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Antenna Selection in MIMO Systems
Published in George Tsoulos, MIMO System Technology for Wireless Communications, 2018
Neelesh B. Mehta, Andreas F. Molisch
Antenna selection is a promising low-complexity solution that solves the pressing problem of the increased hardware and signal processing complexity of MIMO systems. This chapter provides an overview of the extensive work that has been done on antenna selection at the transmitter, or at the receiver, or both. We considered antenna selection for SIMO systems and several different MIMO techniques such as capacity-achieving spatial multiplexing, space–time trellis codes, and orthogonal space–time block codes. We saw in several of these cases that antenna selection achieves full diversity order. However, it incurs an array gain loss, which increases as the number of selected antennas decreases. We also developed several criteria for implementing antenna selection that trade off between complexity and performance. The criteria were tailored to the specific system under consideration. We also considered novel structures that use a RF pre-processing block along with the selection switch and, in the presence of spatial correlation, recover the array gain loss of antenna selection to a great extent.
RF System and Circuit Challenges for WiMAX
Published in Yan Zhang, Hsiao-Hwa Chen, Mobile Wimax, 2007
There are two figures of merit for judging the gain enhancement of an antenna diversity scheme. These are diversity gain and array gain. Under changing channel conditions, diversity gain is equivalent to the decrease in gain variance of local signal strength fluctuations of a multiantenna array system when compared to a single-antenna array system. The result of increased diversity gain is the reduction in fading depth. This is due to each antenna in a multiantenna system experiencing independent fading channels over frequency and time. The second figure of merit, array gain, is the accumulation of antenna gain associated with increased directivity via a multiantenna array system. In a typical system, as the number of antenna array elements grows, the gain increases 10 ∗ log(n), where n is the number of antenna array elements. This means a doubling of gain for every doubling of antenna elements.
Basic Array Theory and Pattern Synthesis Techniques
Published in Lal Chand Godara, Handbook of Antennas in Wireless Communications, 2018
In many applications, the primary objective of an antenna array is to shape a response or beam pattern such that radiation (or reception) in a certain direction is enhanced and the reception in other directions is suppressed. A useful measure of the sharpness of the array is array directivity, which is defined as the ratio of the power radiated by an array in a particular desired direction to the average of the power radiated by the array in all directions. In the context of array synthesis, as the losses in antennas and antenna circuits are not considered, array gain is frequently used interchangeably with array directivity. However, it is important to note that although array directivity and array gain are related, they are not the same.
Antenna Array Pattern Synthesis Using Metaheuristic Algorithms: A Review
Published in IETE Technical Review, 2023
The radiation pattern of conformal antenna array can be optimized by tuning the amplitude and phase of the array elements. The desired goal can be achieved by combining several sub-goals which includes optimized position of main beam, maximum gain, minimum SLL, maximum null depth, and desired half power beamwidth (HPBW). All these sub-goals can be combined using the super-position principle and is defined in a single function as where where , , , and are the actual and desired main beam angular positions; and are the actual and the desired antenna array gain; and are the actual and the allowable SLL; and are obtained and the desired null depth level; and are the actual and the desired HPBW.
An Approach for Energy-Efficient Power Allocation in MIMO–NOMA System
Published in International Journal of Electronics, 2022
Khaleelahmed Sk, VenkateswaraRao N
HP (Zhu et al., 2016) is developed to lower the RF chains in the MIMO system without degrading the performance (Alkhateeb et al., 2015; Ayach et al., 2014; Dai et al., 2018). The idea behind the HP is that the high-dimensional analog precoder is formed by the decomposition of a fully digital precoder, which will increase the low-dimensional digital precoder and antenna array gain to cancel interference. NOMA is used to progress the efficiency of the spectrum evaluated with other traditional methods OMA (Dai et al., 2018; Gao et al., 2016, 2017). NOMA is used in HP architecture, which is fully-connected in (Yuan et al., 2017) by changing the traditional block diagonalisation (BD) precoding method. The researchers used the gain ratio power allocation (GRPA) technique in the NIMO-based visible light communication (VLC) technique (Chen et al., 2018). Multi cluster beamforming is one of the significant keys used to reduce cluster interference. Zero forcing-beam forming (ZF-BF) is a method specifically designed to use in the downlink system for multi-user. The beamforming is developed in the MIMO-NOMA system, where multiple beams are generated from the base station (Sun et al., 2015). The beamforming is carried out through the information of the channel with respect to the maximum channel gain (Ali et al., 2017). The antenna diversity is incorporated with the NOMA system so that only the transmitter knows the information of the channel direction and the distance (Gong et al., 2018). The researchers use the mechanism for power control to offer the service quality in the uplink and the downlink channel in NOMA (Wei et al., 2018).
Design of Low Sidelobe Antenna Array for 24GHz Vehicular Radar
Published in Electromagnetics, 2021
Zhen Xiang, Bin Wang, Xue Tian
The simulated and measured results of the antenna array are shown in Figure 9a. The simulated impedance bandwidth of less than −10 dB is 1.38 GHz (23.35 GHz~24.73 GHz). The measured −10 dB impedance bandwidth is 1.47 GHz (23.6 GHz~25.07 GHz). Compared with the simulation results, the measured results have basically the same bandwidth, but the overall bandwidth has moved 250 MHz to the high frequency. The simulation and measurement results of the antenna array gain are shown in Figure 9b. The antenna gain obtained by simulation is 21.5 dBi. The measured results of antenna array gain fluctuate near the simulated results, but the fluctuation range is small. The measured and simulated results of the antenna array gain remain stable.