Providing diverse Quality of Service (QoS) with ultra-low power consumption and support of mobility is the most important and challenging issue in wireless body area networks (WBANs). The IEEE 802.15.4 standard exhibits a desirable feature for WBAN, but its inability of mobility support makes it insufficient. In this paper, we show what is required for node mobility support and propose two strategies for the support. We observed that the amount of time required for the association process is the key reason IEEE 802.15.4 is unable to handle mobility. In this paper, we present a new fast association technique, which prevents nodes from scanning multiple channels. In the proposed scheme, by scanning just a single channel, a node can learn about all the coordinators working in different channels. The single channel scanning scheme is able to decrease the association time of IEEE 802.15.4 operating in 2.4GHz by 32 times. Furthermore, in this paper, a method to increase the node connectivity time with its coordinator in IEEE 802.15.4 beacon-enabled mode is introduced. The method tries to anticipate whether the node is moving towards or away from the coordinator by analyzing the signal strength of multiple beacons received from the same coordinator. Thus, the connectivity time is increased by choosing the coordinator with good signal strength, but located both furthest from the node and toward the direction which mobile node is moving. Our approach results in significant improvement by reducing the number of times the moving node switches coordinators. Experimental results have verified that our schemes work well in the mobile sensor network environment.

IEEE 802.11ah is a new wireless standard for large-scale wireless connectivity in IoT and M2M applications. One of the major requirements placed on IEEE 802.11ah is the energy-efficient communication of several thousand stations with a single access point. This is especially difficult to achieve during network initialization, because the several thousand stations must rely on the rudimentary approach of random channel access, and the inevitable increase in channel access contention yields a long association delay. IEEE 802.11ah has introduced an authentication control mechanism that classifies stations into groups, and only a small number of stations in a group are allowed to access the medium at a time. Although the grouping strategy provides fair channel access to a large number of stations, the presence of several thousand stations and limitation that only a group can use the channel at a time, causes the association time to remain excessive. In this paper, we propose a novel block association method that enables simultaneous association of all groups. Our experiments verify that our block association method decreases the total association time by many folds.

IEEE 802.11ah is an emerging wireless LAN standard in the sub-1-GHz license-exempt bands for cost-effective and range-extended communication. One of the most challenging issues that need to be overcome in relation to IEEE 802.11ah is to ensure that thousands of stations are able to associate efficiently with a single access point. During network initialization, several thousand stations try to associate with the access point, leading to heavy channel contention and long association delay. Therefore, IEEE 802.11ah has introduced an authentication control mechanism that classifies stations into groups and only a small number of stations in a group are allowed to access the medium in a beacon interval. This grouping strategy provides fair channel access to a large number of stations. However, the approach to grouping the stations and determining the best group size is undefined in the draft of IEEE 802.11ah. In this paper, we first model the authentication/association in IEEE 802.11ah. Our analysis shows that there exists the best group size that results in minimal association delay. Consequently, the analytical model is extended to determine the best group size. Finally, an enhanced authentication control algorithm, which utilizes the best group size to provide the minimum association delay, is proposed. The numerical and the simulation results we obtained with the proposed method demonstrate that our method succeeds in minimizing the association delay.