Ettus Research USRP

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B200.png

Ettus Research provides a wide array of OpenBTS capable devices with varying connectivity options and form factors. This page provides GSM, UMTS, and OpenBTS specific information on USRP products. General product information, datasheets, and announcements can be found on the Ettus Research website.

Devices

All Ettus Research USRP devices are capable of GSM operation.

USB 3.0 and Gigabit Ethernet based devices are capable of UMTS operation.

The USRP1 requires special handling with hardware modification, device clocking, and additional driver configuration.

The following tables describe supported USRP combinations for GSM, UMTS, and respective frequency bands.

Ettus Research Supported Devices
GSM UMTS Transport RF Frequency Stability Notes
B200 Yes Yes USB 3.0 Integrated TCXO 2.0 ppm GPSDO <1 ppb External 10 MHz reference or GPSDO strongly recommended
B210
E310 No AXI DMA
X300 Yes 1 or 10 Gigabit Ethernet SBX, WBX, CBX TCXO 2.5 ppm
X310
N200 1 Gigabit Ethernet
N210
B100 No USB 2.0
E100 No OMAP GPMC
E110 No
USRP2 Yes 1 Gigabit Ethernet VCXO 20 ppm NA External 10 MHz reference required
USRP1 No USB 2.0 RFX, WBX* XO 25 ppm NA Hardware modification and 52 MHz reference required, *WBX Rev. 1.0 only

Frequency Band Coverage

Integrated RF devices provide the widest single unit tuning range and cover all current and proposed 3GPP frequencies.

For discrete RF devices, the SBX daughterboard is recommended for the broadest coverage of currently deployed cellular frequencies. CBX and WBX are also suitable for general applications requiring frequency support above or below current cellular bands. WBX covers all standardized UMTS frequencies with the exception of band 22 (3.5 GHz). CBX extends frequency coverage out to the unlicensed 5 GHz band at the expense of supporting lower cellular frequencies.

The RFX is a older RF design, and no longer recommended for new configurations.

3GPP Band Support
RF Frequency Range GSM Bands UMTS Bands Output Power Notes
B200 Integrated 70 MHz - 6 GHz 850, 900, 1800, 1900 1-14, 19-21, 22, 25, 26, 32 up to 100 mW
B210
E310
All other devices
WBX 50 Mhz - 2.2 GHz 1-14, 19-21, 25, 26, 32
SBX 400 MHz - 4.4 GHz 1-14, 19-21, 22, 25, 26, 32
CBX 1.2 GHz - 6 GHz 1800, 1900 1-4, 7, 9-11, 21, 22, 25, 32
RFX900 750 MHz - 1050 MHz 850, 900 5, 6, 8, 13, 14, 19, 20, 26, 32 up to 200 mW Recommended for USRP1 only
RFX1800 1.5 GHz - 2.1 GHz 1800, 1900 1-4, 9, 10, 25 up to 100 mW

UMTS

In OpenBTS-UMTS the host-side UHD transceiver implements a high-performance polyphase filterbank resampler and root-raised-cosine (RRC) pulse shaping filter. The resampling portion provides sample rate matching between the UMTS chip rate of 3.84 Mcps and selected device sample rate of 6.25 Msps. Additional sample rate conversion and anti-alias filtering takes place on the USRP device.

Optimized host side filtering with Intel SSE instructions is automatically enabled when available.

N200-spectrum.PNG

RRC pulse shaping (0.22 roll-off factor) is specified by 3GPP.

N200-qpsk.png

GSM

The GSM transceiver implementation is implemented with a linear representation of the non-linear GMSK modulator. The implementation is based on a two-pulse Laurent approximation of continuous phase modulated (CPM) signals from the classical paper

  • P. Laurent, “Exact and Approximate Construction of Digital Phase Modulations by Superposition of Amplitude Modulated Pulses (AMP),” Communications, IEEE Transactions on, vol. 34, no. 2, pp. 150 – 160, Feb 1986.

Additional reading on the modulator implementation can be found in the following report.

Optimized host side filtering with Intel SSE instructions is automatically enabled when available.

On ARM platforms, a reduced complexity filter and lower sampling rate are automatically enabled, which results in reduced CPU utilization at some expense to RF performance.

N200-spectrum-gsm.gif

The USRP transceiver is capable of low distortion and high dynamic range. Note that actual performance will be dependent on multiple factors including but not limited to device type, calibration, operating frequency, and gain settings.

N200-gmsk.gif

Frequency Reference

GSM base station operation requires a stable reference oscillator for frequency stability and reliable operation with mobile devices, which expect the base station to serve as a timing reference. The GSM stability requires are specified in the following standards.

  • 3GPP TS 05.05 "Radio Transmission and Reception"
  • 3GPP TS 05.10 "Radio subsystem synchronization"

The general requirement is stated in TS 05.10,

The BTS shall use a single frequency source of absolute accuracy better than 0.05 ppm for both RF frequency generation and clocking the timebase. The same source shall be used for all carriers of the BTS.

In commercial infrastructure applications, this level of accuracy is usually provided by some combination of one or more GPS, synchronous Ethernet, or OCXO (oven-controlled crystal oscillator) components.

For less critical use cases the high level of specified frequency accuracy can be relaxed with potential degradation in handset detection stability.

For carrier grade and operator level timing and frequency stability, the following options are available for USRP products.

GPSDO Kit

Several GPS Disciplined Oscillator (GPSDO) kits are available that cover most models of the USRP.

N200/N210 and E100/E110

X300/X310

B200/B210

When installed, the UHD driver will detect and enable the GPSDO reference automatically. No additional user settings or configuration are required.

External Reference

Most USRP devices can be locked to an external 10 MHz reference signal or use an optional board mounted GPSDO. 10 MHz reference sources are commonly found on electronic test and measurement equipment.

To enable the external 10 MHz reference or GPSDO reference, the entry "TRX.Reference" should be modified or added in the OpenBTS.db configuration. The default setting, which occurs when no entry exists, is to set the reference to 'internal'.

Users with the GPSDO modules should explicitly set the reference setting to 'gpsdo'. Note that UHD versions greater than UHD 3.9.0 will no longer automatically set the GPSDO by default.

'TRX.Reference','internal',0,0,'TRX reference type ("internal", "external", "gpsdo")

Drivers

The Ettus UHD driver provides unified support for all USRP models.

Note that the USRP1, as an older product, requires an alternative driver configuration in addition to hardware modification for use with OpenBTS

UMTS

All UMTS supported USRP devices use the Ettus UHD driver.

  • See the main UMTS page for 3G support.

GSM

All USRP devices - with the exception of the USRP1 - use the Universal Hardware Driver (UHD) for unified firmware and host software support.

  • See the OpenBTS Build-Install-Run page for configuration and setup for all Ettus Research devices.


For the USRP1, an alternative driver framework and FPGA firmware are required for OpenBTS due to custom FPGA requirements for time slot synchronization. Note that non-OpenBTS use (e.g. GNU Radio) with the USRP1 remains fully compatible with the UHD driver.

  • See the OpenBTS USRP1 page for prerequisite configuration and setup with legacy USRP1.
  • Once prerequisite modifications are made, see Build-Install-Run page for remaining setup.


Embedded devices (USRP E310 and E100 series) require special configuration.

  • See the E310 page for information on running OpenBTS with USRP E310 and E100 series.