1,137,640 research outputs found
The Impact of CSI and Power Allocation on Relay Channel Capacity and Cooperation Strategies
Capacity gains from transmitter and receiver cooperation are compared in a
relay network where the cooperating nodes are close together. Under
quasi-static phase fading, when all nodes have equal average transmit power
along with full channel state information (CSI), it is shown that transmitter
cooperation outperforms receiver cooperation, whereas the opposite is true when
power is optimally allocated among the cooperating nodes but only CSI at the
receiver (CSIR) is available. When the nodes have equal power with CSIR only,
cooperative schemes are shown to offer no capacity improvement over
non-cooperation under the same network power constraint. When the system is
under optimal power allocation with full CSI, the decode-and-forward
transmitter cooperation rate is close to its cut-set capacity upper bound, and
outperforms compress-and-forward receiver cooperation. Under fast Rayleigh
fading in the high SNR regime, similar conclusions follow. Cooperative systems
provide resilience to fading in channel magnitudes; however, capacity becomes
more sensitive to power allocation, and the cooperating nodes need to be closer
together for the decode-and-forward scheme to be capacity-achieving. Moreover,
to realize capacity improvement, full CSI is necessary in transmitter
cooperation, while in receiver cooperation optimal power allocation is
essential.Comment: Accepted for publication in IEEE Transactions on Wireless
Communication
Complementary cooperation, minimal winning coalitions, and power indices
We introduce a new simple game, which is referred to as the complementary
weighted multiple majority game (C-WMMG for short). C-WMMG models a basic
cooperation rule, the complementary cooperation rule, and can be taken as a
sister model of the famous weighted majority game (WMG for short). In this
paper, we concentrate on the two dimensional C-WMMG. An interesting property of
this case is that there are at most minimal winning coalitions (MWC for
short), and they can be enumerated in time , where is the
number of players. This property guarantees that the two dimensional C-WMMG is
more handleable than WMG. In particular, we prove that the main power indices,
i.e. the Shapley-Shubik index, the Penrose-Banzhaf index, the Holler-Packel
index, and the Deegan-Packel index, are all polynomially computable. To make a
comparison with WMG, we know that it may have exponentially many MWCs, and none
of the four power indices is polynomially computable (unless P=NP). Still for
the two dimensional case, we show that local monotonicity holds for all of the
four power indices. In WMG, this property is possessed by the Shapley-Shubik
index and the Penrose-Banzhaf index, but not by the Holler-Packel index or the
Deegan-Packel index. Since our model fits very well the cooperation and
competition in team sports, we hope that it can be potentially applied in
measuring the values of players in team sports, say help people give more
objective ranking of NBA players and select MVPs, and consequently bring new
insights into contest theory and the more general field of sports economics. It
may also provide some interesting enlightenments into the design of
non-additive voting mechanisms. Last but not least, the threshold version of
C-WMMG is a generalization of WMG, and natural variants of it are closely
related with the famous airport game and the stable marriage/roommates problem.Comment: 60 page
Fundamental Limits of Cooperation
Cooperation is viewed as a key ingredient for interference management in
wireless systems. This paper shows that cooperation has fundamental
limitations. The main result is that even full cooperation between transmitters
cannot in general change an interference-limited network to a noise-limited
network. The key idea is that there exists a spectral efficiency upper bound
that is independent of the transmit power. First, a spectral efficiency upper
bound is established for systems that rely on pilot-assisted channel
estimation; in this framework, cooperation is shown to be possible only within
clusters of limited size, which are subject to out-of-cluster interference
whose power scales with that of the in-cluster signals. Second, an upper bound
is also shown to exist when cooperation is through noncoherent communication;
thus, the spectral efficiency limitation is not a by-product of the reliance on
pilot-assisted channel estimation. Consequently, existing literature that
routinely assumes the high-power spectral efficiency scales with the log of the
transmit power provides only a partial characterization. The complete
characterization proposed in this paper subdivides the high-power regime into a
degrees-of-freedom regime, where the scaling with the log of the transmit power
holds approximately, and a saturation regime, where the spectral efficiency
hits a ceiling that is independent of the power. Using a cellular system as an
example, it is demonstrated that the spectral efficiency saturates at power
levels of operational relevance.Comment: 27 page
Capacity Gain from Two-Transmitter and Two-Receiver Cooperation
Capacity improvement from transmitter and receiver cooperation is
investigated in a two-transmitter, two-receiver network with phase fading and
full channel state information available at all terminals. The transmitters
cooperate by first exchanging messages over an orthogonal transmitter
cooperation channel, then encoding jointly with dirty paper coding. The
receivers cooperate by using Wyner-Ziv compress-and-forward over an analogous
orthogonal receiver cooperation channel. To account for the cost of
cooperation, the allocation of network power and bandwidth among the data and
cooperation channels is studied. It is shown that transmitter cooperation
outperforms receiver cooperation and improves capacity over non-cooperative
transmission under most operating conditions when the cooperation channel is
strong. However, a weak cooperation channel limits the transmitter cooperation
rate; in this case receiver cooperation is more advantageous.
Transmitter-and-receiver cooperation offers sizable additional capacity gain
over transmitter-only cooperation at low SNR, whereas at high SNR transmitter
cooperation alone captures most of the cooperative capacity improvement.Comment: Accepted for publication in IEEE Transactions on Information Theor
Interference Mitigation Through Limited Receiver Cooperation
Interference is a major issue limiting the performance in wireless networks.
Cooperation among receivers can help mitigate interference by forming
distributed MIMO systems. The rate at which receivers cooperate, however, is
limited in most scenarios. How much interference can one bit of receiver
cooperation mitigate? In this paper, we study the two-user Gaussian
interference channel with conferencing decoders to answer this question in a
simple setting. We identify two regions regarding the gain from receiver
cooperation: linear and saturation regions. In the linear region receiver
cooperation is efficient and provides a degrees-of-freedom gain, which is
either one cooperation bit buys one more bit or two cooperation bits buy one
more bit until saturation. In the saturation region receiver cooperation is
inefficient and provides a power gain, which is at most a constant regardless
of the rate at which receivers cooperate. The conclusion is drawn from the
characterization of capacity region to within two bits. The proposed strategy
consists of two parts: (1) the transmission scheme, where superposition
encoding with a simple power split is employed, and (2) the cooperative
protocol, where one receiver quantize-bin-and-forwards its received signal, and
the other after receiving the side information decode-bin-and-forwards its
received signal.Comment: Submitted to IEEE Transactions on Information Theory. 69 pages, 14
figure
Exploiting Trust Degree for Multiple-Antenna User Cooperation
For a user cooperation system with multiple antennas, we consider a trust
degree based cooperation techniques to explore the influence of the
trustworthiness between users on the communication systems. For the system with
two communication pairs, when one communication pair achieves its quality of
service (QoS) requirement, they can help the transmission of the other
communication pair according to the trust degree, which quantifies the
trustworthiness between users in the cooperation. For given trust degree, we
investigate the user cooperation strategies, which include the power allocation
and precoder design for various antenna configurations. For SISO and MISO
cases, we provide the optimal power allocation and beamformer design that
maximize the expected achievable rates while guaranteeing the QoS requirement.
For a SIMO case, we resort to semidefinite relaxation (SDR) technique and block
coordinate update (BCU) method to solve the corresponding problem, and
guarantee the rank-one solutions at each step. For a MIMO case, as MIMO is the
generalization of MISO and SIMO, the similarities among their problem
structures inspire us to combine the methods from MISO and SIMO together to
efficiently tackle MIMO case. Simulation results show that the trust degree
information has a great effect on the performance of the user cooperation in
terms of the expected achievable rate, and the proposed user cooperation
strategies achieve high achievable rates for given trust degree.Comment: 15 pages,9 figures, to appear in IEEE Transactions on Wireless
communication
Energy Cooperation in Battery-Free Wireless Communications with Radio Frequency Energy Harvesting
Radio frequency (RF) energy harvesting techniques are becoming a potential method to power battery-free wireless networks. In RF energy harvesting communications, energy cooperation enables shaping and optimization of the energy arrivals at the energy-receiving node to improve the overall system performance. In this paper, we proposed an energy cooperation scheme that enables energy cooperation in battery-free wireless networks with RF harvesting. We first study the battery-free wireless network with RF energy harvesting then state the problem that optimizing the system performance with limited harvesting energy through new energy cooperation protocol. Finally, from the extensive simulation results, our energy cooperation protocol performs better than the original battery-free wireless network solution.特
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