Multi-Hop Load Balancing

Abstract

A base station in a wireless communications system defines a plurality of beams which each have an amount of resources for supporting communication links with terminals. A control entity determines if a direct communication link can be supported between a new terminal and a base station using a first beam. If a direct communication link cannot be supported, a relaying equipment is used to provide a multi-hop path between the base station and the terminal. The multi-hop path comprises a link between the base station and the relaying equipment using resources of a different beam. This helps to redistribute load within the cell. The direct communication link can be refused if there are insufficient resources in the first beam, or if accepting the new terminal would cause quality of communication links with existing terminals to deteriorate.

Description

FIELD OF THE INVENTION[0001]This invention relates to wireless communications systems.BACKGROUND TO THE INVENTION[0002]In cellular wireless communications systems a limited range of resources are reused in different, spaced apart, cells. The resources vary according to the type of system, but are generally frequency channels, time slots on a bearer channel, spreading codes or combinations of these. Cells may be subdivided into sectors, with each sector being served by one or more beams formed by directional, higher gain, antennas. The directional antennas increase performance in the uplink and downlink directions by reducing interference, for example, and also help to increase capacity of the overall system as the resources allocated to one beam or sector can be reused in other beams or sectors. Each beam may use a sub-set of the overall resources of the cell or resources may be reused in different beams within the same cell.[0003]One of the problems which can arise in cellular syst...

AI Technical Summary

Benefits of technology

[0009]The invention is particularly applicable to systems where one beam (the first beam) is overloaded and has insufficient resources to support a direct communication link with the terminal. Preferably, the system is arranged to determine if the first beam has sufficient resources to support a direct communication link without reducing quality of communication for existing terminals served by the first beam below a predetermined limit. This can be achieved by determining an amount of resources required to support the direct communication link between the new terminal and the base station, determining a reduced amount of resources available to existing terminals served by the first beam if the base station were to accept the new terminal, and a quality of communication resulting from the reduced amount of resources.

[0010]It is not necessary that the first beam should overlap or be directly adjacent to the second beam. Indeed, it can be advantageous for the second beam to be spaced from the first beam by one or more intermediate beams of a common base station. Alternatively, the second beam can be defined by another base station in the system.

[0011]By using relay equipment in this way the resources of a neighbouring, more lightly loaded, beam can be used to support at least part of the communication path with the base station. Also, the antenna requirements of the base station do not need to be changed. The resources which support the second communication link can be reused on a frequent basis, e.g. for other beams at the base station, since they are only used on a localised basis.

[0012]The invention is particularly advantageous in systems which incorporate AMC / EQT as terminals that would normally require a disproportionate amount of resources to achieve a required service level, when supported directly from the base station in a given beam, may be supported from an alternative beam of the same or an alternative cell in a more efficient manner using a multi-hop path. Thus, the proportion of the resources that such a terminal requires may be lower in the alternative beam and hence the overall efficiency of the cell can be increased, enabling additional terminals to be supported.

[0013]It is preferred that where multiple candidate relay equipments are available in a system a relaying equipment is chosen which offers the best quality of communication. This allows a spectrally efficient modulation scheme to be used and minimises the amount of resources required. By choosing a path to the relay equipment with good propagation characteristics, the resources for the first communication link can also be minimised.

[0014]Normal resources of the cell, i.e. the channels which would normally be used for direct communication between a base station and terminals, may be reused for the link between the relaying equipment and the terminal, or some of the normal resources may be specifically reserved for this purpose. Using the normal resources of the cells has the advantage that the relaying equipments and terminals do not require additional equipment to support other frequency bands, modulation schemes or protocols.

Problems solved by technology

One of the problems which can arise in cellular systems is that the total traffic demand of the terminals in a cell, sector or beam poorly matches the capacity of that cell, sector or beam.

While system operators attempt to provision sufficient resources to meet the expected demand, there can be periods when a cell, sector or beam becomes overloaded to the extent that it cannot provide a service to a new terminal.

Alternatively, providing service to a new terminal may seriously degrade the amount of resources available to be shared among the existing terminals, thus degrading their service level.

The division of cells into sectors increases the likelihood of uneven loading and the division of sectors into beams further increases the likelihood of uneven loading.

While this can more evenly match the load to the available capacity of the base station, it requires a more complicated and expensive antenna arrangement and control system at the base station.

In systems employing adaptive modulation and coding (AMC) combined with equal throughput scheduling (EQT) a further problem arises that cannot easily be addressed by adapting the beam shape provided by the base station.

In such systems, terminals located in areas where the received signal strength, or signal to interference plus noise ratio, in the uplink or downlink directions is badly affected by propagation effects are allocated an increased share of the available resources.

Although all terminals now receive an equal level of service this technique distributes a disproportionately large share of the resources to the affected terminals and results in a reduction in the aggregate capacity of the cell, sector or beam.

Such badly located terminals are not often conveniently positioned to enable support form an adjacent cell, sector or beam and even when they are, the amount of resources required from the adjacent sector or cell will often be equally disproportionate.

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