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Feasibility Analysis of Coexistence of SX1280 Chip and WIFI Technology Module
Wi-Fi technology is currently the most commonly used free ISM band. Although due to channel overcrowding, WiFi modules have expanded into adjacent ISM bands, especially the 5.8 GHz ISM band, most Wi-Fi module traffic still stays in the 2.4 GHz ISM band, typically from 2.4 GHz to 2.4835 GHz (at least in the US and Europe).
There is no doubt that any new technology deployed in this frequency band must be able to withstand the interference of existing WiFi wireless communication technology deployment. Considering that the LoRa module has recently expanded to the 2.4 GHz band, it is of great significance that it coexists with the most common Wi-Fi signals in the 2.4 GHz band.
The figure below shows the usage of the 2.4 GHz ISM band for broadband data communication using Wi-Fi.
Immunity to Wi-Fi technology can come from three methods:
1. Frequency Separation: It is evident from the channel plan shown above that it is possible to avoid certain parts of the spectrum based on prior knowledge of the channel or measurement knowledge. This is an important strategy, but it relies on some management at the MAC layer (media access control layer) to achieve it by sensing what's in the band and intelligently avoiding it. This means, either listening on a certain channel to determine the power level, or sending information about clear channels to the radio, which means management is a layer above the physical layer.
2. Time Spacing: Avoiding communicating in the 2.4 GHz band while avoiding communicating with any Wi-Fi devices in the vicinity is a challenging proposition. Due to the nature of use, Wi-Fi signals are characterized by typically high channel occupancy, such as 50% to 80% occupancy in real-world scenarios.
3. Spatial separation: Simply avoiding co-location with Wi-Fi terminals is one of the easiest and most effective ways to avoid or reduce potential interference between radio systems, as the application use case allows.
So far, the LORA mode of the SX1280 chip has great advantages in intersecting with traditional modulation methods in the case of WIFI wireless communication interference. The use of the LoRa physical layer provides us with some potential additional performance benefits compared to traditional modulation techniques for coexistence and provides additional immunity to in-band and in-channel interference. The specific advantages of lora module wireless communication are as follows:
1. Spread spectrum: LoRa is a spread spectrum modulation technology. A coding gain can be obtained through spread spectrum modulation, because the signal can be received with a negative signal-to-noise ratio. At the same time, in the absence of interference, this is equivalent to reception in noise, and in the presence of co-channel interference, this is equivalent to the ability to receive the desired signal power which is weaker than the interfering signal.
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2. Low bandwidth: Reducing bandwidth has two benefits. First, the lower bandwidth reduces the influence of adjacent signals, making it less likely to fall victim to interference. If we compare the bandwidth of a LoRa signal to a wider band Wi-Fi signal, we see that even a wide LoRa signal occupies only a small fraction of a Wi-Fi channel. This brings us to a second benefit. The power of the Wi-Fi signal is distributed over the entire Wi-Fi channel. Therefore, the energy seen in the narrower part of this channel will be a fraction of this energy. Simply put, even in the case of co-channel interference, we are only exposed to a fraction of the signal power means we receive a fraction of the Wi-Fi signal power.
3. Forward Error Correction and Interleaving Technology: Another advantage of the LoRa modem is the availability of FEC (Forward Error Correction) and interleaving technology. Forward error correction allows redundancy to be introduced into the message, allowing modification and restoration of damaged finite bits.
Even FEC sequential bit errors (i.e. adjacent corrupted bits) are the most difficult to correct. For this reason, the interleaving technique is employed. It's a technique of reallocating information in a packet so that after reconstruction, errors are less likely to come from adjacent bits.
4. Partial symbol loss immunity: In addition to all the previously mentioned benefits of the LoRa physical layer, it is also worth noting that we can lose up to half of a LoRa symbol before losing the data within the symbol. In the case of interference immunity, this gives us enormous immunity to interference (over 100 dB in some cases).
High-power pulsed interferometers can be tolerated if they occupy less than 50% of the LORA symbol duration.
It can be seen that the LORA mode of the SX1280 chip can still maintain a good communication effect under the strong interference of the wireless communication of the WIFI module.
It is worth mentioning that Chengdu Ebyte Electronic Technology Co., Ltd. launched a E28-2G4M12S lora module, which is a wireless module based on Semtech's SX1280. The LoRa module has 2.4G spread spectrum communication (equivalent to the 2.4G of SX1278) G version), the communication distance is better than that of the Zigbee module, and the power consumption is about 1/4 of the power consumption of the Zigbee module. Can
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