An efficient data transmission policy in an integrated voice-data ds-cdma network

CDMA schemes appear to be promising access techniques for coping with the requirements of third-generation mobile systems, mainly because of their flexibility. This paper proposes an adaptive S-ALOHA DS-CDMA access scheme as a method for integrating non-real time (i.e. Internet applications) and real-time (i.e. voice) services, by exploiting the potentials of CDMA under time-varying conditions. The adaptive component terminals autonomously change their transmission rate according to the total (voice+data) channel occupancy, so that the minimum possible data delay is almost always achieved.Peer ReviewedPostprint (published version

A mobile controlled algorithm for improving the throughput in a s-aloha ds-cdma system

This paper presents a novel adaptive DS-CDMA slotted-ALOHA packet random access scheme with transmitter-based spreading codes for mobiles. It is aimed at improving the throughput and message delay delivery when traffic load values below the saturation point of the conventional DS-CDMA slotted-ALOHA system are sensed in the channel. For this purpose a mobile assisted algorithm is envisaged to control the change of the transmission rate according to the traffic load. This algorithm revealed that the optimum behavior, obtained using a Markov chain model, may be almost reached at a low complexity cost. Moreover, priorities between mobiles could be easily established. Finally, a traffic model based on a realistic statistical length distribution of the messages illustrates how the delay delivery can be greatly reduced.Peer ReviewedPostprint (published version

Adaptive algorithms for improving the throughput in an indoor mobile s-aloha ds-cdma system

This paper presents a novel Adaptive DSCDMA Slotted-ALOHA packet random access scheme with transmitter-based spreading codes for mobiles. It is aimed at improving the throughput and message delay delivery when traffic load values below the saturation point of the conventional DS-CDMA Slotted-ALOHA system are sensed in the channel. For this purpose, one Mobile and two Base Station assisted algorithms are envisaged to control the change of the transmission rate according to the traffic load. These algorithms revealed that the optimum behavior, obtained using a Markov Chain model, may be almost reached at a low complexity cost.Peer ReviewedPostprint (published version

Energy-efficient wireless communication

In this chapter we present an energy-efficient highly adaptive network interface architecture and a novel data link layer protocol for wireless networks that provides Quality of Service (QoS) support for diverse traffic types. Due to the dynamic nature of wireless networks, adaptations in bandwidth scheduling and error control are necessary to achieve energy efficiency and an acceptable quality of service. In our approach we apply adaptability through all layers of the protocol stack, and provide feedback to the applications. In this way the applications can adapt the data streams, and the network protocols can adapt the communication parameters

A Mobile Satellite Experiment (MSAT-X) network definition

The network architecture development of the Mobile Satellite Experiment (MSAT-X) project for the past few years is described. The results and findings of the network research activities carried out under the MSAT-X project are summarized. A framework is presented upon which the Mobile Satellite Systems (MSSs) operator can design a commercial network. A sample network configuration and its capability are also included under the projected scenario. The Communication Interconnection aspect of the MSAT-X network is discussed. In the MSAT-X network structure two basic protocols are presented: the channel access protocol, and the link connection protocol. The error-control techniques used in the MSAT-X project and the packet structure are also discussed. A description of two testbeds developed for experimentally simulating the channel access protocol and link control protocol, respectively, is presented. A sample network configuration and some future network activities of the MSAT-X project are also presented

Interference-Based Optimal Power-Efficient Access Scheme for Cognitive Radio Networks

In this paper, we propose a new optimization-based access strategy of multipacket reception (MPR) channel for multiple secondary users (SUs) accessing the primary user (PU) spectrum opportunistically. We devise an analytical model that realizes the multipacket access strategy of SUs that maximizes the throughput of individual backlogged SUs subject to queue stability of the PU. All the network receiving nodes have MPR capability. We aim at maximizing the throughput of the individual SUs such that the PU's queue is maintained stable. Moreover, we are interested in providing an energy-efficient cognitive scheme. Therefore, we include energy constraints on the PU and SU average transmitted energy to the optimization problem. Each SU accesses the medium with certain probability that depends on the PU's activity, i.e., active or inactive. The numerical results show the advantage in terms of SU throughput of the proposed scheme over the conventional access scheme, where the SUs access the channel randomly with fixed power when the PU is sensed to be idle

Channel-Aware Random Access in the Presence of Channel Estimation Errors

In this work, we consider the random access of nodes adapting their transmission probability based on the local channel state information (CSI) in a decentralized manner, which is called CARA. The CSI is not directly available to each node but estimated with some errors in our scenario. Thus, the impact of imperfect CSI on the performance of CARA is our main concern. Specifically, an exact stability analysis is carried out when a pair of bursty sources are competing for a common receiver and, thereby, have interdependent services. The analysis also takes into account the compound effects of the multipacket reception (MPR) capability at the receiver. The contributions in this paper are twofold: first, we obtain the exact stability region of CARA in the presence of channel estimation errors; such an assessment is necessary as the errors in channel estimation are inevitable in the practical situation. Secondly, we compare the performance of CARA to that achieved by the class of stationary scheduling policies that make decisions in a centralized manner based on the CSI feedback. It is shown that the stability region of CARA is not necessarily a subset of that of centralized schedulers as the MPR capability improves.Comment: The material in this paper was presented in part at the IEEE International Symposium on Information Theory, Cambridge, MA, USA, July 201

Adaptive S-ALOHA CDMA as an alternative way of integrating services in mobile environments

Code-division multiple-access (CDMA) schemes appear to be very promising access techniques for coping with the requirements of third-generation mobile systems, mainly because of their flexibility. This paper proposes an adaptive S-ALOHA DS-CDMA access scheme as a method for integrating nonreal-time (i.e., Internet applications) and real-time (i.e., voice) services in a multicell scenario by exploiting the potentials of CDMA under time-varying channel load conditions. The adaptive component makes data terminals autonomously change their transmission rate according to the total (voice+data) channel occupancy, so that the minimum possible data delay, which can be analytically obtained by defining a birth-death process, is almost always achieved. Moreover, by means of a simplified cellular model, the proposed algorithm revealed the same behavior, i.e., it tries to select the most suitable transmission rate at any time slot, when it is affected by intercell interference and even by power control imperfections. Finally, in order to gain more insight into the potentials of such an access strategy, the adaptive S-ALOHA CDMA scheme is then compared to a reservation time-division multiple-access (TDMA)-based protocol (PRMA++), showing the benefits of the CDMA-based solution in terms of capacity, flexibility, and data delay performance.Peer Reviewe

Optimal Spectrum Access for Cognitive Radios

In this paper, we investigate a time-slotted cognitive setting with buffered primary and secondary users. In order to alleviate the negative effects of misdetection and false alarm probabilities, a novel design of spectrum access mechanism is proposed. We propose two schemes. First, the SU senses primary channel to exploit the periods of silence, if the PU is declared to be idle, the SU randomly accesses the channel with some access probability $a_s$. Second, in addition to accessing the channel if the PU is idle, the SU possibly accesses the channel if it is declared to be busy with some access probability $b_s$. The access probabilities as function of the misdetection, false alarm and average primary arrival rate are obtained via solving an optimization problem designed to maximize the secondary service rate given a constraint on primary queue stability. In addition, we propose a variable sensing duration schemes where the SU optimizes over the optimal sensing time to achieve the maximum stable throughput of the network. The results reveal the performance gains of the proposed schemes over the conventional sensing scheme. We propose a method to estimate the mean arrival rate and the outage probability of the PU based on the primary feedback channel, i.e., acknowledgments (ACKs) and negative-acknowledgments (NACKs) messages.Comment: arXiv admin note: substantial text overlap with arXiv:1206.615