ELTRES: a wireless communication standard for LPWA IoT networks.
ELTRES features both long distance and stable communication. The radio wave output from the transmitting terminal is only 20 mW, however the entire Tokyo area can be covered by just a few receiving stations when including the 634m high television broadcast tower “Tokyo Skytree”. In this second part of the ELTRES development team blog, we introduce some unique Sony technologies at the receiver side.

ELTRES performs uplink one-way communication from the transmitter to the receiver. One advantage of one-way only communication is that the transmitting IoT terminal does not need to always be in standby mode and therefore it consumes less power. Furthermore, because it does not use radio wave resources in the downstream direction, more terminals can be connected and the overall communication cost can be reduced. In this article, we would like to introduce the difficulties and technology used to connect many terminals with one receiver station.

ELTRES features long distance and stable communication, but the fact that the radio waves travel over such a long distance means that the area of the light green circle in Figure 1 is very large. Additionally, there are many radio waves traveling from the multiple transmitting terminals to one receiving station. Because radio waves attenuate as the transmission distance increases, there is a large difference in the reception power of radio waves at the receiving station between terminals close compared to those far away from the receiving station. It is very difficult to receive these electric waves when their powers vary so much.

Maybe if we compared this to sound waves that everyone experiences in everyday life, it might be something like this:
- trying to listen to a friend chatting, while you are at a baseball game, in the ninth inning with two out and a full count, as the voices of the cheering fans and the brass band are ringing in your ears
- you are at an outdoor concert with multiple band playing simultaneously, and you are trying to listen to the band from the next booth over while another band is playing right in front of you
In these cases, both low and high-volume sounds are present at the same time – try to imagine listening to the lower volume sound. Difficult!

At the receiving station, both the weaker received signal due to the long communication distance as well as the stronger received signal from the terminals close by must be received at the same time. In order to cope with such reception environments, Sony applied the technologies it has cultivated in TV tuners to the ELTRES receivers.

It's not difficult to send and receive radio waves from a single TV station in an ideal environment such as a laboratory. However, in real life there are various other radio waves, such as smartphones and radios, besides TV broadcasting. In addition, even if it's only TV broadcasting, multiple radio waves are coming from nearby radio towers to one home, and you must choose the TV station you want to watch from among them.

Sony has been making TV tuners since the days of analog broadcasting. In order to display a clear image even in the radio wave environment described above, we have been constantly developing technologies to eliminate radio waves other than those used in television broadcasts (these are called interference waves) and to continue receiving the wanted signal so that the waveform is not distorted.

One example is distortion canceller technology.

The TV tuner is connected to the antenna input terminal of the TV, and since the radio wave (that is, the received signal coming from the antenna) is an analog signal, there is an analog block to process the analog signal. In addition, the analog block consists of a filter to remove the interfering signal, an amplifier to amplify the desired signal, and a mixer to convert the signal frequency. Sony's TV tuners feature a distortion canceller that cancels out distortions caused by strong interference signals.

A distortion canceler is a technology that cancels the distortion caused when a signal with a power larger than that of an antenna is received by adding the distortion to the signal of opposite phase generated from the same received signal.

In terms of the signal waveform of the amplifier output, if the distortion canceller function is not implemented, the waveform will be as shown in Figure 3 (left). However, by implementing the distortion canceller function, the clean sine-wave envelope waveform (without distortion) as shown in Figure 3 (right) can be obtained.

This technology makes it possible to continue receiving the weak desired signals without distortion even in the presence of high-power interference signals.

A TV tuner receives radio waves from a broadcast tower to the receiver antenna at each home, while ELTRES receives radio waves from each terminal to a receiving station.

The following Figure 4 is an image of the received power of various ELTRES receivers. Each ELTRES receiver station receives radio waves of various powers and extracts the needed information.

So in the example above, you can listen to both loud and quiet voices at the same time and understand each one.

Sony's TV tuner LSIs are used for ELTRES receivers. The technology that has been accumulated by receiving TV broadcasts from around the world is incorporated into this system. They use such techniques to understand contents simultaneously, regardless of the loudness of the voice.

So in the example above, you can listen to both loud and quiet voices at the same time and understand each one.

The number of IoT devices will increase in the future. As more IoT devices transmit radio waves, the radio wave environment becomes congested. Receivers for IoT networks are required to retrieve information correctly in this crowded radio wave environment. We believe that this will be the time when the TV tuner technology installed in the ELTRES receiver will be effective.

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