Abstract:
A repeater for re-transmitting signals between first and second wireless devices. The repeater comprises a first antenna array for receiving a forward channel signal transmitted from the first wireless device and a second antenna array for receiving a reverse channel signal transmitted from the second wireless device. The repeater also comprises a first transceiver chain for down-converting the received forward channel signal, processing the down-converted forward channel signal, and up-converting the processed forward channel signal to thereby produce an outgoing forward channel signal. The repeater also comprises a second transceiver chain for down-converting the received reverse channel signal, processing the down-converted reverse channel signal, and up-converting the processed reverse channel signal to thereby produce an outgoing reverse channel signal. The first antenna array comprises a first antenna element and the second antenna array comprises a second antenna element that is cross-polarized with respect to the first antenna element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY 
   The present invention is related to that disclosed in U.S. Provisional Patent Application Ser. No. 60/608,299, filed Sep. 7, 2004, entitled “Method and Procedure for Using a Single RF Chain in a Wireless Repeater For Time-Division Duplexed Signals” and U.S. Provisional Patent Application Ser. No. 60/608,282, filed Sep. 7, 2004, entitled “Method and Procedure for Reduction of Feedback in a Wireless Repeater Using Cancellation of Cross-Polarized Signals”. U.S. Provisional Patent Application Ser. Nos. 60/608,282 and 60/608,299 are assigned to the assignee of the present application. The subject matter disclosed in each of U.S. Provisional Patent Application Ser. Nos. 60/608,282 and 60/608,299 is hereby incorporated by reference into the present disclosure as if fully set forth herein. The present invention hereby claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. Nos. 60/608,282 and 60/608,299. 

   TECHNICAL FIELD OF THE INVENTION 
   The present invention relates generally to communication networks and, more specifically, to a wireless network repeater that uses cross-polarized signals to reduce echo for use in a frequency-division duplexed (FDD) wireless network. 
   BACKGROUND OF THE INVENTION 
   Consumers use a wide range of devices and networks, including cellular phones, paging devices, personal communication services (PCS) systems, and wireless data networks. Wireless service providers create new markets for wireless devices and expand existing markets by making wireless devices and services cheaper and more reliable. Wireless service providers attract new customers by reducing infrastructure costs and operating costs, by increasing handset battery life, and improving quality of service, and new and better features. 
   Inadequate coverage is a persistent problem in the quality of service of any wireless network. Natural and man-made obstacles frequently create radio frequency (RF) “holes” in the coverage area of a wireless network. Voice and data call connections are frequently dropped when a wireless terminal, such as a cell phone or a similar mobile station, enters an RF hole. Mobile stations that are already in an RF hole may not be able to reliably establish new connections. Typical areas in which RF holes occur include underground tunnels, buildings that have large footprints, tall buildings, and underground shopping malls. 
   Wireless service providers may attempt to improve coverage by deploying RF repeater transceivers. A variety of repeaters have been developed to improve the coverage of wireless networks. In U.S. patent application Ser. No. 09/998,238 (Publication No. 20030104781), Son describes a residential wireless repeater that achieves isolation between transmit and receive antennas by physical separation of the antennas. The repeater disclosed by Son requires two separate modular repeaters that communicate simultaneously with each other with low radio frequency. 
   In U.S. Pat. No. 6,731,904, Judd describes a modular repeater that includes a housing having a pair of substantially 180° oppositely facing surfaces. At least one antenna element is mounted to each of these surfaces for radiating energy in a direction opposite that of another antenna element mounted to the other surface. An electronic circuit within the housing operatively couples signals between at least one antenna element on each of the oppositely facing surfaces of the module housing. 
   In U.S. Pat. No. 6,697,603, Lovinggood et al. describe a digital repeater for receiving and retransmitting radio frequency (RF) signals. The Lovinggood repeater down-converts a received RF signal to an intermediate frequency (IF) signal, converts the IF signal into a digital signal, processes and amplifies the digital signal into an amplified signal using the digital signal processor, and converts the amplified signal into an analog signal. The Lovinggood repeater then up-converts the analog signal to an outgoing RF signal suitable for antenna transmission. 
   In U.S. Pat. No. 6,640,112, Lee et al. describe a repeating method for a wireless communication system which provides time and space diversities. The method of repeating a forward link communication signal for a wireless communication system includes the steps of: a) transmitting the forward link communication signal through a first transmitting antenna; b) delaying the forward link communication signal for a predetermined time period; and c) transmitting a delayed forward link communication signal which is generated by step b) through a second transmitting antenna. 
   In U.S. Pat. No. 4,283,795, Steinberger presents an adaptive cross-polarization cancellation arrangement in which a first desired polarized signal and a second interfering orthogonally polarized signal, including cross-polarization components, are concurrently received at an antenna. The orthogonally polarized components of the received signal are separated and transmitted along separate paths and recombined after the phase and amplitude of the separated polarized interfering signal sample have been adjusted for maxim cancellation of cross-polarization components in the other path. 
   Each of the prior art repeaters described above requires at least one of the following: i) physical separation of primary and secondary antenna sets by a significant distance to reduce the magnitude of the transfer function H such that H&lt;1/G, where G is the repeater power gain; ii) precise adjustment of input-output phase adjustment embodied in H such that the vector product G*H is &lt;0 in order to yield negative feedback; iii) separate modules for the reception of external signals and the retransmission of signals internal to the building; and iv) methods for the cancellation of multiple time-delayed echoes that would occur in a home or in-building environment with multiple scattering surfaces. The prior art repeaters generally do not provide a method of canceling any echoes from the output that would lead to unstable operation (i.e., oscillations). 
   Therefore, there is a need in the art for improved repeaters for use in wireless networks. In particular, there is a need for a repeater that cancels echoes and avoids oscillation. 
   SUMMARY OF THE INVENTION 
   The present invention provides a wireless repeater for use in a wireless network that employs frequency-division duplexed (FDD) transmission and reception. A repeater according to the principles of the present invention reduces feedback between an output antenna and an input antenna of the repeater that could cause instabilities or oscillations. The present invention uses a combination of antenna cross-polarization techniques and digital processing techniques to remove time-delayed feedback or echo terms. The signal processing techniques described herein may provide another 20-40 dB of gain isolation. 
   To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a repeater for re-transmitting signals between a first wireless device and a second wireless device. According to an advantageous embodiment of the present invention, the repeater comprises: 1) a first antenna array for receiving a forward channel signal transmitted from the first wireless device; and 2) a second antenna array for receiving a reverse channel signal transmitted from the second wireless device. The repeater further comprises: 3) a first transceiver chain capable of down-converting the received forward channel signal, processing the down-converted forward channel signal, and up-converting the processed forward channel signal to thereby produce an outgoing forward channel signal suitable for transmission to the second wireless device; and 4) a second transceiver chain capable of down-converting the received reverse channel signal, processing the down-converted reverse channel signal, and up-converting the processed reverse channel signal to thereby produce an outgoing reverse channel signal suitable for transmission to the first wireless device. The first antenna array comprises a first antenna element and the second antenna array comprises a second antenna element that is cross-polarized with respect to the first antenna element. 
   According to one embodiment of the present invention, a ground plane associated with the repeater is disposed between the first antenna array and the second antenna array to thereby provide isolation between the first and second antenna arrays. 
   According to another embodiment of the present invention, each of the first and second transceiver chain further comprises an echo processor capable of attenuating in a respective one of the down-converted forward and reverse channel signals an echo signal associated with a respective one of the outgoing forward and reverse channel signals. 
   According to still another embodiment of the present invention, the each echo processor delays transmission of the outgoing one of the forward and reverse channel signals in order to minimize the echo signal in the respective one of the down-converted forward and reverse channel signals. 
   According to yet another embodiment of the present invention, the each echo processor comprises an echo detector for detecting the echo signal in the respective one of the down-converted forward and reverse channel signals. 
   According to a further embodiment of the present invention, the each echo processor further comprises an echo suppressor for suppressing at least a part of the echo signal in the respective one of the down-converted forward and reverse channel signals. 
   According to a still further embodiment of the present invention, the each echo processor comprises a time delay buffer for delaying transmission of the respective one of the down-converted forward and reverse channel signals. 
   According to a yet further embodiment of the present invention, the each echo processor further comprises a test signal generator capable of adding a known test signal to the respective one of the down-converted forward and reverse channel signals. 
   In one embodiment of the present invention, the echo processor is capable of detecting an echo of the test signal in the respective one of the down-converted forward and reverse channel signals and using a delay associated with the test signal echo to determine a delay associated with the delay buffer. 
   In another embodiment of the present invention, the repeater further comprises: 1) a first duplexer capable of coupling the first antenna array to an input of the first transceiver chain and to an output of the second transceiver chain; and 2) a second duplexer capable of coupling the second antenna array to an output of the first transceiver chain and to an input of the second transceiver chain 
   Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
       FIG. 1  illustrates an exemplary wireless network in which a repeater according to the principles of the present invention may be implemented; 
       FIG. 2  illustrates an exemplary repeater according to one embodiment of the present invention; 
       FIG. 3  is an architectural view of the exemplary repeater according to one embodiment of the present invention; 
       FIG. 4  illustrates an exemplary signal processor block according to one embodiment of the present invention; 
       FIG. 5  illustrates an exemplary echo processor block according to one embodiment of the present invention; and 
       FIG. 6  illustrates an exemplary echo processor block according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 through 6 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged RF repeater transceiver. 
     FIG. 1  illustrates exemplary wireless network  100 , which implements repeater  120  according to the principles of the present invention. Wireless network  100  comprises base station (BS)  101  and other base stations (not shown) that communicate with a plurality of mobile stations, such as mobile station (MS)  111 , located in a coverage area of wireless network  100 . In an advantageous embodiment of the present invention, base station (BS)  101  communicates with mobile station (MS)  111  over frequency-division duplexed (FDD) channels. By way of example, the FDD channels may use code division multiple access (CDMA) signals (e.g., CDMA2000). Alternative embodiments of the present invention may use 1xEV-DO, WCDMA, GMS/EDGE, IEEE-802.16, or other cellular signals with frequency division duplexing (FDD) on the forward (downlink) channels and the reverse (uplink) channels. 
   MS  111  may be any suitable wireless device, including a conventional cellular radiotelephone, a PCS handset device, a personal digital assistant (PDA), a portable computer, a telemetry device, or the like, that is capable of communicating with BS  101  via wireless links. The present invention is not limited to mobile devices. Other types of wireless access terminals, including fixed wireless terminals, may be used. For the sake of simplicity, only mobile stations are shown and discussed hereafter. However, it should be understood that the use of the term “mobile station” in the claims and in the description below is intended to encompass the exemplary types of mobile stations described above, as well as portable devices such as, for example, vehicle-mounted wireless devices. 
   Wireless network  100  further comprises wireless repeater  120 . Forward channel (i.e., downlink) signals from BS  101  to MS  111  and reverse channel (i.e., uplink) signals from MS  111  to BS  101  may be blocked by objects  131 - 134 . Repeater  120  may be used in wireless network  100  to extend the coverage range of BS  101  to areas, such as the vicinity of MS  111 , where blockage or scattering causes large propagation losses. Objects  131 - 134  may include, for example, tunnels, terrain features (e.g., mountains, valleys), and large buildings. 
   Repeater  120  comprises donor antenna array  122 , which communicates in the forward and reverse channels with BS  101 , and server antenna array  124 , which communicates in the forward and reverse channels with MS  111 . Repeater  120  is placed in a location where the forward channel signal received from BS  101  exceeds a specified threshold. Repeater  120  filters and amplifies the received signal and retransmits the signal into the regions where the signal from BS  101  is too low for reliable reception. Repeater  120  performs a similar function in the reverse channel from MS  111  to BS  101 . 
     FIG. 2  illustrates exemplary repeater  120  according to one embodiment of the present invention. Repeater  120  implements FDD operations using a single donor antenna array and a single server antenna array. Each antenna array uses a duplexer to support different transmit and receive frequencies. Repeater  120  comprises donor antenna array  122 , duplexer  210 , server antenna array  124 , duplexer  250 , a forward channel transceiver chain, and a reverse channel transceiver chain. The forward channel transceiver chain comprises low-noise amplifier (LNA)  220   a , signal processor  230   a  and high-power amplifier (HPA)  240   a . The reverse channel transceiver chain comprises low-noise amplifier (LNA)  220   b , signal processor  230   b  and high-power amplifier (HPA)  240   b.    
   Donor antenna array  122  receives forward channel (downlink) signals at a downlink frequency, fd, and sends the forward channel signals through duplexer  210  to the input of low-noise amplifier (LNA)  220   a . LNA  220   a  amplifies the forward channel signals to an appropriates level for signal processor  230   a . Signal processor  230   a  removes signal components coupled from the output antenna (i.e., server antenna array  124 ) to the input antenna (i.e., donor antenna array  122 ). Next, HPA  240   a  amplifies the regenerated forward channel signals for transmission via duplexer  250  and server antenna array  124 . 
   Server antenna array  124  receives reverse channel (uplink) signals at an uplink frequency, fu, and sends the reverse channel signals through duplexer  250  to the input of low-noise amplifier (LNA)  220   b . LNA  220   b  amplifies the reverse channel signals to an appropriates level for signal processor  230   b . Signal processor  230 b removes signal components coupled from the output antenna (i.e., server antenna array  124 ) to the input antenna (i.e., donor antenna array  122 ). Next, HPA  240   b  amplifies the regenerated reverse channel signal for transmission via duplexer  210  and donor antenna array  122 . 
   A mobile station (MS) or other access terminal (AT) typically receives downlink transmissions of CDMA 2000  signals in the range of −100 dBm to −80 dBm. The downlink signal fed to the transmit antenna in a wireless repeater in a home environment typically is in the range of +0 dBm to +10 dBm. The amplified and transmitted signal consists of the amplified input signal plus amplified noise. Hence the repeater chain for the downlink signal has an amplifier gain of 80 dB to 110 dB. 
     FIG. 3  is an architectural view of exemplary repeater  120  according to one embodiment of the present invention. Repeater  120  uses ground plane isolation and cross-polarization of antenna elements to minimize feedback between the donor antenna and the server antenna. Repeater  120  uses orthogonally polarized antenna elements  301  and  302  on opposite faces of the housing of repeater  120  to radiate power in directions opposite to each other. Thus, antenna element  301  in antenna array  122  is aligned at right angles with antenna element  302  in antenna array  124 . 
   Electronic circuits mounted within the housing of repeater  120  couple signals between antenna elements  301  and  302  on the oppositely facing surfaces. Circuits that receive low-power signals are isolated from the power amplifier circuits for the down-link and the up-link by shielding techniques well-known in the field. Ground plane  330 , which contains filtered feed-through lines, provides additional isolation between down-conversion circuitry  310  and up-conversion circuitry  320 . This architecture also reduces the length of antenna feeds, a major source of coupling between co-located antennas. 
     FIG. 4  illustrates exemplary signal processor  230  (i.e.,  230   a  or  230   b ) according to one embodiment of the present invention. Signal processor  230  provides further isolation by detecting and attenuating signals coupled from the transmitter antenna to the receiver antenna for both the forward (downlink) channel and the reverse (uplink) channel. Signal processor  230  comprises down-conversion mixer  405 , analog-to-digital converter (ADC)  410 , echo processor  415 , digital-to-analog converter (DAC)  420 , up-conversion mixer  425 , local oscillator (LO)  430 , clock  435  and local oscillator (LO)  440 . 
   The incoming RF signal from LNA  220  is down-converted to baseband (or IF) by down-conversion mixer  405  and LO  430 . ADC  410  converts the output of mixer  405  to digital samples, which are stored in memory in echo processor  415 . Echo processor  415  then removes feedback (i.e., echoes) from the digital samples. The filtered samples are converted back to an analog signal by DAC  420 . mixer  425  and LO  440  then up-convert the output of DAC  420  to an RF signal that is fed to the input of HPA  240 . 
   In alternate embodiments, the ADC sampling may be performed in the RF band of the received signal or at an intermediate frequency (IF) level. The samples are taken over a time interval that represents the maximum propagation time expected for the latest arriving echo, generally less than 1 microsecond, for an in-building or home environment. To reduce the throughput of sampled date (bits/sec), sub-Nyquist sampling rates in either the RF band or in the IF band may be used. ADC  410  has a dynamic range and sampling frequency to differentiate the original, non-delayed signal from the amplified, delayed echo. Clock  435  synchronizes ADC  410  with the data transfer between blocks. 
     FIG. 5  illustrates exemplary echo processor  415  according to one embodiment of the present invention. Echo processor  415  comprises echo detector  505 , echo suppressor  510 , delay buffer  515 , controller  520 , memory  525  and clock  530 . Echo detector  505  searches for any time-delayed echoes in the sampled data. Echo suppressor  510  subtracts any detected echoes from the sampled data stream. In order to reduce the correlation between the original signal and echoed signals, the resulting signal samples are delayed in delay buffer  515  for a time specified by controller  520 . Those familiar with the art will recognize that conventional auto-correlation methods may be used to determine the time delay of each echo. The echo detection and echo subtraction may occur serially or in multiple parallel branches, one for each expected echo. 
     FIG. 6  illustrates exemplary echo processor  415  according to another embodiment of the present invention. In the embodiment shown in  FIG. 6 , repeater  120  processes code division multiple access (CDMA) signals. Echo processor  415  comprises RAKE receiver  605 , echo suppressor  610 , CDMA multiplier  615 , delay buffer  620 , test code generator  625 , controller  630 , memory  635  and clock  640 . RAKE receiver  605  detects multipath signals, including echo signals, in the incoming signal samples. 
   CDMA multiplier  615  receives a low-power test code generated by test code generator  625 . CDMA multiplier  615  multiplies the test code by an unused Walsh code and combines the test code with the signal samples. The low-power test code signal is sufficiently strong so that its echo may be picked up by the receive antenna after transmission. However, the test code signal is too weak to cause interference to a distant mobile station. Since repeater  120  knows the exact value of the test code signal, it is relatively easy to detect the echo of the test code signal. RAKE receiver  605  uses correlation or matched filter techniques to detect any time-delayed, cross-polarized test code signals coupled into the sampled signal from the receiver input antenna. Echo suppressor  610  uses the time-delay information associated with the test code signal to determine the exact propagation delay through repeater  120 . Echo suppressor  610  uses the propagation delay information to subtract each echo signal from the sampled data stored in memory  635 . 
   In an alternate embodiment of the present invention, CDMA multiplier  615  and test code generator  625  may be replaced by a low-frequency (LF) reference modulation signal generator. Echo detector  505  (or RAKE receiver  605 ) uses a lock-in amplifier or phase-shift detection techniques to detect the modulated low-frequency signal coupled into the input. The relative phase shift between the modulation of the received signal and the reference modulation signal provides the echo time delay. 
   To prevent the onset of instabilities or oscillations upon power up of repeater  120 , controller  630  ramps up the output power amplifier gain while echo processor  415  learns of the existence of echo terms. The amplifier gain is increased until either the maximum allowed value is reached or until echo processor  415  no longer provides sufficient suppression of echo signals. 
   Repeater  120  uses a novel combination of techniques to minimize echoes in the transmitted signals. These techniques include the use of orthogonally polarized antenna elements  301  and  302  in the donor and server sides of repeater  120 , coupled with intervening signal processor  230  that removes or greatly attenuates echoes coupled into the opposite polarization. The antennas are oriented at 180-degrees with respect to their high-gain directions, respectively. Antenna arrays  122  and  124  also have high front-to-rear isolation. The echo detection and cancellation processes in signal processor  230  are greatly enhanced by the use of delay buffers  515  and  620  that follow suppression of detected echo components in the input signal. 
   Although the present invention has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.