520 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 (2010ā2014) 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
A Low-Complexity Precoding Scheme for the Downlink of Multi-Cell Multi-User MIMO AF System
Because of its simplicity, amplify-and-forward (AF) is one of the most popular cooperative relaying technique. Relays are used in cooperative communication to improve reliability, coverage or spectral efficiency of cell-edge users. However, relays tend to increase the interferences seen by users of adjacent cells, particularly by the cell-edge users, when used in multi-cell systems. In this paper, we propose a low-complexity precoding scheme to mitigate the effect of other-cell interference (OCI) in cooperative communication. The scheme is designed by taking into account the interference plus noise covariance matrix of each user for mitigating the interference at each receiver by means of precoding at the relay node. Simulation results show the effectiveness of the proposed scheme, both in terms of sum-rate and computational complexity, when compared to other existing OCI-aware precoding algorithms for AF
Layered Steered SpaceāTime-Spreading-Aided Generalized MC DS-CDMA
AbstractāWe present a novel trifunctional multiple-inputā multiple-output (MIMO) scheme that intrinsically amalgamates spaceātime spreading (STS) to achieve a diversity gain and a Vertical Bell Labs layered spaceātime (V-BLAST) scheme to attain a multiplexing gain in the context of generalized multicarrier direct-sequence code-division multiple access (MC DS-CDMA), as well as beamforming. Furthermore, the proposed system employs both time- and frequency-domain spreading to increase the number of users, which is also combined with a user-grouping technique to reduce the effects of multiuser interference
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Physical layer network coding based communication systems in frequency selective channels
PhD ThesisThe demand for wireless communications is growing every day which requiresmore
speed and bandwidth. In two way relay networks (TWRN), physical
layer network coding (PLNC) was proposed to double the bandwidth. A
TWRN is a system where two end users exchange data through a middle node
called the relay. The two signals are allowed to be physically added before being
broadcasted back to the end users. This system can work smoothly in flat
fading channels, but can not be applied straightforward in frequency selective
channels. In a multipath multi-tap FIR channel, the inter-symbol interference
(ISI) spreads through several symbols. In this case, the symbols at the relay
are not just an addition of the sent symbols but also some of the previous
symbols from both sides. This not only causes a traditional PLNC to fail but
also a simple one equalizer system will not solve the problem. Three main
methods have been proposed by other researchers. The OFDM based PLNC
is the simplest in terms of implementation and complexity but suffers from
the disadvantages of the OFDMlike cyclic prefix overhead and frequency offset.
The main disadvantage, however is the relatively low BER performance
because it is restricted to linear equalizers in the PLNC system. Another
approach is pre-filtering or pre-equalization. This method also has some disadvantages
like complexity, sensitivity to channel variation and the need of
a feedback channel for both end nodes. Finally, the maximum likelihood
sequence detector was also proposed but is restricted to BPSK modulation
and exponentially rising complexity are major drawbacks. The philosophy in
this work is to avoid these disadvantages by using a time domain based system.
The DFE is the equalizer of choice here because it provides a non-trivial
BER performance improvement with very little increase in complexity. In
this thesis, the problem of frequency selective channels in PLNC systems can
be solved by properly adjusting the design of the system including the DFE.
The other option is to redesign the equalizer to meet that goal. An AF DFE
system is proposed in this work that provides very low complexity especially
at the relay with little sensitivity to channel changes. A multi-antenna DNF
DFE system is also proposed here with an improved performance. Finally, a
new equalizer is designed for very low complexity and cost DNF approach
with little sacrifice of BER performance. Matlab was used for the simulations
with Monte Carlo method to verify the findings of this work through finding
the BER performance of each system. This thesis opens the door for future
improvement on the PLNC system. More research needs to be done like testing
the proposed systems in real practical implementation and also the effect
of adding channel coding to these systems.Iraqi Government, Ministry of
Higher Educatio
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