Admission control for data connections

ADMISSION CONTROL FOR DATA CONNECTIONS

FIELD OF THE INVENTION

0003The present invention relates to mobile telecommunication systems. In particular, the present in- vention relates to a novel and improved method, system and network node for controlling quality of service for existing data connections using shared radio resources in a wireless communication network.

BACKGROUND OF THE INVENTION

0005The Radio Resource Management (RRM) e.g. in the GERAN (GSM/EDGE Radio Access Network; GSM, Global System for Mobile Communications; EDGE, Enhanced Data rates for GSM Evolution) and the UTRAN (UMTS Terres- trial Radio Access Network) are responsible for utilisation of air interface resources. The RRM is needed for e.g. maintaining the QoS (Quality of Service), planned coverage, and for offering high capacity. The RRM enables optimising service capacity and capabil- ity. The full scope of the RRM is large, and several algorithms are needed to perform various tasks . These algorithms include also Admission Control (AC) .

0006The purpose of admission control is to ensure that there are free radio resources for the intended call or session with required signal-to-interference ratio (SIR) and bit rate. Admission control is always performed when a mobile station initiates communications in a new cell, either through a new call or handover. Furthermore, admission control is performed when a new service is added during an active call. In general, the admission control procedure ensures that the interference created after adding a new call does not exceed a prespecified threshold.

0007Admission control needs to be done separately for uplink and downlink direction. This is especially important if the traffic is highly asymmetric. Typical criteria for admission control are call blocking and call dropping. Blocking occurs when a new user is denied access to the system. Call dropping means that a call of an existing user is terminated. Call dropping is typically considered to be more annoying than blocking.

0008If the air interface load is allowed to increase excessively, the coverage area of the cell is reduced below the planned values, and the quality of service (QoS) of the existing connections cannot be guaranteed. The QoS is the idea that transmission rates, error rates, delay, and other characteristics that can be measured, improved, and, to some extent, guaranteed in advance. The QoS is of particular con- cern for the continuous transmission of video and multimedia information. Transmitting this kind of content dependably is difficult in public networks using ordinary "best effort" protocols. Before admitting a new connection, the admission control needs to check that the. admittance will not sacrifice the planned coverage area or the quality of the existing connections. Admission control accepts or rejects a request for establishing a radio access bearer in the radio access network. The admission control functionality is lo- cated in the Radio Access Node (RNC) in the Universal Mobile Telecommunication System (UMTS) where the load information from several cells can be obtained. The admission control algorithm estimates the load increase that the establishment of the bearer would cause in the radio network. The requesting bearer can be admitted only if both uplink and downlink admission control admit it, otherwise it is rejected because of the excessive interference that is would be generated in the network. The limits for admission control are set by the radio network planning.

0009To support services that require some guarantees (e.g. multimedia streaming services) means that the radio access network (in the RNC and Base Station System (BSS) ) needs to guarantee certain QoS in terms of throughput and delay. If some guarantees are needed, then radio resource reservation is required. Therefore, admission control can be used to calculate what network resources are required to provide the requested QoS, to determine if resources are available, and to reserve them.

0010During the connection the usage of radio re- sources are monitored by a Quality Control (QC) function, which makes sure that the provided QoS is in line with the negotiated ones, i.e. which tackles degraded situations to maintain the QoS for the most of the users at the expense of a few users' QoS. In case of real time (RT) ' traffic, if the target throughput cannot be achieved, QoS renegotiation might be necessary.

0011The main problem is that there is a need for different treatment in the admission control for streaming data flows sharing the same radio resources and experiencing different radio link conditions. The reason for that is that streaming connections are using shared Medium Access Control (MAC) mode, with the aim of increasing the resource utilisation, but at the same time these connections have real time requirements, such as guaranteed bitrate . Since determined radio link conditions lead to a determined experienced throughput, each connection needs to be managed separately to assure that the negotiated QoS requirements are fulfilled.

SUMMARY OF THE INVENTION

0013The present invention describes a method, system and network node for controlling or maintaining quality of service for existing data connections using shared radio resources in a wireless communication network. The wireless communication network is e.g. the UMTS.

0014The Quality Control monitors the satisfaction level of every user as well as the user satisfaction rate in the system. The purpose of this function is to indicate the degraded situation to the Admission Control . In that way, appropriate actions to counteract those situations in which the provision of QoS is not in line with the negotiated QoS (defining the value considered for degradation, i.e. user satisfaction criteria) for a determined amount of users (i.e. user satisfaction rate threshold) can be triggered. The Quality Control indicates Admission Control about the convenience of starting to block users that request guaranteed QoS, such as streaming service users, or non Real Time (nRT) users to avoid the degradation in the provision of QoS for those users already admitted to the system.

0015Therefore, some changes in the admission con- trol policy are one of those possible counteracting actions triggered by the Quality Control when QoS degradation is perceived. In the present invention, the Admission Control evaluates previous indications from the Quality Control in order to deal properly with streaming connections when problems occur.

0016The present invention manages several streaming data flows sharing radio resources, based on calculating the used capacity by the ongoing connections and estimating the needed capacity by the . incoming one. For that purpose, a safety margin concept is defined to take into account the variation of radio link conditions. This parameter may be different for each type of connection (i.e. the safety margin for gold users is bigger than the one for bronze users) and it is dynamically updated, depending on Quality Control feedback. In a preferred embodiment of the present invention, after the Quality Control feedback, the Admission Control will be able to use different safety margins depending on the QoS provisioning that the different ongoing connections are experiencing, so that the system is able to provide the required Quality of Service (QoS) for the most of the streaming users by blocking some users .

0017The present invention improves the user sat- isfaction ratio for streaming users since Admission Control also avoids incoming connections to affect ongoing ones. In the present invention, both Admission Control and Quality Control functionalities work coordinated preventing the users from being unsatisfied.

BRIEF DESCRIPTION OF THE DRAWINGS

0019The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illus- trate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings:

0020Fig 1 illustrates the safety margin concept for those connections that require guaranteed bit rate,

0021Fig 2 illustrates one embodiment of using safety margins,

0022Fig 3 is a block diagram illustrating a preferred embodiment of the system in accordance with the present invention, and

0023Fig 4 is a flow diagram illustrating the functionality of a preferred embodiment of the present invention.

0024DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

0025Figure 1 illustrates the safety margin con- cept for those connections that require guaranteed bit rate. A channel in a wireless communication network has a certain maximum capacity for data connections. To support services that require some guarantees (e.g. multimedia streaming services) means that the radio access network (in the RNC and BSS) needs to guarantee certain QoS in terms of throughput and delay. If some guarantees are needed, then radio resource reservation is required.

0026The largest cylinder 14 refers to the total channel capacity. The sum of the capacities of different data connections cannot exceed the total channel capacity. The cylinder 12 illustrates the capacity used by the data connections on the channel. The cylinder 10 refers to the capacity that is needed for a new data connection. The safety margin is used to depict the excess capacity that is assigned to the existing (streaming) data connections. The safety margin is defined as a percentage of channel capacity that is used as additional used capacity in the admission con- trol algorithm calculations. Hence, an admission request would be accepted if the needed capacity 10 is lower than used capacity 12 plus the safety margin. In case that the needed capacity 10 would be higher, the connection would not be admitted. Figure 2 illustrates one embodiment of the present invention. Figure 2 comprises three connections (1,2,3) , their corresponding safety margins (SM_ιr SM₂, SM₃) , and available capacity (CAP1, CAP2) in two different moments of time (t_n and t_n+1) . When the Quality Control notices that the experienced throughput for a streaming connection is less than the negotiated as guaranteed throughput, and this situation lasts a determined period of time, some actions to counteract such event are triggered. The Admission Control modifies its admission policy related to those connections able to share the resources of the aforementioned connections with throughput troubles. Figure 2 shows how the Admission Control increases the safety margin for connection 2 (from SM₂ to SM₂₂) in order to avoid new connections being allocated to the same channels (i.e. stop admission of connec- tions which are going to affect the ones in trouble because they both are sharing the bandwidth) . The situation in t_n and t_n+1 differ from each other in many ways. Because connection 2 needs more capacity (scheduling time) to achieve the negotiated bit rate, its safety margin is increased (from SM₂ to SM₂₂) . At the same time available capacity for other connections is reduced from CAP1 to CAP2. The connections 1 and 3, and their corresponding safety margins (SM_X and SM₃) do not change . Figure 3 represents an exemplary embodiment of the systems where the present invention can be used. The architecture of Figure 3 comprises three radio access networks: the UTRAN, IP-RAN and GERAN. The GERAN (GSM/EDGE radio access network) is an enhanced GSM radio access network. Enhanced here means that the GERAN uses the EDGE as a radio technology. The EDGE allows use of the UMTS services with 800/900/ 1800/1900 MHz frequency bands. The GERAN offers full advantages of GPRS (General Packet Radio System) to be explored. The base station subsystem (BSS) of the GERAN is connected to the GSM core network by Gb (between the BSS and a GSM SGSN) and A (between a BSS and a GSM MSC) interfaces. The BSS is further connected to the UMTS network by interfaces Iu-ps (between a BSS and a 3G SGSN) and Iu-cs (between a BSS and a 3G MSC) . The BSS is further connected to the RNC of the UTRAN or to another BSS by Iur-g interface. The BSS includes a base station controller (BSC) and base transceiver stations (BTS) . In the GERAN the air interface between the BTS and user equipment (UE) is called Um.

0027The IP-RAN (Internet Protocol Radio Access Network) is a RAN architecture that is fully optimised to carry IP traffic and is based on IP transport technology. In the IP-RAN, most of the functions of the centralised radio network controller (RNC and BSC) are moved to the base station IP-BTS. In this configura- tion the division of functionalities between network elements is fundamentally re-defined to suit the needs of IP traffic. This is clearly different from just using IP as a transport solution with the existing network architectures like the GSM (Global System for Mo- bile Communications) and the CDMA (Code Division Multiple Access) based radio access networks. The radio access networks are connected to the core network CN.

0028Figure 3 comprises also user equipment UE The user equipment UE refers preferably to a mobile termi- nal, e.g. a mobile phone. The user equipment UE is connected to one or more radio access networks.

0029In Figure 3, both the IP-BTS of the IP-RAN and the BSC of the GERAN comprise the Quality Control QC and Admission Control AC functions. In more detail, the Quality Control QC and Admission Control AC are located in the Packet Control Unit (PCU) in the GERAN. The Admission Control AC is arranged for accepting or denying a new data connection to the shared radio resources. The Quality Control QC is arranged for nego- tiating QoS parameter value (s) for each connection using the shared radio resources and for monitoring the experienced QoS for one or more data connections.

0030The Quality Control QC comprises means for detecting DM a degradation situation in the QoS of one or more data connections and means for indicating IM the degradation situation in the QoS to the Admission Control AC. Based on the degradation information the Admission Control AC changes the Admission Control policy for new data connections. Therefore, the Admission Control AC comprises means for adjusting AM the admission control policy of new data connections in response to the degradation situation in the QoS. The Admission Control AC comprises also one or more safety margins parameters SM₁...SM_n.

0031The Quality Control QC may also comprise one or more timers T_x...T_n for measuring the duration of the degradation situation in the QoS. When the Quality Control QC notices that the experienced throughput for a streaming connection is less than the throughput negotiated as guaranteed, and this situation lasts a determined period of time, the Quality Control QC indi- cates Admission Control AC about the convenience of starting to block certain users that request guaranteed QoS to avoid the degradation in the provision of QoS for those users already admitted to the system.

0032The aforementioned means, safety margin pa- rameters and timers are implemented in a way known to a man skilled in the art and therefore are not described in more detail.

0033Figure 4 is a flow diagram illustrating a general principle of how the Quality Control and the Admission Control operate together. For services that require a guaranteed throughput, as e.g. streaming services, the Admission Control needs some information in order to know whether there are available resources to guarantee QoS requirements (throughput requirements as guaranteed and maximum bitrate, and information about the quality of the radio channels such as network planning parameters and statistics) . The radio channel quality information will be used to translate the throughput requirements from a mobile terminal ap- plication side into radio resources on the BSS/RAN side, i.e., into number of time slots needed to assure the guaranteed bitrate. The criteria used for the Admission Control to decide whether a new streaming connection will be accepted or not is based on two concepts: needed capacity (for the new connection to assure its guaran- teed bitrate) and used capacity (by the streaming connections allocated in the network) . It may occur that in some instant an allocation request was accepted because radio conditions were appropriate to provide throughput requirements, but afterwards radio link conditions change in such a way that throughput requirements could not be fulfilled.

0034In order to prevent this problem in advance, safety margin concept has been defined as a percentage of the channel capacity that is used as additional ca- pacity in the admission control algorithm calculations .

0035The function of the Quality Control is to monitor the satisfaction level of every user as well as the user satisfaction rate in the system (phase 20) . The Quality Control indicates the degraded situation to the Admission Control (phases 22 and 24) . By means of changes in the admission control policy it is possible to trigger counteracting actions by the Quality Control when QoS degradation is perceived. The Ad- mission Control updates the safety margi (s) in response to the information received from the Quality Control (phase 26) . Therefore, a new admission request would be accepted when the needed capacity of the incoming connection is lower than capacity used by the ongoing connections plus the safety margi (s). Otherwise, in case the needed capacity is higher, connection would not be admitted.

0036In one embodiment of Figure 4, when the Quality Control notices that the experienced throughput for a streaming connection is less than the throughput negotiated as guaranteed, and this situation lasts a determined period of time, the Quality Control indi- cates the Admission Control about the convenience of starting to block certain users that request guaranteed QoS, such as streaming service users, to avoid the degradation in the provision of QoS for those us- ers already admitted to the system. The Admission Control modifies its admission policy related to those connections able to share the resources of the aforementioned connections with throughput troubles. Thus, the Admission Control increases the safety margin for these particular connections in order to avoid new connections being allocated to the same channels (i.e. stop the admission of connections which are going to affect the ones in trouble because they both are sharing the bandwidth) . Additionally, . increasing the safety margin in such a way that the connection will be able to recover the throughput in an easier manner.

0037In one embodiment of Figure 4, the user profile for updating the safety margin is taken into account, i.e. by categorising users e.g. into "gold", "silver" and "bronze" users, and to allow only "gold" users to update their safety margins, or define different • ranges of variation for different user profiles .

0038In one embodiment of Figure 4, a safety mar- gin parameter is assigned separately to every data connection. Therefore, the safety margin parameters may differ among the users.

0039In another embodiment of Figure 4 , only one safety margin parameter is assigned, the safety margin being common for all data connections using the shared radio resources, i.e. the same channel. Therefore, this common safety margin is increased if the Quality Control detects that some connections are having bad quality. The safety margin concept is a preventive solution for recovering from degraded QoS situations. When a degraded Qos situation is on, new connections willing to allocate onto the same channels may not be admitted at all.

0040It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above, instead they may vary within the scope of the claims .