3,491 research outputs found
Information Exchange Limits in Cooperative MIMO Networks
Concurrent presence of inter-cell and intra-cell interferences constitutes a
major impediment to reliable downlink transmission in multi-cell multiuser
networks. Harnessing such interferences largely hinges on two levels of
information exchange in the network: one from the users to the base-stations
(feedback) and the other one among the base-stations (cooperation). We
demonstrate that exchanging a finite number of bits across the network, in the
form of feedback and cooperation, is adequate for achieving the optimal
capacity scaling. We also show that the average level of information exchange
is independent of the number of users in the network. This level of information
exchange is considerably less than that required by the existing coordination
strategies which necessitate exchanging infinite bits across the network for
achieving the optimal sum-rate capacity scaling. The results provided rely on a
constructive proof.Comment: 35 pages, 5 figur
Dispensing with channel estimation: differentially modulated cooperative wireless communications
As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective
Full-Duplex Cloud Radio Access Network: Stochastic Design and Analysis
Full-duplex (FD) has emerged as a disruptive communications paradigm for
enhancing the achievable spectral efficiency (SE), thanks to the recent major
breakthroughs in self-interference (SI) mitigation. The FD versus half-duplex
(HD) SE gain, in cellular networks, is however largely limited by the
mutual-interference (MI) between the downlink (DL) and the uplink (UL). A
potential remedy for tackling the MI bottleneck is through cooperative
communications. This paper provides a stochastic design and analysis of FD
enabled cloud radio access network (C-RAN) under the Poisson point process
(PPP)-based abstraction model of multi-antenna radio units (RUs) and user
equipments (UEs). We consider different disjoint and user-centric approaches
towards the formation of finite clusters in the C-RAN. Contrary to most
existing studies, we explicitly take into consideration non-isotropic fading
channel conditions and finite-capacity fronthaul links. Accordingly,
upper-bound expressions for the C-RAN DL and UL SEs, involving the statistics
of all intended and interfering signals, are derived. The performance of the FD
C-RAN is investigated through the proposed theoretical framework and
Monte-Carlo (MC) simulations. The results indicate that significant FD versus
HD C-RAN SE gains can be achieved, particularly in the presence of
sufficient-capacity fronthaul links and advanced interference cancellation
capabilities
Cooperative network-coding system for wireless sensor networks
Describes a cooperative network coding system for wireless sensor networks. In this paper, we propose two practical power) and bandwidth)efficient systems based on amplify)and)forward (AF) and decode)and)forward (DF) schemes to address the problem of information exchange via a relay. The key idea is to channel encode each source’s message by using a high)performance non)binary turbo code based on Partial Unit Memory (PUM) codes to enhance the bit)error)rate performance, then reduce the energy consumption and increase spectrum efficiency by using network coding (NC) to combine individual nodes’ messages at the relay before forwarding to the destination. Two simple and low complexity physical layer NC schemes are proposed based on combinations of received source messages at the relay. We also present the theoretical limits and numerical analysis of the proposed schemes. Simulation results under Additive White Gaussian Noise, confirm that the proposed schemes achieve significant bandwidth savings and fewer transmissions over the benchmark systems which do not resort to NC. Theoretical limits for capacity and Signal to Noise Ratio behaviour for the proposed schemes are derived. The paper also proposes a cooperative strategy that is useful when insufficient combined messages are received at a node to recover the desired source messages, thus enabling the system to retrieve all packets with significantly fewer retransmission request messages
Improving Macrocell - Small Cell Coexistence through Adaptive Interference Draining
The deployment of underlay small base stations (SBSs) is expected to
significantly boost the spectrum efficiency and the coverage of next-generation
cellular networks. However, the coexistence of SBSs underlaid to an existing
macro-cellular network faces important challenges, notably in terms of spectrum
sharing and interference management. In this paper, we propose a novel
game-theoretic model that enables the SBSs to optimize their transmission rates
by making decisions on the resource occupation jointly in the frequency and
spatial domains. This procedure, known as interference draining, is performed
among cooperative SBSs and allows to drastically reduce the interference
experienced by both macro- and small cell users. At the macrocell side, we
consider a modified water-filling policy for the power allocation that allows
each macrocell user (MUE) to focus the transmissions on the degrees of freedom
over which the MUE experiences the best channel and interference conditions.
This approach not only represents an effective way to decrease the received
interference at the MUEs but also grants the SBSs tier additional transmission
opportunities and allows for a more agile interference management. Simulation
results show that the proposed approach yields significant gains at both
macrocell and small cell tiers, in terms of average achievable rate per user,
reaching up to 37%, relative to the non-cooperative case, for a network with
150 MUEs and 200 SBSs
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
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