Uplink System Research Articles

PERFORMANCE ANALYSIS AND EVALUATION OF MASSIVE MIMO SYSTEM

This article examines the performance of massive MIMO uplink system over Rician fading channel. The performance is estimated regarding spectral efficiency versus number of base station antennas utilizing three plans of linear detection, maximum-ratio-combining (MRC), zero forcing receiver (ZF), and minimum mean-square error receiver (MMSE). The simulation results reveal that the spectral efficiency increments altogether with expanding the quantity of base station antennas. Additionally, the spectral efficiency with MMSE is superior to that with ZF, and the last is superior to that with MRC. Furthermore, the spectral efficiency diminishes with expanding the fading parameter.

Performance evaluation of companded localized FDMA for LTE uplink communications

The maximum-to-expected power ratio is critical metric in the current day mobile communications. Single-carrier frequency division multiple access is the most promotional scheme to reduce the peak-to-average power ratio in order to compromise the bit error rate for mobile communications. The proposed companding functions play a vital role in SC-FDMA than in OFDMA for LTE uplink systems. Here, in this paper the nonlinear compandings like μ-law, error, logarithmic, exponential, trapezoidal and airy function are more attractive to solve the problem and analyze PAPR and BER. The μ-companding is not recommended to use because of its average power and outband radiation. This paper proposed a companding functions based on special function to limit power ratio without enhancing the average power. The novel airy function gives suitable trade-off with their power ratio PAPR and error rate BER. The suggested method maintains superior performance with and without decompanding function in SC-FDMA systems at the receiver side without effecting the complexity.

Data Traffic Based on Slicing in a 5G Smart Uplink System

The paper considers the data traffic based on slicing in a 5g mobile network uplink system. Slicing is a promising technology for the fifth generation of networks that provides optimal quality of QOS services for each specific user or group of users. Data traffic that is processed by cellular networks increases every year. Therefore, we should consider all set of traffic from VoIP to M2M devices. For example, smart devices in the healthcare system transmit big data that is sensitive to latency, but also a video stream that requires minimal latency in certain cases. The paper focuses on the successful processing of traffic through a relay node, donor microstates, and a base station. All traffic is divided into three levels of QoS segmentation: sensitive, less sensitive, and low-sensitivity, using the AnyLogic simulation program. For fifth-generation 5G networks, achieving minimum latency and maximum data transfer speed within QoS is an important implementation condition. Therefore, in this paper, using simulation modeling, the main and possible results of each segment in the new generation of mobile networks are obtained. The use of a relay node in conjunction with micro-stations can ensure optimal station load and successful data processing. Also, the solutions outlined in this paper will allow you to identify a number of areas for future research to assess possible ways to design new mobile networks, or improve existing ones.

Multiple CFOs Estimation and Implementation of SC-FDMA Uplink System Using Oversampling and Iterative Method

Multiple carrier frequency offsets (CFOs) estimation in high speed single carrier frequency division multiple access (SC-FDMA) uplink system is a challenging issue. Most of the existing blind CFO estimation methods work for a certain type of carrier mapping scheme (CMS) or address a single CFO estimation by utilizing long data over frequency selective fading channel. These estimation methods become irrelevant at high speed and multi-user scenarios where CFO changes with symbols and users. In this paper, we propose a blind multiple CFOs estimation method for all CMS of SC-FDMA and implement over testbed. The proposed method requires only one SC-FDMA symbol to attain reliable estimation even in a high mobility environment, i.e., in a doubly selective channel. It exploits the phase difference present between even and odd samples of the received oversampled signal to estimate CFOs. Subsequently, an iterative joint CFO estimation and compensation (IJCEC) method is introduced to remove residual interference and increase CFOs estimation accuracy. Cramer-Rao lower bound is derived to characterize the CFO estimation accuracy of the proposed method. The work is compared with the conventional methods such as MUSIC, ESPRIT, CAZAC, and some existing methods and validated through Monte Carlo simulations. Finally, we authenticate the proposed IJCEC method by performing implementation and measurement on National Instrument testbed setup in an indoor propagation environment.

A Simplified Zero-Forcing Receiver for Multi-User Uplink Systems Based on CB-OSFB Modulation

A Simplified Zero-Forcing Receiver for Multi-User Uplink Systems Based on CB-OSFB Modulation

Spectral- and Energy-Efficient Hybrid Receivers for Millimeter-Wave Massive Multiuser MIMO Uplink Systems With Variable-Resolution ADCs

A primary difficulty in the practical implementation of millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems is the high hardware complexity and power consumption imposed by the employment of a large number of antennas at the base station. To alleviate this difficulty, we concentrate on a hybrid beamforming architecture consisting of less number of radio-frequency chains with variable-resolution analog-to-digital converters (ADCs) for mmWave massive multiuser MIMO uplink systems. Our objective is to design the ADC resolution profile to maximize system performance while reducing total receiver power consumption. However, the resulting ADC resolution profile design problem incurs high combinatorial complexity and is known to be computationally intractable. We address this problem by devising a simple yet computationally efficient algorithm, namely a coordinate update algorithm, to design the ADC resolution profile. Simulation results show that the proposed algorithm not only provides nearly the same sum rate as full-precision ADC receiver systems but also achieves much higher energy efficiency than existing state-of-the-art receiver architectures.

Layered Inter-Cluster Cooperation Scheme for Backhaul-Constrained C-RAN Uplink Systems in the Presence of Inter-Cluster Interference.

Despite the potential benefits of reducing system costs and improving spectral efficiency, it is challenging to implement cloud radio access network (C-RAN) systems due to the performance degradation caused by finite-capacity fronthaul links and inter-cluster interference signals. This work studies inter-cluster cooperative reception for the uplink of a two-cluster C-RAN system, where two nearby clusters interfere with each other on the uplink access channel. The radio units (RUs) of two clusters forward quantized and compressed version of the uplink received signals to the serving baseband processing units (BBUs) via finite-capacity fronthaul links. The BBUs of the clusters exchange the received fronthaul signals via finite-capacity backhaul links with the purpose of mitigating inter-cluster interference signals. Optimization of conventional cooperation scheme, in which each RU produces a single quantized signal, requires an exhaustive discrete search of exponentially increasing search size with respect to the number of RUs. To resolve this issue, we propose an improved inter-BBU, or inter-cluster, cooperation strategy based on layered compression, where each RU produces two descriptions, of which only one description is forwarded to the neighboring BBU on the backhaul links. We discuss the optimization of the proposed inter-cluster cooperation scheme, and validate the performance gains of the proposed scheme via numerical results.

Frequency synchronization for FBMC-based massive MIMO system uplink

Frequency synchronization and channel equalization are of a great importance in any multicarrier communication system. Hence, in this paper, a joint carrier frequency offset (CFO) and channel estimation approach is proposed for multiuser filter bank multicarrier (FBMC) in the uplink of massive multiple input multiple output (MIMO) systems. Our proposed solution jointly estimates the CFO and channel responses based on the maximum likelihood (ML) criterion. The computational complexity of the estimator is high due to a large number of antennas at the base station (BS). To address this issue, a low-complexity CFO estimation technique is investigated after combining the received signals at the BS antennas. It is worth mentioning that our proposed method estimates both integer and fractional part of CFO values. Also, to characterize the accuracy of our estimation techniques, the asymptotic Cramér–Rao bounds (CRBs) are derived. Furthermore, the CFO correction and channel equalization techniques are performed for FBMC systems. Finally, we show the efficacy of our proposed algorithms through numerical results.

Analysis and Cancellation of Mixed-Numerologies Interference for Massive MIMO-OFDM UL

The extremely diverse service requirements is an important challenge for the future generations of wireless communication technologies. As promising solutions, orthogonal frequency division multiplexing (OFDM)-based massive multiple-input multiple-output (MIMO) and mixed numerologies transmission are proposed. This letter investigates the transmission of different users, sharing the same bandwidth while they are associated to different numerologies. A transceiver design which aims to manage the mixed numerology spectrum sharing (SS) transmission is first presented. Then, we analyze the inter-numerology interference (INI) and derive its corresponding theoretical expressions. Based on the derived closed-form expressions, a new INI cancellation scheme is introduced, which efficiently mitigates the INI and enhances the performance of massive MIMO-OFDM uplink systems.

Joint Estimation of RF Impairments, Channel, and Low Complexity Iterative Equalization Technique for High Mobility SC-FDMA/OFDMA Uplink Systems

In this paper, we consider the problem of joint estimation and equalization of doubly selective channels and all radio frequency impairments, namely transmitter IQ imbalance (TIQI), receiver IQI (RIQI) and carrier frequency offsets (CFO) in the uplink of single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) systems with direct conversion transceiver architecture and high mobility users. We combine the effect of TIQI, RIQI and DSC to a new effective channel and propose the use of a Hermite polynomial based basis expansion model for approximating it to avoid the identifiability issue associated with this complete parameter estimation problem. As the maximum likelihood solution to this joint estimation problem requires complex multi-dimensional searches, we propose a novel subspace nulling based iterative estimation technique that effectively reduces the multi-user interference and replaces the multi-dimensional search with single-dimensional searches. Further, without much compromise on the performance, we also derive a low complexity version of the proposed technique. Additionally, we derive the Cramer-Rao bound for the joint estimation of CFO and effective channel. Moreover, we propose two equalization techniques for iteratively equalizing the mirror subcarrier pairs. The proposed techniques do not put any restriction on the carrier assignment scheme and provide good performance even at high mobile speeds.

Simultaneous Channel Estimation and Data Detection Based on Superimposed Training for Many Access MIMO System in Uplink

Massive Multiple Input Multiple Output (MIMO) has great potential to improve spectrum efficiency in the fifth generation (5G) wireless communication systems. However, the efficiency was disastrously reduced by the heavy burden of overhead for device detection and channel estimation of the large amount of small data packets in the uplink channel. In the paper, we proposed a novel transmission scheme by superposing the training symbols for active device detection and channel estimation on the data symbols in the uplink transmission to improve the efficiency. More specifically, in order to mitigate the cross interference among the superposed signals, we proposed to split the transmission into the training phase and the traffic phase. Then we superposed the training phase in the next transmission with the traffic phase in the current transmission. Furthermore, we give the optimization of power allocation ratio between training phase and traffic phase to obtain the optimal overall performance. The analytic and simulation results show that, with the help of spatial isolation among devices, our proposed transmission scheme can significantly improve the transmission efficiency compared with the existing schemes.

Uplink Null-Space Expansion for Multiuser Massive MIMO in Time-Varying Channels Under Unknown Interference

This article proposes a novel postcoding design scheme for suppressing inter-user interference (IUI) and inter-cell interference (ICI) in uplink multiuser massive multiple-input multiple-output (MIMO) system in time-varying channel environments. In the uplink system, the base station (BS) designs postcoding weight based on estimated channel state information (CSI) to suppress IUI. When user terminals move, the estimated CSI is outdated because actual channels vary with time. This causes IUI and leads to degrading the system capacity. Besides, ICI extensively arises in multiuser massive MIMO systems since many users are simultaneously supported in each cell. The accuracy of CSI estimates is degraded since ICI contaminates the uplink pilot sequences from desired users. Adopting a weight design based on minimum mean square error (MMSE) criteria, we can suppress ICI adequately, and exploiting plentiful degrees of freedom (DoFs) of massive array, we can also suppress IUI even in time-varying channels by steering many nulls for one user based on null-space expansion (NSE) scheme. The computer simulations clarify that the proposed scheme has superior SINR performance in Rayleigh fading channel at low speed, low SIR, and high SNR regions while it is effective at almost all conditions in Rician fading channel.

Impact of Mutual Coupling on Power-Domain Non-Orthogonal Multiple Access (NOMA)

This paper investigates the impact of mutual coupling (MC) on the achievable sum-rate of power-domain non-orthogonal multiple access (NOMA) system in both uplink (UL) and downlink (DL) transmissions. We assume a single-antenna user NOMA system with directional beamforming in the millimeter wave (mmW) channel. Due to the electromagnetic interaction between the antenna elements, called mutual coupling, at the base station (BS), the steering vector of the channel is affected. Consequently, this leads to distorted antenna pattern pointing towards different directions and reduction in channel gain, based on antenna array structure. In this paper, different antenna geometries and configurations, such as one-dimensional (1D) uniform linear array (ULA), two-dimensional (2D), and three-dimensional (3D) uniform circular array (UCA), are implemented at the BS, where induced electromotive force (EMF) and method of moment (MOM) techniques are used to generate the MC coefficients. We first examine the antenna patterns affected by MC, followed by channel gains of user terminals (UT)s. Then sum-rate of the NOMA system is modified in the presence of MC. Furthermore, mutual coupling is compensated successfully for both UL and DL systems for the given antenna structures. Simulation results show that mutual coupling degrades the sum-rate performance of the NOMA system in all three array structures, especially in the UCA structure due to the smaller spacing of the array element in a circular shape, resulting in symmetric mutual coupling from both sides of the circle. On the other hand, it is also shown that compensating the mutual coupling effect by the MOM technique in the case of unknown MC or matrix inversion in the case of known MC significantly improves the system sum-rate in all scenarios.

BER analysis of full duplex NOMA downlink and uplink co-operative user relaying systems over Nakagami-m fading environment

A Co-operative user Relaying Full Duplex Non Orthogonal Multiple Access (CR-FD-NOMA) system is considered, when there is no direct link between base station and the far user. Deriving analytical expressions for probability of error of systems with NOMA technique is a challenging task. In this paper, the Bit Error Rate (BER) performance of pre-paired CR-FD-NOMA users in downlink and uplink scenarios over Nakagami-m fading distribution is investigated. Quadrature Phase Shift Keying and Binary Phase Shift Keying modulations are used for near user and far user information respectively. By exploiting self interference and using the properties of Gaussian Q-functions at high signal to noise ratio regime, an approximated closed form BER expressions of both the users in downlink and uplink systems are derived. The performance of the proposed downlink and uplink CR-FD NOMA systems are compared with the conventional NOMA systems with the existence of direct path for both the users from BS. It is observed that the uplink performance of the CR-FD-NOMA systems outperforms the conventional NOMA systems.

Self-Interference Cancellation in Time-Domain for DOCSIS 3.1 Uplink System With Full Duplex

This paper introduces a self-interference cancellation (SIC) technique for data over cable service interface specification (DOCSIS) 3.1 uplink system with full duplex. At DOCSIS 3.1 uplink environment with full duplex, cable modems (CMs) transmit their request information (upstream) to CM termination system (CMTS), and CMTS transmits its broadcasting data (downstream) through the same frequency band at the same time. Therefore, the upstream becomes a signal of interest (SoI), and consequently the high-power feedback downstream causes self-interference (SI) signal against SoI. However, under the practical DOCSIS 3.1 uplink environment, achieving time and frequency synchronization between upstream and downstream is a challenging problem and additional signal processing technique should be applied. Therefore, in order to improve the processing efficiency and to reflect practical communication environment, the time-domain SIC technique, which does not require any synchronization between upstream and downstream is proposed. Furthermore, since the proposed scheme can consider various practical signal processing aspects, such as multi-path fading channel estimation and nonlinear element estimation of SI signal, it can be efficiently applied for the practical DOCSIS 3.1 uplink system. Test results indicate that the uplink system with 1024QAM (mandatory maximum constellation) can be operated in the case that there is SI estimation interval with two OFDM symbols.

Two-User Network-Coded Cooperation With NOMA and Advanced Successive Interference Cancellation

In this work, we evaluate the outage probability of a two-user network-coded cooperative (NCC) uplink system subjected to non-orthogonal multiple access (NOMA). We consider that the destination performs a recently proposed advanced successive interference cancellation (Adv-SIC) in order to decode the individual messages from the superimposed received signal, which requires only statistical channel state information (CSI). Our results indicate, through mathematical analysis and numerical simulations, that the benefits of Adv-SIC are boosted by NCC, improving the performance of both users, differently from a non-cooperative (NonCooP) NOMA system, where only the user with the worst average channel condition is benefited from Adv-SIC.

Fairness and Sum-Rate Maximization via Joint Subcarrier and Power Allocation in Uplink SCMA Transmission

In this work, we consider a sparse code multiple access uplink system, where $J$ users simultaneously transmit data over $K$ subcarriers, such that $J > K$, with a constraint on the power transmitted by each user. To jointly optimize the subcarrier assignment and the transmitted power per subcarrier, two new iterative algorithms are proposed, the first one aims to maximize the sum-rate (Max-SR) of the network, while the second aims to maximize the fairness (Max-Min). In both cases, the optimization problem is of the mixed-integer nonlinear programming (MINLP) type, with non-convex objective functions, which are generally not tractable. We prove that both joint allocation problems are NP-hard. To address these issues, we employ a variant of the block successive upper-bound minimization (BSUM) \cite{razaviyayn.2013} framework, obtaining polynomial-time approximation algorithms to the original problem. Moreover, we evaluate the algorithms' robustness against outdated channel state information (CSI), present an analysis of the convergence of the algorithms, and a comparison of the sum-rate and Jain's fairness index of the novel algorithms with three other algorithms proposed in the literature. The Max-SR algorithm outperforms the others in the sum-rate sense, while the Max-Min outperforms them in the fairness sense.

A Noncoherent Massive MIMO System Employing Beamspace Techniques

Noncoherent detection schemes are an appealing and low-complexity alternative in multi-user massive MIMO uplink systems compared to classical coherent detection algorithms, since no actual channel knowledge is required at the receiver. For noncoherent multi-user detection to function, the induced power at the base station is utilized to separate the different users. However, spatial separation is impossible when the users are located in the far-field of the receiving antenna array. Consequently, noncoherent detection fails in such scenarios. To this end, beamspace techniques can be applied, focusing the energy of the incident wave to a smaller subset of the receive antennas and enabling again the noncoherent detection scheme. This paper analyzes the beamspace capabilities of a dielectric lens and an analog beamforming network applied at the receiver. Furthermore, a sub-array architecture is proposed, relaxing the design requirements for practical implementation. It is shown that noncoherent detection in combination with beamspace techniques performs comparably to channel-estimation-based detection. In addition, the sub-array architecture revealed a significant performance enhancement accompanied by a reduced user separability.

Spatial Modulation for Uplink Multi-User mmWave MIMO Systems With Hybrid Structure

Spatial modulation is an efficient transmission scheme for RF-chain limited MIMO systems. In this paper, we design a beam-switching based spatial modulation for mmWave MIMO uplink systems. At user side, a power iteration based algorithm is proposed to generate spatial symbols under the constant modulus constraint. With the generated spatial codebook, the optimal transmission mode is determined. At base station side, a round-robin path selection algorithm is proposed to select paths that are separated in angle of arrival. Inter-user interference is then suppressed by constraining the power of the received spatial symbols over selected paths only. Finally, ordered successive interference cancelation is applied to further reduce interference among users. Numerical results show that the proposed beam-switching based spatial modulation is superior to transmission over the strongest propagation path and is able to yield a satisfactory error performance in mmWave MIMO uplink.

Towards energy efficient relay deployment in multi‐user LTE‐A networks

Communication using relay node (RN) cooperation is attractive research interest since it supports wide area coverage and high data rates. RNdeployment problem in multiple users long-term evolution-advanced (LTE-A) network is a challenging issue. In this article, the RN deployment problem for a single carrier-frequency division multiple access uplink system is considered. The total energy efficiency (EE) and average EE for multi-user single-relay in the LTE-A network are considered as the performance measures to select the optimum position of RN. Two types of users are deployed: guaranteed bit rate and non-guaranteed bit rate when performing load balancing that can influence the selection of the optimum position of RN. Simulation results show that the EE is increased by 10% based on load balancing compared to unbalanced loaded network. The optimum position of RN at 75% of a cell radius towards the cell edge can significantly improve the EE.