Patent Publication Number: US-RE42225-E

Title: System and method for timing detector measurements in a wireless communication system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to wireless communication systems, and more particularly to a wireless communication system that provides telephone, data and Internet connectivity to a plurality of users. 
     2. Description of Related Art 
     Several systems are currently in place for connecting computer users to one another and to the Internet. For example, many companies such as Cisco Systems, provide data routers that route data from personal computers and computer networks to the Internet along conventional twisted pair wires and fiber optic lines. These same systems are also used to connect separate offices together in a wide area data network. 
     However, these systems suffer significant disadvantages because of the time and expense required to lay high capacity communications cables between each office. This process is time consuming and expensive. What is needed in the art is a high capacity system that provides data links between offices, but does not require expensive communication cables to be installed. 
     Many types of current wireless communication systems facilitate two-way communication between a plurality of subscriber radio stations or subscriber units (either fixed or portable) and a fixed network infrastructure. Exemplary systems include mobile cellular telephone systems, personal communication systems (PCS), and cordless telephones. The objective of these wireless communication systems is to provide communication channels on demand between the subscriber units and the base station in order to connect the subscriber unit user with the fixed network infrastructure (usually a wired-line system). Several types of systems currently exist for wirelessly transferring data between two sites. 
     In wireless systems using multiple access schemes, frames of time are the basic transmission unit. Each frame is divided into a plurality of slots of time. Some time slots are used for control purposes and some time slots are used for information transfer. Information is typically transmitted during time slots in the frame where the time slots are assigned to a specific subscriber unit. Subscriber units typically communicate with the base station using a “duplexing” scheme which allows for the exchange of information in both directions of connection. 
     Transmissions from the base station to the subscriber unit are commonly referred to as “downlink” transmissions. Transmissions from the subscriber unit to the base station are commonly referred to as “uplink” transmissions. Depending upon the design criteria of a given system, the prior art wireless communication systems have typically used either time division duplexing (TDD) or frequency division duplexing (FDD) methods to facilitate the exchange of information between the base station and the subscriber units. Both the TDD and FDD duplexing schemes are well known in the art. 
     In TDD systems, duplexing of transmissions between a base station and its subscriber units is performed in the time domain. A selected subscriber unit typically communicates with a selected base station using a specific pre-defined radio frequency. The channel is time-divided into repetitive time periods or time “slots” which are employed for uplink and downlink transmissions. In contrast to FDD systems, frequency allocation or frequency reuse patterns are simplified because there is no requirement of frequency separation between the uplink and downlink transmissions. 
     Both the uplink and downlink transmissions occur during different pre-determined time slots using the identical radio frequency. In some current wireless communication systems, there are base stations that act as central points for receiving and transmitting data to a plurality of customer sites. These base stations typically connect to other data systems such as the Internet, the phone system or other systems that provide user data to the customer&#39;s sites. As can be imagined, it is important to maintain a strong signal between the base station and the customer sites. Thus, in conventional systems, power detectors within the base station and customer sites continually monitor wireless transmissions in order to tune the system to receive the strongest possible signal. 
     Unfortunately, prior customer sites relied on complicated control signals to measure transmission power levels. These control signals were implemented because in TDD systems the transmit and receive paths use the same frequency. Thus, it was possible that when the customer site equipment took a power measurement, it was actually measuring a transmission signal from a nearby customer site that was transmitting on the same frequency. The addition of the control signals ensured that power measurements were taken from the base station, and not a nearby customer site. 
     Moreover, in some prior systems, the customer site equipment was separated into indoor units and outdoor units. The indoor units typically included the modem and electronics for connected with the customer&#39;s equipment. The outdoor unit was installed on the exterior of the building and included the antenna for receiving and transmitting wireless user data. However, in these systems, the outdoor unit did not independently know when the base station was transmitting. 
     Some prior systems attempted to solve this problem by including a gating signal between the indoor unit and the outdoor unit. The gating signal could be used to instruct the outdoor unit to sample its receive detectors at a particular time, thus ensuring that the receive detectors would measure signals from the base station. Unfortunately, adding this signal to the transmission cable between the outdoor unit and the indoor unit requires costly hardware changes. In addition, transmitting the extra gating signal across the transmission cable increases spurs and other undesirable effects in the data transmission pathway. 
     This problem is compounded by the fact that the outdoor unit does not contain a modem. A modem could serve as a conduit for the outdoor unit to receive additional commands. Thus, the outdoor unit, by itself, cannot determine the proper time to sample the receive detectors. 
     Thus, what is needed in the art is a convenient system at the customer site for accurately measuring the power of transmission signals from the base station. Such a system is described below. 
     SUMMARY OF THE INVENTION 
     One embodiment of the invention is a wireless communication system having a plurality of base stations and customer sites, wherein data is transferred between said base stations and said customer sites, and wherein said system comprises preset downlink time segments for transmitting said data between the base stations and the customer sites. This embodiment includes: an indoor unit comprising a first modem configured to modulate/demodulate data transmitted between the base stations and the customer sites, wherein the indoor unit is adapted to transmit a control message at a predetermined time with respect to said preset downlink time segments; an outdoor unit comprising a micro controller and a signal detector, said outdoor unit being adapted to receive the control message and, in response to receiving said control message, read said signal detector; and a broadband cable linking the indoor unit to the outdoor unit. 
     Another embodiment of the invention is a wireless communication system having a plurality of base stations and customer sites, wherein data is transferred between said base stations and said customer sites, and wherein said system comprises preset downlink time segments for transmitting said data between the base stations and the customer sites. This embodiment includes: an indoor unit comprising a first modem configured to modulate/demodulate data transmitted between the base stations and the customer sites, said indoor unit further comprising a programmable memory adapted to transmit a control message at a predetermined time with respect to said preset downlink time segments; an outdoor unit comprising a micro controller and a signal detector, said outdoor unit being adapted to receive the control message and, in response to receiving said control message, read said signal detector; and a broadband cable linking the indoor unit to the outdoor unit. 
     Yet another embodiment of the invention is a method for measuring the strength of a signal transmitted from a base station to a customer site in a wireless communication system, wherein said wireless communication system has preset downlink time segments for transmitting data from the base station to the customer site, and wherein said customer site comprises an indoor unit and an outdoor unit. This method provides: transmitting a message from said indoor unit to said outdoor unit, wherein said message is timed to arrive at said outdoor unit at a predetermined time relative to said preset downlink time segment; and reading a detector in said outdoor unit in response to receipt of said message so that said detector is read during said preset downlink time segment. 
     Still another embodiment of the invention is a method for tuning a wireless communication system, wherein said wireless communication system has preset downlink time segments for transmitting data from a base station to a customer site, and wherein said customer site comprises an indoor unit having a processor and an outdoor unit having tunable attenuators. This method includes: transmitting a control message from said indoor unit to said outdoor unit, wherein said message is timed to arrive at said outdoor unit at a predetermined time relative to said preset downlink time segment; reading a detector in said outdoor unit in response to receipt of said message so that said detector will be read during said predetermined downlink time segment; transmitting a response message comprising values from said detector to said indoor unit; determining the appropriate settings said attenuators in said outdoor unit; transmitting a second control message comprising updated attenuator settings to said outdoor unit; and tuning said outdoor unit based on said updated attenuator settings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary broadband wireless communication system for use with the present invention. 
         FIG. 2  is a block diagram of cell site used in the wireless communication system of FIG.  1 . 
         FIG. 3  is a block diagram of an embodiment of an Indoor Unit module from the cell site illustrated in FIG.  2 . 
         FIG. 4  is a block diagram of an embodiment of an Outdoor Unit module from the cell site illustrated in FIG.  2 . 
         FIG. 5  is a block diagram of an embodiment of the micro controller circuitry within the Outdoor unit. 
         FIG. 6  is a state diagram of one embodiment of the initialization process within an Outdoor unit. 
         FIG. 7  is a flow diagram of one embodiment of a preliminary checkout process undertaken in the Outdoor unit. 
         FIG. 8  is a flow diagram of one embodiment of a handshaking process between the Indoor unit and the Outdoor unit. 
         FIG. 9  is a flow diagram of one embodiment of a timing measurement of a detector process undertaken in the Outdoor unit. 
         FIG. 10  is a flow diagram of one embodiment of a loopback process undertaken in the Outdoor unit. 
         FIG. 11  is a block diagram of a commercial customer site that includes customer premises equipment. 
         FIG. 12  is a block diagram of a residential customer site that includes customer premises equipment. 
         FIG. 13  is a block diagram illustrating one embodiment of communications between base stations and consumer premises equipment in wireless systems. 
         FIG. 14  is a block diagram of a time frame for transmitting wireless user data between a base station and consumer premises equipment. 
         FIG. 15  is a flow diagram illustrating one embodiment of a process utilized by an indoor unit to transmit a message to an outdoor unit 
         FIG. 16  is a flow diagram illustrating one embodiment of a process utilized by an outdoor unit to take detector readings during a downlink from a base station. 
         FIG. 17  is a block diagram of an alternate embodiment time frame for transmitting wireless user data between a base station and consumer premises equipment. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention. 
     A. Overview of the Wireless Communication System 
     As described above, embodiments of the present invention relate to a broadband wireless communication system. The system is particularly useful for linking a plurality of customers and businesses together to share data or access the Internet. In general, the system provides base stations that are centrally located from a plurality of customer sites. The base stations are linked to services desired by customers, such as Internet access, satellite access, telephone access and the like. Within the base stations are communication devices, such as routers, switches and systems for communications with the desired services. In addition, each base station includes one or more antennas for connecting wirelessly with one or more customer sites. 
     A customer desiring, for example, access to the Internet will install a set of Customer Premises Equipment (CPE) that includes an antenna and other hardware, as described in detail below, for providing a high speed wireless connection to one or more base stations. Through the high-speed wireless connection, the customer is provided with access to the Internet or to other desired services. As discussed below, the data transmitted wirelessly between a base station and a customer site is termed herein “user data”. Of course, at each customer site, a plurality of simultaneous computers can be provided with wireless access to the base station through the use of hubs, bridges and routers. 
     In one embodiment, the base station comprises a plurality of indoor units that provide an interface between the routers, switches and other base station equipment and a plurality of outdoor units (ODU) that transmit/receive data to/from the customer sites. Each indoor unit typically includes, or communicates with, a modem for modulating/demodulating user data going to/from the outdoor unit. 
     In one embodiment, each of the indoor units is connected to only one outdoor unit and each IDU/ODU pair transmits and receives user data with a unique frequency. This format provides a base station with, for example, 10, 20, 30 or more IDU/ODU pairs that each communicate with customer sites using unique frequencies. This provides the base station with a means for communicating with many customer sites, yet dividing the bandwidth load between several frequencies. Of course, a base station that serves a small community of customer sites might only have a single IDU/ODU pair. 
     Each ODU at the base station is normally located outside of the physical building and includes an integrated broadband antenna for transmitting/receiving wireless user data packets to/from the customer sites. Of course, the antenna does not need to be integrated with the ODU, and in one embodiment is located external to the ODU. 
     The ODU and the IDU communicate with one another through a broadband cable connection, such as provided by an RG-6 cable. In one embodiment the ODU and IDU communicate across about 10 to 100 feet of cable. In another embodiment, the ODU and IDU communicate across about 100 to 500 feet of cable. In yet another embodiment, the ODU and the IDU communicate across about 500 to 1000 feet of cable. 
     In one embodiment, the IDU controls functions within the ODU by sending control messages in addition to the user data stream. The IDU passes messages to the ODU in order for the IDU to control certain aspects of the ODU&#39;s performance. For example, the IDU may determine that the system needs to be tuned in order to maximize the signal strength of the user data being received. The IDU will send a control message in the form of a frequency shift key (FSK) modulated signal, as described below, to the ODU along the broadband cable. The control message preferably includes the identity of a variable voltage attenuator (VVA) or other type of attenuator in the ODU and a new setting for the designated VVA. An onboard micro controller in the ODU reads and interprets the control message coming from the IDU and sends the proper signals to the designated VVA. 
     Once the ODU has adjusted the designated VVA, the micro controller in the ODU sends a response in the form of a response message back along the broadband cable to the IDU. The response message preferably includes a confirmation of the new VVA setting, or other data to confirm that the requested control message has been fulfilled. The following discussion provides a detailed listing and the structure of exemplary control messages and response messages that can be transmitted between the IDU and the ODU. 
     The ODU in a CPE preferably samples its transmit detectors only during a transmission to the base station i.e. during an uplink. Fortunately, the ODU knows when it is transmitting user data, so it can accurately sample transmit detectors during an ODU transmission. 
     In addition to sampling its transmit detectors, the ODU needs to sample its receive detectors to tune the ODU to optimally receive the signal from the base station. 
     Of course, the ODU should only sample the receive detectors during a transmission from the base station i.e. during a downlink. Unfortunately, in a TDD system there are transmissions at the same frequency from other customer premises ODUs directed to the base station. Because both the uplink transmissions and the downlink transmissions are on the same frequency in a TDD system, the customer premises ODU cannot continuously monitor downlink signals because the ODU might receive a transmission from a nearby CPE that is at a higher signal strength than the ODU receives from the base station. If this happened, the ODU might improperly intercept the transmission from a nearby CPE and proceed to sample its receive detectors at a time other than during transmission from the base station. 
     As described in detail below, embodiments of the invention include communication systems that only sample receive detectors in the ODU during times that are known to be during a downlink from the base station to the CPE. These embodiments send regular control messages from the IDU to the ODU that request detector values that are measured at a guaranteed downlink transmission time within the TDD frame. By only sampling the receive detectors during this guaranteed downlink transmission time, the ODU in the customer premises equipment is ensured of reading the base station transmission and not a transmission from a nearby CPE outdoor unit. It should be realized that the base stations and the customer sites each have indoor units and outdoor units that function similarly to provide a communication link between the external antenna and the electronic systems in the interior of the buildings. Of course, in one embodiment within the customer sites, the indoor units are connected through routers, bridges, Asynchronous Transfer Mode (ATM) switches and the like to the customer&#39;s computer systems, which can also include telecommunication systems. In contrast, within the base stations the indoor units are connected to the routers, switches and systems that provide access to the services desired by the customers. 
     Referring now to  FIG. 1 , a wireless communication system  100  comprises a plurality of cells  102 . Each cell  102  contains an associated cell site  104  which primarily includes a base station  106  having at least one base station indoor unit (not shown). The base station receives and transmits wireless user data through a set of base station outdoor units  107 . A communication link transfers control signals and user data between the base station indoor unit (IDU) and the base station outdoor unit (ODU). The communication protocols between the base station IDU and base station ODU will be discussed more thoroughly in the following sections. 
     Each cell  102  within the wireless communication system  100  provides wireless connectivity between the cell&#39;s base station  106  and a plurality of customer premises equipment (CPE) located at fixed customer sites  112  throughout the coverage area of the cell  102 . The customer premises equipment normally includes at least one indoor unit (not shown) and one customer ODU  110 . Users of the system  100  can be both residential and business customers. Each cell can service approximately 1,000 residential subscribers and approximately 300 business subscribers. As will be discussed below, each customer ODU  110  is positioned to receive and transmit user data from and to one of the base station ODUs  107 . As discussed above, the customer IDU (not shown) is located within the site  112  and provides a link between the customer&#39;s computer systems to the ODU. 
     As shown in  FIG. 1 , the cell sites  104  communicate with a communications hub  114  using a communication link or “back haul”  116 . The back haul  116  preferably comprises either a fiber-optic cable, a microwave link or other dedicated high throughput connection. In one embodiment the communications hub  114  provides a data router  118  to interface the wireless communications network with the Internet. In addition, a telephone company switch  120  preferably connects with the communications hub  114  to provide access to the public telephone network. This provides wireless telephone access to the public telephone network by the customers. Also, the communications hub  114  preferably provides network management systems  121  and software that control, monitor and manage the communication system  100 . 
     The wireless communication of user data between the base station ODUs  107  and customer ODU  110  within a cell  102  is advantageously bidirectional in nature. Information flows in both directions between the base station ODUs  107  and the plurality of Customer ODU  110 . Each of the base station ODUs  107  preferably broadcast single simultaneous high bit-rate channels. Each channel comprises different multiplexed information streams. The information in a stream includes address information which enables a selected Customer ODU  110  to distinguish and extract the information intended for it. 
     The wireless communication system  100  of  FIG. 1  also provides true “bandwidth-on-demand” to the plurality of Customer ODU  110 . Thus, the quality of the services available to customers using the system  100  is variable and selectable. The amount of bandwidth dedicated for a given service is determined by the information rate required by that service. For example, a video conferencing service requires a great deal of bandwidth with a well controlled delivery latency. In contrast, certain types of data services are often idle (which then require zero bandwidth) and are relatively insensitive to delay variations when active. One mechanism for providing an adaptive bandwidth in a wireless communication system is described in U.S. Pat. No. 6,016,211 issued on Jan. 18, 2000, the disclosure of which is hereby incorporated by reference in its entirety. 
     The wireless communication system  100  of  FIG. 1  also provides true “bandwidth- on - demand” to the plurality of Customer ODU  110 . Thus, the quality of the services available to customers using the system  100  is variable and selectable. The amount of bandwidth dedicated for a given service is determined by the information rate required by that service. For example, a video conferencing service requires a great deal of bandwidth with a well controlled delivery latency. In contrast, certain types of data services are often idle  ( which then require zero bandwidth )  and are relatively insensitive to delay variations when active. One mechanism for providing an adaptive bandwidth in a wireless communication system is described in U.S. Pat. No.  6 , 016 , 311  issued on Jan.  18 ,  2000 , the disclosure of which is hereby incorporated by reference in its entirety.   
     1. Cell Site 
       FIG. 2  illustrates a block diagram of the cell site  104  of  FIG. 1  used in the wireless communication system  100 . As described above, the cell site  104  comprises the base station  106  linked to a plurality of base station ODUs  107 . As shown in  FIG. 2 , the base station also includes a series of base station indoor units  123 , made up of individual base station indoor units such as indoor unit  122 . Each of the indoor units  123  is linked through a broadband cable to an individual ODU. For example, the indoor unit  122  is linked through a broadband cable  129  to an ODU  108 . The indoor unit  122  sends control messages and user data to the ODU  108  through the cable  129 . The indoor unit  122  also receives response messages and user data from the base station outdoor unit  108 . The indoor units  123  are provided with an interface to a back-haul, for example the back-haul interface equipment  124 . 
     The base station can also alternatively include a video server  128  and direct broadcast satellite (DBS) receiver equipment  130 . The back-haul interface equipment  124  allows the base station to bi-directionally communicate with the hub  114  (FIG.  1 ). 
     The base station  106  is preferably modular in design. The modular design of the base station  106  allows the installation of lower capacity systems that can be upgraded in the field as capacity needs dictate. The IDU  122  in conjunction with the ODU  108  performs both the media access protocol layer and the modulation/de-modulation functions that facilitate high-speed communication over the wireless link. The IDU  122  preferably is connected via the broadband cable  129  to the base station outdoor unit  108  which is preferably mounted on a tower or a pole proximate the base station  106 . The base station outdoor unit  108  contains high-frequency radio electronics (not shown) and antenna elements for transmitting user data to the customer sites. 
     2. Indoor Unit 
     Referring to  FIG. 3 , a more detailed block diagram of the indoor unit  122  is provided. As illustrated, the indoor unit  122  links the base station equipment  124 ,  126 ,  128 , and  130  to the base station outdoor unit  108 . The IDU  122  is preferably under the control of a communications processor  132 . One processor is the Motorola MPC8260 Power-QUICC II (PQII). As illustrated, the communications processor  132  connects through a PowerPC bus  134  to a modem  135 . 
     The modem  135  includes a Field Programmable Gate Array (FPGA)  136  that stores instructions for controlling other subcomponents of the IDU  122 . For example, the FPGA  136  communicates with a Frequency Shift Key (FSK) modem  138  in order to send FSK modulated control messages from the EDU through the broadband cable  129 , to the outdoor unit  108 . A low band pass filter  139  is provided between the cable  129  and the FSK modem  138 . In an alternate embodiment, an Application Specific Integrated Circuit (ASIC) replaces the FPGA in order to provide similar functions. 
     As is discussed in detail below, the IDU and ODU communicate with one another using messages. The IDU sends control messages to the ODU, and the ODU responds with response messages. This communication allows the IDU to request data from ODU detectors, and then send commands instructing the ODU to reset subcomponents in order to be more efficient. 
     Thus, control messages are FSK modulated and sent from the IDU to the ODU. Similarly, response messages from the ODU to the IDU are demodulated by the FSK modem  138  and then interpreted by instructions with the FPGA  136 . These control messages and response messages, and their data structure and format, are discussed in detail below. In one embodiment, the transmission baud rate of the FSK modem  138  is 115 kbps with one start bit, one stop bit and one parity bit. Of course, other data transfer speeds and formats are contemplated to be within the scope of the invention. Moreover, the FSK modem  138  preferably transmits and receives in frequencies between 6-8 MHz. 
     Messages between the IDU and ODU are preferably transmitted independently of the other signals being passed along the cable  129 . In one embodiment, the ODU acts like a slave in that it does not originate messages, but only responds to control messages it receives from the IDU. 
     As illustrated, power is provided to the ODU through a DC power supply  140  that provides, in one embodiment, 48V DC to the ODU. A 20 MHz reference signal  142  is also transmitted across the cable  129  in order to keep components in the IDU and ODU synchronized with one another. 
     The communications processor  132  is also linked to an Input/Output port  150  that attaches to the routers, switches and systems within the base station. The communications processor  132  receives packet data from the Input/Output port  150  and transmits it to a modem  153  for modulation demodulation. The modulated data signal is then placed on a 140 MHz main signal  154  for high throughput transmission to the ODU  108 . It should be realized that the data transmission along the 140 MHz main signal can occur simultaneously with the control message and response message data that is Frequency Shift Key modulated across the cable  129 . 
     In order for the IDU and ODU to effectively and rapidly switch between receiving and transmitting data modes, a 40 MHz switching signal  158  is also linked to the communications processor  132  and carried on the cable  129 . The 40 MHz switching signal  158  is used within the system to switch the ODU and IDU from transmit to receive mode, as will be discussed below with reference to FIG.  4 . 
     In one embodiment, if the 40 MHz signal is present, the ODU and IDU enter transmit mode to send user data from the base station ODU to customer ODUs. However, if the 40 MHz signal is not present, the ODU and IDU enter receive mode wherein user data being transmitted from other ODU&#39;s is received by the base station ODU. The timing of the switching signal is controlled by instructions residing in the FPGA  136 . For example, in a half-duplex Time Division Duplex architecture, the switching signal  158  is preferably set to switch between receive and transmit modes. However, in a full duplex architecture where user data is constantly being received, the switching signal  158  can be programmed to switch between a transmit mode and a null mode. 
     3. Outdoor Unit 
     Still referring to  FIG. 3 , a more detailed block diagram of the outdoor unit  122  is provided. As illustrated, the outdoor unit  122  receives control messages and user data from the IDU across the cable  129 . Depending on the state of the 40 MHz switching signal  142 , a set of switches  160 a, b in the ODU are either in transmit or receive mode. In transmit mode, user data and control messages are sent from the IDU to the ODU. In receive mode, user data and response messages are sent from the ODU to the IDU. As illustrated, and discussed with reference to  FIG. 5 , a microcontroller  400  is linked to the components within the ODU in order to manage data flow. 
     The microcontroller  400  communicates with a multiplexer  170  that separates the signals carried on the cable  129 . Within the microcontroller  400  is a programmable memory  161  that stores instructions for gathering the response data and forming response messages for transmission to the IDU. In addition, the instructions within the memory  161  read incoming control messages from the IDU and send control signals to sub-components of the ODU. A FSK modem  165  is connected to the multiplexer  170  and microcontroller  400  for modulating/demodulating messages to/from the IDU. As shown a Universal Asynchronous Receiver/Transmitter (UART)  166  is connected to the modem  165  and receives modulated serial data from the multiplexer  170 . 
     a. Transmit Mode 
     If the ODU is in transmit mode, the modulated user data being sent from the IDU along the 140 MHz main signal is first routed through the multiplexer  170  to the switch  160 a. If the switch is set to transmit mode, the main signal is sent to an IF UP CONVERSION block  200  that converts the 140 MHz signal to an approximately 2.56 GHz (S band) signal. As illustrated, the IF UP CONVERSION block  200  first provides a variable voltage attenuator (VVA)  210  that is used to compensate for frequency fluctuations from transmission along the cable  129 . The signal then passes to a detector  212  that measures power levels after compensation at the cable input. 
     Although the following discussion relates to a system that transmits user data within the millimeter band at frequencies of approximately 28 GHz, the system is not so limited. Embodiments of the system are designed to transmit user data at frequencies, for example, of 10 GHz to 66 GHz. 
     The user data signal is then up-converted to an S band signal at an IF UP CONVERSION block  216  through an associated local oscillator block  219 . The local oscillator block  219  preferably includes an S band frequency generator  220 . In one embodiment, the frequency generator  220  includes a National Semiconductor LMX 2301 or Analog Devices ADF41117. The signal is then sent through a second VVA  234  that is used for power adjustment at the S band frequency. 
     Once the signal has-been up-converted to the S band frequency, it is sent to an RF UP CONVERSION block  250 . The RF UP CONVERSION block  250  links to a millimeter wave band frequency generator  255  within the local oscillator block  219  for up-converting the 2.56 GHz signal to an approximately 28 GHz signal. The up-converted signal is then passed through a VVA  264  to provide for millimeter wave band power adjustment. Once the signal has been adjusted by the VVA  264  it is sent to a Power Amplifier  268  and then to an output power detector  269 . The signal is then finally passed through the switch  160 b and out an antenna  270 . 
     b. Receive Mode 
     If the ODU is in receive mode, user data is received along a 28 GHz signal (LMDS band) and passed through the antenna  270  and into an RF DOWN CONVERSION BLOCK  272 . Within the RF DOWN CONVERSION BLOCK  272  is a Low Noise Amplifier (LNA)  275  which boosts the received 28 GHz signal. The signal is then sent to a VVA  280  for power adjustment at the millimeter wave band after the LNA  275 . The received 28 GHz signal is then sent to a RF down converter  285  for down conversion to a 2.56 GHz (S band) signal. The RF down converter  285  communicates with the Local Oscillator block  219  to reduce the incoming signal to the S band range. 
     After the received signal has been down converted to 2.56 GHz, it is transmitted to an IF DOWN CONVERSION block  290 . Within the IF DOWN CONVERSION BLOCK  290  is a VVA  292  for adjusting the power at the S band prior to down conversion. Following adjustment by the VVA  292 , the received signal is passed to a detector  294  for measuring power leakage from the transmission path during signal transmission. The signal is then passed to an IF down converter  298  which uses the local oscillator block  219  to down convert the S band signal to a 140 MHz signal for transmission across the cable  129 . 
     After being converted to a 140 MHz signal, the received user data is passed through another VVA  300  for power adjustment at the low frequency band and then a detector  304  to measuring power levels before transmission across the cable  129  (4 dBm at the cable output). 
     c. Message Traffic Between the ODU and IDU 
     It should be realized that the control messages sent by the IDU to the ODU can control components of the ODU. For example, in one embodiment, the controlled components in the ODU are the VVAs and frequency synthesizers. Response messages from the ODU to the IDU are also generated to include data from the detectors, temperature sensor and other components described above. As can be imagined, control messages are sent by the IDU and then interpreted by the microcontroller in the ODU. After interpreting the message, the microcontroller sends the appropriate adjustment signals to components of the ODU. 
     Referring to  FIG. 5 , a hardware schematic of circuitry within the ODU is illustrated. As shown, the ODU is controlled by the micro controller  400  that manages data flow within the ODU. In one embodiment, the micro controller is a Motorola MC68HC908GP20 high-performance 8-bit micro controller. Control messages from the IDU are sent across the cable  129  to the micro controller  400  in the ODU and then forwarded to the appropriate ODU component. In addition data signals generated by the ODU components, such as detectors, are sent from the component to the micro controller  400 . The micro controller  400  builds a response message that is then transmitted via FSK modulation to the IDU. 
     As shown in  FIG. 5 , messages are sent from the IDU along the cable  129  through a 12 Mhz low pass filter  404  to a FSK receiver  408  in the ODU. In one embodiment, the FSK receiver is a Motorola MC13055 FSK receiver. The receiver  408  accepts the FSK modulated data from the IDU and inputs it into the micro controller  400 . As also indicated, the micro controller  400  outputs response messages to the IDU through a voltage controller oscillator  410 . 
     The micro controller  400  is also in communication with the local oscillator block  219 . In addition a digital to analog (D/A) converter  415  communicates with the micro controller  400  in order to control the VVAs within the ODU. In one embodiment, the D/A converter is an Analog Devices model AD8803 D/A converter. 
     The micro controller  400  also provides an input from a temperature sensor in order to provide for temperature compensation of the ODU measurements. In one embodiment, the temperature sensor is a National Semiconductor LM50 temperature sensor. 
     As discussed previously, the IDU transmits FSK modulated control messages to the ODU to control particular components. The structure and format of the control messages sent by the IDU and the response messages returned by the ODU are discussed in detail below. 
     B. Message Format 
     In one embodiment, the maximum data rate of FSK modulated messages that can be handled by the Micro Controller is 125 Kbps. However, in another embodiment, and for compatibility with a conventional personal computer, FSK data is transmitted at a 115.2 kbps data rate. Accordingly, the protocol between the Micro Controller  400  and communications processor  124  can be kept as simple as possible and at the same time flexible for future changes. The message structure presented in the following section takes into account this flexible simplicity. In general, the messages passed between the ODU and the IDU are delivered byte after byte with no delay. In one embodiment, in the ODU, a time gap of more then 0.5 msec between bytes will cause the ODU to re-synchronize on the next preamble. 
     1. Message Structure 
     In one data format, each message, starts with a fixed preamble that is used to identify the beginning of a message. Following the preamble an identifier is sent. The identifier is unique per message, i.e., a specific identifier defines completely the structure of the following message information fields. 
     The variable information within each message is preferably sent after the identifier. In addition, a CRC is added at the end of each message as an integrity check of the message. The Micro Controller  400  in the ODU receives a control message from the IDU, controls the required components in the ODU and prepares a response message. As soon as the IDU finishes sending the control message to the ODU, it switches from transmit mode to receive mode. The ODU then begins to transmit FSK modulated response messages to the IDU. 
     One embodiment of a data structure of the messages is as follows: 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Preamble 
                 Identifier 
                 Information 
                 CRC-8 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Preamble—the preamble is 1 Byte field and it is always 00. 
             Identifier—the identifier is 1 Byte field and unique for each message. 
             Information—the information filed is variable length according to the message data being sent. The information field is always padded to be an integer number of bytes. 
             CRC-8—added for each message for error control. In the IDU, the CRC-8 is implemented inside the FPGA  130  (FIG.  3 ). The CRC-8 is implemented in software in the ODU Micro Controller  400 . 
           
         
       
    
     In general, the messages are delivered byte after byte with no delay. When the ODU detects an error, it waits until the next preamble. No response messages are sent back from the ODU to the IDU. 
     2. Message Traffic 
     In order to keep the protocol simple, only one control message and one response message are preferably used during normal operation mode. This “MEGA” control message/response message includes all the possible basic control/response messages. Additional control messages are needed for such functions such as software updates and technical information such as IDU, ODU serial numbers and software versions. If new control or response messages are needed in the future, they can be easily implemented by following the data structure represented above. Table 1 lists preferable control/response messages and their unique identifiers. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Control and Response Messages 
               
            
           
           
               
               
               
               
            
               
                   
                 Message 
                 Direction 
                 Identifier 
               
               
                   
                   
               
               
                   
                 Master 
                 IDU &lt;=&gt; ODU 
                 0x11 
               
               
                   
                 Identify 
                 IDU =&gt; ODU 
                 0x12 
               
               
                   
                 Identify 
                 IDU &lt;= ODU 
                 0x21 
               
               
                   
                 Unexpected Message 
                 IDU &lt;= ODU 
                 0x22 
               
               
                   
                 Set Mode 
                 IDU &lt;=&gt; ODU 
                 0x33 
               
               
                   
                 Test Control 
                 IDU =&gt; ODU 
                 0x34 
               
               
                   
                 Download Control 
                 IDU =&gt; ODU 
                 0x35 
               
               
                   
                 Download_Ack Control 
                 IDU &lt;= ODU 
                 0x53 
               
               
                   
                 Tune Control 
                 IDU &lt;=&gt; ODU 
                 0x66 
               
               
                   
                 Mega Control 
                 IDU =&gt; ODU 
                 0x96 
               
               
                   
                 Mega Response 
                 IDU &lt;= ODU 
                 0x69 
               
               
                   
                 Mega VVA 
                 IDU =&gt; ODU 
                 0x97 
               
               
                   
                 Mega Det 
                 IDU &lt;= ODU 
                 0x79 
               
               
                   
                 Cal Table Segment 
                 IDU =&gt; ODU 
                 0x44 
               
               
                   
                 Code Segment 
                 IDU =&gt; ODU 
                 0x55 
               
               
                   
                 Segment Received 
                 IDU &lt;= ODU 
                 0x45 
               
               
                   
                   
               
            
           
         
       
     
     In the following tables that describe message data fields, it is assumed that the messages start with a preamble and identifier, and end with an 8 bit CRC that is aligned to be in it&#39;s own byte. 
     a. Master Control Message 
     The Master control message is used in the initialization state for an IDU to identify itself as a Master IDU. During a master IDU configuration, the CPE preferably monitors the IDU/ODU link for a few milliseconds to determine if there is already a master present. The ODU then responds with the same message. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Master Control Message 
               
            
           
           
               
               
               
            
               
                 Field 
                 Bits 
                 Description 
               
               
                   
               
               
                 IDU Identifier 
                 32 
                 32 bit identifier of the IDU. Used to distinguish 
               
               
                   
                   
                 between multiple CPEs in an MDU. 
               
               
                   
               
            
           
         
       
     
     b. Identify Control Message 
     The Identify control messages has no fields, but is simply the preamble, identifier (0×12), and CRC sent from the IDU to the ODU. 
     c. Identity ResDonse Message 
     The Identity response message is the ODU&#39;s response to the Identify control message from the IDU. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Identity Response Message 
               
            
           
           
               
               
               
            
               
                 Field 
                 Bits 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 ODU —   
                 8 
                 0x00 =&gt; ODU has not been calibrated 
               
               
                 Calibrated 
                   
                 0x01 =&gt; ODU has been calibrated 
               
               
                 MaxTxPow 
                 8 
                 Transmission Power level desired minus 45. 
               
               
                   
                   
                 Accordingly, values from 0 to 255 represent 
               
               
                   
                   
                 desired values from 45 to 300. 
               
               
                 MinRxPow 
                 8 
                 Minimum Receive Power 
               
               
                 FrequencyBand 
                 8 
                 ODU Frequency Band in GHz 
               
               
                   
                   
                 24 =&gt; ODU uses 24 GHz Band 
               
               
                   
                   
                 25 =&gt; ODU uses 25 GHz Band 
               
               
                   
                   
                 28 =&gt; ODU uses 28 GHz Band 
               
               
                   
                   
                 31 =&gt; ODU uses 31 GHz Band 
               
               
                 SW Version 
                 32 
                 ASCII Software version number. 
               
               
                   
                   
                 Example: SW version 135 ‘0’, ‘1’, ‘3’, ‘5’ 
               
               
                 Flags 
                 8 
                 ODU Flags 
               
            
           
           
               
               
               
            
               
                   
                  bit 0 (MSB) 
                 Reserved 
               
               
                   
                  bit 1 
                 Reserved 
               
               
                   
                  bit 2 
                 Reserved 
               
               
                   
                  bit 3 
                 Reserved 
               
               
                   
                  bit 4 
                 Reserved 
               
               
                   
                  bit 5 
                 Reserved 
               
               
                   
                  bit 6 
                 Tx MMW detector output is valid 
               
            
           
           
               
               
               
            
               
                   
                   0 
                 No MMW detector 
               
               
                   
                   1 
                 MMW detector valid 
               
            
           
           
               
               
               
            
               
                   
                  bit 7 (LSB) 
                 AFC Polarity 
               
            
           
           
               
               
               
            
               
                   
                   0 
                 AFC Normal 
               
               
                   
                   1 
                 AFC polarity inverted 
               
               
                   
                   
               
            
           
         
       
     
     d. Unexpected Response Message 
     The Unexpected Response Message is the response to a valid control message which is not expected in the current mode. For example, receipt by the ODU of a Mega Control message during initialization, as could happen after a spontaneous reset of the ODU. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Unexpected Response Message 
               
            
           
           
               
               
               
            
               
                 Field 
                 Bits 
                 Description 
               
               
                   
               
               
                 Current Mode 
                 8 
                 0x00 = Initialization State 
               
               
                   
                   
                 0x01 = Normal Mode 
               
               
                   
                   
                 0x02 = Loopback Mode (obsolete) 
               
               
                   
                   
                 0x03 = Code Download Mode (obsolete) 
               
               
                   
                   
                 0x04 = Cal Table Download (obsolete) 
               
               
                   
                   
                 0x05 = Normal 24 GHz (obsolete) 
               
               
                   
                   
                 0x06 = ODU Bootstrap Mode 
               
               
                   
                   
                 0x07 = ODU available for normal operation 
               
               
                   
               
            
           
         
       
     
     e. Set Mode Control Message 
     The Set Mode control message is used by the IDU to change the state of the ODU. The ODU responds by repeating the Set Mode message to the IDU as a response message. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Set Mode Control Message 
               
            
           
           
               
               
               
            
               
                 Field 
                 Bits 
                 Description 
               
               
                   
               
               
                 New Mode 
                 8 
                 0x00 = Initialization State 
               
               
                   
                   
                 0x01 = Normal Mode 
               
               
                   
                   
                 0x02 = Loopback Mode 
               
               
                   
                   
                 0x05 = Normal 24 GHz (obsolete) 
               
               
                   
                   
                 0x06 = ODU Bootstrap Mode 
               
               
                   
                   
                 0x07 = ODU available for normal operation 
               
               
                   
               
            
           
         
       
     
     f. Test Control Message 
     The Test Control Message is used by the IDU to instruct the ODU to perform some kind of test operation as described below. The general form of the message is shown in the table below: 
                     TABLE 6                  Test Control Message                         Field   Bits   Description               Operation   8   The particular test being commanded       Data Byte 1   8   Data pertinent to that command if necessary       Data Byte 2                    
i. Test Control Message—FSK Tone Generation
 
     To conduct testing of the ODU it is useful to have the ODU generate either of the continuous tones corresponding to a 0 or a 1. The format is shown in the table below: 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Test Control Message - FSK tone generation 
               
            
           
           
               
               
               
               
            
               
                   
                 Field 
                 Bits 
                 Description 
               
               
                   
                   
               
               
                   
                 Operation 
                 8 
                 0x1 =&gt; Transmit FSK Tone 
               
               
                   
                 FSK_Tone 
                 8 
                 0x0 =&gt; transmit the ‘0’ tone 
               
               
                   
                   
                   
                 0x1 =&gt; transmit the ‘1’ tone 
               
               
                   
                 Transmit Time 
                 8 
                 Number of seconds to generate the tone 
               
               
                   
                   
                   
                 (0 . . . 255) 
               
               
                   
                   
               
            
           
         
       
     
     The FSK tone generation operation causes the ODU to generate either a continuous ‘0’ tone, or ‘1’ tone for the specified number of seconds. 
     While the tone is being generated the ODU will not respond to control messages since the link is half duplex. When the specified time has elapsed the ODU will resume listening for control messages from the IDU. 
     ii. Test Control Message—Request Break Status (FSK Cut-off Frequency) 
     This command determines from the ODU if a “break” character has been detected on the ODU/IDU message interface. The table below shows the format of this message. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Test Control Message - Request Break Status 
               
            
           
           
               
               
               
               
            
               
                   
                 Field 
                 Bits 
                 Description 
               
               
                   
                   
               
               
                   
                 Operation 
                 8 
                 0x2 =&gt; Request Break Status 
               
               
                   
                 Reserved 
                 8 
               
               
                   
                 Reserved 
                 8 
               
               
                   
                   
               
            
           
         
       
     
     In virtually all cases, the ODU responds with a Test_Command:Break_Status_Report, indicating if it has detected a “break” character since the last request or not. The message is used to test the ODU FSK receive modem function. A “break” character being detected is the result of the ODU detecting a continuous series of zeros. This can only happen by an external source injecting a pure low tone into the ODU. 
     The cut-off frequency of ODU receive circuitry can be determined on a test stand by injecting different frequency tones onto the response data interface and repeatedly requesting the ODU detected a “break” character. Eventually a frequency will be reached where the ODU does not detect a break—hence the cut-off can be determined. 
     iii. Test Control Message—Break Status Report 
     This message is the response to the Request Break Status and is shown in the table below: 
                     TABLE 9                  Test Control Message - Break Status Report                         Field   Bits   Description               Operation   8   0x3 =&gt; Break Status Report       Break_Status   8   0x0 =&gt; No break detected since previous request               0x1 =&gt; Break detected since previous request       Reserved   8                    
iv. Test Control Message—Tune test
 
     This message contains the response to the Test Control—Tune Test. It&#39;s layout is show below: 
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Test Control Message - Tune test 
               
            
           
           
               
               
               
            
               
                 Field 
                 Bits 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Operation 
                 8 
                 Base Frequency in GHz (10-60) 
               
               
                   
                   
                 27 =&gt; works for 28 GHz ODUs 
               
               
                 Data Byte 
                 16 
                 Frequency offset from base in 100 kHz increments i.e. 
               
               
                   
                   
                 1 =&gt; &lt;Base Frequency&gt; .0001 GHz 
               
               
                   
                   
                 1000 =&gt; &lt;Base Frequency&gt; .1000 GHz 
               
               
                   
                   
                 10000 =&gt; &lt;Base Frequency+1&gt; .0000 GHz 
               
               
                   
               
            
           
         
       
     
     The Tune test message attempts to tune the ODU to the specified frequency without regard to the valid frequency range for the ODU, therefore tuning outside of the normal range is permitted. The step resolution of the command is 100 kHz. No range checking is performed so specifying values too far beyond the valid range may have unpredictable results. The ODU may not be able to tune to the precise frequency specified, when this occurs it tunes to the nearest frequency it can. 
     g. Tune Control Message 
     The Tune Control instructs the ODU to tune to a given frequency specified in units of 100 kHz. The ODU responds after performing the tuning operation by echoing the same Tune Control message back to the IDU and reporting the frequency to which the ODU is now tuned. If the specified frequency is outside the valid frequency range for the ODU, the ODU does not retune. Therefore specifying a frequency of 0 is a mechanism for querying the ODU as to the frequency to which it is tuned without changing the frequency. 
     The frequencies of 1 and 4294967295 (or FFFFFFFF hex) are reserved as special query-mode frequencies. If the ODU is told to tune to 0.0001 GHz, the ODU will not retune but will respond with the minimum available frequency. For instance, a 28 GHz ODU would return the number 272000. If the ODU is told to tune to 429496.7295 GHz, it will not retune but will respond with the maximum available frequency, or 286500 for a 28 GHz ODU. 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Tune Control Message 
               
            
           
           
               
               
               
               
            
               
                   
                 Field 
                 Bits 
                 Description 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Frequency 
                 32 
                 The frequency in units of 100 kHz 
               
               
                   
                   
                   
                 Eg. 28 GHz =&gt; 280,000 
               
               
                   
                   
                   
                 28.001 GHz =&gt; 280,001 
               
               
                   
                   
               
            
           
         
       
     
     The ODU may not be able to tune to the precise in-band frequency specified, when this occurs it truncates the value to the nearest possible frequency and tunes to that frequency instead.
         24 GHz ODUs can be commanded to tune from 24.0000 GHz to 25.5000 GHz.   25 GHz ODUs can be commanded to tune from 25.0000 GHz to 25.5000 GHz.   28 GHz ODUs can be commanded to tune from 27.2000 GHz to 28.6500 GHz.   31 GHz ODUs can be commanded to tune from 29.8000 GHz to 31.5000 GHz.       

     h. Mega Control Message 
     The Mega Control is used by the IDU to instruct the ODU to change the values of Attenuators or the Frequency. 
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Mega Control 
               
            
           
           
               
               
               
            
               
                 Field 
                 Bits 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Change Flags 
                 5 
                 1 bit per field that may change 
               
               
                   
                   
                 b10000 =&gt; Enable/Disable PA changed 
               
               
                   
                   
                 b01000 =&gt; Rx Power Level changed 
               
               
                   
                   
                 b00100 =&gt; Tx IF1 VVA changed 
               
               
                   
                   
                 b00010 =&gt; Tx Power Level changed 
               
               
                   
                   
                 OR values to get combinations of 
               
               
                   
                   
                 fields changed For Example, 
               
               
                   
                   
                 b01010 =&gt; Rx Power Level and Tx Power 
               
               
                   
                   
                 Level both changed. 
               
               
                 Enable/ 
                 1 
                 1 = use 40 MHz switching signal 
               
               
                 Disable PA 
                   
                 0 = disable PA 
               
               
                 Rx Power Level 
                 10 
                 Per RX VVA Table in section 1.2 of [1] 
               
               
                 Tx IF1 VVA 
                 8 
                 0 to −30.5 dB in 0.2 dB steps 
               
               
                 Tx Power Level 
                 9 
                 0 to −60 dB in 0.2 dB steps 
               
               
                 LinkAcquired 
                 1 
                 1 =&gt; Link is acquired. 
               
               
                   
                   
                 The ODU reports the value of the RxIF1 the 
               
               
                   
                   
                 detector 10 used immediately following the 
               
               
                   
                   
                 start of the frame (corresponding to the arrival 
               
               
                   
                   
                 of the second byte of the Mega Control). The 
               
               
                   
                   
                 RSL output behaves normally, but with a 
               
               
                   
                   
                 minimum level of 0.5 volts 
               
               
                   
                   
                 0 =&gt; Link is not acquired. The ODU reports 
               
               
                   
                   
                 the value of the RxIF1 detector from the time 
               
               
                   
                   
                 period between any previous command and the 
               
               
                   
                   
                 current Mega Control. The RSL output is 
               
               
                   
                   
                 always 0 volts. 
               
               
                 Padding 
                 14 
                 For byte alignment of CRC 
               
               
                   
               
            
           
         
       
     
     i. Mega Response Message 
     The Mega Response message is the response to the Mega Control message. 
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 Mega Response Message 
               
            
           
           
               
               
               
            
               
                 Field 
                 Bits 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Rx IF1 Detector 
                 8 
                 Temperature compensated and converted to 
               
               
                   
                   
                 the range −11 to 12 dBm, expressed in 0.2 
               
               
                   
                   
                 dBm steps. 
               
               
                 Rx IF2 Detector or 
                 8 
                 Temperature compensated and converted to 
               
               
                 Output Power 
                   
                 the range 5 dBm to 22 dBm, expressed in 0.2 
               
               
                 Detector 
                   
                 dBm steps. 
               
               
                 Tx IF1 Detector 
                 8 
                 Temperature compensated and converted to 
               
               
                   
                   
                 the range −26 to −4 dBm, expressed in 0.2 
               
               
                   
                   
                 dBm steps. 
               
               
                 Tx IF2 Detector 
                 8 
                 Temperature compensated and converted to 
               
               
                   
                   
                 the range −5 to −39 dBm, expressed in 0.2 
               
               
                   
                   
                 dBm steps. 
               
               
                 Temperature 
                 8 
                 −35 to 85° C. 
               
               
                 Pad 
                 5 
                 For byte alignment of CRC. Can add 
               
               
                   
                   
                 additional alarms here in the future. 
               
               
                 Ref PLL Lock 
                 1 
                 Alarm: 1 = fail 
               
               
                 Syn Lock 
                 1 
                 Alarm: 1 = fail 
               
               
                 2.7 GHz Detect 
                 1 
                 Alarm: 1 = fail 
               
               
                   
               
            
           
         
       
     
     j. Mega VVA Control Message 
     The Mega VVA Control is used by the IDU to instruct the ODU to change the values of Attenuators and the Frequency. Unlike the Mega Control message, it contains the explicit VVA settings. 
     
       
         
           
               
             
               
                 TABLE 14 
               
             
            
               
                   
               
               
                 Mega VVA Control Message 
               
            
           
           
               
               
               
            
               
                 Field 
                 Bits 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Rx IF1 VVA 
                 8 
                 Explicit value to set Rx IF1 VVA 
               
               
                 Rx IF2 VVA 
                 8 
                 Explicit value to set Rx IF2 VVA 
               
               
                 Rx MM VVA 
                 8 
                 Explicit value to set Rx MM VVA 
               
               
                 Tx IF1 VVA 
                 8 
                 Explicit value to set Tx IF1 VVA 
               
               
                 Tx IF2 VVA 
                 8 
                 Explicit value to set Tx IF2 VVA 
               
               
                 Tx MM VVA 
                 8 
                 Explicit value to set Tx MM VVA 
               
               
                 Padding 
                 10 
               
               
                 Change Flags 
                 6 
                 1 bit per field that may change 
               
               
                   
                   
                 b100000 =&gt; Rx IF1 VVA changed 
               
               
                   
                   
                 b010000 =&gt; Rx IF2 VVA changed 
               
               
                   
                   
                 b001000 =&gt; Rx MM VVA changed 
               
               
                   
                   
                 b000100 =&gt; Tx IF1 VVA changed 
               
               
                   
                   
                 b000010 =&gt; Tx IF2 VVA changed 
               
               
                   
                   
                 b000001 =&gt; Tx MM VVA changed 
               
               
                   
                   
                 OR values to get combinations of fields changed 
               
               
                   
                   
                 For example, b010100 =&gt; Rx IF2 VVA and Tx 
               
               
                   
                   
                 IF1 VVA values have both changed 
               
               
                   
               
            
           
         
       
     
     k. Mega Det Message 
     The Mega Det message is the response to the Mega VVA control. 
     
       
         
           
               
             
               
                 TABLE 15 
               
             
            
               
                   
               
               
                 Mega Det Message 
               
            
           
           
               
               
               
               
            
               
                   
                 Field 
                 Bits 
                 Description 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Rx IF1 Detector 
                 8 
                 Actual detector value. 
               
               
                   
                 Rx IF2 Detector 
                 8 
                 Actual detector value. 
               
               
                   
                 Tx IF1 Detector 
                 8 
                 Actual detector value. 
               
               
                   
                 Tx IF2 Detector 
                 8 
                 Actual detector value. 
               
               
                   
                 Temperature 
                 8 
                 Actual detector value. 
               
               
                   
                 Pad 
                 5 
                 For byte alignment of CRC. 
               
               
                   
                 Ref PLL Lock 
                 1 
                 Alarm: 1 = fail 
               
               
                   
                 Syn Lock 
                 1 
                 Alarm: 1 = fail 
               
               
                   
                 2.7 GHz Detect 
                 1 
                 Alarm: 1 = fail 
               
               
                   
                   
               
            
           
         
       
     
     l. Download Control Message 
     The Download Control message is used by the IDU to instruct the ODU to perform some kind of test operation. The general form of the message is shown in the table below: 
                     TABLE 16                  Download Control Message                         Field   Bits   Description                                 Operation   8   The particular test being commanded       Data Bytes   88   Data pertinent to that operation if necessary                    
i. Download Control Message—Update Block
 
     The ODU maintains a buffer in its internal RAM for accumulating data to be written to flash memory. This is called the ROW buffer, and is preferably 64 bytes in size. It is sub-divided into 8 blocks, each of which is 8 bytes. A block is updated using this Update Block operation. The format of the operation is defined in the table below: 
                     TABLE 17                  Download Control Message - Update Block                         Field   Bits   Description                                 Operation   8   2 =&gt; Update Block       &lt;reserved&gt;   8   0       Offset   8   Offset from the start of the ROW buffer where the               bytes being sent are to be placed, usually: 0, 8, 16,               24, 32, 40, 48, 56       N_Bytes   8   Number of bytes to be copied to the ROW buffer               (0 . . . 8)       Data_Bytes   64   Up to 8 bytes of data to be written sequentially to               the ROW buffer                    
ii. Download Control Message—Write Row
 
     This message initiates an attempt to write the current content of the ROW buffer in the ODU to flash memory. The format of the operation is defined in the table below: 
                     TABLE 18                  Download Control Message - Write Row                         Field   Bits   Description                                 Operation   8   3 =&gt; Write_Row       Flash_Address   16   Address in flash memory where the ROW buffer               should be written. Must be a multiple of 64, and               not be within the area reserved for the               Boot_Module.       &lt;reserved&gt;   72                    
iii. Download Control Message—Peek Memory
 
     This message reads up to 4 bytes from the specified address in memory. The format of the operation is defined in the table below: 
                     TABLE 19                  Download Control Message - Peek Memory                         Field   Bits   Description                                 Operation   8   4 =&gt; Peek Memory       Address   16   Address in memory from which the bytes are to be               retrieved.       N_Bytes   8   Number of bytes (up to 4 to be retrieved).       &lt;reserved&gt;   64                    
iv. Download Control Message—Software Reset
 
     This message instructs the ODU software to reset. Control is immediately passed through to the address specified in the reset vector. This mimics behavior at power up. There can be a response to this message. If successful, the ODU will behave as is it has just powered on, if not, it will still be in the same state it was before the reset command had been issued. The format of Software 13  Reset is defined in the table below: 
                     TABLE 20                  Download Control Message - Get_Partition_Info                                 Field   Bits   Description                                             Operation   8   8 =&gt; Software Reset           &lt;reserved&gt;   88                        
v. Download Control Message—Get Partition Info
 
     This message requests partition information on the specified partition number. The ODU responds with a download 13  ack:partition_info_report message containing the partition information requested. The format of get 13  partition_info is defined in the table below: 
                     TABLE 21                  Download Control Message - Get_Partition_Info                         Field   Bits   Description                                 Operation   8   9 =&gt; Get_Partition_Info       Partition_number   8   The partition number being requested 0 . . . 255       &lt;reserved&gt;   80                    
vi. Download Control Message—Request CRC
 
     This message requests the ODU to calculate a 16 bit CRC be calculated over the specified range. The IDU uses the request to verify a partition after it has been downloaded. The ODU responds with a download 13  ack:CRC 13  Report message containing the calculated CRC. The format of packet is defined in the table below: 
                     TABLE 22                  Download Control Message - Request_CRC                         Field   Bits   Description                                 Operation   8   12 =&gt; Request_CRC       Start Address   16   The address to start the 16-bit CRC calculation       Length   16   The number of bytes to run the check       &lt;reserved&gt;   56                    
vii. Download Control Message—Get Row Buffer Address
 
     This message requests the address of the ODU ROW buffer. It is used by external software manipulating configuration and hardware parameters to retrieve the values of individual parameters from the ROW buffer using the Download:Peek 13  Memory command as its most primitive operation. The ODU responds with a Download_Ack: Row_Buffer Address packet. The format of Get_Row_Buffer_Address is defined in the table below: 
     
       
         
           
               
             
               
                 TABLE 23 
               
             
            
               
                   
               
               
                 Download Control Message - Get_Row_Buffer_Address 
               
            
           
           
               
               
               
               
            
               
                   
                 Field 
                 Bits 
                 Description 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Operation 
                 8 
                 21 =&gt; Get_Row_Buffer_Address 
               
               
                   
                 &lt;reserved&gt; 
                 88 
               
               
                   
                   
               
            
           
         
       
     
     m. Download Ack Control Message 
     This message contains the response from the ODU to download commands that generate a response. 
     i. Download Ack Control Message—Memory Report 
     This message is the response to a download:peek_memory command. It returns up to 4 bytes from the specified address in memory. The format of the operation is defined in the table below: 
                     TABLE 24                  Download_Ack Control Message - Memory_Report                         Field   Bits   Description                                 Operation   8   5 =&gt; Memory Report       Address   16   Address in memory where these bytes originate       N_Bytes   8   Number of bytes present       Data bytes   32       &lt;reserved&gt;   16                    
ii. Download Ack Control Message—Partition Info Report
 
     This message is the response to a download_get_partition 13  info command. It returns partition information for the partition number requested. The format of partition 13  info 13  report is defined in the table below: 
                     TABLE 25                  Download_Ack Control Message -       Partition_Info_Report                         Field   Bits   Description                                 Operation   8   10 =&gt; Partition_Info_Report       Partition_number   8   The partition number being described 0 . . . 255       Base_Address   16   The starting address of the partition 0 - 0xffff       Type   8   ‘O’ =&gt; Operational Software               ‘C’ =&gt; Calibration tables               ‘H’ =&gt; Hardware parameters               ‘B’ =&gt; Bootstrap module       Is_Valid   8   0 =&gt; the partition is invalid           16   1 =&gt; the partition is valid       Write_Count   16   Number of times this partition has been written       Version_Number   8   A version number indicating the revision of the               partition content 0 . . . 255                    
iii. Download Ack Control Message—Row Written
 
     This message describes the ODU result of a Download: Write 13  Row processed by the ODU. Normally a write will succeed and the status below will return 0. If one or more blocks were not updated, or the ODU was unable to write all the blocks to flash memory correctly, it will respond with a status of 1, and the “Bit 13  Vector” field will indicate which blocks the ODU has. A ‘1’ in a bit position indicates the block is present, a ‘0’ indicates its absence. The remedy to this condition is to resend the missing blocks, and the attempt the write again. The format is shown below: 
                     TABLE 26                  Download_Ack Control Message - Row_Written                         Field   Bits   Description                                 Operation   8   11 =&gt; Row_Written       Flash_Address   16   the address in flash memory where the write was               attempted.       Status   8   0 = row was written successfully to flash memory               1 = some blocks in the ROW have not been               updated, “Bit_Vector” indicates which blocks               are missing               2 = the write to flash was not successful, the               Bit_Vector field indicates which blocks were not               written. This can happen as the write count of the               ODU flash memory approaches its 100 cycle               limit. In an operational system this is indicates               that ODU behavior may become erratic.               3 = =&gt; the flash address is not a legitimate               address for the ODU               4 = flash contents at “flash_address” already               contained the ROW buffer content, no write was               performed       Bit_Vector   8   If status = 1 or 4, bit vector contains a 0 in each               bit position where a block is missing. Block offset               0 is the LSB, block offset 56 is the MSB       &lt;reserved&gt;   16                    
iv. Download Ack Control Message—CRC Report
 
     This message reports a 16 bit CRC calculated by the ODU in response to a previous Download:Request 13  CRC command. The format of packet is defined in the table below. The ODU includes the starting address and the length to identify the CRC being reported. 
                     TABLE 27                  Download_Ack Control Message - CRC_Report                         Field   Bits   Description                                 Operation   8   13 =&gt; CRC_Report       Start_Address   16   The address to start the 16-bit CRC calculation       Length   16   The number of bytes to run the check       Reported_Value   16   The calculated CRC value       &lt;reserved&gt;   16                    
v. Download Ack Control Message—Block Updated
 
     This message is in response to a previous Download:Update 13  Block. The format of the packet is defined in the table below. There are no conditions when an update should not be successful. The only possibility for not receiving a Download 13  Ack:Block_Updated message is that the ODU did not receive the Download:Update_Block request. The remedy is to re-send the packet. 
                     TABLE 28                  Download_Ack Control Message - Block_Updated                         Field   Bits   Description                                 Operation   8   14 =&gt; Block_Updated       &lt;reserved&gt;   8   0       Block_Offset   8   Offset from the start of the ROW buffer where the               bytes being sent are to be placed, may be one of:               0, 8, 16, 24, 32, 40, 48, 56       N_Bytes   8   Number of bytes to be copied to the ROW buffer               (0 . . . 7)       Status   8   0 = Successfully copied, non-zero an error               occurred       &lt;reserved&gt;   32                    
vi. Download Ack Control Message—Row Buffer Address
 
     This message is the response to the Download:Get_Row_Buffer_Address command. It provides the absolute address of the Row buffer, which is where Calibration and Hardware parameters are maintained at runtime. This enables suitable external software to make temporary changes to the operating values of these parameters and observer their effect on the system, without writing them to flash memory (an operation most often performed when an ODU is being calibrated). The format of the packet is defined in the table below: 
                     TABLE 29                  Download_Ack Control Message -       Row_Buffer_Address                                 Field   Bits   Description                                             Operation   8   22 =&gt; Row_Buffer_Address           Address   16   The Address of the Row buffer           &lt;reserved&gt;   72                        
3. Error Detection
 
     When the ODU detects an error in the control message, it normally discards the message. Since all control messages that are sent by the IDU are responded to by the ODU, the IDU detects the failure to receive a response message via a timeout. 
     The IDU, when acting as initiator, sends control messages and then waits for message responses. If the IDU doesn&#39;t receive any response messages after, for example, two (2) milliseconds, it resends the control message again. If it doesn&#39;t receive any response messages after sending several control messages in a row, the IDU takes appropriate corrective action. 
     4. Control of ODU Components 
     Table 30 summarizes the components that may be controlled in the ODU by the IDU, their characteristics and the number of bits required to set/read their values. 
     
       
         
           
               
             
               
                 TABLE 30 
               
             
            
               
                   
               
               
                 ODU Elements Controllable from IDU 
               
            
           
           
               
               
               
            
               
                 Component 
                 Description 
                 Dynamic Range/Bits 
               
               
                   
               
               
                 VVA for 
                 140 MHz VVA used to 
                 0 to −30.5 dB. Controlled via 
               
               
                 Cable Comp 
                 compensate for cable loss 
                 8 bit word. VVA is controlled 
               
               
                 (210) 
                 from the IDU. 
                 in 0.5 dB steps achievable 
               
               
                   
                   
                 through most of the range of 
               
               
                   
                   
                 the VVA. 
               
               
                 Tx IF2 VVA 
                 S-band VVA used to adjust 
                 0 to −30 dB. Controlled via 
               
               
                 (234) 
                 transmit power of the S 
                 7 bit word in 0.5 dB steps. 
               
               
                   
                 band frequency. 
                 Used in conjunction with Tx 
               
               
                   
                   
                 RF VVA (264). 
               
               
                 Tx RF VVA 
                 MM wave band VVA used 
                 0 to −30 dB. Controlled via 
               
               
                 (264) 
                 to adjust transmit power. 
                 8 bit word in 0.5 dB steps 
               
               
                   
                   
                 achievable. Used in conjunc- 
               
               
                   
                   
                 tion with Tx IF2 VVA (234). 
               
               
                 Rx IF1 VVA 
                 140 MHz VVA used to 
                 0 to −32 dB. Controlled via 
               
               
                 (300) 
                 adjust receive attenuation 
                 8 bit word. Used in con- 
               
               
                   
                 prior to transmission along 
                 junction with Rx IF2 VVA 
               
               
                   
                 the cable. Used for 
                 (292) and Rx RF VVA per 
               
               
                   
                 Automatic Gain Control 
                 (280). 
               
               
                   
                 (AGC). 
               
               
                 Rx IF2 VVA 
                 S-band VVA used to adjust 
                 −1 to −27 dB. Controlled via 
               
               
                 (292) 
                 receive attenuation. Used 
                 8 bit word. Used in conjunc- 
               
               
                   
                 for such purposes as AGC. 
                 tion with Rx IF1 VVA (300) 
               
               
                   
                   
                 and Rx RF VVA (280). 
               
               
                 Rx RF VVA 
                 MM wave band VVA used 
                 0 to −24 dB. Controlled via 8 
               
               
                 (280) 
                 to adjust receive attenua- 
                 bit word. Used in conjunction 
               
               
                   
                 tion, for such purposes as 
                 with Rx IF1 VVA (300) and 
               
               
                   
                 AGC. 
                 Rx IF2 VVA (292). 
               
               
                 Syn Freq 
                 Synthesizer frequency to be 
                 34 possibilities space 25 MHz 
               
               
                 (220) 
                 used. 
                 apart. 
               
               
                 Syn Ref 
                 Starting point for frequency 
                 0 to 23.75 MHz in 1.25 MHz 
               
               
                 (308) 
                 mapping. This parameter is 
                 steps. 
               
               
                   
                 dependant upon the Syn 
               
               
                   
                 Ref Parameter. 
               
               
                 Enable/ 
                 Enables or disables the 
                 Enabled means use 40 MHz 
               
               
                 Disable PA 
                 Power Amplifier, allowing 
                 switching signal. Disable 
               
               
                 (268) 
                 transmission to the ODU 
                 means no transmission regard- 
               
               
                   
                 with out transmission over 
                 less of state of 40 MHz 
               
               
                   
                 the air. (Disable causes the 
                 switching signal. 
               
               
                   
                 40 MHz switching signal to 
               
               
                   
                 be ignored.) Typically used 
               
               
                   
                 only in test modes. May be 
               
               
                   
                 necessary during cable loss 
               
               
                   
                 compensation. 
               
               
                   
               
            
           
         
       
     
     Table 31 summarizes the response messages that can be sent from the ODU to the IDU. The bits used to control/read items are not necessarily what will appear in the user data making up the protocol. 
     
       
         
           
               
             
               
                 TABLE 31 
               
             
            
               
                   
               
               
                 Response Messages 
               
            
           
           
               
               
               
            
               
                 Response 
                   
                 Dynamic 
               
               
                 Data 
                 Description 
                 Range/Bits 
               
               
                   
               
               
                 Rx IF1 
                 140 MHz detector located at the output of 
                 Approximately 
               
               
                 Detector 
                 ODU to cable. This detector can be used 
                 −11 to 12 dB. 
               
               
                 (304) 
                 to bring this to 4 dBm. 
                 Expressed as 8 
               
               
                   
                   
                 bit word. 
               
               
                 Rx IF2 
                 S band detector. Can be used to measure 
               
               
                 Detector 
                 Tx power on the Rx path during trans- 
               
               
                 (294) or Out- 
                 mission. Can also be used to determine 
               
               
                 put Power 
                 transmitter saturation points. Optionally 
               
               
                 Detector (not 
                 the absolute output power at the PA in 
               
               
                 shown) 
                 dBm. 
               
               
                 Tx IF1 
                 140 MHz detector at cable input to the 
                 Approximately 
               
               
                 Detector 
                 ODU. Used for cable compensation. 
                 −4 to −26 dB. 
               
               
                 (212) 
                 Expressed as 8 
               
               
                 Tx IF2 
                 S band detector. Can be used to determine 
                 bit word. 
               
               
                 Detector 
                 transmitter saturation points. 
               
               
                 (230) 
               
               
                 Temperature 
                 Temperature detector. 
                 −35 to 85° C. 
               
               
                 Ref PLL 
                 Lock detect signal from the 100 MHz 
                 High = fail. 
               
               
                 Lock 
                 reference clock. the synthesizer lock time 
               
               
                   
                 is 200 msec. 
               
               
                 Syn Lock 
                 Lock detect signal from the channel 
                 High = fail. 
               
               
                   
                 selection synthesizer. The synthesizer lock 
               
               
                   
                 time is 1.5 msec. 
               
               
                 2.7 GHz 
                 Detects failure of the 2.7 GHz local 
                 High = fail. 
               
               
                 Detect 
                 multiplier. 
               
               
                   
               
            
           
         
       
     
     C. Initialization of the System 
     1. Overview 
     Referring now to  FIG. 6 , a software state diagram  500  showing the possible modes in which the ODU may operate is illustrated. The initialization process  500  of the Micro Controller in the ODU includes:
         Initialization of all I/Os (clock generator, SCI, SPI, A/D etc.)   Reset the local oscillator to inhibit any transmission before being tuned   Determine if the memory partitions for operational software, calibration tables and configuration parameters are valid   Determine if memory partitions contents are mutually compatible   Establish communications with a master IDU.       

     On a power-on, or when a watchdog timer expires, the ODU resets and enters a preliminary checkout phase. This phase is explained more completely with reference to FIG.  7 . Briefly, all peripherals are reset to a benign state and the ODU places itself in Mode  6  ( 504 ). The ODU then automatically attempts to transition itself to Mode  7  ( 506 ). This transition entails performing a CRC test on all memory partitions in the ODU to verify that the flash memory is correct and consistent. If it is correct, the initialization procedure in each partition is invoked. This verifies that the content of the memory partition is compatible with the content of any other memory partitions on which it depends. If all memory partitions report compatibility the boot code transition is successful and the system moves to Mode  7 , otherwise it remains in Mode  6 . 
     If the process  501  moves to Mode  7 , a set 13  mode command is given by the micro controller and the system initiates normal operation by transitioning the ODU to Mode  0  ( 512 ). From Initialization Mode  6 , the only valid transition to Mode  0  is through Mode  7 , which requires all the previous system tests be successful. 
     Note that in the State Diagram in  FIG. 6 , download commands are valid in both Mode  6  and Mode  7  so on power-up, new software can always be downloaded to the ODU even if all memory partitions are invalid. 
     While in Mode  0 , the process  501  can also transition to a loopback Mode  2  ( 516 ) and to a normal operational Mode  1  ( 520 ). These other Modes are discussed more completely in reference to  FIGS. 9 and 10  below. 
     2. Preliminary Checkout (Mode  6 ) 
       FIG. 7  illustrates the flow of the first interactions between the IDU  122  and ODU  108 . A preliminary checkout process  600  begins with the ODU  108  resetting its peripherals, checking its flash memory, and checking its memory partition compatibility at a state  602 . 
     Once this is complete, the IDU  122  sends a SET 13  MODE ( 7 ) control message that attempts to transition the ODU from the checkout mode  6  into Mode  7 . The ODU responds with a response message indicating its current mode. A determination of the ODU&#39;s current mode is then made by the IDU  122  at a decision state  610 . If a determination is made that the ODU is still in Mode  6 , and did not transition to Mode  7 , the checkout process  600  moves to a state  614  to begin downloading new software to the ODU in an attempt to help the ODU transition to Mode  7 . 
     However, if a determination was made at the decision state  610  that the ODU was not still in Mode  6 , the IDU then issues a SET 13  MODE ( 0 ) control message to move the ODU into its operational mode ( 0 ). The checkout process  600  then terminates at an end state  616 . 
     When the IDU issues the SET 13  MODE ( 0 ) command, it learns several pieces of information from the response message. If there&#39;s no response it indicates thateither the connection to the ODU is faulty or that the ODU is broken in some way. If there is a response, then the state returned in the response message indicates which of the three possible states the ODU is now in. From the response message the IDU can determine if it must perform some remedial action on the ODU (see the download procedure described later), or if it can begin operation. 
     3. Handshaking Process 
     After the initialization processes of  FIGS. 7  are completed (identical for Base Station and CPE), a handshake process  800  begins, as shown in FIG.  8 . In the handshake process  800 , the Micro Controller in the ODU waits for the first message from the IDU. Because of the complexity of the software in the IDU (whether CPE or base station), the ODU normally finishes initialization before the IDU. 
     The IDU then issues a SET 13  MODE ( 1 ) control message to transition the ODU into Normal Operational Mode  1 . This transition results in the ODU performing the following functions:
         Control the following components:
           1. Set Receive (Rx) VVAs attenuation to minimum.   2. Set Transmit (Tx) VVAs attenuation to maximum.   3. Set reference frequency (LMX2301) to 100 MHz.   4. Disable the Power Amplifier   
               

     Measure test points. 
     Once complete, the process  800  then loops continuously, receiving response messages from the ODU and performing the actions dictated by the control messages from the IDU. The most typical action in this process in the ODU is:
         The ODU receives a MEGA command from the IDU with instructions to alter the values of the VVAs or Frequencies in the Frequency synthesizers and:
           1. Reads the temperature (State  804 ).   2. Adjusts the settings received in the MEGA control message for temperature, if necessary and applies the new values (State  808 ).   3. Calculates and applies the RSL voltage setting (State  810 ).   4. Reads detector values and adjusts values for temperature via the calibration tables (State  812 ).   5. Reads the 3 lock/detect indicators.   6. Builds and transmits a mega response message.
 
4. Reading Detector Values
   
               

     As shown in  FIG. 9 , a process  900  of reading ODU detector values is illustrated. The process  900  begins when the ODU measures the output from the RxIF1 detector  304  ( FIG. 4 ) at a precise instant (state  904 ) in order to send this value in the Mega Response Message. Every time the ODU receives the byte immediately following the preamble byte, it reads the detector  304  at the state  904  and saves the result. Then it holds the detector in reset for a 10 microseconds at a state  908 . The process  900  then de-asserts the reset signal at a state  914  and waits 10 more microseconds at a state  920 . The process  900  then samples the RxIF1 detector  304  again at a state  926  and saves the result. The VVAs and Power Amplifier are then set at a state  930  as commanded by the MEGA control message. 
     A determination is then made at a decision state  934  whether or not the LinkAcquired bit was set in the Mega Control message. If the LinkAcquired bit was set, the ODU reports the measurement taken immediately after the detector reset at a state  938 . However, if the LinkAcquired bit was zero, the ODU reports the measurement taken immediately before the detector reset at a state  940 . 
     The process  900  then waits two milliseconds at a state  942  and proceeds to sample any remaining detectors in the ODU at a state  944 . The Mega response message is then sent from the ODU to the IDU. 
     5. Loopback Mode 
     In the loopback mode process  1000  illustrated in  FIG. 10 , the ODU  108  simply repeats back to the IDU  122  whatever message it has received. It leaves the loopback mode when it receives the set mode control message to transition to a different mode. No other work is performed during loopback mode—no reading of control messages or setting of control values. The control messages sent to the ODU by the IDU during loopback mode preferably have a preamble, a CRC, and at most 14 additional bytes. Other than “set 13  mode” message data which must follow the format described above, the messages sent during loopback mode may be composed of any byte pattern. 
     6. Customer Premises Equipment 
     Although the previous discussion has focused on IDUs and ODUs that are installed as part of a base station, these devices are similarly installed within each customer site for receiving and transmitting wireless data. As illustrated  FIGS. 11 and 12  are block diagrams of the customer premises equipment (CPE)  110  shown in FIG.  1 . As described above, the subscribers of the wireless communication system contemplated for use with the present invention may be either residential or business customers.  FIG. 12  is a block diagram of a residential CPE  110 .  FIG. 11  is a block diagram of a business CPE  110 . 
     As shown in  FIG. 12 , the residential CPE  110  preferably includes an ODU  1140 , IDU  1141  and a residential wireless gateway apparatus  1142 . The residential gateway  1142  is preferably installed on a side of the residence  1144 . The residential gateway  1142  preferably includes a network interface unit (NIU)  1146  and a service gateway unit  1148 . The NIU  1146  performs the functions necessary to allow the residential user to communicate with the wireless communication system, such as performing low frequency RF communication, modem and ATM functions. 
     The NIU  1146  performs the necessary communication interface functions including airlink and protocol interface functions to allow the residential user access to the network. The service gateway unit  1148  allows the residential user to gain access to the services provided over the communications system. 
     For example, as shown in  FIG. 12 , the service gateway unit  1148  preferably includes an MPEG decoder, NTSC video interface, telephone interface and 10-baseT data interface. The residential gateway  1142  interfaces to the various service access points within the residence  1144 . The residential gateway  1142  contains the necessary hardware and software for interfacing to the radio communications airlink and for driving various services into the residence  1144 . In addition, by interfacing with the telephone wiring  1147  within the residence  1144 , the residential gateway  1142  is capable of providing a variety of telephone services to the residence  1144 . 
     Similarly, by interfacing with copper or co-axial wiring  1149  within the residence  1144 , the residential gateway  1142  is capable of providing 10-baseT and other data services to equipment  1150  (such as a personal computer depicted in  FIG. 12 ) within the residence  1144 . Finally, the residential gateway  1142  can also provide broadcast video and data-centric television services to a plurality of television systems  1152  by interfacing with standard cable television co-axial cabling  1154  in the residence  1144 . The residential gateway  1142  is designed in a modular fashion to service multiple data, telephone, and video lines. Thus, a single residential gateway  1142  is sufficiently flexible to accommodate the communication needs of any residential customer. 
       FIG. 11  is a block diagram of the business CPE  110 ′ of FIG.  1 . The business CPE  110 ′ is designed to provision and provide services to a small business customer site  1112 . As shown in  FIG. 11 , the business CPE  110 ′ includes an ODU  108 ′ and IDU  122 ′. The CPE  110 ′ also includes a business wireless gateway apparatus  142 ′. The ODU  108 ′ is affixed to a business site building  144 ′ while the business gateway  142 ′ is installed in a wiring closet within the business site building  144 ′. 
     The communication interfaces of the business gateway  142 ′ are similar to those of the residential gateway  1142  (FIG.  12 ). However, the service interfaces of the business gateway  142 ′ differ from those of the residential gateway  1142 . The business gateway  142 ′ includes interfaces capable of driving voice and data services typically used by small business customers. These include integrated services digital network (ISDN), local area network (LAN), PBX switching and other standard voice and data services. 
     As shown in  FIG. 11 , a “two-box” solution is presently contemplated for implementing the business gateway  142 ′. An “off-the-shelf” multi-service concentrator  1156  can be used to provide the business user services and to convert the outgoing data into a single transport stream. The business gateway  142 ′ also includes a wireless gateway apparatus  1158  which contains the necessary hardware and software for interfacing to the IDU and for driving various services into the business site building  144 ′. 
     Alternatively, the wireless functionality provided by the business gateway  142 ′ can be integrated into the multi-service concentrator  1156  in order to reduce costs and provide a more integrated business gateway solution. Different types of multi-service concentrators  1156  can be used depending upon the size and needs of the business customer. Thus, a network provider can deploy a cost effective solution with sufficient capabilities to meet the business customer&#39;s needs. 
     Various types of services can be provided to the business customer using the CPE  110 ′ of FIG.  11 . For example, by providing standard telephone company interfaces to the business customer, the business CPE  110 ′ gives the customer access to telephone services yet only consumes airlink resources when the telephone services are active. Network providers therefore achieve significant improvements in airlink usage efficiency yet are not required to modify or overhaul conventional interfaces with the business customer&#39;s equipment (e.g., no changes need to be made to PBX equipment). In addition, the business gateway  142 ′ can support HSSI router and 10-BaseT data interfaces to a corporate LAN thereby providing convenient Internet and wide area network (VVAN) connectivity for the business customer. The business gateway  142 ′ will also enable a network provider to provision “frame-relay” data services at the customer&#39;s site. The business gateway  142 ′ can support symmetrical interface speeds of 10 Mbps and higher. 
     Finally, the CPE  110 ′ facilitates the transmission of various types of video services to the business user. The video services primarily includes distance learning and video conferencing. However, in addition, the business CPE  110 ′ can include ISDN BRI interfaces capable of supporting conventional video conferencing equipment. Using these interfaces, the business users will have the option of either viewing or hosting distance learning sessions at the business site building  144 ′. 
     D. Measuring Detectors in the ODU 
       FIG. 13  illustrates a base station  1410  transmitting user data  1440  to an outdoor unit  1422  of customer premises equipment  1420 . As shown, the ODU  1422  is linked to an IDU  1424 . The ODU  1422  might also receive transmissions  1450  from a nearby ODU  1432  of CPE  1430 . As can be imagined, the transmissions  1450  directed towards the base station  1410  would interfere with power measurements taken by the CPE  1420  in a TDD system. This is due to the fact that in TDD systems the CPEs and base stations transmit using the same frequency. 
     Due to the proximity of the CPE  1432  to the CPE  1420 , the ODU  1422  might receive transmissions from the ODU  1432 . This would especially be possible if the signal strength of the transmission  1450  from ODU  1432  is stronger than the signal strength of the transmission  1440  from the base station  1410 . For this reason, it is advantageous for the CPE  1420  to only measure power detectors in the receive pathway during a time when only the base station  1410  is transmitting user data. 
     The communication system uses the known reception time of the Mega Control message to address this problem. Each Mega Control message is timed so that the first byte of the message is received by the ODU at a time that is set aside in each TDD frame for base station downlink transmissions. Thus, when the ODU receives the first byte of the Mega Control message, it can measure the receive path power detectors and be assured that the only transmissions at that time are from a base station. 
     The system is designed such that under normal operation, a Mega Control Message (see Table 12) is sent along a broadband transmission cable (not shown) from the IDU  1424  to the ODU  1422  via FSK modulated signals. The Mega Control Message, as described above, is used by the IDU to control sub-components, such as VVA&#39;s, in the ODU. For this reason, the Mega Control Message is sent repeatedly, very frequently, and for the duration of the normal operation. The ODU responds to the Mega Control Message with the Mega Response Message (see Table  13 ) that includes settings of the detectors in the ODU. 
       FIG. 14  illustrates the timing used by the IDU to send Mega Control Messages to the ODU. As shown, a TDD time frame  1500  is divided into a downlink time  1502  and an uplink time  1504 . The downlink time and uplink time include a plurality of time slots for transmitting or receiving user data from the CPE to the base station. It should be realized that an adaptive time division duplex system dynamically adjusts the number of time slots allocated to uplink and downlink times to provide the most efficient transfer of user data from the CPEs to the base station. Accordingly, when the base station has a tremendous amount of user data to transmit, the number of time slots in the frame  1500  dedicated to downlinking data from the base station to the CPEs will increase. 
     As shown in the  FIG. 14 , at the end of the uplink time  1504  in the frame  1500  is a transition gap of 6.25 microseconds that provides a means for the system to change from an uplink mode to a dedicated downlink time mode. Of course, embodiments of the invention are not limited to systems that provide such a gap. For example, similar systems having no transition gap, or transition gaps of varying times are well within the scope of the invention. 
     At the front of each frame, and following the previous frame&#39;s transition gap, is a dedicated downlink time. In this embodiment, the minimum downlink time lasts 16.25 microseconds. Of course, the invention is not limited to any particular minimum downlink time. The minimum downlink time is used by the system to allow the base station to transmits internal command data to each of the CPEs. This command data, for example, can include the uplink/dowlink times for the next time frame. As discussed herein, the downlink time is only required to be long enough for the detectors to make a measurement from the detectors. Downlink times that are greater or lesser in duration are thus within the scope of the invention. 
     Thus, during this time only the base station is communicating with each CPE. The CPEs do not transmit during the minimum downlink time since they are receiving their instructions for the next frame. Because each time frame is of a fixed duration in the TDD system, and the minimum downlink time occurs at a fixed place (e.g.: at the end) of the frame in this embodiment, the IDU  1424  in the CPE  1420  knows that power measurements taken by the receive detectors during the minimum downlink time are guaranteed to only measure transmissions from the base station  1410 . 
     In one embodiment of the system the micro controller  400  ( FIG. 4 ) continuously polls the Universal Asynchronous Receiver/Transmitter (UART)  166  associated with the FSK modem  165  to determine when a complete byte of data has been received by the ODU. As discussed previously, under normal operating conditions the only control message being sent from the IDU to the ODU is the Mega Control Message. Accordingly, the ODU can be set to begin taking receive power measurements after the first byte of the message is received in the UART  166  from the IDU. By knowing the amount of time it takes the ODU to receive one byte of a message from the IDU, the IDU can be programmed to always begin transmitting the Mega Control Message so that the ODU will receive the first byte of the message at the beginning of each 16.25 microsecond downlink time within every TDD frame. 
     In one embodiment, the FSK modem in the IDU transmits data to the ODU at 115.2 kbps. With this link speed it takes 8.68 microseconds to transmit a single bit of data from the IDU to the ODU. Assuming eight data bits, one start bit and one stop bit, one byte of data can be transmitted from the IDU to the ODU in 86.8 microseconds. If a parity bit is included, the byte of data is transmitted in 8.68×11=95.48 microseconds. 
     For this reason, if the IDU is programmed to begin sending the Mega Control Message 86.8 microseconds before the beginning of the 16.25 microsecond downlink time, the first complete byte of the message will be received at the start of the downlink lime. If the micro controller  400  in the ODU is polling a UART or other buffer in the ODU to determine when the first byte of the message has been received from the IDU, it will be determine that the first byte has been received in the UART  166  at the start of the minimum downlink time. 
     As  FIG. 14  illustrates, once the first byte has been received, the ODU resets the receive detectors. There is then a minimum time provided to allow the detectors to take a proper reading. In one embodiment, the minimum time is approximately 10 microseconds, however other detetctors with other minimum read times are within the scope of the invention, Note that this entire time is within the minimum downlink time, and thus is guaranteed to be measuring transmissions from the base station. Because it only takes 10 microseconds to read the power detectors, there is ample time to reset and read the detector within the 16.25 microsecond downlink time shown in this embodiment. After the detectors are read, the data from them is transmitted to the IDU in a Mega Response message. 
       FIG. 15  illustrates one embodiment of a process  1600  for sending the Mega Control message from the IDU to the ODU to initiate the process of reading receive detectors in a wireless communication system. In one embodiment, this process is stored in a memory, such as the FPGA  136  (FIG.  3 ). The process  1600  begins at start state  1602  and then moves to a state  1608  wherein the proper start time for sending a Mega Control message from the IDU to the ODU is determined. This determination is made to calculate the amount of time it takes to send one byte of data from the IDU to the ODU. Once this figure has been determined, the IDU will send the mega control message so that the last bit of the first byte arrives at the ODU at the start of the minimum downlink command time. Examples of these calculations are described above. 
     Once a determination is made of the proper time to begin sending a Mega control message, the process  1600  moves to a state  1610  wherein software instructions within the IDU begin to build a Mega Control message. Once the mega control message has been built, it is handed to the FPGA  136 . The FPGA  136  is aware of the frame timing and is programmed with an offset time, relative to the start of the frame, at which time the control message should be sent. The process  1600  then moves to a decision state  1612  to determine whether it is the proper time to begin sending the message. If a determination is made that it is the proper time to begin transmitting bits of the message from the IDU to the ODU, the process  1600  moves to a state  1616  wherein the bits comprising the message are handed to the hardware of the IDU in order to be transmitted to the ODU. 
     Once the IDU begins streaming bits from the mega control message to the ODU, the process  1600  moves to a state  1620  wherein a mega response message is received from the ODU. As can be appreciated, the mega response message includes the values that are read from the detectors in the ODU. After the mega response message has been received, the process  1600  moves to a state  1622  wherein the detector measurements stored within the mega response message are read by instructions stored within the IDU. As can be appreciated, these detector measurements are then used to determine whether adjustments need to be made to subcomponents of the ODU in order to more specifically receive, or transmit, user data with the highest efficiency. The process  1600  then terminates at an end state  1624 . 
     If a determination had been made at the decision state  1612  that it was not the proper time to send a mega control message from the IDU to the ODU, the process  1600  moves to a wait state  1628  before returning to the decision state  1612 . Thus, this loop continues until the IDU determines it is the proper time to begin transmitting bits to the ODU. 
     Referring now to  FIG. 16 , a process  1700  running within the FLASH memory  161  of the ODU is exemplified. The process  1700  begins at a start state  1702  and then moves to a state  1704  wherein the transmitted bits corresponding to the mega control message start to be received from the IDU. A determination is then made at a decision state  1708  whether an entire byte of data has been received by the ODU. This determination is preferably made by instructing the microcontroller  400  to continually pole the UART  166  that is buffering the streaming bits from the IDU. Once the microcontroller poles the buffer and determines that an entire byte has been received, the microcontroller moves to a state  1710  wherein the received detectors are reset. The process  1700  then waits 10 microseconds at a state  1714  before taking a reading of the receive detectors in the ODU at a state  1717 . 
     Once the detector readings have been taken at the state  1717 , the process  1700  moves to a state  1720  wherein the mega response message is built by instructions within the FLASH memory of ODU. These instructions then transmit the mega response message to the IDU at a state  1724 . The process  1700  then terminates at an end state  1730 . 
     Of course it should be realized that embodiments of the invention are not limited to any particular TDD frame timing or number of time slots within each frame. For example, while each TDD time frame might be 1 millisecond in duration, the TDD time frame might alternatively be 0.5, 2, 5, 7, 10, 12, 15 or more milliseconds of duration. Moreover, each frame might be divided into any number of time slots. For example, each frame might be divided into 500 to 10000 time slots. 
     Moreover, the location and duration of the minimum downlink time is not limited to the embodiment described in FIG.  14 . For example, the downlink time does not need to be located at the beginning of each frame. In one alternate embodiment, the minimum downlink time is located at the end or middle of each frame. The only requirement being that the minimum downlink time be fixed in relation to each frame so that the mega control message can be timed so that the first byte of the message is received by the ODU at the beginning of the minimum downlink time slot. 
     E. Other Embodiments 
       FIG. 17  illustrates an alternate embodiment of a TDD time frame used to transmit user data and to send Mega Control Messages to the ODU. As shown, a TDD transmission frame  1800  includes several uplink time slots Ta, Ta′, Ta″ and Ta′″ for transmitting user data from the CPE to the base station. In addition, the transmission frame  1800  includes several dowlink time slots Tb, Tb′ and Tb″ for transmitting user data from the base station to a plurality of CPEs. Accordingly, the invention is not limited to TDD time frames wherein a first set of time slots in the frame are dedicated to downlinking and a second set of time slots are dedicated to uplinking user data. Other embodiments of mechanisms for transmitting user data in a TDD manner, as illustrated in  FIG. 17  are also contemplated. 
     Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiment, but only by the scope of the appended claims.