path: root/usrp/doc/usrp_guide.xml

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<article>
  <articleinfo>
  <title>USRP User's and Developer's Guide</title>
    <author>
      <firstname>Matt</firstname>
      <surname>Ettus</surname>
      <affiliation>
	<orgname>Ettus Research LLC</orgname>
	<address>
	  Ettus Research LLC
	  <street>604 Mariposa Ave</street>
	  <city>Mountain View</city>, <state>CA</state> <postcode>94041</postcode>
	  <country>USA</country>
	  <email>matt@ettus.com</email>
	</address>
      </affiliation>
    </author>
    
    <abstract>
      <para>
	This guide explains both basic usage of the USRP as well as how to expand it.
      </para>
    </abstract>
    
  </articleinfo>
  
  <sect1 id="intro">
    <title>Introduction</title>
    <para>
      The Universal Software Radio Peripheral, or USRP (pronounced "usurp") 
      is designed to allow general purpose computers to function as high 
      bandwidth software radios.  In essence, it serves as a digital 
      baseband and IF section of a radio communication system.  In addition, 
      it has a well-defined electrical and mechanical interface to RF 
      front-ends (daughterboards) which can translate between that IF or 
      baseband and the RF bands of interest
    </para>
    <para>
      The basic design philosophy behind the USRP has been to do all of the
      waveform-specific processing, like modulation and demodulation, on the
      host CPU.  All of the high-speed general purpose operations like
      digital up- and downconversion, decimation and interpolation are done
      on the FPGA. 
    </para>
    <para>
      It is anticipated that the majority of USRP users will never need to
      use anything other than the standard FPGA configuration.  However, for
      those users that wish to, the FPGA design may be changed or replaced.
      All of the interfaces are well defined and documented.
    </para>
    <figure id="usrp-board">
      <title>USRP with Daughterboards</title>
      <mediaobject>
	<imageobject><imagedata fileref="usrp.jpg" format="JPG"/></imageobject>
	<caption><para>
	  This USRP has 2 BasicTX and 2 BasicRX boards mounted on it.  
	  Notice that the boards on the left are rotated 180 degrees.
	</para></caption>
      </mediaobject>
    </figure>
    
    <sect2 id="requirements">
      <title>System Requirements</title>
      <para>
	The USRP requires a PC or Mac with a USB2 interface.
      </para>
    </sect2>
    
  <sect2 id="capabilities">
    <title>Capabilities</title>
    <para>
      The USRP has 4 high-speed analog to digital converters (ADCs), each at 
      12 bits per sample, 64 million samples per second.  There are also 
      4 high-speed digital to analog converters (DACs), each at 14 bits per 
      sample, 128 million samples per second.  These 4 input and 4 output 
      channels are connected to an Altera Cyclone EP1C12 FPGA.  The FPGA, in 
      turn, connects to a USB2 interface chip, the Cypress FX2, and on to the 
      computer.  The USRP connects to the computer via a high speed USB2 
      interface only, and will not work with USB1.1.  
    </para>
    <figure id="usrp-block-diagram-fig"><title>Universal Software Radio Peripheral</title>
    <mediaobject>
      <imageobject><imagedata fileref="usrp-block-diagram.eps" format="EPS"/></imageobject>
      <imageobject><imagedata fileref="usrp-block-diagram.png" format="PNG"/></imageobject>
      <caption><para></para></caption>
    </mediaobject>
    </figure>
  </sect2>
  </sect1>
  <sect1 id="getting-started">
    <title>Getting Started</title>
    <sect2 id="the-code">
      <title>Getting all the Software</title>
      <para>
	The first step in using your USRP system is to get all of GNU Radio installed.  This can 
	sometimes be a daunting process, as there are several other libraries which will need to be
	installed first.
      </para>
      <sect3 id="dependencies">
	<title>Library Dependencies</title>
	<itemizedlist>
	  <listitem>
	    <para>SWIG</para>
	    <para>
	      We use SWIG (Simple Wrapper Interface Generator) to tie together the C++ and Python code 
	      in the GNU Radio system.  We require that you have version 1.3.24 or newer.  You'll
	      probably have to compile it from source, which you can find here: <ulink url="http://www.swig.org">SWIG</ulink>
	    </para>
	  </listitem>
	  <listitem>
	    <para>FFTW</para>
	    <para>
	      FFTW is the library which GNU Radio uses for FFTs.  GNU Radio requires version 3.0.1 or
	      newer, and it must be compiled for single precision.  You can get it from the 
	      <ulink url="http://www.fftw.org">FFTW Homepage</ulink>
	    </para>
	  </listitem>
	  <listitem>
	    <para>Boost Library</para>
	    <para>
	      Boost provides several low-level structures used in our C++ code.  If it is not included in
	      your OS distribution, you can get it here:  <ulink url="http://boost.org">Boost</ulink>
	    </para>
	  </listitem>
	  <listitem>
	    <para>CPP Unit</para>
	    <para>
	      CPPUnit provides our unit-testing framework.  This creates automated tests to insure that 
	      code does not break when changes are made.  Get it at the <ulink url="http://cppunit.sf.net">
	      CPP Unit Homepage</ulink>
	    </para>
	  </listitem>
	</itemizedlist>
      </sect3>
      <sect3 id="getting-gradio">
	<title>Getting GNU Radio and the USRP code</title>
	<para>
	  There are several packages of software which make up GNU Radio and the USRP support software.
	  Links to the latest versions of each can be found on the GNU Radio Wiki at
	  <ulink url="http://comsec.com/wiki?GnuRadio2.X">Download Links</ulink>.  Gr-build 
	  can greatly simplify the installation process, and its use it highly recommended.
	</para>
      </sect3>
      <sect3 id="cvs">
	<title>Following CVS Development</title>
	<para>
	  Development for the USRP proceeds very quickly at times, so some users may want to keep up with
	  the latest by following the CVS trees.  There are three separate software repositories 
	  which contain various parts of the USRP system.
	  <itemizedlist>
	    <listitem>
	      <para>
		USRP-HW, containing the hardware and FPGA designs.
	      </para>
	      <para>
		All of the schematics in this repository were created in 
		<ulink url="http://www.geda.seul.org">gEDA</ulink>.  The board 
		layouts were created in <ulink url="http://pcb.sf.net">PCB</ulink>.  
		Verilog designs are compiled in Quartus II Web Edition from 
		<ulink url="http://www.altera.com">Altera</ulink>.
	      </para>
	    </listitem>
	    <listitem>
	      <para>
		<ulink url="https://sourceforge.net/cvs/?group_id=22397">USRP-SW</ulink>, 
		USRP-SW, containing firmware and host drivers for the USRP
	      </para>
	      <para>
		Host side drivers and firmware which runs in the USB2 interface chip on the board.
	      </para>
	    </listitem>
	    <listitem>
	      <para>
		<ulink url="http://comsec.com/wiki?CvsAccess">GNU Radio/gr-usrp</ulink>
		which contains the GNU Radio interface to the USRP
	      </para>
	    </listitem>
	  </itemizedlist>
	</para>
      </sect3>
    </sect2>
    <sect2 id="usrp-start">
      <title>Using your USRP</title>
      <sect3 id="physical">
	<title>Mechanical Connection</title>
	<para>
	  The USRP ships with a complete set of standoffs, nuts and bolts.  There are 20 standoffs, 
	  M3x10mm M-F, of which 4 are intended to be used as "feet" for the USRP.  Place them in the 4
	  corner holes on the main board, inserting the male part from below.  The remaining 16 
	  are used to hold the daughterboards in place.  Four of them should be connected to the male 
	  portion of the 4 standoffs already inserted from below.  The remaining 12 should be
	  connected to the board with the 12 M3x6mm screws from below.  At this point there should be
	  16 standoffs on the board with the male ends up to serve as a guide for the daughterboards.  
	  The 16 M3 nuts are used to fasten the daughterboards down to the main board.
	</para>
	<para>
	  The USRP accomodates 2 TX and 2 RX daughterboards.  The placement of the standoffs is designed
	  to prevent the accidental incorrect connection of daughterboards.  The 2 sides of the USRP have 
	  their daughterboard slots rotated 180 degrees.  The USRP should not be operated without 
	  standoffs, and daughterboards should never be connected or removed while power is applied.
	</para>
      </sect3>
      <sect3 id="electrical">
	<title>Electrical Connections</title>
	<para>
	  The USRP is powered by a 6V 4A power converter included in the kit.  The converter is
	  capable of 90-260 Vac, 50/60 Hz operation, and so should work in any country.
	  If there is a need to use another power supply, the connector is a standard 2.1mm/5.5mm 
	  DC power connector.  The USRP	itself only needs 5V at 2A, but a 6V supply was chosen to 
	  accomodate future daughterboards.  Extra power supplies are available from Ettus Research.
	</para>
	<para>
	  The included USB cable should be connected to a USB2-capable socket on a computer.  The USRP
	  does not support USB 1.1 operation at this time.
	</para>
      </sect3>
      <sect3 id="diagnostics">
	<title>Troubleshooting</title>
	<para>
	  When first powered up, an LED on the USRP should be flashing at about 3-4x per second.
	  This indicates that the processor is running, and has put the device in a low power mode.
	  Once firmware has been downloaded to the USRP, the LED will blink at a slower rate.
	  If there is no blinking LED, check all power connections, and check for continuity
	  in the power fuse (F501, near the power connector).  If the fuse needs replacement, it
	  is size 0603, 3 amps.
	</para>
      </sect3>
    </sect2>
  </sect1>
  <sect1 id="fpga">
    <title>FPGA</title>
    <sect2 id="fpga-std">
      <title>Standard FPGA Configuration</title>
      <para>
	In the standard fpga configuration, usrp_std, all samples sent over
	the USB interface are in 16-bit signed integers in IQ format.  When
	there are multiple channels (up to 4), the channels are interleaved.
	For example, with 4 channels, the sequence would be I0 Q0 I1 Q1 I2 Q2
	I3 Q3 I0 Q0, etc.
      </para>  
      <para>
	The USRP can operate in full duplex mode.  When in this mode, the
	transmit and receive sides are completely independent of one another.
	The only consideration is that the combined data rate over the bus
	must be 32 Megabytes per second or less.  The multiple RX channels
	(1,2, or 4) must all be the same data rate (i.e. same decimation
	ratio).  The same applies to the 1,2, or TX channels, which each must
	be at the same data rate (which may be different from the RX rate).
      </para>
      <para>
	On the RX side, each of the 4 ADCs can be routed to either of I or the
	Q input of any of the 4 downconverters.  This allows for having
	multiple channels selected out of the same ADC sample stream.
      </para>
      <para>
	The digital upconverters (DUCs) on the transmit side are actually
	contained in the AD9862 CODEC chips, not in the FPGA.  The only
	transmit signal processing blocks in the FPGA are the interpolators.
	The interpolator outputs can be routed to any of the 4 CODEC inputs.
      </para>
      <figure id="ddc-fig"><title>Digital Down Converter Block Diagram</title>
      <mediaobject>
	<imageobject><imagedata fileref="ddc.eps" format="EPS"/></imageobject>
	<imageobject><imagedata fileref="ddc.png" format="PNG"/></imageobject>
	<caption><para></para></caption>
      </mediaobject>
      </figure>
      
    </sect2>
  </sect1>
  <sect1 id="dboard-int">
    <title>Daughterboard Interface</title>
    <sect2 id="power-int">
      <title>Power</title>
      <para>
	Daughterboards are provided with clean regulated 3.3V for the analog
	and digital sections.  Additionally there is a 6V connection straight from
	the wall supply which is intended to supply a 5V LDO regulator.  All daughterboards
	may draw a combined total of 1.5 A.
      </para>
    </sect2>
      <sect2 id="logical-int">
      <title>Logical Interface</title>
      <para>
	There are slots for 2 TX daughterboards, labeled TXA and TXB, and 2 
	corresponding RX daughterboards, RXA and RXB.  Each daughterboard slot has 
	access to 2 of the 4 high-speed data converter analog signals (DAC outputs
	for TX, ADC inputs for RX).  This allows each daughterboard which uses real 
	(not IQ) sampling to have 2 independent RF sections, and 2 antennas 
	(4 total for the system).  If IQ sampling is used, each board can support 
	a single RF section, for a total of 2 for the whole system.
      </para>
      <para>
	No antialias or reconstruction filtering is provided on the USRP motherboard.
	This allows for maximum flexibility in frequency planning for the 
	daughterboards.  The analog input bandwidth of the ADCs is over 200 MHz, so
	IF frequencies up to that high may be chosen.  If several decibels of loss
	is tolerable, and IF frequency as high as 500 MHz can be used.
      </para>
      <para>
	Every daughterboard has an I2C EEPROM (24LC024 or 24LC025) onboard 
	which identifies the board to the system.  This allows the host 
	software to automatically set up the system properly based on the 
	installed daughterboard.  The EEPROM may also store calibration values
	like DC offsets or IQ imbalances.  If this EEPROM is not programmed, a
	warning message is printed every time USRP software is run.
      </para>
    </sect2>
    <sect2 id="analog-int">
      <title>Analog Interface</title>
      <para>
	Each RX daughterboard has 2 differential analog inputs 
	(VINP_A/VINN_A and VINP_B/VINN_B) which are sampled at a rate of 64 MS/s.
	The input impedance is approximately 1Kohm.
	The motherboard has a software-controllable programmable gain amplifier 
	on these inputs, with 0 to 20 dB of gain.  With gain set to zero, full 
	scale inputs are 2 Volts peak-to-peak differential.  When set to 20 dB, 
	only .2 V pk-pk differential is needed to reach full scale. 
      </para>
      <para>
	If signals are AC-coupled, there is no need to provide DC bias as long as the
	internal buffer is turned on.  It will provide an approximately 2V bias.
	If signals are DC-couple, a DC bias of Vdd/2 (1.65V) should be provided to
	both the positive and negative inputs, and the internal buffer should be turned off.
	VREF provides a clean 1 V reference.
      </para>
      <para>
	Each TX daughterboard has a pair of differential analog outputs which are 
	updated at 128 MS/s.  The signals (IOUTP_A/IOUTN_A and IOUTP_B/IOUTN_B) are 
	current-output, each varying between 0 and 20 mA.  Since they are high-impedance,
	they can be converted into differential voltages with a resistor.
      </para>
      <para>
	In addition to the high-speed signals, each daughterboard has exclusive access to 2 low-speed ADC inputs 
	(labeled AUX_ADC_A and AUX_ADC_B) which can be read from software.  
	These are useful for sensing RSSI signal levels, temperatures, bias 
	levels, etc.  Additionally, each board has shared access to 4 low-speed DAC
	signals, labeled AUX_DAC_A through AUX_DAC_D.  RXA and TXA share one set
	of these 4 lines, and RXB and TXB share their own independent set.  These
	signals are useful for controlling gain of variable-gain amplifiers, for example.
	AUX_ADC_REF provides a reference level for gain setting if it is necessary.
      </para>
      
    </sect2>
    <sect2 id="dig-int">
      <title>Digital Interface</title>
      <para></para>
    </sect2>
    <sect2 id="mech-int">
      <title>Connector Pinouts</title>
      
      <table frame='all'><title>RX DBoard Connector</title>
      <tgroup cols='3' align='left' colsep='1' rowsep='1'>
	<thead>
	  <row>
	    <entry>Pin #</entry>
	    <entry>Name</entry>
	    <entry>Description</entry>
	  </row>
	</thead>
	<tbody>
	  <row>
	    <entry>1</entry>
	    <entry>power</entry>
	    <entry>This is power</entry>
	  </row>
	  <row>
	    <entry>c1</entry>
	    <entry>c4</entry>
	  </row>
	  <row>
	    <entry>d1</entry>
	    <entry>d4</entry>
	    <entry>d5</entry>
	  </row>
	</tbody>
      </tgroup>
      </table>
    </sect2>
  </sect1>
  <sect1 id="dboards">
    <title>Available Daughterboards</title>
    <sect2 id="basicrx">
      <title>BasicRX</title>
      <para>
      </para>
    </sect2>
    <sect2 id="basictx">
      <title>BasicTX</title>
      <para>
      </para>
    </sect2>
  </sect1>
</article>