Offset Time Research Articles

Network-coded uplink clustered NOMA relay networks: Models and performance comparisons

In this paper, network sum-rate maximization (NSR-MAX) for network-coded (NC) uplink clustered non-orthogonal multiple-access (NOMA) relay networks is considered. In particular, the goal is to maximize network sum-rate via optimal power allocation, where the user clusters communicate with the base-station over an amplify-and-forward relay, subject to quality-of-service (QoS) constraints. Two NC-NOMA transmission models – namely NC-NOMA-I and NC-NOMA-II – are proposed, where in the first model, network-coding is applied at the relay only, while the second model applies network-coding for user clusters’ transmissions and at the relay to further minimize the transmission delay. The formulated NSR-MAX problem happens to be non-convex, and hence, is computationally-intensive. Thus, a low-complexity iterative two-layer algorithm (ITLA) is devised, which decouples the formulated problem and efficiently solves its over two-layers. Specifically, the inner-layer solves the NSR-MAX problem to obtain the optimal relay transmit power, while the outer-layer determines the optimal users’ transmit powers. Numerical results are presented, which illustrate that the proposed ITLA yields near-optimal solutions for all transmission models, in comparison to the formulated NSR-MAX problem (solved via global optimization package) as well as outperforming its OMA-based counterparts. Not only that, but the NC-NOMA-II is shown to be superior to the other NOMA and OMA schemes, while demonstrating resilience to timing offsets as well as successive interference cancellation (SIC) and channel state information (CSI) errors.

A Maximum-Likelihood-Based Two-User Receiver for LoRa Chirp Spread-Spectrum Modulation

Long Range (LoRa) is an emerging low-power wide-area network technology offering long-range wireless connectivity to Internet of Things (IoT) devices. For energy efficiency reasons, LoRa end nodes implement a nonslotted ALOHA multiple access scheme to transmit packets to the gateway. Due to the lack of synchronization between end nodes, collisions between uplink packets have been identified as the main obstacle to the scaling of dense LoRa networks. To tackle this issue, we present in this article a LoRa receiver that is capable of decoding colliding packets from two interfering end nodes. The proposed two-user detector is derived from the maximum-likelihood principle using a detailed model of two colliding LoRa packets. As the complexity of the maximum-likelihood sequence estimation is prohibitive, complexity-reduction techniques are introduced to enable practical implementations of the receiver. An in-depth performance analysis highlights that the proposed two-user detector inherently leverages the differences in received power, time offsets, and frequency offsets between the users to separate and demodulate their respective signals. To demonstrate the practicality of the proposed detector, an interference-robust synchronization algorithm is then designed and evaluated. Simulation results indicate that a LoRa receiver combining the proposed synchronization algorithm and two-user detector is capable of detecting and demodulating two interfering users with satisfactorily error rates.

Delayed circadian rhythms in older Africans living with human immunodeficiency virus (HIV).

The increasing number of people living with human immunodeficiency virus,HIV, (PLWH) have an elevated incidence of risk for noncommunicable comorbidities, the aetiology of which remains incompletely understood. While sleep disturbances are often reported in PLWH, it is unknown to what extent they relate to changes in the circadian and/or sleep homeostatic processes. We studied the relationship between sleep characteristics, circadian phase,and HIV status in older adults from the HAALSI (Health and Ageing in Africa: a Longitudinal Study of an INDEPTH Community in South Africa) subsample of the Agincourt Health and Demographic Surveillance System in South Africa (n = 187, 36 human immunodeficiency virus positive[HIV+], age: 66.7 ± 11.5years, range 45-93years), where HIV prevalence is high and (in contrast to the global north) does not associate significantly with potentially confounding behavioural differences. In participants with valid actigraphy data (n = 172), regression analyses adjusted for age and sex indicated that HIV+ participants had slightly later sleep onset (β = .16, p = .039), earlier sleep offset times (β = -.16, p = .049) and shorter total sleep times (β = -.20, p = .009) compared to the HIV negative (HIV-) participants. In a subset of participants (n = 51, 11 HIV+), we observed a later dim light melatonin onset (DLMO) in HIV+ (21:16 ± 01:47) than in HIV- (20:06 ± 00:58) participants (p = .006). This substantial difference remained when adjusted for age and sex (β = 1.21; p = .006). In 36 participants (6 HIV+) with DLMO and actigraphy data, median phase angle of entrainment was -6 min in the HIV+ group and +1 h 25 min in the HIV- group. DLMO time correlated with sleep offset (ρ = 0.47, p = .005) but not sleep onset (ρ = -0.086, p = .623). Collectively, our data suggest that the sleep phase occurred earlier than what would be biologically optimal among the HIV+ participants. This is the first report of a mistimed circadian phase in PLWH, which has important potential implications for their health and well-being, especially given the well-established relationships between circadian asynchrony and sleep deprivation with poorer health outcomes.

Longitudinal Variations in Equatorial Ionospheric TEC from GPS, Global Ionosphere Map and International Reference Ionosphere-2016 during the Descending and Minimum Phases of Solar Cycle 24

Research on longitudinal discrepancies in local ionospheric variability, especially in equatorial and low-latitude regions, is a focal point of interest for the space weather modeling community. The ionosphere over these regions is influenced by complex electrodynamics, wind, and temperature dynamics that can seriously impact dynamic technological systems such as satellite tracking and positioning, satellite radio communication, and navigation control systems. Here, we researched the longitudinal variability in the ionospheric total electron content (TEC) by analyzing observed global positioning system (GPS)-derived TEC values along with those extracted from the most reliable global ionospheric maps (GIMs) and the International Reference Ionosphere (IRI-2016) model at selected stations in the vicinity of the magnetic equator along the American, African, and Asian longitude sectors. The period of study covered the descending (2016–2017) and deep solar minimum (2018–2019) years in the 24th solar cycle. Apart from the decreasing trend of the TEC from the descending to deep solar minimum period irrespective of season and longitude sector, the results showed a relatively higher magnitude of TEC in the African longitude than the other two longitude sectors. Despite evident overestimation and underestimations of TEC in both models, GIM predictions generally looked better in terms of observed variation patterns, especially in the African longitude. The study also highlights the seasonal and semiannual effects of longitudinal variations in TEC, manifesting in local time offsets and some peculiar anomalies, which seemed to be different from previously reported results, especially during the solar minimum years at the three longitude sectors. The insignificant effects of longitudinal variations on the equinoctial asymmetry are attributed to the diverse electron density distribution and ionospheric morphology at the three longitude sectors that will prompt further investigations in the future. The outcomes from this study may augment the past efforts of scientists to understand the seasonal effects of the longitudinal variations in TEC, thereby complementing the improvements of ionospheric representations in global ionosphere models and maps.

Analysis on the Ecological Concept of Ternary Interactive Education in Business English Writing

In order to improve the effect of business English writing education, this paper combines intelligent algorithms to study the ecological concept of ternary interactive education in business English writing and jointly identifies interference and source signals. Moreover, this paper derives the likelihood function of the received signal under the modulation mode of the interference and the source signal and jointly considers the information of the interference. The modulation recognition can well reduce the influence of interference on algorithm performance. In addition, this paper simulates the recognition performance of the likelihood function-based algorithm when the system has frequency offset and asynchronous time offset. Finally, this paper combines experimental research to verify that the business English education system based on the ternary interaction concept proposed in this paper can effectively improve the effect of business English writing education.

Design, assembly and operation of a Cosmic Ray Tagger based on scintillators and SiPMs

The Mu2e experiment at Fermilab aims to search for the SM forbidden μ−→e− conversion in Al muonic atoms. The signal signature consists of 104.96 MeV electrons, identified by a straw-tube tracker and a crystal calorimeter, made of two annular disks. In order to calibrate the calorimeter disks with minimum ionizing particles (MIP) before the installation, we have realized a Cosmic Ray Tagger (CRT) at Laboratori Nazionali di Frascati (LNF) of INFN. The CRT consists of two planes of eight 2.5×1.5×160 cm3 plastic scintillator (EJ-200) bars, coupled to SiPMs on both edges, so as to estimate longitudinal hit positions from time differences. 3D MIP tracking is achieved by reconstructing hit positions in the two planes, placed above and below the disks, and allows to calibrate the energy response, to align the time offsets, and to study the detector performances dependence along the crystals axis.

Calibration Of Stress Wave Timer for Amazonian Species

Non-destructive testing is increasingly being used on wooden structures. One of the preferred instruments for this task is the Stress Wave Timer, because it is portable and easy to use. This instrument needs to be calibrated to minimize possible reading errors. Tests were performed on samples of different sizes from four Amazonian timber tree species, with differing distances between the start/stop accelerometers and varying gain settings. The aim was to identify errors and find the best ratio between the Metricard SWT’s start and stop accelerometers. The best ratio was observed with settings of 40 for stop and 1 for start. The calculation of the confidence interval for the mean of the stress wave velocities expresses a degree of uncertainty ranging from 2% to 8%, regardless of the species and according to the start/stop ratio. A more in-depth evaluation led to the conclusion that the greatest degree of uncertainty occurs with short pieces. This confirms the need to calibrate the equipment, especially when using the instrument with pieces approximately equal to or less than 70 cm in length. The value for offset time (intersection of the line with the axes) was determined by a simple regression analysis, and indicated that the data correction factor varied from 1.9 to 2.2 depending on the start/stop ratio, at least in the samples studied.

UTC and GNSS system time access using PPP with broadcast ephemerides

The application of precise point positioning with broadcast ephemerides (PPP-BCE) is discussed as an alternative to the established all-in-view technique for multi-GNSS time transfer. It combines the use of broadcast ephemerides with low-noise carrier-phase observations for accessing GNSS system time scales and Coordinated Universal Time (UTC) with improved precision, and can be employed on stationary as well as mobile receivers in offline or real-time analyses. Using calibrated timing receivers, the method is shown to provide estimates of the GNSS-to-GNSS time offsets (XYTOs) with an accuracy at the 2 ns level. In the absence of prior calibrations, 0.5 ns consistency across different stations is achieved for GPS, Galileo, and BeiDou-3 after adjustment of systematic biases in comparison with calibrated reference stations or broadcast XYTO values. Furthermore, access to GNSS-specific UTC realizations can be obtained through predictions of the UTC offset from GNSS system time as provided in the broadcast ephemerides of individual constellations. The overall quality of the PPP-BCE-derived receiver clock offsets from UTC is assessed using calibrated receivers at various timing laboratories along with BIPM-provided UTC-UTC(k) measurements. Over the 1.5 years covered in the study, an accuracy of 1.8 ns for GPS and 2.5 ns for Galileo is demonstrated. For BeiDou, a slightly worse accuracy of 3 ns is obtained for a single timing laboratory over 9 months.

Parallel Greedy Search for Random Access in Wireless Networks

We consider the random access problem in wireless networks such as cellular networks and massive machine type communication networks, where a large number of devices/users are connected to a base station. In order to establish communication with the base station, as a part of the random access procedure, active users select and transmit codes (pilot sequences) randomly from a codebook. Since the active users are typically a small fraction of the total users, sparse signal recovery algorithms are employed to detect the transmitted codes. In this paper, we use multiple measurement vector model for the received signal and develop a parallel greedy search algorithm and it’s stopping criteria to detect the active users. We show through simulations that the proposed scheme, compared with the existing greedy algorithms, gives better detection performance at lower false alarms levels. We study how the code length and the code word size need to be chosen in order to detect a given number of active users. We also address the scenario when there are different timing offsets for signals received from different users.

On the Performance of Precoded OFDM Systems in the Presence of Symbol Timing Offset

This correspondence considers the performance evaluation of precoded orthogonal frequency division multiplexing (P-OFDM) based on Walsh-Hadamard Transform (WHT) in the presence of symbol timing offset (STO). The signal-to-interference plus noise ratio (SINR) is evaluated for flat and frequency-selective fading channels (FSC), where closed-form analytical expressions are derived for the flat fading case. In FSC, the SINR is obtained using Monte Carlo simulation due to the analysis intractability. The bit error rate (BER) performance of OFDM and P-OFDM based on WHT, Haar, and Zadoff-Chu matrix transforms are considered to demonstrate the STO impact on the BER using various precoding transforms. The obtained results show that the impact of STO on P-OFDM is substantially different from conventional OFDM. In particular, it is found that STO affects the SINR of each subcarrier differently, where the SINR of certain subcarriers is severely degraded while others are immune. Furthermore, the diversity gain advantage of the precoding process may vanish for large STOs.

Likelihood based synchronization algorithms in optical pulse position modulation systems with photon-counting receivers.

Deep space optical communication (DSOC) is becoming a hot topic. Pulse position modulation (PPM) is an effective tool to realize DSOC benefiting from the feature of high sensitivity. In this paper, we analyze 2 × 1 optical PPM systems with photon-counting detectors, where the distance difference between the two links causes asynchronous superpositions at the receiving end. Two synchronization algorithms are proposed to estimate the time offsets of the two links, which are the optimal Global Maximum Likelihood Estimation (GMLE) and the suboptimal Integer Comparison - Fractional Likelihood Estimation (ICFLE). The complexities of the two methods are also compared. In order to measure the two proposed algorithms, the Cramer-Rao bounds (CRB) are derived. According to simulation results, both the two proposed algorithms approach the deduced CRBs. Furthermore, an equivalent experiment is designed to verify the feasibility and effectiveness of the proposed algorithms. It's also indicated that the proposed algorithms may be utilized in practical systems.

Cooperative Reflection and Synchronization Design for Distributed Multiple-RIS Communications

To reap the promised gain achieved by distributed reconfigurable intelligent surfaces (RISs)-enhanced communications in a wireless network, timing synchronization among these metasurfaces is an essential prerequisite in practice. This paper proposes a unified framework for the joint estimation of the unknown timing offsets and the RIS channel parameters, as well as the design of cooperative reflection and synchronization algorithm for the distributed multiple-RIS communication. Considering that RIS is usually a passive device with limited capability of signal processing, the individual timing offset and channel gains of each hop of the RIS links cannot be directly estimated. To make the estimation tractable, we propose to estimate the cascaded channels and timing offsets jointly by deriving a maximum likelihood estimator. Furthermore, we theoretically characterize the Cramér-Rao lower bound (CRLB) to evaluate the accuracy of this estimator. By using the proposed estimator and the derived CRLBs, an efficient resynchronization algorithm is devised jointly at the RISs and the destination to compensate the multiple timing offsets. Based on the majorization-minimization framework, the proposed algorithm admits semi-closed and closed form solutions for the RIS reflection matrices and the timing offset equalizer, respectively. Simulation results verify that our theoretical analysis well matches the numerical tests and validate the effectiveness of the proposed resynchronization algorithm.

Sleep Regularity and Predictors of Sleep Efficiency and Sleep Duration in Elite Team Sport Athletes

BackgroundMany elite athletes have suboptimal sleep duration and efficiency, potentially due to factors that may impact sleep onset and offset times. Variability in sleep onset and offset may negatively influence sleep. The sleep regularity index (SRI) is a novel metric for sleep regularity, however there are no published descriptions of SRI in elite athletes. Further, contributors to sleep efficiency and duration in elite athletes using objective measures have not been explored.MethodsSleep was monitored over a minimum of seven consecutive days (7 to 43)—in 203 elite team sport athletes (age range = 19–36 years; female, n = 79; male, n = 124, total sleep nights = 1975) using activity monitoring and sleep diaries. The sleep regularity index (SRI) was calculated to reflect the night-to-night shifts in sleep by accounting for changes in sleep onset and sleep offset. Sleep characteristics were compared between regular and irregular sleepers and important contributors to sleep efficiency and total sleep time were assessed using multiple linear regression models.ResultsThe median sleep regularity index and interquartile range were 85.1 (81.4 to 88.8). When compared to irregular sleepers, regular sleepers demonstrated (1) significantly greater sleep efficiency (p = 0.006; 0.31 medium effect size [ES]), (2) significantly less variability in total sleep time (− p ≤ 0.001; − 0.69, large ES) and sleep efficiency (− 0.34, small ES), (3) similar total sleep time and (4) significantly less variation in sleep onset (p ≤ 0.001; − 0.73, large ES) and offset (p ≤ 0.001; − 0.74, large ES) times. Sleep characteristics explained 73% and 22% of the variance in total sleep time and sleep efficiency, respectively. The most important contributor to total sleep time was a later sleep offset time, while the most important contributors to sleep efficiency were an earlier bedtime and less variable sleep onset times.ConclusionsBedtime and a consistent sleep onset time are important factors associated with sleep efficiency in athletes, while sleep offset is an important factor for total sleep time. Coaches and staff can assist their athletes by providing training schedules that allow for both regularity and sufficiency of time in bed where possible.

Rectangular Orthogonal Digital Filter Banks Based on Extended Gaussian Functions

Rectangular orthogonal digital filter banks (ODFBs) based on square-root-raised-cosine (SRRC) functions are widely utilised to realise flexible and elastic multi-channel aggregations for fixed and mobile networks. However, long digital filter lengths are required to minimize digital filtering-associated signal distortions. In this paper, based on the extended Gaussian function (EGF), a novel rectangular ODFB with excellent robustness against the short digital filter length-induced truncation effect is proposed. Optimum digital filter parameters of the EGF-based ODFBs are identified and verified in multi-channel hybrid OFDM-digital filter multiple access (DFMA) PONs based on intensity modulation and direct detection (IMDD). By making use of the identified optimum digital filter parameters, extensive comparisons of digital filter characteristics and corresponding multi-channel upstream PON performances are made between the EGF-based ODFBs and the SRRC-based ODFBs. It is shown that to achieve a similar aggregated upstream signal transmission capacity, the EGF-based ODFB reduces the digital filter DSP complexity by a factor of 4. For a digital filter length as short as 8, in comparison with the SRRC-based ODFB, the EGF-based ODFB introduces >1.5 dB (>0.8 dB) improvements in upstream receiver sensitivity for 5-bits (8-bits) DACs/ADCs, increases the aggregated upstream signal transmission capacity by >5.5%, enlarges the ONU launch power dynamic range by >2.5 dB and improves the frequency offset tolerance by a factor of >1.5. In addition, the EGF-based ODFB also enhances upstream performance robustness against ONU symbol timing offsets.

Combating Packet Collisions Using Non-Stationary Signal Scaling in LPWANs

LoRa, a representative Low-Power Wide Area Network (LPWAN) technology, has been shown as a promising platform to connect Internet of Things. Practical LoRa deployments, however, suffer from collisions, especially in dense networks and wide coverage areas expected by LoRa applications. Existing collision resolving approaches do not exploit the modulation properties of LoRa and thus cannot work well for low-SNR LoRa signals. We propose <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NScale</i> to decompose concurrent transmissions by leveraging subtle inter-packet time offsets for low SNR LoRa collisions. NScale (1) translates subtle time offsets, which are vulnerable to noise, to robust frequency features, and (2) further amplifies the time offsets by non-stationary signal scaling, i.e., scaling the amplitude of a symbol differently at different positions. In practical implementation, we propose a noise resistant iterative symbol recovery method to combat symbol distortion in low SNR, and address frequency shifts incurred by CFO and packet time offsets in decoding. We propose optimized designs for diminishing the time costs of computation-intensive tasks and meeting the real-time requirements of LoRa collision resolving. We theoretically show that NScale introduces < 1.7 dB SNR loss compared with the original LoRa. We implement NScale on USRP N210 and evaluate its performance in both indoor and outdoor networks. NScale is implemented in software at the gateway and can work for COTS LoRa nodes without any modification. The evaluation results show that NScale improves the network throughput by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.3\times $ </tex-math></inline-formula> for low SNR collided signals compared with other state-of-the-art methods.

The Sleep Behaviors of Elite Australian Rules Footballers Before and After Games During an Entire Season.

Most athletes sleep poorly around competition. The aim of this study was to examine sleep before/after games during an entire season in elite Australian Rules footballers (N = 37) from the same team. Sleep was monitored using activity monitors for 4 consecutive nights (beginning 2 nights before games) during 19 rounds of a season. Differences in sleep on the nights before/after games, and differences in sleep before/after games as a function of game time (day vs evening), location (local vs interstate), and outcome (win vs loss), were examined using linear mixed effects models. Players fell asleep earlier (+1.9h; P < .001), and woke up later (+1h; P < .001) on the night before games compared with the night of games. Players obtained less sleep on the night of games than on the night before games (5.2h vs 7.7h; P < .001), and this reduction was exacerbated when games were played in the evening-after evening games, players obtained approximately 40 minutes less sleep than after day games (P < .001). Sleep duration on the nights before and after games was not affected by game location or game outcome, but players had later sleep onset (P < .001) and offset times (P < .001) on most nights when sleeping away from home. Elite footballers obtain good sleep on the night before games but obtain approximately 30% less sleep on the night of games. Given the role of sleep in recovery, it will be important to determine whether a reduction in sleep duration of this magnitude impairs recovery on the days following games.

Quadrature Filter Approximation for Reconstructing the Complex Envelope of a Bandpass Signal Sampled Directly With a Two-Channel TIADC

A general and flexible technique is proposed for sampling the complex envelope of a bandpass signal by using a nonuniformly interleaved two-channel analog-to-digital converter (TIADC). The signal is sampled directly without any demodulation operation, but the two sampling channels are not uniformly interleaved, since some TIADC timing offsets are rendered forbidden. The proposed complex envelope sampling scheme requires the implementation of two digital FIR filters and a discrete-time modulator. Quadrature sampling, a special case that assumes certain parameter relations, is investigated as an approximation technique. Computer simulations are presented and illustrate a −57dB mean-square error (MSE) can be achieved via quadrature approximation for sufficiently large filter orders.

Associations of chronotype and sleep patterns with metabolic syndrome in the Hispanic community health study/study of Latinos

ABSTRACT Sleep duration, sleep efficiency, and sleep timing have been shown to have potential effects on metabolic functions relevant to circadian rhythms. It is not clear if the impact of sleep patterns on metabolic risk factors is through sociocultural and environmental factors or circadian misalignment. We investigated the associations of sleep patterns, chronotype, and social jet lag with metabolic syndrome among non-shift worker Hispanic/Latino adults. We used cross-sectional data from the Sueño Ancillary Study of The Hispanic Community Health Study/Study of Latinos (HCHS/SOL). Data from a subsample of 2189 participants aged 18–64 years were used in the analysis. Mean nightly sleep duration, mean sleep onset time, mean sleep offset time, mean sleep midpoint time, sleep efficiency, sleep variability (standard deviation (SD) of sleep duration, and SD of sleep midpoint), and time spent above light exposure threshold (1000 lux) in a day were assessed by wrist actigraphy (Acti-watch Spectrum). Chronotype was determined by the reduced Morningness-Eveningness Questionnaire. Medical conditions including dyslipidemia, hypertension, and diabetes mellitus were determined from a fasting blood specimen and physical exam at the baseline visit. To determine whether sleep patterns, light levels, chronotype, and social jetlag are associated with metabolic syndrome, multivariable logistic regression models were fitted, including variables with P < .15 in the univariate analysis. The results of the multivariable analysis demonstrated that in participants older than 40 years, intermediate chronotype (vs early) was significantly associated with a higher risk of metabolic syndrome (Odds ratio (95%CI): 1.33 (1.04,1.7)), while later chronotype (vs. early) in participants younger than 40 years was significantly associated with a lower risk of metabolic syndrome (Odds ratio (95%CI): 0.37 (0.14, 0.96)). Also, higher sleep efficiency was significantly associated with decreased odds of metabolic syndrome (Odds ratio (95%CI): 0.98 (0.96, 0.99)). Nightly sleep duration was not significantly different between two groups of participants with and without metabolic syndrome in multivariable analyses. There was no significant association between social jet lag and metabolic syndrome in multivariable analysis (p = .286). Moreover, there was no significant association between chronotype and social jet lag in multivariable analysis. The association between metabolic syndrome and chronotype is age-dependent. While early chronotype is associated with metabolic syndrome in younger individuals, it tended to be associated with lower odds for metabolic syndrome in older individuals.

Massive Grant-Free OFDMA With Timing and Frequency Offsets

In the massive grant-free orthogonal frequency division multiple access (OFDMA), the timing and frequency offsets between users impose new challenges on joint active user detection (AUD) and channel estimation (CE) for the subsequent data recovery. In the asynchronous OFDMA, the timing and frequency offset effects can be modeled as the phase-shifting on the pilot matrix. As such, by constructing the measurement matrix with timing and frequency offsets, the joint estimation problem can be formulated as a multiple measurement vector (MMV) recovery problem with structured sparsity. However, such structured sparsity cannot be tackled by the existing compressed sensing (CS) techniques. To address this issue, we develop an efficient structured generalized approximate message passing (S-GAMP) algorithm, which includes the parallel AMP-MMV algorithm as a particular case. To deal with the high dimensionality of the measurement matrix, we propose the dynamic S-GAMP algorithm with a dynamic measurement matrix to reduce the computational complexity. Simulation results confirm the superiority of the proposed algorithms in grant-free OFDMA with both timing and frequency offsets.

Deep-Learning-Based Initial Access Method for Millimeter-Wave MIMO Systems

This letter proposes a deep-learning-based initial access (IA) method for a millimeter-wave (mmW) multiple-input multiple-output (MIMO) system. By detecting the primary synchronization signal (PSS) in the IA block, UE can discover and synchronize with the BS. PSS detection can be modeled as a binary hypothesis testing problem with unkonwn channel, carrier frequency offset (CFO), and timing offset (TO). Unlike the conventional methods using energy as the detection statistic, the proposed method uses probability as the detection statistic. Specifically, we first preprocess the received signal, and then input the results into a pre-trained convolutional neural network (CNN). The CNN can output the probability that PSS is present. After comparing the maximum probability with the threshold, the UE can determine whether there is PSS. Once PSS is detected, the estimation of TO can be obtained at the same time. Simulation results demonstrate that, the proposed IA method can outperform the conventional energy-based IA method in both miss detection rate performance of PSS and normalized mean square error (NMSE) performance of TO.