Resource Elements Research Articles

A Simple and Low-Cost Technique for 5G Conservative Human Exposure Assessment

The purpose of this paper is to introduce a simple, low-cost methodology for estimating a conservative value of the maximum field level that can be radiated by a 5G base station useful for human exposure assessment. The method is based on a Maximum Power Extrapolation (MPE) approach and requires the measurement of a reference quantity associated with the SS-PBCH, such as Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), Physical Broadcast CHannel (PBCH), or PBCH Demodulation Reference Signal (PBCH-DMRS). This step requires a simple spectrum analyzer and allows one to obtain the Resource Element (RE) power of a signal transmitted through broadcast beams. In the second phase, the RE power of the signal transmitted through the traffic beam is estimated using the Cumulative Distribution Function (CDF) of the antenna boost factor obtained from the broadcast and the traffic envelope radiation patterns made available by the base station vendor. The use of the CDF allows us to mitigate the problems related to the exact estimation of the direction of the measurement point with respect to the beam of the 5G antenna. The method is applied to a real 5G communication system, and the result is compared with the value given by other MPE methods proposed in the literature.

Analysis on The Effect of Channel Bandwidth Occupying in LTE Frequency Band on Throughput

The maximum channel capacity of a 4G LTE network will be directly correlated to the channel bandwidth that occupies a certain radio frequency on that network. The number of Resource Blocks (RB), subcarriers, and Resource Elements (RE) as channel resources available to serve users concurrently will depend on the bandwidth channel sizes. Mobile service providers in Indonesia provide scalable channel bandwidth LTE 4G networks on a variety of frequency bands, including adjacent and non-adjacent bands. In this study, it was examined how to channel bandwidth, which changes at 10MHz, 15MHz, and 20MHz, affects throughput to give user equipment the best possible performance (UE). This study makes use of actual measurement data from installed and active eNodeB or cells obtained via the drive test approach. According to the test, each channel's maximum throughput varies, however, there is no linear relationship found between channel bandwidth expansion and throughput. The 20MHz channel bandwidth, which is located in the 2300MHz frequency band, has a maximum throughput value of 64666.80 kbps.

Codebook Design for PD-SCMA NOMA Systems

The hybrid power domain sparse code non-orthogonal multiple access (PD-SCMA) scheme multiplexes multiple users on a single resource element (RE) both in power and code domains, thus achieving a superior spectral efficiency. The multiplexing performance of such a scheme can be enhanced not only through deployment of sophisticated resource allocation schemes and low complexity robust multi-user detectors but also prudent multi-user multi-dimensional codebook design. By considering the key codebook design performance indicators (KPIs) in different channel use scenarios, this work assesses various known multi-dimensional constellation (MDC) design criterion on the performance of low-rate turbo-coded PD-SCMA NOMA system. In order to strike a balance with regard to good multi-dimensional modulation (MDM) and low complex detection, a low complex codebook design based on linear error correcting block codes is proposed. Unique user-specific rotation design based on quaternion rotation matrices is proposed with the aim of maintaining users symbol uniqueness for overloaded systems. Simulation results confirm that MDCs that satisfy design KPIs outperform others. Besides, the proposed user-specific rotation design remarkably enhances the BER performance of the block code based codebook design.

A Low-Complexity Codebook Design Scheme for SCMA Systems Over an AWGN Channel

As a promising wireless access technique, sparse code multiple access (SCMA) directly maps the input bits to the transmitted multidimensional codewords according to the SCMA codebook. In general, SCMA codebook optimization and detector simplification are independent of each other. In this article, we propose a simplified SCMA codebook with a separable structure for implementing a low-complexity detector. For codebook design, a separable codebook structure is proposed to simplify the maximization of the minimum Euclidean distance (MED). With this structure, multiple one-dimensional complex codebooks corresponding to one resource element (RE) are determined by maximizing the MED of the superimposed codewords. Then, the entire codebook set is obtained based on a structure indicator matrix and the separable codebook structure. The proposed codebook has a larger MED than obtained by existing codebooks. Benefiting from the separable codebook structure, the signals transmitted over each RE can be independently used to recover the corresponding input bit information. Therefore, we propose a parallel maximum a posteriori (P-MAP) detector consisting of several low-complexity MAP detectors to reduce the complexity of the conventional multiuser message passing (MP) detector in SCMA. At the receiver, each RE is assigned a low-complexity MAP detector. Simulation results show that the proposed codebook outperforms the known optimal codebook over an AWGN channel. Moreover, the run time of the P-MAP detection algorithm is reduced by 99.8% compared to the Log-MPA algorithm. With the proposed codebook design scheme and the P-MAP detector, an SCMA unit can be separated into two independent non-SCMA units, which significantly increases system flexibility.

Capability-based machine layout with a matheuristic-based approach

Capability-based machine layout (CB-ML) problem is firstly introduced in this paper. In the conventional machine layout problem, part flow matrix is generated from parts’ machine routes to minimize total part flows. However, defining part flow matrix based on the machines’ routes (instead of processing capability requirements of parts) restricts facility designers to utilize available flexibility in manufacturing systems. In this research, parts’ processing requirements are defined in terms of Resource Elements (REs), which describe unique processing capabilities and the processing capability overlaps of machines. If part flow matrix is defined in terms of REs, it becomes possible to utilize available flexibility in a more effective manner. However, physical part flows cannot be identified directly from the RE-based flow matrices. Because, the processing requirements of manufactured parts can be satisfied from alternative machines that contain the required REs. Therefore, RE-based part flow matrix must be mapped into the machine flow matrix, which requires defining the machine flow matrix as a decision variable. This makes the proposed CB-ML problem much more complicated than the conventional machine layout problem. We firstly developed an integer non-linear programming model for the proposed CB-ML problem. Because of its NP-completeness and nonlinear structure, a matheuristic-based solution approach is also developed. The extensive computational analysis have shown that the proposed approach is able to provide good quality solutions for the larger problem instances within reasonable computation times.

User Activity Detection for Irregular Repetition Slotted Aloha Based MMTC

Irregular repetition slotted aloha (IRSA) is a grant-free random access protocol for massive machine-type communications, where a large number of users sporadically send their data packets to a base station (BS). IRSA is a completely distributed multiple access protocol: in any given frame, a small subset of the users, i.e., the active users, transmit replicas of their packet in randomly selected resource elements (REs). The first step in the decoding process at the BS is to detect which users are active in each frame. To this end, a novel Bayesian user activity detection (UAD) algorithm is developed, which exploits both the sparsity in user activity as well as the underlying structure of IRSA-based transmissions. Next, the Cramer-Rao bound (CRB) on the mean squared error in channel estimation is derived. It is empirically shown that the channel estimates obtained as a by-product of the proposed UAD algorithm achieves the CRB. Then, the signal to interference plus noise ratio achieved by the users is analyzed, accounting for UAD, channel estimation errors, and pilot contamination. The impact of these non-idealities on the throughput of IRSA is illustrated via Monte Carlo simulations. For example, in a system with 1500 users and 10% of the users being active per frame, a pilot length of as low as 20 symbols is sufficient for accurate user activity detection. In contrast, using classical compressed sensing approaches for UAD would require a pilot length of about 346 symbols. The results also reveal crucial insights into dependence of UAD errors and throughput on parameters such as the length of the pilot sequence, the number of antennas at the BS, the number of users, and the signal to noise ratio.

Methodology Based on Vector and Scalar Measurement of Traffic Channel Power Levels to Assess Maximum Exposure to Electromagnetic Radiation Generated by 5G NR Systems

Maximum-Power Extrapolation (MPE) for mobile telecommunication sources follows an established paradigm based on the identification and measurement of a channel that acts as a power reference. Prior to the 5G era, the role of reference channel has been played by always-on broadcast signals since they had the great advantage of being always transmitted at the maximum power level allowed for a generic signal channel. However, the beamforming implemented by 5G sources obliges us to rethink this approach. In fact, with beamforming the 5G source can transmit data traffic streams through a beam characterized by a much higher gain than the broadcast one. This implies that the detected power for traffic beams could be much higher than the corresponding power of broadcast beams. In this paper, a novel approach for 5G MPE procedure is presented, where the direct measurement of the received power of a traffic beam is used to assess the maximum exposure generated by a 5G system. An innovative specific experimental setup is also proposed, with the use of a User Equipment (UE) with the aim of forcing the traffic beam toward the measurement positions. In this way, it is possible to directly measure the power of each Resource Element (RE) transmitted by the traffic beam. As opposed to other MPE proposals for 5G, the discussed technique does not require any correction of the measured data since it relies only on the traffic beam pointing toward the measurement position, simplifying the overall MPE procedure and thus reducing the uncertainty of the MPE estimated field strength.

Low-latency resource elements scheduling based on deep reinforcement learning model for UAV video in 5G network

We consider the problem of resource elements allocation in a network environment with multiple users. Previous studies have done a lot of works using traditional methods in terms of bandwidth allocation, which is sufficient to serve for 4G network. However, it cannot be neglected to provide more efficient and intelligent scheduling policies in haste, due to growing demands on high resolution video and image transmission in 5G network. To fit the condition taking resource elements as scheduling unit in 5G network, we proposed deep Q network (DQN) algorithm based on the requirement of low time latency and high resource utilization rate to solve resource elements (RE) scheduling problem. Ultimately, we give out the optimal allocation scheme of resource elements (RE) for four users in fixed condition of time latency and resource utilization rate.

Accurate determination of transport block size for 5G new radio

The data payload from the medium access control layer to the physical layer is referred to as the transport block (TB). In fifth-generation new radio, the TB size is determined by using a formula due to large variations of available resource elements (REs) per resource block (RB). To ensure that a matching TB size can easily be scheduled in the retransmission instance, the reference number of REs is used to determine the TB size. As a result, the actual code rate may be much higher than the target code rate. This degrades the performance of the channel coding and increases the likelihood of the decoding failure. To solve these problems, the authors quantise the number of REs within the scheduled duration that are not available for the data transmission and the demodulation reference signal transmission. The difference between the reference number of REs of the traditional scheme and the quantised number is used to determine the TB size in the proposed scheme. Compared to the traditional scheme, the proposed scheme reduces the difference between the actual code rate and the target code rate.

Extensionless Adaptive Transmitter and Receiver Windowing of Beyond 5G Frames

Newer cellular communication generations are planned to allow asynchronous transmission of multiple numerologies (waveforms with different parameters) in adjacent bands, creating unavoidable adjacent channel interference. Most prior work on windowing assume additional extensions reserved for windowing, which does not comply with standards. Whether windowing should be applied at the transmitter or the receiver was not questioned. In this work, we propose two independent algorithms that are implemented at the transmitter and receiver, respectively. These algorithms estimate the transmitter and receiver windowing duration of each resource element (RE) with an aim to improve fair proportional network throughput. While doing so, we solely utilize the available extension that was defined in the standard and present standard-compliant algorithms that also do not require any modifications on the counterparts or control signaling. Furthermore, computationally efficient techniques to apply per-RE transmitter and receiver windowing to signals synthesized and analyzed using conventional cyclic prefix orthogonal frequency division multiplexing are derived and their computational complexities are analyzed. The spectrotemporal relations between optimum window durations at either side, as well as functions of the excess signal to noise ratios, the subcarrier spacings and the throughput gains provided over previous similar techniques are numerically verified.

An Efficient Codebook Design for Uplink SCMA

Sparse code multiple access (SCMA) is one of the most intensively investigated non-orthogonal multiple access (NOMA) techniques for the fifth generation communication (5G) system. In this paper, a new multi-stage optimization approach for codebook design is proposed for the uplink SCMA system. The proposed schemes includes two parts: i) multi-dimensional mother constellation design ii) mapping matrix design. Firstly, the multi-dimensional complex mother constellation design is implemented by a series of two-dimensional real constellations which can be obtained by the lattice theory and the symbol switch algorithm (SSA). The Secondly, we construct user-specific mapping matrix by optimizing the phase rotation of the user constellation to effectively reduce the interference between the multi-user codewords superimposed on every single time-domain resource elements (REs). Finally, the multi-user codebooks are generated by combining the multi-dimensional mother constellation and the user-specific mapping matrix. The simulation results demonstrate that the proposed codebooks can greatly decrease bit error rate (BER) value compared to the existing codebooks under different channels, different codebook sizes and different overloading ratios, and the performance is also improved for the large-scale SCMA codebook. More importantly, in order to verify the proposed codebook applicability, two different message passing algorithm (MPA) are used to simulate the SCMA system with different codebook sizes, both of which obtain faster convergence speed and better BER performance than other existing codebooks.

Biological Resource Allocation Algorithms for Heterogeneous Uplink PD-SCMA NOMA Networks

Due to their ability to multiplex users on a resource element (RE), Non-orthogonal multiple access (NOMA) techniques have gained popularity in 5G network implementation. The features of 5G heterogeneous networks have necessitated the development of hybrid NOMA schemes combining the merits of the individual NOMA schemes for optimal performance. The hybrid technologies on 5G networks make complex air interfaces resulting in new resource allocation (RA) and user pairing (UP) challenges aimed at limiting the multiplexed users interference. Furthermore, common analytical techniques for evaluating the performance of the schemes lead to unrealistic network performance bounds necessitating alternative schemes. This work explores the feasibility of a hybrid power domain sparse code non-orthogonal multiple access (PD-SCMA). The scheme integrates both power and code domain multiple access on an uplink network of small cell user equipments (SUEs) and macro cell user equipments (MUEs). Alternative biological RA/UP schemes; the ant colony optimization (ACO), particle swarm optimization (PSO) and a hybrid adaptive particle swarm optimization (APASO) algorithms, are proposed. The performance results indicate the developed APASO outperforming both the PSO and ACO in sum rate and energy efficiency optimization on application to the PD-SCMA based heterogeneous network.

Random Pattern Multiplexing for Random Access in IoT-Oriented Satellite Networks

In this paper, random pattern multiplexing (RPM) for random access (RA) is proposed to improve the throughput in Internet of Things-oriented satellite networks. The pattern is defined as the mapping scheme of packet onto a resource block (RB) that consists of multiple resource elements (REs). The patterns are randomly selected by active satellite machine-type-communication terminals (SMTs) from a set of available patterns, and are employed to differentiate signals of different SMTs sharing a RB. Message passing detection algorithm is employed to decode multiple superimposed packets, which enables multiple packet reception capability in the RA scheme. The proposed RPM can be combined with contention resolution diversity slotted ALOHA (CRDSA), which generates RPM–CRDSA protocol. In this protocol, the interference cancellation technique can be carried out across RBs to remove the received signals that are already decoded, which further improves the throughput. The performance of RPM–CRDSA is evaluated via mathematical analysis and computer simulation. The probability of preamble collision and an upper bound of throughput are derived, respectively. Simulation results show that the peak normalized throughput of RPM–CRDSA with $N = 4$ REs can reach 2.03 b/symbol, which largely outperforms traditional protocols.

Application of Non-Orthogonal Multiple Access in Wireless Sensor Networks for Smart Agriculture

Agriculture is one of the main economic industries of a country. Application of information technologies in agriculture, smart agriculture, aims to realize precision control of irrigation, fertilizer, diseases, and insect pests prevention in the growing of crops. For the sake of obtaining the interest data, wireless sensor networks (WSNs) are used to collect the interest data in the farm field and send the obtained data to the servers via wireless communication. Since the WSNs usually operate in the unlicensed spectrum, the available resource elements (REs) are scarce especially when a large number of sensor nodes are deployed in the farm field. To accommodate more sensor nodes and prolong the lifetime of the WSNs in agriculture, relay-aided non-orthogonal multiple access is introduced into the uplink transmission stage of the direct transmission from the sensor nodes to the sink node. Non-orthogonal multiple access (NOMA) can transmit multiple symbols simultaneously on the same RE by splitting them in the power domain and distinguish them according to diverse power levels of different symbols. The average sum data rate and outage probability of the relay-aided NOMA in uplink transmission are theoretically analyzed. The numerical simulation results show that the WSNs with relay-aided NOMA outperforms the traditional OMA scheme in uplink transmission in WSNs in agriculture.

Optimal Design of Resource Element Mapping for Sparse Spreading Non-Orthogonal Multiple Access

We propose a new design of the optimal resource element (RE) mapping patterns to maximize the sum-rate of a sparse spreading non-orthogonal multiple access system. In this system, the grouped users who use the same radio resource have different channel conditions. First, we formulate a sum-rate optimization problem subject to sparsity and power constraints. To solve this non-trivial optimization problem, we transform it to an equivalent penalized problem by deriving the closed-form penalty parameters. We then convert this problem to a sequence of subproblems using the difference of convex programming and propose an efficient algorithm to find the optimal solution. Numerical results demonstrate that the proposed algorithm achieves a higher sum-rate and a superior block error rate performance than the conventional RE mapping schemes.

Enabling Sphere Decoding for SCMA

In this paper, we propose a reduced-complexity optimal modified sphere decoding (MSD) detection scheme for SCMA. As SCMA systems are characterized by a number of resource elements (REs) that are less than the number of the supported users, the channel matrix is rank-deficient, and sphere decoding (SD) cannot be directly applied. Inspired by the Tikhonov regularization, we formulate a new full-rank detection problem that it is equivalent to the original rank-deficient detection problem for constellation points with constant modulus and an important subset of non-constant modulus constellations. By exploiting the SCMA structure, the computational complexity of MSD is reduced compared with the conventional SD. We also employ list MSD to facilitate channel coding. Simulation results demonstrate that in uncoded SCMA systems the proposed MSD achieves the performance of the optimal maximum likelihood (ML) detection. Additionally, the proposed MSD benefits from a lower average complexity compared with MPA.

Influence of overhead on LTE downlink performance: a comprehensive model

Overhead resource elements (REs) in Long Term Evolution (LTE) networks are used for some control, signaling and synchronization tasks at both the Physical level and Media Access Control sub-level. Accurately computing all the overhead REs is necessary to achieve an efficient system design, which is difficult because LTE is a complex standard that contains a large number of implementation flexibilities and system configurations. The number of such REs depends on both the system configurations and services demanded. Aiming at exploring the influence of overhead on LTE downlink performance, we first parametrize each system configuration—including parameters corresponding to enhancement techniques such as Adaptive Modulation and Coding and Multi-Antenna Transmissions techniques—and those of the resource allocation mechanisms (which depend on users’ services). Second, using such parametrization, we model all overheads for synchronization, controlling and signaling operations in LTE Physical Downlink Shared/Control Channels. This allows for dynamically computing the useful REs (by subtracting the overhead REs from the total ones), both per Transmission Time Interval (TTI) and per frame (and hence, the corresponding bit rates). Our data rate-based performance model is able to accurately compute: (1) the real, exact system data rate or “throughput” (instead of approximations); and (2) the maximum number of simultaneous multi-service users per TTI that is able to support (called here “capacity”). Aiming at understanding the impact of each overhead mechanism, we have carried out a variety of simulations, including different service provision scenarios, such as multi-user with multi-application. The simulation results prove our starting hypothesis that the influence of overhead on LTE performance should not be neglected. The parametrized and dynamic model quantifies to what extent throughput and capacity are modified by overhead—under a combination of system configurations and services, and may provide these performance metrics, throughput and capacity, as inputs to planning, dimensioning and optimization specialized tools.

CRS interference cancellation algorithm for heterogeneous network

Heterogeneous network is introduced to improve the network capacity in LTE Release 9 and system beyond. The potential traffic congestion due to increased users can be alleviated by the cooperation between macro-cell and pico-cell. However, the inter-cell interference caused by RF signal from macro-cell will reduce the performance severely. Enhanced inter-cell interference coordination is proposed in Rel. 10 to solve this problem using almost blank subframe (ABS). Yet, the cell specific reference signal in ABS can still cause interference to the data resource element (RE) from the pico-cell inevitably for non-colliding scenario. In this Letter, a novel interference cancellation (IC) algorithm is proposed to mitigate the interference. First, the timing and carrier frequency offset of interference signal is estimated and compensated. Second, the interfering channel response is estimated by utilising the channel statistics. Third, the interference signal is reconstructed based on the channel estimation and cancelled in the received signal in time domain. The experiment results show that the performance of proposed IC algorithm is robust.

FAST DETECTION OF NUMBER OF ANTENNA PORTS IN LTE SYSTEM

In LTE system, during initial cell selection UE is unaware about the number of antennas used by eNB for transmission. So, UE blindly tries multiple times to detect the right number of antennas used for transmission in the system. This wastes lot of time and UE processing power, as UE needs to do channel estimation, equalization/demodulation, decoding process multiple times with assumption of 1 or 2 and 4 antenna ports each time. The objective of this paper is to find out a faster and efficient method for detecting the number of antenna ports used by the eNB for signal transmission. A new method is explored for detecting the number of eNB transmit antennas before starting PBCH decoding and CRC checking by exploiting the presence of downlink reference signals at various Resource Element (RE) positions in the Resource Blocks (RB) and using the PBCH SFBC data patterns. This helps for faster detection of number of antennas used for transmission that in turn helps to reduce the UE power consumption as well as reduces the initial cell search time.

RE-Based Weighted Distributed Equipment Layout

Recent industry research shows that the existing layout configuration can not satisfy complex manufacturing of many production types. New layout strategy, especially distributed layout received more attention, has the potential to cope with demand interference. This paper attempts to use the method of resource element (RE) to consider equipment production capacity to design weighted distributed layout. Give a more explicit description of unique and common processing ability of devices and parts processing requirements. Considering the weights between REs and make more relevant REs adjacent, using genetic algorithm to construct RE-based weighted distributed layout, minimizing the total weighted minimum distance between REs to minimize material transportation costs.