SE514244C2 - Improvements to or with regard to wireless telephony - Google Patents

Abstract

The present invention relates to improvements of or relating to cordless telephony and allows a DECT-system to be established at a comparatively low cost by use of the existing public telecommunications network. It further allows that the construction of the radio base stations are simplified and their costs reduced by placing certain functions in a local telephone exchange and to share these functions between radio base stations. Transmission between radio base stations and a local telephone exchange is simplified by the use of an ISDN-protocol, i.e. a transmission format based on the ISDN-standard which utilizes two B-channels with 64 kbit/s, and one D-channel with 16 kbit/s, over one single twisted copper connection. In a WACA-system according to the present invention, much of the higher control layers, for instance NWK and DLC, are placed in a central control unit, for instance located to a local telephone exchange. In this way the system layers can be made comparatively powerful. This makes it possible that subscriber equipment which introduces a radio base station can be simplified for instance by making the MAC-layer thinner. Consequently, the subscriber equipment is not quite independent since its fixed unit is at least partly remote-controlled.

Description

40; 514 244m 1; between the radio base stations: ch the portable stations utilize TDMA / TDD which is used to create a total of 120 duplex channels on 10 carrier frequencies, each carrier frequency carrying 12 uplink channels and 12 downlink channels.

The operating frequency band is between 1880 and 1900 MHz. Typically, the radio base stations have a radio coverage of about 100 m radius and the effective range of a given radio base station can be extended by using covers. Handover can be achieved between different channels and between different radio base stations.

However, handover between different DECT systems can only be achieved with the help of functions that are part of the public switched telephone network. DECT systems can be used for private communication, e.g. in a cordless telephone, and for public access systems, e.g. in a Telepoint system.

Some of the problems associated with setting up DECT systems are briefly outlined below: - it is important for a network operator to provide acceptable surface radio coverage as soon as possible; - network operators need to use their existing wired networks to achieve installation economy; and - DECT systems must be sufficiently attractive to subscribers in public access systems to generate a sufficient customer base to support the system.

The present invention aims to solve at least some of the problems outlined above.

The present invention allows a DECT system to be set up at a relatively low cost using the existing public telephone network. It further enables the construction of the radio base stations to be simplified and their cost reduced by placing certain functions in a local telephone station and dividing these functions between radio base stations. Transmission between radio base stations and a local telephone station is simplified by using an ISDN protocol, ie a transmission format based on the ISDN standard that uses two 64 Kbit / s channels and a 16 Kbit / s D channel over a single twisted copper pair connection. . It should be emphasized that the present invention does not use an ISDN system for communication between radio base stations and a local telephone station, only an ISDN transmission format.

The use of ISDN in connection with DECT is known. For 40-in 514 244 "in 3 examples, ETSI is currently developing a DECT / ISDN collaboration profile. In addition, a number of architectures for DECT-type systems, linked to ISDN, have been proposed in the patent literature.

Examples of such systems are briefly mentioned below.

U.S. Patent 5,297,193 discloses a cordless telephone network having a number of fixed sections linked by radio to portable stations. The fixed stations are connected to an ISDN system. The invention mainly relates to the provision of a centralized maintenance service for the system.

According to the description, the system refers to the provision of ISDN circuits in a radiotelephone system, rather than the use of an ISDN protocol for transmitting speech and signals between a radio base station and a local telephone station.

U.S. Patent 5,040,177 discloses a Telepoint service in which radio base stations are connected to a public ISDN network.

Each radio base station can handle up to 40 voice channels.

The use of radio base stations that handle a mixture of private and public traffic is not described. As with U.S. Patent 297,193, the system relates to the provision of ISDN circuits to a radiotelephone system, rather than the use of an ISDN protocol for transmitting speech and signaling between a radio base station and a local telephone station.

PCT application WO93 / 21719 describes a DECT system which has the ability to cooperate with an ISDN system. A DECT format with a double door is modified to allow the DECT system to transmit an ISDN B-channel and D-channel separately at the same time. This allows ISDN outbound signaling to be handled by a DECT system. The invention relates to the cooperation between DECT and ISDN, rather than the use of an ISDN protocol for transmission between a local telephone station and a radio base station.

U.S. Patent 5,325,419 discloses a PCS with a complete ISDN interface. The invention utilizes intelligent radio base stations.

None of the prior art documents discussed above describe the use of an ISDN protocol to transmit at least three independent voice channels in an ADPCM format, per ISDN channel, between a radio base station and a local telephone station. Other features of the invention which do not exist in the prior art described above are: - that radio base stations process a mixture of private and public traffic; w fi- w-jí-f 40 Q 514 244; - that the system's control functions, including encryption, decryption, coding and decoding, are located in a local telephone exchange; - that radio base stations are powered by a local telephone station; - data compression, interleaving and signal filtering to reduce the bit rates of the D-channel; and - that transmissions are linked to the radio base stations via the public telephone network.

One of the inventive ideas behind a WACA system according to the present invention is that many of the higher control layers, e.g. NWK and DLC, can be located in a central control unit, e.g. located in an LX. In this way, these system layers can be made relatively powerful. This allows subscriber equipment that incorporates a radio base station to be simplified, e.g. by reducing the MAC layer. Thus, the subscriber equipment does not become completely independent because its fixed part FP is at least partially remotely controlled.

According to a first aspect of the present invention, there is provided a wireless telecommunication system for transmitting speech, including at least one radio base station and at least one portable station, in which data, ring and coded speech are transmitted between said at least one radio including signal. base station and said at least one portable station using TDMA / TDD and in which the speech is encoded, using ADPCM, characterized in that said radio base station is linked to a local telephone station, in that signaling and speech are transmitted between said radio base station and said local telephone station with an ISDN protocol, in that speech is transmitted between said radio base station and said local telephone station in the same data format as said speech is received by said radio base station from a portable station or transmitted from said radio base station to a portable station, and in that at least three voice channels per ISDN protocol channel are available for transmission between said radio base station and h said local telephone station; Preferably, four 32 Kbit / s compressed voice channels are available per ISDN protocol channel for 40 s transmission; 514,244 numbers between said radio base station and said local telephone station.

Said radio base station may be arranged to handle both private traffic and public traffic.

Said radio base station may be connected to said local telephone station with a local loop connection in the public telephone network.

Preferably, a control device for said system is located at said local telephone station.

Signaling between said control device and said base station may be digitally compressed.

Alternatively, the signaling between said control device and said base station, intended for or received from different portable stations may be interleaved.

Alternatively, said radio base station may be arranged to remove from the signaling between said control device and said base station any part thereof required only for operation of said radio base station, thereby reducing the signal traffic levels between said radio base station and said control device.

Functions for encryption, decryption, coding and decoding are located in the said local telephone station and are arranged to be shared between a number of radio base stations.

According to a second aspect of the present invention, there is provided a method of constructing a wireless telecommunication system, as described above, characterized by the steps of: - locating a control device for said wireless telecommunication system at a local telephone station; - locating radio base stations of selected subscribers; and - connecting said local telephone station to said radio base stations via an existing public local loop network, using an ISDN transmission protocol.

Said method may comprise the step of installing in a subscriber a radio base station arranged to serve several subscribers. Preferably, a sufficient number of radio base stations are located, located so that their radio coverage overlaps, to provide substantially complete radio coverage, over a predetermined geographical area, substantially greater than a radio coverage for a single radio base station.

Said method may include the steps of: - installing radio base stations in some subscribers; - to install transfer stations with other subscribers; and - linking transmission stations to radio base stations through connections established over an existing public local loop.

According to a third aspect of the present invention, there is provided a wireless telecommunication system having a plurality of radio base stations, each of which is arranged to provide telecommunication services to a plurality of portable stations, characterized in that said wireless telecommunication system is arranged in at least some radio base stations combine functionality with public access and functionality with private access, so that a single radio base station can be used to provide private home service and a public Telepoint service.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates the relationship between the cost of providing wireless telephony and the number of subscribers, for small and large cell units.

Figure 2 is a schematic illustration of a communication link established with a cordless telephone system, in accordance with the present invention, between a portable station and the public telephone network via a radio base station and a local telephone station.

Figure 3 is a schematic illustration of the frame structure of a DECT system.

Figure 4 is a schematic illustration of the radio coverage provided by a wireless telecommunication system in accordance with the present invention.

Embodiments of the present invention described hereinafter use the DECT standard for wireless telephony. It is clearly understood that the invention is not limited to the DECT standard, except as specifically stated in the claims of this patent application, and may be implemented using other wireless telephony standards consistent with the use of TDMA / TDD digital radio transmission. .

In accordance with accepted practice in the field of telecommunications, acronyms and abbreviations are widely used in this application. To help the reader, a list of the terms used is given below: A / D - Analog-digital conversion ADPCM - Adaptive Differential Pulse Code Modulation, ie adaptive differential pulse code modulation B-channel - 64 kbit / s ISDN channel BER - Bit Error Rate, ie bit error rate CFP - Central Fixed Part, ie central fixed unit D / A - Digital analog conversion D-channel - 16 kbit / s ISDN channel DECT - Digital European Cordless Telecommunications, ie digital European wireless telecommunications DLC - Data Link Control, ie data link control ETSI - European Telecommunications Standards Institute, ie European Institute of Telecommunications Standards FP - Fixed Part, ISDN - Integrated Services Digital Network, ie digital ie. fixed unit network for integrated services IWP - Inter-Working Profile, ie collaboration profile LX - Local Telephone Exchange, ie local telephone station MAC - Medium Access Control, ie medium access control NWK - Network layer, ie network layer OSI - Open Systems Interconnection, ie open interconnection of system PCS - Personal Communications System, ie personal communication system PHL - Physical Layer, ie physical layer PP - Portable Part, ie. portable unit PSTN - Public Switched Telephone Network, ie public switched telephone network RFP - Radio Fixed Part, TDD - Time Division Duplex, ie time division duplex ie fixed radio unit 40 514 244 8 TDMA - Time Division Multiple Access, ie time division multiple access U-plane - User plane, ie user plan VPN - Virtual Private Network, ie virtual private network VPN + - Virtual private network with mobility support, sometimes called M-VPN WACA - Wide Access Cordless Access, ie wide access wireless access.

A wireless telecommunication system in accordance with the present invention can be described as a WACA, i.e. the system provides wireless access to telecommunication services over a wide geographical area, certainly an area which is considerably larger than the radio coverage of a single radio base station. However, the invention is not limited to WACA systems.

When designing and installing WACA systems, a telecommunications network operator must ensure that acceptable surface coverage is generated by the system, as quickly and economically as possible.

As can be seen from Figure 1, the initial costs for small cell systems are significantly higher than for large cell systems, ie when the number of users of the system is low. With growth in the number of users or subscribers, however, the costs for small cell systems remain essentially constant, while the costs for large cell systems grow in proportion to the number of users.

In fact, the cost per user can be considered as approximately proportional to the cell size. Provided that a system can quickly attract a relatively large number of users, the small cell alternative is thus economically preferable.

DECT systems are generally small cell systems. Typically, a DECT radio base station has a radio coverage of about 100 m or less in radius.

It is cost-effective for a telecom operator, who is setting up a new system, to make maximum use of installed network infrastructure. When installing a WACA system, the existing twisted copper pair network should ideally be used to establish a connection between radio base stations and local telephone stations. In this way, the need to install a DECT connection network is avoided.

Figure 2 illustrates in schematic form the way in which a portable DECT station can be connected, via a radio base station 40 514 244 9 and local telephone station, to the public telephone network in the so-called U-plane. A system can be schematically illustrated in a number of ways, circuit diagrams. The user plan is a simplified schematic e.g. using block diagrams or illustration of a system that shows how a user "sees" or experiences the system in operation. The PP, ie the portable device, is physically located in a portable station or cordless telephone. The PP comprises a number of layers - NWK, DLC, MAC and PHL.

A radio connection can be established between the physical layer of the handset.

PHL of the portable handset and the physical layer of a fixed radio unit RFP. The fixed radio unit is, of course, physically located in a base station or radio base station. A wired connection that utilizes an ISDN protocol can then access the physical layer of the central fixed unit CFP. The CFP is corrected between the physical layer of the fixed radio unit and is normally located in a radio base station, but the present invention suggests that it may be located in a local telephone station. The CFP is then connected via the local telephone station LX to the public telephone network.

It should be noted that the introduction of the CFP in a radio base station significantly increases the cost of a radio base station.

The CFP performs a variety of functions such as refers to encryption, decryption, coding and decoding. By including these functions in a local telephone station, they can be shared between different radio base stations. This in turn reduces the total cost of the system and allows the construction of particularly cheap and simple radio base stations that have low power requirements.

Radio base stations can be located at the subscriber and connected to the local telephone station via the existing local wire network. This means for the DECT system according to the present invention that the RFP and the CFP are connected (Other connection media can be used if there are available twisted copper pairs used in the local network, eg optical fiber). The connection between the RFP and the CFP must be able to transmit a 32 kbit / s ADPCM signal, in the DECT standards, the signaling. as specified together with the associated DECT- Ideally, the protocol and signaling between the RFP and the CFP should be digital. This facilitates the use of 40,514,244 g coatings. The use of digital transmission further avoids the need for analog-to-digital conversion between the mainline transport network of the public telecommunications network and the subscriber, thus reducing the inevitable distortion and noise generated at each A / D or D / A stage.

The protocol used in the present invention for transmission between the RFP and the CFP is an ISDN protocol used for communication between station equipment and subscriber equipment. ISDN can be successfully transmitted via twisted copper pairs between a local telephone station and subscriber equipment and is thus suitable for use in the present invention for linking the RFP at a radio base station to the CFP at a local telephone station. The ISDN protocol includes two B-channels, ie 64 kbit / s voice channels, and a D-channel, ie a 16 kbit / s channel, which is used for signaling and is normally used in packet transmission mode. It should be clearly noted that the link between the RFP and the CFP does not form part of an ISDN system, this is only an appropriate protocol. In fact, each B-channel can be used in the present invention to carry two voice channels instead of the only voice channel normally used in ISDN.

Using an ISDN protocol link between the RFP and the CFP is shown in Figure 2. The ISDN protocol allows the simultaneous transmission of four 32 kbit / s ADPCM voice channels over the two ISDN B channels. However, there is a problem with the signaling and this is discussed later in this application. The separation of the RFP and the CFP and the use of an ISDN link means that the MAC layer, see Figure 2, in the RFP can be made very "thin" because it only needs to handle the separation of the signaling and the speech and distribute these between the two B-channels and the D-channel in the ISDN protocol. (The MAC layer allocates and releases physical channels depending on what the higher layer requests.) The MAC layer, or media access layer, is present in most telecommunications systems but not in OSI-based systems. The MAC layer lies above the physical layer, which it mainly controls. The "thickness" of the MAC layer, ie its content; determined by the amount of control it needs to perform. In the present invention, the MAC layer is "thin" due to the amount of handling performed in higher layers, e.g. NWK and 40 514 244 11 DLC, and the requirements of PHL.

DECT-specific signaling is transmitted over the ISDN channel that connects the RFP and the CFP.

DECT transmission is illustrated in Figure 3. It can be seen that a Frame structure used for data packets is preceded by a 32-bit synchronization sequence, followed by a data packet containing 388 bits. The data packet can be followed by four bits repeating the last four bits of the data packet, to facilitate detection of slot operation and thereby avoid packet collision. The data packet includes 48 bits of signaling data, followed by 16 error detection / correction followed by another four error detection bits. Thus, 48 ring pieces are generated. The packet includes 320 bits of user data, bits of signaling data per channel per time frame. The length of the time frame is 10 milliseconds. This corresponds to 4.8 kbit / s signaling traffic per voice channel, ie a total of 19.2 kbit / s signaling per four voice channels. It should be noted that the synchronization sequence does not need to be transmitted continuously between the RFP and the CFP as the ADPCM time structure itself can be used to generate a timing clock. However, the requirement for 19.2 kbit / s signaling still exceeds the capacity of a 3.2 kbit / s ISDN D channel. Unless further action is taken, the capacity of the D-channel will limit the capacity of the ISDN protocol link to three DECT voice channels.

However, the ISDN link can be made to support four DECT voice channels by: - using data compression; - signal interleaving; - coordination and reduction of signaling needs; or - a combination of the above.

DECT signaling does not use data compression techniques. The data compression level required to compress the 4.8 kbit / s DECT signaling to the available 4 kbit / s on the ISDN channel is not high - 1: 1.2. Since the BER for wire connections is significantly lower than on radio links, with several orders of magnitude, the low data compression required to squeeze the DECT signaling on the ISDN D channel does not cause any problems. Many suitable data compression techniques to achieve this level of data compression are well known to those skilled in the art. 40 .14 244 12 The greatest signaling need for DECT signaling is made during roaming, during handover between cells and during the call connection. These processes are relatively short, comparatively rare and do not place a continuous need on the signaling capacity. This means that signal interleaving can be used to reduce the average signaling demand placed on the D-channel. Different signals can be interleaved, ie signaling for four simultaneous calls transmitted on the D-channel is interleaved with dynamic shift / delay, as required.

The signaling needs can be reduced by coordinating and reducing the total signal traffic. Parts of the radio-specific signaling do not need to be transferred to the CFP.

Parts of the radio-specific signaling and other signaling can be divided between voice channels. This can be used to reduce the need placed on the D-channel so that it falls within its transmission capacity.

Embodiments of the present invention have a number of advantages including: - low manufacturing costs for the RFP; simple connection of the RFP, simple enough so that a subscriber can connect the RFP himself; - the provision of services to several subscribers, up to four, over the same connection; systems that utilize covers, ie master-slave systems, can be implemented easily so that handover between adjacent cells is easily obtained, thereby increasing the radio coverage; and - the provision of mixed systems.

In a mixed system, a subscriber who has a radio base station installed with him pours one or possibly two DECT channels for his own use. The remaining three (or two) channels will then be available for public use. Overlapping cells from adjacent premises can in this way build up comparatively good radio coverage. Figure 4 illustrates the way in which the radio coverage, which corresponds to the individual radio base stations, is combined to provide almost total radio coverage for a given area. This means that a Telepoint system can be built up using existing local loops and radio base stations located at subscribers. The use of radio base stations by subscribers also facilitates the availability of Telepoint on private property, e.g. a factory site, to the benefit of both the network operator and the subscriber.

The construction of a large number of radio base stations with subscribers means that not all subscribers need to have a dedicated RFP installed with them.

Embodiments of the present invention can be applied to simultaneously provide in a system: - home telephony, ie telephony with private access / limited access; - telephony with public access, e.g. Telepoint; - VPN and VPN +; teleworking, by dynamically allocating the available traffic capacity between data and speech, with mobility.

The present invention provides a DECT-based system in which comparatively high traffic capacity, two speech channels with 64 kbit / s plus a signaling channel with 16 kbit / s can be made available to subscribers. Various developments of the present invention will be apparent to those skilled in the art.

Speech encoders and encryption equipment can be placed centrally in the CFP. This dramatically reduces the cost and power consumption of the RFP. This enables RFP to be supplied with power from a central power source, e.g. located at the local telephone exchange.

Slave base stations, ie covers, can be connected to master base stations via the existing local loop wire network. In this context, it should be noted that many houses are equipped with several telephone sockets. The use of covers increases the surface radio coverage. Handover can be controlled from a master base station with relatively small additions. Control of handover between a radio base station and a cover, from the radio base station, reduces the load on the CFP.

Use of the present invention facilitates system updates to complete ISDN / DECT collaboration.

Since the RFP is designed to work with an ISDN protocol, it is especially easy to ensure that the RFP works directly with ISDN in accordance with DECT / ISDN IWP. 514 244 14 In other words, ISDN services can be distributed from the RFP via a DECT radio interface and / or a "fixed" socket, ie the common ISDN socket. In the latter case (fixed socket), the requirements on the RFP are increased due to the need, among other things, to include a speech encoder. In this case, the RFP becomes part of an ISDN terminal. It should be noted that the operation of an RFP, such as an ISDN terminal, falls outside the scope of the present invention, although the features of the present invention facilitate an upgrade to full ISDN operation.

Claims (15)

10 15 20 25 30 35 40 514 244 ß 'PATENTKRAV A wireless telecommunication system for transmitting speech, comprising at least one radio base station and at least one portable station, in which data, signaling and coded speech are transmitted between said at least one radio base station and said at least one portable including station using TDMA / TDD and in which speech is encoded, using ADPCM, said radio base station being linked to a local telephone station, signaling and speech being transmitted between said radio base station and said local telephone station with an ISDN protocol, speech being transmitted between said radio base station and said local telephone station in the same data format in which voice is received by said radio base station from a portable station or transmitted from said radio base station to a portable station, four 32 kbit / s compressed voice channels are available per two B-channels according to the ISDN protocol for transmitting speech between said radio base station and said local telephone station, and a control device for said s ystem is located at said local telephone station, characterized in that signaling between said control device and said base station is digitally compressed, so that the signaling of the four voice channels can be transmitted over a D-channel according to the ISDN protocol. Wireless telecommunication system according to claim 1, characterized in that signaling between said control device and said base station, intended for or received from different portable stations is interleaved. Wireless telecommunication system according to claim 1, characterized in that said radio base station is arranged to remove from the signaling between said control device and said base station any part thereof required only for operation of said radio base station, thereby reducing the signal traffic levels between said radio base stations and said control device. Wireless telecommunication system according to any one of claims 1-3, characterized in that functions for encryption, decryption, coding and decoding are located in said local telephone station and arranged to be shared between a plurality of radio base stations. Wireless telecommunication system according to any one of claims 1-4, characterized in that said radio base station is supplied with power from said local telephone station. Wireless telecommunication system according to any one of the preceding claims, characterized in that said radio base station is arranged to handle both private traffic and public traffic. Wireless telecommunication system according to any one of the preceding claims, characterized in that said system complies with the DECT standard for wireless telephony. Wireless telecommunication system according to any one of the preceding claims, characterized in that said radio base station is connected to said local telephone station with a local loop connection in the public telecommunications network. Wireless telecommunication system according to any one of the preceding claims, characterized in that it comprises at least one cover linked to a radio base station by a local loop connection in the public telecommunications network. A method of constructing a wireless telecommunication system according to any one of claims 1-9, comprising the steps of: - placing a control device for said wireless telecommunication system at a local telephone station; - to place radio base stations with selected subscribers; - connecting said local telephone station to said radio base stations at an existing public local loop using an ISDN transmission protocol, characterized by compressing signaling, interleaving signaling and / or reducing signaling so that all signaling traffic between a radio base station and a local telephone station can transmitted over an ISDN D channel. A method according to claim 10, characterized by installing said radio base stations so that said radio base stations are powered by transmitting electric current over an existing public local loop network. 10 15 20 514 244 I Method according to claim 107 or 11, characterized by the step of installing in a subscriber a radio base station arranged to serve several subscribers. A method according to claim 12, characterized by installing sufficient radio base stations, positioned so that their radio coverage overlaps to provide substantially complete radio coverage over a predetermined geographical area, substantially greater than a radio coverage of a single radio base station. A method according to any one of claims 10-13, characterized by installing at a subscriber a radio base station arranged to provide a private service to this subscriber and a public service available to other subscribers within the radio coverage of this radio base station. Method according to one of Claims 10 to 14, characterized by the steps of: - installing radio base stations in some subscribers; - to install transfer stations with other subscribers; and - linking transmission stations to radio base stations through connections established over an existing public local loop.