With the massive growth of wireless data in mobile broadband communications, millimeter-wave (mm-wave) communication is an alternative enabling technique for fifth generation (5G) wireless communication systems. More importantly, mm-wave offers large frequency spectrum bands ranging from 30GHz to 300GHz that can be utilized to provide very high capacity (i.e., multigigabits per-second data rates). Moreover, because of the small wavelength at mm-wave frequencies, we can exploit large antenna elements in a small physical area, meaning beamforming schemes are feasible. Nevertheless, high directional antennas should be used due to overcoming the severe path loss and absorption in mm-wave frequencies. Further, the antennas should be steerable in angle and range directions to support point-to-point (multipoint) communications. So far, mm-wave communication has utilized phased-array antennas arrangement which is solely angle dependent. This review paper presents recent array technology, namely, frequency modulated frequency diverse array (FDA) for mm-wave communication applications with an emphasis on beamforming. In FDA, small frequency increment is added across the elements. In doing so, an array beam is generated which is angle-range-time dependent without the need of phase shifters. This feature has several promising potentials in mm-wave communications. In this review, the object is to bring to the fore this advance FDA technology to mm-wave communications community to call for more investigations. We review FDA research progress up to date and highlight the potential applications in mm-wave communications.
Due to massive growth of wireless data in mobile broadband communications, millimeter-wave (mm-wave) communication is put forward as the most attractive solution for 5G technology [
Beamforming schemes in mm-wave communications can be exploited to overcome the path loss at mm-wave frequencies. The mm-wave channel characteristics can influence the choice of physical layer and medium access control layer schemes, as well as the designing of the hardware [
Phased-array antennas have been the most common antennas arrangement widely used in many applications such as wireless communications, radar systems, and others [
In recent years, a new beam technology was proposed, namely, frequency diverse array (FDA) by [
This paper presents a review on recent proposed FDA antenna technology. Specifically, we highlight the potential applications of employing FDA in mm-wave communications and also appeal to wireless communication communities to call for more investigations on FDA antenna development especially in mm-wave 5G communications and even nonorthogonal multiple access (NOMA) schemes. In addition, we present some array configurations suitable for mm-wave communications for consideration.
The rest of this paper is organized as follows: Section
Comparisons of array geometry: (a) conventional phased-array, (b) FDA antenna.
From Figure
According to [
The array factor of FDA antenna can be given as
The following remarks about FDA antennas based on above expressions are in order [ When When If The higher the value of
In this review paper, we highlighted the potentials of employing frequency modulated array (frequency diverse array (FDA)) beamforming rather than the conventional phased-array antennas (PA) in millimeter-wave (mm-wave) applications. The FDA has the capability of providing directional beam gain in angle-range-time focusing dependent due to the tiny (small) frequency increment across each element index. The frequency increment
FDA beamforming comparison using distinct
As shown in Figure The It was observed that as the carrier frequency becomes higher (i.e., as in the case of mm-wave applications), Note that matching filter can be employed at the receiver to handle In fact,
More importantly, in Figure
Actually, FDA beamforming is feasible for mm-wave applications. For instance, channels under mm-wave are correlated not independent and identically distributed (i.i.d). Hence in physical layer security in mm-wave where the desired receiver and undesired receiver are highly correlated (i.e., close-located), FDA is more feasible than PA due to the angle-range focusing dependent. Secondly, as mentioned before, we can suppress range-dependent interferences by choosing appropriate
Range-dependent suppression in FDA transmit beamforming by tuning
Furthermore, Table
FDA versus phased array [
Antenna array | Transmitted signals | Coherent gain (array) | Transmit capabilities | Range-dependent suppression |
---|---|---|---|---|
FDA | coherent | yes | angle-range-time dependent | yes |
Phased array | coherent | yes | angle dependent only | no |
FDA antenna characteristics [
Antenna configuration | frequency increment | Range and Angle | Computation complexity | Interference suppression | User detection capability | Beampattern shape |
---|---|---|---|---|---|---|
Standard FDA | linear | Coupled beampattern | reasonable | good | good | S-shape |
Modified FDA | non-linear | decoupled beampattern | quiet high | better | better | dot-shape |
Very recently, ultrawideband (UWB) FDA has been reported in [
Analogous to [
Comparisons of continuous FDA waveform and pulsed FDA waveform.
In this paper, we consider rectangular pulse
In Figure
Comparisons of transmit beampatterns: (a) FDA using continuous-wave, (b) FDA pulsed-wave, parameters:
Comparisons of transmit beampatterns: (a) FDA using continuous-wave, (b) FDA pulsed-wave, parameters:
According to [
As shown in (
Base station FDA beamforming transmitter for millimeter-wave communications.
As already stated in the previous sections, the standard FDA provides coupled angle-range-dependent beampattern which limits its estimation at the FDA peak output. Herein, we demonstrate the capability of decoupling angle-range-dependent FDA beampattern by considering two communication receivers/users located at the same direction but different ranges. Note that in the literature, several authors have proposed different techniques to decouple angle-range dependent of FDA [
Employing (
Beamforming illustration of two communication receivers: (a) FDA antenna, (b) phased-array antenna: parameters:
Wireless communication systems are the most attractive systems for sharing of information between several users due to the nature of propagation channel. On the other hand, information protection is also important; otherwise, the intended receiver information can be compromised. Therefore, security issues are essential in wireless communication systems. Recently, physical layer security has been widely investigated in the literature due to its degree of freedom as compared to the traditional cryptography keys sharing methods [
It was pointed out in [
Next, we will analyze the bit error rate (BER) distribution of FDA in angle and range dimensions. Suppose that Gray code quadrature phase shift keyed (QPSK) symbols are adopted for transmission. Following the BER formulation in [
FDA BER distributions: (a) angle-dependent, (b) range-dependent: parameters:
In [
FDA
The corresponding radiation pattern at the far-field of the
FDA
In mm-wave 5G communications, tracking of receivers at different locations is very essential. Several papers have made unrealistic assumptions that the users/receivers channel state information (CSI) is accessible at the transmitter [
System model of frequency diverse phase-conjugating retrodirective array for mm-wave 5G communications [
According to [
Large number of transmit arrays can be employed to enable different signals especially for multiple users for mm-wave communication applications. At the receiver, we can utilize matched filters to extract these signals emitted by the transmit arrays separately. Employing MIMO technology, we can achieve spatial diversity; however, it cannot offer directional beam/gain which is useful in wireless communication applications. In recent years combination of MIMO and FDA schemes has been considered for radar applications [
FDA MIMO configuration for multiuser mm-wave 5G communications.
From Figure
Let us assume that subarray comprising of
Without loss of generality, narrow-band channel is considered for the analysis. The signal received at time
In mm-wave communication technology, hybrid beamforming schemes were proposed to overcome the high path loss [
Illustration of FDA hybrid beamforming transmitter for mm-wave communication applications.
It is well known in the literature [
Following the optimization problem in [
where
The optimization problem is formulated as
In this section, we discuss some of the FDA fabrication methods in the literature. The authors in [
All the above mentioned fabrication schemes are suitable for mm-wave applications. In particular, generation of directional beamforming is seen as an attractive technique which can be used to alleviate high propagation path loss in mm-wave. For example, the author thinks that both the base station and communication user can support directional beamforming. The base station can adopt beamforming training to form multiple beams scanning (i.e., directional) which can be radiated simultaneously to multiple users with distinct beams within mm-wave cell. Figure
Mm-wave base station using FDA antennas for directional range-angle focusing dependent.
In the literature, FDA technology arrangement has been focused on monochromatic assumption with identical interelement spacing. In addition, for the sake of simplicity, several authors focused on linearly frequency increments and uniform weighting vector. Since different applications may require different techniques, the author thinks that different design approaches can be useful for particular applications. Amplitude weighting, time modulated [
This review paper discusses a new array technology, namely, FDA antenna from the perspective of narrow-band and ultrawide-band considerations. The employment of FDA technology for mm-wave communications has been discussed. Due to more degrees of freedom that can be derived from using FDA antennas, it is expected to be the most attractive antennas for wireless communication applications which has the following attributes, for example, range-dependent interferences suppression, improving beamforming gain in range-angle-time dependent which is not accessible to phased-array antennas, enhanced secure communications, better energy efficient communications, and others. Several FDA design configurations suitable for mm-wave communications have also been discussed. Further, an optimization algorithm for FDA has been highlighted which can maximize the transmitted energy in angle-time dependent. Certainly, there are more open issues in relation to the development of FDA technology for mm-wave communications. This is just a stepping stone to showcase the capability of FDA technology for 5G communications. Therefore, more support on FDA antennas research on mm-wave 5G wireless communication systems for future is needed.
The author declares that there is no conflict of interest regarding the publication of this paper.