5,565 research outputs found
On the Performance of the Relay-ARQ Networks
This paper investigates the performance of relay networks in the presence of
hybrid automatic repeat request (ARQ) feedback and adaptive power allocation.
The throughput and the outage probability of different hybrid ARQ protocols are
studied for independent and spatially-correlated fading channels. The results
are obtained for the cases where there is a sum power constraint on the source
and the relay or when each of the source and the relay are power-limited
individually. With adaptive power allocation, the results demonstrate the
efficiency of relay-ARQ techniques in different conditions.Comment: Accepted for publication in IEEE Trans. Veh. Technol. 201
Receiver Algorithm based on Differential Signaling for SIMO Phase Noise Channels with Common and Separate Oscillator Configurations
In this paper, a receiver algorithm consisting of differential transmission
and a two-stage detection for a single-input multiple-output (SIMO) phase-noise
channels is studied. Specifically, the phases of the QAM modulated data symbols
are manipulated before transmission in order to make them more immune to the
random rotational effects of phase noise. At the receiver, a two-stage detector
is implemented, which first detects the amplitude of the transmitted symbols
from a nonlinear combination of the received signal amplitudes. Then in the
second stage, the detector performs phase detection. The studied signaling
method does not require transmission of any known symbols that act as pilots.
Furthermore, no phase noise estimator (or a tracker) is needed at the receiver
to compensate the effect of phase noise. This considerably reduces the
complexity of the receiver structure. Moreover, it is observed that the studied
algorithm can be used for the setups where a common local oscillator or
separate independent oscillators drive the radio-frequency circuitries
connected to each antenna. Due to the differential encoding/decoding of the
phase, weighted averaging can be employed at a multi-antenna receiver, allowing
for phase noise suppression to leverage the large number of antennas. Hence, we
observe that the performance improves by increasing the number of antennas,
especially in the separate oscillator case. Further increasing the number of
receive antennas results in a performance error floor, which is a function of
the quality of the oscillator at the transmitter.Comment: IEEE GLOBECOM 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
Estimation of phase noise in oscillators with colored noise sources
In this letter we study the design of algorithms for estimation of phase
noise (PN) with colored noise sources. A soft-input maximum a posteriori PN
estimator and a modified soft-input extended Kalman smoother are proposed. The
performance of the proposed algorithms are compared against those studied in
the literature, in terms of mean square error of PN estimation, and symbol
error rate of the considered communication system. The comparisons show that
considerable performance gains can be achieved by designing estimators that
employ correct knowledge of the PN statistics
Effect of Synchronizing Coordinated Base Stations on Phase Noise Estimation
In this paper, we study the problem of oscillator phase noise (PN) estimation
in coordinated multi-point (CoMP) transmission systems. Specifically, we
investigate the effect of phase synchronization between coordinated base
stations (BSs) on PN estimation at the user receiver (downlink channel). In
this respect, the Bayesian Cram\'er-Rao bound for PN estimation is derived
which is a function of the level of phase synchronization between the
coordinated BSs. Results show that quality of BS synchronization has a
significant effect on the PN estimation
Waveforms for the Massive MIMO Downlink: Amplifier Efficiency, Distortion and Performance
In massive MIMO, most precoders result in downlink signals that suffer from
high PAR, independently of modulation order and whether single-carrier or OFDM
transmission is used. The high PAR lowers the power efficiency of the base
station amplifiers. To increase power efficiency, low-PAR precoders have been
proposed. In this article, we compare different transmission schemes for
massive MIMO in terms of the power consumed by the amplifiers. It is found that
(i) OFDM and single-carrier transmission have the same performance over a
hardened massive MIMO channel and (ii) when the higher amplifier power
efficiency of low-PAR precoding is taken into account, conventional and low-PAR
precoders lead to approximately the same power consumption. Since downlink
signals with low PAR allow for simpler and cheaper hardware, than signals with
high PAR, therefore, the results suggest that low-PAR precoding with either
single-carrier or OFDM transmission should be used in a massive MIMO base
station
Green Communication via Power-optimized HARQ Protocols
Recently, efficient use of energy has become an essential research topic for
green communication. This paper studies the effect of optimal power controllers
on the performance of delay-sensitive communication setups utilizing hybrid
automatic repeat request (HARQ). The results are obtained for repetition time
diversity (RTD) and incremental redundancy (INR) HARQ protocols. In all cases,
the optimal power allocation, minimizing the outage-limited average
transmission power, is obtained under both continuous and bursting
communication models. Also, we investigate the system throughput in different
conditions. The results indicate that the power efficiency is increased
substantially, if adaptive power allocation is utilized. For instance, assume
Rayleigh-fading channel, a maximum of two (re)transmission rounds with rates
nats-per-channel-use and an outage probability constraint
. Then, compared to uniform power allocation, optimal power
allocation in RTD reduces the average power by 9 and 11 dB in the bursting and
continuous communication models, respectively. In INR, these values are
obtained to be 8 and 9 dB, respectively.Comment: Accepted for publication on IEEE Transactions on Vehicular Technolog
HARQ Feedback in Spectrum Sharing Networks
This letter studies the throughput and the outage probability of spectrum
sharing networks utilizing hybrid automatic repeat request (HARQ) feedback. We
focus on the repetition time diversity and the incremental redundancy HARQ
protocols where the results are obtained for both continuous and bursting
communication models. The channel data transmission efficiency is investigated
in the presence of both secondary user peak transmission power and primary user
received interference power constraints. Finally, we evaluate the effect of
secondary-primary channel state information imperfection on the performance of
the secondary channel. Simulation results show that, while the throughput is
not necessarily increased by HARQ, substantial outage probability reduction is
achieved in all conditions.Comment: Published in IEEE Communications Letter
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