Abstract:
A method and apparatus for combining corded and cordless telephone handsets with either analog network lines or a digital network in order to perform intercom and conferencing functions. Specifically, the apparatus comprises a network interface coupled to each analog network line or a digital network line from a digital network, an analog converter coupled to each corded telephone handset, a digital converter coupled to each cordless telephone handset, a signal processing circuit coupled to the network interface as well as the analog converter and the digital converter, and a controller coupled to the signal processing circuit as well as the network interface or interface circuit, the analog converter and the digital converter. In operation, the signal processing circuit receives signals from the network interface, the analog converter and the digital converter in a time division multiplexed manner to generate output signals that are sent to the analog converter, the digital converter and network interface and reconverted to the respective corded telephone handsets, cordless telephone handsets, and analog/digital network lines.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This invention claims benefit to U.S. Provisional Application Serial No. 60/145,690, filed Jul. 26, 1999, and incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to data communication systems. More particularly, the invention involves a method and an apparatus for supporting intercom and conferencing between corded and cordless telephone handsets. 
     BACKGROUND OF THE DISCLOSURE 
     Private Branch Exchange (PBX) devices are used to expand the number of telephone handsets or sets which share a common Plain Old Telephone System (POTS) line or a set of POTS lines from a business or residence to a telephone company Central Office (CO) switch. PBX devices support features such as set-to-set intercom and set-to-CO conferencing. 
     Conventional analog techniques for generating local signals for intercom or summed signals for intercom require analog multiplexers and summing amplifiers. In contrast, digital techniques usually require high speed Digital Signal Processors (DSP). As such, there is difficulty in combining analog and digital techniques for generating intercom and conferencing signals. 
     Therefore, in a multi-handset hybrid telephone system supporting both analog and digital cordless telephone applications, the task of supporting intercom and conferencing features between corded and cordless telephones is problematic. A need exists in the art to support intercom and conferencing features between analog corded telephones and digital cordless telephones. 
     SUMMARY OF THE INVENTION 
     The invention overcomes the disadvantages of the prior art by providing a method and apparatus for combining corded and cordless telephone handsets in intercom and conferencing applications. 
     A first embodiment of the invention is a device that combines corded and cordless telephone handsets to analog network lines. Specifically, the device comprises a codec coupled to each analog network line, an analog to digital converter coupled to each corded telehone handset, a digital converter coupled to each cordless telephone handset, a signal processing circuit coupled to the codec, the analog to digital converter and the digital converter, and a controller coupled to the signal processing circuit, the codec, the analog to digital converter and the digital converter. 
     The codec digitizes a signal from the analog input line, the analog to digital converter digitizes a signal from the corded telephone handset and the digital converter demodulates and possibly decompresses a signal from the digital cordless telephone handset. These signals may comprise audio signals. The signal processing circuit receives the signals from the codec, analog to digital converter and digital converter during time division multiplexed (TDM) slots as determined by the controller. The number of time solts required is equal to the sum of corded telephone handsets, cordless telephone handsets and analog network lines. 
     The signal processing circuit then generates a set of output signals from the received signals. In operation, the signal processing circuit receives a signal during each time slot, multiplies the signal by a set of programmed coefficients to generate one output signal for each corded telephone handset, cordless telephone handset and analog network line. The circuit adds the products for each time frame to values from the previous time slot to provide a running total. As such, the signal processing circuit is generally a multiply and accumulate circuit. 
     The codec, analog to digital converter and digital converter then processes the output signals to the respective analog network lines, corded telephone handsets and cordless telephone handsets and cordless telephone handsets. These components operate in a reverse fashion to that previously described. 
     A second embodiment of the invention is a device that combines corded and cordless telephone handsets to a digital network. In this embodiment, the device comprises a digital interface coupled to the digital network, an analog to digital converter coupled to each corded telephone handset, a digital converter coupled to each cordless handset, signal processing circuit coupled to the digital interface as well as the analog to digital converter and the digital converter, and a digital signal processor coupled to the signal processing circuit as well as the digital interface. 
     The first and second embodiments are similar with the exception of this second embodiment comprising a digital interface instead of a codec, and a digital signal processor instead of a controller. The digital interface may comprise a cable modem or digital subscriber line (DSL) modem for decoding a signal from the digital network and a decompressor/compressor for decompressing a compressed audio signal from the network or compressing an audio signal to the network. The digital signal processor may packetize the signals from the digital interface, the analog converter and the digital converter in substantially the same manner as the controller in the first embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 shows a high level block diagram of a telephone system that integrates corded and cordless telephone handsets with POTS network lines; and 
     FIG. 2 shows a high level block diagram of a telephone system that integrates corded and cordless telephone handsets with a digital telephone system. 
    
    
     To facilitate understanding of the invention, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     FIG. 1 shows a high level block diagram of a telephone system  100  that integrates corded and cordless telephone handsets with POTS lines. As with a conventional Private Branch Exchange (PBX) system, the telephone system  100  coordinates telephone handsets to POTS lines that are connected to a telephone company central office (CO) switch. However, the telephone system  100  in accordance with the present invention supports intercom between corded and cordless telephone handsets, and conferencing between corded telephone handsets, cordless telephone handsets and telephone lines that link other telephone handsets. 
     Specifically, the telephone system  100  includes a coder-decoder or codec  102 A,  102 B and  102 C for each telephone line and for each corded telephone handset, a Subscriber Line Interface Circuit (SLIC)  104 C for each corded telephone handset, a Time-Division-Multiplexed (TDM) bus  106 , a control port  108 , a TDM controller  110 , a Multiply and Accumulate Circuit (MAC)  112 , a radio-frequency (RF) transmitter-receiver or transceiver (XCVR)  114  for the cordless telephone handsets and a baseband processor  116  for the cordless telephone handsets. 
     In operation, each of the codecs  102 A or  102 B samples data, typically an audio signal, entering the telephone system  100  from the respective analog POTS network lines via respective signal lines A and B and encodes the sampled data to digitize the analog data signal. On a system level, the codecs  102 A and  102 B operate as a network interface, coupled to the analog network lines via signal lines A and B, for converting or digitizing the incoming signals into digital network signals. As such, the codecs  102 A and  102 B operate as analog to digital converters for data entering the telephone system  100  and as digital to analog converters for data leaving the telephone system  100 . 
     The codecs  102 A and  102 B couple the MAC  112  via the TDM bus  106  and couple the TDM controller  110  via the control port  108 . After digitizing the analog signals from the POTS lines, each of the codecs  102 A or  102 B writes or drives the respective digitized signals to the TDM bus  106  during a time slot as determined by the TDM controller  110 . Each of the codecs  102 A or  102 B reads output data from the TDM bus  106  during the time slot set by the TDM controller  110 . 
     In addition to processing signals from the analog POTS network lines, the telephone system  100  processes signals from the corded and cordless telephone handsets. The SLIC module  104 C processes signals from the corded telephone handset via signal line C. The SLIC module  104 C couples the codec  102 C via signal path S 1 . 
     The codec  102 C for the corded telephone handset operates in substantially the same manner as codecs  102 A and  102 B for the POTS lines. The codec  102 C samples and encodes the signal from path S 1  to produce a digitized signal for the corded telephone handset. Each paired SLIC module  104 C and codec  102 C, as coupled to the corded telephone handset via signal path C, operates as an analog converter for digitizing the signal from the cordless handset into a digital corded handset signal. 
     The codec  102 C couples the MAC  112  via the TDM bus  106  and couples the TDM controller  110  via the control port  108 . As such, the codec  102 C writes to or reads from the TDM bus  106  during time frames as determined by the TDM controller  110 . 
     The RF XCVR or radio frequency transceiver  114  demodulates the radio frequency signals, from the cordless telephone handsets via signal paths D and E, into baseband signals. The RF XCVR  114  couples the baseband processor  116  via signal path S 2 . The baseband processor  116  decodes the baseband signal into a digital cordless handset signal of a particular cordless telephone handset. As such, the RF XCVR  114  and baseband processor  116  is a digital converter, coupled to the cordless handsets via signal paths D and E, for converting the signal from the cordless handsets into a digital cordless handset signal. This signal is provided to the TDM bus  106  during a time slot determined by the TDM controller  110 . 
     The baseband processor  116  may support multiple cordless telephone handsets illustratively shown via lines D and E. As the telephone system  100  digitizes audio signals from both corded and cordless telephone handsets in the same digitized format on the TDM bus  106 , the TDM controller  110  and the MAC  112  views the baseband processor  116  as multiple codecs, each with an unique time slot. The required number of time slots for the TDM bus  106  equals the total number of telephone handset and external lines. As such, five time slots are required in the example shown in FIG.  1 . 
     As the codecs  102 A,  102 B and  102 C and the baseband processor  116  couple the TDM controller  110  via the TDM bus  106 , the TDM controller  110  sends control signals for enabling the codecs  102 A,  102 B and  102 C, and the baseband processor  116  to write or read from the TDM bus  106  during scheduled time slots. The TDM controller  110  couples the MAC  112  via the control port  108 . The TDM controller.  110  also sets up a desired matrix in the MAC  112  at the beginning of the call and cancels this matrix at the end of the call. 
     The MAC or multiply and accumulate circuit or signal processing circuit  112  generally reads data from different time slots, forms balanced summed signals from the input data and writes output signals onto the TDM bus  106  during a time slot determined by the TDM controller  110 . More specifically, the MAC  112  reads the input values during the appropriate time slots in a TDM frame, multiplies each input value by its coefficient, accumulates the products and writes the resulting sum to the TDM bus  106  during the appropriate time slot in the next frame. Each of these specific steps will be discussed in greater detail below. 
     The MAC  112  initially reads the input data values from the TDM bus  106  during appropriate time slots in a TDM frame. These input values arrive as each codec  102 A,  102 B, or  102 C, or the baseband processor  116  writes to the TDM bus  106  during its scheduled time slot as controlled by the TDM controller  110 . The TDM bus  106 , which couples the MAC  112  with the codecs  102 A,  102 B and  102 C, and the baseband processor  116 , includes two data lines which serve as input and output data lines to the MAC  112 . As the input values arrive through the input data line, the MAC  112  simultaneously writes data to the codec  102 A,  102 B or  102 C, or the baseband processor  116  through the output line of the TDM bus  106 . The number of required time slots is usually equal to the number of corded and cordless telephone handsets plus the number of POTS lines. In this small system example shown in FIG. 1, the MAC  112  requires five time slots. 
     The MAC  112  multiplies each input value by its coefficient and accumulates the products after each succeeding time slot. The coefficients, typically expressed in matrix format for a plurality of telephone lines and telephone handsets, are provided as the TDM controller  110  sets up the desired coefficient matrix at the beginning of the telephone conference or intercom. The coefficient matrix values depend on the corded and cordless handsets that are connected during the conference. These coefficient matrix values may change when other corded and cordless handsets join and/or exit the conference or intercom. As the MAC  112  interacts with the TDM controller  110  only during matrix setup and cancellation, the configuration may significantly reduce digital. signaling requirements for the telephone system  100 . The MAC  112  may comprise a special-purpose sequential circuit to perform the multiply and accumulate functions and to ensure quick operation of the telephone system  100 . 
     As an illustrative example, the telephone system  100  may involve a conferencing application such that POTS lines A and B are linked with telephone handset C. Let Ai represent input to the system from line A, A o  represent output to line A, and k a  represent the multiplying coefficient. Input, output and multiplying coefficients are similarly represented for POTS line B and telephone handset C as B i , B o , k b , C i , C o  and k c . The MAC determines the resulting sums: 
     
       
         
           Ao=k 
           b 
           Bi+k 
           c 
           Ci Bo=k 
           a 
           Ai+k 
           c 
           Ci Co=k 
           a 
           Ai+k 
           b 
           Bi 
         
       
     
     using the multiply and accumulate procedure discussed above. 
     After reading the input data, multiplying the inputs by its coefficient and accumulating the products, the MAC  112  writes the resulting output to the output lines of the TDM bus  106  as determined by the TDM controller  110 . This output is usually delayed one frame time from the input as a particular input signal component may have arrived later in the previous frame. The delay is not perceptible as the frame time is normally about 125 μsec. However, the MAC  112  may also include echo cancellation digital filters to introduce a greater process delay. 
     The codecs  102 A,  102 B and  102 C, and the baseband processor  116  read the output values of the MAC  112  from the TDM bus  106  as determined by the TDM controller  110 . The codecs  102 A,  102 B and  102 C then convert these outputs into analog signals for the respective POTS lines and corded telephone handsets. 
     FIG. 2 shows a high level block diagram of a telephone system  200  that integrates corded and cordless telephone handsets with a digital telephone system. The telephone system  200  is similar to the telephone system  100  shown in FIG. 1 except for the signal processing used for coupling signals from and to the digital telephone system or digital network. 
     The codec  206 , SLIC  208 , RF XCVR  210 , baseband processor  212 , TDM bus  214 , control port  216  and MAC  218  operate in substantially the same manner as the respective codec  102 C, SLIC  104 C, RF XCVR  114 , baseband processor  116 , TDM bus  106 , control port  108  and MAC  112  of the previous telephone system  100 . As such, no further discussion is provided for these components. 
     Specifically, the telephone system  200  includes a network interface  202 , a digital signal processor (DSP) module  204 , a codec  206  for each corded telephone handset, a SLIC  208  for each corded telephone handset, a RF receiver  210  for the cordless telephone handsets, a baseband processor  212  for the cordless telephone handsets, a TDM bus  214 , a control port  216  and a MAC  218 . 
     The network interface  202  processes digital speech from the digital network. The network interface  202 , which typically comprises physical layer and medium access layer components, may include a digital cable modem or a digital subscriber line (DSL) modem for decoding the speech from the digital network. The network interface  202  may also include a compressor/decompressor module for decompressing incoming compressed speech or compressing speech to the digital network in order to better utilize bandwidth. The network interface  202  couples the DSP module  204  via a signal path S 3 . 
     The DSP module  204  provides the control functions of the telephone system  200  in a similar manner to the TDM controller in the previous telephone system  100 . Additionally, the DSP module  204  may provide speech compression, silence suppression and packetization. A lower-powered DSP module  204  is possible as the MAC  218  may perform sum and multiply functions for the DSP  204 . 
     Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.