Performance of Spatial Diversity DCO-OFDM in a Weak Turbulence Underwater Visible Light Communication Channel

The performance of underwater visible light communication (UVLC) system is severely affected by absorption, scattering and turbulence. In this article, we study the performance of spectral efficient DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) in combination with the transceiver spatial diversity in turbulence channel. Based on the approximation of the weighted sum of lognormal random variables (RVs), we derived a theoretical exact bit error rate (BER) for DCO-OFDM systems with spatial diversity. The simulation results are compared with the analytical prediction, confirming the validity of the analysis. It is shown that spatial diversity can effectively reduce the turbulence-induced channel fading. The obtained results can be useful for designing, predicting, and evaluating the DCO-OFDM UVLC system in a weak oceanic turbulence condition

Free-space optical communication employing subcarrier modulation and spatial diversity in atmospheric turbulence channel

An expression for the bit error rate of a multiple subcarrier intensity-modulated atmospheric optical communication system employing spatial diversity is derived. Spatial diversity is used to mitigate scintillation caused by atmospheric turbulence, which is assumed to obey lognormal distribution. Optimal but complex maximum ratio, equal gain combining (EGC) and relatively simple selection combining spatial diversity techniques in a clear atmosphere are considered. Each subcarrier is modulated using binary phase shift keying. Laser irradiance is subsequently modulated by a subcarrier signal, and a direct detection PIN receiver is employed (i.e. intensity modulation/direction detection). At a subcarrier level, coherent demodulation is used to extract the transmitted data/information. The performance of on–off-keying is also presented and compared with the subcarrier intensity modulation under the same atmospheric conditions

Spatial Diversity

Why do Supreme Court opinions denounce some districts as political gerrymanders but say nothing about other superficially similar districts? Why does the Court deem some majority-minority districts unnecessary under the Voting Rights Act, or even unconstitutional, but uphold other apparently analogous districts? This Article introduces a concept - spatial diversity - that helps explain these and many other election law oddities. Spatial diversity refers to the variation of a given factor over geographic space. For example, a district with a normal income distribution is spatially diverse, with respect to earnings, if most rich people live in one area and most poor people live in another. But the district is spatially homogeneous if both rich and poor people are evenly dispersed throughout its territory. Spatial diversity matters, at least in the electoral realm, because it is linked to a number of democratic pathologies. Both in theory and empirically, voters are less engaged in the political process, and elected officials provide inferior representation, in districts that vary geographically along dimensions such as wealth and race. Spatial diversity also seems to animate much of the Court\u27s redistricting case law. It is primarily spatially diverse districts that have been condemned (in individual opinions) as political gerrymanders. Similarly, it is the spatial heterogeneity of the relevant minority population that typically explains why certain majority-minority districts are upheld by the Court while others are struck down. After exploring the theoretical and doctrinal sides of spatial diversity, the Article aims to quantify (and to map) the concept. Using newly available American Community Survey data as well as a statistical technique known as factor analysis, the Article provides spatial diversity scores for all current congressional districts. These scores are then used: (r) to identify egregious political gerrymanders; (2) to predict which majority-minority districts might be vulnerable to statutory or constitutional attack; (3) to evaluate the Court\u27s recent claims about various districts and statewide plans; and (4) to confirm that spatial diversity in fact impairs participation and representation. That spatial diversity can be measured, mapped, and applied in this manner underscores the concept\u27s utility

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

Peak to average power ratio based spatial spectrum sensing for cognitive radio systems

The recent convergence of wireless standards for incorporation of spatial dimension in wireless systems has made spatial spectrum sensing based on Peak to Average Power Ratio (PAPR) of the received signal, a promising approach. This added dimension is principally exploited for stream multiplexing, user multiplexing and spatial diversity. Considering such a wireless environment for primary users, we propose an algorithm for spectrum sensing by secondary users which are also equipped with multiple antennas. The proposed spatial spectrum sensing algorithm is based on the PAPR of the spatially received signals. Simulation results show the improved performance once the information regarding spatial diversity of the primary users is incorporated in the proposed algorithm. Moreover, through simulations a better performance is achieved by using different diversity schemes and different parameters like sensing time and scanning interval

Spatial Diversity Impact in Mobile Quantisation Mapping for Cognitive Radio Networks

Mobile environment especially spatial diversity in spectrum exchange information in cognitive radio networks is an interesting topic for further investigation. Most of the cognitive radio researchers does not consider the spatial diversity of sensing nodes. However, the mobility of the SNs within PU’s coverage area is heavily influencing the detection performance on local observation of energy signals. The movement of the SNs creates spatial diversity in the observation of the PU’s signal. Due to the movement, spatial distance, velocity, Doppler Effect and geo-location information, the signals condition would fluctuate during the sensing process. Spatial diversity also reduces the average received signal strength and must be compensated by detection signal method which appropriate with the signal conditions.  Therefore, it is need to find a comprehensive solution to overcome the effects of spatial diversity. Moreover, this research could give a clearly analysis in spectrum exchange information regarding detection performance for cognitive radio networks. Finally, the cooperation overhead due to spatial diversity effects in master node station could reduce and increased the detection performance of PU’s spectrum hole channels