122 research outputs found
Pushing towards the Limit of Sampling Rate: Adaptive Chasing Sampling
Measurement samples are often taken in various monitoring applications. To
reduce the sensing cost, it is desirable to achieve better sensing quality
while using fewer samples. Compressive Sensing (CS) technique finds its role
when the signal to be sampled meets certain sparsity requirements. In this
paper we investigate the possibility and basic techniques that could further
reduce the number of samples involved in conventional CS theory by exploiting
learning-based non-uniform adaptive sampling.
Based on a typical signal sensing application, we illustrate and evaluate the
performance of two of our algorithms, Individual Chasing and Centroid Chasing,
for signals of different distribution features. Our proposed learning-based
adaptive sampling schemes complement existing efforts in CS fields and do not
depend on any specific signal reconstruction technique. Compared to
conventional sparse sampling methods, the simulation results demonstrate that
our algorithms allow less number of samples for accurate signal
reconstruction and achieve up to smaller signal reconstruction error
under the same noise condition.Comment: 9 pages, IEEE MASS 201
Compressive Spectrum Sensing in Cognitive IoT
PhDWith the rising of new paradigms in wireless communications such as Internet of things
(IoT), current static frequency allocation policy faces a primary challenge of spectrum
scarcity, and thus encourages the IoT devices to have cognitive capabilities to access
the underutilised spectrum in the temporal and spatial dimensions. Wideband spectrum
sensing is one of the key functions to enable dynamic spectrum access, but entails a
major implementation challenge in terms of sampling rate and computation cost since
the sampling rate of analog-to-digital converters (ADCs) should be higher than twice of
the spectrum bandwidth based on the Nyquist-Shannon sampling theorem. By exploiting
the sparse nature of wideband spectrum, sub-Nyquist sampling and sparse signal recovery
have shown potential capabilities in handling these problems, which are directly related
to compressive sensing (CS) from the viewpoint of its origin.
To invoke sub-Nyquist wideband spectrum sensing in IoT, blind signal acquisition with
low-complexity sparse recovery is desirable on compact IoT devices. Moreover, with
cooperation among distributed IoT devices, the complexity of sampling and reconstruc-
tion can be further reduced with performance guarantee. Specifically, an adaptively-
regularized iterative reweighted least squares (AR-IRLS) reconstruction algorithm is
proposed to speed up the convergence of reconstruction with less number of iterations.
Furthermore, a low-complexity compressive spectrum sensing algorithm is proposed to
reduce computation complexity in each iteration of IRLS-based reconstruction algorithm,
from cubic time to linear time. Besides, to transfer computation burden from the IoT
devices to the core network, a joint iterative reweighted sparse recovery scheme with
geo-location database is proposed to adopt the occupied channel information from geo-
location database to reduce the complexity in the signal reconstruction. Since numerous
IoT devices access or release the spectrum randomly, the sparsity levels of wideband spec-trum signals are varying and unknown. A blind CS-based sensing algorithm is proposed
to enable the local secondary users (SUs) to adaptively adjust the sensing time or sam-
pling rate without knowledge of spectral sparsity. Apart from the signal reconstruction
at the back-end, a distributed sub-Nyquist sensing scheme is proposed by utilizing the
surrounding IoT devices to jointly sample the spectrum based on the multi-coset sam-
pling theory, in which only the minimum number of low-rate ADCs on the IoT devices
are required to form coset samplers without the prior knowledge of the number of occu-
pied channels and signal-to-noise ratios. The models of the proposed algorithms are
derived and verified by numerical analyses and tested on both real-world and simulated
TV white space signals
Over-the-air computation for cooperative wideband spectrum sensing and performance analysis
For sensor network aided cognitive radio, cooperative wideband spectrum sensing can distribute the sampling and computing pressure of spectrum sensing to multiple sensor nodes (SNs) in an efficient way. However, this may incur high latency due to distributed data aggregation, especially when the number of SNs is large. In this paper, we propose a novel cooperative wideband spectrum sensing scheme using over-the-air computation. Its key idea is to utilize the superposition property of wireless channel to implement the summation of Fourier transform. This avoids distributed data aggregation by computing the target function directly. The performance of the proposed scheme is analyzed with imperfect synchronization between different SNs. Furthermore, a synchronization phase offset (SPO) estimation and equalization method is proposed. The corresponding performance after equalization is also derived. A working prototype based on universal software radio periphera (USRP) and Monte Carlo simulation is built to verify the performance of the proposed scheme
Some MIMO applications in cognitive radio networks
In the last decade, the wireless communication technology has witnessed a rapid development, which led to a rapid growth in wireless applications and services. However, the radio spectrum resources scarcity resulting from using the traditional methods of fixed spectrum resources allocation has potential constraints on this wireless services rapid growth. Consequently, cognitive radio has been emerged as a possible solution for alleviating this spectrum scarcity problem by employing dynamic resource allocation strategies in order to utilize the available spectrum in a more efficient way so that finding opportunities for new wireless application services could be achieved. In cognitive radio networks, the radio spectrum resources utilization is improved by allowing unlicensed users, known as secondary users, to share the spectrum with licensed users, known as primary users, as long as this sharing do not induce harmful interference on the primary users, which completely entitled to utilize the spectrum. Motivated by MIMO techniques that have been used in practical systems as a means for high data rate transmission and a source for spatial diversity, and by its ease implementation with OFDM, different issues in multi-user MIMO (MU-MIMO) in both the uplink and downlink in the context of cognitive radio are studied in this thesis. More specifically, in the first thrust of this thesis, the spectrum spatial holes which could exist in an uplink MU-MIMO cell as a result of the possible free spatial dimensions resulted from the sparse activity of the primary users is studied; a modified sensing algorithm for these spectrum spatial holes that exploit both the block structure of the OFDM signals and the correlation of their activity states along time are proposed. The second thrust is concerned with cognitive radio relaying in the physical layer where the cognitive radio base station (CBS) relays the PU signal while transmitting its own signals to its SUs. We define secondary users with different priorities (different quality of service requirements); the different levels of priority for SUs are achieved by a newly proposed simple linear scheme based on zero forcing called Hierarchal Priority Zero Forcing scheme HPZF
Sparse Distributed Learning Based on Diffusion Adaptation
This article proposes diffusion LMS strategies for distributed estimation
over adaptive networks that are able to exploit sparsity in the underlying
system model. The approach relies on convex regularization, common in
compressive sensing, to enhance the detection of sparsity via a diffusive
process over the network. The resulting algorithms endow networks with learning
abilities and allow them to learn the sparse structure from the incoming data
in real-time, and also to track variations in the sparsity of the model. We
provide convergence and mean-square performance analysis of the proposed method
and show under what conditions it outperforms the unregularized diffusion
version. We also show how to adaptively select the regularization parameter.
Simulation results illustrate the advantage of the proposed filters for sparse
data recovery.Comment: to appear in IEEE Trans. on Signal Processing, 201
- …