SYSTEMS

Cross-Reference to Related Application

[0001] Priority is claimed to U.S. Provisional Application Serial No. 61/941,272, filed February 18, 2014 and titled "Selectively Combining Uplink Signals in Distributed Antenna Systems," the contents of which are incorporated herein by reference.

Technical Field

[0002] The present disclosure relates generally to telecommunication systems and more particularly (although not necessarily exclusively) to selectively combining uplink signals in distributed antenna systems.

Background

[0003] A distributed antenna system ("DAS") can be used to provide wireless communications coverage in a variety of environments, particularly in large structures such as office buildings, convention halls, airports, stadiums, and the like. A DAS can include one or more master units or other head-end units that are communicatively coupled to one or more base stations. A DAS can also include multiple remote units that are communicatively coupled to each master unit. The remote units, each of which can include one or more transceivers and antennas, can be distributed across a coverage area. The remote units can transmit the downlink signals to mobile phones or other terminal devices within coverage areas serviced by the remote units.

[0004] A master unit of a DAS may combine uplink transmissions received from several remote units into a composite signal. Combining uplink transmissions from different remote units communicating with the same terminal device can boost the power of weak uplink signals received by one or more remote units. The composite uplink signal may be provided to a base station that communicates with the DAS.

[0005] A master unit may combine uplink transmissions regardless of whether the uplink transmissions includes uplink signals from terminal devices or includes only uplink noise. Combining uplink signals regardless of whether uplink signals from terminal devices are present may present disadvantages. For example, uplink transmissions from one or more remote units may include noise on one or more channels, even if no uplink signal has been received by the remote units. Combining the uplink transmissions from each of the remote units to generate a composite uplink signal can combine the received noise in each uplink channel. If some of the uplink transmissions includes noise but does not include an uplink signal, indiscriminately combining uplink transmissions may unnecessarily increase the noise floor for the composite uplink signal and limit the number of remote units used in the DAS.

Summary

[0006] According to one aspect, a method is provided for selectively combining uplink signals in a distributed antenna system ("DAS"). The method involves a unit of the DAS receiving baseband uplink transmissions from remote units of the DAS via a first channel and a second channel. The method also involves generating a first combined uplink signal by combining a first portion of the baseband uplink transmissions received from a first subset of the remote units via the first channel. The first portion of the baseband uplink transmissions includes data for transmission to a base station. The method also involves generating a second combined uplink signal that includes a portion of the baseband uplink transmissions received from a second subset of the remote units via the second channel. In the second combined uplink signal, a portion of the baseband uplink transmissions that are received from the first subset of the remote units via the second channel and that lack data for transmission to the base station are excluded or attenuated. The method also involves transmitting the first combined uplink signal and the second combined uplink signal to the base station.

[0007] According to another aspect, a unit is provided for selectively combining uplink signals in a DAS. The unit can receive baseband uplink transmissions from remote units of the DAS via a first channel and a second channel. The unit can generate a first combined uplink signal by combining baseband uplink transmissions received from a first subset of the remote units via the first channel that include data for transmission to a base station. The unit can generate a second combined uplink signal that includes baseband uplink transmissions received from a second subset of the remote units via the second channel. In the second combined uplink signal, baseband uplink transmissions received from the first subset of the remote units via the second channel and that lack data for transmission to the base station are excluded or attenuated. The unit can transmit the combined uplink signals to the base station.

[0008] According to another aspect, a DAS is provided that can selectively combine channelized uplink signals. The DAS can include a unit that is communicatively coupled to remote units. The remote units can extract baseband uplink transmissions from uplink traffic received in one or more channels in an RF band. The unit can receive baseband uplink transmissions from remote units of the DAS via a first channel and a second channel. The unit can generate a first combined uplink signal by combining baseband uplink transmissions received from a first subset of the remote units via the first channel that include data for transmission to a base station. The unit can generate a second combined uplink signal that includes baseband uplink transmissions received from a second subset of the remote units via the second channel. In the second combined uplink signal, baseband uplink transmissions that are received from the first subset of the remote units via the second channel and that lack data for transmission to the base station are excluded or attenuated. The unit can transmit the combined uplink signals to the base station.

[0009] These illustrative aspects and features are mentioned not to limit or define the disclosure, but to provide examples to aid understanding of the concepts disclosed in this application. Other aspects, advantages, and features of the present disclosure will become apparent after review of the entire application.

Brief Description of the Drawings

[0010] FIG. 1 is a block diagram depicting an example of a distributed antenna system ("DAS") that can selectively combine uplink transmissions according to one aspect of the present disclosure.

[0011] FIG. 2 is a block diagram depicting an example of a unit of the DAS from FIG. 1 that can selectively combine uplink transmissions received from remote units of the DAS according to one aspect of the present disclosure.

[0012] FIG. 3 is a block diagram depicting an alternative example of a unit of the DAS from FIG. 1 that can selectively combine uplink transmissions received from remote units of the DAS according to one aspect of the present disclosure.

[0013] FIG. 4 is a block diagram depicting an example of a baseband processing module used by a remote unit of the DAS from FIG. 1 that obtains channelized baseband uplink transmissions to be selectively combined according to one aspect of the present disclosure.

[0014] FIG. 5 is a partial schematic diagram depicting examples of a signal processing section and a channelizer section of the baseband processing module depicted in FIG. 4 according to one aspect of the present disclosure.

[0015] FIG. 6 is a flow chart depicting an example of a process for selectively combining uplink signals in a DAS according to one aspect of the present disclosure.

Detailed Description

[0016] Certain aspects and features relate to selectively combining uplink transmissions in a distributed antenna system ("DAS"). Selectively combining uplink transmissions can involve combining portions of a spectrum that include uplink signals from terminal devices and excluding or attenuating portions of the spectrum from which uplink signals are absent (i.e., "empty" portions of the spectrum). In some aspects, a unit of a DAS can analyze each channel from a set of channels used by the DAS to identify which remote units have transmitted uplink transmissions with data for that channel. The unit can generate a combined uplink signal for each of the channels. Generating the combined uplink signal can involve excluding or attenuating uplink transmissions that lack data to be transmitted (e.g., uplink transmissions containing only noise or uplink transmissions with an unacceptable signal-to-noise ratio).

[0017] The performance of a DAS can be improved by selectively combining uplink transmissions from different remote units. For example, selecting portions of uplink transmissions from a remote unit having data received from terminal devices and excluding or attenuating other portions of uplink transmissions from remote units that do not have data received from terminal devices can avoid unnecessarily increasing a noise floor for a combined uplink signal. Reducing or minimizing the noise floor for a combined uplink signal may increase the number of remote units that can be used in the DAS.

[0018] 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. The various figures described below depict examples of implementations for the present disclosure, but should not be used to limit the present disclosure.

[0019] FIG. 1 is a block diagram depicting an example of a DAS 102 that can selectively combine uplink signals. The DAS 102 can communicate signals between one or more base stations 101 or other transceiving devices (e.g., repeaters) and terminal devices in one or more coverage zones serviced by the DAS 102. Terminal devices can be electronic devices used to communicate one or more of voice and data via a telecommunication system, such as (but not limited to) mobile phones.

[0020] The DAS 102 can include one or more units 104 having one or more processing modules 106 and one or more combining modules 108. Examples of a unit 104 include a master unit, a base station router, or other suitable unit that can communicate with a base station. In some aspects, the unit 104 can be a master unit or other suitable unit that can communicate with one or more base stations 101 or other transceiving devices in communication with the DAS 102. A master unit can include, for example, an optical transceiver that transmits optical signals to the remote units 1 lOa-d. The master unit or other suitable unit 104 can communicate with remote units HOa-d in different coverage zones of the same DAS 102. In additional or alternative aspects, the unit 104 can be included in a base station router or other suitable unit that can communicate signals between one or more base stations 101 and one or more master units. In additional or alternative aspects, the unit 104 can be included in an extension unit or other suitable unit that can communicate signals between one or more master units and the remote units 1 lOa-d.

[0021] The DAS 102 can also include remote units l lOa-d having respective baseband processing modules 112a-d. The remote units l lOa-d can include transceiving devices that can include or be communicatively coupled to one or more antennas. A non- limiting example of a remote unit is a universal access point. Although FIG. 1 depicts one unit 104 and four remote units l lOa-d, a DAS 102 can include any number of units 104 and any number of remote units.

[0022] The DAS 102 can communicate signals to and from terminal devices via the unit 104 and the remote units 1 lOa-d that service one or more coverage zones. The unit 104 can be communicatively coupled with the base station 101 and the remote units l lOa-d in any suitable manner. Communicatively coupling devices in a DAS 102 or other telecommunication system can involve establishing, maintaining, or otherwise using a communication link (e.g., a cable, an optical fiber, a wireless link, etc.) to communicate information between the devices. Any suitable types of communication links can be used in the DAS 102. A suitable communication link can be a wired connection or a wireless connection. Types of wired connection can include, for example, a connection via a copper cable, an optical fiber, or another suitable communication medium. Types of wireless connections can include, for example, a wireless RF communication link or a microwave link. The type of communication link between the base station 101 and the unit 104 can be the same as or different from the type of communication link between the unit 104 and the remote units 1 lOa-d.

[0023] The unit 104 can provide downlink signals from the base station 101 to the remote units l lOa-d and receive uplink signals from the remote units l lOa-d to be provided to the base station 101. Downlink signals can include signals provided from the base station 101 and transmitted by the remote units 1 lOa-d in coverage zones.

[0024] The remote units l lOa-d can provide signal coverage in one or more coverage zones. Providing signal coverage in the coverage zones can include wirelessly transmitting downlink signals received from the unit 104 to terminal devices in the coverage zones. Providing signal coverage in the coverage zones can also include wirelessly receiving uplink signals from the mobile communication devices or other terminal devices in the coverage zones. Uplink signals are signals at frequencies in an uplink frequency band that are recovered or otherwise received by one or more of the remote units HOa-d from terminal devices. The remote units HOa-d can transmit the uplink signals to the unit 104. The unit 104 can transmit the uplink signals to the base station 101.

[0025] Although FIG. 1 depicts a direct link between the unit 104 and the remote units HOa-d, other implementations are possible. In some aspects, the unit 104 can be communicatively coupled to the remote units 1 lOa-d via one or more extension units or other intermediate devices.

[0026] The unit 104 can combine uplink transmissions received from some or all of the remote units 1 lOa-d into a combined uplink signal, such as a composite signal. A transmitter of the unit 104 can transmit the combined uplink signal to an uplink receiver of the base station 101.

[0027] Uplink transmissions can include uplink signals received by remote units HOa-d from terminal devices. In some aspects, the uplink transmissions can include down- converted versions of these uplink signals. In additional or alternative aspects, the uplink transmissions can include digitized versions of these uplink signals. Uplink transmissions received from remote units HOa-d can also include one or more of noise received by the remote units HOa-d from their surrounding environment, noise from one or more electronic components used by a remote unit to receive signals, and noise generated in an uplink path between a remote unit and the unit 104. In some cases, uplink transmissions can include both uplink signals and uplink noise or weak uplink traffic. In other cases, uplink transmissions may not include uplink signals or may include weak uplink signals with high signal-to-noise ratios. Examples of such cases include cases in which terminal devices are not close enough to a remote unit for received uplink signals to exceed the noise floor.

[0028] The unit 104 can use the processing module 106 and the combining module 108 to selectively combine uplink transmissions received from the remote units 1 lOa-d. Selectively combining uplink transmissions can involve combining portions of the spectrum where uplink signals are present and excluding portions of the spectrum from which uplink signals from terminal devices are absent (e.g., "empty" portions of the spectrum). Selectively combining uplink transmissions can reduce an amount of noise in a combined uplink signal provided to a base station 101. The processing module 106 and the combining module 108 can include one or more devices configured to select uplink signals for a combination, programming instructions executable by a processor to select uplink signals for a combination, or any suitable combination thereof. [0029] In some aspects, the DAS 102 can selectively combine channelized baseband uplink transmissions. Channelized baseband uplink transmissions can include call information for wireless communication with terminal devices. For example, the baseband processing modules 112a-d of the remote units HOa-d can include channelizer sections that can extract, per channel, channelized baseband uplink signals using channel filters and down- converters. The remote units HOa-d can provide the channelized baseband uplink transmissions to the unit 104.

[0030] Selectively combining channelized uplink transmissions can allow the unit 104 to optimize the generation of combined uplink signals to be transmitted to a base station 101. For example, three terminal devices may be geographically located in a coverage area serviced by the DAS 102. A frequency band including at least three frequency channels can be used by the terminal devices to communicate with remote units of the DAS 102. A first terminal device can be geographically located within the communication range of the remote units 110a, 110b and can communicate via a first frequency channel from the frequency band. Uplink transmissions received by the unit 104 from the remote units 110a, 110b can include data corresponding to the first frequency channel. A second terminal device can be geographically located within the communication range of remote units 110a, 110c, 1 lOd and can communicate via a second frequency channel from the frequency band. Uplink transmissions received by the unit 104 from the remote units 110a, 110c, l lOd can include data corresponding to the second frequency channel. A third terminal device can be geographically located within the communication range of remote unit l lOd and can communicate via a third frequency channel from the frequency band. Thus, uplink transmissions received by the unit 104 from the remote units l lOd can also include data corresponding to the third frequency channel. Data corresponding to a frequency channel can include, but may not be limited to, one or more of digitized RF data in the first frequency channel, analog signals in the first frequency channel, analog signals or digital data in an intermediate frequency channel, analog signals or digital data in a baseband frequency channel, etc.

[0031] In this example, the unit 104 can selectively combine uplink transmissions that are received from the different remote units and that correspond to different frequency channels used by the remote units to communicate with the terminal devices. For example, the unit 104 can generate a combined uplink signal for the first frequency channel by combining uplink signals received from the remote units 110a, 110b and having frequencies within or corresponding to the first frequency channel. The combined uplink signal for the first frequency channel can omit or attenuate uplink transmissions corresponding to the first frequency channel that is received from remote units 110c, HOd (e.g., noise on the first frequency channel). The unit 104 can generate a combined uplink signal for the second frequency channel by combining uplink signals received from the remote units 110a, 110c, 1 lOd and having frequencies within or corresponding to the second frequency channel. The combined uplink signal for the second frequency channel can omit or attenuate uplink transmissions corresponding to the second frequency channel that is received from remote units 110c, HOd (e.g., noise on the second frequency channel). For the third frequency channel, the unit 104 can transmit an uplink signal that includes uplink signals received from the remote unit HOd and excludes or attenuates uplink transmissions received from remote units l lOa-c.

[0032] FIG. 2 is a block diagram depicting an example of a unit 104 that can selectively combine uplink transmissions according to one aspect. As depicted in FIG. 2, the processing module 106 can include a processor 202 and a memory 204. The processor 202 can be communicatively coupled to the combining module 108 and the memory 204. The processor 202 can include any processing device or group of processing devices configured for executing program code stored in the memory 204. Examples of the processor 202 include a microprocessor, an application-specific integrated circuit ("ASIC"), a field-programmable gate array ("FPGA"), or other suitable processor. The memory 204 can include, for example, a non-transitory computer-readable medium. The program code can include a selection engine 206 that can be executed by the processor 202.

[0033] The selection engine 206 can include one or more algorithms for selecting portions of uplink transmissions to be combined by the combining 208. The selection engine 206 can select a first portion of the uplink transmissions that includes data to be transmitted to the base station 101 (e.g., uplink transmissions including uplink signals from terminal devices). The selection engine 206 can identify a second portion of the uplink transmissions that does not include data to be transmitted to the base station (e.g., uplink transmissions that includes noise without uplink signals). The identification of the second uplink transmissions portion can cause the processor 202 to configure one or more components of the combining module 108 to exclude or attenuate the second uplink transmissions portion.

[0034] In some aspects, a power measurement device 212 can be included in the unit 104 or another device of the DAS 102. The power measurement device 212 can be communicatively coupled to the processing device 202 and uplink paths from the remote units HOa-d to the unit 104. (Although FIG. 2 depicts a single power measurement device 212, any number of power measurement devices 212 may be used.) The processor 202 can communicate with the power measurement device 212 to obtain data describing signal power levels for uplink transmissions from each of the remote units. In one example, the power measurement device 212 can have an analog output that is electrically connected to the processor 202. The power measurement device 212 can provide a voltage or a current to the processor 202 via the analog output. The voltage or current can be equivalent to or otherwise indicative of the measured power level in the uplink paths from the remote units 1 lOa-d. In another example, the power measurement device 212 can provide a digital output signal to the processor 202 that represents the measured power level in the uplink paths from the remote units 1 lOa-d. The processor 202 can execute the selection engine 206 to compare the data obtained from the power measurement device 212 with data stored in the memory 204 that describes a threshold signal power. Uplink transmissions having a signal power greater than or equal to the threshold signal power can be selected for inclusion in a combined uplink signal. Uplink transmissions having a signal power less than or equal to the threshold signal power can be selected for exclusion from or attenuation in a combined uplink signal.

[0035] In additional or alternative aspects, the unit 104 can use criteria other than signal power measurements to include or exclude uplink transmissions from a combination (e.g., scheduling information or spreading codes received from a base station 101, geographic locations of terminal devices in a coverage area of the DAS 102, etc.). In these aspects, the power measurement device 212 may be omitted.

[0036] The combining module 108 can include a combiner 208 and attenuators 210a-d. The combiner 208 can include any device or group of devices that can add or otherwise combine uplink transmissions into a combined uplink signal. An example of a combiner 208 is an adder. The attenuators 210a-d can include variable gain devices or other suitable devices that can attenuate one or more portions of uplink transmissions received from remote units. For example, the processor 202 can configure one or more of the attenuators 210a-d to attenuate uplink transmissions that does not include data to be transmitted to the base station 101. Attenuating a portion of uplink transmissions selected by the processor 202 can exclude or attenuate that portion of uplink transmissions in a combined uplink signal transmitted to the base station 101 via a transmitter 210 of the unit 104.

[0037] In additional or alternative aspects, the attenuators 210a-d can be used with or replaced by multipliers at inputs of the combiner 208. The processor 202 can configure the multipliers to cancel, minimize, or otherwise attenuate one or more portions of uplink transmissions at one or more inputs of the combiner 208. The multipliers can cause uplink transmissions portions to be excluded from or attenuated in a combined uplink signal transmitted to the base station 101.

[0038] In some aspects, the combining module 108 can be implemented using program code executable by the processor 202. For example, FIG. 3 is a block diagram depicting an alternative example of a unit 104 that can selectively combine uplink transmissions according to one aspect. The unit 104 depicted in FIG. 3 can omit the combiner 208 and the attenuators depicted in 210a-d depicted in FIG. 2.

[0039] As depicted in FIG. 3, the processor 202 can receive or otherwise access digital uplink transmissions that has been received by the unit 104. The selection engine 206 can be executed by the processor 202 to select one or more portions of the digital uplink transmissions to be combined and one or more portions of the digital uplink transmissions to be excluded. A combiner engine 302 can be stored in the memory 204 and can be executed by the processor 202. The combiner engine 302 can include one or more algorithms for combining selected portions of uplink transmissions that have been identified by the selection engine 206. The processor 202 can configure the transmitter 210 of the unit 104 to transmit a combined uplink signal including the selected uplink transmissions portions to the base station 101.

[0040] In some aspects, the unit 104 depicted in FIG. 2 can use a fast Fourier transform ("FFT") or other suitable transform to identify and select portions of uplink transmissions having data for transmission. In a non-limiting example, an FFT can be applied to uplink transmissions received from a remote unit to convert the uplink transmissions from the time domain to the frequency domain. The processor 202 can execute suitable program code to generate an FFT for channels used by the DAS 102. Each bin of the FFT can correspond to a sub-band of the received uplink transmissions. Each bin can include information about the uplink transmissions portion within the bandwidth of the bin, such as a magnitude and a phase for the sub-band in the bin. A length of the FFT being used can determine the bandwidth for each sub-band. For example, the processor 202 can obtain a 1 ,024-point FFT of a signal received by the unit. The sampling rate of the digital signal can be divided into the 1,024 FFT bins. The processor 202 can select at least some of the bins for combination with digitized uplink transmissions from other remote units. For example, the processor 202 can determine that one or more bins of an FFT or other frequency transform include data having a magnitude exceeding a threshold magnitude. The processor 202 can extract or otherwise select portions of uplink transmissions from a remote unit by selecting FFT bins corresponding to the sub-bands of interest. [0041] In some aspects, the DAS 102 can selectively combine channelized baseband uplink transmissions using baseband processing modules of the remote units. For example, the unit 104 can combine uplink transmissions for telecommunication systems using channelized modulation formats (e.g., Global System for Mobile Communications ("GSM") systems). Selective combination of uplink transmissions from different frequency channels can be implemented using channelized squelch functions. For instance, twenty GSM channels may be included within 10 MHz of spectrum. Uplink signals received at each of the remote units HOa-d can be filtered into separate channels. The channelized signals can be transmitted to a unit 104. Each channel from each of the remote units HOa-d can be tested against a programmable threshold. For each channel, if an uplink signal within the channel has a signal strength above the threshold, the uplink signal can be combined into a composite signal for the channel. If the uplink signal does not have a signal strength above the threshold, the uplink signal can be excluded or otherwise omitted from the composite signal for the channel.

[0042] FIG. 4 is a block diagram depicting an example of a baseband processing module 112 used for obtaining channelized baseband uplink transmissions to be selectively combined in the DAS 102 according to one aspect. The baseband processing unit 112 includes a signal processing section 402, a channelizer section 404, and a transport section 406.

[0043] The signal processing section 402 can receive RF signals, amplify and down- convert the RF signals, and convert the RF signals to digital signals. The signal processing section 402 can also convert digital signals to RF signals, and up-convert, amplify, and provide the RF signals.

[0044] The channelizer section 404 can process the digital signals on channel-by-channel bases. For example, the channelizer section 404 can digitally down-convert the digital signals to baseband and provide channelized baseband signals, and digitally up-convert channelized baseband signals and combine the digitally up-converted channelized baseband signals to provide digital signals.

[0045] The transport section 406 can prepare the channelized baseband signals for transport. For example, the transport section 406 can serialize and frame channelized baseband signals for transport and can de-frame and de-serialize the channelized baseband signals.

[0046] FIG. 5 depicts examples of the signal processing section 402 and the channelizer section 404.

[0047] The signal processing section 402 includes an input amplifier 502, a down- converting mixer 504, a bandpass filter 506, and an analog-to-digital converter ("ADC") 508. The input amplifier 502 can amplify uplink signals in an RF band. The RF band may be an RF spectrum including one or more carriers and information carried by the carriers. The down-converting mixer 504 can down-convert uplink signals in the RF band to an intermediate frequency using a mixing frequency. The bandpass filter 506 can filter the RF band at the intermediate frequency. In one example, the bandpass filter 506 has a bandwidth of 75 MHz with a center frequency of 350 MHz. The ADC 508 can convert the filtered RF band at the intermediate frequency according to a selected sample rate to digital signals.

[0048] The channelizer section 404 includes down-converting channel modules 510a-n. Each of the down- converting channel modules 510a-n can be associated with a respective channel. The down-converting channel modules 510a-n can demodulate each channel to baseband using I and Q mixers and numerically controlled oscillators ("NCOs"). Each NCO can be set to the center frequency of the channel. The output of the down-converting channel modules 510a-n can be digital signals sampled at a certain sample rate, such as 200 MHz. The digital signals can be digitally down-sampled by a decimation filter to reduce the sample rate to a level that is suitable for a single channel bandwidth. In an example involving seven active channels, seven decimation processes can be performed in parallel. The seven sets of I and Q data streams can be multiplexed onto a transport communication medium such that call information is transported, but not the RF spectrum or information about the RF spectrum.

[0049] Active channels in an RF band can have different amplitudes. When the RF band is recreated at another location, the channels can be gain equalized, which can allow the system to allocate power per channel by automatically adjusting the gain of the system to maintain a preset power for each carrier in the system. For example, an RF band may be 75 MHz wide and use a sample rate of 150 Msps to meet the Nyquist sampling criteria. Each of seven active channels can be independently demodulated to baseband. Each baseband signal may require a 10 Msps sampling rate to meet the Nyquist sampling criteria, although a 13.5 Msps rate can be used for practical filtering, producing 94.5 Msps (7 x 13.5) of data. A sample rate of 94.5 Msps may be less than half of the sample rate needed for transporting the information and other information about the RF band, such as carrier information and information between call information. The transport communication medium can be an expensive component of a telecommunications system, such as a DAS. Furthermore, transport communication mediums have a fixed bandwidth and a fixed amount of data capacity. Reducing the number of samples can reduce the amount of transport bandwidth that is used for transporting the same amount of call information, along with information from more bands, such as MIMO bands, to be transported.

[0050] The channelizer section 404 can be implemented in a device such as an FPGA, ASIC, or a digital signal processor ("DSP"). The NCOs and I and Q mixers can provide mixing stages for digitally mixing in-phase and quadrature components of signals. Examples of NCOs include modulo-/? NCOs, such as modulo-2000 NCOs. In some aspects, a processor in the channelizer section 404 can be pre-configured with data about the channels, including each channel's center frequency, and can control each module accordingly. In other aspects, the channelizer section 404 can dynamically determine data about each of the channels by analyzing a received spectrum, and can control each module accordingly.

[0051] Any suitable process can be used to selectively combine uplink transmissions. For example, FIG. 6 is a flow chart depicting an example of a process 600 for selectively combining uplink signals in a DAS 102. The process 600 is described with respect to one or more of the aspects and examples described above with respect to FIGs. 1-5. Other implementations, however, are possible.

[0052] The process 600 involves receiving uplink transmissions on a channel from multiple remote units, as depicted in block 602. For example, the unit 104 can receive uplink transmissions from the remote units 1 lOa-d as described in one or more of the examples with respect to FIGs. 1-5.

[0053] In some aspects, the unit 104 can receive baseband uplink transmissions via a channel used to communicate uplink transmissions between one or more of the remote units 1 lOa-d and the unit 104. The remote units 1 lOa-d can receive uplink signals or other uplink transmissions in an RF band. The remote units HOa-d can extract baseband uplink transmissions from the received uplink RF traffic. For example, the remote units 1 lOa-d can extract baseband uplink transmissions using channel filters and down-converters, as described above with respect to FIG. 4. Each of the remote units HOa-d can transmit the extracted baseband uplink transmissions to the unit 104.

[0054] The process 600 also involves determining, for each remote unit, whether the received uplink transmissions for the channel includes data for transmission to a base station, as depicted in block 604. For example, a processor 202 of the unit 104 can execute a selection engine 206. Executing the selection engine 206 can configure the processor 202 to execute one or more algorithms for determining whether the received uplink transmissions for the channel includes data for transmission to a base station 101.

[0055] The process 600 also involves selecting the uplink transmissions received from at least some remote units that includes the data for transmission to the base station, as depicted in block 606. For example, a processor 202 of the unit 104 can execute the selection engine 206. Executing the selection engine 206 can configure the processor 202 to execute one or more algorithms for selecting the uplink transmissions from at least some remote units that includes the data for transmission to the base station 101, as described above with respect to FIGs. 2 and 3. In some aspects, selecting the uplink transmissions can involve configuring at least some of the attenuators 210a-d to attenuate non-selected uplink transmissions portions, as described above with respect to FIG. 2. In additional or alternative aspects, selecting an uplink transmissions portion having data can involve selecting bins from an FFT of the uplink transmissions that include data.

[0056] In some aspects, the unit 104 can determine whether a portion of uplink transmissions received from a given remote unit for a channel includes data by determining whether the uplink transmissions portion has a signal strength equal to or exceeding a threshold. The threshold signal strength can be stored in the memory 204. The processor 202 can access the threshold signal strength and compare the threshold signal strength to a signal strength for the received portion of uplink transmissions. If the signal strength for the received portion of uplink transmissions is greater than or equal to the threshold signal strength, the selection engine 206 can identify the received portion of uplink transmissions as having data for transmission to the base station 101. If the signal strength for the received portion of uplink transmissions is less than the threshold signal strength, the selection engine 206 can identify the received portion of uplink transmissions as lacking data for transmission to the base station 101.

[0057] In some aspects, the unit 104 can determine whether a portion of uplink transmissions received from a given remote unit for a channel includes data by determining whether the uplink transmissions portion includes one or more spreading codes. For example, a base station 101 may be included in a type of telecommunication system (e.g., code division multiple access ("CDMA") systems, Long Term Evolution ("LTE") systems, etc.) that utilizes spreading codes. A list of spreading codes in use by a base station 101 can be provided to a unit 104, the remote units HOa-d, or some combination thereof. Providing the list of spreading codes can allow the selection engine 206 to search for the spreading codes in signals received by the remote units 1 lOa-d or in uplink transmissions received from the remote units HOa-d. The selection engine 206 can select a portion of uplink transmissions for combination based on the portion of uplink transmissions having one or more valid spreading codes. Uplink transmissions without valid spreading codes can be excluded or otherwise omitted from combined uplink signals. In some aspects, a base station 101 can also provide information that can be used to identify frequency channels associated with the spreading codes (e.g., those frequency channels being used with certain spreading codes). The threshold signal strength can be stored in the memory 204. The processor 202 can access the threshold signal strength and compare the threshold signal strength to a signal strength for the received portion of uplink transmissions. If the signal strength for the received portion of uplink transmissions is greater than or equal to the threshold signal strength, the selection engine 206 can identify the received portion of uplink transmissions as having data for transmission to the base station 101. If the signal strength for the received portion of uplink transmissions is less than the threshold signal strength, the selection engine 206 can identify the received portion of uplink transmissions as lacking data for transmission to the base station 101.

[0058] In additional or alternative aspects, the selection engine 206 can use scheduling information for GSM and LTE systems to identify portions of uplink transmissions having data for transmission. For example, in LTE systems, uplink frequency and bandwidth can change from frame to frame. A base station 101 can provide scheduling information about active calls to the unit 104, the remote units HOa-d, or some combination thereof. The selection engine 206 can use the scheduling information to track signal strength for a given terminal device that changes the transmission frequency during a call.

[0059] In additional or alternative aspects, the geographic location of terminal devices can be used to identify portions of uplink transmissions for inclusion in a combined uplink signal. For example, the selection engine 206 can use proximity detection, location detection, or other suitable processes to determine which of the remote units 1 lOa-d are receiving calls from terminal devices served by a base station 101. The base station 101 can communicate information to the unit 104 that identifies terminal devices that are communicating with the base station 101 via the DAS 102. The information from the base station 101 can allow the unit 104 to determine which of the remote units HOa-d are receiving signals from the terminal devices. The unit 104 can select portions of uplink transmissions from a given subset of remote units based on one or more terminal devices using the subset of remote units. For example, the unit 104 can determine from the received information that remote units 110a, 110b are receiving uplink signals from a first terminal device, that remote units 110b, 110c are receiving uplink signals from a second terminal device, and that remote units 110c, 1 lOd are receiving uplink signals from a third terminal device. Thus, the unit 104 can combine uplink transmissions received from 110a, 110b that is associated with a first channel used by the first terminal device, can combine uplink transmissions received from 110b, 110c that is associated with a second channel used by the second terminal device, and can combine uplink transmissions received from 110c, 1 lOd that is associated with a third channel used by the third terminal device.

[0060] The process 600 also involves combining the selected uplink transmissions for transmission to the base station, as depicted in block 608. For example, the unit 104 can combine selected uplink transmissions as described above with respect to FIGs. 1-3.

[0061] The process 600 can return to block 602 to perform selective uplink combining for another uplink channel. The process 600 can be performed for any number of channels used to communicate channelized uplink transmissions from the remote units HOa-d to the unit 104.

[0062] Any suitable process can be used to exclude or omit uplink transmissions from a combined uplink signal. In one example, the unit 104 can mute or otherwise attenuate digital data received from a remote unit that represents wireless traffic to be excluded. In some aspects, the digital data may be attenuated to a low signal level. In other aspects, the digital data may be discarded. In another non-limiting example, the remote unit can refrain from transmitting digital data that represents wireless traffic to be excluded (e.g., noise that is present on an unused uplink frequency channel).

[0063] While the present subject matter has been described in detail with respect to specific aspects and features thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such aspects and features. Each of the disclosed aspects, examples, and features can be combined with one or more of the other disclosed aspects, examples, and features. Accordingly, it should be understood that the present disclosure has been presented for purposes of example rather than limitation, and does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.