Access Point Association Research Articles

Traffic Management for Heterogeneous Networks With Opportunistic Unlicensed Spectrum Sharing

This paper studies how to maximize the per-user-based throughput in an $M$ -tier heterogeneous wireless network (HetNet) by optimally managing traffic flows among the access points (APs) in the HetNet. The APs in the first $M-1$ tiers can use the licensed spectrum at the same time whereas they share the unlicensed spectrum with the APs in the $M$ th tier by the proposed opportunistic CSMA/CA protocol. We characterize the statistical property of the cell load and channel access probability of each AP using a general AP association scheme. For an AP in each tier, the tight bounds on its mean spectrum efficiencies in the licensed and unlicensed spectra are derived in a low-complexity form for general random channel gain and AP association weight models and they can give some insights on how channel gains, AP association weights and void AP probabilities affect the mean spectrum efficiencies. We define the per-user link throughput and per-user network throughput based on the derived the mean spectrum efficiencies and maximize them by proposing the decentralized and centralized traffic management schemes for the APs in the first $M-1$ tiers under the constraint that the per-user link throughput of the tier- $M$ APs must be above some minimum required value. Finally, a numerical example of coexisting LTE and Wi-Fi networks is provided to validate our derived results and findings.

A Framework for Dynamic Network Architecture and Topology Optimization

A new paradigm in wireless network access is presented and analyzed. In this concept, certain classes of wireless terminals can be turned temporarily into an access point (AP) anytime while connected to the Internet. This creates a dynamic network architecture (DNA) since the number and location of these APs vary in time. In this paper, we present a framework to optimize different aspects of this architecture. First, the dynamic AP association problem is addressed with the aim to optimize the network by choosing the most convenient APs to provide the quality-of-service (QoS) levels demanded by the users with the minimum cost. Then, an economic model is developed to compensate the users for serving as APs and, thus, augmenting the network resources. The users' security investment is also taken into account in the AP selection. A preclustering process of the DNA is proposed to keep the optimization process feasible in a high dense network. To dynamically reconfigure the optimum topology and adjust it to the traffic variations, a new specific encoding of genetic algorithm (GA) is presented. Numerical results show that GA can provide the optimum topology up to two orders of magnitude faster than exhaustive search for network clusters, and the improvement significantly increases with the cluster size.

Throughput Optimization via Association Control in Wireless LANs

With the rapid development of the mobile computing, accessing the Internet everywhere is important for mobile device users. Wireless LAN is a stable and reliable technique to provide network access for mobile devices. The Wireless LAN Access Points(APs) have been densely deployed so that a user can access the Internet almost everywhere. However, this fact brings some new challenges. Since the regular AP association strategy is signal-based when a user receive the signals of multiple APs. The APs with strong signal will be too overloaded while the bandwidth resource in other APs is wasted. The throughput of the whole WLAN is not optimized. Moreover, the diverse bandwidth demands among users further exacerbate the situation. In this paper, aiming at optimizing the throughput over the whole WLAN, a joint AP association and bandwidth allocation problem is formulated. The different users' bandwidth demands are added as new constraints. We comprehensively analyze the solution space and prove the problem NP-hard. Our trace-driven evaluations show that the throughput is improved about 23.1 % compared to the conventional schemes.

On-Line AP Association Algorithms for 802.11n WLANs with Heterogeneous Clients

As the latest amendment of IEEE 802.11 standard, 802.11n allows a maximum raw data rate as high as 600 Mbps, making it a desirable candidate for wireless local area network (WLAN) deployment. In typical deployment, the coverage areas of nearby access points (APs) usually overlap with each other to provide satisfactory coverage and seamless mobility support. Clients tend to associate (connect) to the AP with the strongest signal strength, which may lead to poor client throughput and overloaded APs. Although a number of AP association schemes have been proposed for IEEE 802.11 WLANs in the literature, the challenges brought by the new features in 802.11n have not been thoroughly studied nor the impact of legacy 802.11a/b/g clients in 802.11n WLANS on AP association. To fill in this gap, in this paper, we explore AP association for 802.11n with heterogeneous clients (802.11a/b/g/n). We first present a bi-dimensional Markov model to estimate the uplink and downlink throughput of clients and formulate AP association into an optimization problem, aiming at providing each client a bandwidth proportional to its usable data rate. Based on this Markov model, we propose an on-line AP association algorithm under the condition that each client can acquire timely information of all clients associated with nearby APs. Furthermore, for WLANs with densely deployed APs, we provide another on-line AP association algorithm with lower complexity, which takes full advantage of 802.11n transmissions by simply associating different types of clients with different APs. We have conducted extensive simulations and experiments to validate the proposed algorithms. The results show that our algorithms can significantly improve both 802.11n throughput and aggregated network throughput under various network scenarios, compared to previous AP association schemes. Our experiments also confirm the effectiveness of the algorithms in enhancing network throughput, maintaining proportional fairness among clients, and balancing load among APs.

AP Association for Proportional Fairness in Multirate WLANs

In this paper, we investigate the problem of achieving proportional fairness via access point (AP) association in multirate WLANs. This problem is formulated as a nonlinear programming with an objective function of maximizing the total user bandwidth utilities in the whole network. Such a formulation jointly considers fairness and AP selection. We first propose a centralized algorithm Non-Linear Approximation Optimization for Proportional Fairness (NLAO-PF) to derive the user-AP association via relaxation. Since the relaxation may cause a large integrality gap, a compensation function is introduced to ensure that our algorithm can achieve at least half of the optimal in the worst case. This algorithm is assumed to be adopted periodically for resource management. To handle the case of dynamic user membership, we propose a distributed heuristic Best Performance First (BPF) based on a novel performance revenue function, which provides an AP selection criterion for newcomers. When an existing user leaves the network, the transmission times of other users associated with the same AP can be redistributed easily based on NLAO-PF. Extensive simulation study has been performed to validate our design and to compare the performance of our algorithms to those of the state of the art.

SmartAssoc: Decentralized Access Point Selection Algorithm to Improve Throughput

As the first step of the communication procedure in 802.11, an unwise selection of the access point (AP) hurts one client's throughput. This performance downgrade is usually hard to be offset by other methods, such as efficient rate adaptations. In this paper, we study this AP selection problem in a decentralized manner, with the objective of maximizing the minimum throughput among all clients. We reveal through theoretical analysis that the selfish strategy, which commonly applies in decentralized systems, cannot effectively achieve this objective. Accordingly, we propose an online AP association strategy that not only achieves a minimum throughput (among all clients) that is provably close to the optimum, but also works effectively in practice with reasonable computation and transmission overhead. The association protocol applying this strategy is implemented on the commercial hardware and compatible with legacy APs without any modification. We demonstrate its feasibility and performance through real experiments and intensive simulations.

Database-Assisted Distributed Spectrum Sharing

According to FCC's ruling for white-space spectrum access, white-space devices are required to query a database to determine the spectrum availability. In this paper, we study the database-assisted distributed white-space access point (AP) network design. We first model the cooperative and non-cooperative channel selection problems among the APs as the system-wide throughput optimization and non-cooperative AP channel selection games, respectively, and design distributed AP channel selection algorithms that achieve system optimal point and Nash equilibrium, respectively. We then propose a state-based game formulation for the distributed AP association problem of the secondary users by taking the cost of mobility into account. We show that the state-based distributed AP association game has the finite improvement property, and design a distributed AP association algorithm that can converge to a state-based Nash equilibrium. Numerical results show that the algorithm is robust to the perturbation by secondary users' dynamical leaving and entering the system.

Coverage adjustment for load balancing with an AP service availability guarantee in WLANs

In wireless local area networks, adjusting the coverage of access points (APs) may force the clients near the coverage boundaries of congested APs to associate with lightly-loaded ones, thus realizing load-balancing. Such an approach has the advantage of requiring no modification on the client software/hardware compared to other load-balancing techniques. However, its applicability is undermined by the problems of AP service cheating and AP service loophole resulted from coverage adjustment, which significantly affect the AP service availability. Nevertheless, these two problems are largely ignored by the existent research. To tackle this challenge, a variable polyhedron genetic algorithm (GA) is proposed, which not only provides an AP service availability guarantee but also yields a near-optimal beacon range for each AP when the number of evolutions is large enough. Simulation study indicates that our algorithm is superior over the default 802.11 AP association model in terms of load-balancing and network throughput enhancement. In addition, the variable polyhedron GA outperforms the traditional GA in terms of fitness value and convergence speed.

Demo

We present a demo of Odin, an SDN framework to program enterprise wireless local area networks (WLANs). Enterprise WLANs need to support a wide range of services and functionalities. This includes authentication, authorization and accounting, policy, mobility and interference management, and load balancing. WLANs also exhibit unique challenges. In particular, access point (AP) association decisions are not made by the infrastructure, but by clients. In addition, the association state machine combined with the broadcast nature of the wireless medium requires keeping track of a large amount of state changes. To this end, Odin builds on a light virtual AP abstraction that greatly simplifies client management. Odin does not require any client side modifications and its design supports WPA2 Enterprise. With Odin, a network operator can implement enterprise WLAN services as network applications.

Dual access points association in relay networks to conserve mobile terminals' energy

In this study, the authors consider the benefits of mobile terminals (MTs) with different access points (APs) for uplink and downlink transmission to conserve MTs' energy. In traditional cellular networks, an MT is typically associated with a single AP. However, as wireless networks evolve, heterogeneous and/or overlay deployment scenario become viable and an MT can be associated with different APs for uplink and downlink transmission. The authors call this 'dual APs association'. The authors show that allowing dual APs association provides a significant gain on the uplink system capacity and/or the uplink transmit power savings. As a specific example of the use of dual APs, the authors focus on relay networks and show that considering the relay cost further increases the benefits of this approach. Based on extensive simulations using IEEE 802.16m relay network Evaluation Methodology, the authors demonstrate that dual APs can improve the uplink harmonic capacity by 350% or reduce the uplink transmit power by 7 dB. The authors note, however, that there exists a signalling cost in implementing dual APs association, which needs be overcome to achieve these substantial performance improvements.

User-Centric Management of Wireless LANs

With the ever increasing deployment density of Wireless Local Area Networks (WLANs), more and more access points (APs) are deployed within users' vicinity. The effective management of these APs to optimize the users' throughput becomes an important challenge in high-density deployment environments. In this paper, we propose a user-centric network management framework to optimize users' throughput taking into consideration both the network conditions sensed by users and their access priorities. The proposed framework is built around an information pipeline that facilitates the sharing of the information needed for optimal management of communication resources. Theoretical analysis and extensive simulations are presented on two major management activities: AP association and channel selection, and demonstrate that the proposed user-centric network management framework significantly outperforms traditional network management framework in the high-density deployment environment.

Access point selection algorithm for multi-rate WLANs to optimise throughput and guarantee fairness

A novel Access Point (AP) selection algorithm to maximise the system throughput while considering user fairness is proposed for multi-rate WLANs. When a new-coming user enters an overlapping area of multiple APs, it chooses the one to achieve the highest system throughput. For existing users that locate in the overlapping area, they may also need to change their AP associations due to the dynamic nature of traffic load. To enable the fairness among users, each user is guaranteed a minimum transmission opportunity. In-depth theoretical analysis and extensive simulations are performed to verify the throughput optimisation and user fairness.

A game theoretical study of access point association in wireless mesh networks

The process of association to wireless access networks is often driven only by the quality of the wireless link between the accessing mobile station and the wireless access point; such quality is mainly assessed through the Received Signal Strength Indicator (RSSI), which captures the received signal strength to/from the wireless access point. More refined measures have been proposed under different wireless standards to capture traffic-oriented parameters as the current load of the wireless access points. Still the association is mostly driven by “local” measures only which represent the “quality” of the wireless access point only.In case connectivity is provided through a wireless mesh network (WMN), the quality perceived by the user upon association depends also on “global” network-wide parameters. These parameters include the length of the multi-hop wireless path to reach up to the Internet gateway, and the interference level perceived by the traffic flow along such path. This paper addresses access point association in WMNs by resorting to game theoretic tools. The association problem is formalized as a non-cooperative game where accessing stations selfishly play to minimize their own perceived association cost (dually, maximize the perceived association quality) which shall account for the characteristics of the entire path to reach the WMN gateway. The equilibria of the association game are numerically derived and analyzed under two different cost functions capturing in different ways the association interference. Finally, a leader–follower game formulation is given for the case where wireless mesh network operators compete among themselves by properly setting the routing in their managed wireless backbones.

Improved AP association management using machine learning

We propose a distributed scheme by which nodes select an appropriate access point to associate with using each individual device's channel utilization. Specifically, we define a new metric, channel utilization, which is defined as the ratio of required bandwidth to available bandwidth estimation. By incorporating channel utilization into the access point selection protocol, we effectively reduce unnecessary reassociations and improve upper layer performance in terms of throughput, packet delivery delay, etc. We further enhance our protocol by using reinforcement learning to adapt the scheduling of probing neighboring access points (APs), ultimately reducing probing overhead by learning from past experience whether the current operational scenario would suffer from undesirable overhead. When channel utilization is combined with adaptive probing, we observed a significant performance improvement compared to traditional association approaches.

A Cyber Physical Systems Perspective on the Real-time and Reliable Dissemination of Information in Intelligent Transportation Systems

Timely and reliable dissemination of traffic-related information to drivers is a key property that intelligent transportation systems (ITS) should support. Numerous impediments stemming due to (a) physical factors, such as mobility and speed of vehicles, density of vehicles, characteristics of the wireless radio channel, and power and bit rate of radio transceivers, and (b) cyber issues, such as MAC layer access point associations and address resolutions (ARP), network layer addressing, routing and handoffs, and transport layer retransmissions lead to unpredictability in the timely and reliable dissemination of information to drivers. This paper presents compelling arguments in favor of new research directions in this area that are based on a cyber-physical systems (CPS) perspective. In particular, this paper makes three contributions. First, it considers a vehicle-centric perspective to survey and study the physics-and cyber-imposed impediments to the timely and reliable dissemination of information. Second, it presents a promising CPS solution to overcome a subset of the impediments discovered. Third, it outlines lessons learned indicating the need for more focused research and realistic testbeds. The evaluations

Location-based fast handoff for 802.11 networks

This paper presents a location-based approach that reduces handoff overhead in IEEE 802.11 networks. With this approach, a mobile station (MS) can derive the prospective access points (APs) most likely to be visited next, using the current location and the AP topology information acquired from some designated server. The server also provides parameters for AP (re)association so that the MS can re-associate with an AP directly without a probe beforehand. Further along the movement orientation, the MS can resolve a likely set of APs for preauthentication or proactive key distribution purposes. The performance evaluation indicates that our approach is promising.

Location-based fast handoff for 802.11 networks

This paper presents a location-based approach that reduces handoff overhead in IEEE 802.11 networks. With this approach, a mobile station (MS) can derive the prospective access points (APs) most likely to be visited next, using the current location and the AP topology information acquired from some designated server. The server also provides parameters for AP (re)association so that the MS can re-associate with an AP directly without a probe beforehand. Further along the movement orientation, the MS can resolve a likely set of APs for preauthentication or proactive key distribution purposes. The performance evaluation indicates that our approach is promising.