HK1021606A - A dynamic radio backbone transmission system - Google Patents

Description

Dynamic radio backbone transmission system

The present invention relates generally to communication systems comprising a radio link connection between two or more communication units, and in particular to radio communication systems having a plurality of geographically dispersed remote fixed and/or mobile radio communication units.

A typical cellular mobile communications system includes a mobile radio subscriber unit, such as a mobile telephone, a plurality of radio base stations, each of which provides service to a geographical area or cell, and a mobile services switching centre (SMC) or Mobile Telephone Switching Office (MTSO) to which the base stations are connected. The MSC and MTSO are in turn connected to the conventional Public Switched Telephone Network (PSTN) and the Integrated Services Digital Network (ISDN), for example to complete transmissions between mobile radio subscribers and landline subscribers, such as telephone calls.

Current cellular systems provide coverage over a relatively wide area, i.e., a relatively large cell. Analog cellular systems such as AMPS, ETACS, NMT-450 and NMT-900 have been adopted worldwide. The digital cellular system specifies IS-54B in north america and the pan-european GSM system (including DCS1800 and PCS 1900). These and other systems are described, for example, in the book "cellular radio system" written by Balston et al, published by Artech House Press, Norwood, Ma, 1993.

The first generation cellular mobile networks provided service to macro cells with a range of 1 to 5km from base station to cell border and macro cells (5 to 35km) with some satellite cells (> 500 km).

An important issue in wireless cellular communications is effectively providing full coverage costs. This results in the separation of cells in dense traffic zones, adding microcells (10 to 400m for pedestrians and 300n to 2km for vehicles) and small cells (500m to 3km) overlapped by macro-cell structures. The overlapping macro cells serve low service areas and address cells spanned by the mobile subscriber.

As cellular penetration continues as predicted, future cellular mobile networks will also have picocells (a few meters) and femtocells (up to 10 meters), often in street microcell clusters, each cluster being overlapped by a macrocell. In a typical cell overlay configuration, each microcell has its own base station providing services to the respective cell, and several base stations are wired to a concentrator or access unit, which in turn is connected to an MSC or MTSO. These wired links or loops providing a static, fixed backbone infrastructure, especially in the context of pico-and femto-cells, involve substantial networking and transmission costs and do not contribute to the objective of providing cost-effective cellular radio coverage.

However, a picocell, femtocell or microcellular radio network system is an economical installation for capacity and regularity. That is, the various components of the system must be designed so that an optimum between geographic coverage, range, communication capacity, and installation cost is achieved in order to provide a competitive wireless connection.

With respect to capacity and power optimization, the backbone infrastructure constitutes a critical design component for providing viable picocellular, femtocell and microcellular cellular radio networks.

It is therefore an object of the present invention to provide a backbone infrastructure optimally designed for the connection between several base stations of pico-cells, femto-cells and micro-cells and the corresponding network system access units of a cellular mobile communication system.

The present invention provides a dynamic backbone transmission system for connecting a plurality of geographically spread remote radio access units to a mobile radio communication network unit, such as a cellular mobile communication network, said each radio access unit providing services to a particular area or cell of said mobile radio communications network, said backbone transmission system comprising dynamic access node means, the dynamic access node means having radio transceiver means, antenna means and control means operatively connected for accessing said plurality of common radio communication channels, wherein said control means of said dynamic radio access node means and said backbone access unit are arranged for adaptively selecting a free communication channel of said plurality of common radio communication channels, said dynamic access node means being arranged for connecting to said network access unit.

The invention is based on the recognition that: optimization of capacity and power is achieved by a transmission backbone system, whose transmission resources are dynamically allocated when required by Dynamic Channel Access (DCA).

Using DCA as a channel access technology for a radio backbone system according to the present invention, all common radio communication channels of the backbone system can be used by picocell, femtocell and picocell base station sites connected to dynamic radio access node (DAN) devices without the fundamental need for channel or frequency planning. This is because the DCA algorithm automatically prevents the occupation of already occupied communication channels of the cell.

With the dynamic radio backbone transmission system of the invention a very flexible, economical and high traffic handling system is obtained in a cellular mobile network for providing wireless connections between several small-cell radio base stations and a concentrator or MTSO.

In another embodiment of the invention the radio transceiver means, antenna means and control means of said dynamic radio access node means are arranged for accessing said plurality of common radio communication channels in directionally separated transmission sections, wherein said control means are arranged to work in conjunction with said backbone access units in a transmission sector to adaptively select a free radio communication channel of said plurality of common radio communication channels which, when accessed, can be reused by the same dynamic radio access node means but independent means for radio link connection in a transmission sector.

By sectorization the effective range of the radio link connection can be extended. That is, by radiating the RF power of the transmitter device to a directionally limited geographic area, the effective range of the radio transmitter can be extended compared to non-directional coverage. With the interactivity, the same is true for the reception sensitivity of the receiver apparatus.

Moreover, common radio communication channels can be reused from sector to sector within the same DAN, providing efficient use of very efficient transmission resources, if desired.

In a particular embodiment of the invention, the dynamic radio access mode means comprises a plurality of radio access modules, each module having radio transceiver means and control means arranged for accessing a plurality of common radio communication channels. The access module is operatively connected for accessing a common radio communication channel provided in the associated transmission sector. The various radio access modules can operate independently of each other without any control equipment due to the occupation of a common radio communication channel.

The radio node arrangement of the invention can advantageously be equipped with an independently operating access module for operating in accordance with existing commercial cordless technology such as CT2 or DECT, both using DCA as their channel access technology. It should be understood that the access unit is not limited to the use of such radio access modules. Other techniques and modifications of these techniques to provide a communication channel under the control of the DCA algorithm may also be used.

By appropriate placement of the different radio access modules, areas of non-directional coverage or (overlapping) cells can be achieved, so that in each (overlapping) cell and all its neighbouring cells all common radio communication channels of the system are potentially available for establishing radio link connections.

As described above, the DCA algorithm only occupies free channels in a given geographic area. By providing a common radio communication channel in a given sector by at least two radio access modules of the unit, the amount of redundancy required both for repair and maintenance purposes and to account for an increase in communication capacity of the given sector can be easily achieved, the radio access modules being operable simultaneously during normal operation.

To prevent interference when establishing and conducting communications between a node access means and a backbone access unit, the control means according to the invention preferably operates using a modified DCA technique, call Continuous Dynamic Channel Selection (CDCS). The basic characteristics of CDCS are: the radio communication channel with the least interference at its selected moment is accessed.

The radio access module and the backbone access unit preferably comprise transceiver means arranged to provide a plurality of communication channels according to a multiple access technique, such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) and Code Division Multiple Access (CDMA).

A more detailed discussion of DCA and CDCS can be found in us patent 4628152; the article "novel radio access principles useful for third generation mobile radio systems" by akerberg, the third IEEE personal, indoor and mobile radio communications international seminar d.10, 19-21, d.ma., 1992, 4731812 and incorporated herein by reference.

In another embodiment of the dynamic radio backbone transmission system according to the present invention, a plurality of dynamic radio access node devices are connected to the radio node control device. The radio node control means are arranged for connection to a network access unit, such as a mobile services switching centre, a mobile telephone switching office or a base station device of a mobile radio communications network.

A very efficient use of transmission resources is obtained in yet another embodiment of the present invention, wherein the radio node control means and the dynamic radio access node means are operatively connected for adaptively accessing a free communication channel of a plurality of common radio channels accessible at the connection between the radio node control means and the dynamic radio access node means.

In this embodiment, the communication channels of the interface between the radio node control means and the dynamic radio access node means and the radio communication channels of the air interface between the dynamic radio access node means and the backbone access unit are adaptively accessible, depending on the load of the radio access unit or radio base stations of several pico-cells, femto-cells or micro-cells.

For connection over larger distances, according to a further embodiment of the dynamic radio backbone transmission system according to the invention, the transceiver means of the dynamic radio node access means are connected to a range enhancer unit. The range enhancer unit comprises a frequency conversion, an RF amplifier and an antenna arrangement.

The invention also relates to a range enhancer unit for use with a dynamic radio backbone transmission system as described above, the range enhancer unit comprising a frequency conversion, an RF amplifier and an antenna arrangement. The frequency conversion means comprise a receiving and transmitting section, each section comprising mixer conversion means coupled to local oscillator means. These switching means are controlled by a local oscillator for alternately converting the transmitted and received signals to one or the other frequency according to a Time Division Duplex (TDD) communication protocol.

Fig. 1 shows in a very diagrammatic manner a part of a cellular communication network with a dynamic radio backbone transmission system according to the invention, in which several smaller cells are grouped in a transmission sector.

Fig. 2 shows in a very schematic way the backbone system structure used in the network of fig. 1 according to the invention.

Fig. 3 shows a block diagram of a radio module for use in a radio backbone system according to the present invention.

Fig. 4 shows in a very schematic way the backbone system structure with a range enhancer unit according to the invention.

Fig. 5 shows a circuit diagram of the range enhancer unit shown in fig. 4.

Without intending to be limiting, the invention will now be described and illustrated with reference to an exemplary embodiment in a cellular mobile radio communications network.

This is necessary in order to increase the traffic handling capacity of the cellular mobile network in a given area. Also 1 shows an exemplary embodiment of a dynamic radio backbone transmission system in a cellular mobile network, in which a plurality of relatively small cells 4, such as pico cells, femto cells and pico cells, are grouped in a transmission sector 3. These transmission sectors may be contained in or overlapped by a relatively large cell, such as a macrocell. For simplicity, the various cells and transmission sectors are depicted in the form of circles.

Each cell 4 includes a radio access unit that provides services to mobile units in a particular cell 4. The individual radio access units are connected by radio links 5 to a so-called dynamic radio access node arrangement (DAN) 1. The DAN1 is connected to a network access unit such as a Mobile Telephone Switching Office (MTSO), a mobile services switching center (MSC), or a radio base station equipment such as a Base Station Controller (BSC) that provides service to the cellular base stations of the sector or macrocell 3. In this figure, it is assumed that DAN1 is directly connected to MTSO 2.

Particularly in dense homes or metropolitan areas, a large number of small cells 4 may be involved. A typical cellular network may include hundreds of radio access units, thousands of mobile stations and more than one MTSO 2.

Fig. 2 shows a block diagram of a backbone transmission system architecture 10 for use in the network shown in fig. 1. The DAN1 is connected to the MTSO 2 via a so-called Radio Node Controller (RNC) 6. The RNC6 controls one or several DAN1 and is the interface of the radio backbone system to the MTSO 2 and the operation administration maintenance and monitoring (OAMP) unit 7.

The cell 4 comprises a so-called Backbone Access Unit (BAU)8 which is connected to a radio access unit or Radio Base Station (RBS) of the cell 4. In a GSM microcell/picocell cellular system, for example, RGS 9 is actually a small unit that includes a radio transceiver and a control device with an integrated antenna typically located 5-10 meters down the street.

As already stated in the introductory part of the present invention, the radio access node arrangements and the radio backbone units may be based on radio access modules operating according to one of the current commercial cordless technologies, such as CT2, CT3 and DECT, specified, which all use DCA for allocating one of a plurality of common radio channels.

Fig. 3 shows a block diagram of a radio access module 20, which module 20 operates according to the relative protocol of the DECT standard. Briefly, the DECT protocol comprises a multi-carrier/time division multiple access/time division duplex (MC/TDMA/TDD) digital radio access technology, providing 10 radio carriers, each carrier divided into 24 time slots, serving 12 duplex communication channels, called a frame.

The access module 20 is based on a wired output connection 21. The central control and application logic 22 detects incoming and outgoing calls and selects the appropriate carrier and time slot combination according to the DAC/CDCS algorithm and combines the different connections and time slots via the multiplexer 23. The module 20 is based on a frame and slot synchronization unit 24 which controls the slot receive and transmit timing. The central control logic 22 also controls a transmit/receive (T/R) switch 25 and an antenna diversity switch 26 connected to an antenna output 31, respectively, if antenna diversity is implemented. With antenna diversity, if the radio connection does not provide good communication, the control logic first tries another antenna before changing the radio communication channel.

The radio interface of the module 20 is constituted by a receiver/demodulator 27 and a transmitter/modulator 28. Synchronization and control information is separated from the received data by unit 29 and such information is added to the data sent by unit 30 of the connection shown.

According to the invention, each of the 120 radio channels using the unit 20 in the DAN is accessible by the BAU 8 of the dynamic backbone transmission system shown in fig. 2. According to the DCA/CDCS technique, a radio communication channel at the air interface 5 and access from any of these 120 channels for communication purposes is selected, provided that such a channel is not used by another radio link connection in sector 3 or cell 4, whether handled via the same radio access module 20 or not. After selection, such channels are divided into established radio link connections.

As shown, DAN1 is placed at the sector 3 intersection so that the radio access unit (not shown) of each small cell 4 is connected via the radio interface of DAN1 to the MTSO.

In a further embodiment of the invention, the communication channel available at the interface between the RNC6 and the DAN1 is adaptively selected for connecting the radio base station 9 to the MTSO 2. Those skilled in the art will appreciate that a very efficient dynamic radio backbone transport system is provided by the communication channels of the radio interface between the RNC6 and the DAN1 and between the DAN1 and the BAU 8.

It will be appreciated that this is a very efficient way of connecting the various cells, and there is no fundamental need for channel or frequency planning.

Such a dynamic point-to-multipoint backbone radio transmission solution is very efficient and attractive when the traffic generated by several small cells 4 is relatively low and (temporarily) no wired links are regulated and it makes it easy to refer to network redundancy when needed in case of relatively high transmission requirements (e.g. 2 x 64kb/s per radio base station 9). In addition, DAN1 may act as a negotiation point, thereby easily changing from one medium to another.

In a particular embodiment, a plurality of 64kb/s communication channels are (permanently) allocated to the RSB 9 at the MTSO/RNC interface. At the DAN/BAU radio interface 5, the available radio communication channels are dynamically allocated to each RBS according to its load. At the BAU/RBS interface, a limited number of 2-6 64kb/s communication channels are available to the RBS; i.e. 4-12 32kb/s channels between the BAU 8 and DAN1 in case of DECT2 radio air interface. In addition to the communication channels, semi-permanent signaling channels, namely MTSO 2/RNC6/DAN 1, may be provided over the backbone transport system.

From a cost point of view, with very low user densities, it is necessary to interconnect more widely dispersed remote pairs of groups 8, 9. Wherein for use in such suburban areas a so-called Range Enhancer Unit (REU)14 is provided, as shown in fig. 4. The REU14 is placed at the site of the DAN.

In its simplest embodiment, the REU14 carries radio signals over the radio communication link 5, which may be radio signals according to the DECT standard, for example operating in the 1900MHz band to any frequency band, typically 450 or 800 MHz. The transmitted signal is also amplified to a level sufficient to provide a range greater than that of the radio access module 20 or DAN 1. A typical range for the REU14 is 12-15 km.

The REU14 at the DAN1 site may have as many converter, amplifier and antenna combinations as there are radio access modules 20 in the DAN 1. In a particular embodiment, the radio signal at the antenna output 31 of a particular radio access module 20 is fed to the REU 1496 and transformed. At the cell site 4, a further REU 15 is installed to convert the radio signals from the REU14 to the frequency band of the radio communication link 5, which may be for example a radio signal in the DECT band.

The transformed output signal of the REU 15 may be fed to a so-called Radio Relay Station (RRS)17 for providing radio coverage and service to the subscriber cells 4 in accordance with the protocol and frequency of the radio communication link 5. Such RRS 17 may have a wired or wireless link with the REU 15. The RRS 17 is basically configured similarly to the radio access module 20 (see fig. 3). The main differences are that: there is also another transmit/receive output/input (or two if diversity is applied) controlled by the central control and application logic 22, which central control and application logic 22 also connects information on the transmit/receive time slots of the antenna 31 to the appropriate transmit/receive time slots at the transmit/receive output/input. The data from the multiplexer 23 is thus fed into a shift register (not shown) which is controlled to shift the data back to the multiplexer 21 in time, in accordance with the applied repeater protocol, under the control of the central control and application logic 22. This further input/output may be connected to the receiver/demodulator 27 and the transmitter/modulator 28 or may be provided as a wired output/input. See International patent application WO94/19877, incorporated herein by reference.

With the REU concept according to the present invention, it is possible to reestablish subscriber cells anywhere within the combined coverage area of the REUs 14, 15. In the case of an isolated subscriber (at a farm, etc.), the REU 15 may be connected directly to a subscriber remote unit or Fixed Access Unit (FAU), as shown. In the case of a so-called multi-line FAU 19, i.e. FAU 19 having multiple output clients, the REU 15 and FAU 19 may be shared by multiple (adjacent) users, for example.

In the present invention, the DAN1 may be co-located with one or more REUs 14, which greatly reduces the overall system cost per unit.

Also, the antenna output of the radio access module 20 may be directly connected to the antenna and the REU14 by a splitter device (not shown). The signal fed to the REU14 may be relatively weak due to its amplification and therefore have no significant effect on the power to and from the antenna.

If diversity is applied, i.e. two antenna outputs 31 at the radio access module 20 (fig. 3), the REU14 may be connected to each antenna output such that for each diversity link a separate REU may be activated. It is possible to use only one REU 15 on the user side, which is also capable of receiving radio signals of two REUs 14. By inserting the REU14 in the middle path of the antenna diversity switch 26, one REU is sufficient in the case of diversity. However, this may require additional modifications of the existing radio access module 20.

With the REU concept according to the invention, although several radio access modules 20 are installed at the same site, for their operation they are considered to provide service to geographically separated different cells without overlapping coverage, so that each radio access module provides its full capacity to the area it addresses.

Fig. 5 shows in a very schematic way a circuit diagram of a REU for TDD operation. The low noise receiver RX 35 is connected with its input to a transmit/receive (T/R) switch 37 and with its output to an input of a mixer 39. Transmitter TX 36 is connected with its output to T/R switch 37 and with its input to the output of mixer 40. The mixers 39, 40 have their inputs connected to a so-called Local Oscillator (LO) switch 38, the inputs of which are connected to a Local Oscillator (LO) 41. Another output of mixer 39 and another input of mixer 40 are connected to an input and an output, respectively, of a coupler 42. Coupler 106 provides the combined transmit/receive input 43 of the REU, while T/R switch 37 provides the transmit/receive output 44 of the REU.

Due to TDD operation, no filtering is required to separate the transmit and receive paths. Switching between transmit and receive modes is provided by local oscillator switching to any of mixers 39, 40 and T/R switch 37. Suitable control signals may be provided by the radio access module 20 or via a separate signaling path 45 and signaling means (not shown), for example.

Although the present invention has been described with reference to specific embodiments and access units and in more detail with respect to its use in a GSM communication system, it will be appreciated that the novel concept of the present invention can be used with several access technologies and many different dynamic access node arrangements and backbone access units.

Claims (13)

1. A dynamic radio backbone transmission system for connecting a plurality of geographically spread remote radio access units to network elements of a mobile radio communication network, such as a cellular mobile communication network, said each radio access unit providing services to a particular area or cell of said mobile radio communications network, said backbone transmission system comprising dynamic access node means, the dynamic access node means having radio transceiver means, antenna means and control means operatively connected for accessing said plurality of common radio communication channels, wherein said control means of said dynamic radio access node means and said backbone access unit are arranged for adaptively selecting a free communication channel of said plurality of common radio communication channels, said dynamic access node means being arranged for connecting to said network access unit.

2. A dynamic radio backbone transmission system according to claim 1, wherein said radio transceiver means, antenna means and control means of said dynamic radio access node means are arranged for accessing said plurality of common radio communication channels in directionally dispersed transmission sectors, wherein said control means are arranged to co-operate with said backbone access units in transmission sectors for adaptively selecting free radio communication channels of said plurality of common radio communication channels which, when accessed, can be reused by the same dynamic radio access point means but independent of the radio link connections in the transmission sectors.

3. A dynamic radio backbone transmission system according to claim 2, wherein said dynamic radio access node means comprises a plurality of radio access modules, each having radio transceiver means and control means arranged for accessing a plurality of common radio communication channels, wherein said plurality of radio access modules are operatively connected for accessing said plurality of common radio communication channels in the associated transmission sector.

4. A dynamic radio backbone transmission system according to claim 1, 2 or 3, wherein said antenna means are arranged for providing a point-to-point radio link connection between said radio access node means and said backbone access unit.

5. A dynamic radio backbone transmission system according to claim 1, 2, 3 or 4, wherein said control means is arranged for continuously adapting a free radio communication channel for accessing said plurality of common radio communication channels.

6. A dynamic radio backbone transmission system according to claim 1, 2, 3, 4 or 5, wherein said dynamic radio access node module means and said backbone access units are arranged for accessing a plurality of common radio communication channels according to a plurality of radio access technologies.

7. A dynamic radio backbone transmission system according to claim 1, 2, 3, 4, 5 or 6, comprising a plurality of dynamic radio access node means, each dynamic radio access node means being connected to a radio node control means, said radio node control means being arranged for connection to a network access unit, such as a mobile services switching centre, a mobile telephone switching office or a base station equipment of said mobile radio communication network.

8. A dynamic radio backbone transmission system according to claim 7, wherein said radio node control means and said dynamic radio access contact means are operatively connected for adaptively accessing a free communication channel of a plurality of common communication channels connectable between said radio node control means and said dynamic radio access contact means.

9. The dynamic radio backbone transmission system according to claim 7 or 8, wherein a plurality of communication channels are specified on the connection between said radio node control means and said network access units for each of said radio access units.

10. A dynamic radio backbone transmission system according to any of the preceding claims, wherein said transceiver means of said dynamic radio access contact means are connected to a range enhancer unit, said range enhancer unit comprising frequency translation, RF amplifier and antenna means.

11. A dynamic radio backbone transmission system according to any of the preceding claims, wherein said dynamic radio access contact means and said backbone access units operate according to the relative protocols of the Digital Enhanced Cordless Telecommunications (DECT) standard.

12. Use of a dynamic radio backbone transmission system according to any of the preceding claims in a cellular mobile communication network, in particular in a cellular mobile communication network operating according to the global system for mobile communications (GSM) standard.

13. A range enhancement unit for use with a dynamic radio backbone transmission system according to any of the preceding claims, wherein said range enhancement unit comprises frequency translation, RF amplifiers and antenna means, said frequency translation means comprising a receive and transmit path, each path comprising mixer means connected to local oscillator switch means controlled by a local oscillator for alternately translating transmit and receive signals to one or the other frequency according to a Time Division Duplex (TDD) communication protocol.