CZ20001872A3 - Subscriber terminal for wireless telecommunication system, second unit for signal processing and calibration method of the subscriber terminal - Google Patents

Abstract

The subscriber terminal is for communication over a wireless link with a wireless telecommunications central terminal system and includes: a first processing unit (110) a signal associated with the antenna (100) for receiving and receiving signals over a wireless link; second unit (130) for processing the signal remote from the first unit (110) signal processing and associated with element (150) telecommunication signaling equipment between said telecommunication equipment element and first a signal processing unit (110); connecting medium (120) connecting said first and second units (110,130) for signal processing; the calibration logic inside a second signal processing unit (130) for securing on the communication medium (120) of the control signals used for control circuitry in the first signal processing unit (110) and pro feeding an RF signal having a predetermined power level, to the connection medium (120) for enabling calibration logic to determine the RF power loss introduced a coupling medium (120); controlled compensation circuits calibration logic to compensate RF power losses determined by the calibration logic.

Description

The subscriber terminal for the wireless telecommunications system, the second signal processing unit and the subscriber terminal calibration method

Technical field 5

The present invention relates generally to subscriber terminals for wireless telecommunications systems, and particularly relates to calibration techniques for such subscriber terminals.

BACKGROUND OF THE INVENTION

Previously, a wireless telecommunications system has been devised in which a geographic area is divided into cells, each cell having one or more central terminals (CTs) for communicating over wireless links with a plurality of subscriber terminals (STs) in the cell. These wireless links are realized through predetermined frequency channels, the frequency channel usually consisting of one frequency for uplink signals from the ST to the central terminal and another frequency for the downlink signals from the ST to the ST.

This system finds a wide range of possible applications, for example in rural, remote or sparsely populated areas where the cost of laying wired or fiber optic cable networks would be too great, in heavily built-up areas where conventional wiring systems are at full power or the cost of laying such systems would be too large, or the deployment of these systems would be too disruptive to existing infrastructure, and so on.

In one embodiment, the central terminal may be connected

30. With a telephone network, and there is a relay for messages from 4 44 · 4 * 4 subscriber terminals in the cell, controlled by the central terminal, to the telephone network and vice versa. Through this access, the telecommunications equipment element associated with the subscriber terminal can make an outgoing call to the telephone network and receive incoming calls from the telephone network.

However, such a wireless telecommunications system is not limited to use with telephone signals but could instead handle any other suitable type of telecommunications signal, such as video signals or data signals, such as those used to transmit data over the Internet, and could be used for promoting new technologies such as broadband and video on demand technologies.

Giant. 1 illustrates an example of a typical prior art arrangement for a subscriber terminal 20 for such a wireless telecommunications system. Giant. 1 includes a schematic representation of the customer building 22. The customer radio unit (CRU) 24 is typically mounted on the customer building 22. The customer radio unit 24 comprises a flat plate antenna 23 or the like. The customer radio unit 24 is mounted at such a location on the customer building 22, or on a pole or the like, and in an orientation such that the flat plate antenna 23 within the customer radio unit 24 points in the direction 26 to the central terminal 10 for the service area. the customer radio unit 24 is located.

The customer radio unit 24 is typically connected via an outlet line 28 to a PSU 30 within the customer building 22. This power source unit 30 is connected to a local power supply to provide power to the customer radio unit 24 and the network 32 unit. 4 4444

444

4 4 4

4 4 4

44 of the terminal (NTU). The customer radio unit 24 is also connected via the power supply unit 30 to the network terminal unit 32, which is further connected to the telecommunications equipment in the customer building 22, for example one or more telephones 34, facsimile devices 36 and computers 38.

Telecommunication equipment is represented as being inside one customer building. Of course, this may not always be the case, as the subscriber terminal 20 can support more than one line, so that a plurality of subscriber telecommunications equipment elements can be supported by one subscriber terminal 20. The subscriber terminal 20 can also be arranged to support analog and digital telecommunications , such as analog communication at 16, 32, or 64 kbit / s, or ISDN BRA digital communication,

The CRU 24 typically includes all of the necessary processing circuits to convert incoming wireless telecommunications signals into signals recognizable by the telecommunications equipment element, as well as to convert such

0 signals from these elements of telecommunication equipment to wireless telecommunications signals for transmission from the antenna 23.

A significant problem with this approach is that the CRU 24 is a costly equipment feature when replaced. Because this unit is usually located outside the customer buildings, 25 is a frequent target of theft. In addition, all of the components inside the CRU 24 must be able to withstand exposure to varying climatic conditions, as a result of the CRU 24 being mounted externally. For example, these components must be able to withstand significant changes in temperature and changes in humidity.

• · · · · · ··· «

However, one reason why the CRU 24 has already incorporated all of the necessary processing circuits to convert the incoming wireless telecommunications signals into signals recognizable by the wireless equipment elements is because it reduces the technical complexity of the subscriber terminal by having all of the processing circuits in one housing.

In addition, the attenuation problems of the wireless signals transmitted between the central terminal and the ST and vice versa have previously dictated that the processing circuits of the ST are located in the physical vicinity of the antenna 23. To illustrate this phenomenon, it is clear that the signal transmitted from the ST to a predetermined power As soon as the signal has already been received by the antenna 23, there will also be further attenuation within the subscriber terminal as the signal is passed from the antenna to the processing circuits within the subscriber terminal. Obviously, the further away from the antenna these processing circuits are, the more likely attenuation will be. A signal strength threshold below which the signal cannot be processed by the processing circuitry within the subscriber terminal 20 will be determined. Therefore, in order to improve the range of the wireless telecommunications system, it was considered desirable to minimize the distance between antenna 23 and the processing circuitry of the subscriber terminal used to process the received signal. .

The above requirements have led to the creation of subscriber terminals, such as the terminal illustrated in FIG. 1, in which an expensive customer radio unit 24, designed to withstand exposure to changing climatic conditions, has been mounted outside the customer buildings.

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To overcome this problem, International Patent Application No. PCT / GB98 / 0342Q, filed by the same applicant as the present patent application and on the same day as the present patent application, proposes the creation of a subscriber terminal comprising two separate signal processing units, a first processing unit and a second signal processing unit associated with a telecommunications equipment element associated with the subscriber terminal. The signals are transmitted from the antenna and received by the antenna over the wireless link at the first frequencies within the operating frequency band. The first signal processing unit comprises a frequency converter for converting signals between said first frequencies and the second frequency. Usually, the second frequency will be lower than the first frequency.

The first and second signal processing units are coupled through the linking medium, and the telecommunications signals are then transmitted between the first and second signal processing units through the linking medium at the second frequency.

In this approach, the second signal processing unit may then be formed from a signal processing circuit that is independent of the operating frequency band.

Thus, the same signal processing unit may be used regardless of the operating frequency band used for 25 wireless communications between the subscriber terminal and the central terminal. In addition, the approach described above substantially reduces the number of circuits required within the first signal processing unit associated with the antenna, thereby reducing the complexity of the first signal processing unit.

• · · · φ · · · · · · · · φ · φ · φ ·

The actual position of the first and second signal processing units inside the customer buildings is a choice during installation. However, since the first signal processing unit is associated with the antenna, it is probably mounted near the antenna and therefore is probably mounted from the outside. In such an embodiment, the subscriber terminal of the present invention offers significant advantages over the prior art, since the first signal processing unit comprises substantially less processing circuitry than the customer radio unit of the subscriber terminal of the prior art. In addition, a substantial portion of the processing that was previously performed in the customer radio unit is according to the present invention performed in the second signal processing unit associated with the telecommunications equipment element. Assuming that the first signal processing unit is made to withstand outdoor use, then the components inside the first signal processing unit will be able to withstand exposure to changing climatic conditions in the same way that those climatic conditions had to withstand components within a prior art customer radio unit. . However, since the first signal processing unit has considerably fewer components, it is cheaper to manufacture the first signal processing unit with the necessary specifications than to produce a customer radio unit according to the prior art.

Thus, if the first signal processing unit is cheaper than the prior art customer radio unit, then it is also a less desirable target of theft than the prior art customer radio unit.

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9999 999 99 99 99

Although the above described re-arrangement of the subscriber terminal eliminates the above-described problems of the subscriber terminals according to the prior art, there are still several problems to be solved. One problem is how to compensate for the loss of received and transmitted signals resulting from the passage of these signals through the linking medium. It is highly desirable to compensate for these losses so as to limit the dynamic range of the signal received at the distal end of the linking medium, since limiting this dynamic signal range simplifies circuit design. In addition, without some form of compensation, accurate measurements of signal parameters (e.g., levels of received and transmitted signals) cannot be made after the signals have already passed through the link medium.

When creating circuits to determine the necessary compensation. however, it is desirable to maintain a minimum amount of circuitry within the first signal processing unit, since otherwise the formation of these circuits would conflict with the general objective of attempting to limit the number of circuits in the first signal processing unit.

EP0750405 discloses a cable loss compensation system for wireless communication equipment. In this document, RF cable losses are compensated by measuring the DC (DC) resistance. The DC resistance is calculated by measuring the DC current in the cable and the voltage difference at both ends of the cable. From these 25 measurements the voltage drop and then the DC resistance can be calculated. RF losses can be estimated from the DC resistance.

The present inventors are of the opinion that this system can be improved, the system of the present invention

3Q has the advantage of measuring actual RE power losses and not DC • 99 9

9 · 9 • 9 * · ····

9 · 4 • 9 ·· current and voltage at each end of the cables to estimate these RF losses.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a subscriber terminal for communicating over a wireless link with a central terminal of a wireless telecommunications system, the subscriber terminal comprising: a first signal processing unit associated with an antenna for transmitting and receiving signals over the wireless link; a second signal processing unit remote from the first signal processing unit and associated with the telecommunication equipment element for transmitting signals between said telecommunication equipment element and the first signal processing unit; a coupling medium connecting said first and second signal processing units; calibration logic within said second signal processing unit to provide on the control medium the control signals used to control the circuits in the first signal processing unit and for supplying an RF signal having a predetermined power level to the connecting medium to enable the calibration logic to determine the RF power losses introduced binding medium; calibration logic-controlled compensation circuits to compensate for RF power losses determined by the calibration logic.

According to the present invention, the subscriber terminal comprises two separate signal processing units, a first signal processing unit associated with the subscriber terminal antenna, and a second signal processing unit associated with the telecommunications equipment element associated with the subscriber terminal. The first and second signal processing units are coupled through the linking medium, and the telecommunications signals are then transmitted between the first and second signal processing units through the linking medium. As mentioned in the foregoing description, this arrangement provides a number of advantages over prior art arrangements of subscriber terminals.

In addition, according to the present invention, calibration logic is provided within the second signal processing unit to provide control signal coupling media used to control circuits in the first signal processing unit and to supply signals to the coupling media between the first signal processing unit and the second signal processing unit to enable the calibration logic to determine the RF power losses introduced by the coupling medium. Then, a compensation circuit is formed which is controlled by the calibration logic to compensate for the signal losses determined by the calibration logic.

Accordingly, according to the present invention, the linking medium is not only used to transmit the received signals from the first to the second signal processing unit and the transmitted signals from the second signal processing unit to the first signal processing unit, but is also used to transmit the various signals used to calibrate the ST. to compensate for the power loss of the signals resulting from the passage of these signals through the coupling medium.

Through the approach described above, the amount of circuitry required within the first signal processing unit associated with the antenna is reduced, thereby reducing the complexity of the first signal processing unit while still allowing determination of the compensation required to compensate the power loss of the received and transmitted signals, φ φ · Φ φ φ vyplývající φ φ φ vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající vyplývající)

In preferred embodiments of the invention, the compensation circuits are formed within the second signal processing unit, further reducing the number of circuits required within the first signal processing unit.

The signal power losses introduced by the linking medium may vary depending on whether the signal is a signal received by the ST or a signal transmitted by the ST.

Thus, in preferred embodiments of the present invention, the calibration logic is arranged to provide a first pilot signal on the coupling medium to output the first test signal having a predetermined power level to the coupling medium by the first signal processing unit, the calibration logic arranged to determine from the first test signal. the signal loss, as received by the second signal processing unit, of the power loss of the received signal introduced by the linking medium.

Preferably, the compensation circuitry comprises a first variable attenuator that is configured to be adjustable by calibration logic to compensate for determined signal power losses of the received signal.

Further, in preferred embodiments of the present invention, the calibration logic is arranged to provide a second test signal output by the second signal processing unit to the bonding medium, and to output the second pilot signal to the bonding medium to ensure that the first unit e *.

4 4

4 4

4 * 4

4444 ·· ♦ 4 4 4 4

4 · 444 44 4 • * 4 4 4 4 4 · ♦ · 44 44 44 signal processing prevented the second test signal from outputting from the antenna.

Preferably, the first signal processing unit is then arranged to determine the signal strength indication of the second test signal in the first signal processing unit, and to output the indication to the linking medium to the second signal processing unit for use by the calibration logic to determine the signal loss of the transmitted signal. introduced by the binding medium.

In addition, the compensation circuits preferably comprise a second variable attenuator that is arranged to be adjustable by the calibration logic to compensate for the determined signal loss of the transmitted signal.

In preferred embodiments of the present invention, the first signal processing unit comprises a first serial communication control unit for receiving control signals from the second signal processing unit.

In addition, a second serial communication controller is preferably provided in said second signal processing unit, which is arranged to communicate with said first serial communication controller via said connection medium, the calibration logic being arranged to output a signal to the second serial communication controller to provide wherein the second serial communication controller transmits the control signals via the linking medium to the first serial communication controller in the first signal processing unit.

This approach allows a serial communication link to be established through the linking medium for enabling

• Μ v • 4 ·

4 4 • 4444 * 4 * 444

4 4 4 4 4 4

Passing the necessary control signals from the second signal processing unit to the first signal processing unit.

A number of advantages result from the calibration of the ST terminal to compensate for power losses introduced by the linking medium. Once this compensation has been made, the parameters of the received and transmitted signals can be accurately determined, even after the passage of these signals through the linking medium.

One example of a situation in which calibration may be an advantage is the installation of a subscriber terminal where the installer needs to direct the antenna. In preferred embodiments of the present invention, the second signal processing unit includes, for the purpose of directing the antenna: signal strength determination logic to determine the signal strength of the signal received by the first signal processing unit through the antenna and transmitted to the second signal processing unit through the linking medium; the signal is arranged to be provided on a bonding medium of the indicating signal representing the strength of the received signal; wherein the indicator, located or positionable on or near the antenna, may be excited in response to the indication signal provided on the linking medium to provide an indication of the strength of the received signal.

This has the advantage that it is possible for one installer to direct the antenna while providing some indication of the strength of the received signal, although the first signal processing unit associated with the antenna does not include circuits to detect this received signal strength and to drive the indicator. In addition, since the ST has already been calibrated to compensate for the loss introduced by the connection. 9 9 9 9

9 9

99, the indicator signal outputted through the indicator control coupling medium may provide a calibrated value for the strength of the received signal.

The actual indicating device used to provide an indication of the received signal strength is a matter of design choice. In one embodiment, the first signal processing unit comprises an indicator. Alternatively or additionally, however, this indicator may be connected to the output port of the first signal processing unit.

¹⁰

The first signal processing unit may be physically separated from the antenna, providing greater flexibility in selecting the antenna. In such situations, to achieve the greatest advantages of the present invention, it is advantageous that the indicator, either as part of the first signal processing unit or connected to the output port of the first signal processing unit, be positioned so as to be observable by the installer when directing the antenna. Usually this will not be a particular problem, as the first signal processing unit will likely be located near the antenna unit. In addition, in alternative embodiments, the first signal processing unit and antenna may be integrated into a single housing.

The indicator may be arranged to provide any suitable output, either visual or audible, for use by the installer. In preferred embodiments of the invention, however, said indicator comprises a plurality of LEDs to provide an indication of the strength of the received signal.

In alternative embodiments, the indicator need not be associated with or incorporated into the first processing unit.

44 ······· · · 4 444 4444 ·· 4 * 44 «44 44 44 44 signal and may instead be connectable directly to the bonding medium.

In preferred embodiments of the invention, said signal strength determination logic comprises a demodulator for determining the strength of the received signal, and a processor for generating an indicator signal outputted through the linking medium for controlling the indicator.

The linking medium connecting the first and second signal processing units may be any suitable linking medium for transmitting telecommunications signals at a second frequency between the first and second signal processing units. In preferred embodiments, however, the connection medium is a cable over which signals are routed at a second frequency. Preferably, the cable is a coaxial cable. The attenuation of the signal transmitted through the coaxial cable increases with the frequency of the signal. This can be compensated to some extent by suitable signal amplification before it is transmitted over the coaxial cable. On the radio (high) frequencies used for wireless communication between the central terminal and the subscriber terminal, which are of the order of GHz, it has been found that the coaxial cable attenuates the signal to an unacceptable extent. However, by appropriate selection of a second frequency that is lower than that used for the wireless link, it has been found that the coaxial cable provides a suitable medium for transmitting signals between the first and second signal processing units. This is a significant advantage because the coaxial cable is relatively inexpensive and therefore the use of a coaxial cable to transmit signals between the first and second signal processing units helps to reduce

9 9

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999

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999 99 99 99 the total price of the ST. Another advantage of the coaxial cable is that it is relatively easy to terminate.

In a second aspect, the present invention provides a second signal processing unit for a subscriber terminal according to the first aspect of the present invention, wherein the second signal processing unit comprises calibration logic to provide control signal coupling media used to control circuits in the first signal processing unit and supplying signals to the coupling medium between the first signal processing unit and the second signal processing unit to allow the calibration logic to determine the signal losses introduced by the coupling medium.

In a third aspect, the present invention provides a method of calibrating a subscriber terminal configured to communicate over a wireless link with a central terminal of a wireless telecommunications system, wherein the subscriber terminal comprises a first signal processing unit associated with an antenna for transmitting and receiving signals over

2o a wireless link, a second signal processing unit remote from the first signal processing unit and associated with the telecommunication equipment element for transmitting signals between said telecommunication equipment element and the first signal processing unit, and a connecting medium connecting said first and second signal processing units wherein the method comprises the steps of: (a) providing control signal generated by the second signal processing unit on the bonding medium; (b) controlling the circuits in the first signal processing unit in dependence on said control signals to ensure the transmission of signals on the coupling medium of the first • 99 • 9 * 9 ····

999

9 «i

99 a signal processing unit into a second signal processing unit; (c) using the signals generated in step (b) to determine in said second unit the signal loss signal inputted by the binding medium; (d) responsive to the determination in step (c) of controlling the compensation circuits to compensate for signal loss.

The present invention will be described in more detail in the following description only by way of example on preferred embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic illustration of an example of a typical prior art subscriber terminal;

Fig. 2 shows a schematic overview of an example of a wireless telecommunications system in which the present invention may be used;

Giant. 3 is an illustration of an example frequency map for the telecommunications system of FIG. 2;

Giant. 4 is a schematic block diagram of a subscriber terminal according to preferred embodiments of the present invention;

Giant. 5 illustrates a circuit diagram illustrating components in a high frequency block of a ST according to preferred embodiments;

Giant. 6 is a block diagram illustrating the main components of a custom modem unit 9,999,999,999,999

99 «99 999 99 99 99«

a subscriber terminal according to preferred embodiments;

Fig. 7A is a circuit diagram illustrating components within a radio modem card used to perform intermediate frequency processing according to preferred embodiments of the present invention;

Fig. 7B is a block diagram illustrating the main components of a CDMA modem inside a radio modem card that is used to control the circuits of Fig. 7A;

Fig. 8A and Fig. 8B provide more detailed illustrations of the circuitry portions shown in Fig. 7;

Giant. 9 is a diagram illustrating the use of a spectrum of a connection cable used in subscriber terminals according to preferred embodiments of the present invention;

Fig. 10 provides a more detailed illustration of the serial communication controller shown in Fig. 7; and

Fig. 11 illustrates the use of a signal strength measuring means that can be used in embodiments of the present invention to assist in adjusting the antenna during installation of the ST.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be used in conjunction with any suitable type of telecommunications signal, for example

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99 9 • • 9 99 with a telephone, video or data signal, such as those used to transmit data over the Internet, and to support new technologies such as broadband and on-demand video technologies. For the purpose of describing a preferred embodiment of the present invention, however, a wireless telecommunications system that is used to process telephone signals such as POTS (uncoded conventional telephone service) signals will be considered.

For the purpose of describing a subscriber terminal according to the preferred embodiments of the present invention, a wireless telecommunications system in which the exchange is connected to a public telephone network and exists to transmit messages from subscribers in the cell controlled by the exchange to the public telephone network and vice versa will be discussed. Giant. 2 is a schematic overview of an example of such a wireless telecommunications system. The telecommunications system comprises 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 (high frequency) connection to the subscriber terminals (ST) 20 within the corresponding area. The area covered by the central terminal 10 may vary. For example, in a rural area with a low density of subscribers, the service area 12 could cover an area with a radius of 15 to 20 km. Service area 14 in an urban environment with high density of subscriber terminals 20 could only cover an area with a radius of the order of 100m. In suburban area with medium density of subscriber terminals 20, service area X6 could cover an area with a radius of about 1 km. However, it should be understood that the area covered by a particular central terminal 10 can be selected to meet local requirements of the expected or actual subscriber density, the local geographic conditions and the like, and is not limited to the examples illustrated in FIG. 2. In addition, coverage need not be, and usually will not be, circular with its area due to antenna design requirements, geographic conditions, structures, and the like.

The central terminals 10 for the corresponding service areas 12, 14, 16 may be connected to each other via links 13, 15, 17 that connect them, for example, to a public switched telephone network (PSTN) 18. These links may include a conventional telecommunications technology using copper conductors, optical fibers, satellites, microwaves and the like.

The wireless telecommunications system of FIG. 2 is based on establishing fixed radio links between subscriber terminals 20 at fixed locations within a service area (e.g., 12, 14, 16) and a central terminal 10 for that service area. In one embodiment, each subscriber terminal 20 is provided with a permanent fixed access line to its central terminal 10. However, in alternative embodiments, a request-based access could be created so that the number of subscribers that can be supported by the system exceeds the number of telecommunications links (lines). that may just be active.

Wireless telecommunications between the central terminal 10 and the subscriber terminals 20 could operate at different frequencies. In the present example, the wireless telecommunications system is intended to operate in the band defined by CEPT Recommendation SE19. Giant. 3 illustrates the frequencies used for uplink from subscriber terminals 20 to central 444 4

4 4

4 · »4 • 44« 4444 4 • 44 ·· 44 «4 * 4

4 4 4 4 4

44 for terminal 10, and for downlink connection from central terminal 10 to subscriber terminals 20 in preferred embodiments. It should be noted that 12 uplink and 12 downlink radio channels, each of 3.5 MHz, are formed around 3502 MHz. The distance between the receive and transmit channels is 100 MHz.

Therefore, the frequency channel will be defined by one uplink frequency plus the corresponding downlink frequency. Techniques such as code division multi-access (CDMA) can be used to allow a number of wireless links to subscriber terminals to be simultaneously supported on each frequency channel.

Typically, radio traffic from a particular central terminal 10 will extend to an area covered by an adjacent central terminal 10. To prevent or at least reduce interference problems caused by adjacent areas, only a limited number of available frequencies will be used at any given central terminal 10. This is discussed in more detail in GB-A-2,301,751, which also provides further detail about CDMA encoding / decoding and signal processing phases used in the subscriber terminals and the central terminal for managing communications between them.

Following this description of a wireless telecommunications system in which a subscriber terminal according to the preferred embodiments of the present invention can be used, the subscriber terminal according to the preferred embodiments will now be further described with reference to Fig. 54. Giant. 4 is a block diagram illustrating the main components of a ST.

on · 9 9 99 9 9 9 • 9 9 • * 9 • 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 99 9999 999 99 99 99

In preferred embodiments, the function of the ST is divided between the outdoor and indoor units. Thus, an RF (radio frequency) block 110 is provided that is typically mounted on the exterior of the customer building, preferably the RF block 110 is mounted near the customer antenna unit 100 used to transmit and receive wireless telecommunications signals. The customer antenna unit 100 is then connected to the RF block 110 via the RF antenna cable 105. Although the RF block 110 and the customer antenna unit 100 are illustrated in Fig. 4 as separate units connected by the antenna cable 105, those skilled in the art will readily appreciate that, if desired, the antenna unit may be integrated within the RF block 110 to be created one unit for mounting on the outside of the customer building.

In preferred embodiments, all of the electronic circuits that are dependent on the operating frequency band used for wireless communication between the subscriber terminal and the central terminal are located within the RF block 110. The purpose of the RF block is to translate received downlink signals from the RF (radio-high) frequency at a standard intermediate frequency suitable for transmission to the customer modem unit 130 and the like to translate the received (uplink) signals from the customer modem unit 130 at the standard intermediate frequency to an RF uplink signal for transmission from the customer antenna unit 100.

The RF block 110 and the customer modem unit 130 are connected by a connection cable 120, which connection cable 120 is preferably formed by a coaxial cable. The customer modem unit 130 includes a CDMA modem

• »* 4 • 4 4 4 4 4 4 • * · ♦ • · 4 4 • 4 • • 4 • • 4 4 • · 4 4 44 44 ·· • 44 44 • 4 44

operating at a fixed intermediate frequency and also comprising the electronics required to interface with one or more elements of telecommunications equipment associated with the subscriber terminal. In preferred embodiments, the customer modem unit 130 is located within the customer building, for example near the telecommunications equipment element (s). Thus, the telecommunications equipment element 150 is coupled to the customer modem unit 13 via line 155. Further, the customer modem unit is preferably coupled to the AC adapter 140 via a DC power supply cable 145, which AC adapter 140 provides power to the customer modem unit 130.

Within the relevant legal framework of many countries, it is often required that telecommunications equipment operating over wireless links be designed with a separate power source so that such telecommunications equipment can be used in an emergency, even if interruption of the power supply network prevents the telecommunications equipment from connecting main power supply. Thus, in preferred embodiments, a battery backup unit, for example a lead-acid battery, is incorporated within the customer modem unit.

The circuits within the RF block 110 will also require a power supply to operate, and in preferred embodiments, the required power is supplied from the customer modem unit 130 via a connection cable 120.

The architecture illustrated in FIG. 4 allows for a number of cost reductions. For example, if the antenna 100 were integrated within the RF block 110, this would result in a very convenient package, but would require the antenna to be designed for universal use. This usually means designing an antenna with such a high gain, so the gain is so high. ···· ···· ·· ** · ·· ·· ·· as possible, but this contributes to the cost. By keeping the antenna 100 separate from the RF block 110, however, the subscriber terminal may be equipped with a cheap antenna with a common specification that would be suitable for most applications. Then, in situations where the signal strength is unusually low, the subscriber terminal could possibly be equipped with a high gain antenna, for example as a quotation for the customer. This approach increases flexibility and allows the use of cheap antennas for most situations where the antenna will be sufficient.

The subscriber terminal according to preferred embodiments of the invention will preferably be provided with an antenna that is substantially smaller and lighter than the combined antenna / customer radio unit used in the prior art subscriber terminals. By using a smaller and lighter antenna, less hardware placement and mounting is achieved. For example, since this unit is smaller than that used in the subscriber terminals of the prior art, it is more suitable for pole mounting above the roof level. At higher levels, the increased reception signal compensates for any smaller antenna gain resulting from the use of a smaller antenna.

The design of the antenna and / or the choice of technology varies with frequency. In a design for a new operating frequency band, changes in antenna design are likely to result in changes in the mechanical design of the ST and / or in the packaging, resulting in a large number of manufacturing variants. If the mechanics of the ST can not be changed, the antenna power can be adjusted. However, the subscriber terminal according to the preferred embodiments of the present invention allows the choice of creating an easily accessible antenna for a new operating frequency.

- »· 4

4 4 4 4 4 4 • 4 44 4 44 4 • * · 4 4 4 4

444 -44 · 4 4 «band until the sales volume decides to change the design of the ST. Thus, it will be possible to easily create a subscriber terminal that will operate in a different RF working frequency band.

In addition to the above-described cost reductions resulting from the RF block / antenna architecture, a number of additional cost reductions can be realized due to the architecture illustrated in Fig. 4. For example, since all of the frequency band sensitive components are preferably located in the RF block 110 The modem inside the customer modem unit 130 operates at a standard intermediate frequency for all RF operating frequency bands. Thus, the customer modem unit 130 can be manufactured in large volumes regardless of which operating frequency band of the device will operate. Subsequent design modifications would then preferably be limited to RF block 110.

Connection cables used in a prior art subscriber terminal, such as the terminal illustrated in Fig. 1, would typically include a high specification shielded five-pair cable. Such a cable is expensive, including the connectors required for cable termination and network protection. However, in a preferred embodiment of the present invention, a single coaxial cable is used to supply power and transmit the uplink and downlink signals between the RF block 110 and the customer modem unit 130, eliminating the need for expensive cables and connectors.

In preferred embodiments, the customer interface and radio modem functions are separated within the customer

* »· * t « * · · • * · • « • • · · • · · • • ·· ··· « ··· tt ··

««

modem units. A radio modem card is designed that is designed to operate on a standard IF (intermediate frequency) and to establish a solid connection with a customer interface card. The customer interface card is then dependent on a particular element (s) of the telecommunications equipment supported by the ST. Through this arrangement, the radio modem card will operate with any variant of the customer interface, and so the radio modem card can be manufactured in large volumes with a design that is independent of the telecommunications equipment supported by the ST, thereby ensuring cost savings. Advantageously, specific customer variants of the customer interface may be developed and, if desired, such design changes in the customer interface card will not require rearrangement of the radio modem card. In addition, any reduction in the cost of a radio modem card resulting from greater component integration will not require design changes in the customer interface card in preferred embodiments of the invention.

In preferred embodiments, the AC adapter 140 used to supply power to the subscriber terminal is a low cost universal AC adapter supplying 18V DC to the customer modem unit 130 and the RF block 110. The customer modem unit 130 in preferred embodiments also includes a low cost 25

20W lead-acid battery for backup in case of mains failure. The power dissipation and hence the cost of the battery are limited in a preferred embodiment by arranging the logic circuitry to operate from 3.3V where possible and by switching off any circuitry not required when the RF line is not in use, including the circuitry 30.

RF transmission, IF transmission, baseband transmission and

»· 4

4 ·

3 4 «« 4

44 ·· · 4 4 4 | | > 4 4 4 4 4 • 4 444 4 4

444 44 44 «φ encoding and decoding. In addition, processors advantageously utilize power saving modes of operation.

Low energy dissipation results in further cost reductions by facilitating thermal management requirements. In addition, since the outer package of the RF block is smaller and lighter than the prior art customer radio unit, assembly means may be lighter and therefore cheaper. In addition, the internal customer modem unit contains a significant proportion of processing circuitry and cheap plastics and assembly procedures can be used than would normally be required for the prior art customer radio unit of the prior art because the internal environment requires less mechanical integrity.

Having clarified some of the advantages of using the architecture shown in FIG. 4, the RF architecture of the ST will now be discussed in more detail in accordance with preferred embodiments of the invention. As discussed above with reference to FIG. 4, the RF architecture is split between the internal electronics within the customer modem unit 130 which converts the up / down baseband information to a standard IF band, and the external electronics within the RF block 110 that performs the up conversion. / down to RF band.

Giant. 5 is a diagram illustrating the arrangement of components within RF block 110 used to convert signals between IF and RF. Considering the RF signal received by the subscriber terminal first, the received signal will be passed through the antenna 202 to the RF filter 200, which is arranged only to pass signals with frequencies within a predetermined frequency range that it transmits to the path 204. The RF filter 200 and the RF filter 210 together form a duplex (bi-directional) filter, wherein the filter

• • 9 9 in 9 in • : i • 9 9 • 9 9 9 9 9 9 99 •> 99 999 99 99 99

210 is of a type that allows transmitted signals on path 206 to be transmitted to antenna 202 while preventing RF signals from passing from antenna 202 to path 206. Similarly, RF filter 200 is a type that prevents transmitted signals on path 206 from propagating along the path. 204, while allowing received signals through antenna 202 to be passed to path 204. In preferred embodiments, RF filter 200 will allow received downlink signals with center frequencies ranging from 3511.75 to 3550.25 MHz to pass through the filter while RF filter 210 will allow uplink signals with center frequencies ranging from 3411.75 to 3450.25 MHz to pass through the filter.

Thus, in preferred embodiments of the invention, the received RF signal in the antenna 202 will pass through the RF filter 200 through the path 204 to the switch 240. In the normal operation, the switch 240 is arranged to transmit the received signal to a low noise amplifier (LNA) 230. will be discussed in more detail below, but switch 240 may be used to unlock

Any signals received by the antenna 202 and may instead transmit signals from the calibrated noise source 245 to the LNA 230. Once the signal has passed through the switch 240, it is amplified by the LNA 230 and another amplifier 235 before being transmitted to the attenuator network resistors 212, 214, 216. three

5 resistors 212. 214 and 216 operate in combination to attenuate the received signal before passing it to the filter 250. It is desirable to incorporate such a silencer circuit from resistors 212, 214, 216 to ensure that downstream circuits are not exposed to a signal having a higher power level. than they are for

5θ, components designed. Such a high power signal can

9 «· • 9

9 9 9 9 9 • 99 99 can be, for example, received in antenna 202 if the subscriber terminal is located particularly close to the central terminal with which it is to communicate. The attenuation circuit from resistors 212, 214, and 216 then serves to ensure that this initially received signal is attenuated before it propagates through the rest of the processing circuits. If it is subsequently found that attenuation by means of resistors 212, 214 and 216 is unnecessary, then a control signal C2 may be applied to switch 220 to turn on the switch and thereby bypass the attenuation circuit.

in

Once the signal has passed through the attenuator circuit from resistors 212, 214, 316 or through switch 220, it is passed to filter 250. Filter 250 is configured to remove the broadband noise generated by the LNA 230 by allowing only signals within the specified bandwidth centered to pass through the filter. at a predetermined frequency. In preferred embodiments, the bandwidth that is allowed to pass through the filter is 42 MHz centered at 3531 MHz, i.e., the center of the frequency range for the downlink signals transmitted from the antenna 202 through the filter 200.

The signal output from the filter 250 is then transmitted to the mixer 260 (summation) through the resistor matching network 252, 254, 256. This matching network is used to match the impedance of the filter output 250 to the impedance of the input to the mixer 260. from the RF synthesizer 280, wherein the RF synthesizer 280 is controlled by configuration logic 285. In preferred embodiments, the signal output of the RF synthesizer 280 is to a mixer 260 at a frequency of 2596 MHz. Based on two input signals at frequencies f _: and f _{2 a} mixer such as

• ·

9 ···

999 • 9 * 9 · 9 9 9 9 ·· 99 mixer 250, will generate signals at two output frequencies, namely at frequencies + f ₂ and f _x - f ₂ .

The signal output from mixer 260 is then amplified by amplifier 270 prior to receiving a duplex filter including filter 290 and filter 295. In preferred embodiments, filter 290 is arranged to remove a signal component at a frequency f _x + f ₂ formed by mixer 260 to allow passage into the linker. cable 120 only the signal component at frequency f _: - f ₂ . Further, the filter 295 is configured to prevent any signal from the amplifier 270 from propagating along the path 305. Thus, in preferred embodiments of the invention, the intermediate frequency used to transmit the received signals via the connection cable 120 between the RF block 110 and the customer modem unit 130 includes component af. _x - f ₂ generated by the mixer 260 from signals received from both the RF synthesizer 280 and the filter 250.

Considering the signals to be transmitted from the antenna 202, the customer modem unit 130 preferably generates signals at an intermediate frequency in the range of 815.75 to 854.25 MHz and transmits via the connection cable 120 where it is then received by a duplex filter composed of filters 290 and 295. Filter 295 is configured to propagate these signals via path 305 to amplifier 310, while filter 2 90 prevents these signals from passing back to the circuits described above. The amplifier 310 amplifies the signals and then passes them to the mixer 320 via the resistor matching network 312, 314,

316. This matching network matches the impedance at the output of amplifier 310 to the impedance at the input of mixer 320.

The mixer 320 also receives an input from the RF synthesizer 280, with the signal being in preferred embodiments

444 «** 44 * 4¼« • 4 4 4 4 4 4 ··· ·· 4 * 44 same frequency as the signal transmitted from this RF synthesizer 280 to mixer 260. Components f _T + f ₂ and f _x - f ₂ , generated mixer 320, are then passed through another matching network from resistors 322, 324, 326, and via amplifier 330 to filter 340.

The filter 340 is configured to allow only signals in the 42 MHz bandwidth centered at a predetermined frequency to pass through the filter 340, and in preferred embodiments of the invention, the predetermined frequency ^{0 is a} frequency of 3431 MHz so as to remove component af ₁ - f ₂ formed. Subsequently, the amplifiers 350 and 360 amplify the signal to compensate for filter loss 340 before the signal is transmitted via switch 370 to the filter 210 and thence to the antenna 202 for transmission. During normal operation, switch 370 is arranged to pass the signal output from amplifier 360 to RF filter 210. However, during installation calibration procedures, switch 370 may be switched so that the signal is grounded through resistor 380 to prevent transmission of a test signal generated during θ calibration.

Further, the signal output of amplifier 360 to switch 37Q is connected via connector 385 to diode 390. This provides an indication of P signal transmit power level, which power signal P is applied to serial communication control unit 40 within RF block 110, which then transmits this information. via a connection cable 120 to a customer modem unit 130.

The circuits illustrated in Fig. 5 are intended for use in a subscriber terminal using CEPT Recommendation SE19 for wireless telecommunications, where the duplex separation is 100 MHz.

• 4 • 4 4444 • 4 4 4 4 444 I * * 4 4 4 4 4 4 ··· 44

However, other duplex spacings, such as 175 MHz and 94 MHz, can easily be ensured by incorporating an additional fixed frequency synthesizer.

For the Automatic Frequency Control (AFC) loop to work correctly, the RF synthesizer 280 must be phase-coupled to a 13 MHz frequency reference located in the customer modem unit 130. This is achieved by transmitting a 13 MHz tone over the connection cable from the customer modem unit. the tone is isolated using a filter 400. This filter 400 is arranged to allow signals within a 50 kHz bandwidth centered at 13 MHz to be received by the RF synthesizer 280.

Furthermore, certain control signals may be transmitted via a connection cable between the customer modem unit 130 and the RF block 110. To facilitate this transmission of control signals, a serial communication controller 410 is provided within the RF block 110, which is configured to transmit and receive signals centered at a frequency of 455 kHz. To isolate signals within the 20 kHz bandwidth centered at 455 kHz, which are transmitted via a connection cable from the customer modem unit 130 for subsequent processing by the serial communication controller 410, a filter 420 is used. Further, the signals transmitted by the serial communication controller 410 the 455 kHz frequency will be transmitted through the filter 420 and via the connection cable to the customer modem unit 130. Thus, the serial communication controller 410 enables two-way communication with the CDMA modem in the customer modem unit (CMU) 130. The serial communication controller modulates the carrier binary data. In preferred embodiments of the invention, the data transmitted from the RF includes: 4 44 4444 4444

4 4 • 4

444 · «» 4 4 • 4 4 • 4 4

4 4 »

4 · * 4 of block 110 to CMU 130, only the transmitted power level P indication. Preferably, however, the data transmitted from the customer modem unit 130 to the RF block 110 may include the following:

1. Transmit On / Off Control Signal (Cl);

2. Calibration Transmission Control Signal (C4);

3. Calibration receive control signal (C3);

4. Gain Adjustment Control Signal (Volume Switch), (C2); and

5. Indication of received signal strength (used in installation mode).

The above control signals C1 to C4 are then output by the serial communication control unit 410 to the respective components within the RF block 110 as illustrated in FIG. 5. In addition, the received signal strength indication may be used to drive LEDs 430 provided on the RF block 110 so as to provide a visual indication of the strength of the received signal, which, as discussed in more detail later on, is useful during installation. Alternatively or additionally, an indication of received signal strength may be transmitted to DAC 440 (Digital to Analog Converter) to produce an analog signal at the output port of RF block 110. A device, such as a voltmeter, may then be connected to that output port to receive the received signal indicating signal.

In preferred embodiments of the invention, the energy required to operate the RF block 110 is received through the customer modem unit 130 and via a connection cable.

120. The DC-DC converter 450 is formed in the RF block 110 to process the received power signal to generate a regulated voltage to power the circuits within the RF block.

The customer modem unit 130 will now be discussed in more detail with reference to Figs. 6 and 7. As illustrated in Fig. 6, the customer modem unit 130 includes a radio modem card 500 that is connected to a connection cable 120, wherein the radio modem the modem card 500 communicates with the RF block 110 via a connection cable 120 at an intermediate frequency. The radio modem card 500 includes all of the functions required to realize the baseband portions and the IF portions of the CDMA modem. As mentioned earlier, the radio modem card 500 is designed as a generic modem to be manufactured in large volumes independently of the customer interface. The interface with the customer interface card 510 is designed to support all of the envisaged applications, including 1 to 4 line POTS services, base rate ISDN and D128 data services. A more detailed description of the radio modem card will be given later with reference to Fig. 7B.

Customer interface card 510 is coupled to radio modem card 500 and includes the following features:

1. CPE interface, one or two line POTS, or ISDN. Preferably, the POTS CPE interface utilizes a programmable digital signal processor (DSP) to implement voice compression, tone generation and detection. Direct mixed balance and gain adjustment can also be realized through the DSP, but alternatively, these functions can be realized by external circuits;

• 4 · · · · · · · ·

«4

2. A microcontroller with two fully software images stored in FLASH memory for software used to control a customer interface card, downloadable over the air or through a local access terminal (LAT) port. A software image is a specific case of a portion of the software, providing two software images allows one to be active while the other is in a standby mode, allowing the waiting image to be updated while the active image is working;

3. Local Access Terminal (LAT) port;

4. Reset switch;

5. Radio modem card interface 500;

6. Power converter switch, battery charger and backup switch;

7. LED panel driver; and

8. Smart card interface.

As illustrated in FIG. 6, the customer modem unit 130 also includes one lead-acid accumulator 530, the accumulator having a rated output voltage of 12 volts and for backup power supply. In a preferred embodiment, access for the battery is provided by a removable panel on the customer modem unit. Loose or coupled leads can be used to connect the battery to the customer interface card 510, which includes circuitry for charging the battery and switching to battery power in the event of a DC input failure.

The LED panel 520 is also provided in the customer modem unit 130 in preferred embodiments of the invention, the LED panel being utilized to provide a state-of-the-art; <φ • · · * e * * ··· »· ·· In preferred embodiments, the following indications are provided:

Position Type Function Off Flashing On (red) On (green) 1 red error j ednotka he is OK j ednotka requires configuration error 2 green power supply without power supply switched to accumulator - DC input he is OK 3 two- colored connection none connection connection Yippee active Descending connection he is OK

It should be apparent to those skilled in the art that an LCD panel could be used instead of the LED panel.

After this description of the main elements of the customer modem unit 30, the circuits within the radio modem card will now be discussed in more detail with reference to Fig. 7A.

500 used to perform IF processing.

Considering first the IF signal transmitted to the radio modem card 500 from the RF block 110 via the connection cable 120, this signal will be received by a duplex filter formed by filters 600 and 605. The duplex filter is arranged such that the filter 600 allows the IF signal to pass into path 604. while the filter 605 will prevent the signal from passing into the path 602. The received signal is therefore passed via the path 604 to the variable attenuator 640 before it is passed through the amplifier 630 to the mixer 650. The variable attenuator 640 is controlled.

CDMA modem inside the radio modem card (which will be

• ι · ·

discussed in more detail in the description below with reference to FIG. 7B) and is used to compensate for the losses introduced by the connection cable 120.

The mixer 650 also receives a signal from the first IF synthesizer 665, which is referenced to the 13 MHz frequency reference oscillator 700. Oscillator 700 is controlled by a CDMA modem inside the radio modem card 500 as part of the AFC loop. The first synthesizer 665 may be programmed to any of the twelve 3.5 MHz channels within the 42 MHz band dividing the range 815.75 to 854.25 MHz, and thus performs RF channel selection. The components f _x + f ₂ and - f ₂ then formed by the mixer 650 are amplified by the amplifier 655 before being passed to the SAW filter 660 (saw filter). The SAW filter 660 is configured to allow signals in the 3.5 MHz bandwidth centered at 100 MHz to pass through the filter, and thus this SAW filter 660 removes the component f _x + f ₂ generated by the mixer 650. This 3.5 MHz SAW filter 660 actually isolates the RF channel selected by the first IF synthesizer 665.

The output of the SAW filter 660 is then routed through a matching network of resistors 672, 674, 676 to a variable amplifier 680, which amplifier 680 performs automatic gain control (AGC). The signal is then transmitted to the demodulation circuit 690, which performs quadratic demodulation to baseband components I and Q. The I component is then fed via amplifier 694 to the CDMA demodulator inside the radio modem card 500, while the Q component is fed via amplifier 692 to the CDMA demodulator.

A more detailed illustration of the demodulation circuit 690 is provided in FIG. 8A. As can be seen, the AGC signal ’·

4 • 4 * 4444

In 4 * 4

4 •:

The amplifier 680 is divided into two separate signals, one received by the mixer 702 and one received by the mixer 704. The circuit 706 divided by 4 is arranged to produce four 100 MHz signals, phase shifted 90 ° from each other, from the 400 MHz signal generated by the second IF synthesizer 695, wherein the second IF synthesizer 695 is also referenced to an oscillator 700 of the 13 MHz frequency reference. The mixer 702 receives one of these 100 MHz signals and then uses its two input signals to form an I component. Meanwhile, the second

The 100 MHz signal, phase shifted by 90 °, is fed to the mixer

704, and the mixer 704 then extracts the Q component from the phase shifted 100 MHz signal and the second input signal.

Considering now the signals to be transmitted by the subscriber terminal, the I and Q components of the transmitted signal are first passed through the filters 730 and 735, respectively. The two filters have a 2 MHz bandwidth in preferred embodiments of the invention and serve to extract the basis from digitally generated signals. The outputs of filters 730 and 735 are then amplified by amplifiers 740 and 745, respectively, before being fed to circuit 750. Circuit 750 is illustrated in more detail in FIG. 8B. As illustrated in FIG. 8B, the I component of the signal is received by the mixer 752 and the Q component of the signal is received by the mixer 754. Both mixers also receive the signal from the first IF synthesizer 665, although the signal received by the mixer 754 is phase shifted by 90 °. before receiving the mixer 754. As mentioned in the foregoing description, the first IF synthesizer 665 operates at a frequency of from 815.75 to

854.25 MHz and can be programmed to any of the twelve

3.5 MHz channels within the 42 MHz band to perform RF selection

’9 9>« 9 »9 9 * · 9999: ι:.: I:!

9 9 1 <9 8

999 99 99 99 channels. The signals produced by the mixer 752 and 754 are then transmitted to the combiner 756 where they are combined to form a single signal.

The combined signal is then routed through an adaptive network formed by resistors 762, 764, 666 to amplifier 775. The signal output of amplifier 775 is then routed through a variable attenuator 780 and an adaptive network formed by resistors 782, 784 and 786. Then the signal is again fed through variable attenuator 795 before being fed to amplifier 810.

Then, the signal is routed through variable attenuator 815 before it is routed via path 602 to a duplex filter formed by filters 600 and 605. The variable attenuator is arranged to compensate for losses that will be introduced by the connection cable 120. The filter 605 is then arranged to forward the signal on the path 602 to the connection cable 120, while the filter 600 then prevents this signal from propagating on the path 604.

As also illustrated in FIG. 7A, the 13 MHz frequency reference generated by the oscillator 700 is passed through a filter 825 having a bandwidth of 50 kHz centered at a frequency of 13 MHz. The output of the filter 825 is then routed to a connection cable 120 for transmission over that cable to the RF block 110. As mentioned above, for the AFC loop within the RF block 110 to operate correctly, the RF synthesizer 280 within the RF block 110 must be phase bound to 13 MHz frequency reference generated by the oscillator 700 in the customer modem unit 130. By transmitting this 13 MHz tone through the connection cable, this desired phase lock of the RF synthesizer can be provided.

I ί

• * 9 • 9 9999 «

999

Further, as illustrated in Fig. 7A, a serial communication control unit 830 is provided to allow slow speed bidirectional communication with the RF block 110, wherein the serial communication control unit 830 modulates the 455 kHz carrier binary data in amplitude. This signal is then routed through a filter 840 having a bandwidth of 20 kHz centered at a frequency of 455 kHz, and from there the signal is routed to the connection cable 120. The filter 840 also serves to isolate any control signals emitted by the RF block 110 and As mentioned in the foregoing description, in preferred embodiments of the present invention, RF block 110 may, for example, output a control signal identifying the power level of the transmitted signal. The filter 840 then isolates this signal and passes it to the serial communication controller 830.

The radio modem card 500 is configured to provide DC power to the connection cable 120 for transmission to the RF block 110 to power the components of the RF block.

The CDMA modem inside the radio modem card 500, which is used to control the circuit shown in FIG. 7A, will be described in more detail below with reference to FIG. 7B. The CDMA modem according to the preferred embodiments of the present invention consists essentially of a digital signal processor (DSP) 855 that is coupled to both the CDMA modulator 850 and the CDMA demodulator 860. The RXI and RXQ signals generated by the demodulation circuit 690 are routed through an ADC converter 868 and 870, respectively, before being received by the CDMA demodulator 860.

:. ·

· * 99

The CDMA demodulator 860 then performs CDMA demodulation under the control of DSP 855 and outputs the received data (Rx data) and the received clock (RX clock) to the customer interface card 510. The CDMA demodulator 860 also generates a sync signal used to synchronize different circuits within the customer. This synchronization signal is fed to the customer interface card 510 and also fed to the CDMA modulator 850.

CDMA demodulator 860 receives data (Tx data) and clock (Tx clock) signals from ST (subscriber terminal) to connected telecommunications equipment via customer interface card 510. This data is then used by CDMA modulator 850 to generate CDMA modulated I and Q signals under DSP control 855, which signals are routed through respective DACs 862 and 864 to generate TXI and TXQ signals input to the circuit shown in FIG. 7A.

The DSP 855 has a processor host interface with a customer interface card 510 to enable communication with a microcontroller located on the customer interface card. Further, the DSP 855 can receive signals from the CDMA demodulator 860, such as signal strength details used by the DSP during ST installation, as will be described in more detail below.

The DSP 855 is configured to generate various signals used to control the circuit shown in Fig. 7A. Thus, the DSP outputs signals to the multiple DAC 866, which then outputs the AFC signal input to the oscillator 700 to perform automatic frequency control and outputs the TX_GC and RX_GC gain control signals input to the variable attenuators 780, 795 and the variable amplifier 680 for ί. 1 .f 9 I Control the gain of transmitted and received signals during normal operation.

Further, the DSP 855 generates a broadcast enable signal (TX_EN) used to control circuit 750 and amplifiers 775 and 810 to enable transmission. In addition, during circuit calibration (e.g., during installation), DSP 855 generates TX_COMP and RX_COMP signals used to control variable attenuator 815 and 640, respectively, to compensate for losses caused by transmitting uplink and downlink IF signals via interface cable 120. This process will be described in more detail below. description.

Finally, the DSP 855 is responsible for generating the various control signals (SCC_DATA) transmitted to the serial communication control unit 830 for transmission via the connection cable 120 to the RF block 110. In addition, the DSP 855 will receive via the serial communication control unit 830 any control signal emitted by the RF block 110. for example, an indication of the power level of the transmitted signal.

After describing the circuit of the RF block 110 and the radio modem card 500, the signals transmitted between the two units via the connection cable 120 will now be discussed in more detail with reference to FIG. As mentioned in the foregoing, the connection cable 120 preferably includes a two-wire coaxial cable carrying the following signals between the radio modem card 500 and the RF block 110:

scattered spectrum uplink IF signal;

scattered spectrum downlink IF signal;

MHz frequency reference;

· »« * ♦ * 4 »44 *» · · · w • 4 44 4 ¹ 4 • »• 10 4

4. 455 kHz carrier data link; and

5. DC power supply, preferably 10 to 20V.

As mentioned above, the elements of the RF block 110 are in preferred embodiments controlled by a CDMA modem on the radio modem card 500. The digital data is modulated by a pulse position on a 455 kHz carrier, this frequency being selected due to the easy availability of ceramic filters and resonators. since it is not harmonically related to the 13 MHz frequency reference signal (13 / 0.455 = 28.5714). In preferred embodiments of the invention, each data bit is transmitted using a line code that includes a start beat, a data bit, and a stop bit. The correlation between the data bit and the link code is in the preferred embodiments of the present invention as follows:

Data bit Line code 0 100 ALIGN! 1 .... 110

Preferably, the data is transmitted in packets as follows:

Packet element Number of bits Synchronization header 3 Address 1 Useful content 8 Parity 1

1!

♦ * * • 9 9 • 9 · 99

* »9» 9

In preferred embodiments of the invention, packets are multiplexed with a time division every 30 ms. The CMU controller preferably acts as a master protocol controller that begins communication every 30 ms. The header preferably includes a fixed sequence, say 001. In addition, the address is usually set to zero to communicate with the RF block 110, the non-zero address being used to communicate with equipment other than the RF block. for example with a signal strength measuring device.

The payload preferably includes 8 bits and the packet is protected by an error of one parity bit.

Giant. 10 provides a more detailed illustration of the serial communication control unit 830 and the filter 840 illustrated in FIG. 7. The oscillator 900 is configured to generate a carrier signal at 455 kHz. The control inputs transmitted to the serial communication control unit 830 then cause the control data to be output from the serial communication control unit 830 to the switch 910, wherein the switch 910 modulates the data to a 455 kHz carrier signal by pulse position. This signal is then routed to a filter 840 that allows a 20 kHz bandwidth centered at 455 kHz to be output to the connection cable 120.

For the control signal issued by the RF block 110, the filter 840 will isolate the signal and then forward it to the diode 920 which will rectify the signal. The rectified signal is then passed to salt pass 930, which removes the 455 kHz carrier signal.

The output of the low pass filter 930 is then routed to a comparator

940, wherein this signal is compared to a threshold voltage to produce a digital signal output for transmission to the serial communication control unit 830. Controller 830 30 The serial communication then uses this signal for parallel control outputs.

The architecture illustrated in FIG. 10 is also applicable to the serial communication controller 410 and to the RF block filter 420 shown in FIG. 5. The serial communication controller within the RF block 110 may also process the RF synthesizer configuration 280 on power-up. .

Following this detailed description of the ST, according to preferred embodiments of the present invention, the installation of the ST is now discussed. Important aspects of the installation process are unit configuration and antenna alignment.

The configuration data must be loaded into the unit before the ST is switched on. For example, the following minimum information may be required:

1. number of RF channels;

2. PN code; and

3. ST identifier (preferably a six-digit number).

There are two options for entering this data. First, if an LAT port is provided, as in the case of a customer modem unit 130 according to the preferred embodiments of the invention illustrated in Fig. 6, then an external terminal may be used to configure the unit. This technique would generally be used for an ST with an ISDN or D128 interface. An alternative approach is to use a telephone connected to the ST, * * * * * ·· * «·« ·> I t I I I I I I I I t t t t t Whereas such an approach is usually used when the ST is to be used for signaling ΡΟΤΞ. A technique that can be used for this purpose is described in detail in patent application GB-A-2,301,738.

Once the necessary configuration data has been entered, in preferred embodiments of the invention a calibration step ST is performed with respect to signal losses caused by the connection cable. The technique used in preferred embodiments for performing this calibration will now be described with reference to Figs. 5, 7A and 7B.

Firstly, to calibrate the downlink path to compensate for the loss incurred by the connection cable, the DSP 855 generates the control signal C3 to receive the calibration on the SCC_DAT channel, which is then transmitted by the serial communication controller 830 via the connection cable 120 to the serial communication controller 410 in RF block 110. Preferably, the calibrated noise source generates an additive white Gaussian noise at a predetermined power level. This noise signal is then routed through the receive path circuitry of Fig. 5, via the connection cable 120, and through the receive path circuitry of Fig. 7A to form the RXI and RXQ components, which are routed to the CDMA demodulator 860 of the CDMA modem illustrated in Fig. 7B.

Here are stored predetermined criteria that the calibrated noise source should exhibit when received by the CDMA demodulator 860 if the loss of the connection cable has been compensated. By comparing the actually received noise signal with these predetermined criteria, * 446 *

44

44 «

4 «

The CDMA demodulator determines whether the setting of the variable attenuator 640 should be increased or decreased. One example of a predetermined criterion that can be stored is the frequency with which signals outside the number of standard deviations from the Gaussian signal peak should be received.

Since the noise signal is digitized before receiving the CDMA demodulator 860, the CDMA demodulator may be arranged to store the number of times the signal is outside a predetermined number of standard deviations and may alert the DSP 855 if the number exceeds a certain threshold, indicating that variable attenuator setting. 640 should be changed.

When the DSP 855 receives a signal from the CDMA demodulator 860, identifying that the variable attenuator 640 setting should be changed, it generates an RX_COMP signal to be passed to the variable attenuator 640 to change its settings. By appropriately adjusting the variable attenuator 640, the losses introduced by the connection cable into the receiving path can be compensated.

To calibrate the uplink path to compensate for the loss of connection cable, the DSP 855 is arranged to instruct the CDMA modulator 850 to generate, in preferred embodiments of the invention, a calibrated noise signal for transmission through the transmission path circuits of FIGS. 7A and 5. for the noise signal to be transmitted from the antenna 202

The DSP 855 also generates a control signal C4 at the SCC_DATA output that is routed via the radio modem control unit 830 via the connection cable 120 to the serial communication control unit 410 in the RF block 110, causing the serial communication control unit 410 to 30 will issue this one

to ···:

to control signal C4 to switch 370 to ground the transmitted signal.

However, the connector 385 of the RF block 110 still receives the transmitted noise signal and thus provides an indication of the power level P of the transmitted signal. This indication P is applied to the serial communication control unit 410 in RF block 110, which then forwards this information via the connection cable 120 to the serial interface control unit 830 in the radio modem card 500. This data is then fed to DSP 855 via SCC_DATA channel, and The DSP 855 compares the indication s with a predetermined value to determine whether the setting of the variable attenuator 815 should be changed. If a change in setting is needed, then the DSP outputs a suitable TX_COMP signal to variable attenuator 815 to change its setting. Through this approach, losses introduced by the connection cable into the transmission path can be compensated.

Once the necessary calibration steps have been performed, the subscriber terminal antenna 100 is preferably directed toward the central terminal with which it is to communicate. Because the antenna is usually mounted in an elevated position on the outside of the customer building, the installer will usually have to climb up to the antenna mounting location and manually orient the antenna unit.

Where a LAT port is fitted to the subscriber terminal, an external terminal may be connected to monitor the strength of the received signal, which may thus act as an antenna setup guide. However, since the LAT port, if any, will usually be created in the customer modem unit 130 located within the customer building, such access is then very awkward if it is to be performed by one installer and so usually by two installers, one for antenna setup and one for monitoring the received signal strength.

According to preferred embodiments of the present invention, a number of simplified options are available to assist in aligning the antenna. All of these options require the ST to be placed in a special mode of operation that prevents normal operation. This could be achieved, for example, by entering a special code in the subscriber terminal after the unit has been reset. The unit would then remain in antenna alignment mode to allow the device to complete its installation.

The strength of the received signal is measured on the scattered data in the CDMA demodulator 860 within the customer modem unit 130, where the actual signal power can be differentiated into the input noise. One way to eliminate the requirement to mount an external terminal via the LAT port is to use the LED / LCD panel on the customer modem unit to indicate the received signal strength. However, this would still normally require two installers to perform the installation.

Thus, an alternative option is to incorporate the LEDs into the RF block 110 to indicate the strength of the received signal, as discussed in the preceding description with reference to Fig. 5. Because the RF block 110 is likely to be located very close to the antenna unit 100 and additionally in some embodiments both the RF block 110 and the antenna unit 100 will be integrated into the same physical device, then the antenna adjuster can also follow the LED indication on the RF block 100. However, as mentioned in • 444 • 4

4

4

4 ·

4 4 4 '4

4 4 4

4 above, the received signal strength is preferably measured in the CDMA demodulator 860 within the customer modem unit 130. Thus, in preferred embodiments, the received signal strength, as determined by the CDMA demodulator 860, is then routed via DSP 855 to the SCC_DATA output and transmitted back via the linker. cable 120 via a serial communication link and is then displayed on the LEDs on the RF block 110.

As illustrated in FIG. 5, as an alternative or in addition to the LEDs, a DAC 440 ¹⁰ may be formed in the RF block 110 to generate an analog signal (RSSI) of the received signal strength at the RF output port 110. Then, a device such as a voltmeter can be connected by the installer to provide an indication of the strength of the received signal.

In addition, since in preferred embodiments of the present invention, the ST has already been calibrated before performing the antenna alignment process, to compensate for loss introduced by the connection cable, the LEDs or voltmeter can be calibrated to provide a direct value of the received signal strength to the installer.

Yet another alternative approach, shown in FIG. 11, is to place a signal strength measuring device 960 in the line with the connection cable 120.

As before, the received signal level is transmitted to the RF block 110 via a connection cable using a serial communication line, but in this case it is received by the meter 960. The signal strength level is then displayed on an LED or LCD panel formed on the received signal strength meter 960. When the alignment is complete, the measuring device is • 9 · • 9 9999 • 9 φ • 99 99

9 9 9

9 9 9 ··

The received signal strength 960 is removed and the connection cable is attached to the RF block 110.

The main advantage of providing any of the indicating mechanisms in the RF block or a separate meter connected to the cable near the RF block is that the signal strength can be evaluated near that RF block, allowing the ST (central terminal) to be installed by one person. In addition, in preferred embodiments of the present invention, the indication may be calibrated to provide a direct indication of the fading edges, i.e., the amount of deviation in dB prior to loss of the communication path.

It should be apparent to those skilled in the art that the device used to provide an indication of the strength of the received signal is not relevant to the present invention. Any type of visual or audible indication could be used as appropriate.

Although certain embodiments of the present invention have been described herein, it should be understood that the present invention is not limited to this exemplary embodiment and that many modifications and additions may be made within the scope of the present invention. For example, various combinations of features of the following dependent claims could be made with features of the independent claims without departing from the scope of the present invention.

Claims (19)

A subscriber terminal for communication over a wireless link to a central terminal of a wireless telecommunications system, comprising: a first signal processing unit associated with an antenna for transmitting and receiving signals over the wireless link; a second signal processing unit remote from the first signal processing unit and associated with the telecommunication equipment element for transmitting signals between said telecommunication equipment element and the first signal processing unit; a coupling medium connecting said first and second signal processing units; calibration logic within said second signal processing unit to provide on the coupling medium of the control signals used to control the circuits in the first signal processing unit and for supplying an RF signal having a predetermined power level to the coupling medium between the first signal processing unit and the second unit for signal processing, to enable the calibration logic, to determine the RF power losses introduced by the coupling medium; calibration logic-controlled compensation circuits to compensate for RF power losses determined by the calibration logic. The subscriber terminal of claim 1, wherein the compensation circuits are formed in a second signal processing unit. The subscriber terminal according to claim 1 or 2, wherein the calibration logic is arranged to provide a first pilot signal on the bonding medium to provide a &quot; ft &quot; And (e) issuing a first test signal having a predetermined power level to the bonding medium by the first signal processing unit, the calibration logic being arranged to determine from the first test signal; as received by the second signal processing unit, RF power loss of the received signal introduced by the linking medium. The subscriber terminal of claim 3, wherein the compensation circuits comprise a first variable attenuator that is configured to be adjusted by the calibration logic to compensate for the determined RF power loss of the received signal. The subscriber terminal according to any of the preceding claims, wherein the calibration logic is arranged to provide a second test signal having a predetermined power level issued by the second signal processing unit to the bonding medium and to output the second pilot signal to the bonding medium. to ensure that the first signal processing unit prevents the second test signal from outputting from the antenna. The subscriber terminal of claim 5, wherein the first signal processing unit is configured to determine an indication of the signal strength of the second test signal in the first signal processing unit, and to output the indication to the coupling medium to the second signal processing unit. for use by the calibration logic to determine the RF power loss of the transmitted signal introduced by the linking medium. ·· «· ···« ··· • a · a a aaa aa aaaa · * · ·· ·· · The subscriber terminal of claim 5 or 6, wherein the compensation circuits comprise a second variable attenuator that is configured as adjustable by the calibration logic to compensate for the determined RF power loss of the transmitted signal. The subscriber terminal of any one of the preceding claims, wherein the first signal processing unit comprises a first serial communication control unit for receiving control signals from the second signal processing unit. The subscriber terminal of claim 8, wherein a second serial communication controller is provided in said second signal processing unit, which is configured to communicate with said first serial communication controller via said linking medium, wherein the calibration logic is arranged. for outputting a signal to the second serial communication controller to ensure that the second serial communication controller transmits the control signals via the linking medium to the first serial communication controller in the first signal processing unit. The subscriber terminal according to any of the preceding claims, wherein the second signal processing unit additionally comprises: a signal strength determining logic for determining the signal strength of a signal received by the first signal processing unit via the antenna and transmitted to the second signal processing unit via the linking medium, the signal strength determining logic being arranged to be provided on the linking medium of the indicating signal representing the received signal strength 9 ··· · 9 · 9 9 99 99 signal; wherein the indicator, located or positionable on or near the antenna, may be actuated in response to the indicator signal provided on the linker to provide an indication of 5 the received signal strength. The subscriber terminal of claim 10, wherein said first signal processing unit comprises said indicator. The subscriber terminal of claim 10 or 11, wherein the indicator is connectable to an output port of said first signal processing unit. The subscriber terminal of claim 11 or 12, wherein the first signal processing unit 15 and the antenna are integrated into a single housing. The subscriber terminal of any one of claims 10 to 13, wherein said indicator comprises a plurality of LEDs to provide said indication of the strength of the received signal. 15. The subscriber terminal of claim 10, wherein said indicator is connectable to said coupling medium. A subscriber terminal according to any one of claims 10 to 25 15, characterized in that said signal strength determination logic comprises a demodulator for determining the strength of the received signal and a processor for generating an indicator signal outputted through the linking medium for controlling the indicator. • 4 ·· 4 · ·· ♦ ·· The subscriber terminal according to any one of the preceding claims, wherein the connection medium is a coaxial cable. A second signal processing unit for a subscriber terminal according to any one of the preceding claims, characterized in that the second signal processing unit comprises calibration logic to provide control signal coupling media used to control the circuits in the first signal processing unit and / or a second signal processing unit and for supplying one signal having a predetermined power level to the coupling medium between the first signal processing unit and the second signal processing unit to enable the calibration logic to determine the RF power losses introduced by the coupling medium. 19. A method of calibrating a subscriber terminal configured to communicate over a wireless link with a central terminal of a wireless telecommunications system, the subscriber terminal comprising a first signal processing unit associated with an antenna for transmitting and receiving signals over the wireless link, a second signal processing unit remote from the first a signal processing unit associated with the telecommunications equipment element for transmitting signals between said telecommunications equipment element and the first signal processing unit, and a connecting medium connecting said first and second signal processing units, comprising the steps of: (a) providing on the control medium the control signals generated by the second signal processing unit; (b) transmitting the RF signal having a predetermined power level on the coupling medium between the first signal processing unit and the second signal processing unit; (c) using the signal received after step (b) to determine in said second RF power signal processing unit 5 losses introduced by the binding medium; (d) responsive to the determination in step (c) of controlling the compensation circuits to compensate for signal loss.