Smart antenna, the technology of future
Dr Md Abdul Matin | Monday, 2 March 2009
BY enhancing the communication capacity of cellular phone, smart antenna promoted research and development of this exciting technology. Either a fixed or adaptive antenna array is used in wireless communication to improve the service range and reduce interference. With the development of cellular mobile communication they first appeared in AMPS (IS-41) systems several years ago. The limited capacity analog cellular AMPS system is being replaced by more advanced digital cellular CDMA system in some parts of the USA. With the introduction of PCS frequencies, GSM and CDMA technologies are making giant strides in commercial wireless markets across the world. Smart antenna for CDMA, not commercially available on the cellular/PCS market now, is expected to be available in the near future. This paper gives an overview of some general concepts for Smart antennas with focus on the possibility of their applications for CDMA technology.
There is a principal difference between CDMA and other cellular/PCS standards that make it impossible to implement the same type, or equivalent, solution for Smart antennas for CDMA as it is implemented in AMPS (IS-41) or TDMA (IS-54) standards. Namely, in AMPS systems each user occupies a narrow (30 kHz) bandwidth (RF channel) within given cellular bandwidth (12.5 MHz, per link per block) all the time the user is active, making it easy for the Smart antenna to discriminate the particular users' signal against other users' signals (interferors) by simply filtering out the frequency of the user.
In the TDMA system, several users may occupy the same RF channel, but they transmit their signal in bursts, so they are distinguished by different time slots within an RF channel. The time slot synchronisation and their time alignment is controlled by a base station. Therefore, the TDMA Smart antenna system can single out particular user by filtering out RF channel in use within cellular bandwidth, and synchronise its signals with the mobile transmit bursts. The Smart antenna system takes advantage of discretisation of the RF signal in frequency (AMPS) or frequency and time (TDMA), to preprocess the signal on RF level before it gets to a base station radio. Those types of applications are called 'add ons' or 'appliqu
There is a principal difference between CDMA and other cellular/PCS standards that make it impossible to implement the same type, or equivalent, solution for Smart antennas for CDMA as it is implemented in AMPS (IS-41) or TDMA (IS-54) standards. Namely, in AMPS systems each user occupies a narrow (30 kHz) bandwidth (RF channel) within given cellular bandwidth (12.5 MHz, per link per block) all the time the user is active, making it easy for the Smart antenna to discriminate the particular users' signal against other users' signals (interferors) by simply filtering out the frequency of the user.
In the TDMA system, several users may occupy the same RF channel, but they transmit their signal in bursts, so they are distinguished by different time slots within an RF channel. The time slot synchronisation and their time alignment is controlled by a base station. Therefore, the TDMA Smart antenna system can single out particular user by filtering out RF channel in use within cellular bandwidth, and synchronise its signals with the mobile transmit bursts. The Smart antenna system takes advantage of discretisation of the RF signal in frequency (AMPS) or frequency and time (TDMA), to preprocess the signal on RF level before it gets to a base station radio. Those types of applications are called 'add ons' or 'appliqu