Development of communication systems *

In the previous article, we got acquainted with the Meshtastic project. We learned that it's possible to build your own radio chat based on a Mesh network, a regular smartphone, and a radio modem. The next logical questions people started asking were: What's next? How do I build this network? What should I buy?

The second part will describe several commercial kits for a Meshtastic modem from Aliexpress, their differences, and application features. If for some reason you are not interested in ready-made products, you can build a radio modem yourself. It's not difficult at all and is manageable even for the youngest and most novice radio amateur. Interested? Welcome to the second part under the cut.

There is such an interesting data transfer protocol - APRS. A lot has already been told about him on the Internet. There will be no in-depth theoretical material here. This article will describe how to create your own "pocket" AFSK modulator. In the following articles there will be instructions for going on the air and for creating a simple demodulator. Which will allow you to accept APRS packages and display information on the display right on the street. Everything will be implemented for Flipper Zero. If you don't have this gadget yet, then don't worry and try everything on the great and terrible Arduino. It is very interesting to transmit information at a distance "with your own hands".

Different navigation message protocols are used for different navigation signal type. This is true even for a single system like NAVSTAR GPS. For example, L1C/A signals have a LNAV protocol, while L2C and L5 signals utilize a CNAV protocol. The newest L1C signal will use CNAV-2. 

The protocol defines a data distribution into frames, subframes, the subframes structure, transmission intervals, data resolution and so on. 

A navigation receiver use the navigation message data flow for several purposes:

1. The data flow allows to resolve a code ambiguity and set the signal time.

2. Ephemeris and clock values are used for the satellite position calculation, pseudorange corrections and coordinates computation.

3. The received data flow and navigation message data can be used for navigation symbols prediction. As result, we can use the wipe-off technique, expand discriminators and significantly increase tracking sensitivity:

The potential of VoIP to your customers is simply phenomenal. Businesses are experiencing the advantages of VoIP’s cost-efficiency and reliability and now you can pass these benefits onto your own customers very easily. Cloud telecommunication is sophisticated and easily integrated. Confidence in this technology is growing fast. There has never been a better time to start talking to your customers about adopting this solution. It will deliver huge business benefits for them and has the potential to increase business income and profitability.

The "Click to Call" button on the website is an "innovation" that has been around for about 10 years. The technologies under the hood have changed, but the principle remains the same: someone clicks on the button on the site page, then JavaScript launches and requests access to the microphone and establishes a connection to the server — WebRTC SIP gateway. Further, the first client-server leg is a browser gateway, the second leg can be arbitrarily long and through the SIP proxy chain can eventually connect to a mobile or landline phone. Thus, the browser turns, in a sense, into a softphone and becomes a full participant in VoIP telephony.

We used to think of Telegram as a reliable and secure transmission medium for messages of any sort. But under the hood it has a rather common combination of a- and symmetric encryptions. Where’s fun in that? And why would anyone trust their private messages to a third-party anyway?

TL;DR — inventing a private covert channel through users blacklisting each other.