John A. Asenstorfer

Iterative multiuser detection for CDMA with FEC: near-single-user performance

This paper introduces an iterative multiuser receiver for direct sequence code-division multiple access (DS-CDMA) with forward error control (FEC) coding. The receiver is derived from the maximum a posteriori (MAP) criterion for the joint received signal, but uses only single-user decoders. Iterations of the system are used to improve performance, with dramatic effects. Single-user turbo code decoders are utilized as the FEC system and a complexity study is presented. Simulation results show that the performance approaches single-user performance even for moderate signal-to-noise ratios.

Iterative multiuser interference reduction: turbo CDMA

We view the asynchronous random code division multiple-access (CDMA) channel as a time-varying convolutional code. We study the case where the users encode their data, and, therefore, the single user transmitters and the CDMA channel appear as the concatenation of two coding systems. At the receiver we employ serial turbo decoding strategies. Unlike conventional turbo codes where both the inner and outer code may be selected, in our case, the inner code is due to the CDMA channel which we assume to be random. Nevertheless, the decoding system resembles the decoder of a serial turbo code and single-user performance is obtained even for numbers of users approaching the spreading code length.

Near single user performance using iterative multi-user detection for CDMA with turbo-code decoders

This paper discusses a code-division multiple access (CDMA) iterative multi-user receiver with forward error control (FEC) decoding. The maximum a-posteriori probability (MAP) criteria is used to derive the receiver. The decoding is done using a turbo-code decoder with modifications which are discussed. Iterations of the system are used to attain large performance improvements over conventional systems.

Modelling service time distribution in cellular networks using phase-type service distributions

Third generation mobile communication networks are designed to provide a variety of high data rate services with higher quality of service (QoS) than second-generation systems. Handover becomes one of the major problems in such a mobile environment as it is of utmost importance to provide a higher guarantee that the users are able to continue their service during the entire length of the transmission, without it being blocked during the handover or loss of quality or data. Careful dimensioning of the network and the underlying teletraffic analysis plays a major role in determining the various grade of service (GoS) parameters that service providers can provide at various network loads. The channel holding time of a cell is one of the major parameters that needs to be accurately modelled in the teletraffic analysis. This paper focuses on using phase-type distributions of generalised Erlang form to model channel holding time in a mobile environment. We also present the quasi-birth-death process, which characterises the queuing models with generalized Erlang service and exponential inter-arrival distributions. Further we investigate the use of channels exclusively reserved for handover users to improve the handover performance.

Performance of multi-carrier CDMA with iterative detection

We consider a matrix algebraic approach to describe the multi-carrier CDMA (MC-CDMA) system with forward error control coding. We consider the uplink of a mobile communications system and derive the frequency selective channel model and show its similarity with the DS-CDMA channel. We therefore take advantage of a previously published technique that combines iterative decoding and interference cancellation to reduce the multiuser interference (MUI) present in the system and show that the performance approaches single user performance even for moderate signal to noise ratios.

Performance of multi-carrier CDMA with iterative detection for a Doppler shift channel in a LEO mobile-satellite communications environment

In this paper we consider a matrix algebraic approach to derive the coded multi-carrier CDMA (MC-CDMA) system model for a Doppler shift channel. We derive the effects of Doppler shift in a MC-CDMA system for low earth orbit (LEO) mobile-satellite communications and show the similarity of a MC-CDMA channel model under Doppler shift with that of the asynchronous DS-CDMA channel model. We therefore take advantage of a recently proposed technique that combines iterative decoding and interference cancellation in asynchronous DS-CDMA to reduce the multiuser interference and thereby improve the performance of the Doppler shift channel. We show that the performance approaches single user performance even for moderate signal to noise ratio.

Mobility supported by IN in UMTS/B-ISDN

Mobility functions such as personal mobility, terminal mobility, location management and handover control are primary tasks for mobile networks. The next generation mobile network, is proposed to be integrated and become a part of the fixed network. Therefore the fixed network must be able to handle such mobile-specific functions. Intelligent network (IN) could be one of the solutions for integration between mobile and fixed networks. By using the intelligent network concept, a mobility function could be viewed as a type of IN service. Each mobility function could be implemented in a modular way, separated from switches and implemented at the IN service control point. This will avoid switch-by-switch upgrading and reduce switch complexity and cost. In this paper, we describe how the IN could be placed on top of the mobile and fixed network to provide mobility functions.

Congestion control in a CDPA based multimedia network

Future mobile communications have to support multimedia services, operate in multi-cell environments and be able to operate in a multi-operator environments. Towards this end they have to maximise the utilisation of limited spectrum resources while trying to maintain quality of service (QoS) as demanded by multimedia services. This paper focuses on the support of multimedia services and guarantees QoS for these services through efficient call admission control (CAC), media access control (MAC) and related services, which avoid situations of congestion in the air media. Hence we define a congestion control entity (CCE) which enhances the operation of MAC and CAC. By assisting CAC to make an intelligent decision as to whether to admit a call or not we avoid the situation which leads to congestion. By controlling media access among a number of contending users we can implement congestion control by two means. One is by sensing or predicting situations leading to congestion from the present status of traffic and buffer availability; the other scheme is reactive and implements recovery from near congestion situations.