2,471 research outputs found
Sparse Signal Processing Concepts for Efficient 5G System Design
As it becomes increasingly apparent that 4G will not be able to meet the
emerging demands of future mobile communication systems, the question what
could make up a 5G system, what are the crucial challenges and what are the key
drivers is part of intensive, ongoing discussions. Partly due to the advent of
compressive sensing, methods that can optimally exploit sparsity in signals
have received tremendous attention in recent years. In this paper we will
describe a variety of scenarios in which signal sparsity arises naturally in 5G
wireless systems. Signal sparsity and the associated rich collection of tools
and algorithms will thus be a viable source for innovation in 5G wireless
system design. We will discribe applications of this sparse signal processing
paradigm in MIMO random access, cloud radio access networks, compressive
channel-source network coding, and embedded security. We will also emphasize
important open problem that may arise in 5G system design, for which sparsity
will potentially play a key role in their solution.Comment: 18 pages, 5 figures, accepted for publication in IEEE Acces
Artificial-Noise-Aided Physical Layer Phase Challenge-Response Authentication for Practical OFDM Transmission
Recently, we have developed a PHYsical layer Phase Challenge-Response
Authentication Scheme (PHY-PCRAS) for independent multicarrier transmission. In
this paper, we make a further step by proposing a novel artificial-noise-aided
PHY-PCRAS (ANA-PHY-PCRAS) for practical orthogonal frequency division
multiplexing (OFDM) transmission, where the Tikhonov-distributed artificial
noise is introduced to interfere with the phase-modulated key for resisting
potential key-recovery attacks whenever a static channel between two legitimate
users is unfortunately encountered. Then, we address various practical issues
for ANA-PHY-PCRAS with OFDM transmission, including correlation among
subchannels, imperfect carrier and timing recoveries. Among them, we show that
the effect of sampling offset is very significant and a search procedure in the
frequency domain should be incorporated for verification. With practical OFDM
transmission, the number of uncorrelated subchannels is often not sufficient.
Hence, we employ a time-separated approach for allocating enough subchannels
and a modified ANA-PHY-PCRAS is proposed to alleviate the discontinuity of
channel phase at far-separated time slots. Finally, the key equivocation is
derived for the worst case scenario. We conclude that the enhanced security of
ANA-PHY-PCRAS comes from the uncertainty of both the wireless channel and
introduced artificial noise, compared to the traditional challenge-response
authentication scheme implemented at the upper layer.Comment: 33 pages, 13 figures, submitted for possible publicatio
Analysis of Channel-Based User Authentication by Key-Less and Key-Based Approaches
User authentication (UA) supports the receiver in deciding whether a message
comes from the claimed transmitter or from an impersonating attacker. In
cryptographic approaches messages are signed with either an asymmetric or
symmetric key, and a source of randomness is required to generate the key. In
physical layer authentication (PLA) instead the receiver checks if received
messages presumably coming from the same source undergo the same channel. We
compare these solutions by considering the physical-layer channel features as
randomness source for generating the key, thus allowing an immediate comparison
with PLA (that already uses these features). For the symmetric-key approach we
use secret key agreement, while for asymmetric-key the channel is used as
entropy source at the transmitter. We focus on the asymptotic case of an
infinite number of independent and identically distributed channel
realizations, showing the correctness of all schemes and analyzing the secure
authentication rate, that dictates the rate at which the probability that UA
security is broken goes to zero as the number of used channel resources (to
generate the key or for PLA) goes to infinity. Both passive and active attacks
are considered and by numerical results we compare the various systems
Coexistence and Secure Communication in Wireless Networks
In a wireless system, transmitted electromagnetic waves can propagate in all directions and can be received by other users in the system. The signals received by unintended receivers pose two problems; increased interference causing lower system throughput or successful decoding of the information which removes secrecy of the communication. Radio frequency spectrum is a scarce resource and it is allocated by technologies already in use. As a result, many communication systems use the spectrum opportunistically whenever it is available in cognitive radio setting or use unlicensed bands. Hence, efficient use of spectrum by sharing users is crucial to increase maximize system throughput. In addition, secrecy of a wireless communication system is traditionally provided by computational complexity of cryptography techniques employed. However, cryptography systems depend on either a random secret key generation mechanism or a trusted key distribution system. Recent developments in the wireless communication area provided a solution to both key generation and distribution problem via exploiting randomness of the wireless channel unconditional to the computational complexity.
In this dissertation, we propose solutions to the problems discussed. For spectrum sharing, we present a detailed analysis of challenges of efficient spectrum sharing without a central enforcing mechanism, provide insight to already existing power control algorithms and propose a novel non-greedy power allocation algorithm. Numerical simulations show that the proposed algorithm increases system throughput more than greedy algorithms and can use available spectrum to the fullest, yet it is robust to the presence of greedy users. For secrecy, we propose a practical and fast system for random secret key generation and reconciliation. We extend the proposed system to multiple-input-multiple-output systems and increase security via role reversal of the nodes while making it quicker by pre-encoding procedure. Information theory calculation and numerical simulations demonstrates that the proposed system provides a secure channel for legitimate users in the presence of a passive eavesdropper
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