Proc. SPIE. 4865, Internet Performance and Control of Network Systems III
KEYWORDS: Signal to noise ratio, Modulation, Interfaces, Fourier transforms, Interference (communication), Receivers, Lab on a chip, Local area networks, Non-line-of-sight propagation, Standards development
The performance of direct-sequence code-division
multiple access (DS-CDMA) systems in indoor wireless channels
is presented. TCP traffic, channel noise and signal
characteristics are measured using commercial products
that implement the IEEE 802.11b DS-CDMA standard.
The measured throughputs for a
low density mobile network are typically around $4.2$ Mbps
when one of the two end-systems is on the wired segment.
Multipath interference is shown to contribute to significant
degradation in TCP performance. Packet loss rates ranging from $0.02$ to
$0.2$ percent are observed in line-of-sight conditions.
The BER performance of DS-CDMA is estimated using an image source
based channel model of the rectangular room to compute the spatial
variation of the channel impulse response. These impulse responses
provide a quantitative measure of the system performance and
provide estimates of signal power levels required for
supporting high data rates in channels influenced by multipath
Video services to the home are among the driving applications for emerging broadband networks. For residential services to be viable, video quality must be comparable to broadcast video. Video compression technology has well defined standards for high quality video (MPEG). Suitable video delivery techniques are however still under investigation. We consider the problem of delivering constant quality video using variable bit rate encoding. A traffic model is proposed for three different encoding types (H.261, MPEG2: one and two layer). These models are suitable for either stored or real-time video. The statistical multiplexing efficiency of these video sources and call admission based on leaky bucket traffic parameters are evaluated. Two layer encoding is shown to have significantly better statistical multiplexing gains than one-layer video, when the network admits calls based on a leaky-bucket characterization.
The scattering of acoustic waves from three dimensional compressible scatterers is considered. Particular attention is paid to cases where the scatterers have moderate magnitude in compressibility contrast and nondimensional wavenumber. A perturbation method based on Pade approximants is developed. It is shown that the Pade approximant model allows one to represent and evaluate the characteristic features such as internal resonances and mode shapes of the scattered pressure field. These modes are a function of the compressibility contrast and the frequency of the incident pressure wave. Numerical results are in agreement with the analytical solutions for scattering from a sphere.