Capture effects in spread-aloha packet protocols.

Abstract

Research in the field of random access protocols for narrow-band systems started as early as the 1970s with the introduction of the ALOHA protocol. From the research done in slotted narrow-band systems, it is well known that contention results in all the packets involved in the contention being unsuccessful. However, it has been shown that in the presence of unequal power levels, ore of the contending packets may be successful. Ibis is a phenomenon called capture. Packet capture has been shown to improve the performance of slotted narrow-band systems. Recently, much work has been done in the analysis of spread-spectrum ALOHA type code-division multiple access (CDMA) protocols. The issue of designing power control techniques to improve the performance of CDMA systems by reducing multiple access interference (MAl) has been a subject of much research. It has been shown that in the presence of power control schemes, the performance of spread-ALOHA CDMA systems is improved. However, it is also widely documented that the design of power control schemes capable of the ideal of compensation of radio propagation techniques is not possible for various reasons, and hence the imperfections in power control. None of the research known to the author has looked at capture in spread-ALOHA systems, and to a greater extent, looked at expressions for the performance of spreadALOHA systems in the presence of capture. In this thesis we introduce spread-ALOHA systems with capture as a manifestation of the imperfections in power control. We propose novel expressions for the computation of the perfonnance ofspread-ALOHA systems with capture.