347 research outputs found
Achievable Rates of Multi-User Millimeter Wave Systems with Hybrid Precoding
Millimeter wave (mmWave) systems will likely employ large antenna arrays at
both the transmitters and receivers. A natural application of antenna arrays is
simultaneous transmission to multiple users, which requires multi-user
precoding at the transmitter. Hardware constraints, however, make it difficult
to apply conventional lower frequency MIMO precoding techniques at mmWave. This
paper proposes and analyzes a low complexity hybrid analog/digital beamforming
algorithm for downlink multi-user mmWave systems. Hybrid precoding involves a
combination of analog and digital processing that is motivated by the
requirement to reduce the power consumption of the complete radio frequency and
mixed signal hardware. The proposed algorithm configures hybrid precoders at
the transmitter and analog combiners at multiple receivers with a small
training and feedback overhead. For this algorithm, we derive a lower bound on
the achievable rate for the case of single-path channels, show its asymptotic
optimality at large numbers of antennas, and make useful insights for more
general cases. Simulation results show that the proposed algorithm offers
higher sum rates compared with analog-only beamforming, and approaches the
performance of the unconstrained digital precoding solutions.Comment: to be presented in IEEE ICC 2015 - Workshop on 5G & Beyond - Enabling
Technologies and Application
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
Energy Efficiency and Asymptotic Performance Evaluation of Beamforming Structures in Doubly Massive MIMO mmWave Systems
Future cellular systems based on the use of millimeter waves will heavily
rely on the use of antenna arrays both at the transmitter and at the receiver.
For complexity reasons and energy consumption issues, fully digital precoding
and postcoding structures may turn out to be unfeasible, and thus suboptimal
structures, making use of simplified hardware and a limited number of RF
chains, have been investigated. This paper considers and makes a comparative
assessment, both from a spectral efficiency and energy efficiency point of
view, of several suboptimal precoding and postcoding beamforming structures for
a cellular multiuser MIMO (MU-MIMO) system with large number of antennas.
Analytical formulas for the asymptotic achievable spectral efficiency and for
the global energy efficiency of several beamforming structures are derived in
the large number of antennas regime. Using the most recently available data for
the energy consumption of phase shifters and switches, we show that
fully-digital beamformers may actually achieve a larger energy efficiency than
lower-complexity solutions, as well as that low-complexity beam-steering purely
analog beamforming may in some cases represent a good performance-complexity
trade-off solution.Comment: Submitted to IEEE Transactions on Green Communications and Networkin
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