文章目录

Rethinking GPS: Engineering Next-Gen Location at Uber
- 第二段
- 第三段
- 第四段
A bit of background on GPS/GNSS
- 第二段
- 第三段
- 第4段
Why GNSS location is inaccurate in urban environments
- 第二段

Rethinking GPS: Engineering Next-Gen Location at Uber

Location and navigation using GPS
- deeply embedded in our daily lives,
crucial to Uber’s services.

To orchestrate quick, efficient pickups,
need to know
- locations of matched riders and drivers,
- provide navigation guidance
  - from driver’s current location
  - to
  - where the rider needs to be picked up,
- then to rider’s destination.

rider指的是打车的人啊？这么用的吗？

For this process to work seamlessly,
- location estimates for riders and drivers
- need to be precise

第二段

Since (literal!) launch of GPS in 1973
we have advanced our understanding of the world,
- experienced exponential growth in the computational power
- developed powerful algorithms to
  - model uncertainty from fields like robotics.

啥意思啊？啥叫model uncertainty from fields like robotics

fundamentals of how GPS works have not changed that much,
- leads to significant performance limitations.

rethink some of the starting assumptions
- that were true in 1973
  - regarding where and how we use GPS,
- as well as the computational power
- additional information we can bring to bear to improve it.

第三段

GPS works well under clear skies,
wildly inaccurate (with a margin of error of 50 meters or more) when we need it the most:
- densely populated
- highly built-up urban areas,
where many of our users are located.

a software upgrade
- to GPS for Android
improves location accuracy in urban environments
- via a client-server architecture
- utilizes 3D maps
- performs sophisticated probabilistic computations
  - on GPS data
  - available through Android’s GNSS APIs.

第四段

why GPS perform poorly in urban environments
how we fix it using
- advanced signal processing algorithms
- deployed at scale on our server infrastructure.

standard GPS (red)
improved location estimate (blue) for a pickup
- from Uber HQ in San Francisco.
Our estimated location
- follows the true path taken by the rider,
- GPS shows very large excursions.

A bit of background on GPS/GNSS

a quick recap of how GPS works
- in order to understand
- why it can be inaccurate in high-rise urban environments.

第二段

GPS
- network of more than 30 satellites
- an altitude of about 20,000 kilometers.
(Most cell phones can pick up similar Russian “GLONASS” satellites too.)

satellites send out
- radio frequency signals
- that GPS receivers, those found in cell phones, can lock onto.

these satellites advertise the time at which
- they launch their signals.

第三段

For each satellite
the difference between reception time and launch time (time-of-flight),
- multiplied by the speed of light,
- the pseudorange.

If the satellite and receiver’s clocks are synchronized,
signal travels along
- the straight line-of-sight path,
this equal the actual distance to the satellite.

the clocks are not synchronized,
- so the receiver needs to solve for four unknowns,
- its own 3D coordinates on the globe,
- and its clock bias.

a minimum of four satellites (four equations)
- to solve for these four unknowns.

第4段

ignore bias
the location estimate
- intersecting
- spheres centered at the satellites with the radius of each sphere given by the pseudorange.

GPS receiver processes signals
- from a number of satellites (20 GPS and GLONASS satellites are visible in an open field),
more than the minimum number of equations provides extra robustness to noise, blockages, etc.

some new/future receivers
- can/will process signals from other satellite systems.

Other navigation satellite systems coming online
- are Galileo, operated by the European Union,
- IRNSS in India,
- and BeiDou, operated by China.

GNSS (global navigation satellite systems)
- encompasses these systems.
- (use this term in the remainder)

In this simplified interpretation of GPS receiver computation,
spheres intersect at the center of known satellite locations.

球相交于已知卫星位置的中心？？这什么鬼？

Why GNSS location is inaccurate in urban environments

behind GNSS-based positioning
- receiver has a direct line-of-sight to each satellite whose pseudorange it is computing.

really breaks down in urban environments, as shown in Figure 3

Line-of-sight blockage and strong reflections can cause large GPS error

第二段

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Rethinking GPS: Engineering Next-Gen Location at Uber

文章目录

Rethinking GPS: Engineering Next-Gen Location at Uber

第二段

第三段

第四段

A bit of background on GPS/GNSS

第二段

第三段

第4段

Why GNSS location is inaccurate in urban environments

第二段

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