Abstract
Millimeter-wave (mmWave) cellular systems leverage the hybrid analog-digital structure to balance the costs and the capacity performance by using fewer Radio Frequency (RF) chains and the spatial sparsity of the channel. Besides, a more broadband system is the natural outgrowth of the gigantic frequency resource in mmWave band. However, it becomes precarious when the hybrid structure is extended to the wideband systems as the wideband phase shifters are used in the array. In this article, a multi-wideband planar array structure using the concept of Sierpinski carpet fractal is proposed, which exploits the beam squinting property instead of forming several independent beams through an existing hybrid structure. Moreover, multi-subarray can form a larger antenna array without additional costs of phase shifters for the wider range of values. First, we derive several properties of the steering beams from a wideband linear array. Then, we exploit the beam squinting property of the planar arrays employing wideband ideal phase shifters to form multi-beam. The functionality of the phase shifters in an array is simplified by a set of wideband cells connected in series. The maximum cell number needed in the array is derived, and during this derivation, we find a flaw of the beam squinting method. Finally, we present numerical results on the performance of the proposed arrays with the proposed algorithm, based on a cellular scenario of one base station (BS) and multi-user, where the BS has four subarrays and each user has one subarray.
Highlights
In millimeter-wave cellular systems, how to take full advantage of the spatial sparsity of the mmWave channel and the vast amount of frequency resources in the mmWave band is an open problem [1]–[3]
We reveal that the squint beams cannot cover all angles of the hemisphere through the planar array when determining the value of the phase shifters in the array
We validate the usage of the proposed array with simulations in a multi-user scenario, where the proposed algorithm calculates the number of cells of the virtual phase shifters and the working frequencies of the steering beams for the users
Summary
In millimeter-wave (mmWave) cellular systems, how to take full advantage of the spatial sparsity of the mmWave channel and the vast amount of frequency resources in the mmWave band is an open problem [1]–[3]. X. Pan et al.: Compact Multi-Wideband Array for mmWave Communications Using Squint Beams of the RF chains is usually no more than the number of antennas and no less than the number of the signal streams in the baseband [13]. Pan et al.: Compact Multi-Wideband Array for mmWave Communications Using Squint Beams of the RF chains is usually no more than the number of antennas and no less than the number of the signal streams in the baseband [13] This hybrid structure can provide at most as many effective beams as the number of RF chains. We validate the usage of the proposed array with simulations in a multi-user scenario, where the proposed algorithm calculates the number of cells of the virtual phase shifters and the working frequencies of the steering beams for the users. The following notations are adopted throughout this article: Boldface uppercase letters, boldface lowercase letters, and lowercase letters are used to denote matrices, vectors and scalars, respectively; The superscripts (·)T , (·)∗, (·)H denote the transpose, conjugate and conjugate transpose respectively; · F represents the Frobenius norm of a matrix; IN is the N × N identity matrix; ⊗, and ∗ represent Kronecker, Khatri-Rao and Hadamard matrix products, respectively; vec(·) indicates vectorization; {·}mn is the element at mth row and nth column of a matrix; · and · denote floor and ceiling function, respectively; | · | is the amplitude of a complex value
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