Uplink Downlink Research Articles

Uplink–Downlink Cochannel Interference Cancellation in RIS-Aided Full-Duplex Networks

Uplink–Downlink Cochannel Interference Cancellation in RIS-Aided Full-Duplex Networks

Joint Uplink–Downlink Capacity and Coverage Optimization via Site-Specific Learning of Antenna Settings

Joint Uplink–Downlink Capacity and Coverage Optimization via Site-Specific Learning of Antenna Settings

Cooperative NOMA in cognitive radio networks: A study on imperfect CSI, SIC and hardware impairments over Nakagami-m fading channel

This paper proposes a cooperative uplink–downlink non orthogonal multiple access (NOMA) in an overlay cognitive radio network (CR). We examine the impact of imperfect channel state information (impCSI), imperfect successive interference cancellation (impSIC) and residual hardware impairments (RHI) on the cooperative cognitive radio network over Nakagami-m fading channels. We derive the exact outage probabilities of primary user (PU) and multicast secondary users (SUs) under perfect/imperfect conditions for fixed and adaptive power allocations. We show that the use of multiple relays enhances the diversity order, but with fixed power allocation in perfect/imperfect case and adaptive power allocation in imperfect case both suffer from an error floor, which reduces the diversity order to zero. On the other hand, the adaptive power allocation for the perfect case achieves full diversity gain. We validate the analytical results with Monte Carlo simulations and demonstrate the diversity gains of the considered schemes.

Multi-User Downlink Beamforming Using Uplink Downlink Duality With CEQs for Frequency Selective Channels

High-resolution fully digital transceivers are infeasible at millimeter-wave (mmWave) due to their increased power consumption, cost, and hardware complexity. The use of low-resolution converters is one possible solution to realize fully digital architectures at mmWave. In this paper, we consider a setting in which a fully digital base station with constant envelope quantized (CEQ) digital-to-analog converters on each radio frequency chain communicates with multiple single antenna users with individual signal-to-quantization-plus-interference-plus-noise ratio (SQINR) constraints over frequency selective channels. We first establish uplink downlink duality for the system with CEQ hardware constraints and OFDM-based transmission considered in this paper. Based on the uplink downlink duality principle, we present a solution to the multi-user multi-carrier beamforming and power allocation problem that maximizes the minimum SQINR over all users and sub-carriers. We then present a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">per sub-carrier</i> version of the originally proposed solution that decouples all sub-carriers of the OFDM waveform resulting in smaller sub-problems that can be solved in a parallel manner. Our numerical results based on 3GPP channel models generated from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Quadriga</i> demonstrate improvements in terms of ergodic sum rate and ergodic minimum rate over state-of-the-art linear solutions. We also show improved performance over non-linear solutions in terms of the coded bit error rate with the increased flexibility of assigning individual user SQINRs built into the proposed framework.

Energy Efficient Beamforming for Millimeter-Wave Massive MIMO Systems Under User-Wise Asymmetric Uplink–Downlink Traffic

In this paper, a beamforming scheme that aims to support user-wise asymmetric uplink-downlink (UL-DL) traffic in a more energy-efficient manner is proposed for time-division duplex (TDD) millimeter-wave massive multiple-input-multiple-output (MIMO) systems. Assuming that proper data links have been established during the initial access stage for DL or UL traffic, we consider the beamforming problem for UL or DL whose payload traffic is much lighter than the other link. Such asymmetric traffic allows part of the massive MIMO array to be deactivated in order to achieve a higher energy efficiency (EE) while still meeting the spectrum efficiency (SE) requirements for UL or DL. To deal with such a problem, we propose the corresponding phase shifter (PS) deactivation strategies based on different SE constraints for individual mobile stations or users independently, which select the PSs to be deactivated accordingly with low computational complexity. We then propose a novel codebook design method, which relies on the iteratively updated average main beam gain, in order to pursue a flatter beam under asymmetric DL-UL traffic that interacts with the corresponding PS deactivation strategy. The proposed codebook not only offers flexible beam width and flat main beam gain, but also can generate some good candidate codewords to account for the need of beam refinements, after some of the PSs have been deactivated. Simulation results demonstrated the superiority of the proposed energy efficient PS deactivation approach and the corresponding codebook design.

Joint uplink–downlink resource allocation for energy efficient D2D underlaying cellular networks with many-to-one matching

Energy efficiency (EE) is an important parameter for the next generation cellular communications which is not limited to voice and text messages only. Device-to-Device (D2D) communication is being viewed as a promising technology to support heterogeneous applications involved in future cellular networks. Due to its short range communication, less amount of power is sufficient to make a successful transmission. By exploiting this feature of D2D, this paper proposes an energy-efficient resource allocation scheme for joint uplink/downlink (UL/DL) D2D considering many-to-one matching criterion for channel reuse among users. In this paper, total EE of D2D pairs (DPs) is taken as a performance metric to be optimized subject to quality of service (QoS) satisfaction for cellular users (CUs) within the power budgets of all the users. An iterative scheme is designed for joint channel and power optimization problem. Simulation results show the convergence of joint iterative algorithm and verify significant performance improvement over other schemes.

Multicarrier-Division Duplex for Solving the Channel Aging Problem in Massive MIMO Systems

The separation of training and data transmission as well as the frequent uplink/downlink (UL/DL) switching make time-division duplex (TDD)-based massive multiple-input multiple-output (mMIMO) systems less competent in fast time-varying scenarios due to the resultant severe channel aging. To this end, a multicarrier-division duplex (MDD) mMIMO scheme associated with two types of well-designed frame structures are introduced for combating channel aging when communicating over fast time-varying channels. For comparison, the corresponding TDD frame structures related to the 3 rd Generation Partnership Project (3GPP) standards and their variant forms are presented. The MDD-specific general Wiener predictor and decision-directed Wiener predictor are introduced to predict the channel state information, respectively, in the time domain based on UL pilots and in the frequency domain based on the detected UL data, considering the impact of residual self-interference (SI). Moreover, by applying the zero-forcing precoding and maximum ratio combining, the closed-form approximations for the lower bounded rate achieved by TDD and MDD frame structures over time-varying channels are derived. Our main conclusion from this study is that the MDD, endowed with the capability of full-duplex but less demand on SI cancellation than in-band full-duplex (IBFD), outperforms both the conventional TDD and IBFD in combating channel aging.

Design and Build 4G Open Radio Access Network at SmartLab Politeknik Negeri Jakarta

The transition of RAN (Radio Access Network) development from the conventional model to Open RAN is motivated by the fact that Open RAN presents new services by reducing CAPEX (Capital Expenditure) and has the ability to integrate all cellular technologies in one server. One of cellular technology that can be developed using Open RAN is 4G LTE networks. The 4G LTE network produces internet with high data rate and low latency system. Various use case implementations can be carried out, for example to support learning on campus. In this study, the development of Open RAN 4G is implemented as a use case to build the Jakarta State Polytechnic SmartLab which produces its own cellular network. The importance of this research is to be able to ascertain the performance of the Open RAN 4G network using a Centralized RAN scenario. The method used in this research consists of knowing the problem, determining the tools used, determining the implementation scenario, configuring, and testing network performance. Parameters measured to test network performance are uplink downlink speed, RSRP value, and SINR value. Based on the scenarios that have been executed, the results show that the Open RAN 4G network has a maximum downlink speed performance of 13.6 Mbps, a maximum uplink speed of 7.22 Mbps, a maximum SINR of 22 dB, an RSRP of -200 dBm, and a maximum range that can be reached is 5 meters.

Multi-User Downlink Beamforming Using Uplink Downlink Duality With 1-Bit Converters for Flat Fading Channels

The increased power consumption of high-resolution data converters at higher carrier frequencies and larger bandwidths is becoming a bottleneck for communication systems. In this paper, we consider a fully digital base station equipped with 1-bit analog-to-digital (in uplink) and digital-to-analog (in downlink) converters on each radio frequency chain. The base station communicates with multiple single antenna users with individual SINR constraints. We first establish the uplink downlink duality principle under 1-bit hardware constraints under an uncorrelated quantization noise assumption. We then present a linear solution to the multi-user downlink beamforming problem based on the uplink downlink duality principle. The proposed solution takes into account the hardware constraints and jointly optimizes the downlink beamformers and the power allocated to each user. Optimized dithering obtained by adding dummy users to the true system users ensures that the uncorrelated quantization noise assumption is true under realistic settings. Detailed simulations carried out using 3GPP channel models generated from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Quadriga</i> show that our proposed solution outperforms state of the art solutions in terms of the ergodic sum and minimum rate especially when the number of users is large. We also demonstrate that the proposed solution significantly reduces the performance gap from non-linear solutions in terms of the uncoded bit error rate at a fraction of the computational complexity.

Uplink Performance of Narrowband Internet-of-Things Devices in Downlink–Uplink Decoupled-Based Heterogeneous Networks

Uplink Performance of Narrowband Internet-of-Things Devices in Downlink–Uplink Decoupled-Based Heterogeneous Networks

Multi-agent reinforcement learning based joint uplink–downlink subcarrier assignment and power allocation for D2D underlay networks

Multi-agent reinforcement learning based joint uplink–downlink subcarrier assignment and power allocation for D2D underlay networks

Reconfigurable Physical Resource Block Using Novel – Beamforming Filter Circuit for LTE-Based Cell-Edge Terminals

This article presents a novel reconfigurable physical resource block (PRB), where long-term evolution (LTE) and mobile cell-edge terminals are interfaced using low-power tunable second-order <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G_{m}-C$ </tex-math></inline-formula> filter beamforming circuit, hence achieving an uplink–downlink (UL-DL) cellular system. A total of ten wireless multipoint (MP) terminals were structured and investigated. The BS-to-UAV-enabled terminals are propagated by line-of-sight (LoS) and nonline-of-sight (NLoS) beamforming. The subordinate terminals are handled using the derived Rayleigh signal distribution expressions. To guarantee higher frequency shift, the embedded control logic (CL) circuit is modeled upon the NMOS low dropout (LDO) regulator configurations with center frequency of 9.2 MHz and pass band of 1.4 MHz. The quality factors for both the first and second poles remain stable at 4.1 and 6.5 respectively. Stochastic analysis of the anticipated signal impacts with further estimation of its inherent variation challenges within the confined spectrum-sharing zone was corroborated. Our work is validated using an introduced direct and relay network density variations. The model’s performance evaluation compliments a ≥ 45.3-dB gain, an optimal transmission power and robust network sum rates in both LoS and NLoS conditions.

CSI-Impaired Beamforming Optimization for Dense MIMO Communication Networks

This paper studied the robust beamforming for dense transmission systems with imperfect channel state information (CSI). The objective was to maximize the minimum signal to interference plus noise ratio (SINR) in the constraint of the per base station (BS) power. By performing the uplink–downlink duality theory, the referred non-convex optimization problem can be changed into the equivalent uplink decoupling optimization problem. Then, we proposed the instantaneous updating uplink–downlink power algorithm, which relies on instantaneous CSI for the finite system. For the massive MIMO system, to obtain the solution to the problem required for power to instantaneously update, we proposed the updating uplink–downlink power algorithm, which only requires statistical CSI, by applying the random matrix theory. The simulation results show the feasibility and effectiveness of our proposed algorithms.

Optimal Transmission Strategy and Time Allocation for RIS-Enhanced Partially WPSNs

Wireless powered sensor networks (WPSNs) have evolved as a promising paradigm for energy-efficient communications. Recently, the proliferation of reconfigurable intelligent surface (RIS) has further been envisioned as a cost-effective solution for improving wireless power transfer (WPT) efficiency. In this paper, from the practical perspective of balancing the network sustainability and reliability, we consider a RIS-enhanced partially WPSN that composed of wireless-powered energy receivers (ERs) and battery-powered information receivers (IRs). Assuming the partially WPSN operates in time division multiple access (TDMA) mode, the joint optimization of covariance matrices, downlink/uplink (DL/UL) time allocation and RIS reflecting coefficients are investigated under the minimum DL rate constraint among all IRs for maximizing the achievable UL sum rate. Specifically, the single-IR single-ER (SISE) case is first studied based on the assumption of separate DL/UL RIS reflecting coefficients, in which an alternating optimization algorithm is proposed with semi-closed-form optimal solutions. In order to reduce the hardware overhead and signal processing complexity, we also investigate the case of identical DL/UL RIS reflecting coefficients, in which an iterative optimization algorithm is developed to tackle the coupled DL/UL transmissions. Then, we extend our work to the multiple-IRs multiple-ERs (MIME) case, where both the optimization problems corresponding to separate and identical DL/UL RIS reflecting schemes become more challenging to solve. To circumvent this intractability, we propose a successive convex relaxation (SCA) based alternating optimization algorithm and a low-complexity two-step algorithm. Finally, numerical results demonstrate the superior UL sum rate performance of our proposed algorithms over the adopted benchmarks.

Refracting RIS-Aided Hybrid Satellite-Terrestrial Relay Networks: Joint Beamforming Design and Optimization

Reconfigurable intelligent surface (RIS) has been viewed as a promising solution in constructing reconfigurable radio environment of the propagation channel and boosting the received signal power by smartly coordinating the passive elements’ phase shifts at the RIS. Inspired by this emerging technique, this article focuses on joint beamforming design and optimization for RIS-aided hybrid satellite-terrestrial relay networks, where the links from the satellite and base station (BS) to multiple users are blocked. Specifically, a refracting RIS cooperates with a BS, where the latter operates as a half-duplex decode-and-forward relay, in order to strengthen the desired satellite signals at the blocked users. Considering the limited onboard power resource, the design objective is to minimize the total transmit power of both the satellite and BS while guaranteeing the rate requirements of users. Since the optimized beamforming weight vectors at the satellite and BS, and phase shifters at the RIS are coupled, leading to a mathematically intractable optimization problem, we propose an alternating optimization scheme by utilizing singular value decomposition and uplink–downlink duality to optimize beamforming weight vectors, and using Taylor expansion and penalty function methods to optimize phase shifters iteratively. Finally, simulation results are provided to verify the superiority of the proposed scheme compared to the benchmark schemes.

Throughput Maximization for Asynchronous RIS-Aided Hybrid Powered Communication Networks

Hybrid energy supply composed of batteries and radio frequency (RF) signals has been anticipated to be a prominent solution for balancing the reliability and self-sustainability of future IoT networks. The newly emerging reconfigurable intelligent surface (RIS) is also capable of greatly enhancing spectral and energy efficiencies. In this paper, by considering an asynchronous transmission protocol among all energy receivers (ERs) and assuming the perfect self-interference cancellation (SIC) at the hybrid access point (HAP), we aim to maximize sum throughput in the RIS-aided hybrid powered communication networks (HPCNs) by jointly optimizing the transmit covariance matrices of the HAP and all ERs, the RIS reflection matrix and the downlink/uplink (DL/UL) time allocation. Generally, this optimization problem is intractable to solve due to strongly coupled variables and nonconvex unit-modulus constraints. To draw more insights into this joint design, we firstly carry out feasibility analysis on this problem, and then develop a 2-block alternating optimization algorithm, which consists of the semi-closed-form solution based iterative algorithm for deriving the optimal MIMO transceivers together with the DL/UL time allocation and the alternating direction method of multipliers (ADMM) based algorithm for the RIS design. To avoid the potential high complexity of alternating optimization, we also propose a two-stage scheme, where the RIS design is independent of the others and aims to create favorable DL/UL channels. The extension of our proposed algorithms to the practical imperfect SIC case is then discussed. Numerical results illustrate the superior performance of our proposed algorithms over the baselines in terms of the achievable sum throughput, and their time effectiveness in solving large-scale problems.

A survey on downlink–uplink decoupled access: Advances, challenges, and open problems

The emergence of new uplink (UL) intensive applications, coupled with the ambitious vision of the Internet-of-Things (IoT), will soon unleash unprecedented increases in UL wireless data traffic. However, current network designs are mainly concerned with optimizing the downlink (DL) performance, hence cannot give full play to UL communications. Exacerbated by high path-loss and low UL to DL duration ratio in the 5G new radio time division duplex (TDD-NR) spectrum, the UL capacity is much smaller than that of the DL one. To overcome such a problem, a DL–UL decoupled access (DUDe) approach has been proposed, in which the users are allowed to connect to different base-stations (BSs) at different frequency bands in each link direction. Moreover, DUDe can be an add-on to many 5G (and beyond) technologies, such as millimeter-wave communication, multi-connectivity, device-to-device (D2D) communication, cellular-enabled unmanned aerial vehicle (UAV) communication, and mobile edge computing (MEC). However, despite the apparent consensus on its advantages, the realization of DUDe in 5G networks is in its infancy and still requires more efforts from both academia and industry. This survey provides a holistic overview on the DUDe approach, including operating bands DUDe (i.e. supplementary UL) and serving BS DUDe, reviews its fundamentals and explores potential use-cases. Other 5G UL coverage enhancement technologies, such as UL carrier aggregation, evolved universal terrestrial radio access-new radio (EUTRA-NR) dual connectivity (EN-DC), and UL Tx Switching are also compared with DUDe. Lastly, cutting edge research works in this area are summarized along with a discussion on the potential challenges and open research problems.

Impact of fractional power control on downlink uplink decoupled‐based HetNets in varying path loss exponent environment

AbstractUplink power control in cellular networks have proved to be an effective technique for reducing uplink interference levels, resulting in improved uplink signal to interference and noise ratio, especially for cell‐edge user equipments (UEs). Having said that, the impact of fractional power control (FPC) on the performance of downlink uplink decoupled‐ (DUDe) based HetNets while considering varying path loss exponent (PLE) environment has not been investigated as of yet, the reason behind which was to simplify the system model and obtain tractable results. In this article, we have developed a generalized analytical framework, incorporating the effect of FPC, in an effort to investigate its impact on DUDe performance in varying PLE environment. Furthermore, we have considered different small base station's (SBS) transmit powers to study its effect, paired with FPC, on DUDe‐based HetNets. Moreover, we have performed a baseline comparison of DUDe performance against conventional coupled UE association based on maximum downlink received power. Performance indicators like decoupled and coupled uplink coverage probability and decoupled and coupled average spectral efficiency have been analyzed in this paper. The results presented in this paper highlight the impact of the FPC on DUDe performance in varying PLE environment.

Dual-Polarized FDD Massive MIMO: A Comprehensive Framework

We propose a comprehensive scheme for realizing a massive multiple-input multiple-output (MIMO) system with dual-polarized antennas in frequency division duplexing (FDD) mode. Dual-polarized arrays are commonly employed due to the favorable property that, in principle, they can double the number of channel spatial degrees of freedom with a less-than-proportional increase in array size. However, processing a dual-polarized massive MIMO channel is demanding due to the high channel dimension and the lack of Uplink-Downlink (UL-DL) channel reciprocity in FDD mode. In particular, the difficulty arises in common channel training and DL precoding in a multi-user setup. To address this, we develop a unified framework consisting of three steps: (1) covariance estimation to efficiently estimate the UL covariance from noisy UL pilots; (2) a UL-DL covariance transformation method that obtains the DL covariance from the estimated UL covariance, eliminating the need for DL channel covariance training via pilot transmission; <xref ref-type="disp-formula" rid="deqn3a-deqn3b" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(3)</xref> a joint multi-user DL channel training method, which enables the BS to estimate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">effective DL channels</i> given any protocol-specific pilot dimension and to use them for interference-free DL beamforming and data transmission. Through extensive simulations, we show that our scheme is applicable to a variety of communication scenarios in terms of the number of antennas, UL and DL pilot dimensions, and angular scattering properties. Unlike the common trend in the literature, we do <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">not</i> make strong structural assumptions about the wireless channel (such as angular sparsity), ensuring a general treatment of the problem.

X2-Based Signalling Mechanisms for Downlink Uplink Decoupling in Next Generation Communication Systems

Cell selection in cellular networks is an important aspect that impacts the quality of service. The traditional cell selection mechanism is based on downlink received power. Despite the dense deployment of macrocells, mobile network operators are still confronting the daunting challenge of providing capacity and coverage. Deployment of a large number of small cells has emerged as a promising solution towards addressing this problem. However, this success expands the heterogeneous cellular networks where there is a significant disparity in the transmit power of the different base station types. Downlink and Uplink Decoupling (DUDe) can improve efficiency by associating the downlink cell based on the downlink received power and the uplink based on the pathloss. While the higher layer signalling has not been proposed in detail for the DUDe mechanism yet, we aim to propose a solution for the problem. This work addresses four different signalling mechanisms to realise decoupled up/downlinks connections in the radio access network for the next-generation communication systems with handling mobility. Our proposed signalling mechanisms cover uplink decoupling, downlink coupling, downlink decoupling, and uplink coupling scenarios. We analyse the proposed signalling mechanisms using ns3 simulation and present the impact of applying the DUDe mechanism, which mainly shows improvements for the uplink. For the selected mobility scenario, delay and lost packets are reduced by 30% and 26%, respectively. Delay and lost packets are reduced by 36% and 27% for the fix location scenario, respectively. The improvements imply that it reaches particular demand considering next-generation communication systems, with a massive number of smart devices demanding high quality of service requirements.