MIMO HARDWARE REQUIREMENTS

In order to maintain multiple independent data streams, multiple RF and baseband chains are required. There must be at least as many chains on each side as the number of spatial streams. I.e.:
NS = min (NR, NT)

In practice, to obtain better radio link robustness, NR and/or NT are typically chosen to be larger than NS for greater spatial diversity and link budget margin. I.e. for a robust NS = 2 system, NR could be 3. Or for increased link margin, diversity, and performance with a single stream systems, NR = NT = 2 could be used.

Figures 3 and 4 show block diagrams of the MIMO transmitter and receiver, indicating the parallelism and required data rate scaling.

The scaling factors indicate the growth in complexity of each of the blocks as a function of the design variables. This complexity in turn scales the power consumption and area of each block. The complexity scaling is due to both sample rates as well as required sample precision.

As a reference point, an 802.11g single-chip transceiver fabricated in 0.18m CMOS reported in ISSCC 2005 occupies 41mm2 total area, with 72% in digital logic. In transmit mode, the systemon- a-chip consumes 498mW of power, 226mW from the digital components. In receive mode, it consumes 513mW total, 330mW from the digital components.