CSI is not available in the pre-coding and only the signal phase is estimated, the performance loss is minimal and the system can reach its ideal performance by spending limited power. In any case, the closed-forms for the ideal state are a good proxy to predict the performance under non-ideal conditions.

In this paper, we demonstrate the real-time performance of Dedicated Short Range Communication (DSRC) through the design and development of a full-stack testbed based on open-source software that includes the IEEE 802.11p and the IEEE 1609 protocol suite. Vehicles broadcast periodic Basic Safety Messages (BSM). Reference mobility and data traffic models from 3GPP are used for scenario generation using ns-3. We show how to meet the timing requirements of the 802.11p lower layers using low-cost, commercial off-the-shelf components, based on open-source GNU Radio and tested with Ettus USRP B210 Software Defined Radio (SDR), 6 GHz Tx/RxRF frontends and GPS Disciplined Oscillator (GPSDO). The testbed is used to characterize the different contributors to the total delay budget and the Age of Information (AoI), a key metric for vehicle-to-vehicle (V2V). We observe that the AoI is impacted not only by the communication parameters but also by the mobility and traffic conditions. Our results show that more frequent BSM transmission reduces the average peak age but with a higher value relative to the inter-BSM period due to the collisions and packet losses.

This paper evaluates the use of machine learning prediction models for assessing the quality of experience perceived by mobile network subscribers under mobility conditions. Input data are taken from a single measuring point available at commercial subscribers' smartphones. A sequence data classifier based on a type of recurrent neural network, the long shortterm memory network, has been implemented and compared with two simpler machine learning models. A set of nine relevant network parameters, mainly related to the signal level and the signal quality of the serving and the neighbour cells, has been considered as inputs for the prediction model. The prediction model has been applied to estimate the downlink TCP performance on a set of non-intrusive drive tests. The overall performance achieved on the test set is around 80%, a really good result considering the size of the dataset.

In this paper, a novel non-orthogonal multiple access (NOMA)-enabled framework for cloud-radio access networks (CRANs) is proposed. In this framework, two users are scheduled in the same resources according to NOMA; however the performance of cell-edge users is enhanced by means of coordinating beamforming. Stochastic geometry is invoked for modeling the proposed framework, where the positions of BSs follow a cluster point process. In an effort to characterize the performance of the proposed framework, simple expressions in terms of outage probability are derived for both nearby users and the cell-edge users. It is analytically demonstrated that the average beamforming gain is a liner function with respect to the number of cooperating base stations. Numerical results verify the accuracy of analysis and reveal that the proposed framework is capable of greatly enhancing the performance of cell-edge users.

In this work, it is studied the performance of a scheduling algorithm where the Mobile Terminals (MTs) may be turned off if they cause a level of interference greater than a given threshold. This approach, which is referred to as Interference Aware Muting (IAM), may be regarded as an interference-aware scheme that is aimed to reduce the level of interference. The performance of IAM is studied in terms of transmit power, coverage probability, Spectral Efficiency (SE), and Binary Rate (BR). Simplified expressions of SE and BR for adaptive modulation and coding schemes are proposed, which better characterize practical communication systems. Our analysis unveils that, compared with conventional power control schemes, IAM increases the BR and reduces the transmit power.

One of the key ingredients of Intelligent Transportation Systems (ITS) is delivery of broadcast status messages among vehicles for safety purposes. This requires an efficient Medium Access Control (MAC) that provides low average delay and high reliability. To this end, Carrier Sense Multiple Access (CSMA) has been commonly proposed for Vehicle Ad Hoc Networks (VANETs). Nevertheless, the hidden- node problem can jeopardize the reliability of CSMA, whereas the latency when accessing the channel can be unbounded. To overcome these limitations, resource allocation based on the geo-location of the vehicles can be applied in VANETs. For example, a distributed location based access (DLOC) algorithm has been proposed such that vehicles access orthogonal resource blocks based on their position, aiming at maximizing the distance of co-channel transmitters. In this paper we propose a stochastic geometry approach to analyze DLOC taking into account path loss and fading as well as the random location of transmitting vehicles. Analytical results include the average interference, average binary rate and capture probability, i.e. probability of successful message transmission. It is shown that increasing the number of RBs increases reliability but there is a trade off between reliability and average BR.

This paper presents an approach to predict Quality of Experience (QoE) in WLAN networks based on information extracted from non-intrusive measurements which only require control and management frame capture. This procedure avoids costly equipment and it is forward compatible. Specifically, three measurements have been taken: the relative time duration of clear-to-send messages, the percentage of blocked beacons, and the time beacons are deferred. Once the information is stored, a statistical model is trained to estimate a QoE Key Performance Indicator (KPI). Specifically, this paper predicts a basic QoE KPI, the time-to-connect that a newcomer user will experience. Three well-known methods of predictive analysis have been evaluated: decision trees, neural networks and support vector machines. Results obtained from real network measurements encourage further investigation to estimate more complex QoE performance indicators.

Estimation of channel usage is very important to efficiently manage IEEE 802.11-based Wi-Fi networks. The standard approach to estimate the traffic load or busy time of the channel is to passively monitor data frames exchanged over the air interface. However, this method is unfeasible when the network implements the latest versions of the standard or when the interferer is non Wi-Fi traffic such as Bluetooth or the uprising LTE-U. This paper presents an innovative approach to estimate the channel load based on information extracted from the control frames. Control frames are always sent in the legacy format and therefore can be easily captured with any device. Extensive tests have been performed to obtain a correlation between certain control frames metrics and channel achievable throughput.

Inter-cell interference is one of the main limiting factors in current heterogeneous cellular networks. Uplink fractional power control (FPC) is a well-known method that aims to cope with such a limiting factor and to save the battery life of the mobile terminals (MTs). In order to do that, the transmit power of each MT is adjusted as a function of a set of parameters that usually depend only on the link between MTs and serving base station (BS), such as the desired received power at the serving BS or the path loss between the MT and its serving BS. Contrary to these classical FPC schemes, in this paper, we use stochastic geometry to analyze a power control mechanism that keeps the interference generated by each MT under a given threshold. We also consider a maximum transmitted power and a partial compensation of the path loss. Our analysis reveals that such an interference aware method can reduce the average power consumption and increase the average spectral efficiency at once. In addition, the variance of the interference is reduced, thus improving the performance of adaptive modulation and coding schemes, since the interference can be better estimated.

We analyze the coverage probability of multi-user uplink cellular networks with fractional power control. We use a stochastic geometry approach where the mobile users are distributed as a Poisson Point Process (PPP), whereas the serving base station (BS) is placed at the origin. Using conditional thinning, we are able to calculate the coverage probability of k users which are allocated a set of orthogonal resources in the cell of interest, obtaining analytical expressions for this probability considering their respective distances to the serving BS. These expressions give useful insights on the interplay between the power control policy, the interference level and the degree of fairness among different users in the system.

Long Term Evolution (LTE) and its evolved version, LTE-Advanced (LTE-A), are the standards developed by 3GPP to avoid the limitations associated to 3G networks. Efforts have been put on the improvement of system performance in terms of data rates. Coordinated Multipoint (CoMP) and inter-cell interference avoidance techniques have been widely studied in order to do that. However, not only is the increase in data rate important, but also latency reduction is a crucial factor to be considered for some applications. For instance, Machine-to-Machine (M2M) communications are nowadays one of the most promising applications, which are very sensitive to delay. In this work, we evaluate one of the most promising CoMP techniques, i.e. non-precoded Joint Transmission (non-precoded JT) and one of the most widely studied Inter-Cell Interference (ICI) avoidance technique, i.e. Partial Frequency Reuse (PFR). The objective is to determine whether, in addition to increase the data rates, they also reduce the latency. Simulation results show that PFR presents a greater reduction in the mean packet delay than this associated to non-precoded JT.

Global System for Mobile Communications Railways (GSM-R) has been the de facto standard for wireless communications in the field of High Speed Railway (HSR). However due to the increasing requirements associated with HSR, Long Term Evolution for Railways (LTE-R) has been presented as the following wireless communication system. In this paper a complete performance analysis of LTE for HSR is carried out giving results for both Physical (PHY) and Medium Access Control (MAC) layer in order to identify appropriate Quality of Service (QoS) requirements. An adequate Rician channel model with a time-varying Doppler frequency offset has been integrated in a Downlink LTE simulator using Wireless Mobile SIMulator (WM-SIM) platform. The effect of Inter- Carrier Interference (ICI) degrades the Bit Error Rate (BER) whereas the reduced coherence time makes obsolete channel state information reducing the performance of adaptive modulation and coding (AMC). For this reason open loop Multiple Input Multiple Output (MIMO) techniques are attractive. Results illustrate the benefits of LTE in HSR scenario.

Since many years the Gaussian or normal distribution has been a useful tool to model data observations in fields as physics or astronomy. In communication systems, for instance, this distribution is widely used to model thermal noise. However, there exist many natural physical phenomena that exhibit tails decay following a power law that cannot be modelled by the classical Gaussian distribution. In many of these cases, Student's t distributions can be useful for modelling these kind of data because they allow heavy tails which are more realistic. This study provides a brief introduction to those distributions and their convolutions, which are distributed according to the Behrens–Fisher distributions. The goal is to highlight the potential application of non-Gaussian distributions to the analysis of communication systems. With this purpose, the authors present their work applying those distributions to describe the enhanced noise when zero-forcing (ZF) equalisation is used to compensate the effects of a selective fading Rayleigh channel. Obtained results allows the analysis of enhanced noise in three different scenarios: an orthogonal frequency division multiplexing (OFDM) transmission, an OFDM-based relay network and a single carrier frequency division multiple access (SC-FDMA) transmission.

Vehicle-to-vehicle (V2V) communications have seen growing attention in the last few years. In this work, we address the use of the 3GPP Long Term Evolution (LTE) standard technology applied to V2V. We employ empirical models for the V2V channel, and show results from comprehensive computer simulations, based upon both the uplink (UL) and downlink (DL) standards for LTE. We provide results for 10 MHz and 20 MHz channels, in terms of BER, BLER, spectral efficiency and throughput, using multiple MIMO modes. Results show the attractive feasibility of the LTE technology in V2V communication systems.

The sum of ratios of two complex Gaussian random variables appears frequently in the mathematical analysis of telecommunication systems when zero-forcing equalization is applied. This paper is focused on the study of one of those systems: a simple Orthogonal Frequency Division Multiplexing (OFDM) relay network. The reason behind the election of this particular scenario is the recent interest on employing relay networks in wireless and mobile broadband systems to increase the coverage and throughput in a cost-effective way. Thus, the probability distribution of enhanced noise, made up by the sum of ratios of complex Gaussian random variables, is used to obtain a closed-form expression for the BER in the scenario under study.

This work analyzes the joint influence of channel fading and the data outsourcing process in the QoS metrics of a wireless system. As a first contribution, expressions of the channel effective bandwidth function (also known as effective capacity) for time-correlated Rayleigh fading under different adaptive rate policies are obtained. This result allows us to analytically evaluate the maximum constant information rate that can be transmitted over the channel under a probabilistic delay constraint. Later, this Capacity with Probabilistic Delay Constraint CDt,εis generalized for systems with non-constant sources and simple closed-form expressions able to capture the influence of source processes in the probability of over-delay are given. Figures on how much the maximum allowable rate decreases for shorter allowable delays or for more changing rate sources are shown and the expected delay violation is compared to simulations in order to validate our results.

Ergodic capacity is not a suitable information-theoretic measure for delay sensitive applications over fading channels. On the other hand, delay-limited capacity becomes zero for Rayleigh channels. In this case, the Capacity with Probabilistic Delay Constraint becomes useful. In, the maximum constant source rate that may be supported in a wireless system with a probability ¿ of exceeding certain delay bound Dt, CDt,¿, was evaluated for a Rayleigh channel. This contribution extends that work to an OFDM system over a generic Rayleigh frequency selective channel. An analytical expression of the capacity CDt,¿is obtained and figures on how much the maximum allowable rate decreases for higher time or frequency correlation in the channel response are shown. Finally, the expected delay violation is compared to simulations in order to validate our results.

The capacity with probabilistic delay constraint CDt,epsivexpresses the maximum source rate that may be supported in a wireless system with a probability epsiv of exceeding certain delay bound Dt. In a previous paper by the authors (see Proc. IEEE GLOBECOM, November 2007), CDt,epsivwas calculated for a Rayleigh channel carrying a constant rate flow. In this work, the potential of the effective bandwidth theory is shown by evaluating this constrained capacity for a variable rate source modeled as an ON-OFF process. Cross relations among ON-OFF process parameters, fading channel statistics, QoS constraints and maximum allowable mean source rate are displayed by the obtained closed-form expressions. CDt,epsivis measured in different scenarios to exhibit to which extent higher time-correlation of the channel response or longer ON-OFF periods are harmful to the delay behaviour, getting a lower value of the capacity CDt,epsiv.

One of the novelties of the forthcoming LTE technology is the use of SC-FDMA as the transmission technique in the uplink. In this paper a study of the BER in an interleaved SC-FDMA system over a fading channel is presented. This study provides the mathematical grounds to obtain a closed-form expression for the BER for BPSK and square M-QAM. Results are validated by means of comparison with simulations.

In this work, the maximum constant rate that can be supported with a probability epsiv f exceeding certain delay boundDtis evaluated. Following the works in (Wu, 2003), the procedure to derive this capacity with probabilistic delay constraint CDt,epsiv is described. A simple closed form analytical result is given for block fading channel and different adaptive rate policies. The extension to the general correlated Rayleigh fading is also provided based on a semi-analytical strategy and the previous result for independent samples. As expected, CDt,epsiv tends to the ergodic capacity for long allowed delays (Dtrarr infin) and diminishes when the delay constraint is more strict. The expected delay violation probability is compared to simulations in order to validate our results.

The impact of non-ideal adaptive modulation for Nakagami-m flat fading channels is studied. First, the consequences of bounded feedback information rate, not feasible with continuous power or rate variation, are tackled. An optimum fully-discrete AQAM scheme is derived and the signaling information rate is evaluated. Later, degradation due to noisy and delayed pilot symbol assisted channel estimation is analyzed and compared to that of continuous schemes.

Presented here is an approach to analyzing the effect of imperfect channel estimation on adaptive modulation. The sensitivity of the main performance parameters to short-term and long-term estimation error sources is summarized in a set of new formulas that are either closed-form expressions or simple to compute numerically.

Discrete multitone (DMT) modulation is a multicarrier technique that allows the transmission of high speed data over band limited channels. This type of system is very sensitive to synchronization errors when used in digital subscriber loop applications (xDSL), due to the high number of carriers and high density constellations involved. This paper addresses the topic of all-digital timing error correction in a DMT system for xDSL applications, where the timing error correction procedure is based entirely on signal interpolation. An analytical study of the interpolator filter performance is carried out, arriving at an expression for the signal-to-distortion ratio (SDR) at the output of the receiver, as a merit figure. In this derivation, the fixed frequency domain equalizer (FEQ) plays an important role since it compensates for a great part of the distortion introduced by the interpolator. From this study, the design of the optimal interpolator filter in terms of SDR, based on a multirate approach with Kaiser window, is presented. Specific designs for ASIC and for DSP-based implementations are obtained. Performance results are excellent, yielding SDR values above 50 dB for all carriers while keeping the computational cost low.