Let's sum up our achievements over the past month. Relay modes of our modems were worked out in one (devices of single rank) and in different frequency ranges (434 MHz / 2.4 GHz), including usage of high-speed relay links (devices of different rank). The power consumption modes (0.175 / 0.32 / 0.75 / 1.1 W) and adaptive change of processor clock frequency (0 / 64 / 170 / 487.5 MHz) depending on the task being performed were worked out. The 3rd week of continuous operation of one of the repeaters went on (Fig. 1). It works fine, but sometimes it freezes – rebooting is needed. We are working on fixing this issue. We've assembled an intermediate relay device with 2 directional antennas (Fig. 2). 2 modems that are connected directly via UART were used for this. In addition, it was possible to implement spatial transmit diversity.

Directional routing and addressing of zones/cells by different keys of PHY Layer Enc./ “DSSS modulations” (PHY Layer Direct Routing) were worked out to eliminate retransmissions and additional packet collisions when building complex MESH networks (Fig. 3). When placing a network of modules, they are surrounded by stations with only unique PHY Layer Enc. keys. By transmitting a signal with a certain “DSSS modulation”, only the desired station will receive it, while others will be able to do their tasks, and so on in the chain.

fig.3

It's time to sum up. During the month of field testing, we were able to confirm the capabilities of all data rates of our proprietary modulation without correction of the frequency and phase (7.68 / 13.44 / 23.04 / 38.4 / 61.44 / 92.16 / 122.88 kbps, at SF = 1024 / 512 / 256 / 128 / 64 / 32 / 16). In urban conditions at 433.92 MHz and a distance of up to 500m, the quality of communication is good; the signal passes one high-rise building without problems. Further up to 1.5 km, communications can be established only at the EMF diffraction peaks or on the line of sight. Communication at longer distances was not checked. For cases when it is necessary to provide excellent communication over a large area, a relay mode (Ad-Hoc) or targeted/addressed transmission is implemented and tested. With 2 repeaters, the quality is excellent. Generally, the number of repeaters is unlimited; the network capacity is limited by the address space of unique users. To eliminate possible collisions, different frequencies or different PHY Layer Enc. keys / ''DSSS modulations” can be used. Also, we checked the capabilities of the built-in modulations of the IEEE Std 802.15.4g radio chip. At MR-OFDM, data rates up to 2.4Mbps can be reached. Recently, we started testing the simultaneous reception of independent signals with different PHY Layer Enc key at the operation on the same frequency. When receiving signals from 4 devices, the reception itself is successful, but decoding data gives errors, - is being fixed. One modem can simultaneously receive up to 6 independent signals and 8 PHY Layer Enc Key are built-in to each modem.