1,558 research outputs found
Mathematical analysis of the impact of timing synchronization errors on the performance of an OFDM system
This letter addresses the effect of timing synchronization errors that are introduced by an erroneous detection of the start of an orthogonal frequency-division multiplexing (OFDM) symbol. Throughout this letter, the term "timing error" would refer to this type of error. Such errors degrade the performance of an OFDM receiver by introducing intercarrier interference (ICI) and intersymbol interference (ISI). They can occur due to either an erroneous initial frame synchronization or a change in the power delay profile of the channel. In this letter, we provide a mathematical analysis of the effect of timing errors on the performance of an OFDM receiver in a frequency-selective fading environment. The analysis presented in this letter is for the case that no equalization technique has been used to mitigate the introduced ICI and ISI. We find exact formulas for the power of interference terms and the resulting average signal-to-interference ratio. We further extend the analysis to the subsample level. Our results show the nonsymmetric effect of timing errors on the performance of an OFDM system. Finally, simulation results confirm the analysis. The results of this letter can be easily extended to address the effect of such errors on DMT modems
MIMO-UFMC Transceiver Schemes for Millimeter Wave Wireless Communications
The UFMC modulation is among the most considered solutions for the
realization of beyond-OFDM air interfaces for future wireless networks. This
paper focuses on the design and analysis of an UFMC transceiver equipped with
multiple antennas and operating at millimeter wave carrier frequencies. The
paper provides the full mathematical model of a MIMO-UFMC transceiver, taking
into account the presence of hybrid analog/digital beamformers at both ends of
the communication links. Then, several detection structures are proposed, both
for the case of single-packet isolated transmission, and for the case of
multiple-packet continuous transmission. In the latter situation, the paper
also considers the case in which no guard time among adjacent packets is
inserted, trading off an increased level of interference with higher values of
spectral efficiency. At the analysis stage, the several considered detection
structures and transmission schemes are compared in terms of bit-error-rate,
root-mean-square-error, and system throughput. The numerical results show that
the proposed transceiver algorithms are effective and that the linear MMSE data
detector is capable of well managing the increased interference brought by the
removal of guard times among consecutive packets, thus yielding throughput
gains of about 10 - 13 . The effect of phase noise at the receiver is also
numerically assessed, and it is shown that the recursive implementation of the
linear MMSE exhibits some degree of robustness against this disturbance
Random Access in Uplink Massive MIMO Systems: How to exploit asynchronicity and excess antennas
Massive MIMO systems, where the base stations are equipped with hundreds of
antennas, are an attractive way to handle the rapid growth of data traffic. As
the number of users increases, the initial access and handover in contemporary
networks will be flooded by user collisions. In this work, we propose a random
access procedure that resolves collisions and also performs timing, channel,
and power estimation by simply utilizing the large number of antennas
envisioned in massive MIMO systems and the inherent timing misalignments of
uplink signals during network access and handover. Numerical results are used
to validate the performance of the proposed solution under different settings.
It turns out that the proposed solution can detect all collisions with a
probability higher than 90%, at the same time providing reliable timing and
channel estimates. Moreover, numerical results demonstrate that it is robust to
overloaded situations.Comment: submitted to IEEE Globecom 2016, Washington, DC US
Random Access in Massive MIMO by Exploiting Timing Offsets and Excess Antennas
Massive MIMO systems, where base stations are equipped with hundreds of
antennas, are an attractive way to handle the rapid growth of data traffic. As
the number of user equipments (UEs) increases, the initial access and handover
in contemporary networks will be flooded by user collisions. In this paper, a
random access protocol is proposed that resolves collisions and performs timing
estimation by simply utilizing the large number of antennas envisioned in
Massive MIMO networks. UEs entering the network perform spreading in both time
and frequency domains, and their timing offsets are estimated at the base
station in closed-form using a subspace decomposition approach. This
information is used to compute channel estimates that are subsequently employed
by the base station to communicate with the detected UEs. The favorable
propagation conditions of Massive MIMO suppress interference among UEs whereas
the inherent timing misalignments improve the detection capabilities of the
protocol. Numerical results are used to validate the performance of the
proposed procedure in cellular networks under uncorrelated and correlated
fading channels. With UEs that may simultaneously become active
with probability 1\% and a total of frequency-time codes (in a given
random access block), it turns out that, with antennas, the proposed
procedure successfully detects a given UE with probability 75\% while providing
reliable timing estimates.Comment: 30 pages, 6 figures, 1 table, submitted to Transactions on
Communication
Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions
Massive MIMO is a compelling wireless access concept that relies on the use
of an excess number of base-station antennas, relative to the number of active
terminals. This technology is a main component of 5G New Radio (NR) and
addresses all important requirements of future wireless standards: a great
capacity increase, the support of many simultaneous users, and improvement in
energy efficiency. Massive MIMO requires the simultaneous processing of signals
from many antenna chains, and computational operations on large matrices. The
complexity of the digital processing has been viewed as a fundamental obstacle
to the feasibility of Massive MIMO in the past. Recent advances on
system-algorithm-hardware co-design have led to extremely energy-efficient
implementations. These exploit opportunities in deeply-scaled silicon
technologies and perform partly distributed processing to cope with the
bottlenecks encountered in the interconnection of many signals. For example,
prototype ASIC implementations have demonstrated zero-forcing precoding in real
time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing
of 8 terminals). Coarse and even error-prone digital processing in the antenna
paths permits a reduction of consumption with a factor of 2 to 5. This article
summarizes the fundamental technical contributions to efficient digital signal
processing for Massive MIMO. The opportunities and constraints on operating on
low-complexity RF and analog hardware chains are clarified. It illustrates how
terminals can benefit from improved energy efficiency. The status of technology
and real-life prototypes discussed. Open challenges and directions for future
research are suggested.Comment: submitted to IEEE transactions on signal processin
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