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This paper studies the impact of voice traffic on the performance of packet data (PD) transmission in terrestrial trunked radio (TETRA) networks. Particular emphasis is given on the performance of applications characterized by occasionally transmitting small messages between a number of radio terminals and a fixed server while these terminals are also conducting group voice calls. Such applications are constantly increasing in TETRA networks, and so does the need to dimension and configure these networks to meet their reliability, delay, and loss requirements. However, the impact of group voice calls on PD transmission has not been sufficiently studied, and this constitutes the main motivation of our performance analysis. We present simulation results for a variety of practical scenarios, and we discuss how key performance indicators such as PD delay and loss rate are affected by the group call activity of the radio terminals. Our results can help in dimensioning and planning TETRA networks, particularly in determining the number of PD terminals that can be supported in a cell for a given traffic profile and for quality-of-service requirements. Index Terms--Land mobile radio cellular systems, land mobile radio data communication, mobile communication, packet radio.

The media access control (MAC)-layer performance of the cellular digital packet data (CDPD) forward channel is studied and a new technique to improve the performance is proposed. The study is based on a computer simulation model wherein a CDPD base station continuously transmits a sequence of packets to a CDPD mobile station. We consider a Rayleigh fading channel and demonstrate how the performance metrics are affected by the channel characteristics. At the reception stage, we consider both coherent and differential reception. We argue that the throughput at the MAC layer is affected not only by the error performance of the physical layer, but also by several design characteristics of the MAC layer, including the block length and the alignment between blocks and packets. We illustrate the block error rate, packet error rate, and throughput performance by simulation results, and we show how the receiver may discard data, which is correctly received but nevertheless useless. Our main conclusion is that the CDPD forward-channel performance could be significantly improved should the identified deficiencies are eliminated. For this purpose, we propose a new automatic repeat request (ARQ) protocol that operates in the MAC layer to correct the erroneous blocks by means of retransmissions, and we study its performance. In addition, we discuss an adaptive scheme that maximizes the forward-channel performance by automatically enabling and disabling the ARQ protocol according to the channel conditions. Index Terms--Cellular digital packet data (CDPD), coherent detection, differential detection.

In this paper a new protocol is proposed for reducing the power consumption of the battery-powered terminals in a mobile computing environment. We exploit the fact that, in a mobile data network mobile terminals do not continuously receive data and therefore they need not continuously operate their receivers. Nevertheless, they need to periodically check their traffic condition, that is, whether there are pending data for them or not. The proposed energy-efficient protocol is based on a paging procedure wherein a dedicated channel is used to alert (page) the terminals with pending traffic. Each terminal may check its traffic condition whenever it decides to by monitoring the paging channel. The protocol is evaluated through an approximated theoretical model and through computer simulation. We focus on deriving approximate formulas for the mean message delay, the message delay variance and the power consumption. It is shown that the proposed protocol can achieve considerable power saving at a cost of increased message delivery delay. Index Terms--Energy-conserving protocol, energy consumption, energy saving, mobile data networks, power saving, protocol analysis, wireless communications.

This paper deals with the process of constructive and destructive addition of multipath signals in a Rayleigh fading channel. It derives closed formulas associating the number of multipaths with the Rayleigh statistics of the channel and it displays the accuracy of these formulas by means of simulation. The primary conclusion is that multipaths add constructively with high probability, thus the more the multipaths the larger the mean power level experienced at the receiver. In this context, multipath propagation exhibits a beneficial property that could be exploited for designing improved performance receivers. Index terms - Multipath combining, Multipath fading, Rayleigh fading, Mobile channels.

This paper presents the theoretical analysis of a downlink MAC protocol, which features power-saving characteristics and has been previously proposed [3], [7] for implementation in mobile data networks. The main objective of the protocol is to conserve valuable battery energy at the portable terminals of a wireless network. To accomplish this, the terminals employ discontinuous reception, i.e., they periodically power on and off their receive units. The key feature of the protocol, which makes it different from the other power-saving alternatives, is that it does not require system synchronization so the terminals are free to turn on and off their receivers based on their own necessities. The paper discusses the main properties of this protocol and develops a theoretical framework to approximate its performance. Theoretical results for the mean downlink packet delay as well as for the mean downlink power consumption are derived, and these results are compared against simulation outcomes in order to estimate their validity. The main conclusions are that the considered power-saving protocol features great potentials and can be easily implemented and that the developed theoretical model provides an acceptable theoretical tool for its analysis. Index Terms--Energy consumption, energy saving, mobile data networks, power management, power saving, protocol analysis, wireless communications.