Dynamic Load Balance Algorithm (DLBA) for IEEE 802.11 wireless LAN

Many wireless local area network (WLAN) performance estimations are done with the assumption of uniformly distributed stations (STAs). In practice, on the contrary STAs are distributed unevenly among access points (APs), causing hot-spots and under utilized APs in a wireless network. Considering a WLAN is made up of multiple APs, having some APs carrying excessive loads (i.e. hot-spots) degrades both the considered APs as well as the overall network performance. The system performance can be improved by associating incoming STAs effectively throughout the network, in a sense to balance the network load evenly between APs and relieve the hot-spot congestion. Currently employed user association method in IEEE 802.11 WLANs considers only the received signal strength of APs at STAs, and associates STAs to the closest (in signal strength sense) AP, ignoring its load and interference value.Novel user association algorithms are required for congestion relief and network performance improvement. In this work, a new distributed association algorithm taking into consideration not only the received signal strength of the APs at STAs but also AP loadings and interference is proposed. A new AP load calculation method acknowledging the interference between STAs and APs is presented. Our simulations demonstrate that the proposed algorithm can improve the overall system throughput performance more than 50% and offers a better load distribution across the network compared to conventional association algorithm.

In this paper we present a two-dimensional medium access control (MAC) protocol. Orthogonal frequency division multiple access (OFDMA) can make multiple stations (STA) transmit simultaneously on different sub-channels. On the other hand, carrier sense multiple access with collision avoidance (CSMA/CA) could make different stations contend the available channel from the time domain to avoid collision with each other. We propose a two-dimensional MAC protocol based on OFDMA and CSMA/CA in broadband systems. With the new designed MAC protocol different stations will access the channel from the time-frequency domain without interference and collision. The combination of OFDMA with CSMA/CA will improve the system throughput with efficient MAC and decrease the collision probability. We design that different stations will contend the available time-frequency resources dynamically under fairness. The system throughput of the designed protocol is analyzed and simulation results are presented to show the performance under our designed protocol far better than the conventional CSMA/CA protocol.

There has been widespread deployment of IEEE 802.11 wireless local area networks (LANs) because of high demand from mobile terminals, such as iPod and Android terminals. With the increasing energy consumption of the wireless LANs, the development of power saving technologies incorporated into the wireless LANs have become important. In wireless LANs, access points (APs) continuously consume the power regardless of the communication. Therefore, we have proposed the Radio-On-Demand (ROD) wireless LAN, which provides power saving schemes on the basis of the utilization of wireless LANs. In this study, we particularly focus on the power saving scheme of the APs, and propose the decentralized association management of ROD wireless LANs. In our scheme, an AP assigns associated stations (STAs) to new APs before switching to sleep mode. Simulation results show that the proposed scheme can realize sufficient power saving.

Automated interference detection is required for operation and management services in wireless networks as Wireless Local Area Networks (WLANs) based on IEEE 802.11 Standard since co-channel interference from other wireless transmitters occurs irregularly. We propose a new approach for detecting the presence of interference on 802.11 links. Our solution focuses on the Access Point (AP)-initiated monitoring approach without Wireless Station (STA)-initiated additional function and sniffer devices. Our approach uses the geographical distribution of the response delay of the Acknowledgment packet (ACK) to the downlink packet that AP transmitted to STAs. The proposed method consists of a continuous monitoring step and a periodical diagnosis step to measure network statistics by ACK response delay between an AP and STAs and to detect whether and where interference occurs respectively. Comprehensive simulation results show that the proposed approach has a good accuracy and low misdetection ratio for diagnosing the interference existence and location in IEEE 802.11 WLANs.

At present, the theory and algorithm of wireless indoor positioning systems have been widely researched. Some applications of these systems have been successfully used such as inventory management. Nevertheless, positioning using radio signals indoor is subject to multipath propagation and other causes. Therefore, how to determine the location accurately has been recognized as a difficult task. This paper focuses on one of the positioning methods called received signal strength indication(RSSI) in a Wireless Local Area Network(WLAN). To improve the positioning accuracy, we proposed a scheme which to estimate the distance between access point(AP) and mobile station(MS) using the average of pilot signal strength in frequency domain. We then propose another scheme to estimate the position of the MS based on the estimated distances. At last, the simulations results show that the proposed schemes has a higher degree accuracy compared with the conventional methods.

In dense wireless local area network (WLAN) environments, the haphazard deployment of WLAN devices causes them to overlap. In such situations, a coverage adaptation through transmission power control (TPC) is required. At the same time, coverage holes should be taken into consideration for connectivity maintenance among devices. In this paper, a TPC scheme is proposed that reduces overlaps in an autonomous manner, without generating target coverage holes. The problem is formulated as a target coverage problem, in which wireless stations (STAs) are treated as target points, and the transmission power is appropriately controlled by the proposed scheme. In addition, we prove that the target coverage game is a potential game, and the proposed method is guaranteed to converge to a Nash equilibrium after a finite number of iterations. In order to prevent the occurrence of coverage holes that cannot be detected by the available STA information, we propose the exclusion of coverage boundary access points (APs) from reducing transmission power, with the idea that each boundary AP always contains the region covered by it alone. The coverage boundary APs are determined through Delaunay triangulation of all APs. The proposed scheme is evaluated by performing some simulations. The simulation results indicate that the proposed TPC scheme is effective in reducing coverage overlaps without generating coverage holes.

IEEE 802.11ax introduces Uplink Orthogonal Frequency Division Multiple Access (OFDMA)-based Random Access (UORA), a novel feature for facilitating random channel access in Wireless Local Area Networks (WLANs). Similar to the conventional random access scheme in WLANs, UORA employs the OFDMA backoff (OBO) procedure to access the channel’s Resource Units (RUs) and selects a random OBO counter within the OFDMA contention window (OCW) range. The Access Point (AP) can determine and communicate this OCW range to each station (STA). Multiple STAs accessing RUs result in transmission failure due to RU collisions, which occur when specific RUs remain unassessed by any STA, leading to wastage. Efforts to optimize channel efficiency require minimizing both collisions and idle RU despite the challenges arising from UORA’s distributed and random nature. The Fisher-Yates shuffle algorithm introduces a random uniform distribution strategy for managing RU allocations among STAs. The results demonstrate that this approach enables STAs to access RUs in a distributed manner, effectively reducing idle and wasted RUs, especially in scenarios involving a limited number of STAs. Furthermore, this approach effectively mitigates collisions among STAs, even in scenarios with a more significant number of STAs.

Over the past few years, mobile networks have emerged as a promising approach for future mobile IP applications. With limited frequency resources, designing an effective MAC (Medium Access Control) protocol is a hot challenge. IEEE 802.11b/g/a/n networks are currently the most popular wireless LAN products on the market [1]. The conventional IEEE 802.11b and 802.11g/a specification provide up to 11 and 54 Mbps data rates, respectively. However, the MAC protocol that they are based upon is the same and employs a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) protocol with binary exponential back-off. IEEE 802.11 DCF (Distributed Coordination Function) is the de facto MAC protocol for wireless LAN because of its simplicity and robustness [2,3]. Therefore, considerable research efforts have been put on the investigation of the DCF performance over wireless LAN [2]. With the successful deployment of IEEE 802.11a/b/g wireless LAN and the increasing demand for real-time applications over wireless, the IEEE 802.11n Working Group standardized a new MAC and PHY (Physical) layer specification to increase the bit rate to be up to 600 Mbps [3]. The throughput performance at the MAC layer can be improved by aggregating several frames before transmission [3]. Frame aggregation not only reduces the transmission time for preamble and frame headers, but also reduces the waiting time during CSMA/CA random backoff period for successive frame transmissions. The frame aggregation can be performed within different sub-layers. In 802.11n, frame aggregation can be performed either by A-MPDU (MAC Protocol Data Unit Aggregation) or A-MSDU (MAC Service Data Unit Aggregation). Although frame aggregation can increase the throughput at the MAC layer under ideal channel conditions, a larger aggregated frame will cause each station to wait longer before its next chance for channel access. Under errorprone channels, corrupting a large aggregated frame may waste a long period of channel time and lead to a lower MAC efficiency [4]. On the other hand, wireless LAN mobile stations that are defined as the stations that access the LAN while in motion are considered in this chapter. The previous paper analyzed the IEEE 802.11b/g/n MAC performance for wireless LAN with fixed stations, not for wireless LAN with mobile stations [5, 6, 7, 8, 9, 10]. On the contrary, Xi Yong [11] and Ha Cheol Lee [12] analyzed the MAC performance for IEEE 802.11 wireless LAN with mobile stations, but considered only IEEE 802.11 and 802.11g/a wireless LAN specification. So, this chapter summarizes all the reference papers and analyzes the IEEE 802.11b/g/a/n MAC performance for wireless LAN with fixed and mobile stations. In other words, we will present the analytical evaluation of saturation

To achieve a long run-time for battery-operated portable electronic devices that incorporate wireless transceivers, efficient power management of the radio is a critical requirement. The power management function of IEEE 802.11 wireless local area networks (WLANs) allows stations (STAs) to operate in the doze mode so that their power consumption is significantly reduced. Hence, efficient algorithms to manage when and how often a STA enters and exits doze mode are crucial to battery-operated STAs. We address this problem by developing a novel model for stochastic analysis of timer-based power management in infrastructure IEEE 802.11 WLANs. Based on this model, the probabilities that a STA is active, idle, or dozing are derived, and the power consumption of the STA, number of frames buffered, and average delay per frame are obtained. These results enable an efficient power management algorithm that optimizes the idle timer and doze duration at the STA and the frame buffer at the access point. Moreover, similar statistics for the basic power management method in the IEEE 802.11 standard are derived as a special case of the proposed timer-based power management scheme. Numerical results are presented to demonstrate the effectiveness of the proposed algorithms.

With the rapid growth in Internet network infrastructure, there is an urgent need to deploy energy-efficient networking technology. In particular, there is a need for energy-efficient wireless local area networks (WLANs), which are widely used due to their ease of deployment and low installation costs. To realize this, radio-on-demand (ROD) have been proposed. Access points (APs) in ROD are equipped with wake-up receivers that change their status to sleep or active mode based on the network traffic distribution. This study proposes a station aggregation scheme targeting multiple stations (STAs) in ROD. In this scheme, APs cooperate with each other and aggregate their STAs based on their utilization. Simulation results demonstrate the effectiveness of the scheme in terms of power saving and load balancing in ROD networks.

In this paper, we consider the problem of association of wireless stations (STAs) with an access network served by a wireless local area network (WLAN) and a 3G cellular network. There is a set of WLAN Access Points (APs) and a set of 3G Base Stations (BSs) and a number of STAs each of which needs to be associated with one of the APs or one of the BSs. We concentrate on downlink bulk elastic transfers. Each association provides each ST with a certain transfer rate. We evaluate an association on the basis of the sum log utility of the transfer rates and seek the utility maximizing association. We also obtain the optimal time scheduling of service from a 3G BS to the associated STAs. We propose a fast iterative heuristic algorithm to compute an association. Numerical results show that our algorithm converges in a few steps yielding an association that is within 1% (in objective value) of the optimal (obtained through exhaustive search); in most cases the algorithm yields an optimal solution.

Fair and efficient resource allocation in IEEE 802.11ah WLAN with heterogeneous data rates

The next generation wireless local area network (WLAN) needs to significantly improve the area throughput in high-dense deployment scenario. Orthogonal frequency division multiple access (OFDMA), considered as the key technology of the next generation WLAN, has been adopted by IEEE 802.11ax. However, most existing studies have one tricky problem: interference extension problem, i.e., the stations (STAs) placed at dispersive locations from one basic service set (BSS) access channel and transmit data simultaneously through OFDMA, thereby interfering a large area and suppressing the potential transmissions around this BSS. Unfortunately, high-dense deployment scenario exacerbates interference extension problem. This article proposes a spatial clustering group division-based OFDMA (SCGD-OFDMA) protocol, which enables the geographically close STAs to form spatial clustering groups, named SCGs. Each SCG has a leader STA and several member STAs. Each SCG’s leader STA contends for channel resources. After that, the leader STAs that successfully contending channel are scheduled by the access point one by one to trigger its member STAs to transmit uplink data by using OFDMA. Therefore, the geographical interference area is reduced and the area throughput is improved since the concurrent STAs in one SCG are located in limited area. This article theoretically analyzes the optimal SCG establishment, and throughput and area throughput of SCGD-OFDMA. Theoretical analysis is consistent with simulation results. The simulation results also show that when the number of STAs is 200 and all resource units are used for random access, SCGD-OFDMA outperforms IEEE 802.11ax and OMAX in area throughput by 56.13% and 190.97%, respectively.

In the case of a 3G-WLAN interworking architecture, handoff latency is mainly caused by the delays incurred when a mobile station (STA) transfers a current security context to the target access network or establishes connectivity to a new access point (AP). Existing handoff optimization schemes have mostly focused on reducing the scanning time which is to discover nearby access points. Even though the time taken by a mobile STA to authenticate the target APs contributes to the total handoff delay, the schemes to optimize the authentication time have not yet been fully investigated for providing seamless connectivity to mobile users performing handoff in WLANs. As a solution, pre-authentication, a technique performing the authentication of target APs before the completion of the handoff procedure, has attracted considerable attention to reduce the overall delay related with a handoff, which is performed within inter-subnet and/or inter-administrative domain levels. Therefore, in this article, we propose a novel pre-authentication scheme to minimize the handoff delay in 3G-WLAN interworking architecture. The proposed scheme pre-authenticates a new AP directly through a switched channel in a short period of time. Our evaluation shows that the proposed scheme outperforms the existing authentication schemes defined in the IEEE 802.11 standards in terms of authentication delay, signaling cost, and mobility rate. The proposed mechanism offers an additional advantage in that it is easy to implement and deploy by simply modifying the device driver modules of clients' WLAN interfaces.

This paper describes an experimental implementation of a variation of the Reverse Direction (RD) Medium Access Control (MAC) Protocol (RDP) defined in the IEEE 802.11n using the Wireless Open-Access Research Platform (WARP). The proposed approach, named Bidirectional MAC (BidMAC), allows the receiver of a valid data sequence to perform an RD transmission to the transmitter without contending for the channel. Whereas in RDP the RD transmission must be initiated by the transmitter, in BidMAC it can be dynamically initiated by the receiver according to its traffic requirements. Previous results based on mathematical analyses and computer-based simulations have shown that BidMAC can better balance downlink and uplink transmission opportunities in a Wireless Local Area Network (WLAN) where the Access Point (AP) handles bidirectional data flows for some of its wireless stations (STAs). This paper aims at going one step further and demonstrating that such superior performance can be attained in real environments. Towards this end, an implementation of BidMAC has been carried out in a reference design of WARP compatible with the IEEE 802.11a/g and tested in a proof-of-concept network formed by an AP and two STAs. Experimental results confirm the superior performance of BidMAC when compared to the legacy Distributed Coordination Function (DCF) of the IEEE 802.11 versus the traffic load, packet length, and data rate, yielding gains of up to 60%.*