{"id":7531,"date":"2021-02-26T19:26:24","date_gmt":"2021-02-26T19:26:24","guid":{"rendered":"https:\/\/www.use-snip.com\/kb\/?post_type=ht_kb&p=7531"},"modified":"2021-06-27T20:33:57","modified_gmt":"2021-06-27T20:33:57","slug":"creating-dsrc-streams","status":"publish","type":"ht_kb","link":"https:\/\/www.use-snip.com\/kb\/knowledge-base\/creating-dsrc-streams\/","title":{"rendered":"Creating DSRC Streams"},"content":{"rendered":"

The SNIP<\/strong><\/span> NTRIP Caster can be used to create corrections streams suitable for use with the SAE J2735 DSRC Message<\/a> set for delivery to Road Side Units<\/em> (RSUs) which then broadcast the messages for reception by nearby vehicle On Board Units<\/em> (OBUs) and use by the vehicle internal GNSS.\u00a0\u00a0 This allows the vehicle GNSS to use classic code corrections, or RTK methods, or PPP methods, to improve its positional accuracy.<\/p>\n

This article describes how to set up SNIP<\/strong><\/span> to send these data streams to one or more RSU devices (or any remote IP:Port) using the industry format of UDP sending and encoded in an ASN.1 UPER form.<\/p>\n

DSRC<\/strong> = Dedicated Short Range Communication, a short haul 5.9 GHz radio system used for Vehicle to Vehicle<\/em> communications (now more often called V2X = Vehicle to X (everything)).\u00a0 This is one of several international initiatives to deploy “smart cars” “intelligent transportation” or “self driving” vehicles, etc. Today SNIP<\/strong><\/span> is the most widely deployed NTRIP Caster in the world; but was in fact originally created to service this niche<\/span><\/span> market.<\/p>\n

Process Flow<\/h3>\n

SNIP<\/strong><\/span> handles the entire translation process providing the following steps:<\/p>\n

    \n
  1. Decoding the RTCM messages<\/a> (all versions of RTCM are supported as well as the private \/ proprietary message types).\u00a0 The more basic vehicle devices use RTCM2<\/a>, while more advanced devices use RTCM3<\/a>. [spacer height=”15px” id=”3″]<\/li>\n
  2. Filtering and performing integrity monitoring on the RTCM content itself.\u00a0 The complete set of PFAT<\/strong><\/span> operations<\/a> are also supported.[spacer height=”15px” id=”3″]<\/li>\n
  3. Packing the desired RTCM messages into the SAE J2735 message format<\/a> (the ETSI format is also supported).[spacer height=”15px” id=”3″]<\/li>\n
  4. Encoding the resulting DSRC message into ASN.1 UPER format.[spacer height=”15px” id=”3″]<\/li>\n
  5. Further encoding the DSRC message payload into the RSU ‘simple HEX’ format which US RSU devices expect. [spacer height=”15px” id=”3″]<\/li>\n
  6. Sending this payload to multiple RSUs by way of UDP datagrams.<\/li>\n<\/ol>\n

    Each destination device has its own dedicated socket and kernel management to ensure low latency and to prevent cross RSU device performance issues. Up to 32 sockets are supported for each DSRC stream. In a typical deployment a common DSRC message payload is created and delivered to sets of regionally co-located RSUs transmitting on Channel 180 (US numbering plan) at a ~1Hz rate.<\/p>\n

    Within SNIP<\/strong><\/span>\u00ae this process is handled as another PFAT<\/strong><\/span>™ translation, but the control interface is exposed as a Push_Out<\/strong><\/a> stream with a few additional control elements to select the set of IP:Port values where the data is to be sent.\u00a0\u00a0 Once set up, the data simply flows unless there is a detected error which is then reported on the console log<\/a> to the operator.<\/p>\n

    Setup Dialog<\/h2>\n

    The DSRC user dialog is based on the Push-Out<\/a> dialog. But in addition to sending the data to another Caster (in this case the data is sent back to the local SNIP<\/strong><\/span> Caster) some DSRC specific information can also be entered. A typical empty dialog is shown below.<\/p>\n

    \"\"<\/p>\n

    The operator first selects which Base Station data stream will be used.\u00a0 SNIP<\/span><\/strong> provides the normal tool-tip information to further describe the content and general location of the streams.<\/p>\n

    \"\"<\/p>\n

    Note<\/strong><\/span>: Once you select which data stream is to be used from the drop-down, the ‘traditional’ Push-Out setup details are populated for you including appending the word “-dsrc” to the mountPt name, adding the IP and port of your local machine, and adding the default local access password.\u00a0 You do not need to enter these values by hand.<\/p>\n

    [Aside<\/em>: This is an example of the SNIP<\/strong><\/span> Caster folding<\/em> a data stream back into itself for further processing (called loopback).\u00a0 A similar use can be found when a given data stream needs to be sent out in more than one Reference Datum<\/a> using PFAT<\/strong><\/span> to Transform the ECEF antenna location.]<\/p>\n

    The operator then enters the sets of IP:Port address which the final data will be sent to (described next). These are typically RSU devices servicing a region of roadway covered by the selected Base Station.<\/p>\n

    The check box labeled RSU Connections (data sent to UDP)<\/strong> represents the master on\/off<\/strong> switch for sending out the UDP data.\u00a0 To disable sending, you can either un-check this box or disable the stream itself at Push_Out tab <\/a>level.<\/p>\n

    Four additional check boxes are used to control the content which is sent out, and the level of console logging shown. Note<\/strong> <\/span>that the first two of these only have effect when sending RTCM2<\/strong> messages, they are ignored for RTCM3 and other content types.<\/p>\n