Actually, let me be more clear.... The Wikipedia chart lists the first 802.11N MCS0-32 modes standard. The heading "spacial streams" is somewhat mislabeled, and really means "data spacial streams", infering that additiaonl data streams can be enabled if they are spacially apart to allow it. But really that column is representing numberof unique data streams supported.
Modes 0-32 standard specifies "the number of data streams supported" for each mode. But no where does it reference the number of antennas that are specified or required to meet the standard. That I would assume would mean that it is left up to the manufacturer to deside. Wikipedia was clear on how to define MIMO. (A x B : C) A=max number of TR antenna supported B=max number if RCV antennas supported C=max number of data streams supported. 2x2:1 would mean two antennas both that could transmit and receive, but only one data stream, so same data would go across both antennas. 2x2:2 would mean two antennas for tx and rcv, and supports maximum of 2 different unique data streams, to double capacity. 1x1:1 would mean one antenna for tx and one for recv, and supports one data stream. The key here is "max". What is a radio capable of if it isn't configured to do the max? UBNT Mimo supports 2x2:2 in its max configuration, which is enabled by choosing modes MCS 8-15. Thats a known fact. But no where is it documented what happens when select MCS0-7. Does UBNT become a 1x1:1, 2x2:1, 1x2:1, 2x1:1 radio? Thats up to UBNT. Technically the N standard doesn't care one way or the other. All that matters to the standard is how many unique data streams it needs to listen for, and allowed to transmit. Its irrelevent which antenna method gets utilized to get the signal there. To the radio it only distniguishes only the unique data streams. How many antennas used to send one data stream will change the received signal strength, but again the radio's mode doesn't care or isn;t dependant on it because, it is what it is that it hears, with the receiver antenna hearing everything that is in the air regardless of what transmitted it. (That obviously changes in 4x4 or 3x3 modes, since there are only two polarities available, and the additional streams must be achieved via some other spatial method other than polarity such as "space or time" spatial. Anyway, thats why MIMO is confusing. Because there are many options left up to the manufacture, that rarely show up defined on spec sheets. And I find few manufacturer tech support people know the answer when asked which all antenna modes are supported and configurable with their product. They immediately jump to MCS-0-15 that specify only modulation and coding, not antenna selection. Anotehr thing to note, MCS is not limited to 32, there are more. Atleast 64, maybe more modes. I beleive some of the higher modes add teh functionality for two chains to operate at different modes or modulations. I personally feel that functionality is one of the most important features for outdoor professional deployment of MIMO wireless, both to not waste spectrum (operate at highest reliable spectral efficiency per polarity at all times), and to reduce risk of using dual polarity (survive interference per polarity). For some reason the industry has not yet embraces that feature of the standard. It is more complex to consider the higher combinations of having mismatched modulation per polarity. Currently in mode 0-15, both chains must operate on the same modulation, if one chain switches modulation, so does the other. Tom DeReggi RapidDSL & Wireless, Inc IntAirNet- Fixed Wireless Broadband -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
