6 research outputs found
Power minimization for OFDM Transmission with Subcarrier-pair based Opportunistic DF Relaying
This paper develops a sum-power minimized resource allocation (RA) algorithm
subject to a sum-rate constraint for cooperative orthogonal frequency division
modulation (OFDM) transmission with subcarrier-pair based opportunistic
decode-and-forward (DF) relaying. The improved DF protocol first proposed in
[1] is used with optimized subcarrier pairing. Instrumental to the RA algorithm
design is appropriate definition of variables to represent source/relay power
allocation, subcarrier pairing and transmission-mode selection elegantly, so
that after continuous relaxation, the dual method and the Hungarian algorithm
can be used to find an (at least approximately) optimum RA with polynomial
complexity. Moreover, the bisection method is used to speed up the search of
the optimum Lagrange multiplier for the dual method. Numerical results are
shown to illustrate the power-reduction benefit of the improved DF protocol
with optimized subcarrier pairing.Comment: 4 pages, accepted by IEEE Communications Letter
Novel Subcarrier-pair based Opportunistic DF Protocol for Cooperative Downlink OFDMA
A novel subcarrier-pair based opportunistic DF protocol is proposed for
cooperative downlink OFDMA transmission aided by a decode-and-forward (DF)
relay. Specifically, user message bits are transmitted in two consecutive
equal-duration time slots. A subcarrier in the first slot can be paired with a
subcarrier in the second slot for the DF relay-aided transmission to a user. In
particular, the source and the relay can transmit simultaneously to implement
beamforming at the subcarrier in the second slot for the relay-aided
transmission. Each unpaired subcarrier in either the first or second slot is
used by the source for direct transmission to a user without the relay's
assistance. The sum rate maximized resource allocation (RA) problem is
addressed for this protocol under a total power constraint. It is shown that
the novel protocol leads to a maximum sum rate greater than or equal to that
for a benchmark one, which does not allow the source to implement beamforming
at the subcarrier in the second slot for the relay-aided transmission. Then, a
polynomial-complexity RA algorithm is developed to find an (at least
approximately) optimum resource allocation (i.e., source/relay power,
subcarrier pairing and assignment to users) for either the proposed or
benchmark protocol. Numerical experiments illustrate that the novel protocol
can lead to a much greater sum rate than the benchmark one.Comment: 6 pages, accepted by 2013 IEEE Wireless Communications and Networking
Conferenc
Low Complexity Joint Sub-Carrier Pairing, Allocation and Relay Selection in Cooperative Wireless Networks
Multi-carrier cooperative relay-based wireless communication is of particular interest in future wireless networks. In this paper we present resource allocation algorithm in which sub-carrier pairing is of particular interest along with fairness constraint in multi-user networks. An optimization of sub-carrier pair selection is formulated through capacity maximization problem. Sub-carrier pairing is applied in both two-hop Amplify & Forward (AF) and Decode & Forward (DF) cooperative multi-user networks. We develop a less complex centralized scheme for joint Sub-carrier pairing and allocation along with relay selection. The computational complexity of the proposed algorithms has been analyzed and performance is compared with Exhaustive Search Algorithm
On the Optimum Energy Efficiency for Flat-fading Channels with Rate-dependent Circuit Power
This paper investigates the optimum energy efficiency (EE) and the
corresponding spectral efficiency (SE) for a communication link operating over
a flat-fading channel. The EE is evaluated by the total energy consumption for
transmitting per message bit. Three channel cases are considered, namely static
channel with channel state information available at transmitter (CSIT),
fast-varying (FV) channel with channel distribution information available at
transmitter (CDIT), and FV channel with CSIT. A general circuit power model is
considered. For all the three channel cases, the tradeoff between the EE and SE
is studied. It is shown that the EE improves strictly as the SE increases from
0 to the optimum SE, and then strictly degrades as the SE increases beyond the
optimum SE. The impact of {\kappa}, {\rho} and other system parameters on the
optimum EE and corresponding SE is investigated to obtain insight.Some of the
important and interesting results for all the channel cases include: (1) when
{\kappa} increases the SE corresponding to the optimum EE should keep unchanged
if {\phi}(R) = R, but reduced if {\phi}(R) is strictly convex of R; (2) when
the rate-independent circuit power {\rho} increases, the SE corresponding to
the optimum EE has to be increased. A polynomial-complexity algorithm is
developed with the bisection method to find the optimum SE. The insight is
corroborated and the optimum EE for the three cases are compared by simulation
results.Comment: 12 pages, 7 figures, to appear in IEEE Transactions on Communication
Weighted Sum Rate Maximization for Downlink OFDMA with Subcarrier-pair based Opportunistic DF Relaying
This paper addresses a weighted sum rate (WSR) maximization problem for
downlink OFDMA aided by a decode-and-forward (DF) relay under a total power
constraint. A novel subcarrier-pair based opportunistic DF relaying protocol is
proposed. Specifically, user message bits are transmitted in two time slots. A
subcarrier in the first slot can be paired with a subcarrier in the second slot
for the DF relay-aided transmission to a user. In particular, the source and
the relay can transmit simultaneously to implement beamforming at the
subcarrier in the second slot. Each unpaired subcarrier in either the first or
second slot is used for the source's direct transmission to a user. A benchmark
protocol, same as the proposed one except that the transmit beamforming is not
used for the relay-aided transmission, is also considered. For each protocol, a
polynomial-complexity algorithm is developed to find at least an approximately
optimum resource allocation (RA), by using continuous relaxation, the dual
method, and Hungarian algorithm. Instrumental to the algorithm design is an
elegant definition of optimization variables, motivated by the idea of
regarding the unpaired subcarriers as virtual subcarrier pairs in the direct
transmission mode. The effectiveness of the RA algorithm and the impact of
relay position and total power on the protocols' performance are illustrated by
numerical experiments. The proposed protocol always leads to a maximum WSR
equal to or greater than that for the benchmark one, and the performance gain
of using the proposed one is significant especially when the relay is in close
proximity to the source and the total power is low. Theoretical analysis is
presented to interpret these observations.Comment: 8 figures, accepted and to be published in IEEE Transactions on
Signal Processing. arXiv admin note: text overlap with arXiv:1301.293