USB 2.0 Streaming through SMA

Hi All,

We are trying to add a USB interface to one of our wireless modules(a transmitter and a receiver). We would like to demonstrate high speed (480Mbps) data streaming from a PC using USB through the transmitter; and have the receiver stream to another PC. The transmitter and the receiver have a SMA interface, and are capable of handling speeds higher than 480Mbps. Since the wireless modules are not transceivers, we are not sure how to deal with the handshaking process.

Any ideas on how we make a setup for doing something like this?

Thx in advance

- Billu

Reply to
bkamakot
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Saying that the wireless interface has SMA/SMB/SMC, BNC/TNC, N etc. interface does not tell anything usable about the voltage levels or protocol it expects/generates.

Are these modules simple modulators and demodulators ?

Anyway, running 480 Mbit/s would in practice require a _truly_ line of sight path with no obstructions in at least the first Fresnel zone or alternatively COFDM with a heavy ECC, reducing the throughput.

If you claim that speed for the whole system, why do you need handshaking for that. If you just want to demonstrate the speed, why don't you simple send data packets with a serial number and CRC to the USB interface of the first PC and receive the data coming from the USB port of the other PC and check the serial number and CRC for each packet. If you receive packets at 480 Mbit/s without missing packets or CRC errors, then your system operates at 480 Mbit/s.

However, the practical speed for USB is much less, so you would have to add some delay between the packets sent to decrease the effective throughput.

For one way links (such as broadcasting messages to multiple sites), you may have to add a strong ECC to deal with errors in the radio path, which will further reduce the effective throughput by 30-60 %.

Paul

Reply to
Paul Keinanen

Hi Paul,

Thx for your response.

SMA/SMB/SMC, BNC/TNC, N etc.

The voltage swing should be about 0.6V. The module does not really expect a specific protocol, it will just stream any data signals that are sent through the SMA interface. The module consists of a wireless transmitter and receiver.

speed for the whole system, why do you need

At this point, we are just trying to demonstrate a streaming link. (not really concerned about error checking or data integrity) Is it possible to bypass the handshaking process and other initialization procedures associated with the USB protocol and just send out data at highest data rate. Wouldn't this mean non adherence to the USB protocol. Are there any other alternatives, or is there some way we can just use the physical interface of the USB to stream data?

Thx, Billu

Reply to
bkamakot

So what you are saying is you have a radio transmitter with a high- bandwidth analog "modulation in" jack and a radio receiver with a corresponding "modulation out" jack.

You will still need to answer some questions though - for example, are you good down to DC, and up to what maximum modulation frequency? What kinds of distortions can be expected?

As you've rightly noticed, USB is a bidirectional protocol involving handhaking. Simply replacing the wires with your radio boxes is not a very good way of doing things. Yes, I'll admit I once ran S/PDIF digital audio directly into and out of a pair of video sender boxes, making only a gain adjustment... but unless the digital signal already has a fairly robust signaling scheme that's not a good idea.

To do what you want to do right, you need a device on each end which talks USB to the computer, and then talks a more air-channel- apropriate one-way signaling scheme that you can run over your radios. In other words, what you need is a high data rate modem such as might be used for satellite or microwave communcations.

If I had to do your project in a hurry, with little concern for getting it right, I'd ditch USB and try hacking up some 100 megabit or gigabit ethernet cards. You'll want ones with fully open drivers, because you will be needing to convince the trainsceiver chips to go right into the high data rate signalling, despite the abscence of any handshaking to set it up. One way communications on 10 megabit ethernet is pretty simple, even going through the full operating system driver and protocol structure. Doing it faster means you have to persuade the ethernet boards to run at their high speed without first negotiating their way up form a lower one. Of course you might run into other unforseen issues.

Really, you need high rate modems... purchased or kludged together.

Reply to
cs_posting

On 30 Jan, in article snipped-for-privacy@gmail.com " snipped-for-privacy@gmail.com" wrote: ..

So it is a plain old RF transmitter and receiver. Which just HAPPENS to have a SMA connector (they can be used to carry almost any signal) Remember the RCA/Phono connector has uses that are very varied from

75ohm video to many kilohm audio links on the SAME type of connector.

What type of bandwidth do you have on the link? What frequency band is the link in? Is video or data permitted on that band?

If you want to send large amounts of data across the link consider a serialised digital video picture forget the USB. That way you can have a monitor on each end of the link to show the same picture as a demonstration.

I wonder if you are even using the right radio band for what you are trying to do.

--
Paul Carpenter          | paul@pcserviceselectronics.co.uk
    PC Services
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Reply to
Paul Carpenter

SMA/SMB/SMC, BNC/TNC, N etc.

Sounds like a simple FSK link with varactor input and ratio detector (with perhaps a Schmitt trigger) output. Such systems are usable in communication systems between ground and space at any data rate and at very low data rates 1200-9600 bit/s as used in amateur radio packet networks used for decades.

Any ground based systems using high data rates must somehow deal with the multipath issue.

Anyhow, USB is the worst system for PC to PC communication, since USB is simply a master (PC) to slave (any small device) hierarchical communication system in the old IBM SNA tradition :-). With USB you can not transfer data between two PCs, unless you have an "intelligent" cable, which emulates two slaves back to back.

If you want to demonstrate your link, why not connect a signal generator to the transmitter and observe the eye pattern with an oscilloscope.

Paul

Reply to
Paul Keinanen

That's sure to make the money-people's eyes bug out...

Reply to
cs_posting

Thanks for everyones responses.

I guess for the purposes of this discussion (to keep it simple), you can assume that the RF module being considered is a Bluetooth. (or a short range high data rate radio) receiver/transmitter.

Any kind of data is permitted on the device. We have already tested the module by sending a pattern through the signal generator and streaming video from a computer (using a SDI-DVI converter). We are now trying to test it on the more ubiquitous platforms like USB.

We already have a program that does 1Gbps data stream us> >

Reply to
bkamakot

What do you mean by any kind of data? Is the link proportional (analog) or merely digital?

Okay, so what is the transfer function of your link?

So you link does't permit "any kind of data" after all?

You are not going to get that working in any practical way.

Using USB to get data in and out of computer is one thing, but you are not going to get the generic USB peripheral interfaced tunneled over this thing without doing a ton of work.

And it sounds like you don't even understand the problem you are trying to solve.

Reply to
cs_posting

I second the opinion of everyone else here that you have no idea what you're doing. I was staying quiet when I saw your post initially, because I thought I was missing some self-evident truth. I return to this thread a couple of days later to see that there is in fact no missing truth, and it's simply another one of the mystifying semi- troll posts that turn up on c.a.e. so regularly. ("Hi, I need to build a space shuttle, where do I put the diodes? ALL I need to know is where to put the diodes. Come on, I know you're holding out on me. ALL I NEED TO KNOW IS WHERE TO PUT THE DAMN DIODES! I KNOW EVERYTHING ELSE!").

If you want to build a wireless USB link, look at a wireless USB chipset. Of course, this is not as simple as simply connecting a USB host to one end and a USB peripheral to the other end.

If you are selling some proprietary wireless communications modules that you have designed in-house, it completely baffles me how you could be asking questions like this, because you need a better understanding than you have demonstrated here merely to get a reference design from a vendor to function moderately well.

You might - MIGHT - be able to connect a SP/DIF audio channel to your transceiver "directly" (by which I mean you will still need something more than just a piece of wire). You might - MIGHT - be able to connect an analog audio channel to your transceiver "directly" (ditto), but not if the other end already has a slicer built in.

Reply to
larwe

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