365 research outputs found
Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 Years
Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last 5 years (2010–2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input single-output (SISO), multiple-input multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorize the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions
Uplink Contention Based SCMA for 5G Radio Access
Fifth generation (5G) wireless networks are expected to support very diverse
applications and terminals. Massive connectivity with a large number of devices
is an important requirement for 5G networks. Current LTE system is not able to
efficiently support massive connectivity, especially on the uplink (UL). Among
the issues arise due to massive connectivity is the cost of signaling overhead
and latency. In this paper, an uplink contention-based sparse code multiple
access (SCMA) design is proposed as a solution. First, the system design
aspects of the proposed multiple-access scheme are described. The SCMA
parameters can be adjusted to provide different levels of overloading, thus
suitable to meet the diverse traffic connectivity requirements. In addition,
the system-level evaluations of a small packet application scenario are
provided for contention-based UL SCMA. SCMA is compared to OFDMA in terms of
connectivity and drop rate under a tight latency requirement. The simulation
results demonstrate that contention-based SCMA can provide around 2.8 times
gain over contention-based OFDMA in terms of supported active users. The uplink
contention-based SCMA scheme can be a promising technology for 5G wireless
networks for data transmission with low signaling overhead, low delay, and
support of massive connectivity.Comment: Submitted to Golobecom 5G workshop 201
Non-linear echo cancellation - a Bayesian approach
Echo cancellation literature is reviewed, then a Bayesian model is introduced and it is shown how how it can be used to model and fit nonlinear channels. An algorithm for cancellation of echo over a nonlinear channel is developed and tested. It is shown that this nonlinear algorithm converges for both linear and nonlinear channels and is superior to linear echo cancellation for canceling an echo through a nonlinear echo-path channel
Multi-carrier transmission techniques toward flexible and efficient wireless communication systems
制度:新 ; 文部省報告番号:甲2562号 ; 学位の種類:博士(国際情報通信学) ; 授与年月日:2008/3/15 ; 早大学位記番号:新470
Blind user detection in doubly-dispersive DS/CDMA channels
In this work, we consider the problem of detecting the presence of a new user
in a direct-sequence/code-division-multiple-access (DS/CDMA) system with a
doubly-dispersive fading channel, and we propose a novel blind detection
strategy which only requires knowledge of the spreading code of the user to be
detected, but no prior information as to the time-varying channel impulse
response and the structure of the multiaccess interference. The proposed
detector has a bounded constant false alarm rate (CFAR) under the design
assumptions, while providing satisfactory detection performance even in the
presence of strong cochannel interference and high user mobility.Comment: Accepted for publication on IEEE Transactions on Signal Processin
A Survey on Wireless Security: Technical Challenges, Recent Advances and Future Trends
This paper examines the security vulnerabilities and threats imposed by the
inherent open nature of wireless communications and to devise efficient defense
mechanisms for improving the wireless network security. We first summarize the
security requirements of wireless networks, including their authenticity,
confidentiality, integrity and availability issues. Next, a comprehensive
overview of security attacks encountered in wireless networks is presented in
view of the network protocol architecture, where the potential security threats
are discussed at each protocol layer. We also provide a survey of the existing
security protocols and algorithms that are adopted in the existing wireless
network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term
evolution (LTE) systems. Then, we discuss the state-of-the-art in
physical-layer security, which is an emerging technique of securing the open
communications environment against eavesdropping attacks at the physical layer.
We also introduce the family of various jamming attacks and their
counter-measures, including the constant jammer, intermittent jammer, reactive
jammer, adaptive jammer and intelligent jammer. Additionally, we discuss the
integration of physical-layer security into existing authentication and
cryptography mechanisms for further securing wireless networks. Finally, some
technical challenges which remain unresolved at the time of writing are
summarized and the future trends in wireless security are discussed.Comment: 36 pages. Accepted to Appear in Proceedings of the IEEE, 201
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