Take The Slow Modem To The Battlefield

As stated the JTRS radios will offer additional capabilities, including higher data rates.  Two important differences remain, a JTRS radio providing the higher data rate will have less than 10 km range, requiring multiple relays to cover a Bn area.

A JTRS radio will cost closer to 20,000 for a Manpack and upwards of 40,000 for a Mounted radio.  Nothing is free.

I was not aware that higer data rates equalled less range!!!!!  Can you confirm that that is indeed the case, perhaps with a source?  Remeber also that these radios are not going to be used "Standalone" so to speak, vehicle mounted radios are going to have a "Power Amp" and ones used in the various CP's are going to havea PA nad probably be hooked into the good ol OE-254 antenna :

 

This being said I dont think your statement regarding the need for more Retran Stations to cover a Battalions AO is valid.  But  im not a commo guy so what do I know ;)

 

Regards

 

Arty

we had a briefing from the US JTRS prog manager in Oct last year at the Brisbane Conf.  I might have some unclass stuff which I can send you.  Will check in a few days when my workload backs off.

 

Communications in general and the internet in particular is organized around a seven layer model that is composed of discrete steps which are physical, data-link, network, transport, session, presentation, and application.

 

Each step levies a requirement on the step before it in order to perform the transfer of information over the specified environment that the overall link must perform within.  Links that are common with the use of stocastic (connectionless/ probabalistic/ i.e. squishy time) IP driven system are very permissive in that they are usually wire bound with a very high signal to noise ratio (the wireless channels (things like 802.11) are specified to have very high signal to noise ratios or they won't work).  A signal to noise ratio is the amount of useful signal you have above/ against the universal white noise and/ or environmentally generated background RF radiation (accidental or deliberate).  In a shielded cable such as what most IP runs over it is very high; for most free space tactical military applications it is very low. Somewhat counter intuitively it is much easier to transmit and receive for sea or air systems where most of the time you have line of sight, than for land systems.

 

For free space trying to transfer information might be compared to delivering a package.  Within the package is the information you want to transfer.  The package itself is a 3 dimensional box the dimensions of which are time, frequency/ BW, and power.  The problem is thou the more complicated you make the package the bigger the box has got to be to carry the package and the more insulation and layers of wrapping paper you need to insure the safe delivery of the contents.  This goes double when you're trying to ship material from far away.  However you want to limit the ability of the enemy to detect and / or intercept your signal.

 

Each time you try to increase the complexity of a step within the model for an individual link an exponential amount of overhead is generated which means the bigger box you need which won't always be available or convenient to carry around on the battlefield. 

 

Furthermore as you approach closer to the battlefield the routes to and from active users will fade or change associations (what post office the package needs to go to in order to be delivered to its recipient).  What this means is that a user at the edge of the battlefield may send a request up the chain for some piece of data that he requires to complete his mission but the reverse path may not be available when it comes time to send the requested information back down to the entity that originally requested the information.  Then they'll have to have the message just die or start looking for a way to get back to the requester.  The former is bad but the later could be catastrophic because it could gum up ALL of the channels.

 

Remember the enemy gets his vote also, and he'll be attacking our spectrum like we're attacking his.  Plus the natural terrain/ environment, particularly for ground forces, will be negatively effecting the signal.  There is a physical law called Shannon's Law and basically it states that the more data you want to pass over a given link the more power and/or bandwidth you need (the bigger the box you need).  All these things have to taken into account when designing one of these links.

I wonder how compatible they got JTRS to be with SINCGARS while Frequency Hopping?  SINCGARS I've been told is a surprisingly tricky waveform which may be why it is so hard.