Data Transmission Channel Research Articles

Investigative analysis of channel selection algorithms in cooperative spectrum sensing in cognitive radio networks

The proliferation of wireless mobile devices has led to a number of challenges in mobile data communication. The world is experiencinganincreasingusage of finite spectrum bands for social media and other data communication services. It is due to this high usage that the Federal Communications Commission(FCC) sought to open up some spectrum bands to be used opportunistically by secondary users (SUs). However, the coexistence of Primary Users (PUs) and SUs may cause interference which leads to wastage of spectrum resources. This study investigates the impact of interferences between PUs and SUs. To ensure higher detection of PU signal, a cooperative rule was used to decide which SU to share and makea final decision about the availability of the spectrum band. To maximize the throughput of SU, a maximum likelihood function was designed to reduce delays in searching for the next available channel for data transmission. To discover more transmission opportunities and ensuring that a good number of free channels are detected, a parallel sensing technique was employed. Matlabwas used to simulate and generate the results in a distributed cognitive radio environment. The proposed extended generalizedpredictive channel selection algorithm (EXGPCSA) outperformed otherschemes in literature in terms of throughput, service timeandprobability of detection.

Fuzzy logic-based VANET routing method to increase the QoS by considering the dynamic nature of vehicles

Vehicular ad hoc network usually operates in various challenging situations like frequent topology changes, high vehicular mobility and the wide range of communication networks. Due to this it is very hard to maintain a higher data rate and also to achieve low latency during data communication. To overcome these problems, given the dynamic natures of all the vehicles in a given network in the proposed routing method, we have defined two fundamental parameters to determine the forwarding vehicle. The first parameter, which we developed, we call it “Channel quality factor (CQF)” or ‘Z’. The other parameter known as “Communication expiration time” or ‘T’ together with CQF is used in the present method to determine the forwarding vehicle. Fuzzy logic is also used to optimize various Quality of Service matrices. This proposed routing method involves two main parts; one is for forwarding Vehicle selection in the road based on the fuzzy logic. The second one is Road selection at the Road Junction to select the right path to reach the signal to the destination vehicle. The simulation results show that our proposed method performs well compare to other well-known protocols (MoZo, BRAVE, OFAODV) in terms of the average end to end delay, packet delivery ratio and control packet overhead, given any number of vehicles in a set of streets. While we are comparing with VEFR protocol, our proposed method shows higher performance in terms of average E2E delay and control packet overhead. However, it is interesting to see that VEFR gives $$\sim $$ 5% better result than our proposed method when the number of vehicles in the streets are lower. But in the limit, when the number of vehicles reaches close to $$\sim $$ 1900 the difference between the proposed method and method in VEFR goes to zero. At last we compare our proposed method with junction based two V2I protocols. In every cases, it shows better result even though we change the speed of the vehicles, beacon interval, channel data rate and transmission region.

Remote control system for the unmanned floating platform

The paper presents the results of modelling the coverage areas of a communication system in the Wi-Fi range for organizing a wireless data transmission channel between the coastal and onboard control subsystems of an unmanned floating platform, for which the main navigation zones near the coast are determined. It is shown that the use of a communication system based on the IEEE 802.11 standard makes it possible to ensure stable data exchange within the specified navigation zones of the unmanned platform. A generalized block diagram of a remote control system for an unmanned floating platform has been developed. It includes a video surveillance subsystem and a subsystem for engine control and collection of metrological data from various sensors. In this case, the floating platform is controlled both from a stationary post and using a mobile console. Functional diagrams of the onboard video surveillance and control system, as well as the coastal subsystem have been developed.

Integrity of information data flow in meteor communication networks

The paper considers the issues of ensuring the integrity of the flow of information messages between remote objects and identification of the data transmission channel, interrupted randomly by fragmentation-defragmentation processes of this flow as a result of the stochastic appearance and disappearance of traces from meteors burning in the ionosphere, which are used as passive repeaters of VHF radio signals that carry out energy contact between correspondents of a computer network. The problem is posed to implement an algorithm for discontinuous transmission of a continuous data stream over a meteor communication network without distortion and loss of transmitted messages without the inclusion of redundant signs, which contributes to a more rational use of the limited telecommunication resource of the meteor communication network. It is shown that to ensure a reliable exchange of information data between remote infrastructure facilities of the Northern Sea Route, a meteor trail can be used, which will provide a statistically stable connection with the fulfilment of the requirements for the probability of receiving false signs while maintaining the integrity of messages, provided that this type of communication between correspondents is discontinuous.

Восстановление пропущенных отсчетов дискретных сигналов при передаче цифровой информации по инфокоммуникационным каналам связи в приложениях интернета вещей

The paper discusses a method for recovering missing samples of an analog signal during transmission over communication channels in applications of the Internet of Things. The aim of the work is to obtain a mathematical description of the procedure for restoring the values of the signal samples from the output of the analog sensor on the receiving side, which were not transmitted in order to reduce the load on data transmission channels. The procedure is based on the well-known principles of adaptive signal processing, based on the dynamic determination of the parameters of digital filters based on the assessment of the least-mean-square (LMS) deviation of the signal passing through the filter from a reference signal obtained in one way or another. A feature of the proposed method is the solution of the inverse problem of restoring the samples of the original signal with the known parameters of the filter and the reference signal. In this work, the problem of skipping and restoring samples of a discrete signal is formulated, an expression is obtained for the objective function of the method for restoring missing discrete samples, as well as an expression for iterative restoration by Newton's method of the values of the samples of the original analog signal on the receiving side, which were not transmitted via the data transmission channel. The conditions for the applicability of the method are established, which consist in the a priori known parameters of the reference signal and the digital filter, which are determined in advance from the known characteristics of the original signal. Filtration and transmission of electrocardiogram signals through communication channels, for which an electrocardiogram can be obtained as a reference form, as the norm for healthy patients, is considered as a problem for the solution of which the proposed method is applicable. The practical significance of the proposed method lies in the organization of distributed computing for IoT systems, for which it is critically important to ensure energy savings of an autonomous power source for sensors and reduce the load on data transmission channels.

Descriptive model for distributed element synchronization digital radio networks of the IEEE 802.11s and IEEE 802.11p standards

Today, the basic radio communication standards for building self-organizing networks such as MANET, VANET and FANET are IEEE 802.11s and IEEE 802.11p. The link layer is responsible for establishing and conducting a communication session in these networks. It includes a variety of procedures, the main of which are synchronization procedures, random multiple media access, reserved media access and transmitter power control of network elements. Moreover, in digital radio communication networks of the IEEE 802.11 standards family, both centralized synchronization and distributed synchronization of such network elements are used. However, in digital radio networks of the IEEE 802.11s and IEEE 802.11p standards, the key procedure for establishing and conducting a communication session is the distributed synchronization of the network data elements. It should be noted that there is no descriptive model of distributed synchronization of the IEEE 802.11s and IEEE 802.11p standards digital radio communication network elements, taking into account these standards features. All elements of the IEEE 802.11s and IEEE 802.11p digital radio network send Beacons on a competitive basis. This occurs cyclically at the start of the repeating sync interval. In this regard, the occurrence of three events is possible: successful transmission of the synchronizing Beacon packet, its collision with a similar packet and a service or user data packet. To prevent (reduce) the number of collisions in a digital radio communication network, it is necessary to maintain a constant time difference between the internal time of all network elements. It is worth noting that maintaining a constant time difference for all digital radio communication network elements through guaranteed and timely sending of synchronizing Beacon packets is the main mechanism for distributed synchronization of such network elements. In the event that the calculated value of the time difference Toffsetni for one of the neighboring elements of the digital radio communication network does not coincide with the analogous value obtained in the past synchronization interval Toffsetni-1, then the correction of the own internal TTSF time of the IEEE 802.11s and IEEE 802.11p standards digital radio communication network element begins. The procedure for adjusting the network element internal time continues until the maximum value of this element internal time offset TMaxClockDrift is equal to zero. Also, to reduce or prevent collisions of synchronizing Beacon packets in the data transmission channel, each network element both initially, when entering the network, and immediately when collisions of synchronizing packets occur, Beacon selects and sets the timing parameters of synchronization so that they do not coincide with similar parameters of neighboring network elements. The developed descriptive model of the IEEE 802.11s and IEEE 802.11p standards digital radio communication network elements distributed synchronization includes algorithms for the such network elements functioning, adjusting the such elements intrinsic internal time, searching for an alternative value for the start time of a repeating synchronization interval and adjusting it. The presented model is applicable in the development of analytical and simulation models for assessing the IEEE 802.11s and IEEE 802.11p standards digital radio communication network performance, taking into account the distributed synchronization of such network elements.

Visible Light Communication with Input-Dependent Noise: Channel Estimation, Optimal Receiver Design and Performance Analysis

In this paper, single-input single-output (SISO) visible light communication (VLC) subject to signal-dependent shot noise (SDSN) is investigated. We discuss both channel estimation and data transmission. In the former, we introduce least square (LS) and maximum likelihood (ML) estimators. Moreover, we derive the Cram´er–Rao lower bound (CRLB) of the channel estimation error. With regard to data transmission, we present optimal and sub-optimal receiver designs and discuss their bit error rate (BER) performance. In particular, a closed-form expression of the BER is derived for a sub-optimal receiver using the on-off-keying (OOK) modulation technique. An approximated expression is then derived for the optimal receiver. Our analysis shows that the CRLB performance does not have a linear relation with the SDSN, thermal noise, or the fading channel. On the other hand, the SDSN has a dramatic effect on the channel estimation error bound, and it can degrade the BER performance. Increased performance degradation can also be noticed due to the joint effects of the channel estimation error and SDSN.

Effect of Node Mobility on MU‐MIMO Transmissions in Mobile Ad Hoc Networks

In this paper, we investigate the expected outage probability and expected throughput of a multi‐user multiple‐input multiple‐output (MU‐MIMO) transmission in mobile ad hoc networks (MANET) in the presence of co‐channel interference and unpredictable inter‐beam interference. In order to achieve multi‐user diversity gain, the receiving nodes are required to report measured channel information to the transmitting node. During the time gap between channel measurement and data transmission, the channel may change with the location of moving nodes. The unpredictable behavior may cause a mismatch between the weight of beams and the instantaneous channel and the inter‐beam interference in the data transmission phase. In order to obtain the closed form expected outage probability, we categorize the behavior of nodes according to whether the inter‐beam interference exists or not and the number of received interference beams. The probability of each category and the closed form outage probability of an instantaneous MU‐MIMO transmission of each category are derived. Additionally, the expected throughput of an MU‐MIMO transmission which changes with the number of receiving nodes is obtained, and the optimal value of receiving nodes to maximize the expected throughput is discussed. Numeric results show the unpredictable inter‐beam interference degrades the outage probability performance. Reducing the duration of the time gap could improve the expected outage probability and expected throughput.

A Novel Successive-Interference-Cancellation- Aware Design for Wireless Networks Using Software-Defined Networking

In traditional CSMA/CA-based MAC designs supporting successive interference cancellation (SIC), channel utilization is inefficient, because the inherited CSMA/CA-style contention approach often forces the whole channel to remain idle and the early released channel is not utilized. In this paper, we propose Multi-CQ, which is the first software-defined networking (SDN)-based MAC design for wireless LANs that supports SIC and significantly improves the channel utilization. Multi-CQ, adopting SDN’s functional separation idea and OFDMA, makes contention and data transmission be executed over two subchannels independently and concurrently, where the superposition coding are used for decoding combined signals, and multiple CQs (contention queues) are introduced to coordinate the concurrency. This concurrent execution greatly reduces the waste in channel contention. Next, adopting SDN’s central control idea, Multi-CQ controller selects nodes who can finish their frame transmissions in almost equal time, thereby improving the channel utilization. Finally, we develop a theoretical model to optimize bandwidth allocation for channel contention and data transmission. Extensive simulations verify the effectiveness of our design and the accuracy of our theoretical model. This study is also helpful to better design wireless MAC protocols supporting other advanced functionalities such as MU-MIMO.

Analysis of Random Access in NB-IoT Networks With Three Coverage Enhancement Groups: A Stochastic Geometry Approach

NarrowBand-Internet of Things (NB-IoT) is a new 3GPP radio access technology designed to provide better coverage for Low Power Wide Area (LPWA) networks. To provide reliable connections with extended coverage, a repetition transmission scheme and up to three Coverage Enhancement (CE) groups are introduced into NB-IoT during both Random Access CHannel (RACH) procedure and data transmission procedure, where each CE group is configured with different repetition values and transmission resources. To characterize the RACH performance of the NB-IoT network with three CE groups, this paper develops a novel traffic-aware spatio-temporal model to analyze the RACH success probability, where both the preamble transmission outage and the collision events of each CE group jointly determine the traffic evolution and the RACH success probability. Based on this analytical model, we derive the analytical expression for the RACH success probability of a randomly chosen IoT device in each CE group over multiple time slots with different RACH schemes, including baseline, back-off (BO), access class barring (ACB), and hybrid ACB and BO schemes (ACB&BO). Our results have shown that the RACH success probabilities of the devices in three CE groups outperform that of a single CE group network but not for all the groups, which is affected by the choice of the categorizing parameters.This mathematical model and analytical framework can be applied to evaluate the performance of multiple group users of other networks with spatial separations.

Design and Implementation of Port Video Terminals Security Access Authentication System Using Blockchain Technology

In the face of the increasing scale of port video surveillance systems, edge computing is gradually used to improve the real-time processing efficiency of surveillance systems and reduce the load on the cloud with the advantages of distributed computing. In order to improve the security factor of terminal access in the edge computing environment, this paper proposes a decentralized terminal security access authentication system based on blockchain, which realizes the identity registration, revocation and mutual authentication of two interfaces between terminal devices and edge computing through the smart contract technology of blockchain, and establishes a trusted channel for data transmission between terminals and edge nodes. Through the functional test of the system and the security analysis of the system on the Hyperledger Fabric platform, it shows that the system has more security attributes and higher security.

Хвилеводно-щілинний фідерний тракт антен з коловою поляризацією

Modern information systems use circularly polarized signals. Among them are tracking systems, remote sensing systems, satellite television systems. The use of circularly polarized signals in satellite communication systems allows to combat multipath propagation of signals in the environment, which reduces interference. By reflecting signals from different objects, they transform their polarization. This makes it possible to reduce signal distortions in the receiving device, which increases the information capacity of wireless data transmission channels. In satellite communications, multi-band horn antennas are widely used. The use of such devices allows transmission of signals with high power and reception of signals with low noise level. Such systems are used as powering a reflector antenna with a wide bandwidth. For such applications, a horn antenna device has been proposed in which signals can be excited that produce left-hand circularly polarized signals and right-hand circularly polarized signals. The proposed horn antenna was powered through a slot that was cut in a rectangular waveguide. Due to the 45º angle of the slot, the antenna can generate signals with double circular polarization. The proposed design can be used without polarizing devices, which must be developed separately. The developed design of the horn antenna at the operating frequency of 16 GHz provides a peak antenna gain of 24 dB for signals with right circular polarization and a peak value of a gain of 18 dB for signals with left circular polarization. The polarization isolation is greater than 12 dB. Moreover, at the operating frequency, the maximum value of the reflection coefficient takes on a value of –17 dB. Thus, the developed waveguide slot feed section for antennas with circular polarization provide rather good characteristics in a narrow frequency band.

Estimation of hardware and time redundancy when using an additive error vector to correct burst errors in digital data transmission systems

In digital data transmission systems, to improve noise immunity, cyclic codes are widely used, detecting and correcting byte (packet) errors. An error packet is understood to mean errors whose multiplicity does not exceed the number of bits b of the information block. Cyclic codes are used to correct byte errors. The most effective method for correcting byte errors are Reed-Solomon codes, which allow correcting errors in a given number of bytes of information. The main problem of using cyclic (sequential) codes is a long delay time associated with the need to perform a division operation to obtain the remainder, which is not acceptable for digital data transmission systems operating in real time. For example, when using the Reed-Solomon code with a code set length of 69 information bits, the implementation of decoding according to the Euclidean algorithm requires 96 clock cycles, which cannot ensure the channel operation in real time. To eliminate this drawback, one should use codes that correct burst errors that implement an algebraic coding procedure with syndromic decoding of information. However, replacing the cyclic procedure for encoding (decoding) information with a syndromic one leads to a sharp increase in hardware costs associated with the use of a memory unit in the decoder for storing error vector values and a decoder for generating error addresses in accordance with the resulting syndrome. Thus, there is a need to develop a methodological apparatus associated with the construction of a code that corrects errors in a given number of bytes of information and an estimate of the hardware and time costs associated with this purpose. In this work, the need to develop a methodological apparatus associated with the construction of a code that corrects errors in a given number of bytes of information with algebraic syndromic decoding and an assessment of the hardware and time costs associated with this purpose is substantiated. The paper presents the rules for constructing a correcting code that corrects errors in a given number of bytes of information, which implements a linear procedure for constructing a correcting code with syndromic decoding and using an additive error vector, which made it possible to reduce hardware costs for constructing a decoding device (to reduce the amount of memory for storing error vector values). For the developed method for correcting byte errors, expressions for evaluating the number are obtained: checking discharges; additive error vectors that do not require their storage in a memory block; error vectors, for burst errors that occur in adjacent bytes at the same time and require their values to be stored in a memory block. A comparative assessment of hardware and time redundancy in the implementation of the proposed method for correcting packet errors with existing methods is carried out. The proposed method of error correction in a given number of bytes of information with additive formation of the error vector differs from the existing ones in that it allows: carry out the correction of burst errors with algebraic-syndromic decoding (exclude the cyclical procedure for encoding and decoding information); to reduce hardware costs for building a decoding device, since in most cases does not require hardware costs for storing error vectors; to reduce the time spent on encoding and decoding information and to ensure the operation of the data transmission channel in real time; to increase the reliability of the transmitted information by detecting uncorrectable byte errors. Thus, the proposed method for correcting errors in a given number of bytes of information with additive formation of an error vector has a regular and relatively simple procedure for constructing a code, which allows one to reduce the hardware and time costs for encoding and decoding information.

Оптимізація розподілу потужностей мережевих каналів на основі алгоритму Орліна

The article proposes an algorithm for solving the problem of optimal distribution of the capacity of data transmission channels between providers and Internet users. A mathematical model of the problem of distribution of a limited homogeneous resource with transport-type constraints is formulated. A solution method based on Orlin's stream algorithm is considered. A practical application of the algorithm for solving a real distribution problem is proposed. The results of the capacity of the channels of the computer network are obtained with a perspective increase in the capacity of the connections represented by the intervals of the planned changes. An analysis of the solutions obtained with different number of switching servers was made, conclusions about the choice of the provider to meet the optimal information needs of users were made.

Встраивание информации в JPEG-изображения с маскировкой искажений в частотной области

Steganography allows to ensure the confidentiality of information by organizing covert data transmission channels. However, the effectiveness of steganographic information protection directly depends on the invisibility of a secret message, both for the human eye and for steganalysis methods. The paper proposes an approach that allows solving the problem of vulnerability of the popular QIM embedding method to statistical steganalysis. For this, it is proposed to use a variable quantization step, which is adaptively selected for each block of the JPEG cover image. The experimental results demonstrate an increase in the security level of steganographic embedding due to the application of the proposed approach.

Low-RCS and Wideband Reflectarray Antenna With High Radiation Efficiency

Intelligent reflecting surface (IRS) is a promising new paradigm to achieve high spectral and energy efficiency for future wireless networks by reconfiguring the wireless signal propagation via passive reflection. To reap the potential gains of IRS, channel state information (CSI) is essential, whereas channel estimation errors are inevitable in practice due to limited channel training resources. In this paper, in order to optimize the performance of IRS-aided multiuser systems with imperfect CSI, we propose to jointly design the active transmit precoding at the access point (AP) and passive reflection coefficients of IRS, each consisting of not only the conventional phase shift and also the newly exploited amplitude variation. First, the achievable rate of each user is derived assuming a practical IRS channel estimation method, which shows that the interference due to CSI errors is intricately related to the AP transmit precoders, the channel training power and the IRS reflection coefficients during both channel training and data transmission. Then, for the single-user case, by combining the benefits of the penalty method, Dinkelbach method and block successive upper-bound minimization (BSUM) method, a new penalized Dinkelbach-BSUM algorithm is proposed to optimize the IRS reflection coefficients for maximizing the achievable data transmission rate subjected to CSI errors; while for the multiuser case, a new penalty dual decomposition (PDD)-based algorithm is proposed to maximize the users' weighted sum-rate. Simulation results are presented to validate the effectiveness of our proposed algorithms as compared to benchmark schemes. In particular, useful insights are drawn to characterize the effect of IRS reflection amplitude control (with/without the conventional phase shift) on the system performance under imperfect CSI.

Centrally Reserved Access Model to the Medium in Digital Radio Communication Networks

Currently, centrally reserved access to the medium in the digital radio communication networks of the IEEE 802.11 family standards is an alternative to random multiple access to the environment such as CSMA/CA and is mainly used in the transmission voice and video messages in real time. Centrally reserved access to the environment determines the scope of interest in it from attackers. However, the assessment of effectiveness of centrally reserved access to the environment under the conditions of potentially possible destructive impacts was not carried out and therefore it is impossible to assess the contribution of such impacts to the decrease in the effectiveness of such access. Also, the stage establishing of centrally reserved access to the environment was not previously taken into account. Analytical model development of centrally reserved access to the environment under the conditions of destructive influences in digital radio communication networks of the IEEE 802.11 family standards. A mathematical model of centrally reserved access to the environment has been developed, taking into account not only the stage of its functioning, but also the stage of formation under the conditions of destructive influences by the attacker. Moreover, in the model the stage of establishing centrally reserved access to the medium displays a sequential relationship of such access, synchronization elements in digital radio communication networks and random multiple access to the medium of the CSMA/CA type. It was established that collisions in the data transmission channel caused by destructive influences can eliminate centrally reserved access to the medium even at the stage of its establishment. The model is applicable in the design of digital radio communication networks of the IEEE 802.11 family of standards, the optimization of such networks of the operation, and the detection of potential destructive effects by an attacker.

OPTO-ULTRASONIC COMMUNICATION CHANNELS

Ultrasound is widely used in various applications, such as monitoring the state of structures, biomed-ical ultrasound imaging, and information (data) transmission. Ultrasonic transceivers are one of the modern communication systems, both for short-range and remote access. Indeed, the technology of the process of transmitting information using communication channels based on ultrasonic (US) vi-brations and the physical implementation of transmission using optical fiber are widely used in con-ditions of confidentiality of data processing. At the same time, the needs of wireless and wired communication demanded the development of more advanced applications (software, hardware solutions). In particular, new challenges have arisen requiring transceivers to have high frequency, wide bandwidth and compact size. Aim. Consider the “technology – opto-ultrasonic” approach used in data transmission and reception channels. This technology involves the generation of ultrasound by a pulse using the optical-acoustic effect, followed by the reception and processing of ultrasonic vibrations. Optical ultrasonic transceivers based on the photo-acoustic (US) principle of operation have great potential, in particular, to obtain the necessary: (super high) frequency of the transmitted signal; wide bandwidth (speed); ease of use as transceivers; low manufacturing cost. Materials and methods. Various methods of spectral analysis (Fourier and Wavelet) have been in-vestigated to ensure the achievement of the above goal. Results. Compared to traditional technolo-gies of information reception and transmission, optical ultrasonic transceivers provide high-frequency communication, wide bandwidth and compact size. Conclusion. The paper investigates the methods of spectral analysis (Fourier and Wavelet) and proposes, based on these studies, possi-ble options for the implementation of optical ultrasonic transceivers that can generate ultrasonic pulses with a duration on a nanosecond scale using an ultrafast laser and receive confidential data with a high degree of security. At the same time, by combining the principle of generating photo-acoustic ultrasound with the use of optical fiber, it is possible to obtain compact and inexpensive ul-trasonic transceivers.

RACH in Self-Powered NB-IoT Networks: Energy Availability and Performance Evaluation

NarrowBand-Internet of Things (NB-IoT) is a new 3GPP radio access technology designed to provide better coverage for a massive number of low-throughput low-cost devices in delay-tolerant applications with low power consumption. To provide reliable connections with extended coverage, a repetition transmission scheme is introduced to NB-IoT during both Random Access CHannel (RACH) procedure and data transmission procedure. To avoid the difficulty in replacing the battery for IoT devices, the energy harvesting is considered as a promising solution to support energy sustainability in the NB-IoT network. In this work, we analyze RACH success probability in a self-powered NB-IoT network taking into account the repeated preamble transmissions and collisions, where each IoT device with data is active when its battery energy is sufficient to support the transmission. We model the temporal dynamics of the energy level as a birth-death process, derive the energy availability of each IoT device, and examine its dependence on the energy storage capacity and the repetition value. We show that in certain scenarios, the energy availability remains unchanged despite randomness in the energy harvesting. We also derive the exact expression for the RACH success probability of a randomly chosen IoT device under the derived energy availability, which is validated under different repetition values via simulations. We show that the repetition scheme can efficiently improve the RACH success probability in a light traffic scenario, but only slightly improves that performance with very inefficient channel resource utilization in a heavy traffic scenario.

Spectral Efficiency Optimization of Massive MIMO System Under Channel Varying Conditions

In this paper, the performance of the cell free Massive multiple-input multiple-output (MIMO) system with realistic channel impairment conditions is discussed. The channel impairment conditions arise due to various issues like the pilot contamination, high speed user mobility, accumulated phase noise and Doppler shifts etc. At first, we provided a system model with channel aging due to Doppler shift, during uplink and downlink for channel estimation and data transmission. An optimization objective problem is formulated to improve the joint spectral efficiency during both uplink and downlink. The primary objective problem is partitioned into two different sub-problems, which are solved by a user defined joint frame allocation and user matching (JFAUM) algorithm based on efficient allocation of pilot resources and matching techniques for user clustering. Finally, the numerical results prove the improvement in spectral efficiency of massive MIMO system by using the proposed JFAUM algorithm under various practical conditions.