Browsing by Author "Soroushnejad, M."
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Item Collision Resolution Algorithms for Networks with Spread- Spectrum Capture Capability.(1987) Soroushnejad, M.; Geraniotis, Evaggelos A.; ISRIn networks which employ spread-spectrum signaling, capture and correct reception of one out of several packets transmitted to a common receiver by contending users is possible. For the case in which all the contending users employ the same spread-spectrum code, the probability of acquiring and retaining capture is evaluated via accurate approximations and tight bounds for direct-sequence, and frequency-hopped spread-spectrum signaling formats. From this probabilistic capture model, a (deterministic) threshold capture model is also derived. Both these models of capture are then incorporated into the binary tree collision resolution algorithm which takes advantage of the capture capability provided by the spread-spectrum signaling. Stable throughputs are evaluated for two types of feedback: (i) feedback with capture (4-ary), in which case the receiver can distinguish between capture and success slots (as well as between idle slots and collision slots as in the ternary feedback non-capture case), and (ii) feedback without capture (ternary) in which case the receiver can not distinguish between capture and success slots.Item Probability of Capture and Rejection of Primary Multiple-Access Interference in Spread-Spectrum Networks.(1987) Soroushnejad, M.; Geraniotis, Evaggelos A.; ISRThe probability of capture is evaluated for the situation in which several transmitters use the same spread-spectrum code to contend for the attention of a single receiver. The first stage in the capture mechanism is that of acquisition of capture; randomization of the arrival time has been proposed by Davis and Gronemayer to provide delay capture and the probability of this occurence has been derived. We are concerned with the second stage, that of retaining capture in the presence of interference from the contending users. The probability of retaining capture is computed via accurate approximations and upper bounds for direct-sequence, frequency-hopped and hybrid spread-spectrum signaling formats and for different data modulation and demodulation schemes. The calculation of the overall probability of capture is carried out for spread-spectrum systems with and without forward-error-control; in the latter case Reed-Solomon codes, as well as binary convolutional codes, are considered. Finally, the capability of rejecting primary multiple-access interference in spread-spectrum radio networks is examined by computing the maximum number of users which can contend for the same receiver without causing the probability of capture to fall below some desirable level.Item Throughput and Packet Error Probability for Cellular Direct- Sequence and Hybrid Spread-Spectrum Radio Networks.(1988) Geraniotis, Evaggelos A.; Soroushnejad, M.; ISRIn this paper multiple-access interference is characterized for cellular mobile networks, in which users are assumed to be Poisson-distributed on the plane and to employ direct-sequence or hybrid (frequency-hopped/direct-sequence) spread-spectrum signaling with a transmitter-oriented assignment of signature sequences and/or frequencyhopping patterns. Approximations for the bit- and packet-error probabilities are derived for data modulation schemes like binary phase-shift-keying (BPSK) with noncoherent demodulation and forward-error-control codes (like Reed-Solomon codes). In all cases, the effect of varying interference power of the desired signal and the other interfering signals and of Rayleigh nonselective channel fading is taken into account accurately. The throughput in the mobile- to-base transmission mode is then evaluated for the aforementioned data modulation, demodulation, and forward-error- control coding schemes. Furthermore, a comparison of the performance of frequence-hopped, direct-sequence, and hybrid spread-spectrum signaling schemes with the same bandwidth is carried out, to show that, under the varying interference power model, the frequence-hopped system performs best among them.