Descriptive part
Main used protocols in IoT
We have seen the most commonly used protocols in class: LoRA, Sigfox, BLE, ZigBee, NB-IoT (5G) and LTE-m (5G). The similar protocols are grouped 2 by 2. These are the ones generally used for the same purposes i.e. LoRa/Sigfox, BLE/ZigBee and NB-IoT/LTE-m. The tables below gather the main characteristics for each protocol. In my Protocol presentation & report. I give more details about LTE-m.
Specification
LoRa Alliance
Frequency
868 MHz in EU
Max Range (km)
20
Max Data Rate
50 kbps
Payload capacity
243 bytes
Cell Capacity
40 000
Battery Life
15+ yrs
Mobility
Slow
Localization
Yes
Specification
Sigfox
Frequency
868 MHz in EU
Max Range (km)
50
Max Data Rate
600 bps
Payload capacity
12 / 8 bytes (UL/DL)
Cell Capacity
1 000 000
Battery Life
15+ yrs
Mobility
No
Localization
Yes
Specification
3GPP
Frequency
LTE bands
Max Range (km)
50
Max Data Rate
200 kbps
Payload capacity
1 600 bytes
Cell Capacity
200 000
Battery Life
10+ yrs
Mobility
No
Localization
Yes
Specification
3GPP
Frequency
LTE bands
Max Range (km)
50
Max Data Rate
1 mbps
Payload capacity
1 000 bytes
Cell Capacity
1 000 000
Battery Life
10+ yrs
Mobility
Yes
Localization
Yes
Specification
IEEE
Frequency
2.4 GHz
Max Range (m)
50
Max Data Rate
1 mbps
Payload capacity
244 bytes
Cell Capacity
65 536
Battery Life
1 mth
Mobility
Yes
Localization
Yes
Specification
IEEE
Frequency
868/915 MHz, 2.4 GHz
Max Range (m)
100
Max Data Rate
250 kbps
Payload capacity
104 bytes
Cell Capacity
65 536
Battery Life
1 yrs
Mobility
Yes
Localization
Yes
Types of MAC protocols
In the second part of the course, we studied the MAC layers. It serves as an interface between the software part controlling the link of a node and the physical layer. Below you will see a diagram classifying the MAC layers. We categorized those protocols in four categories: Synchronous, Asynchronous, TDMA and hybrid. This is just an overview, I have detailed some protocols in my report & presentation.
Application Case: Software Defined Radio (SDR)
Software Defined Radio is a radio receiver and sometimes a radio transmitter made with software. In this case the open source tool GNU radio is used. For reception the signals are analyzed by an ADC and then processed by GNU radio. For transmission, the data is processed by the software before being converted into signals using a DAC and sent via an antenna.
The advantage of this technology is that with the same antenna it is possible to process several signals on different frequencies. For example, it is possible from the same signal to pick up several radio frequencies or a cellular network or television with the help of filters tailored to the application. We can therefore use a generic hardware with a software part adapted to each technology.
The lab is divided into three parts: showing theoretically that it is possible to transmit a narrowband signal without modifying it with an In-phase/Quadrature transceiver, demodulating recorded signals from an FM radio from a source file and GNU Radio, sending messages via the USRP-2900.
First part:
Theory
The USRP-2900 is the USRP (Universal Software Radio Peripheral) transceiver used to record the radio signal we worked on. The USRP can be summarized in two stages:
• Transposition of the received signal to the zero frequency to process it more easily
• Conversion of the analog signal into a digital signal thanks to an ADC
This part briefly details the theory but without stepping into calculations that you can find in my
report.
The figure above is a diagram representing the Fourier analysis of a signal transmitted in narrow band. Here, we want to keep only the red part of the signal. For this, we use a filter with specific parameters. We must therefore keep the bandwidth within limits.
The figure above is a diagram showing the case where f0 is greater than B/2, ie, in a larger frequency band. We can see that the blue signals interfere with the red signal that we want to recover (yellow area of the graph).
In this second part, we analyze a file containing the recording of radio signals obtained with the USRP-2900. The VHF band includes frequencies from 30 MHz to 300 MHz. In our case, we focus only on the frequencies used for FM radio in France, that is to say, from 87.5 MHz to 108 MHz.
Here is an overview of the scheme to read the audio file and display it.
On the figure below, we observe two frequencies at 99.1 and 100 MHz but also at 99.5 MHz although less obvious on the graph. These three frequencies correspond to the following radios: 99.1 MHz for RFM Toulouse, 99.5 MHz for Nostalgie Toulouse and 100 MHz for Skyrock.
The waterfall display allows us to have a visualization in both frequency and time and thus we can measure the bandwidth more easily.
We have chosen to take measurements at maximum amplitudes and we find a bandwidth of about 250 kHz.
This flow allows the demodulation of the input signal. You can adjust the frequency of observation with a slider and listen to the selected radio.
For this we use a low pass filter with a decimation of 6.
The three peaks corresponding to our three radio stations are more easily observed here.
Second Part:
FM radio reception
Third Part: Implementation of a transmitter/receiver
The purpose of this part is to send audio via radio, then receive it with another radio receiver and demodulate it to listen.
We decided to simply use a sine at a frequency of 20 kHz. We then transmit this complex signal to the UHD: USRP Sink block which will send it via the USRP module. This signal is sent with a carrier fixed at 868 MHz which is a free band in Europe.
Frequency representation of the sine.
Chain of blocks for the demodulation of the signal.
The figure above shows the signal received in waterfall display and in frequency. This is the complex audio. On the waterfall display, we can see the shape of the signal, both audio and sine.