1,228 research outputs found
Cooperative Relaying with State Available Non-Causally at the Relay
We consider a three-terminal state-dependent relay channel with the channel
state noncausally available at only the relay. Such a model may be useful for
designing cooperative wireless networks with some terminals equipped with
cognition capabilities, i.e., the relay in our setup. In the discrete
memoryless (DM) case, we establish lower and upper bounds on channel capacity.
The lower bound is obtained by a coding scheme at the relay that uses a
combination of codeword splitting, Gel'fand-Pinsker binning, and
decode-and-forward relaying. The upper bound improves upon that obtained by
assuming that the channel state is available at the source, the relay, and the
destination. For the Gaussian case, we also derive lower and upper bounds on
the capacity. The lower bound is obtained by a coding scheme at the relay that
uses a combination of codeword splitting, generalized dirty paper coding, and
decode-and-forward relaying; the upper bound is also better than that obtained
by assuming that the channel state is available at the source, the relay, and
the destination. In the case of degraded Gaussian channels, the lower bound
meets with the upper bound for some special cases, and, so, the capacity is
obtained for these cases. Furthermore, in the Gaussian case, we also extend the
results to the case in which the relay operates in a half-duplex mode.Comment: 62 pages. To appear in IEEE Transactions on Information Theor
Relay X Channels without Channel State Information at the Transmit Sides: Degrees of Freedom
This paper focuses on the two-user relay-assisted X channel with no channel state information (CSI) available at the transmitter side. Two relaying modes, namely half-duplex decode-and-forward (DF) and cognitive relays, are considered and the degrees of freedom (DoF) are characterized. It is shown that assisted by a half-duplex DF relay that is equipped with 2M antennas, the X channel with two M-antenna users has 4M/3 DoF, which is achievable through interference alignment (IA). Furthermore, it is shown that in this channel, an M-antenna cognitive relay (with non-causal access to information streams) provides 2M DoF using interference cancellation (IC) technique. In this setting, IC outperforms interference alignment in the cognitive relay mode, since the latter achieves 4M/3 DoF
On the Capacity of the Two-user Gaussian Causal Cognitive Interference Channel
This paper considers the two-user Gaussian Causal Cognitive Interference
Channel (GCCIC), which consists of two source-destination pairs that share the
same channel and where one full-duplex cognitive source can causally learn the
message of the primary source through a noisy link. The GCCIC is an
interference channel with unilateral source cooperation that better models
practical cognitive radio networks than the commonly used model which assumes
that one source has perfect non-causal knowledge of the other source's message.
First the sum-capacity of the symmetric GCCIC is determined to within a
constant gap. Then, the insights gained from the derivation of the symmetric
sum-capacity are extended to characterize the whole capacity region to within a
constant gap for more general cases. In particular, the capacity is determined
(a) to within 2 bits for the fully connected GCCIC when, roughly speaking, the
interference is not weak at both receivers, (b) to within 2 bits for the
Z-channel, i.e., when there is no interference from the primary user, and (c)
to within 2 bits for the S-channel, i.e., when there is no interference from
the secondary user. The parameter regimes where the GCCIC is equivalent, in
terms of generalized degrees-of-freedom, to the noncooperative interference
channel (i.e., unilateral causal cooperation is not useful), to the non-causal
cognitive interference channel (i.e., causal cooperation attains the ultimate
limit of cognitive radio technology), and to bilateral source cooperation are
identified. These comparisons shed lights into the parameter regimes and
network topologies that in practice might provide an unbounded throughput gain
compared to currently available (non cognitive) technologies.Comment: Under second round review in IEEE Transactions in Information Theory
- Submitted September 201
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