WO1996038994A1

WO1996038994A1 - Apparatus and method of authenticating a subscriber terminal in a wireless telecommunications system

Info

Publication number: WO1996038994A1
Application number: PCT/US1996/008912
Authority: WO
Inventors: Martin Lysejko
Original assignee: Dsc Communications Corporation
Priority date: 1995-06-02
Filing date: 1996-06-03
Publication date: 1996-12-05
Also published as: AU5984896A

Abstract

A subscriber terminal (20) receives and transmits telecommunication information from and to a central terminal (10). The subscriber terminal (20) has a serial number (200) associated therewith. The subscriber terminal (20) is programmed with a network identifier (202) associated with the central terminal (10) corresponding to the subscriber terminal (20). The subscriber terminal (20) is also programmed with frequency and transmission codes associated with the central terminal (10). The subscriber terminal (20) transmits a reset indication message (206) encoded with the serial number (200) and the network identifier (202) programmed within the subscriber terminal (20). The central terminal (10) compares the network identifier (202) encoded in the reset indication message with its network identifier (204). If the network identifier (202) matches the network identifier (204), then the central terminal (10) stores the serial number (200) within a serial number slot (208). The central terminal (10) periodically transmits a verify message (210) encoded with the information from the serial number slot (208) to the subscriber terminal (20). The subscriber terminal (20) compares the serial number (200) to the value of the serial number slot (208). If there is no match, the subscriber terminal (20) disables communication to the central terminal (10).

Description

APPARATUS AND METHOD OF AUTHENTICATING A

SUBSCRIBER TERMINAL IN A WIRELESS

TELECOMMUNICATIONS SYSTEM

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to telecommunications systems and more particularly to an apparatus and method of authenticating a subscriber terminal in a wireless telecommunications system.

BACKGROUND OF THE INVENTION

Wireless systems use transmitters and receivers to send and receive radio frequency signals carried over the airwaves. These radio frequency signals are susceptible to interception and eavesdropping by unauthorized users. Such a wireless system is also subject to unauthorized users masquerading as valid users and charging phone calls to the accounts of valid users. Therefore, it is desirable to have a secure wireless system that eliminates unauthorized users from using the resources ^'of the wireless system without compensating for such use.

SUMMARY OF THE INVENTION

An object of the invention is to provide an apparatus and a method of authenticating a subscriber terminal in a wireless telecommunications system that substantially eliminates and reduces the disadvantages and problems associated with conventional wireless systems.

In accordance with an aspect of the present invention, there is provided a method of authenticating a subscriber terminal in a wireless telecommunications system, comprising the steps of: associating a serial number with the subscriber terminal; programming the subscriber terminal with a network identifier associated with a central terminal corresponding to the subscriber terminal; programming the subscriber terminal with frequency and transmission codes associated with the central terminal; sending a reset indication message from the subscriber terminal to the central terminal, the serial number and the network identifier encoded into the reset indication message; receiving a verify message at the subscriber terminal, the verify message encoded with a serial number; comparing the serial number in the verify message with the serial number of the subscriber terminal.

In accordance with another aspect of the invention, there is provided an authenticating subscriber terminal, comprising: a storage element operable to store a serial number associated with the subscriber terminal, the storage element operable to store a network identifier associated with a central terminal corresponding to the subscriber terminal; a receiver operable to receive a verify message, the verify message being encoded with a serial number, the receiver comparing the serial number stored in the storage element with the serial number encoded in the verify message. In accordance with a further aspect of the invention, there is provided a system for authentication in a wireless telecommunications system, comprising: a subscriber terminal having a serial number associated therewith; a central terminal having a network identifier associated therewith, the subscriber terminal having the network identifier corresponding to the central terminal, the subscriber terminal transmitting the serial number and the network identifier to the central terminal encoded into a reset indication message, the central terminal receiving the reset indication message from the subscriber terminal, the central terminal comparing the network identifier encoded in the reset indication message to the network identifier associated with the central terminal, the central terminal storing the serial number encoded in the reset indication signal and associated with the subscriber terminal in response to a match of the network identifier encoded in the reset indication signal with the network identifier associated with the central terminal. According to an embodiment of the present invention, a method of authenticating a subscriber terminal in a wireless telecommunications system includes associating a serial number with the subscriber terminal. The subscriber terminal is also programmed with a network identifier associated with a central terminal corresponding to the subscriber terminal. Frequency and transmission codes corresponding to the central terminal are also programmed into the subscriber terminal. The subscriber terminal sends a reset indication message to the central terminal for authentication. The reset indication message is encoded with the serial number and the network identifier. The subscriber terminal receives a verify message encoded with the serial number. The subscriber terminal compares the serial number encoded in the verify message with the serial number of the subscriber terminal to perform authentication.

The present invention provides various technical advantages over conventional wireless systems. For example, one technical advantage is to authenticate a subscriber terminal in a wireless telecommunications system. Another technical advantage is to provide authentication at a subscriber terminal and a central terminal corresponding to the subscriber terminal. Yet another technical advantage is to disable communications between a subscriber terminal and a corresponding central terminal upon a failure in authentication. Other technical advantages are readily apparent to one skilled in the art from the following figures, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will be described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs are used for like features and in which:

Figure 1 is a schematic overview of an example of a wireless telecommunications system in which an example of the present invention is included;

Figure 2 is a schematic illustration of an example of a subscriber terminal of the telecommunications system of Figure 1;

Figure 3 is a schematic illustration of an example of a central terminal of the telecommunications system of Figure 1; Figure 3A is a schematic illustration of a modem shelf of a central terminal of the telecommunications system of Figure 1;

Figure 4 is an illustration of an example of a frequency plan for the telecommunications system of Figure 1;

Figures 5A and 5B are schematic diagrams illustrating possible configurations for cells for the telecommunications system of Figure 1;

Figure 6 is a schematic diagram illustrating aspects of a code division multiplex system for the telecommunications system of Figure 1;

Figure 7 is a schematic diagram illustrating signal transmission processing stages for the telecommunications system of Figure 1; Figure 8 is a schematic diagram illustrating signal reception processing stages for the telecommunications system of Figure 1; FIGURE 9 illustrates a block diagram of a programmable subscriber terminal for a wireless telecommunications system; and

FIGURE 10 illustrates an example of an authentication process for the subscriber terminal.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 is a schematic overview of an example of a wireless telecommunications system. The telecommunications system includes one or more service areas 12, 14 and 16, each of which is served by a respective central terminal (CT) 10 which establishes a radio link with subscriber terminals (ST) 20 within the area concerned. The area which is covered by a central terminal 10 can vary. For example, in a rural area with a low density of subscribers, a service area 12 could cover an area with a radius of 15- 20Km. A service area 14 in an urban environment where is there is a high density of subscriber terminals 20 might only cover an area with a radius of the order of 100m. In a suburban area with an intermediate density of subscriber terminals, a service area 16 might cover an area with a radius of the order of lKm. It will be appreciated that the area covered by a particular central terminal 10 can be chosen to suit the local requirements of expected or actual subscriber density, local geographic considerations, etc, and is not limited to the examples illustrated in Figure 1. Moreover, the coverage need not be, and typically will not be circular in extent due to antenna design considerations, geographical factors, buildings and so on, which will affect the distribution of transmitted signals. The central terminals 10 for respective service areas

12, 14, 16 can be connected to each other by means of links

13, 15 and 17 which interface, for example, with a public switched telephone network (PSTN) 18. The links can include conventional telecommunications technology using copper wires, optical fibres, satellites, microwaves, etc.

The wireless telecommunications system of Figure 1 is based on providing fixed microwave links between subscriber terminals 20 at fixed locations within a service area

(e.g., 12, 14, 16) and the central terminal 10 for that service area. In a preferred embodiment each subscriber terminal 20 is provided with a permanent fixed access link to its central terminal 10. However, in alternative embodiments demand-based access could be provided, so that the number of subscribers which can be serviced exceeds the number of telecommunications links which can currently be active.

Figure 2 illustrates an example of a configuration for a subscriber terminal 20 for the telecommunications system of Figure 1. Figure 2 includes a schematic representation of customer premises 22. A customer radio unit (CRU) 24 is mounted on the customer's premises. The customer radio unit 24 includes a flat panel antenna or the like 23. The customer radio unit is mounted at a location on the customer's premises, or on a mast, etc., and in an orientation such that the flat panel antenna 23 within the customer radio unit 24 faces in the direction 26 of the central terminal 10 for the service area in which the customer radio unit 24 is located. The customer radio unit 24 is connected via a drop line 28 to a power supply unit (PSU) 30 within the customer's premises. The power supply unit 30 is connected to the local power supply for providing power to_λ the customer radio unit 24 and a network terminal unit (NTU) 32. The customer radio unit 24 is also connected to via the power supply unit 30 to the network terminal unit 32, which in turn is connected to telecommunications equipment in the customer's premises, for example to one or more telephones 34, facsimile machines 36 and computers 38. The telecommunications equipment is represented as being within a single customer's premises. However, this need not be the case, as the subscriber terminal 20 preferably supports either a single or a dual line, so that two subscriber lines could be supported by a single subscriber terminal 20. The subscriber terminal 20 can also be arranged to support analogue and digital telecommunications, for example analogue communications at 16, 32 or 64kbits/sec or digital communications in accordance with the ISDN BRA standard.

Figure 3 is a schematic illustration of an example of a central terminal of the telecommunications system of Figure 1. The common equipment rack 40 comprises a number of equipment shelves 42, 44, 46, including a RF Combiner and power amp shelf (RFC) 42, a Power Supply shelf (PS) 44 and a number of (in this example four) Modem Shelves (MS) 46. The RF combiner shelf 42 allows the four modem shelves 46 to operate in parallel. It combines and amplifies the power of four transmit signals, each from a respective one of the four modem shelves, and amplifies and splits received signals four way so that separate signals may be passed to the respective modem shelves. The power supply shelf 44 provides a connection to the local power supply and fusing for the various components in the common equipment rack 40. A bidirectional connection extends between the RF combiner shelf 42 and the main central terminal antenna 52, typically an omnidirectional antenna, mounted on a central terminal mast 50.

This example of a central terminal 10 is connected via a point-to-point microwave link to a location where an interface to the public switched telephone network 18, shown schematically in Figure 1, is made. As mentioned above, other types of connections (e.g., copper wires or optical fibres) can be used to link the central terminal 10 to the public switched telephone network 18. In this example the modem shelves are connected via lines 47 to a microwave terminal (MT) 48. A microwave link 49 extends from the microwave terminal 48 to a point-to-point microwave antenna 54 mounted on the mast 50 for a host connection to the public switched telephone network 18.

A personal computer, workstation or the like can be provided as a site controller (SC) 56 for supporting the central terminal 10. The site controller 56 can be connected to each modem shelf of the central terminal 10 via, for example, RS232 connections 55. The site controller 56 can then provide support functions such as the localization of faults, alarms and status and the configuring of the central terminal 10. A site controller 56 will typically support a single central terminal 10, although a plurality of site controllers 56 could be networked for supporting a plurality of central terminals 10. As an alternative to the RS232 connections 55, which extend to a site controller 56, data connections such as an X.25 links 57 (shown with dashed lines in Figure 3) could instead be provided from a pad 228 to a switching node 60 of an element manager (EM) 58. An element manager 58 can support a number of distributed central terminals 10 connected by respective connections to the switching node 60. The element manager 58 enables a potentially large number (e.g., up to, or more than 1000) of central terminals 10 to be integrated into a management network. The element manager 58 is based around a powerful workstation 62 and can include a number of computer terminals 64 for network engineers and control personnel.

Figure 3A illustrates various parts of a modem shelf 46. A transmit/receive RF unit (RFU - for example implemented on a card in the modem shelf) 66 generates the modulated transmit RF signals at medium power levels and recovers and amplifies the baseband RF signals for the subscriber terminals. The RF unit 66 is connected to an analogue card (AN) 68 which performs A-D/D-A conversions, baseband filtering and the vector summation of 15 transmitted signals from the modem cards (MCs) 70. The analogue unit 68 is connected to a number of (typically 1- 8) modem cards 70. The modem cards perform the baseband signal processing of the transmit and receive signals to/from the subscriber terminals 20. This includes 1/2 rate convolution coding and x 16 spreading with CDMA codes on the transmit signals, and synchronization recovery, de- spreading and error correction on the receive signals. Each modem card 70 in the present example has two modems, each modem supporting one subscriber link (or two lines) to a subscriber terminal 20. Thus, with two modems per card and 8 modems per modem shelf, each modem shelf could support 16 possible subscriber links. However, in order to incorporate redundancy so that a modem may be substituted in a subscriber link when a fault occurs, only up to 15 subscriber links are preferably supported by a single modem shelf 46. The 16th modem is then used as a spare which can be switched in if a failure of one of the other 15 modems occurs. The modem cards 70 are connected to the tributary unit (TU) 74 which terminates the connection to the host public switched telephone network 18 (e.g., via one of the lines 47) and handles the signaling of telephony information to, for example, up to 15 subscriber terminals (each via a respective one of 15 of the 16 modems) .

The wireless telecommunications between a central terminal 10 and the subscriber terminals 20 could operate on various frequencies. Figure 4 illustrates one possible example of the frequencies which could be used. In the present example, the wireless telecommunication system is intended to operate in the 1.5-2.5GHz Band. In particular the present example is intended to operate in the Band defined by ITU-R (CCIR) Recommendation F.701 (2025-2110MHz, 2200-2290MHz) . Figure 4 illustrates the frequencies used for the uplink from the subscriber terminals 20 to the central terminal 10 and for the downlink from the central terminal 10 to the subscriber terminals 20. It will be noted that 12 uplink and 12 downlink radio channels of 3.5MHz each are provided centered about 2155MHz. The spacing between the receive and transmit channels exceeds the required minimum spacing of 70MHz.

In the present example, as mentioned above, each modem shelf will support 1 frequency channel (i.e. one uplink frequency plus the corresponding downlink frequency) . Up to 15 subscriber links may be supported on one frequency channel, as will be explained later. Thus, in the present embodiment, each central terminal 10 can support 60 links, or 120 lines. Typically, the radio traffic from a particular central terminal 10 will extend into the area covered by a neighboring central terminal 10. To avoid, or at least to reduce interference problems caused by adjoining areas, only a limited number of the available frequencies will be used by any given central terminal 10.

Figure 5A illustrates one cellular type arrangement of the frequencies to mitigate interference problems between adjacent central terminals 10. In the arrangement illustrated in Figure 5A, the hatch lines for the cells 76 illustrate a frequency set (FS) for the cells. By selecting three frequency sets (e.g., where: FS1 = FI, F4, F7, F10; FS2 = F2, F5, F8, Fll; FS3 = F3, F6, F9, F12) , and arranging that immediately adjacent cells do not use the same frequency set (see, for example, the arrangement shown in Figure 5A) , it is possible to provide an array of fixed assignment omnidirectional cells where interference between nearby cells can be avoided. The transmitter power of each central terminal 10 is set such that transmissions do not extend as far as the nearest cell which is using the same frequency set. Thus each central terminal 10 can use the four frequency pairs (for the uplink and downlink, respectively) within its cell, each modem shelf in the central terminal 10 being associated with a respective RF channel (channel frequency pair) .

With each modem shelf supporting one channel frequency

(with 15 subscriber links per channel frequency) and four modem shelves, each central terminal 10 will support 60 subscriber links (i.e., 120 lines). The 10 cell arrangement in Figure 5A can therefore support up to 600 ISDN links or 1200 analogue lines, for example. Figure 5B illustrates a cellular type arrangement employing sectored cells to mitigate problems between adjacent central terminals 10. As with Figure 5A, the different type of hatch lines in Figure 5B illustrate different frequency sets. As in Figure 5A, Figure 5B represents three frequency sets (e.g., where: FS1 = FI, F4, F7, F10; FS2 = F2, F5, F8, Fll; FS3 = F3, F6, F9, F12) . However, in Figure 5B the cells are sectored by using a sectored central terminal (SCT) 13 which includes three central terminals 10, one for each sector SI, S2 and S3, with the transmissions for each of the three central terminals 10 being directed to the appropriate sector among SI, S2 and S3. This enables the number of subscribers per cell to be increased three fold, while still providing permanent fixed access for each subscriber terminal 20.

A seven cell repeat pattern is used such that for a cell operating on a given frequency, all six adjacent cells operating on the same frequency are allowed unique PN codes. This prevents adjacent cells from inadvertently decoding data.

As mentioned above, each channel frequency can support 15 subscriber links. In this example, this is achieved using by multiplexing signals using a Code Division Multiplexed Access (CDMA) technique. Figure 6 gives a schematic overview of CDMA encoding and decoding.

In order to encode a CDMA signal, base band signals, for example the user signals for each respective subscriber link, are encoded at 80-80N into a 160ksymbols/sec baseband signal where each symbol represents 2 data bits (see, for example the signal represented at 81) . This signal is then spread by a factor of 16 using a respective Walsh pseudo random noise (PN) code spreading function 82-82N to generate signals at an effective chip rate of 2.56Msymbols/sec in 3.5MHz. The signals for respective subscriber links are then combined and converted to radio frequency (RF) to give multiple user channel signals (e.g., 85) for transmission from the transmitting antenna 86. During transmission, a transmitted signal will be subjected to interference sources 88, including external interference 89 and interference from other channels 90. Accordingly, by the time the CDMA signal is received at the receiving antenna 91, the multiple user channel signals may be distorted as is represented at 93.

In order to decode the signals for a given subscriber link from the received multiple user channel, a Walsh correlator 94-94N uses the same pseudo random noise (PN) code that was used for the encoding for each subscriber link to extract a signal (e.g, as represented at 95) for the respective received baseband signal 96-96N. It will be noted that the received signal will include some residual noise. However, unwanted noise can be removed using a low pass filter and signal processing. The key to CDMA is the application of orthogonal codes that allow the multiple user signals to be transmitted and received on the same frequency at the same time. Once the bit stream is orthogonally isolated using the Walsh codes, the signals for respective subscriber links do not interfere with each other.

Walsh codes are a mathematical set of sequences that have the function of "orthonormality". In other words, if any Walsh code is multiplied by any other Walsh code, the results are zero.

Figure 7 is a schematic diagram illustrating signal transmission processing stages as configured in a subscriber terminal 20 in the telecommunications system of Figure 1. The central terminal is also configured to perform equivalent signal transmission processing. In Figure 7, an analogue signal from one of a pair of telephones is passed via a two-wire interface 102 to a hybrid audio processing circuit 104 and then via a codec 106 to produce a digital signal into which an overhead channel including control information is inserted at 108. The resulting signal is processed by a convolutional encoder 110 before being passed to a spreader 116 to which the Rademacher-Walsh and PN codes are applied by a RW code generator 112 and PN Code generator 114, respectively. The resulting signals are passed via a digital to analogue converter 118. The digital to analogue converter 118 shapes the digital samples into an analogue waveform and provides a stage of baseband power control. The signals are then passed to a low pass filter 120 to be modulated in a modulator 122. The modulated signal from the modulator 122 is mixed with a signal generated by a voltage controlled oscillator 126 which is responsive to a synthesizer 160. The output of the mixer 128 is then amplified in a low noise amplifier 130 before being passed via a band pass filter 132. The output of the band pass filter 132 is further amplified in a further low noise amplifier 134, before being passed to power control circuitry 136. The output of the power control circuitry is further amplified in a further low noise amplifier 138 before being passed via a further band pass filter 140 and transmitted from the transmission antenna 142.

Figure 8 is a schematic diagram illustrating the equivalent signal reception processing stages as configured in a subscriber terminal 20 in the telecommunications system of Figure 1. The central terminal is also configured to perform equivalent signal reception processing. In Figure 8, signals received at a receiving antenna 150 are passed via a band pass filter 152 before being amplified in a low noise amplifier 154. The output of the amplifier 154 is then passed via a further band pass filter 156 before being further amplified by a further low noise amplifier 158. The output of the amplifier 158 is then passed to a mixer 164 where it is mixed with a signal generated by a voltage controlled oscillator 162 which is responsive to a synthesizer 160. The output of the mixer 164 is then passed via the de-modulator 166 and a low pass filter 168 before being passed to an analogue to digital converter 170. The digital output of the A/D converter 170 is then passed to a correlator 178, to which the same Rademacher-Walsh and PN codes used during transmission are applied by a RW code generator 172 (corresponding to the RW code generator 112) and a PN code generator 174 (corresponding to PN code generator 114), respectively. The output of the correlator is applied to a Viterbi decoder 180. The output of the Viterbi decoder 180 is then passed to an overhead extractor 182 for extracting the overhead channel information. The output of the overhead extractor 182 is then passed via a codec 184 and a hybrid circuit 188 to a two wire interface 190 where the resulting analogue signals are passed to a selected telephone 192.

At the subscriber terminal 20, a stage of automatic gain control is incorporated at the IF stage. The control signal is derived from the digital portion of the CDMA receiver using the output of a signal quality estimator.

Figure 9 shows an example of a programmable subscriber terminal 20. Programmable subscriber terminal 20 includes all the components previously discussed with respect to Figure 2. Programmable subscriber terminal 20 also includes a program request switch 196 that can be set to initiate programming of customer radio unit 24. Though shown in a switch configuration, program request switch 196 may be any activation means including push-button activation. Further, program request switch 196 may be implemented in any of the components of subscriber terminal 20. In order to operate, customer radio unit 24 needs to be programmed with the frequency, pseudo-random noise code, and CDMA code corresponding to central terminal 10 associated with programmable subscriber terminal 20.

Customer radio unit 24 is physically installed at a customer premises and wired down to power supply unit 30 and network termination unit 32. Network termination unit 32 is coupled to one or more subscriber telephone sets 34, facsimile machines 34, and personal computers 36. After installation, programming of customer radio unit 24 begins by activating program request switch 196. The handset of subscriber telephone set 34 is lifted off-hook and a continuous tone is generated indicating that it is safe to proceed with programming. Programming is performed by entering digits through subscriber telephone set 34, either verbally or through use of push-buttons 198. Alternatively, programming may be performed through personal computer 38 with responsive indications provided to personal computer 38.

Preferably, a programming code having twelve digits is entered into customer radio unit 24 through subscriber telephone set 32. The programming code is made up of a frequency field, a pseudo-random noise code field, a CDMA code field, a network identifier field, and a check digit field. The frequency field is a two digit field specifying one possible operating frequency for subscriber terminal 20 corresponding to central terminal 10. The pseudo-random noise code field is a one digit field specifying the proper pseudo-random noise code for transmissions between subscriber terminal 20 and central terminal 10. The CDMA code field is a two digit field specifying the proper CDMA code for transmissions between subscriber terminal 20 and central terminal 10. These three fields comprise the channel code used to define which channel subscriber terminal 20 is allowed to receive and transmit on. The network identifier field is a six digit field specifying the identity of subscriber terminal 20 for central terminal 10. The check digit field is a one digit field specifying a validation of each field in the programming digit code.

The programming code may be entered in the order described above or in a specified scrambled order. Though a specific length has been described for each field, the programming code may have different length fields and any number of fields depending on the design choices selected. A timer may also be implemented to establish a timed interval within which the programming code should be entered. Upon successfully entering the programming code, customer radio unit generates a tone signal having periodic intervals encoded therein to subscriber telephone set 34 indicating successful programming of customer radio unit 24. Programming for subscriber terminal 20 takes effect upon placing the handset of subscriber telephone set 34 in the on-hook condition.

In the event that programming is unsuccessful, customer radio unit 24 generates a tone signal having rapid intervals encoded therein to subscriber telephone set 34 indicating that programming of customer radio unit 24 has not taken place. Unsuccessful programming of customer radio unit 24 may occur if the programming code is not entered within the timed interval, an invalid digit is entered, check digit validation fails, or if any of the fields is detected as being out of range. Programming of customer radio unit 24 does not take effect if any of the above conditions occur.

Once programming is completed, program request switch 196 may be disabled or coupled to a monitoring system. If program request switch 196 is activated during operation of subscriber terminal 20, a tamper alarm will be raised indicating a subsequent attempt at programming customer radio unit 24. The tamper alarm prevents subsequent programming of subscriber terminal 20 by an unauthorized individual. A bypass code may be used to get around the tamper alarm in order to permit authorized subsequent programming of subscriber terminal 20.

After programming is complete, authentication of subscriber terminal 20 may be performed. Figure 10 shows the process involved in authenticating subscriber terminal 20. At manufacture, a unique serial number 200 is placed within customer radio unit 24. Serial number 200 is preferably programmed into an electronic memory within customer radio unit 24. Upon installation, customer radio unit 24 is programmed with a network identifier 202 and channel code 203 as previously discussed. Network identifier 202 of subscriber terminal 20 should correspond to a network identifier 204 of central terminal 10 associated with subscriber terminal 20. When a link is established between subscriber terminal 20 and central terminal 10, subscriber terminal 20 generates a reset indication message 206 for transmission to central terminal 10. Reset indication message 206 is encoded with serial number 200 and network identifier 202.

Central terminal 10 contains its network identifier 204 and a serial number slot 208. Central terminal 10 compares network identifier 202 encoded within reset indication message 206 with its network identifier 204. If network identifier 202 matches network identifier 204, central terminal 10 stores serial number 200 encoded within reset indication message 206 at serial number slot 208. Upon storing serial number 200 of subscriber terminal 20 into serial number slot 208, central terminal begins regular authentication by transmitting a verify message 210 encoded with what is stored in serial number slot 208. Verify message 210 may be sent by central terminal 10 periodically or randomly to subscriber terminal 20 as desired.

Subscriber terminal 20 receives verify message 210 from central terminal 10 and compares serial number 200 to the value of serial number slot 208 encoded within verify message 210. If a match occurs, subscriber terminal 10 continues its operation. If a match does not occur, the telephony functions of subscriber terminal 20 are disabled to prevent unauthorized eavesdropping. The uplink transmission path from subscriber terminal 20 to central terminal 10 is also disabled to prevent access to the network from subscriber terminal 20. In the situation where a subscriber terminal 20 is programmed to listen on a certain channel but does not have the appropriate serial number 200, the transmitter for the subscriber terminal 20 will be disabled to prevent telephony functions from the subscriber terminal 20 to central terminal 10.

Disablement of telephony functions may also occur at central terminal 10. Reset indication message 206 may be sent on a periodic or random basis to central terminal 10. Central terminal 10 can compare network identifier 202 and serial number 200 of subscriber terminal 20 encoded within reset indication message 206 with network identifier 204 and what is stored in serial number slot 208 of central terminal 10. If a match does not occur, central terminal 10 could disable a downlink communication path to subscriber terminal 20 in order to prevent unauthorized communications. The downlink communication path could then be reestablished from central terminal 10 by operator intervention or after a predetermined time. The downlink communication path may also be disabled if central terminal 10 does not receive reset indication message 206 within a selected time period.

In summary, a subscriber terminal may be programmed using the subscriber telephone set in an efficient manner. Programming codes are entered into a customer radio unit of the subscriber terminal through the subscriber telephone set either verbally or by the push-buttons of the subscriber telephone set. After programming, authentication of the subscriber terminal is performed through matching of serial numbers and network identifiers associated with the subscriber terminal and the central terminal. Failure of authentication will cause disablement of telephony functions to prevent unauthorized use of resources in the wireless telecommunications system.

Thus, there has been provided, in accordance with the present invention, an apparatus and method of authenticating a subscriber terminal in a wireless telecommunications system that satisfies the advantages set forth above. Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein. For example, different codes and signal transmissions may be used to implement similar programming or authentication schemes other than those described. Other examples are readily ascertainable by one skilled in the art and may be made without departing from the scope of the present invention.

Claims

WHAT IS CLAIMED IS:

1. A method of authenticating a subscriber terminal in a wireless telecommunications system, comprising the steps of: associating a serial number with the subscriber terminal; programming the subscriber terminal with a network identifier associated with a central terminal corresponding to the subscriber terminal; programming the subscriber terminal with frequency and transmission codes associated with the central terminal; sending a reset indication message from the subscriber terminal to the central terminal, the serial number and the network identifier encoded into the reset indication message; receiving a verify message at the subscriber terminal, the verify message encoded with a serial number; comparing the serial number in the verify message with the serial number of the subscriber terminal.

2. The method of Claim 1, further comprising the steps of: comparing the network identifier in the reset indication message with a network identifier of the central terminal; storing the serial number in the reset indication message corresponding to the subscriber terminal at the central terminal upon initial receipt of the reset indication signal and in response to a match of the network identifier in the reset indication message with the network identifier in the central terminal.

3. The method of Claim 2, further comprising the step of: periodically transmitting the verify message from the central terminal to perform authentication of the subscriber terminal.

4. The method of Claim 2, further comprising the steps of: comparing the network identifier and serial number encoded in the reset indication message transmitted from the subscriber terminal to the network identifier and serial number stored in the central terminal upon subsequent receipts of the reset indication message.

5. The method of Claim 4, further comprising the step of: disabling communications between the central terminal and the subscriber terminal in response to the network identifier and the serial number encoded in the reset indication message not matching the network identifier and serial number stored in the central terminal.

6. The method of Claim 1, wherein the reset indication message is transmitted in a scrambled form.

7. The method of Claim 1, further comprising the step of: disabling the subscriber terminal in response to the serial number encoded in the verify message not matching the serial number of the subscriber terminal.

8. The method of Claim 3, wherein the verify message is transmitted on a random basis.

9. An authenticating subscriber terminal, comprising: a storage element operable to store a serial number associated with the subscriber terminal, the storage element operable to store a network identifier associated with a central terminal corresponding to the subscriber terminal; a receiver operable to receive a verify message, the verify message being encoded with a serial number, the receiver comparing the serial number stored in the storage element with the serial number encoded in the verify message.

10. The authenticating subscriber terminal of Claim 9, wherein the receiver disables telecommunication operation of the subscriber terminal in response to the serial number stored in the storage element not matching the serial number encoded in the verify message.

11. The authenticating subscriber terminal of Claim

9, further comprising: a transmitter operable to transmit a reset indication message, the reset indication method encoded with the network identifier and the serial number.

12. The authenticating subscriber terminal of Claim 9, wherein the receiver receives the verify message on a periodic basis for serial number comparison.

13. The authenticating subscriber terminal of Claim

12, wherein the receiver receives the verify message on a random basis for serial number comparison.

14. A system for authentication in a wireless telecommunications system, comprising: a subscriber terminal having a serial number associated therewith; a central terminal having a network identifier associated therewith, the subscriber terminal having the network identifier corresponding to the central terminal, the subscriber terminal transmitting the serial number and the network identifier to the central terminal encoded into a reset indication message, the central terminal receiving the reset indication message from the subscriber terminal, the central terminal comparing the network identifier encoded in the reset indication message to the network identifier associated with the central terminal, the central terminal storing the serial number encoded in the reset indication signal and associated with the subscriber terminal in response to a match of the network identifier encoded in the reset indication signal with the network identifier associated with the central terminal.

15. The system of Claim 14, wherein the central terminal transmits a verify message, the verify message being encoded with the serial number and network identifier stored in the central terminal, the subscriber terminal receiving the verify message and comparing the serial number and network identifier encoded in the verify message with the serial number and network identifier associated with the subscriber terminal.

16. The system of Claim 15, wherein the subscriber terminal disables communications between the subscriber terminal and the central terminal in response to the serial number and network identifier encoded in the verify message not matching the serial number and network identifier associated with the subscriber terminal.

17. The system of Claim 14, wherein the subscriber terminal periodically transmits the reset indication signal, the central terminal comparing the serial number and network identifier encoded in the reset indication message to the serial number and network identifier stored in the central terminal, the central terminal disabling communications between the central terminal and the subscriber terminal in response to the serial number and network identifier encoded in the reset indication message not matching the serial number and network identifier stored in the central terminal.

18. The system of Claim 17, wherein the subscriber terminal randomly transmits the reset indication signal.

19. The system of Claim 14, wherein the network identifier and serial number are placed into the subscriber terminal prior to activation of the subscriber terminal within the wireless telecommunications system.