99 lines
3.4 KiB
Markdown
99 lines
3.4 KiB
Markdown
[[_TOC_]]
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# USRP device documentation
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## General
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OAI works with most common USRP models, like B200, B200mini/B205mini, B210,
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X310, N300, N310, N320, X410. This is achieved by using the Ettus Universal
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Hardware Driver (UHD) (https://github.com/EttusResearch/uhd). The file
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[`usrp_lib.cpp`](./usrp_lib.cpp) provides an abstraction layer of UHD to OAI.
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Example files can be found in the `ci-scripts/conf_files/` directory with a
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`usrp` in the name, for instance
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[`gnb.sa.band78.106prb.usrpn310.ddsuu-2x2.conf`](../../ci-scripts/conf_files/gnb.sa.band78.106prb.usrpn310.ddsuu-2x2.conf).
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## Configuration
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The USRP can be configured in the RU section of the config file. The field
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`sdr_addrs` uses the [USRP device identification
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string](https://files.ettus.com/manual/page_identification.html). Here are a
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few examples
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```bash
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sdr_addrs = "addr=192.168.10.2" # uses a single 10Gb Ethernet interface on an N3x0 or X3x0 or X4x0
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sdr_addrs = "addr=192.168.10.2,second_addr=192.168.20.2" # uses 2 10Gb Ethernet interfaces on a N3x0 or X3x0 or X4x0 (requires that you flashed the FPGA wth the XG image)
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sdr_addrs = "serial=ABC1234" # globally unique identifier of this device
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```
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you can also use the multi USRP feature and specify multiple USRPs, in which case you will get the aggregated number of channels on all the devices
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```bash
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sdr_addrs = "addr0=192.168.10.2,addr1=192.168.30.2"
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```
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You can specify to use external or interal clock or time source either by
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adding the parameters in the `sdr_addrs` field or by using the fields
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`clock_src` or `time_src`
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```bash
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sdr_addrs = "addr=192.168.10.2,clock_source=external,time_source=external"
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```
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is equivalent to
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```bash
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sdr_addrs = "addr=192.168.10.2"
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clock_src = "external"
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time_src = "external"
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```
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Valid choices for clock and time source are `internal`, `external`, and `gpsdo`.
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Note 1: the USRP remembers the choice of the clock source. If you want to make
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sure it uses always the same, always specify the `clock_source` and
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`time_source`.
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Note 2: when using multiple USRPs they always have to be synchronized using
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`external` or `gpsdo`
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Last but not least you may specify that only a specfic subdevice of the USRP is
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used. See also the section [Specifying the
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Subdevice](https://files.ettus.com/manual/page_configuration.html#config_subdev)
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in the UHD manual.
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For example, on a USRP N310, the following fields will specify that you use
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channel 0 of subdevice A. You can enter this information after providing the ip
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addresses of the USRPs in `sdr_addrs`.
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```bash
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tx_subdev = "A:0"
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rx_subdev = "A:0"
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```
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Here is an example of the RUs configuration for a setup with 2 USRP N310.
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```bash
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RUs = (
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{
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local_rf = "yes"
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nb_tx = 2
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nb_rx = 2
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att_tx = 0
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att_rx = 0;
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bands = [78];
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max_pdschReferenceSignalPower = -27;
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max_rxgain = 75;
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eNB_instances = [0];
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sdr_addrs = "addr0=192.168.10.2,addr1=192.168.20.2,clock_source=external,time_source=external"
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tx_subdev ="A:0 B:0"
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rx_subdev ="A:1 B:1"
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}
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);
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```
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Hint: You cannot see TX/RX spread over multiple USRPs, if you use `internal` as a refrence of the clock and time source.
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Furthur information about synchronization on the USRP N3xx devices can be found here: https://kb.ettus.com/Using_Ethernet-Based_Synchronization_on_the_USRP%E2%84%A2_N3xx_Devices
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When combining this with the multi USRP feature you can create a distributed antenna array with only 1 channel used at each USRP.
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