Abstract We propose the notion of a Secure Virtual Point of Service (SVPOS) as a network‐centric transaction server that facilitates the enhancement of 3G cell phones with a ‘mobile wallet’ capability allowing 3G subscribers to use their cell phones (or, in fact, other preferred mobile gadgets) for their daily transactions and payments. This paper shows how to design an SVPOS and an associated operator/subscriber/merchant protocol for purchasing digital media content over 3G networks. The resulting protocol guarantees a number of desirable privacy and security properties, such as privacy/anonymity of 3G subscribers (i.e. no identities, credit information or credit card numbers are revealed by subscriber to merchants), and protection of 3G operator, merchant, subscriber against various types of malicious behaviour, including transaction repudiation. The proposed SVPOS is ‘built’ on top of the Hypertext Transfer Protocol (HTTP), utilizes the 3rd Generation Partnership Project (3GPP) Generic Authentication Architecture (GAA) for subscriber and merchant authentication, and has an implicit key distribution mechanism that easily provides necessary encryption keys for the novel non‐repudiation mechanism of SVPOS. It also sends the necessary records of the transactions to the accounting entity of the network for charging and billing through standard protocols (e.g. Parlay‐X). Copyright © 2008 John Wiley & Sons, Ltd.

The complementary characteristics of universal mobile telecommunication system (UMTS) and 802.11 wireless local area network (WLAN) networks make them attractive for integration to offer the best of both technologies. However to make their integration effective, seamless mobility between the two networks is necessary. In this paper we address mobility management procedures within and between UMTS and 802.11 WLAN for various integration scenarios. For each integration option we consider, we give the interaction between various networks elements and new procedures required to ensure seamless mobility.

High capacity real-time data communications in sensor networks usually require multihop routing and ad hoc routing protocols. Unfortunately, ad hoc routing protocols usually do not scale well and cannot handle dense situations efficiently. These two issues-scalability and density-are the major limitations when we apply ad hoc routing schemes to sensor networks. Passive clustering (PC) classifies ad hoc/sensor nodes into critical and noncritical nodes without any extra transmission. By 2-b piggybacking and monitoring user traffic (e.g., data polling requests from a sink), PC deploys the clustering structure "for free". Moreover, PC makes even the first flooding as efficient as all subsequent floodings (i.e., no initialization overhead). PC introduces many benefits, including efficient flooding and density adaptation. As a result, PC reduces control overhead of ad hoc routing protocols significantly and, as a consequence, enables ad hoc routing in large, dense sensor networks. The resulting structure can be utilized in cluster-based ad hoc network/sensor networking as well as for active node selection.

We report the performance of the CCITT standard G.721, adaptive differential pulse code modulation, when channel impairment causes erasure of frames of information. The structure of the G.721 decoder is analyzed to explain the behavior observed during frame erasures and when correct transmission is restored. Various techniques have been tried to the decoder when frames are lost and when correct transmission is restored. Though the decoder, at times, takes long to gain synchronism with the encoder, the amplitude of the output signal approaches the error-free output much more rapidly. This fast recovery of amplitude helps in reducing the impact on the perceptual quality of speech. From objective results and informal listening tests, it was found that simple silence substitution performs as well as other frame substitution techniques. Resetting the encoder and decoder simultaneously at the end of erasure is seen to improve the performance. Since silence substitution is the easiest to implement, this technique seems the most appropriate one for application to wireless communications. This work is targeted towards understanding the implications to local exchange networks of wireless system alternatives that could provide access to those networks.>

The authors present a real-time single DSP prototype of a 16-kb/s subband speech coder, using a single digital signal processor, for application to digital portable radio communications. The system architecture, coding algorithm, firmware, and hardware of this coder are addressed. Careful attention has been given to the many special design requirements for interfacing to a time-division multiple-access radio link. The coder uses nonlinear quantization improvement in speech quality with negligible added complexity. A single-board full-duplex prototype, based on a TMS320C25, has been designed and delivers good speech quality.>

Partial response continuous phase modulation (CPM) schemes have found wide acceptance because of their compact spectra and comparable performance with other traditional modulation schemes. Although optimum receivers are complex, simple suboptimum receivers are found to yield very good performance in special cases. Performance of such modulation schemes is of interest in a multiple user environment where adjacent channels are spaced closely to improve the system capacity. This paper presents the performance of partial response CPM in the presence of adjacent channel interference and Gaussian noise. The meansquare crosstalk in CPM systems employing MSK-type receivers is formulated. Based on this formulation, a number of modulation schemes employing different receiver filters are analyzed for their ACI rejection. Comparison of results proves that receiver filters, in addition to the spectral occupancy of the signal, play an important role in deciding the crosstalk. The error performance of various schemes evaluated using simulation technique is compared, and it is found that in the presence of adjacent channel interference, certain schemes perform better than minimum shift keying (MSK). The results of the simulation further prove the inadequacy of Gaussian assumption for the adjacent channel interference. It is seen that judicious choice of modulation scheme and receiver filter can result in better spectrum utilization.