The first ever truly embedded SDR

Jan 14, 2018

Project update 21 of 35

High-bandwidth Progress - See What's Happening in the 2.4 GHz Band

When we launched the campaign, we had our XTRX prototypes running stable at 80 MSPS (both SISO and MIMO), but we were saying that we’re confident we can go up to 120 MSPS. I’m glad to announce that, after a few weeks of blood and tears (and no Xmas and no New Year holidays), we’ve got XTRX to work up to 120 MSPS SISO and 90 MSPS MIMO.

PCIe offers plenty of bandwidth (8 Gbps in PCIe x2 Gen2 mode) and our PCIe implementation works almost at the theoretical throughput limit, so we’re not limited by the host-to-SDR bus. This is a stark difference from all other low-cost SDRs which use and are limited by USB. Optimizing PCIe was a journey in itself (watch our presentation at 33C3 a year ago if you’re curious about details) but it has paid off. Our current limitation is the actual FPGA-to-LMS7 bus. We’re working closely with Lime Micro to see if we can go even further, but at this point, any such improvements will most likely be minor.

For the avoidance of doubt - such high-bandwidth operation does require proper PCIe x2 and you can’t achieve this with the USB 3 Adapter. You’ll need our “PCIe x2 + Front End Adapter” to achieve such high bandwidth. If you want a portable setup, you can buy a PCIe to Thunderbolt 3 adapter like the one we mention in the 33C3 presentation above or a more recent GRCon17 presentation.

Receiving 100 MHz RF Demo

We were thinking what to show as a demo of XTRX high bandwidth operation and decided that visualizing the 2.4 GHz band is the most practical one. I personally would like the ability to look into 2.4 GHz whenever I experience crappy Wi-Fi performance.

The 2.4 GHz band is super popular and is thus super busy. We hear about 2.4 GHz the most when we talk about Wi-Fi, but in reality, there are tens of other technologies using the 2.4 GHz ISM band - from microwave ovens to Bluetooth and car alarm systems. So you never know what’s causing your Wi-Fi issues - your Wi-Fi settings, your neighbors’ interfering Wi-Fi, your microwave, Bluetooth, or something else. The 2.4 GHz band is 100 MHz wide and thus requires 100 MSPS to capture it, which is too much for traditional low-cost SDRs but not for XTRX.

In the demo video above we can clearly see round looking packets which are probably DSSS modulation used in the older 802.11 (Wi-Fi) standards and more rectangular OFDM Wi-Fi packets. At the same time, you can see a lot of narrow-band signals scattered over the spectrum. These are most likely Bluetooth but could be something else as well. Now you can have a lot of fun finding the source of those interfering signals in your house or office.

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