GB2326059A - Path controlled repeating mobile stations - Google Patents

Abstract

A radio communications network comprises at least two base stations in fixed relatively widely spaced-apart positions, and a plurality of relatively closely spaced-apart mobile stations. At least some of the mobile stations act as controlled repeaters to relay traffic signals from a relatively close mobile station to another relatively close mobile station under control of a central control means. The central control means estimates the positions of the mobile stations in order to determine one or more virtual paths for the traffic signals. Control messages telling each mobile station to repeat the call are transmitted to each mobile station via one of the base stations without the use of repeaters. Packet data may be sent over a plurality of virtual paths with different data rates. Base stations may be fixed terrestrial stations, earth-orbiting satellites or aerial stations. The mobile stations may be situated on marine vessels.

Description

COMMUNICATION SYSTEMS This invention relates to communication systems and particularly, but not exclusively, to cellular telecommunications systems.

In order to increase the capacity in cellular networks it is common practice to decrease the cell size and thereby increase the re-use of radio channels.

Small cell size means more base stations (BSs) are required. This means that more cell sites are needed to locate the BSs, and the cell sites must be connected in some fashion to the network. It may be that the BSs are arranged in a local area network by connecting them using radio or optical fibre. The local area network (LAN) may then be connected to other LANs and thence to the network switches and databases.

At the first level of deployment of microcells it is evident that there is a need for a plurality of BSs, cell sites, and the interconnection of the BSs to each other or directly to the next stage of the network.

We consider that BSs and interconnection cost of materials are likely to decrease substantially as the deployment of microcellular networks continue. However, labour costs are likely to rise in line with any inflation. This is also probable with site acquisition costs for base stations.

Methods are therefore required to decrease infrastructure costs associated with high capacity small cell networks.

PRIOR ART SOLUTION Macrocellular sites create cells larger than microcells. A popular concept is to have a network of microcells overlaid by macrocellular network, such that one macrocell may overlay more than one microcell, and possibly clusters of microcells. The macrocells may be used to cover radio deadspots in the microcellular network, or to assist in handovers (HOs) when there is a shortage of microcellular channels due to them being busy at the time of handover requests.

We mean by microcell a small cell relative to a macrocell. The microcell may be provided for users at street level, or at a higher level. In the latter case we are considering three dimensional microcells, as exemplified by a microcell composed of a few floors in a tower block of flats.

SUMMARIES OF THE INVENTION According to one aspect of the invention a communication network comprises at least two base stations located in fixed relatively widely spaced-apart positions, a plurality of relatively closely spaced-apart mobile stations in the space around the two or more base stations, the base stations each comprising base station radio transmitter means and base station radio receiver means, the mobile stations each comprising mobile station radio transmitter means and mobile station radio receiver means, at least some of the mobile stations being arranged to act as controlled repeaters to relay an incoming traffic signal at a mobile station to a nearby mobile station, the repeaters being controlled by a network control means, repeater control signals from the control means to the mobile stations and ancillary control information signals from the mobile stations to the control means being transmitted from or to one or more control signal stations as radio signals on relatively long radio transmission paths as compared with the relatively short distances between the mobile stations.

The relatively short path lengths between the mobile stations allows the known advantages of small cells to be realised in permitting a heavy utilisation of the available wavebands by traffic signals when the mobile stations are operated at relatively low powers for this purpose, but relatively long path lengths can be accommodated for the control signals since the control signals need only convey a relatively small volume of data as compared with the traffic data.

This means that in most applications of the invention relatively few control signal stations need be employed. When the control signal stations are land-based stations this has the advantage that a relatively small number of sites need be acquired for the fixed stations.

The control signal stations may be provided by one or more satellites or aerial stations, in which case the repeating mobile stations are preferably each provided with a suitable signal receiver to receive repeater control signals transmitted from the satellite or aerial station and a suitable signal transmitter to transmit ancillary control signals to the satellite or aerial station.

Preferably the mobile stations are so arranged as to exchange signals (make handshakes) with the nearest one or more mobile stations in order to establish the relative positions of the mobile stations, and preferably the power required to perform the handshake is monitored, and this information is transmitted by the mobile stations to the control signal stations, that is using the control signal network.

The combination of mobile station positional information and information on the quality or integrity of the available individual links between mobile stations provided to the system control, enables the system control to select the preferred route or routes for relaying traffic signals. For dense traffic signals a combination of a plurality of routes may be selected.

According to a second aspect of the invention a communication network comprises a plurality of base stations located in fixed spaced-apart positions, a plurality of mobile stations in the region between the base stations, the base stations each comprising base station radio transmitter means for transmitting signals, and base station radio receiver means for receiving signals, the mobile stations each comprising mobile station radio transmitter means for transmitting signals, and mobile station radio receiver means for receiving signals, at least some of the mobile stations being arranged to act as a controlled repeater to relay an incoming traffic signal to a nearby mobile station, or base station when nearby, the relay action being controlled by a network control means which communicates with the mobile stations by way of the base stations to provide relay action control signals, the signal strength of the mobile station transmitter means when transmitting traffic signals being such as to define a mobile station microcell having a transverse dimension which is generally substantially less than the spacing of the base stations, the base station transmitter means when acting to communicate traffic signals with an adjacent mobile station having a signal strength such as to define a microcell of dimensions comparable with the dimensions of the mobile station microcells, but the base station transmitter means when acting to provide said relay action control signals to the mobile stations having a signal strength sufficient to define a macrocell for control action of dimensions comparable to the spacing between the base stations.

Thus by using the mobile stations to act as repeaters for relaying traffic signals from one mobile station to another mobile station, or to a nearby base station, we avoid the need for a network of closely-spaced base stations. Furthermore we provide centralised control of the virtual path by which the traffic signals flow from mobile station to mobile station and onward.

The control means can communicate with the base stations by any convenient communication link. This can be a land line of any kind or it may be a radio link. In the case of a radio link the base station transmitter means and base station receiver means can form part of this link.

The base station transmitter means, when acting to communicate traffic signals with reduced signal strength compared to the usual signal strength required in conventional macrocells, minimises the interference to the traffic channels of other base station receiver means such that, in the limit, frequencies for traffic use may be allocated with a re-use of unity, thus significantly increasing the capacity of the network.

According to a third aspect of the invention a maritime communication network comprises a plurality of marine vessels spaced-apart on a body of water, each vessel carrying a vessel communication unit, said unit comprising a vessel radio transmitter for transmitting traffic signals generally across the water and a vessel radio receiver for receiving signals transmitted across the water, at least one base station on land provided with a land station radio transmitter and a land station radio receiver for respectively transmitting and receiving radio waves across the water to and from an adjacent one of the vessels, at least one satellite or aerial station, each vessel communication unit being further provided with a transmitter and receiver suitable for communications with the satellite or aerial stations, the vessel communication unit being adapted to receive destination control signals by way of the satellite signal receiver from the satellite, the control signals controlling the principal direction of transmission of traffic signals from the vessel communication unit so as to be directed towards a vessel communication unit carried by another of the vessels, or towards a nearby land station, the vessel communication units comprising repeater means for generating a transmission signal to be emitted by the associated vessel radio transmitter in response to an incoming traffic signal received by the associated vessel radio receiver, and a system control means communicating with, or incorporated in the satellite or aerial station and arranged to monitor the location of the vessels, and to provide the destination control signals.

Thus, the satellite or satellites or aerial station or aerial stations are used for providing destination control signals to the vessel communication units, whereas the traffic signals do not pass via the satellite/s or aerial station/s but are transmitted across the water from one vessel to another, and then from a vessel to a land station.

At least some of the vessel communication units may be arranged to receive radio traffic signals transmitted from an aircraft to provide the aircraft occupants with a telecommunication link.

A further aspect of the invention comprises a mobile station for use in a communication network in accordance with the first or second aspects of the invention, the mobile station being adapted to relay traffic signals from a relatively close further mobile station to another relatively close mobile station under the control of path control signals emitted from a relatively distant fixed base station.

Yet another aspect of the invention comprises a mobile station which is arranged to exchange radio signals with a nearby such mobile station in order to provide information on the relative positions of the mobile stations.

DESCRIPTION OF PREFERRED EMBODIMENTS The various aspects of the invention will now be further described, by way of example only, with reference to the accompanying schematic drawings, in which: Figure 1 is a schematic plan view of a land based mobile communication network in accordance with the first and second aspects of the invention, Figure 2 is a plan view of part of the network of Figure 1 showing the actual positions occupied at a particular time by certain mobile stations MS1 to MS7, Figure 3 is a computer-generated first estimation of the positions of the mobile units of Figure 2, as computed by the network control means of the network of Figure 1, Figure 4 is a plan view, not to scale, of a maritime communication network in accordance with the first and third aspects of the invention, and Figure 5 is a view on the line 5-5 of Figure 4.

The first and second aspects of the invention were based on a consideration of retaining the signalling channels of the previously described prior art solution macrocells for wide area coverage. This means that the signalling channels will be transmitted at a level that the mobile stations could, with appropriate transceivers, receive and transmit signalling information directly via a macrocellular base station.

We then make a radical change. The traffic channels of the macrocell are arranged to have a greatly decreased coverage area, down to the size of a microcell.

The next proposal is to remove all or most of the fixed microcellular BSs, and hence the fixed interconnections between microcellular BSs and the network are removed.

Figure 1 schematically represents the resulting network. It should be appreciated that Figure 1 is not to scale and is merely provided to illustrate the principles involved. As shown, there is a plurality of relatively-widely spaced-apart fixed base stations (BSs): BS1, BS2, BS3, BS4, and in the region around the BSs there is a plurality of mobile stations (MSs): MS1, MS2 to MS34, which are relatively-closely spaced-apart, as compared with the spacing of the BSs.

Each of the MSs comprises a respective mobile station radio transmitter means and a respective mobile station radio receiver means. Each of the BSs comprises a respective base station radio transmitter means and a respective base station radio receiver means. Of course, the transmitter and receiver means associated with a respective mobile station or base station can be combined in a single transceiver unit.

In order for microcells to exist we propose that some mobile stations (MSs) act as repeaters, passing on traffic data from other MSs. This means that a MS must be able to accommodate its own originating calls, and have the capacity to relay traffic from other MSs.

A MS forms a microcell around it when it acts in a repeater mode. For example, in Figure 1 the microcell associated with MS19 is indicated as MCl9. Because of this the transmission power is low. This is significant in keeping down the battery dissipation in hand held MSs.

All MSs signal to the network via the macrocellular signalling BSs in order for network control to estimate their relative positions. This can be done a number of ways. If they have a differential global positioning system (D GPS) they can provide a relatively accurate estimate of their position. If they do not have D-GPS, they may interact with nearby MSs and report to the network who is near them. If this is done by all MSs the network can estimate where each MS is located, as described later.

When a MS wants to make a call it signals a request to do so. The network, via the macrocell signalling channels, gives the MS a routing list.

This list is equivalent to a routing list in a fixed network, setting up a virtual path.

The MS knows which MSs are on the list to repeat its traffic data. It also knows that the MSs on the list have available traffic channels which will not be used by any other MS for the duration of the call made by the MS who has been given the list and permission to make the call. Each MS on the list will have been informed by the network that it is to repeat the call, the channel to use for repeating the call, and suitable side information for the next MS on the list to understand from where it came and to where it is going.

The virtual paths terminate at one of the macrocellular sites, for example BS3 in Figure 1. We recall that all these sites create wide area cells for signalling, the macrocell for site BS1 being indicated in Figure 1 as the region MACROBS1, they are only of microcellular size for traffic, the microcell for BS1 being shown in Figure 1 as the circle MICROBS1. As a consequence there is negligible interference between the traffic channels at each macrocell site, and they are all deployed with a re-use of unity.

In the proposed arrangement there are only macrocellular fixed sites, that is, base stations separated on a macrocellular scale.

Let us now change our definition of cells into those created from fixed sites and those from moving sites.

Fixed sites have two types of channels: signalling channels and traffic channels. Signalling channels take limited capacity, but are operated in a re-use mode that is likely to exceed one. The fixed sites resemble conventional macrocells from a signalling view point. The fixed sites resemble isolated microcells from a traffic point of view. Further, the microcells may be sufficiently isolated from each other that all sites can use the same traffic channels, ie a re-use of one.

There are other microcells that are moving and formed by the repeating action of the MSs. Examples of these are the circles MC19 and MC20 in Figure 1. As a MS has to accept a signal from another MS on the list, and then repeat it, it may be necessary for the repeating MS to change carrier frequency in order to prevent instability in the repeating action.

System control may establish a number of virtual paths consisting of the preferred path, and alternate paths should the preferred path become broken, eg by the rapid movement of a MS resulting in a loss of radio communications between this MS and others in the preferred path. This means that the MSs must be regularly polled by the macrocells signalling system so that preferred and alternative virtual paths are continuously updated. Notice that this means that the packets of data may be replicated at some repeating MSs, so as to retain the virtual path and to sustain an alternative path or paths.

System control may establish a plurality of virtual paths from a MS to a BS. These paths may pass packets that have been replicated at the MS with the view of increased redundancy so that one or more packets may successfully reach the BS. The BS will accept the most likely correct data by comparing the data in the received packets. The reverse procedure applies for the transmission of packets from the BS to the MS.

The plurality of virtual paths may also be used to accommodate variable rate data generated at the MS or the BS. A data rate that exceeds the rate which may be supported by one virtual path can be transmitted by using a plurality of paths. Because the quality of the repeating links in the virtual paths will vary, for example as the repeating MSs and originating MS move, manifesting as an inability to support the desired data rate, it is incumbent on the MSs and BSs to provide buffers to store the data packets when necessary.

The spectral efficiency of the repeating MS system will differ in different situations. The spectral efficiency gains from the fixed traffic stations is large. More importantly, the normal microcellular infrastructure has been removed and replaced by a network of repeating MSs who signal via a conventional large cell arrangement. The macrocell sites become microcell ones in terms of traffic handling.

HOW THE NETWORK IDENTIFIES THE POSITIONS OF MOBILE STATIONS Each MS increases its transmitted power so that it can exchange packets with the nearest one or more MSs. If the MS is relatively isolated the contact may be with only one MS, but if in a pack of MSs, only low power hand shakes may be done with a number of MSs. Each MS signals to its nearest mobile neighbours. The fixed base stations (BSs) also handshake using minimum power with their nearest MSs. Each MS transmits on the signalling network the identity of its nearest neighbours and the power required to perform the handshake in each case, to enable the control network to create a plan of the nearest neighbours to each MS and a crude distance measure of their spacing based on transmitted and received power levels. Figure 2 is a sketch is of the actual positions in our example, but the network control will not have the actual positions, but the relative ones as in Figure 3.

At system time T, a system parameter, the MSs are polled for information relating to their neighbouring MSs as described above. The map is recomputed and thus the network controller may track movements by individual MSs.

High positional accuracy is not the aim. What is required is the relative positions to ensure that a MS can be given a preferred virtual path and a set of alternative paths to a collecting/transmitting BS, and that these paths can be recomputed at system time intervals following the possible movements of MSs from the preferred virtual path, when system control identifies new and better virtual paths.

When there are no MSs to act as a repeater such that no virtual path can be established, the traffic from and to a MS is carried by using the macrocells in the conventional way, ie the traffic is passed directly to the nearest BS.

AD Hoc MARITIME NETWORKS WITH NO INFRASTRUCTURE Referring to Figures 4 and 5 it will be appreciated that the drawings are not to scale and are merely provided to illustrate the principles involved.

Maritime vessels VS1, VS2, VS3, VS4 are used as moving nodes in a telecommunication network. A virtual path consisting of stages P1, P2, P3 across the water is established between fixed terrestrial nodes BSl, BS2 via nodes VSl and VS2.

One or more surveillance satellites, aerial platforms or aircraft shown as SS have a signalling channel via paths SSVSl, SSVS2 to the respective maritime nodes VS1, VS2, and they know the position of each maritime node which they report to the land-based (in this example system control means SC).

If a call is generated in a fixed network on shore, it crosses the ocean/seas along a virtual path Pl, P2, P3 calculated by system control SC which knows not only the location of the origin of the call, but also the destination of the call.

Aircraft and ships acting as moving nodes, and land-based nodes communicate via device SS and thence to system control during the signalling phases of a call. The traffic is then passed from the aircraft/ships/ terrestrial nodes to the maritime repeating network.

For example, a subscriber in an aeroplane JUM flying over the Atlantic would signal via the aircraft system JUMSS to SS and hence system control SC requesting a call to, say, Dallas. System control would set up a virtual path P3 for the data to proceed via data path JUMVS2 to the nearest maritime node VS2 beneath the plane, and then to the nearest USA terrestrial node BS2 and thence by the terrestrial network to Dallas. As the plane flew its point of entry into the maritime network by a data path such as JUMVS2 would change.

The important feature of a system in accordance with the second aspect of the invention is that the relatively low data rates available in satellite systems are be used for control, whereas the ship-to-ship links carry the very high (if required) data rates.

The maritime paths P1, P2, P3 have the virtue of low propagation delay as it is 'free space' rather than optical fibre, and the maritime vessels are capable of taking bulky equipment which can have the ability to accommodate vast amounts of, say, transatlantic teletraffic.

To ensure that links are always available it might be prudent to offer a minimalist service by deploying some vessels on station to act as repeaters if the maritime vessels cluster thereby leaving areas of the oceans with no vessels present.

An alternative to ensure a minimalist network is that if no ships are available to act as a repeater, a satellite link could be used for data traffic.

We also envisage a system in accordance with the invention which is, in effect, an inverse of the system of Figures 4 and 5, in terms of the functions performed by the aircraft and ships. When there are an insufficient number of ships to form a virtual path, such a path may be constructed from links between a plurality of aircraft. A solitary ship may then use a nearby aircraft as the point of entry into the aerial network. The selection and control of the virtual path would still be made by central control.

Claims (12)

Claims

1. A radio communication network comprising a plurality of relatively closely spacedapart mobile stations, each comprising mobile station radio transmitter means and mobile station radio receiver means, at least some of the mobile stations being arranged to act as controlled repeaters to relay an incoming traffic signal to a nearby mobile station or mobile stations, all repeaters being controlled by a central control means able to communicate with each mobile station without the use of repeaters.

2. A radio communication network as claimed in Claim 1 wherein the said central control means communicates with each said mobile station means via fixed relatively widely spaced-apart base stations.

3. A radio communication network as claimed in Claim 2 wherein relatively high power transmissions are used for control messages and relatively low power transmissions are used for relaying traffic signals.

4. A radio communication network as claimed in Claim 3 wherein the fixed relatively widely spaced-apart base stations comprise base station radio transmitter means and base station radio receiver means for transmitting and receiving traffic signals to and from a nearby mobile station or mobile stations, whereby providing a point of access to a fixed communications network.

5. A radio communication network as claimed in Claim 2 wherein the base station means may comprise earth-orbiting satellites or aerial stations.

6. A radio communication network as claimed in Claim 1 wherein the mobile station means is specially constructed to relay traffic signals from a relatively close further mobile station to another relatively close mobile station under the control of the central control means.

7. A radio communication network substantially as described herein with reference to Figures 1-5 of the accompanying drawings.

Amendments to the claims have been fHed as follows 1. A radio communication network comprising a plurality of relatively closely spacedapart mobile stations, each comprising mobile station radio transmitter means and mobile station radio receiver means, at least some of the mobile stations being arranged to act as controlled repeaters to relay an incoming traffic signal to a nearby mobile station or mobile stations, all repeaters being controlled by a central control means able to communicate with each mobile station without the use of repeaters.

2. A radio communication network as claimed in Claim 1 wherein the said central control means communicates with each said mobile station means via fixed relatively widely spaced-apart base stations.

3. A radio communication network as claimed in Claim 2 wherein relatively high power transmissions are used for control messages and relatively low power transmissions are used for relaying traffic signals between mobile stations until their delivery at a fixed base station.

4. A radio communication network as claimed in Claim 2 wherein the said central control means determines virtual communication paths between mobile stations and/or base stations via repeating mobile stations.

5. A radio communication network as claimed in Claim 4 wherein the said central control means may determine a plurality of virtual communication paths between a mobile station originating the traffic and the fixed base stations to provide redundancy for the communication transmissions, or to support a higher transmission rate than can be accommodated by one virtual communication path.

6. A radio communication network as claimed in Claim 5 wherein every mobile station must report periodically to the said central control means the identity of nearby mobile stations and/or base stations. The central control means uses this information periodically to determine the relative location of every mobile station in the network, and to form an alternative virtual path or paths in the event of a virtual path becoming degraded.

7. A radio communication network as claimed in Claim 3 wherein the fixed relatively widely spaced-apart base stations comprise base station radio transmitter means and base station radio receiver means for transmitting and receiving traffic signals to and from a nearby mobile station or mobile stations, thereby providing a point of access to a fixed communications network.

8. A radio communication network as claimed in Claim 2 wherein a base station means may be housed in an earth-orbiting satellite or aerial station.

9. A radio communication network as claimed in Claim 2 wherein the said mobile stations and repeating mobile stations may be housed in maritime vessels or aircraft.

10. A radio communication network as claimed in Claim 9 wherein an alternative virtual path can be constructed from links between a plurality of aircraft under central control, for example, when there are insufficient maritime vessels to form a virtual path.

11. A radio communication network as claimed in Claim 1 wherein the mobile station means is specially constructed to relay traffic signals from a relatively close further mobile station to another relatively close mobile station under the control of the central control means.

12. A radio communication network substantially as described herein with reference to Figures 1-5 of the accompanying drawings.