14 Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits
each user. For M ×N MIMO, as given in (1.1), where M is the number
of transmitter a ntennas, N is the number of receiver antennas. The re-
lationship between the channel capac ity and the SNR is logarithmic.
This implies that trying to increase the data rate (capacity) by sim-
ply transmitting more power is not efficient. Howe ver, due to MIMO
setup, as we can see from (1.1 ), a linear increase in capacity is obtained
with respect to the number of transmitting antennas. T hus, it is more
bene fic ial to transmit data using many different low-powered channels
than by using one single, high-powered channel, which is a benefit of
CMOS implementation as described previously.
C ≈ M × B × log
2
(1 +
M
N
SN R) (1.1)
For NLOS (Non-line-of-sight) transmission, some obstacles appeared
between transmitter and receiver, and the spatial diversity mode
MIMO is applied. Different from low-frequency band diversity where
diversity is only deployed at the receiving side, both transmitter and
receiver multiple-antenna structur e is deployed for THz link, as shown
in Figure 1.7(b). For the transmit side, the beam-forming opera tion is
applied to concentrate all transmitters into one direction with largest
radiation power. For the receiver side, spatial diversity is applied, where
each receiver antenna capture s the signal which experiences a differ-
ent and independent fading environment. Then these received signals
are combined based on an optimal algorithm for signal strength e n-
hancement. As seen from (1.2), in a system with M trans mitters and
N receivers, the same signal is transmitted by each antenna. It is pos-
sible to achieve approximately an M N- fold increase in the SNR and
then maintain a high data rate in a multipath environment with low
error ra te.
C ≈ B × Log
2
(1 + M · N · SN R) (1.2)
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