Issues in DS-CDMA integrated wireless access networks
Date
1997
Authors
Annamalai, Annamalai Jr.
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Abstract
A consequence of the exploding demand for wireless multimedia services is the need to provide a large number of heterogeneous users with various quality requirements, despite the scarcity in the radio spectrum. In light of these considerations, this dissertation addresses three issues pertaining to integrated wireless access networks which use code division multiple access with direct-sequence modulation.
We first assess the performance of a :flexible multi-chip rate multi-processing gain DS-CDMA system architecture which supports teletraffic of different information rates via different spreading bandwidths. This evaluation is particularly important due to the anticipated evolution path of the IWAN architecture from currently proposed 1.25 MHz to wider spreading bandwidths. In addition, we provide a method to efficiently integrate multimedia traffic while ensuring downward compatibility.
Subsequently, we develop an analytical framework to evaluate the performance of different pre-detection diversity techniques in various mobile radio environments. As an example, antenna diversity reception of spread-spectrum signals is illustrated. It is shown that diversity reception is effective for combatting the deep fades experienced on wireless channels. Besides, in an interference hampered network, mitigation of channel fading through the use of diversity can translate into improved interference tolerance. This in turns means greater ability to support additional users, and therefore higher system capacity.
Finally, we devise a simple packet combining mechanism that will enhance the system throughput and delay characteristics of slotted DS-CDMA packet radio networks. Emphasis is placed on improving the system performance without incurring a substantial penalty in terms of implementation complexity or cost. Moreover, the proposed S+I selection scheme is well suited for high data rate transmissions because accurate measurements of the signal-to-noise ratio becomes difficult or expensive.