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Low-cost embeddable SDR occupies a mini-PCIe card

Dec 14, 2017 — by Rick Lehrbaum — 3175 views

[Updated Dec. 16] — The Fairwaves “XTRX” mini-PCIe SDR card is a low-cost embeddable SDR card aimed at high data rate apps including 4G/5G and “massive” MIMO.

Fairwaves Inc.’s “XTRX” SDR mini-PCIe card, which launched on Nov. 30 at Crowd Supply, has earned more than 80 percent of its funding goal with one month remaining. The company claims the full sized mini-PCIe XTRX card (30 x 51mm) is the smallest commercially available SDR card. For comparison, the USB-interfaced LimeSDR Mini and RTL-SDR boards measure 69 x 31.4mm and 40 x 60mm, respectively.

(click images to enlarge)

Fairwaves, which is a small company with staff residing in the U.S. and Europe, says it’s targeting the XTRX SDR at IoT, drone, satellite, and LTE/5G cellular applications. In addition to the XTRX mini-PCIe card, the Crowd Supply campaign also offers an aluminum-enclosed USB3 adapter that contains an XTRX card on a USB3-interfaced carrier, as well as a half-sized PCIe card that adapts the XTRX to a PC’s PCIe x4 slot. There’s also a full-sized PCIe x16 card that accepts up to eight XTRX boards, for use in high-end multiple-SDR applications.

XTRX mini-PCIe card front (left) and back views
(click images to enlarge)

Inside thte XTRX

Fairwaves lists the following features and specs for the initial XTRX boards that will be supplied through the Crowd Supply campaign:

  • RF chipset — Lime Microsystems LMS7002M FPRF
  • FPGA — Xilinx Artix 7 35T
  • Channels — 2×2 MIMO
  • Sample rate — ~0.2 to 120 MSPS
  • Tuning range — 30MHz to 3.8GHz (* see note below)
  • Rx/Tx range:
    • 10MHz to 3.7GHz
    • 100kHz to 3.8GHz with signal level degradation
  • PCIe Bandwidth:
    • PCIe x2 Gen 2.0 — 8 Gbit/s
    • PCIe x1 Gen 2.0 — 4 Gbit/s
    • PCIe x1 Gen 1.0 — 2 Gbit/s
  • Reference clock:
    • Frequency — 26MHz
    • Stability — < 10 ppb stability after GPS/GNSS lock, 500 ppb at start-up
  • Bus latency < 10µs, stable over time
  • Synchronization — synchronize multiple XTRX boards for massive MIMO
  • GPIO:
    • FPC Edge Connector — 4x lines (usable as two diff-pairs)
    • mini-PCIe 8x reserved pins — 2x diff-pairs, 1pps input, 1pps output, TDD switch control, and 3x LEDs
  • Dimensions — 30 x 51mm; full-size mini-PCIe

XTRX block diagram
(click image to enlarge)

According to a September 2017 presentation, Fairwaves plans to eventually add XTRX “Light” and “Pro” flavors, based on Artix7 25T and Artix7 50T FPGAs, whereas the XTRX available through the campaign uses the Artix7 35T. The Pro model would also offer -40 to +85°C operation, GPSDO/GNSS support, DSP FPGA acceleration, faster PCIe speed, and more flash storage, among other differences (see slide below).

Planned XTRX Lite/Pro model features
(click image to enlarge)

Software and open source aspects

XTRX OS support, meanwhile, is expected to include 64- and 32-bit versions of Linux (x86 and Arm) and Windows (x86 only), according the company’s recent presentation (see slide below). Additional software support will likely include GNU Radio, gqrx, SopaySDR (limited features), osmo-trx, Amarisoft LTE, kalibrate, and srsUE/srsLTE,

XTRX software support as of Sept. 2017
(click image to enlarge)

Fairwaves states on the campaign page that “the XTRX card’s main FPGA code is open source and without a viral license, so not only can you modify the code, but you can also develop your own proprietary FPGA blocks.” Host-side software and drivers are also open source, and “you can upload your own firmware with our USB 3 adapter board or with a JTAG cable and our PCIe adapter board,” says the company.

With regard to the hardware designs, “The XTRX hardware itself is proprietary, though the hardware accessories we designed for it (e.g., the USB 3 and PCIe adapters) are open hardware,” states the campaign’s Crowd Source page.

Front end adapters

In addition to the XTRX mini-PCIe card, the Crowd Supply campaign also offers two “front end adapter” options for use with the XTRX: a half-size PCIe card that plugs into a PC’s PCIe x 4 slot; and a USB3 adapter that’s packaged in a slick-looking aluminum enclosure. Below are the photos and block diagrams of the XTRX PCIe x4 card and enclosed USB3 adapters.

XTRX PCIe adapter photo and block diagram
(click images to enlarge)


XTRX USB3 adapter photo and block diagram
(click images to enlarge)

Also, in case you’re planning a “massive MIMO deployment or have a large swath of spectrum you need to monitor,” there’s the XTRX “Octopacks” adapter, shown below. As its name implies, it accommodates up to eight XTRXs, and plugs into a full-length PCIe x16 PC slot.

XTRX Octapack adapter 2-sides photo and block diagram
(click images to enlarge)

To clarify how the XTRX compares, feature-wise, with other maker/hacker-oriented SDR boards, the XTRX Crowd Supply page includes a table comparing key features of several board-level SDR products. Based on that data, we generated the simplified table below that compares key features of the XTRX to those of the LimeSDR and LimeSDR Mini.

XTRX compared to LimeSDR and LimeSDR Mini
(source: XTRX Crowd Supply page)

Tuning range 30 MHz – 3.7 GHz (*) 30 MHz – 3.8 GHz 10 MHz – 3.5 GHz
Duplex Full MIMO Full MIMO Full SISO
Max sampling rate 120 MSPS 61.44 MSPS 30.72 MSPS
ADC/DAC resolution 12-bit 12-bit 12-bit
Max RF bandwidth 120 MHz 61.44 MHz 30.72 MHz
Channels 2 2 1
Transmit power 0 to 10dBm (depends on freq.) 0 to 10dBm (depends on freq.) 0 to 10dBm (depends on freq.)
RF chipset LMS7002M LMS7002M LMS7002M
Embedded yes no no
Industrial temp. range Optional no no
temp. sensors yes yes no
freq. stability ±0.5 ppm initially, <±0.01 ppm after GPS lock ±2.5 ppm ±2.5 ppm
GPS synchronization on board no no
Bus/interface PCIe x2, USB 3 adapter, and more (FPGA based) USB 3 USB 3
Raw bus bandwidth 10 Gbit/s 5 Gbit/s 5 Gbit/s
Dimensions 30 × 51 mm 100 x 60 mm 69 x 31.4 mm
Extra features GPIO, GPS, SIM card interface GPIO GPIO
Multiple boards synchronization Sample clock and timestamps Sample clock Sample clock
Price $199 $299 $139
Price per channel $99.50 $150 $139

(* NOTE: A Dec. 15 update on the XTRX Crowd Supply page notes that “it is possible to use XTRX in the HF band, but it requires the right antenna and perhaps an external filter. We added another FPC header specifically to make working in the HF band easier.”)

Further information

The XTRX mini-PCIe embedded SDR card’s Crowd Supply campaign is currently 80 percent funded, with 32 days left to reach its $90,000 goal. The XTRX board by itself is available starting at $199, with orders expected to ship by May 31, 2018 (shipping is free to the U.S. or $10 elsewhere). Other offered packages include the $79 USB adapter (including aluminum enclosure), the $99 PCIe x4 adapter, and a $2900 PCIe Octopack bundle that includes the adapter card preloaded with 8x XTRX boards. There are also several bundles that include multiple XTRX boards and/or various accessories. More information may be found at the XTRX Crowd Supply page.

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