13 research outputs found
Cooperative Multi-Cell Networks: Impact of Limited-Capacity Backhaul and Inter-Users Links
Cooperative technology is expected to have a great impact on the performance
of cellular or, more generally, infrastructure networks. Both multicell
processing (cooperation among base stations) and relaying (cooperation at the
user level) are currently being investigated. In this presentation, recent
results regarding the performance of multicell processing and user cooperation
under the assumption of limited-capacity interbase station and inter-user
links, respectively, are reviewed. The survey focuses on related results
derived for non-fading uplink and downlink channels of simple cellular system
models. The analytical treatment, facilitated by these simple setups, enhances
the insight into the limitations imposed by limited-capacity constraints on the
gains achievable by cooperative techniques
Cellular Systems with Full-Duplex Compress-and-Forward Relaying and Cooperative Base Stations
In this paper the advantages provided by multicell processing of signals
transmitted by mobile terminals (MTs) which are received via dedicated relay
terminals (RTs) are studied. It is assumed that each RT is capable of
full-duplex operation and receives the transmission of adjacent relay
terminals. Focusing on intra-cell TDMA and non-fading channels, a simplified
relay-aided uplink cellular model based on a model introduced by Wyner is
considered. Assuming a nomadic application in which the RTs are oblivious to
the MTs' codebooks, a form of distributed compress-and-forward (CF) scheme with
decoder side information is employed. The per-cell sum-rate of the CF scheme is
derived and is given as a solution of a simple fixed point equation. This
achievable rate reveals that the CF scheme is able to completely eliminate the
inter-relay interference, and it approaches a ``cut-set-like'' upper bound for
strong RTs transmission power. The CF rate is also shown to surpass the rate of
an amplify-and-forward scheme via numerical calculations for a wide range of
the system parameters.Comment: Proceedings of the 2008 IEEE International Symposium on Information
Theory, Toronto, ON, Canada, July 6 - 11, 200
Optimal Channel Training in Uplink Network MIMO Systems
We consider a multi-cell frequency-selective fading uplink channel (network
MIMO) from K single-antenna user terminals (UTs) to B cooperative base stations
(BSs) with M antennas each. The BSs, assumed to be oblivious of the applied
codebooks, forward compressed versions of their observations to a central
station (CS) via capacity limited backhaul links. The CS jointly decodes the
messages from all UTs. Since the BSs and the CS are assumed to have no prior
channel state information (CSI), the channel needs to be estimated during its
coherence time. Based on a lower bound of the ergodic mutual information, we
determine the optimal fraction of the coherence time used for channel training,
taking different path losses between the UTs and the BSs into account. We then
study how the optimal training length is impacted by the backhaul capacity.
Although our analytical results are based on a large system limit, we show by
simulations that they provide very accurate approximations for even small
system dimensions.Comment: 15 pages, 7 figures. To appear in the IEEE Transactions on Signal
Processin
Uplink CoMP under a Constrained Backhaul and Imperfect Channel Knowledge
Coordinated Multi-Point (CoMP) is known to be a key technology for next
generation mobile communications systems, as it allows to overcome the burden
of inter-cell interference. Especially in the uplink, it is likely that
interference exploitation schemes will be used in the near future, as they can
be used with legacy terminals and require no or little changes in
standardization. Major drawbacks, however, are the extent of additional
backhaul infrastructure needed, and the sensitivity to imperfect channel
knowledge. This paper jointly addresses both issues in a new framework
incorporating a multitude of proposed theoretical uplink CoMP concepts, which
are then put into perspective with practical CoMP algorithms. This
comprehensive analysis provides new insight into the potential usage of uplink
CoMP in next generation wireless communications systems.Comment: Submitted to IEEE Transactions on Wireless Communications in February
201
On an HARQ-based Coordinated Multi-point Network using Dynamic Point Selection
This paper investigates the performance of coordinated multi-point (CoMP) networks in the presence of hybrid automatic repeat request (HARQ) feedback. With an information theoretic point of view, the throughput and the outage probability of different HARQ protocols are studied for slow-fading channels. The results are compared with the ones obtained in the presence of repetition codes and basic HARQ, or when there is no channel state information available at the base stations. The analytical and numerical results demonstrate the efficiency of the CoMP-HARQ techniques in different conditions
Adaptive Spatial Intercell Interference Cancellation in Multicell Wireless Networks
Downlink spatial intercell interference cancellation (ICIC) is considered for
mitigating other-cell interference using multiple transmit antennas. A
principle question we explore is whether it is better to do ICIC or simply
standard single-cell beamforming. We explore this question analytically and
show that beamforming is preferred for all users when the edge SNR
(signal-to-noise ratio) is low ( dB), and ICIC is preferred when the edge
SNR is high ( dB), for example in an urban setting. At medium SNR, a
proposed adaptive strategy, where multiple base stations jointly select
transmission strategies based on the user location, outperforms both while
requiring a lower feedback rate than the pure ICIC approach. The employed
metric is sum rate, which is normally a dubious metric for cellular systems,
but surprisingly we show that even with this reward function the adaptive
strategy also improves fairness. When the channel information is provided by
limited feedback, the impact of the induced quantization error is also
investigated. It is shown that ICIC with well-designed feedback strategies
still provides significant throughput gain.Comment: 26 pages, submitted to IEEE J. Select. Areas Commun. special issue on
Cooperative Communications in MIMO Cellular Networks, Sept. 200