Remote Access Unit Research Articles

Joint Subcarrier Assignment and Power Allocation for OFDMA Full Duplex Distributed Antenna Systems

In this paper, we investigate the resource allocation scheme for orthogonal frequency division multiple access (OFDMA) full-duplex (FD) distributed antenna systems (DASs), in which both remote access units (RAUs) and users having the full-duplex capability. We aim to maximize the system spectral efficiency through jointly optimizing subcarrier assignment and power allocation, where users’ uplink/downlink quality of service requirements, per-user uplink/downlink transmit power constraints, and subcarrier reuse are considered. The user-centric virtual cell approach is adopted to reduce the computational and signaling overhead. Based on the successive convex approximation method and penalty factor, we propose an efficient overall optimization algorithm to tackle the non-convex optimization problem. Simulation results show that the proposed algorithm can achieve performance close to the exhaustive search algorithm, comparable to the hierarchical decomposition algorithm using the optimal subcarrier allocation scheme, and better than other benchmark algorithms. In addition, the proposed algorithm can guarantee fairness among users at a low cost of system spectral efficiency.

Hybrid beamforming design for mmWave OFDM distributed antenna systems

This paper presents a hybrid beamforming design for millimeter-wave (mmWave) orthogonal frequency division multiplexing (OFDM) distributed antenna systems (DASs). First, we derive a downlink signal transmission model that considers the delay spread differences (DSDs) caused by the distributed nature of the network. We then propose a cooperative wideband hybrid beamforming method under the transmitting power constraints of each remote access unit. In a simulation study, the proposed method performed comparably to fully-digital beamforming, even when operated with practical finite-resolution phase shifters. We further confirm that the DSDs are the dominant cause of performance degradation in mmWave OFDM DASs.

Design and analysis of all optical RF transceiver using polarization modulators

All optical multiband radio transceiver is designed using Polarization Modulators. Polarization Modulators have been gaining popularity in recent times as the device is free from bias drift problem that is commonly noticed in Mach Zhender intensity modulator. Two continuous wave (CW) optical frequencies separated by 26.25 GHz are selected from optical frequency comb generator designed using two parallel polarization modulators. Two subcarrier multiplexed (SCM) signal is modulated on a comb frequency using a polarization modulator. The SCM modulated optical signal and another CW optical comb separated by 26.25 GHz are fed to a remote radio access unit (RAU) via a single mode fibre. The two signals are heterodyned in a photo detector at a remote RAU producing multi radios at 27.25 GHz and 28.75 GHz in 5G New Radio frequency band of n258 (24.25–27.5 GHz) and n257 (26.5–29.5 GHz). In the receiver part of the transceiver, the received 5G signals are modulated by a Polarization Modulator with a CW optical comb frequency and the resultant optical sidebands along with the carrier are fed to the baseband unit (BBU) at the central office via a return fiber. At the BBU the signals are heterodyned in a photo-detector with a CW comb frequency to produce the down converted baseband output at the BBU. The proposed transceiver scheme is analysed and simulation is carried out inOptisystem16® platform. BER performance of the received signal with various laser powers show that the scheme is practically implementable. In particular BER of 10−6 is obtained at the photodetector output in the transmitted (downlink) signal and returned link (uplink) signal at 2.25 dBm laser power. Two tone IMD analysis of the transmitted signal provides input and output third order intercept point at 52 dBm and 32 dBm respectively. Spurious free dynamic range (SFDR) between fundamental and 3rd order intermodulation distortion product obtained is 85 dB.Hz2/3 considering a noise floor of − 140 dBc/Hz.

W-band PAM4 signal generation by a modulator driven by binary scheme with different driving voltage

We propose a novel W-band pulse amplitude modulation-4 (PAM4) signal generation to simplify the complexity of central office (CO), remote access unit (RAU) and wireless terminals. Only one dual-polarization Mach–Zehnder Modulator (DP-MZM) is used and no extra optical link is occupied. Moreover, multi-level digital-to analog converter (DAC) is not necessary. In this paper, we theoretically analyze and experimentally demonstrate the proposed method. After 1 m wireless propagation, the 84 GHz W-band signal can carry up 10 G baud data with a bit error rate (BER) less than the hard-decision forward error correction (HD-FEC) threshold of 3.8×10-3 with the photodiode (PD) input power of 0 dBm.

Downlink Transmission of Multicell Distributed Massive MIMO With Pilot Contamination Under Rician Fading

In this paper, we investigate the spectral efficiency (SE) of a multicell downlink (DL) distributed massive MIMO (DM-MIMO) system with pilot contamination operating over Rician fading channels in which each remote access unit (RAU) is equipped with a large number of distributed massive antenna arrays, while each user has a single antenna. In contrast to many previous works about DM-MIMO systems, the channel between users and the RAUs antennas in the same cell is modeled to be Rician fading, which is general for the 5G scenarios like Internet of Things. We explore maximum-ratio transmission (MRT) and line-of-sight (LOS) component-based equal-gain transmission (EGT) under imperfect channel state information. The tractable, but accurate closed-form expressions for the lower bounds of the achievable rate are derived for the MRT and the LOS component-based EGT over Rician fading channels in the DM-MIMO systems. Based on the obtained closed-form expressions, various power scaling laws concerning DL data transmit power and pilot transmit power are analyzed in detail. Numerical results are used to corroborate that these approximations are asymptotically tight, but accurate for systems. They also show that employing the LOS component-based EGT processing is more preferable than the MRT processing for DM-MIMO systems in conditions having a large number of RAU antennas and stronger LOS scenarios. Finally, the simulation results further show that when the number of all antennas for RAUs is fixed, the better SE performance can be obtained with more RAUs.

Polarization Multiplexing-Based Ultra-Wideband Over Fiber Communication Employing Direct Modulation and Carrier Re-Use

A cost-efficient ultra-wideband (UWB) over fiber architecture is proposed and demonstrated through simulation results. A directly modulated laser diode at the central unit (CU) is employed to transport and generate downlink UWB signals at a remote access unit (RAU). The directly modulated carrier is re-used at the RAU for transmission of uplink UWB signal. Therefore, all-optical full-duplex transmission of UWB signals at a rate of 2 Gbps is achieved while maintaining very low-bit-error rate (BER) values.

Improving Central and Remote Access Units in Cloud Based Wi-Fi Network for Better Client and Service

People show attention to cloud computing since it is efficient and scalable. But maintaining the stability of processing so many jobs in the cloud computing environment with load balancing is a very difficult problem and receives much attention by researchers. Load balancing in cloud computing platform has performance impact also. Good load balancing makes cloud computing more efficient and increases user satisfaction. This paper introduces a better load balance model for public cloud based on cloud partitioning concept with a switch mechanism to choose various strategies in different situations. The algorithm applies game theory to load balancing strategy and improves the efficiency in the public cloud environment. MCC is a concept which aims to mitigate these limitations by extending the capabilities of smart devices by employing cloud services, as required. In MCC both the data storage and processing occur external to the mobile device, while in cloud computing it is usually only the data storage which is external. In this following a some of these architectures as categorized in augmented execution, elastic partitioned/modularized applications, application mobility, ad-hoc mobile cloud and add a fifth category; cyber foraging. This system addresses whether MCC techniques can be used to extend the capabilities of resource-constrained mobile-devices to provide the illusion of infinite, elastic resources on demand. The existing system limitations of mobile-devices, and identified five key limited resources as being CPU, memory, battery, data usage and time. In this research explored existing solutions for these limitations and identified offloading computation and storage from the device as a possible solution.

Power Allocation Criteria for Distributed Antenna Systems with D2D Communication

In this paper, we discuss two different optimization objective problems for distributed antenna systems (DAS) with D2D communication. The first objective problem is maximizing spectral efficiency (SE) of the DAS with D2D communication under the constraints of the minimum SE requirements of DAS and D2D pair, maximum transmit power of each remote access unit (RAU) and maximum transmit power of D2D transmitter. We use the subgradient iteration approach to obtain the optimal power allocation and summarize the algorithm. The second objective is maximizing energy efficiency (EE) of the DAS with D2D communication under the same constraints as the first problem. We firstly exploit fractional programming method to transform this difficult problem into an equivalent objective function with subtract form, and then we use the similar method like first problem to obtain the optimal power allocation for the equivalent problem. Simulation results are illustrated the SE and EE of the DAS by using D2D communication are much better than DAS without D2D communication.

Spectral efficiency and energy efficiency of distributed antenna systems with virtual cells

In this paper, we consider user centric virtual cells model in distributed antenna systems (DAS). We investigate different power allocation optimization problems with interferences in DAS with and without user centric virtual cells model, respectively. The first objective problem is maximizing spectral efficiency (SE) of the DAS with user centric virtual cells model under the constraints of the minimum SE requirements of each user equipment (UE), maximum transmit power of each remote access unit (RAU). We firstly transform this non-convex objective function into a difference of convex functions (D.C.) problem, and then we obtain the optimal solutions by using the concave-convex procedure (CCCP) algorithm. The second objective problem is maximizing energy efficiency (EE) of the DAS with user centric virtual cells model under the same constraints as the first objective problem. Firstly, we exploit fractional programming theory to obtain the equivalent objective function of the second problem with subtract form, and then transform it into a D.C. problem and use CCCP algorithm to obtain the optimal power allocation. In each part, we propose the corresponding optimal power allocation algorithm and also use similar method to obtain optimal solutions of the same optimization problems in DAS without using user centric virtual cells model. Simulation results are provided to demonstrate the effectiveness of the DAS with user centric virtual cells model, which can significantly improve the SE and the EE of the communication systems.

Power allocation criteria for distributed antenna systems with D2D communication

In this paper, we discuss four different optimization problems for distributed antenna systems (DAS) with and without D2D communication, respectively. The first and the third problems are maximizing spectral efficiency (SE) and energy efficiency (EE) of the DAS with D2D communication on the conditions of the minimum SE of DAS as well as D2D pair, the maximum transmit power of each remote access unit (RAU) and maximum transmit power of D2D transmitter. The second and the forth problems are maximizing SE of the DAS on the conditions of the minimum SE as well as the maximum transmit power of RAUs. We exploit the sub-gradient iteration method to obtain the optimal power allocation and summarize optimal power allocation algorithms for the first and second problems. We exploit fractional programming method to investigate the third and fourth problems and develop corresponding optimal power allocation algorithms. Simulation results demonstrate the effectiveness of the proposed power allocation algorithms and show the SE and EE of the DAS by using D2D communication are much better than DAS without D2D communication.

Cloud-Based Wi-Fi Network Using Immediate ACK in Uplink Data Transmissions

In a cloud-based network architecture, the central unit (CU) at the cloud coordinates wireless nodes such as the remote access units (RAUs) at the edges of the network and manages most functions for providing wireless connectivity services to clients. The CU facilitates efficient communication resource management such as radio frequency or transmission power of RAUs by global resource coordination. In this paper, we propose a cloud-based Wi-Fi network architecture consisting of a CU and RAUs as an improvement on the conventional Wi-Fi architecture with traditional access points (APs). We then propose a method for uplink data transmission in a cloud-based Wi-Fi network. In a conventional Wi-Fi network with independently operating APs, APs close to each other may not be able to utilize the same frequency band efficiently because of significant amounts of interference. However, in a cloud-based Wi-Fi network, the CU coordinates RAUs so that they can operate in the same frequency band by transmitting or receiving signals through the shared wireless medium to improve spectral efficiency. For each frequency band, the proposed system utilizes a diversity combining that combines multiple signals and introduces a single improved signal with high signal-to-noise ratio for uplink transmission in the cloud-based Wi-Fi network. In our proposed uplink transmission method for a cloud-based Wi-Fi network, we utilize diversity combining with the immediate acknowledgement (ACK) transmission method that transmits the ACK frame to the client immediately before decoding. The proposed uplink data transmission method mitigates the performance degradation caused by the fronthaul propagation delay between the CU and RAUs, without significant modification of the IEEE 802.11 standard. Using an IEEE 802.11n standard-compliant simulation and experiments with software-defined radio equipment, we verify the goodput performance of the proposed method for a cloud-based Wi-Fi network architecture.

Spectral Efficiency and Energy Efficiency of Bidirectional Distributed Antenna Systems With User Centric Virtual Cells

In this paper, we first introduce the bidirectional distributed antenna systems (DAS) and exploit the choosing algorithm to take user-centric virtual cells into this system. Then, we discuss different power allocation optimization problems with interferences in bidirectional DAS with and without user-centric virtual cells, respectively. The first objective problem is maximizing spectral efficiency (SE) of bidirectional DAS satisfying the requirements of the minimum SE of each user equipment and maximum transmit power of each remote access unit. First, we convert this non-convex objective function into a difference of convex functions (D.C.) problem, and then, we obtain the optimal power allocation by using the concave–convex procedure (CCCP) algorithm. The second objective problem is maximizing energy efficiency (EE) of bidirectional DAS under the same constraints as the first problem. First, we exploit fractional programming theory to transform the second problem into an equivalent objective function with subtractive form, and then convert it into a D.C. problem and obtain the optimal solutions by using the CCCP algorithm. In each part, we propose the corresponding optimal power allocation algorithm and also use a similar method to obtain optimal solutions of the same optimization problems in bidirectional DAS with user-centric virtual cells. Simulation results showed the effectiveness of the proposed power allocation algorithms and demonstrate the SE and EE of the bidirectional DAS with user-centric virtual cells which are much better than bidirectional DAS.

Joint Fronthaul Link Selection and Transmit Precoding for Energy Efficiency Maximization of Multiuser MIMO-Aided Distributed Antenna Systems

We jointly select the fronthaul links and optimize the transmit precoding matrices for maximizing the energy efficiency (EE) of a multiuser multiple-input multiple-output-aided distributed antenna system. The fronthaul link’s power consumption is taken into consideration, which is assumed to be proportional to the number of active fronthaul links quantified by using indicator functions. Both the rate requirements and the power constraints of the remote access units are considered. Under realistic power constraints, some of the users cannot be admitted. Hence, we formulate a two-stage optimization problem. In Stage I, a novel user selection method is proposed for determining the maximum number of admitted users. In Stage II, we deal with the EE optimization problem. First, the indicator function is approximated by a smooth concave logarithmic function. Second, a triple-layer iterative algorithm is proposed for solving the approximated EE optimization problem, which is proved to converge to the Karush–Kuhn–Tucker conditions of the smoothened EE optimization problem. To further reduce the complexity, a single-layer iterative algorithm is conceived, which guarantees convergence. Our simulation results show that the proposed user selection algorithm approaches the performance of the exhaustive search method. Finally, the proposed algorithms are capable of achieving an order of magnitude higher EE than its conventional counterpart operating without considering link selection.

Reconfigurable Radio Access Unit for DWDM to W-Band Wireless Conversion

In this letter a reconfigurable remote access unit (RAU) is proposed and demonstrated, interfacing dense wavelength division multiplexed (DWDM) optical and W-band wireless links. The RAU is composed of a tunable local oscillator, a narrow optical filter, and a control unit, making it reconfigurable via software. The RAU allows selection of a DWDM channel and tuning of the radio carrier frequency. Real-time transmission results at 2.5 Gbit/s and performance measurements with offline data processing at 4 and 5 Gbit/s are presented. Error free real-time transmission was achieved after 15 km of standard single mode fiber and 50 m of wireless transmission with carriers between 75 and 95 GHz.

Energy Efficiency Optimization for MIMO Distributed Antenna Systems

In this paper, we propose a transmit covariance optimization method to maximize the energy efficiency (EE) for a single-user distributed antenna system, where both the remote access units (RAUs) and the user are equipped with multiple antennas. Unlike previous related works, both the rate requirement and RAU selection are taken into consideration. Here, the total circuit power consumption is related to the number of active RAUs. Given this setup, we first propose an optimal transmit covariance optimization method to solve the EE optimization problem under a fixed set of active RAUs. More specifically, we split this problem into three subproblems, i.e., the rate maximization problem, the EE maximization problem without rate constraint, and the power minimization problem, and each subproblem can be efficiently solved. Then, a novel distance-based RAU selection method is proposed to determine the optimal set of active RAUs. Simulation results show that the performance of the proposed RAU selection is almost identical to the optimal exhaustive search method with significantly reduced computational complexity, and the performance of the proposed algorithm significantly outperforms the existing EE optimization methods.

A Zigbee and Sip-Based Smart Home System Design and Implementation

This investigation presents a Zigbee and Sip based smart home system(ZSS) that automates home-service operations and remote access. The ZSS home system comprises five subsystems,namely home automation network,home IP netework,home gateway,remote access unit, and cloud service unit. The home automation network is a wireless sensor network , responsible to sample sensors data and control actuators by Zigbee instructions. Security system adopts IP network technology to transmit videos from IP cameras to remote units. A home gateway middleware is designed to extract atomic service provied by a single device, then customize service rules which can meet variable user demands.Peer to peer transparent data channels between remote mobile phones and home devices are set up by Sip framework to overcome connection issues due to network address translation and dymaic public IP address. A novel data stream algorithm named GCOKDE is exploited to get probability density distribution of environmental parameters which can be uesd for the condition value of service rule.At the end,this study constructes a prototype to reveal the procedure of realization.

Energy efficiency of distributed massive MIMO systems

In this paper, we investigate energy efficiency (EE) of the traditional co-located and the distributed massive multiple-input multiple-output (MIMO) systems. First, we derive an approximate EE expression for both the idealistic and the realistic power consumption models. Then an optimal energy-efficient remote access unit (RAU) selection algorithm based on the distance between the mobile stations (MSs) and the RAUs are developed to maximize the EE for the downlink distributed massive MIMO systems under the realistic power consumption model. Numerical results show that the EE of the distributed massive MIMO systems is larger than the co-located massive MIMO systems under both the idealistic and realistic power consumption models, and the optimal EE can be obtained by the developed energy-efficient RAU selection algorithm.

Network Planning for 80211ad and MT-MAC 60 GHz Fiber-Wireless Gigabit Wireless Local Area Networks Over Passive Optical Networks

We present a study concerning the network planning of 60 GHz gigabit wireless local area networks (WLANs) over existing passive optical network (PON) infrastructures. Two fiber-wireless configurations for gigabit WLAN network formations are investigated: i) the Radio & Fiber (RF and ii) the Radio-over-Fiber (RoF) paradigm that employs several remote access units operating under the medium-transparent MAC (MT-MAC) protocol, hence termed as the MT-MACover- PON approach. Simulation-based throughput and delay results are obtained for both network scenarios, revealing the dependence of the 60 GHz enterprise network performance on several network-planning parameters such as load, traffic shape, number of optical wavelengths in the backhaul, and optical backhaul fiber length, highlighting in each case the prevailing architecture. Based on the respective findings we also study a hybrid multitier architecture, termed the GPON-plus-MT-MAC approach, that fuses the abilities of both the RoF and R&F architectures in order to optimally combine their properties and set a framework for next-generation 60 Ghz fiber-wireless networks.

Polarization-Insensitive Remote Access Unit for Radio-Over-Fiber Mobile Fronthaul System by Reusing Polarization Orthogonal Light Waves

To reduce the complexity and cost of remote access units (RAUs), colorless transport architecture is preferred in a wavelength-division multiplexing (WDM) system. The wavelength-reuse technique is commonly adopted to realize colorless RAUs. However, in traditional approaches, RAUs employ crystal-based Mach–Zehnder modulators (MZMs) to modulate the distributed carriers. Hence, polarization tracking systems are necessary to align the polarization state of the distributed carriers with the MZM principal axis. This increases the cost of the RAUs. In this paper, a full-duplex millimeter-wave (MMW) radio-over-fiber (RoF) access architecture employing polarization-insensitive RAUs is proposed. In our proposed RAUs, the upstream signals are generated using polarization-orthogonal lights, and the performance of the upstream signals is independent of the polarization state of the MZM input lights. The proposed system is mathematically formulated and experimentally demonstrated. The 1.2-Gb/s quadrature phase-shift keying (QPSK) orthogonal frequency-division multiplexing (OFDM) downstream signal at the 60-GHz band and 5-Gb/s on–off keying (OOK) polarization-insensitive upstream signal over a 15-km standard single-mode fiber (SSMF) are demonstrated. In our results, a polarization-insensitive RAU is successfully obtained. The power penalty resulting from the interference of downstream signal is about 0.4 and 0.6 dB with a bit error rate (BER) of $10^{-9} $ in back-to-back and 15-km fiber transmission, respectively.

Comparison of three different optimization objectives for distributed antenna systems

In this paper, we discuss three different optimization objectives for a distributed antenna system (DAS). They are: (i) maximize sum-rate under the constraints of the system's minimum spectral efficiency (SE) requirements and overall transmit power of each remote access unit (RAU); (ii) minimize the overall transmit power while satisfying the system's minimum SE requirements and overall transmit power of each RAU; (iii) maximize energy efficiency (EE) while satisfying the system's minimum SE requirements and overall transmit power of each RAU. We use sub-gradient iteration approach to obtain the optimal power allocation algorithms for the maximum sum-rate and minimum the overall transmit power optimization problems. We exploit fractional programming method to investigate energy-efficient power allocation algorithm for the maximum EE optimization problem. Three efficient power allocation algorithms are developed to maximize sum-rate, minimize the overall transmit power, and maximize EE for the downlink multiuser DAS. Simulation results are provided to demonstrate the effectiveness of the developed three power allocation algorithms, and illustrate the EE performance of maximizing EE is higher than the two other optimization objectives.