GB2392352A

GB2392352A - Power or interference control for mobile communications

Info

Publication number: GB2392352A
Application number: GB0327303A
Authority: GB
Inventors: Kiran Anandrao Thakare
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1999-08-20
Filing date: 1999-08-20
Publication date: 2004-02-25
Anticipated expiration: 2019-08-20
Also published as: GB0327303D0; GB9919731D0; GB2392352B; GB2353439A; GB2353439B

Abstract

A method for a Site Selection Diversity Transmission (SSDT) system, a involving a network controller initiating a SSDT capability of a node (base station), wherin the node switches off downlink power when an ID code received from a users mobile telephone is different to that stored in the node. Also, the method notifies an activation time of the SSDT function to the nodes which support SSDT capabilities. This allows a proper timing in order to change cell state from SSDT off to SSDT on (or vice versa).

Description

POWER CONTROL FOR MOBILE COMMUNICATIONS

The present invention relates to mobile telecorrununications systems comprising power control means for diversity transmission and is particularly, but not exclusively, concerned 5 with third generation UMTS systems and diversity transmission conununications.

One particular method for power and interference control in communication systems using diversity transmission is SSDT (Site Selection Diversity Transmission). This method switches on and off the power radiated in one or several of the radio-links of a macro 10 diversity communication, thus reducing interference in the down link by eliminating the contributions of some branches but still keeping the up-links and all other elements of the communication. To achieve that, the User Equipment (UK) must select the best radio links and transr,nit the 15 coded information of the sites or cells that should be kept to all the sites or cells that comprise the set of active radio links. This information can be corrupted due to transmission errors and lead to Ligneous decisions.

A first aspect of this invention is to provide a method, which assures that the correct set of zo radio links, is active in every situation.

Telecornmunicati n networks can be composed of equipment provided by different vendors arid developed according to different standards or different standard releases. This can make that some ofthe base stations or nodes located in the different cell sites involved in a rnacTm 25 diversity transmission are not able to supped site sdection diversity transmission.

A second aspect of this invention addresses this problem.

According to a first aspect, the invention provides a method of operating a mobile 30 telecommunications system supporting Site Selection Diversity Transmission (SSDT). The method comprising means for coding cell site identities with several degrees of protection against error corruption combined with m/eans to set-up different leads of reception quality thresholds for the decoding of the cell site identities.

- 2 Preferably, the method comprises means for controlling the timing and right synchronization for the activation and deactivation of Site Selection Diversity Transmission.

5 Preferably, the method further comprises, means to combine SSDT with other power control, interference control or diversity control methods like Transmit Antenna Array TxAA. According to a second aspect, the invention provides a method of operating a power or o interference control system like SSDT in a mobile teleconununications system, characterized in that means are provided to identify situations where radio links originate from cells with different capabilities The method further comprising means to actuate this power or interference control system accordingly.

15 The invention extends to User Equipment and network components embodying the methods and preferred features above. The invention further extends to signals for use in the above methods. In this specification, terms of the art as defined in the UMTS specification are used for ease

20 of understanding. However, these teens are not intended to be limited to any specific system but are intended to encompass any fimctional equivalents in other systems specially those contemplating macro diversity or soR handover capabilities, for example based on second generation I95 systems or He like.

25 An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates a macroiversity situation.

3 0 The following description of an embodiment relates to application to a UMTS

telecommunications system; as will be explained below, the invention is not so limited.

According to the embodiment, a mechanism is provided to control the operation of SSDT in a UNITS system.

Further infonnation on SSDT can be found in [1], section 5.2.3.4.

s SSDT is a power control scheme for the UE in soft hand-over mode whereby the UE selects one of its cells cites from its active set to be 'primary' in the DL and all others are classed as 'non-primary'.

10 Operation is summarised as follows. The UE selects one of the cells from its active set to be 'primary,' all other cells are classed as 'non primary'. The main objective is to transmit on the DL from the best cell, thus reducing the interference caused by multiple transmissions in a soft handover mode. A second objective is to achieve fast site selection without network intervention thus maintaining the advantage of the soft handover. In 15 order to select a primary cell, each cell is assigned a tempera identification (Coded By: SRNC, cell ID is mapped to [C) label and is mapped to RL Be) and UE periodically informs a primary cell identification to the connecting cells. The non-primaly cells selected by DE switch off the transmission power. The primary cell identity code is delivered via UL DPCCH FBI field.

20 In a situation with three different lengths of coded ID (tamp cell 11)) available denoted as "longs, "medium" and "short". The SRNC decides which length of coded ID is used and notifies it to Node-B and LIE. Two FBI settings FBI with one bit and FBI tenth two bits are supported for AL DPCCH.

When the SRNC makes a decision to enable the SSDT it has to tell node-B which UL 25 DPCCH structure to use. The use of FBI field in UL DPCCH may vary as the other

diversity methods such as TxAA may be used in parallel with the SSDT.

Upon receipt of the primary cell ID by all the involved cells, the cells checks its minimum SSDT quality threshold (Min-Q) value against the received IJL quality. If it is above 30 the minimum threshold value and the received Primary ID does not match its own Id (RL) then the nonprimary cell switches the transmission power off. Otherwise if the received power is below the Qth then the cells continues to transmit normally. The Decoded temp

-4 ld is only validated / acted upon by the Node-B when the link quality is above the minimum SSDT threshold quality value. This minimum threshold value is used so reliable detection of a frame can be achieved.

s The following features are required for the operation of SSDT: Requirementl: The SSDT function is initiated/terminated by the SONIC.

Requirement2: SSDT once set in one state (ON or OFF) will remain in that state for a 10 considerable period of time and will only be changed as the result of some signaling procedure (for ex. NBAP, RNSAP).

Requirement3: NBAP, RNSAP delays are less than 134ms. A typical user plane delay value is of 134ms. If NBAP and RNSAP delay is more than this then it may cause 15 problems with many signaling procedures.

Requirement4:ssDT identifier is set by SRNC to 'on' in Node B for each radio link. This will be set only when UE has more than or equal to 2 RLs, as a power control mechanism.

20 Requirement5:SSDT should be on at Node B upon the SSDT activation at UE and SSDT should be off at UE upon the SSDT termination at Node B. Requirement6: ID label is mapped to RL II), when RL [[)'s are created.

25 Requirement7:LsB field of FBI bits is used for sending temp ID [5].

Requirement8:Temp ID must be terminated within a flame [11.

The Node-B Should act according to the following criteria: 30 If SSDT mode is activated and the received quality is higher than Be quality threshold and the received ID is different than its own ID, then the node B will react switching off the power for the down link.

-5 SSDT activation time: A proper timing is required in order to change Cell state from SSDT off to SSDT on (or 5 on to off) at exactly the same point in time (i.e. same radio frame number). This will avoid the problem of some Node-B's encountering the unexpected UL DPCCH bits rather than that they used to handle in the previous frame. For example, if Tx-AA was operated before SSDT and UE send the Primary 1I) and the SSDT is of at node B then the Node-B may decode FBI bits as Tx-AA weight. In another case, Node-B may handle the FBI bits o as pilot bit.

Radio Cell Capabilities: Node-B SSDT capabilities like any other capabilities would be known by RNC through 15 O&M function, and during son handover, if the radio cell (Node-B) added can not support SSDT, then SRNC would make a decision to switch SSDT off in the previous node-B's (cells) and in UK.

As an example, lets consider the case where a UE has two RL across Node Bl and Node 20 B2, and lets suppose Cat Node B1 supports SSDT and Node B2 does not support SSDT.

In addition, SRNC does not have the prior knowledge whether Node B2 cell supports SSDT or not. In this case SRNC will send a RL configuration message with SSDT on to bow Node-Bs. Node B2 would then respond with a RL Reconfiguration Failure message.

As a consequence, this SRNC has to set SSDT to off by re-sending a RL Reconfiguration as message to Node B1 and an ARC message to the UK.

In a case where SRNC has a prior hlowledge of the Node-Bs capabilities, then SRNC will not set SSDT on in this scenario because it has the knowledge that one of its Node-B does not support SSDT.

The SSDT support capability of Node-B can be indicated in the NBAP O&M Message Node-B capability Exchange Message or Node-B Resource Notification message.

-6 Quality Threshold: The network operators should choose quality threshold values. These values (stated as an 5 example) may be chosen from one of following 8 different Qth settings, (0, -5, -10, -15, 20, -30, -0, -Lnfinity)[dB]. This values would be chosen with respect to the code word length, such as: When the ID code word is "long" then the Qth would be set "low" allowing a low quality o reception level.

When the if) code word is "medium" then the Qth would be set 'rnedium" allowing a medium quality reception level.

5 When the ID code word is "Short" then the Qth would be set "High" to fight against a low quality reception level.

Errors in decoding a short ID code word are more likely to occur, than when decoding a long code word. So when using a "long" code word the quality threshold can be set to a 2 0 bw value.

List of parameters to be exchanged across the Iub/lur interfaces: SSDT indicator.

25 Activation time (for e.g. Cam.

ID code length (long, medium, short).

UL DPCCH Structure Indicator: lbit FBI or 2 bit FBI in FBI Geld of UL DPCCH.

TxAA mode indicator orJoff.

so Parameters related with OHM: Qth: Range of Quality values as discussed above.

ID code and associated Quality level "Long ID code" "Medium ID code" "Shoot ID code" Small Quality Level Medium Quality Level Large Quality Level

- 8 TABLES IN NODE-B

The following is an example of ID Code tables stored in Node-B: 5 Table I Settings of ID codes for I bit FBI ID code ID label " long" " medium" "short" 000000000000000 0000000(0) 00000

111111111]11111 1111111(1) 11111

c 0000000011 1 1 1 1 1, 000011 1(1) 0001 1 d 1 1 1 111110000000 1 111000(0) 11100 e 000011111111000 1 0011110(0) 00110 f 1 1 1 10000000011 1 1100001(1) 11001 Table 2 Settings of R) codes for 2 bit FBI ID code (Column and Row denote slot position and FBI-bit position.) ID label "long" "medium" "short" a 0000000(0) 000(0) 000 0000000(0) 000(0) 000

b 1111111(1) 111(1) 111 1111111(1) 111(1) 111

0000000(0) 0000) 000

1111111(1) 111(1) 111

d 1111111(1) 111(1) 111 0000000(0) 000(0) 000

e 00001 11(1) 001(1) 001 1 1 1 1000(0) 110(0) 100

f I 1 1 1000(0) I 10(0) 1 10 000011 1(1) 001(1) 01 1

NBAP / RNSAP USE for SSDT Indication: The following messages related with SSDT are included in the HEAP, RNSAP protocols: The required infonnation elements for these messages, namely, RL Reconfiguration Prepare, RL Reconfiguration Commit, and R1 Reconfiguration Failure are shown in the following tables: RL Reconfiguration Prepare SSDT Infonnation O SSDT indication On/off M UL DPCCH Structure Indicator Ibit FBI / M 2bit FBI R) code length Short / M Long / Medium TxAA Lndication On/off M RL RecoDflguration comunt SSDT lnfonnation O Activation Time M RL Reconfiguration Failure.

RL D) _ M

Cause (SSDT not supported) M Using the HEAP protocol to convey messages related to SSDT has its advantages and 15 disadvantages the following is a sununa of them: Merits:

- lo -

Assured Delivery.

Software impact only.

Easy to keep track of node-lo hardware status.

If TxAA and SSDT are combined the use of WRAP simplifies the implementation.

Demerits: 3 NBAP/RNSAP messages for each SSDT setting.

Increase in processing load & hence delay.

o A second solution would be to use the DCH control frame protocol to convey messages relating to SSDT: The following is the simplest DCH Control Frame Protocol for SSDT indication triggered by SRNC: SSDT INDICATION

_ RL ID I/D

l SSDT INDICATION On/off B) Code length Long/medium/sho Activation tune CON AL DPCCH Structure Indicator lbit PBI / 2bit FBI TxAA indication [FFS] Onloff Ments: DCH Control frames are very simple.

20 Lower layer and faster to process.

DCH C-FP for SSDT does not need to with every DCH data frame.

Dements: No assured delivery of DCH C-FP.

Hardware as well as software Impact.

s Both ' NBAP/RNSAP" or "DCH control frame" protocols could be used for this purpose depending on implementation priorities.

It will be appreciated that the invention can therefore be implemented in virtually all current and telecommunications systems where diversity transmission or son handover is o implemented. To assist in appreciating how the invention may be extended, a glossary of some term definitions used in the art pertaining to UMTS systems is provided; any of the tams of art may be replaced by functionally equivalent components in a non- l3MTS system.

The following documents are incorporated herein by reference: [1] 3GPP RAN TS 25.214, Physical layer Procedures [2] 3GPP RAN TS 25.427, U19AN IublIur Interface User Plane Protocol for DCH 20 Data Streams [31 3GPP RAN TS 25.433, NBAP SPECIFICATIONS

[4] 3GPP RAN TS 25.423, RNSAP SPECIFICATIONS

[5] 3GPP RAN TS 25.211, Physical Channel and Mapping of Transport channel onto Physical channel.

- 12 Terms and definitions: Node 13: A logical node responsible for radio transmission t reception in one or more cells 5 to /from the UK. It also terminates the lute interface towards the RNC.

Diversity transmission: Situation where the UE has more than one RL at a time. RLs generated by a single source, but conveyed via several parallel physical channels.

10 Sop Handover: Situation similar to diversity transmission where one RNC adds RLs to a UK, which already has RL(s).

Abbreviations: RL Radio Link DL Down Link UL Up Linlc DPCCH Dedicated Physical Control Channel zo SSDT Site Selection Diversity Transmission NBAP Node B Application Part RNSAP Radio Netwoic Subsystem Application Part SRNC Serving Radio Network Controller RNC Radio Network Controller 25 User Equipment FBI Feed Back Infonnation TxAA Transmit Antenna Array SHO Son Handover Qth Quality Threshold 30 O&M Operation & Maintenance CFN Cell Frame Nwnber E Formation Element

7. - 13 O Optional M Mandatory DCH Dedicated Channel DCH C FP DCH Control Frame Protocol 5 TPC Transit Power Control CW Code Word UMTS Universal Mobile Telecommunications System LSB ISIS Significant Bit RRC Radio Resource Control 10 tub Interface between RNC and Node B lur Interface between two RNCs All features described herein can be independently provided unless otherwise stated.

Claims

1. A method for a mobile communication system having user equipment, a plurality of nodes for communicating with the user equipment, and a network controller for controlling the nodes, wherein the network controller initiates a Site Selection Diversity Transmission (SSDT) function of at least one of the nodes, whereby a node of the at least one of the nodes switches off downlink power when an identification code from the user equipment to the node is different from the identification code of the node, the method comprising the step of: notifying an activation time of the SSDT function to the nodes which support SSDT capabilities.

2. The method according to claim 1, wherein the nodes which support SSDT capabilities change their state with regard to the SSDT function at the same point in time, according to the activation time of the SSDT function.

3. The method according to claim 2, wherein the activation time is defined by a frame number.

4. The method according to claim 3, wherein the nodes which support SSDT capabilities change their state with regard to the SSDT function at the same radio frame number.

5. A node in a mobile communication system that includes user equipment for communicating with the node and a network controller for controlling the node, the node comprising: means for sending a message to the network controller in order to inform the network controller whether Site Selection Diversity Transmission (SSDT) capabilities are supported;

- 15 means for receiving an activation time of a SSDT function; and, means for activating the SSDT function at a time according with the received activation time, the activating means thereby switching off power of the downlink when an identification code from the user equipment to the node is different f om the identification code of the node.

6. A network controller for a mobile communication system, comprising: means for receiving a message sent from a node; means for initiating a SSDT function in the node according to the message; and, means for informing the node of an activation time of the SSDT function.

7. A method substantially as herein described with reference to and as shown in the accompanying drawing.

8. A node in a mobile communication system, the node being substantially as herein described with reference to and as shown in the accompanying drawing.

9. A network controller for a mobile communication system, the network controller being substantially as herein described with reference to and as shown in the . accompanying drawing.

10. Method for operating a power or interference control system like SSDT in a mobile telecommunications system, characterized in that means are provided to identify situations where radio links originate from cells with different capabilities.

1 1. Method according to claim 10 further comprising means to actuate this power or interference control system according to those capabilites.

12. Method according to claim 10 or 11 where the power or interference capabilities are activated and deactivated by a Serving Radio Network Controller (SRNC).

- 16

13. Method according to claim 12 where the node owning the cell (Node B) informs these capabilities to the SRNC by means of a signalling message.

14. Method according to claim 12 where the SRNC knows these capabilities through Operation and Maintenance (O&M) functionality.

15. Method of operating a mobile telecommunications system supporting Site Selection Diversity Transmission (SSDT) comprising means for coding cell site identities with several degrees of protection against error corruption combined with means to set-up different levels of reception quality thresholds for the decoding of the cell site identities.

16. Method according to claim I 5 where a Serving Radio Network Controller (SRNC) signals to the nodes owning the cells (Node Bs) and to the mobile units (UEs) the coding length of the cell site identities to be used.

17. Method according to claim 16 where a long coding length corresponds to a low reception quality threshold, a medium coding length corresponds to a medium reception quality threshold and where a short coding length corresponds to a high reception quality threshold.

18. Method according to claims 15 to 17 comprising means for controlling the timing and right synchronization for the activation and deactivation of Site Selection Diversity Transmission.

19. Method according to claim 18 where the frame number is used for synchronization purposes.

20. Method according to claims 15 to 17 comprising means to combine SSDT with otherpowercontrol, interference control ordiversity control methods like Transmit

- 17 Antenna Array (TxAA).

21. Method according to claim 20 where the SNRC signals to the Node B the uplink channel structure to use in order to accommodate the different power/interference/diversity control methods.

22. A Radio Network Controller operating according to a method described in any of claims 10 to 21.

23. A Cell, Node B or Base Station Transceiver operating according to a method described in any of claims 10 to 21.

24. Mobile Station or User Equipment implementing or capable to operate in a telecommunications system implementing any of the methods described in claims 10 to 21 or including equipment as described in claims 22 and 23.

25. Mobile telecommunications system operating a power or interference control strategy of the type Site Selection Diversity Transmission (SSDT) in which means are given to code cell site identities with several degrees of protection against error corruption combined with means to set- up different levels of reception quality thresholds for the decoding of the cell site identities, the system further including signalling means to identify situations where radio links originate from cells with different capabilities in order to activate or deactivate the power or interference control.