Abstract:
The invention discloses a method and apparatus for diagnosing a backhaul communications link between a repeater station and a base transceiver station of a wireless communication system. Adjacent and co-channel interference can severely degrade the performance of the backhaul communication link. As a result, the conditions on the backhaul link channels can be continually monitored to ensure optimal performance of the link. 
     Each RF channel on the backhaul communication link is individually diagnosed. A signal is then sent over the RF channel and the signal strength is measured along with any adjacent and co-channel interference. The measured statistics are then sent back to the base transceiver station. 
     In a further embodiment of the invention, the power level of a RF carrier signal on the backhaul communication link is measured and the carrier signal is then turned off. The power levels on the adjacent channels—above and below are then measured. Based on these measurements and other channel statistics, the power level of the RF carrier signal is accordingly adjusted.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to and claims priority to U.S. Provisional Application Ser. No. 60/173,445 entitled “Backhaul Link Diagnostic System in a Wireless Repeater” filed Dec. 29, 1999, the entirety of which is incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     (Not Applicable) 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention pertains generally to the field of wireless cellular communications. More particularly, the invention describes a method and apparatus for automatically diagnosing the backhaul link of a cellular system that uses RF repeaters. 
     2. Description of the Related Art 
     Conventional wireless cellular communications systems have a common architecture in which one or more defined cell sites are formed by the placement of one or more base transceiver stations within a geographic area. A cell site is typically depicted as a hexagonal area in which a transceiver is located such that a radio communication link can be established between the cellular system and a plurality of mobile stations within the defined geographic area for the cell. 
     In order to extend the coverage of conventional base transceiver station (BTS) systems over a larger geographical area, cell service providers have found it useful to employ translating repeaters. In the uplink direction, signals transmitted by a mobile station (mobile transceiver unit) located in a remote cell are received at the repeater, translated to a different carrier frequency, and then transmitted to the host BTS. Likewise, in the downlink direction, signals transmitted by the host BTS are received by the repeater, translated to a different carrier frequency, and then transmitted to mobile stations. The RF carrier link between the repeater and the BTS is known as the “backhaul channel,” hereinafter, backhaul channel, and the carrier frequency on which the backhaul channel is operated is called the “backhaul frequency.” 
     Some translating repeaters, such as the AirSite® repeater system offered by AirNet Communications Corporation of Melbourne, Fla., advantageously make use of existing inband RF carrier frequencies to backhaul cellular communications traffic. As used herein, the term “in-band” refers to carrier frequencies that are within the frequency spectrum allocation assigned to the service provider for providing cellular communications services to mobile subscribers. Use of in-band radio frequency channels to backhaul cellular communications traffic from remote repeater sites is highly advantageous as it eliminates costly wireline T1 or microwave connections. 
     Interference on the backhaul communications link can be caused by a variety of sources. As the number of subscribers on a cellular system grows, new equipment must be added in order to accommodate the increased usage. The addition of new repeaters in a repeater based cellular communications system can affect the performance of the backhaul communications link. In general, the link conditions can deteriorate due to congestion as the link reaches its full capacity. In addition to more traffic traversing the link, differences in tolerances between the various network entities accessing the bus can also degrade the backhaul communications link. 
     Interference on the backhaul link can be a problem for several reasons. For example, since the repeater station recovers its clock from the downlink channel of the backhaul communications link, the signals on the backhaul link must be maintained at a certain quality in order for the repeater station to maintain synchronization with the base station. Additionally, the slot/frame timing information for the downlink signal is derived as an offset to the uplink signal. Accordingly, interference on the backhaul communications link can adversely affect the uplink timing. Finally, the bit error rate (BER) can be adversely affected by any interference on the backhaul communications link. 
     The backhaul communications link can be diagnosed in a variety of ways. For example, a technician can use test equipment to determine the conditions that exist on the communications link. Alternately, loopback testing for diagnosing the link can be used. However, these systems are not completely satisfactory for testing the backhaul communication link of a repeater based system. For example, manual testing can be expensive and time consuming. By comparison, loopback systems are more convenient and less expensive, but are best used when testing the complete transmit and receive communication path through which a signal must travel. 
     In particular, in order to accurately test the conditions on the RF channel comprising the backhaul communication link, the uplink and downlink transmission paths on the link must be tested independent of the internal path of the repeater system. If a loopback test was employed to test the backhaul communication, then the link statistics would be corrupted by any processing internal to the repeater system. For this reason, loopback systems suffer certain drawbacks for testing the backhaul communication link. 
     SUMMARY OF THE INVENTION 
     The invention concerns a method for diagnosing a backhaul communication link of a repeater based wireless communication system. The wireless communication system has a base station located within a home cell, and a plurality of substantially adjacent cells, at least one of the plurality of cells having a repeater station located therein. The method comprises automatically measuring an interference level for the backhaul communication link and responsive to the measured interference level, selectively modifying the operation of the backhaul link to overcome any adverse effect of the interference level. The modifying step can comprise one or more of increasing a power level of signals transmitted over the backhaul link, decreasing the power level of signals transmitted over the backhaul link, assigning an alternative frequency for use as the backhaul link, or sending a message to an operation maintenance center. 
     The measuring step can comprise automatically measuring the interference level on an RF carrier frequency of a backhaul channel assigned for the backhaul communications link. The measuring step can also include automatically measuring the interference level on one or more RF channels adjacent to the RF carrier frequency of the backhaul channel. Further, the measuring step can include disabling signal transmissions on the backhaul channel and measuring signal levels of noise or interfering signals occurring on the RF carrier frequency of the backhaul channel. Finally, the measuring step further comprises transmitting a test signal on the RF carrier frequency of the backhaul channel and measuring an adverse effect of one or more of a noise level and an interfering signal level on the test signal. The adverse effects of noise or interference on the channel can be measured by determining at least one of a carrier-to-noise level, a carrier-to-interference level, a bit error rate, or a block error rate. The measuring step can be performed at predetermined intervals, upon detection of a predetermined number of detected bit errors, upon detection of a predetermined number of detected block errors, or upon detection of a predetermined number of frame erasures. 
     In a further embodiment of the invention, a system is provided for diagnosing a backhaul communication link of a repeater-based wireless communication system. The system includes a base station located within a home cell, and a plurality of substantially adjacent cells, one or more of which can include a repeater station located therein. The system comprises circuitry and/or software for automatically measuring an interference level for the backhaul communication link. Such measurements can include automatically measuring the interference level on an RF carrier frequency defining a backhaul channel assigned for the backhaul communications link and automatically measuring the interference level on at least one RF channel adjacent to the backhaul channel. The measurements can also include disabling signal transmissions on the backhaul channel and measuring at least one of a noise level and an interfering signal level. Finally, the measurements can include transmitting a test signal on the backhaul channel and measuring any adverse effect of noise or interfering signals on the test signal. Control circuitry and software is also provided so that a transmitter connected to the backhaul communications link can be selectively controlled to modify the operation of the backhaul communication link to overcome any adverse effect of the interference level. This modification can include an increase in power level of signals transmitted over the backhaul link, a decrease in power level of signals transmitted over the backhaul link, the assignment of an alternative frequency for use as the backhaul link, and/or a message being sent to an operation maintenance center. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There are shown in the drawings embodiments which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein: 
     FIG. 1 is a block diagram of a wireless communications system employing wireless translator/repeater stations; 
     FIG. 1A is a block diagram of a wireless communications system as in FIG. 1, illustrating the cell structure and possible proximity of the various entities. 
     FIG. 2 is an exemplary arrangement of the wireless communications system of FIG. 1 showing how wireless links are deployed through the wireless translator/repeater. 
     FIG. 3 is a block diagram of an exemplary single-omni directional type translator repeater station of the type shown in the wireless communication system of FIG.  1 . 
     FIG. 4 is a block diagram of an exemplary base transceiver station of the type shown in the wireless communication system of FIG.  1 . 
     FIG. 5 is an exemplary flow chart illustrating the steps that can be used to diagnose the backhaul communications link. 
     FIG. 6 is illustrates an exemplary alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram of a conventional wireless communications system such as a Personal Communication System (“PCS”) or other similar system. In this system, single-omni directional type wireless translator repeaters are deployed in peripheral cells of a cell cluster to concentrate radio signal traffic to and from a broadband base transceiver station (“BTS”). Those skilled in the art will readily appreciate that sectorized wireless translator repeaters can also be used for this purpose. However, for convenience, the system will first be described relative to the single-omni directional type translator system. 
     The system  10  can include repeater omni-directional antennas  11 - 1 ,  11 - 2 , . . .  11 - i , . . .  11 - n - 2 ,  11 - n - 1  and  11 - n  (collectively omni-directional antennas  11 ), translator repeater stations  12 - 1 ,  12 - 2 , . . .  12 - i , . . .  12 - n - 12 - n - 1  and  12 - n  (collectively repeaters  12 ), repeater directional antennas  13 - 1 ,  13 - 2 , . . .  13 - i , . . .  13 - n - 2 ,  13 - n - 1  and  13 - n  (collectively repeater directional antennas  13 ), BTS omni-directional antennas  14 - 1 , . . .  14 - m  (collectively BTS antennas  14 ), and broadband base transceiver stations  15 - 1 , . . .  15 - m  (collectively BTS&#39;s  15 ). System  10  can further include mobile telephone exchange  16  (MTSO), one or more base station controllers  17 , and a plurality of mobile subscriber units  18 - 1  and  18 - 2  (collectively mobile units  18 ). Repeaters  12  conventionally receive radio signals from mobile units  18  through omni-directional antennas  11  and forward them to BTS&#39;s  15  through repeater directional antennas  13 . Likewise, radio signals transmitted from BTS&#39;s  15  through BTS antennas  14  are forwarded by repeaters  12  to mobile units  18 . BTS&#39;s  15  are responsible for demodulating signals received from repeaters  12  through BTS antennas  14  and connecting these signals to the Public Switched Telephone Network (“PSTN”) through MTSO  16 . In addition, BTS&#39;s  15  modulate signals received from the PSTN (not shown) through MTSO  16  to format them for transmission through BTS antennas  14  to repeaters  12 . 
     FIG. 1A shows the wireless communications system as in FIG. 1, illustrating the cell structure and possible proximity of the various entities. It should be readily understood that FIG. 1A is exemplary and as such, many other configurations with the various entities co-located in one or a plurality of cells are possible. 
     FIG. 2 illustrates the basic operation of a repeater  12 . In particular, repeater  12  transmits signals to and receives signals from BTS  15  through backhaul channel  19 . Similarly, repeater  12  transmits signals to and receives signals from mobile unit  18  through ground link channel  20 . Each of the ground link channel  20  and the backhaul channel  19  is defined by an uplink carrier frequency and a downlink carrier frequency. Because BTS  15  is stationary, repeater  12  preferably employs directional antenna  13  to transmit and receive signals over backhaul channel  19 . In contrast, because mobile units  18  are not stationary and the repeater  12  is not sectorized, repeater  12  preferably employs one or more omni-directional antennas  11 A and  11 B respectively to transmit and receive signals over ground link channel  20 . 
     Communications between mobile units  18 , repeaters  12 , and the BTS  15  can be performed using a variety of multiplexing schemes that are well known in the art. For example, a time division multiplex access (TDMA) scheme may be used for this purpose. 
     FIG. 3 is a detailed block diagram block of a repeater  12  that can be used in connection with the present invention. The repeater  12  can comprise a ground sector transceiver  27  and backhaul transceiver  28 . It will readily be appreciated by those skilled in the art that the particular transceiver architecture shown is not critical to the invention and the invention as described herein is not intended to be so limited. 
     In a preferred embodiment, transceivers  27  and  28  are each capable of transmitting and receiving over a broad range of carrier frequencies allocated to a service provider for multi-carrier operation. However, the invention is not limited in this regard and more narrowbanded transceivers can also be used for the purposes of the present invention. Each transceiver  27 ,  28  is preferably configured so that its operation can be controlled by control processing and master processor  46  and  47 , respectively. 
     FIG. 3 shows a single sector omni directional-type wireless repeater system, it being understood that the invention is not so limited. In fact, a variety of sectorized repeaters can also be used for this purpose. Signals from a mobile unit  18  are received at omni-directional antennas  11 A and/or  11 B attached to ground sector transceiver  27 . These signals are encoded and transmitted by mobile unit  18  using a standard wireless telephony format such as GSM and typically range in power from between about −111 to −25 dBm. The signal passes through cavity filter  29 A on to downconverter  35 A or, alternatively,  35 B where, in conjunction with synthesizer module  36 A and voltage-controlled crystal oscillator  37 A, the signal is mixed down to intermediate frequency or IF. A high-speed analog-to-digital converter  39 A (or  39 B) then converts the analog IF signal into a digital signal. Once the IF signal is digitized, digital downconverter  41 A (or  41 B) translates the signal down to complex baseband. Digital downconverter  41  preferably provides the ability to downconvert, decimate, filter, and control the gain of the signal. After being converted to complex baseband, the signal is demodulated by digital signal processor  42 A. Digital signal processor  42 A is configured for decoding the received signal data from the standard wireless telephony format, such as GSM, to a common format used internally within the repeater  12 . 
     The common format data is then transferred to digital signal processor  42 B in the backhaul transceiver  28  over multi-channel buffered serial port  32 . Subsequently, the signal is re-modulated by digital signal processor  42 B. The re-modulated signal is output as a complex baseband signal and translated to real IF by digital upconverter  40 B. After the signal is translated to real IF, digital-to-analog converter  38 C converts the signal back to an analog signal where it is mixed by upconverter  34 B in conjunction with synthesizer module  36 B and voltage-controlled crystal oscillator  37 B. Now ready to be broadcast, the signal passes through amplifier and cavity filter  29 B and is transmitted through the backhaul channel to the BTS through repeater directional antenna  13 . 
     The transceivers  27  and  28  are preferably controlled by one or more control circuits. The control circuits can be in the form of a general purpose computer interfaced with the transceiver, a programmable microprocessor integrated with the transceivers with appropriate software, a hardware based controller, or any other combination of microprocessors, electronic circuitry and programming as may be necessary or appropriate for controlling the first and second transceivers. 
     As shown in FIG. 3, the control circuits include master processor  47  and control processor  46 . Master processor  47  preferably controls the operation of backhaul transceiver  28 , including selection of transmit and receive frequencies. Master processor  47  is also linked with PCM data and message bus  31  so that it can communicate with control processor  46 , and vice versa. Control processor  46  is preferably a slave processor controlled by master processor  47 . Control processor  46  can also preferably control the operation of ground sector transceiver  27 , including selection of transceiver receive and transmit frequencies. 
     Translation of the downlink signals transmitted from BTS  15  through the backhaul channel is similar to the procedure employed to translate signals transmitted from the mobile units. Specifically, a downlink signal, preferably at −70 dBm but typically ranging anywhere from −111 dBm to −25 dBm, is received from a BTS  15  at repeater directional antenna  13  attached to backhaul transceiver  28 . The signal passes through cavity filter  29 B to downconverter  35 C where, in conjunction with synthesizer module  36 B and voltage-controlled crystal oscillator  37 B, the signal is mixed down to IF. Analog-to-digital converter  39 C converts the analog IF signal to a digital signal where it is subsequently processed by digital downconverter  41 C to complex baseband. 
     Once converted into complex baseband, the signal is demodulated by digital signal processor  42 B and transferred to digital signal processor  42 A over multi-channel buffered serial port  32 . The signal is then re-modulated by digital signal processor  42 A and translated from complex baseband to real IF by digital upconverter  40 A. After the signal is translated to real IF, digital-to-analog converter  38 A converts the signal back to an analog signal. Upconverter  34 A, synthesizer  36 A, and voltage-controlled crystal oscillator  37 A operate together to mix the signal for transmission. The signal is then amplified by high-power amplifier  30 , filtered by cavity filter  29 A and transmitted from omni-directional antenna  11 A to the mobile unit through the ground link channel. 
     Referring now to FIG. 4, a broadband BTS  15  is illustrated, which comprises a receiver section  56  and a transmitter section  55 . It will be readily appreciated by those skilled in the art that the particular transceiver architecture shown is not critical. Accordingly, the invention disclosed herein is not intended to be so limited. Receiver section  56  preferably includes antennas  68 ,  70  and a wideband receiver  51  capable of receiving a plurality of carrier frequency channels. Signals from the received channels can include new power requests, power adjustment requests and traffic channel data from mobile transceiver units. The term “wideband,” as used herein, is not limited to any particular spectral range, and it should be understood to imply a spectral coverage of multiple frequency channels within the communication range over which a wireless communication system may operate (e.g. 5 or 12 MHz). Narrowband, on the other hand, implies a much smaller portion of the spectrum, for example, the width of an individual channel (e.g. 200 or 30 kHz). 
     The output of the wideband receiver  51  is down-converted into a multi-channel baseband signal that preferably contains the contents of all of the voice/data carrier frequency channels currently operative in the communication system or network of interest. This multichannel baseband signal is preferably coupled to high-speed A-D converters  52 - 1  and  52 - 2  operating in parallel for diversity receive capability. Where no diversity capability is required, a single A-D  52 - 1  could be utilized. Additionally, more than one parallel leg may be required for sectorized applications. Hence, it should readily be appreciated by one skilled in the art that the presence of a second parallel processing leg is not intended to be a limitation on the instant invention. The dynamic range and sampling rate capabilities of the A-D converter are sufficiently high (e.g. the sampling rate can be on the order of 25 to 50 Mega-samples per second (Msps)) to enable downstream digital signal processing (DSP) components, including Discrete Fourier Transform (DFT) channelizers  53 - 1  and  53 - 2 , to process and output each of the active channels received by receiver  56 . 
     The channelized outputs from the A-D converters are further processed to extract the individual channel components for each of the parallel streams. FFT channelizers  53 - 1  and  53 - 2  extract from the composite digitized multichannel signals, respective narrowband carrier frequency channel signals. These narrowband signals are representative of the contents of each of the respective individual carrier frequency communication channels received by the wideband receiver  51 . The respective carrier frequency channel signals are coupled via N output links through a common data bus  61  to respective digital signal processing receiver units  63 - 1  . . .  63 - 2 N, each of which demodulates the received signal and performs any associated error correction processing embedded in the modulated signal. In the case where the received signals are destined for the PSTN, these demodulated signals derived from the digital signal processing receiver units  63  can be sent via a common shared bus  54  to a telephony carrier interface, for example, T 1  carrier digital interface  62 , of an attendant telephony network (not shown). 
     The transmitter section  55  includes a second plurality of digital signal processing units, specifically, transmitter digital signal processing units  69 - 1  . . .  69 -N, that are coupled to receive from the telephony network respective ones of a plurality of channels containing digital voice/data communication signals to be transmitted over respectively different individual carrier frequency channels of the multichannel network. Transmitter digital signal processing units  69  modulate and perform pre-transmission error correction processing on respective ones of the plurality of incoming communication signals, and supply processed carrier frequency channel signals over the common bus  54  to respective input ports of an inverse FFT-based multichannel combiner unit  58 . The combiner  58  outputs a composite multichannel digital signal. This composite signal is representative of the contents of a wideband signal, which contains the respective narrowband carrier frequency channel signals output from the digital signal processing transmitter units  69 . A composite signal generated from the output of the multichannel combiner unit  58  is then processed by the digital-to-analog (D-A) converter  59 . The output of D-A converter  59  is coupled to a wideband (multiccarrier) transmitter unit  57 , which can include or have a separate multicarrier high power amplifier (HPA)  57 A. The transmitter unit  57  transmits a wideband (multicarrier) communication channel signal defined by the composite signal output of the inverse fast Fourier transform-based combiner unit  58 . The output of the HPA  57 A is then coupled to antenna  68  for transmission. 
     A central processing unit (CPU) controller  64  is provided for coordinating and controlling the operation of BTS  15 . For example, the CPU  64  can include a control processing unit, memory and suitable programming for responding to transmit power control requests received from mobile transceiver units. CPU  64  can selectively control transmit power levels of each TDM communication channel on a timeslot-by-timeslot basis. The CPU  64  may be a microprocessor, DSP processor, or micro controller having firmware, software, or any combination thereof. 
     DSPs  63  can extract information from each of the narrowband carrier frequency channel signals. Information for each of these channels can be stored in shared memory  75  through the common control and data bus  61 . CPU  64 , under firmware and/or software control, can then access the shared memory  75  through bus  61 . For example, control channel data concerning a particular downlink or control channel can be received at antenna  70  from a repeater station through a backhaul communication link. After the information for each channel in the received signal is processed and separated, DSPs  63  can store the control channel data in the shared memory  75 . CPU  64  can then access shared memory  75  to retrieve the control channel data. CPU  64 , under software and/or firmware control, can then use this data, for example, as an input to a control algorithm. The output from the algorithm can be stored in shared memory  75  for later use. 
     Referring now to FIG. 5, an illustrative flow diagram of exemplary steps used to diagnose the backhaul communications link is shown. For convenience, the inventive arrangements shall be described herein relative to the testing of a downlink channel, it being understood that the uplink channel can be similarly tested. This process can be controlled by the CPU  64 . The diagram starts with step  80 , followed by step  81 , wherein the BTS, for example BTS  15 - 1 , can disable normal backhaul transmissions on a particular backhaul RF carrier channel in order to run the diagnostic. This is achieved by preventing the BTS transmitter from transmitting at that particular RF frequency. The repeater can be notified that the channel will be taken out of service in order to ensure graceful termination of any communication session that is in progress. 
     Once the RF carrier channel is disabled, then traffic will be prevented from accessing the channel. If available, an alternative redundant RF channel can be temporarily used for the backhaul link. The BSC  17  or the BTS  15  will preferably mark a particular backhaul channel as being out-of-service to ensure that it is not allocated for traffic use. 
     In step  82 , a downlink test signal can be sent over the disabled channel from the base transceiver station, for example  15 - 1 , to a repeater  12 , for example  12 - 1 . The signal strength of the test signal and other channel statistics measured at the repeater station  12 - 1  are subsequently reported to the base transceiver station  15 - 1 . These can include the noise and interference levels from co-channel and adjacent channel sources. 
     In step  84 , the downlink channel parameters such as the frame erasure rates (FER), the carrier-to-noise (C/N) and carrier-to-interference (C/I) ratio are determined based on the values measured in step  83 . The methods used to determine the FER, C/N and C/I are well known by those skilled in the art. A bit error rate (BER) and/or a block error rate (BLER) may also be determined from the test signal. Frame erasure rates (FER) which provides an indication of the speech signal that is missing due to lost packets or frames can also provide insight into the interference levels that exist on the backhaul link. Once the downlink channel parameters, for example, FER, C/N, and the C/I are determined, then the uplink and downlink channels can be accordingly adjusted to mitigate adverse effects such as noise and interference as shown in step  85 . 
     A process similar to that described in FIG. 5 can similarly be used for testing the uplink channel. In that case, it may be desirable for the process to be controlled by master processor  47  or control processor  46 . Test signals would preferably be sent from the repeater  12  to the BTS  15 . 
     According to a preferred embodiment of the invention, the uplink and downlink power level used for communicating signals on the backhaul channel can be increased or decreased by transceiver master processor  47  according to predefined FER, C/N, and C/I thresholds. In step  85 , if the FER, C/I and/or C/N are not within acceptable thresholds, the power levels on the uplink and downlink are adjusted in step  86  to mitigate any adverse effects on the channel. If the C/I and C/N are within acceptable thresholds, then the diagnostic ends at step  87 . For example, if the C/I on the backhaul communication link is greater than a predefined threshold of 18 Decibels (dB), then the power level is acceptable and there is no need to adjust the power level. If the C/I is less than the predefined threshold of 18 dB and/or the C/N is less than a predefined threshold of 18 dB, then the power level on the backhaul link can be accordingly adjusted by master processor  47  in an attempt to attain an acceptable C/I ratio greater than 18 dB. 
     In accordance with a further aspect of the invention, the diagnostic test may be run periodically as part of a diagnostic routine, such as in off-peak hours when load on the system is minimal. Alternately, the diagnostic may be run whenever the link statistics such as the Bit Error Rate (BER) or Block Error Rate (BLER) exceed certain thresholds. Since BER and BLER are routinely monitored by the BSC  17 , the master processor  47  can routinely request these values from the BSC  17 . Hence, whenever the main processor  47  receives and compares the received BER or BLER to a predetermined threshold and the threshold is exceeded, the processor  47  can then initiate the diagnostic routine. 
     Instead of, or in addition to adjusting the power as in step  86 , an alarm condition could be set if certain channel statistics fall outside of predetermined ranges. The alarm condition could be designed so that a system operator could be warned of the condition. The alarm could alert and cause an operator at the Operation and Maintenance Center (OMC)  77  to manually remove the link from service and run the diagnostic. Dependent on the link conditions, it might be necessary to remove the link temporarily from service and use a spare RF carrier channel as a replacement. In this case, the BSC  17  can change the channel status from marked as out-of-service, to being marked as bad. The selection of the spare RF channel could be performed manually by the operator. In a preferred embodiment however, the spare RF channel can be automatically selected for use by the backhaul link if power adjustments in step  86  prove insufficient to eliminate the effects of noise or interference. 
     It should be readily understood by one skilled in the art that although the uplink and downlink power levels can be adjusted according to measurements taken on the downlink channel of the backhaul link, both the uplink and the downlink power levels do not have to be so adjusted. While adjustment of the downlink power level is advantageous, adjustment of the uplink power based on measurements taken on the downlink channel alone are at best, a mere representation of the reciprocal path loss. Hence, factors such as uplink co-channel interference are not taken into account when the uplink power is adjusted based on the downlink channel measurements. 
     In a further embodiment of the invention, various power levels on the uplink and downlink RF carrier frequency for the backhaul communications link as well as respective adjacent channels can be monitored. In particular, the noise power level and the power level of interfering signals can be measured. These interfering signals might be from adjacent channels, co-channel, or due to various types of noise. Accordingly, the conditions on the uplink and downlink RF carrier channel of the backhaul communication link can be diagnosed by comparing these various power levels with and without transmission on the backhaul channel. For convenience, the process according to the inventive arrangements shall be described relative to the downlink carrier frequency. However, it should be understood that the method can also be used in connection with the uplink carrier frequency. In this regard, it is noted that the backhaul channel is comprised of a pair of carrier frequencies, one for uplink transmission and the other for downlink transmission. 
     Referring now to FIG. 6, the method starts at step  90  followed by the measurement of the downlink RF carrier power level (RF 1 ) in step  91 . This measured downlink carrier power level is the power level as received at the repeater station. This signal may be a special test signal or a signal being used for communication. The measured carrier power level RF 1  is used as a reference power level. In step  92 , following the measurement of the downlink RF carrier power, the RF carrier is disabled by BTS master processor  47 . The noise and interference signal power level on the downlink of the backhaul channel is then measured as illustrated in step  93 . Although the measurement can be taken at the BTS, the invention should not be so limited. For example, measurements could be taken anywhere along the downlink path using suitable test instruments. According to a preferred embodiment, the measurements can be made at the repeater station  12  and reported back to the BTS  15 . Measurements taken at the repeater station give the best indication of the noise and interference levels to which the repeater station  12  may be subjected. 
     In steps  94  and  95 , the RF carrier levels on the downlink channels adjacent to the backhaul channel are measured, for example, at the BTS  15  or at the repeater  12 . Thus, for example, in a GSM based system, the RF carrier power (RF 2 ) can be measured in step  94  for a channel that is 200 kHz below RF 1 , or the next lower downlink channel to RF 1 . Similarly, in step  95 , the RF carrier power (RF 3 ) is measured for a downlink channel that is 200 kHz above RF 1 , or the next higher channel to RF 1 . 
     In step  96 , the measured carrier power for the adjacent downlink channels are compared to upper and lower power thresholds, RF UT/hold  and RF LT/hold  defined by RF 1 . For example, the thresholds can be predefined to be ±9 dBm above and below the measured RF 1  value. Thus, if RF 1  is −70 dBm, then RF UT/hold  would be −61 dBm and RF LT/hold  would be −79 dBm. 
     Returning to step  96 , the power level for the lower RF carrier RF 2  and RF carrier RF 3  are compared to the predefined threshold, RF LT/hold . If RF 2  or RF 3  is greater than the upper threshold RF UT/hold , then the downlink power level on the backhaul channel can be increased as in step  101 . Otherwise, the carrier power lever for the higher adjacent downlink channel is compared against the lower threshold as in step  97 . If RF 2  and RF 3  are less than the threshold RF L/Thold , then the downlink power level on the backhaul channel can be decreased in step  100 . If RF 2  and RF 3  are not less than the threshold RF L/Thold , then the system proceeds to step  98 . 
     In step  98 , a comparison is made between the noise and interference signal power level that was measured in step  93 , and a co-channel upper power threshold, which is preferably defined relative to RF 1 . For example, the co-channel upper threshold can be selected to be −9 dBc, that is, −9 dB relative to the carrier. If the measured noise and interference levels on the downlink channel of the backhaul link are greater than the upper threshold, then the power level on the downlink channel of the backhaul link is increased as illustrated in step  101 . If the measured noise and interference levels on the downlink channels of the backhaul link are not greater than the co-channel upper threshold, then the measured levels are compared to a co-channel lower threshold as illustrated in step  99 . The co-channel lower threshold is preferably defined relative to RF 1 . For example, this lower threshold can be selected to be 9 dBc. If the measured noise and interference levels are less than the co-channel lower threshold, then the power levels on the downlink channel of the backhaul link are decreased as illustrated in step  100 . Otherwise, the adjustment then ends as shown in step  102 . 
     It should readily be understood that the uplink channel could be tested in a similar manner as described for the downlink channel. To achieve this, the signals would originate at the repeater station and would be measured at the BTS. The measurement would be carried out in the same manner as done with the downlink measurement. Once the measurements are done, the power levels of signals transmitted over the backhaul link can be increased or decreased accordingly. 
     While exemplary systems and methods embodying the present invention are shown by way of example, it will be understood that the invention is not limited to these embodiments. Modifications can be made by those skilled in the art, particularly in light of the foregoing teachings. For example, each of the elements of the aforementioned embodiments may be utilized alone or in combination with elements of the other embodiments.