26 research outputs found
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
Distributed MIMO Systems with Oblivious Antennas
A scenario in which a single source communicates with a single destination
via a distributed MIMO transceiver is considered. The source operates each of
the transmit antennas via finite-capacity links, and likewise the destination
is connected to the receiving antennas through capacity-constrained channels.
Targeting a nomadic communication scenario, in which the distributed MIMO
transceiver is designed to serve different standards or services, transmitters
and receivers are assumed to be oblivious to the encoding functions shared by
source and destination. Adopting a Gaussian symmetric interference network as
the channel model (as for regularly placed transmitters and receivers),
achievable rates are investigated and compared with an upper bound. It is
concluded that in certain asymptotic and non-asymptotic regimes obliviousness
of transmitters and receivers does not cause any loss of optimality.Comment: In Proc. of the 2008 IEEE International Symposium on Information
Theory (ISIT 2008), Toronto, Ontario, Canad
Cooperation in Wireless Sensor Networks with Intra and Inter Cluster Interference
Virtual MIMO configuration, a common model for cooperation in sensor networks, trades off cooperation cost in front of MIMO gains. Most of proposed approaches rely mainly on the fact that cooperation at transmitter side alone seems to be much more powerful than receiver cooperation alone. The scenario that is analysed in this contribution includes the effect of interference of other clusters located closely that clearly degrades whatever cooperation type aforementioned. Under these circumstances, the use of additional sensors at receiver side helps creating a set of virtual beamformers, optimally designed to cancel the undesired signal. So, transmitter cooperation based on Dirty Paper Coding (DPC) strategies to minimize intra-cluster interference and virtual beamformers to minimize inter-cluster interference seems to be a very satisfactory combination
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
The Approximate Capacity Region of the Gaussian Z-Interference Channel with Conferencing Encoders
A two-user Gaussian Z-Interference Channel (GZIC) is considered, in which
encoders are connected through noiseless links with finite capacities. In this
setting, prior to each transmission block the encoders communicate with each
other over the cooperative links. The capacity region and the sum-capacity of
the channel are characterized within 1.71 bits per user and 2 bits in total,
respectively. It is also established that properly sharing the total limited
cooperation capacity between the cooperative links may enhance the achievable
region, even when compared to the case of unidirectional transmitter
cooperation with infinite cooperation capacity. To obtain the results,
genie-aided upper bounds on the sum-capacity and cut-set bounds on the
individual rates are compared with the achievable rate region. In the
interference-limited regime, the achievable scheme enjoys a simple type of
Han-Kobayashi signaling, together with the zero-forcing, and basic relaying
techniques. In the noise-limited regime, it is shown that treating interference
as noise achieves the capacity region up to a single bit per user.Comment: 25 pages, 6 figures, submitted to IEEE Transactions on Information
Theor
H2-ARQ-relaying: spectrum and energy efficiency perspectives
In this paper, we propose novel Hybrid Automatic Repeat re-Quest (HARQ) strategies used in conjunction with hybrid relaying schemes, named as H2-ARQ-Relaying. The strategies allow the relay to dynamically switch between amplify-and-forward/compress-and-forward and decode-and-forward schemes according to its decoding status. The performance analysis is conducted from both the spectrum and energy efficiency perspectives. The spectrum efficiency of the proposed strategies, in terms of the maximum throughput, is significantly improved compared with their non-hybrid counterparts under the same constraints. The consumed energy per bit is optimized by manipulating the node activation time, the transmission energy and the power allocation between the source and the relay. The circuitry energy consumption of all involved nodes is taken into consideration. Numerical results shed light on how and when the energy efficiency can be improved in cooperative HARQ. For instance, cooperative HARQ is shown to be energy efficient in long distance transmission only. Furthermore, we consider the fact that the compress-and-forward scheme requires instantaneous signal to noise ratios of all three constituent links. However, this requirement can be impractical in some cases. In this regard, we introduce an improved strategy where only partial and affordable channel state information feedback is needed