WO1999023772A1 - Procede et appareil servant a reduire l'effet d'une condition d'evanouissement dans un systeme de communication - Google Patents

Procede et appareil servant a reduire l'effet d'une condition d'evanouissement dans un systeme de communication Download PDF

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Publication number
WO1999023772A1
WO1999023772A1 PCT/US1998/023449 US9823449W WO9923772A1 WO 1999023772 A1 WO1999023772 A1 WO 1999023772A1 US 9823449 W US9823449 W US 9823449W WO 9923772 A1 WO9923772 A1 WO 9923772A1
Authority
WO
WIPO (PCT)
Prior art keywords
condition
power
signal
transmit power
radio frequency
Prior art date
Application number
PCT/US1998/023449
Other languages
English (en)
Inventor
John Douglas Reed
John Stephen Ruppel
Original Assignee
Motorola Inc.
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 Motorola Inc. filed Critical Motorola Inc.
Publication of WO1999023772A1 publication Critical patent/WO1999023772A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/18—TPC being performed according to specific parameters

Definitions

  • the present invention generally relates to radio frequency communication systems, and more particularly, a cellular communication system.
  • Radio Frequency (RF) communication systems very often adopt a power control mechanism to reduce the effects of problems associated with the RF signal propagation channel whereby improving the system performance.
  • An RF signal experiences what is commonly known as fading as it propagates through an RF channel between a transmitting unit and a receiving unit.
  • the effects of fading condition in an RF channel result from summing the scattered rays at the antenna.
  • the scattered rays are normally produced by one or more dominant rays that arrive at or near the receiving unit.
  • a fade condition occurs when vector addition of rays at the antenna results in a reduction in the resulting signal quality compared to an average or some other threshold.
  • the reduction in the signal quality is the result of a destructive condition of summing the scattered rays and the dominant rays that are received at the receiving antenna. Fading is furthermore characterized by the rate which the amplitude and phase of the resulting signal are changing. In a fast fade condition, the resulted RF signal amplitude and phase are rapidly changing. In a slow fade condition, the average amplitude and phase may remain substantially constant for a long period of time. Although both slow and fast fading may be present at any time, slow fades occur more often where transmit and receive units are stationary.
  • a mobile unit does not experience the destructive effects of a slow fade condition for a sustained period since it is constantly moving. A slight change in the position of the antenna is sufficient to move away from a deep null in the RF signal amplitude that has been created by the destructive condition of summing the rays which is a characteristic of the slow fading condition.
  • a recently proposed type of duplex radio telephone system called Fixed Wireless Terminal (FWT) requires that the terminals be at fixed locations. When a terminal is stationary, a slow fade is likely to happen, and may last for a long time.
  • the cellular system through its communication protocol standard commands the transmitting unit to increase the transmitting power in response to the fade condition occurring at the receiving unit.
  • the transmitter has only a limited available power.
  • the limited available power is due to the power amplifier saturating or reaching a pre-defined operating maximum limit.
  • the basestation has a system pre-defined maximum transmit power limit which is established due to practical system constraints. When the limited power level is reached, the communication link would severely degrade if additional signal power is needed to respond to a slow fade condition.
  • FIG. 1 depicts general components of a cellular communication system.
  • FIG. 2 depicts general block diagram of a transceiver.
  • FIG. 3 depicts a flow chart of a power control loop according to prior art.
  • FIG. 4 depicts a flow chart of a power control loop according to various aspects of the present invention.
  • a method of reducing an effect of a fading condition of the radio frequency signal at the receiver includes detecting the fading condition, monitoring the radio frequency signal for detecting a transmit power limiting condition occurring at the transmitting source, and changing the radio frequency signal frequency when the transmit power limiting condition and the fading condition are present.
  • the occurrence of transmitter power limiting condition is reported by the unit performing the monitoring step.
  • a quality of the radio frequency signal such as bit error rate, determines the effect of the fading condition at the receiving unit.
  • the transmit power limiting condition is characterized as the transmit power saturating condition or a pre-defined maximum transmit power limiting condition.
  • the transmit power limiting condition is detected when said transmitting source fails to respond to a power increase command. Furthermore, in the monitoring step the transmit power limiting condition is detected when a threshold associated with a cumulative number of the power increase commands is reached, or the threshold is reached over a period of time. The monitoring step is performed in either the transmitting source or the receiving unit or both.
  • a cellular communication system 100 is conceptually shown to include a basestation 101, and a number of remote units 1021-1024. Although only four remote units are shown in FIG. 1, the number of remote units in system 100 may exceeds thousands depending on the capacity of basestation 101.
  • Each remote unit has a two way communication link with the basestation 101. The direction of each communication link, in FIG. 1, is shown by the direction of arrow heads.
  • Each of the communication links from the basestation to remote units is called a forward link, a communication link in the opposite direction is called a reverse link.
  • Other names, such as uplink, for reverse, and down link, for forward have been used in other communication systems.
  • CDMA Code Division Multiple Access
  • GSM Group Special Mobile
  • the remote unit 1021 in response to a command by its controller 201 adjusts the transmitter 202 output power.
  • the reverse link signal 105 may be received at a higher power level at the basestation 101.
  • the command in 201 is generated in response to forward link 106 carrying a message that the signal received at the basestation 101 is degraded, and, therefore, requesting an increase of signal power.
  • the degradation in signal is either due to far location of the remote unit 1021 from the transmitting unit which would cause large propagation loss or a fade condition in the RF channel.
  • the maximum power level may be set at any valid transmit power level as defined by the system requirements.
  • the controller 201 detects that at a step 301. If the power control bit is at logic zero, in this example, it means that the transmitter should reduce its power level. However, if the power level is at the predetermined minimum level already, the transmitter should not reduce its transmit power level. If the power control bit is at logic 1, in this example, and the transmit power level is not at its maximum level, the transmit power is increased. The entire process is shown in FIG. 3 at steps 301-306.
  • a continuous stream of power control bits is being communicated to the fix unit from the basestation based on CDMA protocols.
  • the control bit stream includes step up and step down power control bits alternatively at an 800 Hz rate. If each step up is followed by a down step, then the power level will be toggling up and down by approximately a dB which then keeps the average power level at a constant level. If the signal power level is low, the power up commands are communicates at more intervals than power down commands.
  • the subscriber sends a request for more transmit power from the basestation transmitter when it is detecting poor received frames signal quality. In response, the basestation transmits at a predetermined higher power level.
  • the power control loop is modified to include a step 407 of initiating a carrier frequency change when at step 305 is determined that the transmitter is in a saturating condition or has reached a pre-defined maximum limit and a fading condition is present in the RF channel.
  • a level below saturation as a safe operating point, and this may be used to establish the maximum limit.
  • This limited level may be as much as 10 to 20 dB below the transmit power saturating level to control the effect of interference or improve battery life among many other reasons.
  • it is common to set different power limits for the transmitting units which may depends on the location of each transmitting unit.
  • the effect of signal degradation due to fading is closely tied to the carrier frequency since even small percentage changes in frequency will change the vector sum of rays at the receiving antenna. Therefore, fading conditions are in general, different at different carrier frequencies.
  • the change in carrier frequency in response to a power-up command when the transmitter is in a limiting condition most likely changes the fading effect occurring at the remote receiving unit.
  • the change in carrier frequency is a form of carrier hand-off which is controlled and maintained by the system controller.
  • step 305 There are a number of ways to determine in step 305 when a transmitter is in a saturating condition, or when the transmitter is at its pre-defined maximum limit.
  • One method is to monitor the transmit power level when requesting transmit power increase. If the transmit power level does not change accordingly, the transmitter is considered to be in a saturating condition, or at its maximum limit.
  • Another method is to characterize the transmitter power output characteristics before installation, and then during operation, the controller knowing this characteristic monitors the transmitter for finding the saturating condition or its pre-defined maximum limit.
  • the receiving unit requests power increase from the transmitting unit repeatedly.
  • the receiving unit can make the determination at step 305 that the transmitting unit is in a saturating condition.
  • a message then will be send out to indicate the transmitting unit saturating condition or a limiting condition.
  • the signal quality generally improve if the transmitting unit is actually increasing the signal transmit power level.
  • the quality of the signal is measured either by received errors or received signal strength indicator based on the received signal strength. In this case, the number of requests to increase power level made by the receiving unit should go above a predetermined threshold level if a saturating condition, or pre-defined maximum limit is present at the transmitting unit.
  • the block 408 is shown to generate a threshold signal 409 whenever the condition to change carrier frequency according to present invention is satisfied. If the number of power up commands exceeds a threshold number over a period of time, the condition to initiate a carrier frequency change has been satisfied. If the power up command is for the basestation to increase its power level, the condition to change the carrier frequency is satisfied when the basestation has reached its predetermined maximum power level allocated to the subscriber unit after the basestation receives a number of power up requests repeatedly from the subscriber unit.
  • the command to change the carrier frequency at step 407 can be executed from either the transmitting or receiving unit.
  • a transmitter saturating condition or pre-defined maximum limit is detected in the transmitting unit, the same unit also initiates the process of changing the transmitting carrier frequency.
  • the receiving unit which is experiencing the effect of the fading condition can initiate the process of changing the receiving signal carrier frequency. This is accomplished by transmitting a message to the transmitting unit to change its carrier frequency which is basically initiating a carrier frequency hand-off. Since the forward and reverse links are independently controlled, a change of carrier frequency in one link does not require a change of carrier frequency in another link in the general case.
  • changing the frequency of one link will also results in changing the frequency of the other link since forward and reverse links are paired in practice.
  • a message is transmitted to the preferred unit. The message indicates that a power limiting condition has been detected in a transmitting unit.

Abstract

Dans un système (100) de communications dans lequel un signal haute fréquence est émis à partir d'une source d'émission, et reçu à une unité de récepteur, l'invention concerne un procédé et un appareil servant à réduire un effet d'une condition d'évanouissement du signal haute fréquence au récepteur. Le procédé et l'appareil comportent les étapes consistant à détecter la condition d'évanouissement, surveiller le signal haute fréquence en vue de détecter une condition de limitation de la puissance d'émission se produisant à la source d'émission, et modifier la fréquence du signal haute fréquence au moment de la détection de la condition de limitation de puissance d'émission et de la condition d'évanouissement. Au cours de l'étape de surveillance, la condition de limitation de puissance d'émission est détectée lorsqu'un seuil associé à un nombre cumulatif de commandes d'augmentation de puissance est atteint.
PCT/US1998/023449 1997-11-04 1998-11-04 Procede et appareil servant a reduire l'effet d'une condition d'evanouissement dans un systeme de communication WO1999023772A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US96373197A 1997-11-04 1997-11-04
US08/963,731 1997-11-04

Publications (1)

Publication Number Publication Date
WO1999023772A1 true WO1999023772A1 (fr) 1999-05-14

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PCT/US1998/023449 WO1999023772A1 (fr) 1997-11-04 1998-11-04 Procede et appareil servant a reduire l'effet d'une condition d'evanouissement dans un systeme de communication

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WO (1) WO1999023772A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001091333A1 (fr) * 2000-05-23 2001-11-29 Littlefeet, Inc. Appareil reduisant dans des systemes de radiocommunication les effets d'evanouissement rapide des signaux radio propages pour postes stationnaires, et mobiles a deplacements lents
WO2001091334A1 (fr) * 2000-05-23 2001-11-29 Littlefeet, Inc. Appareil reduisant dans des systemes de radiocommunication les effets d'evanouissement rapide des signaux radio propages pour postes stationnaires, et mobiles a deplacements lents

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4613990A (en) * 1984-06-25 1986-09-23 At&T Bell Laboratories Radiotelephone transmission power control
US5491837A (en) * 1994-03-07 1996-02-13 Ericsson Inc. Method and system for channel allocation using power control and mobile-assisted handover measurements
US5579373A (en) * 1992-11-05 1996-11-26 Samsung Electronics Co., Ltd. Transmission power control method in cellular radiotelephone system
US5697056A (en) * 1995-05-08 1997-12-09 Motorola, Inc. Communication system in which radio subscriber units mitigate interference
US5805995A (en) * 1996-10-28 1998-09-08 Northern Telecom Limited Channel reservation and power control for improved handoff performance

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4613990A (en) * 1984-06-25 1986-09-23 At&T Bell Laboratories Radiotelephone transmission power control
US5579373A (en) * 1992-11-05 1996-11-26 Samsung Electronics Co., Ltd. Transmission power control method in cellular radiotelephone system
US5491837A (en) * 1994-03-07 1996-02-13 Ericsson Inc. Method and system for channel allocation using power control and mobile-assisted handover measurements
US5697056A (en) * 1995-05-08 1997-12-09 Motorola, Inc. Communication system in which radio subscriber units mitigate interference
US5805995A (en) * 1996-10-28 1998-09-08 Northern Telecom Limited Channel reservation and power control for improved handoff performance

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001091333A1 (fr) * 2000-05-23 2001-11-29 Littlefeet, Inc. Appareil reduisant dans des systemes de radiocommunication les effets d'evanouissement rapide des signaux radio propages pour postes stationnaires, et mobiles a deplacements lents
WO2001091334A1 (fr) * 2000-05-23 2001-11-29 Littlefeet, Inc. Appareil reduisant dans des systemes de radiocommunication les effets d'evanouissement rapide des signaux radio propages pour postes stationnaires, et mobiles a deplacements lents

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