497 research outputs found
An Efficient Precoder Design for Multiuser MIMO Cognitive Radio Networks with Interference Constraints
We consider a linear precoder design for an underlay cognitive radio
multiple-input multiple-output broadcast channel, where the secondary system
consisting of a secondary base-station (BS) and a group of secondary users
(SUs) is allowed to share the same spectrum with the primary system. All the
transceivers are equipped with multiple antennas, each of which has its own
maximum power constraint. Assuming zero-forcing method to eliminate the
multiuser interference, we study the sum rate maximization problem for the
secondary system subject to both per-antenna power constraints at the secondary
BS and the interference power constraints at the primary users. The problem of
interest differs from the ones studied previously that often assumed a sum
power constraint and/or single antenna employed at either both the primary and
secondary receivers or the primary receivers. To develop an efficient numerical
algorithm, we first invoke the rank relaxation method to transform the
considered problem into a convex-concave problem based on a downlink-uplink
result. We then propose a barrier interior-point method to solve the resulting
saddle point problem. In particular, in each iteration of the proposed method
we find the Newton step by solving a system of discrete-time Sylvester
equations, which help reduce the complexity significantly, compared to the
conventional method. Simulation results are provided to demonstrate fast
convergence and effectiveness of the proposed algorithm.Comment: Accepted to appear in IEEE Trans. Vehicular Technology, 13 pages, 8
figure
Cooperative Precoding with Limited Feedback for MIMO Interference Channels
Multi-antenna precoding effectively mitigates the interference in wireless
networks. However, the resultant performance gains can be significantly
compromised in practice if the precoder design fails to account for the
inaccuracy in the channel state information (CSI) feedback. This paper
addresses this issue by considering finite-rate CSI feedback from receivers to
their interfering transmitters in the two-user multiple-input-multiple-output
(MIMO) interference channel, called cooperative feedback, and proposing a
systematic method for designing transceivers comprising linear precoders and
equalizers. Specifically, each precoder/equalizer is decomposed into inner and
outer components for nulling the cross-link interference and achieving array
gain, respectively. The inner precoders/equalizers are further optimized to
suppress the residual interference resulting from finite-rate cooperative
feedback. Further- more, the residual interference is regulated by additional
scalar cooperative feedback signals that are designed to control transmission
power using different criteria including fixed interference margin and maximum
sum throughput. Finally, the required number of cooperative precoder feedback
bits is derived for limiting the throughput loss due to precoder quantization.Comment: 23 pages; 5 figures; this work was presented in part at Asilomar 2011
and will appear in IEEE Trans. on Wireless Com
Energy-Efficient Symbol-Level Precoding in Multiuser MISO Based on Relaxed Detection Region
This paper addresses the problem of exploiting interference among
simultaneous multiuser transmissions in the downlink of multiple-antenna
systems. Using symbol-level precoding, a new approach towards addressing the
multiuser interference is discussed through jointly utilizing the channel state
information (CSI) and data information (DI). The interference among the data
streams is transformed under certain conditions to a useful signal that can
improve the signal-to-interference noise ratio (SINR) of the downlink
transmissions and as a result the system's energy efficiency. In this context,
new constructive interference precoding techniques that tackle the transmit
power minimization (min power) with individual SINR constraints at each user's
receiver have been proposed. In this paper, we generalize the CI precoding
design under the assumption that the received MPSK symbol can reside in a
relaxed region in order to be correctly detected. Moreover, a weighted
maximization of the minimum SNR among all users is studied taking into account
the relaxed detection region. Symbol error rate analysis (SER) for the proposed
precoding is discussed to characterize the tradeoff between transmit power
reduction and SER increase due to the relaxation. Based on this tradeoff, the
energy efficiency performance of the proposed technique is analyzed. Finally,
extensive numerical results show that the proposed schemes outperform other
state-of-the-art techniques.Comment: Submitted to IEEE transactions on Wireless Communications. arXiv
admin note: substantial text overlap with arXiv:1408.470
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