MOBILE COMMUNICATIONS NETWORKS
This invention is concerned with the control of resources in 5 mobile communications systems. In particular the invention allows for the management of the trade-off between radio resources and Quality of Service (QoS), and more particularly, the commitment which can be given to defined QoS parameters. 10
In mobile wireless communications systems user terminals (e.g., mobile phones) are able to move. This means that com- 15 munication requirements will vary from time to time and from place to place, and also that the communication channel over which information is sent will vary in quality over time. Various techniques have been designed to allow for efficient use of the physical air interface when this occurs, including 20 (but not limited to) handover (where the wireless link is changed from one base site to another), macrodiversity (where a link is maintained with two or more base sites at the same time), Dynamic Channel Allocation (DCA) where the air interface resources available to different base sites are 25 pooled and shared out between the sites dynamically depending on current demand, Link Adaptation (where the channel coding is changed in response to the channel quality) Adaptive Modulation (where the modulation is changed in response to the channel quality) and Adaptive Power Control 30 (APC) where the transmission power is changed in response to the channel quality. These different techniques all trade resource on the air interface against quality of the user data stream (the user Quality of Service), and therefore have to be controlled in a coordinated manner. However, efficient con- 35 trol of a system with so many variables is very difficult.
The generic definition of Quality of Service (QoS) is "The collective effect of service performances which determine the degree of satisfaction of a user of the service". The satisfaction of the user depends significantly on the service being 40 considered. For example, QoS measures for speech would include clipping (loss of the start of speech bursts), echoes, crosstalk, distortion, acoustic noise, quantisation noise, and overall signal to noise ratio. For a video service, the QoS parameters would include block distortion, blurring, edge 45 busyness (distortion concentrated at the edge of objects, like edges shimmering), jerkiness, tiling or pixelation, frame freezing, or colour cycling (where colour stability is lost, and colours cycle through a range of hues).
While there are a large number of different QoS measures 50 which are service dependent, it is possible at the transmission level of the system to map these different measures to generic QoS measures related to the network capabilities. These QoS measures are:
bit rate, both in terms of mean bit rate (throughput) and 55
variation of bit rate (burstiness); delay, both in terms of absolute delay (network transit
delay) and delay variation (jitter); data corruption, in terms of Bit Error Rate (BER) and
Frame Erasure Rate (FER) (where packets are lost or 60
dropped rather than received with error).
According to the present invention there is provided a 65 mobile communications system comprising a radio access network having a multiplicity of network sites, and a traffic
flow management system for controlling the routing of traffic flows through the network, wherein the management system is adapted to trade resource at the various network sites against a plurality of user Quality of Service parameters to achieve required contractual levels of commitment to a multiplicity of users.
The invention allows for the management of the trade-off between resources and QoS and, in particular, the commitment which can be given to defined QoS parameters. This enables network operators to converge their communication technologies by enabling the selection of the air interface technology that will best serve the user requirements dynamically.
By way of example in an embodiment the present invention allows the high level control functions of a communications system to choose between different air interface technologies and cell types in a cost effective manner in order to minimise resource use and the cost of providing the service. This is achieved by two key features: the definition of the commitment which is mapped between entities, and a division of control functionality of the management system between three separate entities, one of which is responsible for the data flow wherever it is within the network, a second one of which is responsible for a specific link or network site, and the third one of which is responsible for a specific transmission medium or air interface. This allows devolution of air interface specific functions to low level entities and allows mapping of QoS parameters and commitment levels in a practical and achievable fashion.
The radio access network is preferably organised in a multi-layer hierarchy of network sites and by virtue of the present invention the upper layers of the network can specify not only the Quality of Service they wish to obtain, but also the reliability of the connection in terms of the lower (transport) layers' ability to maintain this quality (the commitment), and furthermore allows the network to cost this commitment.
It is preferred to utilise an explicit trade-off between cost and reliability so that the user can choose the level of reliability required and the communication of QoS requirements to the lower layers in the form of standardised contracts which are independent of the air interface.
In combination with the division into separate entities, these requirements are mapped to transmission medium or air-interface specific requirements at the low levels whilst commitment levels offered by the transmission medium or air-interface are mapped back to the upper layers in a consistent format across different air interfaces so that application level functions maintain QoS without requiring explicit details of the low level functionality. This allows for:
the effective management of resources between different types of communications technologies and air interfaces within the same network;
costs of service for different areas and air interfaces to be reported and the optimal choice made (either to minimise cost of service or to maximise revenue for the network);
the practical implementation of such decision-making mechanisms in a devolved manner allowing dynamic selection of the most cost effective technology of a particular mobile at a particular time;
the convergence of telecommunications technologies expected in future wireless communications systems.
Where the upper network layers express their QoS requirements in service specific forms, these will be mapped in a Flow Controller (FC) forming part of the management system to the generic QoS requirements. However, usually the user application will undertake this conversion. The user could