984,783 research outputs found
Commutator estimates in -algebras
Let be a -algebra and let be the algebra
of all locally measurable operators affiliated with . It is shown
that for any self-adjoint element there exists a
self-adjoint element from the center of , such that
for any there exists a unitary element from
, satisfying . A
corollary of this result is that for any derivation on
with the range in a (not necessarily norm-closed) ideal
, the derivation is inner, that is
, and . Similar results are
also obtained for inner derivations on .Comment: 30 page
On the Exact BER of Bit-Wise Demodulators for One-Dimensional Constellations
The optimal bit-wise demodulator for M-ary pulse amplitude modulation (PAM)
over the additive white Gaussian noise channel is analyzed in terms of uncoded
bit-error rate (BER). New closed-form BER expressions for 4-PAM with any
labeling are developed. Moreover, closed-form BER expressions for 11 out of 23
possible bit patterns for 8-PAM are presented, which enable us to obtain the
BER for 8-PAM with some of the most popular labelings, including the binary
reflected Gray code and the natural binary code. Numerical results show that,
regardless of the labeling, there is no difference between the optimal
demodulator and the symbol-wise demodulator for any BER of practical interest
(below 0.1)
On the BER of Multiple-Input Multiple-Output Underwater Wireless Optical Communication Systems
In this paper we analyze and investigate the bit error rate (BER) performance
of multiple-input multiple-output underwater wireless optical communication
(MIMO-UWOC) systems. In addition to exact BER expressions, we also obtain an
upper bound on the system BER. To effectively estimate the BER expressions, we
use Gauss-Hermite quadrature formula as well as approximation to the sum of
log-normal random variables. We confirm the accuracy of our analytical
expressions by evaluating the BER through photon-counting approach. Our
simulation results show that MIMO technique can mitigate the channel
turbulence-induced fading and consequently, can partially extend the viable
communication range, especially for channels with stronger turbulence
FWM-based wavelength conversion of 40 Gbaud PSK signals in a silicon germanium waveguide
We demonstrate four wave mixing (FWM) based wavelength conversion of 40 Gbaud differential phase shift keyed (DPSK) and quadrature phase shift keyed (QPSK) signals in a 2.5 cm long silicon germanium waveguide. For a 290 mW pump power, bit error ratio (BER) measurements show approximately a 2-dB power penalty in both cases of DPSK (measured at a BER of 10-9) and QPSK (at a BER of 10-3) signals that we examined
BER and outage probability of DPSK subcarrier intensity modulated free space optics in fully developed speckle.
In this paper a differential phase shift keying (DPSK) subcarrier intensity modulated (SIM) free space optical (FSO) link is considered in negative exponential atmospheric turbulence environment. To mitigate the scintillation effect, the selection combining spatial diversity scheme (SelC) is employed at the receiver. Bit error rate (BER) and outage probability (Pout) analysis are presented with and without the SelC spatial diversity. It is shown that at a BER of 10-6, a maximum diversity gain 25 dB is predicted. And about 60 dBm signal power is required to achieve an outage probability of 10-6, based on a threshold BER of 10-4
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