Distributed point coordination function for IEEE 802.11 wireless ad hoc networks J. Alonso-Zárate a,⇑ , C. Crespo b , Ch. Skianis c , L. Alonso b , Ch. Verikoukis a a Centre Tecnològic de Telecomunicacions de Catalunya (CTTC), Castelldefels, Barcelona, Spain b Department of Signal Theory and Communications, Universitat Politècnica de Catalunya (UPC-EETAC), Castelldefels, Barcelona, Spain c University of the Aegean, Greece article info Article history: Received 16 February 2011 Received in revised form 28 July 2011 Accepted 8 September 2011 Available online 8 October 2011 Keywords: MAC DCF PCF IEEE 802.11 DPCF DQCA DQMAN abstract The Distributed Point Coordination Function (DPCF) is presented in this paper as a novel Medium Access Control Protocol (MAC) for wireless ad hoc networks. DPCF extends the operation of the Point Coordination Function (PCF) defined in the IEEE 802.11 Standard to operate over wireless networks without infrastructure. In PCF, a central point coordina- tor polls the users to get access to the channel and data collisions are completely avoided, thus yielding high performance. In order to extend its high performance to networks with- out infrastructure, the DPCF is proposed in this paper as a combination of the Distributed Coordination Function (DCF) and the PCF. The general idea is to combine a dynamic, tem- porary, and spontaneous clustering mechanism based on DCF with the execution of PCF within each cluster. The backwards compatibility of DPCF with legacy 802.11 networks is also assessed in this paper. Comprehensive computer-based simulations demonstrate the high performance of this new protocol in both single-hop and multi-hop networks. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The Medium Access Control (MAC) layer defines the set of rules that the mobile stations of a wireless network should obey to get access to the radio channel in an effi- cient manner. The IEEE 802.11 Standard, which defines the MAC and physical (PHY) layers for Wireless Local Area Networks (WLANs), was first released in 1999 and reis- sued later in 2007 grouping some of the subsequent amendments [1]. Since the first release, it has been widely accepted as the most commonly used interface for short-range wireless connectivity. The Distributed Coordination Function (DCF) is defined in this standard as the mandatory access method for any compliant de- vice. This access method is based on Carrier Sensing Mul- tiple Access (CSMA), i.e., listen before transmit, in combination with a Binary Exponential Backoff (BEB) mechanism. An optional Collision Avoidance (CA) mecha- nism is also defined by which a handshake Request to Send (RTS) – Clear to Send (CTS) can be established be- tween source and destination before the actual transmis- sion of data. This CA mechanism aims at reducing the impact of the collisions of data packets and to combat the hidden terminal problem. The DCF can be executed in either ad hoc or infrastructure-based networks and, in- deed, is the only access method implemented in most commercial wireless cards. However, the Point Coordina- tion Function (PCF) is also defined in the IEEE 802.11 Standard as an optional polling-based access method for infrastructure-based networks. In PCF, there is no conten- tion to get access to the channel since the access point (AP) polls the stations of the network to transmit data. Therefore, collisions of data packets can be completely avoided. This access method, which may achieve superior performance under heavy traffic loads and can provide some degree of Quality of Service (QoS), has received less attention in the literature. 1570-8705/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.adhoc.2011.09.004 ⇑ Corresponding author. Tel.: +34 936452900; fax: +34 936452901. E-mail address: jesus.alonso@cttc.es (J. Alonso-Zárate). Ad Hoc Networks 10 (2012) 536–551 Contents lists available at SciVerse ScienceDirect Ad Hoc Networks journal homepage: www.elsevier.com/locate/adhoc