[aprssig] APRS vs. SPOT
earl.kd5xb at gmail.com
Thu Sep 8 08:41:31 CDT 2011
It isn't really Wifi, it's using a sat phone as a data connection -- I'd
guess it's more in line with dial-up service. Pretty slow, too.
Vy 7 3
On Thu, Sep 8, 2011 at 7:18 AM, Jim Alles <kb3tbx at gmail.com> wrote:
> 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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>> aprssig at tapr.org
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