114 research outputs found
On the Number of RF Chains and Phase Shifters, and Scheduling Design with Hybrid Analog-Digital Beamforming
This paper considers hybrid beamforming (HB) for downlink multiuser massive
multiple input multiple output (MIMO) systems with frequency selective
channels. For this system, first we determine the required number of radio
frequency (RF) chains and phase shifters (PSs) such that the proposed HB
achieves the same performance as that of the digital beamforming (DB) which
utilizes (number of transmitter antennas) RF chains. We show that the
performance of the DB can be achieved with our HB just by utilizing RF
chains and PSs, where is the rank of the
combined digital precoder matrices of all sub-carriers. Second, we provide a
simple and novel approach to reduce the number of PSs with only a negligible
performance degradation. Numerical results reveal that only PSs per RF
chain are sufficient for practically relevant parameter settings. Finally, for
the scenario where the deployed number of RF chains is less than ,
we propose a simple user scheduling algorithm to select the best set of users
in each sub-carrier. Simulation results validate theoretical expressions, and
demonstrate the superiority of the proposed HB design over the existing HB
designs in both flat fading and frequency selective channels.Comment: IEEE Transactions on Wireless Communications (Minor Revision
Design of Full-Duplex Millimeter-Wave Integrated Access and Backhaul Networks
One of the key technologies for the future cellular networks is full duplex
(FD)-enabled integrated access and backhaul (IAB) networks operating in the
millimeter-wave (mmWave) frequencies. The main challenge in realizing FD-IAB
networks is mitigating the impact of self-interference (SI) in the wideband
mmWave frequencies. In this article, we first introduce the 3GPP IAB network
architectures and wideband mmWave channel models. By utilizing the
subarray-based hybrid precoding scheme at the FD-IAB node, multiuser
interference is mitigated using zero-forcing at the transmitter, whereas the
residual SI after successfully deploying antenna and analog cancellation is
canceled by a minimum mean square error baseband combiner at the receiver. The
spectral efficiency (SE) is evaluated for the RF insertion loss (RFIL) with
different kinds of phase shifters and channel uncertainty. Simulation results
show that, in the presence of the RFIL, the almost double SE, which is close to
that obtained from fully connected hybrid precoding, can be achieved as
compared to half duplex systems when the uncertainties are of low strength
Spatial modulation schemes and modem architectures for millimeter wave radio systems
The rapid growth of wireless industry opens the door to several use cases such as internet of things and device-to-device communications, which require boosting the reliability and the spectral efficiency of the wireless access network, while reducing the energy consumption at the terminals. The vast spectrum available in millimeter-wave (mmWave) frequency band is one of the most promising candidates to achieve high-speed communications. However, the propagation of the radio signals at high carrier frequencies suffers from severe path-loss which reduces the coverage area. Fortunately, the small wavelengths of the mmWave signals allow packing a large number of antennas not only at the base station (BS) but also at the user terminal (UT). These massive antenna arrays can be exploited to attain high beamforming and combining gains and overcome the path-loss associated with the mmWave propagation. In conventional (fully digital) multiple-input-multiple-output (MIMO) transceivers, each antenna is connected to a specific radio-frequency (RF) chain and high resolution analog-to-digital-converter. Unfortunately, these devices are expensive and power hungry especially at mmWave frequency band and when operating in large bandwidths. Having this in mind, several MIMO transceiver architectures have been proposed with the purpose of reducing the hardware cost and the energy consumption.
Fully connected hybrid analog and digital precoding schemes were proposed in with the aim of replacing some of the conventional RF chains by energy efficient analog devices. These fully connected mapping requires many analog devices that leads to non-negligible energy consumption. Partially connected hybrid architectures have been proposed to improve the energy efficiency of the fully connected transceivers by reducing the number of analog devices. Simplifying the transceiver’s architecture to reduce the power consumption results in a degradation of the attained spectral efficiency.
In this PhD dissertation, we propose novel modulation schemes and massive MIMO transceiver design to combat the challenges at the mmWave cellular systems. The structure of the doctoral manuscript can be expressed as
In Chapter 1, we introduce the transceiver design challenges at mmWave cellular communications. Then, we illustrate several state of the art architectures and highlight their limitations. After that, we propose scheme that attains high-energy efficiency and spectrum efficiency.
In chapter 2, first, we mathematically describe the state of the art of the SM and highlight the main challenges with these schemes when applied at mmWave frequency band. In order to combat these challenges (for example, high cost and high power consumption), we propose novel SM schemes specifically designed for mmWave massive MIMO systems. After that, we explain how these schemes can be exploited in attaining energy efficient UT architecture. Finally, we present the channel model, systems assumptions and the transceiver devices power consumption models.
In chapter 3, we consider single user SM system. First, we propose downlink (DL) receive SM (RSM) scheme where the UT can be implemented with single or multiple radio-frequency chains and the BS can be fully digital or hybrid architecture. Moreover, we consider different precoders at the BS and propose low complexity and efficient antenna selection schemes for narrowband and wideband transmissions. After that, we propose joint uplink-downlink SM scheme where we consider RSM in the DL and transmit SM (TSM) in the UL based on energy efficient hybrid UT architecture.
In chapter 4, we extend the SM system to the multi-user case. Specifically, we develop joint multi-user power allocation, user selection and antenna selection algorithms for the broadcast and the multiple access channels.
Chapter 5 is presented for concluding the thesis and proposing future research directions.Considerando los altos requerimientos de los servicios de nueva generación, las infraestructuras de red actual se han visto obligadas a evolucionar en la forma de manejar los diferentes recursos de red y computación. Con este fin, nuevas tecnologÃas han surgido para soportar las funcionalidades necesarias para esta evolución, significando también un gran cambio de paradigma en el diseño de arquitecturas para la futura implementación de redes.En este sentido, este documento de tesis doctoral presenta un análisis sobre estas tecnologÃas, enfocado en el caso de redes inter/intra Data Centre. Por consiguiente, la introducción de tecnologÃas basadas en redes ópticas ha sido estudiada, con el fin de identificar problemas actuales que puedan llegar a ser solucionados mediante el diseño y aplicación de nuevas técnicas, asimismo como a través del desarrollo o la extensión de los componentes de arquitectura de red.Con este propósito, se han definido una serie de propuestas relacionadas con aspectos cruciales, asà como el control de dispositivos ópticos por SDN para habilitar el manejo de redes hÃbridas, la necesidad de definir un mecanismo de descubrimiento de topologÃas ópticas capaz de exponer información precisa, y el analizar las brechas existentes para la definición de una arquitectura común en fin de soportar las comunicaciones 5G.Para validar estas propuestas, se han presentado una serie de validaciones experimentales por medio de escenarios de prueba especÃficos, demostrando los avances en control, orquestación, virtualización y manejo de recursos con el fin de optimizar su utilización. Los resultados expuestos, además de corroborar la correcta operación de los métodos y componentes propuestos, abre el camino hacia nuevas formas de adaptar los actuales despliegues de red respecto a los desafÃos definidos en el inicio de una nueva era de las telecomunicaciones.Postprint (published version
Integrated Sensing and Communications with Joint Beam Squint and Beam Split for Massive MIMO
Integrated sensing and communications (ISAC) has attracted tremendous
attention for the future 6G wireless communication systems. To improve the
transmission rates and sensing accuracy, massive multi-input multi-output
(MIMO) technique is leveraged with large transmission bandwidth. However, the
growing size of transmission bandwidth and antenna array results in the beam
squint effect, which hampers the communications. Moreover, the time overhead of
the traditional sensing algorithm is prohibitive for practical systems. In this
paper, instead of alleviating the wideband beam squint effect, we take
advantage of joint beam squint and beam split effect and propose a novel user
directions sensing method integrated with massive MIMO orthogonal frequency
division multiplexing (OFDM) systems. Specifically, with the beam squint
effect, the BS utilizes the true-time-delay (TTD) lines to steer the beams of
different OFDM subcarriers towards different directions simultaneously. The
users feedback the subcarrier frequency with the maximum array gain to the BS.
Then, the BS calculates the direction based on the subcarrier frequency
feedback. Futhermore, the beam split effect introduced by enlarging the
inter-antenna spacing is exploited to expand the sensing range. The proposed
sensing method operates over frequency-domain, and the intended sensing range
is covered by all the subcarriers simultaneously, which reduces the time
overhead of the conventional sensing significantly. Simulation results have
demonstrated the effectiveness as well as the superior performance of the
proposed ISAC scheme.Comment: 13 pages, 11 figures, submitted to IEEE journa
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