Wednesday, April 28, 2010

Cisco Location Tracking Overview

I've been doing a lot of work on real-time location tracking as part of the Cisco Unified Wireless Network (CUWN) as of lately. Recently, I visited a large warehouse, over 1 million sq. feet large in fact, to perform a location evaluation and tune performance as best possible. I thought I would share my findings and some tips on improving location accuracy.

First, a note on how Cisco's location server and Mobility Services Engine (MSE) perform locationing. Several methods are available to RTLS engineers, whether they use Wi-Fi, GPS, cellular or other technologies as the underlying transport. Those include:

  • Cell of Origin - simple; indicates only the cell to which the mobile device is currently registered.
  • Distance (lateration) - multiple algorithms available; most rely on very precise time measurements and clock synchronization between the mobile device and multiple sensors (GPS for example). Received signal strength (RSS) is one sub-type which does not rely on time measurements but rather on signal strength measurements and a knowledge of the path loss characteristics of the environment (we'll get back to this in a bit...)
  • Angle (angulation) - just as it sounds, uses the angle of incidence at which signals arrive at the receiving sensors to locate the mobile station. Relies heavily on geometric relationships between multiple sensors. Generally sensors use multiple antenna arrays to sample the receiving signal.
  • Pattern Recognition - uses the sampling and recording of radio signal behavior patterns in specific environments. Assumes unique signal characteristics are present at each possible location, creating a unique RF signature. Patterning solutions rely on one of the above mentioned algorithms for the basis of the observed signatures, with RSS being most common.
Cisco's implementation uses what they like to call "RF Fingerprinting". Think of this system as a hybrid between a pure RSS lateration algorithm and a full Pattern Recognition algorithm. Essentially, the network administrator gets the ease of setup of the RSS lateration while still being able to create unique RF signatures of a Pattern Recognition method.

However, Cisco makes it easy on network administrators by supplying 3 pre-defined Pattern Recognition models. Have you noticed the pre-defined RF calibration models in Cisco WCS when you import a floor map - Cubes and Walled Offices, Drywall Office Only, and Outdoor Open Space? In addition, network administrators have the ability to define custom RF calibration models suited to unique environments (like a warehouse for example). In this manner, customers get out-of-the-box functionality for simple deployments while retaining the ability to customize the algorithm for more complex deployments or challenging environments.

In future posts, I'll discuss setting up location tracking and provide some tips for improving location accuracy.


1 comment:

  1. This is really great info. I did not have a clear understanding of locationing methods until I read your post!