Designing energy efficient access points with Wi-Fi Direct Daniel Camps-Mur a,⇑ , Xavier Pérez-Costa a , Sebastià Sallent-Ribes b a NEC Network Laboratories, Kurfürsten-Anlage 36, Heidelberg, Germany b i2cat Foundation/UPC, c/ Gran Capita 2-4, Barcelona, Spain article info Article history: Received 3 February 2011 Received in revised form 23 May 2011 Accepted 11 June 2011 Available online 22 June 2011 Keywords: Wi-Fi Direct AP power saving QoS abstract Wi-Fi Direct is a new technology defined by the Wi-Fi Alliance in order to enable efficient device-to-device communication. Portable devices are a main target of this technology and hence, power saving is a key objective. In this paper we analyze the power saving protocols defined in Wi-Fi Direct and design two algorithms to efficiently use them: Adaptive Single Presence Period (ASPP) and Adaptive Multiple Presence Periods (AMPP). Operating only with layer two information, our proposed algorithms allow Wi-Fi Direct mobile devices to address the trade-off between performance and energy consumption in a configurable manner when offering access to an external network. The two algorithms presented, ASPP and AMPP, are evaluated by OPNET simulations. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The Wi-Fi technology 1 has enjoyed since its conception a tremendous market success. Most of this success has been built around the infrastructure mode of operation defined in the IEEE 802.11 standard [1], which allows a set of clients to share an Internet connection through an access point (AP). Following this success, the infrastructure mode has continuously evolved to address an increasing set of require- ments covering an ever growing number of use cases and devices. Examples of this evolution are the addition of QoS and advanced power saving capabilities through the Wi-Fi Multimedia (WMM) and WMM-PowerSave (WMM-PS) tech- nologies [2], or advances in security and ease of use through the Wi-Fi Protected Setup technology [3]. However, unlike infrastructure mode, the ad-hoc mode defined in the 802.11 standard, aimed at providing de- vice-to-device connectivity, has not enjoyed a similar mar- ket success. In order to address this market void, the Wi-Fi Alliance (WFA) [4] has recently developed the Wi-Fi Direct technology, which is however based on a different ap- proach than the 802.11 ad-hoc mode. Instead of having a network of equally capable devices, in Wi-Fi Direct devices negotiate the roles of AP and client to set up an infrastruc- ture-like network. Hence, Wi-Fi Direct can immediately benefit from the technologies defined for infrastructure mode, and can seamlessly integrate all the existent basis of Wi-Fi devices in the market, which will simply see a Wi-Fi Direct device as a traditional AP. Targeting a successful device-to-device connectivity experience, the Wi-Fi Direct technology goes beyond hav- ing a device acting as a traditional Wi-Fi AP and introduces the following new functionalities: (i) AP power saving capabilities, critical in portable devices like mobile phones, (ii) Concurrent Operation, allowing devices to maintain simultaneous connections to different Wi-Fi Direct net- works, and (iii) Layer two service discovery, allowing de- vices to discover available services prior to establishing a connection. For a detailed description of each of these fea- tures the interested reader is referred to [5]. Our work in this paper focuses on the AP power saving protocols defined by Wi-Fi Direct. Specifically, we target the case where the Wi-Fi Direct device acting as AP is a battery limited device (e.g. a mobile phone) and offers its connected clients access to an external network (e.g. a 1389-1286/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.comnet.2011.06.012 ⇑ Corresponding author. E-mail addresses: camps@netlab.nec.de (D. Camps-Mur), perez@netlab.nec.de (X. Pérez-Costa), sebastia.sallent@i2cat.net (S. Sallent-Ribes). 1 In this paper we refer indistinctly to the set of technologies derived from the work of the IEEE 802.11 group as Wi-Fi or 802.11. Computer Networks 55 (2011) 2838–2855 Contents lists available at ScienceDirect Computer Networks journal homepage: www.elsevier.com/locate/comnet