5,678 research outputs found
Out-of-Band Radiation Measure for MIMO Arrays with Beamformed Transmission
The spatial characteristics of the out-of-band radiation that a multiuser
MIMO system emits in the environment, due to its power amplifiers (modeled by a
polynomial model) are nonlinear, is studied by deriving an analytical
expression for the continuous-time cross-correlation of the transmit signals.
At a random spatial point, the same power is received at any frequency on
average with a MIMO base station as with a SISO base station when the two
radiate the same amount of power. For a specific channel realization however,
the received power depends on the channel. We show that the power received
out-of-band only deviates little from the average in a MIMO system with
multiple users and that the deviation can be significant with only one user.
Using an ergodicity argument, we conclude that out-of-band radiation is less of
a problem in massive MIMO, where total radiated power is lower compared to SISO
systems and that requirements on spectral regrowth can be relaxed in MIMO
systems without causing more total out-of-band radiation
Scaling up MIMO: Opportunities and Challenges with Very Large Arrays
This paper surveys recent advances in the area of very large MIMO systems.
With very large MIMO, we think of systems that use antenna arrays with an
order of magnitude more elements than in systems being built today, say a
hundred antennas or more. Very large MIMO entails an unprecedented number of
antennas simultaneously serving a much smaller number of terminals. The
disparity in number emerges as a desirable operating condition and a practical
one as well. The number of terminals that can be simultaneously served is
limited, not by the number of antennas, but rather by our inability to acquire
channel-state information for an unlimited number of terminals. Larger numbers
of terminals can always be accommodated by combining very large MIMO technology
with conventional time- and frequency-division multiplexing via OFDM. Very
large MIMO arrays is a new research field both in communication theory,
propagation, and electronics and represents a paradigm shift in the way of
thinking both with regards to theory, systems and implementation. The ultimate
vision of very large MIMO systems is that the antenna array would consist of
small active antenna units, plugged into an (optical) fieldbus.Comment: Accepted for publication in the IEEE Signal Processing Magazine,
October 201
Indoor wireless communications and applications
Chapter 3 addresses challenges in radio link and system design in indoor scenarios. Given the fact that most human activities take place in indoor environments, the need for supporting ubiquitous indoor data connectivity and location/tracking service becomes even more important than in the previous decades. Specific technical challenges addressed in this section are(i), modelling complex indoor radio channels for effective antenna deployment, (ii), potential of millimeter-wave (mm-wave) radios for supporting higher data rates, and (iii), feasible indoor localisation and tracking techniques, which are summarised in three dedicated sections of this chapter
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