GB2452794A - Base station having means for indicating its data capacity - Google Patents

Abstract

A telecommunications system includes a radio access network having a plurality of network elements configured to communicate wirelessly with one or more mobile terminals, one of those network elements being a micro base station having a backhaul connection to a core component of the system. The micro base station is adapted to determine the resources available to it, and to transmit an indication of those resources to the user terminal. Preferably the resource indication is determined using a cost-function that includes terms representative of backhaul capacity and radio conditions. In this way the network capacity can be maximised by steering mobile terminals away from cells which have a reduced capacity, or a capacity not suited to the mobile terminals communication requirements. The cost function provides an indication of a micro base station's available capacity based upon the resources currently available to them.

Description

DATA CAPACITY

Field of the Invention

The present invention relates to a system and method for managing capacity in a telecOmniiinjcatioiis network. The present invention is particularly applicable to a telecomniunjcatioiis network including a fixed backhaul network and a radio access network (RAN) for wirelessly transmitting between a mobile telecommunications device and a base stdtion (BS). The present invention also relates to a method and arrangement for optimising the potential data capacity across both RAN and backhaul.

Background

There have recently been proposals to allow access to the features and services provided by GSM (Global System for Mobile conimunications) and IJMTS (Universal Mobile Telecoiiimunication Services) networks other than by accessing those networks in the conventional manner. In this regard, the conventional manner involves signalling between the mobile terminal and a standard base statioii (macro base station) that has a dedicated backhaul connection to an MSC (Mobile Switching Centre) or RNC (Radio Network Controller), and provides coverage in the cell occupied by the mobile terminal using cellular telecommunication (e.g. GSM or UMTS) transport protocols.

To increase network capacity, it has been proposed to provide additional special base stations (micro base stations), often referred to as femto cells, femto base stations, pico cells, pico base stations or access points (APs). These micro base stations may be a dedicated network access point, or may be enhanced wireless internet hubs (i.e. providing wireless internet access, as well as wireless telecommunications network access). The range of micro base stations is significantly smaller than macro base stations, typically oniy providing coverage of the order of 20 to 30 metres, making them suitable for use, for example at a subscriber's honie or office.

An advantage of using an Access Point connected to the core network via an IP network is that existing broadband DSL connections can be used to link mobile terminals with the network core without using the capacity of the radio access network or transmission network of a mobile telecommunications network. In this regard, these access points coninlunicate with the core network via IP based conimunications, such as a (fixed) broadband IP network, and are typically routed via the Internet. Using such base stations will allow a proportion of the data required for the provision of features or services to be carried through a fixed network and onto the backhaul network without requiring radio network capacity (the so-called "backhaul margin").

They are also able to provide mobile network access where there is no conventional radio access network coverage. For example, UMTS coverage could be provided by an access point where there is no conventional UMTS coverage (perhaps only GSM coverage).

It has also been proposed to use these APs in the Long Term Evolution (LTE) telecommunications network which is currently being developed. An industry body, 3GPP (Third Generation Partnership Project) is overseeing the production of technical specifications for implementing this next generation mobile system, which is based on an evolved GSM core network. LTE is likely to be the next network implementation after the current 3G UMTS etc. In future networks, there is likely to be a heterogeneous mixture of micro base stations serving very small areas and macro base stations serving significantly larger areas. These micro base stations will coexist with the conventional macro base statioiis with the coverage area of one macro base station likely to overlap with a number of micro base stations. Overall, the use of APs as an additional or alternative means for accessing the network will advantageously increase the network capacity.

However, since these access points are not conventional macro base stations, additional challenges arise. In particular, communications between the access point and the network are IP based communications, and may be, for example, transmitted via an ADSL backhaul connection to an IP network, such as the Internet. However, the capacity of such ADSL backhauls are limited, and not under the control of the telecommunications network provider. In view of this limited capacity, there needs to be a degree of control in relation to which APs a user terminal (UE) accesses, in order to maintain an acceptable degree of service quality for the UEs.

Currently, the UE cell selection and handover focus in 3GPP is on radio signal quality, received power and load balancing, in an attempt to maximise spectral efficiency within the RAN.

As femto base stations become more ubiquitous in a RAN, the radio conditions which are currently crucial for the efficient operation of a RAN will become less important to the overall capacity of the network to carry data. Consequently, the current focus is seen to provide an incomplete model.

Summary of the Invention

In accordance with an aspect of the invention, there is provided a telecomiiiunicatiojis system including a base station or access point that advertises its resource to the user terminal (UE) based on a cost-function that includes terms representative of both backhaul inangin and radio conditions.

In order to deliver an improved user experience in future access systems, it is therefore desirable to optimise system capacity by including knowledge of the backhaul capability of the access points, in addition to knowledge of radio conditions.

If each available femto base station advertises its backhaul margin and radio conditions, the user equipment can select the most suitable access point for any specific feature or service (e.g. voice call, messaging, Mobile TV, etc.).

It is recognised that if open-access femto base stations were to become ubiquitous, the potential data transmission capacity per unit of geographical area could become very much larger than is currently available through the conventional GSM arid UMTS networks. The limitation of user performance is then more likely to be constrained by the limited backhaul capacity than by the radio performance. Given that the performance of the backhaul from individual femto base stations may be variable, and will depend on an individual user's installation and (fixed) DSL connection, then this aspect of the invention allows the cell selection procedure to be biased towards cells which have greater backhaul capacity.

An important feature of these aspects of the invention is that they seek to maximise network capacity and better distribute user terminals about the base stations before network congestion occurs, rather than addressing the problem once overloading has been detected.

Brief Descrft,tioli of the Drawings The present invention will now be described in greater detail, with reference to the following drawings: Figure 1 which illustrates an_example mobile telecommunications network for receiving IP based communications from an access point in addition to comnlulljcatiojis from a conventional base station, in which the embodiments of the present invention may be implemented.

Detailed Description

Key elements of a mobile telecommunications network, and its operation, will now briefly be described with reference to Figure 1. 1 0

Figure 1 shows the elements for providing access to a GSM or UMTS network by both a conventional base station 3 and a micro base station (AP 20). The AP provides a radio link 21 to mobile terminal I. Each base station (e.g. base station 3 and AP 20) corresponds to a respective cell of its cellular or mobile telecommunications network and receives calls from and transiiiits calls to a niobile terminal in that cell by wireless radio communication in one or both of the circuit switched or packet switched domains. Such a subscriber's mobile terminal (yE) is shown at 1. The mobile terminal may be a handheld mobile telephone, a personal digital assistance (PDA) or a laptop computer equipped with a datacard.

In a GSM mobile telecommunications network, each base station 3 comprises a base transceiver station (BTS) 22 and a base station controller (BSC) 26. A BSC may control more than one BTS. The BTSs and BSCs comprise the radio access network.

In a UMTS mobile telecommunications network, each base station 3 comprises a node B 22 and a radio network controller (RNC) 26. An RNC may control more than one node B. The node B's and RNC's comprise the radio access network.

In the proposed LIE mobile telecommunications network, each base station 3 comprises an eNode B, which effectively combines the functionality of the iiode B and the RNC of the UMTS network.

Conventionally, in a GSM/UMTS network, the base stations are arranged in groups and each group of base stations is controlled by a mobile switching centre (MSC) 2 and a Serving GPRS Support Node (SGSN) 16. MSC 2 supports communications in the circuit switched domain -typically voice calls, and corresponding SGSN 16 supports communications in the packet switched domain -such as GPRS data transmissions. SGSN 1 6 functions in an analogous way to MSC 2. The base station 3 has a dedicated (not shared) connection to its MSC 2, typically a cable connection. This prevents transmission speeds being reduced due to congestion caused by other traffic.

In the LTE network, it is proposed that the base stations are arranged in groups and each group of base stations is controlled by a Mobility Management Eiitity (MME) and a User Plane Entity (UPE).

The radio link 2 1 from the AP 20 to the mobile terminal I uses the same cellular telecommunication transport protocols as the conventional base station 3 but with a smaller range -for example 25m. The AP 20 appears to the mobile terminal I as a conventional base station, and no modification to the mobile terminal 1 is required to operate with the AP 20. The AP 20 performs a role corresponding to that of a GSM BTS 22 and BSC 26 and/or UMTS Node B and RNC and/or an LTE eNode B. Communications between the access point 20 and the core network 12 are IP based communications, and may be, for example, transmitted over a broadband IP network (and routed via the Internet). The communications are routed via MSC 32 or SGSN 34. The access point 20 converts the cellular telecommunications transport protocols used between the mobile terminal I and the AP 20 to IP based signalling.

The connection 23 between the access point 20 and the core network 1 2 may use the PSTN telephone network. Typically a Digital Subscriber Line (DSL) cable connection (a backhaul connection) connects the access point 20 to the PSTN network. The data is transmitted between the access point 20 and the core network 12 by IP transport/DSL transport. The bandwidth of the cable connection between the access point and the telephone exchange is shared with multiple other users (typically between 20 and 50 other users). This means that the speed of transmission of data between the access point 20 and the telephone exchange varies significantly in dependence upon the activities of the other access point devices sharing the connection.

The backhaul connection between the access point 20 and the core network 12 may be effected by means other than a DSL cable and the PSTN network. For example, the access point 20 may be connected to the core network 12 by a dedicated cable connection that is independent of the PSTN, Or by a satellite connection between the access point 20 and the network core 12.

AP 20 would typically be configured to serve a Wireless Local Area Network (WLAN) located in a home or office, in addition to GSM/UMTS/LTE networks.

The WLAN could belong to the subscriber of the mobile terminal 1, or be an independently operated WLAN. The owner of AP 20 can prescribe whether the AP is either open or closed, whereby an open AP is able to carry communications from any mobile device in the GSM/UMTS/LTE network, and a closed AP is only able to carry communications from specific pre-designated mobile devices.

From the description above, it will be understood that the coverage area of a mobile telecommunications network is divided into a plurality of cells, each of which is served by a respective base station. Traditionally, when a mobile terniinal is idle, it will "canip" in a cell which provides it with the best network coverage. The terminal monitors the signal strength of its neighbouring cells so that it knows when a neighbouring cell becomes its best cell. When this happens, the terminal will initiate a cell reselection so that it will he camped in the better neighbouring cell.

Similarly, if a mobile terminal is active, it will be communicating with the core network through its serving cell. Where the active terminal moves outside the coverage area of its serving cell, the call will be handed to an alternative cell, providing better coverage, automatically. The terminal will be monitoring the signal strength from its neighbouring cells, but since the terminal is active, it is usual for the handover determination to be made by the serving base station.

Handover is a time critical process requiring action to be taken before the radio link with the original cell degrades to-such an extent that the call is lost.

Handover requires synchronisation of events between the mobile terminal and the network.

With this background in mind, an implementation of the first embodiment of the invention will iiow be described, which seeks to maximise network capacity by steering mobile terminals away from cells which have a reduced capacity, or a capacity not suited to the mobile terminals communication requirements.

This is achieved by calculating a cost function in relation to all micro base stations in the network, which provides an indication of their capacity/service quality based upon the resources currently available to them. The cost function information can then be used for determining whether a mobile terminal should be handed over to the micro base station (as determined by the UE when in idle mode and tile serving base station when the terminal is active).

To perform the calculation tile base station draws upon various factors related to its available capacity. Examples of these various factors are: a) Backhaul illfornlatjon at cell level; b) Radio condition measurements such as uplink channel capacity and/or downiink channel capacity; c) Quality of Service (QoS) requirement of any connected users; d) QoS requirement of a potential new user; e) Estimation of throughput for offered Modulation Coding Scheme (MCS); and/or Noise Rise (NR) measurement, e.g. as experienced by the AP on its OTA communication channels, the ratio of total received wideband power to

Is background noise.

Preferably tile capacity indication uses at least (1) backhaul information and (2) radio condition measurements, as these are two broad factors that generally provide the greatest influence on tile capability of an access point, or base station, to accept a call.

The backhaul information or "backhaul margin" is a measure of the capacity currently available over tile backhaul connecting the micro base station to the core network. Preferably this backhaul margin is a measure of tile utilised backhaul, relative to the predicted peak capacity of the backhaul (this will be obtained by periodic polling and monitoring of delays on its Own link).

The radio condition Component is preferably a measure of the channel quaiity on the RAN down! ink, and a measure of the RAN uplink capacity margin.

The Quality of Service (QoS) indication of any connected users preferably takes into account the services already being provided through the AP. For instance, if the AP already has one connected user, if that user is being provided with a video streaming service via the AP, their required QoS is much higher than if they were merely involved in a data download, as data download can be delayed without unduly degrading the service being provided. The AP can determine the service being provided via the communications transmitted between it and the existing user, such as the communications that take place to set up tile connection. Other factors may be taken into consideration in determining the QoS indication, such as a priority factor given to different users. A normalised QoS in the range of 0 to I is preferably determined, where 0 indicates the existing users require a high quality of service taking up all the current backhaul capacity, and 1 indicates there are no existing users with quality of service requirements.

A similar QoS indication can be used in relation to the potential new user, whereby 0 indicates the user requires a high quality of service at the maximum service level possible, and I indicates the potential user requires a service with no specific quality requirements.

The QoS indication is an optional feature, and where it is not used, or BOW known, it can be set to "background" in the cost function.

Depending upon the Modulation Coding Scheme being utilised, an approximation of the throughput �n the available channel can also be utilised in determining the capacity indicator. Including this estimation in the calculations essentially takes into account the fact that some coding schemes are more efficient than others. Examples of Modulation Coding Schemes (MCS) that may be used include QPSK, 1ÔQAM and 64QAM.

As will readily be appreciated by the reader, there are various algebraic forms of the capacity indicator or "cost-function" that could be considered. For example, in one embodiment of the invention, the cost-function is a simple linear combination of (I) backhaul margin, and (2) radio conditions, as f'ollows:

S

Cost of admitting call (where O' is a high cost) = Backhaul margin x Downlink channel capacity x Uplink capacity where: a) backhaul margin is in the range of 0 to 1, where 1 indicates unlimited resource is available and 0 indicates backhaul is completely congested b) downlink channel capacity is normalised in the range of 0 to 1, where I represents the peak capability of the radio system (=highest MCS) and 0 represents a condition beyond that which can be supported by the lowest MCS; and c) uplink capacity is normalised in the range of 0 to I, where I represents unused uplink resources (based �n either noise rise, or channel utilisation) and 0 represents noise rise beyond planned limit, or fully utilised resource.

The resulting output from the cost-function is advertised by each access point for use by user terminals in determining which AP to use. The advertisement of the cost function may for instance be made in a broadcast message, in a multicast message addressed to specific user terniinals or may be provided in a response message as a result of a request for such information for a specific user terminal.

More specifically, considering UE I in idle mode, it would be measuring the signal strength of broadcasts from Node B 22 and AP 20. The strength of these signals is used by the UE in determining upon which base station to camp. In addition, the UE would extract the cost function from the AP's broadcast

II

message and use this in its determination, such as by using it as a weighting factor against the signal strength measurement.

For example, if the cost function is "I ", this indicates that AP 20 has full capacity. This value would therefore not alter the value of the AP's signal strength relative to the other neighbouring cells, so that it would be considered as a reselection candidate equally with the other neighbouring cells.

If however the cost function was less than 1, say "0.3", this would be an Jo indication that AP 20 only had about a third of its capacity available for new terminals, and so would serve to reduce the AP's value relative to the other neighbouring cells. For instance, if the signal strength of AP 20 was higher than that of Node B 22, without the cost function, UE I would be more likely to select AP 20 as the cell to camp on.

By taking the "0.3" cost function into consideration, however, the "effective" signal strength of AP 20 would be reduced, potentially below the measurement for Node B 22. Therefore, the cost function serves to make AP 20 less attractive to IJE I as a reselectjon/handover candidate.

Advantageously, where the calculation of the cost function takes into account factors such as the backhaul margin, requiring an estimation of the instantaneous, and average, usage of the AP's backhaul, together with a measure of the QoS of those users currently connected, it is becomes possible to allow a more informed haiidover/cell reselection decision to be made, rather than just using signal strength measurements.

This embodiment has been described in relation to the micro base station itself calculating the service quality indication. Alternatively, however, the core network may determine the indication on the micro base station's behalf Further, the micro base station could determine all the factors necessaiy for the calculation, and communicate the factors to the mobile terminal for the mobile terminal itself to do the final service quality indication. In this way, each mobile terminal could have its own formula for determining the service quality, according to its own needs. In a still further alteiiiative, the mobile terminal could communicate its required algorithm to a micro base station, and the micro base station would determine the service quality indication based upon the provided algoIthI11.

The embodiments of the present invention have generally been described in relation to the capacity indication being determined in relation to micro base stations. In an alteniatjve embodiment, however, the inventive concept may be applied to macro base stations, wherein the backhaul capacity indication is replaced by an indication of the core network capacity. For instance, where the network is a UMTS network, the indication may relate to the available capacity of the base station's RNC and/or SGSN.

The invention has been generally described in relation to selecting a cell when a communication is being initiated or handing over to a new cell when the serving cell nO longer provides the best radio access conditions (i.e. the signal strength is non-optimal). According to another embodiment, the invention may be implemented in the situation of the serving cell having a highly loaded backhaul connection. For instance, if the serving cell's cost function is no longer optimal, handover may be initiated to a cell with a more optimal cost function.

Claims (14)

1. CLAIMS: 1. in a telecommunications system including a radio access network having a plurality of network elements configured to wirelessly communicate with oiie or s more mobile terminals, at least one of those network elements being a micro base station having a backhaul connection to a core component of the system, a method of a network element providing a user terminal with a resource indication, the method including: determining the resource indication using information relating to the resource capacity of the network element; and the network element advertising its resource capacity by transmitting the resource indication to the user terminal.
2. 2. The method of claim I wherein the network element advertisiiig its resource is the micro base station, and the resource indication is determined using a cost-function that includes terms representative of backhaul capacity and radio conditions.
3. 3. In a telecommunications system including a radio access network having a plurality of network elements configured to wirelessly communicate with one or more mobile terminals, at least one of those network elements being a micro base station having a backhaul connection to a core component of the system, a method of a network element of providing a user terminal with a resource indication, the method including: determining one or more of the following service factors: a) An indication of the capacity on the backhaul connection associated with tile network element, where the network element is a micro base station; b) An indication of a downlink channel capacity associated with the network element; c) An indication of an uplink channel capacity associated with the network element; d) An indication of the Liser's terminal's required quality of service; e) An indication of a quality of service required by one or more existing users of the network element; f) A throughput estimation relating to a coding scheme utilised on the backhaul connection, the downlink channel and/or the uplink channel; g) A noise rise measurement relating to the backhaul connection, the downlink chamiel and/or the uplink channel; using the determined service factor or factors to calculate the resource indicator; transmitting the resource indicator to the user terminal.
4. 4. The method of claim 3 wherein the indication of backhaul capacity is determined by obtaining a measure of the backhaul capacity currently being utilised relative to an estimated maximum capacity of the backhaul connection associated with the network element.
5. 5. The method of claim 3 or 4 wherein the required quality of service indication is determined based upon the user terminal's required form of communication.
6. 6. The method of any one of claims 1 to 5 wherein the resource indicator is transmitted to the user terminal in a multicast message addressed to the user terminal.
7. 7. The method of any one of claims 1 to 5 wherein tile resource indicator is transmitted to the iser terminal in a broadcast message.
8. 8. A network element configured for use ill a telecommunications network including a radio access network having a plurality of base stations configured to wirelessly communicate with one or more mobile terminals, at least one of those network elements being a micro base station having a backhaul connection to a core component of the system, the network element being further configured to provide a user terminal with a resource indication by: determining one or more of tile following service factors: a) an indication of a backhaui capacity associated with the network element, wllere the network element is a micro base station; b) an indication of a downiink channel capacity associated with tile network element; c) an indication of an uplink channel capacity associated witil tile network element; d) all indication of tile user's terminal's required quality of service; e) an indication of a quality of service required by one or more existing users of the network element; using tile determined service factor or factors to calculate a resource indicator; and transmitting tile resource indicator towards the user terminal.
9. 9. Tile network element of claim 8 wherein the network element is a micro base statioii.
10. 10. Tile network element of claim 8 or 9 wherein tile backhaul connection is a DSL cable connection.
11. 11 A mobile temiinal configured for use in a telecommunications network including a radio access network having a plurality of base stations configured to wireless coniniunjcate with the mobile terminal, at least one of those base stations being of a micro base station]iaving a backhaul connection to a core component of the system, the mobile terminal being further configured to: receive a communication from at least one of the plurality of base stations, the communication including a resource indication relating to the particular base station; utilise the resource indication in one or more of: a) detennining which base station to connect to in regard to a network service required by the terminal; b) determining which base station to handover to in regard to a network service currently being provided to the teniinal.
12. 1 2. A telecommunications system including a base station or access point that advertises its resource to the user terminal (UE) based on a cost-function that includes terms representative of both backhaul margin and radio conditions.
13. 13. A method substantially as herein described with reference to the accompanying drawings.
14. 14. A network element substantially as herein described with reference to the accompanying drawings.

    1 5. A telecommunications system substantially as herein described with reference to the accompanying drawings.