EVALUATION OF INFLUENCE OF UNINTENTIONAL NON-STATIONARY INTERFERENCE ON FUNCTIONING OF SATELLITE COMMUNICATION SYSTEM WITH MULTIFREQUENCY TIME-DIVISION MULTIPLE ACCESS

The article considers the effect of non-Stationary unintentional interference on the earth station of a satellite communications system with Multi-Frequency Time-Division Multiple Access. The influence of non-stationary interference and white Gaussian noise on the earth station reception channel is compared using simulation modeling. The simulation model takes into account the effect of unintentional interference on the synchronization subsystem and the allocation of the boundaries of the transmitted packet of the receiver of the earth station of the satellite communication system. The probability of a bit error was used as a criterion for the quality of the satellite channel operation. The article shows the dependence of the protective ratio on the ratio of the preamble length to the packet length under the influence of pulsed interference. The obtained dependence can be used to assess the noise immunity of an earth station in a satellite communications system under the influence of pulsed interference.

Decision fusion for composite hypothesis testing in wireless sensor networks over a shared and noisy collision channel

We consider the composite hypothesis testing problem of time-bandwidth-constrained distributed detection. In this scenario, the probability distribution of the observed signal when the event of interest is happening is unknown. In addition, local decisions are censored and only those uncensored local decisions will be sent to the fusion center over a shared and noisy collision channel. The fusion center also has a limited time duration to collect transmitted decisions and make a final decision. Two types of medium access control that the sensor nodes apply to send their decisions are investigated: time division multiple access and slotted-Aloha. Unlike using the time division multiple access protocol, the slotted-Aloha-based distributed detection will experience packet collisions. However, in this article, since only uncensored decisions are sent, packet collisions are informative. We derive fusion rules according to generalized likelihood ratio test, Rao test, and Wald test for both the time division multiple access–based distributed detection and the slotted-Aloha-based distributed detection. We see that the fusion rules for the slotted-Aloha-based distributed detection here also exploit packet collisions in the final decision-making. In addition, the asymptotic performances and energy consumption of both schemes are analyzed. Extensive simulation and numerical results are provided to compare the performances of these two schemes. We show that, for a given time delay, the slotted-Aloha-based distributed detection can outperform the time division multiple access–based distributed detection by increasing the number of sensor nodes which results in higher energy consumption.

Preamble time-division multiple access fixed slot assignment protocol for secure mobile ad hoc networks

Mobile ad hoc networks are the “spontaneous networks” which create a temporary network in any place and any time without using any extra fixed radio device of a full infrastructure network. Each device in this network works as a router to develop end-to-end communication connections and move independently in any direction. Mostly, mobile ad hoc networks use the IEEE 802.11b protocol with carrier-sense multiple access with collision avoidance medium access control layer protocol for sharing a common medium among the nodes simultaneously. Due to this distributed medium, the routing and medium access control layer of the mobile ad hoc network are prone to attacks. Among several attackers, blackhole attacker is the dangerous one which causes the loss of all data packets of devices in the network. Efficient medium access control protocol designs in this respect play a key role in determining channel utilization, network delay, and, more importantly, network security. In the proposed work, preamble information is used with time-division multiple access medium access control. The preamble time-division multiple access uses time synchronization for each time slot and does not assign much time to the blackhole attacker due to a fixed time slot. As a result, blackhole is not stable in all communications and such an attack is effectively defended. Simulation results show that, in the presence of the blackhole attacker, carrier-sense multiple access with collision avoidance has a high packet loss ratio and low network throughput as compared to the proposed preamble time-division multiple access.

СИСТЕМА ОЦЕНКИ ЭНЕРГОЭФЕКТИВНОСТИ СИНХРОНИЗИРОВАННОГО ДОСТУПА В ИМИТАЦИОННОЙ МОДЕЛИ БЕСПРОВОДНОЙ СЕНСОРНОЙ СЕТИ

В статье исследуются энергоэффективность узлов в структуре имитационной модели синхронизированного доступа беспроводной сенсорной сети, приводятся обоснования и доказательства применения имитационного моделирования на основе метода Time Division Multiple Access (TDMA), для оценки надежности используется алгоритм определения пути f узла к базовой станции в нижней границе оценки стабильности. Основной задачей исследуемого синхронизированного доступа канального уровня является настройка временных параметров протокола. Предложенная имитационная модель исправляет дефекты спецификации сети и производит оценку объема в момент передачи и за единицу времени на раннем этапе настройки архитектуры сети. Основное преимущество имитационной модели заключается в высокой энергоэффективности беспроводных сенсорных узлов при развертывании беспроводной сенсорной сети.

Priority Based Time-Division Multiple Access Algorithm for Medium Range Data Communication in Very High Frequency Radios

In this paper, A novel and efficient time division multiple access (TDMA) algorithm for military last-mile data communication is designed. A dynamic slot assignment method coupled with an out-of-band control mechanism is used for the proposed design. In out-of-band, there is a well-defined control segment along with the data segment. So, if a new node specifically a high priority node arrives at the network, it can signal its arrival by a response in the designated mini-slots and can also check the slot in the network, if no idle slots are available. Assigning priority to the nodes would also ensure the delivery of the important messages first. Query messages are broadcasted by the Central node in order to detect new nodes. This reduces nodes working time and also ensures that the nodes don’t interrupt any existing communication. Furthermore, we describe the feasibility and the reliability of this algorithm for military’s last-mile (end user) data communication.