• DDH-MAC: a novel dynamic de-centralized hybrid MAC protocol for cognitive radio networks

      Shah, Munam Ali; Safdar, Ghazanfar Ali; Maple, Carsten (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011)
      The radio spectrum (3kHz - 300GHz) has become saturated and proven to be insufficient to address the proliferation of new wireless applications. Cognitive Radio Technology which is an opportunistic network and is equipped with fully programmable wireless devices that empowers the network by OODA cycle and then make intelligent decisions by adapting their MAC and physical layer characteristics such as waveform, has appeared to be the only solution for current low spectrum availability and under utilization problem. In this paper a novel Dynamic De-Centralized Hybrid “DDH-MAC” protocol for Cognitive Radio Networks has been presented which lies between Global Common Control Channel (GCCC) and non-GCCC categories of cognitive radio MAC protocols. DDH-MAC is equipped with the best features of GCCC MAC protocols but also overcomes the saturation and security issues in GCCC. To the best of authors' knowledge, DDH-MAC is the first protocol which is hybrid between GCCC and non-GCCC family of protocols. DDH-MAC provides multiple levels of security and partially use GCCC to transmit beacon which sets and announces local control channel for exchange of free channel list (FCL) sensed by the co-operatively communicating cognitive radio nodes, subsequently providing secure transactions among participating nodes over the decided local control channel. This paper describes the framework of the DDH-MAC protocol in addition to its pseudo code for implementation; it is shown that the pre-transmission time for DDH-MAC is on average 20% better while compared to other cognitive radio MAC protocols.
    • Effects of iterative block ciphers on quality of experience for Internet Protocol Security enabled voice over IP calls

      Safdar, Ghazanfar Ali; Sant, Paul; Epiphaniou, Gregory; Maple, Carsten (IET, 2012)
      Voice over IP (VoIP) is the technology used to transport real-time voice over a packet-switched network. This study analyses the effects of encrypted VoIP streams on perceived Quality of Experience (QoE) from a user's perspective. An in-depth analysis on how the transparent nature of encryption can influence the way users perceive the quality of a VoIP call have been investigated by using the E model. A series of experiments have been conducted using a representative sample of modern codecs currently employed for digitising voice, as well as three of the most commonly used iterative block ciphers for encryption (DES, 3DES, AES). It has been found that the Internet Protocol Security encryption of VoIP strongly relates to the payload sizes and choice of codecs and this relationship has different effects on the overall QoE as measured by the E model, in terms of the way that users perceive the quality of a VoIP call. The main result of this paper is that the default payload shipped with the codecs is not the optimal selection for an increased number of VoIP calls, when encryption is applied and a minimum level of QoE has to be maintained, per call.