End-to-end performance enhancement of W-CDMA mobile satellite systems for Web traffic

The performance of W-CDMA for third generation (3G) land mobile satellite systems for Web traffic is examined. It is assumed that the satellite channel is Rice-lognormal.; It is found that slow fading (due to low mobility) and power control error (due to uncompensated shadowing) inherits in mobile satellites severely degrades the performance of 3 G W-CDMA mobile satellite systems. Hence, a combination of powerful error correction and diversity techniques is proposed to enhance the performance of both the uplink and downlink of 3G W-CDMA mobile satellite systems for Web traffic.; The W-CDMA mobile satellite links must operate at low Eb/No, since they are power limited in the downlink while they are interference limited in the uplink. Thus, this work proposes different error correction and diversity schemes for the uplink and the downlink to minimize both the required Eb/No and fading margin in both links for enhanced performance.; A macrodiversity scheme is proposed for the downlink, which must be employed at the mobile Web terminal rather than at the satellite itself due to the space limitation on board the satellite. Meanwhile, a space-time transmit diversity (STTD) technique is examined for the uplink. The error correction techniques include turbo code for the downlink, convolutional code for the uplink, a radio link protocol (RLP) and interleaving. The RLP uses the same retransmission mechanism as that used in the IS-99 standard for terrestrial code division multiple access (CDMA) systems.; The use of convolutional coding instead of turbo coding in the uplink is justified by the fact that the uplink operates at low data rate (i.e. 12.5 kbps), as it will be used to carry only TCP acknowledgements and HTTP object requests. It is known that at such low data rates the performance of convolutional code outperforms that of turbo code, it is also due to the fact that convolutional decoding is much simpler to implement especially on board the satellite. The use of STTD diversity in the uplink instead of macrodiversity is due to the fact that macrodiversity cannot be employed on board the satellite due to the space limitation as explained earlier.; This research has shown that the use of diversity techniques and especially macrodiversity in the downlink greatly enhances the Web traffic capacity of 3 G W-CDMA mobile satellite systems in the presence of major degradation factors such as slow fading and power control errors. On the basis of this work, it is strongly recommended that diversity techniques be employed as an essential and integral part of the satellite component of the universal mobile telecommunication services (UMTS). This improvement in performance will also lead to significant reduction in the channel operational cost, which represents a major challenge in the deployment of the satellite component of UMTS.