Users In Uplink Research Articles

Decoupled Association With Rate Splitting Multiple Access in UAV-Assisted Cellular Networks Using Multi-Agent Deep Reinforcement Learning

In unmanned aerial vehicles (UAVs) assisted cellular networks, user association plays an important role in interference control and spectrum efficiency. In this paper, we study the performance of uplink-downlink decoupled (UDDe) user association in a multi-UAV assisted network in which each user can associate with different UAVs or the macro base station (MBS) for uplink (UL) and downlink (DL) transmissions. Since some popular data may be requested by multiple users, grouping these users and applying multicasting can significantly improve spectral efficiency. Unlike traditional linear precoding that treats interference entirely as noise, we propose a rate-splitting multiple access (RSMA) policy that employs rate splitting at the transmitter and successive interference cancellation (SIC) at the receiver. To be specific, the transmitted signal is split into a common part and a private part, and the interference is partially decoded and partially treated as noise. In this context, we formulate a joint optimization problem of UL-DL association and beamforming for maximizing the sum-rate of users in UL and that of multicast groups in DL under the constraints of UAV backhaul capacity and power budget. Since the formulated problem is non-convex with intricate states and an individual UAV may not know the rewards of other UAVs, we convert it into a robust partially observable Markov decision process (POMDP). Then we resort to multi-agent deep reinforcement learning (MADRL) that enables each UAV to learn and optimize its policy in a distributed manner. To achieve an optimal policy, we further propose an improved clip and count-based proximal policy optimization (PPO) algorithm to train actor and critic networks. Simulation results demonstrate the superiority of the proposed decoupled association strategy with RSMA and the MADRL learning algorithm.

QoS-Aware Content Dissemination Based on Integrated Social and Physical Attributes Among Cellular and V2V Users

With the recent advancement in intelligent transportation systems (ITS), the vehicular network has become the major force in content dissemination, and it is essential to improve efficiency in content delivery and quality and service (QoS). The rapid growth in vehicular data traffic and limited resources in the vehicular network have created a bottleneck in content dissemination. In addition, the demand of high data rate, low latency and user's satisfaction on content make content dissemination more challenging. To address the above problem which involves vehicle to vehicle (V2V) peer discovery and resource allocation, we propose an efficient content dissemination scheme which integrates both social and physical attributes of the users. V2V users are paired to share content based on the similarity in their preferences and link reliability, while considering the QoS of vehicle to network (V2N) users in both uplink and downlink phases. Moreover, we present an improved matching algorithm for channel allocation, which maximizes the sum rate of V2V pairs weighted by the intensity of their social relationship. Simulation results demonstrate the performance of the proposed scheme in terms of weighted sum rate and user's satisfaction on content.

5G uplink interference simulations, analysis and solutions: The case of pico cells dense deployment

The launch of the new mobile network technology has paved the way for advanced and more productive industrial applications based on high-speed and low latency services offered by 5G. One of the key success points of the 5G network is the available diversity of cell deployment modes and the flexibility in radio resources allocation based on user’s needs. The concept of Pico cells will become the future of 5G as they increase the capacity and improve the network coverage at a low deployment cost. In addition, the short-range wireless transmission of this type of cells uses little energy and will allow dense applications for the internet of things. In this contribution, we present the advantages of using Pico cells and the characteristics of this type of cells in 5G networks. Then, we will do a simulation study of the interferences impact in uplink transmission in the case of PICO cells densified deployment. Finally, we will propose a solution for interference avoidance between pico cells that also allows flexible management of bands allocated to the users in uplink according to user’s density and bandwidth demand.

Massively Concurrent Non-Orthogonal Multiple Access for 5G Networks and Beyond

We propose a new signal spreading-based non-orthogonal multiple access (NOMA) schemes that exploits the frame-theoretic design principles to enable the efficient concurrence of multiple users in both downlink (DL) and uplink (UL). In contrast to many other NOMA schemes, the proposed method does not require built-in sparsity on the usage of resources by any individual users, hence referred to as massively concurrent non-orthogonal multiple access (MC-NOMA). Instead, MC-NOMA leverages frames as vectorized ensembles of the individual complex-valued waveform signatures, optimized for low mutual coherence so as to minimize the multi-user interference. A theoretical analysis of the MC-NOMA is offered, which reveals that it can theoretically reach the capacity of the multi-user MIMO channel and outmatches the state of the art in terms of maximum achievable rate over discrete constellations. A detailed description of both the frame-based transmitter design and a newly developed low-complexity efficient decoder is given, which, via simulations, are used to demonstrate that MC-NOMA outperforms the well-established NOMA schemes, such as sparse-coded multiple access (SCMA) and pattern division multiple access (PDMA).

Joint power allocation and subcarrier assignment for device to device in 5G time division duplex networks

The explosive demands for mobile broadband service bring a major challenge to 5G wireless networks. Device-to-device communication, adopting side links for user-direct communication, is regarded as a main technical source for offloading large volume of mobile traffic from cellular base station. This article investigates the joint power and subcarrier allocation scheme for device-to-device communication in 5G time division duplex systems. In time division duplex system, instead of utilizing an exclusive portion of the precious cellular spectrum, device-to-device pairs reuse the subcarriers occupied by cellular users, thus producing harmful interference to cellular users in both uplink and downlink communication, and strongly limiting the spectrum efficiency of the system. To this end, we focus on the maximization of device-to-device throughput while guaranteeing both uplink and downlink channel quality of service of cellular users as well as device-to-device pairs. The problem is formulated as a mixed integer non-linear programming (MINLP) problem. To make it tractable, we separate the original MINLP problem into two sub problems: power allocation and sub-carrier reusing. The former is to develop optimal power allocation for each device-to-device pair and each cellular user, with the constraints of maximum power and quality of service. It is solved by geometric programming technique in convex optimization method. The latter is derived as a one-to-many matching problem for scheduling multiple subcarriers occupied by cellulars to device-to-device pairs. It is solved by Hungarian method. Simulation results show that the proposed scheme significantly improves system capacity of the device-to-device underlay network, with quality of service of both device-to-device users and cellular users guaranteed.

AN EFFICIENT CFO ESTIMATION AND ICI REDUCTION IN MC-CDMA SYSTEM THROUGH CONJUGATE WEIGHTED MUSIC BASED RPRCC SCHEME

Multicarrier code division multiple access (MC-CDMA) is one of the most attractive method for future broadband wireless systems and long term evolution (LTE) standard. The performance of MC-CDMA systems is greatly deteriorated by carrier frequency offset (CFO) which is due to oscillator instability and Doppler shifts. CFO leads to loss of orthogonality between the subcarriers and introduces intercarrier interference (ICI). Among the numerous ICI cancellation techniques, the proposed receiver phase rotated conjugate cancellation (RPRCC) offers greater ICI reduction compared to other methods. The distributed nature of networks and concurrent transmission from multiple users in uplink, RPRCC needs multiple frequency offset estimation at the receiver. Multiple signal classification (MUSIC) algorithm is the best suited CFO estimation technique in multiuser environment. However the performance of MUSIC algorithm is inferior for closely spaced CFOs. To achieve precise CFO estimation and greater ICI reduction, RPRCC with conjugate weighted MUSIC based CFO estimation is proposed in this paper. The simulation results depict that the ICI power reduction capability and BER performance of the suggested method outperforms the conventional techniques in both properly and closely spaced CFOs.

Wireless Powered Communications With Initial Energy: QoS Guaranteed Energy-Efficient Resource Allocation

This letter considers a wireless powered communication network (WPCN) where users first harvest energy in the downlink (DL) and then use the energy to transmit information signals in the uplink (UL). Furthermore, each user is also equipped with some initial energy, which generalizes the previous works on energy transfer and initial energy. Our goal is to maximize the system energy efficiency while guaranteeing the user's quality of service via joint time allocation and power control in both DL and UL. We find that the power station always transmits with the maximum power in DL while the transmit power of users in UL follows the waterfilling structure. In addition, the time allocation between DL and UL can be simplified into a linear programming problem. Finally, we propose an efficient algorithm to obtain the optimal solution. Simulation results demonstrate the system EE analysis for the WPCN as well as the special cases.

Cognitive and Energy Harvesting-Based D2D Communication in Cellular Networks: Stochastic Geometry Modeling and Analysis

While cognitive radio enables spectrum-efficient wireless communication, radio frequency (RF) energy harvesting from ambient interference is an enabler for energy-efficient wireless communication. In this paper, we model and analyze cognitive and energy harvesting-based device-to-device (D2D) communication in cellular networks. The cognitive D2D transmitters harvest energy from ambient interference and use one of the channels allocated to cellular users (in uplink or downlink), which is referred to as the D2D channel, to communicate with the corresponding receivers. We investigate two spectrum access policies for cellular communication in the uplink or downlink, namely, random spectrum access (RSA) policy and prioritized spectrum access (PSA) policy. In RSA, any of the available channels including the channel used by the D2D transmitters can be selected randomly for cellular communication, while in PSA the D2D channel is used only when all of the other channels are occupied. A D2D transmitter can communicate successfully with its receiver only when it harvests enough energy to perform channel inversion toward the receiver, the D2D channel is free, and the signal-to-interference-plus-noise ratio (SINR) at the receiver is above the required threshold; otherwise, an outage occurs for the D2D communication. We use tools from stochastic geometry to evaluate the performance of the proposed communication system model with general path-loss exponent in terms of outage probability for D2D and cellular users. We show that energy harvesting can be a reliable alternative to power cognitive D2D transmitters while achieving acceptable performance. Under the same SINR outage requirements as for the non-cognitive case, cognitive channel access improves the outage probability for D2D users for both the spectrum access policies. When compared with the RSA policy, the PSA policy provides a better performance to the D2D users. Also, using an uplink channel provides improved performance to the D2D users in dense networks when compared to a downlink channel. For cellular users, the PSA policy provides almost the same outage performance as the RSA policy.

Adaptive Resource Allocation in MIMO-OFDMA based on Subcarrier Allocation (SA) and (GA)

In recent years, the eyes of scholars has been on the road to an proficient allocation scheme of signalling dimension between users in both uplink and downlink channels, since bandwidth is usually limited and/or very expensive. This paper covenants with the rate adaptive MIMO-OFDMA (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) downlink resource allocation scheme. It has an objective of maximizing the total system capacity subject to constraints on total power, bit error rate and proportional fairness. The proposed algorithm determines the number of subcarriers for each user and then handing over the subcarrier to each user. Two optimization methods, one based on Subcarrier Allocation (SA) and the other, based on Genetic Algorithm (GA) are used for resource allocation. In the optimization technique based on SA, using SVD (Singular Value Decomposition), the MIMO fading channel of each subcarrier is transformed into an equivalent bank of parallel SISO (Single Input Single Output) subchannels, which leads to a better trade-off strategy among system capacity, computational complexity and proportional fairness. Paralleled to static allocation schemes, the new algorithm has significantly lower complexity and in simulation fruitages higher system capacity. Simulation results show that the subcarrier allocation based on GA can provide capacity improvement with the reduction in fairness.

A Performance Summary of the Evolved 3G (E-UTRA) for Voice Over Internet and Best Effort Traffic

Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (E-UTRA) is a new technology that targets the long-term evolution (LTE) of third generation. The E-UTRA technology has recently been standardized by the Third-Generation Partnership Project (3GPP) as a set of (series_36) specifications. The standardization process is almost complete; this paper does not focus on comparing specific proposed schemes but instead aims to outline the system performance more in general. E-UTRA operates in the packet-switched domain; hence, all traffic is handled by the packet protocols. The analysis is shown for Voice over Internet Protocol (VoIP) and Best Effort (BE) data, as these are common examples of real-time and non-real-time traffic, respectively. The performance is given in the VoIP study as the number of satisfied voice users per cell and in the BE study as the cumulative probability distribution of user (or cell) throughput, which was scaled to the spectral efficiency values, given both at the mean and at the cell edge. The VoIP capacity extends beyond 350 users in downlink and 230 users in uplink, which is a considerable increase compared with the high-speed packet-access (HSPA) reference. The BE spectral efficiency meets the 3GPP targets and yields impressive gains of order 2.5-3 times the well-performing HSPA reference. This clearly exceeds the mean of 1.5 b/s/Hz/cell in downlink and 0.8 b/s/Hz/cell in uplink for a baseline antenna configuration with penetration loss of 20 dB. In some scenarios, these mean gains exceed four times the reference.

On antijamming in general CDMA systems-part I: multiuser capacity analysis

The capacity of a general multiuser CDMA jamming channel is analyzed when the receiver has or lacks jammer state information. Analyses are carried out for noncooperative and cooperative users in uplink and downlink static and Nakagami fading channels. The results are applied to a versatile multiaccess channel model which is based on the time-bandwidth dimensionality and is considered for the user capacity analysis of a variety of multiuser spread spectrum systems contaminated by jamming. In this model, different users are distinguished by signatures of either direct sequence or hopping type. It is found that the jammer should spread its energy evenly over all degrees of freedom in order to minimize the average capacity. Also, the capacity behavior appears to be dominated more by knowledge of jammer state information than by the effects of fading. The capacity of downlink channels in cooperative schemes is found to be more sensitive to changes in fading severity, compared with the capacity of other kinds of channels.

Low complexity subcarrier and power allocation for utility maximization in uplink OFDMA systems

We consider the joint subcarrier and power allocation problem with the objective of maximizing the total utility of users in the uplink of an OFDMA system. Our formulation includes the problems of sum rate maximization, proportional fairness and max-min fairness as special cases. Unlike some previous algorithms, which are iterative and time consuming, our proposed one is non-iterative and with time complexity of only O(KN log2 N), where K and N are the number of users and subcarriers respectively. We prove that it provides a solution that is Pareto optimal within a large neighborhood of itself. Besides, we derive an efficiently computable upper bound of the optimal solution. Simulation results show that our algorithm is nearly optimal.

On Antijamming in General CDMA Systems-Part II: Antijamming Performance of Coded Multicarrier Frequency-Hopping Spread Spectrum Systems

In the first part of the paper, the capacity of a general multiuser code division multiple access (CDMA) jamming channel was analyzed for noncooperative and cooperative users in uplink and downlink static and Nakagami fading channels when the receiver has or lacks jammer state information. The results were applied to a unified channel model encompassing a variety of multiuser spread spectrum systems contaminated by jamming. It was found that the jammer should spread its energy evenly over all degrees of freedom in order to minimize the average capacity. In the second part of the paper, using a standard orthogonal frequency division multiplexing (OFDM) model, the performance of a coded version of a multicarrier frequency-hopping (MC-FH) CDMA system in static and Rayleigh fading jamming uplink channels is analyzed. The MC-FH system under study is a hybrid of the OFDM and frequency hopping concepts, and is also a practical example of the model developed in the first part. It is demonstrated that in the cases where the receiver knows the jammer state and the receiver lacks the jammer state, spreading and contracting the jamming power over the system bandwidth, respectively, will give rise to the worst performance for the communicators. Optimal decorrelator weights for the receiver soft outputs in different channels, valuable for practical system design, are also obtained.

Performance comparison of MRC and EGC on a MC-CDMA system with synchronization errors over fading channels

This work derives the average bit error rate (BER) of the uplink and downlink multicarrier code division multiple access (MC-CDMA) systems using maximum ratio combining (MRC) and equal gain combining (EGC) with synchronization errors over fading channels. The derived equation can simultaneously incorporate the parameters of the fading channel and all of the synchronization errors, including frequency offset, carrier phase jitter, and timing jitter. Numerical results indicate that those two combining schemes on the uplink and downlink MC-CDMA systems are degraded by all of the normalized synchronization errors over 10?2. The comparison outcomes between MRC and EGC reveal that the MRC generally outperforms EGC in the uplink MC-CDMA system. However, EGC achieves better performance when the number of users is small, the normalized synchronization errors are low and the signal to noise ratio (SNR) is high. In the downlink system, EGC mainly outperforms MRC when the SNR and the number of users are gradually increased and the normalized synchronization errors are low. Therefore, the selection of MRC or EGC depends on the SNR, the synchronization errors and the number of users in uplink and downlink MC-CDMA systems.