Differene between DPMR and DMR

[n9upc]

Not really. DMR (TRBO) uses a 12.5 kHz channel (2.5 kHz dev), period. Due to the time division, you get 2 channels in that 12.5 kHz step so it is equivalent in terms of occupied band width to running twin 6.25 kHz channels (at 1.25 kHz dev).

NXDN (NextEdge, iDAS) only gives a single channel. It can be either 12.5 kHz wide or 6.25 kHz wide. So to get two channels in 6.25 kHz would require two repeaters.

Thus the debate between NXDN and DMR (in the US). NXDN subscribers are cheaper (roughly 40% the cost of DMR subscribers). However, the 6.25 kHz thing means it is much more expensive to get two channels in a 12.5 kHz space requiring either 2 times the number of sites or a multicoupler (couple thousand dollars right there) at each site to get the same system capacity as DMR. NXDN favors the consumers, DMR favors the system owners due to same capacity on half the hardware (minus 1 time slot for control on a trunk system).

Yes thank you for restating what was stated there. However, C4FM is more like a format where as FDMA Is more of the roadway. You can run CQPSK on FDMA also and then do not forget vocoding.

As for C4FM with Fusion if you really look at the comparison to p 25 you will see that the frequencies used between the two technologies are different as well as some slight data framing. It is not surprising that Yaesu did that in order to not have to pay large sums of money for patents. If you search the internet you will see some experiments that have been done already with software defined radio that allow the reception of fusion and p25.

As a matter of fact a classic example of this is the new DV4mini that allows transports of data streams for fusion, DStar, and P 25.

 

[slicerwizard]

NXDN favors the consumers, DMR favors the system owners due to same capacity on half the hardware (minus 1 time slot for control on a trunk system).

DMR does not favor the system owners. System owners need customers and customers aren't interested in radios that cost twice as much, if not more.

I suppose a DMR system owner could eat some of the subscriber radio costs, but there goes any savings made on site hardware. In fact, those savings wouldn't be anywhere near enough to subsidize subscriber units in a meaningful way.

 

[Voyager]

Sorry P25 Phase 1 is FDMA feel free to google search and see white papers and reports from all the manufacturers of P25 Phase 1

If it's FDMA, why can't more than one user share a transmitter?

Why did they need to release Phase II which is a multiple access (2-slot) mode if Phase I can do more than one slot?

 

[n9upc]

If it's FDMA, why can't more than one user share a transmitter?

Why did they need to release Phase II which is a multiple access (2-slot) mode if Phase I can do more than one slot?

Let's go to the image Bob....FDMA breaks it down via frequency paths like a roadway whereas TDMA is in time slots. Thus with FDMA it takes up a whole width of a frequency in 6.25Khz where as TDMA takes up a 6.25 Khz slot interlaced with another 6.25 Khz slot in a 12.5 khz width

 

[Project25_MASTR]

DMR does not favor the system owners. System owners need customers and customers aren't interested in radios that cost twice as much, if not more.

I suppose a DMR system owner could eat some of the subscriber radio costs, but there goes any savings made on site hardware. In fact, those savings wouldn't be anywhere near enough to subsidize subscriber units in a meaningful way.

The reality of it, DMR Tier 3 infrastructure to obtain the same capacity per site costs about 58% that of NXDN. (To the system owner). DMR subscribers cost roughly 28% more compared to NXDN.

In the long run, a consumer pays roughly 24% more for NXDN for a trunked system. The consumer pays roughly 10% less for NXDN for a conventional system.

 

[hitechRadio]

If it's FDMA, why can't more than one user share a transmitter?

Why did they need to release Phase II which is a multiple access (2-slot) mode if Phase I can do more than one slot?

Also FDMA can be either analog or digital. TDMA is digital. At least as far as today.

Technically Ham Radio's are FDMA.

The MA part can be confusing, engineers look at things differently then most people.

I may be over simplifying this, and I am sure I will be corrected if wrong.

Look at it like this:

Imagine you have 4 repeaters that are narrowband 12.5khz in your area, The 12.5khz repeaters frequencies are the FD part in FDMA. Now, your portable has these 4 repeaters frequencies ( actually 8 frequencies, but I think you get the point) programed so you can access the 4 repeaters. This is the MA part of FDMA.
As you know, on an analog ham repeater only one person can talk at one time, so while your talking on that one repeater other hams can be talking on the other 3 having there own separate conversation seperate from you, AKA, Multiple Access.

The MA part can be confusing, but if you consider for those 4 repeaters you install a device that automatically assigns or allocates frequencies for you (AKA trunking controller) then maybe its easier to understand. Although trunking is not FDMA to be clear.

In TDMA those same 4 repeaters/frequencies can handle 2 simultaneous conversations, effectively doubling capacity in the same 12.5khz spectrum.

A side note both NXDN and dPMR both of which are FDMA support 6.25khz. you could fit two 6.25khz repeaters into a 12.5khz frequency location. Even though you can fit both repeaters into a 12.5khz frequency allocation, the repeaters/frequencies themselves still only support one conversation at a time. But you have doubled your capacity in the 12.5khz frequency allocated.



A lot of the terms we use today in radio came from telephone.
In fact FDMA is a form of FDM (Frequency Division Multiplex) where a defined bandwidth on a analog telephone circuit was divided up frequency wise. Today though Digital TDM (Time Division Multiplex) has replaced FDM, and is similar in some ways to TDMA we are used to in the radio world today.

 

[hitechRadio]

It is actually C4FM, a subset of FDMA. FDMA (see why some of us are complaing about Yaesu building a new C4FM protocol that can't play with an existing standard).

C4FM is not a subset FDMA.

C4FM is the way data is sent over the air.

C4FM=Continuous 4 level FM

C4FM is a type of FSK where by 4 levels +3,+1,-1,-3 and each Symbol represent 2 bits of 00,01,10,11.

 

[Voyager]

Technically Ham Radio's are FDMA.

No. Ham radio is not FDMA, or TDMA, or any-MA. Ham radio uses single user transmitters with the exception of the DMR/NXDN networks.

Look at the graphic UPC posted. It shows the accurate depiction of FDMA - a single transmitter broken into two (or more) voice paths.

I understand that some people think multiple transmitters equals FDMA, but that is simply not true. CB is not FDMA. It is 40 channels of single-user transmitters, not 40-slot FDMA.

A 5-channel trunk system uses 5 transmitters. That does not make it 5-slot FDMA. If it were 5-slot FDMA it would have a single transmitter on a single frequency that is divided into 5 slots.

 

[hitechRadio]

No. Ham radio is not FDMA, or TDMA, or any-MA. Ham radio uses single user transmitters with the exception of the DMR/NXDN networks.

Look at the graphic UPC posted. It shows the accurate depiction of FDMA - a single transmitter broken into two (or more) voice paths.

.

Your wrong, and I see where you are getting confused.
You need to read the graphic again,,, pay attention to the WORD Channels (PLURAL) describing FDMA!
In comparison to TDMA Channel (SINGULAR)!

The graphic that UPC posted of FDMA. It is NOT a single transmitter broken into 2 (or more) voice paths.

IT is in FACT TWO transmitters!!!!! NOT one.

Additionally fitting two transmitters 6.25khz into a 12.5khz channel does NOT define FDMA.

 

[Voyager]

No confusion. That is an accurate depiction of FDMA. Note that both are using a single 12.5 kHz wide transmitter. That's why the brackets indicate 12.5 kHz. Read the description - two users SHARE 12.5 kHz worth of bandwidth. That is true FDMA.

The key to multiple access (MA) is the multiple users have access to a single transmitter.

Using your definition, the entire spectrum is FDMA (including DMR) which makes the term FDMA meaningless.

Likewise, ham radio is not TDMA just because one user can use a frequency followed by another user. TDMA can be twisted just the same as FDMA.

Using these twisted definitions, everything is FDMA and everything is TDMA.

 

[hitechRadio]

No confusion. That is an accurate depiction of FDMA. Note that both are using a single 12.5 kHz wide transmitter. That's why the brackets indicate 12.5 kHz. Read the description - two users SHARE 12.5 kHz worth of bandwidth. That is true FDMA.

The key to multiple access (MA) is the multiple users have access to a single transmitter.

Using your definition, the entire spectrum is FDMA (including DMR) which makes the term FDMA meaningless.

You need to read the graphic again. And it is an accurate depiction!

Pay close attention to the WORD Channels (PLURAL) describing FDMA!
In comparison to TDMA Channel (SINGULAR)!

AGAIN THE GRAPHIC OF FDMA IS TWO CHANNELS/FREQUENCIES OR TWO REPEATERS!
TDMA IN THE GRAPHIC IS ONE CHANNEL/FREQUENCY ONE REPEATER!
Within a 12.5khz bandwidth!

I can't be any clearer than this!

Please reread my post #29

 

[nd5y]

Note that both are using a single 12.5 kHz wide transmitter. That's why the brackets indicate 12.5 kHz.

The graphic indicates two separate 6.25 kHz transmitters on adjacent 6.25 kHz spaced frequencies in a 12.5 kHz wide channel.
As far as I know nobody makes a repeater that is capable of operating on two seperate adjacent 6.25 kHz channels. In order to do that you need two repeaters or Icom's repeater with the optional second RF module in the same chassis.

 

[Project25_MASTR]

The graphic indicates two separate 6.25 kHz transmitters on adjacent 6.25 kHz spaced frequencies in a 12.5 kHz wide channel.
As far as I know nobody makes a repeater that is capable of operating on two seperate adjacent 6.25 kHz channels. In order to do that you need two repeaters or Icom's repeater with the optional second RF module in the same chassis.

You also need a multi-coupler to run at the same site to have a single antenna system.


Sent from my iPhone using Tapatalk

 

[Voyager]

The graphic indicates two separate 6.25 kHz transmitters on adjacent 6.25 kHz spaced frequencies in a 12.5 kHz wide channel.
As far as I know nobody makes a repeater that is capable of operating on two seperate adjacent 6.25 kHz channels. In order to do that you need two repeaters or Icom's repeater with the optional second RF module in the same chassis.

Whether or not anyone truly makes FDMA equipment for Land Mobile is irrelevant. FDMA has been used in satellite communications for decades. I thought Icom made FDMA equipment, but if it uses separate adjacent transmitters, that is close, but is still separate transmitters and no Multiple Access of the same transmitter exists.

Regardless, TDMA slices the carrier in time. FDMA slices the carrier in frequency. Both methods give Multiple Access to the same transmitter. The number of times it is divided will dictate the number of simultaneous users. But, for Land Mobile I think the most slots available is 4 (Open Sky).

The only true ham use of FDMA I am aware of are (some) satellites and Linear Translators (basically satellites on the ground). Both can carry multiple users on the same transmitter.

Again, if you use twisted definitions, all RF is both FDMA and TDMA which makes both terms meaningless.

 

[Voyager]

You also need a multi-coupler to run at the same site to have a single antenna system.

All multicouplers I've seen have much larger frequency separation specs. I wonder what Icom uses to combine two transmitters 6.25 kHz apart. (assuming they are two separate transmitters).

 

[hitechRadio]

Whether or not anyone truly makes FDMA equipment for Land Mobile is irrelevant. FDMA has been used in satellite communications for decades. I thought Icom made FDMA equipment, but if it uses separate adjacent transmitters, that is close, but is still separate transmitters and no Multiple Access of the same transmitter exists..

So your saying that, ICOM, Yaesu, Motorola, Kenwood, Tait and all the other radio manufactures that sell FDMA equipment. Are actually not FDMA because you cant have 2 simultaneous transmissions on the same repeater or frequency? You should probably contact all the manufactures and voice your opinion.

Regardless, TDMA slices the carrier in time. FDMA slices the carrier in frequency. Both methods give Multiple Access to the same transmitter.

FDMA will not give access to the same transmitter/repeater. Even though it is still FDMA, only TDMA allows that. I don't make the rules or terminologies.
Have you not seen the arguments of DMR vs. NXDN on RR. The Arguments being NXDN requires double of everything on site side (repeaters, RF conditioning equipment, power supplies, Etc., Etc) to equal DMR capacity wise.
To equal the same capacity as 2slot TDMA (DMR) you would need two 12.5khz FDMA (NXDN) repeaters either on two 12.5khz frequencies or two 6.25khz FDMA repeaters within a 12.5khz frequency.

To equal the spectral efficiency of DMR you need two 6.25khz FDMA repeaters within a 12.5khz BW.

There are Pro's and Con's to both FDMA and TDMA. I am not choosing one over the other, just to clear.

But, for Land Mobile I think the most slots available is 4 (Open Sky)..

Open Sky is a TDMA system Supports 4 slots in 25khz BW, additionally it can also support 2 slots in a 12.5khz BW. There is also TETRA.

The only true ham use of FDMA I am aware of are (some) satellites and Linear Translators (basically satellites on the ground). Both can carry multiple users on the same transmitter .

It has been along time since I read up on Sat comms But, These are typically broad band, and you are only using a small portion of the transmitted frequencys BW. If someone was on the same exact carrier as you, there would be interference.

Again, if you use twisted definitions, all RF is both FDMA and TDMA which makes both terms meaningless.

Not sure why there needs to be any twisting, facts are facts.

All multicouplers I've seen have much larger frequency separation specs. I wonder what Icom uses to combine two transmitters 6.25 kHz apart. (assuming they are two separate transmitters).

I would guess they would need to use a hybrid combiner, as it allows for zero spacing. Lot of loss with a hybrid combiner.
And no assuming about it, for NXDN or IDAS or DPMR there will be separate transmitters/repeaters.

You do realize, that if you purchased a single Kenwood NXR-700 NXDN repeater or any FDMA repeater for that matter, that it will only support one conversation at a time, right? No matter if the repeater is set for 12.5khz or 6.25khz BW.

 

[Voyager]

I don't need to contact the manufacturers because they are not selling their radios as FDMA.

As for the rest, I simply don't subscribe to the argument that all RF is both FDMA and TDMA. Multiple Access means more than one user can use a transmitter at the same time. DMR is true TDMA. P25 Phase II is true TDMA. Linear translators are true FDMA (and several uses DO share the same carrier without interference - the reason? They are using different frequency segments of that carrier - much like your CTCSS shares your carrier without interference, as it's using frequencies below those you are using, but CTCSS is not a second user.)

If a transmitter allows only one talk path, it is neither FDMA nor TDMA. I guess you could call it Conventional or Legacy RF. There is no Multiple Access - period. One transmitter - one user at a time.

 

[Raccon]

Perhaps you guys should not think of FDMA as access to the same carrier but rather the same repeater site / base station with multiple carriers.

From the Wiki:

FDMA
FDMA (Frequency Division Multiple Access) is a way of sharing radio spectrum by assigning multiple users to different frequencies in a radio system.

Sharing "radio spectrum", not sharing a single frequeny.

Also keep in mind that TDMA and FDMA are very generic terms that are not even limited to RF things, as such they are a poor choice when arguing about the technology of a radio system.

I agree however that all RF is not both FDMA and TDMA.

 

[hitechRadio]

Just not sure how Voyager can argue with the graphic in post #24.

I simply pointed out to him that dPMR is FDMA as described in a system. He believed and probably still does that you get 2 talk paths with ONE FDMA transmitter. FDMA is by definition a way to divide/separate users by Frequency.

My next point here is FDMA does not signify a single band either, it can be spread across multiple bands.
Example a P25p1 system that has a VHFsite, UHFsite,700site and 800site and all sites controlled by a controller that can assign users with an APX8000 or Harris multiband subscriber radios. IS FDMA.

And there does not have to be a controller involved for it to be FDMA.

Example: Sheriff department has 2 repeaters/transmitters analog or digital. One is used for dispatching located at tower site A and the other is used for 28/29 located at tower site B. There is no controller, but it is FDMA.
The sheriffs office removes the 28/29 repeater from service. The dispatch channel is still FDMA by definition.

All user in the spectrum for example VHF, farmers, taxi, towing company and public safety. All have AKA "Multiple access" to the allocated VHF spectrum and are separated from each other in the Frequency Domain. They do not have to know each other, be on the same system, same tower, controller, Etc.. They are all sharing the spectrum and is in essence FDMA.

FDMA describes how the users one frequency is being used, as TDMA describes how the users one frequency is being used.
FDMA gives users an individual allocation of one or several frequency bands, or channels.


Also as I pointed out, manufactures will label there radios FDMA. Yeasu System Fusion, they call it
C4FM FDMA. NXDN is technology is FDMA, dPMR is FDMA, P25p1 is absolutely FDMA. They do not say FDMA only if it is located at the same site, is trunking or has a specific separation between channels.

Analog before digital came around was never called FDMA. In the past there was not a need. We all understood that one LMR or Ham repeater could only handle one single conversation with the bandwidth allocated to the repeater. Then came along Digital and with that the terms FDMA and TDMA (the terms we are accustom to in LMR). The terms became used more often especially when it came to digital technologies, to distinguish what was being used FDMA or TDMA as there is a huge difference between the two. Saying that repeater is DIGITAL does not provide enough basic information of the technology implemented. TDMA and FDMA are usually used when talking about digital to distinguish the 2 on simple channel access. Of course Just saying TDMA DIGITAL only gives basic information on the channel access, as there is P25p2, DMR, Tetra etc. same goes with Digital FDMA, as there are many different implementations.



All voyager would have to do is "google it" and lots of examples come up.
here is one from ICOM.
Key Differences between FDMA vs. TDMA Technology

 

[kayn1n32008]

All multicouplers I've seen have much larger frequency separation specs. I wonder what Icom uses to combine two transmitters 6.25 kHz apart. (assuming they are two separate transmitters).

Sinclair Technologies has transmit combiners that are rated @ 0 kHz separation.