GNSS接收机的集成

Integrating aGNSS receiver How to build a test plan for designers anddevelopers of GNSS-dependent products Contents Introduction 1.Establishing your product’s PNT requirements32.Reviewing GNSS chipset specifications43.Selecting a GNSS receiver for your product54.Integration testing with your prototype75.Testing application-specific performance86.Testing the antenna107.Verification testing in the real world118.Testing on the production line129. A GNSS receiver test checklist13Get help with building your GNSS test plan14 1.Establishing your product’s PNT requirements Introduction The receiver tests you conduct will be largely determined by howyou need your product to perform from a PNT perspective. The importance of GNSS receiver testing Positioning, navigation and timing(PNT) are becoming ever-more criticalcapabilities in an ever-growing arrayof electronic products. Drawing up a list of your PNT performance requirements will allow you to evaluate differentchipsets and modules from different vendors, and assess the performance of the chosenchipset once it has integrated into your device. Performance requirements will vary depending on the nature, function and user expectationsof your product. For example: From a fitness tracker that records the route the weareris running to a delivery drone carrying emergencymedical supplies, and from a master clock that keepsan energy grid in sync to a farming robot that preciselywaters each plant – all rely on global navigationsatellite systems (GNSS) to function. •A fitness trackermay need to achieve position accuracy to within 10m, even if thewearer is running through a wooded area or urban canyon where satellite visibility isrestricted. •A delivery dronemust be able to fly a defined route within stringent horizontal andvertical accuracy limits, and avoid unforeseen obstacles. It must be able to land safelyat the required location, and return to the operator once delivery has been completed.It must be highly resistant to radio frequency (RF) interference, including maliciousinterference for high-value loads. Companies integrating GNSS receivers into productslike these must be confident that the receiver willdeliver the promised level of performance. That meansselecting the best receiver for the product, and testingit at successive stages of the product developmentcycle to identify and fix any issues before launch. If PNTcapabilities are essential to the proper functioning ofthe product, this can’t be left to chance – it requiresrigorous, repeatable testing, both in the lab and in thereal world. •A master clockusing GNSS as a source of precision time in an electricity grid willrequire high levels of resilience and reliability and provide sufficient accuracy for timingand synchronization. •An agricultural robotmay need to achieve position accuracy to within 10cm and to dothis repeatably, as GNSS drift can prevent the robot from returning to the same positionwith sufficient accuracy. This eBook is a guide for product designers anddevelopers on what to consider when building atest plan for an integrated GNSS receiver. It offersadvice on what and how to test at each stage of thedevelopment cycle, and ends with a checklist to helpyou build the right test plan for your product. The performance requirements you draw up here will then form the basis of your test plan. 2. ReviewingGNSSchipsetspecifications Did you know? Some designers may be content to rely on the performanceinformation provided in the GNSS chipset’s product specifications.However, while these will have been generated under stringenttest conditions, there are several good reasons to validate theperformance of each chipset by conducting your own testing: Understanding manufacturers’accuracy measurements Satellite position data is stochastic, makingit impossible to provide a simple ‘accurate towithin…’ figure without an accompanying measureof probability that a reading will fall within thatradius of the true position. There are severaldifferent positioning accuracy measures, including: 1.There are no universal test standards or test frameworks that all chipset manufacturers mustfollow. Each manufacturer determines their own test regime and the conditions under whichtests are carried out. Evaluating different receivers based purely on their spec sheets canmean you’re not comparing like with like. 2.Often, tests can be carried out in ‘ideal’ conditions, with perfectly simulated signals and noneof the impairments the receiver is likely to encounter in the real world. While that does providea good idea of its peak performance, its day-to-day performance may be at variance withthe specification – and perhaps unacceptably so for your product. •Circular error probable (CEP):The radius ofa circle centred at the true position, at which50% of estimated positions occur. This is a 2Dmeasure of accuracy. •Spherical error probable (SEP):The radius ofa sphere centred at the true position, at which50% of