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New Radio Unlicensed (NR-U), a fifth-generation cellular communication technology, allows base stations to use multichannel transmissions in the unlicensed frequency band, which is of great practical interest. However, the simultaneous operation of several NR-U operators in the same frequency channels leads to an increase in the number of collisions in the network when gaining access to an unlicensed channel. In this paper, we study the effectiveness of the collision resolution method previously proposed for single-channel transmissions when base stations use the multi-channel access method of access of Type A defined in the NR-U specification. Scenarios of coexistence of two NR-U operators with a various choice of active channels are considered. The normalized network throughput and the uniformity of the distribution of channel resources between the base stations of operators are estimated. It is shown that the use of the collision resolution method makes it possible to increase the total throughput by up to 20% compared to the standard method. [ABSTRACT FROM AUTHOR]

In existing dynamic spectrum sharing (DSS) systems, each node arbitrates channel access independently based on carrier-sensing mechanisms such as the listen-before-talk (LBT) protocol. Owing to the uncoordinated channel access between all nodes, the channel is occupied in a random pattern. This makes it difficult to reduce the mismatch in channel quality indicator (CQI) while increasing the spatial reuse gain between the different nodes; therefore, the areal capacity gain obtained by adding nodes is much lower in existing DSS systems than in the cellular system. In this paper, we propose a different means of improving the areal capacity for downlink DSS systems. It is a group-wise DSS approach that ensures full frequency reuse in each group of base stations (BSs) by performing LBT only between the representative BSs, each of them selected by each group. Once a channel is secured by each group, all its member BSs share a channel simultaneously. This approach makes closed-loop feedback-based link adaptation practical while boosting spatial reuse gain even in the DSS environment. To implement the group-wise DSS, we propose a single unified framework that employs elementary algorithms for BS grouping and carrier-sensing threshold adjustment. Our system-level simulation results demonstrate that the proposed framework boosts the areal capacity gain by approximately 4.42 times as much as the conventional approach.

Device-to-Device communications (D2D) are being used to improve the spectral efficiency and to reduce the load of the base station (BS) by reutilizing the licensed spectrum. However, the primary cellular users may face high interference from D2D users. There is also a scarcity of licensed spectrum due to the dense deployment of smart devices. To alleviate this problem, in this paper, we are extending the D2D users to the unlicensed band. In this scenario, the D2D users are allowed to reuse the licensed spectrum or share the unlicensed spectrum with the incumbent WiFi users. However, cellular and WiFi users experience high interference if an efficient interference management scheme is not used. In this paper, we propose a joint mode selection, channel allocation, and power control algorithm using particle swarm optimization to manage the interference and improve the overall throughput of cellular and D2D users such that the minimum data rate requirement of WiFi users is guaranteed. Through numerical simulations, we show that the proposed algorithm can significantly mitigate the interference and improve the throughput of the system.

Despite that the LoRa technology has its salient features such as long transmission range and low power consumption, it suffers from data collision and signal suppression. The signal suppression problem not only degrades reliability in data transmission, but also tends to incur the unfairness such that a receiver demodulates only the strongest one of multiple received signals. To tackle this problem, the proposed approach tries to avoid the situation that multiple nodes send data simultaneously. It allows every node to transmit data only at the boundary of transmission slots and uses both random delay slots and the listen-before-talk (LBT) mechanism for collision avoidance. It is proven by experiments that the proposed approach, named ST/CA, achieves high reliability and fairness against the variation of traffic loads compared with LoRaWAN. [ABSTRACT FROM AUTHOR]

Frame-based listen-before-talk (FB-LBT) has been adopted as one of the channel access mechanism for Wi-Fi/LTE coexistence. We aim to explore the limits of FB-LBT by developing theoretical models to characterize the FB-LBT channel access performance under the coexistence of LTE and Wi-Fi. We first derive a steady-state model to calculate the spectrum share occupied by LTE under the assumption that the Wi-Fi transmissions have stationary distributions. The assumption does not hold when the time between two LTE transmissions is short, where the system is dominated by a dynamic phenomenon. A second model is developed that accounts for the dynamics of the Wi-Fi channel access mechanism. Our models, validated by simulation results, accurately calculate the spectrum share occupied by LTE over a range of FB-LBT frame periods and Wi-Fi traffic loads. We obtain upper bounds on the FB-LBT spectrum share when competing with heavy Wi-Fi traffic, which confirm the weakness of FB-LBT. Moreover, we demonstrate that our models can be used to control the FB-LBT spectrum share within a modest range. [ABSTRACT FROM AUTHOR]

We study the performance optimization problem of the long term evolution (LTE) network operating in the unlicensed band and sharing it with an existing WiFi network. We consider the LTE network to be based on the frame-based listen-before-talk protocol. We formulate the joint channel assignment and channel occupancy time optimization problem using a stochastic integer programming (IP) model. By applying the Lyapunov drift-plus-penalty theorem, we develop an asymptotically optimal solution with polynomial time-complexity for the stochastic IP problem. Numerical results are presented and the performance of the proposed solution is compared to the performance of two alternative approaches in which the channel assignment and channel occupancy time are determined sequentially. [ABSTRACT FROM AUTHOR]

Abstract Licensed-assisted access (LAA) is a new operation mode of carrier aggregation for the Long Term Evolution Advanced systems to transmit data on both licensed and unlicensed spectrum. To deal with the issue of co-existence with WiFi systems, LAA is required to perform listen-before-talk, which can significantly impact its resource utilization. In this paper, the concept called multi-subframe scheduling (MSS) which can enhance the performance of uplink LAA data transmission is presented. MSS allows a user equipment to have multiple channel sensing opportunities and/or to transmit data continuously for multiple subframes. Both scheduling-based and random access schemes are evaluated and compared. The optimum configuration of MSS which maximizes resource utilization of LAA is also provided. Numerical results show that MSS improves resource utilization on the unlicensed spectrum significantly.

With the release of the 5 GHz unlicensed spectrum has emerged licensed-assisted access, in which long-term evolution (LTE) operators compete with Wi-Fi users for a share of the unlicensed spectrum so as to augment their licensed spectrum. Subsequently, there has been the need to develop a LTE channel access mechanism that enables harmonious coexistence between Wi-Fi and LTE. Load-based listen-before-talk (LB-LBT) has been adopted as this LTE channel access mechanism by the 3rd Generation Partnership Project (3GPP). Theoretical modelling of LB-LBT schemes has focused on throughput and fair channel-time sharing between Wi-Fi and LTE technologies. We explore a LB-LBT scheme that belongs to LBT category 4, as recommended by the 3GPP, and develop a model for the distribution of the medium access control (MAC) delays experienced by the Wi-Fi packets and LTE frames. The model, validated by simulations, reveals design insights that can be used to dynamically adjust the LB-LBT parameters not only to achieve channel-time fairness, but also to guarantee MAC-delay bounds, with specified probability.

In licensed-assisted access using the LTE (LAA) standard, carrier sensing via the listenbefore-talk (LBT) procedure is a vital feature for fair sharing with the Wi-Fi systems. Furthermore, it has been designed to support frequency reuse-1 operation among all cells by the virtue of licensed spectrum. As opposed to the two existing channel-access schemes for frequency reuse-1, transmission start time alignment (TSTA) and energy detection threshold adaptation (EDTA), which may not be able to maximize the LAA system throughput without violating the requirement of fair coexistence, we propose a new frequency-reuse-1 scheme, referred to as the alignment reference interval adaptation-based LAA (ARIALAA). It attempts to combine the advantages of TSTA and EDTA into a unified access framework, in which the alignment reference interval (ARI) is adaptively adjusted to control the channel-access probability for LAA and Wi-Fi systems. Meanwhile, to operate the ARIA-LAA effectively toward our design objective, we design the fuzzy Q-learning system that adapts the continuous variable ARI to the dynamically changing wireless network environment. Based on the analytical system models and formation of the optimization problem, it employs a model-free learning algorithm that interacts with the state, defined as the current level of fairness achieved by adaptation, and the Q-learning function to determine the ARI as a global action. Our simulation results demonstrate that the ARIA-LAA is a novel scheme of spectrum sharing with spatial reuse for LAA that enhances the overall system capacity while satisfying the fair-coexistence requirement in the unlicensed spectrum.

In this paper, a novel technology, namely, device-to-device communications in the unlicensed spectrum (D2D-U) is proposed, which can allow D2D users to transmit on the unlicensed spectrum and coexist with the incumbent Wi-Fi networks. In D2D-U networks, D2D users can share the licensed spectrum with the existing cellular users or share the unlicensed spectrum with legacy Wi-Fi networks. Therefore, mutual interference across different networks and different users should be properly coordinated to optimize the system performance. In this paper, within the framework of D2D-U, we propose a joint mode selection and resource allocation algorithm to minimize the overall interference that cellular and Wi-Fi users suffer from the D2D communications while guaranteeing the signal-to-noise-and-interference ratio requirements of all users, including those of cellular, D2D, and Wi-Fi. Through theoretical analysis and numerical simulation, we show that using unlicensed spectrum can significantly mitigate the interference to both cellular and Wi-Fi users. Moreover, the duty cycle-based unlicensed spectrum access method achieves better system throughput than the listen-before-talk-based access method in most of the cases.

Future mobile networks will exploit unlicensed spectrum to boost capacity and meet growing user demands cost-effectively. The 3rd Generation Partnership Project (3GPP) has recently defined a License Assisted Access (LAA) scheme to enable global Unlicensed LTE (U-LTE) deployment, aiming at 1) ensuring fair coexistence with incumbent WiFi networks, i.e., impacting on their performance no more than another WiFi device; and 2) achieving superior airtime efficiency as compared with WiFi. We show the standardized LAA fails to simultaneously fulfill these objectives, and design an alternative orthogonal (collision-free) listen-before-talk coexistence paradigm that provides a substantial improvement in performance, yet imposes no penalty on existing WiFi networks. We derive two optimal transmission policies, ORLA and OLAA, that maximize LAA throughput in both asynchronous and synchronous (i.e., with alignment to licensed anchor frame boundaries) modes of operation, respectively. We present a comprehensive evaluation through which we demonstrate that, when aggregating packets, IEEE 802.11ac WiFi can be more efficient than LAA, whereas our proposals attains 100% higher throughput, without harming WiFi. We further show that long U-LTE frames incur up to 92% throughput losses on WiFi when using 3GPP LAA, whilst ORLA/OLAA sustain >200% gains at no cost, even in the presence of non-saturated WiFi and/or in multi-rate scenarios. [ABSTRACT FROM AUTHOR]

License Assisted Access (LAA) LTE (LAA-LTE) is a new type of LTE that aggregates the licensed LTE bands with the unlicensed bands via carrier aggregation. To operate in unlicensed bands, LAA-LTE adopts the listen-before-talk policy and designs its channel access mechanism similar to WLAN's DCF. This paper considers an LAA-LTE eNB coexisting with asymmetric hidden Wi-Fi APs where the eNB can detect the APs while the APs cannot, which is caused by the asymmetric CCA thresholds. The behavior of such a network is modeled by a joint Markov chain (MC), using which steady-state probabilities, throughput, and channel access delay are derived analytically. An extensive evaluation confirms that the proposed analysis correctly models the dynamics of LAA-WLAN coexistence, and identifies important design guidelines for fair coexistence as follows. First, LAA-LTE should enable channel access priority class 4 to exploit its large contention window (CW). Second, LAA-LTE should re-design its CW doubling policy to restore the balance between LAA-LTE and WLAN in throughput and channel access delay. Third, to protect Wi-Fi, the maximum CW stage should be used more times by increasing the retry count. [ABSTRACT FROM AUTHOR]

Licensed-assisted access (LAA) is a new operation mode of carrier aggregation for the Long Term Evolution Advanced systems to transmit data on both licensed and unlicensed spectrum. To deal with the issue of co-existence with WiFi systems, LAA is required to perform listen-before-talk, which can significantly impact its resource utilization. In this paper, the concept called multi-subframe scheduling (MSS) which can enhance the performance of uplink LAA data transmission is presented. MSS allows a user equipment to have multiple channel sensing opportunities and/or to transmit data continuously for multiple subframes. Both scheduling-based and random access schemes are evaluated and compared. The optimum configuration of MSS which maximizes resource utilization of LAA is also provided. Numerical results show that MSS improves resource utilization on the unlicensed spectrum significantly. [ABSTRACT FROM AUTHOR]

The existence of relatively long LTE data blocks within the licensed-assisted access (LAA) framework results in bursty machine-type communications (MTC) packet arrivals, which cause system performance degradation and present new challenges in Markov modeling. We develop an embedded Markov chain to characterize the dynamic behavior of the contention arising from bursty MTC and Wi-Fi data traffic in the LAA framework. Our theoretical model reveals a high-contention phenomenon caused by the bursty MTC traffic, and quantifies the resulting performance degradation for both MTC and Wi-Fi data traffic. The Markov model is further developed to evaluate three potential solutions aiming to alleviate the contention. Our analysis shows that simply expanding the contention window, although successful in reducing congestion, may cause unacceptable MTC data loss. A TDMA scheme instead achieves better MTC packet delivery and overall throughput, but requires centralized coordination. We propose a distributed scheme that randomly spreads the MTC access processes through the available time period. Our model results, validated by simulations, demonstrate that the random spreading solution achieves a near TDMA performance, while preserving the distributed nature of the Wi-Fi protocol. It alleviates the MTC traffic contention and improves the overall throughput by up to 10%. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a concept of interference load to analyze the performance of spectrum sharing technologies in unlicensed frequency bands. The interference load can quantitatively compare the technical properties of various spectrum sharing technologies, such as frequency hopping(FH), duty cycle(DC), listen-before-talk(LBT). Therefore, it can help to evaluate whether a local regulation about spectrum sharing is reasonably established or not. In order to verify the suggested concept, we applied it to 2.4 GHz frequency bands. Also, we demonstrated a real-time test-bed. Two bit error rate(BER) curves for FH with 10 random channels and DC of 10%, show such good agreement that our proposed concept is expected to be widely used to assess various spectrum sharing technologies. [ABSTRACT FROM AUTHOR]

In this paper, we have shown the performance analysis results of the LoRa low power wide area network under duty cycle local regulation in Korean RFID/USN frequency band. Especially, we analyzed uplink throughput and data transmission time of a single LoRa end device. From the analysis results, duty cycle regulation, in which a data transmission should be ended within 0.4 second, limits the performance of LoRa network. Therefore, it is necessary to revise Korea's duty cycle regulation referencing EU regulation in order to assess LoRa network in Korea. [ABSTRACT FROM AUTHOR]

The Internet of Things (IoT) architecture is quickly becoming popular even outside of its originating scenario of home automation. This paper reports the design, implementation, and performance of an IoT hardware and software architecture conceived for the continuous monitoring of livestock located in barns and during grazing. We have adopted the LoRa low power wide area network (LPWAN) technology to cover the diverse environments, and a suitable configuration of web services to perform data storage, analysis, and visualization. Since the LoRa LPWAN (LoRaWAN) medium access control (MAC) layer does not provide a listen-before-talk (LBT) mechanism, we propose a custom MAC layer with LBT-based carrier-sense multiple access with collision avoidance (CSMA/CA). The devised system has been implemented using off-the-shelf hardware, and its performance has also been estimated with the help of a C++ event-based simulator. The preliminary results of our HW implementation on the field confirm the stability of the conceived system and its reliability. [ABSTRACT FROM AUTHOR]