Abstract:
Full-duplex, coherent transceivers are provided which can directly interface between exisiting data interface modules (e.g., cable modems) and wireless cable providers to facilitate the flow of high-speed downlink communication signals and high-speed uplink data signals. Currently, a speed bottleneck is formed between consumers and various communication resources (e.g., the internet) by low transfer rates of telephones and conventional modems. This bottleneck is removed by transceivers of the invention. The transceiver structure prevents frequency inversion and reduces cost because it can form the required interface without requiring additional interface modules.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to transceivers and more particularly to wireless cable transceivers. 
     2. Description of the Related Art 
     FIG. 1 illustrates signal bands that are associated with a variety of communication services that deliver communication signals to consumers. In the oldest of these communication services, off-air television and frequency modulation signals are received through a consumer antenna. Off-air television channels are arranged in three different signal bands that are included in a frequency span of 54-800 MHz and off-air frequency modulation signals extend across a signal band of 88-108 MHz. Subsequently, consumers were offered the alternative of cable television (CATV) in which hard cables deliver television and frequency modulation signals to consumer dwellings over a CATV signal band of 54-648 MHz. Off-air and CATV communication signals are, therefore, substantially contained within a consumer signal band  10  of FIG. 1 that spans 5-750 MHz. 
     Consumers can presently choose between an additional pair of communication services. In a first one of these services, communication signals are provided by a direct broadcast satellite (DBS) system. In this system, satellites radiate microwave signal beams in C-band frequencies (e.g., 3.7-4.2 GHz) and Ku-band frequencies (e.g., 11.7-12.75 GHz). Upon direct receipt at a consumer antenna, these satellite signals are initially downconverted to a signal band of 950-1450 MHz before further downconversion and detection at either 479 MHz or 70 MHz. 
     In a second one of these services, communication signals are provided by a wireless cable system in which signals are directed from a service provider&#39;s antenna to a plurality of subscriber antennas. The signals can be sent over two different wireless cable signal bands. One band is the multipoint distribution service (MDS) frequency band  11  of FIG. 1 that spans 2150-2162 MHz. The other band is the multichannel multipoint distribution service (MMDS) frequency band  12  that extends across 2500-2686 MHz. Signals in these wireless cable bands are typically downconverted at subscriber dwellings by low noise block downconverters (LNB&#39;s) that use a converter signal  13  at 2278 MHZ to form MDS and MMDS intermediate frequency bands  14  and  15  that respectively span 116-128 MHz and 222-408 MHz. 
     The communication signals provided by these consumer services were initially limited to television and frequency modulation signals. Consumers are now being offered, however, an increasing list of other communication options. For example, a communication service can operate as an internet service provider (ISP) who provides access to the internet. It was also initially envisioned that signals were only downlinked to consumers but some of these communication services have now become two-way streets in which consumers uplink data signals (e.g., signals associated with the activities of pay-for-view, banking, home shopping, medical alarm and fire/security). 
     In the past, uplink data from consumers has typically been channeled over telephone lines. As a first example, consumers communicate home shopping selections over their telephones to wireless cable providers. As a second example, consumer computers communicate through modems and telephone lines with internet ISP&#39;s. Telephone lines and conventional modems, however, form a speed bottleneck in these data communications because of their low transmission rates (typically less than 56 kbps). 
     To provide a path around this bottleneck, the signal band  10  of FIG. 1 is now generally divided into an uplink signal band  16  of 5-65 MHz for consumer uplinking of data signals and a downlink signal band  17  of 50-750 MHz for provider downlinking of communication signals. Recently introduced data interface modules (e.g., cable modems) take advantage of the higher uplink bandwidth. Accordingly, these modules have significantly higher data transmission rates (e.g., 500 kbps-3 Mbps). 
     The provider antenna-subscriber antenna structure of wireless cable is especially suited for two-way signal flow. As stated previously, communication signals from wireless cable headends are typically downconverted at subscriber dwellings by LNB&#39;s and subscriber data is presently communicated back to the headend by telephone lines which have the speed limitation referred to above. This data path limitation could be removed by provision of a high-speed uplink path. In anticipation of this, a pair of data-uplink signal bands have been proposed. One is a limited-bandwidth (2686.0625-2689.8125 MHz) instructional television fixed service (ITFS) signal band and the other is a wider-bandwidth (2305-2360 MHz) wireless communication service (WCS) signal band. These are respectively shown in FIG. 1 as signal bands  18 A and  18 B. 
     In an exemplary uplink path proposed in U.S. Pat. No. 5,437,052 (issued Jul. 25, 1995 to Hemmie, et al.), a bi-directional converter has a downconverter for downconverting MMDS programming signals (i.e., signals in the MMDS band  13  of FIG. 1) to converted signals in the 222-408 MHz range (i.e., intermediate frequency band  16  in FIG. 1) and an upconverter that converts data/information signals in the 116-128 MHz range (i.e., intermediate frequency band  15  in FIG. 1) to the MDS signal band (i.e., MDS band  12  in FIG.  1 ). 
     This proposed uplink path, however, ignores a frequency gap  19  between the uplink signal band  16  and the intermediate frequency MDS band  14  of FIG.  1 . Subscribers wishing to access this uplink path with data interface modules that operate in the uplink signal band  16 , would have to purchase additional interface modules that could span the frequency gap  19 . In addition, if this upconversion structure is used to communicate data to the MDS band ( 11  in FIG.  1 ), it will invert the data&#39;s frequency order in contrast to the conventional MMDS downconversion process which does not invert frequency order. This inversion typically creates problems in communication and data transfer systems. 
     SUMMARY OF THE INVENTION 
     The present invention addresses full-duplex, coherent transceivers that can directly couple exiting data interface modules to wireless cable providers and thus establish a high-speed uplink path for subscriber data flow that complements an existing high-speed downlink path for communication signals. 
     In particular, such transceivers can directly couple data interface modules (e.g., cable modems) operating in the uplink and downlink signal bands  16  and  17  of FIG. 1 to wireless cable providers through signal bands at the providers&#39; transmission antennas. With this direct interface, subscriber communication devices (e.g., computers, telephones and television displays) can be coupled in high-speed two-way paths with wireless cable providers (and, from there, to other resources such as the internet). Equipment to provide this two-way access is limited to the transceiver, a subscriber antenna and a hookup cable between the externally-positioned transceiver and communication devices inside the subscriber&#39;s dwelling. Subscribers are thus spared the cost of additional interface devices (e.g., devices that can span the frequency gap  19  of FIG.  1 ). 
     These goals are achieved with transceivers that position a downconverter mixer in a downconversion path and serially-arranged first and second upconverter mixers in an upconversion path. A stable signal source (e.g., a microwave oscillator phase-locked to a crystal) provides mixer signals to the downconverter mixer and the second upconverter mixer and a frequency divider couples the signal source and the first upconverter mixer. 
     Accordingly, all mixers convert with coherent signals and the phase coherency required for two-way flow of provider-subscriber signals (e.g., television, internet and telephony signals) is preserved. The division of the frequency divider can be chosen to place the upconverted data signals into selected microwave signal bands at a wireless cable transmission antenna (e.g., signal bands  11 ,  12 ,  18 A and  18 B of FIG.  1 ). In addition, the double upconversion facilitates the use of frequency plans which select or avoid frequency inversion. This feature of the invention also enhances its use in carrying provider-subscriber signals. 
     A downconverter input port and an upconverter output port can be coupled through a diplexer to a subscriber antenna or, alternatively, each coupled to a respective antenna. 
     Subscriber equipment cost is further reduced by integration of the transceiver and the subscriber antenna into a single unit. Additional cost reduction is obtained by coupling a primary supply voltage through the hookup cable to a power conditioner in the transceiver. This eliminates the need for expensive and bulky dc power conversion circuits in the transceiver. 
     The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of frequency bands that are associated with existing communication services; 
     FIG. 2 is a block diagram of a wireless cable system in accordance with the present invention; 
     FIG. 3A is a block diagram of a full-duplex, coherent transceiver in the wireless cable system of FIG. 2; 
     FIG. 3B is a partial block diagram which is similar to FIG. 3A but shows variations of another full-duplex, coherent transceiver embodiment; 
     FIG. 4 is a cross sectional view through filters in the transceiver of FIG. 3A; 
     FIG. 5 is a block diagram of an exemplary mixer signal source in the transceiver of FIG. 3A; and 
     FIG. 6 is a flow chart which illustrates process steps in the transceiver of FIG.  3 A and the wireless cable system of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 illustrates a wireless cable system  20  of the present invention in which a wireless cable headend  22  receives programming inputs from a variety of sources. These sources may include video tapes  24 , direct-feed sources  25  and transmissions  26  received via satellite receivers  27  and a receive antenna  28  from a broadcast satellite  30 . From the programming sources, the headend  22  prepares communication signals  32  with various signal conditioning equipment (e.g., decoders  34 , modulators  35 , upconverters  36  and power amplifiers  37 ) and transmits the communication signals to a plurality of subscriber antennas  38  from a transmit antenna  39 . 
     In an exemplary subscriber dwelling  40 , various subscriber communication devices (e.g., television-display device  42 , computer  44  and telephone  46 ) are coupled into a data interface module in the form of a cable modem  48 . Other exemplary interface modules include an analog decoder  49  which would typically couple to an analog television set as indicated in broken lines. In the following description, it is assumed the data interface module is represented by the cable modem  48 . 
     A hookup cable  50  connects the cable modem with an externally-positioned transceiver  60 . The cable modem  48  is thus directly coupled through the transceiver  60  and the subscriber antenna  38  to thereby transmit data signals  52  to the headend&#39;s transmit antenna  39 . Accordingly, a high-speed two-way flow of communication signals  32  and data signals  52  is established between subscribers and a wireless cable headend  22 . 
     In particular, the transceiver  60  is shown in FIG. 3A to include a frequency downconverter  62  and a frequency upconverter  64 . The downconverter&#39;s input port  63  and the upconverter&#39;s output port  65  are coupled through a diplexer  66  to the subscriber antenna  38 . The downconverter&#39;s output communication signals are available at a downconverter output port  70  for coupling through the hookup cable ( 50  in FIG. 2) to the cable modem ( 48  in FIG.  2 ). Data signals from the cable modem are coupled through the hookup cable to an upconverter input port  72 . 
     The downconverter  62  has a mixer  74  between the diplexer  66  and the downconverter&#39;s output port  70  and the upconverter  64  has first and second mixers  76  and  78  that are serially arranged between the upconverter&#39;s input port  72  and the diplexer  66 . The diplexer  66  has an input/output port  80  that couples to the antenna  38 . 
     The output of a stable mixer signal source  84  is directly coupled through a signal divider  81  to the downconverter mixer  74  and the second upconverter mixer  78  and is coupled through a frequency divider  86  to the first upconverter mixer  76 . 
     In more detail, the downconverter  62  positions a low-noise amplifier  90  and a radio-frequency (rf) bandpass filter  92  between the diplexer  66  and the downconverter&#39;s mixer  74 . Although the low-noise amplifier  90  is positioned ahead of the bandpass filter  92  in FIG. 3A to enhance the downconverter&#39;s noise figure, other embodiments of the invention may reverse this arrangement to enhance filtering of image and intermediate frequency (if) signals. Between its mixer  74  and its output port  70 , the downconverter includes a serially-arranged if amplifier  94  and an if bandpass filter  96 . 
     Between its input port  72  and its first mixer  76 , the upconverter  64  has a serially-arranged if amplifier  98  and an if bandpass filter  100 . Similarly, the upconverter has a serially-arranged if amplifier  102  and an if bandpass filter  104  between its first and second mixers  76  and  78 . Finally, a serially-arranged radio frequency (rf) bandpass filter  106  and rf amplifier  108  are arranged between the second upconverter mixer  78  and the diplexer  66 . The rf filter  104  is preferably before the rf amplifier  106  to reduce unwanted mixing products (e.g., image and intermodulation signals) before they are amplified. 
     In addition, the transceiver  60  has a switched-mode DC power conditioning module  110  that can be coupled through a selected one of low-pass filters  112  to either of the downconverter output port  70  and the upconverter input port  72 . A primary DC voltage can therefore be generated elsewhere (e.g., the cable modem  48  of FIG. 2) and coupled into the transceiver where the power conditioning module uses it to form biasing voltages for the transceiver. This feature of the invention lowers the transceiver&#39;s power dissipation and increases its efficiency. 
     In one embodiment, the transceiver&#39;s diplexer  66  is formed with a receive filter  113  that couples the input/output port  80  to the downconverter&#39;s input port  63  and a transmit filter  114  that couples the upconverter&#39;s output port  65  to the input/output port  80 . The receive filter is configured to pass microwave signals in a communication signal band from the input/output port  80  to the downconverter input port  63 . Similarly, the transmit filter is configured to pass microwave signals in an upconverted signal band from the input/output port  80  to the antenna  38 . Various other conventional diplexer structures can be substituted. In another diplexer embodiment, for example, the filters  113  and  114  are replaced by an isolator  115  as indicated by the replacement arrow  115 R. 
     FIG. 3B shows a partial block diagram of another transceiver embodiment  116  which is similar to the transceiver  60  with like elements indicated by like reference numbers. In the transceiver  60 , the downconverter input port  63  and the upconverter output port  65  are coupled through a diplexer  66  to a subscriber antenna  38 . In contrast, these ports are available for other connections in the transceiver  116 . For example, the downconverter input port  63  and the upconverter output port  65  can be respectively coupled along signal paths  117  to a receive antenna  118  and a transmit antenna  119 . 
     To reduce crosstalk between the frequency downconverter  62  and the frequency upconverter  64 , the transceiver  60  of FIG. 3A preferably includes bandpass filters  120  and  121 . Filter  120  is arranged to couple the signal of the signal source  84  to downconverter mixer  74  and filter  121  is arranged to couple the signal to upconverter mixer  78 . 
     Each of these filters passes only the signal source&#39;s signal and is preferably received and isolated by a cavity in the transceiver&#39;s frame. This structure reduces the transciever&#39;s size while also enhancing signal isolation. It is exemplified in FIG. 4 where the filter  120  is formed by microwave transmission lines  122  on the underside of a microwave circuit board  124 . Other microwave circuits of the transceiver are formed by microwave transmission lines  126  on the upper side of the circuit board. 
     A transceiver frame  128  defines a cavity  130  which surrounds and isolates the filter  120  (for clarity of illustration, the frame is slightly spaced from the circuit board). The microwave transmission lines can be any of several conventional transmission lines (e.g., microstrip, slot line and coplanar waveguide). The lines  122  and  126  are preferably separated by a ground plane  132  and signal connections between the lines are formed by via holes  134 . 
     FIG. 5 shows that an exemplary stable mixer signal source  84  is formed with a microwave oscillator  142 . The oscillator is phase locked to a crystal  144  that is contained within a control loop  146 . This forms a highly stable crystal-controlled signal source which enhances the phase coherence of the transceiver  60 . 
     Basic operation of the transceiver  60  of FIG.  3 A and the system  20  of FIG. 2 is shown in process steps of the flow chart  150  of FIG.  6 . In a process step  152 , headend communication signals (communication path  32  in FIG. 2) in a communications signal band (e.g., MMDS band  12  in FIG. 1) are downconverted with a converter signal (output of the signal source  84  in FIG. 3A) to a downlink signal band (e.g., signal band  15  in FIG. 1) for use by wireless cable subscribers. In FIG. 2, this downlink signal band is accessed by the cable modem  48 . 
     In process step  154 , the converter signal is divided (by divider  86  in FIG. 3A) to form a lower-frequency initial converter signal. In process step  156 , data signals from an uplink signal band (e.g., uplink band  16  in FIG. 1 provided by the cable modem  48  in FIG. 2) are double upconverted (in mixers  76  and  78  of FIG. 3A) with the initial converter signal and the converter signal to form signals in an upconverted signal band (e.g., a selected one of the signal bands  11 ,  12 ,  18 A and  18 B in FIG.  1 ). These upconverted signals are transmitted to the wireless cable headend (data path  52  in FIG.  2 ). 
     In its operation, the transceiver thus downconverts and upconverts with stable and phase coherent mixing signals to preserve phase coherency between the communication and data paths  32  and  52  of FIG.  2 . Because of its double upconversion, the transceiver can directly interface between the cable modem ( 48  in FIG. 2) and the headend ( 22  in FIG. 2) without requiring any additional interface modules. 
     In the absence of the first upconverter mixer  76 , a data signal band at the upconverter input port  72  would be frequency inverted by the upconversion process of the second mixer  78 . With double upconversion, however, frequency inversion can be selected or avoided and, accordingly, frequency order preserved in both of the downconversion and upconversion processes of the transceiver  60 . 
     By choice of the divider ratio in the frequency divider  86  of FIG. 3A, the upconverted signal band can be adjusted to match any selected one of various wireless cable signal bands. As a first example, with the signal source  84  generating a 2278 MHz signal and the divider  86  set to a divider ratio of  16 , the first upconverter mixer  76  is supplied with a ˜142.4 MHz drive signal. In this example, input data signals at input port  72  in the approximate range of 14.37-26.37 MHz will be upconverted (with difference frequencies selected by the bandpass filters  104  and  106 ) at the output port  65  to the MDS frequency band ( 11  in FIG. 1) that spans 2150-2162 MHz. 
     In FIG. 2, data can be therefore be sent directly from the uplink signal band ( 16  in FIG. 1) through the cable modem  48  to the headend  22  without the need for any interface modules and without frequency inversion. Simultaneously, communication signals in the MMDS band of 2500-2686 MHz (band  12  in FIG. 1) can be downconverted to an MMDS intermediate frequency band of 222-408 MHz (band  15  in FIG.  1 ). 
     As a second example, with the signal source  84  generating a 2143 MHz signal and the divider  86  again set to a divider ratio of  16 , the first upconverter mixer  76  is supplied with a ˜133.94 MHz drive signal. In this second example, input data signals at input port  72  in the approximate range of 28.06-43.06 MHz will be upconverted (with sum frequencies selected by the bandpass filters  104  and  106 ) at the output port  65  to a lower frequency portion 2305-2320 MHz of the WCS band  18 B of FIG.  1 . 
     In FIG. 2, data can again be sent directly from the uplink signal band ( 16  in FIG. 1) through the cable modem  48  to the headend  22  without the need for any interface modules and without frequency inversion. Simultaneously, communication signals in the MMDS band of 2500-2686 MHz (band  12  in FIG. 1) can be downconverted to an MMDS intermediate frequency band of 357-643 MHz. 
     In other exemplary applications of the transceivers of the invention, the divider ratio of the frequency divider  86  can be set to other conventional divider ratios (e.g.,  2 ,  4  and  8 ) to facilitate coupling between a variety of communication and data signal bands (e.g., the WCS signal band ( 18 B in FIG.  1 ), an Industrial, Scientific and Medical (ISM) band of 2400-2483.5 MHz and a Personal Communication Services (PCS) band of 1850-1990 MHz). 
     The downconverter port ( 70  in FIG. 3A) and upconverter port ( 72  in FIG. 3A) can be connected to the cable modem with double microwave cables or, preferably, with any of various microwave two-path cables (e.g., a microwave triaxial cable). Alternatively, ports  70  and  72  can be coupled to external circuits through a diplexer similar to the diplexer  66 . 
     The teachings of the invention facilitate enhanced data transfer rates because they provide direct coupling of dow ed communication signals and uplinked data signals between wireless cable subscribers and providers. Although these teachings have been illustrated with reference to a cable modem ( 48  in FIG.  2 ), other data interface modules can be used in practicing the invention. 
     The preferred embodiments of the invention described herein are exemplary and numerous modifications, variations and rearrangements can be readily envisioned to achieve an equivalent result, all of which are intended to be embraced within the spirit and scope of the invention as defined in the appended claims.