WO2002047248A1

WO2002047248A1 - Very low noise local oscillator for use in wireless communication transceiver

Info

Publication number: WO2002047248A1
Application number: PCT/US2001/050947
Authority: WO
Inventors: Moti Kabelly; Yossi Keren
Original assignee: Ensemble Communications, Inc.
Priority date: 2000-11-03
Filing date: 2001-10-26
Publication date: 2002-06-13
Also published as: AU2002241754A1

Abstract

Disclosed is a wireless communication system including base stations and customer sites. Each of the base stations and customer sites has an indoor unit and an outdoor unit. The indoor unit has a modem for modulating/demodulating data transmitted between the base stations and customer sites. The outdoor unit is controlled based on control message from the indoor unit. The outdoor unit includes a local oscillator, which generates two frequency signals: a fixed frequency signal and a variable frequency signal. Both of the signals are phase locked to the data transmitted between the base stations and customer sites. The fixed frequency signal is used in composing the variable frequency signal. The outdoor unit receives a signal loading the data from the indoor unit and up-converts the frequency of the data-loading signal using the fixed and variable frequency signals before wireless transmission of the signal. Also, the outdoor unit down-converts the frequency of the data-loading signal which is wirelessly received using the fixed and variable frequency signals before transmission to the indoor unit.

Description

VERY LOW NOISE LOCAL OSCILLATOR FOR USE IN WIRELESS COMMUNICATION TRANSCEIVER

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a wireless communication transceiver. More particularly, the present invention pertains to low noise frequency synthesis for use in a wireless communication transceiver. Description of the 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. For example, prior art wireless communication systems have typically used a Code Division

Multiple Access (CDMA), Time Division Mutiple Access (TDMA) or Frequency Division Multiple Access (FDMA) type system to facilitate the exchange of information between two users. These access schemes are well known in the art.

In a wireless communication system, regardless of the access scheme, the data is loaded on a carrier frequency before transmission and unloaded after receipt in either of the base station and subscriber unit. Thus, a transceiver in both of the base station and subscriber unit requires a carrier frequency source. For high performance of a wireless communication system, a low noise and stable carrier frequency signal needs to be synthesized.

SUMMARY OF THE INVENTION

One aspect of the present invention provides an electronic circuit for synthesizing a frequency signal. The electronic circuits comprises a first oscillator configured to generate a first fixed frequency signal; a multiplier configured to multiply the frequency of the first fixed frequency signal to generate a second fixed frequency signal; a second oscillator configured to generate a first variable frequency signal; and a mixer configured to mix the second fixed frequency signal and the first variable frequency signal to generate a second variable frequency signal.

Another aspect of the present invention provides a method of generating an electromagnetic frequency. The method comprises providing a reference signal; generating a first fixed frequency signal phase-locked to the reference signal; multiplying the frequency of the first fixed frequency signal to generate a second fixed frequency signal; generating a first variable frequency signal phase-locked to the reference signal; and generating a second variable frequency signal by either combining the second fixed frequency signal with the first variable frequency signal or subtracting the first variable frequency signal from the second fixed frequency signal. Still another aspect of the present invention provides an outdoor unit for a wireless communication system, wherein the wireless communication system comprises a plurality of stations, each of which comprises the outdoor unit and an indoor unit comprising a modem. The outdoor unit comprises a first frequency generator for generating a fixed frequency signal; a second frequency generator for generating a variable frequency signal; a frequency converter configured to convert a frequency of a data signal using the fixed and variable frequency signals. The data signal comprises at least one of a signal received from the modem of the indoor unit for frequency conversion and a signal to be transmitted to the modem of the indoor unit after frequency conversion.

Still another aspect of the present invention provides a method of shifting a frequency of a data signal for wireless communication among a plurality of stations, each of which comprises an indoor unit comprising a modem and the outdoor unit comprising an antenna. The data signal comprises at least one of a signal generated by the modem of the indoor unit and a signal wirelessly received by the antenna of the outdoor unit and a signal. The method comprises receiving the data signal at a frequency; generating a fixed frequency signal; generating a variable frequency signal using the fixed frequency signal; and shifting the frequency of the data signal using the fixed and variable frequency signals.

A still further aspect of the present invention provides a wireless communication system operating among a plurality of stations. The system comprises an outdoor unit comprising a local oscillator and a frequency converter; an indoor unit comprising a modem for modulating/demodulating a data signal transmitted between the stations, wherein the indoor unit is further configured to generate a reference signal; and a broadband cable disposed between the indoor unit and the outdoor unit, wherein the cable is configured to carry the data transmitted between the stations. The local oscillator of the outdoor unit comprises a first phase locked loop, a frequency multiplier, a second phase locked loop, and a mixer. The first phase locked loop comprises a fixed frequency oscillator and a phase detector, wherein the fixed frequency oscillator is configured to generate a first fixed frequency signal and wherein the phase detector is configured to detect phases difference between the first fixed frequency signal and the reference signal from the indoor unit and to control the fixed frequency oscillator to minimize the phase difference. The frequency multiplier is configured to multiply the frequency of the first fixed frequency signal and to filter the multiplied signal with a predetermined bandwidth to generate a second fixed frequency signal. The second phase locked loop comprises a variable frequency oscillator and a phase detector, wherein the variable frequency oscillator is configured to generate a first variable frequency signal and wherein the phase detector is configured to detect phases difference between the first variable frequency signal and the first fixed frequency signal from first phase locked loop and to control the variable frequency oscillator to minimize the phase difference. The mixer is configured to combine the second fixed frequency signal and the first variable frequency signal so as to generate a second variable frequency signal. The frequency converter of the outdoor unit is configured to receive the data signal and to convert the frequency of the data signal to another frequency for wireless transmission between stations or for transmission to the indoor unit.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of an exemplary broadband wireless communication system for use with the present invention.

Figure 2 is a block diagram of cell site used in the wireless communication system of Figure 1. Figure 3 is a block diagram of an embodiment of an Indoor Unit module from the cell site illustrated in Figure 2.

Figure 4 is a block diagram of an embodiment of an Outdoor Unit module from the cell site illustrated in Figure 2.

Figure 5 is a block diagram of an embodiment of the micro controller circuitry within the Outdoor unit. Figure 6 is a block diagram of a commercial customer site that includes customer premises equipment. Figure 7 is a block diagram of a residential customer site that includes customer premises equipment. Figure 8 illustrates a block diagram of an embodiment of the local oscillator of the outdoor unit shown in Figure 3.

Figure 9 illustrates a block diagram of an embodiment of the 2JGHz frequency multiplier. Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 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 preferred 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 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. Preferably, 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'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.

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'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 Figure 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 base station outdoor units 108. 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'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 will preferably 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 the base station ODU 108. As discussed above, the customer IDU (not shown) is located within the site 112 and provides a link between the customer's computer systems to the ODU.

As shown in Figure 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 ODU 108 and customer ODU 110 within a cell 102 is advantageously bi-directional in nature. Information flows in both directions between the base station ODU 106 and the plurality of Customer ODU 110. The base station ODU 106 preferably broadcasts single simultaneous high bit-rate channels. Each channel preferably 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 Figure 1 also preferably 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. Patent 6,016,211 issued on January 18, 2000, the disclosure of which is hereby incorporated by reference in its entirety.

1. Cell Site Figure 2 illustrates a block diagram of the cell site 104 of Figure 1 used in the wireless communication system 100. As described above, the cell site 104 preferably comprises the base station 106 and at least one base station ODU 108. As shown in Figure 2, the base station also preferably includes at least one base station indoor unit 122, back-haul interface equipment 124, an Asynchronous Transfer Mode (ATM) switch 126, a video server control computer 128 and direct broadcast satellite (DBS) receiver equipment 130. The base station can also alternatively include a video server (not shown in Figure 2). The indoor unit 122 sends control messages and user data to the ODU. The indoor unit 122 also receives response messages and user data from the base station outdoor unit 108.

The back-haul interface equipment 124 allows the base station to bi-directionally communicate with the hub 114 (Figure 1 ). The ATM switch 126 functions at the core of the base station 106 to interconnect the various services and systems at appropriate service and bandwidth levels. 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 a 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 preferably contains high-frequency radio electronics (not shown) and antenna elements for transmitting user data to the customer sites.

2. Indoor Unit

Referring to Figure 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 preferred processor is the Motorola

MPC8260 PowerQUICC 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 IDU 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 between transmit and receive modes, as will be discussed below with reference to Figure 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'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

Now referring to Figure 4, 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 (shown in Figure 3), a set of switches 160a,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 Figure 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. 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 160a. 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 wave 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 then finally through the switch 160b and out an antenna 270. The up-converted signal is then passed to another detector 269 to measure the transmit power at the 28 GHz mm wave band before transmission. 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 a preferred 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 Figure 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 Figure 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 MC 13055 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.

4. 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 Figures 6 and 7 are block diagrams of the customer premises equipment (CPE) 110 shown in Figure 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. Figure 7 is a block diagram of a preferred residential CPE 110. Figure 6 is a block diagram of a preferred business CPE 110.

As shown in Figure 7, 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 Figure 7 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 Figure 7) 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.

Figure 6 is a block diagram of the preferred business CPE 110' of Figure 1. The preferred business CPE 110' is designed to provision and provide services to a small business customer site 1112. As shown in Figure 6, the business CPE 110' preferably includes an ODU 108' and IDU 122'. The CPE 110' also includes a business wireless gateway apparatus 142". The ODU 108' is preferably affixed to a business site building 144' while the business gateway 142' is preferably 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 (Figure 7). However, the service interfaces of the business gateway 142' differ from those of the residential gateway 1142. The business gateway 142' preferably 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 Figure 6, 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's needs.

Various types of services can be provided to the business customer using the CPE 110' of Figure 6. 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'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 (WAN) connectivity for the business customer. The business gateway 142' will also enable a network provider to provision "frame-relay" data services at the customer'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 preferably primarily include 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'.

B. Local Oscillator

Now one embodiment of the local oscillator block 219 (See Figure 4) for use in the outdoor unit 108 is further discussed in detail. As shown in Figure 8, the local oscillator block 219 includes the S band frequency generator 220 and the millimeter wave band frequency generator 255. The 20 MHz reference signal 142 from the indoor unit 122 (Figure 3) is provided to the local oscillator block 219 to synchronize the phase of the signals generated therein with the 140 MHz main signal 154 from the indoor unit 122.

The S band frequency generator 220 includes a frequency synthesizer 1302 and a frequency multiplier 1304. The frequency synthesizer 1302 is preferably composed of a phase locked loop (PLL) with a voltage controlled oscillator (VCO). Further, the voltage controlled oscillator can be a crystal oscillator. In the alternative, the frequency generator 220 is a low noise fixed S band oscillator phase locked to the 20 MHz source.

For example, the PLL of the frequency synthesizer 1302 has a phase-sensitive detector 1320, an amplification and filtering block 1322, and a voltage controlled crystal oscillator (VCXO) 1324. The phase-sensitive detector 1320 outputs a DC voltage proportional to the phase difference between its two inputs, i.e., the 20 MHz reference signal 142 and the output signal of the VCXO 1324. The amplification and filtering block 1322 amplifies the DC voltage from the phase sensitive detector 1320 with a high gain and low-pass filters it. The VCXO 1324 generates a fixed frequency sine wave signal with low phase noise. The fixed frequency generated by the frequency synthesizer 1302 can be 100 MHz, although not limited thereto. For example, the frequency which can be used in this construction includes any frequency in the UHF range of 50 to 200 MHz. The loop arrangement of the PLL minimizes any phase difference between its input and output signals and locks the phase of the 100 MHz output signal 1326 to that of the 20 MHz reference signal 142. The frequency synthesizer 1320 is advantageously constructed using a single chip integrated circuit PLL, examples of which are LMX2301 available from National Semiconductor or ADF4117 from Analog Devices and a VCXO or other controllable oscillator.

The 100 MHz signal 1326 is inputted to the frequency multiplier 1304. The frequency multiplier 1304 multiplies the frequency of the input signal to generate a fixed higher frequency signal 1328. For example, the frequency multiplier 1304 multiplies the 100 MHz signal by 27, generating a 2.7 GHz signal 1328. The multiplication factor of the frequency multiplier 1304 may be bigger or smaller than 27 depending upon the frequency requirements where the multiplied frequency is used with or without changes in the following circuits or building blocks. The frequency of the resulting multiplied frequency signal preferably ranged from about 1 GHz to about 4 GHz. An example of the construction of the frequency multiplier 1304 will be discussed in detail later with reference to Figure 9.

The 2J GHz signal 1328 is provided to the IF (intermediate frequency) UP CONVERSION block 200 (see Figure 4) for the IF up conversion operation (block 216), which combines the 2J GHz signal 1328 and the 140 MHz main signal 154 to generate the IF S band signal.

The 2J GHz signal 1328 is also provided to the IF DOWN CONVERSION block 290. The S band signal from the RF DOWN CONVERSION block 272 is converted to approximately 140 MHz by the IF down conversion (block 292).

The millimeter wave band frequency generator 255 also receives the 2J GHz signal 1328. The millimeter wave band frequency generator 225 generates a variable or tunable RF carrier signal. Preferably, the millimeter wave band frequency generator synthesizes a fixed frequency signal and a variable frequency signal, and then combines the fixed and variable frequency signals to form a variable RF carrier signal. The 2J GHz signal 1328 from the S band frequency generator 220 is preferably used in the synthesis of the fixed frequency signal. Preferably, a frequency multiplier 1306 multiplies the 2J GHz signal 1328, for example by 4, to generate the fixed frequency (10.8 GHz) signal 1330. The multiplicand (4) of this frequency multiplier 1306 may vary depending upon the frequency of the input signal and the subsequent processing of the output frequency. The frequency multiplier 1306 multiplies the frequency for example by 6 in other bands. On the other hand, the 100 MHz signal 1326 generated by the S band frequency generator 220 is preferably used in the synthesis of the variable frequency signal. A frequency divider 1308 divides the 100 MHz frequency by 4, generating a 25 MHz signal, which is supplied to a variable frequency synthesizer 1310. Alternatively, the 100 MHz frequency may be divided by another divisor, bigger or smaller than 4. The exemplary chips for the frequency divider 1308 include UPB1509 by Cal Eastern Labs (CEL). Further alternatively, the 100 MHz signal 1326 can be directly provided to the synthesizer 1310 without the frequency division.

The resulting 25 MHz signal is inputted to the variable frequency synthesizer 1310, which synthesizes a frequency tunable signal 1338. The variable frequency synthesizer 1310 is for example composed of a phase locked loop (PLL), which includes a phase-sensitive detector 1332, an amplification and filtering block 1334, and a voltage controlled oscillator (VCO) 1336. The output signal from the oscillator 1336, and the 25 MHz signal from the frequency divider 1308 are inputted to the phase-sensitive detector 1332, which outputs a DC voltage proportional to the phase difference between the two inputted signals. The DC voltage is amplified and filtered by the amplification and filtering block 1334, and locks the variable frequency signal 1338 of the oscillator 1336 to the phase of the 25 MHz reference signal. The frequency synthesizer 1310 is advantageously a single chip integrated circuit PLL, for example LMX2326 National Semiconductor and a and a VCXO or other controllable oscillator. Alternatively, the variable frequency synthesizer 1310 can be constructed with ADF4112 by Analog Devices.

The frequency of the output signal 1338 of the variable frequency synthesizer 1310 ranges from about 1 GHz to about 3 GHz. Preferably, the frequency is from about 1.5 GHz to about 2.5 GHz , more preferably from about 1.67 GHz to about 2.095 GHz. The output variable frequency signal 1338 is locked to the phase of the 25 MHz signal and is further synchronized with the 2J GHz signal 1328 and the 10.8 GHz signal 1330 because these (25 MHz, 2.7 GHz and 10.8 GHz) signals are results of multiplication or division of the 100 MHz signal 1326 with a low phase noise.

A mixer 1312 combines the 10.8 GHz signal 1330 and the variable frequency signal 1338 to generate another variable frequency signal 1340. A band-pass filter 1314 filters the mixed variable frequency signal 1340 with a frequency band from about 11.8 GHz to about 13.8 GHz. Preferably, the frequency band for filtering is from about 12.3 GHz to about 13.3 GHz, more preferably from about 12.47 GHz to about 12.895 GHz. The mixer 1312 and bandpass filter 1314 can be implemented by any comparable circuits or chips.

The band-passed variable frequency signal is then inputted to a frequency multiplier 1316, which raises the frequency of the variable signal. Preferably, the frequency multiplier 1316 which doubles the frequency and generates a radio frequency (RF) signal. Preferably, the RF signal is further filtered by a band-pass filter 1318 to remove unwanted frequency components. The frequency of the resulting RF carrier signal 1342 ranges from about 23.6 GHz to about 27.6 GHz, preferably, from about 24.6 GHz to about 26.6 GHz, more preferably from about 24.94 GHz to about 25.79 GHz.

Although not illustrated, the local oscillator block 219 may include various amplifiers and filters for signal amplification and filtering where appropriate. The RF carrier signal 1342 is provided to the RF UP CONVERSION block 250 as shown in Figure 4. The RF carrier signal 1342 is combined with the S band frequency carrying the message transferred from the IF UP CONVERSION block 200, generating a millimeter wave band frequency signal. The RF signal 1342 is also used for the RF down conversion operation 285 in the RF DOWN CONVERSION block 272 (see Figure 4), in which the RF carrier frequency component is stripped from a millimeter wave band signal received by the antenna 270. Now referring to Figure 9, the construction of the frequency multiplier 1304 within the S band frequency generator 220 is discussed in detail. The frequency multiplier 1304 raises the frequency of the input signal 1326 from the crystal oscillator (VCXO) 1324 to the 2J GHz signal 1328. The multiplier is advantageously composed of 3 consecutive multiplication units 1402, 1404 and 1406. Each multiplication unit multiplies its input frequency by 3 to achieve the overall multiplication of 27. The 100 MHz signal 1326 from the frequency synthesizer 1302 is provided to the first multiplication unit

1402, in which a first multiplier 1408 multiplies the inputted 100 MHz signal 1326 by 3. Examples for the first multiplier 1408 includes an unbiased transistor NE85633 available from Cal Eastern Labs (CEL). The first multiplier 1408 generates various harmonic components of the input frequency, including a strong third harmonic component. A 300 MHz band-pass filter (BPF) 1410 filters the resulting signal to remove the unwanted harmonics and passes the third harmonic component, a 300 MHz signal. The 300 MHz BPF 1410 is advantageously implemented by an LC filter.

Then, a surface acoustic wave (SAW) filter 1412 further filters the signal to lower the noise floor of the resulting signal with a narrow bandwidth of from about 50 to 300 KHz, preferably about +/-140 KHz. The SAW filter

1412 can be implemented using TFD300 available from Telefilter Vectron. The noise filtering with this narrow SAW filter 1412 enables the multiplication unit 1402 to achieve a low system noise floor even after total frequency multiplication of over 200 times within this frequency multiplier 1304 and in the following millimeter wave band frequency generator 255. In addition, this SAW filter 1412 further attenuates remaining harmonics of the signal.

The 300 MHz signal 1413 obtained in the first multiplication unit 1402 is provided to the second multiplication unit 1404 for further multiplication and processing. An amplifier 1414 pre-amplifies the 300 MHz signal 1413. The amplifier 1414 is advantageously a tuned transistor amplifier such as HBFP420 from Agilent. The amplified signal is multiplied by 3 at a multiplier 1416. An exemplary multiplier includes HBFP420. The multiplied signal is then provided to a 900 MHz band-pass filter (BPF) 1418, which filters the multiplied signals to remove unwanted harmonic components generated in the previous multiplication. The 900 MHz BPF 1418 can be implemented using a ceramic filter, for example TDFS8A-904A available from TOKO. Although not illustrated, the 900 MHz BPF 1418 can include two ceramic filters with an interposed LC filter. Any common LC filter and the TDFS8A-904A ceramic filter can be used to construct the 900 MHz BPF 1418. In the third multiplication unit 1406, the resulting 900 MHz signal 1419 is also pre-amplified at an amplifier 1420, which is advantageously a tuned HBFP420 transistor amplifier. The amplified signal is multiplied by 3 at a multiplier 1422, which is advantageously a transistor multiplier. The transistor multiplier 1422 preferably has a collector thermistor for temperature compensating the output power. The collector bias is filtered to generate a DC voltage that is relative to the signal level. This level is sensed by a comparator to detect failure of the multiplier chain or the VCXO 1324. Exemplary transistor multiplier includes HBFP420 from Agilent. The multiplied signal is filtered at a 2.7 GHz BPF 1424, examples of which include a PCB printed filter. The filtered signal is then amplified at an amplifier 1426, which is for example amplifier ERA2 available from Mini Circuits. Preferably, the resulting 2.7 GHz signal has phase noise of about -103 dbc/Hz at 1 KHz; about -117 dbc/Hz at 10 KHz; about -125 dbc/Hz at 100 KHz; about -142 dbc/Hz at 1 MHz; about -146 dbc/Hz at 10 MHz.

In this embodiment of the local oscillator block 219, the fixed frequency (100 MHz) of the VCXO signal 1326 is increased to the fixed 10.8 GHz signal 1330 by way of multiplication. On the other hand, the variable frequency signal 1338, which is phase locked to the VCXO signal 1326, is synthesized independently of the frequency multiplication. Then, the fixed 10.8 GHz signal 1330 and the variable signal 1326 are combined. The fixedness of the frequency up to 10.8 GHz enables narrow band filtering in the frequency multipliers 1304 and 1306, especially before up/down conversions and amplifications, thereby keeping the noise level low. The local oscillator block 219 does not require frequency tuning in the course of raising the frequency. Rather, a tunable frequency is simply mixed with a multiplied fixed frequency with low phase noise. All of these attributes contribute to creating a reliable local oscillator at a low cost with very good repeatability in production. Moreover, this local oscillator demonstrates very good phase transient performance under voltage pushing spikes and load pulling, which makes this design a very good solution for burst/TDD systems. C. Other Embodiments

Although this invention has been described in terms of a certain preferred embodiment, other embodiments will become apparent to those of ordinary skill in the art, in view of the disclosure herein. Accordingly, the present invention is not limited by the specific illustrated embodiment, but , but only by the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An electronic circuit for synthesizing a frequency signal, comprising: a first oscillator configured to generate a first fixed frequency signal; a multiplier configured to multiply the frequency of the first fixed frequency signal to generate a second fixed frequency signal; a second oscillator configured to generate a first variable frequency signal; and a mixer configured to mix the second fixed frequency signal and the first variable frequency signal to generate a second variable frequency signal.

2. The electronic circuit as defined in Claim 1, wherein the first fixed frequency signal has a frequency in a range from about 50 MHz to about 200 MHz.

3. The electronic circuit as defined in Claim 1, wherein the second fixed frequency signal has a frequency in a range from about 1 GHz to about 4 GHz.

4. The electronic circuit as defined in Claim 1, wherein the first variable frequency signal has a frequency in a range from about 1 GHz to about 3 GHz.

5. The electronic circuit as defined in Claim 1, wherein the second variable frequency signal has a frequency in a range from about 11.8 GHz to about 13.8 GHz.

6. The electronic circuit as defined in Claim 1, wherein the first oscillator comprises a crystal oscillator.

7. The electronic circuit as defined in Claim 1, wherein the first oscillator comprises a phase locked loop.

8. The electronic circuit as defined in Claim 1, wherein the second oscillator comprises a non-crystal oscillator.

9. The electronic circuit as defined in Claim 1, wherein the second oscillator comprises a phase locked loop.

10. The electronic circuit as defined in Claim 1 , wherein the multiplier comprises a band-pass filter with a pass bandwidth from about 50 KHz to about 300 KHz.

11. The electronic circuit as defined in Claim 10, wherein the band-pass filter is one selected from the group consisting of an LC filter, a surface acoustic wave (SAW) filter, and a ceramic filter.

12. The electronic circuit as defined in Claim 1, wherein the multiplier comprises at least one multiplication unit, each of which comprises a sub-multiplier and a band-pass filter, wherein the sub-multiplier is configured to multiply an input frequency, and wherein the band-pass filter is configured to filter the multiplied frequency at the sub-multiplier with a predetermined bandwidth.

13. The electronic circuit as defined in Claim 12, wherein the multiplier comprises three multiplication units connected in series.

14. The electronic circuit as defined in Claim 1, further comprising a band-pass filter configured to filter the second variable frequency signal.

15. The electronic circuit as defined in Claim 14, wherein the band-pass filter having a bandwidth from about 0.5 MHz to 2 MHz.

16. The electronic circuit as defined in Claim 1, further comprising a multiplier configured to multiply the frequency of the second variable frequency signal to generate a third variable frequency signal.

17. The electronic circuit as defined in Claim 15, wherein the third variable frequency signal is a radio frequency (RF) signal.

18. The electronic circuit as defined in Claim 17 wherein the RF signal has a frequency ranged from about 20 GHz to about 30 GHz.

19. The electronic circuit as defined in Claim 19, wherein the first oscillator comprises a phase locked loop circuit and the second oscillator comprises a phase locked loop circuit, and wherein both the first and second oscillators are adapted to use a common signal as a phase reference to which output phases thereof are locked.

20. The electronic circuit as defined in Claim 19, wherein the first oscillator comprises a phase locked loop circuit and the second oscillator comprises a phase locked loop circuit, and wherein the second oscillator is adapted to use the first fixed frequency signal as a phase reference.

21. The electronic circuit as defined in Claim 20, further comprising a divider interveningly connected to the first and second oscillators, the divider being configured to divide the frequency of the first frequency signal to generate a third fixed frequency signal, the second oscillator is adapted to use the third fixed frequency signal as the phase reference.

22. A method of generating an electromagnetic frequency, comprising providing a reference signal; generating a first fixed frequency signal phase-locked to the reference signal; multiplying the frequency of the first fixed frequency signal to generate a second fixed frequency signal- generating a first variable frequency signal phase-locked to the reference signal; and generating a second variable frequency signal by either combining the second fixed frequency signal with the first variable frequency signal or subtracting the first variable frequency signal from the second fixed frequency signal.

23. The method as defined in Claim 22, further comprising multiplying the frequency of the second variable frequency signal so as to generate a radio frequency (RF) signal.

24. The method as defined in Claim 23 wherein the RF signal has a frequency ranged from about 23.6 GHz to 27.6 GHz.

25. The method as defined in Claim 22, wherein the generating the first fixed frequency signal comprises: generating a fixed frequency signal; comparing phases of the fixed frequency signal and the reference signal; and adjusting the phase of the fixed frequency signal so as to generate the first fixed frequency signal phase-locked to the phase of the reference signal.

26. The method as defined in Claim 25, wherein the generating the first fixed frequency signal is performed by a crystal oscillator.

27. The method as defined in Claim 22, wherein the first fixed frequency signal has a frequency in a range from about 50 MHz to about 200 MHz.

28. The method as defined in Claim 22, wherein the generating the first variable frequency comprises: generating a variable frequency signal- comparing phases of the variable frequency signal and the reference signal; and adjusting the phase of the variable frequency signal so as to generate the first variable frequency signal phase-locked to the phase of the reference signal.

29. The method as defined in Claim 22, wherein the generating the first variable frequency comprises: generating a variable frequency signal; comparing phases of the variable frequency signal and the first fixed frequency signal; and adjusting the phase of the variable frequency signal so as to generate the first variable frequency signal phase-locked to the phase of the first fixed frequency signal.

30. The method as defined in Claim 22, wherein the first variable frequency signal has a frequency in a range from about 1 GHz to about 3 GHz.

31. The method as defined in Claim 29, wherein the frequency of the first fixed frequency signal is reduced before the inputting thereof to the phase locked loop.

32. The method as defined in Claim 22, wherein the multiplying comprises: generating a plurality of harmonic components of the frequency of the first fixed frequency signal; and separating a desired harmonic component from the plurality of harmonic components.

33. The method as defined in Claim 32, wherein the separating comprises filtering the plurality of harmonic components with a band-pass filter having a bandwidth from about 50 KHz to about 300 KHz.

34. The method as defined in Claim 33, wherein the band-pass filter is one selected from the group consisting of an LC filter, a surface acoustic wave (SAW) filter, and a ceramic filter.

35. The method as defined in Claim 22, wherein the multiplying comprises at least two sequential sub- multiplying an input frequency thereof.

36. The method as defined in Claim 35, wherein each of the sub-multiplying comprises: generating a plurality of harmonic components of the input frequency thereof; and separating a desired harmonic component from the plurality of harmonic components of the input frequency.

37. The method as defined in Claim 36, wherein the separating of the sub-multiplying comprises filtering the plurality of harmonic components of the input frequency with a band-pass filter having a bandwidth ranged about +/- 140 KHz.

38. The method as defined in Claim 35, wherein the multiplying comprises three sub-multiplication in series.

39. The method as defined in Claim 22, further comprising filtering the second variable frequency signal with a bandwidth ranged from about 11.8 GHz to about 13.8 GHz.

40. An outdoor unit for a wireless communication system, wherein the wireless communication system comprises a plurality of stations, wherein each station comprises an indoor unit and the outdoor unit, and wherein the indoor unit comprises a modem, the outdoor unit comprising: a first frequency generator for generating a fixed frequency signal; a second frequency generator for generating a variable frequency signal; a frequency converter configured to convert a frequency of a data signal using the fixed and variable frequency signals; and wherein the data signal comprises at least one of a signal received from the modem of the indoor unit for frequency conversion and a signal to be transmitted to the modem of the indoor unit after frequency conversion.

41. The outdoor unit as defined in Claim 40, wherein the first frequency generator comprises a phase locked loop configured to receive a reference signal from the indoor unit and generating the fixed frequency signal.

42. The outdoor unit as defined in Claim 41, wherein the phase locked loop comprises a crystal oscillator.

43. The outdoor unit as defined in Claim 40, wherein the first frequency generator comprises: a frequency oscillator generating an intermediary fixed frequency signal; and a frequency multiplier multiplying the frequency of the intermediary fixed frequency signal so as to generate the fixed frequency signal.

44. The outdoor unit as defined in Claim 43, wherein the frequency multiplier comprises at least one multiplication unit, which comprises a sub-multiplier and a band-pass filter, wherein the sub-multiplier is configured to multiply an input frequency thereof, and wherein the band-pass filter is configured to filter the multiplied frequency at the sub-multiplier with a predetermined bandwidth.

45. The electronic circuit as defined in Claim 44, wherein the multiplier comprises three multiplication units connected in series.

46. The electronic circuit as defined in Claim 44, wherein the predetermined bandwidth is ranged from about 50 KHz to about 300 KHz

47. The outdoor unit as defined in Claim 40, wherein the second frequency generator comprises: an variable frequency oscillator configured to generate an intermediary variable frequency; and a mixer configured to combine the fixed frequency signal from the first frequency generator and the intermediary variable frequency from the variable frequency oscillator.

48. The outdoor unit as defined in Claim 47, wherein the variable frequency oscillator comprises a phase locked loop configured to receive the fixed frequency signal as a reference signal and to generate the intermediary variable frequency signal phase-locked to the first frequency signal.

49. The outdoor unit as defined in Claim 48, wherein the second frequency generator further comprises a frequency divider configured to divide the frequency of the fixed frequency signal and to provide the resulting divided frequency signal to the phase locked loop as the reference signal.

50. The outdoor unit as defined in Claim 47, wherein the second frequency generator further comprises a frequency multiplier configured to multiply the frequency of the fixed frequency signal and to provide the resulting signal to the mixer.

51. The outdoor unit as defined in Claim 47, wherein the second frequency generator further comprises a frequency multiplier to multiply the frequency of an output signal of the mixer to generate the variable frequency signal.

52. The outdoor unit as defined in Claim 40, wherein the frequency converter comprises an up- conversion unit configured to receive the data signal from the indoor unit and to convert the frequency of the data signal to another frequency using the fixed and variable frequency signals.

53. The outdoor unit as defined in Claim 52, wherein the up-conversion unit comprises: a first up-conversion unit configured to convert the frequency of the data signal from the indoor unit using the fixed frequency signal from the first frequency generator; and a second up-conversion unit configured to convert the frequency of the output of the first up- conversion unit using the variable frequency signal from the second frequency generator.

54. The outdoor unit as defined in Claim 40, wherein the frequency converter further comprises a down-conversion unit configured to convert the frequency of the data signal to another frequency using the fixed and variable frequency signal and to transmit the frequency-converted data signal to the indoor unit.

55. The outdoor unit as defined in Claim 54, wherein the down-conversion unit comprises: a first down-conversion unit configured to convert the frequency of the data signal, which is wirelessly received, using the variable frequency signal; and a second down-conversion unit configured to convert the frequency of the output of the first down- conversion unit using the fixed frequency signal.

56. A method of shifting a frequency of a data signal for wireless communication among a plurality of stations, each of which comprises an indoor unit comprising a modem and the outdoor unit comprising an antenna, wherein the data signal comprises at least one of a signal generated by the modem of the indoor unit and a signal wirelessly received by the antenna of the outdoor unit and a signal, the method comprising: receiving the data signal at a frequency; generating a fixed frequency signal; generating a variable frequency signal using the fixed frequency signal; and shifting the frequency of the data signal using the fixed and variable frequency signals.

57. The method as defined in Claim 56, wherein the variable frequency signal is a carrier frequency of the wireless communication.

58. The method as defined in Claim 56, wherein the fixed frequency signal and the variable frequency signal are phase-locked with each other.

59. The method as defined in Claim 56, wherein the generating the fixed frequency signal is performed by a phase locked loop including a crystal oscillator.

60. The method as defined in Claim 56, wherein the frequency of the variable frequency signal is higher than the frequency of the fixed frequency signal.

61. The method as defined in Claim 56, wherein the generating the fixed frequency signal comprises: generating an intermediary fixed frequency signal; and multiplying the frequency of the intermediary frequency signal so as to generate the fixed frequency signal.

62. The method as defined in Claim 60, wherein the multiplying comprises: generating a plurality of harmonic components of the frequency of the intermediary fixed frequency signal; and separating a desired harmonic component from the plurality of harmonic components.

63. The method as defined in Claim 62, wherein the separating comprises filtering the plurality of harmonic components with a band-pass filter having a pass bandwidth raged from about 50 KHz to about 300 KHz.

64. The method as defined in Claim 63, wherein the band-pass filter is one selected from the group consisting of an LC filter, a surface acoustic wave (SAW) filter, and a ceramic filter.

65. The method as defined in Claim 60, wherein the multiplying comprises at least two sequential sub- multiplying an input frequency thereof.

66. The method as defined in Claim 56, wherein the generating the variable frequency comprises: generating-an intermediary variable frequency signal; and combining the intermediary variable frequency signal with the fixed frequency signal.

67. The method as defined in Claim 66, wherein further comprising multiplying the frequency of a signal generated by the combining.

68. The method as defined in Claim 66, wherein the generating the intermediary variable frequency signal uses the fixed frequency signal as a reference signal to which the intermediary variable frequency signal is phase-locked.

69. The method as defined in Claim 68, wherein the frequency of the fixed frequency signal is divided and the divided fixed frequency signal is used as the reference signal.

70. The method as defined in Claim 66, wherein the generating the variable frequency signal further comprises: multiplying the frequency of the fixed frequency signal; and combining the multiplied fixed frequency signal with the intermediary variable frequency.

71. The method as defined in Claim 56, wherein the data signal is one generated by the modem of the indoor unit and to be wirelessly transmitted by the antenna after the frequency shifting, and wherein the shifting the frequency of the data signal comprises: combining the data signal with the fixed frequency signal so as to up-convert the frequency of the data signal to an intermediate frequency; and combining the up-converted data signal with the variable frequency signal so as to further up- convert the intermediate frequency of the data signal to a frequency for wireless transmission.

72. The method as defined in Claim 56, wherein the data signal is one wirelessly received by the antenna of the outdoor unit and to be transmitted to the modem of the indoor unit after the frequency shifting, and wherein the shifting the frequency of the data signal comprises: removing a component of the variable frequency signal from the wirelessly received data signal so as to down-convert the frequency of the data signal to an intermediate frequency; and removing a component of the fixed frequency signal from the down-converted data signal so as to further down-convert the intermediate frequency of the data signal to a frequency for transmission to the modem of the indoor unit.

73. A wireless communication system operating among a plurality of stations, the system comprising: an indoor unit comprising a modem for modulating/demodulating a data signal transmitted between the stations, wherein the indoor unit is further configured to generate a reference signal; an outdoor unit comprising a local oscillator and a frequency converter, wherein the frequency is converter configured to receive the data signal and to convert the frequency of the data signal to another frequency for wireless transmission between stations or for transmission to the indoor unit, and wherein the local oscillator comprises a first phase locked loop comprising a fixed frequency oscillator and a phase detector, wherein the fixed frequency oscillator is configured to generate a first fixed frequency signal and wherein the phase detector is configured to detect phases difference between the first fixed frequency signal and the reference signal from the indoor unit and to control the fixed frequency oscillator to minimize the phase difference, a frequency multiplier configured to multiply the frequency of the first fixed frequency signal and to filter the multiplied signal with a predetermined bandwidth to generate a second fixed frequency signal, a second phase locked loop comprising a variable frequency oscillator and a phase detector, wherein the variable frequency oscillator is configured to generate a first variable frequency signal and wherein the phase detector is configured to detect phases difference between the first variable frequency signal and the first fixed frequency signal from first phase locked loop and to control the variable frequency oscillator to minimize the phase difference, and a mixer configured to process the second fixed frequency signal and the first variable frequency signal so as to generate a second variable frequency signal; and a broadband cable disposed between the indoor unit and the outdoor unit, wherein the cable is configured to carry the data transmitted between the stations.

74. The system as defined in Claim 73, wherein the fixed frequency oscillator comprises a crystal oscillator.

75. The system as defined in Claim 73, wherein the frequency converter comprises a first frequency shifter configured to receive the data signal from the modem of the indoor unit and shift the frequency of the data signal to an intermediate frequency using the second fixed frequency signal and a second frequency shifter configured to shift the intermediate frequency to the other frequency using the second variable frequency signal.

76. The system as defined in Claim 73, wherein the frequency multiplier comprises a plurality of sub- multiplication units connected in series, each of which comprises a sub-multiplier and a band-pass filter.

77. The system as defined in Claim 76, wherein the band-pass filter is one selected from the group consisting of an LC filter, a surface acoustic wave (SAW) filter, and a ceramic filter.

78. The system as defined in Claim 73, wherein the frequency of the first fixed frequency signal is adapted to be divided prior to being provided to the second phase locked loop.

79. The system as defined in Claim 73, wherein the frequency of the second fixed frequency signal is adapted to be further multiplied prior to being mixed with the first variable frequency signal.