Instrumentation & Measurement Magazine 23-9 - 60

and retrieving spectrum data, are independent of each
other. This allows topological flexibility and resilience.
◗◗ The SCOS sensor network protocol and data exchange
protocols can be implemented over any suitable mechanisms. This allows for exchanging of messages, for
transport layer security and authentication/authorization to be done using popular methods such as REST or
MQTT for message/data exchange, TLS for transport
security, OpenID for authorization, etc.
◗◗ Sensor network management and task management
uses explicit action/response control messages for reliable state maintenance and for audit and log analysis for
robust operation.
Transmission of spectrum data is independent of both
management of the sensor network and control/configuration messages to individual sensors. This is to provide greater
security and flexibility. Messages are structured as nestable
" containers of containers " so command/response messages
are the same structure as sensing task messages to sensors or
data transmission messages from sensors. These types of message objects can in turn contain any necessary metadata objects
(sensing task definition, task or sensor state, system configuration, etc.) or sensed data objects (raw IQ data, energy density
frequency series, etc.). All of the metadata and data objects
are strictly defined in terms of a " Transfer Specification " in
the standard, which allows explicit and accurate definition of
sensor state, configuration and task performed through a comprehensive set of metadata items. This Transfer Specification
is aligned with work by the GNU Radio project [9], an open
source SDR community.

The Proposed SCOS Architecture
The purpose of this system is the characterization and the assessment of spectrum resources towards supporting its more
efficient and effective use. To this aim, the standard under development defines functional entities that are part of the SCOS

architecture, their interfaces, the structure of the messages that
they can exchange, the possible interactions between them
and the format of the measurement data and metadata. As reported in Fig. 1, there are two primary entities that compose
the SCOS system. A measurement device able to perform spectrum measurement and sensing, hereinafter called Sensor, and
a management system, hereinafter called Manager, able to expose the capabilities of the SCOS platform to users (Clients)
and manage and mediate task requests by users to the sensors. A SCOS system is composed of one or more Sensors and
a Manager.

The Sensor
Sensors allow users (whether individuals or other applications, e.g., an instance of a Manager) to interact with them via
an API and (optionally) provide a data distribution service to
allow sensed data to be flexibly transmitted to multiple users.
The API allows users to discover capabilities, schedule actions, and download data. Sensors package data with required
metadata in a standardized data format for transmission or
retrieval.
Fig. 2 illustrates the Sensor hardware model that is composed of the following elements:
Antenna: Converts environmental electromagnetic waves into
an oscillating voltage.
Preselector: Provides preselection filtering, improved sensitivity via low noise amplification, calibration signal sources,
etc.
Signal Analyzer: Required sensor hardware components, that
capture discrete raw data (e.g., baseband representation of the
signal) and can apply digital signal processing algorithms to
the raw data to achieve a desired metric.
Computer: The computer offers the system control and data
packaging and transfer functionality and may provide control
signals and messages to the preselector and signal analyzer,

Fig. 1. Conceptual SCOS Block Diagram.
60	

Fig. 2. Simplified Block Diagram of the Sensor. Dashed lines represent data
and/or metadata information exchange, solid lines represent the sensed data
signal.

IEEE Instrumentation & Measurement Magazine	

December 2020



Instrumentation & Measurement Magazine 23-9

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