165,415 research outputs found
Space-time processing for wireless mobile communications
Intersymbol interference (ISI) and co-channel interference (CCI) are two major
obstacles to high speed data transmission in wireless cellular communications
systems. Unlike thermal noise, their effects cannot be removed by
increasing the signal power and are time-varying due to the relative motion
between the transmitters and receivers. Space-time processing offers a signal
processing framework to optimally integrate the spatial and temporal properties
of the signal for maximal signal reception and at the same time, mitigate
the ISI and CCI impairments. In this thesis, we focus on the development of
this emerging technology to combat the undesirable effects of ISI and CCL
We first develop a convenient mathematical model to parameterize the
space-time multipath channel based on signal path power, directions and
times of arrival. Starting from the continuous time-domain, we derive compact
expressions of the vector space-time channel model that lead to the
notion of block space-time manifold, Under certain identifiability conditions,
the noiseless vector-channel outputs will lie on a subspace constructed from
a set. of basis belonging to the block space-time manifold. This is an important
observation as many high resolution array processing algorithms Can be
applied directly to estimate the multi path channel parameters.
Next we focus on the development of semi-blind channel identification
and equalization algorithms for fast time-varying multi path channels. Specifically.
we develop space-time processing algorithms for wireless TDMA networks that use short burst data formats with extremely short training data.
sequences. Due to the latter, the estimated channel parameters are extremely
unreliable for equalization with conventional adaptive methods. We approach
the channel acquisition, tracking and equalization problems jointly, and exploit
the richness of the inherent structural relationship between the channel
parameters and the data sequence by repeated use of available data through a forward- backward optimization procedure. This enables the fuller exploitation
of the available data. Our simulation studies show that significant performance
gains are achieved over conventional methods.
In the final part of this thesis, we address the problem identifying and
equalizing multi path communication channels in the presence of strong CCl.
By considering CCI as stochasic processes, we find that temporal diversity
can be gained by observing the channel outputs from a tapped delay line. Together with the assertion that the finite alphabet property of the information
sequences can offer additional information about the channel parameters and
the noise-plus-covariance matrix, we develop a spatial temporal algorithm,
iterative reweighting alternating minimization, to estimate the channel parameters
and information sequence in a weighted least squares framework.
The proposed algorithm is robust as it does not require knowledge of the
number of CCI nor their structural information. Simulation studies demonstrate
its efficacy over many reported methods
A Software-Defined Channel Sounder for Industrial Environments with Fast Time Variance
Novel industrial wireless applications require wideband, real-time channel
characterization due to complex multipath propagation. Rapid machine motion
leads to fast time variance of the channel's reflective behavior, which must be
captured for radio channel characterization. Additionally, inhomogeneous radio
channels demand highly flexible measurements. Existing approaches for radio
channel measurements either lack flexibility or wide-band, real-time
performance with fast time variance. In this paper, we propose a correlative
channel sounding approach utilizing a software-defined architecture. The
approach enables real-time, wide-band measurements with fast time variance
immune to active interference. The desired performance is validated with a
demanding industrial application example.Comment: Submitted to the 15th International Symposium on Wireless
Communication Systems (ISWCS 2018
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