11,483 research outputs found
DSP Linearization for Millimeter-Wave All-Digital Receiver Array with Low-Resolution ADCs
Millimeter-wave (mmWave) communications and cell densification are the key
techniques for the future evolution of cellular systems beyond 5G. Although the
current mmWave radio designs are focused on hybrid digital and analog receiver
array architectures, the fully digital architecture is an appealing option due
to its flexibility and support for multi-user multiple-input multiple-output
(MIMO). In order to achieve reasonable power consumption and hardware cost, the
specifications of analog circuits are expected to be compromised, including the
resolution of analog-to-digital converter (ADC) and the linearity of
radio-frequency (RF) front end. Although the state-of-the-art studies focus on
the ADC, the nonlinearity can also lead to severe system performance
degradation when strong input signals introduce inter-modulation distortion
(IMD). The impact of RF nonlinearity becomes more severe with densely deployed
mmWave cells since signal sources closer to the receiver array are more likely
to occur. In this work, we design and analyze the digital IMD compensation
algorithm, and study the relaxation of the required linearity in the RF-chain.
We propose novel algorithms that jointly process digitized samples to recover
amplifier saturation, and relies on beam space operation which reduces the
computational complexity as compared to per-antenna IMD compensation.Comment: 2019 IEEE 20th International Workshop on Signal Processing Advances
in Wireless Communications (SPAWC
Hybrid Analog-Digital Precoding for Interference Exploitation
We study the multi-user massive multiple-input-single-output (MISO) and focus
on the downlink systems where the base station (BS) employs hybrid
analog-digital precoding with low-cost 1-bit digital-to-analog converters
(DACs). In this paper, we propose a hybrid downlink transmission scheme where
the analog precoder is formed based on the SVD decomposition. In the digital
domain, instead of designing a linear transmit precoding matrix, we directly
design the transmit signals by exploiting the concept of constructive
interference. The optimization problem is then formulated based on the geometry
of the modulation constellations and is shown to be non-convex. We relax the
above optimization and show that the relaxed optimization can be transformed
into a linear programming that can be efficiently solved. Numerical results
validate the superiority of the proposed scheme for the hybrid massive MIMO
downlink systems.Comment: 5 pages, EUSIPCO 201
Sub-Nyquist Sampling: Bridging Theory and Practice
Sampling theory encompasses all aspects related to the conversion of
continuous-time signals to discrete streams of numbers. The famous
Shannon-Nyquist theorem has become a landmark in the development of digital
signal processing. In modern applications, an increasingly number of functions
is being pushed forward to sophisticated software algorithms, leaving only
those delicate finely-tuned tasks for the circuit level.
In this paper, we review sampling strategies which target reduction of the
ADC rate below Nyquist. Our survey covers classic works from the early 50's of
the previous century through recent publications from the past several years.
The prime focus is bridging theory and practice, that is to pinpoint the
potential of sub-Nyquist strategies to emerge from the math to the hardware. In
that spirit, we integrate contemporary theoretical viewpoints, which study
signal modeling in a union of subspaces, together with a taste of practical
aspects, namely how the avant-garde modalities boil down to concrete signal
processing systems. Our hope is that this presentation style will attract the
interest of both researchers and engineers in the hope of promoting the
sub-Nyquist premise into practical applications, and encouraging further
research into this exciting new frontier.Comment: 48 pages, 18 figures, to appear in IEEE Signal Processing Magazin
Interference Exploitation-based Hybrid Precoding with Robustness Against Phase Errors
Hybrid analog-digital precoding significantly reduces the hardware costs in
massive MIMO transceivers when compared to fully-digital precoding at the
expense of increased transmit power. In order to mitigate the above shortfall,
we use the concept of constructive interference-based precoding, which has been
shown to offer significant transmit power savings when compared with the
conventional interference suppression-based precoding in fully-digital
multiuser MIMO systems. Moreover, in order to circumvent the potential
quality-of-service degradation at the users due to the hardware impairments in
the transmitters, we judiciously incorporate robustness against such
vulnerabilities in the precoder design. Since the undertaken constructive
interference-based robust hybrid precoding problem is nonconvex with infinite
constraints and thus difficult to solve optimally, we decompose the problem
into two subtasks, namely, analog precoding and digital precoding. In this
paper, we propose an algorithm to compute the optimal constructive
interference-based robust digital precoders. Furthermore, we devise a scheme to
facilitate the implementation of the proposed algorithm in a low-complexity and
distributed manner. We also discuss block-level analog precoding techniques.
Simulation results demonstrate the superiority of the proposed algorithm and
its implementation scheme over the state-of-the-art methods
On the Number of RF Chains and Phase Shifters, and Scheduling Design with Hybrid Analog-Digital Beamforming
This paper considers hybrid beamforming (HB) for downlink multiuser massive
multiple input multiple output (MIMO) systems with frequency selective
channels. For this system, first we determine the required number of radio
frequency (RF) chains and phase shifters (PSs) such that the proposed HB
achieves the same performance as that of the digital beamforming (DB) which
utilizes (number of transmitter antennas) RF chains. We show that the
performance of the DB can be achieved with our HB just by utilizing RF
chains and PSs, where is the rank of the
combined digital precoder matrices of all sub-carriers. Second, we provide a
simple and novel approach to reduce the number of PSs with only a negligible
performance degradation. Numerical results reveal that only PSs per RF
chain are sufficient for practically relevant parameter settings. Finally, for
the scenario where the deployed number of RF chains is less than ,
we propose a simple user scheduling algorithm to select the best set of users
in each sub-carrier. Simulation results validate theoretical expressions, and
demonstrate the superiority of the proposed HB design over the existing HB
designs in both flat fading and frequency selective channels.Comment: IEEE Transactions on Wireless Communications (Minor Revision
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