Ultra-wideband (UWB) transmission is an emerging wireless communication technology that is gaining significant interest for future broadband wireless access. This transmission technique based mainly on the Impulse-Radio (IR) paradigm, has the potential to deliver high-speed wireless connectivity at low power and low proximity, characteristics that makes it an ideal choice for wireless sensor networks (WSNs). The distinct physical layer properties call, however, for innovative solutions at the medium access control (MAC) layer. Various MAC protocols with different objectives were proposed for these pulse-based networks. In this article, we first outline the issues related to MAC layer design relying on an IR-UWB physical layer. Then, we describe several MAC protocols emphasizing their strengths and weaknesses. Finally, we identify the cross-layer dependencies between the specified physical and the higher layers of the communication stack and investigate open research issues.
In wireless communications networks with multiple service classes (SCs) of calls, Call Admission Control (CAC) schemes is an essential radio resource management (RRM) function for networks consistency. Apart from the calculation of the call blocking probability (CBP) appropriate criteria and metrics should be considered to evaluate the efficiency of various schemes. Fairness among different services is an important efficiency criterion for CAC in wireless networks with multimedia services while throughput is an efficiency criterion of general validity. In the present paper, four CAC schemes based on guard channel algorithms are proposed for multiclass services, offering priority to real time service class calls while ensuring a certain level of Quality of Service (QoS). The proposed schemes investigate the CAC problem in terms of ongoing users and occupied channels. Fairness among calls of different classes is evaluated and the network performance is compared with respect to input load.
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