Low-speed Users Research Articles

On the performance of multiple association with mobility support in 5G ultra‐dense networks: Realistic network simulation

AbstractA user equipment (UE) in ultra‐dense networks (UDN) has a high chance of being in close proximity to many cells. multiple association (MA) can be used to serve users with high data rate demands in such a deployment scenario. However, because of the small footprint of the low power node (LPN), mobile users may experience highly frequent cell re‐association issues. This paper focuses on solutions for UEs with high data rate demands as well as mobility management. User‐centric clustering, control, and user‐plane split usages are designed and investigated in coordination with the MA scheme. The clustering involves two stages: a master clustering and user‐centric clustering. This approach goes with mobility management in long term evolution advanced (LTE‐A)/fifth generation (5G) and can easily be integrated with the existing system. By setting some predefined threshold, the scheme attempts to treat UEs separately, based on their speed. In addition, a clustering approach was developed that generates virtual cells with which UEs are associated. The combination of MA with clustering and mobility support improves cooperation between the most appropriate cells to serve a specific UE. To validate the performance gains, synthetic system level and realistic network deployment simulations were used. The results show that the proposed scheme solves the frequent re‐association issues and improves the user throughput performance. In the realistic network evaluation, up to 65.7% decrease in re‐association frequency was obtained for the UEs average speed of 90 Km/h with cluster size . In addition, the percentile UE throughput when showed about 5.5% increase compared with the case when for pedestrian and low speed users.

A novel angle of arrival tracking method in large-scale-array systems

In this paper, we investigate the problem of angle of arrival (AOA) tracking for the large-scale array in terahertz (THz) communication, which has a large size and a narrow beam, highly demanding an accurate angle estimation. On the one hand, the system usually adopts a hybrid structure with limited radio-frequency (RF) chains, which increases the difficulty of angle estimation; on the other hand, the rapid mobility of users also brings new challenges to angle estimation. To address the above challenges, a two-stage tracking framework is proposed in this paper, which employs the random phase matrix and orthogonal long pilots in the first stage to reduce the complicated multi-user estimation to multiple single-user estimations, followed by using both wide and narrow beams in the second stage to serve high-speed and low-speed users. Furthermore, a generalized-approximated-message-passing (GAMP) method is proposed for facilitating a low-accuracy estimation of the angles, followed by adopting a modified expectation-maximization (EM) algorithm based phase estimation to unbiased estimate the instantaneous angle with the help of high-gain characteristics of the beams. The proposed structure can not only simplify the estimation complexity, but also improve the estimation accuracy due to its capability of transferring the non-linear problem of angle observation into a linear gaussian model. In addition, the Kalman tracking framework is employed for performing a continuous angle tracking. Numerical results show that the angle estimation based on the random phase matrix in the initial stage can obtain a high enough estimation accuracy, while the GAMP algorithm implemented in the second stage can quickly capture the angle range under the Rayleigh limit. The performance of the proposed EM-based tracking method is shown to outperform the traditional extended Kalman filter (EKF) method.

A Novel Cooperative Cache Policy for Wireless Networks

Mobile edge caching is an emerging approach to manage high mobile data traffic in fifth‐generation wireless networks that reduces content access latency and offloading data traffic of backhaul links. This paper proposes a novel cooperative caching policy based on long short‐term memory (LSTM) neural networks considering the characteristics between the features of the heterogeneous layers and the user moving speed. Specifically, LSTM is applied to predict content popularity. Size‐weighted content popularity is utilised to balance the impact of the predicted content popularity and content size. We also consider the moving speeds of mobile users and introduce a two‐level caching architecture consisting of several small base stations (SBSs) and macro base stations (MBSs). To avoid content requests of fast‐moving users affecting the content popularity distribution of the SBS since fast‐moving users frequently handover among SBSs, fast‐moving users are served by MBSs no matter which SBS they are in. SBSs serve low‐speed users, and SBSs in the same cluster can communicate with one another. The simulation results show that compared to common cache methods, for example, the least frequently used and least recently used methods, our proposed policy is at least 8.9% lower and 6.8% higher in terms of the average content access latency and offloading ratio, respectively.

Wireless Information-Theoretic Security: Theoretical analysis & experimental measurements with multiple eavesdroppers in an outdoor obstacle-dense MANET

Wireless Information-Theoretic Security (WITS) has been suggested as a robust security scheme, especially for infrastructure-less networks. Based on the physical layer, WITS considers quasi-static Rayleigh fading instead of the classic Gaussian wiretap scenario. In this paper, the key parameters of WITS are investigated by implementing an 802.11n ad-hoc network in an outdoor obstacle-dense topology. Measurements performed throughout the topology allow for a realistic evaluation of a scenario with multiple moving eavesdroppers. Low speed user movement has been considered, so that Doppler spread can be discarded. A set of discrete field test trials have been conducted, based on simulation of human mobility throughout an obstacle-constrained environment. Average Signal-to-Noise Ratio (SNR) values have been measured for all moving nodes, and the Probability of Non-Zero Secrecy Capacity has been calculated for different eavesdropping cooperative schemes (Selection Combining and Maximal-Ratio Combining). In addition, the Outage Probability has been estimated with regard to a non-zero target Secrecy Rate for both techniques. The results have been compared with the respective values of WITS key parameters derived from theoretical analysis.

Multi-Hop WiMAX Networks: A New Opportunistic Algorithm Using AMC and PUSC Mode for Different Mobility Users

Resource allocation algorithms play the main role in provisioning high throughput in broad band wireless communications. The previous studies in WiMAX networks have considered either AMC or PUSC techniques for the resource allocation algorithms. In this way, AMC based algorithms have presented high throughput for low speed users. Conversely, PUSC based algorithms have not been affected by users' speed, whilst the throughput is low. To date, the importance of presenting proportional fair and maintaining the network throughput for the users with different speeds has not been acknowledged yet. This paper presents a novel opportunistic algorithm which is suitable for the users with different mobility speeds. The new algorithm uses two modes of AMC and PUSC simultaneously. The simulation results reveal that in comparison to similar algorithms, the proposed algorithm presents more proportional fair throughput when there are both high and low speed users.

A Novel Scheduling Algorithm for Low and High Mobility Users in Multi-hop WiMAX Network

QoS provisioning and high capacity for high mobility users are considered as the distresses of broadband wireless communications (BWC) and specifically the key technology of WiMAX. Hence, the scheduling and resource allocation algorithms play the main role in this regard. In the research conducted on scheduling algorithms in WiMAX network, two principal methods of AMC and PUSC are used. The high capacity in AMC mode algorithms is achieved by considering the low speed users. Conversely, in PUSC mode algorithms, speed does not affect the network performances; however, the capacity is low. To date, the importance of presenting QoS and maintaining the network capacity for the users with different speeds has not been acknowledged yet. This paper presents novel scheduling algorithms and also new frame partitioning scheme which are proper for the users with different mobility speeds. The new algorithm uses two modes of AMC and PUSC simultaneously to maintain the high capacity of the network. QoS is also provided. The simulation results reveal that our algorithm increases capacity while it presents low packet delay and packet loss rate in the presence of both high and low mobility speed users.

New Subcarrier Allocation for Uplink-OFDMA under Time-Varying Channels

Inter-carrier interference (ICI) and multiuser interference (MUI) occur in an uplink orthogonal frequency division multiple access system if a channel between a mobile user and a base station is rapidly time-varying. To reduce the ICI and MUI, this letter proposes a subcarrier allocation method. The key idea is to allocate a high-speed user's subcarrier near a low-speed user's one. Then, a wide Doppler spread of a high-speed user can be spilled over a low-speed user's subcarrier band with insignificant influence, and the signal-to-interference-plus-noise ratio (SINR) at each high-speed user's subcarrier can be maximized. This can provide a significant performance improvement of multiuser detection in an uplink-OFDMA.

Wireless Information-Theoretic Security in an Outdoor Topology with Obstacles: Theoretical Analysis and Experimental Measurements

This paper presents a Wireless Information-Theoretic Security (WITS) scheme, which has been recently introduced as a robust physical layer-based security solution, especially for infrastructureless networks. An autonomic network of moving users was implemented via 802.11n nodes of an ad hoc network for an outdoor topology with obstacles. Obstructed-Line-of-Sight (OLOS) and Non-Line-of-Sight (NLOS) propagation scenarios were examined. Low-speed user movement was considered, so that Doppler spread could be discarded. A transmitter and a legitimate receiver exchanged information in the presence of a moving eavesdropper. Average Signal-to-Noise Ratio (SNR) values were acquired for both the main and the wiretap channel, and the Probability of Nonzero Secrecy Capacity was calculated based on theoretical formula. Experimental results validate theoretical findings stressing the importance of user location and mobility schemes on the robustness of Wireless Information-Theoretic Security and call for further theoretical analysis.

No guarantees [mobile Internet

While various radio-based access networks are available for mobile users, the most commonly available network that offers performance sufficient for video applications is the third generation (3G) mobile phone. Download data rates are expected to improve when high-speed downlink packet access (HSDPA) becomes widely available. The network of choice may shift to WiMAX networks as soon as they become more available but when this will happen remains unclear. For low speed users, Wi-Fi hotspots are available as these offer the highest download data rates and the adoption of WMM allows QoS levels to be defined.

Modeling and analysis of queuing handoff calls in single and two-tier cellular networks

Two-tier cellular networks consist of a group of contiguous microcells overlaid by a macrocell. This design provides an enhanced use of the networks’ resources for both high and low speed users because of the availability of additional channels. However, this causes an increase in the number of handoffs between cells due to having smaller cell sizes in the microcell tier. Since, handoff call blocking is less desirable than new call blocking, delaying the handoff calls using a queue is an effective approach used to prevent the dropping of ongoing calls in a cellular network. Several techniques have been previously proposed to solve this problem. In this study, we extended the analysis of a previously proposed model by taking into account the effect of having different queue times for each type of users in the cellular network. We proposed new Markov models for single and two-tier cellular networks to solve the handoff call dropping problem. The paper presents solutions, performance analysis and comparisons of the proposed models with previously done work. As a result, it is shown that the proposed two-tier models have superior performance.

Speed control in developing countries: issues, challenges and opportunities in reducing road traffic injuries

Speed has been determined to be one of the most common contributing factors in vehicle crashes. This study explores vehicle speed as a factor in the causation of road traffic crashes, using the example of Ghana. It examines the effectiveness of various speed control measures, based on policereported traffic crashes in Ghana and published works on speed control measures in both industrialized and developing countries. In Ghana, pedestrians were the main victims of road traffic injuries. The dominant driver error assigned by traffic police was loss of control, with the underlying factor being excessive vehicle speeds. The ‘speed factor’ alone accounted for more than 50% of all Ghanaian road traffic crashes between 1998 and 2000. While the enforcement of speed limits by traffic police may not be affordable for most developing countries, rumble strips and speed humps were found to be effective on Ghanaian roads. Rumble strips installed on the main Accra-Kumasi highway reduced crashes by about 35% and fatalities by about 55%. Reducing vehicle speeds may be one of the most effective interventions to stem traffic crashes in low-income countries. However, setting lower speed limits is not an effective intervention without the traffic law enforcement resources to ensure that limits are followed. Developing countries must also look to other speed reduction measures such as speed bumps and rumble strips, roads that segregate high- and low-speed users, and technological solutions such as speed governors, as well as greater public awareness of the problem.