CR-LBT: Listen-before-Talk with Collision Resolution for 5G NR-U Networks
To achieve higher throughputs in cellular networks, 3GPP proposes to use unlicensed frequency bands and develops technologies - the latest one is NR-U - allowing a cellular base station to transmit in unlicensed bands, which are already occupied by Wi-Fi networks. To enable fair channel sharing between two technologies, the base station uses a sort of CSMA/CA with binary exponential backoff similar to Wi-Fi. However, the base station can start data transmission only at strictly periodic time moments. Many papers propose sending a reservation signal between the end of the backoff procedure and such a moment to prevent nearby devices from accessing the channel. However, this approach significantly reduces Wi-Fi performance. The paper proposes a novel method CR-LBT of transmitting a reservation signal that greatly decreases channel resource waste caused by collisions and improves channel resource sharing fairness. With developed analytical models and simulations, it is shown that CR-LBT may simultaneously increase the throughput of both NR-U and Wi-Fi networks. The effect is more noticeable for the Wi-Fi network, the throughput of which may rise three times compared with the traditional method of sending the reservation signal. Finally, the influence of various factors on CR-LBT performance is studied.
To improve the reliability of data delivery, in Wi-Fi networks stations can reserve for their transmissions periodic time intervals of the same duration in which they are allowed to transmit, while adjacent stations do not have that right. Here there arises the problem of choosing the parameters of reserved intervals that would ensure quality of service requirements for transmitted data in the smallest possible amount of reserved channel time. We consider the data transmission process in periodic intervals with the block acknowledgement policy that lets us reduce the costs by acknowledgement the set of packets with a single service message. We propose a method for mathematical modeling of such a transmission.
Для передачи по mesh-сети потоковых данных, предъявляющих высокие требования к качеству обслуживания, удобно использовать описанный в стандарте IEEE 802.11s механизм MCCA детерминированного доступа к среде. При использовании этого механизма станции резервируют для своих передач определенные периодически повторяющиеся интервалы времени, тем самым получая бесконкурентный доступ к каналу связи. Однако, чтобы обеспечить успешную доставку данных в условиях помех, необходимо устанавливать дополнительные резервирования под повторные попытки передачи. В работе построена аналитическая модель процесса передачи неординарного потока по многошаговым беспроводным сетям с помощью механизма MCCA. Модель позволяет определить наибольший период резервирований, при котором выполнены требования на время доставки и долю потерянных пакетов.
This article is devoted to the origin of the third “coexistence’ (1997–2002) in France of V Republic explained by its main participant – President Jacques Chirac. Particular attention is paid to his decision to dissolve Parliament and to lead pre-term elections in 1997.
Proceedings of 16th International Conference on Next Generation Wired/Wireless Advanced Networking
Proceedings of Wireless Communications and Networking Conference (WCNC) 2016
The grouping consisting of Brazil, Russia, India and China (BRIC) was initially meant to be nothing more than clever investment jargon referring to the largest and most attractive emerging economies. However, these countries identified with the BRIC concept, and started to meet annually as a group in 2008. At their fourth summit in 2011, they added South Africa to become the BRICS. By then the BRICS had fully morphed from investment jargon to a name for a new economic and political grouping that had the potential to challenge the unipolar hegemony of the United States and its Western allies. This work analyses the extent to which the concept of coexistence explains the individual foreign policies of the BRICS countries. The editors define coexistence as a strategy that promotes the establishment of a rule-based system for co-managing the global order. It recognizes that different states may legitimately pursue their own political and economic interests, but they have to do so within the bounds of a rule-based international system that ensures the peaceful coexistence of states. The BRICS and Coexistence addresses the political dimension of the emergence and influence of the BRICS in the international system and will be of interest to students and scholars of Politics, Development and International Relations.
In Wi-Fi networks, preliminary channel reservation protects transmissions in reserved time intervals from collisions with neighboring stations. However, making changes in established reservations takes long time spent on negotiating changes with neighboring stations and dissemination of information about these changes. This complicates serving of Variable Bit Rate (VBR) flows which intensity varies with time, what leaves no choice but to reserve some additional time for handling data bursts and packet retransmissions (caused by random noise and interference from remote stations). In the paper, we consider a more flexible approach when bursts and retransmissions are handled by some random access method while a constant part of an input flow is served in preliminarily reserved intervals. We build a mathematical model of a VBR flow transmission process with this heterogeneous access method and use the model to find transmission parameters which guarantee that Quality of Service requirements of the flow are satisfied at the minimal amount of used channel time.
Generalized error-locating codes are discussed. An algorithm for calculation of the upper bound of the probability of erroneous decoding for known code parameters and the input error probability is given. Based on this algorithm, an algorithm for selection of the code parameters for a specified design and input and output error probabilities is constructed. The lower bound of the probability of erroneous decoding is given. Examples of the dependence of the probability of erroneous decoding on the input error probability are given and the behavior of the obtained curves is explained.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
Let G be a semisimple algebraic group whose decomposition into the product of simple components does not contain simple groups of type A, and P⊆G be a parabolic subgroup. Extending the results of Popov , we enumerate all triples (G, P, n) such that (a) there exists an open G-orbit on the multiple flag variety G/P × G/P × . . . × G/P (n factors), (b) the number of G-orbits on the multiple flag variety is finite.
I give the explicit formula for the (set-theoretical) system of Resultants of m+1 homogeneous polynomials in n+1 variables