Method of broadcasting over-the-air multicast

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Background of invention] [Technical field to which the invention belongs] The present invention relates to a telecommunications system, and more particularly to a method of broadcasting quality by multicast over an air interface to a plurality of mobile communication terminals. [0002]

[Conventional technology] Multicast is convenient whenever there is a group of subscribers with a common interest, and information that is of interest to the group is broadcast to that group in a single transmission. For example, at a sporting event, a PDA (Personal Digital) Multiple spectators with mobile terminals such as Assistants (personal portable information terminals) may wish to receive broadcasts such as highlights and game stats. In broadcast transmission, the same data is transmitted to all users at the same time, and no response from the mobile communication terminal is required. Multicast processing is used only on downlink channels, not on uplink channels. On the other hand, other channels on the network are open for use by other users. Billing for a particular broadcast may be set to a flat rate. The information to be broadcast may be encrypted, or a code entry may be requested to ensure that only signed-up subscribers can receive the broadcast information. In the GSM (Global System for Mobile Communications) system, a key can be set on the SIM card so that the mobile communication terminal can receive multicast. [0003]

Multicast is effective and requires minimal resources to send. However, the quality of service (QoS, ie, transmission quality, etc.) depends on the bearer. The multicast protocol is implemented at a higher network layer that does not consider the transfer medium at the time of transmission, and the system operator asks whether the information to be multicast is received by the mobile communication terminal with sufficient transmission quality for the data type to be transmitted. I don't know during multicast. Point-to-point unicast, on the other hand, can ensure communication by requiring an acknowledgment by the recipient. This technique is often used in wired networks where the potential for packet loss is low. However, when a wireless network relays multicast packets over an air interface, the potential for packet loss is quite high. To compensate for this, data networks such as GPRS (General Packet Radio Service) send multicast packets to each radio terminal as point-to-point unicast packets. For example, Group Call Service (PTM-G) is defined in GSM's GPRS standard, which provides multicast inputs, for example, corporate LAN: Obtain from trusted sources such as Wireless Ethernet® and send them to a wireless GPRS receiver as a point-to-point unicast. To achieve this, PTM-G utilizes a list of individual receivers subscribed to the multicast and sends a copy of the data to each receiver individually. The acknowledgment is sent from each receiver to the network. This type of transmission utilizes retransmissions at the wireless link layer and is therefore a high bandwidth transmission that is not well suited in real time. In addition, increasing the number of recipients of multicast services may reduce scalability and require significant network resources. [0004]

Alternatively, there is an easy way to eliminate the acknowledgment from the recipient and simply broadcast the packet in the cellular coverage area. The problem with this method is that the multicast service is a billing service, and a mechanism that measures the transmission and adjusts it according to the QoS of the transmission is indispensable. [0005]

In addition, it should be noted that GPRS, like most other networks, has different bandwidths that each mobile terminal supports and the ability to support current applications. Current multicast processing does not take into account different mobile communication terminal classes and their performance. [0006]

In overcoming the shortcomings of existing solutions, it would be beneficial to have a way to broadcast quality over multicast over air interfaces to multiple mobile terminals. The method should be fully extended as the number of recipients of multicast services increases and should take into account different mobile terminal classes and their performance. Furthermore, it should allow the system operator to measure transmissions and make adjustments according to the QoS of the transfer. On the other hand, it is not necessary to receive an acknowledgment from each mobile communication terminal that has received the multicast. The present invention provides such a method.

[Outline of Invention] In one aspect, the present invention is a method of broadcasting data by multicast to a group of mobile communication terminals via an air interface in a wireless telecommunications network. The method determines the minimum transmission quality (TQmin) that a mobile communication terminal must receive for the data type to be broadcast, broadcasts a test transmission to the mobile communication terminal, and responds from the mobile communication terminal representing the group. Is started by receiving. The response includes an indication of the received transmission quality, and the method determines if the received transmission quality is greater than or equal to TQmin. If the received transmission quality is TQmin or higher, the data is broadcast by multicast to the group of mobile communication terminals via the air interface. [0007]

On the other side, the present invention is a method of broadcasting data by multicast to a group of mobile communication terminals via an air interface, and the mobile communication terminal must receive the data type to be broadcast. It includes a step of determining the minimum transmission quality (TQmin) and a step of broadcasting a test transmission including the maximum transmission quality threshold (TQmax) to a mobile communication terminal. The mobile communication terminal is instructed not to respond to the test transmission when the transmission quality received by the mobile communication terminal exceeds TQmax. Following this, the response timer is activated to receive a response, including an indication of the received transmission quality, from the mobile communication terminal representing the group. At this time, each of the responses includes an indication of the transmission quality received by the mobile communication terminal transmitting the response. Next, it is determined whether the received transmission quality is TQmin or higher. If the received transmission quality is less than TQmin and the response timer expires, the TQmin is lowered and the test transmission to the mobile communication terminal is broadcast again at the lowered TQmin. If the received transmission quality is TQmin or higher, the data is broadcast by multicast to the group of mobile communication terminals via the air interface. [0008]

In yet another aspect, the present invention is a method of broadcasting data by multicast to a group of mobile communication terminals via an air interface, unless the mobile communication terminal receives the data type to be broadcast. It includes a step of determining the minimum transmission quality (TQmin) that must not be required and a step of broadcasting a test transmission including the maximum transmission quality threshold (TQmax) to a mobile communication terminal. The mobile communication terminal is instructed not to respond to the test transmission when the transmission quality received by the mobile communication terminal exceeds TQmax. Following this, responses are received from a plurality of mobile communication terminals in the group. Here, each of the responses includes an indication of the transmission quality received by the mobile communication terminal that transmits this response. Then, it is determined whether or not the received transmission quality is TQmin or higher. If the received transmission quality of the received response of a predetermined threshold number is TQmin or higher, the data is broadcast by multicast to the group of mobile communication terminals via the air interface. [0009]

By referring to the accompanying drawings, along with a detailed description, the invention will be better understood and many purposes and benefits will become more apparent to those skilled in the art. [0010]

[Detailed description of the embodiment] The present invention determines the downlink transmission mode used in a multicast broadcast that is the most effective mode and is most likely to reach a particular group of mobile communication terminals envisioned as recipients. .. This method is used prior to the multicast transmission of the payload in order to coordinate the transmission for the best transmission to all receiving subscribers. The present invention defines a minimum broadcast quality while adapting the broadcast based on the performance of the multicast receiver. Suitable embodiments of the present invention are described below in the context of GPRS. [0011]

Other than the present invention, if the operator needs to push the data to a group of subscribers, the operator attempts to send the data, but there is no way to know what bit rate to use. In most cases, the operator will transmit the data at the optimum bit rate to produce the best transmission quality. However, for any data transmission, there are thresholds for defining bad quality, medium quality and good quality, and for some transmissions, lower than optimal transmission quality may be sufficient. .. The present invention makes it possible to transmit to an operator with a quality lower than the optimum quality and to determine that there is a mobile communication terminal capable of receiving the transmission. [0012]

When multicast targets a group of subscribers within a cell, the methods of the invention apply certain QoS criteria and extract one response that represents a member of the group. This maximizes the likelihood that the multicast packet will reach all group members without error, without requiring a separate response from each mobile terminal. Appropriate representative members must be identified as ensuring that all members are likely to receive multicast transmissions. Once the network receives the response, the group is notified of this fact to prevent other mobile terminals from responding. [0013]

FIG. 1 is a diagram showing a cellular service area surrounding the base station 10 and an area 11 in which the multicast service is provided by the base station. The outer boundary 12 defines a multicast area defined by the minimum transmit quality (TQmin) required to carry a particular broadcast service. TQmin can vary depending on the content of the transmission, including loss-sensitive data such as software, images, text documents, or loss-tolerant data such as audio and video. [0014]

Statistical data of cells are collected based on common point-to-point cellular transmissions to build a database for each base station. Statistical data show the optimum signal quality that users typically experience when operating in a cell. Based on the signal quality, TQmin is determined for a particular data content (eg, audio stream, etc.). If TQmin is, for example, 3 out of 5 time slots, the test broadcast requires the mobile communication terminal to have a receive transmission quality (tq) that responds to 3 out of 5 time slots. [0015]

The method applies the network in response to changing QoS levels. If most of the mobile communication terminals are close to the base station 10, the quality threshold increases as well as the bit rate. However, if most of the mobile communication terminals in the group move farther away from the base station, the signal quality threshold may be lowered. The threshold range within the query is selected based on statistical data. [0016]

The inner border 13 of the multicast area is defined by the highest transmit quality (TQmax). It is defined to avoid flooding the network with responses from mobile terminals that measure transmission quality better than TQmin. Moreover, the highest quality level is defined because any response with a notification tq above that level is not fairly representative of the group and is not useful. TQmin and TQmax are defined and broadcast to groups within the test broadcast. When the base station receives the first response notifying tq within the range of TQmin <tq <TQmax, the other mobile terminals are notified not to respond from the base station. [0017]

The present invention solves a problem in an existing system in which a base station must receive an acknowledgment from each mobile communication terminal. This saves uplink traffic and processing at the base station. In a general on-point-to-point cellular connection from a provider to a mobile communication terminal, there are both a downlink connection and an uplink connection that transmit signal strength information. This is not the case for multicast, which has only downlink connections. The methods of the invention provide statistical sampling to increase the likelihood that all members of the group will receive good reception. [0018]

The service area for multicast may be smaller than the area covered by the cell. The mobile communication terminal at the edge position of the multicast service area may be used as a reference mobile communication terminal for controlling the transmission quality. In this case, the mobile communication terminal located outside the desired multicast area cannot receive the multicast transmission. [0019]

If the first method performed does not produce definitive results, the method is repeated using a wider range between TQmin and TQmax, or with improved transmission quality of the test broadcast. Different QoS thresholds may be set depending on the type of information transmitted. Different coding techniques are used, for example, for audio, data, and video. Since it depends on the data type transmitted in this way, there is a minimum threshold encoding scheme that requires guarantee that the data can be transmitted, and a minimum signal quality that the response should exceed. .. [0020]

FIG. 2 is a simplified flowchart showing the relationship between the multicast quality procedure 20 of the present invention and the multicast broadcast. The multicast quality procedure comprises a bandwidth optimization procedure 21 and a transmit quality procedure 22. The purpose of the bandwidth optimization procedure is to determine which bandwidth the multicast transmission should be allocated to, and to identify TQmin and TQmax. The bandwidth allocated to the multicast service may be affected by the current traffic in the system, the minimum bandwidth required by the multicast transmission, and the performance of the mobile communication terminal trying to receive the multicast transmission. .. The time slot assigned to the service can have a range of 1 to 8 in GPRS, so the bandwidth may vary from 14 kbs to 115 kbs. In principle, the minimum multicast service request and the bandwidth allocated by the network operator for multicast transmissions determines the minimum and maximum number of time slots allocated for multicast transmissions. In practice, the mobile terminal class in the receiving group determines the actual number of time slots utilized for multicast transmission, as determined in the methods of the invention. [0021] [0021]

In the bandwidth optimization procedure, the transmission quality in a given cell is evaluated by transmitting the test packet over the broadcast channel. The test packet is transmitted using a downlink transmission method that assumes an ideal state on the link (ie, 1 time slot, minimal coding, etc.). The transmission specifies the minimum bandwidth required for this transmission. Bandwidth optimization procedures are described in more detail below in connection with Figure 3. [0022]

In step 22, the transmission quality procedure is executed to obtain the response from the representative mobile communication terminal. The purpose of the transmit quality procedure is to improve the true multicast model, i.e. send only one packet to many users. In this procedure, the quality of multicast transmission is measured from the viewpoint of the mobile communication terminal (end user), and the parameters of layer 1 (physical layer) and layer 2 (link layer) are adjusted. For wireless, transmission quality can be measured in relation to signal strength and bit error rate (BER). [0023]

In the transmission quality procedure, the transmission quality within a given cell can be evaluated by transmitting a test packet over a broadcast channel. The test packet is transmitted using a downlink transmission method that assumes an ideal state on the link (ie, 1 time slot, minimum coding, etc.). The test packet also identifies the highest transmission quality TQmax. A mobile terminal that is camping on the cell where the broadcast transmission is taking place and is interested in receiving a particular broadcast service associated with the test packet ensures that the transmission can be received at a given level of quality, TQmin. If the received signal quality of a particular mobile communication terminal is TQmax or higher, the mobile communication terminal is not suitable for replying. This is because it is likely to be located close to the base station and is not representative of a mobile communication terminal located near the edge of the cell / service area. [0024]

All mobile terminals with a receive / transmit quality (tq) less than TQmax initiate a reply of that tq to the network. When a tq equal to the TQmin of the broadcast service is received at the base station, an instruction to stop transmitting further tq measurements is broadcast to the mobile communication terminal. If within a given time window the base station does not receive a response indicating that the mobile terminal will receive the test packet at a tq greater than TQmin, lower the required downlink tq and follow the multicast quality procedure. repeat. The transmission quality procedure is described in more detail in connection with FIG. [0025]

The results of the bandwidth optimization procedure 21 and the transmission quality procedure 22 are used for multicast transmission in step 23. In this embodiment of the invention, the bandwidth optimization and transmission quality procedures are not repeated during multicast. This embodiment is used in multicasting to relatively stationary users, such as spectators at sporting events and concerts. [0026]

FIG. 3 is a flowchart showing the processing of the preferred embodiment of the multicast quality procedure 20 of FIG. In step 31, the system operator specifies TQmin, the minimum bandwidth required for the type of data transmitted by multicast. As mentioned above, the operator may determine the TQmin from statistical data about cells collected from common point-to-point cellular communications of the same data type that are multicast transmitted. In step 32, TQmax is specified. In step 33, the test packet is broadcast on the broadcast channel using a method that assumes an ideal downlink situation. The test packet identifies TQmin and TQmax, and the mobile communication terminal that receives the test packet having the transmission quality (tq) in the range between TQmin and TQmax is instructed to respond. [0027]

The response timer is started in step 34. The response timer handles a situation in which a test packet is broadcast but there is no mobile communication terminal that notifies tq within a predetermined range. In that case, the mobile communication terminal is located far away from the base station, for example, and receives a signal having a quality lower than TQmin, or is located considerably closer to the base station, far more than TQmax. You may be receiving a signal of high quality. The response timer is used to measure the response period, and when it expires, the network stops listening to the response. Therefore, when the timer expires, it can be seen that there is no mobile communication terminal in the cell capable of receiving the signal within a predetermined transmission quality range. [0028]

In step 35, all mobile terminals that have received the broadcast with a tq lower than TQmax begin transmitting the response to base station 10. The response includes the received tq and the class of the mobile communication terminal. GPRS includes different classes of mobile terminals, so multicast may be sent to mobile terminals with different performance. The present invention makes it possible to use these classes when transmitting multicast to the operator. The class of the mobile communication terminal is indicated in the response and identifies whether the responding mobile communication terminal is multi-slot and the reception performance of the responding mobile communication terminal. [0029]

In step 36, base station 10 receives a response with the notified tq and class of mobile communication terminals. At 37, it is determined whether the notified tq is TQmin or more. If it is less than TQmin, the process proceeds to step 38 to determine if the response timer has expired. If it does not expire, the process returns to step 36 and the base station continues to receive the response from the mobile communication terminal. If the response timer expires at 38, then no mobile terminal has received a transmission with a tq greater than or equal to TQmin. Therefore, in step 39, the TQmin is lowered, the process returns to step 32, and the test sequence is restarted. TQmax may be adjusted in step 32 to increase the predetermined range between TQmax and TQmin. [0030]

However, if in step 37, a response notifying tq of TQmin or higher is received, the process proceeds to step 41 and the system instructs the remaining mobile communication terminals to stop responding. The intent is to receive only acknowledgments from the first qualified mobile terminal that successfully receives the test packet. When this acknowledgment is received, it means that acceptable transmission quality has been achieved. As a result, in order to avoid further responses from other mobile communication terminals, rebroadcasting into the cell is performed to reduce the load on the network. [0031]

In this method, in step 42, the bandwidth supported by the mobile communication terminal and the air interface is determined. In step 43, multicast transmission is initiated. GPRS broadcasts may fill time slots from 1 to 8. If all mobile terminals can receive 4 out of 8 time slots, the operator may start the broadcast in 4 time slots. If the operator transmits video, a minimum of 4 time slots are set, and mobile communication terminals that can operate in 4 time slots or less cannot benefit. If one mobile terminal can receive 4 time slots and others can receive 8 time slots, the operator will probably send in 4 time slots so that the maximum number of users can receive the data. There will be. However, if higher data rates are preferred and all mobile terminals have reception performance in 8 time slots, the operator will probably broadcast in 8 time slots. [0032]

FIG. 4 is a flowchart of processing according to another embodiment of the present invention. In this embodiment, the multicast quality procedure 20 is broadcast periodically to ensure that the target mobile terminal is still receiving the multicast and to respond to any mobile terminal that meets the reception criteria. .. This embodiment may be effective when the target mobile communication terminal is moving in a wide area and there is a large change in the received tq. The use of this embodiment may depend on system performance and transmitted data. This is because system resources are used to perform multicast quality procedures. [0033]

In step 21, the bandwidth optimization procedure is performed. The transmission quality procedure performed in step 22 and the results of these procedures are utilized to perform the multicast transmission in step 23. Optionally, the operator may set a periodic timer in step 45. If it is determined that the timer has expired in step 46, the process returns to step 21 and the bandwidth optimization procedure and the transmission quality procedure are repeated. [0034]

FIG. 5 is a flowchart of processing according to still another embodiment of the present invention. For a given type of data, the transmission quality procedure may be broadcast during the dead time when the transmission data does not exist. In this embodiment, the bandwidth optimization procedure is performed in step 21 and the transmission quality procedure is performed in step 22. The results of these steps will be used for multicast transmission in step 23. If it is determined in step 51 that there is a dead time in the data transmission, the operator may choose to repeat the transmission quality procedure in the dead time in step 52. Then, the multicast transmission is continued in step 23. [0035]

FIG. 6 shows a flow chart of processing in another embodiment of the multicast quality procedure in the present invention. In this embodiment, the operator is allowed to respond to one or more mobile terminals in order to obtain sampling and to ensure that multiple mobile terminals are receivable at the minimum quality level. You may. This embodiment may be used when the load on the network is light. However, if the network is congested, the operator may not want to use system resources for multiple responses, and a single that can be received with a given QoS, as shown in Figure 3. It may request a response from the mobile terminal only. The present embodiment also reveals a stepwise algorithm that reduces transmission quality if all mobile communication terminals are receivable. Here, subsequent test transmissions are performed at lower transmission quality to see if there is still a suitable response. [0036]

The method is initiated as shown in Figure 3 and similar steps are given for the same citation number. In step 31, the system operator specifies TQmin, the minimum bandwidth required for the type of data transmitted by multicast. In step 32, TQmax is specified. At 33, the test packet is broadcast on the broadcast channel using a method that assumes an ideal downlink situation. The test packet identifies TQmin and TQmax, and the mobile communication terminal that receives the test packet having the transmission quality (tq) in the range between TQmin and TQmax is instructed to respond. [0037]

The response timer is started in step 34. In step 35, all mobile terminals that have received the broadcast with a tq lower than TQmax begin transmitting the response to base station 10. The response includes the received tq and the class of the mobile communication terminal. In step 61, the base station receives a sampling of the response having the notification tq and the class of mobile communication terminals from the plurality of mobile communication terminals. In step 62, it is determined whether multiple responses have been received such that the notified tq is TQmin or greater. If not received, the process proceeds to step 38 to determine if the response timer has expired. If the timer has not expired, the process returns to step 61 and the base station continues to receive the response from the mobile communication terminal. If the response timer expires in step 38, the process proceeds to step 39, the TQmin is lowered, and then the process returns to step 32 to restart the test sequence. TQmax may be adjusted in step 32 to increase the predetermined range between TQmax and TQmin. [0038]

However, if a plurality of responses notifying tq of TQmin or more are received in step 62, the process proceeds to step 63, and the system instructs the remaining mobile communication terminals to stop responding to the reception. The process proceeds to step 64 to determine whether all responses signal tq greater than or equal to TQmin. If not, multicast is performed in step 65. Alternatively, the operator may specify that multicast be initiated when tq is greater than or equal to TQmin in a number of responses that exceed a predetermined threshold. However, if all responses signal tq greater than or equal to TQmin, the broadcast transmission quality may be reduced in step 66 and processing may return to step 34 to conserve network resources. [0039]

Various parameters may be adjusted to reduce transmission quality in the downlink to the mobile communication terminal. The parameters include channel coding, power control, diffusion coefficient and the like. The actual radio parameters can vary from network to network. For channel coding, there are various MPEG coding methods for different situations. For example, MPEG-4 is an option in multimedia coding where only low data rates are feasible in air interfaces. Other examples of available codecs can include H261, H263 and RealVideo. The parameters that can be controlled in the downlink depend on the particular radio interface, such as GPRS, EDGE, wideband CDMA, etc. Transmission quality measurement also depends on the wireless interface. [0040]

It is believed that the operation and configuration of the present invention have been clarified by the above description. While the methods, devices and systems shown and described above are characterized as suitable, various changes and modifications are made without departing from the scope of the invention as defined in the claims. It will be immediately understood that it is possible.

[Simple explanation of drawings]

[Figure 1]

It is a figure which shows the cellular service area which surrounds a base station, and the area which is serviced by multicast from a base station.

[Figure 2]

It is a simplified flowchart which shows the relationship between the multicast quality procedure of this invention and a multicast broadcast.

[Fig. 3]

It is a flowchart of the process in a preferred embodiment of the multicast quality procedure of the present invention.

[Fig. 4]

It is a simplified flowchart of the process in another embodiment of the present invention.

[Fig. 5]

It is a flowchart of the process in still another embodiment of this invention.

[Fig. 6]

It is a flowchart of the process in the further embodiment of the multicast quality procedure of this invention.