MIMO

[Titanium]

in MIMO systems, is there really a need to do the RF downconversion of a received signal to baseband then after sometime upconvert it for transmission? can we just tap the RF signal (the raw data) and just make a loopback for it to ready for retransmission? What if i dont want any signal processing involved with my signal, can i just disable this down/upconversion path then just use a direct path like a loopback?

[ErikL]

The message includes the term MIMO but what you seem to be describing is relaying. Virtual MIMO combines relaying with a SISO link to provide MIMO-like bennefits. There are many ways to implement all of these approaches with Software defined radio. There are tradeoffs in implementation. Take for instance the relaying approach you describe, if you recieve and transmit on the same frequency with no delay how would you keep from overwhelming the reciever with the transmitter? HAM / Amateur Radio repeaters for example Rx on one frequency and Tx on another to avoid this problem.

[Titanium]

yes, received and transmit the signal with delay...so it will be possible of no more downconversion? or still need to have different freq for Tx & Rx?

[Tim-C]

For MIMO communication one of the key inputs is carrier frequency. It's important for converting to baseband. If you follow MIMO best practices and the device intended use then you will be downcoverting and reconstructing the signal.

[ErikL]

Its common to decode and re-encode the signal for transmission to remove the noise introduced by the channel on the first hop.  Answers to all of these questions really depend on what you're trying to accomplish and/or research.