4,784 research outputs found
Underlay Cognitive Radio with Full or Partial Channel Quality Information
Underlay cognitive radios (UCRs) allow a secondary user to enter a primary
user's spectrum through intelligent utilization of multiuser channel quality
information (CQI) and sharing of codebook. The aim of this work is to study
two-user Gaussian UCR systems by assuming the full or partial knowledge of
multiuser CQI. Key contribution of this work is motivated by the fact that the
full knowledge of multiuser CQI is not always available. We first establish a
location-aided UCR model where the secondary user is assumed to have partial
CQI about the secondary-transmitter to primary-receiver link as well as full
CQI about the other links. Then, new UCR approaches are proposed and carefully
analyzed in terms of the secondary user's achievable rate, denoted by ,
the capacity penalty to primary user, denoted by , and capacity
outage probability. Numerical examples are provided to visually compare the
performance of UCRs with full knowledge of multiuser CQI and the proposed
approaches with partial knowledge of multiuser CQI.Comment: 29 Pages, 8 figure
On Discrete Alphabets for the Two-user Gaussian Interference Channel with One Receiver Lacking Knowledge of the Interfering Codebook
In multi-user information theory it is often assumed that every node in the
network possesses all codebooks used in the network. This assumption is however
impractical in distributed ad-hoc and cognitive networks. This work considers
the two- user Gaussian Interference Channel with one Oblivious Receiver
(G-IC-OR), i.e., one receiver lacks knowledge of the interfering cookbook while
the other receiver knows both codebooks. We ask whether, and if so how much,
the channel capacity of the G-IC- OR is reduced compared to that of the
classical G-IC where both receivers know all codebooks. Intuitively, the
oblivious receiver should not be able to jointly decode its intended message
along with the unintended interfering message whose codebook is unavailable. We
demonstrate that in strong and very strong interference, where joint decoding
is capacity achieving for the classical G-IC, lack of codebook knowledge does
not reduce performance in terms of generalized degrees of freedom (gDoF).
Moreover, we show that the sum-capacity of the symmetric G-IC- OR is to within
O(log(log(SNR))) of that of the classical G-IC. The key novelty of the proposed
achievable scheme is the use of a discrete input alphabet for the non-oblivious
transmitter, whose cardinality is appropriately chosen as a function of SNR
Accessible Capacity of Secondary Users
A new problem formulation is presented for the Gaussian interference channels
(GIFC) with two pairs of users, which are distinguished as primary users and
secondary users, respectively. The primary users employ a pair of encoder and
decoder that were originally designed to satisfy a given error performance
requirement under the assumption that no interference exists from other users.
In the scenario when the secondary users attempt to access the same medium, we
are interested in the maximum transmission rate (defined as {\em accessible
capacity}) at which secondary users can communicate reliably without affecting
the error performance requirement by the primary users under the constraint
that the primary encoder (not the decoder) is kept unchanged. By modeling the
primary encoder as a generalized trellis code (GTC), we are then able to treat
the secondary link and the cross link from the secondary transmitter to the
primary receiver as finite state channels (FSCs). Based on this, upper and
lower bounds on the accessible capacity are derived. The impact of the error
performance requirement by the primary users on the accessible capacity is
analyzed by using the concept of interference margin. In the case of
non-trivial interference margin, the secondary message is split into common and
private parts and then encoded by superposition coding, which delivers a lower
bound on the accessible capacity. For some special cases, these bounds can be
computed numerically by using the BCJR algorithm. Numerical results are also
provided to gain insight into the impacts of the GTC and the error performance
requirement on the accessible capacity.Comment: 42 pages, 12 figures, 2 tables; Submitted to IEEE Transactions on
Information Theory on December, 2010, Revised on November, 201
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