9 research outputs found
On the multiplexing gain of MIMO Microwave backhaul links affected by Phase Noise
We consider a multiple-input multiple-output (MIMO) AWGN channel affected by phase noise. Focusing on the 2 × 2 case, we show that no MIMO multiplexing gain is to be expected when the phase-noise processes at each antenna are independent, memoryless in time, and with uniform marginal distribution over [0,2π] (strong phase noise), and when the transmit signal is isotropically distributed on the real plane. The scenario of independent phase-noise processes across antennas is relevant for microwave backhaul links operating in the 20–40 GHz range
Multi-sample Receivers Increase Information Rates for Wiener Phase Noise Channels
A waveform channel is considered where the transmitted signal is corrupted by
Wiener phase noise and additive white Gaussian noise (AWGN). A discrete-time
channel model is introduced that is based on a multi-sample receiver. Tight
lower bounds on the information rates achieved by the multi-sample receiver are
computed by means of numerical simulations. The results show that oversampling
at the receiver is beneficial for both strong and weak phase noise at high
signal-to-noise ratios. The results are compared with results obtained when
using other discrete-time models.Comment: Submitted to Globecom 201
Capacity bounds for MIMO microwave backhaul links affected by phase noise
We present bounds and a closed-form high-SNR expression for the capacity of
multiple-antenna systems affected by Wiener phase noise. Our results are
developed for the scenario where a single oscillator drives all the
radio-frequency circuitries at each transceiver (common oscillator setup), the
input signal is subject to a peak-power constraint, and the channel matrix is
deterministic. This scenario is relevant for line-of-sight multiple-antenna
microwave backhaul links with sufficiently small antenna spacing at the
transceivers. For the 2 by 2 multiple-antenna case, for a Wiener phase-noise
process with standard deviation equal to 6 degrees, and at the medium/high SNR
values at which microwave backhaul links operate, the upper bound reported in
the paper exhibits a 3 dB gap from a lower bound obtained using 64-QAM.
Furthermore, in this SNR regime the closed-form high-SNR expression is shown to
be accurate.Comment: 10 pages, 2 figures, to appear in IEEE Transactions on Communication
On the Capacity of the Wiener Phase-Noise Channel: Bounds and Capacity Achieving Distributions
In this paper, the capacity of the additive white Gaussian noise (AWGN)
channel, affected by time-varying Wiener phase noise is investigated. Tight
upper and lower bounds on the capacity of this channel are developed. The upper
bound is obtained by using the duality approach, and considering a specific
distribution over the output of the channel. In order to lower-bound the
capacity, first a family of capacity-achieving input distributions is found by
solving a functional optimization of the channel mutual information. Then,
lower bounds on the capacity are obtained by drawing samples from the proposed
distributions through Monte-Carlo simulations. The proposed capacity-achieving
input distributions are circularly symmetric, non-Gaussian, and the input
amplitudes are correlated over time. The evaluated capacity bounds are tight
for a wide range of signal-to-noise-ratio (SNR) values, and thus they can be
used to quantify the capacity. Specifically, the bounds follow the well-known
AWGN capacity curve at low SNR, while at high SNR, they coincide with the
high-SNR capacity result available in the literature for the phase-noise
channel.Comment: IEEE Transactions on Communications, 201
Capacity of SIMO and MISO Phase-Noise Channels with Common/Separate Oscillators
In multiple antenna systems, phase noise due to instabilities of the
radio-frequency (RF) oscillators, acts differently depending on whether the RF
circuitries connected to each antenna are driven by separate (independent)
local oscillators (SLO) or by a common local oscillator (CLO). In this paper,
we investigate the high-SNR capacity of single-input multiple-output (SIMO) and
multiple-output single-input (MISO) phase-noise channels for both the CLO and
the SLO configurations.
Our results show that the first-order term in the high-SNR capacity expansion
is the same for all scenarios (SIMO/MISO and SLO/CLO), and equal to , where stands for the SNR. On the contrary, the second-order
term, which we refer to as phase-noise number, turns out to be
scenario-dependent. For the SIMO case, the SLO configuration provides a
diversity gain, resulting in a larger phase-noise number than for the CLO
configuration. For the case of Wiener phase noise, a diversity gain of at least
can be achieved, where is the number of receive antennas. For
the MISO, the CLO configuration yields a higher phase-noise number than the SLO
configuration. This is because with the CLO configuration one can obtain a
coherent-combining gain through maximum ratio transmission (a.k.a. conjugate
beamforming). This gain is unattainable with the SLO configuration.Comment: IEEE Transactions on Communication
Massive MIMO with Non-Ideal Arbitrary Arrays: Hardware Scaling Laws and Circuit-Aware Design
Massive multiple-input multiple-output (MIMO) systems are cellular networks
where the base stations (BSs) are equipped with unconventionally many antennas,
deployed on co-located or distributed arrays. Huge spatial degrees-of-freedom
are achieved by coherent processing over these massive arrays, which provide
strong signal gains, resilience to imperfect channel knowledge, and low
interference. This comes at the price of more infrastructure; the hardware cost
and circuit power consumption scale linearly/affinely with the number of BS
antennas . Hence, the key to cost-efficient deployment of large arrays is
low-cost antenna branches with low circuit power, in contrast to today's
conventional expensive and power-hungry BS antenna branches. Such low-cost
transceivers are prone to hardware imperfections, but it has been conjectured
that the huge degrees-of-freedom would bring robustness to such imperfections.
We prove this claim for a generalized uplink system with multiplicative
phase-drifts, additive distortion noise, and noise amplification. Specifically,
we derive closed-form expressions for the user rates and a scaling law that
shows how fast the hardware imperfections can increase with while
maintaining high rates. The connection between this scaling law and the power
consumption of different transceiver circuits is rigorously exemplified. This
reveals that one can make the circuit power increase as , instead of
linearly, by careful circuit-aware system design.Comment: Accepted for publication in IEEE Transactions on Wireless
Communications, 16 pages, 8 figures. The results can be reproduced using the
following Matlab code: https://github.com/emilbjornson/hardware-scaling-law