Improvement on WLAN Multicast Key Management 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.

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.

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.

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.

Cognitive Radio (CR) is expected to bring about a more flexible wireless communication environment by the efficient utilization of spectrum resources. In this paper, a CR coexisting with IEEE 802.11 Wireless Local Area Networks (WLANs) is proposed. In the Distributed Coordination Function (DCF) access scheme in IEEE 802.11 WLAN, a station (STA) transmits a data frame by executing a random backoff procedure after Distributed Inter Frame Space (DIFS) period, and the destination STA of the data frame responds with Ack frame to the source STA after Short Inter Frame Space (SIFS) period. After the Ack frame is transmitted, the same procedures are repeated. The proposed CR terminal recognizes the DIFS period and the SIFS period, and then it transmits CR signals during these periods with the transmission power that does not affect the IEEE 802.11 WLAN protocol. Thus, the proposed CR terminals recognize the periods during which IEEE 802.11 STAs do not transmit any frames and they use the periods to transmit CR signals. In this paper, IEEE 802.11 WLAN STA that has the capability for the proposed CR technique in addition to the normal 802.11 WLAN capability is considered and the improved average throughputs by the CR communications are evaluated in the computer simulation, and then the effectiveness of the proposed method is clarified.

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.

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.

Recently, IEEE 802.11 wireless LAN (WLAN) has emerged as a widely accepted technology for broadband wireless networking. A WLAN handoff operation, which occurs when a wireless station (STA) changes its association from one access point (AP) to another, has not been well understood so far since the mobility has not been a major concern for typical WLAN environments. However, the mobility within WLAN is becoming more and more important as the portable WLAN devices, e.g., voice over WLAN (VoWLAN) devices, emerge today. In this paper, we introduce an empirical approach to evaluate the 802.11 handoff process in a public WLAN service network, i.e., KT (Korea Telecom) NESPOT. We analyze the handoff delay by characterizing individual delay components in terms of protocol-oriented delays and network configuration-dependent ones. From the analysis, we identify that the user authentication-related procedure, especially, with delay terms not rooted in the employed protocols, could become a major delay in a public service WLAN, and hence should be reduced in order to achieve a faster handoff

This paper presents a novel medium access control (MAC) mechanism for wireless local area network (WLAN) systems, called visual recognition based medium access control (VRMAC) mechanism. VRMAC exploits Wi-Fi and visible light communications techniques, using LEDs and a camera to facilitate collision-less medium access with low overhead. In VRMAC, stations (STAs) equipped with LEDs send medium-access request messages by blinking their LEDs and an access point (AP) equipped with a camera receives the messages via the camera. In this paper, we introduce the fundamentals of the mechanism and present an example protocol. Our simulation results indicate that the mechanism improves WLAN throughput over that of the conventional MAC mechanism in WLANs.

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%.*

Over the past few years, wireless local area networks (WLANs) have gained an increased attention and a large number of WLANs are being deployed in universities, companies, airports etc. Majority of the IEEE 802.11 based WLANs employ distributed coordination function (DCF) in wireless access points (AP) to arbitrate the wireless channel among Wireless Stations (STAs). However, DCF poses serious unfairness problem between uplink and downlink flows. To overcome this unfairness problem, we propose a simple enhancement to the IEEE 802.11 DCF which provides priority to the AP and thus enables it to acquire a larger share of the channel when required. We have demonstrated the unfairness problem through systematic measurements in an experimental test bed of WLAN using the legacy 802.11 DCF. We also developed analytical models to calculate the throughput of AP and the STAs and verify these results through thorough simulations in ns-2. We observe that our simulation results find in good agreement with our analytical models. Results show that our proposed enhancement achieves a fair distribution of bandwidth and improves the throughput (by nearly 300%) for the downlink flows as compared to the DCF, without severely affecting the performance of uplink flows

IEEE 802.11ax uplink orthogonal frequency division multiple access (OFDMA)-based random access (UORA) is a new feature for random channel access in wireless local area networks (WLANs). Similar to the legacy random access scheme in WLANs, UORA performs the OFDMA backoff (OBO) procedure to access the channel and decides on a random OBO counter within the OFDMA contention window (OCW) value. An access point (AP) can determine the OCW range and inform each station (STA) of it. However, how to determine a reasonable OCW range is beyond the scope of the IEEE 802.11ax standard. The OCW range is crucial to the UORA performance, and it primarily depends on the number of contending STAs, but it is challenging for the AP to accurately and quickly estimate or keep track of the number of contending STAs without the aid of a specific signaling mechanism. In addition, the one for this purpose incurs an additional delay and overhead in the channel access procedure. Therefore, the performance of a UORA scheme can be degraded by an improper OCW range, especially when the number of contending STAs changes dynamically. We first observed the effect of OCW values on channel efficiency and derived its optimal value from an analytical model. Next, we proposed a simple yet effective OBO control scheme where each STA determines its own OBO counter in a distributed manner rather than adjusting the OCW value globally. In the proposed scheme, each STA determines an appropriate OBO counter depending on whether the previous transmission was successful or not so that collisions can be mitigated without leaving OFDMA resource units unnecessarily idle. The results of a simulation study confirm that the throughput of the proposed scheme is comparable to the optimal OCW-based scheme and is improved by up to 15 times compared to the standard UORA scheme.

In an infrastructure wireless LAN, the access point (AP) is responsible for connecting mobile stations (STA) and wired stations. Each access point is assigned on one channel. Traditionally, one station selects AP to connect is based on the received signal strength indicator (RSSI). This approach may cause all active mobile stations to connect to few APs and lots of contentions/collisions will occur by the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol. Consequently, the total network throughput will be degraded. Contrarily, if all STAs can be equally distributed to all APs and the signal strength of any pair of STA and connected AP is still kept in an acceptable range, the spare bandwidth in wireless LAN (WLAN) will be utilized in a more efficient way. In this paper, a novel dynamic load balance algorithm is proposed for WLAN. Simulation results show the proposed algorithm has the ability to fairly distribute all STAs among APs. Moreover, it also maximizes the average RSSI between AP and connected STAs.