Independent Data Streams Research Articles

Chip-to-Chip Interfaces for Large-Scale Highly Configurable mmWave Phased Arrays

This article presents a chip-to-chip (C2C) interface for constructing reconfigurable phased arrays to be used in fifth-generation (5G)/sixth-generation (6G) wireless systems. The C2C interface further facilitates building phased array panels by allowing the use of grid-based PCB routing, thus providing flexibility in the system design. An eight-element RFIC capable of handling two independent data-streams is fabricated using 45-nm CMOS technology. The RFIC incorporates four C2C interfaces operating at 27 GHz, two C2C interfaces operating at 9 GHz, and a complex baseband (BB) with single-sided bandwidth in excess of 400 MHz. The architecture is tested by flip-chip bonding two fabricated RFICs on an eight-layer Megtron 7 PCB. In this article, only the receiver path of the RFIC and the phased array is described. Performance of both the single RFIC and the combination using the 27-GHz C2C interface is demonstrated using conductive and over-the-air (OTA) measurements. OTA measurements are conducted using 5GNR FR2 OFDM waveforms with a signal bandwidth of up to 800 MHz. The measured RF to BB conversion gain for a single element is larger than 23 dB and the minimum measured noise figure (NF) is 6.2 dB. The nominal dc power consumed by the receiver per element per stream is 116.5 mW. The RFIC occupies a normalized area per element per data stream of 2.7 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^2$</tex-math> </inline-formula> . The RFIC is capable of supporting dual-polarized antennas or in a large-scale panel utilizing the same antenna elements to two independently weighted data streams as part of the hybrid beamforming architecture.

Generation of Photon Orbital Angular Momentum and Its Application in Space Division Multiplexing

In the last three decades, light’s orbital angular momentum (OAM) has been of great interest because it has unique characteristics that make it sought after in many research fields, especially in optical communications. To address the exponentially increasing demands for higher data rates and capacity in optical communication systems, OAM has emerged as an additional degree of freedom for multiplexing and transmitting multiple independent data streams within a single spatial mode using the spatial division multiplexing (SDM) technology. Innumerable research findings have proven to scale up the channel capacity of communication links by a very high order of magnitude, allowing it to circumvent the reaching of optical fiber’s non-linear Shannon limit. This review paper provides a background and overview of OAM beams, covering the fundamental concepts, the various OAM generators, and the recent experimental and commercial applications of the OAM-SDM multiplexing technique in optical communications.

ACDC: Online unsupervised cross-domain adaptation

We consider the problem of online unsupervised cross-domain adaptation, where two independent but related data streams with different feature spaces – a fully labeled source stream and an unlabeled target stream – are learned together. Unique characteristics and challenges such as covariate shift, asynchronous concept drifts, and contrasting data throughput arise. We propose ACDC, an adversarial unsupervised domain adaptation framework that handles multiple data streams with a complete self-evolving neural network structure that reacts to these defiances. ACDC encapsulates three modules into a single model: A denoising autoencoder that extracts features, an adversarial module that performs domain conversion, and an estimator that learns the source stream and predicts the target stream. ACDC is a flexible and expandable framework with little hyper-parameter tunability. Our experimental results under the prequential test-then-train protocol indicate an improvement in target accuracy over the baseline methods, achieving more than a 10% increase in some cases.

Closed Form Approximation of the Actual Spectral Power Emission of Commercial Color LEDs for VLC

Multi-color Light-Emitting Diode (LED) technology enables a simple approach to increase the throughput of a Visible Light Communications (VLC) system, by using Wavelength-Division Multiplexing (WDM) to transmit independent data streams on different <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">colors</i> . However, to compute the data rate that is achievable in such WDM VLC link, the optical power that leaks between the different colors needs to be estimated accurately, especially when low-cost optical filters are used in reception. So far, the approximations that have been reported in the literature to model the spectral power emission of different color LEDs are not good enough to perform these calculations. Starting from the theoretical spectral emission of a color LED, a closed form expression is derived based on an asymmetric Pearson type VII function, which is shown to approximate accurately the measured spectra of the color LEDs at different working regimes. In addition, the effect that the DC-bias current has on the key parameters of the approximated spectral power emissions, namely the peak and half-maximum wavelengths, as well as the peak spectral emission, are studied. Finally, a new approach is proposed to assess the level of fitness of the derived closed form approximations, using for this purpose the step-size of the MacAdam ellipses that corresponds to the different color LED spectral emissions in the CIE 1931 chromaticity diagram.

Robust change detection for large-scale data streams

Robust change point detection for large-scale data streams has many real-world applications in industrial quality control, signal detection, and biosurveillance. Unfortunately, it is highly nontrivial to develop efficient schemes due to three challenges: (1) the unknown sparse subset of affected data streams, (2) the unexpected outliers, and (3) computational scalability for real-time monitoring and detection. In this article, we develop a family of efficient real-time robust detection schemes for monitoring large-scale independent data streams. For each data stream, we propose to construct a new local robust detection statistic called the -CUSUM (cumulative sum) statistic that can reduce the effect of outliers by using the Box-Cox transformation of the likelihood function. Then the global scheme will raise an alarm based upon the sum of the shrinkage transformation of these local -CUSUM statistics to filter out unaffected data streams. In addition, we propose a new concept called false alarm breakdown point to measure the robustness of online monitoring schemes and propose a worst-case detection efficiency score to measure the detection efficiency when the data contain outliers. We then characterize the breakdown point and the efficiency score of our proposed schemes. Asymptotic analysis and numerical simulations are conducted to illustrate the robustness and efficiency of our proposed schemes.

Visible light communication performance using MIMO‐ADO‐OFDM system

AbstractVisible light communications (VLC) and optical orthogonal frequency division multiplexing (O‐OFDM) have recently been identified as hopeful wireless techniques. Asymmetrically clipped DC‐biased O‐OFDM (ADO‐OFDM) is a modern performance enhancement technology used in VLC. This article proposes a performance improvement model using a novel approach that collaborates with ADO‐OFDM and multiple‐input multiple‐output (MIMO) in different design scenarios. In the first scenario, the bit‐error‐rate (BER) performance improvement is examined using different setups of MIMO‐ADO‐OFDM with maximal ratio combining (MRC). 8 × 8 MIMO good performance can be attained with about 15 dB signal‐to‐noise ratio for BER = 10−4. Another scenario is to boost the spectral efficiency of MIMO‐ADO‐OFDM by employing spatial multiplexing (SMX). However, 8 × 8 MIMO with SMX can improve spectral efficiency eight times that of single‐input single‐output ADO‐OFDM by fragmenting source data into numerous independent data streams. In the last scenario, multi‐user MIMO is developed by adopting ADO‐OFDM with zero‐forcing equalisers, allowing each user to consume all available bandwidth. The proposed technologies are evaluated by comparison with other MIMO systems, different O‐OFDM, and under a non‐linear LED model.

Utilizing Non-Orthogonal Polarization With Polarization Reuse Technique for 4 × 4 MIMO Capacity Enhancement

5G communication promises fast and large data stream which requires higher capacity of a cellular wireless network. A higher capacity could be achieved with wider bandwidth and network densification, but they are expensive approaches. Instead, upgrading the wireless network with higher-order Multiple Input Multiple Output (MIMO) antenna system with polarization diversity can inexpensively escalate the peak data rate for higher capacity. We present a 4x4 MIMO cellular network scheme utilizing polarization reuse scheme and using 4 polarization to reform the cellular network from current state of the art of dual polarization 4x4 MIMO scheme. 4 Polarizations (vertical, Horizontal, ±45° slant) is used in 2 orthogonal polarization pair form, with a beam-separation among pair, to intensify polarization diversity and maximize the MIMO network channel capacity. This beam-separated polarization reuse technique minimizes the channel correlation which maximizes the probability of four independent data streams (rank 4). The simulated result of the channel capacity with the proposed scheme achieves a 30% higher capacity compared to the baseline configuration of 3-sector 4x4 MIMO. The field trial of the presented network indicates a higher portion of rank 4, supporting four independent data streams in the rich scattering environment of a cellular network.

An Adaptive CMT-SCTP Scheme: A Reinforcement Learning Approach

With the continuous increase of end users and types of services, the scale of the network has shown explosive growth, which has brought tremendous pressure and challenges to network data transmission. How to achieve high-quality data transmission has become a core issue. Single-path transmission has been difficult to meet the above requirements. The concurrent multipath transfer extension for stream control transmission protocol (CMT-SCTP), which supports multipath and independent data streams, can solve this problem. However, the current transmission path assessment scheme has too large granularity to make full use of the resources of the transition zone. Most studies ignore the different requirements of different services, a single transmission strategy, and the lack of an intelligent dynamic adjustment mechanism. Therefore, we designed a QCMT(Q-learning based CMT-SCTP) scheduling method. This method considers the multi-dimensional characteristics of the path and the characteristic preferences of different services, periodically evaluates and trains the reinforcement learning model for service adaptation, and makes scheduling decisions dynamically. Experimental results show that dynamic scheduling based on path parameters and service preferences can reduce message delay and improve network throughput.

DESIGN OF 6G COMMUNICATION SYSTEM AT THZ FREQUENCY BANDS

Toward increasing the data rates further, Teraherk (THz) frequency bands (0.1 -10 THz) became the central aspect of sixth-generation (6G) networks that support massive connectivity, low-latency, highly secure communications, data rates [hundreds of gigabytes per second (Gbps)], and denser networks. THz transmission is a complementary wireless technology for high-speed wireless extension of the optical fibers for 6G. The availability of materials for antenna fabrication and feasibility in designing ultra-massive multi-input-multi-output (U-mMIMO) systems motivates one to explore its peak performance at THz frequency bands. In this paper, a multiuser U-mMIMO system was designed with hybrid beam-forming features and its performance was tested at 0.142 THz bands for different numbers of base station antennas and modulation orders. Each user had one or more number of independent data streams, and the total number of users considered in the multiuser U-mMIMO system were 4 and 8. The metrics we considered in evaluating the performance were error vector magnitude, antenna array radiation patterns, and equalized symbol constellations. The results of simulations strongly recommend exploring the THz frequency bands for building next-generation wireless systems that satisfy the needs of the near future.

Design and Feasibility Verification of 6G Wireless Communication Systems with State of the Art Technologies

Frequencies above 100 GHz are the promising frequency bands for 6G wireless communication systems because of the abundant unexplored and unused spectrum. The increasing global demand for ultra-high spectral efficiencies, data rates, speeds and bandwidths in next-generation wireless networks motivates the exploration of peak capabilities of massive MIMO (Multi–Input–Multi–Output) wireless access technology at THz bands (0.1–10 THz). The smaller wavelengths (order of microns) of these frequencies give an advantage of making high gain antennas with smaller physical dimensions and allows massive spatial multiplexing. This paper presents the design of ultra-massive MIMO (ultra-mMIMO) hybrid beamforming system for multi users and its feasibility to function at THz frequency bands. The functionality of the proposed system is verified at higher order modulation schemes to achieve higher spectral efficiencies using performance metrics that includes error vector magnitude, symbol constellations, and antenna array radiation beams. The performance results suggest to use a particular mMIMO antenna configuration based on number of independent data streams per user and strongly recommended to use higher number of data streams per user in order to achieve higher throughputs that satisfy the needs of 6G wireless systems. Also the performance of the proposed system at 0.14 THz is compared with mmWave systems that operate at 28 GHz and 73 GHz bands to justify the feasibility of the proposed work.

Reconfigurable Intelligent Surface Based Orbital Angular Momentum: Architecture, Opportunities, and Challenges

Orbital angular momentum (OAM) has gained a lot of attention due to its potential in enhancing the spectral efficiency for wireless communications. Using different OAM modes, multiple independent data streams are simultaneously transmitted by using spatial distribution of helical phase, which enables OAM as a new form of multiple access technique for wireless communications. Controlling the phases of incoming electromagnetic waves, the reconfigurable intelligent surface (RIS) is suitable for implementing OAM. In this article, an RIS-based OAM framework is introduced. The basic concepts and features of RIS and OAM are presented. Then classifications and comparisons of different RIS-based OAM schemes are summarized. Simulation results verify that RIS-based OAM transmission can achieve nearly 100 percent higher spectral efficiency of wireless communication systems compared to the conventional RIS scheme.

Micro-Workflows Data Stream Processing Model for Industrial Internet of Things

The fog computing paradigm has become prominent in stream processing for IoT systems where cloud computing struggles from high latency challenges. It enables the deployment of computational resources between the edge and cloud layers and helps to resolve constraints, primarily due to the need to react in real-time to state changes, improve the locality of data storage, and overcome external communication channels’ limitations. There is an urgent need for tools and platforms to model, implement, manage, and monitor complex fog computing workflows. Traditional scientific workflow management systems (SWMSs) provide modularity and flexibility to design, execute, and monitor complex computational workflows used in smart industry applications. However, they are mainly focused on batch execution of jobs consisting of tightly coupled tasks. Integrating data streams into SWMSs of IoT systems is challenging. We proposed a microworkflow model to redesign the monolith architecture of workflow systems into a set of smaller and independent workflows that support stream processing. Micro-workflow is an independent data stream processing service that can be deployed on different layers of the fog computing environment. To validate the feasibility and practicability of the micro-workflow refactoring, we provide intensive experimental analysis evaluating the interval between sensor messages, the time interval required to create a message, between sending sensor message and receiving the message in SWMS, including data serialization, network latency, etc. We show that the proposed decoupling support of the independence of implementation, execution, development, maintenance, and cross-platform deployment, where each micro-workflow becomes a standalone computational unit, is a suitable mechanism for IoT stream processing.

Performance analysis of multi user massive MIMO hybrid beamforming systems at millimeter wave frequency bands

Millimeter-wave (mmWave) and massive multi-input–multi-output (mMIMO) communications are the most key enabling technologies for next generation wireless networks to have large available spectrum and throughput. mMIMO is a promising technique for increasing the spectral efficiency of wireless networks, by deploying large antenna arrays at the base station (BS) and perform coherent transceiver processing. Implementation of mMIMO systems at mmWave frequencies resolve the issue of high path-loss by providing higher antenna gains. The motivation for this research work is that mmWave and mMIMO operations will be much more popular in 5G NR, considering the wide deployment of mMIMO in major frequency bands as per 3rd generation partnership project. In this paper, a downlink multi-user mMIMO (MU-mMIMO) hybrid beamforming communication system is designed with multiple independent data streams per user and accurate channel state information. It emphasizes the hybrid precoding at transmitter and combining at receiver of a mmWave MU-mMIMO hybrid beamforming system. Results of this research work give the tradeoff between multiple data streams per user and required number of BS antennas. It strongly recommends for higher number of parallel data streams per user in a mmWave MU-mMIMO systems to achieve higher order throughputs.

Demonstrating the use of OAM modes to facilitate the networking functions of carrying channel header information and orthogonal channel coding.

We experimentally demonstrate the use of orbital angular momentum (OAM) modes as a degree of freedom to facilitate the networking functions of carrying header information and orthogonal channel coding. First, for carrying channel header information, we transmit a 10 Gb/s on-off keying (OOK) data channel as a Gaussian beam and add to it a 10 Mb/s OOK header carried by an OAM beam with the mode order ℓ=3. We recover the header and use it to drive a switch and select the output port. Secondly, for orthogonal channel coding, we configure transmitters to generate orthogonal spatial codes (orthogonal spatial beam profiles of OAM modes), each carrying an independent data stream. We measure the correlation between the OAM codes and demonstrate their use in a multiple access system carrying two 10 Gb/s OOK data channels. At the end of this Letter, we combine the concepts of using OAM modes for carrying channel header information and orthogonal channel coding in one experiment. We transmit a 10 Gb/s OOK data channel as a Gaussian beam and add to it two 10 Mb/s OOK header waveforms carried by different OAM codes. In the routing node, we recover one of the headers to drive the switch.

Development of algorithms of self-organizing network for reliable data exchange between autonomous robots

Factors affecting the reliability of data transmission in networks with nodes with periodic availability were considered. The principles of data transfer between robots are described; the need for global connectivity of communications within an autonomous system is shown, since the non-availability of information on the intentions of other robots reduces the effectiveness of the robotics system as a whole and affects the fault tolerance of a team of independent actors performing distributed activities. It is shown that the existing solutions to the problem of data exchange based on general-purpose IP networks have drawbacks; therefore, as the basis for organizing autonomous robot networks, we used developments in the domain of topological models of communication systems allowing us to build self-organizing computer networks. The requirements for the designed network for reliable message transfer between autonomous robots are listed, the option of organizing reliable message delivery using overlay networks, which expand the functionality of underlying networks, is selected. An overview of existing popular controlled and non-controlled overlay networks is given; their applicability for communication within a team of autonomous robots is evaluated. The features and specifics of data transfer in a team of autonomous robots are listed. The algorithms and architecture of the overlay self-organizing network were described by means of generally accepted methods of constructing decentralized networks with zero configurations. As a result of the work, general principles of operation of the designed network were proposed, the message structure for the delivery algorithm was described; two independent data streams were created, i.e. service and payload; an algorithm for sending messages between network nodes and an algorithm for collecting and synchronizing the global network status were developed. In order to increase the dependability and fault tolerance of the network, it is proposed to store the global network status at each node. The principles of operation of a distributed storage are described. For the purpose of notification on changes in the global status of the network, it is proposed to use an additional data stream for intra-network service messages. A flood routing algorithm was developed to reduce delays and speed up the synchronization of the global status of a network and consistency maintenance. It is proposed to provide network connectivity using the HELLO protocol to establish and maintain adjacency relations between network nodes. The paper provides examples of adding and removing network nodes, examines possible scalability problems of the developed overlay network and methods for solving them. It confirms the criteria and indicators for achieving the effect of self-organization of nodes in the network. The designed network is compared with existing alternatives. For the developed algorithms, examples of latency estimates in message delivery are given. The theoretical limitations of the overlay network in the presence of intentional and unintentional defects are indicated; an example of restoring the network after a failure is set forth.

A QPSK 110-Gb/s Polarization-Diversity MIMO Wireless Link With a 220–255 GHz Tunable LO in a SiGe HBT Technology

In this article, a polarization-diversity technique multiple-input multiple-output (MIMO) is demonstrated to double the spectral efficiency of a line-of-sight quadrature phase-shift keying (QPSK) wireless link at 220-255 GHz with a pair of highly integrated single-chip transmitter (TX) and receiver (RX) front-end modules in 0.13-μm SiGe HBT technology ( f T/ f max = 350/550 GHz) exploiting only a low-cost wire-bonded chip-on-board packaging solution for high-speed baseband (BB) signals. Both TX and RX chips accommodate two independent fundamentally operated direct-conversion in-phase and quadrature (IQ) paths with separately tunable on-chip multiplier-based (×16) local oscillator (LO) generation paths driven from a single external highly stable 13.75-16-GHz frequency synthesizer. On the RX side, a mixer-first architecture is implemented to improve the symmetry between upper and lower sidebands (USB and LSB) at the cost of an increased noise figure (NF), whereas, on the TX chip, each upconversion mixer is followed by a gain-bandwidth (BW)-limited fourstage power amplifier (PA) to support the link budget at a meter distance. Next, two independent IQ data streams from the upconversion/downconversion paths on each chip are directed to a common lens-coupled broadband on-chip slot antenna system. This way, two orthogonal circular polarizations [left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP)] can be transmitted with sufficient isolation for link operation without the need for a high-speed depolarizer in the BB for any relative orientation between TX and RX modules. The antenna combined with a 9-mm diameter Si-lens provides a directivity of 23.5-27 dBi at 210-270 GHz for each of the modules. This, along with a peak radiated power of 7.5 dBm/ch from the TX module, and the cascaded conversion gain (CG)/single sideband (SSB) NF of 18/18 dB/ch for the RX module followed by a broadband amplifier (PSPL5882) from Tektronix allowed successful transmission of two independent QPSK data streams with an aggregate speed of 110 and 80 Gb/s over 1 and 2 m, respectively, at 230 GHz with a board-level limited channel BB bandwidth (BW) of 13.5 GHz.

Subcarrier Wise Scheduling Methods for Multi-antenna and Multi-carrier Systems

In this paper, multiuser scheduling algorithms are evaluated for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) networks. These scheduling schemes allocate M [number of transmit antennas at base station (BS)] number of independent data streams from BS to the M most favourable users experiencing the highest signal-to-interference-plus-noise-ratio (SINR). Here, SINR is used to convey the channel state information (CSI) to the BS. We have investigated the system throughput and feedback overhead attained by these scheduling schemes for different scenarios as: (a) the maximum CSI is sent to the BS by every user and (b) the maximum CSI sent to the BS corresponding to every BS antenna. The overall feedback overhead incurred by MIMO-OFDM system increases linearly with number of users, number of subcarriers and number of transmit antennas. Hence, to reduce the feedback overhead, a scheme is proposed where users with SINR values greater than or equal to a predefined threshold value are only allowed to feedback the channel state information to BS. The relation between system throughput and various thresholds is also studied. The achievable system throughput results are validated by comparing the probability density function of achieved SINR values by different scheduling schemes.

Antenna Preprocessing and Element-Pattern Shaping for Multi-Band mmWave Arrays: Multi-Port Receivers and Antennas

Classical MIMO arrays employ a series of identical transceiver elements with periodically spaced identical and static antenna elements at a given frequency. The fixed antenna spacing limits the frequency of operation of the array due to the appearance of severe grating lobes at frequencies where the spacing approaches one wavelength. In this article, we propose element-level programmability, where each element in an array can be independently reconfigured to synthesize a set of element patterns. Through the control of element lobe and notch, new array patterns can be synthesized with strict control of side and grating lobes over a wide spectral range for multi-band arrays. In addition, we present the co-design methodology between the unit transmitter element and the integrated electromagnetic (EM) interface that allows broadband operation and unique antenna-level processing of signals that are distinct from classical arrays. This includes signal combination through the antenna, thus creating reconfigurable element patterns, dual beams for supporting wide angles of arrival and departure, and processing of more than one independent data stream in a single radiating surface (and reciprocal properties in a receiver). As a proof of concept, we present a four-port transmitter and EM interface implemented in a 65-nm bulk CMOS process. The chip demonstrates a wide effective isotropic radiated power (EIRP) bandwidth approximately across 40–70 GHz at the broadside and a peak EIRP of 25.6 dBm at 60 GHz with the ability to create a wide array of transmitter element patterns in a single aperture. The multi-functional EM interface and the broadband transmitters can enable future efficient and compact MIMO arrays for reliable links exploiting frequency and pattern diversities.

A Leakage-Based Directional Modulation Scheme for Frequency Diverse Array in Robot Swarm Networks

Robot swarms, which constitute typical multi-user systems, have played more and more important roles in many areas. In this paper, a directional modulation (DM) scheme for frequency diverse array (FDA) based on the leakage power minimization criterion is proposed, which can be used in a robot swarm system as well as other multi-user scenarios. Based on this scheme, location-dependent secure transmission can be obtained in the multi-user downlink channels under certain circumstances, where independent data streams can be sent to different legitimate users safely. Meanwhile, the difficulty for perfect eavesdropping is significantly increased compared with phased-array-based DM. We also use the block successive upper-bound minimization algorithm to optimize the frequency offsets of the array, and the algorithm can be effectively performed. This scheme utilizes the baseband model of the FDA, which is another contribution of this paper. It solves the problems brought by the time-varying nature of the FDA and reveals the distance-angle correlation of the FDA more fundamentally. Based on that, besides the proposed FDA-DM scheme, a novel multiple access technique, named as link division multiple access, is also preliminarily proposed. It allows the transmitter to distinguish multiple users in the same or proximal locations without the help of time division, frequency division, or code division. At last, numerical results are presented to verify the superiorities of LDMA and the proposed FDA-DM scheme.

3D Angular-Based Hybrid Precoding and User Grouping for Uniform Rectangular Arrays in Massive MU-MIMO Systems

This paper proposes a new user grouping algorithm and three-dimensional (3D) angular-based hybrid precoding (AB-HP) scheme for massive multi-user multiple-input multiple-output (MU-MIMO) systems using uniform rectangular arrays (URA). At first, the users clustered in multiple spots are efficiently grouped according to the proposed user grouping algorithm, which only utilizes the user angle-of-departure (AoD) information and does not require prior knowledge of the number of user groups. By employing the AoD support of the user groups, the RF-beamformer of AB-HP is designed to reduce the inter-group interference, the channel state information (CSI) overhead, and the number of RF chains. Then, the digital baseband precoder of AB-HP is constructed via regularized zero-forcing (RZF) using the effective channel seen from baseband to simultaneously serve the users clustered in multiple groups, by considering three approaches: joint-group-processing (JGP), per-group-processing (PGP) and common-group-processing (CGP). For each approach, the signal-to-interference-plus-noise ratio (SINR) expressions as well as their tight deterministic approximations are derived. To further reduce the number of RF chains, we also propose a new transfer block design, which reduces the number of RF chains down to the number of independent data streams without penalizing the sum-rate performance. Illustrative results reveal that the proposed AB-HP schemes with the relaxed CSI estimation overhead and reduced hardware cost/complexity can closely approach to the sum-rate performance of the single-stage fully-digital precoding (FDP). Furthermore, AB-HP has considerably higher energy efficiency performance compared to FDP due to the reduced number of RF chains. We show through simulation that the proposed AB-HP can offer significantly better performance than existing HP techniques. The computational complexity of AB-HP is also analyzed.