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A HIGH-RESOLUTION DIRECTION FINDING ALGORITHM FOR CELLULAR SYSTEMS

IP.com Disclosure Number: IPCOM000009162D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2002-Aug-12
Document File: 5 page(s) / 205K

Publishing Venue

Motorola

Related People

Ray Owen: AUTHOR

Abstract

Adaptive antennas and mobile subscriber based location are just two techniques that can involve the use of high-resolution direction finding algorithms such as MUSIC or ESPRIT. Angle of arrival infor- mation can give clues to the RF propagation channel characteristics enabling direction and/or weighting estimates to be utilized in location and beam steer- ing respectively.

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m MOTOROLA

A HIGH-RESOLUTION DIRECTION FINDING ALGORITHM FOR CELLULAR SYSTEMS

by Ray Owen

INTRODUCTION

  Adaptive antennas and mobile subscriber based location are just two techniques that can involve the use of high-resolution direction finding algorithms such as MUSIC or ESPRIT. Angle of arrival infor- mation can give clues to the RF propagation channel characteristics enabling direction and/or weighting estimates to be utilized in location and beam steer- ing respectively.

THE PROBLEM

  Angle of arrival information can be used to detect the constituent multipath effects in the chan- nel and/or to detect co-channel interferers. In many urban cellular systems the cell-site re-use is the capacity limiting factor with up to 2 or more chan- nel propagation induced multipath components and 2 or more interfering mobiles in adjacent cells. Adaptive antennas can be used to place nulls at the interfering mobiles and lobes at the wanted mobiles and thus improve the muse factor and consequently system performance. However an assumption is made that it is possible to detect the multipath and adjacent user energy. Two multipath components per user and 2 interferes would require at least 5 anten- na elements to distinguish the 4 arriving energy sources. There are many techniques that can be used to estimate the arriving angle of arrival of radio frequency energy at a linear array. Two of the most common methods are to estimate the energy in a given direction by 'looking' or applying a 'steering vector' to the received power at a linear array. When the steering vector phase matches the incom- ing phase across the array elements a maximal ener- gy peak occms. This technique has limited resolu- tion proportional to the number of elements in the array. Typically cellular systems at the PCS fre-

quencies can accommodate no more than 4-8 ele- ments before the environmental/physical size of the panel antennas becomes unacceptable.

  A second approach to obtain more AOA resolu- tion is to use a high-res,olution approach such as MUSIC or ESPRIT. These approaches rely on the co-variance matrix and its constituent Eigen analysis to be able to achieve relatively high resolution with a limited number of antenna elements. Simplifying the mathematics the NxN co-variance matrix, where N is the number of antenna elements in a panel, can be broken down into two orthogonal Eigen-spaces: the first being the noise Eigen-values and the second being the signal Eigen-values. Provided both are separable then much higher resolution can be achieved. See Figure 1.

  However this approach suffers from two major practical drawbacks in cellular systems:

1) The number of impinging signal somces at the array must be known in' advance of applying the high-resolution algorithm. This is equivalent to say- ing that the separation between defming the signal and noise Eigen-values must be estimated or known in advance. Typically numerical source estimation techniques can be used such as t...