Institute for Systems Research

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Author: search.filters.author.Ghaffari, BehzadSubject: search.filters.subject.multi-user systems

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    Voice, Data, and Video Integration for Multi-Access in Broadband Satellite Networks
    (1993) Ghaffari, Behzad; Geraniotis, Evaggelos A.; ISR; CSHCN
    Multi-media integration of broadband services in a broadband satellite network is considered. Voice, data, video teleconferencing, and television with broad range of service (bit) rates are multiplexed through a broadband satellite, channel in a multiple-access fashion. Large (but finite) population sizes are considered with arrivals modeled by binomial distributions. A two-state minisource model is used for voice signals. For video, variable rate interframe coding is utilized to reduce the bandwidth requirements, and Markov phase processes model the modulation of the rates of the video teleconferencing and television signals.

    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.

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    Comparison of Coherent WDMA and Hybrid WDMA/CDMA for the Multiplexing of Optical Signals
    (1992) Ghaffari, Behzad; Geraniotis, Evaggelos A.; ISR
    In this paper, we provide an accurate analysis of the performance of coherent dense wavelength-division multiple-access (WDMA) schemes introduced for use in high-capacity optical networks. In our analysis, the effects of interference from other signals due to the frequency overlap caused by the instability of the carrier frequency of laser, or to mistakes in frequency coordination and assignment, are taken into account. Phase noise and thermal noise are also taken into consideration. Dense WDMA is then coupled with spread-spectrum direct-sequence modulation in order to mitigate the effect of interference from other signals. The performance of this hybrid of WDMA and code-division multiple- access (CDMA) scheme is also analyzed and compared to that of pure WDMA.

    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.

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    Analysis of Coherent Random-Carrier Code-Division Multiple- Access for High-Capacity Optical Networks
    (1992) Ghaffari, Behzad; Geraniotis, Evaggelos A.; ISR
    In this paper we provide an accurate analysis of the performance of a random-carrier (RC) code-division multiple-access (CDMA) scheme recently introduced for use in high-capacity optical networks. According to this scheme coherent optical techniques are employed to exploit the huge bandwidth of single-mode optical fibers and are coupled with spread-spectrum direct-sequence modulation in order to mitigate the interference from other signals due to the frequency overlap caused by the instability of the carrier frequency of the laser, or to the mistakes in the frequency coordination and assignment.

    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.