2,008 research outputs found
Achievable Sum Rates of Half- and Full-Duplex Bidirectional OFDM Communication Links
While full-duplex (FD) transmission has the potential to double the system
capacity, its substantial benefit can be offset by the self-interference (SI)
and non-ideality of practical transceivers. In this paper, we investigate the
achievable sum rates (ASRs) of half-duplex (HD) and FD transmissions with
orthogonal frequency division multiplexing (OFDM), where the non-ideality is
taken into consideration. Four transmission strategies are considered, namely
HD with uniform power allocation (UPA), HD with non-UPA (NUPA), FD with UPA,
and FD with NUPA. For each of the four transmission strategies, an optimization
problem is formulated to maximize its ASR, and a (suboptimal/optimal) solution
with low complexity is accordingly derived. Performance evaluations and
comparisons are conducted for three typical channels, namely symmetric
frequency-flat/selective and asymmetric frequency-selective channels. Results
show that the proposed solutions for both HD and FD transmissions can achieve
near optimal performances. For FD transmissions, the optimal solution can be
obtained under typical conditions. In addition, several observations are made
on the ASR performances of HD and FD transmissions.Comment: To appear in IEEE TVT. This paper solves the problem of sum
achievable rate optimization of bidirectional FD OFDM link, where joint time
and power allocation is involve
A gauge-invariant and current-continuous microscopic ac quantum transport theory
There had been consensus on what the accurate ac quantum transport theory was
until some recent works challenged the conventional wisdom. Basing on the
non-equilibrium Green's function formalism for time-dependent quantum
transport, we derive an expression for the dynamic admittance that satisfies
gauge invariance and current continuity, and clarify the key concept in the
field. The validity of our now formalism is verified by first-principles
calculation of the transient current through a carbon-nanotube-based device
under the time-dependent bias voltage. Moreover, the previously well-accepted
expression for dynamic admittance is recovered only when the device is a
perfect conductor at a specific potential
- …