Patent Description:
Telecommunications operators use telecommunication systems to provide signal coverage to coverage zones in which wireless devices are located. A distributed antenna system ("DAS") may be used to extend the coverage of such telecommunication systems. Such distributed antenna systems include signal paths between base stations or other signal sources operated by telecommunication operators and remote antenna units positioned in one or more geographical coverage areas.

In some implementations, a DAS may be configured for time division duplexing ("TDD") operations in which downlink and uplink signals are respectively transmitted and received using at least some common frequencies or common portions of a signal path. A DAS configured for TDD operations may include one or more switches for isolating downlink signal paths from uplink signal paths.

In some cases, multiple telecommunication operators may use the same DAS for extending the coverage of their respective telecommunication systems. An entity responsible for configuring or otherwise operating the DAS may be independent of the telecommunication operators that use the DAS. The entity being independent of the telecommunication operators may present disadvantages. For example, it may be difficult or infeasible to configure the switching operations of the DAS in accordance with the TDD configuration used by the telecommunication operators.

Systems and methods for optimizing TDD switching operations for a DAS are desirable. Relevant background art is disclosed in <CIT> and <CIT>.

Further aspects are disclosed in the dependent claims.

Certain aspects and examples are directed to switching sub-systems for a distributed antenna system ("DAS") configured for time division duplexing ("TDD") operations. For example, the DAS can use a switching sub-system to switch between an uplink mode for communicating TDD signals in an uplink direction and a downlink mode for communicating TDD signals in a downlink direction. The switching sub-system can automatically determine switching times for the DAS based on determining whether a signal level for downlink signals exceeds a threshold level. One or more switches of the switching sub-system can switch a remote antenna unit of the DAS to the downlink mode by selectively connecting one or more components of the downlink path in the remote antenna unit and disconnecting one or more components of a corresponding uplink path in the remote antenna unit. One or more switches of the switching sub-system can switch a remote antenna unit of the DAS to the uplink mode by selectively connecting one or more components of the uplink path in the remote antenna unit and disconnecting one or more components of a corresponding downlink path in the remote antenna unit. In some aspects, the switching sub-system can switch a remote antenna unit of the DAS to a standby mode or other mode by disconnecting one or more components of the uplink path and the downlink path in the remote antenna unit of the DAS.

In accordance with some aspects, the switching sub-system can include a switching control module that detects the downlink/uplink ratio of base stations in communication with the DAS. The switching control module can determine an initial clock setting based on the downlink/uplink ratio. The initial clock setting can determine the timing for sending command signals to the switches of the switching sub-system that instruct the switches to switch the DAS between an uplink mode and a downlink mode.

The switching control module can also optimize a clock setting that controls switching times for the switches. Optimizing the switching times can maximize or otherwise improve data throughput via the DAS. The switching control module can optimize the clock setting by determining start or end times for respective downlink subframes transmitted via the downlink path. The switching control module can determine the start or end times based on when signal power measurements for the downlink path exceed a threshold signal power. The switching control module can statistically determine a switching time adjustment based on a set of switching time differentials between the initial clock setting and the determined start or end times for the downlink subframes. For example, the switching time adjustment may be the statistical mean of the set of switching time differentials. The switching control module can update the clock setting based on the switching time adjustment.

The switching control module can be used to automatically determine a TDD configuration for one or more telecommunication operators using the DAS. Automatically determining the TDD configuration can reduce or eliminate the need for manual configuration of the DAS with respect to each telecommunication operator. Reducing or eliminating the need for manual configuration of the DAS can reduce or avoid problems resulting from missing information with respect to the configuration settings of different telecommunication operators. The switching control module can also compensate for uplink or downlink pulsing variation or other deficiencies components of the DAS in the uplink or downlink direction, such as a jitter or clock frequency drift experienced by one or more reference clock devices in the DAS.

Detailed descriptions of certain examples are discussed below. These illustrative examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional aspects and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative examples but, like the illustrative examples, should not be used to limit the present disclosure.

<FIG> is a block diagram depicting an example of DAS <NUM> having a TDD switching sub-system <NUM> according to an aspect of the present disclosure. The DAS <NUM> can include a master unit <NUM> in communication with remote antenna units 104a, 104b and with base stations 101a, 101b. In some aspects, different base stations can communicate signals associated with different telecommunication operators. The DAS <NUM> can be positioned in a geographical area (e.g., a stadium, an office building, etc.) to extend wireless communication coverage of the base stations 101a, 101b into geographical coverage areas 108a, 108b.

The DAS <NUM> or other telecommunication system can include downlink paths for transporting downlink signals from the base stations 101a, 101b to one or more of the remote antenna units 104a, 104b. The DAS <NUM> can receive downlink signals from the base stations 101a, 101b via a wired or wireless communication medium. Downlink signals can include signals provided from the base stations 101a, 101b and transmitted by the remote antenna units 104a, 104b in the coverage areas 108a, 108b. A non-limiting example of a remote antenna unit is a universal access point.

The DAS <NUM> or other telecommunication system can also include uplink paths for transporting uplink signals from one or more of the remote antenna units 104a, 104b to one of more of the base stations or repeaters. Uplink signals are signals at frequencies in an uplink frequency band that are recovered or otherwise received by one or more of the remote antenna units 104a, 104b from communication devices in the coverage areas 108a, 108b.

The master unit <NUM> can communicate signals between the base stations 101a, 101b and the remote antenna units 104a, 104b. An example of a master unit <NUM> is a wireless conversion station. The master unit <NUM> and remote antenna unit(s) 104a, 104b can communicate via any suitable communication medium. The communication medium can be any suitable medium for providing a serial communication link between the master unit <NUM> and the remote antenna unit 104a, 104b. In some aspects, the communication medium can be an optical fiber. In other aspects, the communication medium can include copper cables, microwave links, etc. The master unit <NUM> and remote antenna units 104a, 104b can include analog-to-digital and digital-to-analog converters for digital communication over a serial link.

For illustrative purposes, <FIG> depicts a single master unit <NUM> in communication with two base stations 101a, 101b and two remote antenna units 104a, 104b. However, a distributed antenna system <NUM> can include any number of master units and any number of remote antenna units for communicating signals between any number of base stations or other signal sources and any number of coverage areas.

A DAS <NUM> can include other devices in addition to master units and remote antenna units. For example, in some aspects, the DAS <NUM> may include a base station router or other interface device that receives signals from base stations 101a, 101b and provides the signals to the master unit <NUM>. In some aspects, the DAS <NUM> may include one or more extension units that communicate signals between the master unit <NUM> and the remote antenna units 104a, 104b.

The DAS <NUM> can be configured for TDD operations that support multiple operators communicating signals via the DAS <NUM>. For example, the DAS <NUM> can switch between an uplink mode for communicating TDD signals in an uplink direction and a downlink mode for communicating TDD signals in a downlink direction.

The remote antenna units 104a, 104b can respectively include TDD switching sub-systems 110a, 110b used to connect components of the downlink path in response to detecting downlink signals having signal levels exceeding a threshold level. The TDD switching sub-systems 110a, 110b can analyze downlink signals to determine if signal levels for the downlink signals exceed specified threshold levels. Each of the TDD switching sub-systems 110a, 110b can include switches that switch a respective one of the remote antenna units 104a, 104b to the downlink mode by selectively connecting one or more components of the downlink path in the remote antenna unit and disconnecting one or more components of a corresponding uplink path in the remote antenna unit.

<FIG> is a block diagram depicting an example of a remote antenna unit <NUM> with a TDD switching sub-system <NUM> according to an aspect of the present disclosure. In a downlink direction, downlink signals received from the master unit <NUM> via an interface <NUM> can traverse a downlink path <NUM> and can be coupled to an antenna <NUM> via an interface <NUM> for transmission to communication devices in a coverage area. In an uplink direction, uplink signals received by the antenna <NUM> can be coupled to an uplink path <NUM> via the interface <NUM> and can traverse the uplink path <NUM> for transmission to the master unit <NUM> via the interface <NUM>.

The TDD switching sub-system <NUM> can include one or more components of the downlink path <NUM> and the uplink path <NUM>. For example, <FIG> depicts a TDD switching sub-system <NUM> that includes a switching control module <NUM>, switches <NUM>, <NUM> in the downlink path <NUM>, and a switch <NUM> in the uplink path <NUM>. The switching control module <NUM> can be coupled to the downlink path <NUM> in any suitable manner. The switch <NUM> can be positioned in the downlink path <NUM> between the interface <NUM> and a power amplifier <NUM>. The switch <NUM> can be positioned in the downlink path <NUM> between the power amplifier <NUM> and the interface <NUM>. The switch <NUM> can be positioned in the uplink path <NUM> between the interface <NUM> and a low noise amplifier <NUM>.

The switching control module <NUM> can control the operation of the switches <NUM>, <NUM>, <NUM> to selectively allow communication of downlink signals via the downlink path <NUM> or uplink signals via the uplink path <NUM>. The switching control module <NUM> can control the switches <NUM>, <NUM>, <NUM> by sending switching signals to the switches <NUM>, <NUM>, <NUM> or devices actuating the switches <NUM>, <NUM>, <NUM> (not depicted in <FIG>). The switching control module <NUM> can be communicatively coupled to the switches <NUM>, <NUM>, <NUM> or devices actuating the switches <NUM>, <NUM>, <NUM> via any suitable mechanism. For example, the remote antenna unit <NUM> may include a printed circuit board or other communication bus via which switching signals from the switching control module <NUM> can provided to the switches <NUM>, <NUM>, <NUM> or devices actuating the switches <NUM>, <NUM>, <NUM>. For downlink transmission, the switching control module <NUM> can provide switching signals that cause the switches <NUM>, <NUM> to be closed and the switch <NUM> to be opened, thereby completing the downlink path <NUM> between the interfaces <NUM>, <NUM> and opening the uplink path <NUM> between the interfaces <NUM>, <NUM>. For uplink transmission, the switching control module <NUM> can provide switching signals that cause the switches <NUM>, <NUM> to be opened and the switch <NUM> to be closed, thereby opening the downlink path <NUM> between the interfaces <NUM>, <NUM> and completing the uplink path <NUM> between the interfaces <NUM>, <NUM>. Any suitable switches <NUM>, <NUM>, <NUM> can be used. Non-limiting example of suitable switches <NUM>, <NUM>, <NUM> include RF switches, RF attenuators, digital attenuators in a digital signal path, digital switches interrupting a digital signal in a digital signal path, etc..

Although <FIG> depicts the switching control module <NUM> as a separate module coupled to the downlink path <NUM> for illustrative purposes, other implementations are possible. In some aspects, the downlink path <NUM> may include one or more digital signal processing components, such as a processing device (e.g., an application-specific integrated circuit ("ASIC"), a field-programmable gate array ("FPGA"), etc.). The functions of the switching control module <NUM> can be performed by the processing device using digital downlink signals in the downlink path <NUM> between the interfaces <NUM>, <NUM>.

The switching control module <NUM> can provide switching signals based on a detection of downlink signals in the downlink path <NUM>, an internal clock, or a combination thereof. For example, <FIG> is a block diagram depicting an example of the switching control module <NUM> according to an aspect of the present disclosure. The switching control module <NUM> can detect the downlink/uplink ratio of the base stations 101a, 101b or other signals sources. The switching control module <NUM> can determine an initial clock setting for the TDD switching sub-system based on the downlink/uplink ratio. The initial clock setting can determine the timing of sending switching signals to the switches <NUM>, <NUM>, <NUM>. The switching control module <NUM> can optimize switching times for the switches <NUM>, <NUM>, <NUM>. Optimizing the switching times can maximize or otherwise improve data throughput via the DAS <NUM>.

The switching control module <NUM> can include a measurement receiver <NUM>, a comparator <NUM>, and a processor <NUM> communicatively coupled to a memory <NUM>.

The measurement receiver <NUM> can include any suitable device for measuring a signal power level in the downlink path <NUM>. A non-limiting example of a measurement receiver <NUM> is a power detector. For example, the measurement receiver can be a received signal strength indicator (RSSI) detector or the like. The measurement receiver <NUM> can be coupled to the downlink path <NUM> in any suitable manner, such as (but not limited to) a directional coupler.

The comparator <NUM> can include a first input coupled to an output of the measurement receiver <NUM> and a second input coupled to processor <NUM>. The measurement receiver <NUM> can provide a voltage or current representative of a signal power measurement for the downlink path <NUM> to the first input of the comparator <NUM>. The processor <NUM> can provide a voltage or current representative of a threshold signal power to the second input of the comparator <NUM>. The comparator <NUM> can compare the representative voltages or currents for the downlink signal power measurement and the threshold signal power. The comparator <NUM> can output a voltage or current representative of whether the downlink signal power measurement exceeds the threshold signal power. The threshold signal power can be modified by modifying the voltage or current provided by the processor <NUM>. In the example embodiment shown in <FIG>, the threshold signal power provided to the comparator <NUM> is controlled by the processor <NUM>. It should be understood that the threshold signal power can be provided directly by the processor <NUM> or the processor <NUM> can be configured to control a separate reference source device or circuit to provide the threshold signal power.

The processor <NUM> can receive the voltage or current representative of whether the downlink signal power measurement exceeds the threshold signal power. The processor <NUM> can control switching operations of the TDD switching sub-system <NUM> based on the comparison of the downlink signal power measurement and the threshold signal power by executing a switching control engine <NUM> or other executable instructions stored to the memory <NUM>, as described in further detail below. The processor <NUM> can control the switching operations by generating switching signals that are provided to the switches <NUM>, <NUM>, <NUM> or the devices used for actuating the switches <NUM>, <NUM>, <NUM>.

Although <FIG> depicts a switching control module <NUM> including a comparator <NUM> for outputting a signal indicative of whether the downlink signal power exceeds a threshold signal power, other implementations are possible. For example, in some aspects, the comparator <NUM> and the reference source <NUM> can be omitted, and the processor <NUM> can communicate with the measurement receiver <NUM> to obtain data describing signal power levels in the downlink path <NUM> and directly compare the output from the measurement receiver <NUM> to the threshold signal power. For example, the processor <NUM> can compare the data obtained from the measurement receiver <NUM> with data stored in the memory <NUM> that describes the threshold signal power, and the threshold signal power can be modified by providing updated data describing the threshold signal power to the processor <NUM> for storage in the memory <NUM>. In such embodiments, the processor <NUM> produces the signal indicative of whether the downlink signal power exceeds a threshold signal power. In one non-limiting example the measurement receiver <NUM> can have an analog output electrically connected to the processor <NUM>. The measurement receiver <NUM> can provide a voltage or a current to the processor <NUM> via the analog output. The voltage or current can be equivalent to or otherwise indicative of the measured power level in the downlink path <NUM>. In another non-limiting example, the measurement receiver <NUM> can provide a digital output signal to the processor <NUM> that represents the measured power level in the downlink path <NUM>. In additional or alternative aspects, the measurement receiver <NUM> can include a digital input that is coupled to the downlink path <NUM>.

The processor <NUM> can include any device or group of devices suitable for accessing and executing executable instructions stored in the memory <NUM>. Non-limiting examples of the processor <NUM> include a microprocessor, an ASIC, a FPGA, or other suitable processing device. The processor <NUM> may include one processor or any number of processors. The memory <NUM> may be any non-transitory computer-readable medium capable of tangibly embodying executable instructions and can include electronic, magnetic, or optical devices. Examples of memory <NUM> include random access memory ("RAM"), read-only memory ("ROM"), magnetic disk, an ASIC, a configured processor, or other storage device. Instructions can be stored in memory <NUM> as executable code. The instructions can include processor-specific instructions generated by a compiler and/or an interpreter from code written in any suitable computer-programming language, such as C, C++, C#, Visual Basic, Java, Python, Perl, JavaScript, and ActionScript.

At the time of installation, synchronization must be established prior to operation. A primary concern for establishing synchronization relates to the accurate detection of the entire downlink signal. Since the processor <NUM> uses the determination of whether the measured signal power exceeds the threshold signal when determining when to switch the switches <NUM>, <NUM>, <NUM>, the threshold signal power input to the comparator <NUM> or used directly by the processor <NUM> is critical for proper synchronization for communication between the base station and user equipment for the TDD system. Typically, this threshold signal power is calibrated in the factory during production. However, the specific characteristics of the entire system are not known until installation of the system that includes the switching control module <NUM>. For example, the particular characteristics (for example, signal power) of the downlink signal from the base station will be affected by other components of the system. It is likely that the factory calibration of the threshold signal power is not optimal to ensure synchronization in the field.

A particularly challenging situation for establishing synchronization occurs when portions of the downlink signal have reduced signal power compared to other portions of the downlink signal. A particular example of this occurs with Long-Term Evolution (LTE) TDD communication. <FIG> is a graph of different LTE TDD frame configurations and <FIG> illustrates the first two subframes of each of the LTE TDD frame configurations. As shown in <FIG>, when switching from a downlink subframe to an uplink subframe, there is a Special Sub Frame (SSF) in between to facilitate the switch. The SSF includes the Downlink Pilot Time Slot (DwPTS), a Guard Period (GP), and the Uplink Pilot Time Slot (UpPTS) and also has different configurations for the subframe. The DwPTS is part of the downlink signal and must be detected using the threshold signal power for proper synchronization.

As shown in <FIG>, the power level of the downlink signal at the end of the downlink subframe can be significantly lower than the power level of the downlink signal at the beginning of the downlink subframe. In the example shown in <FIG>, the LTE signal contains <NUM> resource blocks. Slot <NUM> and slot <NUM> of the LTE TDD signal in <FIG> include the Physical Broadcast Channel (PBCH) and the Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS), which are placed in six resource blocks. In other words, the power level of the symbols for the PBCH, PSS, and SSS is about <NUM>% of the power level for the LTE TDD downlink signal. This means that the power level of the symbols for the PBCH, PSS, and SSS is about <NUM> dB lower than in symbols with all occupied resource blocks.

The effect of the lower power level for the PBCH, PSS, and SSS is that the comparator <NUM>, and ultimately the processor <NUM>, may miss these signal parts if the threshold signal power is not appropriately set. For example, this is shown in contrasting <FIG> and <FIG>, which are example graphs of a simplified LTE TDD signal <NUM> and a signal <NUM> output from a comparator of a switching control module of the TDD switching sub-system. In <FIG>, the calibrated threshold signal power (THcal) is low enough to determine the actual downlink signal time (t<NUM>) as none of the peaks of the downlink signal are missed. In <FIG>, the threshold signal power (THcal) is too high to detect the downlink signal at the end of the DwPTS. In order to avoid missing these signal parts, the TDD switching sub-system dynamically adjusts the threshold signal power during installation in an offline process as described below with respect to <FIG>.

<FIG> is a flow chart of an example method for determining a threshold signal power for the of the switching control module of the TDD switching sub-system according to an aspect of the present disclosure. The embodiment of method <NUM> shown in <FIG> is described here as being implemented using the switching control module of the TDD switching sub-system <NUM> of <FIG>, though it is to be understood that other embodiments can be implemented in other ways.

The DAS <NUM> is set to an offline mode for performing the method <NUM>. For example, the DAS <NUM> may be automatically set to an initialization mode upon entering operation. An initialization or other offline mode can be used to set one or more system parameters of the DAS <NUM> used for TDD operation. In an offline mode, the switching control module <NUM> may perform one or more configuration operations based on signal power measurements in the downlink path <NUM> without controlling the switches <NUM>, <NUM>, <NUM>. For example, in an offline mode, the switches <NUM>, <NUM>, <NUM> may be set to an open position such the DAS <NUM> does not communicate signals between the base stations 101a, 101b and the coverage areas 108a, 108b. Thus, no uplink signals are communicated during the offline mode because the user equipment in the coverage areas 108a, 108b cannot connect to the base stations 101a, 101b.

Method <NUM> includes setting a threshold signal power to a first value (block <NUM>). As discussed above with respect to <FIG>, the threshold signal power can be provided as an input to the comparator <NUM> or can be used directly by the processor <NUM>. In exemplary embodiments, the first value of the threshold signal power is set to be a maximum value usable for the DAS. For example, for a LTE TDD signal, the maximum value of the threshold signal power (THmax) can correspond to a value that is just below the lowest power level of the high signals of the downlink signal in a downlink signal only subframe. This is shown in <FIG>, which are example graphs of a simplified LTE TDD signal <NUM> and an example signal <NUM> output from a comparator of a switching control module of the TDD switching sub-system. In other embodiments, the first value for the threshold signal power can be other values, such as, for example, the factory calibrated threshold signal power.

Method <NUM> further includes determining the downlink signal time using the first value of the threshold signal power (block <NUM>). In exemplary embodiments, the determined downlink signal time corresponds to the time elapsed from when the downlink signal is first detected (shown as <NUM>) to when the downlink is no longer detected (shown as <NUM>). As discussed above with respect to <FIG>, the downlink signal is first detected when the downlink signal power of the signal from the base station, which can provided to the comparator <NUM> or directly to the processor <NUM>, exceeds the threshold signal power. In <FIG>, the threshold signal power (THmax) is too high to detect the downlink signal in the DwPTS, so the determined downlink signal time (t<NUM>) is shorter than the actual downlink signal time (t<NUM>).

Method <NUM> further includes adjusting the threshold signal power to a reduced value (block <NUM>). In exemplary embodiments, the threshold signal power is reduced by a predetermined fixed amount. For example, the threshold signal power can be reduced in <NUM> dB increments.

Method <NUM> further includes determining the downlink signal time using the reduced value of the threshold signal power (block <NUM>). In exemplary embodiments, the downlink signal time using the reduced value of the threshold signal power is determined in a similar manner to that described above with respect to block <NUM>. In <FIG>, the reduced threshold signal power (THx') is low enough to detect one of the peaks in the DwPTS, but not all of the peaks. Therefore, the downlink signal time (tx') determined using the reduced threshold signal power (THx') is also shorter than the actual downlink signal time (t<NUM>).

Method <NUM> further includes determining a difference between the measured downlink signal times determined using the different values of the threshold signal power (block <NUM>). In particular, for the first instance of the determination, the difference between the measured downlink time determined using the first value (shown as t<NUM>) of the threshold signal power and the measured downlink signal time determined using the reduced value of the threshold signal power (shown as tx') is determined.

Method <NUM> further includes determining whether the determined difference exceeds a threshold time (block <NUM>). The threshold time is a predetermined, fixed value. If a determined downlink signal time is not correct, it can be assumed that at least one symbol was cut off. In other words, the determined downlink signal time is not correct if another downlink signal time was measured with a different offset time of more than one symbol, which is approximately <NUM> for LTE. Therefore, in exemplary embodiments, the threshold time is selected based on the duration of one symbol. In particular, the threshold time is selected to be less than the duration of one symbol by a desired offset. In the context of LTE, one symbol has a duration of approximately <NUM>, so the threshold time can be selected to be less than <NUM>. For example, the threshold time is set at approximately <NUM> for LTE signals.

When the determined difference exceeds the threshold time, method <NUM> proceeds with adjusting the threshold signal power to a further reduced value (block <NUM>) and determining the downlink time using the further reduced value of the threshold signal power (block <NUM>). Method <NUM> proceeds with determining the difference between the measured downlink signal times determined using the different values of the threshold signal power (block <NUM>) and determining whether the difference exceeds the time threshold (<NUM>). The difference is determined for each iteration of the method steps and the two most recent measured downlink signal times are compared. The sequence can be repeated sequentially until the difference between the measured downlink signal times does not exceed the threshold.

When the determined difference does not exceed the threshold time, method <NUM> proceeds with determining whether the downlink signal time determined using the reduced value is valid (block <NUM>). In exemplary embodiments, the determination is made by comparing the downlink signal time determined using the reduced value with known valid times for the system. TDD frame configurations have particular timing for downlink and uplink subframes and different downlink/uplink ratios for different TDD configurations. For LTE TDD signals, there is also particular timing for different configurations of the SSF for the DwPTS, GP, and UpPTS. Since the DwPTS is part of the downlink signal, the valid downlink signal times used for comparison include the total time for the downlink subframes and the DwPTS. In exemplary embodiments, the switching control engine <NUM> can access data describing the timing and different downlink/uplink ratios for different TDD configurations. In some aspects, the switching control engine <NUM> can select a TDD configuration based on a standardized downlink/uplink ratio in a telecommunication standard, such as a 3rd Generation Partnership Project ("3GPP") specification. Selecting the TDD configuration based on a standardized downlink/uplink ratio in a telecommunication standard can minimize or otherwise reduce errors with respect to incorrect switching intervals. If the downlink signal time determined using the reduced value matches a valid downlink time, then it is validated.

When the downlink signal time determined using the reduced value is not valid, method <NUM> proceeds with adjusting the threshold signal power to a further reduced value (block <NUM>) and determining the downlink time using the further reduced value of the threshold signal power (block <NUM>) similar to when the determined difference exceeds the threshold time as discussed above.

When the downlink signal time determined using the reduced value is valid, method <NUM> proceeds with setting the threshold signal power value for use during online operation of the switching control module (block <NUM>). In exemplary embodiments, the threshold signal power is set at the reduced value used during the most recent iteration of method <NUM> (for example, the value used in block <NUM>). In some embodiments, setting the threshold signal power includes reducing the threshold signal power by a fixed amount from the value used during the most recent iteration of method <NUM>. Such embodiments provide a buffer for instances where the downlink signal power is reduced over time.

A certain level of isolation between the downlink signal power and the uplink signal power should be maintained for proper operation of a TDD switching sub-system. Since the processor <NUM> uses the determination of whether the measured signal power exceeds the threshold signal when determining when to switch the switches <NUM>, <NUM>, <NUM>, there is also a minimum level for the threshold signal power (THmin), which corresponds to a level that is above the power level of the peaks of the uplink signals.

While method <NUM> has been described above with respect to setting the threshold signal power to a first value and successively reducing the threshold signal power until an optimal threshold signal power is identified, it should be understood that alternative methods can be implemented in similar ways. For example, in some embodiments, the first value of the threshold signal power can correspond to the minimum signal power necessary for isolation between the downlink and the uplink paths and the threshold signal power can be successively increased until an optimal threshold signal power is identified. In such embodiments, the method would continue until there was a reduction in the downlink signal time that exceeded a threshold similar to the threshold described above. In some aspects, optimal threshold signal power would provide additional isolation between the downlink and uplink signals while also detecting the entire downlink signal. In such aspects, it is assumed that the isolation can be increased. However, in certain implementations, it may not be possible to increase isolation in this manner and also detect the entire downlink signal.

Method <NUM> provides a more accurate determination of the threshold signal power compared to the calibrated threshold signal power based on estimation in the factory setting. In particular, the threshold signal power is calibrated to ensure detection of all components of the downlink signal for synchronizing the TDD switching sub-system with the TDD signals provided by the base stations.

Once the threshold signal power is set using the offline mode, the DAS <NUM> is switched to an online mode where signals are transmitted between the base stations 101a, 101b and user equipment in the coverage areas 108a, 108b. In operation, the base stations 101a, 101b provide downlink signals to a downlink path <NUM> and the measurement receiver <NUM> measures the power of the signals on the downlink path <NUM>. The signal power in the downlink path <NUM> exceeding the threshold power can indicate that a downlink frame is being transmitted via the downlink path <NUM>. The signal power in the downlink path <NUM> being less than or equal to the threshold power can indicate that a downlink frame is not being transmitted via the downlink path <NUM> and that an uplink frame is being transmitted via the uplink path <NUM>. In operation, there may be slight discrepancies between the determined downlink signal time and the timing of the downlink signal provided by the base stations 101a, 101b. In some aspects, the discrepancies could be a result of some SSF configurations having the last portion of the DwPTS used for data channels only, which do not include synchronization signals. Thus, the duration of the downlink signal can be varied due to adding throughput to the downlink, which includes extending the duration with respect to the data load.

<FIG> is a flow chart of an example method <NUM> for operating the switching control module of the TDD switching sub-system according to an aspect of the present disclosure. The embodiment of method <NUM> shown in <FIG> is described here as being implemented using the switching control module of the TDD switching sub-system <NUM> of <FIG>, though it is to be understood that other embodiments can be implemented in other ways.

Method <NUM> optionally includes detecting a start time of the downlink signal (block <NUM>). For example, the switching control engine <NUM> can receive or otherwise access data describing power measurements by the measurement receiver <NUM>. The switching control engine <NUM> can detect the start time for a respective downlink signal based on a signal indicative of the signal power in the downlink path <NUM> exceeding the threshold signal power. Such a signal can be provided by a comparator <NUM> or directly from the processor <NUM> as discussed above.

Method <NUM> proceeds with determining whether a predetermined time window of an expected transition from a downlink signal to an uplink signal is reached (<NUM>). In exemplary embodiments, the predetermined time window is selected using an initial clock setting for the switching control module <NUM> based on the offline mode described above with respect to <FIG>. For example, the determined downlink signal time identified using the set threshold signal power can be used for the initial clock setting. The start of the time window can correspond to a fixed period of time before the expected switching time based on the initial clock setting. The fixed period of time before the expected switching time is sufficient so the final transition from high to low when the downlink signal ends is detected. For example, the start of the time window can be approximately <NUM> prior to the expected switching time.

Essentially, the time window can be used to determine when the processor <NUM> begins looking for a transition from the downlink signal to the uplink signal. In exemplary embodiments, the processor <NUM> operation is interrupted until the time window is reached. In other words, the processor <NUM> does not listen to the output of the comparator <NUM> or output of the measurement receiver <NUM> until the time window is reached. By using the interrupt, transitions across the threshold signal power during the downlink subframe or uplink subframe (for example, extraneous power spikes when user equipment is close to the antenna) do not trigger an incorrect, early switch from the downlink to the uplink.

When the predetermined time window of an expected transition from a downlink signal to an uplink signal is reached, method <NUM> proceeds with monitoring a signal indicative of whether the power of the downlink signal on the downlink path exceeds a threshold (block <NUM>). In exemplary embodiments, the power of the downlink signal is measured using a measurement receiver, such as measurement receiver <NUM>, and the measured power signal is provided to a comparator, such as comparator <NUM>. The comparator determines whether the measured power of the downlink signal exceeds the threshold signal power determined using the offline mode and outputs the signal indicative when the measured power of the downlink signal exceeds the threshold signal power. In other embodiments, the power of the downlink signal is provided directly to the processor <NUM> from the measurement receiver <NUM>. In such embodiments, the processor determines whether the measured power of the downlink signal exceeds the threshold signal power determined using the offline mode and generates the signal indicative when the measured power of the downlink signal exceeds the threshold signal power.

When the measured power of the downlink signal on the downlink path exceeds the threshold signal power (for example, when a signal is received from the comparator), method <NUM> continues to monitor the signal indicative of whether the power of the downlink signal on the downlink path exceeds a threshold.

Since there may be gaps in the downlink signal, once the measured power of the downlink signal on the downlink path does not exceed the threshold signal power (for example, when a signal is not received from the comparator), method <NUM> proceeds with determining whether a filter time period has passed since the measured power of the downlink signal did not exceed the threshold signal power (<NUM>). In other words, method <NUM> waits for the filter time period to ensure that the end of the downlink signal has been detected rather than a gap in the downlink signal. In exemplary embodiments, the filter time period is a fixed, predetermined amount of time and is selected based on the duration of one symbol. In some embodiments, the filter time period is selected to be greater than the duration of one symbol by a desired offset. In the context of LTE, one symbol has a duration of approximately <NUM>, so the filter time period can be selected to be greater than <NUM>. For example, the filter time period can be set at approximately <NUM> for LTE signals. In other embodiments, the filter time period is selected to be less than the duration of one symbol by a desired offset. In the context of LTE, one symbol has a duration of approximately <NUM>, so the filter time period can be selected to be less than <NUM>. For example, the filter time period is set at approximately <NUM> for LTE signals.

When the filter time period has not passed, method <NUM> continues to monitor the signal indicative of whether the power of the downlink signal on the downlink path exceeds a threshold (block <NUM>). If a signal indicating that the power of the downlink signal on the downlink path exceeds the threshold signal power is received or determined during the filter time period, then the process is reset and method <NUM> continues to monitor the signal indicative of whether the power of the downlink signal on the downlink path exceeds a threshold (block <NUM>).

If a signal indicating that the power of the downlink signal on the downlink path exceeds the threshold signal power is not received or determined and the filter time period has passed, method <NUM> proceeds with determining an end time for the downlink signal (block <NUM>). The switching control engine <NUM> can identify an end time for a respective downlink signal based on the time the power of the downlink signal on the downlink path dropped from a level exceeding the threshold signal power to a level below the threshold signal power.

Method <NUM> proceeds with updating the initial clock setting of the switching control module of the TDD switching sub-system based on the detected end time and/or the detected start time of the downlink signal (block <NUM>). The clock setting of the switching control module of the TDD switching sub-system controls a timing for generating switching signals sent to the switches <NUM>, <NUM>, <NUM> or devices actuating the switches <NUM>, <NUM>, <NUM>. The processor <NUM> provides switching signals to the switches <NUM>, <NUM>, <NUM> based on the updated clock setting.

In exemplary embodiments, method <NUM> can further include determining switching time differentials and using statistical analysis to identify switching time adjustments, as discussed in <CIT>, titled "Switching Sub-System for Distributed Antenna Systems Using Time Division Duplexing, which is incorporated herein by reference. For example, in some aspects, sampled values for switching time differentials can be obtained over different frames in which an operator using the DAS <NUM> switches between an uplink mode and a downlink mode. The switching control engine <NUM> can generate or otherwise obtain a statistical distribution of the sampled values for the switching time differentials and determine the switching time adjustment based on the statistical distribution. A non-limiting example of a switching time adjustment statistically determined from sampled values for the switching time differentials is a mean value of the sampled values of the switching time differentials.

The TDD switching sub-system can be implemented in any suitable DAS <NUM> configured for TDD operations. For example, <FIG> is a schematic depicting examples of a master unit <NUM> and remote antenna units 104a-n for an optical TDD distributed antenna system that can utilize an optimized clock setting for a TDD switching sub-system according to an aspect of the present disclosure.

The master unit <NUM> can include splitter-combiners 802a-n for isolating uplink and downlink signals communicated with base stations or other signal sources. The master unit <NUM> can also include mixers 803a-n and local oscillators 804a-n for frequency-shifting downlink signals to intermediate frequency ("IF") bands, as described in greater detail below. The master unit <NUM> can also include a combiner <NUM> for combining downlink signals from different operators for serial transmission to remote antenna units 104a-n. The master unit <NUM> can also include an electrical-to-optical converter <NUM> for converting the serialized electrical downlink signals into serialized optical downlink signals. The serialized optical downlink signals can be transmitted to the remote antenna units 104a-n via the optical communication link <NUM>. The master unit <NUM> can also include an optical-to-electrical converter <NUM> for converting optical uplink signals received via the optical communication link <NUM> into serialized electrical uplink signals. The master unit <NUM> can also include a splitter <NUM> for separating the serialized electrical uplink signals into separate uplink signals for transmission to base stations or other receivers of uplink signals.

The remote antenna units 104a-n can include respective optical splitter-combiners 816a-n for isolating optical downlink signals from optical uplink signals. The remote antenna units 104a-n can also include respective optical-to-electrical converters 818a-n for converting optical downlink signals into electrical downlink signals. The remote antenna units 104a-n can also include respective mixers 820a-n and local oscillators 821a-n for frequency shifting downlink signals to RF frequency bands, as described in detail below. The remote antenna units 104a-n can also include respective bandpass filters 822a-n for attenuating unwanted frequency components of the RF downlink signals outputted by the mixers 820a-n. The remote antenna units 104a-n can also include switching control modules 210a-n and switches 212a-n, 214a-n, 216a-n that perform the same or similar functions with respect to the power amplifiers 218a-n and low noise amplifiers 220a-n as described above with respect to <FIG>. The remote antenna units 104a-n can also include respective circulators 824a-n for coupling downlink signals from the downlink paths to the antennas 209a-n and for coupling uplink signals from the antennas 209a-n to the uplink paths. The remote antenna units 104a-n can also include respective electrical-to-optical converters 828a-for converting electrical uplink signals to optical uplink signals for transmission via the optical communication link <NUM>.

Multiple telecommunication operators utilizing the DAS <NUM> can use a common optical communication link <NUM> between the master unit <NUM> and the remote antenna units 104a-n. In some aspects, the DAS <NUM> can support an "uncoordinated operator mode. " In the uncoordinated operator mode, different operators using the DAS <NUM> do not coordinate with one another in switching between an uplink TDD mode and a downlink TDD mode.

The DAS <NUM> can be configured to reduce or eliminate uplink blocking by unsynchronized operators transmitting signals using adjacent frequencies. For example, downlink signals from multiple operators can be closely spaced within a frequency band (e.g., a few MHz). The mixers 803a-n and the local oscillators 804a-n of the master unit <NUM> can be used to frequency-shift downlink signals to IF bands. Frequency shifting the downlink signals to IF bands can separate downlink signals from uncoordinated operators use closely spaced frequencies for transmitting TDD signals. The mixers 820a-n and local oscillators 821a-n of the remote antenna units 104a-n can be used to frequency-shift the IF downlink signals back to RF bands for transmission. A reference clock <NUM> in the master unit <NUM> can be used for synchronizing the local oscillators 804a-n, 821a-n. In some aspects, the reference clock <NUM> can also be used for synchronizing the threshold signal power used by the switching control module <NUM>. The reference clock <NUM> can be communicatively coupled to the local oscillators 804a-n via any suitable mechanism, such as a printed circuit board or other communication bus (not depicted in <FIG>). Signals from the reference clock <NUM> can be communicated from the master unit <NUM> to the remote antenna units 104a-n via the optical communication link <NUM>.

The TDD switching sub-system can be implemented in any suitable single-node repeater configured for TDD operations. <FIG> illustrates one exemplary embodiment of a single-node repeater <NUM> in which the TDD synchronization techniques described here can be implemented.

In the exemplary embodiment shown in <FIG>, the single-node repeater <NUM> is coupled to one or more base stations <NUM> using a donor antenna <NUM>.

The single-node repeater <NUM> comprises a first duplexer <NUM> having a common port that is coupled to the donor antenna <NUM> via a cable <NUM>, a downlink port that is coupled to downlink circuitry <NUM>, and an uplink port that is coupled to uplink circuitry <NUM>. The single-node repeater <NUM> comprises a second duplexer <NUM> having a common port that is coupled to the coverage antenna <NUM>, a downlink port that is coupled to the downlink circuitry <NUM>, and an uplink port that is coupled to the uplink circuitry <NUM>.

In general, the single-node repeater <NUM> is configured to receive one or more downlink signals from one or more base stations <NUM>. Each base station downlink signal includes one or more radio frequency channels used for communicating in the downlink direction with user equipment <NUM> over the relevant one or more wireless air interfaces. The downlink circuitry <NUM> is configured to amplify the downlink signals received at the repeater <NUM> and re-radiate the amplified downlink signals via the coverage antenna <NUM>. As a part of doing this, the downlink circuitry <NUM> can be configured to filter the downlink signals to separate out the individual channels, individually amplify each filtered downlink channel signal, combine the individually amplified downlink channel signals, and re-radiate the resulting combined signal.

Similar processing is performed in the uplink. The single-node repeater <NUM> is configured to receive one or more uplink signals from user equipment <NUM>. Each user equipment uplink signal includes one or more radio frequency channels used for communicating in the uplink direction with one or more base stations <NUM> over the relevant one or more wireless air interfaces. The uplink circuitry <NUM> is configured to amplify the uplink signals received at the repeater <NUM> and re-radiate the amplified uplink signals via the donor antenna <NUM>. As a part of doing this, the uplink circuitry <NUM> can be configured to filter the uplink signals to separate out the individual channels, individually amplify each filtered uplink channel signal, combine the individually amplified uplink channel signals, and re-radiate the resulting combined signal.

The single-node repeater <NUM> can be configured to implement one or more features to provide sufficient isolation between the donor antenna <NUM> and the coverage antenna <NUM>. These features can include gain control circuitry and adaptive cancellation circuitry. Other features can be implemented. These features can be implemented in one or more of the downlink circuitry <NUM> and/or the uplink circuitry <NUM>. These features can also be implemented in separate circuitry.

The various circuitry and features of the single-node repeater <NUM> can be implemented in analog circuitry, digital circuitry, or combinations of analog circuitry and digital circuitry. The downlink circuitry <NUM> and uplink circuitry <NUM> can comprise one or more appropriate connectors, attenuators, combiners, splitters, amplifiers, filters, duplexers, analog-to-digital converters, digital-to-analog converters, electrical-to-optical converters, optical-to-electrical converters, mixers, field-programmable gate arrays (FPGAs), microprocessors, transceivers, framers, etc., to implement the features described above. Also, the downlink circuitry <NUM> and uplink circuitry <NUM> may share common circuitry and/or components.

In this embodiment, the signal node repeater <NUM> is configured to repeat time-division duplexing (TDD) signals. The downlink circuitry <NUM> and the uplink circuitry <NUM> includes one or more switches that are switched in order to either couple or isolate the output and/or input of that circuitry to or from corresponding ports of the duplexers <NUM> and <NUM>. The techniques described above for determining the threshold signal power and TDD synchronization timing can be used in such a repeater <NUM>. In exemplary embodiments, the repeater <NUM> includes a switching control module and TDD switching sub-system similar to those described above.

Claim 1:
A method (<NUM>) for determining threshold signal power for a switching control module of a time-division-duplexing, TDD, switching sub-system comprising:
setting (<NUM>) a threshold signal power to a first value, wherein the threshold signal power is compared to a measured signal power of a downlink signal of a downlink path of a telecommunication system from a measurement receiver;
determining (<NUM>) a first downlink signal time using the first value, wherein the first downlink signal time is an amount of time elapsed from when a first downlink signal is first detected to when the first downlink signal is no longer detected, wherein the first downlink signal is detected when its downlink power exceeds the threshold signal power set to the first value;
characterized in that the method further comprises:
adjusting (<NUM>) the threshold signal power to a second value;
determining (<NUM>) a second downlink signal time using the second value, wherein the second downlink signal time is an amount of time elapsed from when a second downlink signal is first detected to when the second downlink signal is no longer detected, wherein the second downlink signal is detected when its downlink power exceeds the threshold signal power adjusted to the second value;
determining (<NUM>) a difference between the first downlink signal time and the second downlink signal time;
when the difference between the first downlink signal time and the second downlink signal time does not exceed a predetermined threshold time, determining (<NUM>) whether the second downlink signal time corresponds to a known valid downlink signal time;
when the second downlink signal time corresponds to the known valid downlink signal time, setting (<NUM>) a fixed threshold signal power for use during online operation of the switching control module.