Personal Wi-Fi Hotspot, the Wi-Fi tethering function, is widely deployed on mobile devices to allow other wireless clients to share Internet access via a broadband connection. Its advantages include no connection fee and support of non-3G/LTE devices. However, utilizing this function can rapidly deplete the battery power of the tethering device because both interface connections (3G/LTE and Wi-Fi) are always on. To address this problem, this paper proposes the Energy Management Mechanism for Wi-Fi Tethering Mode on Mobile Devices (EMWT). The mechanism is designed to effectively manage both interfaces by adjusting certain sleep durations according to the incoming traffic. Short, Long, and Deep sleep durations are introduced for saving energy. EMWT can also guarantee the packet delay bound by limiting the maximum sleep period. Five traffic rates, composed of very low, low, medium, high, and very high, are evaluated. NS-3 simulation results reveal that energy savings of up to 52.52% can be achieved with only a slight impact on system performance, in terms of end-to-end delay, throughput, and packet loss.

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 longer 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.