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Bandwidth Sharing over Wireless

Process for determining wireless bandwidth requirements. Should be agnostic to frequency, band or protocol. It should accommodate interoperability of multiple transmitters/receivers in the environment and inside the product.

The first thing to understand is your use cases. Once you understand what your product is supposed to do the protocols and bands required usually follow directly due to the need to be compatible with 3rd party hardware.

The next step is to determine the number of antennas you'll require. There are different approaches here. Sometimes it makes sense to have one antenna for every transmitter / protocol you're implementing. If your protocol supports FDM (frequency division multiplexing) then you scale the number of antennas with your required bandwidth. However sometimes it is necessary to share an antenna with more than one transmitter. This can be due to cost or the result of physical limitations. If you need an antenna that is required to available to intercept asynchronous transmissions then you must have a dedicated antenna for this purpose.

So I would do this in the following steps:

  1. Make a list of bands/protocols.
  2. Choose one antenna per band/protocol.
  3. For each protocol scale up the number of antennas needed to meet bandwidth/speed requirements.
  4. For any antennas that must be dedicated, temporarily remove them from the list.
  5. Look at bandwidth requirements and use cases and see if any antennas can be shared. A good example of this is combining a low bandwidth protocol onto one leg of a multiple antenna high speed protocol.
  6. Reassemble your list.
  7. We've satisfied product requirements but there is work yet to prove out performance. The problem is desense. We have to make sure that the antennas are sufficiently isolated from each other so that they don't interfere. Specifically if antenna A is transmitting then antenna B nearby can still receive legitimate signals. How to determine sufficient isolation and how much isolation you need is beyond the scope of this article.

    Summary:
    1.) Determine your use cases.
    2.) Map use cases to bandwidth and frequency (or protocol) requirements.
    3.) Determine # antennas
    4.) Determine isolation requirements.

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