(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2011/0281579 A1
`(43) Pub. Date:
`Nov. 17, 2011
`Kummetz
`
`US 20110281579A1
`
`(54) SYSTEMAND METHOD FOR DETECTING
`AND MEASURING UPLINK TRAFFIC IN
`SIGNAL REPEATING SYSTEMS
`
`(76)
`
`Inventor:
`
`Thomas Kummetz, Forest, VA
`(US)
`
`(21)
`
`Appl. No.:
`
`12/778,312
`
`(22)
`
`Filed:
`
`May 12, 2010
`
`Publication Classification
`
`(51)
`
`Int. C.
`H04/24/00
`
`(2009.01)
`
`(52) U.S. Cl. ........................................................ 455/424
`(57)
`ABSTRACT
`A signal repeating system for a wireless network includes an
`antenna configured for transceiving signals between a base
`station and a user equipment device. Repeating circuitry is
`coupled to the antenna and defines an uplink path for signals
`from the user equipment device to the base station and a
`downlink path for signals from the base station to the user
`equipment device. The repeating circuitry includes gain cir
`cuitry and gain control circuitry that is coupled to the gain
`circuitry. The gain control circuitry is operable for varying the
`gain of the repeating circuitry according to a waveform. Mea
`Surement circuitry measures the receive power in the uplink
`path over time from the user equipment device. Processing
`circuitry cross-correlates the inverted gain variation wave
`form with the measured receive power for determining the
`existence of traffic from user equipment devices in the uplink
`path.
`
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`Patent Application Publication
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`Patent Application Publication
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`Patent Application Publication
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`Nov. 17, 2011 Sheet 7 of 7
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`
`
`BTS DESENSITISATION (P in BTS total)
`
`TRAFFICLOAD dBm)
`— - - -110
`-107
`-104
`-101
`-98
`-95
`-92
`-89
`-86
`-83
`-80
`-77
`-74
`BTSEOUV.
`MPUT NOISE
`
`TRAFFICLOAD dBm
`-110
`
`-104
`-101
`-98
`-95
`-92
`-89
`-86
`-83
`-30
`-77
`-74
`REPEATEREOUV.
`NPUT NOISE
`
`10O
`REPEATER GAINdE)
`
`REPEATER RSSI (P in rep)
`
`REPEATER GAIN dB
`
`FIG. 6
`
`

`

`US 2011/028 1579 A1
`
`Nov. 17, 2011
`
`SYSTEMAND METHOD FOR DETECTING
`AND MEASURING UPLINK TRAFFIC IN
`SIGNAL REPEATING SYSTEMS
`
`FIELD OF THE INVENTION
`
`0001. The present invention is directed generally to signal
`repeating systems, such as repeaters or distributed antenna
`systems, for wireless communications, and more particularly
`to a system and method for detecting uplink traffic from
`mobile user equipment within those systems.
`
`BACKGROUND OF THE INVENTION
`
`0002. In existing wireless technologies, signal repeating
`devices. Such as repeaters or distributed antenna systems
`(DAS), are used to extend the coverage of an overall wireless
`system beyond the ranae of traditional base stations. For
`example, an overall wireless communication system may
`consist of a plurality of base transceiver stations (BTS) or
`base stations that communicate with each other and with user
`equipment, such as cellular phones, to provide a defined
`coverage area. In Such coverage areas, there are often Smaller
`geographical areas that have very low signal coverage, as
`provided by one or more of the base stations. For example,
`Such areas of low signal coverage may be within buildings or
`in areas that are otherwise obstructed, such as by terrain
`features or man-made structures. Rather than simply imple
`menting another costly and large base station to provide coV
`erage in Such low signal areas, repeaters and distributed
`antenna systems are often utilized.
`0003) While repeaters and distributed antenna systems
`(herein collectively, “signal repeating systems') may
`adequately extend coverage, it may be desirable to eventually
`install a dedicated BTS in order to increase the amount of
`capacity offered in the area. To that end, it is desirable to be
`able to determine the relative loading and traffic of a signal
`repeating system so that a building owner or other system
`operator is aware of the traffic requirements for that wireless
`environment.
`0004 One method of detecting traffic within a mobile
`network is to utilize the receive signal strength indication
`(RSSI) measurement of the power that is present in a received
`radio signal. The RSSI is a well-known parameter in the
`operation of signal repeating systems. The RSSI-based detec
`tion method for determining traffic within a wireless environ
`ment or network is used extensively in GSM repeaters and
`distributed antenna systems. Usually, the uplink RSSI is uti
`lized to determine the uplink traffic from mobiles that are
`within the coverage range of a signal repeating system. The
`signal repeating system identifies the channels used by the
`adjacent base stations and it then distributes and amplifies the
`signals in order to monitor the equivalent uplink (UL) fre
`quencies. If the RSSI level on a UL channel exceeds a certain
`threshold, the system can detect the UL traffic. The threshold
`level is usually a level above the receiver input noise floor for
`the signal repeating system. The specific delta with respect to
`the noise floor depends upon the acceptable probability of
`having false positive detections, which might be triggered by
`regular thermal noise peaks. In addition to the independent
`measurement of the RSSI levels, the signal repeating system
`can determine the RSSI within a certain timeslot by synchro
`nizing itself with the base station through the detection of the
`downlink (DL) signal. Therefore, for such a gated RSSI mea
`
`Surement, the repeater or distributed antenna system can mea
`Sure UL activity on a timeslot-per-timeslot basis.
`0005. However, while such a methodology works
`adequately for GSM repeaters and distributed antenna sys
`tems, the implementation of Such a traffic detection and mea
`Surement system in a spread spectrum environment, such as
`CDMA or WCDMA, is more difficult. Generally, in a CDMA
`or CDMA network, the mobile devices or other user equip
`ment (UE) devices are driven so that the transmit power is
`controlled in order to be close to or below the noise level of the
`receiving base station. In a typical configuration, the repeater
`or distributed antenna system operating in Such a network
`essentially acts to extend the UL receiver of the base station.
`In that regard the repeater/DAS experiences the same low
`level receive signal from the user equipment devices. That is,
`the receive signal level from those devices is at the noise level,
`or even below the noise level, for the repeater/DAS. As such,
`this makes the use of RSSI-based uplink traffic detection and
`measurement generally unfeasible for Such networks.
`0006. There are other mechanisms for determining the
`uplink traffic within a CDMA system, but those mechanisms
`require the specific spreading codes that are used for the
`various uplink signals received from the mobile UE devices.
`However, those spreading codes are known to the base station
`system, and are not necessarily known by the repeater or
`DAS. Therefore, a system that incorporates uplink traffic
`detection that relies upon correlation with dynamically-as
`signed uplink spreading codes generally will not be a feasible
`alternative for detecting and measuring uplink traffic within a
`repeater or DAS.
`0007 Accordingly, there is a need for providing a traffic
`measurement system for a repeater/DAS that can adequately
`detect and measure the uplink traffic within a spread spectrum
`network, such as a CDMA or WCDMA network or another
`network where the UL signal is at or close to the noise level of
`the system.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`0008 FIG. 1 is a schematic view of a repeater system for
`implementing an embodiment of the present invention.
`0009 FIG. 2 is a schematic diagram of a distributed
`antenna system for implementing an embodiment of the
`present invention.
`0010 FIG. 3 is a more detailed schematic illustration of a
`repeater system for implementing an embodiment of the
`present invention.
`0011
`FIG. 3A is a schematic of another repeater system
`for implementing an embodiment of the present invention.
`0012 FIG. 4 is a more detailed schematic illustration of a
`distributed antenna system implementing an embodiment of
`the present invention.
`0013 FIG. 4A is a schematic of another distributed
`antenna system for implementing an embodiment of the
`present invention.
`0014 FIG. 5 is a graphical illustration of the effect of
`repeater gain variation on the received power of a base station
`with UL power control in operation.
`(0015 FIG. 6 is a graphical illustration of the effect of
`repeater gain variation on the power received at the repeater.
`0016. The accompanying drawings, which are incorpo
`rated in and constitute a part of this specification, illustrate
`
`

`

`US 2011/028 1579 A1
`
`Nov. 17, 2011
`
`embodiments of the invention and, together with a general
`description of the invention given below, serve to explain the
`principles of the invention.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENTS OF THE INVENTION
`0017. The present invention incorporates a system and
`method that utilizes an RSSI-based mechanism to determine
`the presence of uplink (UL) traffic within a CDMA network
`or other network to measure the strength of the detected UL
`traffic. In one aspect of the invention, the gain of a signal
`repeating system, Such as a repeater or DAS, is periodically
`varied in the uplink direction. The uplink received power, or
`RSSI, for the expected uplink channel of the repeating system
`is measured over time. For the purposes of measuring the
`RSSI, a suitable measurement receiver is utilized. The mea
`Surement receiver is tuned to match the center frequency and
`signal bandwidth that is to be measured for the purposes of the
`invention. The measurement receiver may be configured for
`receiving either an analog signal or a digital signal within the
`signal processing uplink path, and will generally be coupled
`in the signal path at a point that precedes the stage providing
`the gain variation. The waveform that is utilized to provide the
`periodic gain variation in the uplink path is then inverted due
`to the inverse relationship between the gain and RSSI values
`and the inverted waveform is then cross-correlated with the
`received UL time-variant RSSI values. When one or more
`peaks are detected associated with Such cross-correlation, the
`level of the peak, or the number of peaks, are analyzed to
`determine the amount of traffic in the system. If no peak is
`detected, then the system determines that there is no UL
`traffic in the repeater. Generally, the correlation process might
`only provide a single peak wherein the peak is higher or
`wider, depending on the amount of traffic handled by the
`repeater.
`0018. In accordance with another aspect of the invention,
`the inventive system takes into account that the base station
`(BTS) may experience an increased amount of traffic, which
`will increase the UL input power to the BTS for the same
`amount of UL traffic in the repeater/DAS cell, which will
`inherently increase the transmit power received (RSSI) at the
`input to the uplink path of the repeater/DAS. But since the
`correlation between the gain variation waveform and the mea
`sured RSSI is sensitive to the dynamic RSSI change caused
`by the mobiles in the repeater cell and less to the relative to the
`gain change assumed Static BTS loading the invention will
`allow the detection of mobile traffic under different BTS
`loading conditions in a similar fashion.
`0019 FIGS. 1 and 2 illustrate exemplary signal repeating
`systems that may incorporate embodiments of the present
`invention. Referring to FIG. 1, a basic wireless communica
`tion system 10, incorporating a signal repeating system 14, is
`shown. System 10 includes a base station (BTS) 12 that
`communicates with a repeater system 14 that has at least one
`donor antenna 16, at least one coverage antenna 18, and
`processing electronics 20 that are coupled between the anten
`nas 16 and 18 to process and amplify the repeated signal. The
`present invention may be used with MIMO systems and com
`munication schemes, and thus, may have multiple donor
`antennas and multiple coverage antennas, as would be under
`stood by a person of ordinary skill in the art. Therefore,
`antennas 52, 58 are reflective of one or more antennas. The
`downlink signals (BTS to mobile device/UE) are indicated by
`direction DL, while the uplink signals (mobile device/UE to
`
`BTS) are indicated by direction UL. Accordingly, downlink
`wireless signals 22 are received from the BTS 12 by the donor
`antenna 16 of the repeater, and are then amplified, processed,
`and repeated through the coverage antenna 18 as downlink
`signals 22a. The downlink signals 22a are received by one or
`more wireless communication devices, such as mobile
`phones or other user equipment (UE) device 24. Similarly, in
`an uplink direction, as indicated by reference numerals 26 and
`26a, the wireless UE devices 24 communicate uplink signals
`26a back to the coverage antenna and the repeated uplink
`signals 26 are then provided back to the BTS 12. Also in the
`system 10 are UE devices 24a that communicate with BTS 12
`directly rather than through a repeater 14. Such devices 24a
`contributed to the overall traffic handled by the BTS 12. As
`will be readily understood by a person of ordinary skill in the
`art, Such signal repeating systems 14 can take many different
`forms and are not limited only to devices conventionally
`called “repeaters'.
`0020 For example, FIG. 2 illustrates a schematic diagram
`for another exemplary signal repeating system that may
`implement the invention. A distributed antenna system (DAS)
`30 may be appropriately coupled to a BTS, such as BTS12 in
`a wired or wireless fashion. The distributed antenna system
`30 might be incorporated into a building environment and
`includes a number of remote antenna units 32 that are distrib
`uted in the environment to provide coverage within a service
`area of the DAS30. In that way, the remote antenna units 32
`service a number of different UE devices 24 operating in the
`environment of the DAS30. Generally, each remote antenna
`unit 32 typically includes at least one antenna 36 and suitable
`electronics 38. As noted above, if the invention is imple
`mented in a MIMO system, multiple antennas 36 might be
`used. Therefore, antennas 36 are reflective of one or more
`antennas. Remote antenna units 32 are coupled to one or more
`master units 40, which combine and process the signals from
`the remote antenna units 32 to interface appropriately with the
`BTS 12. A system controller 42 couples to and controls the
`operation of each of the master units 40 for handling and
`processing the signals 33 associated with the remote antenna
`units 32. Similar to the repeater system 10 illustrated in FIG.
`1, the signals 33 of the remote antenna units 32 are reflective
`of the uplink and downlink signals of the DAS 30 for com
`municating with UE devices 24. Such a DAS 30 may incor
`porate any number of remote antenna units and master units,
`and thus, would not be limited to the illustrated example
`shown in FIG. 2.
`0021. In accordance with one aspect of the invention, peri
`odic gain variation is provided in the repeater or DAS uplink
`path. For example, the gain in the UL path might be varied
`according to a periodic waveform. Ideally, the periodic gain
`variation and waveform is synchronized with the framing
`interval of the spread spectrum network, such as a CDMA
`network, although Such synchronization is not necessary.
`With the periodic gain variation, the UL receive power (UL
`RSSI value) in the selected UL channel is measured over time
`by the signal repeating system. The waveform that is utilized
`to periodically vary the gain in the uplink path is then cross
`correlated with the UL received time-variant RSSI values.
`Based upon Such cross-correlation of those signals, the exist
`ence of one or more peaks is determined. If there is no peak
`detected, then the signal repeating system would provide an
`indication that there is generally no repeater traffic as the
`periodic gain variation would not cause any variation in the
`uplink RSSI values. However, if the periodic gain variation
`
`

`

`US 2011/028 1579 A1
`
`Nov. 17, 2011
`
`causes variations in the uplink RSSI values, then the cross
`correlation performed by the signal repeating system would
`yield one or more signal peaks. Such peaks are an indication
`that if there is uplink traffic from UE devices within the
`coverage area of the signal repeating system. The level of the
`peak and its width as well as the energy in the peak if inte
`grated over the time delay of the cross-correlation may be
`indicative of the amount of traffic within the coverage area of
`the signal repeating system. However, the overall traffic in the
`BTS can affect the peak levels, as discussed below.
`0022. In one embodiment of the invention, the measured
`uplink RSSI values might be averaged according to an aver
`aging scheme over time that reduces fast RSSI value fluctua
`tions without affecting or reducing the correlation peak. The
`present invention works not only with COMA-type signals,
`but also other system signals and network signals that allow
`for the received power at the BTS to be close to the noise floor
`and even below the input noise floor of the BTS. For example,
`OFDM modulated systems such as LTE systems might ben
`efit from the present invention.
`0023. In accordance with one aspect of the present inven
`tion, the periodic gain variation in the signal repeating system
`is performed without significantly affecting the noise figure
`of the signal repeating system. To that end, the gain of the
`system is varied by changing the gain in an amplification
`stage of the repeater or DAS that is not very close to the input
`of the uplink path. That is, a latter gain stage in the uplink path
`is used for the periodic gain variation. To provide for suitable
`cross-correlation in accordance with the present invention, a
`selected periodic waveform is used to periodically vary the
`gain of the UL path of the signal repeating system. Such a
`waveform may be adapted to the specific mobile standard that
`is used within the signal repeating system. To that end, the
`periodic gain variation is controlled so that the size of the gain
`variation and its time period is not faster than the mobile
`standard allows or can handle. For example, CDMA mobile
`devices can handle 800 power control steps of one dB per
`second. As such, in accordance with one feature of the inven
`tion, the implemented periodic UL gain variation does not
`exceed that rate of change when the invention is utilized
`within a CDMA system. As will be appreciated, other sys
`tems will have other gain variation constraints that would be
`implemented in the invention.
`0024. In one embodiment of the invention, the gain varia
`tion is provided by reducing the gain in a periodic fashion in
`the signal repeating system. For the purposes of the invention,
`various different waveforms might be utilized to periodically
`reduce the system gain in the UL path. For example, an
`inverted Sawtooth function with gaps may be used as a pos
`sible periodic gain variation function. The present invention
`provides maximization of the cross-correlation peak between
`the inverted gain variation function and measured UL input
`RSSI. To that end, in one aspect of the invention, the gain
`variation function may be aligned in phase and frequency
`with the mobile standard (e.g. CDMA). In accordance with
`another feature of the invention, the sensitivity of the traffic
`detection may be increased by averaging multiple consecu
`tive (i.e. several consecutive frames) cross-correlation curves.
`The periodic nature of the gain variation allows such averag
`ing of the cross-correlation curves. To that end, the length of
`the data that is measured is ideally an integer multiple of a
`frame length of the particular mobile standard, such as the
`CDMA standard.
`
`0025. The bandwidth and center frequency settings of the
`RSSI measurement receiver will depend on the used channel
`and expected Standard. The used channel and Standard can be
`determined through the detection and decoding of the equiva
`lent DL signal using a decoding receiver. This DL signal
`decoding does not necessarily have to be performed with a
`dedicated receiver as the standard is not expected to change.
`A scanning DL decoding receiver would be sufficient.
`0026. In cases in which the repeater/DAS system pro
`cesses a variety of standards a sub-band architecture will
`allow a different gain variation in time or in amplitude within
`two or more different sub-bands. A sub-band is a section
`within the RF band that represents a subset of the entire
`bandwidth. There can be multiple sub-bands with the RF
`band. Sub-bands might be adjacent to each other or have a
`section between them with no amplification. In the imple
`mentation of the sub-bands a surface acoustic wave filter
`(SAW) might be used to define the sub-band. In a digital
`implementation of the invention, a digital filter such as a FIR
`filter or IIR filter could be used instead to define the sub-band.
`This will allow optimizing the cross-correlation function for
`each standard. For each Sub-band, only one mobile commu
`nication standard is allowed for optimization.
`0027 FIGS. 3,3A, 4, and 4A illustrate detailed schematics
`of possible implementations of the invention. FIGS. 3 and 3A
`illustrate repeater systems. FIGS. 4 and 4A illustrate imple
`mentation within a DAS system, as illustrated in FIG.1. Like
`reference numerals are used for like elements in the various
`Figures.
`0028 Referring to FIG.3, a schematic block diagram of a
`repeater 50 is illustrated. FIG. 3 shows the uplink path (UL)
`62 for the repeater for illustration purposes. It will be readily
`understood that the repeater 50 also incorporates a suitable
`downlink (DL) path 64 that would use some similar compo
`nents as the downlink paths between the BTS 12 and devices
`24. Diplexers 55, 95 are utilized to handle the UL and DL
`paths through the antennas 52, 58. A repeater 50 incorporates
`a receive antenna 52 (or coverage antenna) for processing
`input signals 54 from one or more mobile UE devices 24. The
`input signals 54 represent the input signals from the UE
`devices 24 that are to be repeated. Thus, signals 54 represent
`the UE traffic to be detected in accordance with the invention.
`The repeated transmit signals 56 illustrated in FIG.3 include
`the transmitted signals or signal portions that are directed in
`the uplink to BTS 12 by a coverage antenna 58. Throughout
`the application, the terms 'signal' or 'signals are used inter
`changeably herein to refer to the signal(s) handled by the
`signal repeating system and are not limited to just a single
`signal or plurality of signals.
`0029. For proper signal repeating, repeater 50 includes
`suitable electronics 60 that are operably coupled between the
`antennas 52, 58. Generally, such electronics will include gain
`control circuitry 84 that provides a desired or selected gain G
`in the repeater and processing 72 and correlation 100 circuitry
`to implement the invention.
`0030) Referring to FIG. 1, the repeater circuitry 20 might
`process the signals in the analog domain in accordance with
`aspects of the invention. Alternatively, electronics 20 of the
`repeater might provide the various aspects of the invention in
`the digital domain.
`0031 Turning again to FIG. 3, as noted, that figure sets
`forth a schematic diagram with respect to one embodiment of
`the invention in the form of a repeater device. It will be
`understood by one of ordinary skill in the art that the features
`
`

`

`US 2011/028 1579 A1
`
`Nov. 17, 2011
`
`of the invention might be incorporated in other signal repeat
`ing systems, such as a distributed antenna system, as illus
`trated in FIGS. 2, 4, and 4A. As noted, components are shown
`in an uplink path 62 in the repeater 50. Various similar com
`ponents will exist in the downlink path 64 for handling down
`link traffic between wireless UE devices 24 and a BTS 12 for
`example. Accordingly, various components within the uplink
`path 62 will be described herein in further detail with the
`assumption that Some similar functionality and components
`would be utilized in the downlink path 64 as well, although
`the periodic gain variation of the invention might only be used
`in the uplink path.
`0032 Receive or coverage antenna 52 receives the input
`traffic signals 54 from UE devices 24. Those signals 54 are
`coupled through diplexer 55 to a low noise amplifier (LNA)
`66 for amplifying uplink the RF receive signals from device
`24. A mixer component 68 is fed by an appropriate local
`oscillator (LO) signal and converts the RF receive signal 54 to
`an intermediate frequency (IF) signal at a different IF fre
`quency or a frequency at or near the baseband frequency for
`ease of later processing in the repeater 50. The signal may
`then be filtered by an appropriate filter component or circuitry
`70. In the embodiment illustrated in FIG. 3, the repeater
`circuitry incorporates both analog and digital components.
`Digital signal processing circuitry 72 is implemented for
`providing the filtering and further frequency conversion of the
`signals, as well as for periodically adjusting gain and for
`providing the necessary cross-correlation and signal process
`ing to detect UL traffic in accordance with the invention.
`Appropriately, an A/D converter circuit 74 converts the ana
`log signal to an appropriate digital signal for further digital
`processing. The DSP circuitry 72 might bean FPGA, ASIC,
`digital signal processor or other such element. The DSP cir
`cuitry might include an additional digital mixer circuit 76 fed
`by a suitable numerically-controlled oscillator (NCO) signal
`to provide digital downconversion for ease of further process
`ing. The signal might also be filtered by an appropriate digital
`filter 78. Filter 78 might also change the amplitude of the
`signal. Gain circuitry 80 or amplification circuitry provides
`gain amplification to the repeated signals. Components 80
`and 84 represent Suitable circuitry for periodically adjusting
`or varying the gain within repeater 50 for the invention. The
`signals might then be digitally upconverted by appropriate
`digital upconversion circuitry 86 fed by a transmit NCO. The
`signals may then be converted back to analog signals by D/A
`circuitry 88.
`0033. Various of the gain and filtering aspects illustrated in
`the digital circuitry 72 of FIG.3 might also be implemented in
`an analog fashion. FIG. 3A shows an analog repeater for
`implementing the present invention. Like reference numerals
`are utilized for those components similar between FIGS. 3
`and 3A. Therein, gain stages 81, 82, and 83 might be imple
`mented in an analog fashion with analog filters, such as SAW
`filters 85 and 87 providing the desired filtering. In the
`embodiment illustrated in FIG. 3A, the correlation circuitry
`100 might still be implemented by appropriate digital signal
`processing (DSP) circuitry. Also, certain portions of the gain
`control circuitry 84 might be implemented digitally.
`0034. The analog signals, such as at analog IF, are further
`upconverted with mixer circuitry 90 fed by an appropriate
`transmit LO to an appropriate RF signal. The RF signal is
`filtered by filter circuitry 92, and then fed to an RF power
`amplifier 94 before being transmitted as a repeated signal 56
`through the transmit or donorantenna 58. The various mixing
`
`and filter elements are typical of a repeater. There can be more
`or fewer mixing elements than illustrated in the examples and
`still implement a functional repeater.
`0035. In the embodiments illustrated in FIGS. 3, 3A, the
`noted cross-correlation functionality is provided by suitable
`processing circuitry and correlation circuitry 100. Such as
`within the digital signal processing (DSP) circuitry 72, or
`otherwise implement digitally, as in FIG. 3A. The cross
`correlations to determine UL traffic are performed by captur
`ing samples 102 of the signals in the UL path at the UL input
`and providing RSSI values reflective of the receive power of
`the signals at the UL input for the cross-correlation.
`0036. Accordingly, as illustrated in FIGS. 3-4A, a suitable
`measurement receiver 101 is utilized to capture signals in the
`uplink path and to provide RSSI values reflective of the
`received power of such signals. The bandwidth and center
`frequency of the RSSI measurement receiver 101 are turned
`and configured to detect the RF signal of interest. Therefore,
`the bandwidth and center frequency would depend on the
`used channel and the expected Standard for the signal. The
`used channel and standard may be determined through the
`detection decoding of the equivalent downlink signal Such as
`by using a decoding receiver. The downlink signal decoding
`would not necessarily have to be performed with a dedicated
`receiver, as the signal standard would not be expected to
`change. A Scanning downlink decoding receiver would be
`sufficient. One example of such decoding receiver 105 is
`illustrated in the downlink path 64 of the figures. As illus
`trated in FIG. 3, the capture point for the signal is illustrated
`close to the coverage antenna wherein an appropriate coupler
`107 captures the signal that is then directed to the measure
`ment receiver 101. For the purposes of the invention, the
`capture point for such data can be anywhere between the
`coverage antenna and the amplification stage that performs
`the periodic gain changes. Accordingly, as illustrated in FIG.
`3A, the capture point is indicated following filter 70. Accord
`ingly, the capture point can be directed at various different
`points along the uplink path, with the condition that it is
`before the components or stages that perform the periodic
`gain changes. The measurement receiver 101 can either be
`implemented as analog circuitry with an A/D converter to
`provide the digitized measured RSSI to the correlation cir
`cuitry or as digital circuitry on a repeater system with digital
`signal processing where the input to the measurement
`receiver is captured at a point after the A/D converter 74.
`0037. In the illustrated embodiments, the correlation cir
`cuitry 100 coupled to the measurement receiver 101 samples
`the RSSI values for repeated signal 102 via suitable connec
`tions and is also coupled to obtain information regarding the
`waveform 104 used in the repeater path to periodically vary
`the UL gain. It will be understood by a person of ordinary skill
`in the art that the various different functionalities discussed
`within the correlation circuitry 100 digital signal processing
`circuitry 72 might be implemented in a number of different
`ways to achieve the functionality of the invention. Accord
`ingly, the illustrations of FIGS. 3-4A are not limiting with
`respect to the DSP circuitry. That is, the specific details
`regarding how the various components are utilized and
`arranged within DSP circuitry 72, or the analog and digital
`circuitry 72a, and the overall repeater or DAS circuitry of
`FIGS. 3-4A are illustrative, and not meant to be limiting.
`0038 FIGS. 4 and 4A illustrate implementation of the
`invention within a distributed antenna system, particularly
`within a remote antenna unit component 38. In the embodi
`
`

`

`US 2011/028 1579 A1
`
`Nov. 17, 2011
`
`ment of FIG. 4, digital circuitry is utilized for implementing
`the gain and gain control within the system. Furthermore, for
`putting signals in the necessary form for serial transmission,
`Such as back to a master unit, the digital signal circuitry 72 of
`FIG. 4 utilizes the necessary signal processing element 78A
`and conversion circuitry 79 for providing the necessary par
`allel-to-s