[Ground-station] Functional Requirements

[Michelle Thompson]

Greetings all!

Here's the developing set of functional requirements for Phase 4 Ground
(and Space Weather Station). We are doing our best to develop a set of
boards that will serve both projects, reduce risk, and reduce cost.

Plain text is in the body of this email below. Formatted pdf attached too!

Comment and critique welcome and encouraged (as always). Discuss in
#general on our Slack and here on the list.

This is not a complete list. The next set is operating ranges, RF
bandwidths, air interface, and annexes supported.

I'd like an accessibility requirement. I have reached out to both handihams
and several local people would are caretakers for disabled hams for help.
In general, SDRs have poor accessibility. Being a new design, we have an
opportunity to design accessibility in from the beginning, and make a
better product for users often left out. This is in general a user
interface requirement. However spending some time now will reduce the risk
of designing something unnecessarily difficult to use. Ease of use helps
everyone.

-Michelle W5NYV

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Terms:

SWS
Space Weather Station, an effort from HamSci to build a distributed radio
network for atmospheric scientific research.
P4G
Phase 4 Ground, an open source broadband microwave multiple-access radio
network for amateur radio. Implements DVB-S2/X on the 10GHz downlink and an
FDMA 4-ary MSK on the 5GHz uplink.
TAPR
Tucson Amateur Packet Radio, a non-profit devoted to advancing the digital
arts in amateur radio.
ORI
Open Research Institute, a non-profit dedicated to open source hardware and
software solutions in amateur radio, especially in the open source amateur
satellite service.
Who and What

Introduction

Space Weather Stations are networked radio stations that implement one or
more of the sensors discussed in the HamSci Space Weather Station project.
Diverse in geography, architecture, and capability, there is a need for an
internetworking protocol and philosophy to unite them. Very similar needs
are shared by the Phase 4 Ground network. This document contains functional
requirements work applicable to both radio networks.

Mission statement: A successful distributed radio network must be reliable,
scaleable, and maintainable.

Required Functions

Remote Command and Control Function
Stations need to be controlled remotely.

For SWS: First, to schedule recording of particular events. Second, to
allow rapid reconfiguration based on updated parameters from the
centralized machine learning models. Third, to ensure the secure remote
operation of the station. Unauthorized access or transmission must be
prevented.

For P4G: First,  modes where communications access to a limited resource
such as a satellite need to be controlled, such as during emergency
communications or for experiments. Second, to ensure the secure remote
operation of the station. Unauthorized access or transmission must be
prevented.
Remote Command and Control Functional Requirement Statement
Each station accepts one or more command and control connections. These are
cryptographically authenticated.




Distributed Radio Network Flexibility
Stations in the network can be source of radio information, a consumer of
radio information, or both. Stations should be able to connect to multiple
receivers and multiple transmitters in order to carry out their
experiments.
The heterogenous nature of the hardware anticipated means that some
stations are less capable than others. This puts limits on the amount of
connections that can be supported and maintained at each radio.
The number of receiver and transmitter connections supported depends on the
capability of the hardware.  Receive-only stations accept zero transmit
connections. Transmit-only stations accept zero receive connections.
Each radio maintains information on capabilities and availability.
A multicast implementation that allows subscribers has been proposed.
Distributed Radio Network Flexibility Requirement Statement
Each station accepts zero or more receiver connections. Each station
accepts zero or more transmitter connections.
Transmissions connections work only if authorized and authenticated.



Time Resolution
For SWS, observations of the ionosphere are radio reflections from the
ionized layers of gas. The sizes of the structures can be as small as
single-digit meters in size.
Sensitivity and spatial resolution are increased by using a phased array.
Stations can reveal cross sections of the ionosphere if multiple receive
and transmit signals can be cohered into a phased array. For phased arrays
to be effective, the integration period must be limited to the time over
which the phase of the signal (compared to a reference phase) does not
change. This lowers the effective sampling rate and lowers the Nyquist
frequency.
The repercussion is that we need nanosecond accuracy and stability in the
clock edges. Variance needs to be low as well. Calibrating the variance
between clocks involved in phased arrays needs to be discussed and
accounted for so that variance won’t dominate as a source of timing error.

This clock scheme does not need to be in the base unit, because P4G does
not need this level of clock accuracy.  A modular approach dramatically
increases the number of potential customers for the radio, as the more
expensive clock circuits are optional for many non-SWS applications.
For Phase 4 Ground receive, the DVB-S2/X specification has a phase noise
mask. This sets the acceptable amount of phase noise at a series of
offsets. [Citation needed]
For Phase 4 Ground transmit, the scheme is frequency division multiple
access. The uplink is channelized. Occupied bandwidth and channelization is
flexible. The most straightforward polyphase filter bank applications have
the number of channels as a power of two. Anticipated first deployment is
to use all of the 10MHz satellite or experimental terrestrial sub-bands.
Ideally, the 10MHz would be divided into segments of approximately 100kHz
per channel. At 64 uplink channels, the channels are 156,250Hz. At 128
uplink channels, the channels are 78,125Hz wide. Based on observations from
the Phase 4A amateur radio satellite (Es’Hail2), 128 uplink channels is a
good starting point. Uplink clock stability requirements depend on the
receiver in the payload.


Time Resolution Requirement Statement
The base unit must be able to accept an external clock source.
External clock source for SWS needs to have 3.3nS timing accuracy in order
to resolve structures 1m in size.
External clock source for Phase 4 Ground downlink must meet the phase noise
requirement in the DVB-S2/X specification (available for free from dvb.org).
Uplink clock must be good enough to achieve channelization and be
successfully received. Stratum 3 has been proposed.
Stratum 3 has three frequency stability specifications.
Free Run (±4.6 ppm/20 years Stratum 3 and 3E)
Holdover (±0.37 ppm/24 hours for Stratum 3 and ±0.01 ppm/24 hours for
Stratum 3E)
Drift (in a lab environment: ±0.04 ppm/24 hours for Stratum 3 and ±0.001
ppm/24 hours for Stratum 3E)
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