Joint Routing and Scheduling in Multi-hop Wireless Networks with Directional Antennas
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Long-distance multi-hop wireless networks have been used in recent years to provide connectivity to rural areas. The salient features of such networks include TDMA channel access, nodes with multiple radios, and point-to-point long-distance wireless links established using high-gain directional antennas mounted on high towers. It has been demonstrated previously that in such network architectures, nodes can transmit concurrently on multiple radios, as well as receive concurrently on multiple radios. However, concurrent transmission on one radio, and reception on another radio causes interference. Under this scheduling constraint, given a set of source-destination demand rates, we consider the problem of satisfying the maximum fraction of each demand (also called the maximum concurrent flow problem). We give a novel joint routing and scheduling scheme for this problem, based on linear programming and graph coloring. We analyze our algorithm theoretically and prove that at least 50% of a satisfiable set of demands is satisfied by our algorithm for most practical networks (with maximum node degree at most 5).We present an analytic method to determine the provably smallest possible slot length that must be allocated in a TDMA resource, to serve an event-triggered hard real-time load with arbitrary deterministic timing behavior. Based on this method, we then present constructive methods to find all feasible as well as the optimal cycle length in a TDMA resource, and we show how to determine the minimum required band-width of a TDMA resource. We demonstrate the applicability and computational efficiency of the presented methods in a case study of a large distributed embedded system with a TDMA bus, where we will find the optimal parameter set for the TDMA bus.
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In this paper, an optimal time slot allocation scheme (O-TDMA) supporting hard real-time communication in wireless sensor networks (WSNs) is studied. In mission-critical system, O-TDMA scheme based on TDMA protocol and a real-time performance analysis method based on WCAU (the worst case achievable utilization) are proposed. Analytical proof that O-TDMA has better performance than other schemes is given. Finally simulative examples are presented to promote the conclusion.
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A shipborne ad-hoc network (SANET), a maritime counterpart of the terrestrial vehicle ad-hoc network, can provide ships with diverse multimedia services by substituting digital maritime VHF communications for expensive satellite communications. This article proposes ad-hoc self-organizing TDMA (ASO-TDMA), a medium access control (MAC) protocol targeting SANETs. Frames in ASO-TDMA are divided into several sub-frames, and based on the proposed rules for assigning time slots, ships can only reserve time slots for data transfers through their available sub-frames. Accordingly, ASO-TDMA provides better performance in terms of reducing receiver collisions from hidden terminal problems compared to self-organizing TDMA (SO-TDMA) and carrier-sensing TDMA (CS-TDMA), two existing MAC protocols for maritime VHF communications. In addition, the article compares the performance of the three MAC protocols in terms of delays and collision rates (CRs). The results suggest that, given the same delay, ASO-TDMA can reduce the CR by as much as 30% in comparison with SO-TDMA and CS-TDMA. Similarly, given the same CR, ASO-TDMA can reduce delays by as much as 26% in comparison with SO-TDMA and CS-TDMA.
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Due to the fact that sensor nodes are untethered and unattended, energy management is a critical issue in communication mechanism of a wireless sensor network. In this paper, we address this problem and propose a novel solution based on media access control technique. Our protocol STDMA (for Sensor-Time Division Multiple Access) exploits the inherent features of TDMA to avoid the main sources of energy wastage. It assigns sensors with consecutive time slots to reduce the frequency of state transitions. S-TDMA is carefully designed to overcome the high latency of traditional TDMA protocols. It also conserves energy when a node may not be transmitting or receiving packets. Simulation results show that the S-TDMA protocol functions well.
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A survey is given covering synchronization techniques for large-capacity time-division multiple-access (TDMA) systems using geosynchronous satellites. Five important classes are identified and compared. Also, several methods of initial acquisition are described. The fundamentals of multiple access and TDMA in particular are presented. Summary descriptions and comparisions of the TDMA systems developed to date are given for experimental, prototype, and operational systems. Some important related technologies are introduced. It is concluded that TDMA is in a maturing period.
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Mode (computer interface)
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This paper investigates the information freshness of two time division multiple access (TDMA) systems: round-based TDMA and user-based TDMA. The age of information (AoI) metric is used to represent the freshness of information, measured by the time since the generation of the most recently received packet. In a conventional round-based TDMA system, multiple users send their packets in rounds, regardless of whether their packets are successfully received by the receiver, possibly leading to a high average AoI of the system. In contrast, we propose a user-based TDMA system that guarantees successful packet reception for each user through feedback before proceeding to the next user. We evaluate the average AoI and average Peak AoI (PAoI) of both TDMA systems. Our theoretical and simulation results indicate that while both systems exhibit the same average PAoI, the user-based TDMA system has a lower average AoI compared with its round-based counterpart. Our findings provide new insights into the design of TDMA systems with different information freshness requirements.
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MF-TDMA technology is from the combination of FDMA and TDMA technologies,it has frequency-division channel and time-division channel,and can implement system extension and compatibility of small station and large station based on the advantages of TDMA technology. From flexible networking of MF-TDMA system,multiple networking modes,network planning and simulation estimation for MF-TDMA system are described in this paper. The network planning decision support software is used for providing the best configuration and simulation estimation for MF-TDMA system parameters and,achieving the maximum efficiency of MF-TDMA satellite communication system.
Communications satellite
Frequency-division multiple access
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Time division multiple access (TDMA) schemes are intensively being the main solution to provide predictability and timeliness in data communication systems requiring real-time operation. In this paper we investigate the problem of low efficiency and channel utilization, common to the TDMA algorithms. As a solution, we propose a general slot stealing version of TDMA, able to significantly increase the channel utilization factor, while preserving the required level of predictability, both in wired and in wireless real-time networks.
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The paper presents a specialty wireless telemedicine application, namely wireless ultrasound, and describe its place in the growing wireless telemedicine market. We address the needs of current wireless telemedicine applications by presenting software additions that will enhance our application. Preliminary testing has been done with a 2 Mbps WLAN (wireless local area network) to establish transmission/retrieval times of a patient file, but new wireless technology is expected to reduce these times. We describe two wireless implementation schemes to achieve improved transmission and retrieval times.
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