941 research outputs found
Doubly Massive mmWave MIMO Systems: Using Very Large Antenna Arrays at Both Transmitter and Receiver
One of the key features of next generation wireless communication systems
will be the use of frequencies in the range 10-100GHz (aka mmWave band) in
densely populated indoor and outdoor scenarios. Due to the reduced wavelength,
antenna arrays with a large number of antennas can be packed in very small
volumes, making thus it possible to consider, at least in principle,
communication links wherein not only the base-station, but also the user
device, are equipped with very large antenna arrays. We denote this
configuration as a "doubly-massive" MIMO wireless link. This paper introduces
the concept of doubly massive MIMO systems at mmWave, showing that at mmWave
the fundamentals of the massive MIMO regime are completely different from what
happens at conventional sub-6 GHz cellular frequencies. It is shown for
instance that the multiplexing capabilities of the channel and its rank are no
longer ruled by the number of transmit and receive antennas, but rather by the
number of scattering clusters in the surrounding environment. The implications
of the doubly massive MIMO regime on the transceiver processing, on the system
energy efficiency and on the system throughput are also discussed.Comment: Accepted for presentation at 2016 IEEE GLOBECOM, Washington (DC),
USA, December 201
A Comparison of Hybrid Beamforming and Digital Beamforming with Low-Resolution ADCs for Multiple Users and Imperfect CSI
For 5G it will be important to leverage the available millimeter wave
spectrum. To achieve an approximately omni- directional coverage with a similar
effective antenna aperture compared to state of the art cellular systems, an
antenna array is required at both the mobile and basestation. Due to the large
bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog
front-end of the receiver with a large number of antennas becomes especially
power hungry. Two main solutions exist to reduce the power consumption: hybrid
beam forming and digital beam forming with low resolution Analog to Digital
Converters (ADCs). In this work we compare the spectral and energy efficiency
of both systems under practical system constraints. We consider the effects of
channel estimation, transmitter impairments and multiple simultaneous users.
Our power consumption model considers components reported in literature at 60
GHz. In contrast to many other works we also consider the correlation of the
quantization error, and generalize the modeling of it to non-uniform quantizers
and different quantizers at each antenna. The result shows that as the SNR gets
larger the ADC resolution achieving the optimal energy efficiency gets also
larger. The energy efficiency peaks for 5 bit resolution at high SNR, since due
to other limiting factors the achievable rate almost saturates at this
resolution. We also show that in the multi-user scenario digital beamforming is
in any case more energy efficient than hybrid beamforming. In addition we show
that if different ADC resolutions are used we can achieve any desired
trade-offs between power consumption and rate close to those achieved with only
one ADC resolution.Comment: Submitted to JSTSP. arXiv admin note: text overlap with
arXiv:1610.0290
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