304 research outputs found
Dynamic Resource Allocation in Cognitive Radio Networks: A Convex Optimization Perspective
This article provides an overview of the state-of-art results on
communication resource allocation over space, time, and frequency for emerging
cognitive radio (CR) wireless networks. Focusing on the
interference-power/interference-temperature (IT) constraint approach for CRs to
protect primary radio transmissions, many new and challenging problems
regarding the design of CR systems are formulated, and some of the
corresponding solutions are shown to be obtainable by restructuring some
classic results known for traditional (non-CR) wireless networks. It is
demonstrated that convex optimization plays an essential role in solving these
problems, in a both rigorous and efficient way. Promising research directions
on interference management for CR and other related multiuser communication
systems are discussed.Comment: to appear in IEEE Signal Processing Magazine, special issue on convex
optimization for signal processin
A General Rate Duality of the MIMO Multiple Access Channel and the MIMO Broadcast Channel
We present a general rate duality between the multiple access channel (MAC)
and the broadcast channel (BC) which is applicable to systems with and without
nonlinear interference cancellation. Different to the state-of-the-art rate
duality with interference subtraction from Vishwanath et al., the proposed
duality is filter-based instead of covariance-based and exploits the arising
unitary degree of freedom to decorrelate every point-to-point link. Therefore,
it allows for noncooperative stream-wise decoding which reduces complexity and
latency. Moreover, the conversion from one domain to the other does not exhibit
any dependencies during its computation making it accessible to a parallel
implementation instead of a serial one. We additionally derive a rate duality
for systems with multi-antenna terminals when linear filtering without
interference (pre-)subtraction is applied and the different streams of a single
user are not treated as self-interference. Both dualities are based on a
framework already applied to a mean-square-error duality between the MAC and
the BC. Thanks to this novel rate duality, any rate-based optimization with
linear filtering in the BC can now be handled in the dual MAC where the arising
expressions lead to more efficient algorithmic solutions than in the BC due to
the alignment of the channel and precoder indices.Comment: Submitted to IEEE Globecom 2008; Fixed dimensions of channel matrix
H_k and covariance matrix Z_k, slightly modified conclusio
Code designs for MIMO broadcast channels
Recent information-theoretic results show the optimality of dirty-paper coding (DPC) in achieving the full capacity region of the Gaussian multiple-input multiple-output (MIMO) broadcast channel (BC). This paper presents a DPC based code design for BCs. We consider the case in which there is an individual rate/signal-to-interference-plus-noise ratio (SINR) constraint for each user. For a fixed transmitter power, we choose the linear transmit precoding matrix such that the SINRs at users are uniformly maximized, thus ensuring the best bit-error rate performance. We start with Cover's simplest two-user Gaussian BC and present a coding scheme that operates 1.44 dB from the boundary of the capacity region at the rate of one bit per real sample (b/s) for each user. We then extend the coding strategy to a two-user MIMO Gaussian BC with two transmit antennas at the base-station and develop the first limit-approaching code design using nested turbo codes for DPC. At the rate of 1 b/s for each user, our design operates 1.48 dB from the capacity region boundary. We also consider the performance of our scheme over a slow fading BC. For two transmit antennas, simulation results indicate a performance loss of only 1.4 dB, 1.64 dB and 1.99 dB from the theoretical limit in terms of the total transmission power for the two, three and four user case, respectively
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