27,063 research outputs found
Convolutive superposition for multicarrier cognitive radio systems
Recently, we proposed a spectrum-sharing paradigm for single-carrier
cognitive radio (CR) networks, where a secondary user (SU) is able to maintain
or even improve the performance of a primary user (PU) transmission, while also
obtaining a low-data rate channel for its own communication. According to such
a scheme, a simple multiplication is used to superimpose one SU symbol on a
block of multiple PU symbols.The scope of this paper is to extend such a
paradigm to a multicarrier CR network, where the PU employs an orthogonal
frequency-division multiplexing (OFDM) modulation scheme. To improve its
achievable data rate, besides transmitting over the subcarriers unused by the
PU, the SU is also allowed to transmit multiple block-precoded symbols in
parallel over the OFDM subcarriers used by the primary system. Specifically,
the SU convolves its block-precoded symbols with the received PU data in the
time-domain, which gives rise to the term convolutive superposition. An
information-theoretic analysis of the proposed scheme is developed, which
considers different amounts of network state information at the secondary
transmitter, as well as different precoding strategies for the SU. Extensive
simulations illustrate the merits of our analysis and designs, in comparison
with conventional CR schemes, by considering as performance indicators the
ergodic capacity of the considered systems.Comment: 29 pages, 8 figure
Cognitive Multiple Access Network with Outage Margin in the Primary System
This paper investigates the problem of spectrally efficient operation of a
multiuser uplink cognitive radio system in the presence of a single primary
link. The secondary system applies opportunistic interference cancelation (OIC)
and decode the primary signal when such an opportunity is created. We derive
the achievable rate in the secondary system when OIC is used. This scheme has a
practical significance, since it enables rate adaptation without requiring any
action from the primary system. The \emph{exact} expressions for outage
probability of the primary user are derived, when the primary system is exposed
to interference from secondary users. Moreover, approximated formulas and tight
lower and upper bounds for the ergodic sum-rate capacity of the secondary
network are found. Next, the power allocation is investigated in the secondary
system for maximizing the sum-rate under an outage constraint at the primary
system. We formulate the power optimization problem in various scenarios
depending on the availability of channel state information and the type of
power constraints, and propose a set of simple solutions. Finally, the
analytical results are confirmed by simulations, indicating both the accuracy
of the analysis, and the fact that the spectral-efficient, low-complexity,
flexible, and high-performing cognitive radio can be designed based on the
proposed schemes
Capacity scaling law by multiuser diversity in cognitive radio systems
This paper analyzes the multiuser diversity gain in a cognitive radio (CR)
system where secondary transmitters opportunistically utilize the spectrum
licensed to primary users only when it is not occupied by the primary users. To
protect the primary users from the interference caused by the missed detection
of primary transmissions in the secondary network, minimum average throughput
of the primary network is guaranteed by transmit power control at the secondary
transmitters. The traffic dynamics of a primary network are also considered in
our analysis. We derive the average achievable capacity of the secondary
network and analyze its asymptotic behaviors to characterize the multiuser
diversity gains in the CR system.Comment: 5 pages, 2 figures, ISIT2010 conferenc
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