Principles of Multiple Input Multiple Output Transmission
In the following sections, we introduce the principles of signal transmission over a Multiple Input Multiple Output (MIMO) channel and emphasize on wireless links. We will derive a block diagram of a MIMO system and compact it using the concept of the equivalent baseband channel, which is described in Part I for single input single output (SISO) channels. We characterize the physical channels between the various inputs and outputs of the MIMO system by the delay spread functions, which are functions of two variables t and \(\tau \) to prepare for the case of time-variant wireless channels. For time-invariant MIMO channels, such as cables composed of many two-wire electrical lines or optical fibers, the delay spread function turns into the impulse response and just depends on the delay variable \(\tau \), which is then renamed as t.
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