Packet access in wireless CDMA networks

The research focus of this dissertation is on random access methods for wireless networks, so called pocket radio; and it is of particular interest to study random access methods in code division multiple access (CDMA) networks. The contents falls into two parts. The first part includes a study of channel fading-incurred capture effect on slotted Aloha (S-Aloha) in cellular systems and a reduced-rate retransmission (RRR) protocol for S-Aloha. The second part focuses on packet access problems for third generation (3G) wireless networks. A performance improvement scheme for random access channel (RACH) in wideband CDMA (WCDMA) systems is developed.; S-Aloha is widely implemented in wireless packet networks as a multiple access scheme. Due to fading in wireless channels, S-Aloha possesses capture effect, that is, a strong signal overrides others and is correctly received from out of the interference. In our work, the capture effect in S-Aloha systems due to Nakagami fading channels and with the presence of in-cell as well as cochannel-cell interference is investigated. Both synchronized and asynchronous cochannel cells are considered. The analysis gives the system throughput as a function of channel fading parameters and network traffic toad. Certain additional system parameters are also examined including the cellular cluster size.; The RRR protocol is proposed for improving the throughput performance of packet radio networks in high traffic region. It assumes that several versions of a data packet of different sizes are available. The transmission of a packet starts from its full-size version. If the full-size version is not correctly received, then the half-size version is used in retransmission. Since the reduction of packet size reduces effective multiple access interference, the system throughput can be increased. This improvement is especially significant for CDMA systems in which the throughput is "softly" dependent on the interference level. The RRR protocol is suitable for multimedia applications for which codes of variable rate for the source data are possible and which can tolerate gracefully degraded quality of service.; RACH is a variant of multichannel Aloha for WCDMA systems. Our improvement to RACH is based on the idea to expand the access preamble (AP) set. The method is to let a mobile station modulate a random sequence on the AP. The random sequence is bounced back from the base station together with the acknowledgment signal. Only that mobile station whose AP is acknowledged and random sequence coincides the one bounced back obtains access to the message channel. Since it is less probable that two or more mobile stations happen to choose the same AP signature and identical random sequences, the probability of collisions in the message channel is greatly reduced and the channel throughput increased. The proposed scheme is fully compatible with the RACH signaling in the WCDMA standard.