Addressing key management in mobile multicast communication is currently a booming topic due to the convergence of wireless and mobile technologies. With the proliferation of multiple group based services that are possible to co-exist within a single network, mobile subscribers could subscribe to these services concurrently while ubiquitous. However, the existing group key management (GKM) protocols intend to secure group communication for just a single group service. The GKM approaches involve inefficient use of keys and huge rekeying overheads, hence unsuitable for multiple multicast group environments. In this paper, we propose a novel GKM protocol for multiple multicast groups, called slot based multiple group key management (SMGKM) scheme. SMGKM supports the movement of single and multiple members across a homogeneous or heterogeneous wireless network while participating in multiple group services with minimized rekeying transmission overheads. Unlike conventional GKM protocols, SMGKM protocol can mitigate one-affect-n phenomenon, single point of failure and investment pressure of signaling load caused by rekeying at the core network. Numerical analysis and simulation results of the proposed protocol show significant resource economy in terms of communication bandwidth overhead, storage overheads at the Domain Key Distributor (DKD), mobile receiver and Area Key Distributors while providing intense security.

Mobile multicast is recently becoming a hot research in the convergence of wireless and mobile technologies. With the emergence of various multicast-based services, multiple multicast groups are possible to exist within a single network, and mobile subscribers could subscribe to multiple groups concurrently. However, the existing group key management (GKM) protocols intend to secure group communication for just a single group service. The GKM approaches involve inefficient use of keys and huge rekeying overheads, hence unsuitable for multiple multicast group environments. In this paper, we propose a novel GKM protocol for multiple multicast groups, called slot based multiple group key management (SMGKM) scheme. SMGKM supports the movement of single and multiple members across a homogeneous or heterogeneous wireless network while participating in multiple group services with minimized rekeying transmission overheads. Unlike conventional GKM protocols, SMGKM protocol mitigates 1-affect-n phenomenon, single point of failure and investment pressure of signaling load at the core network. The results of the proposed protocol show resource economy in terms of communication bandwidth and storage overheads.

Security is a serious bottleneck for the future of VoIP. Because of the time-critical nature of VoIP most of the same security measures currently implemented in today's data networks could not be used in VoIP networks. Two main factors affect voice traffic over secure IP channels. The first is the time required to encrypt payload and headers and the construction of the new ones. The second is the increased packet size because of the headers added to the original IP packet. Techniques that could be adopted to overcome these two problems in addition to the compression QoS issues associated with audio codecs put more strain on end-point CPU's. In this paper we propose a new QoS control scheme that uses a simple protocol to detect the end-point CPU capabilities, and according to this information, we choose dynamically the most suitable techniques for the transmission of voice over a secure IP channel to provide a superior QoS control performance, in terms of perceived speech quality.

This paper addresses the problem of selecting the optimum training sequence for channel estimation in communication systems over time-dispersive channels. By processing in the frequency domain, a new explicit form of search criterion is found, the gain loss factor (GLF), which minimizes the variance of the estimation error and is easy to compute. Theoretical upper and lower bounds on the GLF are derived. An efficient directed search strategy and optimal sequences up to length 42 are given. These sequences are optimal only for frequency domain estimation, not for time domain estimation.

In order to fulfil the need of users in wireless ATM, the system has to acquire features. One of the system features for wireless ATM is functionality, especially the security aspect. There is so far little security consideration in developing wireless ATM standards. Therefore a wide range of features in security functions needs consideration. This paper tries to define the features of security in wireless ATM networks considering the features from existing fixed ATM networks and wireless network security functions. It does not attempt to define the cryptographic system, but rather provide a template in making a cryptographic system for those required features.

This paper uses some computational results to show that the peak envelope power (PEP) of orthogonal frequency-division multiplex (OFDM) waveforms can be reduced very substantially by coding to select only those messages with low peak factor as valid codewords in the scheme. It is shown that the asymptotic limit of the PEP is between two and three, and that only four bits of redundancy are necessary to limit the PEP to within 10% of this optimum value as the number of carriers becomes large.

This paper describes a new approach to the security of wireless ATM networks. Firstly, the generic wireless ATM model is summarised in terms of architectural principles. Then, a mapping from the fixed ATM network protocol stack to the wireless ATM equivalent is described. The provision of security services and facilities within the fixed ATM model is then covered. Finally, a migration methodology for mapping these security services to the wireless ATM environment is presented.

This paper presents an efficient key exchange protocol for cryptographically secure CDMA systems which uses no more than the single REQUEST-RESPONSE protocol of conventional systems. The protocol, based on the Diffie-Hellman scheme, makes synchronisation of the cryptographic spreading sequence easy and uses the existing cryptographic sequence generation hardware for the key protocol computations.

Hussain and Barton (see Seventh IEE European Conference on Mobile Personal Communications, p.95-98, 1993) have shown that noncoherent binary frequency shift keying (BFSK) is subject to an irreducible error rate in the presence of phase noise. This paper extends the analysis of the performance degradation caused by oscillator phase noise to non-coherent orthogonal M-ary frequency shift keying (MFSK). It is shown that for a given bit rate, a particular level of MFSK may prove more robust than others before being subject to an irreducible enter rate. Results are presented in the form of bit error rate (BER) versus Eb/No plots for M=2, 4, 8 and 16. The performance degradation for higher M can also be determined by this analysis.>