In this paper, we discuss the implementation of Linear Constrained
Minimum Variance (LCMV) beamforming (BF) for a novel Wireless Local
Position System (WLPS). WLPS main components are: (a) a dynamic
base station (DBS), and (b) a transponder (TRX), both mounted on
mobiles. WLPS might be considered as a node in a Mobile Adhoc
NETwork (MANET). Each TRX is assigned an identification (ID) code.
DBS transmits periodic short bursts of energy which contains an ID
request (IDR) signal. The TRX transmits back its ID code (a signal
with a limited duration) to the DBS as soon as it detects the IDR
signal. Hence, the DBS receives non-continuous signals transmitted
by TRX.
In this work, we assume asynchronous Direct-Sequence Code Division
Multiple Access (DS-CDMA) transmission from the TRX with antenna
array/LCMV BF mounted at the DBS, and we discuss the implementation
of the observed signal covariance matrix for LCMV BF. In LCMV BF,
the observed covariance matrix should be estimated. Usually sample
covariance matrix (SCM) is used to estimate this covariance matrix
assuming a stationary model for the observed data which is the case
in many communication systems. However, due to the non-stationary
behavior of the received signal in WLPS systems, SCM does not lead
to a high WLPS performance compared to even a conventional
beamformer. A modified covariance matrix estimation method which
utilizes the cyclostationarity property of WLPS system is introduced
as a solution to this problem. It is shown that this method leads to
a significant improvement in the WLPS performance.
A novel wireless local positioning system (WLPS) for airport (or indoor) security is introduced. This system is used by airport (indoor) security guards to locate all of, or a group of airport employees or passengers within the airport area. WLPS consists of two main parts: (1) a base station that is carried by security personnel; hence, introducing dynamic base station (DBS), and (2) a transponder (TRX) that is mounted on all people (including security personnel) present at the airport; thus, introducing them as active targets. In this paper, we (a) draw a futuristic view of the airport security systems, and the flow of information at the airports, (b) investigate the techniques of extending WLPS coverage area beyond the line-of-sight (LoS), and (c) study the performance of this system via standard transceivers, and direct sequence code division multiple access (DS-CDMA) systems with and without antenna arrays and conventional beamforming (BF).
A smart antenna with a carefully controlled time-varying beam pattern can create a channel with a small coherence time. This small channel coherence time can be used by the mobile station to achieve time diversity benefit, thereby enhancing performance. In this work, the coherence time induced by antenna arrays with time-varying beam-patterns is evaluated using the so-called geometric-based stochastic channel model (GSCM). Here, we assume a circular coverage area in an urban environment and we treat buildings (or parts of buildings) as point scatterers (dimensionless). We demonstrate a relationship between coherence time and antenna array control parameters, and show that 9-fold-time diversity can be created via time-varying beam patterns.
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