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Medium Access Control Protocols for Wireless Sensor Networks in a Pervasive Computing Paradigm
Published in Syed Ijlal Ali Shah, Mohammad Ilyas, Hussein T. Mouftah, Pervasive Communications Handbook, 2017
Muhammad K. Dhodhi, Syed Ijlal Shah, Marwan Fayed
As we have learned, CSMA is ideal for low traffic loads while it suffers from traffic contention under high traffic. On the other hand, TDMA avoids contentions and provides high channel utilizations under high traffic. In TDMA, nodes can only transmit during scheduled slots and under low contentions slots are wasted and channel utilization is reduced. The Z-MAC protocol combines the advantages of both TDMA and CSMA while offsetting their weaknesses. This is achieved by utilizing CSMA as a baseline protocol while switching to TDMA under high traffic contentions. Therefore, Z-MAC achieves high channel utilization and low-latency under low contention as in CSMA and it achieves high channel utilization under high contention and reduces collision among two-hop neighbors at a low cost similar to TDMA. Therefore, Z-MAC can dynamically adjust the behavior of MAC between CSMA and TDMA depending on the traffic contention and provide high performance at both ends of the utilization spectrum.
Satellite orbital parameters and outline satellite communication principles
Published in L. Tetley, D. Calcutt, Understanding GMDSS, 2012
As shown in figure 4.14 the total time slots occupied by all users constitute a frame. The frame structure repeats so that a fixed TDMA assignment is composed of time slots that re-occur with successive frames. There are short time periods between successive slots, called guard times, which assist in separating successive time slot bursts and thus minimizing interference. Advantages of TDMA include: no inter-modulation problems since the transponder only has to deal with one carrier at a time, thus the transponder is able to operate at full power; the system is highly flexible, allowing channels of differing capacity to be accommodated by altering the number of equally spaced time slots allocated to a user. Disadvantages include the requirement for complex, and expensive, earth stations.
Contemporary Wireless Technologies
Published in G. S. V. Radha Krishna Rao, G. Radhamani, WiMAX, 2007
G. S. V. Radha Krishna Rao, G. Radhamani
In TDMA systems, several callers time-share a frequency channel. A call is sliced into a series of time slots, and each caller gets one time slot at regular intervals. Typically, a 39-kHz channel is divided into three time slots, which allows three callers to use the same channel. In this case, nine callers use three channels. The main advantage of the TDMA system is increased efficiency of transmission; TDMA systems can be used for transmission of both voice and data. They offer data rates from 64 kbps to 120 Mbps, which enables operators to offer personal communication services such as fax, voice-band data, and short messaging services (SMS). TDMA technology separates users in time, thus ensuring that they will not have interference from other simultaneous transmissions. It provides extended battery life because transmission occurs only part of the time. One of the disadvantages of TDMA is caused by the fact that each caller has a predefined time slot. The result is that when callers are roaming from one cell to another, all time slots in the next cell are already occupied, and the call might be disconnected. GSM is the best-known European implementation of services that use TDMA air interface technology. The other systems that deploy TDMA are DECT, the IS-136 standard, and Integrated Digital Enhanced Network (iDEN).
Fuzzy-based fault-tolerant and instant synchronization routing technique in wireless sensor network for rapid transit system
Published in Automatika, 2019
K. M. Karthick Raghunath, S. Thirukumaran
After the conclusion of defuzzification process, phase-IV commences for data transmission event, in which sr has multi-optional optimal NN to route the packets. Based on the fuzzy logic outcome each and every sr determines the NN to route the packets. As an initial step, the sender selects the NN and assigns a transmission timing slot. For allotting transmission slot, TDMA [20] technique is utilized. TDMA is a well-known channel access scheme which provides the capability to utilize maximum bandwidth without any collision. Once the NN receives the time slot and has the free channel to receive the packets, immediately sends its TS for synchronization with the sender. Then, the sender adjusts its clock according to the received TS and start sending its data packets.
A hybrid-spatially distributed multichannel MAC protocol for vehicular ad-hoc networks
Published in International Journal of Electronics, 2023
Jahnvi Tiwari, Madhuri Purna, Arun Prakash, Rajeev Tripathi
The MAC protocols must be adaptable to channel access based on vehicle density. Since anticipating the behaviour of cars is challenging due to the dynamicity of nodes, the channel frame structure must be constructed so that it can be adaptable and flexible (Javed et al., 2015). Time division multiple access (TDMA) is currently being used to divide the full-time interval into an equal number of slots so that each node may send a security message (Javed et al., 2015). The adoption of TDMA results in higher throughput and quicker data transmission. TDMA has several advantages, but it does not deliver bandwidth efficiency, necessitating an improvement to the access mechanism. The spatial hybrid division multiple access (SDMA) is intended to partition the whole network region into many distinct dimensions. By utilising orthogonally polarised antennas in other locations, nodes from various locations can utilise the same frequency, increasing bandwidth efficiency. However, this reduces scalability and increases network complexity (Booysen et al., 2012). The authors offer a system that combines TDMA and SDMA to improve throughput and spectrum efficiency in a VANET scenario (Booysen et al., 2012). The issue to be addressed in this study is to efficiently integrate TDMA and SDMA in a MAC protocol that delivers high throughput with minimal latency. The SDMA network, which is based on the slotted TDMA network, increases capacity by permitting multiple terminals in each slot, and spatial broadcasting is used to acquire packets from multiple devices within each slot. In essence, SDMA expands the spectrum resource by turning each slot into a space slot, resulting in a massive boost in system throughput in the best-case scenario.
A permanent wireless dynamic monitoring system for the Colosseum in Rome
Published in Journal of Structural Integrity and Maintenance, 2018
Giorgio Monti, Fabio Fumagalli, Giuseppe Quaranta, Marco Sgroi, Marcello Tommasi
Communication is based on a proprietary protocol, which uses a Time Division Multiple Access (TDMA) mechanism to assign nodes of the network the time slots in which they can transmit. Frame duration and number of slots are configurable parameters. In a typical configuration, like the one used in the implementation deployed at the Colosseum, each frame has a duration of 250 ms and is divided in 32 slots. Two slots are allocated to the network coordinator, which transmits: (1) the ID of the transmission slots for all the terminals in the network as specified in the system configuration file, and (2) a synchronization message.