Abstract: In this paper, we derive an expression for the bit error rate (BER) of a multiple subcarrier intensity modulated atmospheric optical communication system employing spatial diversity. Spatial diversity is used to mitigate scintillation caused by atmospheric turbulence which is assumed to obey log normal distribution. We consider the optimal but complex maximum ratio (MRC), the equal gain combining (EGC) and the relatively simple selection combing (SelC) spatial diversity techniques in clear atmosphere. We modulate each subcarrier using binary phase shift keying (BPSK) and demodulate coherently. The performance of on-off-keying (OOK) is also presented and compared with subcarrier intensity modulation (SIM) under the same atmospheric conditions
Abstract: The performance of dual header pulse interval modulation (DHPIM)
employing a linear zero forcing equaliser (L-ZFE) in
diffused optical wireless indoor environment is presented. The
work is based on the ceiling bounce channel model and the Monte
Carlos simulation. A 3-tap L-ZFE is used and the results are
compared with unequalised DH-PIM as well as with digital pulse
interval modulation (DPIM), pulse position modulation (PPM) and
on-off keying (OOK) schemes. The power penalty due to
intersymbol interference is presented for each of the signalling
techniques. The results presented show that equalisation does
reduce the error probability and power requirements of high data
rate DH-PIM in a highly dispersive environments
Abstract: The bit error rate (BER) expression and performance of free-space optical communication link in clear but turbulent atmosphere using subcarrier intensity modulation (SIM) with differential phase shift keying (DPSK) is presented. The practical linear combining technique suitable for differentially modulated data (selection combining) is considered and its performance evaluated under weak atmospheric turbulence. The theoretical link margin obtainable from using selection combining under weak turbulence modeled as log normal distribution is also discussed.
Abstract: Free-space optical communication is reputable for its ability to proffer solution to the access network bottle-neck but when used for long range communication, it suffers from scintillation caused by atmospheric turbulence. The probability of outage based performance of subcarrier intensity modulated free-space optical communication in log normal atmospheric turbulence is hereby presented. The bit-error-rate of subcarrier intensity modulated FSO employing phase shift keying (PSK) is also discussed. The atmospheric turbulence is modelled using log normal distribution and its effect mitigated by using an array of PIN photodetectors
Abstract: Free-space optical communications (FSO) propagated over a clear atmosphere suffers from irradiance fluctuation caused by small but random atmospheric temperature fluctuations. This results in decreased signal-to-noise ratio and consequently impaired error performance. In this paper, the error performance of the FSO using a subcarrier intensity modulation (SIM) based on a binary phase shift keying scheme in clear but turbulent atmosphere is presented. To evaluate the system error performance in turbulence regimes from weak to strong, the probability density function of the received irradiance after traversing the atmosphere is modelled using the gamma-gamma distribution and the effect of turbulence induced irradiance fluctuation is mitigated using spatial diversity
Abstract: The paper presents upper bound theoretical analysis and
simulation results for uncoded and convolutional coded
Digital Pulse Interval Modulation (CC-DPIM) scheme for
non-diffuse optical wireless link. We have shown that
with convolutional encoder and the Viterbi decoder the
error performance is significantly improved compared
with the standard uncoded DPIM scheme achieving a
code gain of more than 5 dB at the slot error rate of 10-4
Abstract: Digital Pulse Interval Modulation (DPIM) technique
coded using a 1/3 code rate convolutional codes with 3-
constraint length is presented. The channel model used is that of
the non-diffuse environment with no multipath induced
dispersion. Coding DPIM results in an improved packet error
rate performance compared with uncoded DPIM but at the
price of increased bandwidth requirement while maintaining the
same energy per symbol. Results also show that DPIM with one
guard band does not significantly out perform DPIM without a
guard band in a non-distorting channel.
Abstract: The performance of dual heard pulse interval
modulation (DH-PIM) employing least mean square
error equaliser (LMSE) in diffuse infrared indoor
environment is presented. The work is based on the
ceiling bounce channel model and the Monte Carlos
simulation. A 3-tap LMSE equaliser is used and results
are compared with unequalised DH-PIM and with DHPIM
employing linear zero forcing equaliser (L-ZFE).
The error performance and power penalties are
compared with on-off keying (OOK), pulse position
modulation (PPM) and digital pulse interval modulation
(DPIM) techniques. The results show that DH-PIM with
short pulse duration gives the best error performance and
the most power penalty in highly dispersive environment.
