3,161 research outputs found
Multiuser Diversity Gain in Cognitive Networks
Dynamic allocation of resources to the \emph{best} link in large multiuser
networks offers considerable improvement in spectral efficiency. This gain,
often referred to as \emph{multiuser diversity gain}, can be cast as
double-logarithmic growth of the network throughput with the number of users.
In this paper we consider large cognitive networks granted concurrent spectrum
access with license-holding users. The primary network affords to share its
under-utilized spectrum bands with the secondary users. We assess the optimal
multiuser diversity gain in the cognitive networks by quantifying how the
sum-rate throughput of the network scales with the number of secondary users.
For this purpose we look at the optimal pairing of spectrum bands and secondary
users, which is supervised by a central entity fully aware of the instantaneous
channel conditions, and show that the throughput of the cognitive network
scales double-logarithmically with the number of secondary users () and
linearly with the number of available spectrum bands (), i.e., . We then propose a \emph{distributed} spectrum allocation scheme, which does
not necessitate a central controller or any information exchange between
different secondary users and still obeys the optimal throughput scaling law.
This scheme requires that \emph{some} secondary transmitter-receiver pairs
exchange information bits among themselves. We also show that the
aggregate amount of information exchange between secondary transmitter-receiver
pairs is {\em asymptotically} equal to . Finally, we show that our
distributed scheme guarantees fairness among the secondary users, meaning that
they are equally likely to get access to an available spectrum band.Comment: 32 pages, 3 figures, to appear in the IEEE/ACM Transactions on
Networkin
Exact Outage Performance Analysis of Multiuser Multi-relay Spectrum Sharing Cognitive Networks
In this paper, we investigate the outage performance of dual-hop multiuser multi-relay cognitive radio networks under spectrum sharing constraints. Using an efficient relay-destination selection scheme, the exact and asymptotic closed-form expressions for the outage probability are derived. From these expressions it is indicated that the achieved diversity order is only determined by the number of secondary user (SU) relays and destinations, and equals to M+N (where M and N are the number of destination nodes and relay nodes, respectively). Further, we find that the coding gain of the SU network will be affected by the interference threshold at the primary user (PU) receiver. Specifically, as the increases of the interference threshold, the coding gain of the considered network approaches to that of the multiuser multi-relay system in the non-cognitive network. Finally, our study is corroborated by representative numerical examples
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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