Next Point-Of-Interest (POI) recommendation aim to predict users’ next visits by mining their movement patterns. Existing works attempt to extract spatial–temporal relationships from historical check-ins; however, the following critical factors have not been adequately considered: (1) structured features implied in trajectory that reflect individual visit tendency; (2) collaborative signals from other users and (3) dynamic user preference. To this end, we jointly take into full consideration the graph-structured information as well as sequential effects of user trajectory sequences and propose the Trajectory Graph enhanced Spatial–Temporal aware Attention Network (TGSTAN). Given the general preference among users and the shifts of individual interests over time, we present a novel trajectory-aware dynamic graph convolution network module (TDGCN) to facilitate the capturing of local spatial correlations. Specifically, TDGCN dynamically adjusts the normalized adjacency matrix of the trajectory graph by element-wise multiplication with self-attentive POI representations. The local trajectory graph is generated from the same training batch to reflect real-time and collaborative signals, while also following causality. Moreover, we explicitly integrate spatial–temporal interval information with bilinear interpolation to comprehensively attach relative proximity to attention mechanism when capturing long-term dependence. Extensive experiments on three real-world Location-Based Social Networks datasets (Foursquare_TKY, Weeplaces and Gowalla_CA) demonstrate that the proposed TGSTAN consistently outperforms the existing state-of-the-art baselines with an average of 8.18%, 6.59%, and 9.60% improvement on the three datasets, respectively.

Abstract Named entity recognition (NER) is one of the widely studied natural language processing tasks in recent years. Conventional solutions treat the NER as a sequence labeling problem, but these approaches cannot handle nested NER. This is due to the fact that nested NER refers to the case where one entity contains another entity and it is not feasible to tag each token with a single tag. The pyramid model stacksLflat NER layers for prediction, which subtly enumerates all spans with length less than or equal toL. However, the original model introduces a block consisting of a convolutional layer and a bidirectional long short-term memory (Bi-LSTM) layer as the decoder, which does not consider the dependency between adjacent inputs and the Bi-LSTM cannot perform parallel computation on sequential inputs. For the purpose of improving performance and reducing the forward computation, we propose a Multi-Head Adjacent Attention-based Pyramid Layered model. In addition, when constructing a pyramid structure for span representation, the information of the intermediate words has more proportion than words on the two sides. To address this imbalance in the span representation, we fuse the output of the attention layer with the features of head and tail words when doing classification. We conducted experiments on nested NER datasets such as GENIA, SciERC, and ADE to validate the effectiveness of our proposed model.

For cognitive radio (CR), cooperation in spectrum sensing (SS) using energy detection can increase the detection of primary user signal. However, it also brings extra cooperative sensing overhead due to mutual exchange of large information among CR users. To reduce cooperative sensing overhead and improve sensing performance, the authors propose a novel clustering scheme consists of three stages: pruning , selecting , and clustering . In pruning stage, the CR users without sensing results will not join the following two stages; in the subsequent selecting stage, the CR user who has the most reliable sensing data is selected as the cluster header. For CR network, channel availability is an essence cause of cluster change. Hence, the authors proposed cluster constructing based on SS results correlation in the clustering stage. The simulation results show that the proposed clustering scheme not only has low overhead but also suit to perform in the low signal noise ratio environment.

The solar powered energy harvesting sensor node is a key technology for Internet of Things (IoT), but currently it offers only a small amount of energy storage and is capable of harvesting only a trivial amount of energy. Therefore, new technology for managing the energy associated with this sensor node is required. In particular, it is important to manage the transmission interval because the level of energy consumption during data transmission is the highest in the sensor node. If the proper transmission interval is calculated, the sensor node can be used semi‐permanently. In this study, the authors propose an energy prediction algorithm that uses the light intensity of fluorescent lamps in an indoor environment. The proposed algorithm can be used to accurately estimate the amount of energy that will be harvested by a solar panel using a weighted average for light intensity. Then, the optimal transmission interval is calculated using the amount of predicted harvested energy and residual energy. The results from the authors’ experimental testbeds show that their algorithm's performance is better than the existing approaches. The energy prediction error of their algorithm is approximately 0.5%.

Coordinated multi‐point (CoMP) – joint processing (JP) is a technique which improves the cell edge user data rate and spectral efficiency. The practical requirements for CoMP‐JP in terms of capacity and latency constraints should be solved by considering backhaul network. The possibility of deploying CoMP‐JP in practical cellular systems strongly depends on the backhaul network capabilities. The authors propose a selective clustering scheme which is able to selectively form clusters in order to decrease the traffic load of the backhaul network for CoMP‐JP. In addition, the authors propose a new frequency reuse scheme for downlink CoMP‐JP. The authors are able to decrease intra‐cell and inter‐cell interference with our proposed frequency reuse scheme. Therefore the authors increase the spectral efficiency and SINR (signal to interference and noise ratio) performance of the system.

In this paper, we propose a mobility-based prediction algorithm with dynamic LGD (Link Going Down) triggering for vertical handover by applying the IS (information server) of IEEE 802.21 MIH (media independent handover). The proposed algorithm predicts a possible moving area (PMA) of the mobile terminal based on mobility information (the velocity, coordinate values, position, movement detection, etc) in IS. Since the PMA indicates a next target cell for handover, it can advance the LGD trigger point dynamically to prepare for handover beforehand. The analytical results show that our prediction algorithm can reduce handover latency for MIPv6 (mobile IPv6), FMIPv6 (fast handover for mobile IPv6) by advancing the LGD trigger point.

In this paper, we propose a novel MAC protocol (RP-MAC) with a receiver preamble for wireless sensor networks. Energy efficiency is the most critical and fundamental factor in wireless sensor networks, because sensor nodes rely on the limited power source. For energy efficiency, the existing MAC protocols such as B-MAC and X-MAC change the active and sleep states periodically with a duty cycle. Even if these protocols work well in the sleep state, transmission overhead due to the preamble is very large when changing to the active state, because the sender transmits a preamble repetitively. In our approach, the receiver transmits instead a preamble only once, thereby minimizing the overhead. With this concept we implement real source code working on the telosb platform with TinyOS 1.1.15 version. The test results show that the proposed protocol provides better performance in terms of energy efficiency and delay compared to X-MAC.

In this paper, we propose a novel network selection algorithm considering power consumption in hybrid wireless networks for vertical handover. CDMA, WiBro, WLAN networks are candidate networks for this selection algorithm. This algorithm is composed of the power consumption prediction algorithm and the final network selection algorithm. The power consumption prediction algorithm estimates the expected lifetime of the mobile station based on the current battery level, traffic class and power consumption for each network interface card of the mobile station. If the expected lifetime of the mobile station in a certain network is not long enough compared the handover delay, this particular network will be removed from the candidate network list, thereby preventing unnecessary handovers in the preprocessing procedure. On the other hand, the final network selection algorithm consists of AHP (analytic hierarchical process) and GRA (grey relational analysis). The global factors of the network selection structure are QoS, cost and lifetime. If user preference is lifetime, our selection algorithm selects the network that stays longer due to low power consumption. Also, we conduct some simulations using the OPNET simulation tool. The simulation results show that the proposed algorithm provides longer lifetime in the hybrid wireless network environment.

In this paper, we propose a novel MAC protocol with the patterned preamble technique to improve performance in terms of low power, channel utilization, and delay in wireless sensor networks. B-MAC is one of typical MAC protocols for wireless sensor networks using the duty cycle in order to achieve low-power operation. Since it works in an asynchronous fashion, B-MAC employs extended preamble and preamble sampling techniques. Even if it has outstanding performance in idle state, the overhead of these techniques is very large when packets are sent and received, because there is a lot of waste in the traditional preamble method. Instead of the simple preamble, our proposed MAC solution is to introduce more intelligent preamble with some patterns consisting of 2 phases (Tx phase & Ack phase). With this concept we implement real source code working on the mica2 platform with Tinyos-1.x version. Also, the test set-up is presented, and the test results demonstrate that the proposed protocol provides better performance in terms of delay compared to B-MAC.

In wireless sensor networks, the existing routing protocols do not support bi-directional routing, uplink and downlink both simultaneously due to the insufficient resources. While tree-based uplink routing is used for collecting data from the sensor nodes, downlink routing is used to send any interests to the sensor nodes by flooding. As a result, it causes a lot of overhead in the downlink direction. In this paper, we propose an efficient bi-directional routing protocol with a new address notation for wireless ssor networks, thereby minimizing the memory requirement on each node. The proposed protocol has been validated by conducting some experiments on a test bed. The test results show that our routing protocol provides higher efficiency in terms of the number of control packets compared to the traditional flooding approach in the downlink direction for wireless sensor networks.

A wireless sensor network consists of a large number of sensor nodes that are spread densely to observe the phenomenon. The whole network lifetime relies on the lifetime of each sensor node. If one node dies, it could lead to a separation of the sensor network. Thus each and every sensor node should live long to extend the lifetime of the wireless sensor network. In this paper, we propose a path selection algorithm with energy efficiency for wireless sensor networks. The key idea in the algorithm is that all the paths are utilized evenly and the paths with enough available energy are selected, so that the network lifetime can be maximized. To evaluate its performance, some simulations are carried out. In conclusion, we find out that our protocol is more efficient than the other routing protocols in terms of energy.

In this paper, we propose a novel anti-collision algorithm for generation 2 RFID system to estimate the number of tags and to use the optimal frame size. Depending on the number of tags, there exists the optimal frame size in the sense that the system efficiency is maximized. The number of tags can be estimated from the collision ratio in terms of collided slots per frame. In addition, we compare our proposed algorithm with other existing schemes by simulation. The proposed scheme is easy to implement, and the simulation results show that its performance improves significantly compared to other schemes in terms of the identification time and the number of consumed slots.

The stream control transport protocol (SCTP) is a new transport layer protocol that has been designed to provide reliable transport over IP networks. While the transmission control protocol (TCP) is the most. popular transport protocol in IP networks, it falls short with regard to security - more specifically, resilience to denial-of-service (DoS) attacks, such as SYN attacks. The need for resilience to DoS attacks is obvious, and SCTP provides for this resilience via its improved handshake mechanism and the cookie feature. The paper discusses SCTP simulation with particular emphasis on resilience to DoS attacks. As revealed by our detailed simulation study, the increased DoS resilience comes with increased overheads. While DoS resilience is extremely critical, reducing overheads in the resource-constrained wireless environment also assumes paramount importance. Hence, we propose an innovative cookie mechanism with a combination of cache and INIT packet repetition to minimize the communication overhead and simultaneously to maximize security associated with SCTP's DoS resilience over mobile ad-hoc networks.

This paper describes the design and performance of a routing protocol for mobile ad-hoc networks. Our routing protocol is named "hybrid routing" in that it attempts to take advantage of both proactive and reactive approaches. The protocol is based on the concept of multipoint relaying (MPR) to minimize flooding traffic. For most applications over mobile ad-hoc networks, it is expected that a major portion of communication will be done in the two-hop region. Therefore, when a node needs a route to a destination in the two-hop region, it consults with the routing table as the proactive approach to find the route directly. Outside this region, on the other hand, it discovers a route on demand as the reactive approach through the use of MPR flooding. The proposed protocol has been validated using the ns network simulator with wireless and mobility extensions. The simulation results show that our MPR-HR protocol provides higher efficiency in terms of routing overhead compared to AODV one of the most efficient routing protocols released for mobile ad-hoc networks.

A new adaptive forward-error-correction scheme (AFEC) is introduced at the link layer for TCP/IP data traffic in wireless ATM networks. The fading and interference in wireless links cause high and variable error rates, as well as bursty errors. The purpose of the AFEC scheme is to provide a dynamic error-control mechanism by using Reed-Solomon coding to protect the ATM cell payload, as well as the payload type indicator/cell loss priority fields in the ATM cell header. In order to enhance the error tolerance in cell framing and correct delivery, the AFEC scheme functions within a new concept called LANET framing and addressing protection mechanisms. The AFEC scheme has been validated using a simulation testbed of a low-speed wireless ATM network.

This paper describes the design and performance of a medium access control protocol (called reservation CSMA/CA) for multimedia traffic over mobile ad-hoc networks. The reservation CSMA/CA protocol is based on a hierarchical approach consisting of two sublayers. The lower sublayer of the MAC protocol provides a fundamental access method using CSMA/CA to support asynchronous data traffic over mobile ad-hoc networks. The upper sublayer is designed to support real-time periodic traffic by making a slot reservation with the three-way handshake prior to actual data transmission. The proposed protocol has been validated using a software emulator which was carried out with the UNIX implementation. The simulation results show that the reservation CSMA/CA offers higher throughput for real-time periodic traffic compared to the IEEE 802.11 standard, while providing deterministic delay performance.

This paper describes the design and performance of a new AAL protocol (AAL-UDP) for UDP/IP over wireless ATM networks. The wireless links are characterized by higher error rates and burstier error patterns in comparison with the fiber-based links for which ATM was designed. The purpose of AAL-UDP is to support time-critical UDP traffic over wireless ATM networks. The key ideas in the design consist of no discard at AAL level and header protection with sequence number mechanism. The UDP/IP header is repeated for reliability, because it contains the most important information such as address and port number. The proposed AAL has been validated using a software emulator on the simulated wireless ATM network. The simulation results show that the AAL-UDP provides significant improvement in throughput as well as application level performance compared to the conventional AAL 5 case.

In future wireless multimedia networks, there will be a mixture of different traffic classes which have their own maximum tolerable bit error rate (BER) requirements. In this paper, a novel medium access control (MAC) protocol called wireless multimedia access control protocol with BER scheduling (in short form, WISPER) for CDMA-based systems is proposed. WISPER utilizes the novel idea of scheduling the transmission of multimedia packets according to their BER requirements. The scheduler assigns priorities to the packets, and performs an iterative procedure to determine a good accommodation of the highest-priority packets in the slots of a frame so that packets with equal or similar BER requirements are transmitted in the same slots. The proposed WISPER protocol has been validated using a software emulator on the cellular environment. Performance evaluation results based on the implementation are also included.

This paper describes the design and performance of a new ARQ protocol for wireless ATM networks. The wireless channel is characterized by a higher and variable error rate in comparison with fiber-based networks for which ATM was designed. The purpose of the protocol is to provide a capability to dynamically support ATM-based communications in a fluctuating transmission environment by using selective retransmission. The key ideas in the protocol design consist of variable packet size and periodic status message. The packet size is changed adaptively with the optimal size according to the time-varying conditions of the wireless channel, as a result maximizing the throughput efficiency. The proposed protocol has been validated using a software emulator which incorporates a wireless channel model. Experimental performance results based on the implementation are presented.

Thii paper describes the design and performance of a hybrid ARQ scheme with the concatenated FEC for wireless ATM networks.The wireless channel is characterized by burstier error patterns, and a higher and time-varying error rate when compared with the fiber-based network for which ATM was designed.The purpose of the hybrid ARQ scheme with the concatenated FEC is to provide a capability to dynamically support survivable ATM-based communications on a wireless channel by using a combination of ARQ and FEC schemes.The key ideas of the proposed hybrid scheme are the adaptation of the code rate to the channel conditions using incremental redundancy and the increase of the starting code rate as high as possible with the concatenated FEC to maximize the throughput efficiency.The simulation results show that our proposed scheme outperforms other hybrid ARQ schemes for all SNR values.