GB2366951A

GB2366951A - Multi-hop wireless network

Info

Publication number: GB2366951A
Application number: GB0025910A
Authority: GB
Inventors: Keith Edward Mayers; Rajadurai Vijithan; Arulalingam Arulkkumaran; Alan Law
Original assignee: Vodafone Group PLC; Vodafone Ltd
Current assignee: Vodafone Group PLC; Vodafone Ltd
Priority date: 2000-09-12
Filing date: 2000-10-23
Publication date: 2002-03-20
Anticipated expiration: 2020-10-23
Also published as: AU2001286068A1; GB0025910D0; DE60133397T2; GB0022335D0; GB2367208B; DE60133397D1; GB2367208A; GB2366951B; WO2002023829A1

Abstract

A telecommunications system is described, for transmitting data between any one of a number of radio transceiving nodes (A,B,C and D) and a concentration point (CP) around which they are arranged. The data is transmitted in a series of hops (e.g. h1,h2,h3...h6), each hop terminating in an intermediate node (not shown) which then re-transmits the data to produce the next hop. In order to produce an even distribution of radio interference over the geographical area encompassed by the nodes and hence provide the optimum capacity for the system, the length of the hops closer to the concentration point is less than the length of the hop farther away from the concentration point (CP), the lengths of the hops in any particular one of the transmission paths preferably decreasing successively in the direction towards the concentration point (CP). In this way, the radio power dissipated in each hop is reduced immediately adjacent the concentration point (CP) to compensate for the inevitable concentration there of the converging transmission path.

Description

<Desc/Clms Page number 1> TELECOMMUNICATIONS SYSTEM The invention relates to telecommunications systems. A telecommunications system embodying the invention, and to be described in more detail below, by way of example only, is for transmitting data in a radio network, such as a cellular telecommunications network.

According to the invention, there is provided a method of transmitting data in a wireless network between two spaced radio transceiving nodes in a network, one of the nodes being a concentration point and the other node being a selectable one of a plurality of the nodes spatially positioned with reference to the concentration point, by means of a transmission path including a plurality of hops involving at least one intermediate one of the nodes, including the step of constraining the radiated energy dissipation in a hop close to the concentration point to be lower than the radiated energy dissipation in a hop in the same transmission path but further from the concentration point.

According to the invention, there is further provided a method of transmitting data in a wireless network between two spaced radio transceiving nodes in the network, one of the nodes being a concentration point and the other node being a selectable one of a plurality of the node spatially positioned with reference to the concentration point, the data being transmitted between each selected one of the nodes and the concentration point in a

respective transmission path comprising a plurality of hops involving at least one intermediate one of the nodes, and including the step of constraining the transmission energy which produces each of the hops in each transmission path such that the level of radio interference tends to be uniform along the length of the path.

According to the invention, there is also provided a telecommunications system for transmitting data in a wireless network between two spaced radio transceiving nodes in a network, one of the nodes being a concentration point and the other node being a selectable one of a plurality of the nodes spatially positioned with reference to the concentration point, by means of a transmission path including a plurality of hops involving at least one :.ntermediate one of the nodes, comprising constraining means for constraining the radiated energy dissipation in a hop close to the concentration point to be lower than the radiated energy dissipation in a hop in the same transmission path but further from the concentration point.

According to the invention, there is still further provided a telecommunications system for transmitting data in a wireless network between two spaced radio transceiving nodes in the network, one of the nodes being a concentration point and the other node being a selectable one of a plurality of the node spatially positioned with reference to the concentration point, the data being transmitted between each selected one of the nodes and the concentration point in a respective transmission path comprising a plurality of hops involving at least one intermediate one of the nodes, including constraining means

for constraining the transmission energy which produces each of the hops in each transmission path such that the level of radio interference tends to be uniform along the length of the path.

Telecommunications systems embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 diagrammatically illustrates a problem underlying the invention in one of its aspects; Figure 2 illustrates the operation of one of the telecommunications systems embodying the invention; Figures 3A,3B and 3C illustrates principles underlying the telecommunications system embodying the invention; Figure 4 illustrates the operation of another of the telecommunications systems embodying the invention; Figure 5 illustrates the operation of a further one of the telecommunications systems embodying the invention; and

Figure 6 is a flow chart illustrating the operational steps employed in one of the telecommunications systems embodying the invention.

The telecommunications systems to be described employ wireless networks, such as cellular telecommunications networks. In the networks to be described, data, normally packet data, is transmitted from a source node in the network to a destination node. The network normally includes one node in the form of a concentration point (CP), which may be a base station, and a plurality of other nodes spaced around the concentration point. The nodes may be radio transceivers of any suitable type. The nodes around the concentration point may, for example, be represented by cellular telephone handsets. The source node may be any of the distributed nodes in the network and the destination node may then be the CP. Instead, the CP may be the source node, transmitting data to a destination node comprising one of the distributed nodes. Data is transmitted by hopping, that is, data is communicated between the source node and the destination node in a series of hops, in which the data is received by an intermediate node and then transmitted to another intermediate node, this process continuing until the data reaches the destination node. Such a hopping technique reduces the transmission power required and thus reduces the possibility of radio interference, as compared with an attempt to transmit the data between the source and the destination nodes by means of a single transmission. In principle, of course, there may be only one intermediate node and thus two hops.

Figure 1 shows a concentration point (CP) around which are arranged a plurality of radio

transceiving nodes, such as in the form of a plurality of mobile transceivers (MS), shown at A,B,C and D. It is assumed that each MS wishes to act as a source and to transmit data to the CP. In accordance with known protocols, each MS transmits data to the CP by means of a series of hops shown, for example, at hl,h2,..h3..h6.. Thus hl starts at the MS A and terminates at the first intermediate MS. This intermediate MS then retransmits the data, in a second hop h2, to a second intermediate MS. This process continues until the data reaches the CP. For clarity, the intermediate MSs are not shown. The other MSs B,C and D operate in similar fashion.

In a network operating in this way, therefore, each MS involved in the hopping process must select the next MS in the hopping process. If each MS acts to keep radio interference within the network to a minimum level, it will tend to retransmit its data in a hop of relatively small length, as shown by the hops hl,h2,h3 in Figure 1, thus involving low transmission power. However, each message to be transmitted to the CP will in general be time-constrained (that is, it must reach the CP within a certain time). Therefore, as the hopping process continues, the effect of the time constraint will be to increase the lengths of the hops (as shown at h5 and h6), as the system strives to deliver the message at the CP by the correct time. Therefore, there will be a tendency in such a system for the hops to be of small size at the beginning of each data transmission path from the source MS to the CP, the hops becoming progressively larger and being of maximum length in the immediate vicinity of the CP.

Because the CP is, by definition, the concentration point to which a number of MS's are transmitting data, the result will be high power concentration in the immediate vicinity of the CP, resulting in a tendency for excessive radio interference thus reducing the overall capacity for network.

The invention aims to overcome this problem.

Date transmission in the reverse direction, that is, from the CP to the outlying Mss A,B,C and D do not in general cause a problem. Thus, if they initially start off with a small hop size in the vicinity of the CP, which then progressively increases in order to ensure that the message reaches its destination in due time, the overall power, and thus the radio interference, will be low in the concentrated region around the CP. The increased power causes by the larger hops near the outlying Mss will not be of significance because of the spatial separation of the Mss.

Figure 2 diagrammatically illustrates the operation of a system embodying the invention. Items in Figure 2 corresponding to items in Figure I are similarly referenced.

From Figure 2, it will be seen that the system operates by ensuring that each data transmission from the source MS towards the CP proceeds by means of initial relatively large-sized hops which progressively reduce in length as they approach the CP. Therefore, when a number of surrounding MSs are transmitting data to the CP, the data

transmission paths ensure that the sizes of the hop in the immediate vicinity of the CP are small. Therefore, the power and the radio interference is significantly reduced, and the capacity of the network is increased accordingly.

According to one feature of the invention, therefore, a protocol is set up for controlling the sizes of the hops involved in transmitting data from a source node to the CP so as to minimise hop length, and thus transmission power, in the vicinity of the CP. In accordance with this protocol, the source node or MS first estimates the distance between itself and the CP. This estimation can be carried out in various ways: for example, the difference could be estimated by measuring the amount of power received at the MS from the CP, assuming -a known value for the transmission power and a particular radio path loss model. Alternatively, the distance could be estimated using GPS location data for the CP and the MS. The protocol then decides on the most efficient number and length of hops for the data transmission, based on the estimated distance and on interference measurements. Such a protocol could be stored in each MS, or could be stored at the CP; in the latter case, the decisions would be made by the CP and transmitted to the source node and to the intermediate nodes.

Figure 3A,313 and 3C illustrate the operating principles of such a protocol in more detail. Figure 3A shows a cell or part of a cell in a telecommunications network which is notionally divided up into circular layers L1,L2,L3 of equal width and with progressively

reducing radial distance from the CP. Superimposed on the layers is a graph showing the average number of users (that is, MSs transmitting data at any time) in each layer. Plainly, the number of such users is greater for the larger radius layers than for the smaller radius layers.

Figure 3B shows the layers L1,L2,L3... again, and the CP. Here, there is superimposed a graph showing the cumulative distribution of data transmission traffic from the outlying MSs to the CP, assuming that the data communication is sent through each of the layers. Plainly, cumulative traffic increases progressively in the direction towards the CP.

For optimum transmission speed and minimum radio interference (and thus maximum capacity for the network), the protocol therefore needs to operate as illustrated in Figure 3C. This Figure shows a graph plotting the interference level on the vertical axis and the distance from the CP on the horizontal axis.

The protocol operates by setting a maximum interference level V.

At the maximum distance from the CP, the originating Mss are widely spaced. Therefore, an originating MS can transmit the data to the first intermediate MS in a single hop Hl, which produces the maximum radio interference V, as shown at 1.

At a position nearer to the CP, shown at 11, there will be a smaller number of originating

users, but potentially more radio interference because there will be potentially interfering transmissions from the more outward layers of the cell. Therefore, the data transmission how takes place by means of two hops H2 and H3, each of shorter lengths than the hop Hl. The total interference produced is again at the level V.

As is shown at 111, IV and V in Figure 3C, the number of hops progressively increases, and their sizes progressively decrease, for positions closer to the CP. However, in each case the total cumulative level of interference which is produced is maintained constant at V. Therefore, the protocol advantageously operates by adjusting the hop length to maintain the cumulative level of interference constant.

Although in general the hop lengths will be smaller at positions closer to the CP than at positions further away, the important factor is the level of potential interference which will be a function of the power or energy dissipated in the hop. This will depend, at least to some extent, on the local radio propagation characteristics. For a given level of radiated energy (which determines potential interference), the actual permitted hop length can be greater where the radio propagation characteristics are good than where those characteristics are bad.

The principles illustrated in Figures 3A,3B and 3C can be implemented by notionally dividing the cell into circular regions around the CP which are sized so that their radiusses increase to a disproportionately greater extent further from the CP, and then arranging for

each data hop to start in one region and then in the next region.

Figure 4 shows such an arrangement in a cell of a cellular telephone system, with regions R1,R2 and R3 arranged around the concentration point CP. The inner and outer radial limits for each such region are spaced apart by a greater distance than the inner and outer radial limits for of the next region closer to the CP.

Within each region, there will be a respective plurality of MSs. Assuming that the MSs are distributed within the cell substantially evenly, there will be more MSs in the outer regions than in the regions closer to the CP. The MSs within each region are given a particular identifying "tag", corresponding to the region in which they are situated. For example, tags of different "colour" could be attached, with MSs in regions Rl,R2 and R3 being respectively given red, yellow and green tags? If the protocol constraining the hopping process is such that data has to take place by means of successive hops each of which starts with a node or MS in one region and ends at an MS or node in the next region, it follows that data transmission starting from an MS in an outer region will take place by means of hops of progressively shorter length in the direction towards the CP. In this way, therefore, an approximation to the required constant cumulative level of interference V shown in Figure 3C will be achieved. Obviously, this will not be achieved exactly because the length of the hops between adjacent regions in Figure 4 will depend on the positions within their respective regions

of the MSs at the beginning and end of each hop.

Figure 5 shows a more complex arrangement of where regions close to the CP have a small size, the size disproportionately increasing as the distance from the regions increases from the CP. Again, the protocol ensures that data transmission takes place by means of hops starting in one region and ending in the next, so that the hops have progressively shorter length as they approach the CP.

It will also be appreciated that, with the arrangements described, data transmission from the CP towards an outlying MS takes place by means of short-length hops which progressively increase in length. Again, therefore, radio interference is minimised. Figure 6 shows a flow chart illustrating steps which can take place in implementing the arrangements illustrated.

At step S 1, the protocol responds to receipt of data at a particular node which is to be transmitted towards the CP by means of a hop. In principle, this node can be the originating MS or an intermediate node.

At step S2, the protocol determines whether the node is a tagged node in one of a series of regions such as shown in Figure 4 or Figure 5. If the node is determined to be such a node, then it is merely necessary for the protocol to calculate the power level in order to

achieve a hop to a node in the next region (step S4). As explained, in connection with Figures 4 and 5, the respective sizes of the regions ensures that the hop will have the correct length.

If at step S2 it is determined that the node does not lie in a particular region as illustrated in Figure 4 or 5. At step S4 the protocol determines the position of the node relative to the CP (e.g. using GPS information or power loss information as described above).

At step S5, the system obtains the "radio and/or system parameters". At step S6, the protocol uses this information to determine the optimal size of the next hop. Finally, at step S7 the protocol calculates the required power level to achieve this hop.

In summary, therefore, the network systems described aim to produce an even distribution of radio interference over a particular geographical area and thus provide optimum capacity for any interference-limited system.

Claims

CLAIMS 1. A method of transmitting data in a wireless network between two spaced radio transceiving nodes in a network, one of the nodes being a concentration point and the other node being a selectable one of a plurality of the nodes spatially positioned with reference to the concentration point, by means of a transmission path including a plurality of hops involving at least one intermediate one of the nodes, including the step of constraining the radiated energy dissipation in a hop close to the concentration point to be lower than the radiated energy dissipation in a hop in the same transmission path but further from the concentration point.
2. A method according to claim 1, in which the constraining step includes the step of dynamically determining the lengths of the hops in a said data transmission path in dependence on the radio properties in and adjacent to the transmission path.
3. A method according to claim 2, in which the constraining step includes the step of dynamically determining the lengths of the hops in a said data transmission path in dependence on the distance from the source node to the concentration point.
4. A method according to any preceding claim, in which the length of a hop close to the concentration point is shorter than the length of a hop in the same transmission path

<Desc/Clms Page number 14>

but further from the concentration point.
5. A method according to claim 4, in which the constraining step includes the step of defining a plurality of spatial regions, a first one of which includes the source node, a second one of which includes the concentration point and at least a third one of which includes an intermediate node, at least the first and third regions including others of the nodes, the regions successively closer to the concentration point being of successively reduced size, and the step of defining each hop to start in one of the regions and to end in an adjacent one of the regions.
6. A method according to claim 5, in which the regions are arranged around the concentration point.
7. A method of transmitting data in a wireless network between two spaced radio transceiving nodes in the network, one of the nodes being a concentration point and the other node being a selectable one of a plurality of the node spatially positioned with reference to the concentration point, the data being transmitted between each selected one of the nodes and the concentration point in a respective transmission path comprising a plurality of hops involving at least one intermediate one of the nodes, and including the step of constraining the transmission energy which produces each of the hops in each transmission path such that the level of radio interference tends to be uniform along the length of the path.

<Desc/Clms Page number 15>
8. A method according to claim 7, in which in each transmission path the hops successively closer to the concentration point have successively reduced lengths.
9. A telecommunications system for transmitting data in a wireless network between two spaced radio transceiving nodes in a network, one of the nodes being a concentration point and the other node being a selectable one of a plurality of the nodes spatially positioned with reference to the concentration point, by means of a transmission path including a plurality of hops involving at least one intermediate one of the nodes, comprising constraining means for constraining the radiated energy dissipation in a hop close to the concentration point to be lower than the radiated energy dissipation in a hop in the same transmission path but further from the concentration point.
10. A system according to claim 9, in which the constraining means comprises means for dynamically determining the lengths of the hop in a said data transmission path in dependence on the radio properties in and adjacent to the transmission path.
11. A system according to claim 10, in which the constraining means comprises means for dynamically determining the lengths of the hops in a said data transmission path in dependence on the distance from the source node to the concentration point.
12. A system according to any one of claims 9 to 11, in which the constraining means constrains the length of a hop close to the concentration point to be shorter than the length

<Desc/Clms Page number 16>

of a hop in the same transmission path but further from the concentration point.
13. A system according to claim 12, in which the constraining means comprises means for defining a plurality of spatial regions, a first one of which includes the source node, a second one of which includes the concentration point and at least a third one of which includes an intermediate node, at least the first and third regions including others of the nodes, the regions successively closer to the concentration point being of successfully reduced size, and means for defining each hop to start in one of the regions and to end in an adjacent one of the regions.
14. A system according to claim 13, in which the regions are concentrically arranged around the concentration point.
15. A telecommunications system for transmitting data in a wireless network between two spaced radio transceiving nodes in the network, one of the nodes being a concentration point and the other node being a selectable one of a plurality of the node spatially positioned with reference to the concentration point, the data being transmitted between each selected one of the nodes and the concentration point in a respective transmission path comprising a plurality of hops involving at least one intermediate one of the nodes, including constraining means for constraining the transmission energy which produces each of the hops in each transmission path such that the level of radio interference tends to be uniform along the length of the path.

<Desc/Clms Page number 17>
16. A system according to claim 15, in which in each transmission path the hops successively closer to the concentration point have successively reduced lengths.
17. A method of transmitting data in a wireless network, substantially as described with reference to the accompanying drawings.
18. A telecommunications system for transmitting data in a wireless network? substantially as described with reference to the accompanying drawings.