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OpenSky = CDPD?

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S

SCPD

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Apparently so ...

From this MA/COM website ...
A fully integrated IP voice and data controller, based on CDPD architecture. As the heart of the OpenSky® network, it administers frequency re-use and automatic hand-off through the OpenSky® IP packet-switched backbone.
Click to expand...

http://www.opensky.com/network/index.asp

From this white pager ...
OpenSky is a wireless data solution developed by AMP originally for Federal Express use for its urban operations. Federal Express required a new wireless mobile data system that would provide four times the message data of its previous system. In addition, Federal Express also needed occasional voice communications to handle exceptions that would not be conveyed over the data system.
A partnering with Federal Express allowed AMP to develop a wireless data and wide-area
network solution that is reviewed here. Most systems deployed today are voice systems that support data, whereas OpenSky is a wireless data system based on data communications technology. The system currently supports public-safety 800-MHz channels and cellular AMPS channels16. The Commonwealth of Pennsylvania is currently deploying a statewide OpenSky system.
OpenSky is an 800-MHz system that utilizes TDMA with two time slots to support both voice
and data services. The two time slots can be used for both voice and data simultaneously or can be aggregated to support 19.2-kbps throughput on a 25-kHz channel. The two time slots can be split to enable full duplex voice operation or can provide a single simplex digital voice channel and a single data channel with 9.6-kbps data throughput.
What is interesting about this for Tompkins County is that, under a hybrid network scenario, the urban agencies, which may have higher data needs, could use OpenSky radios for data. This would take some of the load off the voice system and increase capacity. Also OpenSky could be used where some of the carriers have Cellular Digital Packet Data (CDPD) channels on their network.
Click to expand...

http://www.co.tompkins.ny.us/pubinfo/pscs/options.pdf

So basically, OpenSky is a private LMR version of CDPD that does voice and data.

-rick
 
N

N_Jay

Guest
rfmobile said:
Apparently so ...
From this white pager ...

http://www.co.tompkins.ny.us/pubinfo/pscs/options.pdf

So basically, OpenSky is a private LMR version of CDPD that does voice and data.

-rick
Click to expand...

Yep, OpenSky is/was based on CDPD standards (for the channel access and channel control layers)

As for the "Hybrid" network described in the 2001 white paper, I don't think the idea was ever implemented anywhere, and now that CDPD is being decommissioned, I doubt it ever can be.
 
datainmotion

datainmotion

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Has anyone heard any updated baud rates on OpenSky? LMR can't seem to break out of the 1980s data rates. I'm sure someone far more educated than me can explain why.

19.2k is pretty pitiful considering other radio modem manufacturers range all the way up to to 1Mb/sec baud rates and even cellular carriers are running at 300k w/ EV-DO.
 
N

N_Jay

Guest
datainmotion said:
Has anyone heard any updated baud rates on OpenSky? LMR can't seem to break out of the 1980s data rates. I'm sure someone far more educated than me can explain why.

19.2k is pretty pitiful considering other radio modem manufacturers range all the way up to to 1Mb/sec baud rates and even cellular carriers are running at 300k w/ EV-DO.
Click to expand...
It all has to do with "occupied bandwidth" and "Signal to Noise ratios".

A 25 kHz LMR channel carries a lot less than a 1.25 MHz cellular carrier.

Trying to "break out" of this issue is not going to happen soon.
 
E

EnidPuceflange

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Location
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datainmotion said:
Has anyone heard any updated baud rates on OpenSky? LMR can't seem to break out of the 1980s data rates. I'm sure someone far more educated than me can explain why.

19.2k is pretty pitiful considering other radio modem manufacturers range all the way up to to 1Mb/sec baud rates and even cellular carriers are running at 300k w/ EV-DO.
Click to expand...

There ARE modulation schemes that do provide very much greater bit rates, even in narrow SMR channels. OFDMA (a variant of which is used in the Nextel system) springs to mind. However, in nature nothing is free, and as the data rate increases, the effective range falls off. Now this is actually an advantage with high bit rate cellular providers, as they are limited by frequency reuse and have lots of money for base stations and fiber, but in SMR systems the cost of a base station every mile is prohibitive.

There is a sweet spot at around 9600 symbols/sec in terms of range vs data rate which is why P25 and OpenSky use variants of C4FM/CQPSK but the problem (for SMR/LMR anyway) is that these modulation schemes don't work real well in Simulcast - you have to have linear modulation which is expensive.

I guess that was rather more information than you wanted :)
 
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