Method of providing point-to-multipoint service in mobile communication system

Abstract

A method of providing a point-to-multipoint service in a mobile communication system and transmission controlling method thereof are disclosed, by which a better quality of a point-to-multipoint service can be provided in a manner of coping with time-variable channel situation variable adaptively. In a mobile communication system providing a point-to-multipoint service, the present invention includes the steps of receiving data for the point-to-multipoint service from a base station, measuring a reception quality for the received point-to-multipoint service data, and transmitting reception quality information for the point-to-multipoint service data to the base station.

Description

If a BCMCSQualityReportTimer value becomes Identical to the timer expiry value QualityReportTimerMax, a mobile station feeds back BCMC service quality information to a base station via BCMCSQualityReport message. As the feedback information transmitted through the BCMCSQualityReport, at least one of PER and SNR can be used.

Table 3 shows an example of BCMCSQualityReport message.

TABLE 3

Field                   Length (bits)

MessageID               8
ChannelQuality          5
BCMCSFlowFormat         1
BCMCSFlowIDLength       2
zero or one occurrence of the following record:
BCMCSFlowCount          6
BCMCSFlowCount occurrence of the following three fields:
BCMCSFlowID             (BCMCSFlowIDLength + 1) * 8
TotalPackets            20
ErrorPackets            10
zero or one occurrence of the following record:
ProgramCount            6
ProgramCount occurrences of the remaining fields
(expect Reserved field):
ProgramIDLSBLength      5
ProgramIDLSBs           ProgramIDLSBLength
FlowDiscriminatorCount  6
FlowDiscriminatorLength 0 or 3
TotalPackets            20
ErrorPackets            10
FlowDiscriminateorCount occurrence of the following three fields:
FlowDiscriminator       FlowDiscriminatorLength
TotalPackets            20
ErrorPackets            10
Reserved                0-7 (as needed)

In Table 3, MessageID field is an identifier indicating a type of the present message and can be set to ‘0×05’ for example. ChannelQuality field is a field indicating channel status information and can be represented as a signal to noise ratio (SNR) using pilot signals of a base station. If a BCMC Flow Identifier included in the message shown in Table 3 is specified to a Program IdentifierFlowDiscriminator format, BCMCSFlowFormat field is set to ‘1’. Otherwise, It is set to ‘0’.

Meanwhile, BCMCSFlowIDLength field is set to a value of BCMCFlowLwngth received via a broadcast overhead message. BCMClowCount field is omitted if BCMCSFlowFormat field has a value of ‘1’. Otherwise, it is set to the number of BCMCS flow Identifiers. BCMCSFlowID field indicates a BCMC flow identifier. The BCMCSFlowID field is omitted if BCMCSFlowFormat field has a value of ‘1’. TotalPackets field means the number of packets received during a reception quality measuring interval. The TotalPackets field is omitted if BCMCSFlowFormat field has a value of 1′.

ErrorPackets field indicates the number of erroneous packets among the packets received for the reception quality measuring interval. The ErrorPackets field is omitted if BCMCSFlowField has a value of ‘1’. ProgramIDLSBLength field is set to the number of LSB (least significant bits) of ProgramID included in the present message. The ProgramIDLSBLength field is omitted if BCMCSFlowFormat field has a value of ‘1’. ProgramIDLSBs field is set to ProgramIDLSBLength LSB (least significant bits) of ProgramID.

FlowDiscriminatorCount field means the number of flow discriminators associated with a program to be registered by a mobile station. The FlowDiscriminatorCount field is omitted if BCMCSFlowFormat field has a value of FlowDiscriminatorLength field represents a length of a flow discriminator. The FlowDiscriminatorLength field is omitted if BCMCSFlowFormat field has a value of ‘0’ or if FlowDiscriminatorCount field has a value of ‘000000’. FlowDiscriminator field indicates a flow discriminator. The Flow Discriminator field is omitted if BCMCSFlowFormat field has a value of ‘0’.

As shown in Table 3, one general information for a channel status such as SIR is transmitted. Yet, TotalPackets information and ErrorPackets information used in indicating PER corresponding to each BCMCS flow are transmitted as many as the number of BCMCS flows. After the SCMCSQualityReport message has been transmitted, the BCMCSQualityReportTimer timer, TotalPackets counter and ErrorPackets counter are reset to zero.

Meanwhile, a base station transmits a broadcast overhead message including fields associated with the feedback information transmission. For example, QialityReportMode field, MeasureStartTime field and MeasureEndTime field can be used as the fields representing the feedback associated information.

Referring to Table 1, if QualityReportMode field is set to ‘00’, it means that a mobile station needs not to transmit the feedback for a BCMC service. If QualityReportMode field is set to ‘01’, it means that all mobile stations receiving the BCMC service need to periodically transmit the feedback. If QualityReportMode field is set to ‘10’, it means that prescribed mobile stations in poor channel status (e.g., PER is over 1%) among a plurality of mobile stations receiving the BCMC service need to transmit the feedback information.

MeasureStartTime field and MeasureEndTime field have information for an interval for measuring PER. MeasureStartTime is used In deciding a starting point of a PER measurement. And, the starting point of the PER measurement is decided as a timing point that meets Formula 2 for example.
(SystemTime−MeasureStartTime)mod N=0  [Formula 2]

In Formula 2, a unit of SystemTime or MeasureStartTime is slot (1.66..ms) and ‘N’ means a period for transmitting BCMCSQualityReport to a base station.

MeasureEndTime is used in deciding an ending point of a PER measurement. And, the ending point of the PER measurement is decided as a timing point that meets Formula 3 for example.
(SystemTime−MeasureEndTime)mod N=0  [Formula 3]

In Formula 3, a unit of SystemTime or MeasureEndTime is slot (1.66..ms) and ‘N’ means a period for transmitting BCMCSQualityReport to a base station.

In Formula 2 and Formula 3, a base station is able to decide and transmit a value of N to a mobile station. Alternatively, a value preset between a base station and a mobile station can be used as a value of N. Preferably, the preset value is 218 slots (7.28 minutes). Thus, a mobile station measures PER from one timing point meeting Formula 2 and to the other timing point meeting Formula 3.

So, a base station is able to accurately know the interval for which a mobile station measures PER to recognize a distribution of broadcast packets and unicast packets for the corresponding measurement interval. Hence, the base station is able to compensate inaccuracy of feedback information from the mobile station due to the unicast packets.

Besides, in order to solve a problem caused by the mixed existence of the broadcast and unicast packets, the base station is able to restrict the broadcast packets to be transmitted only for a specific interval for the generation of the feedback information.

A base station may use MeasureStartTime and MeasureDuration fields to transmit PER measurement interval information. In particular, the base station uses MeasureStartTime to indicate a starting point of measuring PER and MeasureDuration to indicate an interval for measuring PER from the starting point. In this case, the starting point of measuring PER is decided using Formula 2 and an ending point of the PER measurement can be decided using Formula 4.
{SystemTime−(MeasureStartTime+MeasureDuration)} mod N=0  [Formula 4]

The PER measurement is executed until a timing point that SystemTime meets Formula 4. In Formula 4, a unit of SystemTime, MeasureStartTime or MeasureDuration is slot (1.66..ms) and ‘N’ means a period for transmitting BCMCSQualityReport to a base station.

In Formula 4, a base station is able to decide and transmit a value of N to a mobile station. Alternatively, a value preset between a base station and a mobile station can be used as a value of N. Preferably, the preset value is 218 slots (7.28 minutes). Thus, a mobile station measures PER from one timing point meeting Formula 2 and to the other timing point meeting Formula 4.

A base station has a timer named BCMCSQualityReportTimer that operated by a unit of slot (1.66..ms). The timer is set to a pseudorandom value between 0 and {N-(MeasureEndTime-MeasureStartTime)−1) mod N}×1.66..ms. The timer is decreased by slot unit (1.66..ms). And, BCMCSQualityReport message is transmitted at a timing point at which the timer becomes zero. By enabling the timer set value to have a pseudorandom value, it is able to prevent excessive loads from being given to a base station if mobile stations transmit feedback Information simultaneously.

FIG. 7 is a diagram of a feedback timing point of BCMC service quality information according to another embodiment of the present invention.

Referring to FIG. 7, a first mobile station (1^st MS) measures PER according to Formula 2 and Formula 3 and then transmits BCMCSQuaityReport message according to the BCMCSQualityReportTimer timer. A second mobile station (2^nd MSS) measures PER according to Formula 2 and Formula 3 and then transmits BCMCSQualityReport message according to the BCMCSQualityReportTimer timer. However, since the first and second mobile stations have pseudorandom values as BCMCSQualityReportTimer set values, respectively, they transmit the BCMCSQualityReport messages at different timing points, respectively.

A mobile station sets a status indicator value and is then able to perform the operation shown in FIG. 7 using the status indicator value. For instance, a first status indicator (RqualityReportEnabled), a second status indicator (RqualityReportTimerEnabled) and a third status Indicator (RqualityMeasureEnabled) can be used. The first status indicator (RqualityReportEnabled) is set to ‘NO’ only if a value of QualityReportMode field is ‘00’. Otherwise, the first status Indicator (RqualityReportEnabled) is set to ‘YES’.

If the first status indicator (RqualityReportEnabled) is ‘YES’, the third status indicator (RqualityMeasureEnabled) is set to ‘YES’ each time. Formula 2 is met. If the first status indicator (RqualityReportEnabled) is ‘YES’, the third status indicator (RqualityMeasureEnabled) is set to ‘NO’ each time Formula 3 or Formula 4 is met. Meanwhile, if the first status indicator (RqualityReportEnabled) is ‘NO’, the third status indicator (RqualityMeasureEnabled) is set to ‘NO’.

If a value of the third status indicator (RqualityMeasureEnabled) is changed into ‘NO’ from ‘YES’, the second status indicator (RqualityReportTimerEnabled) is set to ‘YES’. If BCMCSQuaiityReport message is transmitted, the second status indicator (RqualityReportTimerEnabled) is set to ‘NO’.

A mobile station is able to transmit feedback information if the first status indicator (RqualityReportEnabled) is set to ‘YES’. A mobile station is able to measure feedback information for an interval during which the third status indicator (RqualityMeasureEnabled) is set to ‘YES’. And, a mobile station activates QualityReportTimer if the second status indicator (RqualityReportTimerEnabled) is set to ‘YES’.

In case of transmitting the feedback information on an access channel, the mobile station decides that the feedback is successful if receiving transmission success information (TransmissionSuccessful indication). In case of transmitting the feedback information on a reverse traffic channel, the mobile station decides that the feedback is successful by transmitting BCMCSQuaiityReport message.

Meanwhile, in transmitting feedback information, a mobile station is able to transmit its position Information as well as PER and SNR. If a base station obtains the position information of the mobile station as well as PER or SNR, the base station is able to recognize an area having a poor channel situation. Hence, necessary management can be provided to such an area.

Besides, if a predetermined condition is met for a mobile communication terminal, it is able to stop the feedback information transmission. For Instance, if a mobile station, which measures PER and SNR and transmits feedback information, performs a handoff into another cell area, a base station may be confused in understanding whether the received feedback information it the information corresponding to an old base station or a current serving base station. So, in such a case, it is able to make the mobile station stop the feedback information transmission.

As explained in the foregoing description, a base station having received feedback information from a mobile station performs a BCMC service transmission based on the received feedback information.

In particular, according to the received feedback information, in case that a channel status is not good, a transmission is performed by lowering a data rate. If the channel status becomes better, the transmission can be performed by raising the data rate. In the example shown in FIG. 3, in case that a channel status is degraded like the cell D, mobile stations within the cell transmit feedback information. A base station controls reception quality of the BCMC service based on the feedback information. The reception quality of the BCMC service can be controlled by changing a transmission format with which the BCMC service data is transmitted. The transmission format means a combination of at least two transmission parameters (e.g. a number of data bits included in a frame, a modulation scheme, a channel coding rate, or a channel coding scheme) with which the base station transmits the BCMC service data to the mobile stations.

For example, if the number of mobile stations transmitting the feedback information, which indicates that the channel status becomes good, exceeds a first threshold, the data rate and the coding rate can be raised. If the number of mobile stations transmitting the feedback information, which indicates that the channel status becomes poor, exceeds a second threshold, the data rate and the coding rate can be lowered. Moreover, the data rate can be raised only if the feedback information indicating that the channel statuses of the entire mobile stations become good is received. And, the data rate can be lowered only if the feedback Information indicating that the channel statuses of the entire mobile stations become poor is received.

Thus, in case that a base station decides a new data rate using feedback information, the base station transmits the decided data rate information to mobile stations within a cell via a broadcast overhead message and then performs a BCMC service according to the decided data rate.

Meanwhile, in aspect of a service provider, a smooth service can be performed on an area, of which channel situation is decided poor according to feedback information, by redesigning a cell or installing a repeater additionally. And, the feedback information can be used as a database for customer management. So, the customer management can be enhanced in a manner of recognizing a user failing to receive the BCMC service correctly using the feedback information.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

1. A method of controlling a point-to-multipoint service transmission in a mobile communication system, the method comprising:

receiving point-to-multipoint service data from a base station;

receiving control information from the base station, the control information associated with reception quality information of the received point-to-multipoint service data;

measuring a reception quality of the received point-to-multipoint service data; and

transmitting the reception quality information for the point-to-multipoint service data to the base station according to the control information,

wherein the control information includes an indicator of at least one mobile station that transmits the reception quality information,

wherein the control information further includes information for a reception quality information transmission mode,

wherein the reception quality information transmission mode corresponds to at least a periodic mode or a threshold mode,

wherein the control information further includes a transmission period of the reception quality information if the reception quality information transmission mode corresponds to the periodic mode;

wherein the control information further includes threshold information for the reception quality information transmission if the reception quality information transmission mode corresponds to the threshold mode; and

wherein the control information further includes the transmission period of the reception quality information and the threshold information for the reception quality information transmission if the reception quality information transmission mode corresponds to the periodic mode and the threshold mode.

2. The method of claim 1, wherein the control information includes information for a transmission condition of the reception quality information, the transmission condition being to stop transmitting the reception quality information during performance of a handoff.

3. The method of claim 1, wherein:

the reception quality information is transmitted when a packet error rate or a signal to noise ratio (SNR) exceeds a threshold and the reception quality information transmission mode corresponds to the threshold mode; and

the reception quality information is transmitted to the base station according to the transmission period if the reception quality information transmission mode corresponds to the periodic mode.

4. The method of claim 1, wherein

measuring the reception quality comprises checking the reception quality during a reception quality measuring interval

according to information in the control information for a reception quality measurement starting point and a reception quality measurement ending point.

5. The method of claim 4, wherein:

the reception quality measurement starting point is a timing point that meets (SystemTime−MeasureStartTime) mod N=0;

the information for the reception quality measurement starting point is MeasureStartTime; and

N is a reception quality information transmission period.

6. The method of claim 5, wherein:

the reception quality measurement ending point is a timing point that meets (SystemTime−MeasureEndTime) mod N=0; and

the information for the reception quality measurement ending point is MeasureEndTime.

7. The method of claim 5, wherein:

the reception quality measurement ending point is a timing point that meets {SystemTime−(MeasureStartTime+MeasureDuration)} mod N=0; and

the information for the reception quality measuring interval is MeasureDuration.

8. The method of claim 7, wherein the reception quality information is transmitted at a pseudorandom timing point after the reception quality measurement ending point with the transmission period.

9. The method of claim 4, wherein a unicast packet is not received during the reception quality measuring interval.

10. A method of providing a point-to-multipoint service in a mobile communication system, the method comprising:

transmitting point-to-multipoint service data to a plurality of mobile stations;

transmitting control information to the plurality of mobile stations, the control information associated with reception quality information of the point-to-multipoint service data to;

receiving the reception quality information for the point-to-multipoint service data, the reception quality information transmitted from at least one of the plurality of mobile stations according to the control information; and

controlling a quality of the point-to-multipoint service according to the reception quality information,

wherein the control information includes an indicator of at least one mobile station that shall transmit the reception quality information,

wherein the control information further includes information for a reception quality information transmission mode,

wherein the reception quality information transmission mode corresponds to at least a periodic mode or a threshold mode,

wherein the control information further includes a transmission period of the reception quality information if the reception quality information transmission mode corresponds to the periodic mode;

wherein the control information further includes threshold information for the reception quality information transmission if the reception quality information transmission mode corresponds to the threshold mode; and

wherein the control information further includes the transmission period of the reception quality information and the threshold information for the reception quality information transmission if the reception quality information transmission mode corresponds to the periodic mode and the threshold mode.

11. The method of claim 10, wherein the control information includes information for a transmission condition of the reception quality information.

12. The method of claim 10, wherein controlling the quality of the point-to-multipoint service comprises adjusting a data rate of the point-to-multipoint service data.