413 research outputs found
An Uplink Interference Analysis for Massive MIMO Systems with MRC and ZF Receivers
This paper considers an uplink cellular system, in which each base station
(BS) is equipped with a large number of antennas to serve multiple
single-antenna user equipments (UEs) simultaneously. Uplink training with pilot
reusing is adopted to acquire the channel state information (CSI) and maximum
ratio combining (MRC) or zero forcing (ZF) reception is used for handling
multiuser interference. Leveraging stochastic geometry to model the spatial
distribution of UEs, we analyze the statistical distributions of the
interferences experienced by a typical uplink: intra-cell interference,
inter-cell interference and interference due to pilot contamination.
For a practical but still large number of BS antennas, a key observation for
MRC reception is that it is the intra-cell interference that accounts for the
dominant portion of the total interference. In addition, the interference due
to pilot contamination tends to have a much wider distribution range than the
inter-cell interference when shadowing is strong, although their mean powers
are roughly equal. For ZF reception, on the other hand, we observe a
significant reduction of the intra-cell interference compared to MRC reception,
while the inter-cell interference and the interference due to pilot
contamination remains almost the same, thus demonstrating a substantial
superiority over MRC reception.Comment: 7 pages, 4 figures, accepted by IEEE Wireless Communications and
Networking Conference (WCNC) 201
Power Scaling of Uplink Massive MIMO Systems with Arbitrary-Rank Channel Means
This paper investigates the uplink achievable rates of massive multiple-input
multiple-output (MIMO) antenna systems in Ricean fading channels, using
maximal-ratio combining (MRC) and zero-forcing (ZF) receivers, assuming perfect
and imperfect channel state information (CSI). In contrast to previous relevant
works, the fast fading MIMO channel matrix is assumed to have an arbitrary-rank
deterministic component as well as a Rayleigh-distributed random component. We
derive tractable expressions for the achievable uplink rate in the
large-antenna limit, along with approximating results that hold for any finite
number of antennas. Based on these analytical results, we obtain the scaling
law that the users' transmit power should satisfy, while maintaining a
desirable quality of service. In particular, it is found that regardless of the
Ricean -factor, in the case of perfect CSI, the approximations converge to
the same constant value as the exact results, as the number of base station
antennas, , grows large, while the transmit power of each user can be scaled
down proportionally to . If CSI is estimated with uncertainty, the same
result holds true but only when the Ricean -factor is non-zero. Otherwise,
if the channel experiences Rayleigh fading, we can only cut the transmit power
of each user proportionally to . In addition, we show that with an
increasing Ricean -factor, the uplink rates will converge to fixed values
for both MRC and ZF receivers
On the Performance of MRC Receiver with Unknown Timing Mismatch-A Large Scale Analysis
There has been extensive research on large scale multi-user multiple-input
multiple-output (MU-MIMO) systems recently. Researchers have shown that there
are great opportunities in this area, however, there are many obstacles in the
way to achieve full potential of using large number of receive antennas. One of
the main issues, which will be investigated thoroughly in this paper, is timing
asynchrony among signals of different users. Most of the works in the
literature, assume that received signals are perfectly aligned which is not
practical. We show that, neglecting the asynchrony can significantly degrade
the performance of existing designs, particularly maximum ratio combining
(MRC). We quantify the uplink achievable rates obtained by MRC receiver with
perfect channel state information (CSI) and imperfect CSI while the system is
impaired by unknown time delays among received signals. We then use these
results to design new algorithms in order to alleviate the effects of timing
mismatch. We also analyze the performance of introduced receiver design, which
is called MRC-ZF, with perfect and imperfect CSI. For performing MRC-ZF, the
only required information is the distribution of timing mismatch which
circumvents the necessity of time delay acquisition or synchronization. To
verify our analytical results, we present extensive simulation results which
thoroughly investigate the performance of the traditional MRC receiver and the
introduced MRC-ZF receiver
Spectral Efficiency of One-Bit Sigma-Delta Massive MIMO
We examine the uplink spectral efficiency of a massive MIMO base station employing a one-bit Sigma-Delta ( \Sigma \Delta ) sampling scheme implemented in the spatial rather than the temporal domain. Using spatial rather than temporal oversampling, and feedback of the quantization error between adjacent antennas, the method shapes the spatial spectrum of the quantization noise away from an angular sector where the signals of interest are assumed to lie. It is shown that, while a direct Bussgang analysis of the \Sigma \Delta approach is not suitable, an alternative equivalent linear model can be formulated to facilitate an analysis of the system performance. The theoretical properties of the spatial quantization noise power spectrum are derived for the \Sigma \Delta array, as well as an expression for the spectral efficiency of maximum ratio combining (MRC). Simulations verify the theoretical results and illustrate the significant performance gains offered by the \Sigma \Delta approach for both MRC and zero-forcing receivers
Spectral Efficiency of Mixed-ADC Massive MIMO
We study the spectral efficiency (SE) of a mixed-ADC massive MIMO system in
which K single-antenna users communicate with a base station (BS) equipped with
M antennas connected to N high-resolution ADCs and M-N one-bit ADCs. This
architecture has been proposed as an approach for realizing massive MIMO
systems with reasonable power consumption. First, we investigate the
effectiveness of mixed-ADC architectures in overcoming the channel estimation
error caused by coarse quantization. For the channel estimation phase, we study
to what extent one can combat the SE loss by exploiting just N << M pairs of
high-resolution ADCs. We extend the round-robin training scheme for mixed-ADC
systems to include both high-resolution and one-bit quantized observations.
Then, we analyze the impact of the resulting channel estimation error in the
data detection phase. We consider random high-resolution ADC assignment and
also analyze a simple antenna selection scheme to increase the SE. Analytical
expressions are derived for the SE for maximum ratio combining (MRC) and
numerical results are presented for zero-forcing (ZF) detection. Performance
comparisons are made against systems with uniform ADC resolution and against
mixed-ADC systems without round-robin training to illustrate under what
conditions each approach provides the greatest benefit.Comment: To appear in IEEE Transactions on Signal Processin
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