350 research outputs found
Full-Duplex Systems Using Multi-Reconfigurable Antennas
Full-duplex systems are expected to achieve 100% rate improvement over
half-duplex systems if the self-interference signal can be significantly
mitigated. In this paper, we propose the first full-duplex system utilizing
Multi-Reconfigurable Antenna (MRA) with ?90% rate improvement compared to
half-duplex systems. MRA is a dynamically reconfigurable antenna structure,
that is capable of changing its properties according to certain input
configurations. A comprehensive experimental analysis is conducted to
characterize the system performance in typical indoor environments. The
experiments are performed using a fabricated MRA that has 4096 configurable
radiation patterns. The achieved MRA-based passive self-interference
suppression is investigated, with detailed analysis for the MRA training
overhead. In addition, a heuristic-based approach is proposed to reduce the MRA
training overhead. The results show that at 1% training overhead, a total of
95dB self-interference cancellation is achieved in typical indoor environments.
The 95dB self-interference cancellation is experimentally shown to be
sufficient for 90% full-duplex rate improvement compared to half-duplex
systems.Comment: Submitted to IEEE Transactions on Wireless Communication
Cognitive Radio Systems
Cognitive radio is a hot research area for future wireless communications in the recent years. In order to increase the spectrum utilization, cognitive radio makes it possible for unlicensed users to access the spectrum unoccupied by licensed users. Cognitive radio let the equipments more intelligent to communicate with each other in a spectrum-aware manner and provide a new approach for the co-existence of multiple wireless systems. The goal of this book is to provide highlights of the current research topics in the field of cognitive radio systems. The book consists of 17 chapters, addressing various problems in cognitive radio systems
A Distributed Approach to Interference Alignment in OFDM-based Two-tiered Networks
In this contribution, we consider a two-tiered network and focus on the
coexistence between the two tiers at physical layer. We target our efforts on a
long term evolution advanced (LTE-A) orthogonal frequency division multiple
access (OFDMA) macro-cell sharing the spectrum with a randomly deployed second
tier of small-cells. In such networks, high levels of co-channel interference
between the macro and small base stations (MBS/SBS) may largely limit the
potential spectral efficiency gains provided by the frequency reuse 1. To
address this issue, we propose a novel cognitive interference alignment based
scheme to protect the macro-cell from the cross-tier interference, while
mitigating the co-tier interference in the second tier. Remarkably, only local
channel state information (CSI) and autonomous operations are required in the
second tier, resulting in a completely self-organizing approach for the SBSs.
The optimal precoder that maximizes the spectral efficiency of the link between
each SBS and its served user equipment is found by means of a distributed
one-shot strategy. Numerical findings reveal non-negligible spectral efficiency
enhancements with respect to traditional time division multiple access
approaches at any signal to noise (SNR) regime. Additionally, the proposed
technique exhibits significant robustness to channel estimation errors,
achieving remarkable results for the imperfect CSI case and yielding consistent
performance enhancements to the network.Comment: 15 pages, 10 figures, accepted and to appear in IEEE Transactions on
Vehicular Technology Special Section: Self-Organizing Radio Networks, 2013.
Authors' final version. Copyright transferred to IEE
PAPR Reduction and Sidelobe Suppression in Cognitive OFDM - A Survey
Cognitive radio (CR) is one of the key technology providing a new way to enhance the utilization of available spectrum effectively. The multicarrier modulation (MCM) technique which is widely used is Orthogonal Frequency Division Multiplexing (OFDM) system, is an excellent choice for high data rate application. The main two limitations of this technology is the high peak-to-average power ratio (PAPR) of transmission signal and large spectrum sidelobe. This article describes some of the important PAPR reduction techniques and sidelobe suppression techniques
PAPR Reduction and Sidelobe Suppression in Cognitive OFDM - A Survey
Cognitive radio (CR) is one of the key technology providing a new way to enhance the utilization of available spectrum effectively. The multicarrier modulation (MCM) technique which is widely used is Orthogonal Frequency Division Multiplexing (OFDM) system, is an excellent choice for high data rate application. The main two limitations of this technology is the high peak-to-average power ratio (PAPR) of transmission signal and large spectrum sidelobe. This article describes some of the important PAPR reduction techniques and sidelobe suppression techniques
Power spectrum characterization of systematic coded UW-OFDM systems
Unique word (UW)-OFDM is a newly proposed multicarrier technique that has shown to outperform cyclic prefix (CP)-OFDM in fading channels. Until now, the spectrum of UW-OFDM is not thoroughly investigated. In this paper, we derive an analytical expression for the spectrum taking into account the DFT based implementation of the system. Simulations show that the proposed analytical results are very accurate. Compared to CP-OFDM, we show that UW-OFDM has much lower out-of-band (OOB) radiation, which makes it suitable for systems with strict spectral masks, as e. g. cognitive radios. Further, in this paper, we evaluate the effect of the redundant carrier placement on the spectrum
Narrowband Signal Detection in OFDM Systems Using Spectral Shaping Techniques
Abstract: Orthogonal Frequency Division Multiplexing (OFDM) allow data to be transmitted efficiently and reliably by using multiple orthogonal subcarriers. It provides robustness against noise and corruption in the channel. The channel can be either wired or wireless depending on the particular application. Due to the close spacing of subcarriers, OFDM is susceptible to corruption caused by various narrowband signals such as Narrowband Interference (NBI). Spectral shaping shapes the Power Spectral Density (PSD) in order to have certain properties. Spectral shaping might improve the effectiveness of OFDM and make it sustainable in the long run for applications beyond the 4th generation of mobile communications (4G) and Long Term Evolution (LTE). We make use of spectral null codes and load them onto OFDM subcarriers. Introducing narrowband signals in the channel degrades the system’s performance and also eliminates the designed spectral properties. From this observation we infer that some narrowband noise is present in the channel. Previously, carriers hit by NBI or other narrowband noise had to be switched off manually. We found that combining OFDM with spectral shaping allows the presence of Narrowband signals in the channel to be detected and conclusions can be drawn over the channel quality. This did not improve the system in terms of bit error rate performance
Thirty Years of Machine Learning: The Road to Pareto-Optimal Wireless Networks
Future wireless networks have a substantial potential in terms of supporting
a broad range of complex compelling applications both in military and civilian
fields, where the users are able to enjoy high-rate, low-latency, low-cost and
reliable information services. Achieving this ambitious goal requires new radio
techniques for adaptive learning and intelligent decision making because of the
complex heterogeneous nature of the network structures and wireless services.
Machine learning (ML) algorithms have great success in supporting big data
analytics, efficient parameter estimation and interactive decision making.
Hence, in this article, we review the thirty-year history of ML by elaborating
on supervised learning, unsupervised learning, reinforcement learning and deep
learning. Furthermore, we investigate their employment in the compelling
applications of wireless networks, including heterogeneous networks (HetNets),
cognitive radios (CR), Internet of things (IoT), machine to machine networks
(M2M), and so on. This article aims for assisting the readers in clarifying the
motivation and methodology of the various ML algorithms, so as to invoke them
for hitherto unexplored services as well as scenarios of future wireless
networks.Comment: 46 pages, 22 fig
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