1,454 research outputs found
Multiuser detection in a dynamic environment Part I: User identification and data detection
In random-access communication systems, the number of active users varies
with time, and has considerable bearing on receiver's performance. Thus,
techniques aimed at identifying not only the information transmitted, but also
that number, play a central role in those systems. An example of application of
these techniques can be found in multiuser detection (MUD). In typical MUD
analyses, receivers are based on the assumption that the number of active users
is constant and known at the receiver, and coincides with the maximum number of
users entitled to access the system. This assumption is often overly
pessimistic, since many users might be inactive at any given time, and
detection under the assumption of a number of users larger than the real one
may impair performance.
The main goal of this paper is to introduce a general approach to the problem
of identifying active users and estimating their parameters and data in a
random-access system where users are continuously entering and leaving the
system. The tool whose use we advocate is Random-Set Theory: applying this, we
derive optimum receivers in an environment where the set of transmitters
comprises an unknown number of elements. In addition, we can derive
Bayesian-filter equations which describe the evolution with time of the a
posteriori probability density of the unknown user parameters, and use this
density to derive optimum detectors. In this paper we restrict ourselves to
interferer identification and data detection, while in a companion paper we
shall examine the more complex problem of estimating users' parameters.Comment: To be published on IEEE Transactions on Information Theor
Adaptive Interference Removal for Un-coordinated Radar/Communication Co-existence
Most existing approaches to co-existing communication/radar systems assume
that the radar and communication systems are coordinated, i.e., they share
information, such as relative position, transmitted waveforms and channel
state. In this paper, we consider an un-coordinated scenario where a
communication receiver is to operate in the presence of a number of radars, of
which only a sub-set may be active, which poses the problem of estimating the
active waveforms and the relevant parameters thereof, so as to cancel them
prior to demodulation. Two algorithms are proposed for such a joint waveform
estimation/data demodulation problem, both exploiting sparsity of a proper
representation of the interference and of the vector containing the errors of
the data block, so as to implement an iterative joint interference removal/data
demodulation process. The former algorithm is based on classical on-grid
compressed sensing (CS), while the latter forces an atomic norm (AN)
constraint: in both cases the radar parameters and the communication
demodulation errors can be estimated by solving a convex problem. We also
propose a way to improve the efficiency of the AN-based algorithm. The
performance of these algorithms are demonstrated through extensive simulations,
taking into account a variety of conditions concerning both the interferers and
the respective channel states
Co-existence Between a Radar System and a Massive MIMO Wireless Cellular System
In this paper we consider the uplink of a massive MIMO communication system
using 5G New Radio-compliant multiple access, which is to co-exist with a radar
system using the same frequency band. We propose a system model taking into
account the reverberation (clutter) produced by the radar system at the massive
MIMO receiver. Then, we propose several linear receivers for uplink
data-detection, ranging by the simple channel-matched beamformer to the
zero-forcing and linear minimum mean square error receivers for clutter
disturbance rejection. Our results show that the clutter may have a strong
effect on the performance of the cellular communication system, but the use of
large-scale antenna arrays at the base station is key to provide increased
robustness against it, at least as far as data-detection is concerned.Comment: To be presented at 2018 IEEE SPAWC, Kalamata, Greece, June 201
Joint Design of Overlaid Communication Systems and Pulsed Radars
The focus of this paper is on co-existence between a communication system and
a pulsed radar sharing the same bandwidth. Based on the fact that the
interference generated by the radar onto the communication receiver is
intermittent and depends on the density of scattering objects (such as, e.g.,
targets), we first show that the communication system is equivalent to a set of
independent parallel channels, whereby pre-coding on each channel can be
introduced as a new degree of freedom. We introduce a new figure of merit,
named the {\em compound rate}, which is a convex combination of rates with and
without interference, to be optimized under constraints concerning the
signal-to-interference-plus-noise ratio (including {\em signal-dependent}
interference due to clutter) experienced by the radar and obviously the powers
emitted by the two systems: the degrees of freedom are the radar waveform and
the afore-mentioned encoding matrix for the communication symbols. We provide
closed-form solutions for the optimum transmit policies for both systems under
two basic models for the scattering produced by the radar onto the
communication receiver, and account for possible correlation of the
signal-independent fraction of the interference impinging on the radar. We also
discuss the region of the achievable communication rates with and without
interference. A thorough performance assessment shows the potentials and the
limitations of the proposed co-existing architecture
Communications and Radar Coexistence in the Massive MIMO Regime: Uplink Analysis
This paper considers the uplink of a massive MIMO communication system using
5G New Radio-compliant multiple access, which is to co-exist with a radar
system using the same frequency band. A system model taking into account the
reverberation (clutter) produced by the radar system onto the massive MIMO
receiver is proposed. In this scenario, several receivers for uplink channel
estimation and data detection are proposed, ranging from the simple
channel-matched beamformer to the zero-forcing and linear minimum mean square
error receivers for clutter disturbance rejection, under the two opposite
situations of perfectly known ad completely unknown clutter covariance. A
theoretical analysis is also given, deriving a lower bound on the achievable
uplink spectral efficiency and the mutual information between the input
Gaussian-encoded symbols and the observables available at the communication
receiver of the cellular massive MIMO system: regarding the latter, in
particular, we show that, in the large antenna number regime, the radar clutter
effects at the base station is suppressed and single-user capacity is restored.
Numerical results, illustrating the performance of the proposed detection
schemes, confirm the findings of the theoretical analysis, and permit
quantifying the system robustness to clutter effect for increasing number of
antennas at the base station.Comment: 15 pages, 8 figures, paper accepted for publication in IEEE
Transactions on Wireless Communications. arXiv admin note: text overlap with
arXiv:1805.0779
Using Massive MIMO Arrays for Joint Communication and Sensing
One of the trends that is gaining more and more importance in the field of
beyond-5G and 6G wireless communication systems is the investigation on systems
that jointly perform communication and sensing of the environment. This paper
proposes to use a base station (BS), that we call \textit{radar-BS}, equipped
with a large-scale antenna array to execute, using the same frequency range,
communication with mobile users and sensing/surveillance of the surrounding
environment through radar scanning. The massive antenna array can indeed both
operate as a MIMO radar with co-located antennas -- transmitting radar signals
pointing at positive elevation angles -- and perform signal-space beamforming
to communicate with users mainly based on the ground. Our results show that
using a massive MIMO radar-BS the communication and the radar system can
coexist with little mutual interference.Comment: 5 pages, 4 figures, presented at 53th Asilomar conference, Nov. 201
- …