Abstract:
A method and apparatus for controlling and maintaining a tower top low noise amplifier (TTL) module coupled to an antenna, where the TTL module includes a plurality of TTLs, each for amplifying signals received by the antenna on an associated cell sector. The method includes: reading alarm information concerning alarm conditions present in the TTL module during a read mode; and, writing commands to control circuitry coupled to the TTL module in a write mode to control switching states of bypass switches therein in response to the alarm information.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to wireless communications equipment and more particularly to a method and apparatus for controlling and maintaining a tower top low noise amplifier. 
     2. Description of the Related Art 
     When an antenna located at the top of a tower is distant from the base station communication equipment it connects to, excessive signal attenuation through tower to ground cabling can produce an increase in the signal to noise ratio of signals received by the antenna. To alleviate this problem, a tower top low noise amplifier (hereafter, “TTL”, not to be confused with transistor-transistor logic) is typically employed at the base of the antenna on the tower to immediately amplify receive signals and thereby prevent deterioration of signal quality. The TTL acts as a preamplifier to the main low noise amplifier (LNA) of the receiving equipment at the bottom of the tower. 
     Since tower top amplifiers are oftentimes difficult to access due to their location on the tower top, it is customary to utilize some sort of automatic bypassing mechanism in the event of a TTL failure. One example of such a bypassing scheme is disclosed in U.S. Pat. No. 5,418,490 which employs both primary and backup amplifiers at the tower top. The system in that patent generates a primary failure signal in the event of an abnormal current draw of the primary amplifier, whereupon the backup amplifier is automatically switched into operation. If the backup amplifier fails, a backup failure signal is generated to switch in a bypass circuit in place of the backup amplifier. 
     SUMMARY OF THE INVENTION 
     In an illustrative embodiment of the present invention, there is provided an apparatus for controlling and maintaining a tower top low noise amplifier (TTL) module coupled to an antenna, where the TTL module has a plurality of TTLs, each for amplifying signals received by the antenna on an associated cell sector. The apparatus includes a control box configured to control the TTL module and to determine whether or not an alarm condition is present, and to control bypass switches, each associated with a TTL, so as to route receive signals from the antenna to a bypass path when an alarm condition is present. An alarm board, interfaced with the control box, functions to receive data indicative of alarm conditions within the TTL module and to transmit write commands to the control box in response to commands from a base transceiver system control processor (BCP), where the write commands serve to selectively control the bypass switches within the TTL module. 
     An illustrative method of the present invention for controlling and maintaining a tower top low noise amplifier module coupled to an antenna includes: reading alarm information concerning alarm conditions present in the TTL module during a read mode; and, writing commands to control circuitry coupled to the TTL module in a write mode to control switching states of bypass switches therein in response to the alarm information. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to exemplary embodiments thereof, taken in conjunction with the accompanying drawings in which like reference numerals indicate like elements or features, wherein: 
     FIG. 1 is a block diagram of a TTL controlling module arrangement; 
     FIG. 2 is a flow chart depicting a read mode of a method for controlling and maintaining the TTL in accordance with the present invention; 
     FIG. 3 is a schematic diagram of a pin array of the read mode of FIG. 2; 
     FIG. 4 is a schematic diagram for controlling a write operation utilizing four bits of data; 
     FIG. 5 is a schematic diagram of the pin array of the alarm board for the four bit write operation; 
     FIG. 6 is a schematic diagram illustrating write operation control utilizing three data bits and a latch; 
     FIG. 7 is a schematic diagram of the pin array of the alarm board for the three bit write case; 
     FIG. 8 is a flow chart of a read mode of a method for controlling and maintaining a TTL according to the present invention; and 
     FIG. 9 is a block diagram illustrating tower top amplifiers and associated switches within a tower top amplifier module. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a block diagram of a tower top low noise amplifier controlling module arrangement is shown. A tower top low noise amplifier module  10  includes a number of TTLs, each of which amplifies signals received by an antenna AT and routes the amplified signals through a coaxial cable (or cables)  18  that runs down the tower to the base station receiver. A control box  12  controls TTL module  10  and monitors whether or not an alarm condition is present, which indicates that a TTL therein has failed or is in dancer of failing. When an alarm condition is present, control box  12  changes the switching state of a switch within TTL module  10  so as to turn off the TTL or switch the TTL out of operation and switch in a bypass circuit or path within TTL module  10  in its place. When a base station manager or automated test system desires to control the TTL or TTL switch in order to perform a VSWR test (e.g., on the antenna/antenna cables), Base Transceiver System (BTS) Control Processor (BCP)  16  writes a corresponding command to the control box  12 , which responds with an appropriate control signal to TTL module  10 . 
     The alarm board  14 , comprised of a Rack Alarm Control Assembly (RACA) and a Cell Site Alarm Assembly (CSAA), interfaces with control box  12  and receives and stores alarm signals from control box  12  corresponding to alarm conditions present in the TTL module. Alarm board  14  also transmits write commands originating from BCP  16  to control box  12 . Alarm board  14  is connected to the BCP  16  through a telephony device bus (TDBus). 
     A base transceiver system (BTS) fault measurement block (BFMB), located in the BTS, collects and manages the various alarms reported to BCP  16  by alarm board  14 . The BFMB reads the register of the alarm board received through the TDBus to gather alarm information, and transmits the alarms to the base station manager. The BFMB also conducts the TTL write operation upon receipt of the TTL write command from the BSM, and controls the TTL switch when testing the VSWR. 
     In order to control the TTL module  10 , read and write modes are utilized. These modes are as follows: 
     1. Read Mode 
     In the alarm board  14 , each pin is allocated for a respective alarm. If an alarm condition is present in TTL module  10 , information indicating the same is reported to the corresponding pin of the alarm board. 
     FIG. 2 is a flow chart of an exemplary routine by which the BFMB periodically reads data on the alarm board pins and monitors whether or not an alarm has occurred in TTL module  10 . In this example, a pin value of  0  indicates a normal condition and a pin value of  1  indicates an alarm condition. The routine first checks in step s 201  whether or not the corresponding system is equipped with a TTL module by reading data stored in program memory. If the system is so equipped, a register corresponding to the TTL module is periodically read by the alarm board RACA through the TDBus, and a location index and alarm flag corresponding to the read register bit are set in an alarm table (step s 202 ). (If the system is not equipped with a TTL module, the process terminates in step s 210 .) Next, in step s 203 , a check is performed to ascertain whether or not the TTL module is equipped in the desired location by comparing the location index to values stored in memory. If the TTL is not equipped in the desired location, the procedure is terminated (step s 210 ). Other vise, the set alarm flag is compared with the previous alarm flag stored in a buffer (step s 204 ). 
     If the set alarm flag is different from the previous alarm flag, the alarm flag is updated and the location index, alarm code, and alarm flag are transmitted to the Base Station Manager (BSM) in step s 205 . The transmitted alarm information is reported to the administrator, and the TTL mode is updated according to the alarm results (step s 206 ). 
     Referring to FIG. 9, a simplified block diagram of an exemplary TTL module  10  is shown. TTL module  10  is designed to amplify signals received by a multi-sector antenna AT, which, in this example, separately outputs signals from three sectors, α, β and γ. The receive signals of each sector are normally provided to a pair of TTLs in two paths, A and B. At the input of each TTL pair is a single pole, double throw switch S which ordinarily routes the incoming signal to the TTL pair. However, if an alarm condition exists in one of the TTLs in the corresponding TTL pair, the switch is controlled to route the receive signal to a bypass path. 
     FIG. 3 illustrates respective pins allocated in the alarm board and the related alarm information. The alarms are transmitted from control box  12 . Each pin is associated with an alarm condition for one of the TTLs in TTL module  10 . Thus, the logic level of pin  0  indicates whether an alarm condition is present in the TTL of path A in sector α, the logic level of pin  3  indicates whether an alarm condition is present in the TTL of path B of sector β, and so forth. 
     If an alarm occurs in a TTL, the associated switch in the TTL path is turned on, and the signals received from the antenna bypass the TTL having the alarm condition. Therefore, managing the operation state of a TTL is identical to managing the operation state of the associated switch mode of that TTL. The BFMB has a state-managing buffer to manage the alarm state of TTL module  10 . 
     2. Write Mode 
     When a user inputs a command to the base station manager to conduct a VSWR test diagnosing the antenna path, or to manually turn on one of the TTL bypass switches, the BFMB receives the command to perform these operations, and responds by performing the write operation to TTL module  10  through the alarm board. 
     The write method may be classified into two types according to the number of bits controlling the write operation. The first approach controls the corresponding TTL switch by utilizing one bit. This approach also includes two methods. The first method causes the switch to be turned on upon the detection of a low to high transition of the one bit signal, and to be turned off upon detection of a high to low transition, or vice versa. This is called the rising and falling detection method. In the second method, when a pulse having a constant cycle is inputted, the switch mode is converted by toggling. This is called the pulse method. 
     In the second approach, the corresponding TTL switch is controlled by combining data of a plurality of write pins. This approach can also be performed with two methods. The first method involves using the write data bits. Referring to FIG. 4, a table showing illustrative pin data and corresponding functions is shown. Four data bits D 0  to D 3  are employed to form code words, each intended to control a unique combination of switching states. For instance, if the four bits form codeword [0000], all the signals are bypassed, if they form codeword [1000] the α sector switch (or switches) is turned on to bypass the corresponding α sector TTL, and so forth. The four bits of D 0  to D 3  are switched by a toggling method. 
     FIG. 5 illustrates the pin array of alarm board  14  writing the information to the control box in the above-described method. If the register bit is 1, pin  0  indicates D 0  information, pin  1  indicates D 1  information, etc. 
     The second method utilizes 3 bit data and a latch. FIG. 6 shows an illustrative pin description for the 3 bit data method. As illustrated, to control the write mode, 3 data bits D 0  to D 2  and a latch are employed. If the 3 bits indicate [000], all the signals are bypassed, if the 3 bits indicate [100], the α switch is turned on, and so forth. 
     FIG. 7 illustrates the pin array of the alarm board writing the information to the control box in the above-discussed method. If the register bit is 1, pins  0 ,  1  and  2  indicate D 0 , D 1  and D 2  information, respectively, and pin  3  indicates latch information. 
     The BFMB uses a periodic latch signal to write a command corresponding to a specific operation to the alarm board. After reading the inputted bit information, at the moment the latch falls, the control box recognizes the value written to the alarm board, thereby performing the predefined operations. 
     FIG. 8 is a flow chart of an illustrative routine for implementing the write mode operations. The values of the switch mode and the corresponding sector&#39;s switch state are first received from the BSM or BTS Diagnostic Block (BDIAB) (step s 801 ). The TTL switch&#39;s state of the corresponding sector is then compared to the value of the switch mode (step s 802 ). If the comparison is favorable, the results are reported to the BSM and BDIAB (step s 806 ). If the compared results are different, the compared results are written to the corresponding sector cell and switch mode through the Rack Alarm Control Assembly (step s 803 ). The TTL switch&#39;s state is then read in step s 804 . The switch mode and the updated switch&#39;s state are compared in step s 805 , and the comparison results are reported to the BSM and BDIAB (step s 806 ). 
     While the present invention has been described above in reference to exemplary embodiments thereof, it is understood that many modifications can be made to these embodiments without departing from the spirit and scope of the invention as defined by the appended claims.