WO2002093969A1 - Procede et arrangement d'informations de transmission dans un systeme de telecommunications - Google Patents

Procede et arrangement d'informations de transmission dans un systeme de telecommunications Download PDF

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Publication number
WO2002093969A1
WO2002093969A1 PCT/IT2001/000240 IT0100240W WO02093969A1 WO 2002093969 A1 WO2002093969 A1 WO 2002093969A1 IT 0100240 W IT0100240 W IT 0100240W WO 02093969 A1 WO02093969 A1 WO 02093969A1
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WO
WIPO (PCT)
Prior art keywords
downlink
cells
dlas
uplink
transmission
Prior art date
Application number
PCT/IT2001/000240
Other languages
English (en)
Inventor
Nicola Binucci
Mirko Masi
Eros Gaiani
Original Assignee
Telefonaktiebolaget Lm Ericsson
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 Telefonaktiebolaget Lm Ericsson filed Critical Telefonaktiebolaget Lm Ericsson
Priority to PCT/IT2001/000240 priority Critical patent/WO2002093969A1/fr
Publication of WO2002093969A1 publication Critical patent/WO2002093969A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/16—Performing reselection for specific purposes
    • H04W36/18—Performing reselection for specific purposes for allowing seamless reselection, e.g. soft reselection
    • 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
    • H04W52/38—TPC being performed in particular situations
    • H04W52/40—TPC being performed in particular situations during macro-diversity or soft handoff

Definitions

  • the present invention relates to a method and arrangement in a wireless communication system, such as a cellular communication system, which includes mobile radio communication stations. More particularly, the present invention relates to a method and arrangement for better usage of available radio resources in CDMA and WCDMA system. DESCRIPTION OF RELATED ART
  • Fig. 1 illustrates ten cells C1-C10 in a typical cellular mobile radio communication CDMA-system. Normally a cellular mobile radio communication system would be implemented with more than ten cells.
  • Each cell, C1-C10 is related to at least a logical base station, called Node B in the 3GPP standard specification.
  • the Node b BS A covers the cells CI, C6, C7.
  • the Node b BS B covers the cells CI, C2, C3.
  • the Node b BS C covers the cells C4, C5.
  • the Node b BS D covers the cells C4, C8.
  • the Node b BS E covers the cells C9, CIO.
  • Fig. 1 illustrates the Node b as situated at the cell border and provided with two or "" three antennas.
  • Fig. 1 also illustrates, nine mobile stations MS1-MS9 which are movable within the cells and from one cell to another.
  • a mobile station is defined as any mobile station, e.g. e mobile phone or a mobile computer provided with equipment for wireless communication.
  • a typical cellular mobile radio communication system there would normally be more Node b and mobile stations. In fact, there is typically many times the number of mobile stations as there are Node b.
  • a radio network controller RNC is also illustrated in fig. 1 a radio network controller RNC.
  • the interface between a RNC and a Node b is also called Iub interface.
  • the radio network controller RNC is connected to the Core Network CN through an Iu interface.
  • the Iu interface is not shown.
  • the RNC selects the cell, which is to be inserted in the active set of a mobile station.
  • the active set is the set of cells connected simultaneously to a given mobile station.
  • a Core Network is the network connected to a set of RNC, e.g. a fixed network.
  • a Node b is connected to one and only one RNC.
  • the radio network controller RNC, the Node b, and the mobile stations are all computer-controlled.
  • Each RNC is responsible for the resources in its set of Node b.
  • Two or more RNCs may be interconnected by means of an Iur interface.
  • An Iur interface can be conveyed over direct physical connection between two or more RNCs or virtual networks using any suitable transport network.
  • An Iur interface is an interface, which allows soft handover between different RNCs. The term soft handover will be disclosed below.
  • Iu and Iur are logical interfaces.
  • a System employing code separation is called a CDMA system.
  • the transmission of signals from a mobile station to a Node b is called uplink.
  • the transmission of signals from a Node b to a mobile station is called downlink.
  • Three main resources are managed in a radio access system using CDMA technology: • Interference in uplink due to power transmitted in the uplink • Power.
  • Soft handover implies that the mobile station is power controlled by several cells on the uplink or that several cells are power controlled by one mobile station on the downlink • Code, i.e. OVSF (Orthogonal Variable Spreading Factor) codes in downlink.
  • OVSF Orthogonality between downlink physical channels of different rates and spreading factors .
  • Soft handover is a handover operation in which one mobile station MSI simultaneously communicates with several cells, e.g.
  • a soft handover is seamless and no information is lost during the handover process.
  • two or more Nodes b receive a signal from the mobile station, whereupon the signal is combined in the network. Normally, selection combining is used if the two cells belong to different Nodes b.
  • a mobile station receives a signal from two or more base stations, whereupon the signal is combined in the receiver, e.g. a rake receiver, of the mobile station. Normally, maximum ratio combining (MRC) is used.
  • MRC maximum ratio combining
  • a RAKE-receiver performs a correlation of receivers called fingers.
  • a finger is reserved for each path in order to provide diversity between multi-path components. Each finger is synchronized to one path. A rake finger picks up one multi-path component and suppresses the other. Normally, a maximum ratio combining (MRC) is output from the RAKE-receiver.
  • selection combining is performed in the radio network controller (RNC) , when the mobile station is connected to different Nodes b (BS A , BS B ) . The transmitted signal from the mobile station is received and decoded in all connected Node b (BS A , BS B ) and the signal power data is sent to the RNC.
  • RNC radio network controller
  • a softer handover is a handover process performed between two cells (C6, C7) belonging to the same Node b (BS A ) .
  • a softer handover operation entails less signaling in the network than a soft handover operation.
  • combining can be performed in the rake receiver of the Node b instead of in the network. Maximum ratio combining may be used in both uplink and downlink.
  • the set of cells to which a mobile station is connected is called the active set (AS) .
  • a mobile station can use different base station or nodes b on the uplink and downlink, respectively. Soft handover can thus be performed on the uplink and downlink, respectively.
  • An important soft handover parameter is the Add threshold parameter.
  • the Add threshold parameter is a threshold value based on which decision is taken, by a RNC, if a given cell can be inserted in the active set (AS) or not.
  • a given cell C6 is inserted in the active set if the difference between the best received signal power and the power of the signal received from the cell C6 is higher than the Add threshold value.
  • the best received signal power is the signal having the maximum power received from the cells in the active set.
  • the power is evaluated at the mobile station on the downlink and is typically measured on a primary common pilot channel (CPICH) .
  • the active set includes the best cell and at least a further cell having the above mentioned power difference higher than the Add threshold parameter, if the terminal is in soft handover. However, the maximum amount of cells in the active set limits the number of connected cells.
  • the Add threshold parameter and the maximum number of cells in the active set determines the number of cells that are involved in a soft/softer handover process in the system. If the Add threshold parameter value is small, the precentage of users in soft/softer handover will be small and vice versa.
  • the signaling aspects for the link between the Node b and the RNC, the Iub interface, for the link between two RNC, the Iur, and the UTRAN (Universal mobile telecommunications systems. Terrestial Radio Access Network) and the core network CN are not considered.
  • the probability of transmitting at a minimum power level increases with the number of cells in the active set. I.e., the more cells there are in the active set, the greater is the probability that one or more of these has a minimum absolute power.
  • every cell in the active set is transmitting, and thus the interference is increased.
  • Another important factor is the transmission resources in the fixed network. For a mobile station MSI in soft handover, all connected Node b (BS A , BS B ) belonging to different cells, require a transmission link to the Radio Network Controller RNC. Thus, a large percentage of mobile stations in soft handover will require a large amount of extra transmission resources in the access network.
  • the RNC controls every soft handover process that take place in a Node b.
  • the soft handover procedure is composed of a number of single functions :
  • the soft handover algorithm • Execution of handover Based on the measurements of the set of monitored cells, the soft handover function evaluates if any cell should be added to, removed from, or replaced in the active set.
  • the transmission uplink uses I/Q/code multiplexing for user data and control information for physical layer.
  • the physical layer control information is carried by the Dedicated Physical Control Channel (DPCCH) having a fixed spreading factor of 256.
  • the higher layer information, including user data, is carried on one or more Dedicated Physical Data Channels (DPDCHs) , having a spreading factor ranging from 4 to 256.
  • the uplink transmission may consist of one or more Dedicated Physical Data channels (DPDCH) having a variable spreading factor, and a single dedicated Physical Control Channel (DPCCH) having a fixed spreading factor.
  • the DPDCH data rate may vary on a frame-by-frame basis.
  • the DPDCH data is transmitted continuously and rate information is transmitted using a Transport Format Combination Indicator (TFCI) and DPCCH information related to the data rate on the current DPDCH frame. If the TFCI is not decoded correctly, the whole data frame is lost. Because the TFCI indicates the transport format of the same frame, the loss of TFCI does not affect any other frames. The reliability of the TFCI is higher than the reliability of the user data detection on the DPDCH. Therefore, the loss of TFCI is a rare event.
  • the uplink DPCCH uses a slot structure having 15 slots over a radio frame of 10 milliseconds. This results in a slot duration of 2560 chips or about 666 microseconds.
  • Each slot is provided with four fields allocated for pilot bits, TFCI, Transmission Power Control (TPC) bits and Feedback Information (FBI) bits.
  • the pilot bits are used for estimating the channel condition at the receiver end, and the TPC bits carry power control commands used by the Node b for the downlink power control.
  • SSDT is a method for power control for the downlink that can be applied while a mobile station is in soft handover in order to reduce the interference on the downlink.
  • the principle of SSDT is that the best cell (Cl) in the active set (CI, C2, C3) is dynamically chosen as the transmitting Node b (Cl) , and the other Node b (C2, C3) in the active set turns off their Dedicated Physical Data Channel (DPDCH) . Only one cell transmits data, but all cells transmit power control information, and other type of control information.
  • DPDCH Dedicated Physical Data Channel
  • DPDCH Dedicated Physical Control Channel
  • Each Node b is given a temporary identification number.
  • Computer simulations have been carried out in order to investigate the behavior of SSDT under ETSI & ITU-R guidelines for IMT-200ORTT evaluation. The results are compared to a conventional power control method, where the transmit power of all involved cells is controlled in order to reach a predetermined value for the Signal-to-Interference Ratio (SIR) .
  • SIR Signal-to-Interference Ratio
  • the capacity is enhanced by approximately 40% without diversity at the mobile station, and 50% with diversity at the mobile station, when transported at a walking speed.
  • the advantage of SSDT gradually diminishes.
  • the performance degradation of SSDT at higher speed is caused by the limited update frequency of the primary cell identity.
  • US patent 5,487,174 filed March 23, 1993 by Bengt Y. Person and assigned to LM Ericsson is disclosed a method in a cellular mobile radio system having cells of substantially different sizes or cells transmitting with substantially different output power. Decisions on which cell to use for the downlink of a bidirectional connection with a mobile station are made more or less independently of which cell is used for the uplink e.g.
  • the network resources are not exploited in an optimal way.
  • a more efficient usage of the system resources may be obtained by introducing separate management of the active uplink and downlink, i.e. a separate management of parameters for the uplink and downlink management, which parameters are related to the algorithms used for the management of soft handover in the RNC.
  • the necessity of having a self-configuring system i.e. a Radio Network Management capable of managing traffic load variations over space and time without delay, in order to optimize the usage of transmission resources.
  • the method disclosed herein does not function in a GSM system, since soft handover is not used in GSM systems.
  • the method disclosed herein is aimed to function in CDMA systems, systems according to the IS-95 specification and WCDMA systems for the UMTS standard.
  • a purpose of the method and arrangement disclosed herein is to provide separate system optimization, ' in order to improve the total Quality of Service provided by the network during the performance of a soft handover operation between cells belonging to two different Node b and a softer handover operation between cells belonging to the same Node b, respectively. Therefore, as in a CDMA-based- radio access system, the mobile stations are spending a large amount of time in soft handover, a separate system optimization would contribute to a better exploitation of the available radio resources.
  • a further purpose of the method disclosed herein is to provide different management of active links for transmission on the uplink and the downlink, respectively.
  • Fig. 1 is a schematic view of the basic layout of a cellular communication system.
  • Fig. 2 is a diagram illustrating simulation results obtained using different Add threshold values. DETAILED DESCRIPTION
  • a mobile station MSI and a Node b BS A ' perform measurements on the cells belonging to an active set, i.e. the set of cells (Cl, C2, C3, C4, C5) being active during the soft handover operation.
  • the mobile station MSI and the Node b BS A evaluate the result from these measurements with respect to specific events, such as loss of connection, or when the received power, measured on a common pilot channel (CPICH) from a cell of an active set exceeds a predefined threshold value (Add threshold) .
  • CPICH common pilot channel
  • Add threshold a predefined threshold value
  • the measurements reports are transmitted to the radio network controller RNC.
  • the radio network controller RNC uses a handover evaluation procedure in order to take a final decision on which cells to add, delete or replace in the active set.
  • a cell that has been inserted in the Active Set of a certain mobile station transmits data information on the DPDCH and control information on the DPCCH to the mobile station on the downlink.
  • the cell receives data from the mobile station on the uplink. Therefore, the radio network controller RNC uses the same algorithm and the same parameters when selecting cells that are to be inserted in the active set of a certain mobile station.
  • the radio network controller RNC uses different algorithms for selecting a cell to be used for transmission uplink or downlink, respectively, to a determined mobile station MSI.
  • the radio network controller RNC can also use the same algorithm for selecting a cell to be used for transmission on the uplink and for transmission on the downlink, but uses different parameters or predetermined threshold values for selecting said cell.
  • the cell that has been selected for transmission on the downlink will transmit both control and data information, whereas the cell that has been selected for transmission on the uplink transmits only control information in order to reduce the power consumption of the cell.
  • Two separate active sets of cells belongin to the same or different Node b,,i.e.
  • the sets of active links are considered, one set for transmission uplink (upAS) , and one set for transmission downlink (dlAS) .
  • the Active Set comprises five cells (Cl, C2, C3, C4, C5)
  • the active set for the downlink (dlAS) comprises three cell (Cl, C2, C3)
  • the active set for the uplink (upAS) comprises five cells (Cl, C2, C3, C4, C5) .
  • the cells in the active set for transmission downlink transmit both on the control channel DPCCH and the data channel DPDCH, and the cells receive data and speech from the mobile station MSI on the uplink.
  • the cells in the active set for transmission uplink transmit on the control channel DPCCH on the downlink and receive data and speech from the mobile station MSI on the uplink.
  • the construction of the RNC only require minor changes, since it has only to set and control different active sets for transmission uplink and downlink, respectively. Possibly some changes in the code allocation and spreading factor selection for the control channels enable the reduction of code tree occupancy.
  • the mobile station takes advantage from a large number of links on the uplink, which increase the performance of soft/softer handover on the uplink, while reducing the amount of data information transmitted on the downlink, as only relevant data is transmitted.
  • the reduced interference on the downlink results in a reduction of transmitted power.
  • Each cell in the Active Set (upAS and dlAS) continues to transmit control information, e.g. Transmit Power Control (TPC) on the Dedicated Physical Control Channel (DPCCH) in both directions .
  • TPC Transmit Power Control
  • DPCCH Dedicated Physical Control Channel
  • the above method is an evolution of the SSDT method disclosed above.
  • the object of the above method is to provide different management of active links for transmission on the uplink and the downlink, respectively.
  • the object of the SSDT method is to transmit downlink only from the best cell while in soft/softer handover, in order to reduce the interference for transmission on the downlink, but to the cost of no advantage of using maximum ratio combining MRC.
  • MRC maximum ratio combining
  • different predetermined thresholds are used. Said threshold values are separately tuned for the uplink and the downlink.
  • the radio network controller RNC applies the same handover evaluation procedure but uses different threshold values for transmission on the uplink and downlink, respectively.
  • the predetermined threshold values for performing soft/softer handover are dynamically set depending on the traffic load conditions .
  • the usage of different values for the "Add Threshold" parameter can be advantageous for the . total system quality.
  • the Add Threshold parameter can be load depending. I.e. different values of the Add Threshold parameter are used for performing a soft/softer handover operation depending on the traffic load in the system.
  • the advantages of performing a soft/softer handover operation for transmission on the downlink are entirely dependent on the traffic load in the system or the cell.
  • the number of active links for transmission on the downlink should be reduced, i.e. a reduced active set in the downlink (dlAS) , when the system or cell gets more loaded.
  • Add_th_dl Aexp /(limit Pdl - max ( Pdl ) ) for transmission downlink
  • Add_th_ul B for transmission uplink
  • a and B are constant values that are optained by means of computer simulations and thereafter tuned according to empiric data.
  • max(Pdl 3 ) is defined as the value for maximum power.
  • the maximum power is defined as the power transmitted by a cell on the downlink under a predefined time period.
  • mean (Pdl.,) is the mean value of the output power from all the considered cells on the downlink.
  • limit Pdl is the power limit for one cell on the downlink. Power limit is here defined as the total power available for each cell. When the power on the downlink is close to the limit or is far from the mean value, the value of Add threshold is small.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention concerne un procédé et un arrangement destinés à fournir une optimisation de système séparé dans un système de communication radiocellulaire comprenant au moins deux noeuds et une station mobile, permettant d'améliorer la qualité globale du service fourni par le réseau lors d'un transfert souple entre des cellules appartenant aux deux différents noeuds b et un transfert plus souple entre les cellules appartenant aux mêmes noeuds b, respectivement. C'est pourquoi, comme dans un système d'accès radio ARMC, les stations mobiles utilisent une grande quantité de temps dans le transfert souple, et une optimisation du système séparé contribue à mieux exploiter les ressources radio disponibles.
PCT/IT2001/000240 2001-05-16 2001-05-16 Procede et arrangement d'informations de transmission dans un systeme de telecommunications WO2002093969A1 (fr)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005034384A1 (fr) * 2003-10-01 2005-04-14 Telefonaktiebolaget Lm Ericsson (Publ) Procede et appareil visant a ameliorer les performances de liaisons inverses amrc
CN100362899C (zh) * 2004-09-02 2008-01-16 华为技术有限公司 一种高速尽力而为业务频内过渡切换方法
WO2008130300A1 (fr) * 2007-04-23 2008-10-30 Telefonaktiebolaget Lm Ericsson (Publ) Procede de transmission de donnees de liaison descendante
EP2713667A1 (fr) * 2008-02-04 2014-04-02 NTT DoCoMo, Inc. Procédé de communication mobile et station de base radio
EP2836048A3 (fr) * 2013-08-08 2015-09-23 Alcatel Lucent Procédés et dispositifs de découplage des liaisons descendante et montante dans un réseau de communication mobile

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5487174A (en) * 1992-03-24 1996-01-23 Telefonaktiebolaget Lm Ericsson Methods in a cellular mobile radio communication system
US5781861A (en) * 1995-12-06 1998-07-14 Electronics And Telecommunications Research Institute Method for shedding traffic load in code division multiple access mobile communication system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5487174A (en) * 1992-03-24 1996-01-23 Telefonaktiebolaget Lm Ericsson Methods in a cellular mobile radio communication system
US5781861A (en) * 1995-12-06 1998-07-14 Electronics And Telecommunications Research Institute Method for shedding traffic load in code division multiple access mobile communication system

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005034384A1 (fr) * 2003-10-01 2005-04-14 Telefonaktiebolaget Lm Ericsson (Publ) Procede et appareil visant a ameliorer les performances de liaisons inverses amrc
US8532664B2 (en) 2003-10-01 2013-09-10 Telefonaktiebolaget Lm Ericsson (Publ) Method and apparatus to improve CDMA reverse link performance
CN100362899C (zh) * 2004-09-02 2008-01-16 华为技术有限公司 一种高速尽力而为业务频内过渡切换方法
WO2008130300A1 (fr) * 2007-04-23 2008-10-30 Telefonaktiebolaget Lm Ericsson (Publ) Procede de transmission de donnees de liaison descendante
EP2140701A1 (fr) * 2007-04-23 2010-01-06 Telefonaktiebolaget LM Ericsson (PUBL) Procede de transmission de donnees de liaison descendante
CN101652937A (zh) * 2007-04-23 2010-02-17 艾利森电话股份有限公司 发射下行链路数据的方法
EP2140701A4 (fr) * 2007-04-23 2012-07-04 Ericsson Telefon Ab L M Procede de transmission de donnees de liaison descendante
US8385958B2 (en) 2007-04-23 2013-02-26 Telefonaktiebolaget Lm Ericsson (Publ) Method of transmitting down link data
EP2713667A1 (fr) * 2008-02-04 2014-04-02 NTT DoCoMo, Inc. Procédé de communication mobile et station de base radio
US10154441B2 (en) 2008-02-04 2018-12-11 Ntt Docomo, Inc. Mobile communication method and radio base station
EP2836048A3 (fr) * 2013-08-08 2015-09-23 Alcatel Lucent Procédés et dispositifs de découplage des liaisons descendante et montante dans un réseau de communication mobile

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