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XBee Range Testing

October 22, 2009

Link to Part II

XBee Range Test.  Write-up: 091021

Proposal: To test the ranges of the various XBee models in different conditions.

Initially, XBee range-testing appeared to be a simple experiment involving mostly legwork.

Initial Testing Grid:

Measure transmission distance for each model

  • 2.4 GHz
    • Series 1
    • Series 2
  • 900 MHz
  • Antenna Type
    • Integrated Whip, Chip, RPSMA, or U.FL Connector

Network Type

  • Peer-to-Peer
  • Non-Beacon
  • ZigBee

Indoors

  • LOS
  • Through-wall
    • Wall Type

Outdoors

  • Open Field
  • Over water
  • In forest
    • w/different vegetation types

Power Consumption/Model

Test 1: 091019.

Location: ITP, 4th Floor.

We formatted (2) Series 1 XBees, hooked them up to our laptops, and communicated with each other by typing characters, words and sentences, while moving down the hall from each other simultaneously.

LOS: Strings were exchanged without garbling line-of-sight (LOS) from John Duane’s desk to Dan’s Wooden Mirror.  Beyond that and out of sight, we began dropping characters.

Through-wall: I stayed fixed at the column opposite Dan’s Mirror, while Michael made his way through the quiet lounge, down the opposite hall, and back around through the lounge.   The main impediment is a structural brick wall approximately 18-24″ thick, plus miscellaneous partitions.  There was almost never 100% transmission, and frequently no transmission at all.  Transmission returned to 100% once we regained LOS.

Error checking.  This quickly became a significant problem.  At first we had no pre-agreed string to expect, and we relied on cell phones to tell each other whether a transmission had been sent or received.  We moved to a pre-agreed string, but timing was still an issue, and we still needed the cell phones to cross-check.

Range testing.  This can be easily worked out with tape or laser measures at this scale, but the issue of error checking needs to be clarified first as it helps to define what range actually is.  Is it 100% error-free transmission, or is it a percentage of transmission that is still comprehensible, and if so, what is that?

Equipment and Software:

MLF: Power PC G5 & X-Bee Explorer tethered w/USB Cable.  Tom’s Processing XBee Terminal Sketch.

MZD: PC & X-Bee Explorer tethered w/USB Cable.  X-CTU.

Radio configurations:

Radio            ATMY            ATDL            ATDH            ATID

1                     1234            5678            0                  B00B

2                     5678            1234            0                  B00B

Proposed Data Representation:

A map of the XBee ranges on the floor at various times of day.  The proposition being that there are varying levels of RF interference at various times.

Variables that need to be clarified:

  • Network Type
  • Transmitter Location(s)
  • Receiver Location(s)
  • Interference Sources, Types & Strengths
  • Range & Error definitions

Need to understand:

What are the impediments to the simplicity of this test?

The simplest correction would be to redo it with two PCs and X-CTU on both.

In addition:

  • Radio mechanics & physics–more knowledge
  • How XBees communicate–their protocol
    • Zigbee Protocol 802.15.4, 2.4 GHz
    • Synchronous vs Asynchronous: XBees use asynch
  • Error tracking
    • to filter noise: limit transmission character range (eg, to ASCII) — see Making Things Talk on error checking: pp 189-191
      • noise–do XBees filter?
    • UART checksums: better understanding of this mechanism, as partial/garbled transmissions were still received.
  • Radio comparisons
    • XBee data rate up to 115,200 bps (benefits error tracking, as listening > speaking)
  • Test design issues
    • how is range defined?
      • 0% error?  how do you track error?
    • methods of automating the more routine procedures

Further Reading & Research:

  • Making Things Talk–ch 6 & 7 experiments
  • Digi data sheets
  • Digi white papers
  • Digi antenna application note
  • Faludi Blog: XBee
  • ITP Tutorials: XBee
  • Compare other radio mfrs
  • Build a radio
  • Build some antennas
  • And….”Please read up on the very basics of IEEE 802.15.4….[esp for]  use of MAC layer ACKs for error correction”

Source: http://forum.sparkfun.com/viewtopic.php?p=77007&sid=32a41fe3421ce99d464f886ee343822a

Links

Link to Part II

RF Links: http://docs.google.com/Doc?docid=0AZFXfifnCf8DZGQybm1tMzdfNzFkc3I3dDlnaw&hl=en

RF Devices: http://spreadsheets.google.com/ccc?key=0ApFXfifnCf8DdHd6QjhDU2pkWmptbnNvb01hclJzMkE&hl=en

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