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SUMMARYIEEE802.11 WLAN (Wireless LAN) has been widely used in enterprises and public spaces such as airports. In these large WLAN networks, RRM (Radio Resource Management) is necessary for efficient use of radio resources, and also load balancing among APs (Access Point) has to be taken into account. Since, in IEEE802.11, STA (Station) has the right to select an AP with which it will associate, the AP selection mechanism implemented in STA is important for load balancing. This paper proposes an association mechanism called HRFA (High-Rate First Association) in order to achieve load balancing and efficient use of radio resources. Furthermore, IEEE802.11e was developed by Task Group E of the IEEE802.11 working group and specified a MAC protocol to provide QoS in the MAC layer and to support real-time traffic over WLAN. In order for WLAN to be more widely used, the functionalities of IEEE802.11e must be provided in WLAN devices. Our proposed HRFA can be applied to WLANs compliant with IEEE802.11e. Since the HRFA can be implemented without any modifications in the IEEE802.11 and IEEE802.11e standards, it is useful from the implementation-cost and compatibility point of views. Simulation results show that HRFA can efficiently utilize radio resources and can also achieve load balancing in IEEE802.11e WLAN networks.

IEEE802.11 WLAN (Wireless LAN) has been widely used in enterprise and public space such as air port. In these large WLAN networks, RRM (Radio Resource Management) is necessary for the efficient use of radio resource and also for load balancing among APs (Access Point) Since, in IEEE802.11, STA (Station) has the right to select an AP with which it will associate, AP selection mechanism implemented in STA is important for RRM. This paper proposes an AP selection mechanism, called HRFA (High-Rate First Association) in order to achieve load balancing and the efficient use of radio resource. Furthermore, IEEE802.11e is currently standardizing a MAC protocol to provide QoS (Quality of Service) in MAC layer and support real-time traffic over WLAN. In order for WLAN to be more widely used and to provide QoS in WLAN networks, the functionalities of IEEE802.11e have to be provided in WLAN devices. Our proposed HRFA can be applied to IEEE802.11e WLAN and can be implemented without any modifications in IEEE802.11 and 802.11e standard. Therefore it is useful from implementation-cost and compatibility point of views. Simulation results show that HRFA can efficiently ultilize radio resource and also achieve load balancing in IEEE802.11e WLAN networks.

Ad hoc networks have recently become a hot topic. In ad hoc networks, battery power is an important resource, since most terminals are battery powered. Terminals consume extra energy when their network interfaces are in the idle state or when they overhear packets not destined for them. They should, therefore, switch off their radio when they do not have to send or receive packets. IEEE802.11 features a power saving mechanism (PSM) in Distributed Coordination Function(DCF). In PSM for DCF, nodes must stay awake for a fixed time, called ATIM window (Ad-Hoc Traffic Indication Map window). If nodes do not have data to send or receive, they enter the doze state except for during ATIM window. However, ad hoc networks with PSM have larger end-to-end delays to deliver packets and suffer lower throughput than the standard IEEE802.11. To solve this problem, this paper proposes a protocol that reduces delay and achieves high throughput and energy efficiency. Simulation results show that our proposal outperforms other PSMs in terms of throughput, end-to-end delay and energy efficiency.

The IEEE802.11e defines a MAC protocol, which provides EDCA (enhanced distributed channel access) and HCCA (HCF controlled channel access) to support differentiation service over WLAN (wireless LAN). In IEEE802.11e WLAN, real-time application such as VoIP (Voice over IP) can have more chance to access the WM (wireless medium) than non realtime application. In addition to QoS support in WLAN, power consumption is a critical issue when WLAN is used in handheld devices. For power saving in the use of real-time applications like VoIP under EDCA, U-APSD (Unscheduled Automatic Power Save Delivery) was proposed in [2] and [4]. In fact, it can save power consumption and works well when it is used for bi-directional voice connections generated at constant bit rate. However, when it is used for real-time applications like ON-OFF traffic, buffuring delay at AP (access point) increases. To reduce the buffereing delay, this paper proposes two mechanisms. Simulation results show that they can alleviate buffering delay generated at AP.