PointPerfect MQTT Distribution - (Legacy)

PointPerfect Topics in MQTT 

When using MQTT, your device must be configured to subscribe to the appropriate topics needed to access the service.  The device will need these topics to receive the correct stream for PointPerfect data and to obtain the decryption keys that may be needed for the encrypted SPARTN messages. 

A list of topics specific to your PointPerfect plan can be found under the Topics tab of your Thing.  Note:  If you have multiple Things with different plans in your domain, please pay attention to the differences and apply the proper data topics as you configure your device. 

MQTT Topic Structure 

The MQTT topic structure follows the service distribution model for the MQTT delivery option and supports all solution combinations.  Currently, we support these distributions: 

• Continental IP

• Localized IP

• L-band+IP

• L-band (for key collection only) 

 
NOTE:  Data topics for the L-band+IP distribution are only applicable when the IP option is used. 

MQTT PointPerfect Data Topics

When connecting using the MQTT protocol, PointPerfect corrections are provided through service data topics.  These topics will vary between selected plans and applicable regions.  

Below is an example screenshot of the Topics tab on the Thingstream Portal, showing the service data topics for an IP plan with the EU region (using the Filter by Region button.)  The IP correction topic for each <region> includes all of the data needed for PointPerfect.  Deserialized data topics (/gad, /hpac, /ocb, /clk) are also available if needed for your application.  

Note: The list of topics may change in the future. 

Once you configure the topics for the PointPerfect data streams, the device is ready to access and consume the service.

MQTT Key Topics 

About Dynamic Keys and MQTT Key Topics

Dynamic Keys are provided to decrypt only our Continental-wide correction streams, which are used only with our L-band or IP delivery plans when a Continental distribution is selected for an MQTT client.  Clients using the Localized distribution via MQTT or NTRIP do not need these dynamic keys. 

Encryption keys change every month.  Your device is required to use the current encryption key to decrypt the data. “Current” and “Next” keys are provided with valid to/from start dates to provision two keys simultaneously. 

You can acquire these dynamic keys in multiple ways:

• Your device can subscribe to the MQTT key distribution topic associated with its plan.  By subscribing to the key distribution topic, updated keys will be continuously received by your device regardless of the time it was originally published.

• Keys can be manually collected from the Thingstream platform under the Credentials tab of your Thing.

  • In the ‘MQTT Credentials’ section, you will find the u-center config file (downloads in JSON format) that includes the Current and Next Keys along with their start date and duration.

  • Within the ‘L-band + IP Dynamic keys’ section the current and Next Keys are displayed with their expiration date.

See the Dynamic Keys Lease section of the PointPerfect Service Description document for an example of dynamic key messages in .JSON format.

Dynamic Key Topics in UBX format

For u-blox receivers, users can subscribe to the key distribution topic for their plan and collect the keys in UBX format. The data generated by the topic is in binary format and not encapsulated in any envelope, so it can be transferred to the receiver as it is. 

• /pp/ubx/0236/ip                    (Topic for IP dynamic keys in UBX format)

• /pp/ubx/0236/Lb             (Topic for L-band + IP dynamic keys in UBX format)

Below is an example screenshot of the Topics tab on the Thingstream Portal showing the IP key distribution topic for an IP plan.   

Configuration

MQTT Client Authorization (Key and Certificate)

To provision a device, you will need the Client Key and Client Certificate associated with the location Thing with a PointPerfect plan. This information is found under the Credentials tab > MQTT Credentials section and can be downloaded separately or together within the u-center config (JSON) file.  Once the keys and certificates are stored on your host, you can transfer them to your system to authorize its connection to the service.

Download u-center to Evaluate your PointPerfect Solution 

u-center is the software provided by u-blox for easy installation and configuration of high precision GNSS modules such as the F9.  You can download the latest version of u-center from the PointPerfect Location Services portal on Thingstream.   Please also check the PointPerfect u-center guide for more details.

Additional Features 

AssistNow MQTT Topics with PointPerfect

Devices using PointPerfect via MQTT can subscribe to the AssistNow topics over the PointPerfect broker, with no additional charges! 

AssistNow significantly reduces the time to first fix (TTFF) after a cold start by providing the latest ephemerides data (with updates) from satellite constellations. This saves time by not downloading this data from the satellites.

To get started, simply subscribe to the /pp/ubx/mga topic to receive ephemerides data for all constellations. With a message size of around 8 kB, you'll have access to all the data you need to get started.

Once you've received this data, it's time to unsubscribe and subscribe to the /pp/ubx/mga/updates topic to get incremental ephemerides updates with a message size of around 80 bytes for each satellite as they are updated.

With this bandwidth-optimized approach, your device will have the latest ephemerides data available, even during poor sky visibility and signal loss such as in urban canyons.

It is true incremental updates can reduce the amount of bandwidth required, but we should keep in mind these updates still have an impact on overall data traffic. Unless the assistance data is crucial for operations in challenging environments (such as urban canyons) we suggest avoiding subscribing to the aforementioned topics. This way you can effectively conserve valuable data traffic and reduce operational costs.

The table below shows the two different topics and their respective message size and update frequency.

Python sample script:  PointPerfect MQTT Client

If you are interested to evaluate PointPerfect with an MQTT Client built-in your host application, you may please refer to PointPerfect MQTT Client sample python script available in the Thingstream Downloads PointPerfect section to get started. The script demonstrates on how to authenticate the MQTT client with the broker and subscribe to the MQTT topics. 

MQTT Deserialized Topics for PointPerfect

The SPARTN correction data IP topics (e.g. /pp/ip/eu) provide the SPARTN messages in a sequential order, where clock corrections come every 5 seconds and GAD, HPAC and OCB messages come every 30 seconds.  The GAD, HPAC and OCB messages are required by the receiver to achieve a PointPerfect solution. 

To reduce the time the receiver takes to start using the correction data and achieve a PointPerfect solution, the device can subscribe to each of the SPARTN message topics individually. This enables the device to get the required data right away, rather than waiting for 30 seconds while subscribed to the assembled SPARTN topic. 

The device needs to subscribe to the individual topics in the required order to utilize them.  Once the receiver has a fix (position information), the device shall first subscribe to the GAD topic.  The device shall then subscribe to the HPAC topic, and finally to the OCB topic.  After the data from these three topics have been received, the device shall subscribe to the CLK topic to receive the clock corrections.  Please refer to the message sequence diagram shared below. 

The individual topics used by PointPerfect for SPARTN messages for IP based plan are described in the table below.

Reference Documentation

[1] ZED-F9P Integration manual, UBX-18010802
[2] u-center User guide, UBX-13005250
[3] u-blox F9 HPG 1.32 Interface description, UBX-22008968
[4] C099-F9P application board User guide, UBX- 18063024
[5] EVK-F9P-01 evaluation kit User guide, UBX-22038408  
[6] Thingstream Knowledge Base – Services Support