Page 82 - ITU Journal, Future and evolving technologies - Volume 1 (2020), Issue 1, Inaugural issue
P. 82
ITU Journal on Future and Evolving Technologies, Volume 1 (2020), Issue 1
In this section, we present the API that grants access to is parameterized by a discrete variable corresponding to
the tile’s metamaterial applications by defining an ab- the number of outgoing beams, their directivity ampli-
stract representation of the metamaterial, its switch ele- tudes, and an appropriate number of (θ, ϕ) pairs, in-
ment configurations and their respective functionalities. dicating the steering angles. The most complex func-
Specifically, the API resides between a user, operating a tionality can be generally described by a custom scat-
common PC (desktop, smartphone, etc.) and a tile gate- tering pattern and represented herein by a collection of
way, linked to the network of switch element controllers. variables that indicate the reflected power towards all
The case diagram of the proposed concept, presented in directions within the tile’s viewing area.
Fig. 7(a), involves the following main entities: It is, also, worth noting that the data objects being
passed as arguments in the callbacks are primarily de-
A Configuration Database which stores all informa-
scriptions of wavefronts. A simplified data structure is
tion regarding the tiles, the switch element config-
illustrated in Fig. 7(b). Hence, a wavefront is described
urations, and their corresponding functionalities.
by a type (string identifier), such as “Planar”, “Elliptic”,
A User which initiates all API callbacks though ei- “Gaussian”, “Custom”, etc. For each type, a series of
ther the source code or button click events in the headers defines the location and attributes of the cre-
Graphical User Interface (GUI). ating source (for impinging wavefronts only) as well as
the coordinate system origin with respect to which all
The HyperSurface Gateway which represents the
distances are measured. Moreover, the direction of ar-
electronic controller of the hardware.
rival and departure are arrays that can be used to define
An Interrupt handling service which acts as a per- multiple impinging or departing wavefronts at the same
sistent daemon, receiving and dispatching com- time. Notably, the information within the headers may
mands to the Hypersurface Gateway. be sufficient to produce any value of the wavefront via
simply analytical means. In such cases, the data part
4.1 Data Structures of the Metamaterial API can be left empty. In custom wavefronts, the data is
populated accordingly. A mechanism for defining peri-
In the configuration Database (DB), each tile is associ- odicity is supplied via the notion of ranges (i.e. coor-
ated with an element array S that represents all possible dinate ranges where the energy field is approximately
arrangements of switch element states on the metama- equal), to potentially limit the size of the overall data
terial under study. Each switch element is represented object.
by either a discrete or a continuous variable, creating a
The parameters that represent the functionalities and
mathematical space of V 1 × N × M + · · · + V n × N × M
configurations of a tile constitute the set of variables
dimensions, where V i is the number of elements of the
that are exposed to the programmer through the meta-
same type (e.g. capacitors) and N, M the number of
material API. They are organized in a unified manner
unit cells towards the two perpendicular directions. Fur-
within the Database, as shown in Fig. 7(c) which pro-
thermore, every object in this space corresponds to a dif-
vides an illustration of the unique association between
ferent state of S and therefore a different configuration.
all primary tables. Particularly, the ¡Tile¿ table stores
As an example, a tile with two controllable resistive and
all information of a tile’s hardware implementation, such
one diode elements per unit cell is parameterized by a
as the number of variables per unit cell and the type of
2×N ×M +1×N ×M array, where the first and second
switch elements. The ¡Functionality¿ table stores the
sets span a continuous [R min , . . . , R max ] and a discrete
representation scheme described in subsection 2 for all
[0, 1] range, respectively. In this case, 0 and 1 corre-
available metamaterial functionalities. Each parameter
spond to the OFF and ON states of the diode. This
associated with a functionality is organized in a separate
representation will then acquire the following form
table, including a table that stores an identification vari-
F ←− [(d 1 , d 2 , i 1 ) n=1 , . . . , (d 1 , d 2 , i 1 ) n=N×M ] (1) able representing the type of functionality. This table
ID enumerates all possible operations supported by the
where d 1 , d 2 are double-type variables, i 1 is an inte- tile, including full power absorption, wavefront manipu-
ger variable, and F is the appointed functionality. The lation (steering, splitting, etc.), and wavefront sensing.
primitive data types of all variables should be selected Finally, the ¡Configuration¿ table combines, in an exclu-
so as to minimize the total parameter space of com- sive manner, both primary tables (¡Tile¿ and ¡Function-
bined states without any loss of relevant information. ality¿) to link each stored functionality with a specific
This lays a better optimized communication and com- set of switch element states, acquired from the pool of
putational burden to both the API and the Compiler, available entries in the secondary table ¡States¿.
especially during the compilation process where a siz-
able amount of mathematical computations is required. 4.2 API Callbacks and Event Handling
Accordingly, all functionalities are, also, associated with
their own representation and classified pertinent to their Using the Database as a reference point, the API is re-
own type and defining parameters. For instance, a com- sponsible for interpreting a configuration array to the
plex beam-splitting and polarization control operation proper set of hardware commands, when a suitable call-
62 © International Telecommunication Union, 2020
