WO2004047334A1 - Monitoring stability of an on-frequency repeater - Google Patents
Monitoring stability of an on-frequency repeater Download PDFInfo
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- WO2004047334A1 WO2004047334A1 PCT/CA2003/001755 CA0301755W WO2004047334A1 WO 2004047334 A1 WO2004047334 A1 WO 2004047334A1 CA 0301755 W CA0301755 W CA 0301755W WO 2004047334 A1 WO2004047334 A1 WO 2004047334A1
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- Prior art keywords
- signal
- pulse
- signature
- repeater
- function
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/155—Ground-based stations
- H04B7/15528—Control of operation parameters of a relay station to exploit the physical medium
- H04B7/15535—Control of relay amplifier gain
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/155—Ground-based stations
- H04B7/15564—Relay station antennae loop interference reduction
- H04B7/15578—Relay station antennae loop interference reduction by gain adjustment
Definitions
- the present application relates to wireless access networks and, in particular, to a method and system for monitoring stability of an on- frequency repeater.
- On-frequency repeaters are known in the art, for amplifying an input signal without otherwise altering its frequency spectrum.
- an on-frequency repeater may also employ various types of active circuitry in order to enhance the signal-to-noise (S/N) ratio, in addition to simply increasing the power level.
- S/N signal-to-noise
- a typical application of on-frequency repeaters is for improving wireless services within defined regions of a wireless network, where signal levels would otherwise be too low for satisfactory quality of service. For example, within a building, or a built-up urban area, signal attenuation, shadowing by buildings and/or hills; noise generated by various radio frequency sources, and multi-path effects can seriously degrade the quality of desired RF signals.
- a wireless network provider may install a repeater in order to improve service in a region lying at an edge of the coverage area serviced by a base station, thereby effectively extending the reach of the base-station.
- On-frequency repeaters are characterized by the fact that the input and output signals (in either the uplink or downlink path directions) have the same frequency.
- the term "on-frequency repeater” shall be understood to refer to any amplifier system that has this characteristic, irrespective of whether the system is used as part of an wireless communications network, or in any other context.
- the external input signal received by the repeater e.g. from a base station or a subscriber's wireless communications device - WCD
- the external input signal received by the repeater can be represented by:
- G is the repeater gain and d is the time delay through the repeater at the carrier frequency ? .
- the output signal (So) radiated by the repeater is a replica of the input signal received by the repeater, that has been amplified and subject to a time delay d due to electrical delays within the repeater. Part of this delay is inherent to the amplification process, but is primarily caused by band-pass filters used in the repeater to prevent the unwanted amplification of signals outside the frequency band of interest. Generally this delay is inversely proportional to the bandwidth of the filters.
- the repeater gain (G) provides the increase in signal level that makes the repeater useful.
- L is the signal loss in the feedback path (that is, the antenna isolation), and ? is the time delay in the feedback path at the carrier frequency ? .
- V . L repeater will be the vector sum of the external input signal Se (Equ. 1) and the feedback signal Sf (Equ. 3).
- the magnitude of the input signal (Si) is a function of both the amplitude of the external input signal (Se) and the feedback signal Sf, and their relative phases.
- the magnitude of the output signal (So), and thus the feedback signal (Sf) will be held approximately constant over a wide range of input power. Such a system will remain stable if the feedback signal Sf is always smaller than the input signal (Se).
- system stability can be obtained by ensuring that antenna isolation (L) is equal to or greater than the system gain (G).
- antenna isolation is difficult to predict, and will frequently change over time. Accordingly, conventional on-frequency repeater gain is manually adjusted by a technician to be less than the expected antenna isolation by a significant margin, in order to provide conditional stability in a changing RF environment. This margin significantly decreases the effectiveness of the repeater and yet does nto prevent oscillation for all potential scenarios.
- United States Patent Nos. 5,125,108 and 5,584,065 disclose methods of removing interfering signals that are present along with a desired communications signal traffic, using a sample of the interfering signal recieved by a separate, auxiliary antenna.
- adaptive techniques are employed to adjust the amplitude and phase of the sample so that, when it is combined with the output of the communication system's receiving antenna, the interfering signal is cancelled.
- United States Patent No. 4,475,243 describes an apparatus for minimizing the "spillover" signal from the transmitter to the receiver in a repeater.
- the received signal is translated to baseband (i.e., the carrier is removed) for amplification (regeneration), then translated back up to the same carrier frequency (i.e., remodulating a carrier) for retransmission.
- An "injection signal” based on sampling the regenerated communication signal is used in conjunction with mixing and correlation techniques to isolate the spillover component of the input signal so that it can be removed at an intermediate frequency (IF) stage of the receiver.
- IF intermediate frequency
- This system is designed to handle a single communication signal with narrowband analog voice modulation, and thus is not suitable for use with broadband signal traffic carrying multiple parallel communication signals.
- a digital microwave radio repeater in which the desired digital signal is a single signal and is regenerated (amplified) at baseband.
- the transmitter- to-receiver coupled interference component that appears at baseband is canceled by subtracting an estimated baseband interference signal.
- the estimated baseband interference signal is produced by means of an equalization technique implemented by transversal filters whose characteristics are adaptively determined.
- United States Patent No. 4,383,331 teaches a system in which a "tag", in the form of one or more side-frequencies, is added to the output signal prior to its retransmission.
- the detection of the tag in a received input signal allows the power level of the feed back signal to be measured, and this information allows the repeater to subtract out the interference.
- this technique could be applied to monitor antenna isolation in a repeater operating in a broadband RF environment.
- the tag suffers the limitation that the tag must be located in a side-band (i.e., lying above or below the bandwidth of the desired communications signal traffic) in order to avoid interference corrupting the desired communications signal traffic and/or interfering with other network components. Because antenna isolation can vary strongly with frequency, measurements based on side-band "tags" can, at best, provide only an rough approximation of the antenna isolation at the frequencies of the desired communications signal traffic.
- United States Patent No. 5,835,8408 teaches a repeater in which antenna isolation is determined using a calibration procedure that is executed during periods in which no communications traffic is present.
- the calibration procedure involves opening a switch to prevent transmission of signals received at the input antenna; transmitting a test (pilot) signal from the output antenna; and then detecting the signal power of the test signal received through the input antenna.
- the test signal can be transmitted at any desired frequency, so it is possible to measure antenna isolation, as a function of frequency, across the entire operating bandwidth of the communications traffic.
- Applicant's co-pending United States Patent Application No. 09/919,888 proposes a solution in which a unique bit-sequence is encoded as a signature signal that is transmitted through an output antenna as a low-level fade impressed on a broadband RF signal.
- the signal received through the input antenna is correlated with the bit- sequence, and the degree of correlation used as an indirect indicator of system stability. Impressing the signature signal onto the broadband RF signal (i.e., the desired communications signal traffic) as a low-level fade allows the system stability to continuously monitored without interfering with the communications signal traffic of other devices within the network.
- An object of the present invention is to provide a method and system for monitoring stability of an on-frequency repeater.
- an aspect of the present invention provides a method of monitoring stability of an on-frequency repeater.
- a signature signal comprising a sequential series of signal pulses is generated. Each signal pulse has a selected pulse function and duration.
- the signature signal is transmitted through an output of the repeater.
- a respective quiescent power level of an input signal component received through an input of the repeater, and having a frequency corresponding to the selected pulse function is detected.
- a respective transmit power level of the input signal component is detected.
- the transmitted signature signal, and the detected quiescent and transmit power levels of the input signal component are then used to estimate stability of the repeater.
- the present invention utilizes a pulsed signature signal, which is detected in the input signal Si during both the transmission of signal pulses and the quiescent period between pulses.
- This arrangement enables the signal components corresponding to the signature signal appearing in the input signal (Si) (via the leakage path) to be positively distinguished from ambient noise having the same frequency as the signature signal.
- the signature signal By transmitting the signature signal as a low-level amplitude modulation of the output signal (So), continuous, real-time monitoring of stability can be obtained without interfering with desired communications signal traffic.
- Information of the system stability can be used in various ways, such as , for example, to control system gain.
- Fig. 1 is a block diagram schematically illustrating principle elements of an isolation monitoring system in accordance with an embodiment of the present invention, deployed in an on-frequency repeater;
- FIG. 2 is a flow-chart illustrating principle operations of the stability monitoring system of FIG. 1;
- FIGs. 3a-3c are signal charts illustrating operation of the stability monitoring system of FIG. 1.
- FIG. 1 is a block illustrating principle elements of an exemplary system in accordance with an embodiment of the present invention.
- an on-frequency repeater includes an input 2 for receiving an input signal (Si); an output 4 for radiating an output signal (So); and a signal path 6 coupled between the input 2 and output 4 in order to amplify the received input signal (Si) for retransmission as the output signal (So).
- the signal path 6 may include an Intermediate Frequency (IF) section (not shown) to facilitate filtering, amplification, and other signal processing functions.
- IF Intermediate Frequency
- FIG. 1 shows a single RF signal path 6 coupled between the input 2 and output 4, both of which are provided by respective antennas.
- This arrangement will clearly be suitable for unidirectional RF signal traffic.
- Bi-directional signal traffic through the repeater can readily be accommodated by duplicating the system of FIG. 1, or by coupling a pair of signal paths between the two antennas via diplexers. Both of these solutions are well known in the art, and accordingly will not be described in greater detail.
- the bandwidth of the signal path 6 will be determined in accordance with the communications network within which the repeater will operate.
- the communications network within which the repeater will operate.
- publicly accessible cellular communications networks utilize a 25MHz uplink and downlink channel bandwidth centered on 836.5MHz and 881.5MHz, respectively.
- the radiated output signal (So) is an amplified (and phase shifted) replica of the received input signal (Si)
- a feedback signal (Sf) will couple between the output 4 and the input 2 via a leakage path 8, as described above and shown in FIG. 1.
- the received input signal (Si) will be the vector sum of the external input signal (Se) and the feedback signal (Sf).
- Sf may become greater than (Se), and unstable operation of the repeater (in the form of oscillation) will occur.
- the present invention operates by adding a signature signal to the output signal (So), and detecting corresponding signal components appearing in the received input signal (Si) via the leakage path 8.
- the signature signal is designed such that the corresponding signal components can be unambiguously discriminated from noise in the received input signal (Si).
- the signature signal is added to the output signal (So) in such a manner that it does not interfere with subscriber traffic. Correlation between the signature signal added into the output signal (So) with the signal components detected within the input signal (Si) provides an indirect indication of the stability of the repeater.
- FIG. 1 illustrates an exemplary stability monitoring system in accordance with the present invention.
- the isolation monitoring system includes a modulator
- a tunable isolator 12 coupled to the signal path 6 for isolating signal components corresponding to the transmitted signature signal appearing in the received input signal (Si); a detector 14 for detecting the isolated signal component, and a micro-controller 16 operating under suitable software control for controlling operation of the modulator and tunable detector, and for evaluating the system stability.
- phase modulation has an advantage in that it is less susceptible to distortion in the leakage path 8. However, in this case, careful design is required to ensure that insertion of the signature signal does not add significant frequency-domain noise in the frequency-modulated RF signal traffic being conveyed through the signal path 6.
- a variable gain amplifier is used as a modulator 10 controlled by the micro-controller 16.
- This arrangement enables the gain of the signal path 6 to be varied in accordance with the signature signal, effectively superimposing the signature signal onto the output signal (So) as a broadband amplitude modulation.
- the output signal (So) radiated by the repeater can be represented by:
- C(t) is the amplitude modulation applied by the variable gain amplifier 10 in accordance with the signature signal. This amplitude modulation will also appear in the feedback signal, which can then be represented as:
- the received input signal (Si) will include a signal component that corresponds with the amplitude modulation appearing in the feedback signal (Sf), and this signal component is isolated and detected by the tunable detector 12 and detector 14.
- the modulation power level of the signal component measured by the detector 14 is then sampled by a conventional analog-to-digital (A/D) converter 18, and the digitized sample value passed to micro-controller 16.
- A/D analog-to-digital
- Correlation between the respective power levels of the transmitted signature signal and the detected signal components within the input signal (Si) provides a direct indication of total signal leakage, and an indirect indication of system stability.
- the micro-controller 16 can implement various control functions such as, for example, controlling the gain of the signal path 6 to ensure unconditional system stability.
- the signature signal may be provided as any signal pattern that can be reliably detected within the received input signal (Si), without disrupting normal operation of the repeater or other transceivers of the wireless communications network.
- the signature signal is composed as a stream of signal pulses separated by corresponding quiescent periods, as may be seen in Fig. 3 a.
- Each signal pulse is defined by a pulse function Sp(t), which governs the waveform (shape), frequency and amplitude of the pulse.
- the pulse function Sp(t) defines a sinusoidal waveform having a selected amplitude and pulse frequency (Fp), both of which are substantially constant values (at least during any one pulse).
- any pulse waveform that can be positively detected in the input signal (Si), such as, for example, square, sinusoidal, or triangular waveforms may be used.
- the amplitude of the pulse waveform may remain constant, or may be varied (e.g. following an amplitude modulation pattern) as desired.
- the pulse frequency (Fp) of the pulse waveform can be constant or may be varied (e.g. chirped or frequency modulated).
- the duration (Np)of each pulse can be controlled using any or a variety of well known means, such as, for example, a desired number of cycles of the pulse waveform.
- Various means can be used to generate the signature signal.
- the micro-controller 16 may be programmed to synthesize the signature signal by sequentially reading successive values from a read-only-memory (ROM).
- ROM read-only-memory
- D/A digital-to-analog converter
- other techniques may equally be used. Any of these techniques are considered to be well within the purview of those of ordinary skill in the art, and thus will not be described further.
- Correlation between the signature signal superimposed on the output signal (So) and corresponding signal components within the received input signal (Si) can be accomplished by detecting respective magnitudes of the received input signal (Si) at a frequency corresponding to the pulse function Sp(t) during a quiescent period between successive pulses, and during transmission of the next successive pulse.
- the pulse frequency (Fp) is a constant
- this can be accomplished by suitably tuning a detector to the appropriate pulse frequency (Fp).
- the detector is tuned to follow the frequency profile of the pulse function Sp(t). In either case, the resulting measured magnitudes, in combination with the known modulation power of the signature signal within the output signal (So) enables estimation of system stability, as will be described in greater detail below with reference to FIGs. 2 and 3.
- FIG. 2 is a flow chart showing principle steps in a process of estimating system stability in accordance with the present invention.
- the pulse duration (Np) of each pulse, and the modulation power (Pm) are initialized, and the pulse function Sp(t) (including the waveform and pulse frequency - Fp) is selected (at 304).
- the pulse function Sp(t) including the waveform and pulse frequency - Fp) is selected (at 304).
- any desired pulse frequency (Fp) may be used.
- the frequency (Fp) should be high enough to ensure that the signature signal can be detected in the input signal (Si) in a timely manner, and low enough to avoid interference with subscriber signal traffic.
- selection of different pulse function parameters (principally the frequency) for each repeater can minimize the risk of faulty operation due, for example, to erroneous detection of a signature signal transmitted by another repeater.
- Effective discrimination can also be obtained by the use of multiple different pulse functions.
- parameters for a set of predetermined "candidate" pulse functions can be stored in memory.
- the micro-controller 16 can then select one of the candidate functions, and control generation of the signature signal using the selected function.
- This selection process can be "static", or “dynamic”, as desired.
- the micro-controller 16 may select a pulse function once (e.g., as part of a start-up sequence), and then use the parameters associated with that function (including the waveform, frequency etc.) thereafter.
- the pulse function may be a "fixed” default value, in which case a discrete operation step of "selecting the pulse function" (step 304) may be eliminated.
- Dynamic selection processes can be implemented in various ways.
- the micro-controller 16 can select each candidate function in turn, with the parameters associated with each selected candidate function being used as the pulse function for a predetermined period of time (e.g., a desired number of successive pulses).
- Selection of candidate functions can follow a predetermined order, or be random, as desired.
- the use of multiple candidate functions reduces the probability that two neighboring repeaters will be simultaneously using the same pulse function. As will be appreciated, this effectively eliminates the risk that a repeater will erroneously estimate system stability based on a signature signal transmitted by a neighbor repeater.
- the isolator 12 is tuned (at 306) to facilitate detection of the signal (or modulation) power within a narrow-band centered on the pulse frequency (Fp).
- this can be accomplished using a tunable narrow band-pass filter tuned to the pulse frequency (Fp) of the selected pulse function.
- a pair of cascaded tunable filters 20,22 are used, as shown in FIG. 1.
- a first tunable filter 20 is tunable across the entire frequency band of the signal path 6, and thus can be used to select a desired narrow band channel within the signal path 6.
- the second filter 22 is then tuned to the pulse frequency (Fp), in order to isolate a signal component that corresponds to the signature signal within the selected narrow band channel.
- Fp pulse frequency
- the power level measured by the detector 14 is sampled (at 308). Because this power level measurement is sampled during a quiescent period (initially, before transmission of the first pulse, and thereafter between successive pulses) it may be referred to as the "quiescent" power level (Po), and is directly indicative of the level of ambient noise, at the selected pulse frequency (Fp), within the input signal Si. This value can be used to calculate a noise metric (M) at 310. In simple embodiments, the noise metric (M) may simply be the quiescent power (Po) level itself.
- the noise metric (M) may be a calculated parameter that also takes into account the known characteristics of the system (e.g., phase delay, signal gain, filter characteristics, detector sensitivity, A/D precision etc.) as well as the waveform, frequency (Fp) and duration (Np) of each signal pulse.
- the noise metric (M) calculated using an equation of the form: Po
- the pulse duration Np is counted as the number of cycles of each pulse.
- This formulation reflects the fact that the noise tolerance of the system improves with pulse duration.
- other equations may be used as desired. Development of a suitable noise metric equation is considered to be well within the perview of one of ordinary skill in the art, and thus will not be described in further detail.
- the use of a calculated noise metric offers an advantage in that the noise metric (M) can then be directly indicative of the ability of the system to accurately evaluate system stability under the current conditions of ambient noise, using the selected pulse function.
- ambient noise can vary dramatically with location and time. In an ideal situation, ambient noise will be minimal, and thus the detected quiescent power (Po) will be close to zero. However, in practice, this will frequently not be the case, particularly if multiple noise sources are present. If the ambient noise level is too high, then accurate detection and sampling of signal components corresponding to a subsequently transmitted pulse, and consequently accurate estimation of stability, will not be possible.
- the noise metric (M) is compared to a threshold level (Mmax) at 312 that represents the maximum tolerable ambient noise level. If the noise metric (M) is greater than the threshold level (Mmax), then the duration (Np) of each pulse can be increased (at 314) to improve detection performance. However, increasing the duration (Np) has the effect of reducing system responsiveness, by reducing the rate at which successive pulses can be transmitted. At some point, the increased sensitivity afforded by increasing the duration of each pulse is offset by the degraded system response time.
- the pulse duration (Np) is then compared (at 316) with a predetermined maximum permissible pulse length (Nmax). If Np is greater than Nmax, then it is assumed that the ambient noise level is too high to permit satisfactory estimation of stability using the current pulse function. In this case, the current pulse function is discarded in favor of a new function (e.g. having a different pulse frequency- Fp) (at 318); and processing continues from step 306 above.
- Example exit conditions include, but are not limited to: a pulse function is found for which M ⁇ Mmax; or it is determined that there is no pulse function for which M ⁇ Mmax. If a satisfactory pulse function is found (i.e., M ⁇ Mmax), operation of the system can continue using the new function. Otherwise, ambient noise is assumed to be too severe to permit accurate monitoring of system stability, and the system may enter a "recovery" mode (not shown), in which the total gain of signal paths is restricted to a predetermined level in order to provide unconditional stability.
- the system can continue selection of pulse function 304; detection of the quiescent power level (Po) 308; calculation of the noise metric M 310; and comparison with Mmax 312 until a pulse function is found for which M ⁇ Mmax.
- Po quiescent power level
- a corresponding signal pulse of the signature signal can be generated (at 324) and inserted into the signal path 6.
- the signal pulse is superimposed onto the RF signal traffic in the signal path 6 as an amplitude modulation across the entire operating bandwidth of the signal path 6.
- the signature signal is used as an variable gain amplifier control signal to modulate the gain of the signal path 6.
- the modulation power (Pm) of the signal pulse is preferably held to a low level (e.g., less than about 3dB).
- the power level detected by the tunable detector at 328
- PI transmit power level
- the transmit power value (PI) detected at step 328 represents the vector sum of ambient noise (Po) and the pulse within the feedback signal (Sf).
Abstract
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Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE60329934T DE60329934D1 (en) | 2002-11-20 | 2003-11-14 | STABILITY MONITORING OF A SAME FREQUENCY INTERMEDIATE AMPLIFIER |
EP03811314A EP1563615B1 (en) | 2002-11-20 | 2003-11-14 | Monitoring stability of an on-frequency repeater |
CA002506907A CA2506907A1 (en) | 2002-11-20 | 2003-11-14 | Monitoring stability of an on-frequency repeater |
AU2003302097A AU2003302097A1 (en) | 2002-11-20 | 2003-11-14 | Monitoring stability of an on-frequency repeater |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US10/299,797 US7035321B2 (en) | 2002-11-20 | 2002-11-20 | Monitoring stability of an on-frequency repeater |
US10/299,797 | 2002-11-20 |
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WO2004047334A1 true WO2004047334A1 (en) | 2004-06-03 |
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PCT/CA2003/001755 WO2004047334A1 (en) | 2002-11-20 | 2003-11-14 | Monitoring stability of an on-frequency repeater |
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US (1) | US7035321B2 (en) |
EP (1) | EP1563615B1 (en) |
CN (1) | CN1714520A (en) |
AU (1) | AU2003302097A1 (en) |
CA (1) | CA2506907A1 (en) |
DE (1) | DE60329934D1 (en) |
WO (1) | WO2004047334A1 (en) |
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2002
- 2002-11-20 US US10/299,797 patent/US7035321B2/en not_active Expired - Fee Related
-
2003
- 2003-11-14 AU AU2003302097A patent/AU2003302097A1/en not_active Abandoned
- 2003-11-14 CA CA002506907A patent/CA2506907A1/en not_active Abandoned
- 2003-11-14 WO PCT/CA2003/001755 patent/WO2004047334A1/en not_active Application Discontinuation
- 2003-11-14 EP EP03811314A patent/EP1563615B1/en not_active Expired - Fee Related
- 2003-11-14 DE DE60329934T patent/DE60329934D1/en not_active Expired - Lifetime
- 2003-11-14 CN CN200380103769.6A patent/CN1714520A/en active Pending
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US4317217A (en) * | 1980-08-11 | 1982-02-23 | Motorola, Inc. | Tag generator for a same-frequency repeater |
EP0851606A2 (en) * | 1996-12-30 | 1998-07-01 | Lucent Technologies Inc. | Range repeater for a transmission system |
US20020044594A1 (en) * | 2000-10-18 | 2002-04-18 | Spotwave Wireless Inc. | Coverage area signature in an on-frequency repeater |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN1777074B (en) * | 2005-11-28 | 2011-06-29 | 三维通信股份有限公司 | Method for monitoring wireless high-frequency-amplification station isolation degree using pilot frequency multi-channel signal |
Also Published As
Publication number | Publication date |
---|---|
DE60329934D1 (en) | 2009-12-17 |
CA2506907A1 (en) | 2004-06-03 |
AU2003302097A1 (en) | 2004-06-15 |
EP1563615A1 (en) | 2005-08-17 |
US20040095992A1 (en) | 2004-05-20 |
CN1714520A (en) | 2005-12-28 |
US7035321B2 (en) | 2006-04-25 |
EP1563615B1 (en) | 2009-11-04 |
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