A Novel Two-Relay Collaborative Multihop Inter-Vehicle Communication Systems

We propose a time division multiple access (TDMA) scheme for the BPSK modulated single carrier block transmission with frequency domain equalization (SC-FDE) over ultra-wideband (UWB) communications. The transmitter and receiver matrices for the proposed TDMA SC-FDE system are derived to achieve the multiple access interference (MAI) free and interblock-interference (IBI) free transmission without the insertion of cyclic prefix (CP) between blocks, circumventing the need for long CP and large FFT size in high speed UWB communications. The performance of the proposed TDMA SC-FDE system over UWB channels is investigated and compared with that of the block spread code division multiple access (CDMA) scheme. The effects of oversampling diversity and imperfect channel estimation are also investigated. Results show that the proposed TDMA scheme can effectively eliminate the error floor in CDMA due to insufficient CP, and it is more efficient to accommodate larger number of users than CDMA in high data rate transmission

We examine the performance of inter-vehicle communication (IVC) systems using the IEEE802.11b standard CSMA scheme and a proposed system in which packet transmission timing is decided by the vehicle position. For the realization of safety cruise-assist systems by IVC systems, the spread of transceivers on vehicles is important. To improve the equipped rate of transceivers on vehicles, it is necessary that the implementation of more simple and cheaper IVC systems. One of the solutions is using conventional wireless LAN systems for IVC systems. So we evaluate the performance of an IVC system using the conventional IEEE802.11b CSMA system. In addition, we propose and evaluate an improvement scheme for solving the performance degradation caused by packet collision. The results of simulation show that the proposed scheme is superior to other schemes when the bit rate is low. Also, it is shown that the proposed scheme has the same or higher performance than the other schemes in high bit rate.

This paper discusses the IVC (Inter Vehicle Communication) system using the UWB (Ultra Wideband) radar. DSUWB (Direct Sequence - UWB) signal is used for this IVC system because it has CDMA (Code Division Multiple Access) Capability. However, there is the near-far problem due to difference of signal power from each vehicles, it becomes the cause of degradation of communication characteristics and detection accuracy of the signal. In this paper, we propose the iterative detection system using the SIC (Successive Interference Cancellation) to improve detection rate of the signal and the bit error rate (BER) performance. The signals except the desired signal detected by the SIC is subtracted from the original received signal. As the result, the performance was improved.

Radio Frequency Identification (RFID) systems are one of the enabling technologies for the ubiquitous computing paradigm. At the moment, the EPCglobal organization leads the development of industry-driven standards for this field and has settled the EPC "Gen 2" as a reference standard. In this paper, we analyze the anti-collision procedure of EPC "Gen 2" to find the time needed to identify a population of tags, by means of the finite Markov-chain of the system. In addition, a UHF multi-reader prototype based on time division multiple access (TDMA) scheme is evaluated in this work. In this TDMA scheme, the reader time-slot duration is allocated according to the computations obtained from our analytical study. The main conclusions derived from this implementation are summarized in this work.

To address the straggler problem in wireless federated learning (WFL) networks, a novel hybrid non-orthogonal multiple access (NOMA) - time division multiple access (TDMA) scheme is proposed, where not only local model training and uploading of different users are performed in parallel, but also the model uploading of different users is performed in a hybrid NOMA-TDMA manner. Particularly, users that complete their local training form dynamic NOMA groups across different time slots in a TDMA fashion to upload their models efficiently. The latency per training round minimization problem is formulated to jointly optimize the user scheduling, time allocation, computing frequency allocation, and energy allocation. An efficient algorithm, combining one-dimensional search and successive convex approximation, is developed. Simulation results demonstrate that the proposed scheme can outperform the state-of-the-art NOMA and TDMA schemes under various system parameter setups.

We analyze the actual condition of wireless resource environment for AIS system used in maritime communication, and propose a method to detect malfunctioning wireless communication device. When an AIS system is transmitted in a manner incompatible with the slot timing due to malfunction, the AIS wireless apparatus of the Carrier Sense Time Division Multiple Access (CSTDMA) scheme can communicate but the usable slot available becomes smaller and the AIS wireless apparatus of the Self Organized Time Division Multiple Access (SOTDMA) scheme may fail to receive an AIS message due to transmission data collision on the wireless. Through the analysis of the experimental results, it was confirmed that a large number of malfunctioning AIS radio devices are actually transmitting at the actual sea. In this paper, we propose a method to improve the performance of the maritime wireless communication by improving the wireless interference environment due to malfunctioning transponder by finding out the malfunctioning AIS wireless communication device and compensating or removing it to secure the occupied slot by erroneous operation.

Co-channel interference in the downlink of LiFi attocell networks significantly decreases the network performance in terms of rate. Analysis of multiple access schemes is essential to mitigate interference and improve rate. The light-emitting diodes (LEDs) being centrally monitored, the time division multiple access (TDMA) scheme over the LEDs will be suitable to analyze. This work considers the interference characterization in Ref. (Surampudi A, Ganti RK. Interference characterization in downlink Li-Fi optical attocell networks. J Lightwave Technol 2018;36:3211–28) over M-PAM modulated signals to derive an exact expression for the goodput G of the time scheduled attocell network, which is arranged as a deterministic square lattice in two dimensions. Given this TDMA over the LEDs, numerical simulations show that the LEDs can be optimally time scheduled to maximize the goodput, which implies that the TDMA mitigates interference in an attocell network compared to the case when the LEDs are unscheduled.

High speed optical communications systems are evolving rapidly. Commercial systems achieve high aggregate data rates utilizing wavelength division multiplexing, where multiple wavelength channels carry information at electronic rates, typically 2.5 Gb/s. Data encryption in these systems will most likely be implemented electronically. However, future system may also utilize time division multiple access (TDMA) schemes and technologies for 100 Gb/s, single stream TDMA networks are currently being developed. These high speed TDMA networks will rely on all-optical switches and processors to interface the high-speed electronics in the users nodes to the ultra-high-speed optical data bus. Data encryption in these networks may need to be implemented using optical logic gates. Straightforward duplication of electronic encryption circuits using optical logic gates is not feasible because optical logic gates have low fan-out, require high optical powers, are difficult to synchronize and have high latency. In this paper, we propose a high- speed electro-optic scheme for reconfigurable feedback shift registers (RFSRs) that relies upon electronic encryption circuits to reconfigure a sequence of optical logic gates and which makes use of the latency in the optical gates as memory. We show that, for linear RFSRs, the low number of optical gates is not a drawback and that the period of the sequences is generally very large. Non-linear feedforward functions, such as all-optical bit swapping, many also be introduced to improve the pseudo-random properties of the sequences.

This paper analyzes the characteristics of time division multiple access (TDMA) scheme to improve the performance of data transmissions in wireless networks. After analyzing these characteristics, we design an efficient medium access control (MAC) mechanism based on our analysis. Because of the variable characteristics of TDMA we analyzed, we could get a time slot period to achieve the system throughput more optimal. Our proposed protocol is based on our analysis and schedule with a carefully computation. The slot(s) can be divided into several minislots as the contention interval which is used by subscribers to transmit the control packets to base station. We conclude with an approximate optimal throughput through our MAC mechanism.

In this paper, a new concept for ultrasonic indoor positioning based on instantaneous frequency of ultrasonic signals is presented. Nonlinear phase characteristics of ultrasonic transducers introduce a frequency deviation in ultrasonic signals. By sweeping at very fast rates, a large spike in the deviation is introduced. The artefacts observable in instantaneous frequency estimations are highly localized and present an opportunity for accurate frequency detection. In order to be useful, the artefacts need to take place within the pulse and have sufficient magnitude for accurate processing. The system consists of a transducer transmitter and receiver pair, which have a center frequency of 40kHz and a bandwidth of 460Hz. In order to incorporate more transmitters, a time-division multiple access (TDMA) scheme is applied to ensure orthogonality of signals. The concept includes four ultrasonic transmitters and a single receiver, which can uniquely identify each transmitter by a distinct signal sweep. Linear chirp signals are used to form narrow pulses and ensure no interference in the TDMA scheme. The received signal is amplified and passed through a phase-locked loop (PLL) to detect the chirp signals. Accurate instantaneous frequency detection can be done on the voltage-controlled oscillator (VCO) of the PLL, which has a narrower bandwidth than the overall signal sweep. The instantaneous frequency estimation methods are largely explored in this work and consider two methods: the Hilbert transform and a zero-crossings method. This work highlights some of the advantages and disadvantages of both methods. Time of flight (ToF) in this system can ultimately be obtained by considering the instantaneous frequency estimations and the time for one particular frequency to be transmitted and received.

Networking methods and applications of the inter-vehicle packet communication system are discussed. In a proposed system, vehicles and roadside beacons broadcast individual ID, position, speed in a cyclic manner using time-dots allocated with a distributed algorithm. Other information is transmitted with the random access. The routing method using 1-hop cyclic information is applied to relay the information packet to farther terminals efficiently. This communication system is extensible and realize its applications efficiently. As a new remarkable application of the inter-vehicle communication system, we propose the drive control of vehicles. >

In this paper, we consider a multiple-access channel, where multiple users equipped with energy harvesting batteries communicate to an access point. To avoid consuming extra energy on competition for the channel, the users are supposed to share the channel via time division multiple access (TDMA). In many existing works, it is commonly assumed that the users' energy harvesting processes and storage status are known to all the users before transmissions. In practice, such knowledge may not be readily available. To avoid excessive overhead for real-time information exchange, we consider the scenario where the users schedule their individual transmissions according to the users' statistical energy harvesting profiles. We first study the optimal transmission scheme in the case where each node has an infinite-capacity battery. By optimization theory, we show that, to maximize the average system throughput, all the users should transmit at an identical optimal power, which solely depends on the energy harvesting rate per time slot. We then study the equal-power TDMA scheme in the case where each node is equipped with a battery of finite capacity. The system is formulated as a polling system consisting of multiple energy queues and one server. By the Markov chain modeling method, we derive the performance of equal-power TDMA in this case, in terms of the energy loss ratio and average system throughput. In addition, we develop an algorithm to efficiently compute the optimal transmission power in the finite-capacity battery case. We also consider an equal-time TDMA scheme, which assigns equal-length subslots to each user, and analyze its system performance. It is found that equal-power TDMA always outperforms equal-time TDMA in the infinite-capacity battery case, whereas equal-time TDMA exhibits compatible or even slightly better performance in some scenarios when the batteries have finite capacities.

An airdropped meteorological parameters measurement network (AMPMN) is introduced in this paper. AMPMN with star topology is composed of two kinds of nodes, sensor nodes and one relay node, all equipped with nRF905 radio frequency (RF) modules. A three-layer protocol is built on nRF905 in terms of its configuration. The RF configuration parameters and the payloads formats are set to enable the implementation of carrier sense multiple access with collision avoidance (CSMA/CA) or time division multiple access (TDMA) schemes through programming. The performances of two presented CSMA/CA schemes and one designed TDMA scheme are evaluated by simulation. Based on the simulation results and the difficulty of practical implementation, the CSMA/CA scheme without RTS/CTS is selected for AMPMN. AMPMN will be used in unmanned meteorological parameters measuring over hazard area.

Joint user grouping and frequency allocation for multiuser SC-FDMA transmission

The demand for global telephony services for mobile users requires the use of constellations of non-geostationary orbits. The proposed S-PCNs are Iridium, Inmarsat-P, Globalstar, Odyssey and Ellipso. The first two systems propose to use a time division multiple access (TDMA) scheme and the others code division multiple access (CDMA) scheme. It is claimed that CDMA based S-PCNs can share the allocated frequency bands due to the interference resistant property of CDMA. Spectrum sharing must be based on defined interference criteria being satisfied. The interference events are based on the statistics of carrier to interference ratio (C/I). For this a computer simulation was developed to model the dynamic nature of any constellation, and produces all the statistical values of C/I to a mobile in a fading channel. The simulation includes constellations results of proposed S-PCNs with multi-spotbeam antennas (MBA). We present the results of the investigation on the effect of imperfect power control on the total system capacity for a totally overlapped band sharing scenario. Results for a band segmented scenario are also presented for comparison.