431 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
Compound Multiple Access Channels with Partial Cooperation
A two-user discrete memoryless compound multiple access channel with a common
message and conferencing decoders is considered. The capacity region is
characterized in the special cases of physically degraded channels and
unidirectional cooperation, and achievable rate regions are provided for the
general case. The results are then extended to the corresponding Gaussian
model. In the Gaussian setup, the provided achievable rates are shown to lie
within some constant number of bits from the boundary of the capacity region in
several special cases. An alternative model, in which the encoders are
connected by conferencing links rather than having a common message, is studied
as well, and the capacity region for this model is also determined for the
cases of physically degraded channels and unidirectional cooperation. Numerical
results are also provided to obtain insights about the potential gains of
conferencing at the decoders and encoders.Comment: Submitted to IEEE Transactions on Information Theor
Strong Secrecy for Multiple Access Channels
We show strongly secret achievable rate regions for two different wiretap
multiple-access channel coding problems. In the first problem, each encoder has
a private message and both together have a common message to transmit. The
encoders have entropy-limited access to common randomness. If no common
randomness is available, then the achievable region derived here does not allow
for the secret transmission of a common message. The second coding problem
assumes that the encoders do not have a common message nor access to common
randomness. However, they may have a conferencing link over which they may
iteratively exchange rate-limited information. This can be used to form a
common message and common randomness to reduce the second coding problem to the
first one. We give the example of a channel where the achievable region equals
zero without conferencing or common randomness and where conferencing
establishes the possibility of secret message transmission. Both coding
problems describe practically relevant networks which need to be secured
against eavesdropping attacks.Comment: 55 page
Gaussian Broadcast Channels with an Orthogonal and Bidirectional Cooperation Link
This paper considers a system where one transmitter broadcasts a single
common message to two receivers linked by a bidirectional cooperation channel,
which is assumed to be orthogonal to the downlink channel. Assuming a
simplified setup where, in particular, scalar relaying protocols are used and
channel coding is not exploited, we want to provide elements of response to
several questions of practical interest. Here are the main underlying issues:
1. The way of recombining the signals at the receivers; 2. The optimal number
of cooperation rounds; 3. The way of cooperating (symmetrically or
asymmetrically; which receiver should start cooperating in the latter case); 4.
The influence of spectral resources. These issues are considered by studying
the performance of the assumed system through analytical results when they are
derivable and through simulation results. For the particular choices we made,
the results sometimes do not coincide with those available for the discrete
counterpart of the studied channel
- …