Edge sensor detection is often used in identifying regions that are affected by various factors in wireless sensor networks. A statistical methodology based on distributed detection theory and the Neyman-Pearson criterion is developed for edge sensor detection in this research. The input sensor statistics are assumed to be identically independently distributed in our framework. Edge regions and sensors are determined using a hypothesis test, where the observation model for each hypothesis is derived. A sub-optimal distributed detection scheme, which is optimal among detectors having the same test at all local sensors, and the way of choosing the optimal operating point are described. The condition under which the proposed scheme outperforms the optimum detector based on a single sensor is presented. Furthermore, the noisy channel effect is considered, and a method to overcome this noisy effect is addressed. The performance of the proposed distributed edge sensor detection scheme is studied via computer simulation, where the ROC curves are used to demonstrate the tradeoff between the cost (in terms of the sensor density) and detection accuracy.
The effects of inter-carrier interference (ICI) and aperiodic
random spreading sequences on the performance of asynchronous
multicarrier code division multiple access (CDMA) systems with
correlated fading among sub-carriers are investigated in this
research. To obtain the maximal ratio combining (MRC) filter,
random parameters including asynchronous delays, correlated
Rayleigh fading and spreading sequences are averaged to find the
unconditional covariance matrix of the interference-plus-noise
vector. We demonstrate that the ICI in the system proposed by
Kondo and Milstein can be mitigated by
assigning a common random spreading sequence over all sub-carriers
for each user, rather than using a set of distinct spreading
sequences. Moreover, the analytic expression for the bit error
probability (BEP) can be obtained with the Gaussian approximation.
Simulation results are used to demonstrate the accuracy of our
analysis. Finally, various design tradeoffs including the number
of sub-carriers, fading correlations, ICI and multipath effect are
also presented in simulation.
The bit error probability (BEP) of a multistage linear parallel interference canceller (LPIC) is a long-code code division multiple access (CDMA) s ys tem with chip-synchronized asynchronous transmission is analyzed in this work. By assuming the decision statistic to be a Gaussian random variable, the BEP can be obtained by plugging the conditional mean and variance of the decision statistic into the Q function. We formulate the effective correlation matrix D(i) in the asynchronous environment, and show that the conditional mean and the variance of the decision statistic can be expressed as functions of moments of D(i). The computation of moments of D(i) can be divided into two parts. One is the expectation of cosine terms, which can be solved by the method introduced in our previous work of a synchronous system . The ot her is the expectation of cross-correlation terms, which is much more complex than the case in . Besides tools in , we develop an evolutionary forest to deal with manipulations of D(i) and show that the computation of the expectation of cross-correlation terms is equivalent to solving a list coloring problem.
The performances of direct sequence-code division multiple access (DS-CDMA), multicarrier-CDMA (MC-CDMA) and multicarrier-direct sequence-CDMA (MC-DS-CDMA) systems under different channel conditions are compared in this work. In a frequency-selective slowly fading channel, MC-CDMA and MC-DS-CDMA outperform DS-CDMA, since the former two systems partition the frequency band into sub-channels, each of which has a nearly constant frequency response. Thus, MC-CDMA and MC-DS-CDMA do not suffer much from the multipath effect. The performance of MC-CDMA and MC-DS-CDMA can be further differentiated in severe fading conditions. In a frequency-selective fast fading channel, the larger spreading ratio of MC-DS-CDMA in the time domain prevents the chip duration of a sub-carrier from being longer than the channel coherence time. Hence, the sub-carrier orthogonality is maintained in MC-DS-CDMA, leading to its better performance in this case.
In this paper, we analyze the bit error probability of the multistage linear parallel interference canceller in a long- code code division multiple access (CDMA) system. To obtain the bit error probability, we approximate the decision statistic as a Gaussian random variable, and compute its mean and variance. The mean and variance of the decision statistic can be expressed as functions of the moments of (R-I), where R is the correlation matrix of the signature sequences. Since the complexity of calculating the moments increases rapidly with the growth of the stage index, a graphical representation for the moments is developed to alleviate the complexity. Propositions are presented to interpret the calculation of moments as several graph problems that are well known in the literature, i.e., the coloring, graph decomposition and Euler tour problems. It is shown that the graphical representation facilitates the analytic evaluation of the bit error probability, and the analytic results match well with the simulation results.
Effective transmission of multiple video signals over a CDMA system
simultaneously is investigated in this work. A channel code assignment
scheme that efficiently protects compressed bitstreams while minimizing
multiple access interference (MAI) is proposed. First, each video
signal is coded with a two-layer structure that consists of the base and
the enhanced bitstreams according to the bit importance. Then, these
bitstreams are protected against transmission errors with channel codes
such as RCPC. Better protection of higher bit-rate video requires more
multicodes in spreading, which can lead to a severe multiple access
interference problem. We set up a framework to a joint design of
channel codes and spreading codes with the feedback of the channel
status, and provide a solution to deal with the trade-off between
channel coding rates and the assigned number of multicodes to achieve
efficient transmission. Preliminary experimental results are presented
to demonstrate the performance of the proposed channel code assignment