933 research outputs found
Channel Acquisition for Massive MIMO-OFDM with Adjustable Phase Shift Pilots
We propose adjustable phase shift pilots (APSPs) for channel acquisition in
wideband massive multiple-input multiple-output (MIMO) systems employing
orthogonal frequency division multiplexing (OFDM) to reduce the pilot overhead.
Based on a physically motivated channel model, we first establish a
relationship between channel space-frequency correlations and the channel power
angle-delay spectrum in the massive antenna array regime, which reveals the
channel sparsity in massive MIMO-OFDM. With this channel model, we then
investigate channel acquisition, including channel estimation and channel
prediction, for massive MIMO-OFDM with APSPs. We show that channel acquisition
performance in terms of sum mean square error can be minimized if the user
terminals' channel power distributions in the angle-delay domain can be made
non-overlapping with proper phase shift scheduling. A simplified pilot phase
shift scheduling algorithm is developed based on this optimal channel
acquisition condition. The performance of APSPs is investigated for both one
symbol and multiple symbol data models. Simulations demonstrate that the
proposed APSP approach can provide substantial performance gains in terms of
achievable spectral efficiency over the conventional phase shift orthogonal
pilot approach in typical mobility scenarios.Comment: 15 pages, 4 figures, accepted for publication in the IEEE
Transactions on Signal Processin
Analysis of cyclic delay diversity on DVB-H systems over spatially correlated channel
The objective of this work is to research and analyze the performance of Cyclic Delay Diversity (CDD) with two transmit antenna on DVB-H systems operating in spatially correlated channel. It is shown in this paper that CDD can achieve desirable transmit diversity gain over uncorrelated channel with or without receiver diversity. However, in reality, the respective signal paths between spatially separated antennas and the mobile receiver is likely to be correlated because of insufficient antenna separation at the transmitter and the lack of scattering effect of the channel. Under this spatially correlated channel, it is apparent that CDD cannot achieve the same diversity gain as obtained under the uncorrelated channel. In this paper, a new upper bound on the pairwise error probability (PEP) of the CDD with spatial correlation of two transmit antennas is derived. The upper bound is used to study the CDD theoretical error performance and diversity gain losses over a generalized spatially correlated Rayleigh channel. This theoretical analysis is validated by the simulation of DVB-H systems with two transmit antennas and the CDD scheme. Both the theoretical and simulated results give the valuable insight that the CDD ability to perform well with a certain amount of channel correlation
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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