WO2000002329A1 - Method for decreasing fading in a telecommunication system - Google Patents

Method for decreasing fading in a telecommunication system Download PDF

Info

Publication number
WO2000002329A1
WO2000002329A1 PCT/SE1999/001226 SE9901226W WO0002329A1 WO 2000002329 A1 WO2000002329 A1 WO 2000002329A1 SE 9901226 W SE9901226 W SE 9901226W WO 0002329 A1 WO0002329 A1 WO 0002329A1
Authority
WO
WIPO (PCT)
Prior art keywords
loss
base station
lobes
path
lobe
Prior art date
Application number
PCT/SE1999/001226
Other languages
French (fr)
Inventor
Per Zetterberg
Original Assignee
Radio Design Innovation Tj Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Radio Design Innovation Tj Ab filed Critical Radio Design Innovation Tj Ab
Priority to AU49499/99A priority Critical patent/AU4949999A/en
Publication of WO2000002329A1 publication Critical patent/WO2000002329A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W48/00—Access restriction; Network selection; Access point selection
    • H04W48/20—Selecting an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0408—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas using two or more beams, i.e. beam diversity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/24—Cell structures

Definitions

  • the present invention relates to a method for reducing fading in a telecommunication system, and more particularly the down-link fading in a mobile 0 telecommunication system having transmit lobe diversity.
  • the signal strength is often subject to so called Rayleigh fading, i.e. rapid changes with deep dips caused by multiple path propagation in a changing environment.
  • the purpose of the invention is to eliminate this problem in the down-link direction, i.e. in the communication from the base station to the mobile 5 station. The result is an improved link performance which can be traded for coverage, and capacity improvement as well as reduced power consumption.
  • the invention combines measurements in the up-link as well as the downlink for respectively selecting a set of lobes and a communication lobe.
  • the base station measures the average path-loss while the mobile station measures the 0 instantaneous path-loss between the base station and the mobile terminal.
  • antenna diversity techniques are based on the idea of 5 creating several independent channels. By selecting the best or by combining the channels, the probability of a deep fade can be made small. Most antenna diversity techniques are implemented at the receiver while only a few are implemented at the transmitter. For down-link, i.e. base to mobile communication, transmit diversity techniques are favourable since they put most of the complexity on the 0 base station, where higher costs generally can be tolerated.
  • Prior art transmit diversity techniques include delayed signal transmission and antenna array transmission with feed back. Delayed signal transmission has the drawback of increasing the channel delay spread and requiring complex channel equalisation techniques at the receiving end.
  • Array transmission with feedback is 5 an attractive alternative.
  • US 5,634,199 discloses a method for using feedback to reduce cross-talk between mobile receivers in a wireless communications system comprising an adaptive transmitting antenna array.
  • US 5,471,647 discloses a method for using feedback signals to optimise the directional properties of information signals with respect to their intended receivers, where information 0 signals are applied to the transmitting elements of a transmitting antenna array. These methods are based solely on feedback of measurement data resulting in high feedback rates.
  • the present invention take advantage of measurements in the up-link signals as well as mobile feedback to gauge the antenna patterns. This significantly reduces the feedback data rates which are otherwise to high to be practical.
  • the present invention provides a method for decreasing fading in a telecommunication system comprising at least one base station having an antenna array providing lobe diversity, and communicating with mobile terminal units.
  • the average path-loss between the base station and a mobile terminal unit is measured in order to select a set of alternative lobes.
  • the instantaneous path-loss between the base station and the mobile terminal unit is also measured in order to select a communication lobe.
  • Figure 1 is a schematic illustration of various multipaths between a base station and a mobile station using a set of lobes in accordance with the invention.
  • FIG. 1 there is shown a base station (BS) transmitting to a mobile station (MS).
  • BS base station
  • MS mobile station
  • One possible path is represented by a solid line and another possible path by a broken line.
  • dips may be caused.
  • the base station uses lobe diversity, several lobes are used having different direction characteristics, such as are shown by the two lobes illustrated in Figure 1. Since the lobes have different phase and gain characteristics as a function of angle, the fading dips occur in a different pattern in each lobe. Thus, by appropriately combining the lobes the probability of a fading dip at a particular mobile location can be significantly reduced.
  • the base station is equipped with an array of antenna elements being combined into up-link reception lobes.
  • a distribution network forms a set of down-link transmission lobes.
  • the up- and down-link communication is performed at different frequencies but this is not a requirement in this invention.
  • the base station selects a set of lobes (the alternative lobes) to be used in down-link transmission. These lobes should typically be selected to have low average path- loss. Transmission is then performed in the lobe which is estimated to have the lowest instantaneous path-loss among the alternative lobes. Information of which has the lowest instantaneous path-loss is obtained by the base through an arrangement which enables the mobile to measure the instantaneous path-loss of the alternative lobes and feed sufficient information back to the base-station.
  • a set of alternative lobes is selected.
  • the set includes only two lobes but a greater number of lobes may be used. These lobes are selected to have low average path-loss.
  • the average path-loss is defined as the quotient of the power transmitted to the power received, where the powers are averaged over a time interval which is in the order of seconds.
  • the average path-loss is typically log-normal distributed and largely independent of frequency. Thus, even if different frequencies are used for the down-link, the up-link signals can be used for the estimation of the average downlink path-loss.
  • the base station BS is in charge of measuring the average path-loss and the mobile terminal is not involved.
  • a communication lobe has to be selected in which to perform the communication between the base station (BS) and the mobile station (MS).
  • the instantaneous path-loss of the alternative lobes must be measured.
  • the instantaneous path-loss is defined as the quotient of the power transmitted to the power received, where the powers are averaged over a time interval which is in the order of milliseconds or shorter.
  • the measurements of the instantaneous path-loss are made by the mobile-station.
  • the base-station measures the correlation of the receiving lobes. Generally, it is better to select lobes having low correlation, such that they complement each other and have their respective dips at different locations.
  • lobes having low path-loss but strong correlation are not always the best choice for the alternative set of lobes.
  • two alternative lobes are utilised and the mobile sends back a signal to the base station ordering a change of the communication lobe, if necessary. Otherwise, the communication continues in the same lobe.
  • the base sends short bursts in the alternative lobe so that the mobile station may perform its measurements.
  • the mobile knows when these bursts are sent and no information is carried in them.
  • the base station sends whole bursts.
  • the present invention provides a methodhaving several advantages over the prior art.
  • the method implements down-link antenna diversity without the use of multiple antennas or receivers at the mobile, and utilises measurements by the base as well as the mobile which reduces feedback rates considerably as compared with the use of feed-back only. Furthermore, even though the mobile stations make some measurements, no measurement results are required to be fed back to the base station, except a simple switching signal. This significantly reduces the feedback data rates.

Abstract

The present invention provides a method for decreasing fading and more particularly the down-link fading in a mobile telecommunication system having transmit lobe diversity. The telecommunication system comprises at least one base station having an antenna array providing lobe diversity, and communicating with mobile terminal units. According to the invention, the average path-loss between the base station and a mobile terminal unit is measured by the base station in order to select a set of alternative lobes. The instantaneous down-link path-loss of the alternative lobes between the base station and the mobile terminal unit is also measured by the mobile in order to select a communication lobe from said set of alternative lobes, such that the communication is effected in the communication lobe.

Description

TITLE OF INVENTION: METHOD FOR DECREASING FADING IN A
TELECOMMUNICATION SYSTEM
:>
Field of the invention
The present invention relates to a method for reducing fading in a telecommunication system, and more particularly the down-link fading in a mobile 0 telecommunication system having transmit lobe diversity. In mobile communications, the signal strength is often subject to so called Rayleigh fading, i.e. rapid changes with deep dips caused by multiple path propagation in a changing environment. The purpose of the invention is to eliminate this problem in the down-link direction, i.e. in the communication from the base station to the mobile 5 station. The result is an improved link performance which can be traded for coverage, and capacity improvement as well as reduced power consumption.
The invention combines measurements in the up-link as well as the downlink for respectively selecting a set of lobes and a communication lobe. The base station measures the average path-loss while the mobile station measures the 0 instantaneous path-loss between the base station and the mobile terminal.
State of the art
It is previously known to use antenna diversity techniques to reduce the rate of deep Rayleigh fading dips. Antenna diversity techniques are based on the idea of 5 creating several independent channels. By selecting the best or by combining the channels, the probability of a deep fade can be made small. Most antenna diversity techniques are implemented at the receiver while only a few are implemented at the transmitter. For down-link, i.e. base to mobile communication, transmit diversity techniques are favourable since they put most of the complexity on the 0 base station, where higher costs generally can be tolerated.
Prior art transmit diversity techniques include delayed signal transmission and antenna array transmission with feed back. Delayed signal transmission has the drawback of increasing the channel delay spread and requiring complex channel equalisation techniques at the receiving end. Array transmission with feedback is 5 an attractive alternative. US 5,634,199 discloses a method for using feedback to reduce cross-talk between mobile receivers in a wireless communications system comprising an adaptive transmitting antenna array. US 5,471,647 discloses a method for using feedback signals to optimise the directional properties of information signals with respect to their intended receivers, where information 0 signals are applied to the transmitting elements of a transmitting antenna array. These methods are based solely on feedback of measurement data resulting in high feedback rates.
The present invention take advantage of measurements in the up-link signals as well as mobile feedback to gauge the antenna patterns. This significantly reduces the feedback data rates which are otherwise to high to be practical.
Summary of the invention
Thus, the present invention provides a method for decreasing fading in a telecommunication system comprising at least one base station having an antenna array providing lobe diversity, and communicating with mobile terminal units.
According to the invention, the average path-loss between the base station and a mobile terminal unit is measured in order to select a set of alternative lobes. The instantaneous path-loss between the base station and the mobile terminal unit is also measured in order to select a communication lobe. The method according to the invention is defined in claim 1, while preferred embodiments of the invention are set forth in the dependent claims.
Brief description of the drawings
The invention will be described below with reference to the accompanying drawings, in which Figure 1 is a schematic illustration of various multipaths between a base station and a mobile station using a set of lobes in accordance with the invention.
Detailed description of preferred embodiments The mechanism of Rayleigh fading is well known in the art and is only discussed briefly here. It is caused by multiple propagation paths from a transmitter to a receiver. In Figure 1. there is shown a base station (BS) transmitting to a mobile station (MS). One possible path is represented by a solid line and another possible path by a broken line. When the signals interfere, dips may be caused. If the base station uses lobe diversity, several lobes are used having different direction characteristics, such as are shown by the two lobes illustrated in Figure 1. Since the lobes have different phase and gain characteristics as a function of angle, the fading dips occur in a different pattern in each lobe. Thus, by appropriately combining the lobes the probability of a fading dip at a particular mobile location can be significantly reduced.
Thus, the base station is equipped with an array of antenna elements being combined into up-link reception lobes. Correspondingly, a distribution network forms a set of down-link transmission lobes. Typically, the up- and down-link communication is performed at different frequencies but this is not a requirement in this invention. Based on estimates of the signal strength in the up-link lobes, the base station selects a set of lobes (the alternative lobes) to be used in down-link transmission. These lobes should typically be selected to have low average path- loss. Transmission is then performed in the lobe which is estimated to have the lowest instantaneous path-loss among the alternative lobes. Information of which has the lowest instantaneous path-loss is obtained by the base through an arrangement which enables the mobile to measure the instantaneous path-loss of the alternative lobes and feed sufficient information back to the base-station.
In other words, first a set of alternative lobes is selected. In the embodiment shown in the Figure, the set includes only two lobes but a greater number of lobes may be used. These lobes are selected to have low average path-loss. The average path-loss is defined as the quotient of the power transmitted to the power received, where the powers are averaged over a time interval which is in the order of seconds. The average path-loss is typically log-normal distributed and largely independent of frequency. Thus, even if different frequencies are used for the down-link, the up-link signals can be used for the estimation of the average downlink path-loss. Thus, the base station (BS) is in charge of measuring the average path-loss and the mobile terminal is not involved.
Second, a communication lobe has to be selected in which to perform the communication between the base station (BS) and the mobile station (MS). In order to select the best lobe, the instantaneous path-loss of the alternative lobes must be measured. The instantaneous path-loss is defined as the quotient of the power transmitted to the power received, where the powers are averaged over a time interval which is in the order of milliseconds or shorter. The measurements of the instantaneous path-loss are made by the mobile-station. Before selecting a communication lobe, the base-station measures the correlation of the receiving lobes. Generally, it is better to select lobes having low correlation, such that they complement each other and have their respective dips at different locations. Thus, lobes having low path-loss but strong correlation are not always the best choice for the alternative set of lobes. In one embodiment of the invention, two alternative lobes are utilised and the mobile sends back a signal to the base station ordering a change of the communication lobe, if necessary. Otherwise, the communication continues in the same lobe.
In one embodiment, the base sends short bursts in the alternative lobe so that the mobile station may perform its measurements. The mobile knows when these bursts are sent and no information is carried in them. In the communication lobe, the base station sends whole bursts.
As may be seen from the above, the present invention provides a methodhaving several advantages over the prior art. The method implements down-link antenna diversity without the use of multiple antennas or receivers at the mobile, and utilises measurements by the base as well as the mobile which reduces feedback rates considerably as compared with the use of feed-back only. Furthermore, even though the mobile stations make some measurements, no measurement results are required to be fed back to the base station, except a simple switching signal. This significantly reduces the feedback data rates.
A person skilled in the art will realise that the present invention may be implemented by various combinations of hardware and software. All those combinations are intended to fall within the scope of the following claims.

Claims

1. Method for decreasing fading in a telecommunication system comprising at least one base station (BS) having an antenna array providing lobe diversity, and communicating with mobile terminal units (MS), characterised by the steps of: measuring the average path-loss between the base station and a mobile terminal unit, to select a set of alternative lobes: measuring the instantaneous path-loss of the alternative lobes; the mobile terminal unit feeding back sufficient information to allow the base to select a communication lobe from said set of alternative lobes .
2. Method according to claim 1, characterised in that the average path-loss is measured by the base station.
3. Method according to claim 1 or 2, characterised in that the instantaneous path-loss is measured by the mobile terminal unit.
4. Method according to any one of the preceding claims, characterised in that the mobile terminal unit sends back a signal to the base station to request a switching to an alternative lobe.
5. Method according to any one of the preceding claims, characterised in that the base station transmits a whole burst in the communication lobe and transmits short bursts in the alternative lobes.
6. Method according to any one of the preceding claims, characterised in that the base-station measures the correlation of receiving lobes before selecting a communication lobe.
7. Method according to any one of the preceding claims, characterised in that the average path-loss is measured by averaging the path-loss over a time in the order of some seconds.
8. Method according to any one of the preceding claims, characterised in that the instantaneous path-loss is measured by averaging the path-loss over a time in the order of milliseconds.
PCT/SE1999/001226 1998-07-06 1999-07-06 Method for decreasing fading in a telecommunication system WO2000002329A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU49499/99A AU4949999A (en) 1998-07-06 1999-07-06 Method for decreasing fading in a telecommunication system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9802414-4 1998-07-06
SE9802414A SE512656C2 (en) 1998-07-06 1998-07-06 Procedure for reducing fading in a telecommunications system

Publications (1)

Publication Number Publication Date
WO2000002329A1 true WO2000002329A1 (en) 2000-01-13

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2817894A4 (en) * 2012-02-21 2015-12-02 Samsung Electronics Co Ltd Method and apparatus for transmitting and receiving signal in communication system

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5437055A (en) * 1993-06-03 1995-07-25 Qualcomm Incorporated Antenna system for multipath diversity in an indoor microcellular communication system
US5471647A (en) * 1993-04-14 1995-11-28 The Leland Stanford Junior University Method for minimizing cross-talk in adaptive transmission antennas
WO1996004738A1 (en) * 1994-08-02 1996-02-15 Ericsson Inc. Method of and apparatus for interference rejection combining in multi-antenna digital cellular communications systems
US5634199A (en) * 1993-04-14 1997-05-27 Stanford University Method of subspace beamforming using adaptive transmitting antennas with feedback
WO1997044978A1 (en) * 1996-05-22 1997-11-27 Nokia Telecommunications Oy Method and system for selecting an antenna beam of a base station of a radio system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5471647A (en) * 1993-04-14 1995-11-28 The Leland Stanford Junior University Method for minimizing cross-talk in adaptive transmission antennas
US5634199A (en) * 1993-04-14 1997-05-27 Stanford University Method of subspace beamforming using adaptive transmitting antennas with feedback
US5437055A (en) * 1993-06-03 1995-07-25 Qualcomm Incorporated Antenna system for multipath diversity in an indoor microcellular communication system
WO1996004738A1 (en) * 1994-08-02 1996-02-15 Ericsson Inc. Method of and apparatus for interference rejection combining in multi-antenna digital cellular communications systems
WO1997044978A1 (en) * 1996-05-22 1997-11-27 Nokia Telecommunications Oy Method and system for selecting an antenna beam of a base station of a radio system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2817894A4 (en) * 2012-02-21 2015-12-02 Samsung Electronics Co Ltd Method and apparatus for transmitting and receiving signal in communication system
US9775114B2 (en) 2012-02-21 2017-09-26 Samsung Electronics Co., Ltd. Method and apparatus for transmitting and receiving signal in communication system

Also Published As

Publication number Publication date
AU4949999A (en) 2000-01-24
SE9802414L (en) 2000-01-07
SE9802414D0 (en) 1998-07-06
SE512656C2 (en) 2000-04-17

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