Patent Description:
A distributed antenna system (DAS) may have various topologies in consideration of particularity of its installation areas and application fields (e.g., in-building, subway, hospital, stadium, etc.). Moreover, in the DAS, a hub unit (HUB) may be introduced when it is difficult to install remote units (RUs) as many as a number required to be installed due to a limited number of branches of a main unit (MU).

According to a topology form, a plurality of MUs may be connected to a single HUB, and a plurality of RU may be connected in a star or cascade structure through the HUB. In this case, there is required a method in which, when different sub-band signals in the same service band are transmitted from each MU to the HUB, signals can be efficiently transmitted to the RUs posterior to the HUB.

<CIT> for example discloses an architecture for a Digital Capacity Centric Distributed Antenna System (DCC-DAS) comprising a hub apparatus according to the preamble of annexed claim <NUM>.

An embodiment of the inventive concept is directed to a method for summing downlink digital signal applicable to a distributed antenna system.

To solve the above technical problems, the present invention provides a hub apparatus for a distributed antenna system according to claim <NUM> and a method for summing a signal in a hub apparatus for a distributed antenna system according to claim <NUM> and a digital summing device according to claim <NUM>. Preferred embodiments are disclosed in claims <NUM>-<NUM>, <NUM>, <NUM>.

According to embodiments of the inventive concept, a method of summing digital downlink signal is performed on different sub-band signals in the same service band in the distributed antenna system, thereby improving the efficiency of digital transmission.

Exemplary embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which:.

Exemplary embodiments of the inventive concept will be described below in more detail with reference to the accompanying drawings. The inventive concept may, however, be embodied in different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Throughout the disclosure, like reference numerals refer to like parts throughout the various figures and embodiments of the inventive concept.

In description of the inventive concept, detailed explanation of known related functions and constitutions may be omitted to avoid unnecessarily obscuring the subject manner of the inventive concept.

It will be understood that when an element is "connected" or "coupled" to another element, the element may be directly connected or coupled to another element, and there may be an intervening element between the element and another element. To the contrary, it will be understood that when an element is "directly connected" or "directly coupled" to another element, there is no intervening element between the element and another element.

Hereinafter, a distributed antenna system (DAS) will be mainly described as an application example to which embodiments of the inventive concept are applicable. However, the embodiments of the inventive concept are identically or similarly applicable to other signal distributed transmission systems such as a base transceiver station distributed antenna system, as well as the DAS.

<FIG> is a diagram illustrating an example of a topology of a DAS as one form of a signal distributed transmission system to which the inventive concept is applicable.

Referring to <FIG>, the DAS may include a base station interface unit (BIU) <NUM> and a main unit (MU) <NUM>, which constitute a head-end node of the DAS, a hub unit (HUB) <NUM> serving as an extension node, and a plurality of remote units (RUs) <NUM> respectively disposed at remote service positions. The DAS may be implemented as an analog DAS or a digital DAS. When necessary, the DAS may be implemented as a hybrid of the analog DAS and the digital DAS (e.g., to perform analog processing on some nodes and digital processing on the other nodes).

However, <FIG> illustrates an example of the topology of the DAS, and the DAS may have various topologies in consideration of particularity of its installation areas and application fields (e.g., in-building, subway, hospital, stadium, etc.). In view of the above, the number of the BIU <NUM>, the MU <NUM>, the HUB <NUM>, and the RUs <NUM> and connection relations between upper and lower nodes among the BIU <NUM>, the MU <NUM>, the HUB <NUM>, and the RUs <NUM> may be different from those of <FIG>. In the DAS, the HUB <NUM> may be used when the number of branches to be branched in a star structure from the MU <NUM> is limited as compared with the number of RUs <NUM> required to be installed. Therefore, the HUB <NUM> may be omitted when only the single MU <NUM> sufficiently covers the number of RUs <NUM> required to be installed, when a plurality of MUs <NUM> are installed, or the like.

Hereinafter, nodes in the DAS applicable to the inventive concept and their functions will be sequentially described based on the topology of <FIG>.

The BIU <NUM> serves as an interface between a base station transceiver system (BTS) <NUM> and the MU <NUM>. Although a case where three BTSs BTS#<NUM> to BTS#<NUM> are connected to the single BIU <NUM> is illustrated in <FIG>, the BIU <NUM> may be separately provided for each provider, each frequency band, or each sector.

In general, a base station signal transmitted from the BTS <NUM> is a radio frequency (RF) signal of high power. Hence, the BIU <NUM> converts the RF signal of high power into a signal with power suitable to be processed in the MU <NUM> and transmits the converted signal to the MU <NUM>. According to an embodiment, the BIU <NUM>, as shown in <FIG>, may receive base station signals for each frequency band (or each provider or each sector), combine the received signals, and then transmit the combined signal to the MU <NUM>.

When the BIU <NUM> converts RF signals of high power, transmitted from the BTS <NUM>, into mobile communication signals of low power, combines the RF signals, and then transmits the combined RF signal to the MU <NUM>, the MU <NUM> may distribute the combined and transmitted RF signal for each branch. In this case, when the DAS is implemented as the digital DAS, the BIU <NUM> may be separated into a unit for converting RF signals of high power, transmitted from the BTS <NUM>, into RF signals of low power, and a unit for converting RF signals of low power into intermediate frequency (IF) signals, performing digital signal processing on the converted IF signals, and then combining the processed digital signals. Alternatively, when the BIU <NUM> performs only the function of converting the RF signals of high power, transmitted from the BTS <NUM>, into the RF signals of low power, the MU <NUM> may combine the transmitted RF signals and distribute the combined RF signal for each branch.

As described above, the combined RF signal distributed from the MU <NUM> may be transmitted to the RUs <NUM> through the HUB <NUM> or directly transmitted to the RUs <NUM>, for each branch (see Branch #<NUM>,. , Branch #k,. , Branch #N of <FIG>). Each RU <NUM> may separate the transmitted combined RF signal for each frequency band and perform signal processing (analog signal processing in the analog DAS and digital signal processing in the digital DAS). Accordingly, each RU <NUM> can transmit RF signals to user terminals in its own service coverage through a service antenna. Specific components and functions of the RU <NUM> will be described in detail below with reference to <FIG>.

In <FIG>, it is illustrated that the BTS <NUM> and the BIU <NUM> are connected through an RF cable, the BIU <NUM> and the MU <NUM> are connected through an RF cable, and all nodes from the MU <NUM> to lower nodes thereof are connected through optical cables. However, a signal transport medium between nodes may be variously modified. As an example, the BIU <NUM> and the MU <NUM> may be connected through an RF cable, but may be connected through an optical cable or a digital interface. As another example, the MU <NUM> and HUB <NUM> may be connected through an optical cable, the MU <NUM> and the RU <NUM> directly connected thereto may be connected through an optical cable, and the cascade-connected RUs <NUM> may be connected through an RF cable, a twist cable, a UTP cable, etc. As still another example, the MU <NUM> and the RU <NUM> directly connected thereto may also be connected through an RF cable, a twist cable, a UTP cable, etc..

Hereinafter, this will be described based on <FIG>. Therefore, in this embodiment, each of the MU <NUM>, the HUB <NUM>, and the RUs <NUM> may include an optical transceiver module for electrical-to-optical (E/O) conversion/optical-to-electrical (O/E) conversion. When node units are connected through a single optical cable, each of the MU <NUM>, the HUB <NUM>, and the RUs <NUM> may include a wavelength division multiplexing (WDM) element.

The DAS may be connected to an external monitoring device, e.g., a network management server or system (NMS) <NUM>. Accordingly, a manager can remotely monitor states and problems of the nodes in the DAS through the NMS <NUM>, and can remotely control operations of the nodes in the DAS through the NMS <NUM>.

<FIG> is a block diagram illustrating an embodiment of the RU in the DAS to which the inventive concept is applicable.

Here, the block diagram of <FIG> illustrates an embodiment of the RU <NUM> in the digital DAS in which nodes are connected through an optical cable. In addition, the block diagram of <FIG> illustrates only components related to a function of providing service signals to terminals in service coverage through a forward path and processing terminal signals received from the terminals in the service coverage through a reverse path.

Referring to <FIG>, with respect to a downlink signal transmission path (i.e., a forward path), the RU <NUM> includes an optical-to-electrical (O/E) converter <NUM>, a serializer/deserializer (SERDES) <NUM>, a deframer <NUM>, a digital signal processor (DSP) <NUM>, a digital-to-analog converter (DAC) <NUM>, an up converter <NUM>, and a power amplification unit (PAU) <NUM>.

In the forward path, an optical relay signal digital-transmitted through an optical cable may be converted into an electrical signal (serial digital signal) by the O/E converter <NUM>. The serial digital signal may be converted into a parallel digital signal by the SERDES <NUM>. The parallel digital signal may be deformatted by the deframer <NUM>. The DSP <NUM> performs functions including digital signal processing, digital filtering, gain control, digital multiplexing, etc. on relay signals for each frequency band. The digital signal passing through the DSP <NUM> is converted into an analog signal through the DAC <NUM> posterior to a digital part <NUM>, based on the signal transmission path. In this case, when the converted analog signal is an IF signal or a baseband signal, the analog signal may be frequency up-converted into an analog signal in the original RF band through the up converter <NUM>. The converted analog signal (i.e., the RF signal) in the original RF band is amplified through the PAU <NUM> to be transmitted through a service antenna (not shown).

With respect to an uplink signal transmission path (i.e., a reverse path), the RU <NUM> includes a low noise amplifier (LNA) <NUM>, a down converter <NUM>, an analog-to-digital converter ADC <NUM>, the DSP <NUM>, a framer <NUM>, the SERDES <NUM>, and an electrical-to-optical (E/O) converter <NUM>.

In the reverse path, an RF signal (i.e., a terminal signal) received through the service antenna (not shown) from a user terminal (not shown) in a service coverage may be low-noise amplified by the LNA <NUM>. The low-noise amplified signal may be frequency down-converted into an IF signal by the down converter <NUM>. The converted IF signal may be converted into a digital signal by the ADC <NUM> to be transmitted to the DSP <NUM>. The digital signal passing through the DSP <NUM> is formatted in a format suitable for digital transmission through the framer <NUM>. The formatted digital signal is converted into a serial digital signal by the SERDES <NUM>. The serial digital signal is converted into an optical digital signal by the E/O converter <NUM> to be transmitted to an upper node through an optical cable.

Although not clearly shown in <FIG>, in the state in which the RUs <NUM> are cascade-connected to each other as illustrated in <FIG>, the following method may be used when a relay signal transmitted from an upper node is transmitted to a lower adjacent RU cascade-connected to the upper node. For example, when an optical relay signal digital-transmitted from an upper node is transmitted to a lower adjacent RU cascade-connected to the upper node, the optical relay signal digital-transmitted from the upper node may be transmitted to the adjacent RU in an order of the O/E converter <NUM> → the SERDES <NUM> → the deframer <NUM> → the framer <NUM> → the SERDES <NUM> → the E/O converter <NUM>.

In <FIG>, the SERDES <NUM>, the deframer <NUM>, the framer <NUM>, and the DSP <NUM> may be implemented as a field programmable gate array (FPGA). In <FIG>, it is illustrated that the SERDES <NUM> and the DSP <NUM> are commonly used in the downlink and uplink signal transmission paths. However, the SERDES <NUM> and the DSP <NUM> may be separately provided for each path. In <FIG>, it is illustrated that the O/E converter <NUM> and the E/O converter <NUM> are provided separately from each other. However, the O/E converter <NUM> and the E/O converter <NUM> may be implemented as a single optical transceiver module (e.g., a single small form factor pluggable (SFP) (see reference numeral <NUM> of <FIG>)).

In the above, one form of the topology of the DAS and an embodiment of the RU have been described with reference to <FIG> and <FIG>. Particularly, the RU in the digital DAS in which digital signals are transmitted through a transport medium has been mainly described in <FIG>. However, it will be apparent that the inventive concept may be applied to various application examples.

<FIG> is a diagram illustrating a topology form of the DAS to which a method for summing downlink digital signal is applied according to an embodiment of the inventive concept.

The method for summing downlink digital signal according to the embodiment of the inventive concept may be applied to a topology form of the DAS as shown in <FIG>, which includes a plurality of HEUs 100A, 100B, and 100C, a single HUB <NUM>, and a plurality of RUs connected in a star structure or/and a cascade structure to the single HUB <NUM>.

In addition, it will be apparent that the method for summing downlink digital signal according to the embodiment of the inventive concept may be applied to various types of signal distributed systems each including a plurality of upper nodes constituting an upper stage based on a signal transmission direction, and a middle node receiving a plurality of mobile communication signals from the plurality of upper nodes, the middle node distributing the mobile communication signals to a plurality of lower nodes branch-connected thereto. Hereinafter, for convenience of illustration, the embodiment of the inventive concept will be described in detail based on <FIG>.

Referring to <FIG>, each of the HEUs 100A, 100B, and 100C receives mobile communication signals from a plurality of BTSs through transport mediums. In this case, each of the HEUs 100A, 100B, and 100C may perform digital signal conversion on the plurality of mobile communication signals from the plurality of BTSs and transmit the digital-converted mobile communication signals to the HUB <NUM>.

In this embodiment, it is assumed that each of the HEUs 100A, 100B, and 100C receives mobile communication signals of different mobile communication operators. Although it is assumed in <FIG> that one HEU and one mobile communication operator are matched one by one, the inventive concept is not limited thereto. That is, base stations covered by each HEU may not be base stations of different operators. In this case, the base station may be a base station unit concentrated on a remote place such as a BTS hotel. Hereinafter, for convenience of illustration, a case where each HEU receives signals for each mobile communication service band from base station units of different operators will be mainly described.

In the topology illustrated in <FIG>, when different sub-band signals in the same mobile communication service band (e.g., an LTE serve band using a band of <NUM>) are transmitted to the HUB <NUM> from different HEU 100A, 100B, and 100C, the HUB <NUM> may perform the downlink digital signal summing method according to the embodiment of the inventive concept. Hereinafter, this will be described with reference to <FIG>.

<FIG> is a block diagram illustrating components for performing the method for summing downlink digital signal as a digital part of a hub unit according to the embodiment of the inventive concept.

Referring to <FIG>, in order to perform the method for summing downlink digital signal, the digital part of the HUB <NUM> may include a signal input unit <NUM>, a band extractor <NUM>, a signal summer <NUM>, and a reformatter <NUM>.

The signal input unit <NUM> allows mobile communication signals transmitted from each of the HEUs 100A, 100B, and 100C to be input to the band extractor <NUM>. In this case, the signal input unit <NUM> may receive mobile communication signals input from each of the HEUs 100A, 100B, and 100C and then deframed.

For example, it is assumed that mobile communication signals (see reference numeral (A) of <FIG>) of a mobile communication operator A are input to the HUB <NUM> from the HEU of reference numeral 100A, mobile communication signals (see reference numeral (B) of <FIG>) of a mobile communication operator B are input to the HUB <NUM> from the HEU of reference numeral 100B, and mobile communication signals (see reference numeral (C) of <FIG>) of a mobile communication operator C are input to the HUB <NUM> from the HEU of reference numeral 100C. Here, the signals input to the HUB for each mobile communication operator may include mobile communication signals in the WCDMA band, the LTE band, and the LTE-A band. In this case, the mobile communication signals for each mobile communication operator may be input, through the signal input unit <NUM>, to a digital filter for each service band (see a digital filter for separating the WCDMA band, a digital filter for separating the LTE band, and a digital filter for separating the LTE-A band in <FIG>).

The band extractor <NUM> is provided with the digital filter for each service band, to separate only a signal corresponding to the service band. Referring to <FIG>, the mobile communication signals (A) of the mobile communication operator A, the mobile communication signals (B) of the mobile communication operator B, and the mobile communication signals (C) of the mobile communication operator C are band-separated by the digital filter for each service band. Here, reference numeral (a1) designates a signal in the WCDMA band among the mobile communication signals (A) of the mobile communication operator A, reference numeral (b1) designates a signal in the WCDMA band among the mobile communication signals (B) of the mobile communication operator B, and reference numeral (c1) designates a signal in the WCDMA band among the mobile communication signals (C) of the mobile communication operator C. In the same manner, reference numeral (a2), (b2), or (c2) designate a signal in the LTE band among the mobile communication signals of each mobile communication operator, and reference numeral (a3), (b3), or (c3) designate a signal in the LTE-A band among the mobile communication signals of each mobile communication operator.

In <FIG>, the case where the band extractor <NUM> is implemented with digital filters for each band is illustrated as an example. However, it will be apparent that various methods may be applied in addition to the band extraction method.

As described above, if the signals for each mobile communication operator pass through the band extractor <NUM>, sub-band signals (see Sub-band <NUM>, Sub-band <NUM>, and Sub-band <NUM>) in the same mobile communication service band may be extracted as shown in reference numeral 220A of <FIG>. Here, the Sub-band <NUM> conceptually illustrates a frequency band used by the mobile communication operator A in a process of providing a specific mobile communication service, the Sub-band <NUM> conceptually illustrates a frequency band used by the mobile communication operator B in a process of providing a specific mobile communication service, and the Sub-band <NUM> conceptually illustrates a frequency band used by the mobile communication operator C in a process of providing a specific mobile communication service.

The sub-band signals extracted for each of the same mobile communication service bands through the band extractor <NUM> as described above are input to the signal summer <NUM>. In the embodiment of the inventive concept, the signal summer <NUM> digitally sums the different sub-band signals in the same mobile communication service band, input through the band extractor <NUM>. If the sub-band signals pass through the signal summer <NUM>, the summing of the sub-band signal in the same mobile communication service band is performed as shown in reference numeral 230A of <FIG>, and a digital frame signal suitable for a transmission standard defined in the DAS is generated based on the summed signal through the reformatter <NUM>. The digital frame signal passing through the reformatter <NUM> may be transmitted each RU branch-connected to the HUB <NUM> via a framer, an SERDES, and an E/O converter.

As described above, according to the inventive concept, digital downlink signal summing is performed on sub-band signals in the same service band, transmitted from a plurality of operators, in the DAS, thereby improving the efficiency of digital transmission.

Claim 1:
A hub apparatus (<NUM>, <NUM>) for a distributed antenna system comprising:
a band extractor (<NUM>) configured to receive downlink mobile communication signals from different operators, wherein each of the downlink mobile communication signals includes a plurality of sub-band signals having different service bands each other, and
extract sub-band signals corresponding to a same service band, with respect to each of the service bands, from the downlink mobile communication signals; and
a signal summer (<NUM>) configured to digitally sum the extracted sub-band signals with respect to each of the service bands.