WO2014032733A1

WO2014032733A1 - Method for energy saving in a communication system

Info

Publication number: WO2014032733A1
Application number: PCT/EP2012/067021
Authority: WO
Inventors: Peter Legg; Henrik Lundqvist
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2012-08-31
Filing date: 2012-08-31
Publication date: 2014-03-06
Also published as: CN104604302A

Abstract

The present invention relates to a method for energy saving in a communication system, said communication system including: at least one wireless access network comprising one or more wireless access nodes and one or more mobile stations, and at least one associated wireless backhaul network comprising one or more wireless backhaul nodes; said method comprising the steps of: controlling a first power consumption P₁ of said one or more wireless access nodes, and jointly controlling a second power consumption P₂ of said one or more wireless backhaul nodes such that a sum P_Sum of said first power consumption P₁ and said second power consumption P₂ is minimised. Furthermore, the invention also relates to a computer program, and a computer program product, and a control device.

Description

METHOD FOR ENERGY SAVING IN A COMMUNICATION SYSTEM

Technical Field

The present invention relates to a method for energy saving in a communication system. Furthermore, the invention also relates to a computer program, and a computer program product, and a control device.

Background of the Invention

Cellular communication systems are designed for peak hour traffic despite the fact that the traffic activity in a certain area normally is high only during short periods of the day. Considering the traffic activity in a residential area, it is usually low during daytime when people have left homes for work while it increases in the evenings when people are at home. The opposite pattern prevails for an office area. In a heterogeneous network environment different infrastructures are differently utilised throughout the duration of a day, e.g. macro cells are serving traffic in a residential area during working hours while a vast amount of the traffic is carried by pico or femto cells during evenings and late hours. At the opposite end of the city in the working areas these indoor femto cells or outdoor pico cells that provide indoor coverage are not fully utilised at the end of business days or during evenings and nights. In all cases, under-utilization of the radio infrastructure and radio resources is a waste of power and significant power savings could be achieved by reducing the number of radio resources that the network provides in time (and in space and frequency), e.g. by switching off a number of base stations at different tiers (micro, pico, femto, etc.). One simple approach to obtain energy efficiency is based on the activation of network resources on demand, thus avoiding to always power on all the resources that are necessary to serve the users during peak traffic periods. This necessitates the implementation of a power on/off strategy that refers to switching on or off radio infrastructure nodes and cells of a radio network. The radio network could be a heterogeneous network (HetNet) consisting of sites with different power transmission, coverage and capacity profiles. One of the key optimisation problems in such HetNet scenario is to maximize or maintain user throughput and coverage at a minimum of energy consumption cost. In future mobile networks the density of cell sites must increase to meet growing traffic demands. Many of the nodes will be low power nodes with limited coverage but high capacity. A major deployment and operating expense for such low-cost nodes is the backhaul provision. In many cases wired backhaul using fibre or coaxial cable is not an economically viable option. Instead wireless backhaul is gaining attention as a lower cost alternative.

Furthermore, given a meshed network of wireless backhaul nodes it is relatively straightforward to install new base stations or move existing base stations provided that the mesh capacity is sufficient. Different technologies offer meshed wireless capability, including members of IEEE 802.11 and 802.16 families. Some technologies require line of sight connectivity, whilst others work with non-line of sight. Meshes employ distributed routing protocols that determine the path traversed by data packets. The mesh is resilient to node failure by being able to establish new routes. Figure 1 shows a typical wireless access network with meshed wireless backhaul. The access nodes communicate directly with mobile stations and the traffic is backhauled to a neighbouring mesh node. The meshed nodes are wirelessly linked together to reach a single gateway node in this example. Access nodes with low power are typically attached to the side of buildings whilst the mesh nodes often are raised higher and placed on roof-tops. More elaborate networks could include: backhaul via a neighbouring access node and integration of access node and mesh node, which is illustrated in figure 2.

Some prior art solutions for energy saving consider switching off a group of cells, whilst others focus on specific radio access technologies characteristics (e.g. UMTS) and/or use of different optimisation approaches. However, these solutions do not consider the trade-off between throughput and power consumption, and secondly do not consider the details of switching on and off individual cells.

Another drawback of the prior art solutions are that they are not feasible in practice. By switching off a group of cells according to a pattern one cannot flexibly address mobile users' needs in locations where non-uniform user distribution and non-uniform service demands occur.

Summary of the Invention An object of the present invention is to provide a solution which mitigates or solves the drawbacks and problems of prior art solutions relating to energy saving.

Especially, an object of the invention is to provide a solution which minimizes the total power consumption of access nodes and backhaul nodes.

According to a first aspect of the invention, the above mentioned objects are achieved by a method for energy saving in a communication system, said communication system including: at least one wireless access network comprising one or more wireless access nodes and one or more mobile stations, and

at least one associated wireless backhaul network comprising one or more wireless backhaul nodes; said method comprising the steps of:

- controlling a first power consumption P of said one or more wireless access nodes, and jointly

- controlling a second power consumption P₂ of said one or more wireless backhaul nodes such that a sum P_Sum of said first power consumption P and said second power consumption P₂ is minimised.

According to a second aspect of the invention, the above mentioned objects are achieved with a control device for a communication system, said communication system including:

at least one wireless access network comprising one or more wireless access nodes and one or more mobile stations, and

at least one associated wireless backhaul network comprising one or more wireless backhaul nodes;

wherein said control device is arranged to control said one or more wireless access nodes and said one or more wireless backhaul nodes; and said control device further being arranged to:

- control a first power consumption P of said one or more wireless access nodes, and jointly

- control a second power consumption P₂ of said one or more wireless backhaul nodes such that a sum Psum of said first power consumption and said second power consumption P₂ is minimised. With a solution according to the present invention the energy consumption of the whole communication network can be minimized. This can also be achieved while taking into account the number of present mobile stations and their locations in the communication network.

Further applications and advantages of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different embodiments of the present invention in which:

Fig. 1 shows an example of a wireless meshed backhaul;

Fig. 2 shows an example of a more sophisticated wireless meshed backhaul architecture;

- Fig. 3 shows an exemplary scenario in a communication network;

Fig. 4 shows a communication network before energy saving;

Fig. 5 shows a communication network after energy saving; and

Fig. 6 illustrates some different connectivity options. Detailed Description of the Invention

To achieve the aforementioned and other objects, the present invention relates to a method for energy saving in a communication system of the type including at least one wireless access network comprising one or more wireless access nodes (ANs) and one or more mobile stations; and further at least one associated wireless backhaul network comprising one or more wireless backhaul nodes (e.g. meshed backhaul nodes, MNs). The present communication system can e.g. be a communication system according a 3GPP standard or any other suitable system, and the wireless access nodes may e.g. be base stations, remote radio heads, relay stations, or any other suitable communication devices with corresponding function(s). Further, the wireless backhaul network is a mesh network according to preferred embodiment of the present invention, which is illustrated in the appended figures.

The present method comprises the steps of: controlling a first power consumption P of the one or more wireless access nodes, and jointly controlling a second power consumption P₂ of the one or more wireless backhaul nodes such that a sum P_Sum. of the first power consumption P and the second power consumption P₂ is minimised. The first power consumption P is preferably the total power consumption of the one or more wireless access nodes, and the second power consumption P₂ is preferably the total power consumption of the one or more wireless backhaul nodes.

The inventors have realized that a joint optimization of access nodes and backhaul nodes offers better performance with respect to energy consumption for a given traffic demand than prior art solutions. This is because there are multiple access network configurations that can serve the mobile stations (and their traffic) of the communication system and each access network configuration has an optimal backhaul configuration so there are a number of combinations to consider. In this context an access network configuration is e.g. the on/off settings of the nodes (or cells) of the network. The backhaul configuration considers e.g. the on/off settings and also the network topology, e.g. which node connects to which other node(s).

According to an embodiment of the invention the steps of controlling of the present method involves switching the one or more wireless access nodes and the one or more wireless backhaul nodes between energy saving mode and non-energy saving mode. The energy saving mode and the non-energy saving mode may be ON-mode and OFF-mode, respectively, which means that the nodes are either in on or off state. However, the energy saving mode could also relate to different energy consumption levels. For example, when the full capacity of a node is not needed, the node may be configured with sleep periods and active periods. During the sleep periods parts of the node are switched to a low energy state, and no data can be sent or received. All data reception and transmission is performed during the active periods of the node. In another example of a node in energy saving mode, the capacity may be reduced by switching off some antennas while maintaining continuous service.

In the example of Table 1 access network configuration A meshed network configuration D is the best (lowest) for total power consumption with the present joint optimisation method. Thus, the access network with the highest power consumption gives the lowest total power consumption in this particular example. Access Network Power Meshed network Power Total power Configuration consumption configuration (best consumption consumption for access network

configuration)

A 8 kW D 19.5kW 27.5kW

B 7.5 kW E 22kW 29.5kW

C 6.5 kW F 22kW 28.5kW

Table 1

Further, the fact that the access node power consumption includes a component for its backhaul link(s) have been ignored and this may vary according to which mesh node(s) it connects to. Thus, the sum power consumption (P + P₂) may further depend on:

• Access network configuration: which access nodes are in energy saving mode, type of energy saving mode, which mobile connects to which cell, etc.

• Mesh network configuration: which backhaul nodes are in energy saving mode, type of energy saving mode, which backhaul links exist, etc.

· Association of access nodes to backhaul nodes: i.e. for each active access node which backhaul node(s) does it connect to.

In the following two examples some examples of joint optimization are described. Example 1

Figure 3: a new mobile station wants to connect to the internet. Its closest AN is AN3 but this is currently switched off (sleeping). Also, if AN3 is enabled then meshed node MN3 must be switched on to allow backhaul. The alternative is to force the mobile to connect to AN2. This choice probably has lower total power consumption although consumption for that specific mobile station will be larger.

Example 2

Figures 4 and 5: in the example in figure 4 ANl and AN2 are lightly loaded while AN3 is heavily loaded. It makes sense to switch off ANl or AN2. If ANl is switched off then MN1 can also be switched off so this will save the most total energy. This energy saving state is illustrated in figure 5.

A question to be addressed is: how can joint optimization of access and backhaul networks be implemented? In principle, a central entity (e.g. an optimization server in network management system) could determine the optimum state of the complete network using standard optimization techniques such as simulated annealing. For example, if a mobile station is assumed to connect to its nearest AN, and each AN connects to its nearest MN (only), and the mesh nodes are fully meshed, then the state of the system can be described as an on/off vector of length equal to the sum of the number of ANs and the number of MNs. The power consumption of each possible vector value would be estimated and the search would look for a global minimum in this space.

According to another embodiment of the invention a constraint that certain minimum Quality of Service (QoS) should be met may be added, hence the sum P_Sum is minimised subject to at least one QoS requirement for mobile stations in the access network. The QoS requirement may relate to any of: latency, cell downlink throughput, cell uplink throughput, cell edge downlink throughput, cell edge uplink throughput, or traffic QoS. Since the QoS requirement of the mobile stations may vary, only taking into account the presence of mobile stations at certain locations does not give a very accurate view of the required capacity. Therefore, adding constraints for the specific services of each mobile station at a given time will allow a more accurate optimization of the energy consumption for a required service level.

A more advanced algorithm could consider a balance of QoS requirements and power consumption requirements which mean that the sum P_Sum is ^al^so minimised subject to at least one power consumption requirement. Preferably, the power consumption requirements relates to any of: mobile station power consumption, network radio frequency power radiation, downlink network coverage, or uplink network coverage. This allows the optimization algorithm to take into account limitations of the communication equipment with respect to maximum power, which otherwise could cause problems with coverage. It also allows the optimization algorithm to take into account the limited battery capacity of mobile stations, which makes the energy consumption of the mobile stations more critical than the energy consumption of other nodes in the communication system. Moreover, multiple criteria may be included in a utility function which should be minimised for minimum power consumption of the communication network. Therefore, the following capabilities may be included in the present method:

• The AN can connect to one of several MNs,

· The AN can connect to multiple MNs simultaneously,

• In the case that the backhaul network is a mesh network, the mesh is not fully-meshed but the enabled links and nodes should be chosen considering the optimisation.

Including any of the above capabilities increases the number of possible configurations of the network compared to a simpler network topology. However, the optimization problem becomes more complex (the state space becomes much larger) with a more sophisticated network topology.

Furthermore, the optimization should be performed regularly as mobile stations move or new mobiles transition to/from active state. Even changes in a traffic bearer to one mobile user, e.g. from ftp download to video streaming could induce a re-optimization. The rate at which the energy optimization can be performed depends on the speed of the optimization and the speed at which nodes can be reconfigured, e.g. switched on or off. Impacts on mobile stations are also a consideration, handovers that are forced by switching an AN off may impact the perceived Quality of Experience (QoE) of the mobile users. It should further be noted that a distributed implementation of the optimization would in principle also be possible. This scales better with network size but is likely to give poorer performance compared to a centralised solution.

To allow a flexible association of access node to backhaul node(s), the access node may support a steerable antenna for connecting to the backhaul (mesh) nodes in its neighbourhood, either by mechanical or electrical adjustment (such as beam switching) or multiple beams.

To reduce installation expanses and operational expenses (opex) of an access node or backhaul node, the management of the nodes may be executed using the backhaul link itself. The alternative could be to employ a permanent wired communications link to the node such that OAM management or management from a central control entity could take place. This link could be of low bandwidth since management traffic is generally light, so fibre would not be necessary. The link could possibly be implemented together with the power provision to the node, e.g. using IEEE 1901.

If energy management uses the backhaul wireless then there needs to be a mechanism to "page" the access nodes that are in energy saving mode (e.g. sleep mode) when downstream management information is to be sent. For example, the management signal could be to switch the access node on. The paging could work as follows:

1. A backhaul node sends wireless page message to an access node at predetermined time - this could be at one of a periodic set of paging occasions,

2. The access node wakes up on every paging occasion and on this occasion it reads the page message,

3. The access node sends a response to the backhaul node and fully wakes up, and

4. The backhaul node sends management signalling to the access node. Clearly, the frequency of paging occasions is a trade off between the time that the nodes need to be in wake up mode and the delay that will be incurred before a node can be paged.

In some cases the backhaul node nearest to the access node may itself be asleep. In this case the wake up delay can be reduced by synchronizing the paging occasions of the backhaul nodes and access nodes. The access node paging occasions should slightly lag those of the backhaul node to allow the backhaul node to wake-up and then itself to page the access node according to an embodiment. Furthermore, there may be a need to page a mobile station under the access node which has just been woken, so further synchronization here will minimize the delay. It should however be noted that it is also possible that the wake up periods for the backhaul nodes lag the wake up periods for the access nodes depending on the scenario. This means that the different wake up periods may be synchronised with some time shifts between them. In principle the wake up periods of the interfaces of two different nodes that they use to communicate with each other shall wake up at the same time, but when a node has two interfaces in different directions there may be a time lag between the two interfaces. So a mobile station wakes up at the same time as the radio interface of the access node, and one interface of a backhaul node wakes up at the same time as the access node backhaul interface. Hence, the lag in the wake up periods between different interfaces of a node may be configurable in a way which corresponds to the requirements of control signalling. According to another embodiment of the invention, the access node may wake up first and broadcast a reference signal that the mobile stations within its coverage area can detect. This access node may be called a probing access node. The mobile stations may report the presence of the probing access node to the access node they are currently connected to. Mentioned access node can then decide to trigger the probing access node to wake up and start serving the mobile stations. In this embodiment the control signalling will be sent after the wake up of the access node, hence the wake up time of the backhaul nodes would lag that of the access nodes.

The wake up times can also be used for broadcasting probing signals to detect if there are any mobile stations that may connect to an access node that is in sleep mode. The access node wake up times would then be synchronized with the mobile network signalling, and also mobile stations with discontinuous reception (DRX) configuration could have their active periods synchronized with the same wake up times.

Hence, according to an embodiment it is proposed to use synchronized wake up periods to allow connectivity during sleep state:

• For both backhaul nodes and access nodes,

· For access nodes and mobile stations, e.g. paging occasions, ES probing, etc.

One advantage of such synchronization is that the on time for all nodes is minimized without reducing the connectivity or causing additional delay. If the wake up periods would not be synchronized the control signalling would either have to be delayed in the access nodes or backhaul nodes or the connectivity opportunity would be lost. Alternatively, longer wake up periods would be needed for non-synchronized nodes to guarantee that the nodes would have overlapping wake up times and thereby allow the nodes to connect.

Furthermore, as understood by the person skilled in the art, any method according to the present invention may also be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprises of essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive. Moreover, the present invention also relates to a control device arranged to control one or more wireless access nodes of at least one wireless access network and one or more wireless backhaul nodes of at least one associated wireless backhaul network. The control node is further arranged to control a first power consumption P of the one or more wireless access nodes, and jointly control a second power consumption P₂ of the one or more wireless backhaul nodes such that a sum P_Sum of the first power consumption and the second power consumption is minimised. It must further be considered obvious that the control device above may be modified, mutatis mutandis, according to different embodiments of the present method. Finally, it should be understood that the present invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

1. Method for energy saving in a communication system, said communication system including:

2. Method according to claim 1 , wherein

said first power consumption P is the total power consumption of said one or more wireless access nodes, and

said second power consumption P₂ is the total power consumption of said one or more wireless backhaul nodes.

3. Method according to claim 1 , further comprising the step of:

- estimating a first power consumption and estimating a second power consumption, and

- using said estimated first power consumption and said estimated second power consumption for minimising said sum P_Sum -

4. Method according to claim 1 , wherein the steps of controlling involves:

- switching said one or more wireless access nodes and said one or more wireless backhaul nodes between energy saving mode and non-energy saving mode.

5. Method according to claim 4, wherein said energy saving mode and said non-energy saving mode are ON-mode and OFF-mode, respectively.

6. Method according to claim 1, wherein said sum P_Sum is minimised subject to at least one quality of service (QoS) requirement for said one or more mobile stations.

7. Method according to claim 6, wherein said at least one quality of service (QoS) requirement relates to: latency, cell downlink throughput, cell uplink throughput, cell edge downlink throughput, cell edge uplink throughput, or traffic quality of service (QoS).

8. Method according to claim 6 or 7, wherein said sum P_Sum is minimised subject to at least one power consumption requirement relating to: mobile station power consumption, network radio frequency power radiation, downlink network coverage, or uplink network coverage.

9. Method according to claim 1, wherein each wireless access node is associated with only one wireless backhaul node.

10. Method according to claim 1, wherein each wireless access node is simultaneously associated two or more wireless backhaul nodes.

11. Method according to claim 9 or 10, wherein said one or more wireless access nodes support steerable or switchable antenna beams for connecting to its backhaul node(s).

12. Method according to claim 1, wherein the steps of controlling involves:

- using said wireless backhaul network for controlling said first power consumption P and said second power consumption P₂ by means of control signalling.

13. Method according to claim 12, further comprising the step of:

- paging wireless access nodes and/or wireless backhaul nodes which are in energy saving mode.

14. Method according to claim 13, wherein wake up periods for wireless access nodes and wireless backhaul nodes in energy saving mode are synchronised.

15. Method according to claim 14, wherein the wake up periods for wireless access nodes time lag the wake up periods for wireless backhaul nodes, or vice versa.

16. Method according to claim 14 or 15, wherein wake up periods for mobile stations in energy saving mode are synchronised with the wake up periods for wireless access nodes and wireless backhaul nodes.

17. Method according to claim 16, wherein the wake up periods for mobile stations time lag the wake up periods for wireless access nodes and/or the wake up periods for wireless backhaul nodes, or vice versa.

18. Method according to claim 1, wherein

said one or more wireless access nodes are any of: base stations, remote radio heads, or relay stations; and/or

said wireless backhaul network is a meshed backhaul network.

19. Computer program, characterised in code means, which when run by processing means causes said processing means to execute the method according to any of claims 1-17.

20. Computer program product comprising a computer readable medium and a computer program according to claim 19, wherein said computer program is included in the computer readable medium, and comprises of one or more from the group: ROM (Read-Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically EPROM) and hard disk drive.

21. Control device for a communication system, said communication system including: at least one wireless access network comprising one or more wireless access nodes and one or more mobile stations, and

wherein said control device is arranged to control said one or more wireless access nodes and said one or more wireless backhaul nodes; and said control device being characterised in that further being arranged to: - control a first power consumption P of said one or more wireless access nodes, and jointly

- control a second power consumption P₂ of said one or more wireless backhaul nodes such that a sum P_Sum of said first power consumption and said second power consumption is minimised.