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[aprssig] APRS vs. SPOT

Jim Alles kb3tbx at gmail.com
Thu Sep 8 13:18:16 UTC 2011


Iridium just announced Wifi from their satellites, good for an Igate app,
maybe ($$$).

Axcess Point<http://news.cnet.com/8301-30686_3-20102904-266/iridium-brings-wi-fi-to-remote-corners-of-the-world/>

Jim A. KB3TBX

On Wed, Sep 7, 2011 at 5:35 PM, <jjesson at voyager.net> wrote:

>
> From my ~10 years of designing-in commercial satellite/cellular tracking
> and telematics systems:
>
>   SPOT technology originally was designed by Axonn's then CTO and this
> technology is based on simplex protocol talking to Globalstar.... protocol
> is interesting as it chips between Globalstar's native CDMA duplex protocol
> (native to Globalstar). Their form of simplex is also known as send-and-pray
> as not an ARQ protocol with Simplex... but a form of repeat packet
> transmissions improve the odds of correctly receiving packets and this is a
> setting in their engineering configuration tool.
>
> Unfortunately, the fade margin (C/N) is marginal so trees or roof structure
> attenuate the signal to the point of not working and the lack of
> confirmation was a major issue.  Not exactly the product or wireless
> satellite protocol I would use if my life was riding on packet reception but
> ok for a lightweight tracking unit.  I used these for a quick light fleet
> tracking system.
>
> The new Iridium ASIC provides a true duplex portable unit and offers a
> solid ARQ protocol. I have evaluated their ASIC and it works great and would
> be my life-saving product of choice.  Hey, all the ice road truckers use
> Iridium tracking devices and they do bet their life on this satellite
> network!  One word of caution - Iridium data costs are not for the typical
> experimenter but if needed commercially a good deal if you need  very
> low-latency duplex data transmission.
>
>  Incidentally, for the best cost/packet  and if you can live with a longer
> latency and larger antennas - such as for heavy equipment and 53' trailer
> fleets - you cannot beat Orbcomm.  While both Globalstar and Iridium use
> L-band, Orbcomm uses 136-150 MHz for its operation.  Now you understand the
> antenna size issue :-)  Orbcomm is getting ready to relaunch this year and
> they will, IMHO, become the leader for global large asset tracking.
>
> 73, Joe Jesson, KC2VGL
>
>
>
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