Sum Capacity Research Articles

A Two-Stage Approach of Joint Route Planning and Resource Allocation for Multiple UAVs in Unmanned Logistics Distribution

Unmanned aerial vehicles (UAVs) can serve as means of delivery to enhance the effectiveness and accuracy of logistics distribution in various scenarios, such as emergency items delivery for disaster areas and logistics services for remote areas. This paper focuses on the problem of route planning for UAVs, which is the basis for UAVs to complete distribution tasks. Besides, to enhance the collaboration of UAVs during the delivery mission, this work also studies wireless resource (spectrum, power) allocation problem for multiple UAVs enabled communication networks. Due to the non-convex and combinatorial characteristics, it is challenging to obtain an optimal strategy for joint route planning and resource allocation issues within a finite time. To this end, the paths of UAVs are planned by the simulated annealing (SA) method in the first stage. Based on the preplanned paths, a double deep Q network (DDQN) based resource allocation method is proposed to maximize the average sum capacity of UAV-to-UAV (U2U) links and reduce transmission delay while minimizing the interference to UAV-to-infrastructure (U2I) links. Multi-UAV communication networks are reconnected according to the positions of UAVs changing in each time slot. Then each U2U link acting as an agent learns to improve spectrum and power allocation policy with imperfect knowledge of the environment. Simulation results demonstrate that the proposed DDQN-based resource management scheme can achieve higher system communication capacity than a random scheme. Moreover, the successful transmission probability of U2U links obtained by the DDQN-based method is much higher than a Particle Swarm Optimization (PSO) based method.

Blockage-Aware Flow Control in E-UTRA-NR Dual Connectivity for QoS Enhancement

Millimeter-wave (mmWave) communication included in new radio (NR) provides high throughput to meet the stringent requirements of modern applications. However, its performance is highly dependent on whether obstacles are blocking line-of-sight (LOS) paths. Blockages on the LOS paths jeopardize reliable connections. E-UTRA-NR dual connectivity (EN-DC) is one option for managing unstable connectivity using robust long-term evolution (LTE) as well as mmWave NR. EN-DC aggregates and utilizes multiple links to provide a better quality of service (QoS) to users. However, the performance of EN-DC is strongly affected by flow control due to the possibility of out-of-order packet delivery at the packet data convergence protocol (PDCP) layer. In this paper, we propose a blockage-aware flow control scheme (BAFC) that appropriately responds to the dynamics of mmWave links in the presence of mobile blockages and improves users’ QoS. To this end, we also develop PDCP scheduling schemes that satisfy various users’ QoS requirements. Through extensive simulations, we verify that BAFC exploits over 99% of the sum capacity of links on average under rapidly changing channels due to mobile blockages. Moreover, BAFC combined with PDCP scheduling achieves higher throughput or reduces latency by up to 43.9% with minimal throughput degradation.

Nullforming-Based Precoder for Spectrum Sharing Between HAPS and Terrestrial Mobile Networks

Ultra-wide coverage is one of the important concepts of the sixth generation (6G) mobile communications. High-altitude platform stations (HAPSs) have attracted considerable attention as a leading candidate for coverage extension of cellular networks. HAPSs should share a frequency band with terrestrial cellular networks and provide users with mobile communication services using the common frequency band to improve spectral efficiency in service links. However, the signals from HAPS strongly interfere with terrestrial cells in the service area of HAPS, which leads to a considerable deterioration in the system capacity of terrestrial cells. This study proposes a novel two-stage precoding scheme that realizes spectrum sharing between HAPS and terrestrial networks. The proposed scheme mitigates HAPS interference with terrestrial cells using beamforming techniques in phased array antenna systems. In the first stage, nulls are created in directions of terrestrial cells. In the second stage, user-specific beams are formed in directions of users connected to HAPS. Results demonstrate that the proposed scheme improves the signal-to-interference-plus-noise ratio of users in terrestrial cells by up to 10 dB compared with a conventional minimum mean square error (MMSE) precoder without nullforming when the HAPS uses a cylindrical array antenna with 196 elements. Furthermore, for ten terrestrial cells, the proposed scheme achieves 128% of total capacity of the conventional MMSE precoder. Total capacity is defined as the sum capacity of HAPS and all terrestrial cells.

Fundamental Limits of Full-Duplex Spectrum Sharing Under Peak Interference Power Constraint

Cognitive radio (CR) and full-duplex (FD) have received extensive attention and research due to their high spectrum efficiency, which can effectively solve the problem of low spectrum efficiency in current communication systems. Based on CR and FD techniques, in this paper, a FD spectrum sharing CR networks is considered, in which both secondary users (SU1 and SU2) are each equipped with dual antennas, one antenna is used to transmit signals, and the other antenna is used to receive signals at the same time and frequency. Under peak interference power and peak transmit power constraints, we analysis the ergodic sum capacity and the outage probability based on the FD spectrum sharing CR networks and the conventional spectrum sharing CR networks. Furthermore, under no peak transmit power constrain and perfect self-interference cancellation (SIC), based on the FD spectrum sharing CR networks and the conventional spectrum sharing CR networks, the closed-form expressions of the theoretical performance upper bound of the ergodic sum capacity and the outage probability are derived by two lemmas and four propositions. Accurate mathematical analysis display, under the same bandwidth, the upper bound of ergodic sum capacity for the full-duplex spectrum sharing CR networks is twice as much as the traditional spectrum sharing CR networks, and the FD spectrum sharing CR networks based on SU1, also has better performance upper bound on the outage probability than the traditional spectrum sharing CR networks. Simulations results also validate that, the FD spectrum sharing CR networks obtains better communication performance than the conventional spectrum sharing CR networks, especially when the mean of self-interference channel power gain is small. Finally, we also can see that the simulation performance upper bound is completely consistent with the theoretical analysis performance upper bound, whether in the FD spectrum sharing CR networks or the conventional spectrum sharing CR networks. So also verifies the correctness of the theoretical performance upper bound derivation.

Performance Analysis of Optical Backhauled Cooperative NOMA Visible Light Communication

Optical wireless networks, particularly free-space optical (FSO) in outdoor environments and visible light communication (VLC) in indoor environments, suffer from severe deterioration in signal quality due to various factors such as the availability of line-of-sight link, the turbulence of the atmosphere, or pointing errors. To enable high-quality service point-to-point transmission through optical wireless communication, an efficient and reliable backhaul link is essential. Towards this objective, this paper proposes a novel optical backhauled non-orthogonal multiple access (NOMA) in VLC systems. Unlike earlier works, our model considers the effects of various transmission parameters in a mixed cooperative FSO/radio over a fiber backhaul link with NOMA-VLC to serve two users. The closed-form expressions of outage probability, sum throughput, ergodic sum capacity, and average bit error rate are delivered for a variety of channel conditions using Meijer's G and Gaussian hypergeometric functions. More specifically, both the theoretical and simulation results demonstrate that the performance gain of the proposed optical-based NOMA systems can improve the performance of the users in comparison with the conventional OMA systems at medium to high SNR ranges. Furthermore, a deep learning-based framework is proposed to accurately estimate the ergodic capacity of the proposed system and significantly reduce the complexity cost of the theoretical analysis.

5G NOMA user grouping using discrete particle swarm optimization approach

Non-orthogonal multiple access (NOMA) technology meets the increasing demand for high-seed cellular networks such as 5G by offering more users to be accommodated at once in accessing the cellular and wireless network. Moreover, the current demand of cellular networks for enhanced user fairness, greater spectrum efficiency and improved sum capacity further increase the need for NOMA improvement. However, the incurred interference in implementing NOMA user grouping constitutes one of the major barriers in achieving high throughput in NOMA systems. Therefore, this paper presents a computationally lower user grouping approach based on discrete particle swarm intelligence in finding the best user-pairing for 5G NOMA networks and beyond. A discrete particle swarm optimization (DPSO) algorithm is designed and proposed as a promising scheme in performing the user-grouping mechanism. The performance of this proposed approach is measured and demonstrated to have comparable result against the existing state-of-the art approach.

Comparative Analysis of Ergodic Sum Capacity of Cooperative NOMA Aided with Spatial Modulation

Comparative Analysis of Ergodic Sum Capacity of Cooperative NOMA Aided with Spatial Modulation

Backscatter Assisted NOMA-PLNC Based Wireless Networks

In this paper, sum capacity maximization of the non-orthogonal multiple access (NOMA)-based wireless network is studied in the presence of ambient backscattering (ABS). Assuming that ABS is located next to far nodes, it improves the signal strength of far node cluster. By applying suitable successive interference cancellation (SIC) operation, far node cluster act as an internet of things (IoT) reader. Moreover, to improve the uplink performance of the nodes, a physical layer network coding (PLNC) scheme is applied in the proposed network. Power optimization is employed at the access point (AP) to enhance the downlink performance with total transmit power constraint and minimum data rate requirement per user constraint using Lagrangian’s function. In addition, end-to-end outage performance of the proposed wireless network is analyzed to enhance each wireless link capacity. Numerical results evident that the outage performance of the proposed network is significantly improved while using the ABS. Furthermore, the average bit error rate (BER) performance of the proposed wireless network is studied to improve the reliability. Simulation results are presented to validate the analytical expressions.

RIS-Assisted Multi-User MISO Communications Exploiting Statistical CSI

Reconfigurable intelligent surface (RIS) is a promising solution to build a programmable wireless environment with reconfigurable passive elements, which can achieve high spectral and energy efficiency. In this paper, we investigate the ergodic capacity of RIS-assisted multi-user multiple-input single-output (MISO) wireless systems in both uplink and downlink scenarios. Unlike most of prior works, where instantaneous channel state information (CSI) is assumed, we consider the realistic scenario with only statistical CSI. For both scenarios, we first present an analytical expressions for the ergodic sum capacity of the system. Based on which, the joint power control (or transmit beamforming) and phase shift design problem maximizing the ergodic sum capacity is formulated. Capitalizing on the alternating direction method of multipliers (ADMM), fractional programming (FP) and alternating optimization (AO) methods, efficient suboptimal solutions are obtained for the non-convex design problems. Simulation results are presented to validate the accuracy of the analytical ergodic sum capacity expressions and evaluate the impact of key system parameters such as CSI, Rician <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> factor, number of RIS elements, and RIS location on the ergodic capacity performance. The findings suggest that the proposed statistical CSI design achieves decent performance compared with the instantaneous CSI based design. Moreover, a signal hot spot can be created when placing the RIS close to the users.

Cooperative Multiple-Access Channels With Distributed State Information

This paper studies a memoryless state-dependent multiple access channel (MAC) where two transmitters wish to convey a message to a receiver under the assumption of causal and imperfect channel state information at transmitters (CSIT) and imperfect channel state information at receiver (CSIR). In order to emphasize the limitation of transmitter cooperation between physically distributed nodes, we focus on the so-called distributed CSIT assumption, i.e., where each transmitter has its individual channel knowledge, while the message can be assumed to be partially or entirely shared a priori between transmitters by exploiting some on-board memory. Under this setup, the first part of the paper characterizes the common message capacity of the channel at hand for arbitrary CSIT and CSIR structure. The optimal scheme builds on Shannon strategies, i.e., optimal codes are constructed by letting the channel inputs be a function of current CSIT only. For a special case when CSIT is a deterministic function of CSIR, the considered scheme also achieves the capacity region of a common message and two private messages. The second part addresses an important instance of the previous general result in a context of a cooperative multi-antenna Gaussian channel under i.i.d. fading operating in frequency-division duplex mode, such that CSIT is acquired via an explicit feedback of perfect CSIR. The capacity of the channel at hand is achieved by distributed linear precoding applied to Gaussian codes. Surprisingly, we demonstrate that it is suboptimal to send a number of data streams bounded by the number of transmit antennas as typically considered in a centralized CSIT setup. Finally, numerical examples are provided to evaluate the sum capacity of the binary MAC with binary states as well as the Gaussian MAC with i.i.d. fading.

Experimental Analysis of Concentrated versus Distributed Massive MIMO in an Indoor Cell at 3.5 GHz

This paper presents a measurement-based comparison between distributed and concentrated massive multiple-input multiple-output (MIMO) systems, which are called D-mMIMO and C-mMIMO systems, in an indoor environment considering a 400 MHz bandwidth centered at 3.5 GHz. In both cases, we have considered an array of 64 antennas in the base station and eight simultaneously active users. The work focuses on the characterization of both schemes in the up-link, considering the analysis of the sum capacity, the total spectral efficiency (SE) achievable by using the zero forcing (ZF) combining method, as well as the user fairness. The effect of the power imbalance between the different transmitters or user terminal (UT) locations, and thus, the benefits of performing an adequate power control are also investigated. The differences between the C-mMIMO and D-mMIMO channel performances are explained through the observation of the structure of their respective measured channel matrices through parameters such as the condition number or the power imbalance between the channels established by each UT. The channel measurements have been performed in the frequency domain, emulating a massive MIMO system in the framework of a time-domain duplex orthogonal frequency multiple access network (TDD-OFDM-MIMO). The characterization of the MIMO channel is based on the virtual array technique for both C-mMIMO and D-mMIMO systems. The deployment of the C-mMIMO and D-MIMO systems, as well as the distribution of users in the measurement environment, has been arranged as realistically as possible, avoiding the movement of people or machines.

On Linearly Precoded Rate Splitting for Gaussian MIMO Broadcast Channels

In this paper, we consider a general $K$ -user Gaussian multiple-input multiple-output (MIMO) broadcast channel (BC). We assume that the channel state is deterministic and known to all the nodes. While the private-message capacity region is well known to be achievable with dirty paper coding (DPC), we are interested in the simpler linearly precoded transmission schemes. In particular, we focus on linear precoding schemes combined with rate-splitting (RS). First, we derive an achievable rate region with minimum mean square error (MMSE) precoding at the transmitter and joint decoding of the sub-messages at the receivers. Then, we study the achievable sum rate of this scheme and obtain two findings: 1) an analytically tractable upper bound on the sum rate that is shown numerically to be a close approximation, and 2) how to reduce the number of active streams – crucial to the overall complexity – while preserving the sum rate to within a constant loss. The latter results in two practical algorithms: a stream elimination algorithm and a stream ordering algorithm. Finally, we investigate the constant-gap optimality of linearly precoded RS with respect to the capacity. Our result reveals that, while the achievable rate of linear precoding alone can be arbitrarily far from the capacity, the introduction of RS can help achieve the capacity region to within a constant gap in the two-user case. Nevertheless, we prove that the RS scheme’s constant-gap optimality does not extend to the three-user case. Specifically, we show, through a pathological example, that the gap between the sum rate and the sum capacity can be unbounded.

Reuse of Multiple Channels by Multiple D2D Pairs in Dedicated Mode: A Game Theoretic Approach

Device-to-device communication (D2D) is expected to accommodate high data rates and to increase the spectral efficiency of mobile networks. The D2D pairs can opportunistically exploit channels that are not allocated to conventional users in a dedicated mode. To increase the sum capacity of D2D pairs in the dedicated mode, we propose a novel solution that allows the reuse of multiple channels by multiple D2D pairs. In the first step, the bandwidth is split among D2D pairs so that each pair communicates at a single channel that guarantees a minimal capacity for each pair. Then, the channel reuse is facilitated via a grouping of the D2D pairs into coalitions. The D2D pairs within one coalition mutually reuse the channels of each other. We propose two approaches for the creation of the coalitions. The first approach reaches an upper-bound capacity by optimal coalitions determined by the dynamic programming. However, such approach is of a high complexity. Thus, we also introduce a low-complexity algorithm, based on the sequential bargaining, reaching a close-to-optimal capacity. Moreover, we also determine the transmission power allocated to each reused channel. Simulations show that the proposed solution triples the sum capacity of the state-of-the-art algorithm with the highest performance.

A Comparative Study of Perfect and Imperfect SIC in Downlink PD-NOMA based on Sharing Bandwidth

In this paper, a scheme for sharing bandwidth-non-orthogonal multiple access (SB-NOMA) based on coordinated multi-point (CoMP) is proposed to improve total sum capacity and user capacity. The proposed algorithm is implemented in a cellular network platform, and the performance is analysed via two cases. First, the network performance is evaluated considerning both channel conditions and interference effects, which is addressed as the worst-case condition. The total network capacity is evaluated assuming Channel Estimation Error (CEE) and Imperfect Successive Interference cancelation (SIC). Second, the network is tested assuming ideal case condition materialized by canceling the effect of inter-channel interference (ICC) of the Base Station (BS) on Near User (NUE). The simulation results show that the capacity increases for SB-NOMA with installed by increasing the number of Cooperative BS (CBSs), where (2bits/Hz/s) is the gain in total capacity that is achieved by increasing the CBSs by one. Moreover, power allocation to the proposed scheme shown (0.15 - 0.85) represents the best value for maintaining capacity achievement.

Exploiting non-orthogonal multiple access in device-to-device communication

This paper proposes an uplink non-orthogonal multiple access (NOMA) system with device-to-device (D2D) communication, enabling NOMA users to communicate with other users/devices using D2D communication to improve the system capacity. In the NOMA-D2D system, two cellular users communicated with the BS using uplink NOMA, and two cellular users simultaneously communicated with the D2D users using downlink NOMA. Closed-form solutions for the ergodic sum capacity of the proposed system are derived analytically. The analytical results are validated via simulations and they are compared with the results obtained from conventional schemes. The comparison shows that, in scenarios where efficient interference cancellation can be achieved, the proposed NOMA system with the D2D model can achieve higher capacity gains than conventional benchmark schemes. When dB, NOMA-D2D achieves capacity gains of 192.2% and 157.5% over the conventional OMA and the time-sharing-based NOMA, respectively.

Coordinated Direct and Relay Transmission for Multiuser Networks: NOMA or Hybrid Multiple Access?

This letter proposes non-orthogonal multiple access (NOMA) based coordinated direct and relay transmission (CDRT) and hybrid multiple access (HMA) protocols for a general CDRT system, where a base station directly serves cell-center users (CCUs), while it communicates with cell-edge users (CEUs) via a relay. The ergodic sum capacity (ESC), capacity scaling and the number of successive interference cancellation (SIC) operations are derived correspondingly. If the number of CCUs is less than that of CEUs and the interference level of imperfect SIC is small, the proposed NOMA-based CDRT can achieve much better ESC than HMA. Otherwise, the proposed HMA achieves a better performance-complexity tradeoff. Numerical results verify the effectiveness and superiority of the proposed protocols.

Power Optimization for Spectrum Sharing in Vehicular Networks

The main goal of vehicular communication is to provide a more safe and efficient vehicular operation. The challenge in a Vehicle-to-Everything (V2X) network is to provide reliable connectivity for the Vehicle-to-Vehicle (V2V) links and high data rate connectivity for the Vehicle-to-Infrastructure (V2I) links at the same time. This requirement leads to spectrum sharing in vehicular communication. As the vehicular systems increases, the transmit power levels increases in the environment which in turn causes harmful effects on the atmosphere. The objective of this paper is to analyze the graph-based spectrum sharing algorithms that are available for vehicular communication and to develop a power optimization algorithm based on Hidden Markov Model (HMM) and to incorporate it into these algorithms in such a way to achieve better sum capacity for the V2I links along with a guaranteed reliability for the V2V links.

QoS-Driven Spectrum Sharing for Reconfigurable Intelligent Surfaces (RISs) Aided Vehicular Networks

Reconfigurable intelligent surfaces (RISs) have the capability of reconfiguring the wireless environment in a favorable way to improve the quality-of-service (QoS) of wireless communications. This makes RISs a promising candidate to enhance vehicle-to-everything (V2X) applications. This paper investigates the spectrum sharing problem in RIS-aided vehicular networks, in which multiple vehicle-to-vehicle (V2V) links reuse the spectrum already occupied by vehicle-to-infrastructure (V2I) links. To overcome the difficulty of acquiring instantaneous channel state information (CSI) due to the fast varying nature of some V2X channels, we rely upon large-scale (slowly varying) CSI in order to fulfill the QoS requirements of V2I and V2V communications. Particularly, we aim to maximize the sum capacity of V2I links that are used for high-rate content delivery and to guarantee the reliability of V2V links that are used for the exchange of safety information. The transmit power of vehicles, the multi-user detection (MUD) matrix, the spectrum reuse of V2V links, and the RIS reflection coefficients are jointly optimized, which results in a mixed-integer and non-convex optimization problem. To tackle this problem, the outage probability of each V2V link is first approximated by introducing an analytical expression to simplify the formulated problem. By leveraging the block coordinate descent (BCD) method, the considered optimization problem is decomposed into three sub-problems, whose optimal solutions are provided independently and updated alternately to obtain a near-optimal solution. Simulation results verify the theoretical analysis and the effectiveness of the proposed algorithm, as well as unveil the benefits of introducing RISs for enhancing the QoS performance of vehicular communications.

A coordinated non-orthogonal multiple access strategy for integrated terrestrial-satellite networks.

In this paper, we investigate the outage probability and ergodic sum capacity of the downlink of the integrated satellite-terrestrial networks (ISTN) with a cooperative non-orthogonal multiple access (CNOMA) scheme, in which a user with better channel condition acts as a relay node and forwards information to the other users. In this paper, a pilot-based channel estimation method is considered which can verify the performance of this scheme with the imperfect channel state information. In this model, all these users are equipped with multi-antennas, and all of them are both in the coverage of a same beam of the satellite. Specifically, the exact analytical expression for the outage probability and ergodic sum capacity of the system is derived. The result shows that this coordinated non-orthogonal multiple access (CNOMA) scheme performs better than that of OMA (TDMA) in this model. Finally, the future research directions are given to further enhance the system capacity.

Distributed Adaptive Cooperative Bandwidth Spectrum Sensing for Cognitive MIMO Radios

To allow secondary and primary concurrent transmissions achieving optimal spectrum utilization in cognitive radio networks (CRNs), this paper proposes an innovative distributed cooperative spectrum sensing methodology using adaptive sensing bandwidth entitled distributed adaptive cooperative bandwidth spectrum sensing (DACB-SS) scheme when multiple secondary users (SUs) use part of the bandwidth to collaboratively perform spectrum sensing throughout the whole frame to detect the primary user (PU)'s reappearance in time. The SU’s spectrum efficiency is maximized by jointly optimizing the sensing bandwidth proportion, the number of cooperative SUs, and the detection probability, subject to the constraints on the SUs’ interference and the false alarm probability. A gripping slant of DACB-SS regime is provided to maintain overall maximum spectral efficiency. Another contribution of DACB-SS algorithm is the benefit to make great improvement on the sum capacity to obtain better performance of spectrum coexistence. Simulation results illustrate that the proposed analytical model investigates characteristic changes of the spectrum usage affected by the outage probability of PR and the coexisting secondary transmission bandwidth in terms of overall spectral efficiency as well as the outage capacity which can be characterized by the outage probability of SR and the interference from ST to PR in multiuser multiple-input multiple-output broadcast channel (MU-MIMO-BC). Besides, the sum capacity is impacted by channel gains, primary transmit power and secondary transmit power in Gaussian cognitive inference channel (G-CIFC).