HK1217385B - Method for operating a distributed antenna system and method of communicating in the system - Google Patents

Description

Method of operating a distributed antenna system and method of communicating in the system

This patent application is a divisional application of a patent application with an international application date of August 16, 2011, national application number 201180050052.4, and invention name “Remotely Reconfigurable Distributed Antenna System and Method”.

This application claims the benefit of US Patent Application No. 61/382,836, filed September 14, 2010, entitled "REMOTELY RECONFIGURABLEDISTRIBUTED ANTENNA SYSTEM AND METHODS."

Technical Field

The present invention generally relates to wireless communication systems that employ distributed antenna systems (DAS) as part of a distributed wireless network. More particularly, the present invention relates to DAS utilizing software defined radio (SDR).

Background Art

Wireless and mobile network operators face the ongoing challenge of building networks that effectively manage high data traffic growth rates. The increasing level of mobility and multimedia content available to end users requires end-to-end network adaptation to support both new services and the growing demand for broadband and flat-rate internet access. One of the greatest challenges facing network operators arises from the physical movement of users from one location to another, particularly when wireless users gather in large numbers in a single location. A prominent example is an industrial facility during lunchtime, when a large number of wireless users visit the building's cafeteria. During this time, many users are away from their offices and typical work areas. It's likely that during lunchtime, there are numerous locations throughout the facility with few users. If indoor wireless network resources are properly estimated during the design process for user load, as they would during normal working hours when users are in their normal work areas, it's likely that this lunchtime scenario will present unexpected challenges with regard to available wireless capacity and data throughput.

In order to adapt to the change of user load, there are several available existing methods.

One approach is to deploy multiple low-power, high-capacity base stations throughout the facility. The number of base stations is determined based on the coverage area of each base station and the total space to be covered. Each of these base stations is provided with sufficient radio resources—capacity and bandwidth data handling capacity—to accommodate the peak user load experienced during the workday and workweek. While this approach generally achieves high-quality service, a significant drawback is that much of the base station capacity is wasted during most of the time. Because typical indoor wireless network deployments involve capital and operating costs estimated for each base station on a per-user basis, the high lifecycle costs typically associated with a given enterprise facility are far from optimal.

A second alternative approach involves the deployment of a DAS and a centralized group of base stations dedicated to that DAS. Conventional DAS deployments fall into one of two categories. The first type of DAS is "fixed," where the system configuration does not change based on the time of day or other usage information. The remote units associated with the DAS are established during the design process so that a specific block of base station radio resources is deemed sufficient to serve each small group of DAS remote units. A significant disadvantage of this approach is that most enterprises appear to experience frequent adjustments and reorganizations of the various groups within the enterprise. Therefore, the initial setup will most likely need to be constantly changed, requiring the deployment of additional personnel and contract resources with the appropriate level of expertise in wireless networks.

The second type of DAS is equipped with a network switch that enables the location and number of DAS remote units associated with any particular centralized base station to be manually changed. While this approach appears to allow for dynamic reconfiguration based on the needs of the enterprise or based on the time of day, it often requires the deployment of additional personnel resources for real-time management of the network. Another problem is that it is not always correct or optimal to have the same DAS remote unit configuration changed back and forth at the same time every day of the week. Often, it is difficult or impractical for the enterprise IT manager to monitor the user load on each base station. And it is almost certain that the enterprise IT manager has no practical way to determine the load for each DAS remote unit at a given time of day; they can only guess.

Another major limitation of existing DAS deployments relates to their installation, commissioning, and optimization processes. Challenging issues that must be overcome include selecting remote unit antenna sites to ensure adequate coverage while minimizing downlink interference from outdoor macrocell sites, minimizing uplink interference to outdoor macrocell sites, and ensuring proper intra-system handover when indoors and when moving from outdoor to indoor (and vice versa). The process of performing such deployment optimization is often described as a trial-and-error approach, and as such, the results may not be consistent with high-quality service.

A major limitation of existing DAS devices that utilize digital transmission links, such as fiber or wired Ethernet, is that existing RF-to-digital conversion techniques utilize a system's method of converting a single, wide RF bandwidth, such as 10 MHz to 25 MHz, to digital. Consequently, all signals within the wide bandwidth, whether weak or strong, desired or undesired, are converted to digital, regardless of whether those signals are desired or not. This approach often results in inefficiencies within the DAS that limit the capacity of the DAS network. It would be preferable to employ alternative approaches that achieve higher efficiency and improved flexibility, particularly for neutral host applications.

In 2008, the US Federal Communications Commission (FCC) further clarified its E-911 requirements for Phase 2 accuracy for mobile wireless networks. The required information in Phase 2 is the mobile phone number and the physical location within a few dozen yards of the call originating from. The Canadian government is reportedly considering similar requirements. Furthermore, the FCC is eager to see US mobile network operators provide E-911 location services with enhanced accuracy for indoor users. Reports indicate that the FCC is working to approve Phase 2 accuracy for indoor wireless communications within the next two years.

Many wireless networks employ mobile and fixed broadband wireless terminals that use GPS-based E-911 location services. GPS signals from outdoor satellites have been shown to not propagate well indoors. Therefore, alternative, more robust E-911 location determination methods are needed indoors, especially if FCC regulations become more stringent.

Several US operators have expressed concerns about how they can practically and cost-effectively obtain these enhanced positioning accuracy capabilities. Operators are very eager to identify a cost-effective method for enhanced positioning accuracy that can be deployed indoors.

One proposed approach for enhancing indoor positioning accuracy for CDMA networks employs a separate unit known as a CDMA pseudo-pilot (Pilot Beacon). A significant disadvantage of this approach for indoor DAS applications is that, since the CDMA pseudo-pilot is a separate and dedicated device and is not integrated into the DAS, its deployment is likely to be expensive. The pseudo-pilot approach for CDMA networks uses pseudo-pilots with unique PN codes (in that area) that effectively divide a specific CDMA network coverage area (e.g., indoors) into multiple small zones (each corresponding to the coverage area of a low-power pseudo-pilot). The network knows the location, PN code, and RF power level of each pseudo-pilot. Each pseudo-pilot must be synchronized to the CDMA network via GPS or a local base station connection. A variable delay setting enables each pseudo-pilot to have appropriate system timing to allow triangulation and/or cell identity location determination. An alternative, but potentially expensive, enhancement to this approach would employ a wireless modem for each pseudo-pilot to provide remote alarming, control, and monitoring of each CDMA pseudo-pilot. For WCDMA networks, there are no known solutions publicly proposed for indoor positioning accuracy enhancement.

An alternative, technically proven approach to indoor positioning accuracy enhancement for GCM networks employs a separate unit known as a Location Measurement Unit or LMU. A significant disadvantage of this approach for indoor DAS applications is that, since the LMU is a separate, dedicated device and is not integrated into the DAS, its deployment is likely to be expensive. Each LMU requires backhaul infrastructure to a central server where the LMU measurements are analyzed. The LMU backhaul cost increases the overall cost of deploying an enhanced accuracy E-911 solution for GCM networks. Although the technically proven KMU approach is available, it has not yet been widely deployed in conjunction with indoor DAS.

Based on the prior art approaches described herein, it is apparent that efficient, easily deployable, and dynamically reconfigurable wireless networks cannot be achieved through prior art systems and capabilities.

Summary of the Invention

The present invention substantially overcomes the limitations of the prior art described above. The advanced system architecture of the present invention provides a high degree of flexibility to manage, control, enhance and promote the radio resource efficiency, usage and overall performance of distributed wireless networks. This advanced system architecture enables specialized applications and enhancements, including flexible simulcasting, automatic traffic load balancing, network and radio resource optimization, network calibration, autonomous/assisted commissioning, carrier polling, automatic frequency selection, radio frequency carrier positioning, traffic monitoring, traffic tagging and indoor location determination using pseudo pilots. The present invention can also serve multiple operators, multi-mode radios (modulation independent) and multiple frequency bands per operator to improve the efficiency and traffic capacity of the operator's wireless network.

Accordingly, the object of the present invention is to provide a capability for flexible simulcasting. With flexible simulcasting, the amount of radio resources (such as RF carriers, CDMA codes or TDMA time slots) allocated by each RRU access module to a specific RRU or RRU group can be set via software control as described below to meet the desired capacity and total processing power targets or the needs of wireless users. To achieve these and other purposes, one aspect of the present invention uses software-programmable frequency-selective digital up converters (DUCs) and digital down converters (DDCs). A software-defined remote radio head architecture is used for cost-effective optimization of radio performance. The frequency-selective DDCs and DUCs at the remote radio head make it possible to achieve a high signal-to-noise ratio (SNR) that maximizes the total processing power data rate. The embodiment described in Figure 1 describes the basic structure and provides an example of a flexible simulcast downlink transmission script. Figure 2 describes an embodiment of the basic structure of a flexible simulcast uplink transmission script.

Another object of the present invention is to facilitate the conversion and transmission of several discrete, relatively narrow RF bandwidths. In another aspect of the present invention, embodiments convert only specific, relatively narrow bandwidths that carry useful information. Thus, this aspect of the present invention enables more efficient use of available fiber transmission bandwidth for neutral host applications and facilitates the transmission of more operator bandwidth segments over fiber. To achieve the above results, the present invention utilizes frequency-selective filtering at the remote radio head to enhance system performance. In some embodiments of this aspect of the invention, noise reduction via frequency-selective filtering at the remote radio head is used to maximize the signal-to-noise ratio (SNR) and, therefore, data throughput. Another object of the present invention is to provide enhanced indoor location accuracy for CDMA and WCDMA. In one aspect of the present invention, embodiments provide enhanced location accuracy performance by employing pseudo pilots. Figure 3 depicts a typical indoor system employing multiple remote radio head units (RRUs) and a central digital access unit (DAU). The remote radio heads have unique beacons that identify specific indoor cells. Mobile users use the beacon information to assist in locating a specific cell.

Another object of the present invention is to enhance indoor location accuracy for GCM and LTE. In another aspect, one embodiment of the present invention provides user location based on the radio signature of a mobile device. Figure 4 illustrates a typical indoor system employing multiple remote radio head units (RRUs) and a central digital access unit (DAU). According to the present invention, each remote radio head provides unique header information on data received by the remote radio head. The system of the present invention uses this header information in conjunction with the mobile user's radio signature to locate the user in a specific cell. Another object of the present invention is to reroute local traffic to Internet VoIP, Wi-Fi, or WiMAX. In this aspect of the present invention, one embodiment determines the radio signature of each user within a DAU or DAU island and uses this information to identify whether the user is within the coverage area associated with a particular DAU or DAU island. The DAU tracks the radio signatures of all active users within its network and maintains a running database containing information about the users. As shown in Figure 6, one embodiment of the present invention enables a network operations center (NOC) to notify a DAU that, for example, two specific users are located within the same DAU or DAU island. The DAU then reroutes the users to Internet VoIP, Wi-Fi, or WiMAX as needed. Another embodiment of the present invention determines the Internet Protocol (IP) address of each user's Wi-Fi connection. If the IP addresses of the users are within the same DAU or DAU island, the data calls of these users will be rerouted on the internal network.

The present invention is suitable for use with distributed base stations, distributed antenna systems, distributed repeaters, mobile devices and wireless terminals, portable wireless devices, and other wireless communication systems such as microwave and satellite communications. The present invention is also field upgradeable through a link such as an Ethernet connection to a remote computing center.

An embodiment of the present invention provides a method for operating a distributed antenna system, the method comprising: providing one or more remote radio units, each of the one or more remote radio units being configured to receive one or more downlink radio frequencies and to transmit one or more uplink radio frequencies; providing at least one digital access unit configured to communicate with at least some of the one or more remote radio units; receiving a signal from a signal source at the at least one digital access unit; digitizing the received signal at the at least one digital access unit to provide a digitized signal; performing I/Q mapping and framing on the digitized signal at the at least one digital access unit to provide a packetized signal; and transmitting the packetized signal from the at least one digital access unit to the one or more remote radio units.

An embodiment of the present invention also provides a method for communicating in a distributed antenna system, the method comprising: receiving a downlink optical signal at a remote radio unit, the downlink optical signal being received from a digital access unit, the downlink optical signal comprising a plurality of carriers; converting a portion of the downlink optical signal received at the remote radio unit into a downlink signal, the portion of the downlink optical signal corresponding to a subset of the plurality of carriers, wherein the number of carriers in the subset of the plurality of carriers is less than the number of carriers in the plurality of carriers, and the number of carriers in the subset of the plurality of carriers is configurable; sending the downlink signal from the remote radio unit; receiving an uplink signal at the remote radio unit; converting the uplink signal received at the remote radio unit into an uplink optical signal, wherein the uplink optical signal corresponds to the subset of the plurality of carriers; and sending the uplink optical signal from the remote radio unit to the digital access unit.

An embodiment of the present invention also provides a system for sending signals, the system comprising: a plurality of remote radio units; and a plurality of digital access units, each digital access unit being coupled to another digital access unit of the plurality of digital access units, wherein a first digital access unit of the plurality of digital access units is coupled to a first signal source and a second digital access unit of the plurality of digital access units, the first digital access unit being configured to communicate with at least a first part of the plurality of remote radio units, and wherein each of the first part of the plurality of remote radio units is configured to packetize a first uplink signal for sending to the first digital access unit, and the first digital access unit is configured to packetize a first downlink signal for sending to the first part of the plurality of remote radio units.

An embodiment of the present invention also provides a system for sending signals, the system comprising: a plurality of remote radio units; and a plurality of digital access units, each digital access unit being coupled to another digital access unit of the plurality of digital access units, wherein a first digital access unit of the plurality of digital access units is coupled to a first signal source, and a second digital access unit of the plurality of digital access units is configured to communicate with at least a first part of the plurality of remote radio units, wherein each of the first part of the plurality of remote radio units is configured to packetize a first uplink signal for sending to the first digital access unit via the second digital access unit, and wherein the first digital access unit is configured to packetize a first downlink signal for sending to the first part of the plurality of remote radio units via the second digital access unit.

Appendix 1 is a glossary of terms including acronyms used in this document.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present invention may be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG1 is a block diagram illustrating a basic structure and example based on a flexible simulcast downlink delivery scenario with 2 DAUs and 4 DRUs according to an embodiment of the present invention.

2 is a block diagram illustrating a basic structure and example based on a flexible simulcast uplink delivery scenario with 2 DAUs and 4 DRUs according to an embodiment of the present invention.

FIG3 illustrates an embodiment of an indoor system employing multiple remote radio head units (RRUs) and one central digital access unit (DAU).

FIG4 shows an embodiment of an indoor system according to the present invention using multiple remote radio head units (RRUs) and a central digital access unit (DAU)

FIG5 illustrates an embodiment of a cellular network system employing multiple remote radio heads according to the present invention.

FIG. 6 is a depiction of local connectivity according to one embodiment of the present invention.

FIG. 7 shows an embodiment of the basic structure of an embedded software control module for managing key functions of a DAU and an RRU according to the present invention.

DETAILED DESCRIPTION

The present invention is a novel reconfigurable distributed antenna system that provides a high degree of flexibility to manage, control, reconfigure, enhance, and improve the radio resource efficiency, utilization, and overall performance of the distributed antenna system. An embodiment of the reconfigurable distributed antenna system according to the present invention is shown in FIG1 . The operation of flexible simulcast for downlink signals can be explained using a flexible simulcast system 100 . The system utilizes a digital access unit (hereinafter referred to as a "DAU") function. The DAU serves as an interface to a base station (BTS). The DAU is connected to the BTS (at one end) and to multiple RRUs on the other. For the downlink (DL) path, RF signals received from the BTS are individually downconverted, digitized, and converted to baseband (using a digital downconverter). The data streams are then I/Q mapped and framed. Specific parallel data streams are then independently serialized and translated into optical signals using pluggable SFP modules and delivered to different RRUs over optical cables. For the uplink (UL) path, optical signals received from the RRUs are dedigitized, deframed, and digitally upconverted using a digital upconverter. The digital streams are then independently converted to the analog domain and up-converted to the appropriate RF frequency band. The RF signals are then passed to the BTS. The system embodiment generally includes a DAU1, designated 101, an RRU1, designated 103, an RRU2, designated 104, an RRU3, designated 105, and an RRU4, designated 106. A composite downlink input signal 107 from, for example, a base station belonging to one wireless operator enters DAU1 at its DAU1 RF input port. Composite signal 107 includes carriers 1 through 4. A second composite downlink input signal from, for example, a second base station belonging to the same wireless operator enters DAU2 at its DAU2 RF input port. Composite signal 108 includes carriers 5 through 8. The functions of DAU1, DAU2, RRU1, RRU2, RRU3, and RRU4 are explained in detail in U.S. Provisional Application No. 61/374,593, filed on August 17, 2010, and attached hereto as an appendix, entitled "Neutral Host Architecture for a Distributed Antenna System." One optical output of DAU1 is fed to RRU1. A second optical output 113 of DAU1 is fed to DAU2 via a bidirectional optical cable 113. This connection facilitates networking of DAU1 and DAU2, meaning that, depending on the software settings within the networked DAU system including DAU1 and DAU2, carriers 1 through 8 are all available within DAU1 and DAU2 for transmission to RRU1, RRU2, RRU3, and RRU4. The software settings within RRU1 are configured manually or automatically so that carriers 1 through 8 are present in the downlink output signal 109 at the antenna port of RRU1. The presence of all eight carriers means that RRU1 can potentially access the full capacity of both base stations feeding DAU1 and DAU2. One possible application for RRU1 is in a wireless distribution system, for example, a cafeteria within a corporate building where a large number of wireless users gather during lunchtime. RRU2 is fed by RRU1's second optical port via a bidirectional optical cable 114 leading to RRU2. Optical cable 114 performs the function of daisy-chaining RRU2 with RRU1. Software settings within RRU2 are manually or automatically configured so that carriers 1, 3, 4, and 6 are present in the downlink output signal 110 at RRU2's antenna port. The capacity of RRU2 is set to a value significantly less than that of RRU1, depending on its specific digital upconverter settings. Each remote radio unit has integrated frequency-selective DUCs and DDCs with gain control for each carrier. The DAU can remotely turn individual carriers on and off via gain control parameters.

In a manner similar to that described previously for RRU1, software settings within RRU3 are manually or automatically configured so that carriers 2 and 6 appear in the downlink output signal 111 at RRU3's antenna port. Compared to the downlink signal 110 at RRU2's antenna port, the capacity of RRU3, as configured via RRU3's software settings, is much smaller than the capacity of RRU2. RRU4 is fed by RRU3's second optical port via a bidirectional optical cable 115 leading to RRU4. Optical cable 115 performs the function of daisy-chaining RRU4 with RRU3. Software settings within RRU4 are manually or automatically configured so that carriers 1, 4, 5, and 8 appear in the downlink output signal 112 at RRU4's antenna port. The capacity of RRU4 is set to a value much smaller than the capacity of RRU1. As discussed in conjunction with FIG. 7 , the relative capacity settings of RRU1 , RRU2 , RRU3 , and RRU4 may be dynamically adjusted to meet capacity requirements within a coverage area determined by the physical locations of the antennas connected to RRU1 , RRU2 , RRU3 , and RRU4 , respectively.

The present invention facilitates the conversion and transmission of several discrete, relatively narrow RF bandwidths. This approach enables conversion of only those specific, relatively narrow bandwidths carrying useful or specific information. This approach also enables neutral host applications to more efficiently use available fiber transmission bandwidth and enables transmission of more bandwidth segments of various operators over fiber. As disclosed in U.S. Provisional Application No. 61/1374,593, filed on August 17, 2010, entitled "Neutral Host Architecture for a Distributed Antenna System," and also referenced in FIG1 of the present patent application, a dynamically software-programmable digital up-converter (DDC) located within an RRU, as described below, can be reconfigured to transmit any specific narrow frequency band or bands, RF carriers, or RF channels available at the respective RF input ports of any DAU from the DAU input to any specific RRU output. FIG1 illustrates this capability, wherein only specific frequency bands or RF carriers appear at the output of a given RRU.

A relevant capability of the present invention is not only that the digital upconverter within each RRU can be configured to pass any specific narrowband from the DAU input to any specific RRU output, but also that the upconverter within each RRU can be configured to pass any specific time slot or timeslots per carrier from the DAU input to any specific RRU output. The DAU detects which carriers and corresponding timeslots are active. This information is relayed to each RRU via the management control and monitoring protocol software described below. This information is then used by the RRU to turn off and on individual carriers and their corresponding timeslots as needed.

With reference to Figure 1 of the present patent application, an alternative embodiment of the present invention can be described as follows. In the foregoing description of Figure 1, the foregoing embodiment involves having downlink signals from two separate base stations belonging to the same wireless operator enter the DAU1 and DAU2 input ports respectively. In an alternative embodiment, a second composite downlink input signal from, for example, a second base station belonging to a different wireless operator enters DAU2 at the DAU2RF input port. In this embodiment, the signals belonging to both the first operator and the second operator are converted and sent to RRU1, RRU2, RRU3 and RRU4 respectively. This embodiment provides an example of a neutral host wireless system in which multiple wireless operators share a common infrastructure including DAU1, DAU2, RRU1, RRU2, RRU3 and RRU4. All of the features and advantages mentioned above belong to each of the two wireless operators.

As disclosed in U.S. Provisional Application No. 61/374,593, filed on August 17, 2010, entitled “Neutral Host Architecture for a Distributed Antenna System,” and also referenced in FIG. 1 of the present application, the digital upconverters present in the RRUs can be programmed to handle a variety of signal formats and modulation types, including FDMA, CDMA, TDMA, OFDMA, and the like. Furthermore, the digital upconverters present in each RRU can be programmed to operate signals to be transmitted within a variety of frequency bands, subject to the capabilities and limitations of the system architecture disclosed in U.S. Provisional Application No. 61/374,593, filed on August 17, 2010, entitled “Neutral Host Architecture for a Distributed Antenna System.” In one embodiment of the present invention, where a wideband CDMA signal is present within a bandwidth corresponding to, for example, carrier 1 at the input port to DAU1, the signals transmitted at the antenna ports of RRU1, RRU2, and RRU4 will be a wideband CDMA signal that is substantially identical to the signal present within the bandwidth corresponding to carrier 1 at the input port to DAU1.

As disclosed in U.S. Provisional Application No. 61/374,593, filed on August 17, 2010, entitled "Neutral Host Architecture for a Distributed Antenna System," and also referenced in FIG. 1 of the present application, it is understood that the digital upconverters present in each RRU can be programmed to transmit any desired composite signal format to each of the RRU antenna ports. For example, the digital upconverters present in RRU1 and RRU2 can be dynamically software reconfigured as previously described so that the signal present at the antenna port of RRU1 corresponds to the spectral profile shown as 110 in FIG. 1 and the signal present at the antenna port of RRU2 corresponds to the spectral profile shown as 109 in FIG. 1 . An application for such dynamic reconfiguration of RRU capacity could be, for example, if a company meeting is unexpectedly convened within the area of the enterprise corresponding to the coverage area of RRU2. Although the description of some embodiments in this application refers to base station signals 107 and 108 at different frequencies, because the base station signals are digitized, packetized, routed, and switched to the desired RRU, the systems and methods of the present invention easily support the following configurations: one or more carriers are part of the base station signals 107 and 108 and are of the same frequency.

FIG2 illustrates another embodiment of a distributed antenna system according to the present invention. As disclosed in U.S. Provisional Application No. 61/374,593, filed on August 17, 2010, entitled "Neutral Host Architecture for a Distributed Antenna System," and also shown in FIG2 , flexible simulcast system 200 can be used to explain the operation of flexible simulcast for uplink signals. As previously discussed with respect to downlink signals and with reference to FIG1 , the uplink system shown in FIG2 primarily includes DAU 1, designated 201, RRU 1, designated 203, RRU 2, designated 204, RRU 3, designated 205, and RRU 4, designated 206. The operation of the uplink system shown in FIG2 can be understood in a manner similar to the downlink operation explained with reference to FIG1 .

As previously described, the digital down-converters present in each of RRU1, RRU2, RRU3, and RRU4 are dynamically software-reconfigured so that uplink signals of the appropriate desired signal format or formats present at the respective receive antenna ports of RRU1, RRU2, RRU3, and RRU4 are selected based on the desired uplink frequency band to be processed and filtered, converted, and transmitted to the appropriate uplink output port of DAU1 or DAU2. The DAUs and DRUs use the Common Public Interface Standard (CPRI) to frame individual data packets corresponding to their respective broadcast signatures. Other interface standards are applicable as long as they uniquely identify data packets through each DRU. Header information is transmitted along with the data packets identifying the RRU and DAU corresponding to each data packet.

In one example embodiment shown in Figure 2, RRU1 and RRU3 are configured to receive uplink signals within the carrier 2 bandwidth, while RRU2 and RRU4 are configured to reject uplink signals within the carrier 2 bandwidth. When RRU3 receives a sufficiently strong signal within the carrier 2 bandwidth at its receive antenna port to be properly filtered and processed, the digital down-converter within RRU3 facilitates processing and conversion. Similarly, when RRU1 receives a sufficiently strong signal within the carrier 2 bandwidth at its receive antenna port to be properly filtered and processed, the digital down-converter within RRU1 facilitates processing and conversion. Based on an active signal combining algorithm, the signals from RRU1 and RRU3 are combined and fed to a base station connected to the uplink output port of DAU1. The term "simulcast" is often used to describe the operation of RRU1 and RRU3 for both uplink and downlink signals within the carrier 2 bandwidth. The term "flexible simulcast" refers to the fact that the present invention supports dynamic and/or manual adjustment of the specific RRUs involved in the signal combining process for each carrier bandwidth.

Referring to Figure 2, the digital down-converter present in RRU1 is configured to receive and process signals within the bandwidths of carriers 1 to 8. The digital down-converter present in RRU2 is configured to receive and process signals within the bandwidths of carriers 1, 3, 4, and 6. The digital down-converter present in RRU3 is configured to receive and process signals within the bandwidths of carriers 2 and 6. The digital down-converter present in RRU4 is configured to receive and process signals within the bandwidths of carriers 1, 4, 5, and 8. The respective high-speed digital signals generated by the processing performed in each of the four RRUs are routed to two DAUs. As previously described, the uplink signals from the four DRUs are combined in the corresponding DAUs corresponding to each base station.

One aspect of the present invention includes an integrated pseudo pilot function within each RRU. In an embodiment, as discussed below, each RRU includes a unique software-programmable pseudo pilot. This approach is intended for use in CDMA and/or WCDMA indoor DAS networks. A very similar approach may be effective for indoor positioning accuracy enhancement for other types of networks such as LTE and WiMAX. Because each RRU is already controlled and monitored via the DAUs that make up the network, remote monitoring and control of the pseudo pilot does not require the expensive deployment of additional dedicated wireless modems.

The RRU-integrated pseudo-pilot approach is used for both CDMA and WCDMA networks. Each active pseudo-pilot within the RRU uses a unique PN code (in that area), which effectively divides the WCDMA or CDMA indoor network coverage area into multiple small "zones" (each small "zone" corresponds to the coverage area of a low-power pseudo-pilot). The network knows the location, PN code, and RF power level of each pseudo-pilot. Each pseudo-pilot is synchronized to the WCDMA or CDMA network via its connection to the DAU.

Unlike the "dynamic" transmissions from the base station, the pseudo pilot transmissions will be "static" in effect and their downlink messages will not change over time based on network conditions.

For WCDMA networks, each mobile user terminal can perform pilot signal measurements on downlink signals transmitted by the base station and pseudo pilots in idle mode. When a WCDMA mobile user terminal transitions to active mode, it reports all its pilot signal measurements for the base station and pseudo pilots to the serving cell. For CDMA networks, the operation is very similar. For an RRU deployed in an indoor network, the RRU can be configured to either perform pseudo pilot operations or to provide services to mobile users within a specific operator's bandwidth, but not both simultaneously.

For WCDMA networks, existing, inherent capabilities of globally standardized networks are utilized. WCDMA mobile user terminals can measure the strongest CPICH RSCP (Pilot Signal Code Power) in idle mode or any of several active modes. Furthermore, CPICH Ec/No measurements are possible by the mobile user terminal in idle mode or any of several active modes. Therefore, the mobile user terminal reports all available RSCP and Ec/No measurements to the network via the serving base station (whether indoors or outdoors). Based on this information, the most likely location of the mobile user terminal can be calculated and/or determined. For CDMA networks, the process is very similar to the one described above.

The embodiment of the present invention described above with reference to FIG1 involves having a wideband CDMA signal present within the bandwidth corresponding to, for example, carrier 1 at the input port to DAU1. In the embodiment described above, the signal transmitted at the antenna ports of RRU1, RRU2, and RRU4 is a wideband CDMA signal that is nearly identical to the signal present within the bandwidth corresponding to carrier 1 at the input port to DAU1. An alternative embodiment of the present invention is one in which the wideband CDMA signal is present within the bandwidth corresponding to, for example, carrier 1 at the input port to DAU1. However, in this alternative embodiment, the signal transmitted at the antenna port of RRU1 differs slightly from the previous embodiment. In this alternative embodiment, the wideband CDMA signal is present within the bandwidth corresponding to, for example, carrier 1 at the input port to DAU1. The signal transmitted from RRU1 is a combination of the wideband CDMA signal present at the input port to DAU1 and a specialized WCDMA dummy pilot signal. The WCDMA dummy pilot signal is intentionally set to a level significantly lower than the base station pilot signal.

Another alternative embodiment can be explained with reference to FIG1 , which is applicable to the case where the CDMA signal is generated by a base station connected to the input of DAU 1. In this alternative embodiment of the present invention, the signal transmitted at the antenna port of RRU 1 is a combination of the CDMA signal present at the input port to DAU 1 and a dedicated CDMA pseudo pilot signal. The CDMA pseudo pilot signal is intentionally set to a level much lower than the base station pilot signal.

One embodiment of the present invention provides enhanced accuracy for determining the location of indoor wireless users. Figure 4 depicts a typical indoor system employing multiple remote radio head units (RRUs) and a central digital access unit (DAU). Each remote radio head provides unique header information on the data received by the remote radio head. This header information is used in combination with the mobile user's radio signature to locate the user to a specific cell. DAU signal processing can identify each carrier and its corresponding time slot. A header is included with each data packet that uniquely identifies the corresponding RRU. The DAU can detect the carrier frequency and corresponding time slot associated with each RRU. The DAU has a running database that identifies each carrier frequency and time slot by each RRU. The carrier frequency and time slot uniquely identify the radio signature of a GSM user.

As shown in Figure 5, the DAU communicates with the Network Operations Center (NOC) via an Ethernet connection or an external modem. Once an E911 call is initiated, the Mobile Switching Center (MSC) in conjunction with the NOC can identify the corresponding Base Transceiver Station (BTS) from which the user is making the call. The user can be located within the BTS cell. The NOC then sends a request to each DAU to determine whether the E911 radio signature is active within their indoor cell. The DAU checks its database for the carrier frequency and time slot that are active. If the radio signature is active in the DAU, the DAU will provide the DAU with the location information of the corresponding RRU.

Another embodiment of the present invention incorporates LTE to provide enhanced accuracy for determining the location of indoor wireless users. While GSM uses individual carriers and timeslots to distinguish users, LTE uses multiple carrier and timeslot information to distinguish users. The DAU can simultaneously detect multiple carriers and their corresponding timeslots to uniquely identify LTE users. The DAU maintains a running database that identifies the carrier frequency and timeslot radio signature for each RRU. This information can be retrieved from the NOC upon request to the DAU.

Referring next to Figure 7, the DAU embedded software control module and the RRU embedded software control module can be better understood in conjunction with the operation of the key functions of the DAU and RRU. One such key function is to determine and/or set the appropriate amount of radio resources (such as RF carriers, CDMA codes or TDMA time slots) allocated to a specific RRU or RRU group to meet the desired capacity and overall processing power targets. The DAU embedded software control module includes a DAU monitoring module that detects which carriers and corresponding time slots are active for each RRU. The DAU embedded software control module also includes a DAU management and control module that communicates with the RRU via a control protocol with the RRU management and control module on a fiber link control channel. Accordingly, the RRU management and control module sets various parameters of all RRU digital up-converters to enable or disable the transmission of specific radio resources by a specific RRU or RRU group, and also sets various parameters of all RRU digital down-converters to enable or disable the processing of specific uplink radio resources by a specific RRU or RRU group.

In one embodiment, an algorithm running within a DAU monitoring module (which detects which carriers and corresponding time slots in each carrier are active for each RRU) provides information to the DAU management and control module to help identify, for example, when a particular downlink carrier is loaded at a percentage greater than a predetermined threshold, the value of which is communicated to the DAU management and control module via the DAU remote monitoring and control function. If the above situation occurs, the DAU management and control module adaptively modifies the system configuration to slowly begin deploying additional radio resources (such as RF carriers, CDMA codes, or TDMA time slots) for use by specific RRUs within its coverage area, where those additional radio resources are required by that specific RRU. At the same time, in at least some embodiments, the DAU management and control module adaptively modifies the system configuration to slowly begin removing specific radio resources (such as RF carriers, CDMA codes, or TDMA time slots) for use by specific RRUs within its coverage area, where those specific radio resources are no longer required by that specific RRU. Another such key function of the DAU embedded software control module and the RRU embedded software control module is to determine and/or set and/or analyze the appropriate transmission parameters and monitoring parameters for the integrated pseudo pilots contained within each RRU. These pseudo pilot transmission parameters and monitoring parameters include beacon enable/disable, beacon carrier frequency, beacon transmission power, beacon PN code, beacon downlink BCH message content, beacon alarm, beacon delay setting, and beacon delay adjustment resolution. The RRU pseudo pilot control module communicates with the pseudo pilot generator function in the RRU to set and monitor the pseudo pilot parameters listed here.

In summary, the reconfigurable distributed antenna system of the present invention described herein effectively saves resources and reduces costs. Since the algorithm can be adjusted at any time like software in a digital processor, the reconfigurable system is adaptively or manually field programmable.

Although the present invention has been described with reference to preferred embodiments, it will be understood that the invention is not limited to the details described herein. Various substitutions and modifications have been suggested in the foregoing description, and other substitutions and modifications will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be included within the scope of the present invention as defined by the appended claims.

Inventive concept

The present invention provides the following inventive concepts:

1. A method for routing and switching carrier RF signals, comprising:

providing one or more remote radio units, each remote radio unit being configured to receive one or more downlink radio frequencies and to transmit one or more uplink radio frequencies,

providing at least one digital access unit configured to communicate with at least some of the remote radio units,

Converts uplink and downlink signals between RF and baseband as needed,

Packetize uplink and downlink baseband signals, and

Packetized signals are routed and switched between the one or more radio units and the at least one digital access unit.

2. A method for locating a wireless network user within a network of radio units, comprising:

generating a unique pseudo pilot at each radio unit suitable for reception by user equipment,

receiving, at a central location, from a user equipment a signature identifying the at least one pseudo pilot received by the user equipment, and

An approximate location of the user is determined based on the received marker.

3. A method for locating a wireless network user within a network of radio units, comprising:

receiving, at at least one radio cell within the network of radio cells, an emergency signal on a carrier frequency and time slot from a user equipment and forwarding the emergency signal to a remote station,

receiving, at a plurality of radio units, inquiries from the remote station as to whether the identified carrier frequency and time slot used by the emergency signal are active,

responding at the radio unit in which the identified carrier frequency and time slot are active, and

An approximate location of the user is determined based on the response.

Appendix 1

Glossary

ACLR Adjacent Channel Leakage Ratio

ACPR Adjacent Channel Power Ratio

ADC analog-to-digital converter

AQDM Analog Quadrature Demodulator

AQM Analog Quadrature Modulator

AQDMC Analog Quadrature Demodulator Corrector

AQMC Analog Quadrature Modulator Corrector

BPF Bandpass Filter

BTS Base Transceiver System or Base Station

CDMA Code Division Multiple Access

CFR Crest Factor Reduction

DAC Digital-to-Analog Converter

DAU Digital Access Unit

DET detector

DHMPA Digital Hybrid Mode Power Amplifier

DDC Digital Down Converter

DNC Downconverter

DPA Doherty Power Amplifier

DQDM Digital Quadrature Demodulator

DQM Digital Quadrature Modulator

DSP digital signal processing

DUC Digital Up Converter

EER Envelope Elimination and Restoration

EF Envelope Follower

ET Envelope Tracking

EVM Error Vector Magnitude

FFLPA Feedforward Linear Power Amplifier

FIR Finite Impulse Response

FPGA Field Programmable Gate Array

GSM Global System for Mobile Communications

I-Q In-Phase/Quadrature

IF (Intermediate Frequency)

LINC Linear amplification using nonlinear elements

LO Local Oscillator

LPF Low-pass filter

MCPA Multi-Carrier Power Amplifier

MDS Multi-Directional Search

OFDM Orthogonal Frequency Division Multiplexing

PA power amplifier

PAPR Peak to Average Power Ratio

PD Digital Baseband Predistortion

PLL Phase-Locked Loop

PN Pseudo Noise

QAM Quadrature Amplitude Modulation

QPSK Quadrature Phase Shift Keying

RF radio frequency

RRH Remote Radio Head

RRU Remote Radio Head Unit

SAW Surface Acoustic Wave Filters

UMTS Universal Mobile Telecommunications System

UPC Upconverter

WCDMA Wideband Code Division Multiple Access

WLAN Wireless Local Area Network

Claims (18)

1. A method for operating a distributed antenna system, the method comprising: One or more remote radio units are provided, each of the one or more remote radio units being configured to receive one or more downlink radio frequencies and transmit one or more uplink radio frequencies; Provide at least one digital access unit configured to communicate with at least some of the one or more remote radio units; Receive a signal from a signal source at the at least one digital access unit; The received signal is digitized at the at least one digital access unit to provide a digital signal; At the at least one digital access unit, the digitized signal is I/Q mapped and framed to provide packetized signal; and The packetized signal is transmitted from the at least one digital access unit to the one or more remote radio units. 2. The method according to claim 1, wherein digitizing the received signal includes down-converting the received signal, converting the down-converted signal into a digital signal, and converting the digital signal to baseband. 3. The method of claim 2, wherein the conversion of the digital signal to baseband is performed using a digital down-converter. 4. The method according to claim 1, wherein sending the packetized signal comprises sending an optical signal via an optical fiber cable. 5. The method according to claim 1, wherein framing is performed in accordance with a common public interface standard. 6. The method of claim 1, wherein each packetized signal includes a destination address that associates the data packet with a corresponding remote radio unit. 7. The method of claim 6, wherein the destination address is included in header information identifying the corresponding remote radio unit. 8. The method according to claim 1, further comprising: At the at least one digital access unit, optical signals are received from the one or more remote radio units; The optical signal is deframed to provide an uplink digital signal; The uplink digitized signal is upconverted to provide an upconverted digitized signal; The up-converted digitized signal is converted into an uplink signal; and The uplink signal is sent to the signal source. 9. The method of claim 8, wherein the upconversion of the uplink digitized signal is performed using a digital upconverter. 10. The method of claim 8, wherein converting the upconverted digitized signal comprises converting the upconverted digitized signal into an analog signal and converting the analog signal into the uplink signal. 11. The method of claim 8, wherein the optical signal includes a destination address that associates the optical signal with the digital access unit. 12. A method for communication in a distributed antenna system, the method comprising: A downlink optical signal is received at a remote radio unit, the downlink optical signal being received from a digital access unit at the remote radio unit, the downlink optical signal comprising multiple carriers; A portion of the downlink optical signal received at the remote radio unit is converted into a downlink signal, the portion of the downlink optical signal corresponding to a subset of the plurality of carriers, wherein the number of carriers in the subset of the plurality of carriers is less than the number of carriers in the plurality of carriers, and the number of carriers in the subset of the plurality of carriers is configurable. The downlink signal is transmitted from the remote radio unit; Receive uplink signals at the remote radio unit; The uplink signal received at the remote radio unit is converted into an uplink optical signal, wherein the uplink optical signal corresponds to the subset of the plurality of carriers; and The uplink optical signal is transmitted from the remote radio unit to the digital access unit. 13. The method of claim 12, further comprising converting a second portion of the downlink optical signal received at the remote radio unit into a downlink signal, the second portion of the downlink optical signal corresponding to a second subset of the plurality of carriers, wherein the number of carriers in the second subset of the plurality of carriers is different from the number of carriers in the subset of the plurality of carriers. 14. The method of claim 12, further comprising increasing the number of carriers in the subset of the plurality of carriers. 15. The method of claim 12, further comprising reducing the number of carriers in the subset of the plurality of carriers. 16. The method of claim 12, wherein each of the plurality of carriers corresponds to a corresponding RF band. 17. A system for transmitting signals, comprising: Multiple long-range radio units; and A plurality of digital access units, each digital access unit coupled to another digital access unit among the plurality of digital access units, wherein a first digital access unit among the plurality of digital access units is coupled to a first signal source and a second digital access unit among the plurality of digital access units, the first digital access unit being configured to communicate with at least a first portion of the plurality of remote radio units, and Each of the first portions of the plurality of remote radio units is configured to packetize a first uplink signal for transmission to the first digital access unit, and the first digital access unit is configured to packetize a first downlink signal for transmission to the first portions of the plurality of remote radio units. 18. A system for transmitting signals, comprising: Multiple long-range radio units; and A plurality of digital access units, each digital access unit coupled to another digital access unit among the plurality of digital access units, wherein a first digital access unit among the plurality of digital access units is coupled to a first signal source, and a second digital access unit among the plurality of digital access units is configured to communicate with at least a first portion of the plurality of remote radio units. Each of the first portions of the plurality of remote radio units is configured to packetize a first uplink signal for transmission to the first digital access unit via the second digital access unit, and The first digital access unit is configured to packetize a first downlink signal for transmission via the second digital access unit to the first portion of the plurality of remote radio units.