Secondary Access Points Research Articles

Multi‐slot‐based dynamic clustering in cognitive radio network

Multi‐slot‐based dynamic clustering in cognitive radio network

Exploiting Underlay Spectrum Sharing in Cell-Free Massive MIMO Systems

We investigate the coexistence of underlay spectrum sharing in cell-free massive multiple-input multiple-output (MIMO) systems. A primary system with geographically distributed primary access points (P-APs) serves a multitude of primary users (PUs), while a secondary system serves a large number of secondary users (SUs) in the same primary/licensed spectrum by exploiting the underlay spectrum sharing. To mitigate the secondary co-channel interference inflected at PUs, stringent secondary transmit power constraints are defined for the secondary access points (S-APs). A generalized pilots sharing scheme is used to locally estimate the uplink channels at P-APs/S-APs, and thereby, conjugate precoders are adopted to serve PUs/SUs in the same time-frequency resource element. Moreover, the effect of a user-centric AP clustering scheme is investigated by assigning a suitable set of APs to a particular user. The impact of estimated downlink (DL) channels at PUs/SUs via DL pilots beamformed by P-APs/S-APs is investigated. The achievable primary/secondary rates at PUs/SUs are derived for the statistical DL and estimated DL CSI cases. User-fairness for PUs/SUs is achieved by designing efficient transmit power control policies based on a multi-objective optimization problem formulation of joint underlay spectrum sharing and max-min criteria. The proposed orthogonal multiple-access based analytical framework is also extended to facilitate non-orthogonal multiple-access. Our analysis and numerical results manifest that the primary/secondary performance of underlay spectrum sharing can be boosted by virtue of the average reduction of transmit powers/path-losses, uniform coverage/service, and macro-diversity gains, which are inherent to distributed transmissions/receptions of cell-free massive MIMO.

Channel Load Aware AP / Extender Selection in Home WiFi Networks Using IEEE 802.11k/v

Next-generation Home WiFi networks have to step forward in terms of performance. New applications such as on-line games, virtual reality or high quality video contents will further demand higher throughput levels, as well as low latency. Beyond physical (PHY) and medium access control (MAC) improvements, deploying multiple access points (APs) in a given area may significantly contribute to achieve those performance goals by simply improving average coverage and data rates. However, it opens a new challenge: to determine the best AP for each given station (STA). This article studies the achievable performance gains of using secondary APs, also called Extenders, in Home WiFi networks in terms of throughput and delay. To do that, we introduce a centralized, easily implementable channel load aware selection mechanism for WiFi networks that takes full advantage of IEEE 802.11k/v capabilities to collect data from STAs, and distribute association decisions accordingly. These decisions are completely computed in the AP (or, alternatively, in an external network controller) based on an AP selection decision metric that, in addition to RSSI, also takes into account the load of both access and backhaul wireless links for each potential STA-AP/Extender connection. Performance evaluation of the proposed channel load aware AP and Extender selection mechanism has been first conducted in a purpose-built simulator, resulting in an overall improvement of the main analyzed metrics (throughput and delay) and the ability to serve, at least, 35% more traffic while keeping the network uncongested when compared to the traditional RSSI-based WiFi association. This trend was confirmed when the channel load aware mechanism was tested in a real deployment, where STAs were associated to the indicated AP/Extender and total throughput was increased by 77.12%.

Cross-Tier Dual-Connectivity Designs of Three-Tier Hetnets With Decoupled Uplink/Downlink and Global Coverage Performance Evaluation

In the conventionally coupled uplink (UL) and downlink (DL) association (CUDA) scheme, the UL performance is limited greatly by the DL parameters such as the density and power of base stations (BSs). To overcome this issue, this paper focuses on a novel three-tier heterogeneous network (HetNet) as well as global performance evaluation, where the cross-tier dual-connectivity (DC) and decoupled UL and DL association (DUDA) are integrated. On one hand, with the cross-tier DC, in DL or UL, typical user equipment is associated simultaneously with the primary and secondary BSs that are located at different tiers. On the other hand, with DUDA the primary and secondary access points of UL and DL are not necessarily the same. The proposed cross-tier DC scheme meets the need of the next generation networks where control channel comes from Macro BS and data channels from small cell BSs. For such HetNets, the work first presents a comprehensive investigation of the cross-tier DC design of all possible DUDA modes and the corresponding association conditions. Second, by simplifying the association conditions the work gives the comprehensive derivations in terms of the association probabilities and the statistical descriptions of the primary and secondary UL access distances. Third, by using the method from stochastic geometry this paper derives the general form of UL coverage probabilities by creating a common model of DUDA designs so that the global UL average coverage probability (ACP) of the whole network is achieved. The presented numerical and simulated analysis first validates the derivations. Then, the analysis focuses on the global UL ACP comparison of the whole HetNet between the DUDA and CUDA designs. The comparison of global ACP shows that the ACP of DUDA design is higher than the one of the CUDA design. Although the powers and densities of BSs impose the outstanding impact on the ACP of the CUDA designs, they have a very limited effect on one of the DUDA designs due to the utilization of decoupling association.

Improving Smart Home Security: Integrating Logical Sensing Into Smart Home

This paper explains various security issues in the existing home automation systems and proposes the use of logic-based security algorithms to improve home security. This paper classifies natural access points to a home as primary and secondary access points depending on their use. Logic-based sensing is implemented by identifying normal user behavior at these access points and requesting user verification when necessary. User position is also considered when various access points changed states. Moreover, the algorithm also verifies the legitimacy of a fire alarm by measuring the change in temperature, humidity, and carbon monoxide levels, thus defending against manipulative attackers. The experiment conducted in this paper used a combination of sensors, microcontrollers, Raspberry Pi and ZigBee communication to identify user behavior at various access points and implement the logical sensing algorithm. In the experiment, the proposed logical sensing algorithm was successfully implemented for a month in a studio apartment. During the course of the experiment, the algorithm was able to detect all the state changes of the primary and secondary access points and also successfully verified user identity 55 times generating 14 warnings and 5 alarms.

Secondary Access Points Placement in Cognitive Radio Networks: A Spatial Game Model With Power Discrimination

This paper studies the problem of determining the locations of secondary access points (SAPs) that belong to two competitive service providers in a certain region. Secondary users (SUs) connect to SAPs according to their preferences. A key feature of the proposed model is that it permits SAPs to set discriminatory powers for SUs, i.e., SUs in different locations will be scheduled with different transmission powers. Profit-maximizing SAPs compete with each other by setting locations and delivered power schedules to attract SUs, taking into account the impact of the revenue obtained and the power cost incurred. To study this competitive situation, an appropriate extensive form game is defined. The game can be viewed as two-staged. The selection of transmission powers by SAPs can be investigated for each pair of locations. Then, the problem of location choice can be analyzed, anticipating what transmission powers will be chosen. We make an important observation: The Nash equilibrium of the game exists, and the global revenue maximum strategy is a Nash equilibrium strategy. Finally, we explore the equilibrium for a circular region having uniform SU distribution and illustrate how to locate SAPs for such a region.

Collaborative bibliography

A bibliography is traditionally characterized by the judgments, bounded by explicit selection criteria, made by a single compiler. Because these criteria concern the attributes ascribed to a work and the needs of readers, bibliographic work is largely conceptual even across technological eras and domains. Yet, the development of networked information services, made possible by WWW infrastructure, has enabled very large numbers of people to discover, organize, and publish information, including bibliographies. Indeed, bibliographies, or at least bibliography-like artifacts, are a common genre of website, often published by people without specialized skills in information organization who follow nonrigorous selection procedures. Nevertheless, even if the items from these lists are poorly selected and described, this publishing activity is fundamentally important because it structures information locally, creating a patchy network of secondary access points. In turn, these access points enable information discovery, the formation and development of communities of interest, the estimation of document relevance by search engines, and so on. In sum, this activity, and the enabling technical infrastructure, invites bibliographies to take on new interactive possibilities. The aim of this article is to extend the traditional view of bibliography to encompass collaborative possibilities for wide, or narrow, participation in the shaping of bibliographies and the selection of items. This is done by examining the nature of bibliography on the Web, by proposing a conceptual model that opens bibliography to participatory practices, and by discussing a case study where a team sought to develop a bibliography of electronic resources. This examination reveals splendid opportunities for expanding the notion of bibliography with participatory policies while remaining true to its ancient roots.