The authors study spread slotted ALOHA (SSA) techniques which combine certain characteristics of both spread spectrum and slotted ALOHA (SA) systems to achieve better performance than the constituent systems. Their results demonstrate that SSA offers significant improvements in terms of throughput, delay and network stability against excessive loading at very acceptable levels of receiver implementation complexities. Also, SSA is found to be highly robust to errors in the time of arrivals (a serious and frequently encountered problem in satellite networks) and eliminates the need to allocate guard time. Some of the candidate SSA schemes studied show great promise for practical implementation both from the performance and complexity points of view.>

A global positioning system (GPS) receiver has been modelled and implemented in software. A digital full-time delay lock loop (DDLL) is designed for the pseudorange time delay measurement and a digital phase-locked loop (DPLL) is applied for measurements of the carrier beat phase and Doppler shift. The closed form expressions of the detection and false-alarm probabilities for the code phase acquisition process and the variance of the code phase tracking error for the code phase fine synchronization process are derived. The performance of the modelled static receivers is validated by computer simulations.>

The objective is to develop a general theoretical framework for a class of spread slotted ALOHA (SSA) systems. The contributions include: modeling of a generalized spread slotted ALOHA (SSA) system; derivation of computationally efficient closed form expressions for the SSA system throughput and delay taking into account receiver complexity; and presentation of numerical results to validate the derivation as well as to substantiate the superior performance of the proposed scheme. The results demonstrate that SSA schemes offer significant improvements in terms of throughput, delay, and network stability against excessive loading at very acceptable levels of receiver implementation complexities. Also, SSA is found to be highly robust to errors in the time of arrivals and eliminates the need for a guard time.>

The authors describe the modeling and simulation of a frequency-division multiple-access (FDMA) satellite bandwidth-on-demand (BOD) service. The class of resource allocation processes to which the satellite BOD application belongs is identified and contrasted with more common resource allocation processes. Several unique features of BOD service complicate the performance specification, modeling, and analysis. The authors divide the modeling problem into three fundamental components: modeling the resource algorithm and modeling the processing of individual resource requests. These modeling components are illustrated with the satellite BOD application. In addition, simulation of the resource allocation requires three additional components: an easy-to-use user input interface, performance measures and statistics gathering, and presentation of simulation results (user output interface). The architecture of the simulation software (resource allocation analysis program, or RAAP) is presented in terms of these six components. To illustrate RAAP's capabilities, example simulation results are given.>

The authors consider the network modeling and performance analysis of multimedia file transfer between workstations connected to remotely located local area networks (LANs). The LANs are linked by a satellite wide-area network (SWAN) with a high bandwidth and high path delay. Four areas are addressed: (1) development of a fairly accurate interconnection network model using measured delay values for different network elements; (2) derivation of tight upper and lower bounds for the network throughput for both error-free and error-prone channels using mean value analysis; (3) validation of the model using computer simulation; and (4) analysis of the SWAN performance using numerical results for a wide range of parameters (file sizes, window size, link speed, number of workstations, etc.) for the case of a multimedia SWAN. Based on the analyses, performance bottlenecks for different operating conditions that could be used to evolve design criteria for better overall system performance are identified.>