12 research outputs found
Asymmetric Compute-and-Forward with CSIT
We present a modified compute-and-forward scheme which utilizes Channel State
Information at the Transmitters (CSIT) in a natural way. The modified scheme
allows different users to have different coding rates, and use CSIT to achieve
larger rate region. This idea is applicable to all systems which use the
compute-and-forward technique and can be arbitrarily better than the regular
scheme in some settings.Comment: in International Zurich Seminar on Communications, 2014; minor update
on example
Secure Compute-and-Forward Transmission With Artificial Noise and Full-Duplex Devices
We consider a wiretap channel with an eavesdropper (Eve) and an honest but
curious relay (Ray). Ray and the destination (Bob) are full-duplex (FD)
devices. Since we aim at not revealing information on the secret message to the
relay, we consider the scaled compute-and-forward (SCF) where scaled lattice
coding is used in the transmission by both the source (Alice) and Bob in order
to allow Ray to decode only a linear combination of the two messages. At the
same time Ray transmits artificial noise (AN) to confuse Eve. When Ray relays
the decoded linear combination, Alice and Bob are transmitting AN against Eve.
This can be a 5G cellular communication scenario where a mobile terminal (MT)
aims at transmitting a secret message to a FD base station (BS), with the
assistance of a network FD relay. With respect to existing literature the
innovations of this paper are: a) Bob and Ray are FD devices; b) Alice, Ray and
Bob transmit also AN; and c) the channel to Eve is not known to Alice, Bob and
Ray. For this scenario we derive bounds on both the secrecy outage probability
under Rayleigh fading conditions of the channels to Eve, and the achievable
secrecy-outage rates.Comment: submitted to PIMR
Lattice Codes for Many-to-One Interference Channels With and Without Cognitive Messages
A new achievable rate region is given for the Gaussian cognitive many-to-one
interference channel. The proposed novel coding scheme is based on the
compute-and-forward approach with lattice codes. Using the idea of decoding
sums of codewords, our scheme improves considerably upon the conventional
coding schemes which treat interference as noise or decode messages
simultaneously. Our strategy also extends directly to the usual many-to-one
interference channels without cognitive messages. Comparing to the usual
compute-and-forward scheme where a fixed lattice is used for the code
construction, the novel scheme employs scaled lattices and also encompasses key
ingredients of the existing schemes for the cognitive interference channel.
With this new component, our scheme achieves a larger rate region in general.
For some symmetric channel settings, new constant gap or capacity results are
established, which are independent of the number of users in the system.Comment: To appear in IEEE Transactions on Information Theor
Gaussian Multiple Access via Compute-and-Forward
Lattice codes used under the Compute-and-Forward paradigm suggest an
alternative strategy for the standard Gaussian multiple-access channel (MAC):
The receiver successively decodes integer linear combinations of the messages
until it can invert and recover all messages. In this paper, a multiple-access
technique called CFMA (Compute-Forward Multiple Access) is proposed and
analyzed. For the two-user MAC, it is shown that without time-sharing, the
entire capacity region can be attained using CFMA with a single-user decoder as
soon as the signal-to-noise ratios are above . A partial analysis
is given for more than two users. Lastly the strategy is extended to the
so-called dirty MAC where two interfering signals are known non-causally to the
two transmitters in a distributed fashion. Our scheme extends the previously
known results and gives new achievable rate regions.Comment: to appear in IEEE Transactions on Information Theor