Patent Description:
In mobile communications, wireless coverage is dependent, to large extent, on a base transceiver station (BTS). Due to high costs of installing BTSs, there has been an attempt to expand wireless coverage through a remote radio head (RRH) device. The RRH device is connected with a BTS via a fiber optic cable using common public radio interface (CPRI) protocols.

Further, a distributed antenna system (DAS) may be introduced in order to enhance in-building coverage. <CIT> discloses an example of the DAS.

A typical analog DAS includes a headend unit and remote units. The headend unit is connected to BTSs or RRH devices via coaxial cables, converts radio frequency (RF) signal inputs from the connected BTSs or RRH devices into optical RF signals, and outputs the optical RF signals, and the remote units are connected to the headend unit via optical fibers and distribute downlink optical RF signals to wireless terminals.

Such an analog DAS is difficult to reconfigure once it has been deployed, and cannot scale dynamically to a required service capacity.

Meanwhile, as mobile communication technology evolves into long term evolution (LTE)-Advanced, a small cell technology emerges as one approach to maximize usage efficiency within limited resources. Small cells are low-powered wireless access BTSs, which are each defined as having an operational range from at least <NUM> meters to a few hundred meters. Small cells are classified as femtocells, picocells, metrocells, and microcells according to their usage range and purpose of use. In addition, the classification of small cells may be made according to an installation site and purpose of service, and small cells for home, enterprise, urban areas, and rural areas may exist.

<CIT> discloses a system for managing a small cell telecommunication system servicing multiple network operators. The management sub-system disclosed in <CIT> encompasses a controller, multiple baseband units and a transport module. Each of the baseband units includes one processor, I/Q modules, PHY modules and MAC modules. The output of the baseband units is connected to a transport module encompassing several mixers, which combine the I and Q components of the complex digital signal, a combining module and a backplane. The backplane routes the signal to one or more of the remote antenna units.

It is the object of the present mention to provide an adaptable small cell signal source for use in a cellular communication system. This object is solved by the subject matter of independent claim <NUM>. Preferred embodiments are the subject matter of the dependent claims.

The following description relates to a cellular communication system, which uses an analog distributed antenna system (DAS) that is readily reconfigurable according to a required service capacity.

The following description relates to a cellular communication system, which uses an analog DAS whose capacity is scalable according to a required service capacity.

The following description relates to a cellular communication system, which uses an analog DAS that is readily reconfigurable according to a required service capacity while minimizing addition of hardware devices or components at the customer sites.

Throughout the drawings and the detailed description, the same drawing reference numerals should be understood as referring to the same elements, features, and structures unless otherwise described.

The following description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Also, although configurations of selectively described aspects or selectively described aspects in below are illustrated as a single integrated configuration in the drawings, it should be understood that these configurations may be freely combined with each other as long as a technological contradiction of such a combination is not apparent for those skilled in the art unless otherwise described. It should also be noted that each block of the block diagrams may represent a physical element, and in some cases, may represent part of a function of one physical element or a logical representation of a function over a number of physical elements. A block or a portion of a block may sometimes be a set of program instructions. All or some of the blocks may be implemented by hardware, software, or a combination thereof.

<FIG> is a diagram illustrating an example of an analog distributed antenna system (DAS) to which the present invention is applicable. As shown in <FIG>, the analog DAS includes a headend unit <NUM> and a plurality of remote units <NUM>. In the illustrated example, the remote units are represented as remote optical units <NUM>. The headend unit <NUM> and the plurality of remote optical units <NUM> are connected via optical cables. The term "remote unit" indicates that the headend unit may be connected to the plurality of remote optical units <NUM> via coaxial cables or other analog cables instead of the optical cables. The headend unit <NUM> mixes and converts a plurality of radio frequency (RF) signals from a plurality of base transceiver stations (BTSs) into an optical RF signal. Each of the remote optical units <NUM> is disposed at each site, converts the optical RF signal received from the headend unit into an electrical RF signal, and transmits the electrical RF signal to the antenna. A description regarding a downlink signal may be applied to an uplink signal in a symmetrical manner.

For example, the headend unit <NUM> includes a base station interface unit (BIU) <NUM> and an optical distribution unit (ODU) <NUM>. The BIU <NUM> includes a plurality of base-station signal driving units <NUM>, which receive a signal of each band from a BTS, up/down convert the band of the signal if necessary, and output the resultant signal, and a combine-divider <NUM>, which mixes RF signals input from the plurality of base-station signal driving units and output a resultant signal. In the drawing, according to the names used in an applicant's commercialized system, the base-station signal driving unit is denoted as a main driver BTS unit (MDBU) and the combine-divider <NUM> is denoted as a main combiner/divider unit (MCDU). In the present exemplary aspect, the base-station signal driving units <NUM> are connected to an output of BTS equipment of each mobile communication service operator via coaxial cables. However, the present invention is not limited to the above, and the base-station signal driving units <NUM> may also be connected via optical cables. The base-station driving units <NUM> may deal with different frequency bands or different signal specifications according to specifications of a mobile communication service operator or specifications of BTS equipment. The combine-divider <NUM> has a plurality of outputs, through each of which a mixture of the RF signals output from the base-station signal driving units <NUM> is output according to needs of the remote optical units <NUM>.

The ODU <NUM> converts the RF signal output from the combine-divider <NUM> into an optical RF signal, and distributes and outputs the optical RF signal through a plurality of output ports.

The remote optical unit <NUM> receives the optical RF signals from the ODU <NUM>. Each output port of the ODU <NUM> may be connected with the remote optical unit <NUM>. For example, in <FIG>, an ODU <NUM>-<NUM> is connected with remote optical units <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>. Also, an ODU <NUM>-<NUM> is connected with remote optical units <NUM>-<NUM> and <NUM>-<NUM>.

<FIG> is a block diagram illustrating an example of a configuration of a remote optical unit of <FIG>. In one exemplary aspect, the remote optical unit <NUM> includes three types of modules which are a photoelectric conversion unit <NUM> configured to convert the optical RF signals received from the ODU <NUM> into electrical RF signals, a plurality of remote drive units (RDUs) <NUM>-<NUM> and <NUM>-<NUM>, and a combine unit configured to combine signals generated from the RDUs. In one exemplary aspect, the remote optical units <NUM> may include the plurality of RDUs.

Each of the RDUs <NUM>-<NUM> and <NUM>-<NUM> includes a bandpass filter <NUM> which filters only a required band in an RF signal on a downlink path, a modulation/demodulation unit <NUM> which up/down converts a band of the filtered RF signal when necessary and outputs a resultant signal, and a power amplifier <NUM>. Each of the RDUs <NUM>-<NUM> and <NUM>-<NUM> includes a low noise amplifier <NUM> which amplifies a signal from an antenna on an uplink path and a modulation/demodulation unit <NUM> which up/down converts a band of output from the low noise amplifier <NUM> and outputs a resultant signal when necessary. A plurality of RF signals of different bands may be multiplexed and transmitted through a single optical fiber.

<FIG> is a block diagram illustrating a configuration of a cellular communication system according to one exemplary aspect. As illustrated in <FIG>, the cellular communication system includes equipment for a small cell signal source <NUM>, a headend unit <NUM>, and remote units <NUM>-<NUM> and <NUM>-<NUM>. The small cell signal source <NUM> includes an upper small cell unit <NUM> and a lower small cell unit <NUM>. The upper small cell unit <NUM> includes a plurality of upper protocol processors <NUM>. Each upper protocol processor <NUM> processes a first part of a protocol stack of a small cell from an uppermost protocol of the protocol stack of the small cell.

The lower small cell unit <NUM> includes a plurality of lower protocol processors <NUM>. Each lower protocol processor <NUM> processes a remaining second part of the protocol stack of the small cell.

According to one aspect, the first part processed by the upper protocol processor <NUM> may be a media access control (MAC) layer and/or higher in the protocol stack of the small cell. In this case, the remaining second part processed by the lower protocol processor may be a physical (PHY) layer in the protocol stack of the small cell. Such function splitting is possible on various levels.

In regard to long term evolution (LTE) radio interface protocols, a number of technical materials have been available, for example, there is the article entitled "<NPL>. As described in the article, the LTE radio interface protocols may be classified as radio resource control (RRC), packet data convergence protocol (PDCP), radio link control (RLC), MAC, and PHY layer protocols. Among PDCP, RLC, and MAC layers that correspond to a second layer in seven layers of open system interconnection (OSI), the PDCP layer receives an RRC packet and processes header compression, a cipher of an RRC message, and integrity protection. The RLC layer segments and concatenates protocol data unit (PDU) packets from the PDCP layer to generate an RLC PDU with an appropriate packet size. In particular, the RLC layer performs automatic repeat request (ARQ) control according to a response from a receiving side. The MAC layer performs scheduling of shared channel resources. Also, the MAC layer processes a hybrid ARQ (HARQ). The PHY layer performs cell search and channel-dependent scheduling in a frequency domain, and performs a random access procedure when making a call.

Although the illustrated aspect is described as an example of an LTE system, the present invention is not limited thereto and can be applied to general mobile communication technologies or a combination thereof, as is typical for a DAS.

Virtualization technique of a radio access network (RAN), which has been recently discussed in the Small Cell Forum (http://www. smallcellforum. org), may be considered as a reference technique, although it is not directly related to the present invention. According to this technique, some upper layers among RAN layers for mobile communication are virtualized and implemented in cloud space in a software manner, and the remaining layers are implemented as physical network functions. In this forum, the discussion on "function splitting" is in progress regarding which layers are to be virtualized and which layers are to be implemented as physical network functions among the RAN layers. According to the ongoing discussion, because splitting is performed on higher layers, transport costs are advantageously reduced, while RF gains are also reduced. Important factors for considering function splitting in RAN virtualization which can secure smooth communications between virtualized functional blocks and physical lower layer functional blocks include bandwidth and latency. According to the materials disclosed by the Small Cell Forum, function splitting between a MAC layer and a PHY layer may provide a trade-off in terms of bandwidth and latency.

Referring back to <FIG>, the small cell signal source <NUM> of the cellular communication system in accordance with the exemplary aspect includes a first matching switch <NUM> and a common controller <NUM>. The first matching switch <NUM> respectively matches lower protocol processors to the plurality of remote units <NUM> connected to the BIU by switching on or off an output path of each of the lower protocol processors. According to a required service capacity, the common controller <NUM> activates a plurality of upper protocol processors of the upper small cell unit and a plurality of lower protocol processors of the lower small cell unit, and accordingly, controls an operation of the first matching switch <NUM>.

In one exemplary aspect, the upper protocol processors <NUM> may be implemented in a software manner, as well as in a circuitry manner. For example, each of the upper protocol processors <NUM> may be programmed in a general programming language (e.g., C/C++ language, etc.), then be compiled and executed as a task or a process on a central processing unit (CPU). In one exemplary aspect, the lower protocol processors <NUM> may be implemented in a circuit manner. For example, each of the lower protocol processors <NUM> may be implemented in the form of a gate array or firmware.

According to one aspect, a plurality of upper protocol processors <NUM>-<NUM> to <NUM>-p of the upper small cell unit <NUM> may be implemented as software tasks whose execution is controlled by the common controller <NUM>. Similarly, a plurality of lower protocol processors <NUM>-<NUM> to <NUM>-q of the lower small cell unit <NUM> may be implemented as software tasks whose execution is controlled by the common controller <NUM>. As is already known, since the upper protocol processors <NUM>-<NUM> to <NUM>-p are implemented as software tasks, they do not physically or logically reside within the upper small cell unit <NUM>, and no corresponding program modules exist on a program code. Rather, the upper protocol processors may be considered as entities which are newly generated and executed on memory under the control of a scheduler. Although, due to the technical difficulty in representation, it is stated that the small cell unit includes a plurality of upper protocol processors, such statement or similar expressions are intended to be construed to imply a case in which the plurality of upper protocol processors are implemented as software tasks, as well as a case in which the upper protocol processors are implemented physically, that is, as circuitry, in the upper small cell unit.

In another exemplary aspect, some of logical modules of the upper protocol processor <NUM> may be implemented in a circuit manner. For example, a part of each of the upper protocol processors <NUM> may be implemented in the form of a gate array or firmware, and the remaining part may be implemented as a software task. Similarly, in one exemplary aspect, some of logical modules of the lower protocol processor <NUM> may be implemented in a circuit manner. For example, a part of each of the lower protocol processor <NUM> may be implemented in the form of a gate array or firmware, and the remaining part may be implemented as a software task.

In another exemplary aspect, the upper protocol processor <NUM> may be implemented as a software task, and the lower protocol processors <NUM>-<NUM> to <NUM>-q may be implemented in a circuit manner.

In this case, the common controller <NUM> schedules execution of shared resources of the upper small cell unit <NUM>. According to another aspect, the common controller <NUM> may be implemented as one of components included in the upper small cell unit. In the illustrated exemplary aspect, the small cell is an LTE small cell, and, for example, the common controller may be implemented as a function of a scheduler that processes scheduling of shared channel resources in the MAC layer. Additionally, the common controller <NUM> operates to mitigate interference which may occur when a plurality of PHY layers transmit different RF signals using the same frequency in a multi-cell or multi-sector environment.

The first matching switch <NUM> may be a physical switch that switches on or off output, or may be implemented as a software input/output interface for using an output of a program module as input or a program code, such as an input/output command. In the illustrated exemplary aspect, the first matching switch <NUM> is included in the lower small cell unit <NUM>, but it is not limited thereto and may be configured as a separate device.

In the illustrated exemplary aspect, the first matching switch <NUM> connects an output of each of the lower protocol processors <NUM> to a plurality of headend units <NUM> by switching on or off an output path of each of the lower protocol processors <NUM>.

According to one aspect, when the number of users increases in a region where a DAS provides services, that is, in a service region, the common controller <NUM> additionally activates the upper protocol processor <NUM> of the upper small cell unit.

According to another aspect, when additional bandwidth or capacity is required due to an increase in the use of the frequency band by users in a region where the DAS provides services, i.e., in a service region, the common controller <NUM> additionally activates the lower protocol processor <NUM> of the lower small cell unit <NUM>. The common controller <NUM> controls the first matching switch <NUM> to connect the activated lower protocol processor <NUM> to the remote unit that needs additional capacity.

<FIG> is a block diagram illustrating a configuration of a cellular communication system according to another exemplary aspect. As illustrated in <FIG>, the cellular communication system includes a small cell signal source <NUM>, a headend unit <NUM>, and a plurality of remote units <NUM>-<NUM> and <NUM>-<NUM>. The small cell signal source <NUM> includes an upper small cell unit <NUM>, a lower small cell unit <NUM>, and a second matching switch <NUM>'. The upper small cell unit <NUM> includes a plurality of upper protocol processors <NUM>-<NUM> to <NUM>-n that process an upper first part of a protocol stack of a small cell. The lower small cell unit <NUM> includes a plurality of lower protocol processors <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-I that process a remaining second part of the protocol stack of the small cell.

The second matching switch <NUM>' switches on or off connections between each lower protocol processor of the lower small cell unit and each upper protocol processor of the upper small cell unit. The second matching switch <NUM>' may be a physical switch that switches on or off output, or may be implemented as a software input/output interface for using an output of a program module as input, or a program code such as an input/output command. Since configurations corresponding to those of <FIG> are similar to those in <FIG>, detailed descriptions thereof are omitted.

According to one aspect, when the number of users increases in a region where a DAS system provides services, i.e., in a service region, the common controller <NUM> additionally activates the upper protocol processor <NUM> of the upper small cell unit and the lower protocol processor <NUM> of the lower small cell unit, and in turn, controls an operation of the second matching switch <NUM>'. According to another aspect, when additional bandwidth or capacity is required due to an increase in the use of the frequency band by users in a region where a DAS system provides services, i.e., in a service region, the common controller <NUM> additionally activates the lower protocol processor <NUM> of the lower small cell unit <NUM>.

<FIG> is a block diagram illustrating a configuration of a cellular communication system according to still another exemplary aspect. As illustrated in <FIG>, the cellular communication system includes a small cell signal source <NUM>, a headend unit <NUM>, and a plurality of remote units <NUM>-<NUM> and <NUM>-<NUM>. The small cell signal source <NUM> includes an upper small cell unit <NUM>, a lower small cell unit <NUM>, a first matching switch <NUM>, and a second matching switch <NUM>'. The upper small cell unit <NUM> includes a plurality of upper protocol processors <NUM>-<NUM> to <NUM>-n that process an upper first part of a protocol stack of a small cell. The lower small cell unit <NUM> includes a plurality of lower protocol processors <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-I that process a remaining second part of the protocol stack of the small cell.

The first matching switch <NUM> switches on or off an output path of each lower protocol processor. The second matching switch <NUM>' switches on or off a connection between each lower protocol processor of the lower small cell unit and each upper protocol processor of the upper small cell unit. Each of the first matching switch <NUM> and the second matching switch <NUM>' may be a physical switch which switches on or off output, or may be implemented as a software input/output interface for using an output of a program module as input, or a program code such as an input/output command. Since configurations corresponding to those of <FIG> are similar to those in <FIG>, detailed descriptions thereof will be omitted.

According to one aspect, when the number of users increases in a region where a DAS system provides services, that is, in a service region, the common controller <NUM> additionally activates the upper protocol processor <NUM> of the upper small cell unit and the lower protocol processor <NUM> of the lower small cell unit, and in turn, controls an operation of the second matching switch <NUM>'.

According to another aspect, when additional bandwidth or capacity is required due to an increase in the use of the frequency band by users in a region where a DAS system provides services, i.e., in a service region, the common controller <NUM> additionally activates the lower protocol processor <NUM> of the lower small cell unit <NUM>, and in turn, controls an operation of the first matching switch <NUM>. Thus, a plurality of lower protocol processors <NUM> may be connected to a single upper protocol processor <NUM>.

As should be apparent from the exemplary aspects illustrated, one or both of the first matching switch <NUM> and the second matching switch <NUM>' may be provided.

<FIG> is a block diagram illustrating one aspect of a configuration of the lower small cell unit <NUM> in the exemplary aspect shown in <FIG> or <FIG>. According to one aspect, in the lower small cell unit <NUM>, the lower protocol processor <NUM> includes wireless converters <NUM>'-<NUM> to <NUM>'-q. In the present aspect, an output from the small cell is an RF signal, and the first matching switch <NUM> switches the RF signal from the lower protocol processor <NUM>.

<FIG> is a block diagram illustrating another aspect of a configuration of the lower small cell unit <NUM> in the exemplary aspect shown in <FIG> or <FIG>. As shown in <FIG>, the first matching switch includes wireless converters <NUM>-<NUM> to <NUM>-q at a receiving side. The small cell outputs a digital signal, for example, an LTE IQ signal, and the first matching switch <NUM> converts the IQ signal into an RF signal by modulating the IQ signal in the receiving side, and then transmits the RF signal to the remote optical unit which matches the small cell.

<FIG> is a block diagram illustrating still another aspect of a configuration of the lower small cell unit <NUM> in the exemplary aspect shown in <FIG> or <FIG>. As shown in <FIG>, the first matching switch <NUM> includes the wireless converters <NUM>-<NUM> to <NUM>-q at an output side. The small cell outputs a digital signal, for example, an LTE IQ signal, and the first matching switch <NUM> respectively connects the small cells to the remote optical units so that outputs of the small cells respectively match the remote optical units, and then the first matching switch <NUM> converts the IQ signal into an RF signal by modulating the IQ signal, and outputs the RF signal.

<FIG> is a block diagram illustrating one aspect of a configuration of the remote optical units <NUM>-<NUM> and <NUM>-<NUM> in the exemplary aspects shown in <FIG>. Referring to <FIG>, the remote optical unit <NUM> includes three types of modules which are the photoelectric conversion unit <NUM> configured to convert optical RF signals received from ODUs <NUM> into electrical RF signals, the plurality of RDUs <NUM>-<NUM> and <NUM>-<NUM>, and a combine unit <NUM> configured to combine signals generated from the RDUs. In one exemplary aspect, the remote optical unit <NUM> may include the plurality of RDUs <NUM>-<NUM> and <NUM>-<NUM>. The RDUs may have different configurations from each other.

The RDU <NUM>-<NUM> includes a bandpass filter <NUM>-<NUM> which filters only a required band in an RF signal on a downlink path, and a power amplifier <NUM>-<NUM> which amplifies the filtered RF signal. The RDU <NUM>-<NUM> includes a low noise amplifier <NUM>-<NUM> which amplifies a signal from an antenna on an uplink path.

The RDU <NUM>-<NUM> includes a bandpass filter <NUM>-<NUM> which filters only a required band in the RF signal on the downlink path, and a power amplifier <NUM>-<NUM> which amplifies the filtered RF signal. The RDU <NUM>-<NUM> includes a low noise amplifier <NUM>-<NUM> which amplifies the signal from the antenna on the uplink path. Outputs from the two RDUs <NUM>-<NUM> and <NUM>-<NUM> are combined by the combine unit <NUM> and are transmitted to a single antenna.

In this case, the bandpass filter <NUM>-<NUM> of the RDU <NUM>-<NUM> and the bandpass filter <NUM>-<NUM> of the RDU <NUM>-<NUM> may have different pass bands. A plurality of RF signals with different bands may be multiplexed and transmitted through a single optical fiber.

In the illustrated exemplary aspects, the remote optical unit <NUM> may have a suitable configuration capable of transmitting RF signals of two different bands which are output from the headend unit <NUM>.

<FIG> is a block diagram illustrating another aspect of a configuration of the remote optical units <NUM>-<NUM> and <NUM>-<NUM> in the exemplary aspects shown in <FIG>. Referring to <FIG>, the remote optical unit <NUM> includes three types of modules which are the photoelectric conversion unit <NUM> configured to convert the optical RF signals received from the ODUs <NUM> into electrical RF signals, the plurality of RDUs <NUM>-<NUM> and <NUM>-<NUM>, and the combine unit <NUM> configured to combine signals generated from the RDUs. In the exemplary aspect, the remote optical unit <NUM> may include the plurality of RDU modules <NUM>-<NUM> and <NUM>-<NUM>. The RDUs may have different configurations from each other.

The RDU <NUM>-<NUM> includes the bandpass filter <NUM>-<NUM> which filters only a required band in an RF signal on a downlink path, a demodulation unit <NUM>-<NUM> which demodulates the filtered RF signal by converting a band of the signal when necessary, and the power amplifier <NUM>-<NUM> which amplifies the demodulated signal. The RDU <NUM>-<NUM> includes the low noise amplifier <NUM>-<NUM> which amplifies a signal from an antenna on an uplink path, and a modulation unit <NUM>-<NUM> which modulates the amplified signal by converting a band of the signal when necessary.

The RDU <NUM>-<NUM> includes a bandpass filter <NUM>-<NUM> which filters only a required band in the RF signal on the downlink path, a demodulation unit <NUM>-<NUM> which demodulates the filtered RF signal by converting a band of the signal when necessary, and a power amplifier <NUM>-<NUM> which amplifies the demodulated signal. The RDU <NUM>-<NUM> includes a low noise amplifier <NUM>-<NUM> which amplifies the signal from the antenna on the uplink path and a modulation unit <NUM>-<NUM> which modulates the amplified signal by converting a band of the signal when necessary. The modulated signal outputs from the two RDUs <NUM>-<NUM> and <NUM>-<NUM> are in different bands.

According to one aspect, the headend unit may modulate RF signals of the same bands and transmit the modulated signals in order to increase coverage or capacity. These RF signals of different bands are transmitted through different remote optical units. Outputs of the two RDUs <NUM>-<NUM> and <NUM>-<NUM> having different frequencies are combined by the combine unit <NUM> and are transmitted to a single antenna.

<FIG> is a block diagram illustrating still another aspect of a configuration of the remote optical units <NUM>-<NUM> and <NUM>-<NUM> in the exemplary aspects shown in <FIG>. Referring to <FIG>, the remote optical unit <NUM> includes three types of modules which are the photoelectric conversion unit <NUM> configured to convert the optical RF signals received from the ODUs <NUM> into electrical RF signals, the plurality of RDUs <NUM>-<NUM> and <NUM>-<NUM>, and the combine unit <NUM> configured to combine signals generated from the RDUs. In one exemplary aspect, the remote optical unit <NUM> may include the plurality of RDU modules <NUM>-<NUM> and <NUM>-<NUM>. The RDUs may have different configurations from each other.

The RDU <NUM>-<NUM> includes the bandpass filter <NUM>-<NUM> which filters only a required band in an RF signal on a downlink path, and the power amplifier <NUM>-<NUM> which amplifies the filtered RF signal. The RDU <NUM>-<NUM> includes the low noise amplifier <NUM>-<NUM> which amplifies a signal from an antenna on an uplink path.

The RDU <NUM>-<NUM> includes the bandpass filter <NUM>-<NUM> which filters only a required band in the RF signal on the downlink path, the demodulation unit <NUM>-<NUM> which demodulates the filtered RF signal by converting a band of the signal when necessary, and the power amplifier <NUM>-<NUM> which amplifies the demodulated signal. The RDU <NUM>-<NUM> includes the low noise amplifier <NUM>-<NUM> which amplifies the signal from the antenna on the uplink path, and the modulation unit <NUM>-<NUM> which modulates the amplified signal by converting a band of the signal when necessary. Outputs of the two RDUs <NUM>-<NUM> and <NUM>-<NUM> are combined by the combine unit <NUM> and are transmitted to a single antenna.

In the illustrated exemplary aspect, since the RDU <NUM>-<NUM> does not include a modulation/demodulation unit, the RDU <NUM>-<NUM> performs bandpass filtering on the RF signal output from the headend unit <NUM>, then amplifies the filtered signal and outputs the amplified signal. The RDU <NUM>-<NUM> extracts an RF signal of a specific frequency band using the bandpass filter <NUM>-<NUM>, demodulates the extracted RF signal through band-down conversion using the modulation/demodulation unit <NUM>-<NUM>, and outputs a resulting signal.

In the exemplary aspects illustrated in <FIG>, scalability of the small cell is addressed from two perspectives. One is the number of users, and the other is bandwidth, i.e., total throughput. The proposed invention can improve both the number of users and the bandwidth/throughput. According to one aspect, the common controller <NUM> may additionally activate the upper protocol processor <NUM> in the upper small cell unit <NUM>, thereby increasing the number of users that can be supported. According to another aspect, the common controller <NUM> may allocate more computational resources, for example, memory or CPU resources, to the upper protocol processor <NUM> being executed in the upper small cell unit <NUM>, thereby enabling the increase of the number of users.

According to still another aspect, the common controller <NUM> may additionally activate the lower protocol processor <NUM> being executed in the lower small cell unit <NUM>, thereby increasing the bandwidth that can be supported. According to yet another aspect, the common controller <NUM> may allocate more computational resources, for example, memory or CPU resources, to the lower protocol processor <NUM> being executed in the lower small cell unit <NUM>, thereby enabling the increase of the bandwidth. In this case, the common controller <NUM> may need to appropriately control the first matching switch <NUM> or the second matching switch <NUM> in the lower small cell unit <NUM>. Hereinafter, the above-described aspects will be described in detail with reference to <FIG>.

<FIG> is a diagram for describing a first operation mode of a cellular communication system in accordance with the exemplary aspect shown in <FIG>. In the illustrated first operation mode, only one upper protocol processor <NUM>-<NUM> is being executed in the upper small cell unit <NUM>, and only one lower protocol processor <NUM>-<NUM> is being executed in the lower small cell unit <NUM>. The first matching switch <NUM> distributes output from the lower protocol processor <NUM>-<NUM>, i.e., a PHY layer <NUM>-<NUM>, into two signals and transmits the two signals to two input ports, which are an RF_1_SISO port and an RF_1_MIMO port of the BIU <NUM>.

In the illustrated exemplary aspect, the BIU <NUM> includes two types of base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM>, one of which does not include a demodulator but has the RF_1_SISO input port, and the other of which includes a demodulator and has the RF_1_MIMO input port. Alternatively, both of the base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> may have the same configurations and may include demodulator modules therein, but the base-station signal driving unit <NUM>-<NUM> may be configured not to use the included demodulator module and the base-station signal driving unit <NUM>-<NUM> may be configured to use the included demodulator module. In this case, a band of a signal output from the base-station signal driving unit <NUM>-<NUM> is represented as RF_1_SISO, and a band of a signal output from the base-station signal driving unit <NUM>-<NUM> is represented as RF_1_MIMO.

The common controller <NUM> has information about such a system configuration, and controls the first matching switch <NUM> according to the information so that interference among RF signals of the same frequency band can be avoided.

The two base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM> each receive the distributed RF signal. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_1_SISO input port, outputs the received RF signal intact to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_1_MIMO input port, modulates the RF signal to up or down convert a band thereof, and outputs a resulting signal to the combine-divider <NUM>. The combine-divider <NUM> mixes the two RF signals and outputs a mixture of the RF signals to the ODU <NUM>. The reason why the base-station signal driving unit <NUM>-<NUM> modulates the RF signal is because otherwise the mixed signal output from the combine-divider <NUM> cannot be separated later.

The ODU <NUM> converts the mixed signal into an optical RF signal and distributes the optical RF signal. The remote optical units <NUM>-<NUM> and <NUM>-<NUM> receive the distributed optical RF signal. In the illustrated exemplary aspect, the remote optical unit <NUM>-<NUM> has a suitable configuration capable of transmitting an RF signal of an RF_1_SISO band, which is output from the base-station signal driving unit <NUM>-<NUM> of the BIU <NUM>. In addition, the remote optical unit <NUM>-<NUM> has a suitable configuration capable of transmitting an RF signal of an RF_1_MIMO band, which is output from the base-station signal driving unit <NUM>-<NUM> of the BIU <NUM>. That is, the remote optical unit <NUM>-<NUM> does not include a modulation/demodulation unit, while the remote optical unit <NUM>-<NUM> includes a modulation/demodulation unit to convert the RF signal of the RF_1_MIMO band into an RF signal of the RF_1_SISO band.

The remote optical unit <NUM>-<NUM> photoelectrically converts the received optical RF signal into an electrical RF signal, then extracts an RF signal of a specified frequency band, i.e., the RF_1_SISO band, using the bandpass filter, amplifies the RF signal, and transmits the amplified signal to the antenna. The remote optical unit <NUM>-<NUM> photoelectrically converts the received optical RF signal into an electrical RF signal, then extracts an RF signal of another specified frequency band, i.e., the RF_1_MIMO band, using the bandpass filter, up or down converts a band of the extracted RF signal to a specified frequency band, amplifies the converted signal, and outputs a resulting signal to the antenna. Consequently, the two remote optical units <NUM>-<NUM> and <NUM>-<NUM> transmit the same data through RF signals of the same band. Since the two remote optical units <NUM>-<NUM> and <NUM>-<NUM> provide services to different floors of a building, coverage may be expanded.

<FIG> is a diagram for describing a second operation mode of the cellular communication system in accordance with the exemplary aspect shown in <FIG>. The second operation mode described herein is an example of a response that the system in accordance with the proposed invention may make when it is necessary to increase the number of users and the bandwidth/capacity in the first operation mode illustrated in <FIG>.

According to one aspect, when it is necessary to increase bandwidth or capacity, the common controller <NUM> controls an operation of the first matching switch and controls whether the headend unit performs modulation. In the illustrated second operation mode, the common controller <NUM> generates and executes new tasks such that the common controller <NUM> generates and executes a new upper protocol processor <NUM>-<NUM> and a new lower protocol processor <NUM>-<NUM> and connects both of the processors. In this case, MAC+#<NUM> processes different data as the new upper protocol processor <NUM>-<NUM> from data processed by MAC+#<NUM>. In the illustrated second operation mode, the new lower protocol processor <NUM>-<NUM> outputs a signal of the same frequency band as that of the existing lower protocol processor <NUM>-<NUM>.

The first matching switch <NUM> disconnects the existing connection between the lower protocol processor PHY#<NUM><NUM>-<NUM> and the RF_1_MIMO input port of the base-station signal driving unit <NUM>-<NUM>, and connects the newly generated and executed lower protocol processor PHY#<NUM><NUM>-<NUM> to the RF_1_MIMO input port of the base-station signal driving unit <NUM>-<NUM>. The two upper protocol processors <NUM>-<NUM> and <NUM>-<NUM> and the two lower protocol processors <NUM>-<NUM> and <NUM>-<NUM> are executed, which is generally identical to the case of two small cells being executed.

The two base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM> receive RF signals through two input ports. The base-station signal driving unit <NUM>-<NUM> outputs the received RF signal intact to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM> modulates the received RF signal to up or down convert a band thereof, and outputs a resulting signal to the combine-divider <NUM>. The reason why the base-station signal driving unit <NUM>-<NUM> modulates the RF signal is because otherwise the mixed signal output from the combine-divider <NUM> cannot be separated later.

The ODU <NUM> converts the mixed signal into an optical RF signal and distributes the optical RF signal. The remote optical units <NUM>-<NUM> and <NUM>-<NUM> receive the distributed optical RF signal. The remote optical unit <NUM>-<NUM> photoelectrically converts the received optical RF signal into an electrical RF signal, then extracts an RF signal of a specified frequency band, i.e., the RF_1_SISO band, using the bandpass filter, amplifies the RF signal, and transmits the amplified signal to the antenna. The remote optical unit <NUM>-<NUM> photoelectrically converts the received optical RF signal into an electrical RF signal, then extracts an RF signal of another specified frequency band, i.e., the RF_1_MIMO band, using the bandpass filter, up or down converts a band of the extracted RF signal to a specified frequency band, amplifies a converted signal, and outputs a resulting signal to the antenna. Consequently, since the two remote optical units <NUM>-<NUM> and <NUM>-<NUM> transmit different LTE data through RF signals of the same band, it is possible to form two mobile communication cells and to double the number of users and the bandwidth/capacity in comparison to the first operation mode illustrated in <FIG>.

<FIG> is a diagram for describing a third operation mode of the cellular communication system in accordance with the exemplary aspect shown in <FIG> or <FIG>. The third operation mode described herein is an example of a response that the system in accordance with the proposed invention may make when a necessity to increase bandwidth/capacity used by users arises in the first operation mode illustrated in <FIG>.

According to one aspect, when it is necessary to increase bandwidth/capacity, the common controller <NUM> additionally activates the lower protocol processor, controls an operation of the first matching switch, and controls whether the lower protocol processor performs modulation. In the illustrated third operation mode, the common controller <NUM> generates and executes new tasks such that the common controller <NUM> generates and executes a new lower protocol processor <NUM>-<NUM>. The common controller <NUM> controls the second matching switch <NUM>' to connect the newly generated lower protocol processor <NUM>-<NUM> to the upper protocol processor <NUM>-<NUM>.

In the illustrated third operation mode, the new lower protocol processor <NUM>-<NUM> outputs a signal of the same frequency band as that of the existing lower protocol processor <NUM>-<NUM>.

The first matching switch <NUM> disconnects the existing connection between the lower protocol processor PHY#<NUM><NUM>-<NUM> and the RF_1_MIMO input port of the base-station signal driving unit <NUM>-<NUM>, and connects the newly generated and executed lower protocol processor PHY#<NUM><NUM>-<NUM> to the RF_1_MIMO input port of the base-station signal driving unit <NUM>-<NUM>.

The base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM> receive RF signals through two input ports. The base-station signal driving unit <NUM>-<NUM> outputs the received RF signal intact to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM> modulates the received RF signal to up or down convert a band thereof, and outputs a resulting signal to the combine-divider <NUM>. The reason why the base-station signal driving unit <NUM>-<NUM> modulates the RF signal is because otherwise the mixed signal output from the combine-divider <NUM> cannot be separated later.

The ODU <NUM> converts the mixed signal into an optical RF signal and distributes the optical RF signal. The remote optical units <NUM>-<NUM> and <NUM>-<NUM> receive the distributed optical RF signal. The remote optical unit <NUM>-<NUM> photoelectrically converts the received optical RF signal into an electrical RF signal, then extracts an RF signal of a specified frequency band, i.e., the RF_1_SISO band, using the bandpass filter, amplifies the RF signal, and transmits the amplified signal to the antenna. The remote optical unit <NUM>-<NUM> photoelectrically converts the received optical RF signal into an electrical RF signal, then extracts an RF signal of another specified frequency band, i.e., the RF_1_MIMO band, using the bandpass filter, up or down converts a band of the extracted RF signal to a specified frequency band, amplifies the converted signal, and outputs a resulting signal to the antenna. Consequently, the bandwidths of both the remote optical units <NUM>-<NUM> and <NUM>-<NUM> can be widened more than that of the first operation mode of <FIG>.

In the first to third operation modes shown in <FIG>, extending coverage is dependent on the modulation/demodulation in the base-station signal driving unit of the headend unit and the modulation/demodulation in the corresponding remote unit. However, aspects of the proposed invention are not limited to the above, that is, by controlling the wireless converters, as shown in <FIG>, to convert a signal into a different frequency band that is used by the same service operator, the modulation/demodulation in the headend side may not be necessary. Although such an aspect may be applied to any operation mode which has been described with reference to <FIG> or will be described below, an exemplary operation in a case in which the aspect is applied to the second operation mode shown in <FIG> will be described herein.

<FIG> is a diagram illustrating an example of another cellular communication system that implements the second operation mode described with reference to <FIG>. The example shown in <FIG> is substantially the same as the exemplary aspect of <FIG>, but the base-station signal driving unit <NUM>-<NUM> and the corresponding remote unit <NUM>-<NUM> do not need a modulation/demodulation unit. Rather, the lower protocol processors of the lower baseband unit <NUM> are connected with the wireless converters <NUM>'-<NUM> and <NUM>'-<NUM>, respectively. As should be apparent to those skilled in the art, the respective lower protocol processors of the exemplary aspects illustrated in <FIG> require wireless converters, which are simply omitted in the drawings. The difference between the above aspects and the present aspect is that modulation/demodulation frequencies of the wireless converters are controlled by the common controller <NUM>.

Mobile communication service operators use multiple frequencies for the same service in order to support as much bandwidth and/or as many users as possible. Terminal devices search all of multiple frequencies for services of the same service operator. The common controller <NUM> controls modulation/demodulation frequencies of the wireless converters in order to increase the number of users and/or the bandwidth. For example, in the exemplary aspect shown in <FIG>, the upper protocol processor <NUM>-<NUM> and the lower protocol processor <NUM>-<NUM> are additionally activated for the same service operator, and the wireless converter <NUM>'-<NUM> and the wireless converter <NUM>'-<NUM> are controlled to select two of the multiple frequencies used by the service operator and modulate/demodulate the selected frequencies. In this case, the bandpass filter <NUM>-<NUM> of the remote unit <NUM>-<NUM> is tuned to a band of the wireless converter <NUM>'-<NUM>, and the bandpass filter <NUM>-<NUM> of the remote unit <NUM>-<NUM> is tuned to a band of the wireless converter <NUM>'-<NUM>. As such, the coverage as well as the bandwidth and the number of users can be substantially increased for the same service operator. Although the exemplary aspect of <FIG> employs the configuration illustrated in <FIG>, it should be understood by those skilled in the art that the configuration of <FIG> or <FIG> can be applied to <FIG> through the exemplary aspect of <FIG>.

Similar schemes use the configurations illustrated in <FIG>, and may be applied to the exemplary aspect of <FIG>.

<FIG> is a diagram for describing a fifth operation mode of the cellular communication system in accordance with the exemplary aspect illustrated in <FIG> or <FIG>. When it is necessary to increase the number of users or the throughput in the first operation mode as illustrated in <FIG>, the fifth operation mode may be initiated. Alternatively, the fifth operation mode may be initiated in order to increase the throughput in the second operation mode illustrated in <FIG>. In the fifth operation mode, the common controller <NUM> generates and executes the additional upper protocol processor <NUM>-<NUM> in the upper small cell unit <NUM>, generates and executes the additional lower protocol processor <NUM>-<NUM> in the lower small cell unit <NUM>, and connects the upper protocol processor <NUM>-<NUM> and the lower protocol processor <NUM>-<NUM>. In the case where PHY#<NUM> and PHY#<NUM> are hardware circuits, the common controller <NUM> transmits only an output of the newly executed upper protocol processor <NUM>-<NUM> to PHY#<NUM>.

MAC+#<NUM>, which is the existing upper protocol processor <NUM>-<NUM>, outputs data D1, while MAC+#<NUM>, which is the newly executed upper protocol processor <NUM>-<NUM>, outputs data D2. PHY#<NUM>, which is the existing lower protocol processor <NUM>-<NUM>, transmits a signal of an RF_1 band, while PHY#<NUM>, which is the newly executed lower protocol processor <NUM>-<NUM>, outputs a signal of an RF_2 band.

The first matching switch <NUM> distributes each output of each lower protocol processor <NUM>-<NUM> and <NUM>-<NUM>, i.e., PHY#<NUM> and PHY#<NUM><NUM>-<NUM> and <NUM>-<NUM>, into two, and transmits the distributed output to one pair of the RF_1_SISO port and the RF_1_MIMO port and the other pair of an RF_2_SISO port and an RF_2_MIMO port, which are pairs of input ports of the BIU <NUM>.

In the illustrated exemplary aspect, the BIU <NUM> includes two activated base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> that receive RF signals of the RF_1 band as an input such that one base-station signal driving unit does not include a modulator but has the RF_1_SISO input port while the other includes a modulator and has the RF_1_MIMO input port. In this case, a band of the signal output from the base-station signal driving unit <NUM>-<NUM> is represented as RF_1_SISO, and a band of the signal output from the base-station signal driving unit <NUM>-<NUM> is represented as RF_1_MIMO.

In the illustrated exemplary aspect, the BIU <NUM> includes two activated base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> that receive RF signals of the RF_2 band as inputs such that one base-station signal driving unit does not include a modulator but has the RF_2_SISO input port while the other includes a modulator and has the RF_2_MIMO input port. In this case, a band of the signal output the base-station signal driving unit <NUM>-<NUM> is represented as RF_2_SISO, and a band of the signal output from the base-station signal driving unit <NUM>-<NUM> is represented as RF_2_MIMO.

The two base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM> each receive the distributed RF signal. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_1_SISO input port, outputs the received RF signal intact to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_1_MIMO input port, modulates the RF signal to up or down convert a band thereof, and outputs a resulting signal to the combine-divider <NUM>.

The two base-station signal driving unit <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM> each receive the distributed RF signal. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_2_SISO input port, outputs the received RF signal intact to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_2_MIMO input port, modulates the RF signal to up or down convert a band thereof, and outputs a resulting signal to the combine-divider <NUM>.

The combine-divider <NUM> mixes the four signals and outputs a mixture of the signals to the ODU <NUM>. The ODU <NUM> converts the mixed signal into an optical RF signal and distributes the optical RF signal.

The remote optical units <NUM>-<NUM> and <NUM>-<NUM> receive the distributed optical RF signal.

In the illustrated exemplary aspect, the remote optical unit <NUM>-<NUM> may be configured as the exemplary aspect of <FIG> and the remote optical unit <NUM>-<NUM> may be configured as the exemplary aspect of <FIG>. The operations of the remote optical units <NUM>-<NUM> and <NUM>-<NUM> in accordance with the exemplary aspect of <FIG> will be described with reference to <FIG> and <FIG>.

Referring to <FIG>, the remote optical unit <NUM>-<NUM> processes signals of two channels and has a configuration suitable to transmit RF signals of two bands, i.e., the RF_1_SISO band and the RF_2_SISO band, which are output from the base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM>.

An upper channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of a specified frequency band, i.e., the RF_1_SISO band, from a photoelectrically converted RF signal output from the photoelectric conversion unit (<NUM>) through the bandpass filter <NUM>-<NUM>, amplifies the extracted RF signal, and outputs a resulting signal to the antenna. A lower channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of a specified frequency band, i.e., the RF_2_SISO band, from the photoelectrically converted RF signal output from the photoelectric conversion unit (<NUM>) through the bandpass filter <NUM>-<NUM>, amplifies the extracted RF signal, and outputs a resulting signal to the antenna. The RF signal of RF_1_SISO band and the RF signal of RF_2_SISO band are mixed in a forward direction by the combine unit <NUM> and then transmitted to the antenna. Descriptions of an uplink will be omitted.

Referring to <FIG>, the remote optical unit <NUM>-<NUM> processes signals of two channels and has a configuration suitable to transmit RF signals of two bands, i.e., the RF_1_MIMO band and the RF_2_MIMO band, which are output from the base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM>. More specifically, the remote optical unit <NUM>-<NUM> does not include a modulation/demodulation unit, whereas the remote optical unit <NUM>-<NUM> includes the modulation/demodulation unit <NUM>-<NUM>, which converts the RF signal of the RF_1_MIMO band into an RF signal of the RF_1 band, and the modulation/demodulation unit <NUM>-<NUM>, which converts the RF signal of the RF_2_MIMO band into an RF signal of the RF_2 band.

An upper channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of another specified frequency band, i.e., the RF_1_MIMO band, from a photoelectrically converted RF signal output from the photoelectric conversion unit (<NUM>) through the bandpass filter <NUM>-<NUM>, demodulates the extracted RF signal to a specified frequency band, i.e., the RF_1 band, through band-down conversion by the modulation/demodulation unit <NUM>-<NUM>, amplifies the demodulated RF signal in the amplifier <NUM>-<NUM>, and outputs a resulting signal to the antenna. A lower channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of another frequency band, i.e., the RF_2_MIMO band, from the photoelectrically converted RF signal through the bandpass filter <NUM>-<NUM>, demodulates the extracted RF signal to a specified frequency band, i.e., the RF_2 band, through band-down conversion by the modulation/demodulation unit <NUM>-<NUM>, amplifies the demodulated RF signal in the amplifier <NUM>-<NUM>, and outputs a resulting signal to the antenna. The RF signal of the RF_1_MIMO band and the RF signal of the RF_2_MIMO band are mixed in the forward direction by the combine unit <NUM> and then transmitted to the antenna. Descriptions of an uplink will be omitted.

As a result, both of the remote optical units <NUM>-<NUM> and <NUM>-<NUM> transmit the data D1 through the RF signal of the RF_1 band and the data D2 through the RF signal of the RF_2 band. That is, since different data D1 and D2 are transmitted using two frequency bands RF_1 and RF_2, it is the same as functions of two cells or a single cell sectorized into two sectors.

<FIG> is a diagram for describing a sixth operation mode of the cellular communication system in accordance with the exemplary aspect illustrated in <FIG> or <FIG>. When it is necessary to additionally increase the throughput in the fifth operation mode as illustrated in <FIG>, the sixth operation mode may be initiated. In the sixth operation mode, the common controller <NUM> generates and executes another additional upper protocol processor <NUM>-<NUM> in the upper small cell unit <NUM>, generates and executes another additional lower protocol processor <NUM>-<NUM> in the lower small cell unit <NUM>, and connects the upper protocol processor <NUM>-<NUM> and the lower protocol processor <NUM>-<NUM>. In the case where PHY#<NUM>, PHY#<NUM>, and PHY#<NUM> are hardware circuits, the common controller <NUM> transmits only an output of the newly executed upper protocol processor <NUM>-<NUM> to PHY#<NUM>.

MAC+#<NUM> and MAC+#<NUM>, which are the existing upper protocol processors <NUM>-<NUM> and <NUM>-<NUM>, output data D1 and data D2, respectively, while MAC+#<NUM>, which is the newly executed upper protocol processor <NUM>-<NUM>, outputs data D3. PHY#<NUM>, which is the existing lower protocol processor <NUM>-<NUM>, transmits a signal of the RF_1 band, while PHY#<NUM>, which is the newly executed lower protocol processor <NUM>-<NUM>, outputs a signal of the RF_2 band as does the existing lower protocol processor <NUM>-<NUM>.

In the same manner as above, the first matching switch <NUM> distributes an output of the lower protocol processor <NUM>-<NUM>, i.e., PHY#<NUM>, into two signals, and transmits the distributed output to the RF_1_SISO port and the RF_1_MIMO port, which are input ports of the BIU <NUM>. Also, the first matching switch <NUM> connects output of the lower protocol processor <NUM>-<NUM>, i.e., PHY#<NUM>, with the RF_2_SISO port, which is an input port of the BIU <NUM>. In addition, the first matching switch <NUM> disconnects the existing connection between the lower protocol processor <NUM>-<NUM>, i.e., PHY#<NUM>, and the RF_2_MIMO input port of the BIU <NUM>, and connects the newly generated and executed lower protocol processor <NUM>-<NUM>, i.e., PHY#<NUM><NUM>-<NUM>, with the RF_2_MIMO input port of the BIU <NUM>.

In the illustrated exemplary aspect, the BIU <NUM> includes two activated base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> that receive RF signals of the RF_2 band as an input such that one base-station signal driving unit does not include a modulator/demodulator but has the RF_2_SISO input port while the other includes a modulator/demodulator and has the RF_2_MIMO input port. In this case, a band of the signal output from the base-station signal driving unit <NUM>-<NUM> is represented as RF_2_SISO, and a band of the signal output from the base-station signal driving unit <NUM>-<NUM> is represented as RF_2_MIMO.

The two base-station signal driving unit <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM> each receive the distributed RF signal. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_1_SISO input port, outputs the received RF signal intact to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_1_MIMO input port, modulates the RF signal to up or down convert a band thereof, and outputs a resulting signal to the combine-divider <NUM>.

The two base-station signal driving unit <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM> receive the RF signal from PHY#<NUM> and PHY#<NUM>, respectively. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_2_SISO input port, outputs the received RF signal intact to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_2_MIMO input port, modulates the RF signal to up or down convert a band thereof, and outputs a resulting signal to the combine-divider <NUM>.

In the illustrated exemplary aspect the remote optical unit <NUM>-<NUM> may be configured as the exemplary aspect of <FIG> and the remote optical unit <NUM>-<NUM> may be configured as the exemplary aspect of <FIG>. The operations of the remote optical units <NUM>-<NUM> and <NUM>-<NUM> in accordance with the exemplary aspect of <FIG> will be described with reference to <FIG> and <FIG>.

Referring to <FIG>, the remote optical unit <NUM>-<NUM> processes signals of two channels and has a suitable configuration capable of transmitting RF signals of two bands, i.e., the RF_1_SISO band and the RF_2_SISO band, which are output from the base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM>.

An upper channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of a specified frequency band, i.e., the RF_1_SISO band, from a photoelectrically converted RF signal output from the photoelectric conversion unit (<NUM>) through the bandpass filter <NUM>-<NUM>, amplifies the extracted RF signal, and outputs a resulting signal to the antenna. A lower channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of a specified frequency band, i.e., the RF_2_SISO band, from the photoelectrically converted RF signal output from the photoelectric conversion unit (<NUM>) through the bandpass filter <NUM>-<NUM>, amplifies the extracted RF signal, and outputs a resulting signal to the antenna. The RF signal of RF_1_SISO band and the RF signal of RF_2_SISO band are mixed in the forward direction by the combine unit <NUM> and then transmitted to the antenna. Descriptions of an uplink will be omitted.

Referring to <FIG>, the remote optical unit <NUM>-<NUM> processes signals of two channels and has a suitable configuration capable of transmitting RF signals of two bands, i.e., the RF_1_MIMO band and the RF_2_MIMO band, which are output from the base-station signal driving units <NUM>-<NUM> and <NUM>-<NUM> of the BIU <NUM>. More specifically, the remote optical unit <NUM>-<NUM> does not include a modulation/demodulation unit, whereas the remote optical unit <NUM>-<NUM> includes the modulation/demodulation unit <NUM>-<NUM>, which converts the RF signal of the RF_1_MIMO band into an RF signal of the RF_1 band, and the modulation/demodulation unit <NUM>-<NUM>, which converts the RF signal of the RF_2_MIMO band into an RF signal of the RF_2 band.

An upper channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of another specified frequency band, i.e., the RF_1_MIMO band, from a photoelectrically converted RF signal output from the photoelectric conversion unit (<NUM>) through the bandpass filter <NUM>-<NUM>, demodulates the extracted RF signal to a specified frequency band, i.e., the RF_1 band through band-down conversion by the modulation/demodulation unit <NUM>-<NUM>, amplifies the demodulated RF signal in the amplifier <NUM>-<NUM>, and outputs a resulting signal to the antenna. A lower channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of another frequency band, i.e., the RF_2_MIMO band, from the photoelectrically converted RF signal through the bandpass filter <NUM>-<NUM>, demodulates the extracted RF signal to a specified frequency band, i.e., the RF_2 band through band-down conversion by the modulation/demodulation unit <NUM>-<NUM>, amplifies a demodulated RF signal in the amplifier <NUM>-<NUM>, and outputs a resulting signal to the antenna. The RF signal of RF_1_MIMO band and the RF signal of RF_2_MIMO band are mixed in the forward direction by the combine unit <NUM> and then transmitted to the antenna. Descriptions of an uplink will be omitted.

As a result, the remote optical unit <NUM>-<NUM> transmits the data D1 through the RF signals of the RF_1 band and the data D2 through the RF signals of the RF_2 band, while the remote optical unit <NUM>-<NUM> transmits the data D1 through the RF signals of the RF_1 band and the data D3 through the RF signals of the RF_2 band. That is, since different data D1, D2, and D3 are transmitted using two frequency bands RF_1 and RF_2, it is the same as functions of three cells or a single cell sectorized into three sectors.

<FIG> is a diagram for describing a seventh operation mode of the cellular communication system in accordance with the exemplary aspect illustrated in <FIG> or <FIG>. When it is necessary to additionally increase the throughput in the sixth operation mode as illustrated in <FIG>, the seventh operation mode may be initiated. In the seventh operation mode, the common controller <NUM> generates and executes another additional upper protocol processor <NUM>-<NUM> in the upper small cell unit <NUM>, generates and executes another additional lower protocol processor <NUM>-<NUM> in the lower small cell unit <NUM>, and connects the upper protocol processor <NUM>-<NUM> and the lower protocol processor <NUM>-<NUM>. In the case where PHY#<NUM>, PHY#<NUM>, PHY#<NUM>, and PHY#<NUM> are hardware circuits, the common controller <NUM> transmits only an output of the newly executed upper protocol processor <NUM>-<NUM> to PHY#<NUM>.

MAC+#<NUM>, MAC+#<NUM>, and MAC+#<NUM>, which are the existing upper protocol processors <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, output data D1, data D2, and data D3, respectively, while MAC+#<NUM>, which is the newly executed upper protocol processor <NUM>-<NUM>, outputs data D4. PHY#<NUM>, which is the existing lower protocol processor <NUM>-<NUM>, and PHY#<NUM>, which is the newly executed lower protocol processor <NUM>-<NUM>, both transmit signals of the RF_1 band, while the remaining existing lower protocol processors <NUM>-<NUM> and <NUM>-<NUM> output signals of the RF_2 band.

The first matching switch <NUM> disconnects the existing connection between the lower protocol processor <NUM>-<NUM>, i.e., PHY#<NUM><NUM>-<NUM>, and the RF_1_MIMO input port of the BIU <NUM>, and connects the newly executed lower protocol processor <NUM>-<NUM>, i.e., PHY#<NUM><NUM>-<NUM>, with the RF_1_MIMO input port of the BIU <NUM>. Connections of the remaining two input ports are maintained in the same state as the sixth operation mode.

The configurations of the BIU <NUM> and the remote optical units <NUM>-<NUM> and <NUM>-<NUM> are similar to those in the sixth operation mode. The common controller <NUM> has information about such a system configuration, and controls the first matching switch <NUM> according to the information so that interference among RF signals of the same frequency band can be avoided.

The four base-station signal driving units <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> of the BIU <NUM> receive an RF_1_SISO RF signal, an RF_2_SISO RF signal, an RF_2_MIMO RF signal, and an RF_1_MIMO RF signal, respectively. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_1_SISO input port, outputs the RF signal intact to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_2_SISO input port, outputs the RF signal intact to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_2_MIMO input port, modulates the received RF signal to up or down convert a band thereof and outputs a resulting signal to the combine-divider <NUM>. The base-station signal driving unit <NUM>-<NUM>, which receives the RF signal through the RF_1_MIMO input port, modulates the RF signal to up or down convert a band thereof and outputs a resulting signal to the combine-divider <NUM>.

An upper channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of a specified frequency band, i.e., the RF_1_SISO band, from a photoelectrically converted RF signal output from the photoelectric conversion unit (<NUM>) through the bandpass filter <NUM>-<NUM>, amplifies the extracted RF signal, and outputs a resulting signal to the antenna. A lower channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of a specified frequency band, i.e., the RF_2_SISO band, from the photoelectrically converted RF signal output from the photoelectric conversion unit (<NUM>) through the bandpass filter <NUM>-<NUM>, amplifies the extracted RF signal, and outputs a resulting signal to the antenna. The RF signal of the RF_1_SISO band and the RF signal of the RF_2_SISO band are mixed in the forward direction by the combine unit <NUM> and then transmitted to the antenna. Descriptions of an uplink will be omitted.

An upper channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of another specified frequency band, i.e., the RF_1_MIMO band, from a photoelectrically converted RF signal output from the photoelectric conversion unit (<NUM>) through the bandpass filter <NUM>-<NUM>, demodulates the extracted RF signal to a specified frequency band, i.e., the RF_1 band through band-down conversion by the modulation/demodulation unit <NUM>-<NUM>, amplifies the demodulated RF signal in the amplifier <NUM>-<NUM>, and outputs a resulting signal to the antenna. A lower channel of the remote optical unit <NUM>-<NUM> extracts an RF signal of another frequency band, i.e., the RF_2_MIMO band, from the photoelectrically converted RF signal through the bandpass filter <NUM>-<NUM>, demodulates the extracted RF signal to a specified frequency band, i.e., the RF_2 band through band-down conversion by the modulation/demodulation unit <NUM>-<NUM>, amplifies the demodulated RF signal in the amplifier <NUM>-<NUM>, and outputs a resulting signal to the antenna. The RF signal of RF_1_MIMO band and the RF signal of RF_2_MIMO band are mixed in the forward direction by the combine unit <NUM> and then transmitted to the antenna. Descriptions of an uplink will be omitted.

As a result, the remote optical unit <NUM>-<NUM> transmits the data D1 through the RF signals of the RF_1 band and the data D2 through the RF signals of the RF_2 band, while the remote optical unit <NUM>-<NUM> transmits the data D4 through the RF signals of the RF_1 band and the data D3 through the RF signals of the RF_2 band. That is, since different data D1, D2, D3, and D4 are sent out using two frequency bands RF_1 and RF_2, it is the same as functions of four cells or a single cell sectorized into four sectors.

That is, a band of the RF signal output from the first matching switch <NUM> of the lower small cell unit <NUM> matches a frequency of the bandpass filter of the RDU in the matched remote optical unit. In addition, in a case in which the band of the RF signal is converted in the base-station signal driving unit <NUM> of the BIU <NUM>, the band matches the frequency of the bandpass filter of the RDU inside the matched remote optical unit.

By generalizing the aspects of the proposed invention, it is possible to flexibly increase throughput when service capacity is additionally required. In other words, by varying a passband of the bandpass filter in each remote unit, the common controller additionally activates and allocates another physical layer, or controls the base-station signal driving unit to up or down convert a band of the signal to a band of the bandpass filter of a remote unit to be connected thereto in order to increase throughput for a physical layer that uses the same frequency band, and thereby an increase in throughput is generally achieved.

According to the proposed invention, it is possible to provide an expanded cellular communication using an existing analog DAS.

Claim 1:
A small cell signal source (<NUM>) for use in a cellular communication system the small cell signal source (<NUM>) comprising:
an upper small cell unit (<NUM>) comprising a plurality of upper protocol processors (<NUM>) configured to process an upper first part of a protocol stack of a small cell,
a lower small cell unit (<NUM>) comprising a plurality of lower protocol processors (<NUM>) configured to process a remaining second part of the protocol stack of the small cell,
a first matching switch (<NUM>) configured to switch on or off an output path of each of the lower protocol processors (<NUM>),
a common controller (<NUM>) configured to control activation of the plurality of upper protocol processors (<NUM>) of the upper small cell unit (<NUM>) and the plurality of lower protocol processors (<NUM>) of the lower small cell unit (<NUM>) according to a required service capacity and configured to control an operation of the first matching switch (<NUM>) and the second matching switch (<NUM>'), characterized by
a second matching switch (<NUM>') configured to switch on or off connections between each lower protocol processor of the lower small cell unit and each upper protocol processor of the upper small cell unit and wherein the common controller is configured to control operation of the second matching switch.