PATENT DOCUMENT

Abstract:
A repeater mediates traffic between a network transceiver and a user transceiver in a wireless communication system. The repeater comprises a network unit that maintains a network link with the network transceiver, a user unit that maintains a user link with the user transceiver, a two-way communication pathway between the network unit and the user unit; that facilitate the communication of signals between the network transceiver and the user transceiver in autonomous repeater hops between the network transceiver and the network unit, between the user transceiver and the user unit, and between the network unit and the user unit, and a gain controller that compensates for propagation losses between the network unit and user unit alone.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application, filed under 35 U.S.C. §371, of and claims priority to International Application No. PCT/US2004/029123, filed on Sep. 23, 2004, which in turn claims priority to U.S. Provisional Pat. App. Ser. No. 60/499,693, filed on Sep. 23, 2003. 
     BACKGROUND 
     The existing cellular networks, such as (Global System for Mobile Communications (GSM) and IS95, are intended to provide a contagious and continuous coverage, so as to support the high terminal mobility expected from such systems. However, despite careful network design, indoor (in-building) coverage, or the coverage of places with high shadowing attenuation (e.g. tunnels) of such networks is often “patchy”, with “coverage Holes” at best, and no coverage at worst. The reason for the impaired indoor coverage is that the cellular base stations are usually placed outside buildings, higher than the average building heights, to provide large area coverage. Although the signal may be adequate at “street-level”, it is severely attenuated by the building material, reducing the signal power in-building, resulting in the poor converges. Loss of signal power (attenuation) depends on the building material and can be tens of dBs for each wall penetration. The problem is exacerbated in the 3 rd  generation systems such as Wideband Code Division Multiple Access (WCDMA) and cdma2000, as these new systems have the capability of high data transmission, which results in lower information bit energy (E b ), and much reduced link budget and cell foot-print. Currently, the common solutions for providing indoor coverage are:
         I) More outdoor base stations in the same geographical area, supporting smaller cell sizes.   II) Microcells.   III) Picocells (in-building cells).   IV) Conventional repeaters.       

     Clearly all the above solutions (except the repeater solution) are very expensive and involve extensive investment in the cellular network infrastructure and are much more complex in planning and operation. There are other solutions such as repeaters that can be used to boost the signal in a given geographical area. 
     The repeater solution, although cheaper than a base station, has several drawbacks. These outdoor repeaters are still too expensive for a private user, and involve careful planning. Most use large directional antennas, or additional backhaul frequencies to reduce antenna gain specifications, which results in lower spectral efficiency and are capacity limited. The repeaters often cause increased interference in the network, as they are outdoor devices, similar to base stations, and hence are not popular as a viable solution for providing high performance indoor coverage. The indoor repeaters are still cheaper than the outdoor version, but typically involve installation of high directional antennas on the roof, and ensured antenna isolation, creating costly demand for skilled installation and operation. Therefore, the system generally remains too complicated for an unskilled user and not sufficiently inexpensive for usage in a very localized coverage area. 
     SUMMARY 
     In accordance with an embodiment of a communication device, a repeater mediates traffic between a network transceiver and a user transceiver in a wireless communication system. The repeater comprises a network unit that maintains a network link with the network transceiver, a user unit that maintains a user link with the user transceiver, a two-way communication pathway between the network unit and the user unit; that facilitate the communication of signals between the network transceiver and the user transceiver in autonomous repeater hops between the network transceiver and the network unit, between the user transceiver and the user unit, and between the network unit and the user unit, and a gain controller that compensates for propagation losses between the network unit and user unit alone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention relating to both structure and method of operation, may best be understood by referring to the following description and accompanying drawings whereby: 
         FIG. 1  is a schematic block diagram illustrating an embodiment of a cellular network with two base stations; 
         FIG. 2  is a schematic block diagram depicting an embodiment of a forward-link part of a repeater; 
         FIG. 3  is a schematic block diagram showing an embodiment of a reverse-link part of a repeater; 
         FIG. 4  is a schematic block diagram illustrating an embodiment of a system including a Network unit and a User unit; 
         FIG. 5  is a schematic block diagram that illustrates an embodiment of a system including a Network unit implementing antenna diversity; 
         FIG. 6  is a schematic block diagram depicting an embodiment of a repeater that uses two antennas for antenna diversity; 
         FIGS. 7-11  are flow charts depicting embodiments of system operation flow for a network unit ( 7 - 9 ) and a user unit ( 10 - 11 ); 
         FIGS. 12 and 13  are schematic block diagrams showing embodiments of digital repeater implementations; 
         FIG. 14  is a schematic block diagram showing an embodiment of an analog implementation of a back-to-back repeater; 
         FIG. 15  is a schematic block diagram showing an embodiment of a digital implementation of a back-to-back repeater; 
         FIG. 16  is a flow chart showing an embodiment of operation flow of a back-to-back repeater; 
         FIGS. 17 and 18  are a simplified block diagram to illustrate a channel filtering operation; 
         FIGS. 19-22  are schematic block diagrams showing other repeater embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The system disclosed herein provides better, and localized indoor coverage without causing excess interference in the network, usage of costly equipment or network planning. The system increases the overall network capacity, reducing the mobile and BTS transmit power, increasing the battery life and reducing the “harmful” radiation to the user. 
     Descriptions of the illustrated embodiments are based on a GSM (Global System for Communications) network, which is a TDMA based system operating at various spectrum bands, depending on the country and the region&#39;s regulations. However, the disclosure, with minor modifications, is equally applicable to any other cellular system, including (but not limited to) IS95, cdma2000 and WCDMA, and wireless LAN systems such as 802.11a, b, and g. Although the description is given for cellular systems, with minor modifications, it can equally be applied to other systems such as GPS or any other system that uses signal-boosting capability. The operating frequency can be at any desired part of communications spectrum used for mobile communications (e.g. PCS 1900, or DCS1800 or GSM900 or UMTS 2000, ISM or UNII band). The description here is only intended as an example and as such utilization of the booster is not only limited to the in-building coverage and can be used in other places such as trains, planes, cars, tunnels, etc. Also, the example may not include all minute or unimportant design details. Units and sub-units discussed and explained hereafter meet regulations of the respective licensed and unlicensed band of operation. Therefore, for the different example implementations and embodiments disclosed, specifications including maximum transmit power, spectral mask, out of band radiation, and others for transmitters, receivers, repeaters and boosters, are met for both licensed and unlicensed bands of operation. 
     Analogue Implementation Example 
       FIG. 1  shows a cellular network  100  with two base stations (BTS 1  ( 101 ) &amp; BTS 2  ( 102 )). A typical network supports more than two base stations. The disclosed system may be applied in any size network, regardless of the supported number of base stations. BTS 1   101  is connected to Base Station Controller BSC 1   107 . BTS 2   102  is connected to Base Station Controller BSC 2   108 . BTS 2   102  can also be connected to Base Station Controller BSC 1   107 , instead of BSC 2   108 . BSC 1   107  is connected to Mobile Switching Center MSC  109 . BSC 2   108  is connected to MSC  109 , or instead may be connected to another MSC in the network. MSC  109  is connected to PSTN  110 . BTS 1   101  has an associated coverage area  103 . BTS 2   102  has an associated coverage area  104 . These coverage areas may or may not overlap. However, usually the network is planned such that there is considerable overlap, to facilitate handoffs. The mobile terminal  105  is inside building  106 , in the coverage area  103  communicating with BTS 1   101 , using a traffic channel transmitted at around frequency f 1  in the forward-link and its associated reverse-link frequency, f 1 ′. The traffic channel can be one of the available time slots on the BCCH carrier, or may be on a TCH carrier, where frequency hopping may be used to reduce interference. Mobile terminal  105  may or may not be in coverage area  104 , but the mobile unit  105  is well within the coverage area  103  and average signal power from BTS 1   101  is much stronger than the average signal power from BTS 2   102 , within the building  106 , and the locality of mobile unit  105 . Root-mean-square (rms) forward-link signal level Ŝ 1 , outside the building  106  is higher than the rms signal level Ŝ 2  inside the building by the wall penetration loss α. The loss α may be such that Ŝ 2  is not at sufficiently high level for the User unit  105  to maintain reliable communication with BTS 1   101 , or BTS 2   102 , or both BTS 1   101  and BTS 2   102 . Further, the signal level Ŝ 2  may be such that mobile unit  105  may have difficulty to setup and maintain a communication link with BTS 1   101  or BTS 2   102 , or both BTS 1   101  and BTS 2   102 , or the communication link does not have the desired performance and reliability, in all or some of the in-building areas. The coverage problem inside the building  106  may be solved by more transmit power from BTS 1   101  in the down-link to combat the signal loss, by the wall penetration loss, a. The r.m.s. reverse-link signal level Ŝ 1 , inside the building  106  is higher than the r.m.s. signal level Ŝ′ 2 , outside the building, by the wall penetration loss α′. The loss α′ may be such that Ŝ′ 2  is not at sufficiently high level for the User unit  105  to maintain reliable communication with BTS 1   101 , or BTS 2   102 , or both BTS 1   101  and BTS 2   102 . Further, the signal level Ŝ′ 2  may be such that mobile unit  105  may have difficulty to setup and maintain a communication link with BTS 1   101  or BTS 2   102 , or both BTS 1   101  and BTS 2   102 , or the communication link does not have the desired performance and reliability, in all or some of the in-building areas. The coverage problem inside the building  106  may be solved by more transmit power from mobile unit  105  in the up-link to combat the signal loss, by the wall penetration loss, α′. Usually the forward and reverse link frequency pairs are sufficiently close, such that a level is substantially similar to α′ level. 
       FIG. 2  depicts a forward-link part  230  of the repeater  200 . The forward-link portion  230  in a simple form supplies improved indoor coverage by boosting the signal level in building in the forward-link of the cellular network. BTS 1   213  has a BCCH radio channel (beacon channel) transmitted substantially close to f 1 . BTS 1   213  is in communications with the mobile unit  214  at a frequency substantially close to f 1  (the BCCH carrier frequency) or another carrier frequency, f 2 , that may or may not be frequency hopping. There may or may not be other frequencies that are transmitted by BTS 1   213 , or other base stations in the same area, which are not shown in the  FIG. 2 . 
     The device has two separate units, the “Forward-link Network unit”  201 , which is placed where good signal coverage exists, indoor or outdoors, and the “Forward-link User unit”  202 , which is placed where good signal coverage does not exist, indoor or outdoors. The Forward-link Network unit  201  is connected to an antenna  203 , tuned to operate at the cellular network operating frequency band. The Forward-link Network unit  201  is also connected to an antenna  204  tuned to operate at a suitable Unlicensed National Information Infrastructure (known as U-NII) bands, where the system is designed to operate at U-NII spectrum bands. Subject to the relevant regulations, the system can also be designed to operate at Unlicensed Personal Communications Services (U-PCS) band or at Industrial, Scientific and Medical (ISM) band of frequencies. The choice of the unlicensed frequency depends on the design of the equipment and the system specification. Frequencies defined in the portion of the radio spectrum known as U-NII bands may be implemented in some embodiments. Some design modifications are useful, for ISM band operation. The modifications are related to the minimum spreading factor of 10 specified for the ISM band operation, and the maximum allowed transmit power. If the system is designed to operate in ISM band, the signal may use further spread spectrum modulation/demodulation and other modifications to meet FCC 47 CFR Part-15, subpart E specifications. 
     The frequency bands defined for U-NII operations are as follows:
         1) 5.15-5.25 GHz @ Max Transmit power of 2.5 mW/MHz   2) 5.25-5.35 GHz @ Max Transmit power of 12.5 mW/MHz   3) 5.725-5.825 GHz @ Max Transmit power of 50 mW/MHz       

     Any unlicensed operation in U-NII band is allowed, as long as the signal transmissions meet FCC 47 CFR Part-15. So operation of the described booster generally complies with standards of the FCC 47 CFR Part-15 (subpart E for U-NII frequencies). Regulations commonly specify transmit power, emission limits, and the antenna gain limits and are implemented for an acceptable device. 
     The “Forward-link User Unit”  202  is connected to an antenna  205  tuned to operate in the same frequency band as antenna  204 , which is U-NII band in some embodiments. The Forward-link User unit  202  is also connected to an antenna  206  tuned to operate at the cellular network operating band. 
     Antenna  203  is connected to a (Low Noise Amplifier) LNA unit  207 , which is further connected to a bandpass filter  232 . LNA unit  207  may be a high performance amplifier, with a typical gain of 15 dB and a noise figure of 1.5 dB with sufficient bandwidth to cover the appropriate portion of the spectrum. The bandpass filter  232  can be designed to pass all or a desired part of the interested cellular spectrum, or can be a bank of overlapping bandpass filters, covering the full spectrum of the interested cellular system, with a RF switch, such that the desired band and bandwidth can be selected. The bandpass filter  232  is connected to frequency converter  208 . The frequency converter  208  is capable of converting the cellular network operating spectrum band to a desirable part of the U-NII spectrum, and includes components such as mixers and filters for correct operation. The frequency converter  208  is connected to the Forward-link Network unit transmitter  209 . The transmitter unit  209  is designed to operate in U-NII band and conforms to the FCC 47 CFR Part-15, subpart E regulations, and can be as simple as a single amplifier operating at the desirable U-NII operation band, or more complex transmitter with amplifiers and filters, or even a WLAN transmitter such as 802.11a. The transmitter unit  209  is connected to antenna  204 . 
     Antenna  205  is connected to the Forward-link User unit receiver  210 , which is designed to receive the signal transmitted by unit  201 . The receiver  210  which is connected to frequency converter  211 , can be as simple as a single LNA operating at desirable U-NII band of device operation, or it can be better designed with additional functionalities such as variable attenuator and variable channel select filters, or even a WLAN receiver such as 802.11a (where the transmitter part of 802.11a is used in the Network unit  209 ). Frequency converter unit  211 , which is connected to receiver unit  210  and variable gain amplifier unit  212 , converts the input signals, from U-NII band, to the cellular network operating frequencies, and includes all components such as mixers and filters for correct operation. The frequency converter unit  211  performs the opposite conversion operation of the frequency converter unit  208 , and includes all components such as mixers and filters for correct operation. The frequency converter  211  is connected to the Variable Gain (VG) amplifier  212 , operating at the cellular network operating frequency band. The variable gain amplifier  212  is connected to antenna  208 . Antenna  208  will be transmitting signals with substantially similar frequencies to the frequencies transmitted by base station  213 , and meets cellular system specifications. 
     The signal radiated by antenna  208 , which is an amplified repeated version of the original incident signal received by antenna unit  203 , will experience some loss in the power level, before returning and re-entering the antenna  203  again. The re-entered signal into antenna  203  is termed “Down-link Returned-Signal” hereafter. The ratio of the r.m.s. signal value of the Down-link Returned-Signal to the r.m.s. value of the original incident signal at the output of the antenna  203  terminator, with all the system and propagation path delays between the antenna units  208  and  203  removed, is the Down-link Returned-Signal path loss, and is termed here as the “Down-link System Path Loss” and referred to as PL d1 . 
     Further, the “Down-link System Link Gain”, which is here referred to as G d1 , is defined as “the ratio of the r.m.s. signal value at the input to the antenna  208  terminator, to the r.m.s. signal value, at the antenna  203  terminator, where the Down-link System Path Loss, PL d1 , as defined above, is infinite (i.e. no EM coupling path between antenna  208  and antenna  203 ), and all the system and propagation path delays (from antenna  203 , through the system to antenna  208 ) are removed”. 
     The variable gain amplifier unit  212  gain is set such that Down-link System Link Gain, G d1 , is less than the Down-link System Path Loss, PL d1 , by dg d1 , so as to avoid a “positive feed-back” loop in the system, i.e.
 
 G   d1   =PL   d1   −dg   d1 ( dB )
 
     Note that all values of PL d1 , G d1 , and dg d1  are all in dB. The value of dg d1  ranges from 0 to PL d1 , and can be assumed to be 3 dB for the purposes of the description here. However, it is possible to select better values for dg d1 , where the system performance is optimized further. 
       FIG. 3  depicts an embodiment of the reverse-link part  330  of a repeater  300 . The reverse-link portion  330  in a simple form improves indoor coverage by boosting signal level in building in the reverse-link of the cellular network to such level that attains acceptable link performance. BTS 1   302  has a BCCH radio channel (beacon channel) transmitted substantially close to f 1 , and a frequency pair, f′ 1  on the reverse-link. BTS 1   302  is in communications with the mobile unit  324  at a frequency substantially close to f′ 1  (the BCCH carrier frequency) or another carrier frequency, f′ 2 , that may or may not be frequency hopping. There may or may not be other frequencies that are transmitted by BTS 1   302 , or other base stations in the same area, which are not shown in the  FIG. 3 . 
     The device has two separate units, the “Reverse-link Network unit”  326 , which is placed where good signal coverage exists, indoor or outdoors, and the “Reverse-link User unit”  328 , which is placed where good signal coverage does not exist, indoor or outdoors. The Reverse-link Network unit  326  is connected to an antenna  304 , tuned to operate at the cellular network operating frequency band. The Reverse-link Network unit  326  is also connected to an antenna  312  tuned to operate at a suitable Unlicensed National Information Infrastructure (U-NII) bands, where the system is designed to operate at U-NII bands. Subject to the relevant regulations, the system can also be designed to operate at Unlicensed Personal Communications Services (U-PCS) band or at Industrial, Scientific and Medical (ISM) band of frequencies. The choice of the unlicensed frequency depends on the design of the equipment and the system specification. Frequencies defined in the portion of the radio spectrum known as U-NII bands may be used in some system designs. Some design modifications are used for ISM band operation. The modifications are related to the minimum spreading factor of 10 used for ISM band operation, and the maximum allowed transmit power. If the system is designed to operate in ISM band, the signal uses further spread spectrum modulation/demodulation and other modifications to meet the FCC 47 CFR Part-15, subpart E specifications. 
     The frequency bands defined for U-NII operations are as follows:
         1) 5.15-5.25 GHz @ Max Transmit power of 2.5 mW/MHz   2) 5.25-5.35 GHz @ Max Transmit power of 12.5 mW/MHz   3) 5.725-5.825 GHz @ Max Transmit power of 50 mW/MHz       

     Any unlicensed operation in U-NII bands is allowed, as long as the signal transmissions meet with FCC 47 CFR Part-15. Operation of the illustrative booster meets specifications of FCC 47 CFR Part-15 (subpart E for U-NII frequencies). 
     The “Reverse-link User Unit”  328  is connected to an antenna  314  tuned to operate in the same frequency band as antenna  312 , which is U-NII band for example. The Reverse-link User unit  328  is also connected to an antenna  322  tuned to operate at cellular network operating band. 
     Antenna  322  is connected to a LNA unit  320 , which is further connected to a bandpass filter  321 . LNA unit  320  may be a high performance amplifier with a typical gain of 15 dB and a noise figure of 1.5 dB with sufficient bandwidth to cover the appropriate portion of the spectrum. The bandpass filter  321  can be designed to pass all or a desired part of the cellular spectrum, or can be a bank of overlapping bandpass filters, covering the full spectrum of the interested cellular system, with a RF switch, such that the desired band and bandwidth can be selected. The bandpass filter  321  is connected to frequency converter  318 . The frequency converter  318  is capable of converting the cellular network operating spectrum band to a desirable part of the U-NII spectrum, and includes all components such as mixers and filters for correct operation. The frequency converter  318  is connected to the Reverse-link User unit transmitter  316 . The transmitter unit  316  is designed to operate in U-NII band and conforms to the FCC 47 CFR Part-15, subpart E regulations, and can be as simple as a single amplifier operating at the desirable U-NII operation band, or a more complex transmitter with amplifiers and filters or even a WLAN transmitter such 802.11a. The transmitter unit  316  is connected to antenna  314 . The desired portion of the U-NII band of operation for the reverse-link part of the booster is different to the desired portion of the U-NII band of operation for Forward-link part of the booster, and sufficiently apart, so that no substantial interference is experienced from the operation of one link, to the other. 
     Antenna  312  is connected to the Reverse-link Network unit receiver  310 , which is designed to receive the signal transmitted by unit  328 . The receiver  310  which is connected to frequency converter  308 , can be as simple as a single LNA operating at desirable U-NII band of device operation frequency, or it can be better designed with additional functionalities such as variable attenuator and variable channel select filters or even a WLAN receiver such as 802.11a (where the transmitter part of 802.11a is used in the User unit  316 ). Frequency converter unit  308 , which is connected to receiver unit  310  and variable gain amplifier unit  306 , converts the input signals, from U-NII band, to the cellular network operating frequencies, and includes all components such as mixers and filters for correct operation. The frequency converter unit  308  performs the opposite conversion operation of the frequency converter unit  318 . The frequency converter  308  is connected to the variable gain amplifier  306 , operating at the cellular network operating frequency band. The variable gain amplifier  306  is connected to antenna  304 . Antenna  304  will be transmitting signals with substantially similar frequencies to the frequencies transmitted by mobile unit  324 . 
     The signal radiated by antenna  304 , which is an amplified repeated version of the original incident signal received by antenna unit  322 , will experience some loss in the power level, before returning and re-entering the antenna  322  again. The re-entered signal into antenna  322  is termed “Up-link Returned-Signal” hereafter. The ratio of the r.m.s. signal value of the Up-link Returned-Signal, to the r.m.s. value of the original incident signal, at the output of the antenna  322  terminator, with all the system and propagation path delays between the antenna units  304  and  322  removed, is the Up-link Returned-Signal path loss, and is termed here as the “Up-link System Path Loss” and referred to as PL u1 . 
     Further, the “Up-link System Link Gain” which here is referred to as G u1 , is defined as “the ratio of the r.m.s. signal value at the input to the antenna  304  terminator, to the r.m.s. signal value, at the antenna  322  terminator, where the Up-link System Path Loss, PL u1 , as defined above, is infinite (i.e. no EM coupling path between antenna  304  and antenna  322 ), and all the system and propagation path delays (from antenna  322 , through the system to antenna  304 ) are removed”. 
     The variable gain amplifier unit  306  gain is set such that Up-link System Link Gain, G u1 , is less than the Up-link System Path Loss, PL u1 , by dg u1 , so as to avoid a “positive feed-back” loop in the system, i.e.
 
 G   u1   −PL   u1   −dg   u1 ( dB )
 
     Note that all values of PL u1 , G u1 , and dg u1  are in dB. The value of dg u1  ranges from 0 to PL u1 , and can be assumed to be 3 dB for the purposes of the description here. However, it is possible to select better values for dg u1 , where the system performance is optimized further. 
     Usually the forward and the reverse links frequency pairs are sufficiently close, such that G u1  level is substantially similar to G d1  level, and PL u1  level is substantially similar to PL d1  level and dg u1  level is substantially similar to dg d1  level. 
     The unique booster unit identity code and optionally the device location can be transmitted to the cellular network. The information can be used to locate a user in an indoor environment, for example by generating a heavily coded (protected), low bit rate data containing a long known preamble, the unique identity code, optionally the longitude, and the latitude of the reverse-link Network unit  326 . The information can then be pulse-shaped for low spectral leakage and superimposed on the reverse-link signal of a given channel by an appropriate modulation scheme, within the reverse-link Network unit  326 . The choice of the modulation scheme depends on the operating cellular system. For example, for GSM, which enjoys a constant envelope modulation such as GMSK, amplitude modulation (with low modulation index) can be used. For CDMA systems with fast reverse-link power control, DBPSK can be used as the modulation scheme. Extraction of information from the received channel signal at base station may involve base station receiver modifications, but does not effect the normal operation of the cellular link. 
       FIG. 4  shows an embodiment of a system  500  including the Network unit  502 , together with the User unit  504  in the same diagram. The Forward-link Network unit  514  ( 201  in  FIG. 2 ) and the Reverse-link Network unit  516  ( 326  in  FIG. 3 ) are now in one unit, referred to hereafter as the Network unit  502 . The Forward-link User unit  518  ( 202  in  FIG. 2 ) and the Reverse-link User unit  520  ( 328  in  FIG. 3 ) are now in one User unit, referred to hereafter as the User unit  504 . In  FIG. 4 , the transmit/receive antenna  203  in  FIG. 2  and transmit/receive antenna  304  in  FIG. 3  are replaced by a single antenna  506  and duplex filter  528 . The duplex filter unit  528  is designed for optimum performance, and meets specifications for cellular operation. Also, the transmit/receive antenna  204  in  FIG. 2  and transmit/receive antenna  312  in  FIG. 3  are replaced by a single antenna  508  and duplex filter  526 . Further, the transmit/receive antenna  205  in  FIG. 2  and transmit/receive antenna  314  in  FIG. 3  are replaced by a single antenna  510  and duplex filter  524  in  FIG. 4 . Equally, the transmit/receive antenna  208  in  FIG. 2  and transmit/receive antenna  322  in  FIG. 3  are replaced by a single antenna  512  and duplex filter  522  in  FIG. 4 . The duplex filter unit  522  is designed for optimum performance, and complies with specifications for cellular operation. GSM system is a FDD system, and as such reverse-link frequencies are different to that of the forward-link frequencies. In such system a duplex filter provides appropriate functionality. However, if the Network unit  502  and the User unit  504  are designed for a TDD system, the duplexers  528  and  522  can be replaced by hybrid combiners or “circulators”. However, duplexers  526  and  524  are still used, since forward-link and reverse-link frequencies in the U-NII band are kept separate (i.e. FDD). With minor modifications, it is possible that, instead of antennas  508  and  510 , a coaxial cable (such as RG58 or IS inch heliax) is used to connect the Network unit  502  to the User unit  504 . In such an arrangement, where coaxial cable is used for the link connection, although still possible, up-conversion to U-NII bands is superfluous, and the system can operate with the Forward and reverse-link signals kept at original cellular frequencies. 
     The described booster system typically operates satisfactorily in limited scenarios. To ensure the correct operation of the booster system in all propagation and operating conditions, several features may be included in the system design.
         1. Since both the Network unit  502  and the User unit  504  are for most time stationary relative to each other, and possibly other network elements such as base stations, antenna (space) diversity is used for transmit and receive operations.   2. The signals transmitted by antenna  506 , in the reverse-link, are substantially at the same operating frequency band as the reverse-link signals received by antenna unit  512 . Equally, the signals transmitted by antenna  512 , in the forward-link, are substantially at the same operating frequency band as the forward-link signals received by antenna unit  506 . As the signals received by the Forward-link Network unit  514  are transmitted to Forward-link User unit  518 , via antenna units  508  and  510 , and further, as the signal received by the Forward-link User unit  518  is then amplified before the retransmission via antenna unit  512 , a feed-back loop, through the antennas  512  and  506 , between the two Forward-link Network unit  502  and Forward-link User unit  518  exists. Any gain in the loop causes “positive feed-back”, which results in unstable operation, a phenomenon that is also true for reverse-link operation of the Network unit  502  and the User unit  504 . To keep the two feed-back loops in a stable operating region, in the forward-link the Down-link System Link Gain, G d1 , is less than the Down-link System Path Loss, PL d1 , by dg d1 , so as to avoid a “positive feed-back” loop in the system, i.e. G d1 =PL d1 −dg d1  (dB). Equally, in the reverse-link, the Up-link System Link Gain, G u1 , is less than the Up-link System Path Loss, PL u1 , by dg u1 , so as to avoid a “positive feed-back” loop in the system. i.e. G u1 =PL u1 −dg u1 (dB). The propagation losses, PL u1  and PL d1 , may be due to shadowing, distance, antenna radiation pattern and multipath propagation as well as wall penetration loss. The levels of these propagation losses, PL u1  and PL d1 , are not readily available and are measured.   3. Continuous and correct operation of the Network unit  502  and User unit  504  is monitored. Any operational problem at the Network unit  502  or the User unit  504  can result in unwanted transmissions in either forward or reverse (or both) links. Further, the system may rely on radio channels operating at unlicensed frequency bands, which are prone to interference from other unlicensed devices. Also, operation of the Network unit  502  and the User unit  504  is coordinated. Therefore a control-signaling channel is inserted between the two Network  502  and the User  504  units.   4. The local oscillators of the network unit  502  and the User unit  504  are substantially similar in frequency, as any large frequency error between the Network  502  and the User  504  units will result in an unacceptable cellular link performance. In some embodiments, a pilot signal can be transmitted in a control link from the network unit  502  to the user unit  504  and used for synchronization of local oscillators of the two units. In other examples, an electric power supply waveform can be used for synchronization of local oscillators in the two units.       

     Advanced Features 
     Illustrative advanced features include design solutions that are useful in countering the enumerated problems. 
       FIG. 5  shows a system  600  including the Network unit  602  ( 502  in  FIG. 4 ) with the new design features included. Two antennas  610  and  608  are used for antenna diversity, instead of a single antenna  506  in  FIG. 4 . Also two antennas  636  and  638  are used for antenna diversity, instead of a single antenna  512  in  FIG. 4 . Although any diversity-combining scheme such as Maximal Ratio Combining, etc. can be used for the receiver chain, and transmit diversity schemes such as random phase change in one or both antennas for the transmitter chain, a simple scheme that is based on antenna switched diversity with “continuous switching” strategy is suggested here. The continuous switching strategy, with the switching rate selected for optimum performance (e.g. at, or twice, the GSM Timeslot rate which is 4.6 msec), can be used for both transmit and receive operation, and will result in a nominal average transmit/receive signal power, provided the antennas are placed sufficiently apart. The continuous-switch diversity scheme is also simple to implement, using only a simple RF switch at the antenna ports. Therefore, the RF switch  612  connected to antennas  610  and  608  and the duplex filter  614  will provide switching operations for the cellular transmit/receive operation of the Network unit  602 . Also the RF switch  634 , connected to antennas  636  and  638  and the duplex filter  634 , will provide switching operations for the U-NII band transmit/receive operation of the Network unit  602 . The duplex filter  614  is connected to Forward-link Network unit  604  ( 514  in  FIG. 4 ), and the Reverse-link Network unit  606  ( 516  in  FIG. 4 ) via the directional coupler  618 . Directional couplers may be 17 dB directional couplers. Also, the duplex filter  634  is connected to Forward-link Network unit  604  via the directional coupler  630 , and Reverse-link Network unit  606  via the directional coupler  616 . It is also possible to use hybrid combiners instead of the directional couplers  618 ,  630  and  616 . It is also possible, and is more desirable, to place the Reverse-link Network receiver unit  310  internal LNA amplifier, before the directional coupler  616  (or the hybrid combiner replacement) in diagram  600 . 
     A calibration signal generator/transmitter unit  622  is coupled to the reverse-link transmitter path of the Network unit  602 , via the directional coupler  618 . The unit  622  will provide a calibration signal, at the desired power levels, which is used to establish the level of the above-mentioned Up-link System Path Loss, PL u1 , which exists between the Network unit  602  ( 502  in  FIG. 4 ) and the User unit  702  in  FIG. 6  ( 504  in  FIG. 4 ). The calibration signal generated by unit  622  is transmitted via the diversity antennas  610  and  608  at a set transmit level which is substantially below any expected signal level from cellular network (e.g. 20 dB below the minimum expected cellular signal level). The calibration signal generated by unit  622  is a direct-sequence spread spectrum signal modulated by a known Pseudo Random (PN) code with a known code phase (referred to hereafter as “own code” phase) and with a chipping rate comparable to the forward and reverse links of the Network unit  602  and User unit  702  (in  FIG. 6 ) operating bandwidths. The code phases are selected such that the minimum code phase difference is larger than the maximum expected path delay (measured in multiple number of chips), and after that the code phases should be multiple integer of the minimum code phase. The calibration signal receiver unit  620  which is coupled to the reverse-link receive path of the Network unit  602 , by directional coupler  616 , using the known PN code and the transmit code phase is then capable of detecting and demodulating the calibration signal transmitted by unit  622 , which has entered the reverse-link path via the mentioned closed-loop mechanism that exists between the Network unit  602  and the User unit  702  in  FIG. 6  ( 504  in  FIG. 4 ). The calibration signal receiver unit  620  is capable of establishing the received signal strength, which is then used to estimate the Up-link System Path Loss, PL u1 , that exists between the Network unit  602  ( 502  in  FIG. 4 ) and the User unit  702  in  FIG. 6  ( 504  in  FIG. 4 ). The calibration signal receiver unit  620  includes many sub-units, including a frequency converter similar to frequency converter unit  308  (in  FIG. 3 ), to return the calibration signal, to its original operating frequency. The PN code phase can be assigned uniquely, or drawn according to a random algorithm, such that the probability of two units having the same code phase can be very low. Other code offset assignment strategies are also possible, such as dynamic assignment, where the code offset is selected, if no such offset was detected in that geographical area. The feature enables the calibration signal receiver  620  to be able to scan and receive “other code” phases, and hence establishing if there is any other signal coupling to or from other units, that may be operating in the same geographical area. Further, more than one code phases can be used, to establish the Up-link System Path Loss, PL u1 , so that the probability of detection by other systems is increased. The PN code used for the calibration signal can be modulated with information about the identity of the Network unit  602 . The carrier frequency of the transmitted calibration signal may be at the operating cellular frequency band. However, carrier frequencies in other bands, such as ISM band at 2.4 GHz, may be used for transmission of the calibration signal so that the calibration signal generator and transmitter  622  carrier frequency are placed as near as possible to the operating frequency band. The chipping rate and the transmit power of the calibration signal PN code is configured so that the calibration signal complies with the FCC 47 CFR Part-15 rules. Although the mentioned ISM band is not the same as the cellular operating band, nevertheless, the band is sufficiently close to enable the system to establish the antenna coupling and the Up-link and Down-link System Link Gains, (G u1 , G d1 ), at the cellular operating band (the instantaneous amplitude and phase values are no longer relevant operating at ISM band). Any antenna and propagation differences in average signal power between the ISM and cellular operating bands can be investigated in the design phase and taken into account in the final system design. The calibration signal generator and transmitter unit  622 , and the calibration signal receiver  620 , are both in the Network unit  602 , operating in the desired cellular band. However, one or both of the units including calibration signal generator and transmitter unit  622 , and the calibration signal receiver  620 , can also be placed in the User unit  702 , with certain modifications and considerations. In some cases, a calibration mechanism for the forward-link, similar to the one described for the reverse-link, includes parts such as the unit,  622 ,  618 ,  616  and  620 , which can be placed in the User unit  702 . 
     Further, it can be assumed that Up-link System Path Loss, PL u1 , and the Down-link System Path Loss, PL d1 , are the same, i.e. PL d1 ≈PL u1 . The assumption enables measurement of only one of the entities to be sufficient. Validity of the assumption can be investigated for each system, and should hold true if the frequency separation between the forward and reverse links of the system is not excessively high. The assumption simplifies description. However, if the assumption is not made, a similar technique may be used in the forward-link of the Network unit  602 , or User unit  702  in  FIG. 6 . 
     The Equipment ID and reference frequency unit  624  basically generates a Binary Phase Shift Keying (BPSK) signal, modulated by the equipment ID number and placed at a suitable part of U-NII band, and is coupled in the transmitter path of the forward-link of the Network unit  602  via the directional coupler  630 . The unit is “frequency locked” to the local oscillator of the Network unit  602 . The carrier frequency of the signal is selected to avoid an unacceptable interference to the main cellular signal in the transmit path of the forward-link of the Network unit  602 , but is sufficiently close for an optimum transmission bandwidth. Where the Network unit  602  and the User unit  702  use the mains electricity supply for their operations, the 60 Hz or 50 Hz mains oscillations can be used to “lock” the local oscillators of the two units to a common frequency source. The 60 Hz or 50 Hz mains oscillations are converted, by suitable circuitry, to the desired frequency for the operation of the Network unit  602  and the User unit  702 . 
     The Control Link unit  628  is a radio link between the two, Network unit  602  and the User unit  702  in  FIG. 6 . It may be a simple proprietary link that operates in one of the unlicensed band of frequencies, or may be an in-band control signaling, multiplex with the cellular signal path. It may also be a standard wireless link such as 802.11b, 802.11a or Bluetooth, designed to operate in unlicensed frequency band. The control link unit  628  is connected to micro-controller unit  626 , and is able to communicate through an appropriate interface. The control link unit  628  is also connected to antenna  644  and  642  for transmission and reception of the control signals. If operating bandwidth and frequencies allow, with minor modifications to unit  602 , antenna units  636  and  638  can also be used for the operation of control link unit  628 . In some embodiments, the User unit  702  can be a very simple device with all signal processing and control functionalities supported in the Network unit  602 . If so, the control link can be eliminated or may implement very simple control signaling such as in-band frequency tones to set the system bandwidth and gain in the User unit  702 . Provided that the antenna bandwidth allows, with minor modifications to unit  602 , antenna units  636  and  638  can also be used for control link unit  628  operations. 
     Micro-controller unit  626  is a simple micro-processor such as ARM7 or ARM9 with all the appropriate memory and interfaces. The micro-controller unit  626  is controlling the operation of the Network unit  602 , and may perform some additional signal conditioning and processing such as signal level averaging and estimation, where useful. Some of the task of the micro-controller unit  626  is to set the operating bandwidth and gain of the forward and reverse links of the Network units  604  and  606 , communicate with and control the User unit  702  in  FIG. 6 , via the control link unit  628 , control and communicate with the calibration signal generator and transmitter  622  and calibration signal receiver  620 . Other tasks of the micro-controller  626  are discussed later by way of an example given in  FIGS. 7 ,  8  and  9 . Micro-controller unit  626  is connected to units  628 ,  622 ,  606 ,  604 ,  620  and  624 . 
     Units  628 ,  622 ,  606 ,  604 ,  620 ,  624 ,  602  are all connected to local oscillator unit  640 , and derive their clock and reference frequencies from the local oscillator  640  signal. 
     A simple user interface unit  627 , which can be a keypad or simple dipswitch, is connected to micro-controller unit  626 . 
     The Network unit  602  has a unique “identity code”, which can be set by the user interface unit  627 , which is known to the micro-controller unit  626  and can be communicated to the User unit  702  micro-controller unit  728 , or any other User units that may be within the operating range of Network unit  602 . 
       FIG. 6  shows an embodiment of a repeater  700  including the User unit  702  ( 504  in  FIG. 4 ) with the new design features included. Two antennas  734  and  736  are used for antenna diversity, instead of a single antenna  512  in  FIG. 4 . Also, two antennas  704  and  706  are used for antenna diversity, instead of a single antenna  510  in  FIG. 4 . Although any diversity-combining scheme such as Maximal Ratio Combining, etc. can be used for the receiver chain, and transmit diversity schemes such as random phase change in one or both antennas for the transmitter chain, a simple scheme that is based on antenna switched diversity with “continuous switching” strategy is suggested here. The continuous switching strategy, with the switching rate selected for optimum performance (e.g. at, or twice, the GSM Timeslot rate 4.6 msec), can be used for both transmit and receive operation, and will result in a nominal average transmit/receive signal power, provided the antennas are placed sufficiently apart. The continuous-switch diversity scheme can be easily implemented using a simple RF switch at the antenna ports. Therefore the RF switch  732  connected to antennas  734  and  736  and the duplex filter  730  will provide switching operations for the cellular transmit/receive operation of the User unit  702 . Also the RF switch  712  connected to antennas  704  and  706  and the duplex filter  714  will provide switching operations for the U-NII band transmit/receive operation of the User unit  702 . The duplex filter  712  is connected to Forward-link User unit  724  ( 518  in  FIG. 4 ), via the directional coupler  718 , and the Reverse-link User unit  726  ( 520  in  FIG. 4 ). Also, the duplex filter  732  is connected to Forward-link User unit  724 , and Reverse-link User unit  726 . It is also possible to use a hybrid combiner instead of the directional coupler  718 . It is also possible, and is more desirable, to place the Forward-link User unit  328  receiver  210  internal LNA, before the directional coupler  718  (or the hybrid combiner replacement), in diagram  700 . 
     The Reference signal receiver unit  716 , which is capable of receiving the transmitted signal generated by the equipment ID and reference frequency generator  624  in  FIG. 5 , is connected to the directional coupler  718 . The receiver is capable of extracting the reference frequency and the ID code transmitted by the Network unit  602  equipment ID and reference frequency generator  624 . The extracted reference frequency is then used to provide a reference local oscillator  722 , as reference frequency signal. The directional coupler  718  is connected to the Forward-link User unit  724 . Reverse-link User unit  726  is connected to duplex filters  730  and  714 . The reference signal and the local oscillator unit  722  can alternatively be based on the control link unit  720  oscillator, if the unit  726  is capable of locking to the received signal carrier frequency which has been transmitted by control link unit  628  of the Network unit  602 . 
     The Control Link unit  720  is a radio link between the two, Network unit  602  and the User unit  702 . It may be a proprietary link that operates in one of the unlicensed band of frequencies, or may be a standard wireless link such as 802.11b, 802.11a or Bluetooth, designed to operate in unlicensed band. The control link unit  720  is connected to micro-controller unit  728 , and is able to communicate through an appropriate interface. The control link unit  720  is also connected to antennas  708  and  710  for transmission and reception of the control signals. Note that provided that the antenna bandwidth and operating frequency allow, with minor modifications to unit  702 , antenna units  704  and  706  can also be used for the control link unit  720  operations. 
     Micro-controller unit  728  is a simple microprocessor such as ARM7 or ARM9 with all the appropriate memory and interfaces. The micro-controller unit  728  is controlling the operation of the User unit  702  and may perform some additional signal conditioning and processing such as signal level averaging and estimation. Some of the task of the micro-controller unit  728  is to set the operating bandwidth and gain of the Forward and Reverse link User units  724  and  726 , to communicate with the Network unit  602  in  FIG. 5  via the control link unit  720 . Other tasks of the micro-controller  728  are discussed later by way of an example given in  FIGS. 10 and 11 . Micro-controller unit  728  is connected to units  720 ,  726 ,  724  and  722 . The micro-controller unit  720  is not strictly essential since the control unit  626  can perform appropriate tasks in the User unit  702  via the control link units  628  and  720  based on a simple acknowledgement scheme. 
     Units  720 ,  726 ,  724  and  728  are all connected to local oscillator unit  722 , and derive their clock and reference frequencies from the local oscillator  722  signal. 
     Techniques, such as the use of vertical polarization for antennas units  610  and  608 , and horizontal polarization for antennas  734  and  736  can further improve the system performance. It is also possible to improve system performance by the use of directional antennas, as in conventional booster and repeater systems. 
     A simple user interface unit  721 , which can be a keypad or simple dipswitch, is connected to micro-controller unit  728 . 
     The User unit  702  has a unique “identity code”, which can be set by user interface unit  721 , which is known to the micro-controller unit  728  and can be communicated to the Network unit  602  micro-controller unit  626 , or any other Network units that may be within the operating range of User unit  702 . 
     The unique Network unit  602  identity code and optionally device location can be transmitted to the cellular network. The information can be used to locate a user in an indoor environment, for example by generating a heavily coded (protected), low bit rate data, containing a long known preamble, the unique identity code and optionally the longitude and the latitude of the Network unit  602 . The information can then be pulse-shaped for low spectral leakage and superimposed on the reverse-link signal of a given channel by an appropriate modulation scheme, within the Network unit  602 . The choice of the modulation scheme depends on the operating cellular system. For example, for GSM, which enjoys a constant envelope modulation such as GMSK, amplitude modulation (with low modulation index) can be used. For CDMA systems, with fast reverse-link power control, DBPSK can be used as the modulation scheme. The extraction of the above mentioned information from the received channel signal at base station may involve base station receiver modifications, but does not effect the normal operation of the cellular link. 
     An example of the above system operation is shown in  FIGS. 7 ,  8 ,  9 ,  10  and  11 .  FIGS. 7 ,  8  and  9  are the system operation flow diagrams for the Network unit  602  and  FIGS. 10 and 11  are the flow diagrams for the User unit  702 . There are mainly two independent control flow operations that are executed concurrently on the micro-controller  626 . The first control-flow is to establish normal operation of the booster, with the second one to monitor the correct operation of the control link between the Network unit  602  and the User unit  702 . On “power-up” or “reset” of the Network unit  602 , the VG amplifier  306  gain is always set to minimum and is switched “OFF”. The system is said to be “operational” when VG amplifier  306  is switched “ON”, after the correct gain setting by instruction from micro-controller  626 . On “power-up” or “reset” of the Network unit  602  (assuming that the “identity code” of the interested User unit  702  is known by or pre-entered into the Network unit  602  via the user interface unit  627 ), the micro-controller unit  626  will start the control-flow (step  802 ) in  FIG. 7 . The micro-controller unit  626  instructs the control link unit  628  to establish link with the User Unit  702  (step  804 ). The control link unit  628 , using the appropriate protocols, will continue trying to establish a communication link with the control unit  720  of the User unit  702  until such link is established (step  806 ). The micro-controller unit  626  will select the desired U-NII band of operation (step  808 ) and instruct the calibration signal receiver unit  620  to attempt to receive all the possible code offsets (step  8 ) in the frequency band, ensuring no signal paths from other User units are operational in the geographical area directed to the Network unit  602 , and facilitating selection of an unused code offset and transmission channel. If an unintended signal path exists between the Network unit  602  and other operating User units (step  812 ), depending on the severity of the coupling path and the strength of the “other units” received calibration signal(s) strength, several different actions can be taken, after a comparison of the received signal SNR with threshold SNR (SNR th ) (step  814 );
         1) If the strength of the received calibration signal(s) from other User units is below the threshold (SNR th ), indicating NO interference with the operation of the Network unit  602  and User unit  702 , an appropriate different code phase is selected, and the micro-controller proceeds as normal.   2) If the strength of the received calibration signal(s) from other User units is above the threshold (SNR th ), indicating interference with the operation of the Network unit  602  and User unit  702 , the Network unit  602  will try to select another U-NII frequency band of operation (step  816 ), and if more U-NII operating band available, steps  808 ,  8 , and  812  are repeated (step  816 ).   3) If the strength of the received calibration signal(s) from other User units is above the threshold (SNR th ), indicating interference with the operation of the Network unit  602  and User unit  702 , and no new clean U-NII operating frequency band can be found, the Network unit  602  will issue an appropriate error signal (block  818 ) and instruct User unit  720  to stop operation (step  9 ), and the Network unit  602  stops operation (step  822 ).       

     After the successful establishment of the control link between the Network unit  602  and the User unit  702 , and successful selection of an U-NII operation band, the control flow would be at point “A” in  FIG. 7 . Point “A”, shown in  FIG. 8 , is the continuation of point “A” in  FIG. 7 . With reference to  FIG. 8 , after the point “A”, the Network unit  602  will select an unused code offset ( 824 ), and start the transmission of the calibration signal with the known code offset, at the lowest possible transmit power (step  826 ). The task is performed by an instruction from the micro-controller  626  to the calibration signal generator and transmitter unit  622 . The micro-controller  626  will also instruct the calibration signal receiver unit  620  to try to receive the calibration signal for the above mentioned code offset, used by the transmitter unit  622  (block  828 ). The Network unit  602  instructs the User unit  702 , via the control link  628 , to commence operation, with the minimum possible transmitter powers for Reverse-link and Forward-link User units  726  and  724  respectively (step  830 ). If no signal is detected with a desired strength by receiver  620  (step  832 ), and the maximum transmit power of the transmitter unit  622  has not been reached (step  834 ), the micro-controller unit  626  will instruct the transmitter unit  622  to increase the power of the transmitted signal by a predetermined step size, dG, (step  836 ). The operation continues until a signal is detected at the output of the receiver  620 , or until establishment that no signal can be detected with even the maximum transmit power of the transmitter unit  622 . Then, the Network unit  602  is capable of calculating the Up-link System Path Loss, PL u1 , and hence the Up-link System Link Gain, G u1 , and accordingly, supplies appropriate transmitter power of the Reverse-link Network unit  606  (step  838 ). Assuming the Up-link System Path Loss, PL u1 , and the Down-link System Path Loss, PL d1 , are the same, i.e. PL d1 =PL u1 , the maximum gain of the transmitter amplifier  212  of the Forward-link User unit  724  can be calculated (step  838 ) and forwarded to User unit  702 , via the control link unit  628  (step  840 ). After the establishment of the system gain, the micro-controller  626 , via link control unit  628 , informs the User unit  702  of the correct amplifier  212  gain setting (block  840 ). After the completion of the system calibration (steps  804  to  840 ), the micro-controller  626  sets the amplifier  306  at the correct gain for transmission (step  842 ) and instructs the User unit  702  to commence operation with the stated amplifier  212  gain setting (block  844 ). The calibration signal receiver  620  continues to receive the signal transmitted by the calibration signal transmitter  622  (step  846 ). If the safe average signal power level is exceeded for a substantial amount of time (step  848 ), the micro-controller  626  will instruct the User unit  702 , via the control link unit  628 , to stop operation (step  850 ), and also Network  602  will stop transmission of signals by the Reverse-link Network unit  606  (step  852 ), and the system steps  802  to  844  are repeated. If the average signal power level is within the expected range, the calibration signal receiver  620  is instructed to receive and detect signals with all other possible code offsets (step  856 ). If no signal with substantial average signal power level is detected, the Network unit  602  will return to step  846 . If a signal with substantial average signal power level is detected, the Network unit  602  will go to step  850 . In order to speed up the search and detection of other code offsets, it is also possible to have two (or more) replicas of the calibration signal receiver  620 , such that the “own code” detection can be continuous and uninterrupted, while other receiver replicas can scan for “other code” offsets. 
     The second control-flow operation starts after step  806 , and is shown in  FIG. 9 . The second operation checks the quality and performance of the control links of the control units  628  and  720  operation, by monitoring such quantities as BER, SNR, background noise and interference (step  860 ). If the operation of the link is not satisfactory (step  862 ), an error signal is flagged (step  864 ), all transmissions in the forward and reverse cellular link, of the Network unit  602  are stopped (step  866 ), and the User unit  702  is instructed to stop operation (step  868 ), and finally the Network unit  602  will go back to step  802  (step  870 ). 
       FIGS. 10 and 11  are the system operation flow diagram for the User unit  702 . There are mainly two independent control flow operations that are executed concurrently on the micro-controller  728 . The first control-flow is to establish normal operation of the booster ( FIG. 10 ), with the second one to monitor the correct operation of the control link between the Network unit  602  and the User unit  702  ( FIG. 11 ). On “power-up” or “reset” of the User unit  702 , the VG amplifier  212  gain is always set to minimum and is switched “OFF”. The system is said to be “operational” when VG amplifier  212  is switched “ON”, after the correct gain setting by instruction from micro-controller  728 . On “power-up” or “reset” of the User unit  702  (assuming that the “identity code” of the interested Network unit  602  is known by or pre-entered into the User unit  702  via the user interface unit  721 ), the micro-controller  728  will start the control-flow (step  902  in  FIG. 10 ). The micro-controller unit  728  instructs the control link unit  720  to establish link with the Network Unit  602  (step  904 ). The control link unit  728 , using the appropriate protocols, will continue trying to establish a communication link with the control unit  620  of the Network unit  602  until such link is established (step  906 ). After the successful establishment of the control link between the User unit  702  and the Network unit  602 , the User unit  702  monitors the control channel for instruction from the Network unit  602  (step  908 ). If a “stop” instruction is issued by the Network unit  602  (step  11 ), the User unit  702  will stop the forward-link and reverse-link transmissions (step  912 ). If the instruction is to set parameters (step  916 ) such as the “operation bandwidth”, or the “U-NII spectrum channel number”, or “the cellular channel number”, or any or all of the above, and any other system parameters to be set, the User unit  702  sets the parameters as specified by the instruction (step  918 ). If the instruction is to “set the amplifier  212  gain” (step  920 ), the User unit  702  sets the requested gain for the VG amplifier  212  (step  922 ). If the instruction is to “commence transmission” (step  923 ), the User unit  702  begins operation in the forward  724  and the reverse  726  links of the unit (step  924 ). Other instructions that are not mentioned in the example may be used. The instructions are executed by the User unit  702  if the instructions are received by the User unit  702  (step  925  &amp;  926 ). After instruction execution, the User unit  702  returns to step  908 . 
     The second control-flow operation starts after step  906 , and is shown in  FIG. 11 . The second operation checks the quality and performance of the control links of the control units  628  and  720  operation, by monitoring such quantities as BER, SNR and the background noise and interference (step  930 ). If the operation of the link is not satisfactory (step  932 ), an error signal is flagged (step  934 ), all transmissions in the forward  724  and reverse  726  link units, are stopped by the User unit  702  (step  936 ), and finally the User unit  702  will go back to step  902  (step  938 ). 
     The description is merely an example a system implementation. Other possible methods and solutions may be implemented. Several points may be noted.
         1. The Network unit  602  can control several User units, such as the User unit  702 . In such setups, the example control flow, shown in  FIGS. 7 ,  8 ,  9 ,  10  and  11  may be modified such that the Network Unit  602  can initialize each User unit independently. For stable operation, the Reverse-link Network unit  606  amplifier  306  gain is set for the minimum Up-link System Path Loss, PL u1 , for operation with all the active User units. Thus, if the Down-link System Path Loss, PL d1 , is based on the Up-link System Path Loss, PL u1 , calculations (i.e. PL d1 ≈PL u1 ), the minimum amplifier  306  gain is used for all the User units in the forward-link under the control of the Network unit  602 . If the Down-link System Path Loss, PL d1 , is NOT based on the Up-link System Path Loss (i.e. a separate calibration loop exists for estimating PL d1 ), the amplifier  306  gain can be set independently for each User units in the forward-link, under the control of the Network unit  602 .   2. Another modification used for a multiple-User unit (several User units  702 ) operation is that the final Down-link System Path Loss, PL d1 , and the Up-link System Path Loss, PL u1 , measurements can be performed with all User units under the control of the Network unit  602  (including Network unit  602 ), active such that aggregate signal power levels do not exceed the desired Down-link System Link Gain, G d1 , or the desired Up-link System Link gain, G u1 . If combined signal from the User Units exceeds the acceptable level for either of the reverse or forward system link gains, the appropriate amplifier gains are reduced in iterative step increments to such level that the maximum allowed system link gain, or the forward and the reverse links are met.   3. Additional hardware, similar to the calibration signal generator and transmitter  622 , and the calibration signal receiver  620 , may be included in the forward-link path of either the Network unit  602  or the User unit  702 , to assess the Down-link System Path Loss, PL d1 , independently (for each User unit  702  controlled by Network unit  602 ).   4. Although the signal path in both the Network unit  620  and the User unit  702 , in the forward link, is constantly active, to boost the beacon (BCCH in GSM) transmissions of the base stations, the reverse-link path signal path of the Network unit  620  and the User unit  702  may be active, unless a substantial signal level is detected (i.e. “gated”). Therefore, in the User unit  702 , based on the received signal power level on reverse-link, which can be measured after the LNA unit  320  or filter unit  321 , the micro-controller unit  728  switches the transmitter unit  316  “OFF” if the signal power level is below the desired threshold, or “ON” if the signal power level is above the desired threshold. Equally, in the Network unit  602 , based on the received signal power level on reverse-link, which can be measured after the receiver unit  310  or converter unit  308 , the micro-controller unit  626  switches the variable gain amplifier unit  306  “OFF” if the signal power level is below the desired threshold, or “ON” if the signal power level is above the desired threshold. Care is taken that the reverse-link “gated” operation does not interfere with the calibration signal path and mechanism involving the units  622  and  620 . Therefore, either the “gated” operation is replaced by continuous operation during the calibration process, or where possible, a forward-link calibration is placed and used in a manner similar to the reverse-link mechanism for both Down-link System Path Loss, PL d1  and Up-link System Path Loss, PL u1  calculations.   5. With certain modifications in the hardware and the control software, the Network unit  602  and the User unit  702  can be merged into a single unit, connected “back-to-back”. The design and operation of the back-to-back option is shown in  FIG. 14  and discussed later.   6. The unique Network unit  602  identity code and optionally device location can be transmitted to the cellular network. The information can be used to locate a user in an indoor environment, for example by generating a heavily coded (protected), low bit rate data, containing a long known preamble, the unique identity code and optionally the longitude and the latitude of the Network unit  602 . The information can then be pulse-shaped for low spectral leakage and superimposed on the reverse-link signal of a given channel by an appropriate modulation scheme, within the Network unit  602 . The choice of the modulation scheme depends on the operating cellular system. For example, for GSM, which enjoys a constant envelope modulation such as GMSK, amplitude modulation (with low modulation index) can be used. For CDMA systems, with fast reverse-link power control, DBPSK can be used as the modulation scheme. The extraction of the above mentioned information from the received channel signal at base station may involve base station receiver modifications, but does not effect the normal operation of the cellular link.       

     The above discussion is applicable to all the different analogue implementations of all the various disclosed boosters. 
     Digital Implementation Example 
       FIG. 12  shows an example of digital implementation of the Network unit  602  (labeled  1002  in  FIG. 12 ), which is placed where good signal coverage exists, indoor or outdoors. Two antennas  1004  and  1006  are used for antenna diversity for the cellular band transmitter and receiver of the Network unit  1002 . Also two antennas  1036  and  1038  are used for antenna diversity of the U-NII band operation of the Network unit  1002 . Although, any diversity-combining scheme such as Maximal Ratio Combining, etc. can be used for the receiver chain, and transmit diversity schemes such as random phase change in one or both antennas for the transmitter chain, a simple scheme that is based on antenna switched diversity with “continuous switching” strategy is suggested here. The continuous switching strategy, with the switching rate selected for optimum performance (e.g. at, or twice the GSM Timeslot rate ˜4.6 msec), can be used for both transmit and receive operations, and will result in a nominal average transmit/receive signal power, provided the antennas are placed sufficiently apart. The continuous-switch diversity scheme can be simply implemented using only a simple RF switch at the antenna ports. Therefore, the RF switch  1008  connected to antennas  1004  and  1006  and the duplex filter  1010 , and the micro-controller  1060 , under the control of the micro-controller  1060 , will provide switching operations for the cellular transmit/receive operation of the Network unit  1002 . Also, the RF switch  1032  connected to antennas  1036  and  1038  and the duplex filter  1034  will provide switching operations for the U-NII band transmit/receive operation of the Network unit  1002 . The duplex filter  1010  is connected to forward-link LNA  1012  and the directional coupler  1056 . LNA  1012  is connected to the frequency converter unit  1014 . Frequency converter  1014  is connected to Automatic Gain Control (AGC) unit  1018 . The frequency converter  1014  converts the frequency band of the incoming signal from the cellular band to baseband, or “near baseband” frequency band. The frequency converter unit  1014  may supply appropriate filtering for the correct operation of the receiver chain. The operating frequency of the frequency converter unit  1014  is set by micro-controller unit  1060 . The AGC unit  1018  is connected to Analogue to Digital Converter (AD/C) unit  1020  and the Signal Conditioning (SC) unit  1022 . The AGC  1018  is optional, and its task is to place the received signal level substantially close to the middle of the dynamic range of the AD/C  1020 . If included, the design and operation of the unit  1018  is configured so that in the presence of low signal power noise within the operating bandwidth does not dominate the operation of the AGC unit  1018 . Also care is taken so that the gain contribution of the AGC unit  1018  is compensated in the final Down-link System Link Gain G d1  calculations or the gain value of the AGC  1018  is compensated in the SC unit  1022 . If the AGC unit  1018  is not included, the AD/C unit  1020  has to provide the appropriate dynamic range, which can be as high as 144 dB (24-bits). The AD/C unit  1020  is connected to the Signal Conditioning unit  1022 . The Signal Conditioning unit  1022  performs such tasks as channel select filtering for the desired operating frequency band, frequency conversion, insertion of reference frequency, signal level estimation, AGC algorithm, WLAN transmitter algorithms, and any other features that use signal conditioning and processing. For example, the channel select filters that can be implemented as poly-phased filters can be set for a given operating bandwidth of 1.3, 5, 10 or 15 MHz, operating at any position within the forward-link cellular or PCS or desired frequency spectrum. The Signal Conditioning unit  1022  clock frequency is derived from a local reference frequency  1070  and provided by clock unit  1024 . Depending on the system parameters and the appropriate operational bandwidth and the load of the supported operations, such as filtering, the Signal Conditioning unit  1022  may be implemented by a variety of technologies such as FPGAs, ASICs and general purpose DSPs such as Texas Instruments TMS320C6416-7E3 processor. The Signal Conditioning unit  1022  may include all appropriate interfaces and memory. The Signal Conditioning unit  1022  is connected to Digital to Analogue Converter (DA/C) unit  1026 . The DA/C unit  1026  may include appropriate post filtering after digital to analogue conversion. The DA/C unit  1026  is connected to frequency converter unit  1028 . Frequency converter unit  1028  up-converts the frequencies of the input signal to the desired portion of U-NII band of frequencies. The frequency converter unit  1028  may supply all filtering for the correct operation of the transmitter chain. The operating frequency of the frequency converter unit  1028  is set by micro-controller unit  1060 . Therefore, Dynamic Channel Allocation (DCA) algorithm can be used to select the best operating frequency band. The frequency converter unit  1028  is connected to the variable gain amplifier unit  1030 . The gain of the amplifier  1030  is set by the micro-controller unit  1060 , and in most time is set to maximum allowed power for transmission in U-NII band. The variable gain amplifier unit  1030  is connected to Duplex filter  1034 . 
     The duplex filter  1034  is connected reverse-link LNA  1040  an the VG amplifier  1030 . LNA  1040  is connected to the frequency converter unit  1042 . Frequency converter unit  1042  is connected to the directional coupler unit  1041 . The frequency converter  1042  converts the frequency band of the incoming signal from the U-NII band to baseband, or “near baseband” frequency band. The frequency converter unit  1042  includes filtering for the correct operation of the receiver chain. The operating frequency of the frequency converter unit  1042  is set by micro-controller unit  1060 . Directional coupler unit  1041  is connected to Automatic Gain Control (AGC) unit  1044 , and the calibration signal receiver unit  1016 . The AGC unit  1044  is connected to Analogue to Digital Converter (AD/C) unit  1046  and the Signal Conditioning unit  1048 . The AGC  1044  is optional, and its task is to place the received signal level substantially close to the middle of the dynamic range of the AD/C  1046 . If included, the design and operation of the unit  1044  are configured so that in the presence of low signal power noise within the operating bandwidth does not dominate the operation of the AGC unit  1044 . Also care can be taken so that the gain contribution of the AGC unit  1044  is compensated in the final Up-link System Link Gain G u1  calculations or the gain value of the AGC  1044  is compensated in the SC unit  1048 . If the AGC unit  1044  is not included, the AD/C unit  1046  supplies suitable dynamic range, which can be as high as 144 dB (24-bits). The AD/C unit  1046  is connected to the Signal Conditioning unit  1048 . The Signal Conditioning unit  1048  performs such tasks as channel select filtering for the desired operating frequency band, frequency conversion, signal calibration receiver, signal level estimation, AGC algorithm, WLAN receiver algorithms and any other features that use signal conditioning and processing. For example, the channel select filters that can be implemented as poly-phased filters can be set for a given operating bandwidth of 1.3, 5, 10 or 15 MHz, operating at any position within the forward-link U-NII or any desired frequency spectrum. The Signal Conditioning unit  1048  clock frequency is derived from a local reference frequency  1070  and provided by clock unit  1024 . Depending on the system parameters such as appropriate operational bandwidth and the load of the supported operations, such as filtering, the Signal Conditioning unit  1048  may be implemented by a variety of technologies such as FPGAs, ASICs and general purpose DSPs such as Texas Instruments TMS320C6416-7E3 processor. The Signal Conditioning unit  1048  may include all appropriate interfaces and memory. The Signal Conditioning unit  1048  is connected to Digital to Analogue Converter (DA/C) unit  1050 . The DA/C unit  1050  is connected to frequency converter unit  1052 . The DA/C unit  1050  supplies post filtering subsequent to digital to analogue conversion. Frequency converter unit  1052  up-converts the frequencies of the input signal to the desired portion of cellular or PCS band of frequencies. The frequency converter unit  1052  includes filtering for the correct operation of the transmitter chain. The operating frequency of the frequency converter unit  1052  is set by micro-controller unit  1060 . The frequency converter unit  1052  is connected to the variable gain amplifier unit  1054 . The gain of the amplifier  1054  is set by the micro-controller unit  1060 . The variable gain amplifier unit  1054  is connected to directional coupler  1056 . The directional coupler  1056  is connected to Duplex filter  1010 . It is also possible to use hybrid combiners instead of the directional couplers  1041  and  1056 . 
     A calibration signal generator/transmitter  1058  is coupled to the reverse-link transmitter path via the directional coupler  1056 . The unit  1058  will provide a calibration signal, at desired power levels, which is used to establish the level of the above mentioned Up-link System Path Loss, PL u1 , that exists between the Network unit  1002  ( 502  in  FIG. 4 ) and the User unit  2002  in  FIG. 13  ( 504  in  FIG. 4 ). The calibration signal generated by unit  1058  is transmitted via the diversity antennas  1004  and  1006  at a set transmit level which is substantially below any expected signal level from cellular network (e.g. 20 dB below the minimum expected cellular signal level). The calibration signal generated by unit  1058  is a direct-sequence spread spectrum signal modulated by a known Pseudo Random (PN) code with a known code phase (“own code” phase) and with a chipping rate comparable to the forward and reverse links of the Network unit  1002  and User unit  2002  operating bandwidths. The code phases are selected such that the minimum code phase difference is larger than the maximum expected path delay (measured in multiple number of chips) and after that, the other code phases should be multiple integer of the minimum code phase. The calibration signal receiver  1016  which is connected to the reverse-link of the Network unit  1002 , by using the known PN code and the transmit code phase (“own code” phase), is then capable of detecting and demodulating the calibration signal transmitted by unit  1058 , which has entered the reverse-link path via the mentioned closed-loop mechanism that exists between the Network unit  1002  and the User unit  2002  in  FIG. 13  ( 504  in  FIG. 4 ). The calibration signal receiver unit  1016  is capable of establishing the received signal strength, which is then used to estimate the Up-link System Path Loss, PL u1 , that exists between the Network unit  1002  ( 502  in  FIG. 4 ) and the User unit  2002  in  FIG. 13  ( 504  in  FIG. 4 ). The PN code phase can be assigned uniquely, or drawn according to a random algorithm, such that the probability of two units having the same code phase can be very low. The feature enables the calibration signal receiver  1016  to be able to scan and receive “other code” phases, and hence, establishing if there is any other signal coupling to or from other units that may be operating in the same geographical area. The code can also be modulated with information about the identity of the Network unit  1002 . The carrier frequency of the transmitted calibration signal may be at the operating cellular frequency band. However, carrier frequencies in other bands, such as ISM band at 2.4 GHz, may be used for the transmission of the calibration signal so that the calibration signal generator and transmitter  1058  carrier frequency is placed as near as possible to the operating frequency band. The chipping rate and the transmit power of the calibration signal PN code are such that the calibration signal complies with the FCC 47 CFR Part-15 rules. Although the ISM band is not the same as the cellular operating band, nevertheless, the band is sufficiently close to enable the system to establish the antenna coupling and the Up-link and Down-link System Link Gains, (G u1 , G d1 ), at the cellular operating band. The instantaneous amplitude and phase values are no longer relevant operating at ISM band. Any antenna and propagation differences in the average signals level between the two ISM and cellular operating bands can be investigated in the design phase and taken into account in the final system design. 
     The calibration transmitter unit  1058  and the calibration receiver unit  1026  baseband functions can be integrated and supported by the Signal Conditioning unit  1048 . The calibration transmitter unit  1058  and the calibration receiver unit  1016  functions can also be integrated into reverse-link signal path. In the example, the calibration signal generator and transmitter unit  1058  and the calibration signal receiver  1016  are both in the Network unit  1002 . However, both or one of the units including calibration signal generator and transmitter unit  1058 , and calibration signal receiver  1016 , can also be placed in the User unit  2002  with certain modifications and considerations. In some cases, a calibration mechanism for the forward-link, similar to the one described for the reverse-link, includes components such as the units,  1056 ,  1058 ,  1016  and  1041 , which is placed in the User unit  2002 . 
     The Equipment ID and reference frequency unit  624  shown in  FIG. 5 , in the forward-link path, is now supported by the Signal Conditioning unit  1022  in the digital Network unit  1002 , with the description and function remaining the same as the one discussed for unit  624 . 
     The control link unit  1062  is a radio link between the two Network  1002  and the User  2002  (in  FIG. 13 ) units. It may be a proprietary link that operates in one of the unlicensed band of frequencies, or may be a standard wireless link such as 802.11b, 802.11a, 802.11g or Bluetooth, designed to operate in the unlicensed band. The control link unit  1062  is connected to micro-controller unit  1060  and is able to communicate through an appropriate interface. The control link unit  1062  is also connected to antennas  1066  and  1064  for transmission and reception of the control signals. Note that provided that the antenna bandwidth and operating frequency allow, with minor modifications to unit  1002 , antenna units  1036  and  1038  can also be used for the control link unit  1062  operations. With minor modifications to unit  1002 , and where the selected operating frequencies allow, the baseband functionality of the control link unit  1062  can be included in the Signal Conditioning units  1022  and  1048 , with the transmit/receive control link unit  1062  signals multiplexed (in frequency or time) with the transmit/receive signals of the forward and the reverse-link Network unit  1002 , that are transmitted and received by antennas  1038  and  1036 . 
     Micro-controller unit  1060  is a simple micro-processor such as ARM7 or ARM9 with all the appropriate memory and interfaces. The micro-controller unit  1060  is controlling the operation of the Network unit  1002  and may perform some additional signal conditioning and processing such as signal level averaging and estimation. Some of the task of the micro-controller unit  1060  is to set the operating bandwidth and gain of the forward and reverse link Network unit  1002  components, communicate with the User unit  2002  in  FIG. 13  via the control link unit  1062 , control and communicate with the calibration signal generator and transmitter  1058  and calibration signal receiver  1016 . Other tasks of the micro-controller  1060  are discussed by way of an example given in  FIGS. 7 ,  8  and  9 . Micro-controller unit  1060  is connected to units  1062 ,  1016 ,  1058 ,  1052 ,  1048 ,  1042 ,  1030 ,  1028 ,  1022  and  1014 . 
     Units  1062 ,  1016 ,  1058 ,  1052 ,  1042 ,  1060 ,  1028 ,  1046 ,  1020 ,  1024  and  1014  are all connected to local oscillator unit  1070 , or derive their clock and reference frequencies from the local oscillator  1070  signal. 
     A simple user interface unit  1061 , which can be a keypad or simple dipswitch, is connected to micro-controller unit  1060 . 
       FIG. 13  shows an example of digital implementation of the User unit  702  (labeled  2002  in  FIG. 13 ), which is placed where good signal coverage does not exist, indoor or outdoors. Two antennas  2034  and  2036  are used for antenna diversity for the cellular band transmitter and receiver operation of the User unit  2002 . Also, two antennas  2004  and  2006  are used for antenna diversity of the U-NII band operation of the User unit  2002 . Although any diversity-combining scheme such as Maximal Ratio Combining, etc. can be used for the receiver chain, and transmit diversity schemes such as random phase change in one or both antennas for the transmitter chain, a simple scheme that is based on antenna switched diversity with “continuous switching” strategy is suggested here. The continuous switching strategy, with the switching rate selected for optimum performance (e.g. at, or twice the GSM Timeslot rate ˜4.6 msec), can be used for both transmit and receive operation, and will result in a nominal average transmit/receive signal power, provided the antennas are placed sufficiently apart. The continuous-switch diversity scheme is simply implemented as a simple RF switch at the antenna ports. Therefore, the RF switch  2032  connected to antennas  2034  and  2036  and the duplex filter  2030  and the micro-controller  2054 , under the control of the micro-controller  2054 , will provide switching operations for the cellular transmit/receive operation of the User unit  2002 . Also the RF switch  2008  connected to antennas  2004  and  2006  and the duplex filter  2010  will provide switching operations for the U-NII band transmit/receive operation of the User unit  2002 . The duplex filter  2010  is connected to forward-link LNA  2012  and VG amplifier  2052 . LNA  2012  is connected to the frequency converter unit  2014 . Frequency converter  2014  is connected to Automatic Gain Control (AGC) unit  2016 . The frequency converter  2014  converts the frequency band of the incoming signal from the cellular band to baseband, or “near baseband” frequency band. The frequency converter unit  2014  includes all appropriate filtering for the correct operation of the receiver chain. The operating frequency of the frequency converter unit  2014  is set by micro-controller unit  2054 . The AGC unit  2016  is connected to Analogue to Digital Converter (AD/C) unit  2018  and the Signal Conditioning unit  2020 . The AGC  2016  is optional, and its task is to place the received signal level substantially close to the middle of the dynamic range of the AD/C  2018 . If included, design and operation of the unit  2016  are arranged so that in the presence of low signal power noise within the operating bandwidth does not dominate the operation of the AGC unit  2016 . Also care may be taken so that the gain contribution of the AGC unit  2016  is compensated in the final Down-link System Link Gain G d1  calculations, or the gain value of the AGC  2016  is compensated in the SC unit  2020 . If the AGC unit  2016  is not included, the AD/C unit  2018  supplies a suitable dynamic range, which can be as high as 144 dB (24-bits). The AD/C unit  2018  is connected to the Signal Conditioning unit  2020 . The Signal Conditioning unit  2020  is programmed to perform such tasks as channel select filtering for the desired operating frequency band, frequency conversion, extraction of reference frequency, signal level estimation, AGC algorithm, WLAN receiver algorithms and any other features that usesignal conditioning and processing. For example, the channel select filters that can be implemented as poly-phased filters can be set for a given operating bandwidth of 1.3, 5, 10 or 15 MHz, operating at any position within the forward-link cellular or PCS or desired frequency spectrum, and set similar to the same parameters as the Network unit  1002 . The Signal Conditioning unit  2020  extracts the reference frequency transmitted by the Network unit  1002 . The DA/C  2021 , which is connected to the Signal Conditioning unit  2020  provides the analogue form of the reference frequency  2023 . Where the Network unit  1002  and the User unit  2002  use the mains electricity supply for their operations, it is possible to use the 60 Hz (or 50 Hz) mains oscillations, to “lock” the local oscillators of these two units, to a common frequency source. The 60 Hz or 50 Hz mains oscillations are converted, by suitable circuitry, to the desired frequency, for the operation of the Network unit  1002  and the User unit  2002 . The Signal Conditioning unit  2020  clock frequency is derived from a local reference frequency  2023  and provided by clock unit  2022 . Depending on the system parameters such as operational bandwidth and load of the supported operations, such as filtering, the Signal Conditioning unit  2020  may be implemented by a variety of technologies such as FPGAs, ASICs and general purpose DSPs such as Texas Instruments TMS320C6416-7E3 processor. The Signal Conditioning unit  2020  includes suitable interfaces and memory. The Signal Conditioning unit  2020  is connected to Digital to Analogue Converter (DA/C) unit  2024 . The DA/C unit  2024  is connected to frequency converter unit  2026 . The DA/C unit  2024  includes post filtering that is appropriate after the digital to analogue conversion. Frequency converter unit  2026  up-converts the frequencies of the input signal to the desired portion of cellular (or PCS) band of frequencies. The frequency converter unit  2026  includes filtering for correct operation of the transmitter chain. The operating frequency of the frequency converter unit  2026  is set by micro-controller unit  2054 . The frequency converter unit  2026  is connected to the variable gain amplifier unit  2028 . The gain of the amplifier  2028  is set by the micro-controller unit  2054 . The variable gain amplifier unit  2028  is connected to Duplex filter  2030 . 
     The Duplex filter  2030  is also connected to the reverse-link LNA  2038 . LNA  2038  is connected to the frequency converter unit  2040 . Frequency converter  2040  is connected to Automatic Gain Control (AGC) unit  2042 . The frequency converter  2040  converts the frequency band of the incoming signal from the cellular (or PCS) band to baseband, or “near baseband” frequency band. The frequency converter unit  2040  includes filtering for correct operation of the receiver chain. The operating frequency of the frequency converter unit  2040  is set by micro-controller unit  2054 . The AGC unit  2042  is connected to Analogue to Digital Converter (AD/C) unit  2044  and the Signal Conditioning unit  2046 . The AGC  2042  is optional, and its task is to place the received signal level substantially close to the middle of the dynamic range of the AD/C  2044 . If included, design and operation of the unit  2042  are configured so that in the presence of low signal power noise within the operating bandwidth does not dominate the operation of the AGC unit  2042 . Also care may be taken so that the gain contribution of the AGC unit  2042  is compensated in the final Up-link System Link Gain, G u1  calculations, or the gain value of the AGC  2042  is compensated in the SC unit  2046 . If the AGC unit  2042  is not included, the AD/C unit  2044  supplies an appropriate dynamic range, which can be as high as 144 dB (24-bits). The AD/C unit  2044  is connected to the Signal Conditioning unit  2046 . The Signal Conditioning unit  2046  performs such tasks as channel select filtering for the desired operating frequency band, frequency conversion, signal level estimation, AGC algorithm, WLAN transmitter algorithms and any other features that usesignal conditioning and processing. For example, the channel select filters that can be implemented as poly-phased filters can be set for a given operating bandwidth of 1.3, 5, 10 or 15 MHz, operating at any position within the forward-link U-NII or any desired frequency spectrum and set similar to the same parameters as the Network unit  1002 . The Signal Conditioning unit  2046  clock frequency is derived from a local reference frequency  2023  and provided by clock unit  2022 . Depending on system parameters such as operational bandwidth and supported operation load, for example filtering, the Signal Conditioning unit  2046  may be implemented by a variety of technologies such as FPGAs, ASICs and general purpose DSPs such as Texas Instruments TMS320C6416-7E3 processor. The Signal Conditioning unit  2046  includes appropriate interfaces and memory. The Signal Conditioning unit  2046  is connected to Digital to Analogue Converter (DA/C) unit  2048 . The DA/C unit  2048  is connected to frequency converter unit  2050 . The DA/C unit  2048  includes post filtering that is appropriate the digital to analogue conversion. Frequency converter unit  2050  up converts the frequencies of the input signal to the desired portion of U-NII band of frequencies. The frequency converter unit  2050  includes appropriate filtering for the correct operation of the transmitter chain. The operating frequency of the frequency converter unit  2050  is set by micro-controller unit  2054 , and therefore Dynamic Channel Allocation (DCA) algorithm can be used to select the best operating frequency band. The frequency converter unit  2050  is connected to the variable gain amplifier unit  2052 . The gain of the amplifier  2052  is set by the micro-controller unit  2054  and in most time is set to maximum allowed power for transmission in U-NII band. The variable gain amplifier unit  2052  is connected to Duplex filter  2010 . 
     The Control Link unit  2056  is a radio link between the Network unit  1002  and the User unit  2002 . It may be a proprietary link that operates in one of the unlicensed band of frequencies, or may be a standard wireless link such as 802.11b, 802.11a or Bluetooth, designed to operate in unlicensed band. The control link unit  2056  is connected to micro-controller unit  2054  and is able to communicate through an appropriate interface. The control link unit  2056  is also connected to antenna  2058  and  2060  for transmission and reception of the control signals. Note that provided that the antenna bandwidth and operating frequency allow, with minor modifications to unit  2002 , antenna units  2004  and  2006  can also be used for the control link unit  2056  operations. Also, with minor modifications to unit  2002 , and where the selected operating frequencies allow, the baseband functionality of the control link unit  2056  can be included in the Signal Conditioning units  2046  and  2020  respectively, with the transmit/receive control link unit  2056  signals multiplexed (in frequency or time) with the transmit/receive signals of the forward and reverse User unit  2002 , that are transmitted and received by antennas  2004  and  2006 . 
     Micro-controller unit  2054  is a simple micro-processor such as ARM7 or ARM9 with all the appropriate memory and interfaces. The micro-controller unit  2054  is controlling the operation of the Network unit  2002  and may perform some additional signal conditioning and processing such as signal level averaging and estimation. Some of the task of the micro-controller unit  2054  is to set the operating bandwidth and gain of the forward and reverse link network components, and to communicate with the Network unit  1002  in  FIG. 12  via the control link unit  2056 . Other tasks of the micro-controller  2054  are discussed by way of an example given in  FIGS. 10 and 11 . Micro-controller unit  2054  is connected to units  2056 ,  2052 ,  2050 ,  2046 ,  2040 ,  2028 ,  2026 ,  2020  and  2014 . 
     A simple user interface unit  2055 , which can be a keypad or simple dipswitch, is connected to micro-controller unit  2054 . 
     Units  2056 ,  2052 ,  2050 ,  2040 ,  2028 ,  2026 ,  2054 ,  2018 ,  2044 ,  2022  and  2014  are all connected to local oscillator unit  2023 , or derive their clock and reference frequencies from the local oscillator  2023  signal. 
     Considering only the reverse-link operation of the Network unit  1002  and the User unit  2002 , as an example, the signals received through antenna units  2034  and  2036 , are re-transmitted through the antenna units  1004  and  1006 , at a higher signal power. These re-transmitted signals can be received again through the antenna units  2034  and  2036  (and have been termed above as the “Up-link Returned-Signal”), causing a signal return path in the system that may cause instability in the operation of the booster. In the digital implementation of the Network unit  1002  and the User unit  2002 , it may be possible to reduce the magnitude of the returned signal (Up-link Returned-Signal) by various signal-processing techniques. The choice, design and effectiveness of the illustrative techniques depend on the system parameters and operating conditions. Most known multipath mitigation algorithms can also be applied for return signal reduction, however, due to the extremely small propagation delays between the Network unit  1002  and the User unit  2002 , and the limited temporal resolution of the system, the above conventional algorithms may be practically hard and expensive to implement, at best, or ineffective and detrimental, at worst. Therefore, an example of a filtering technique is supplied, for example in the “Channel Filtering” section, where a “deliberate” delay in the re-transmission of the received signal is used, to separate the returned signal (Up-link Returned-Signal), from the original incident signal, at the output of the antenna unit  2034  and  2036  terminators. For example, a delay of about 1 usec, will ensure the time separation of the re-transmitted signal, from the original received signal, and hence the ability to mitigate the re-transmitted signal by the example “Channel Filtering” technique, which is discussed later. The delay can be introduced in the Signal Conditioning unit  1048 , provided that there is a digital data buffer of sufficient size available. The Channel Filtering operation can also be performed by the Signal Conditioning unit  1048  (or SC unit  2046 ), or can be performed by a separate ASIC or FPGA, connected to the AD/C unit  1046 , and the Signal Conditioning unit  1024 . Alternatively, with minor modifications, the ASIC or the FPGA units can be placed in the User unit  2002 , connected to the AD/C unit  2042  and Signal Conditioning unit  2046 . The calibration signal can be used for channel estimation purposes, so that the amplitude and the phase of the overall channel response (including the return path) can be estimated, for the setting of the Channel Filter taps. The introduction of Channel Filter in the signal path also has an impact on the operation of the antenna diversity scheme. Channel estimation is performed so that antenna switching operations are synchronized so that, out of possible four channels, only two possible propagation channels exist. Since the antenna switching (selection) is under the control of micro-controller unit  1060  in the Network unit  1002 , and micro-controller  2054  in the User unit  2002 , channel estimation can be performed for both propagation paths, and two sets of Channel Filter coefficients can be determined for filtering operation. Therefore, it is possible to select (or switch to) the relevant filter coefficients, synchronized and in harmony with the antenna selection operation. The Channel Filtering mechanism is not used to totally mitigate the returned signal but is rather used to suppress the signal sufficiently so that some system gain is possible for the signal boosting operation. The introduction of the “deliberate delay” may also be used in conjunction with any other known signal-processing algorithm. 
     The above discussion is also relevant to the forward-link of the Network unit  1002  and the User unit  2002 , and therefore the above “delay” and “Channel Filtering”, with the aid of the forward-link calibration signal (not included in the  FIGS. 12 and 13 ) is performed in the forward-link of the Network unit  1002  (or User unit  2002 ). 
     Other techniques, such as the use of vertical polarization for antenna units  1004  and  1006 , and horizontal polarization for antennas  2034  and  2036  can further improve the system performance. It is also possible to improve system performance by the use of directional antennas, as in conventional booster and repeater systems. 
     The control-flow description given for  FIGS. 7 ,  8 ,  9 ,  10  and  11 , with minor modifications, can also be used for the digital implementation of the Network unit  1002  and User unit  2002 , which is discussed above in  FIGS. 12 and 13 . 
     The illustrative description is only an example of how the system may be implemented, and is not the only possible method and solution. Several points are noted, as follows:
         1. The Network unit  1002  may control several User units, such as the User unit  2002 . In such setups, the example control flow, shown in  FIGS. 7 ,  8 ,  9 ,  10  and  11  may be modified such that the Network Unit  1002  can initialize each User unit independently. For stable operation, the reverse-link Network unit  1002  variable gain amplifier unit  1054  gain is set for minimum Up-link System Path Loss, PL u1 , for operation with all the active User units. Thus, if the Down-link System Path Loss, PL d1 , is based on the Up-link System Path Loss, PL u1 , calculations (i.e. PL d1 ≈PL u1 ), the minimum variable gain amplifier unit  2028  gain is used for all the User units in the forward-link under the control of the Network unit  1002 .   2. Another modification for multiple User unit (several User units  2002 ) operation is that the final Down-link System Path Loss, PL d1 , and the Up-link System Path Loss, PL u1 , measurements should be carried out with all User units, under the control of the Network unit  1002  (including Network unit  1002  itself), active such that aggregate signal power levels do not exceed the desired Down-link System Link Gain, G d1 , or the desired Up-link System Link gain, G u1 . If combined signal from the User Units exceeds the acceptable level for either of the reverse or forward system link gains, the appropriate amplifier gains are reduced in iterative step increments to such level that the maximum allowed system link gain, or the forward and the reverse links are met.   3. Additional hardware may be included, similar to the calibration signal generator and transmitter  1058 , and the calibration signal receiver  1016  in the forward-link path of either the Network unit  1002  or in the User unit  2002  to assess the Down-link System Path Loss, PL d1 , independently (for each User unit  2002  controlled by Network unit  1002 ).   4. Although the signal path in both the Network unit  1002  and the User unit  2002 , in the forward link, is constantly active, to boost the beacon (BCCH in GSM) transmissions of the base stations, the reverse-link path signal path of the Network unit  1002  and the User unit  2002  may be inactive, unless a substantial signal level is detected (i.e. “gated”). Therefore, in the User unit  2002 , based on the received signal power level on reverse-link, which can be measured after the LNA unit  2038  or in Signal Conditioning unit  2046 , the micro-controller unit  2054  switches the VG amplifier unit  2052  “OFF” and if the signal power level is below the desired threshold, or “ON” if the signal power level is above the desired threshold. Equally, in the Network unit  1002 , based on the received signal power level on reverse-link, which can be measured after the LNA unit  1040  or in Signal Conditioning unit  1048 , the micro-controller unit  1060  switches the VG amplifier unit  1054  “OFF” and if the signal power level is below the desired threshold, or “ON” if the signal power level is above the desired threshold. Care is taken that the reverse-link “gated” operation does not interfere with the calibration signal path and mechanism involving the units  1058  and  1026 . Therefore, either the “gated” operation is replaced by continuous operation during the calibration process, or, where possible, a forward-link calibration is placed and used in a manner similar to the reverse-link mechanism for both Down-link System Path Loss, PL d1 , and Up-link System Path Loss, PL u1 , calculations.   5. With certain modifications in the hardware and the control software, it is possible to merge the Network unit  1002  and the User unit  2002  into a single unit, connected “back-to-back”. The design and operation of the back-to-back option is shown in  FIG. 15  and discussed later.   6. It is also possible to transmit the unique Network unit  1002  identity code, and optionally device location, to the cellular network. The information can be used to locate a user in an indoor environment, for example by generating a heavily coded (protected), low bit rate data, containing a long known preamble, the unique identity code and optionally the longitude and the latitude of the Network unit  1002 . The information can then be pulse-shaped for low spectral leakage and superimposed on the reverse-link signal of a given channel by an appropriate modulation scheme, within the Network unit  1002 . The choice of the modulation scheme depends on the operating cellular system. For example, for GSM, which enjoys a constant envelope modulation such as GMSK, amplitude modulation (with low modulation index) can be used. For CDMA systems, with fast reverse-link power control, DBPSK can be used as the modulation scheme. Extraction of information from the received channel signal at base station may be improved by base station receiver modifications, but does not affect normal operation of the cellular link.       

     The noted points are applicable to many different digital booster implementations. 
     Back-To-Back Booster 
     In a Back-to-Back arrangement, transmission and reception in U-NII band and the control link that exists between the Network unit  602  and the User unit  702  is superfluous. FIG.  14  depicts an analogue implementation example of such an arrangement, where the booster is placed where good signal coverage exists, indoor or outdoors. The back-to-back unit  2252  consists of antennas  2254 ,  2256 ,  2282  and  2280 , all operating in the cellular spectrum of interest. Antennas  2254  and  2256  are connected to the RF switch  2258 , where antenna switched diversity operation for transmit and receive operation is provided as discussed for Network unit  602  and User unit  702 . In the forward-link, the RF switch unit  2258  is connected to the duplex filter unit  2260 . The duplex filter unit  2260  is connected to the LNA  2288  in the Forward-link unit  2264 . The LNA  2288  is connected to the filter unit  2286 . The bandpass filter unit  2286  can be designed to pass all or a desired part of the interested cellular spectrum, or can be a bank of overlapping bandpass filters, covering the full spectrum of the interested cellular system, with a RF switch, such that the desired band and bandwidth, can be selected. Filter unit  2286  is connected to the variable gain amplifier  2284 . The gain of the VG amplifier unit  2284  is set by micro-controller unit  2270 . The variable gain amplifier unit  2284  is connected to the duplex filter  2276 . The duplex filter  2276  is connected to RF switch  2278 . The antennas  2282  and  2280  are both connected to the RF switch  2278 . On the reverse-link, the RF switch unit  2278  is connected to the duplex filter  2276 . The duplex filter unit  2276  is connected to directional coupler unit  2274 . The directional coupler unit  2274  is connected to calibration signal receiver  2272  and LNA  2290  in the Reverse-link unit  2266 . The calibration signal receiver unit  2272  which is coupled to the reverse-link receive path of the booster unit  2252 , by directional coupler  2272 , using the known PN code and the transmit code phase is then capable of detecting and demodulating the calibration signal transmitted by unit  2268 , which has entered the reverse-link path via the mentioned closed-loop mechanism that exists between the antenna units  2254 ,  2256  and the antenna units  2280 ,  2282 . The calibration signal receiver unit  2272  is capable of establishing the received signal strength, which is then used to estimate the Up-link System Path Loss, PL u1 . The LNA  2290  is connected to filter unit  2292 , which is connected to variable gain amplifier unit  2294 . The bandpass filter  2292  can be designed to pass all or a desired part of the interested cellular spectrum, or can be a bank of overlapping bandpass filters, covering the full spectrum of the interested cellular system, with a RF switch, such that the desired band and bandwidth can be selected. The gain of the VG amplifier unit  2294  is set by micro-controller unit  2270 . The variable amplifier  2294  is connected to directional coupler unit  2262 . Directional coupler unit  2262  is connected to the calibration signal generator and transmitter unit  2268 , and duplex filter  2260 . The micro-controller  2270  is connected to calibration signal generator and transmitter unit  2268 , the calibration signal receiver  2272 , the Reverse-link unit  2266  and Forward-link unit  2264 . A simple user interface unit  2271 , which can be a keypad or simple dipswitch, is connected to micro-controller unit  2270 . 
     Although many functional units of the Network unit  602  and the User unit  702  can be eliminated in the back-to-back unit  2252 , operation and the remaining units of the booster remain fundamentally the same as the one described for the Network unit  602  and User unit  702 . Calibration signal transmission and reception are shown just for the Reverse-link. However, the same mechanism can be placed for the forward-link if desired, which also results in better system performance. Since the antenna units  2254 ,  2256 ,  2282  and  2280  are placed close to each other, antenna isolation can be provided by highly directional antennas, with increased front-to-back radiation ratios. 
     The unique unit  2252  identity code and optionally device location can be transmitted to the cellular network. The information can be used to locate a user in an indoor environment, for example by generating a heavily-coded (protected), low bit rate data, containing a long known preamble, the unique identity code and optionally the longitude and the latitude of the unit  2252 . The information can then be pulse-shaped for low spectral leakage and superimposed on the reverse-link signal of a given channel by an appropriate modulation scheme, within the unit  2252 . Choice of the modulation scheme depends on the operating cellular system. For example, for GSM, which enjoys a constant envelope modulation such as GMSK, amplitude modulation (with low modulation index) can be used. For CDMA systems, with fast reverse-link power control, DBPSK can be used as the modulation scheme. Extraction of the illustrative information from the received channel signal at base station may involve base station receiver modifications, but does not effect normal operation of the cellular link. 
       FIG. 15  depicts a digital implementation example of Back-to-Back arrangement, where the booster is placed where good signal coverage exists, indoor or outdoors. The back-to-back unit  2302  consists of antennas  2304 ,  2306 ,  2328  and  2330 , all operating in the cellular spectrum of interest. Antennas  2304  and  2306  are connected to the RF switch  2308 , where antenna switched diversity operation for transmit and receive operations is provided as discussed for Network unit  1002  and User unit  2002 . In the forward-link, the RF switch unit  2308  is connected to the duplex filter unit  2310 . The RF switch unit  2308  is also connected to micro-controller  2350 . The duplex filter unit  2310  is connected to the LNA  2312 . The directional coupler unit  2311  is connected to output of the LNA  2312 , and the calibration receiver unit  2305 . The calibration receiver  2305  is also connected to micro-controller  2350 . The directional coupler unit  2311  is also connected to the frequency converter unit  2313 . Frequency converter  2313  is connected to Automatic Gain Control (AGC) unit  2314 . The frequency converter  2313  converts the frequency band of the incoming signal from the cellular band to baseband, or “near baseband” frequency band. The frequency converter unit  2313  includes filtering for the correct operation of the receiver chain. The operating frequency of the frequency converter unit  2313  is set by micro-controller unit  2350 . The AGC unit  2314  is connected to Analogue-to-Digital Converter (AD/C) unit  2316 . The AGC  2314  is optional, and its task is to place the received signal level substantially close to the middle of the dynamic range of the AD/C  2316 . If included, design and operation of unit  2314  are configured so that in the presence of low signal power, noise within the operating bandwidth does not dominate the operation of the AGC unit  2314 . Also care is taken so that the gain contribution of the AGC unit  2314  is compensated in the final Down-link System Link Gain, G d1  calculations, or alternatively the gain value of the AGC  2314  is compensated in the SC unit  2318 . If the AGC unit  2314  is not included, the AD/C unit  2316  supports a suitable dynamic range, which can be as high as 144 dB (24-bits). The AD/C unit  2316  is connected to Signal Conditioning unit  2318 . The Signal Conditioning unit  2318  performs such tasks as channel select filtering for the desired operating frequency band, frequency conversion, signal level estimation, AGC algorithm, and any other features that usesignal conditioning and processing. For example, the channel select filters that can be implemented as poly-phased filters can be set for a given operating bandwidth of 1.3, 5, 10 or 15 MHz, operating at any position within the forward-link cellular or PCS or desired frequency spectrum. Depending on the system parameters such as operational bandwidth and supported operation load, for example filtering, the Signal Conditioning unit  2318  may be implemented by a variety of technologies such as FPGAs, ASICs and general purpose DSPs such as Texas Instruments TMS320C6416-7E3 processor. The Signal Conditioning unit  2318  includes appropriate interfaces and memory. The Signal Conditioning unit  2318  is connected to Digital-to-Analogue Converter (DA/C) unit  2320 . The DA/C unit  2320  includes post filtering that is appropriate the digital to analogue conversion. The DA/C unit  2320  is connected to frequency converter unit  2321 . Frequency converter unit  2321  up-converts the frequencies of the input signal to the original band of cellular frequencies. The frequency converter unit  2321  includes appropriate filtering for the correct operation of the transmitter chain. The operating frequency of the frequency converter unit  2321  is set by micro-controller unit  2350 . The frequency converter unit  2321  is connected to the variable gain amplifier unit  2322 , which is connected to the directional coupler unit  2325 . The gain of the VG amplifier unit  2322  is set by micro-controller unit  2350 . The directional coupler unit  2325  is connected to the calibration signal generator and transmitter unit  2323  and the duplex filter  2324 . The calibration signal generator and transmitter unit  2323  is also connected to the micro-controller  2350 . The duplex filter  2324  is connected to RF switch  2326 . The antennas  2328  and  2330  are both connected to the RF switch  2326 . 
     On the reverse-link, the RF switch unit  2326  is connected to the duplex filter  2324 . The RF switch unit  2326  is also connected to micro-controller  2350 . The duplex filter unit  2324  is connected to LNA unit  2332 . The LNA unit  2332  is connected to the directional coupler unit  2334 . The directional coupler unit  2334  is connected to the frequency converter unit  2335 . Frequency converter  2335  is connected to Automatic Gain Control (AGC) unit  2336 . The frequency converter  2335  converts the frequency band of the incoming signal from the cellular band to baseband, or “near baseband” frequency band. The frequency converter unit  2335  includes filtering for the correct operation of the receiver chain. The operating frequency of the frequency converter unit  2335  is set by micro-controller unit  2350 . The directional coupler unit  2334  is also connected to calibration signal receiver unit  2348 . The frequency converter unit  2335  is connected to AGC unit  2336 . The AGC unit  2336  is connected to Analogue-to-Digital Converter (AD/C) unit  2338 . The AGC  2336  is optional, and its task is to place the received signal level substantially close to the middle of the dynamic range of the AD/C  2338 . If included, design and operation of the unit  2336  are configured so that in the presence of low signal power, noise within the operating bandwidth does not dominate the operation of the AGC unit  2336 . Also care is taken so that the gain contribution of the AGC unit  2336  is compensated in the final Up-link System Link Gain, G u1  calculations, or alternatively the gain value of the AGC  2336  is compensated in the SC unit  2340 . If the AGC unit  2336  is not included, the AD/C unit  2338  supports a suitable dynamic range, which can be as high as 144 dB (24-bits). The AD/C unit  2338  is connected to Signal Conditioning unit  2340 . The Signal Conditioning unit  2340  performs such tasks as channel select filtering for the desired operating frequency band, frequency conversion, signal level estimation, AGC algorithm, and any other features that usesignal conditioning and processing. For example, the channel select filters that can be implemented as poly-phased filters can be set for a given operating bandwidth of 1.3, 5, 10 or 15 MHz, operating at any position within the forward-link cellular or PCS or desired frequency spectrum. Depending on the system parameters such as operational bandwidth and the load of the supported operations, such as filtering, the Signal Conditioning unit  2340  may be implemented by a variety of technologies such as FPGAs, ASICs and general purpose DSPs such as Texas Instruments TMS320C6416-7E3 processor. The Signal Conditioning unit  2340  includes appropriate interfaces and memory. The Signal Conditioning unit  2340  is connected to Digital-to-Analogue Converter (DA/C) unit  2342 . The DA/C unit  2342  includes post filtering that is appropriate the digital to analogue conversion. The DA/C unit  2342  is connected to the Frequency converter unit  2343 , which up-converts the frequencies of the input signal to the desired portion of cellular or PCS band of frequencies. The frequency converter unit  2343  includes filtering for the correct operation of the transmitter chain. The operating frequency of the frequency converter unit  2343  is set by micro-controller unit  2350 . The frequency converter unit  2343  is connected to the variable gain amplifier unit  2344 , which is connected to the directional coupler unit  2346 . The gain of the VG amplifier unit  2344  is set by micro-controller unit  2350 . The directional coupler unit  2346  is connected to the duplex filter  2310 . The duplex filter  2310  is connected to RF switch  2308 . The antennas  2304  and  2306  are both connected to the RF switch  2308 . A simple user interface unit  2351 , which can be a keypad or simple dipswitch, is connected to micro-controller unit  2350 . Units  2305 ,  2323 ,  2313 ,  2321 ,  2348 ,  2335 ,  2343 ,  2352  and  2350  are all connected to local oscillator unit  2356 , or derive their clock or reference frequencies from the local oscillator  2356 . The Signal Conditioning units  2318  and  2340  clock frequencies are derived from a local reference frequency  2356  provided by clock unit  2353 . 
     Although, many functional units of the Network  1002  and the User  2002  units can be omitted in the back-to-back unit  2302 , the operation and the function of the most of the units of the booster  2302  remain fundamentally the same as the one described for the Network unit  1002  and User unit  2002 . As before, the calibration signal transmission and reception are shown just for the reverse-link. In the digital implementation of booster unit  2302 , the functional blocks for calibration signal generator and transmitter unit  2352 , and the calibration receiver unit  2348  can be included in the Signal Conditioning unit  2340  for the uplink, and in the Signal Conditioning unit  2318  for the downlink operation. Since the antenna units  2304 ,  2306 ,  2328  and  2330  are placed close to each other, antenna isolation can be provided by highly directional antennas, with increased front-to-back radiation ratios. 
     Considering only the reverse-link operation of the booster  2303 , as an example, the signals received through antenna units  2328  and  2330  are re-transmitted through the antenna units  2304  and  2306 , at a higher signal power. These re-transmitted signals can be received again through the antenna units  2330  and  2328  (and have been termed above as the “Up-link Returned-Signal”), causing a signal return path in the system that may cause instability in the operation of the booster. In the digital implementation of the booster unit  2302 , it may be possible to reduce the magnitude of the returned signal (Up-link Returned-Signal) by various signal-processing techniques. The choice, design and effectiveness of a technique depends on system parameters and operating conditions. Most known multi-path mitigation algorithms can also be applied for return signal reduction, however, due to the extremely small propagation delays between the antenna units  2304 ,  2306  and the antenna units  2328 ,  2330 , and the limited temporal resolution of the system, conventional multi-path mitigation algorithms may be practically hard and expensive to implement, at best, or ineffective and detrimental, at worst. Therefore, an example of a filtering technique is provided for example in the “Channel Filtering” section, where a “deliberate” delay in the re-transmission of the received signal is used, to separate the returned signal (Up-link Returned-Signal), from the original incident signal, at the output of the antenna unit  2328  and  2330  terminators. A delay of about 1 usec will ensure the time separation of the re-transmitted signal from the original received signal, and hence the ability to mitigate the re-transmitted signal, by the example channel filtering technique. The delay can be introduced in the Signal Conditioning unit  2340 , provided that there is a digital data buffer of sufficient size available. The Channel Filtering operation can also be performed by the Signal Conditioning unit  2340 , or can be performed by a separate ASIC or FPGA, connected to the AD/C unit  2338 , and the Signal Conditioning unit  2340 . The calibration signal can be used for channel estimation purposes, so that the amplitude and the phase of the overall channel response (including the return path) can be estimated, for the setting of the Channel Filter taps. The introduction of Channel Filter in the signal path also has an impact on the operation of the antenna diversity scheme. Because channel estimation is performed, antenna switching operations are synchronized so that, out of possible four, only two possible propagation channels exist. Since the antenna switching (selection) is under the control of micro-controller unit  2350 , channel estimation can be performed for both propagation paths, and two sets of Channel Filter coefficients can be determined for filtering operation. Therefore, it is possible to select (or switch to) the relevant filter coefficients, synchronized and in harmony with the antenna selection operation. The Channel Filtering mechanism is not used to totally mitigate the returned signal but rather to suppress the signal sufficiently so that some system gain is possible for the signal boosting operation. Introduction of the “deliberate delay” may also be used in conjunction with any other known signal-processing algorithm. 
     The above discussion is also relevant to the forward-link of the booster unit  2302 , and therefore the above “delay” and “Channel Filtering” are performed in the forward-link as well. 
     Other techniques, such as the use of vertical polarization for antenna units  2304  and  2306 , and horizontal polarization for antennas  2328  and  2330  can further improve the system performance. It is also possible to improve system performance by the use of directional antennas, as in conventional booster and repeater systems. 
     It is also possible to transmit the unique unit  2302  identity code, and optionally device location, to the cellular network. The information can be used to locate a user in an indoor environment, for example by generating a heavily coded (protected), low bit rate data, containing a long known preamble, the unique identity code and optionally the longitude and the latitude of the unit  2302 . The information can then be pulse-shaped for low spectral leakage and superimposed on the reverse-link signal of a given channel by an appropriate modulation scheme, within the unit  2302 . The choice of the modulation scheme depends on the operating cellular system. For example, for GSM, which enjoys a constant envelope modulation such as GMSK, amplitude modulation (with low modulation index) can be used. For CDMA systems, with fast reverse-link power control, DBPSK can be used as the modulation scheme. Extraction of information from the received channel signal at base station may involve base station receiver modifications, but does not effect the normal operation of the cellular link. 
     An example of the system operational flow diagrams is shown in the  FIG. 16 . With reference to  FIGS. 15 and 16 , on “power-up” or “reset” of the booster unit  2303 , the VG amplifiers  2322  and  2344  gain are always set to minimum and are switched “OFF”. The system is said to be “operational” when VG amplifiers  2322  and  2344  are switched “ON”, after the correct gain setting by instruction from micro-controller  2350 . Also, on “power-up” or “reset” action, the operation starts (step  2402 ), with the micro-controller  2350  instructs the reverse-link calibration receiver  2348  to scan for all possible code offsets (step  2404 ). If a substantial signal power transmitted by other units, operating within the same geographical area, is detected by the receiver unit  2348  (step  2406 ), the received signal powers are stored (step  2408 ). If no substantial signal is detected (step  2410 ), the micro-controller  2350  instructing the forward-link calibration receiver  2305  to scan for all possible code offsets (step  2410 ). If a substantial signal power transmitted by other units, operating within the same geographical area, is detected by the receiver unit  2305  (step  2416 ), the received signal powers are stored (step  2414 ). After the test for all possible code offsets is finished for the forward and reverse links of the system, and if other units signal power detected (step  2417 ), the received signals for each offset are tested and the largest signal power is selected (step  2412 ). If the selected signal power is above a safe threshold (step  2418 ), the unit  2302  displays an error message (step  2419 ) and stops operation (step  2422 ). If the selected signal power is below the safe threshold, the unit proceeds to step  2420 . If no substantial signal is detected or the detected signals are below the safe threshold (step  2416 ), the micro-controller  2350  selects an unused code offset (step  2420 ) and instructs both the forward and reverse link calibration signal generator and transmitter units  2323  and  2352 , which have not been transmitting so far, to commence transmission (step  2424 ). The micro-controller  2350  also instructs the forward and reverse calibration receivers  2305 ,  2348  to receive signal with the selected code offset (step  2425 ). Based on the forward and reverse calibration receivers  2305 ,  2348  outputs, the micro-controller  2350  calculates the Up-link and Down-link system gains, G u1  and G d1 , and the subsequent variable amplifier gains for the forward and reverse links (step  2426 ). Micro controller  2350  sets the gains of the forward and reverse link variable gain amplifier units  2322  &amp;  2346  to the calculated levels, which so far have been at a minimum and “OFF” (step  2428 ). The system commences full operation (step  2430 ), with the variable gain amplifier units  2322  &amp;  2346  switched “ON”. 
     Channel Filtering Example 
     The example provided here can be applied to the booster system described here to combat the effect of mentioned feed-back loop and the above mentioned Up-link Returned-Signal that may exist in the reverse-link of the system and Down-link Returned-Signal that may exist in the forward-link of the system. The “Channel Filtering” technique, discussed here, for the forward and the reverse links is autonomous and can either be applied to both or just one of the forward or the reverse links of the system, and can be implemented in the Network unit  1002  or the User unit  2002 , or both. To explain the working of Channel filtering, a simplified block diagram of the booster is shown in  FIG. 17 , and only the reverse-link operation is discussed for the Network unit  1002  and User unit  2002  (the Channel Filtering discussed here is applicable to all digital implementations). In the representation, no antenna diversity is assumed for either the Network unit  2452  (which is substantially similar to  1002  in  FIG. 12 ) or the User unit  2454  (which is substantially similar to  2002  in  FIG. 13 ). The processing and propagation delays within the booster system can be categorized as the following:
         τ Us =the User unit  2454  processing delay (relatively negligible).   τ P1 =the unlicensed band propagation delay.   τ Nrx =the Network unit  2452  receiver processing delay (relatively negligible).   τ Ntx =the Network unit  2452  transmitter processing delay (relatively negligible).   τ d =the “deliberate” delay introduced in the transmission path of the Network unit  2452 .   τ P2 =the licensed band propagation delay of the Up-link Returned-Signal.       

     The overall impulse response of the booster unit  2451  is shown in  2464 . The original incident pulse, entering from antenna  2462  (A 1 ), arrives at the input to the Network unit  2452  receiver after a delay of τ f , (the pulse is marked as  2468 ), where:
 
τ f =τ Us +τ P1 ≅τ P1  
 
     The pulse is amplified and transmitted  2470 , after the “deliberate” time delay τ d , from antenna  2456  (marked A 4  in  FIG. 17 ). The transmitted signal re-enters the antenna  2462  (A 1 ) after the propagation delay τ P2 , and arrives at the input to the Network unit  2452  receiver after a delay of τ f  (marked as  2472 ). So the overall delay for the Up-link Returned-Signal at the input to the Network unit  2452  receiver can be stated as τ t  and is substantially equal to:
 
τ t =τ Nrx +τ d +τ Ntx +τ P2 +τ f ≅τ d +τ P1 +τ P2  
 
     The returned pulse  2472  is delayed by the propagation path delays τ P1  and τ P2 , which can be very small in the booster&#39;s operating environment. The “deliberate” delay is introduced to sufficiently separate the Up-link Returned-Signal from the original incident pulse, such that filter coefficients can be estimated easily, and filtering can be performed more effectively. Introduction of another “deliberate” delay in the transmit path of the User unit  2454  ensures separation of the boosted transmitted pulse and the Up-link Returned-Signal, a condition that may be desirable to reduce the effect of the multipath experienced by the boosted transmitted pulse on the operation of the Channel filtering. 
     In the example here, the “Channel Filtering” unit  2512  (in  FIG. 18 ) is placed only on the reverse-link of the Network unit  1002 . The channel filtering process involves estimating the complex propagation channel impulse response, including amplitude and phase for all time delays, up to the maximum expected multipath delay. The complex channel impulse response, C(t,τ), can be provided by the calibration signal receiver unit  1016  shown in  FIG. 12 , as the information is readily available at the output of the unit, for the reverse-link path of the system. Note that based on the described design of the calibration signal mechanism shown in  FIG. 12  (also  FIG. 15 ), the channel impulse response, provided by the calibration signal receiver unit  1016 , will not include the delay contributions of the “deliberate” delay (τ d ), and the τ Nrx +τ Ntx  components. While τ Nrx +τ Ntx  is sufficiently small to ignore, the “deliberate” delay (τ d ) is added in the overall impulse response, in the Network unit  1002 , for the estimation of the Channel Filter coefficients. Similarly, if Channel Filtering operation is also used for the forward-link, a separate complex channel impulse response is used for the link. As a result, a similar calibration technique to the reverse-link is performed on the forward-link. An example of the estimated power of the channel impulse response, C(tτ),  2510 , at the output of the calibration signal receiver  1016  is shown in  FIG. 18 . The impulse response  2510  is for a maximum delay of 1 usec, assuming a calibration signal PN code chipping rate of 5 Mchips/sec and 2 samples per chip. In  FIG. 18 , C(t,τ)  2510  has three substantial distinguishable propagation paths at delays of 0.2 (P 1 ), 0.4 (P 2 ) and 1.0 (P 3 ) usec respectively. The maximum expected time delay corresponds to a signal path of about 300 meters, which is reasonable for the booster range and operational environment. The 1.0 usec maximum time delay, together with a “deliberate delay of 1 usec (τ d =1 usec), may be implemented using a 21-tap complex FIR filter, with half-chip tap spacing, for Channel Filtering operation.  FIG. 18  shows the Channel Filter unit  2512 . The Channel Filter unit  2512  has a 21-tap FIR filter  2506 , with tap delay of D=0.1 usec spacing, and with the variable complex coefficients set to the values shown in table  2508 . The FIR filter  2506  output is connected to one of the inputs of the adder unit  2504 , and the input of the FIR filter unit  2506  is connected to the output of the adder unit  2504 . The other input of the adder unit  2504  is connected to the AD/C  2502 . In the example, the AD/C is the unit  1046  in  FIG. 12 . The FIR filter  2506  will produce a replica of the received signal, at the desired time delay with the respective complex coefficient specifying the magnitudes and the phases of the received Up-link Returned-Signal, to “wipe off” the incoming first (P 1 ), second (P 2 ) and third (P 3 ) return signal components. The FIR filter  2506  can either be implemented by a FPGA, ASIC or by the Signal Conditioning unit  1048  in  FIG. 12 . The processes of channel estimation, C(t,τ), and hence up-dating the FIR filter  2506  filter coefficients, are performed continuously, with an update rate that depends on the channel coherence time. For the example, a value of 100 msec can be assumed, as the indoor channels exhibit large coherence time. Alternatively, it is possible to use an adaptive algorithm such as Normalized LMS (NLMS), or RLS, converging on the received calibration signal at the Network unit  1002 , to estimate the filter coefficients, on an on-going basis. 
     Wire Connected Booster 
       FIG. 30  shows an example of analogue implementation of the Network unit  600  using a transmission cable as the physical medium for communication with the User unit  20  ( 702  in  FIG. 6 ). The Network unit  602  shown in  FIG. 5  is modified to the unit  3005  shown in  FIG. 30  to transmit to, and receive signals from, the User unit  4005  ( FIG. 20 ), which is modified version of the User unit  702  shown in  FIG. 6 , over a cable capable of supporting the operating bandwidth and the frequencies of the Network unit  3005  and User unit  4005  signals. The cable interface unit  3020  consists of a line interface unit  3160  which is connected to the transmission/reception cable  3170  and two hybrid combiners  3140  and  3150  on the forward-link and  3150  on the reverse link of the Network sub unit  3010 . The line interface unit  3160  will provide the means for the load matching for connection to a transmission line  3170 , and other appropriate components such as the amplifiers, modulation and frequency converters (modem functionalities), for reliable transmission over the transmission line  3170 . The design of the line interface unit  3160  is dependent on the transmission line  3170  characteristics, and is well known in the art. For example, even the in-building power lines or telephone lines can be used as the transmission line  3170  (as in homePNA), where the line interface unit  3160  is designed for such operation. The hybrid combiner (or directional coupler)  3140  is used to combine the control link  3110  signal with the forward-link signal. Alternatively, the outputs of the directional coupler unit  3040  and the control link unit  3110  can directly be connected to line interface unit  3160 , where they are modulated on adjacent carriers for simultaneous transmission to the User unit  4005 . The hybrid combiner (or directional coupler)  3150  is used to extract sufficient signal for reception and detection of control link  3110  received signal. Alternatively, the inputs to the directional coupler unit  3130  and the control link unit  3110  can directly be connected to line interface unit  3160 , if the control and data signals are modulated on adjacent carriers for simultaneous transmission from the User unit  4005 . It is also possible to use hybrid combiners instead of the directional couplers  3040 ,  3130  and  3085 . It is also possible, and is more desirable, to place the Reverse-link Network unit  3060  receiver internal LNA amplifier before the directional coupler  3130  (or the hybrid combiner replacement), in  FIG. 19 . 
     The operation of the units  3015 ,  3030 ,  3050 ,  3120 ,  3110 ,  3060 ,  3100 ,  3105 ,  3070 ,  3074 ,  3078 ,  3080 ,  3085 ,  3040 ,  3130  and  3090  in  FIG. 30  is similar, in operation and description, to  640 ,  624 ,  604 ,  620 ,  628 ,  606 ,  626 ,  627 ,  614 ,  610 ,  608 ,  612 ,  618 ,  630 ,  616  and  622  respectively, as discussed for  FIG. 5 . In the modified Network unit  3005 , the directional coupler  3040  ( 630  in  FIG. 5 ) is connected to hybrid combiner  3140 , and the directional coupler  3130  ( 616  in  FIG. 5 ) is connected to hybrid combiner  3150 . 
       FIG. 20  shows an example of analogue implementation of the User unit  702  ( FIG. 6 ) using a transmission cable as the physical medium for communication with the Network unit  3005  ( 602  in  FIG. 5 ). The User unit  702  shown in  FIG. 6  is modified to the unit  4005  shown in  FIG. 20  to transmit to, and receive signals from, the Network unit  3005 , which is a modified version of the Network unit  602  shown in  FIG. 5 , over a cable capable of supporting the operating bandwidth and the frequencies of the Network  3005  and User  4005  units signals. The cable interface unit  4020  consists of a line interface unit  4150  which is connected to the transmission/reception cable  4160  and two hybrid combiners  4130  on the forward-link and  4140  on the reverse link of the User sub unit  4010 . The line interface unit  4150  will provide the means for the load matching for connection to a transmission line  4160 , and other suitable components such as the amplifiers, modulation and frequency converters (modem functionalities), for reliable transmission over the transmission line  4160 . The design of the line interface unit  4150  is dependent on the transmission line  4160  characteristics, and is well known in the art. For example, even the in-building power lines or telephone lines can be used as the transmission line  4160  (as in homePNA), where the line interface unit  4150  is designed for such operation. The hybrid combiner (or mixer or directional coupler)  4140  is used to combine the control link  4120  signal with the reverse-link signal. The hybrid combiner (or duplexer)  4130  is used to extract sufficient signal for reception and detection of control link  4120  received signal. It is also possible to use hybrid combiners instead of the directional coupler  4110 . It is also possible, and is more desirable, to place the Forward-link Network unit  4080  internal LNA amplifier, before the directional coupler  4110  (or the hybrid combiner replacement), in diagram  20 . 
     The operation of the units  4015 ,  4030 ,  4040 ,  4050 ,  4060 ,  4070 ,  4075 ,  4080 ,  4090 ,  4100 ,  4110  and  4120  in  FIG. 20  is similar, in operation and description, to  722 ,  734 ,  736 ,  732 ,  730 ,  728 ,  721 ,  724 ,  726 ,  716 ,  718  and  720  respectively, as discussed for  FIG. 6 . In the modified User unit  4005 , the directional coupler  4110  ( 718  in  FIG. 6 ) is connected to hybrid combiner  4130 , and the Reverse-link User unit  4090  ( 726  in  FIG. 6 ) is connected to hybrid combiner  4140 . 
     Apart from the mentioned differences, the operation of Network unit  3010  is similar to the operation of the Network unit  602  and the operation of User unit  4010  is similar to the operation of the User unit  702 . 
     The control-flow description given for  FIGS. 7 ,  8 ,  9 ,  10  and  11  can also be used for the digital implementation of the Network unit  3005  and User unit  4005 , which is discussed above in  FIGS. 19 and 20 . 
       FIG. 40  shows an example of digital implementation of the Network unit  5005  ( 1002  in  FIG. 12 ), using a transmission cable as the physical medium for communication with the User unit  6005  ( 2002  in  FIG. 13 ). The Network unit  1002  shown in  FIG. 12  is modified to the unit  5005  shown in  FIG. 40  to transmit to, and receive signals from, the User unit  6005  (in  FIG. 50 ), which is the modified version of the User unit  2002  shown in  FIG. 13 , over a cable capable of supporting the operating bandwidth and the frequencies of the Network  5005  and User  6005  units signals. The modified cable interface unit  5020  consists of a line interface unit  5220 , which is connected to the transmission/reception cable  5210  and the Line Modem unit  5250 . 
     The line interface unit  5220  and the Line Modem unit  5250  will provide the means for the load matching for connection to transmission line  5210 , and other suitable components such as the amplifiers, modulation and frequency converters, for reliable transmission over the transmission line  5210 . The design of the line interface unit  5220  is dependent on the transmission line  5210  characteristics, and is well known in the art. For example, even the in-building power lines or telephone lines can be used as the transmission line  5210  (as in homePNA), where the line interface unit  5220  is designed for such operation. The line modem unit  5250  may be used for modulation and demodulation AD/C, DA/C and all other modem functionalities for transmission of the signal generated by the unit  5010  and reception of signal generated by unit  6010 . Also, the design of the modem unit  5250  is well known in the art, and as example technologies, homePNA and Home Networking can be mentioned. The line modem unit  5250  is connected to data muliplexer unit  5260  and data demultiplexer unit  5270 . The line modem unit  5250  can be implemented in either analogue or digital technology (or a mix). In the example it is assumed that the line modem unit  5250  is implemented in digital domain. 
     Data multiplexer unit  5260  is also connected to Signal Conditioning unit  5110  and the control link unit  5145 , and is used to multiplex control samples generated by control link unit  5145  and the signal samples generated by the Signal Conditioning unit  5110 . The multiplexer unit  5260  can be integrated within the Signal Conditioning unit  5110 . Alternatively, the output of the Signal Conditioning unit  5110  and control link unit  5140  can be separately connected to the line modem unit  5250 , where they are modulated on adjacent carriers for simultaneous transmission to the User unit  6005 . 
     Data Demultiplexer unit  5270  is also connected to Signal Conditioning unit  5130  and the control link unit  5145 , and is used to demultiplex received control samples and the signal samples generated by the User unit  6005 . The demultiplexer unit  5270  can be integrated within the Signal Conditioning unit  5130 . Alternatively, the input to the Signal Conditioning unit  5130  and control link unit  5145  can be separately connected to the line modem unit  5250 , if the control and data signals are modulated on adjacent carriers for simultaneous transmission by the User unit  6005 . 
     In Network unit  5005 , the calibration signal receiver unit ( 1016  in  FIG. 12 ) is no longer implemented separately. As no analogue signal path is available in the reverse-link of the Network unit  5005 , the calibration signal receiver unit ( 1016  in  FIG. 12 ) is integrated and performed in the Signal Conditioning unit  5130 . 
     The operation of the units  5110 ,  5120 ,  5130 ,  5140 ,  5141 ,  5145 ,  5300 ,  5100 ,  5150 ,  5090 ,  5160 ,  5080 ,  5170 ,  5070 ,  5180 ,  5190 ,  5060 ,  5050 ,  5040  and  5030  in  FIG. 30  is similar, in operation and description, to  1022 ,  1024 ,  1048 ,  1060 ,  1061 ,  1062 ,  1070 ,  1020 ,  1050 ,  1018 ,  1052 ,  1014 ,  1054 ,  1012 ,  1056 ,  1058 ,  1010 ,  1008 ,  1004  and  1006  respectively, as discussed for  FIG. 12 . 
       FIG. 50  shows an example of digital implementation of the User unit  6005  ( 2002  in  FIG. 13 ) using a transmission cable as the physical medium for communication with the Network unit  5005  ( 1002  in  FIG. 12 ). The User unit  2002  shown in  FIG. 13  is modified to the unit  6005 , shown in  FIG. 50 , to transmit to, and receive signals from, the Network unit  5005 , which is a modified version of the Network unit  1002 , shown in  FIG. 12 , over a cable capable of supporting the operating bandwidth and the frequencies of the Network  5005  and User  6005  units signals. The modified cable interface unit  6020  consists of a line interface unit  6230  which is connected to the transmission/reception cable  6240  and the line modem unit  6220 . 
     The line interface unit  6230  and the Line Modem unit  6220  will provide the means for the load matching for connection to transmission line  6240 , and other suitable components such as the amplifiers, modulation and frequency converters, for reliable transmission over the transmission line  6240 . The design of the line interface unit  6230  is dependent on the transmission line  6240  characteristics, and is well known in the art. For example, even the in-building power lines or telephone lines can be used as the transmission line  6240  (as in homePNA), where the line interface unit  6230  is designed for such operation. The line modem unit  6220  may be used for modulation and demodulation, AD/C, DA/C and all other functionalities for transmission of the signal generated by the unit  6010  and reception of signal generated by unit  5005 . Also, the design of the modem unit  6220  is well known in the art, and as example technologies, homePNA and Home Networking can be mentioned. The line modem unit  6220  is connected to data muliplexer unit  6200  and data demultiplexer unit  6210 . The line modem unit  6220  can be implemented in either analogue or digital technology (or a mix). In the example it is assumed that the line modem unit  6220  is implemented in digital domain. 
     Data multiplexer unit  6210  is also connected to Signal Conditioning unit  6140  and the control link unit  6150 , and is used to multiplex control samples generated by control link unit  6150  and the signal samples generated by the Signal Conditioning unit  6140 . The multiplexer unit  6210  can be integrated within the Signal Conditioning unit  6140 . Alternatively, the output of the Signal Conditioning unit  6140  and control link unit  6150  can be separately connected to the line modem unit  6220 , where they are modulated on adjacent carriers for simultaneous transmission to the Network unit  5005 . 
     Data Demultiplexer unit  6200  is also connected to Signal Conditioning unit  6100  and the control link unit  6150 , and is used to demultiplex received control samples and the signal samples generated by the User unit  5005 . The demultiplexer unit  6200  can be integrated within the Signal Conditioning unit  6100 . Alternatively, the input to the Signal Conditioning unit  6100  and control link unit  6150  can be separately connected to the line modem unit  6220 , if the control and data signals are modulated on adjacent carriers for simultaneous transmission by the Network unit  5005 . 
     The operation of the units  6150 ,  6100 ,  6110 ,  6140 ,  6155 ,  6151 ,  6120 ,  6130 ,  6090 ,  6160 ,  6170 ,  6080 ,  6180 ,  6070 ,  6190 ,  6060 ,  6050 ,  6030  and  6040  in  FIG. 50  is similar, in operation and description, to  2056 ,  2020 ,  2022 ,  2046 ,  2054 ,  2055 ,  2021 ,  2023 ,  2024 ,  2044 ,  2042 ,  2026 ,  2040 ,  2028 ,  2038 ,  2030 ,  2032 ,  2034 , and  2036  respectively, as discussed for  FIG. 13 . 
     The control-flow description given for  FIGS. 7 ,  8 ,  9 ,  10  and  11  can also be used for the digital implementation of the Network unit  5005  and User unit  6005 , which is discussed above in  FIGS. 21 and 22 . 
     Apart from the mentioned differences, the operation of Network unit  5010  is similar to the operation of the Network unit  1002  and the operation of User unit  6010  is similar to the operation of the User unit  2002 .