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Semtech provides a new family LoRa with extremly high link budget and low power consumption.For example SX1276 has a 168 dBm link budget. This is much more that CC1125 provides (145 dBm).Difference is 23 dBm. It's approximately 16x times more range. It's possible?Semtech presented a new type of modulation in this product family - LoRa. What can TI provide for competing with this technology?Application requirements - 868 MHz, 4.8 kBod, output power 10-100 mW, lowest power consumption in receiving mode. SX1276 has a 9.9 mA in RX mode, TI has a maximum current 17 mA.
The 168 dBm link budget comes from the SX datasheet number of -148 dBm sensitivity. This sensitivity is at 18 bps (yes, 18 bits per second), which is not a usable rate for any application, just a showcase number for the datasheet frontpage. For a rate of 4.8 kbps, a solution based on TI Narrowband technology will give more range and a more robust link than a link using LoRa.
The modulation format in LoRa is Chirp Spread Spectrum (CSS), a technology invented in the 1930's. CSS is widely used in radar and ranging applications, but not in communications systems. The main reason CSS is not used in communication systems is the very weak co-existence performance, i.e. the ability to reliably operate in presence of interference. LoRa spread the signal information over a wide bandwidth (500 kHz), but will be jammed by any other system operating in this bandwidth (check out the co-channel rejection on page 21 in the SX1276 datasheet.....). Semtech claim LoRa has great co-existence, but their own datasheet measurements show performance 50 dB worse than TI narrowband solutions.
Using a wide bandwidth to send a low rate signal, using a modulation format that does not tolerate any activity in the used bandwidth, this is something that will not work in a real environment with real interference. The de-facto standard for long range communication is narrow band, this offers the best range, co-existence and robustness. For more details also check out the white paper on long range RF communication:
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In reply to terje lassen:
Note also that you can take advantage of the RF Sniff Mode feature to lower the CC112x/CC120x RX current consumption. Please refer to www.ti.com/lit/SWRA428
I have no affiliation with Semtech, but the CC1125 is obsolete versus the SX1276. If you compare co-channel rejection, and sensitivity at equivalent bit-rates, the SX1276 wins, in both narrow and wide band specs, and power consumption. That being said, Semtech may be fudging their specs, who knows unless a real world comparison is done.
For their Lora receiver, they spec positive co-channel rejection numbers. This means it is pulling a signal out of the noise!!!! If you look at page 87 of the SX1276 spec, "Due to the nature of the LoRa modulation, it is possible to receive packets below the noise floor." See page 26, for an explanation, and table showing negative SNRs.
I like TI's high speed solutions, but they are behind in the sub-GHz ISM transceiver low-speed, long-distance solutions assuming Semtech's specs are true. I would also say that TI could likely implement a similar solution to Semtech's, but with better specifications. It's just a matter of taking the time to do it. The CC1310 looks more competitive since it has an integrated CPU, but it's still not available. It appears IOT support won out over making the transceiver specs better, but that's unfortunate since the power consumed by the transceiver outweighs the power consumed by the CPU. The SX1276 wins in the power consumption category vs the CC1125, but not against the pre-release specs for the CC1310. Unfortunately, the CC1310 still can't compete with the SX1276 in terms of transceiver performance, but that's more palatable given the clear power consumption savings.
In reply to David Elam:
I would recommend to test the CC112x and the Lora system together in parallel and to perform a range test. We have performed this test, as well as several customers and the results have been the same every time. CC112x is far superior with respect to blocking and selectivity.
With the IoT trend, blocking and selectivity are becoming more important since the number of wireless devices are increasing on a daily basis.
Perform the range test and let me know your results.
Out-of-office until 17th of August
In reply to RGW:
Hi Richard, thanks for the response. I don't really have time to do this test, which is why I searched online hoping your applications engineers had already done so. Until then, I will use the specifications.
If you take a look at the white paper linked below (www.ti.com/.../swry006), you will find a detailed technical explanation of difference between coded (wideband) and non-coded (narrow band) signals. You do not gain sensitivity by adding coding gain, as you use the coding gain to combat the higher noise you get from the wide channel. The practical sensitivity is a function of the datarate, lower datarate, better sensitivity, longer range, pretty straight forward.
The problem of using modulations like LoRa, is that you waste a lot of bandwidth. This becomes a big issue for capacity, escpecially in a long range network. Semtech knows this fact very well, but this is of course not part of their marketing pitch. Semtech have done system simulations of LoRa vs. narrowband and found that narrowband has 13000x better capacity compared to LoRa for a given bandwidth, you can find the simulations in the following public document, a Semtech proposal document from March 2015:
Using spectrally in-efficient modulation for the limited frequencies available for ISM band communication is just not a good idea, it does not scale
Moreover, using wideband modulation for low rate, you are also very vulnerable to interference. We have performed apples to apples comparison of CC1120 and SX1276, using same frequency (868 MHz) and same datarate (1.2 kbps), running range test side by side. As you can see from the video below, the LoRa link totally breaks down in presence of a single interferer, even if the interferer is several 100 meters away. I expected it to be bad from the datasheet values, but I was shocked by how bad it handled a real world environment. See for yourself and judge, would you like to deploy a system with this kind of issues?
For an RF system, it is really the range in a real life environment that matters. See for yourself how Richard Wallace and Rodney Farrow achieved 114 km (!) range using CC1120 devices. As you can understand from this test, it is not the sensitivity that limits the range, it is the ability to operate in a real RF environment - The CC112x family has the best co-existence properties of any ISM band devices on the market
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