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Are ALL of the application capabilities that are available built in to the latest reference design, or do some categories come as "extras" that we can add into the reference design?? For example, the things in the "Research " folder or Educational Apps folder.??
Specifically,
Is Alamouti mode something that is built in as part of the 12.1 reference design, or is it something you have to add and then rebuild the system??
What options are there for receiver processing when it is set to Alamouti??
Are you required to use single receive antenna with Almouti coding?? Does WARP only separate the two data streams or does it have some type of signal optimization also??
Can v 12.1 do 2 antenna Alamouti transmit with MRC processing on two receive antennas??
Is there any other STBC coding available or coming soon??
Is there any type of receive diversity capability??
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Ref design v12.1 does not support Alamouti mode. Since posting v12.1, we have added Alamouti mode to the PHY (alongside SISO and 2x2 multiplexing MIMO) and will include this when we post v13 sometime soon. The Alamouti receiver uses a single receive antenna, which is selected statically in code or by auto-antenna selection per packet (i.e. selection diversity, based on measured received power in the preamble).
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When you say "autoselection Diverstiy based on SNR," does that mean the system will select either 2 x 2 spatial multiplex or Alamouti 2 x 1 for the transmitter (based on preset SNR from RSSI)?? Then the receiver will set itself to the appropriate mode based on header information??
If I sellect the link under v 12.1 for documentation, there is a wide variety of different options, that includes 4 x 4 SM-MIMO. Is that really included in the current reference design, or is it necessary to use WARP lab to test 4 x 4 MIMO??
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The PHY includes logic to read the AGC gain choices for both Rx antennas, then route the antenna with lower gain (higher SNR) to the Rx pipeline. This scheme works for SISO and 2x1 Alamouti modes, where the Rx processing is single-antenna, but the antenna is selected automatically. The selection of SISO, 2x2 multiplexing and 2x1 Alamouti must be made a-priori; this isn't communicated in the header (as the choice affects how the header waveform is constructed).
Our latest real-time PHY doesn't support 4x4. The latest WARPLab design flow does (more details here).
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Thanks, Patrick. I think I almost have it now.
This sounds like the system evaluates header (<5 microseconds stated in one of your papers) and adjusts gain according to the signal level, then uses that data to select which single antenna it will use for incoming data stream. Do I understand correctly that this is an implementation of "Receive Switching Diversity?" (Assuming of course that you have two radios hooked up to the system.
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It's exactly receive switching diversity. The evaluation is actually done in the preamble, before the header samples are received, so an antenna is selected long before the Rx pipeline starts receiving the header.
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To those who have written recently asking about use of MIMO/Almouti with only one board:
I believe that all of the systems are Time Division Multiplexed, so that you have to set for EITHER transmit OR receive at any given time. Thus, you CAN both transmit AND receive with the same system, but you could not do it at the same time, so a direct use of MIMO/Almouti system would not be possible with code available now.
Two alternatives may be possible:
1) transmit code and capture it with a Vector Signal analyzer. then use the playback mode of Vector signal generator as your transmitter. Now you could set the WARP board to receive the signal.
2) IF you are very good at coding, you may be able to basically start from scratch and write your own code to have transmit and receive operational at the same time. As was mentioned in the RICE comments, you may have to use only a subset of the waveform in order to have enough processor power left to do this. You may have to modify your hardware also, as I do not think it is intended to behave this way.
Although the hardware may be able to somewhat support your desires, I think you would be using your time and other resources much better by purchase of a second system and thoroughly learn how everything works before you try to do this. Even if you are successful, I think there is not much practical application for the system you propose...
More comments:
You are correct that the RICE site makes substantial assumptions about the basic knowledge and familiarity with OFDM and SDR conepts that should be understood by users. This is a weakness. However, I do not think there is another site anywhere that does anywhere near as good a job as they do. I have spoken literally with over a hundred suppliers, sales people, researchers, etc. and very few among them understand basic concepts either.
The term, MIMO, refers to Multiple Input Multiple Output of RADIOS into AND out of a CHANNEL. The strong implication for this is that you MUST have TWO radio BOARDS, each having at least two radios (2x2), and the two boards must be separated by a channel. Since the WARP boards each support 4 radios and the software required to use those radios in either or Tx or RX mode at any given time, they ARE, by definition, MIMO boards (not SISO) but you need two of them, each with two radios, to operate in 2 x 2 MIMO mode. Although, as I mentioned, it would be theoretically possible to use a single board for both the input and output of the channel, this is not the intention of the system and it would have very limited usefulness, except for example, as a possible channel emulaton tester....
In terms of using two receive anttenas as one end of the MIMO link, this is NOT SISO and has no relation to SISO. This can, and has been, implemented in WARP software as MIMO-switched diversity on the receive end, and has very clear (several dB) advantages over SISO in radio performance.
sincerely,.
Claude Setzer
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I just want to add one more thought about trying to do MIMO stuff on a single device. Claude is totally right; if you really want to take this approach, it would take a significant amount of effort to start things from scratch. However, even beyond the practical considerations of that time investment, I'd seriously recommend against having a transmitter and receiver on a single board operating simultaneously. The radios themselves leak a small amount of RF energy themselves. In general, this is negligible compared to the amount of radiation coming from the antenna. However, if you have both a transmitter and receiver radio on a single board, I doubt this effect is negligible.
Even if you had really long antennas and separated them far apart from one another, there might be a nontrivial RF link that would be established across the ~3 inches from transmit radio to receive radio. So, any results you wanted to measure could have a strong line-of-sight component to them with potentially nontrivial SNR. On a single board, I'd venture a guess that results would get skewed by this behavior. I'm basing this almost completely on intuition, so don't take this as a "it can't work" post. I'm just trying to emphasize that there are a number of reasons why going to >1 kit might be a good idea.
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