Patent Description:
A contemporary wireless communication system for repeating wireless signals, such as distributed antenna system <NUM>, is shown in <FIG>, and includes a number of remote units <NUM> distributed to provide coverage within a service area of the system <NUM>. In particular, each remote antenna unit <NUM> typically includes an antenna <NUM> and suitable electronics. Each remote unit is coupled to a master unit <NUM> with a suitable media, such as a coaxial cable or optical fiber. Each master unit <NUM> is, in turn, coupled to an RF combination network <NUM> that combines the signals from one or more (<NUM>-N) base transceiver stations ("BTS," or more simply, "base station") <NUM> (hereinafter, "BTS" <NUM>). As illustrated in <FIG>, the system <NUM> may include a plurality of master units <NUM> and may couple to a plurality of BTSs <NUM>, each master unit <NUM> configured to provide a combination of the signals from the BTSs <NUM> to the various remote units <NUM>. The link <NUM> between the BTSs <NUM> and the RF combination network <NUM> and various master units <NUM> may be a wired or wireless link.

In <FIG>, each remote unit <NUM> broadcasts a wireless signal <NUM> that, in turn, is transceived with a wireless device <NUM> that may be a mobile device, such as a telephone device or a computing device. In particular, and as discussed above, the wireless signal <NUM> from each remote unit <NUM> may be a combination of signals from the BTSs <NUM>. Thus, the wireless device <NUM> may communicate with the system <NUM> through any of the wireless signals <NUM> from the remote units <NUM>. Specific embodiments of the system <NUM> illustrated in <FIG> may include ION-B systems and ION-M systems, both of which are distributed by Andrew LLC, a division of CommScope, Inc. , of Hickory, NC.

To improve wireless communications, such as communications from a base station to mobile devices, Multiple-lnputlMultiple-Output ("MIMO") technology might be utilized to provide advanced solutions for performance enhancement and broadband wireless communication systems. Substantial improvements may be realized utilizing MIMO techniques with respect to the traditional SISO systems. MIMO systems have capabilities that allow them to fully exploit the multi-path richness of a wireless channel. This is in contrast with traditional techniques that try to counteract multi-path effects rather than embrace them. MIMO systems generally rely upon multi-element antennas at both of the ends of the communication links, such as in the base station and also in the wireless device. In addition to desirable beam-forming and diversity characteristics, MIMO systems also may provide spatial multiplexing gain, which allows multi data streams to be transmitted over spatially-independent parallel sub-channels. This may lead to a significant increase in the system capacity without extending the bandwidth requirements. Generally, a SISO system, such as that illustrated in <FIG>, cannot increase spectral efficiency by taking advantage of spatial MIMO technology.

For example, the wireless device <NUM> of <FIG> receives one signal communication signal only, though it may be in the range of a plurality of remote units <NUM>. The wireless signals <NUM> from each remote unit are typically at the same frequency and carry the same data, and communication between a plurality of remote units <NUM> and the wireless device <NUM> simultaneously may result in signal degradation and collisions. In a best case scenario, the multipath nature of the communication channel can be turned into an advantage by sophisticated equalizer algorithms. However, data bandwidth from the wireless device <NUM> is constricted to the speed of reception and processing of data from one remote unit <NUM>.

It is therefore, desirable to take advantage of spatial MIMO signals within a distributed antenna system.

Prior art document <CIT> is considered to be the closest prior art and discloses a distributed antenna system and associated method according to the preambles of claims <NUM> and <NUM>, respectively.

Embodiments of the invention provide a distributed antenna system ("DAS") that is configured to operate in a multiple-input and multiple-output ("MIMO") mode of operation. Alternative embodiments of the invention provide a DAS that normally operates in a single-input and single-output ("SI SO") mode of operation but that has been converted to operate in a MIMO mode of operation with the addition of specified components.

The Invention is expressly defined by the attached claims. Any contradiction between the claims and the following disclosure is understood to describe related information useful for understanding the claimed invention.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of embodiments of the invention. The specific design features of the system and/or sequence of operations as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes of various illustrated components, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments may have been enlarged, distorted or otherwise rendered differently relative to others to facilitate visualization and clear understanding.

<FIG> is a diagrammatic illustration of a MIMO DAS <NUM> consistent with embodiments of the invention that further shows downlink ("DL") and uplink ("UL") gain of that MIMO DAS <NUM>. The MIMO DAS <NUM> includes a plurality of remote units <NUM> distributed to provide coverage within a service area of the MIMO DAS <NUM>, such as inside a building or some other enclosed area. Each remote unit <NUM>, in turn, includes at least two antennas 44a-b and suitable electronics. In various of the disclosed embodiments, a <NUM> x <NUM> MIMO arrangement is illustrated or discussed. It should be understood that other MIMO scenarios, such as <NUM> x <NUM> or <NUM> x <NUM>, etc., would also benefit from the invention. Each remote unit <NUM> is coupled to a master unit <NUM> through at least one optical link <NUM>, which may include one or more optical fibers (not shown), optical splitters (not shown), or other optical transmission components (not shown). As illustrated in <FIG>, one remote unit <NUM> may be connected directly to the master unit <NUM> through a direct optical link, such as at link 48a. Alternatively, a plurality of remote units <NUM> may be connected to the master unit <NUM> in a series connection optical link, such as at link 48b. Or a plurality of remote units <NUM> may be connected to the master unit <NUM> in a tree connection optical link, such as at link 48c. The master unit <NUM> is configured with a respective electrical-to-optical conversion circuit <NUM> for each optical link <NUM> to convert electrical signals at the master unit <NUM> to optical signals for transmission over the respective optical links <NUM>.

In the downlink direction (e.g., from the master unit <NUM> to the remote unit <NUM>), the master unit <NUM> receives at least one signal from at least one MIMO BTS (not shown in <FIG>). The master unit <NUM> may receive signals from other BTSs as well. Specifically, the master unit <NUM> may receive the signals for the remote units <NUM> over an input optical link (not shown), or some other suitable fashion, then separate and/or combine the signals within a particular optical link for transmission over the optical link <NUM> to the remote units <NUM>. The signals from the BTSs may be electrical RF signals, or in some other form for processing. As illustrated in <FIG>, the master unit <NUM> receives two signals from at least one MIMO BTS (illustrated as "BTS SIG1" and "BTS SIG2") as well as a signal in the <NUM> frequency band (illustrated as "<NUM> SIG") at a first input optical link.

The master unit <NUM> may frequency convert and/or combine the signals received at an input optical link for the remote unit <NUM> in a conversion module <NUM>, in accordance with aspects of the invention. Conversion modules 52a-c are illustrated in <FIG> for handling the various BTS signals. The master unit <NUM> then converts the electrical signals to optical signals with appropriate electrical-to-optical circuits <NUM> (50a, 50b, and 50c) and transmits or sends the optical signals to the remote units <NUM>. Similar frequency conversion, combining, and electrical-to-optical conversion takes place for the various optical links 48a-c. In the uplink direction (from the remote unit <NUM> to the master unit <NUM>), the master unit <NUM> receives optical signals from the remote units <NUM> and converts the signals from optical signals to electrical signals, then may split and/or frequency convert the signals prior to sending them to the MIMO BTS as discussed further herein.

In the downlink direction (e.g., from the master unit <NUM> to the remote unit <NUM>), the master unit <NUM> of the embodiment of <FIG> is configured to receive various communication signals in suitable frequency bands as used by service providers, such as a signal in the <NUM> communication range labeled "<NUM> SIG". Some such signals might be typical signals for conventional SISO systems. The master unit <NUM> is also configured to receive and process a plurality of MIMO signals for MIMO services. In accordance with one aspect of the invention, the MIMO signals are frequency converted so that the multiple MIMO signals may be handled over a single fiber-optic cable in the uplink and/or downlink directions without loss of the benefits of those multiple signals, such as diversity and spatial multiplexing gain benefits. For example, in accordance with one exemplary embodiment of the invention, the MIMO signals may be in a <NUM> range, including a first MIMO signal, such as that labeled "BTS SIG1". BTS SIG1 is frequency converted or translated to a signal that falls into a first frequency band FB1. A second MIMO signal in the <NUM> communication range, such as that labeled "BTS SIG2", is frequency converted to a signal that falls into a second frequency band FB2 (See <FIG>). The first frequency band FB1 is different from the second frequency band FB2 so that the signals may be combined on a single fiber-optic cable while maintaining their unique MIMO information. Referring to <FIG>, the master unit <NUM> then combines the signals in the <NUM> frequency band, the frequency converted MIMO signals and an LO reference having an LO frequency LO1. The master unit <NUM> directs the combined signals to a remote unit <NUM> through the optical link <NUM>. As seen in <FIG>, the various downlink signals are appropriately converted from electrical to optical signals, and are then transmitted over fiber link <NUM> to one or more remote units.

In the uplink direction (e.g., to the master unit <NUM> from the remote unit <NUM>), the master unit <NUM> is configured to receive the first signal in the <NUM> communication range. The master unit <NUM> also receives uplink MIMO signals in a third frequency band FB3 or a fourth frequency band FB4 and converts the signals into uplink MIMO signals with a frequency at their original MIMO frequency. The master unit also receives additional MIMO signals from an additional antenna at the remote unit in a fifth frequency band FB5 or a sixth frequency band FB6 and converts the signals into uplink MIMO signals with a frequency at the frequency of the original MIMO signals, such as in the <NUM> band (See <FIG>). In the uplink direction, the uplink MIMO signals might be received in various uplink MIMO sub-bands. Therefore, for frequency conversion, those MIMO uplink sub-bands may be converted to appropriate sub-bands F3/F4 and F/<NUM>/F6 associated with each of the multiple MIMO antennas. The master unit <NUM> then sends the frequency converted plurality of MIMO signals back to the MIMO BTS. Similar operations may occur for each of the signals for the other optical paths 48b-c depending on whether they are frequency converted MIMO signals or non-MIMO signals. While only one particular portion of the master unit <NUM> and specific remote unit <NUM> are discussed with respect to the MIMO aspect of the invention in <FIG>, it will be understood that the other portions and various associated remote units <NUM> might also handle MIMO signals.

In some embodiments of the invention, the DAS system and the master unit <NUM> may be an ION-M series system and master units as distributed by Andrew LLC, a division of CommScope, Inc. of Hickory, North Carolina. The master unit <NUM> thus includes a controller <NUM> that operates similar to previous controllers <NUM> for ION-M master units <NUM>. As such, the controller <NUM> controls the operation of the master unit <NUM> and can be configured across the Internet (the Web) as well as using simple network management protocol ("SNMP") communications or short messaging service ("SMS") communications. The controller <NUM>, in turn, manages the operation of the master unit <NUM>, such as the operation of the electrical-to-optical circuits 50a-c through RS485 communications, as well as a modem <NUM>. The controller <NUM> is also configured to receive data, such as through the modem <NUM>, from a service computer through RS232, summary alarm messages, and data about alarm messages. In turn, the controller <NUM> outputs data about alarm messages. With respect to the conversion modules 52a-c, the controller <NUM> is further configured to provide alarms related thereto, such as a ConvMod X communication failure (indicating that communication with a conversion module X is lost), a ConvMod X Current alarm (indicating that a current monitored in a conversionmodule X is too high or too low, and a ConvMod X DL LO level too low (indicating that a local oscillator for a conversion module X has received too low a level). The master unit <NUM> also includes a power supply unit <NUM> to provide power thereto.

Turning to the remote unit <NUM>, this may be an ION-M7P/7P/85P series repeater as also distributed by Andrew LLC. In the disclosed embodiment of <FIG>, the uplink and downlink paths between the remote unit <NUM> and master unit <NUM> are handled by a single fiber <NUM>. <FIG> illustrates that the remote unit <NUM> may include a wave division multiplexer <NUM> to split the optical signals for the single fiber-optical link <NUM> into downlink and uplink signals. In the downlink direction (e.g., from the master unit <NUM> to the antennas 44a-b), the remote unit <NUM> converts the downlink signals from optical signals to electrical signals using an appropriate optical-to-electrical circuit 72a. Circuit 72a outputs the signal in the <NUM> frequency band, the converted plurality of MIMO signals, and the LO signal LO1. The converted MIMO signals are processed by a conversion module <NUM>, which frequency converts the converted MIMO signals back to a specific MIMO band, such as the <NUM> MIMO band. Such a conversion module is discussed herein below.

In particular, the conversion module <NUM> converts the downlink MIMO signals in the first and second frequency bands FB1, FB2 into MIMO signals in the original <NUM> range (See <FIG>). The signals are then amplified and transmitted over an air interface by the remote unit. The remote unit <NUM> amplifies the downlink signals in the <NUM> communication range and the plurality of MIMO signals with respective power amplifiers <NUM> (76a, 76b, and 76c). The signals are then directed to appropriate antennas. The signal in the <NUM> communication range is combined with one of the MIMO signals in a first duplexer 78a for communication through the first antenna 44a. Another of the MIMO signals is processed through a second duplexer 78b for transmission by the second antenna 44b. As such, the remote unit <NUM> is configured to send and/or receive signals, such as from a wireless device <NUM>, which may also be MIMO enabled and include multiple antennas. As discussed herein, the embodiments discuss essentially two MIMO signals and a remote unit <NUM> with two antennas 44a-b. However, as noted above, it will be readily understood that the invention is also applicable with systems using a greater number of MIMO signals than two.

In the uplink direction (e.g., from the remote unit <NUM> to the master unit <NUM>), the remote unit <NUM> separates the signal in the <NUM> communication range from one of the MIMO signals, which has a frequency in one of the <NUM> sub-bands used for uplink MIMO signals, via the duplexer 78a. The other MIMO signal also has a frequency in one of the <NUM> MIMO sub-bands. The duplexer, in the uplink, is configured to handle the different frequency bands or sub-bands associated with the MIMO uplink signals.

The remote unit <NUM> then amplifies the <NUM> and MIMO uplink signals via respective amplifiers 80a-c, such as LNAs, and then frequency converts the MIMO signals in the conversion module <NUM>. In particular, the remote unit <NUM> converts one of the MIMO signals to a frequency in the third or fourth frequency band or sub-band FB3, FB4, and converts the other MIMO signal to a frequency in the fifth or sixth frequency band or sub-band FB5, FB6. The conversion module <NUM> then combines the multiple MIMO signals, and the remote unit <NUM> provides the <NUM> signal and the combined MIMO signals for conversion to optical signals to the electrical-to-optical circuit 72b. The remote unit <NUM> then wave division multiplexes the uplink optical signal onto an optical link <NUM> using the wave division multiplexer <NUM>. A controller <NUM> controls the operation of the remote unit <NUM>. As illustrated in <FIG>, the controller <NUM> is illustrated controlling the electrical-to-optical circuits 72a-b as well as monitoring power provided by a power supply unit <NUM> and through various buffers 86a-d, though one having ordinary skill in the art will appreciate that the controller <NUM> controls additional operations thereof, such as status, alarm management, and alarm reporting, as noted above.

As illustrated in <FIG> and <FIG>, the MIMO DAS <NUM> may have a downlink gain in the <NUM> frequency band (whether a normal communication band or a MIMO specific communication band) of about <NUM> dB, whether that gain is measured using ICP3 optimized methods or NF optimized methods. Moreover, the MIMO DAS <NUM> has a downlink gain in the <NUM> frequency band) of about <NUM> dB, also whether that gain is measured using ICP3 optimized methods or NF optimized methods. Similar gains are illustrated in the <NUM> frequency band, <NUM> MIMO specific communication band, and <NUM> frequency band for ICP3 optimized measurements of uplink gain. However, the MIMO DAS <NUM> includes, for uplink gain measured using NF optimized methods, about <NUM> dB of gain for the <NUM> frequency band, <NUM> MIMO specific communication band, and <NUM> frequency band.

in some embodiments, a DAS system might utilize dedicated MIMO remote units, rather than combining the MIMO service with other service frequency bands. As such, the master unit <NUM> may transceive the two signals from at least one MIMO BTS on an optical link 48a with one or more MIMO remote units <NUM>. In particular, two or more MIMO signals in the <NUM> frequency band (e.g., signals labeled "BTS SIG1" and "BTS SIG2") are utilized. <FIG> is a diagrammatic illustration of a MIMO DAS <NUM> that includes such a dedicated remote MIMO unit <NUM>. The remote units <NUM> are configured to transmit two MIMO signals, such as BTS SIG1 and BTS SIG2 in a <NUM> frequency band. As such, the remote units <NUM> of <FIG> include many similar components to the remote units <NUM> illustrated in <FIG>. It utilizes power amplifiers 76a-b, duplexers 78a-b, amplifiers 80a-b, such as LNAs, and buffers 86a-c. The frequency conversion module <NUM> converts the two signals similarly to the manner as disclosed above for the plurality of MIMO signals discussed in connection with <FIG>. The remote unit <NUM> transmits one MIMO signal via the first antenna unit 44a and transmits the other MIMO signal via the second antenna unit 44b. Thus, the remote unit <NUM> may be an ION-M7P/7P series repeater unit, as also distributed by Andrew LLC.

As illustrated in <FIG> and <FIG>, the MIMO DAS <NUM> may have a downlink gain in the <NUM> frequency band (whether a normal communication band or a MIMO specific communication band) of about <NUM> dB, whether that gain is measured using ICP3 optimized methods or NF optimized methods. Similar gains are illustrated in the <NUM> frequency band and the <NUM> MIMO specific communication band for ICP3 optimized measurements of uplink gain. However, the MIMO DAS <NUM> includes, for uplink gain measured using NF optimized methods, about <NUM> dB of gain for the <NUM> frequency band and the <NUM> MIMO specific communication band.

In various scenarios, legacy DAS systems may be set up as SISO systems without MIMO operable remote units. In alternative embodiments of the invention, an extension unit may be utilized in combination with the remote units to extend the range of a MIMO DAS. <FIG> is a diagrammatic illustration of a MIMO DAS <NUM> that includes a remote unit <NUM> configured to communicate with an extension unit <NUM> through an extension port. As illustrated in <FIG>, the master unit <NUM> may be configured to receive appropriate service signals from the BTS, including a signal in the <NUM> frequency band labeled "<NUM> SIG", as well as a signal in the <NUM> frequency band labeled "<NUM> SIG", and the master unit <NUM> also receives a plurality of MIMO signals in the <NUM> frequency band. As such, the master unit <NUM> frequency converts MIMO signals in the <NUM> frequency band to frequencies in the first or second frequency band FB1, FB2 and combines the frequency shifted MIMO signals with the signals in the <NUM> frequency band to send over the optical link. The master unit <NUM> then combines and sends the <NUM> SIG, the combined <NUM> SIG and converted MIMO <NUM> SIG, and an LO reference signal across the optical link 48a to the remote unit <NUM>.

In the downlink direction and as illustrated in <FIG>, the remote unit <NUM> receives the combined signals and converts them from optical signals to a plurality of electrical signals. As such, the remote unit <NUM> includes wave division multiplexer <NUM> and the optical-to-electrical circuits 72a-b, as discussed above. In particular, the remote unit <NUM> provides the signal in the <NUM> frequency service band along a different path than the signal that contains the combined <NUM> frequency band service signal and the converted <NUM> frequency MIMO band signal. As shown in <FIG>, the <NUM> signals are provided directly to an antenna port 126a through duplexer 124a. The combined <NUM> signals are provided to a duplexer 118a that splits the <NUM> frequency service band signals from the frequency converted <NUM> frequency MIMO band signals. The <NUM> frequency band signal and the <NUM> frequency band signal are then amplified by respective amplifiers <NUM> (122a, 122b, and 122c). In turn, the <NUM> frequency band signals are duplexed by duplexer 124a and transmitted via a first antenna 44a that may be coupled to antenna port 126a. The <NUM> frequency band signals are duplexed by duplexer 124b and transmitted via a second antenna 44b that may be coupled to antenna port 126b. Therefore, the remote unit handles transceiving the <NUM> and <NUM> signals. In the uplink direction, the <NUM> frequency band signals and the <NUM> frequency band signals are amplified by respective amplifiers <NUM> (125a and 125b), such as LNA's. The amplified <NUM> frequency band signals are then provided back to the electrical-to-optical circuit 72b while the amplified <NUM> frequency band signals are provided to the duplexer 118b for combination with any uplink frequency shifted <NUM> frequency MIMO band signals.

With respect to the frequency converted <NUM> frequency MIMO band signals, they are provided, along with the LO reference, in the downlink direction, to an extension port <NUM> through duplexer 118a. The exterior port is connected to extension unit <NUM>. <FIG> is an illustration of one embodiment of such an extension unit <NUM>.

The extension unit <NUM> receives the converted <NUM> frequency MIMO band signals, which are in the first or second frequency band FB1, FB2, and converts the signals back to the MIMO band for the air interface through the extension unit. Specifically, the extension unit converts the MIMO signals in a conversion module <NUM> to signals in the range of the original MIMO frequency and splits that signal. The split signals are amplified by respective power amplifiers <NUM> (130a and 130b) then output through respective duplexers <NUM> (131a and 131b) to respective antenna ports and antennas 132a and 132b. Thus, the MIMO DAS <NUM> transmits the signals in the <NUM> band and the <NUM> band on respective antennas <NUM> of the remote unit <NUM>, while transmitting the MIMO signals in the <NUM> band on both antennas <NUM> of the extension unit <NUM>.

In the uplink direction, the extension unit <NUM> provides MIMO signals that are received via antennas 132a and 132b in the original MIMO frequency through the respective duplexers 131a and 131b to be amplified by respective low noise amplifiers 134a and 134b. The MIMO signals are then converted into a seventh frequency band or sub-band FB7, or an eighth frequency band or sub-band FB8 in the extension unit <NUM> using frequency conversion module <NUM>. This converted <NUM> frequency band signal is, in turn, provided over the extension port <NUM> back to remote unit <NUM> to be forwarded to the master unit. In the illustrated embodiment, the MIMO signals are duplexed with the uplink <NUM> band frequency signal received by the remote unit and provided at duplexer 118b. The output of duplexer 118b is then processed by the electrical-to-optical circuit 72b for transmission over the optical link <NUM>.

As illustrated in <FIG>, the extension unit <NUM> also includes a connecting board <NUM> that receives the RS485 signal from controller <NUM> of the remote unit <NUM> through the extension port <NUM>. The extension unit <NUM> further includes a control unit <NUM> that controls the operation of the extension unit <NUM> and a power supply unit <NUM> that powers the extension unit <NUM>. As illustrated in <FIG>, the extension unit <NUM> may include one or more buffers 146a-c.

As illustrated in <FIG>, the MIMO DAS <NUM> may have a downlink gain in the <NUM> frequency band (whether a normal communication band or a MIMO specific communication band) of about <NUM> dB, whether that gain is measured using ICP3 optimized methods or NF optimized methods. Similar gains are illustrated in the <NUM> frequency band and the <NUM> MIMO specific communication band for ICP3 optimized measurements of uplink gain. However, the MIMO DAS <NUM> includes, for uplink gain measured using NF optimized methods, about <NUM> dB of gain for the <NUM> frequency band and the <NUM> MIMO specific communication band.

Thus, <FIG>, <FIG>, and <FIG> illustration various MIMO DAS's consistent with embodiments of the invention.

in disclosed embodiments, each frequency conversion module <NUM>, <NUM>, and/or <NUM> for the master, remote, and extension units, generally includes a downlink portion and an uplink portion for handling the signal traffic. <FIG> is one embodiment of a downlink portion <NUM> of a frequency conversion module <NUM>/<NUM>/<NUM> for a master unit <NUM> that may be used to frequency convert signals in the <NUM> frequency band as well as to combine those converted signals with another service signal, such as a signal in the <NUM> frequency band. In particular, the downlink portion <NUM> receives the various service signals, as well as the MIMO signals, from an appropriate source, such as the BTS. The conversion module section <NUM> may attenuate any of the <NUM> frequency band signals, the <NUM> frequency band signals, or the <NUM> frequency MIMO band signals with respective attenuators <NUM> (162a, 162b, 162c, and 162d). Those signals might then be forwarded for further processing, such as amplification and/or frequency conversion, in accordance with the present invention. The downlink portion <NUM> provides frequency conversion by mixing with mixer 164a, the MIMO BTS SIG1 with an LO having a first frequency LO1 signal generated by a suitable LO circuitry <NUM> to produce a first converted MIMO signal in the first frequency band FB1. The downlink portion <NUM> also mixes, with mixer 164b, the MIMO BTS SIG2 with an LO signal at the second LO frequency LO2 (which is an integral multiple of the first LO signal frequency LO1) to produce another converted MIMO signal in the second frequency band FB2. These converted signals are then filtered further by respective filters <NUM> (166a and 166b), amplified by respective amplifiers <NUM> (168a and 168b), filtered further by respective filters <NUM> (170a and 170b), and amplified by respective amplifiers <NUM> (172a and 172b).

As illustrated in <FIG>, a frequency conversion module might also provide some combination of other service signals with the MIMO signals that have been frequency converted. Other service signals might pass directly from the master unit to the remote unit, without being significantly affected. For example, as shown in <FIG>, a service signal, such as a non-MIMO <NUM> signal, might be forwarded directly through to a remote unit. Alternatively, a non-MIMO <NUM> signal might be combined or duplexed with the converted MIMO signals. As would be readily understood, the combination of such signals may depend upon the frequency conversion that takes places with respect to the MIMO signals and their frequency as presented onto the fiber link. In <FIG>, the <NUM> frequency band signal or other service is combined with the two converted MIMO signals by duplexer <NUM> to provide a combined MIMO signal to an optical-to-electrical circuit <NUM>.

<FIG> is an illustration of an uplink portion <NUM> of a frequency conversion module <NUM> for a master unit <NUM> that may be used to split frequency converted MIMO signals in the <NUM> frequency band from a non-converted service signal in the <NUM> frequency band, and to further convert the converted MIMO signals. Thus, the uplink portion <NUM> generally acts in the opposite manner of the downlink portion <NUM>. For example, referring to <FIG>, the uplink signal from a remote unit may include frequency converted MIMO signals that are combined with a <NUM> signal. As such, the uplink portion <NUM> includes a duplexer <NUM> that splits the <NUM> frequency band signals from converted <NUM> frequency MIMO band signals (e.g., one or more signals in the third, fourth, fifth, or sixth frequency bands/sub-bands FB3, FB4, FB5, FB6). The duplexer circuitry further splits a signal in the fifth or sixth frequency band/sub-band FB5, FB6 and the signal in the third or fourth frequency band/sub-band FB3, FB4 into two separate, frequency converted channels. The signals in the frequency converted channels are thus filtered by respective filters <NUM> (180a and 180b) and mixed by respective mixers <NUM> (182a and 182b). In particular, the signals in the fifth or sixth frequency band FB5, FB6 are mixed, by mixer 182a, with an LO signal at the first LO frequency LO1 to produce MIMO signals in desired MIMO uplink frequency bands. The signals in the third or fourth frequency band/sub-band FB3, FB4 are mixed, by mixer 182b, with the LO signal at the second LO frequency LO2 to also produce MIMO signals also in the desired MIMO uplink frequency bands. The MIMO signals in the <NUM> frequency band in the two channels are then filtered by respective filters <NUM> (184a and 184b) and amplified by respective amplifiers <NUM> (186a and 186b), and/or then attenuated by respective attenuators <NUM> (188c and 188d) to output as MIMO signals BTS SIG1 and BTS SIG2 to transmit back to a BTS or other location. The <NUM> frequency band signals and <NUM> frequency band signals are likewise attenuated by respective attenuators <NUM> (188a and 188b) as necessary.

<FIG> is an illustration of a downlink circuit portion 189a of a frequency conversion module <NUM>, <NUM> that may be included in a remote unit <NUM>, <NUM>, and/or <NUM>, or an extension unit <NUM>. The downlink circuit portion 189a receives an LO reference signal (which is the LO signal at the first LO frequency LO1) from the master unit. The circuit also receives frequency converted MIMO signals, such as an converted <NUM> frequency MIMO band signal, and duplexes the converted MIMO signals into two channels with a duplexer <NUM>. The signals in each channel are then filtered with respective filters <NUM> (191a and 191b). In turn, the signal in one channel, which is in the first frequency band FB1, is mixed by mixer 192a with the LO signal at the first LO frequency LO1 to produce a first signal in the <NUM> MIMO downlink frequency band. The signal in the other channel, which is in the second frequency band FB2, is mixed by mixer 192b with an LO signal at the second LO frequency LO2 (which is an integral multiple of the first LO frequency LO1) to produce a second signal in the <NUM> MIMO downlink frequency band. The MIMO signals are then filtered via respective filters <NUM> (193a and 193b) and amplified by respective amplifiers <NUM> (194a and 194b) before being output from the conversion circuitry for eventual transmission.

Similarly, <FIG> is an illustration of an uplink circuitry portion 189b of a frequency conversion module <NUM>, <NUM> that may be included in a remote unit <NUM>, <NUM>, and/or <NUM>, or an extension unit <NUM>. Thus, the uplink portion 189b generally acts in an opposite manner to the downlink portion 189a. The uplink portion 189b includes two channels that each receives signals in the <NUM> MIMO uplink frequency bands or sub-bands from suitable antennas and antenna ports. The signals in the channels are filtered by respective filters <NUM> (195a and 195b). In turn, the signal in one MIMO channel is mixed by mixer 196a with the LO signal at the first LO frequency LO1 to produce a first frequency converted uplink signal having a frequency in the fifth frequency band FB5 and the sixth frequency band FB6. The signal in the other MIMO channel is mixed by mixer 196b with a an LO signal at the second LO frequency LO2 (which is an integral multiple of the first LO signal at frequency LO1) to produce another converted uplink signal having a frequency in the third frequency band FB3 and the fourth frequency band FB4. The first and second converted signals are then filtered by respective filters <NUM> (197a and 197b), amplified by respective amplifiers <NUM> (198a and 198b), and combined by a suitable duplexer <NUM>. The combined converted MIMO signal is then presented for transmission, in the uplink direction, over fiber link <NUM>, back to the master unit.

In accordance with one aspect of the invention, as illustrated in <FIG>, the converted MIMO signals and other service signals are transmitted between the master unit and the various remote units and extension units implementing a single fiber that handles both the uplink signals and the downlink signals. Because of the frequency conversion provided for the various MIMO signals, the integrity of the MIMO process is maintained when the multiple MIMO signals originally having the same frequency are transmitted over a single cable, such as a single fiber-optic cable or link. In such a scenario, each of the individual MIMO signals is maintained at different frequencies in both the uplink direction and the downlink direction. That is, all the uplink MIMO signals have different frequencies, and all the downlink MIMO signals have different frequencies. Furthermore, to maintain the segregation between uplink and downlink signals over a single fiber-optic cable, all of the MIMO signals being transmitted in the downlink direction are at different frequencies from those that are being transmitted in the uplink direction.

In accordance with a further embodiment of the invention, the DAS system may incorporate separate cables, such as separate fiber-optic cables, between the master unit and any remote units or extension units. In such a case, the downlink signals are handled on a separate fiber-optic cable from the uplink signals.

<FIG> is a diagrammatic illustration of another embodiment of a MIMO DAS <NUM> that may be configured using a legacy DAS system, and in particular a legacy SISO DAS. Specifically, the MIMO DAS <NUM> includes a master unit <NUM>. For example, the master unit might be an ION-B master unit, as distributed by Andrew LLC. The master unit is configured to provide signals to a plurality of remote units <NUM>, such as ION-B remote units, which are also distributed by Andrew LLC. The present invention, therefore, might be used to provide a legacy system with MIMO capabilities. In a normal mode of operation, the master unit <NUM> is configured to send and receive signals from one or more plurality of BTSs, such as through a BTS point of interface component <NUM>. Such BTS Bands <NUM>-n might be conventional, non-MIMO service bands, for example. To implement a MIMO operation, the master unit <NUM> is additionally configured to send and receive signals through a MIMO point of interface component <NUM>. For purposes of illustration, the MIMO signals are illustrated as a MIMO signal in the <NUM> frequency band (illustrated as "<NUM> LTE CH1) and another, different MIMO signal in the <NUM> frequency band (illustrated as "<NUM> LTE CH2").

in the downlink direction, the BTS point of interface component <NUM> is configured to provide each of the BTS signals to a splitting/combining network <NUM> of the master unit <NUM> through a respective downlink connection, such as a coaxial cable. The MIMO point of interface component <NUM> is similarly configured to provide the plurality of MIMO signals in the <NUM> frequency MIMO band to the splitting/combining network <NUM> through a corresponding downlink connection, such as a coaxial cable. In turn, the splitting/combining network <NUM> is configured to split and/or otherwise combine signals from the BTS point of interface component <NUM> and/or MIMO point of interface component <NUM> for transceiving with respective remote units <NUM>. In operation, the splitting/combining network <NUM> is configured to provide the Band <NUM>-n service signals from at least one BTS, as well as the multiple MIMO signals in the <NUM> frequency band, to optical transceiver circuitry <NUM> through a suitable downlink connection, such as a coaxial cable. The various optical transceiver circuits <NUM>, in turn, provide downlink signals to respective remote units <NUM> through a downlink optical link, which may be an optical fiber. As is illustrated in <FIG>, the uplink (UL) and downlink (DL) paths are handled over separate fiber links.

Each remote unit <NUM> of the MIMO DAS <NUM> is configured to receive the optical signals from the master unit <NUM>, convert those signals into appropriate electrical signals, transmit various of the signals for that remote unit <NUM> through one or more antennas 216a-b, and couple the plurality of MIMO signals in the <NUM> MIMO frequency band to an extension unit <NUM> through downlink auxiliary channels for transmission on respective antennas 218a-b thereby.

In the uplink direction, the extension unit <NUM> receives uplink MIMO signals in the <NUM> frequency band or other MIMO frequency band on respective antennas 218a-b and provides those signals to the remote unit <NUM> over the auxiliary channels or ports. The remote unit <NUM>, in turn, receives other service signals via the antennas 216a-b and combines those signals with the MIMO signals from the extension unit <NUM>. The remote unit provides them via an uplink optical link, which may be an optical fiber, to the optical transceiver <NUM> of the master unit <NUM> after appropriate conversion from electrical signals, such as using suitable optical transceiver circuitry, as noted below. The optical transceiver <NUM>, in turn, provides the combined signals to the splitting/combining network <NUM> through an uplink connection, which may be a coaxial cable. The splitting combining network <NUM> splits the combined signals back to the MIMO point of interface <NUM> through an uplink connection, which may be a coaxial cable, as well as the signals for the respective BTS bands <NUM>-n for transmission back to that BTS through the BTS point of interface component <NUM>.

Thus, the MIMO DAS <NUM> operates to simultaneously transmit the signal from at least one BTS through the remote unit <NUM> as well as a plurality of MIMO signals in the <NUM> frequency band or other MIMO band through the extension unit <NUM> using a legacy DAS communication system and additional components.

In accordance with the aspects of the invention, the DAS <NUM> as illustrated in <FIG> also provides frequency translation or frequency conversion of a plurality of MIMO signals for maintaining the integrity of the MIMO system. All of the MIMO signals, including any additional service signals, are sent over dual fiber-optic cables. One fiber link is for the uplink signals and another fiber link is for the downlink signals. As illustrated in the <FIG>, <FIG>, and <FIG>, although the downlink and uplink paths are handled over separate fiber-optic cables, all the MIMO signals in the downlink direction, as well as all of the MIMO signals in the uplink direction, are present on the same fiber-optic cable. As such, the present invention addresses the integrity of the MIMO process by providing suitable frequency conversion and frequency translation of the MIMO signals discussed herein.

<FIG> is a diagrammatic illustration of another embodiment of the MIMO DAS <NUM> somewhat similar to the DAS system of <FIG>, except in which the signals from the remote unit <NUM> and the extension unit <NUM> are combined prior to being transmitted via the appropriate antennas 216a-b and/or 218a-b. The extension unit <NUM> processes the various MIMO signals, however, antennas from the remote units <NUM> are used fortransceiving the MIMO signals, in addition to antennas coupled to the extension unit <NUM>. As such, a combiner 217a and 217b is placed between the remote unit <NUM> and the respective antennas 216a and 216b of the remote unit. The combiners 217a and 217b, in turn, receive signals from a splitter 219a that is coupled with the extension unit <NUM>. The other splitter 219b is placed between the extension unit <NUM> and respective antennas 218a and 218b. A first output of splitter 219a is provided to a first antenna 216a of the remote unit <NUM>, while a second output of the splitter 219a is provided to the second antenna 216b of the remote unit <NUM>. As for splitter 219b, a first output is provided to the first antenna 218a of the extension unit <NUM>, while a second output is provided to the second antenna 218b of the extension unit <NUM>. In this manner, the MIMO DAS <NUM> operates to simultaneously transmit the signals from at least one BTS service band, and one of the signals in the <NUM> MIMO frequency band through a first antenna 216a of the remote unit <NUM>, simultaneously transmit the signals from at least one BTS service band and one of the signals in the <NUM> frequency band through a second antenna 216b of the remote unit <NUM>, and simultaneously transmit another signal in the <NUM> MIMO frequency band through the antennas 218a and 218b of the extension unit <NUM>. As such, the MIMO transmission is shared between the remote unit and extension unit.

<FIG> is a diagrammatic illustration of another alternative embodiment of a MIMO DAS <NUM> that may be configured from a pre-existing SISO DAS, and in particular a DAS that does not use an extension unit for handling the MIMO signals. As such, the MIMO DAS <NUM> includes at least one master unit 202a-b for each of the multiple MIMO signals in the <NUM> frequency band. Specifically, the MIMO DAS <NUM> includes a point of interface component 222a-b for each master unit 202a-b that combines multiple MIMO signals in the <NUM> frequency band (e.g., illustrated as "MIMO BTS1 CH1," "MIMO BTS2 CH1," "MIMO BTS1 CH2," and "MIMO BTS2 CH2") with one or more other service signals from a plurality of BTSs.

In the downlink direction, for example, the point of interface component 222a combines a signal from a first MIMO BTS in a MIMO band, such as the <NUM> frequency band, (e.g., MIMO BTS1 CH1) with a signal from a second MIMO BTS in a MIMO band, such as the <NUM> frequency band (e.g., MIMO BTS2 CH1) and at least one service signal from at least one additional BTS. This combined signal is provided to the master unit 202a via a downlink connection, such as a coaxial cable. The master unit 202a, in turn, provides the combined signals, through the optical transceiver circuitry 212a, to remote units 204a over a set of uplink and downlink fiber cables for transmission by antennas 216a-b. Therefore, the remote units 204a handle one MIMO signal for the various MIMO bands MIMO BTS1 and MIMO BTS <NUM>.

Similarly, the point of interface component 222b combines a signal from the first MIMO BTS in a MIMO band, such as the <NUM> frequency band, (e.g., MIMO BTS1 CH2) with a signal from the second MIMO BTS in a MIMO band, such as the <NUM> frequency band, (e.g., MIMO BTS2 CH2) and at least one service signal from at least one additional BTS. This combined signal is provided to the master unit 202b via a downlink connection, such as a coaxial cable, which in turn provides the combined signals to another set of remote units 204b over a separate set of uplink and downlink fiber cables for transmission by its antennas 216c-d. Therefore, the remote units 204b handle an additional MIMO signal for the various MIMO bands MIMO BTS1 and MIMO BTS2.

in that way, the segregation between various MIMO signals is maintained by implementing various master units and associated remote units, each handling a specific MIMO signal. In that way, the plurality of MIMO signals might be transmitted throughout a space, such as the inside of a building or other confined area where the DAS system might be utilized in accordance with the principles of the invention. Master unit 202a incorporates a set of downlink and uplink fiber-optic cables 215a for handling one of the MIMO signals for each of the various different MIMO services. Alternatively, the master unit 202b handles another of the MIMO signals of the various different MIMO services. As such, in accordance with one aspect of the invention, the segregation of the different MIMO signals, CH1 and CH2, for example, are maintained without requiring frequency conversion or frequency translation, as is utilized in various of the other embodiments of the invention disclosed herein.

<FIG> is a diagrammatic illustration of another alternative embodiment of a MIMO DAS 220a that may be configured from a pre-existing SISO DAS. The MIMO DAS 220a includes one or more extension units for handling additional MIMO signals, thereby allowing a single remote unit to accommodate more than two MIMO BTSs. In contrast to the system illustrated in <FIG>, which provides an optical link between a master unit and remote unit with separate uplink and downlink cables, the system in <FIG> is configured so that the uplink and downlink optical signals between a master unit and remote unit share a single fiber. Advantageously, this configuration may allow a legacy SISO system that uses separate fibers for uplink and downlink signals (such as those illustrated in <FIG> and <FIG>) to handle additional MIMO signal bands, as compared to the system illustrated in <FIG>. The additional MIMO signals may be coupled to extension units through extension ports on a single remote unit 204c for transmission to existing antennas. The MIMO DAS 220a may thereby provide MIMO signals to the service area without the need for frequency conversion or additional optical fibers with respect to an existing legacy system having separate uplink and downlink fiber cables.

To this end, the MIMO DAS 220a includes separate master units 202c-d for each of the multiple MIMO signals in the <NUM> frequency band. Specifically, the MIMO DAS 220a includes point of interface components 222c-d for each of the separate master units 202c-d. The point of interface components 222c-d are coupled to appropriate sources of communication signals, such as one or more BTSs, and combine multiple MIMO signals in the <NUM> frequency band (e.g., illustrated as "MIMO BTS1 CH1," "MIMO BTS2 CH1," "MIMO BTS3 CH1," "MIMO BTS4 CH1," "MIMO BTS1 CH2," "MIMO BTS2 CH2," "MIMO BTS3 CH2," and "MIMO BTS4 CH2") with one or more other service signals (BTS Band <NUM>-n) from one or more BTSs.

In the downlink direction, for example, the point of interface component 222c combines signals from four MIMO BTSs in chosen MIMO bands, such as the <NUM> frequency band and other bands (e.g., MIMO BTS1 CH1, MIMO BTS2 CH1, MIMO BTS3 CH1, and MIMO BTS4 CH1), with at least one service signal from at least one additional BTS (BTS Band). This combined signal is provided to the master unit 202c via a downlink connection, such as a coaxial cable. The master unit 202c, in turn, provides the combined signals, through the optical transceiver circuitry 212c, to a remote unit 204c over a single fiber cable 215c for transmission by antennas 216e-f. To reduce the total number of fiber cables required, the downlink signal shares the fiber cable 215c with its associated uplink signal. To this end, the uplink and downlink signals are multiplexed in optical units at either end of the fiber using appropriate combining or multiplexing circuitry, such as illustrated in <FIG>, <FIG>, and <FIG>.

Similarly, the point of interface component 222d combines signals from the four MIMO BTSs in a MIMO band, such as the <NUM> frequency band, (e.g., MIMO BTS1 CH2, MIMO BTS2 CH2, MIMO BTS3 CH2, and MIMO BTS4 CH2) with at least one service signal from at least one additional BTS. This combined signal is provided to the master unit 202d via a downlink connection, such as a coaxial cable, which in turn provides the combined signals to remote unit 204c over a separate fiber cable 215d for transmission by antennas 216c-d. Therefore, the MIMO DAS 202a handles the additional MIMO signals or Channel <NUM> signals for the various MIMO bands MIMO BTS1, MIMO BTS2, MIMO BTS3, and MIMO BTS <NUM> by utilizing a second fiber (which may have served as an uplink fiber in the legacy SISO system) to deliver MIMO CH2 signals from the plurality of BTSs. The remote unit 204c receives the various different MIMO signals and processes and directs those signals appropriately for the interface. Because the Channel <NUM> and Channel <NUM> MIMO signals are handled over separate fiber links, the MIMO information on those channels remains intact without frequency translation and segregation. The remote unit 204c communicates MIMO BTS1 CH1 and CH2; and MIMO BTS2 CH1 and CH2, and other appropriate signal bands over antennas 216e and 216f.

The additional MIMO signals in the downlink direction originating from the third and fourth MIMO BTSs in the MIMO band (e.g., MIMO BTS3 CH1, MIMO BTS4 CH1, MIMO BTS3 CH2, MIMO BTS4 CH2) are received by the remote unit 204c and communicated through extension or auxiliary ports to extension units 213a-b for transmission by antennas 216e, 216f. To accommodate these additional MIMO signals, the remote unit 204c may include one or more extension ports each configured to accept connections from an extension unit 213a-b. When the extension units 213a-b are coupled to the remote unit 204c via the extension ports, additional separate uplink and downlink paths are provided through the remote unit 204c to the various extension units. The multiple extension units might be configured to handle separate MIMO channels, as shown for the MIMO <NUM> and MIMO <NUM> bands. For example, extension unit 213a handles Channel <NUM> signals for the additional bands, and extension unit 213b handles Channel <NUM> signals.

Segregation between various MIMO signals is thereby maintained by implementing various master units and associated extension units coupled by a single remote unit. The remote unit handles transmission of the MIMO signals from the first and second MIMO BTSs, and the extension units each handle specific MIMO channel signals from the third and fourth MIMO BTS's. Each of the MIMO antennas 216e, f are coupled with the remote unit and extension units to handle the Channel <NUM> and Channel <NUM> signals respectively for multiple MIMO services. In that way, the plurality of MIMO signals may be transmitted throughout a space, such as the inside of a building or other confined area where the DAS system may be utilized in accordance with the principles of the invention. Master unit 202c utilizes one fiber-optic cable 215c for handling the uplink and downlink signals for one of the MIMO channel signals for each of the various different MIMO services; and master unit 202d utilizes a second fiber-optic cable 215d for handling the other of the MIMO channel signals. Additional master units may be added as required to handle additional MIMO BTSs, with corresponding extension units 213a-b coupling the additional MIMO signals to the antennas 216e-f through signal combiners 211a-b. As such, in accordance with one aspect of the invention, the segregation of the different MIMO signals, CH1, CH2 for example, is maintained without requiring frequency conversion or frequency translation, as is utilized in various of the other embodiments of the invention disclosed herein.

<FIG> is a diagrammatic illustration of at least a portion of the MIMO point of interface component <NUM> that may be used within the MIMO DAS <NUM> of <FIG>, <FIG>. Returning to <FIG>, the MIMO point of interface component <NUM> processes the various MIMO signals in the MIMO band, such as a <NUM> frequency band, in much the same way, apart from the frequencies to which they are converted/translated and combined in the end.

More specifically, the MIMO point of interface is coupled with the master unit in DAS <NUM> such that the interface circuit <NUM> handles the frequency conversion or translation rather than the master unit, and thus delivers the frequency converted MIMO signals to the master unit to then be forwarded to the various remote units. For the purposes of discussion, the different MIMO signals will be referred to as Channel <NUM> or CH1 and Channel <NUM> or CH2. As discussed above, while a <NUM> x <NUM> MIMO arrangement is disclosed and discussed herein, additional MIMO arrangements might be utilized, and therefore, there may be additional MIMO signals such as CH3, CH4, etc. In accordance with the invention, those signals would have to be handled in a similar fashion to provide the desirable frequency conversion and/or separate handling of the various MIMO channel signals to maintain the integrity of the MIMO process.

As such, the MIMO point of interface component <NUM> is configured to accept both duplexed or un-duplexed signals. In the case of duplexed signals, the signals are processed through a respective duplexer circuitry, such as triplexers <NUM> (230a and 230b) that separate the downlink MIMO signals from uplink MIMO signal sub-bands. When the signals are not duplexed, the downlink (DL) signal is processed through a respective triplexer <NUM> with the uplink (UL) signal sub-bands connected to a respective separate connector <NUM> (232a and 232b).

With respect to the downlink path, the MIMO channel signals are attenuated by a fixed amount with an attenuator <NUM> (234a, 234b) then processed through two digital attenuators <NUM> (236a, 236b) and <NUM> (238a, 238b), one of which <NUM> is responsible for automatic level control ("ALC") and the other of which <NUM> is used to adjust the gain (e.g., in the 30dB range, in 1dB steps). A filter <NUM> (240a and 240b) filters the respective channel signals. The signals are then mixed with an appropriate LO reference in a respective mixer <NUM> (242a and 242b) to produce respective frequency converted signals. As illustrated in <FIG>, the signal of the first MIMO channel CH1 is mixed by mixer 242a with an LO reference at a third LO frequency LO3. The signal of the second MIMO channel CH2 is mixed by mixer 242b with an LO reference at a fourth LO frequency LO4. As such, in the embodiment of <FIG>, the MIMO signals CH1, CH2 are converted into a ninth frequency band FB9 (CH1) and a tenth frequency band FB10 (CH2). The frequency converted signals are filtered again with a respective filter <NUM> (244a and 244b), and amplified by respective amplification circuits <NUM> (246a and 246b). After amplification, the two downlink signals CH1 and CH2 are combined in a duplexer 248a. The combined signal is then further amplified by amplifier circuit <NUM> before being combined with another attenuated and filtered frequency reference as at <NUM> by duplexer <NUM>. The MIMO point of interface component <NUM> then provides the combined signals to the master unit <NUM> as described above.

In the uplink (UL) direction, the MIMO uplink signals from the master unit <NUM> are split appropriately into two signals by a duplexer <NUM>. For example, the MIMO signals from the various remote units might be in an eleventh frequency band FB11 and a twelfth frequency band FB12. As noted above, the MIMO uplink signals may be in various sub-bands of FB11, FB12. Each signal is then filtered by a respective filter <NUM> (258a and 258b), attenuated by a respective attenuator <NUM> (260a and 260b), filtered again by respective filter <NUM> (262a and 262b), and again attenuated by respective attenuator <NUM> (264a and 264b). Each signal is then frequency converted by a respective mixer <NUM> (266a and 266b). In particular, the signal on the first channel is mixed by mixer 266a with an LO reference at a fifth LO frequency LO5, while the signal on the second channel is mixed by a mixer 266b with an LO reference at a sixth LO frequency LO6. This yields MIMO uplink signals in the original MIMO uplink band. In any event, the frequency converted signals are filtered by a respective filter <NUM> (268a and 268b), and amplified by a respective amplifier <NUM> (270a and 270b) prior to being provided back to a MIMO BTS as described above.

in particular, the signals in the uplink direction are split by respective splitter <NUM> (272a and 272b) and duplexed into respective MIMO uplink sub-bands by respective duplexer <NUM> (274a and 274b). Each sub-band is attenuated by respective attenuator <NUM> (276a-276b) then combined with the downlink signals by the respective duplexer circuits <NUM>. Alternatively, the signals in the uplink direction are provided directly back to the respective MIMO BTSs via the respective connectors <NUM>.

<FIG> is a diagrammatic illustration of frequency conversion circuitry <NUM> that may be used inside the MIMO point of interface component <NUM> for providing desirable LO's or other frequency references for frequency conversion, A voltage controlled crystal oscillator <NUM> provides a reference frequency signal, such as a signal at a first reference frequency R1. A frequency divider <NUM> produces stabilized reference signals that are subsequently filtered. The frequency divider <NUM> further divides the reference frequency signal into additional paths to generate the reference signals for the synthesizers of the LO references for the MIMO point of interface component <NUM>. The reference signals are level adjusted, amplified, and/or filtered, as necessary. In specific embodiments, the frequency conversion circuitry <NUM> produces a frequency reference at frequency R1 and LO references at frequencies LO3, LO4, LO5, and LO6.

<FIG> is a diagrammatic illustration of at least a portion of optical transceiver circuitry <NUM> that may be used with the MIMO DAS <NUM> of <FIG>, <FIG>, or the MIMO DAS <NUM> of <FIG>, or <FIG>. Returning to <FIG>, the optical transceiver circuitry <NUM> includes main channel and auxiliary downlink inputs, as well as main channel and auxiliary uplink inputs. In the downlink direction, the signal received on the main channel downlink input is combined with any signal received on the auxiliary downlink input in a directional coupler <NUM>, processed through a matching network <NUM>, amplified in amplifier <NUM>, and converted to an optical signal by an electrical-to-optical circuit <NUM>. The optical signal may then be split by a series of optical splitters 302a-c to output various outputs, such as to one of four optical outputs. The outputs include the signals combined from the main channel and auxiliary downlink Inputs. The downlink signals are provided by appropriate downlink optical links, such as fiber-optic cables, to remote units <NUM>. As illustrated in <FIG>, the optical transceiver <NUM> may include a microprocessor <NUM> to control its operation,.

In the uplink direction, signals received from the remote units <NUM> on suitable optical links, such as fiber-optic cables, provide various (e.g., one of four) inputs that are converted from an optical signal to an electrical signal by a respective electrical-to-optical circuit <NUM> (304a-d). The signals are amplified by a respective amplifier <NUM> (306a-d), and attenuated by a respective attenuator <NUM> (308a-d). The signals are then amplified by another respective amplifier <NUM> (310a-d). Each of the uplink signals received is then combined by a series of RF couplers 312a-c, processed through a matching network <NUM>, and split between the corresponding main channel and auxiliary uplink inputs for transmission to the splitting/combining network <NUM> of the master unit.

<FIG> is a diagrammatic illustration of at least a portion of a remote unit <NUM> that may be used with the MIMO DAS <NUM> of <FIG>, or the MIMO DAS <NUM> of <FIG>. The remote unit <NUM> couples with a master unit over multiple fiber-optic cables, one dedicated for the uplink traffic, and another for the downlink traffic. In the downlink direction, the remote unit <NUM> receives an optical signal across a downlink optical connection and converts that signal to an electrical signal using an electrical-to-optical circuit 320a under control of a suitable microprocessor <NUM>. The electrical signal is then amplified by an amplifier <NUM> and attenuated by an adjustable automatic gain control attenuator <NUM> also under control of the microprocessor <NUM>. The attenuated signal is again amplified by an amplifier <NUM>. In accordance with one aspect of the invention, the signal is split into separate signals for the remote unit <NUM> and for an extension unit <NUM> using a directional coupler <NUM>.

The directional coupler <NUM> separates the main signal for the remote unit <NUM> to include an auxiliary signal for provision to an auxiliary signal port <NUM> in the remote unit. An extension unit <NUM> is coupled to the auxiliary port <NUM>. Thus, the auxiliary signal is amplified by an amplifier <NUM> then provided to extension unit <NUM>. The main signal, in turn, is attenuated by an adjustable attenuator <NUM>, which may compensate for temperature variances, and duplexed by a duplexer <NUM> into its high frequency and low frequency band components, such as a signal in the <NUM> frequency band (e.g., a "high" band) and a signal in the <NUM> frequency band (e.g., a "low" band). The high and low band signals are amplified by respective amplifiers <NUM> (336a and 336b), filtered by respective filters <NUM> (338a and 338b), and again amplified by respective high or low band amplifiers <NUM> (high band amplifier 340a and low band amplifier 340b). The high and low band signals are then filtered via a respective filter <NUM> (344a and 344b), and coupled to each antenna 216a-b via a respective coupler <NUM> (346a and 346b). The high and low band signals combined by respective duplexers <NUM> (348a and 348b) for transmission on a plurality of antennas 216a-b of that remote unit <NUM>. Thus, the remote unit <NUM> simultaneously provides the high and low band signals for each antenna 216a-b.

In the uplink direction, the signals from the antennas 216a-b are separated by the duplexers 348a-b and couplers 346a-b into their respective high and low band signals. Each of the high and low band uplink signals is then filtered by a respective filter <NUM> (350a and 350b), amplified by a respective amplifier <NUM> (high band amplifier 352a and low band amplifier 352b), and attenuated by a respective adjustable attenuator <NUM> (354a and 354b), which may adjust the gain of the respective band. The high band signal is then amplified by an amplifier <NUM> while the low band signal is filtered by a filter <NUM>. The high and low band signals are then combined into a common uplink signal via a duplexer <NUM>. The uplink signal is attenuated by a programmable and adjustable attenuator <NUM> that is controlled by the microprocessor <NUM>. The signals handled by the remote unit are then combined with any auxiliary signals from the extension unit <NUM> by a combiner <NUM>. The combined uplink and auxiliary signal is then amplified by an amplifier <NUM> before being converted into an optical signal by an electrical-to-optical circuit 320b for being directed to a master unit over the fiber link.

As discussed above with respect to <FIG> and <FIG>, for implementing a MIMO service within an existing DAS system, an extension unit might utilized and coupled with the remote unit for handing one or more of the plurality of MIMO signals. Such an extension unit is coupled with the remote unit, such as through an auxiliary port that has individual uplink and downlink connections, as illustrated. Such a connection might be made using a suitable link, such as a coaxial cable link.

<FIG> is a diagrammatic illustration of an extension unit <NUM> that may be used with the MIMO DAS <NUM> of <FIG>, or the MIMO DAS <NUM> of <FIG>. In <FIG>, the downlink signal coming into the extension unit <NUM> is attenuated by attenuator <NUM> and duplexed by duplexer <NUM> to separate the main signal from any frequency reference that might be utilized for the frequency conversion of the MIMO signals. The frequency reference is then filtered by filters 404a-b, amplified by amplifier <NUM>, and level controlled through an automatic level control circuit <NUM> prior to use for signal frequency conversion.

The downlink signal, however, is amplified by amplifier <NUM> then duplexed by duplexer <NUM> into the multiple MIMO signals, such as the two MIMO signals corresponding to those provided to the MIMO point of interface component <NUM> and/or point of interface component <NUM>. Each signal is level adjusted via another respective automatic level control component <NUM> (414a and 414b), amplified by a respective amplification circuit <NUM> (416a and 416b), filtered by a respective filter <NUM> (418a and 418b), and frequency converted with a respective active mixer <NUM> (420a and 420b). In particular, the signal on the first channel (e.g., the signal in the ninth frequency band FB9) is mixed by active mixer 420a with an LO reference at the third LO frequency LO3 and frequency converted to a range of the MIMO downlink band. The signal on the second channel (e.g., the signal the tenth frequency band FB10) is mixed by active mixer 420b with an LO reference at the fourth LO frequency LO4, and frequency converted to the MIMO downlink band. Each frequency converted signal is then filtered by a respective filters <NUM> (422a and 422b), amplified by a respective amplifier <NUM> (424a and 424b), filtered by another respective filter <NUM> (426a and 426b), attenuated by a respective attenuator <NUM> (428a and 428b), and amplified by a respective amplification circuit <NUM> (430a and 430b) before being isolated via a respective isolator <NUM> (432a and 432b) and duplexed with uplink signals via a respective duplexer <NUM> (434a and 434b). The isolators 432a-b provide adequate matching between the output of each amplification circuit 430a-b and the antennas 218a-b.

The MIMO signals might then be directed to appropriate antennas for providing an air interface for the signals. As illustrated in the embodiment of <FIG>, the extension unit <NUM> might handle the MIMO signals exclusively with the antennas coupled to the extension unit. Alternatively, as Illustrated in <FIG>, MIMO signals might be directed from the extension unit to other antennas, such an antennas coupled to the remote unit <NUM>. In accordance with MIMO principles, it is desirable to transmit the MIMO downlink signals over separate antennas to provide the advantages of a MIMO scheme.

In the uplink direction, each signal received from the antennas 218a-b is separated into uplink bands or sub-bands by the respective duplexers 434a-b. Each sub-band is amplified by a respective amplifier <NUM> (436a-d) and attenuated by a respective attenuator <NUM> (438a-d). The uplink sub-bands from the first antenna 218a are combined by duplexer 440a, while the uplink sub-bands from the second antenna are combined by duplexer 440b. The respective combined uplink signals then have their levels adjusted via a respective level control component <NUM> (442a and 442b) and are amplified by a respective amplifier <NUM> (444a and 444b), filtered by a respective filter circuit <NUM> (446a and 446b), and attenuated by a respective attenuator <NUM> (448a and 448b). The combined signals are then frequency converted by a respective mixer <NUM> (450a and 450b). In particular, the signal on the first channel is mixed by active mixer 450a with an LO reference at the fifth LO frequency LO5 and frequency converted to the eleventh frequency band FB11, while the signal on the second channel is mixed by active mixer 450b with an LO reference of at the sixth LO frequency LO6, and thereby frequency converted into the twelfth frequency band FB12. The frequency converted signals are then duplexed together by duplexer <NUM>. The
duplexed signal is then filtered by filter <NUM>, attenuated by attenuator <NUM>, amplified by amplifier <NUM>, attenuated by attenuator <NUM>, and provided to a respective remote unit <NUM> over an auxiliary uplink (UL) path in an auxiliary port.

<FIG> is a diagrammatic illustration of frequency conversion circuitry <NUM> that may be used with the extension unit <NUM>. In particular, a frequency reference filtered from the downlink path (e.g., a frequency reference having a frequency of R1) is provided to a frequency divider <NUM> which divides the frequency reference by four to generate the references for the synthesizers of the LO references for the extension unit <NUM>, each of which is level adjusted, amplified, and/or filtered, as necessary. In specific embodiments, the frequency conversion circuitry <NUM> produces reference signals of LO3, LO4, LO5, and LO6.

<FIG> together present an exemplary embodiment of the distributed antenna system (DAS) <NUM> that provides broadband coverage to an extended service area. The DAS <NUM> is configured to accommodate multiple bands having both MIMO and SISO signals so that the extended service area is provided with coverage from a plurality of service providers and/or broadband services operating in different bands over one single transport media, such as an optical fiber <NUM>. Such signals are provided by one or more BTS's. For the purposes of clarity, the description of <FIG> is limited to the downlink signal paths. However, persons having ordinary skill in the art will understand that each downlink path has an associated uplink path which is provided in essentially the same manner using similar frequency conversions and sharing the same signal links.

Referring now to <FIG>, the DAS <NUM> includes one or more master units <NUM> that interface with a plurality of service signals <NUM>-<NUM> such as from one or more base station transceivers (BTSs), an optical module <NUM> that couples the outputs of the master unit <NUM> to one or more remote units <NUM> over fiber-optic links, and a filter unit <NUM> that couples the outputs of the remote units <NUM> to a plurality of extension units, such as, for example three extension units <NUM>, <NUM>, <NUM>. The master units <NUM> include uplink and downlink BTS connection modules <NUM>, <NUM>, frequency conversion modules <NUM>, <NUM>, and band combining modules <NUM>, <NUM>, Each of the uplink and downlink BTS connection modules <NUM>, <NUM> includes a plurality of radio frequency (RF) signal attenuators <NUM>-<NUM> and <NUM>-<NUM>, which couple uplink signals from the DAS <NUM> back to the signal sources or BTSs <NUM>-<NUM> and downlink signals from the signal sources or BTSs <NUM>-<NUM> to the DAS <NUM>, respectively,.

The plurality of BTSs <NUM>-<NUM> may include BTSs operating in different frequency bands and supporting different air interfaces. A low-band BTS <NUM> transmits and receives low-band MIMO (L-MIMO or L1/L2) signals over the evolved NodeB (eNB) air interface and operates in the <NUM> band. To support MIMO, the low-band BTS <NUM> has two outputs or channels, with the first output providing a L-MIMO-<NUM> or L1 signal and the second output providing an L-MIMO-<NUM> or L2 signal. As noted, although a 2x2 MIMO scheme is shown in the examples illustrated, the invention is not so limited to such a MIMO scheme.

A low-band legacy BTS <NUM> transmits and receives GSM signals in the <NUM> band. The LL-BTS <NUM> of the exemplary embodiment does not support MIMO, and thus has a single output.

A mid-band BTS <NUM> transmits and receives mid-band MIMO (M-MIMO) signals over the eNB air interface and operates in the <NUM> band. As with the low-band BTS <NUM>, the mid-band BTS <NUM> has two outputs or channels, with the first output providing an M-MIMO-<NUM> or M1 signal and the second output providing an M-MIMO-<NUM> or M2 signal.

A mid-band legacy BTS <NUM> transmits and receives mid-band Universal Mobile Telecommunications System (MM-UMTS) signals in the <NUM> band. As with the low-band legacy BTS <NUM>, the mid-band legacy BTS <NUM> of the exemplary embodiment does not support MIMO, and thus has a single output.

An upper-band BTS <NUM> transmits and receives upper-band MIMO (U-MIMO) signals over the eNB air interface and operates in the <NUM> band. As with the low-band and mid-band BTSs <NUM>, <NUM>, the upper-band BTS <NUM> has two outputs or channels, with the first output providing a U1 or U1 signal and the second output providing a U-MIMO-<NUM> or U2 signal.

The low band L1 and L2 signals from the low-band BTS <NUM> are coupled to the master unit <NUM> by duplexers <NUM>, <NUM>, which separate the L-MIMO signals into a uplink signals 554a, 554b and downlink signals 556a, 556b. The L1 and L2 downlink signals pass through signal attenuators <NUM> and <NUM>, respectively, which couple a portion of the downlink signals to the downlink frequency conversion module <NUM>. While embodiments of the invention herein provide frequency translation for all the MIMO signals, the embodiment in <FIG> and <FIG> provide a translation of only one of the signals. The downlink frequency conversion module <NUM> provides the L1 downlink signal 556a to the band combining module <NUM> relatively unaltered or at its original frequency. However, to preserve the information contained in the L2 downlink signal 556b, the L2 downlink signal 556b is frequency shifted by a first appropriate shift frequency amount SF1, so that the shifted L2 downlink signal 556b* is frequency shifted from an original frequency to a different frequency such as into a thirteenth frequency band FB13. For consistency with respect to the other described embodiments, the different bands used for frequency shifting are numbered consecutively, but that does not mean that as between different embodiments the bands must be unique. Rather, an appropriate frequency band is chosen so as to provide the desired signal segregation in accordance with the invention. The L1 and shifted (as designated with an *) L2 downlink signals 556a, 556b* are provided to the downlink band combining module <NUM> where they are combined with other downlink signals as described in more detail below.

In a similar fashion as described with respect to the low-band BTS signals <NUM>, <NUM>, the LL-GSM signal from the low-band legacy BTS <NUM> is a non-MIMO signal, such as a SISO signal, and is coupled to the master unit <NUM> by duplexer <NUM>, which separate the LL-GSM signal into a downlink signal <NUM> and an uplink signal <NUM>. The LL-GSM downlink signal <NUM> passes through signal attenuator <NUM>, which couples a portion of the downlink signal <NUM> to the downlink frequency conversion module <NUM>. The downlink frequency conversion module <NUM> provides the LL-GSM downlink signal <NUM> to the band combining module <NUM> relatively unaltered or unshifted or at the original frequency, where it is combined with other downlink signals.

The M-MIMO-<NUM> (M1) and M-MIMO-<NUM> (M2) signals from the mid-band BTS <NUM> are coupled to the master unit <NUM> by duplexers <NUM>, <NUM>, which separate the M-MIMO signals into uplink signals 568a, 568b and downlink signals 570a, 570b. The M1 and M2 downlink signals 570a, 570b pass through signal attenuators <NUM> and <NUM>, respectively, which couple portions of the downlink signals 570a, 570b to the downlink frequency conversion module <NUM>. Similarly to the low-band MIMO signals, the downlink frequency conversion module <NUM> provides the M1 downlink signal 570a to the band combining module <NUM> relatively unaltered or unshifted or at an original frequency. However, to preserve the information contained in the M2 downlink signal 570b, the M2 downlink signal 570b is frequency shifted by a shift frequency amount SF2, so that the M2 downlink signal 570b* is shifted from an original frequency to a different frequency such as into a fourteenth frequency band FB14. The M1 and shifted M2 downlink signals 570a, 570b* are provided to the downlink band combining module <NUM> where they are combined with other downlink signals.

The MM-UMTS signal from the mid-band legacy BTS <NUM> is a non-MIMO signal, such as a SISO signal, and is coupled to the master unit <NUM> by duplexer <NUM>, which separate the MM-UMTS signal into an uplink signal <NUM> and a downlink signal <NUM>. The MM-UMTS downlink signal <NUM> passes through signal attenuator <NUM>, which couples a portion of the downlink signal <NUM> to the downlink frequency conversion module <NUM>. The downlink frequency conversion module <NUM> provides the MM-UMTS downlink signal <NUM> to the band combining module <NUM> relatively unaltered or unshifted or at the original frequency, where it is combined with other downlink signals.

The U-MIMO-<NUM> (U1) and U-MIMO-<NUM> (U2) signals from the upper-band BTS <NUM> are coupled to the master unit <NUM> by duplexers <NUM>, <NUM>, which separate the U-MIMO signals into uplink signals 582a, 582b and downlink signals 584a, 584b. The U1 and U2 downlink signals 584a, 584b pass through signal attenuators <NUM> and <NUM>, respectively, which couple portions of the downlink signals 584a, 584b to the downlink frequency conversion module <NUM>. Similarly to the low and mid-band MIMO signals, the downlink frequency conversion module <NUM> provides the U1 downlink signal 584a to the band combining module <NUM> relatively unaltered of unshifted or at an original frequency. However, to preserve the information contained in the U2 downlink signal 584b, the U2 downlink signal 584b is frequency shifted a shift frequency amount SF3, so that the shifted U2 downlink signal 584b* is shifted from an original frequency to a different frequency such as into a fifteenth frequency band FB15. The U1 and shifted U2 downlink signals 584a, 584b* are provided to the downlink band combining module <NUM> where they are combined with other downlink signals for transmission to the remote unit <NUM>.

In order to keep the MIMO channel signals for each MIMO band or MIMO set the master unit from interfering with each other, the master unit is operable to convert the various MIMO channel signals to different frequencies wherein the different frequency of one set of MIMO channel signals is different from the different frequency of another set of MIMO channel signals. For example, as discussed above, each of the FB13, FB14, and FB15 frequencies or frequency bands are different so that they may be transceived over the same fiber optic cable without interfering with each other.

The downlink band combining module <NUM> includes a low-band duplexer <NUM>, and a high band duplexer <NUM>. The low band duplexer <NUM> is coupled to L1 signal 556a, LL-GSM signal <NUM>, frequency converted M2 signal 570b*, and frequency converted U2 signal 584b*. The aforementioned signals are thereby combined into a composite low band downlink signal <NUM> that includes signals in the fourteenth and fifteenth frequency bands FB14, FB15 as well as frequencies in about the <NUM> and <NUM> ranges. Similarly, the high band duplexer <NUM> is coupled to the frequency converted L2 signal 556b*, the MM-UMTS signal <NUM>, and the U1 signal 584a. The aforementioned signals are thereby combined into a composite high band downlink signal <NUM> that includes signals in the thirteenth frequency band FB13 as well as frequencies in about the <NUM> and <NUM> ranges. The remaining M1 signal 570a is passed through the band combining module relatively unaltered. The bands used for frequency shifting may be chosen so as to be close to existing service bands that are already being handled. That is one or more of the MIMO channel signals are converted to a different frequency that is close to the original frequency of the unshifted or original frequency of the MIMO or non-MIMO signals. In that way, the signals may be efficiently combined and separated at the remote and master units using appropriate band combining and band separating circuit components such as combiners and duplexers. For example, the frequency converted M2 and U2 signals are converted so as to be close to the L-band (<NUM>) and LL-Band (<NUM>). Alternatively, the shifted L2 signal is shifted so as to be close to the MM-band (<NUM>) and U-band (<NUM>). As such efficient use of components is provided.

The M1 downlink signal 570a, composite low-band downlink signal <NUM>, and composite high-band downlink signal <NUM> are coupled to the optical module <NUM>. The optical module <NUM> includes an appropriate electrical-to-optical circuit <NUM>, an optical-to-electrical circuit <NUM>, and a wavelength-division multiplexer <NUM>. The wavelength-division multiplexer <NUM> couples the composite optical downlink signal having a first wavelength, or color onto the optical fiber <NUM> and extracts the composite uplink signal having a second wavelength, or color from the same optical fiber <NUM>. The M1 and composite downlink signals 570a, <NUM>, <NUM> are coupled to the input of electrical-to-optic circuit <NUM>, which converts the signals into a composite downlink optical signal <NUM>. The composite downlink optical signal <NUM> is coupled to the optical fiber <NUM>, for transporting the composite downlink optical signal <NUM> to the remote unit <NUM>.

Referring now to <FIG>, the remote unit <NUM> is configured to receive and transmit optical signals over the optic fiber <NUM>, convert between optical signals and electrical signals, and receive and transmit RF electrical signals via one or more extension units <NUM>, <NUM>, <NUM> and via one or more antennas <NUM>. The remote unit <NUM> thereby provides wireless coverage to the extended service area. To this end, the remote unit <NUM> includes an optical module <NUM>, a low-band downlink duplexer <NUM>, a high-band downlink duplexer <NUM>, power amplifiers <NUM>-<NUM>, a post-amplification duplexer <NUM>, an antenna feed duplexer <NUM>, an antenna <NUM>, and one or more extension ports <NUM>.

The optical module <NUM> includes a wavelength-division multiplexer <NUM> that is coupled to an optical-to-electrical downlink receiver circuit <NUM> and an electrical-to-optical uplink transmitter circuit <NUM>. The composite downlink optical signal <NUM> is coupled from the optic fiber <NUM> to the optical-to-electrical circuit <NUM> by the wavelength-division multiplexer <NUM>. In turn, the optical-to-electrical circuit <NUM> converts the composite downlink optical signal <NUM> into a composite downlink electrical signal, thereby recovering the M1 signal 570a, low-band composite downlink signal <NUM>, and high-band composite downlink signal <NUM>.

The low-band and high-band composite downlink signals <NUM>, <NUM> are coupled to the low-band and high-band downlink duplexers, <NUM>, <NUM> respectively. In turn, the low-band downlink duplexer <NUM> separates the low-band composite downlink signal <NUM> into L1 signal 556a, LL-GSM signal <NUM>, and a U/M-MIMO-<NUM> composite signal <NUM> comprising the frequency shifted M2 and U2 signals 570b*, 584b*. Similarly, the high-band downlink duplexer <NUM> separates the high-band composite signal <NUM> into the frequency shifted L2 signal 556b*, MM-UMTS signal <NUM>, and U1 signal 584a.

The LL-GSM signal <NUM>, M1 signal 570a, and MM-UMTS signal <NUM> are coupled to power amplifiers <NUM>, <NUM>, and <NUM> respectively, which amplify the signals to a level suitable for providing wireless coverage. In turn, the resulting amplified signals are coupled to antenna <NUM> by the post-amplification and antenna duplexers <NUM>, <NUM>. The remote unit <NUM> thereby provides wireless coverage to the extended service area by extending the coverage of the low-band and mid-band legacy BTSs <NUM>, <NUM>. The remote unit <NUM> also extends the service area for the M1 signal 570a.

In the specific embodiment illustrated in <FIG>, the remaining L1 signal 556a, frequency shifted L2 signal 556b*, U1 signal 584a, and U/M-MIMO-<NUM> composite signal <NUM> are coupled to an appropriate filter unit <NUM> through the extension port <NUM>, which is coupled to an input port <NUM> of the filter unit <NUM> via suitable transmission lines. However, it should be understood that in alternative embodiments, a suitably configured extension unit may be coupled directly to the extension port <NUM>, in which case the filter unit <NUM> would be omitted. In the embodiment illustrated in <FIG>, the filter unit <NUM> includes, in addition to the input port <NUM>, three output ports <NUM>-<NUM> and a duplexer <NUM> that separates the frequency shifted M2 and U2 signals 570b*, 584b*. The filter unit <NUM> is thereby configured so that:.

The first extension unit <NUM> includes a frequency conversion circuit <NUM>, transmit/receive duplexers <NUM>, <NUM>, power amplifiers <NUM>, <NUM> and antennas <NUM>, <NUM>. The frequency shifted L2 signal 556b* is coupled to the input of the frequency conversion circuit <NUM>, which shifts the signal by the first shift frequency amount SF1 so that the frequency range of the L2 signal 556b is restored to the same frequency range as the original L1 signal 556a for the air interface. The L1 and restored L2 signals. 556a, 556b are coupled to the inputs of appropriate power amplifiers <NUM>, <NUM>, which in turn amplify the signals to a power level sufficient to cover the extended service area. The outputs of the power amplifiers <NUM>, <NUM> are coupled to antennas <NUM>, <NUM> by the transmit/receive duplexers <NUM>, <NUM>. The first extension unit <NUM> thereby extends the coverage of the low-band BTS <NUM> into the service area.

The second extension unit <NUM> includes a frequency conversion circuit <NUM>, a transmit/receive duplexer <NUM>, a power amplifier <NUM>, and an antenna <NUM>. The frequency shifted M2 signal 570b* is coupled to the input of the frequency conversion circuit <NUM>, which shifts the signal by the second shift frequency amount SF2 so that the frequency range of the M2 signal 570b is restored to the same frequency range as the original M1 signal 570a. The restored M2 signal 570b is coupled to the input of power amplifier <NUM>, which in turn amplifies the signal to a power level sufficient to cover the extended service area. The output of the power amplifier <NUM> is coupled antenna <NUM> by the transmit/receive duplexer <NUM>. The second extension unit <NUM>, working in cooperation with the remote unit <NUM> (which transmits the M1 signal 570a) thereby extends the coverage of the mid-band BTS <NUM> into the service area.

The third extension unit <NUM> includes a frequency conversion circuit <NUM>, transmit/receive duplexers <NUM>, <NUM>, power amplifiers <NUM>, <NUM> and antennas <NUM>, <NUM>. The frequency shifted U2 signal 584b* is coupled to the input of the frequency conversion circuit <NUM>, which shifts the signal by the third shift frequency amount SF3 so that the frequency range of the U2 signal 584b is restored to the same frequency range (<NUM>-<NUM>) as the U1 signal 584a. The U1 and restored U2 signals 584a, 584b are coupled to the inputs of power amplifiers <NUM> and <NUM>, which in turn amplify the signals to a power level sufficient to cover the extended service area. The outputs of the power amplifiers <NUM>, <NUM> are coupled to antennas <NUM>, <NUM> by the transmit/receive duplexers <NUM>, <NUM>. The third extension unit <NUM> thereby extends the coverage of the upper-band BTS <NUM> into the service area.

The frequency conversion circuits <NUM>, <NUM>, <NUM> in the extension units <NUM>, <NUM>, <NUM> may include local oscillators, mixers, and filters as is known in the art. To synchronize the local oscillators in the extension units <NUM>, <NUM>, <NUM> with the local oscillators in the frequency conversion modules <NUM>, <NUM> in the master unit <NUM>, the frequency conversion circuits <NUM>, <NUM>, <NUM> may receive a common reference signal transmitted via the same downlink path as the BTS signals. This common reference signal transmitted from the master unit to the remote unit and to the filter unit and all extension units may be used to synchronize the offset frequencies of the frequency conversion circuits <NUM>, <NUM>, <NUM> with their associated frequency conversion circuits in the frequency conversion module <NUM> and to frequency lock all of the frequency synthesizers used for frequency conversion. The common reference signal or signals may thereby allow the frequency converted signals to be recovered to their original frequency with minimal error. In an alternative embodiment, high stability reference sources may be used in the conversion modules <NUM>, <NUM> and extension units <NUM>, <NUM>, <NUM> to provide frequency matching between the conversion stages.

For example, embodiments of the invention may shift or convert frequencies by either downconverting or upconverting the frequency. Thus, in a downlink direction, at least one MIMO signal received by a master unit may be upconverted before such signal is passed over an optical link to a remote unit and/or extension unit. This upconverted signal may then be downconverted to the appropriate MIMO band by the remote unit and/or extension unit before it is transmitted. Alternative embodiments of the invention may, instead, downconvert at least one signal received by the master unit before such signal is passed over an optical link to the remote unit and/or extension unit, then upconvert that signal to the MIMO band at the remote unit and/or extension unit. Therefore, the direction of the frequency conversion is not limiting, as described herein, for the exemplary embodiments. Correspondingly, in an uplink direction, at least one signal received by the remote unit and/or extension unit may be upconverted before such signal is passed over an optical ink to the master unit. This upconverted signal may then downconverted to the MIMO band by the master unit before it is transmitted back to a BTS. Alternative embodiments of the invention may, instead, downconvert at least one signal received by the remote unit and/or extension unit before such signal is passed over an optical link to the master unit, then upconvert that signal at the master unit to the appropriate MIMO band.

Moreover, the DAS systems of <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, and the components or circuits or <FIG> and <FIG> may include more or fewer components consistent with embodiments of the invention. In particular, each master unit <NUM> of a MIMO DAS system may communicate with more than three sets of remote units and receive more signals than those shown or described. Such a master unit <NUM> can support up to <NUM> remote units in point to point architecture and or up to <NUM> optical links in cascaded architecture with up to <NUM> remote units per optical link in one embodiment of the invention. As such, the systems of <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> may be configured with more or fewer master units, remote units, extension units, or other components consistent with embodiments of the invention.

Claim 1:
A distributed antenna system (<NUM>), comprising:
a master unit (<NUM>) configured to:
receive at least one set of multiple input multiple output, MIMO, channel signals at original MIMO radio frequencies in a service provider frequency band from at least one signal source, the at least one set of the MIMO channel signals including at least a first MIMO channel signal at a first original MIMO radio frequency and a second MIMO channel signal at a second original MIMO radio frequency;
generate a local oscillator signal;
frequency convert the first MIMO channel signal having the first original MIMO radio frequency into a frequency converted first MIMO channel signal having a frequency different than the first original MIMO radio frequency using the local oscillator signal;
maintain the second MIMO channel signal at the second original MIMO radio frequency;
combine the frequency converted first MIMO channel signal, the second MIMO channel signal, and the local oscillator signal into a combined signal for transmission;
an optical link (<NUM>) operably coupled with the master unit (<NUM>);
a remote unit (<NUM>) communicatively coupled with the master unit (<NUM>) via the optical link (<NUM>) for receiving the combined signal from the master unit (<NUM>) via the optical link (<NUM>), the remote unit further configured to process the combined signal to obtain the frequency converted first MIMO channel signal, the second MIMO channel signal, and the local oscillator signal;
at least one extension unit (<NUM>) in communication with the remote unit (<NUM>), wherein the at least one extension unit (<NUM>) includes conversion circuitry and is configured to receive the frequency converted first MIMO channel signal and the local oscillator signal from the remote unit and to frequency convert the frequency converted first MIMO channel signal from the frequency different than the first original MIMO radio frequency back to the first original MIMO radio frequency for transmission over at least one antenna (44a, 44b, 132a, 132b, 216a, 216b, 216c, 216d).