406 research outputs found
Joint Subcarrier Pairing and Power Allocation for OFDM Transmission with Decode-and-Forward Relaying
In this paper, a point-to-point Orthogonal Frequency Division Multiplexing
(OFDM) system with a decode-and-forward (DF) relay is considered. The
transmission consists of two hops. The source transmits in the first hop, and
the relay transmits in the second hop. Each hop occupies one time slot. The
relay is half-duplex, and capable of decoding the message on a particular
subcarrier in one time slot, and re-encoding and forwarding it on a different
subcarrier in the next time slot. Thus each message is transmitted on a pair of
subcarriers in two hops. It is assumed that the destination is capable of
combining the signals from the source and the relay pertaining to the same
message. The goal is to maximize the weighted sum rate of the system by jointly
optimizing subcarrier pairing and power allocation on each subcarrier in each
hop. The weighting of the rates is to take into account the fact that different
subcarriers may carry signals for different services. Both total and individual
power constraints for the source and the relay are investigated. For the
situations where the relay does not transmit on some subcarriers because doing
so does not improve the weighted sum rate, we further allow the source to
transmit new messages on these idle subcarriers. To the best of our knowledge,
such a joint optimization inclusive of the destination combining has not been
discussed in the literature. The problem is first formulated as a mixed integer
programming problem. It is then transformed to a convex optimization problem by
continuous relaxation, and solved in the dual domain. Based on the optimization
results, algorithms to achieve feasible solutions are also proposed. Simulation
results show that the proposed algorithms almost achieve the optimal weighted
sum rate, and outperform the existing methods in various channel conditions.Comment: 33 pages, 11 figure
Filter and nested-lattice code design for fading MIMO channels with side-information
Linear-assignment Gel'fand-Pinsker coding (LA-GPC) is a coding technique for
channels with interference known only at the transmitter, where the known
interference is treated as side-information (SI). As a special case of LA-GPC,
dirty paper coding has been shown to be able to achieve the optimal
interference-free rate for interference channels with perfect channel state
information at the transmitter (CSIT). In the cases where only the channel
distribution information at the transmitter (CDIT) is available, LA-GPC also
has good (sometimes optimal) performance in a variety of fast and slow fading
SI channels. In this paper, we design the filters in nested-lattice based
coding to make it achieve the same rate performance as LA-GPC in multiple-input
multiple-output (MIMO) channels. Compared with the random Gaussian codebooks
used in previous works, our resultant coding schemes have an algebraic
structure and can be implemented in practical systems. A simulation in a
slow-fading channel is also provided, and near interference-free error
performance is obtained. The proposed coding schemes can serve as the
fundamental building blocks to achieve the promised rate performance of MIMO
Gaussian broadcast channels with CDIT or perfect CSITComment: submitted to IEEE Transactions on Communications, Feb, 200
Clean relaying aided cognitive radio under the coexistence constraint
We consider the interference-mitigation based cognitive radio where the
primary and secondary users can coexist at the same time and frequency bands,
under the constraint that the rate of the primary user (PU) must remain the
same with a single-user decoder. To meet such a coexistence constraint, the
relaying from the secondary user (SU) can help the PU's transmission under the
interference from the SU. However, the relayed signal in the known dirty paper
coding (DPC) based scheme is interfered by the SU's signal, and is not "clean".
In this paper, under the half-duplex constraints, we propose two new
transmission schemes aided by the clean relaying from the SU's transmitter and
receiver without interference from the SU. We name them as the clean
transmitter relaying (CT) and clean transmitter-receiver relaying (CTR) aided
cognitive radio, respectively. The rate and multiplexing gain performances of
CT and CTR in fading channels with various availabilities of the channel state
information at the transmitters (CSIT) are studied. Our CT generalizes the
celebrated DPC based scheme proposed previously. With full CSIT, the
multiplexing gain of the CTR is proved to be better (or no less) than that of
the previous DPC based schemes. This is because the silent period for decoding
the PU's messages for the DPC may not be necessary in the CTR. With only the
statistics of CSIT, we further prove that the CTR outperforms the rate
performance of the previous scheme in fast Rayleigh fading channels. The
numerical examples also show that in a large class of channels, the proposed CT
and CTR provide significant rate gains over the previous scheme with small
complexity penalties.Comment: 30 page
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