Institute for Systems Research

Among these services, video and voice are real-time signals and can not tolerate large random delays. In our attempt to satisfy this, video and voice use the Synchronous Transfer Mode (STM) with a frame structure, while the data users (with their bursty traffic) send (and retransmit, if necessary) their packets randomly within a frame. The video and voice users make their schedules in advance by using a pre- assigned slot (status slot). The first portion of a frame is assigned to the variable rate video users, while the variable rate voice users fill up the last portion of the frame. Data packets fill up the remaining slots between these two movable boundaries in a random-access fashion. In this protocol, the delay introduced by the satellite is taken into consideration. This multiple-access integration protocol is optimized with respect to performance measures, such as the blocking probabilities for voice and video, the average delay for data, and the average throughput for voice, video, and data.

First the exact multireception probabilities for synchronous uncoded systems are evaluated at the bit level; these results are essential for checking the accuracy of the other approximations used here. Our results establish that the Independent Receiver Operation Assumption (IROA) yields very good approximations whose accuracy increases as the number of chips per bit N increases. The IROA accuracy is not as satisfactory for colocated receivers when Eb/No is small; for this case we develop an approximation based on the Guassian multivariate distribution, which is ore accurate than the IROA. Extensive comparisons of the exact expressions with the Guassian and the IROA approximations are conducted. For convolutional code systems, we derive the multireception packet probabilities following a new approach, the Joint First Error Event Approximation (JFEEA), which is based on the lower bound of the probabilities of all-correct packet receptions and the moments of random variables. We compare this approximation with the IROA and observe good agreement between the two.

The detection problem is formulated as a zero-sum game involving two players: the detector designer and the deceptive signal designer. The payoff is the probability of error of the detector which the detector designer tries to minimize and the deceptive signal designer to maximize. For this detection game, saddle point solutions --- whenever possible --- or otherwise maximin and minimax solutions are derived under three distinct constraints on the deceptive signal power; these distinct constraints involves bounds on (i) the peak power, (ii) the probabilistic average power, and (iii) the time average power. The cases of i.i.d. and correlated signals are both considered.

The average bit error probability of dense WDMA and WDMA/CDMA schemes is evaluated in integrating the characteristic function of other-user interference at the output of the matched optical filter. Gaussian approximation techniques are also employed. Time-synchronous and as asynchronous systems are analyzed in this context. Binary phase-shift-keying (BPSK) data modulation is considered. Our analysis quantifies accurately for first time the multiple-access capability of dense WDMA schemes and the advantages offered by employing hybrids of WDMA and CDMA.

The average bit error probability of this multiple-access scheme is evaluated by using the characteristic function of the other-user interference at the output of the matched optical filter. Both phase noise and thermal noise are taken into account in the computation. Time- Synchronous as well as asynchronous systems are analyzed in this context. Binary phase-shift-keying (BPSK) and on-off-keying (OOK) data modulation schemes are considered. The analysis is valid for arbitrary values of the spreading gain and the number of interfering users. The performance evaluation of RC CDMA established the potential advantage in employing hybrids of wavelength-division multiple-access )WDMA) and CDMA to combat inter-carrier interference in dense WDMA systems.

To develop the ADF methodology, a mathematical foundation is laid consisting of a sequence of definitions, lemmas, and theorems, an outline of which is included in the paper. The most significant result is that the ADF of signal plus noise is the convolution of the ADF of signal and the ADF of noise taken separately. These ideas are applicable through the definition of the Amplitude Moment Statistic (AMS), a statistical transform that converges to the moment generating function of the ADF. Hence, the AMS is the vehicle for indirectly estimating the ADF from observations. For the particular problem of detecting a modulated sinusoid in stationary Gaussian noise, a detector is developed around the AMS. The detector's performance is analyzed, compared with that of a radiometer, and shown superior for small (10) time-bandwidth products.

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