Power control is essential in the use of direct-sequence code-division multiple-access (CDMA) techniques over fading radio channels. This paper investigates a feedback power control approach that allows power commands to be updated at a higher rate than the rate of multipath fading. The signal and interference statistics as received at the base stations after power control are obtained for a simulated CDMA system which includes multiple base stations with diversity receivers and a large number of power-controlled users continuously movmg at various speeds. We show that often-used analyses based on perfect average power control lead to optimistic capacity results (by 25 to 60 %) because interference is underestimated by 1 to 2 dB.
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Power control is essential in the use of directsequence code-division multiple-access (CDMA) techniques. Early system-level performance analyses of a CDMA approach to wireless mobile and personal communications have assumed the ability of power control to equalize the absolute signal powers of CDMA users received at each base station. This paper studies a more practical, although analytically more complicated, uplink power control technique that uses measurements of the received signal-to-interference ratio (SIR) instead. A combination of discrete-event link simulation and analysis of the obtained SIR statistics is used to explore the previously little-known behavior of a CDMA system using SIRbased power control and to obtain performance estimates for such a system under various operating assumptions. The overall results indicate that power control based on SIR has the potential for somewhat higher system performance than power control based on absolute signal strength assumed in the early analyses.
The Mobile IP (MIP) protocol for IP version 4 provides continuous Internet connectivity to mobile hosts.However, currently it has some drawbacks in the areas of survivability, performance, interoperability with protocols for providing QoS. We have proposed an alternative protocol, Mobile IP with Location Registers (MIP-LR), which overcomes some of these drawbacks and is closer to the "service node" database approach used in the Public Switched Telephone Network (PSTN): before launching a packet to the mobile host, the sender first queries a database, called the Home Location Register (HLR), to obtain the recipient's current location. MIP-LR is designed for operation in enterprise environments or within logical administrative domains.In this paper we focus on showing how MIP-LR enhances the survivability of MIP by eliminating some of the functions which MIP introduces for mobility support, allowing the HLR to be placed outside the mobile's home network in case the latter is particularly vulnerable, and replicating and distributing HLRs. We present two schemes for managing the multiple HLRs and enabling mobile and correspondent hosts to dynamically discover the addresses of the HLRs serving a given mobile host. The first scheme introduces a set of Translation Server (TS) databases while the second uses a form of quorum consensus based on the Triangle Lattice (TL); for the latter we present an enhanced protocol called the Optimistic TL (OTL). For both schemes we present algorithms for mobile host registration and packet delivery, protocols for recovery from HLR failures, and complexity analysis of the overhead involved.
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