Abstract:
A system for communicating wireless signals includes a passive optical network (PON) between a central office (CO) and network subscribers. The CO has an optical line terminal (OLT) and a wireless base station. An RF/Optic converter converts base station radio frequency (RF) signals to and from corresponding optical signals. An optical combiner combines signals of the OLT and signals of the RF/Optic converter for communication over the PON with at least one optical network unit (ONU) at a location of one or more of the network subscribers, so that signals of the OLT and converted wireless base station signals are carried together over the PON. A fiber mounted wireless antenna unit (FMCA) having an optical interface and a wireless antenna, and communicating wireless signals of the wireless antenna with the ONU, including performing conversions between wireless RF signals and optical signals.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a Passive Optical Network (PON) used to deliver native wireless signals into buildings, where a small Customer Premises Equipment (CPE) is used to transmit and receive the signals to and from the wireless devices. 
       BACKGROUND 
       [0002]    One of the major challenges of wireless networks, such as cellular networks, is in-building coverage. Wireless antennas are typically located outside buildings, while in many cases the users are located inside the buildings. As a result, the wireless signals have to penetrate the walls of the buildings. While penetrating the walls, the signal is attenuated, causing degradation of the communication quality. 
         [0003]    This challenge of in-building coverage is well known and there are some methods to address this challenge, mainly repeaters and in-building Distributed Antenna Systems (DAS). Both methods are typically used for highly populated locations, such as office buildings, public buildings, shopping centers and campuses. 
         [0004]    Now a brief overview of PON architecture will be provided. A PON is an access network based on optical fibers. The network is built as a Point to Multi-point network, where a single optical interface, known as Optical Line Terminal (OLT), is located at the Central Office (CO) or Head-End (HE) and serves multiple users (typically 16 to 64 users). The OLT is connected via optical fiber (usually called feeder) to a passive splitter, which splits the optical signal among multiple optical fibers (usually called distribution lines or drops). The passive splitter may be located at the CO (centralized split) or at a passive cabinet in the field (distributed split). The distribution lines (or drops) terminate with an Optical Network Unit (ONU) which converts the optical signals to electrical signals. The ONU may be located at the subscriber&#39;s home (AKA FTTH—Fiber To The Home), at the subscriber&#39;s building (AKA FTTB) where the electrical signals are forwarded to the end users using the building&#39;s infrastructure (e.g. CAT 5) or at the curb (AKA FTTC) where the electrical signals are forwarded to the end users using copper wires (e.g. DSL). There are several flavors of PON, such as APON, BPON, EPON, GPON and GePON. All flavors share the same basic architecture of passive splitting and differ from each other by the data rate and the protocols.  FIG. 1  illustrates a typical PON. 
         [0005]    There is a need for improved in-building coverage for wireless communications such as cell phones, but no prior solution has effectively taken advantage of the possibilities of employing the PON architecture in this regard. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention addresses the challenge of in-building coverage for residential locations such as private houses and apartment buildings as well as commercial and public buildings. According to the invention, in which a Passive Optical Network (PON) is used to deliver native wireless signals into buildings, where a small Customer Premises Equipment (CPE) is used to transmit and receive the signals to and from the wireless devices, support is provided for multiple types of wireless technologies such as cellular technologies (i.e. GSM900, GSM1800, PCS, UMTS, CDMA, iDEN etc.), wireless LAN technologies (e.g. WiFi), WiMAX and other OFDM/OFDMA technologies.1. 
         [0007]    According to one aspect of the invention, there is provided a system for communicating wireless signals, which includes a passive optical network (PON) between a central office (CO) and network subscribers, the CO having an optical line terminal (OLT) and a wireless base station. An RF/Optic converter converts base station radio frequency (RF) signals to and from corresponding optical signals. An optical combiner combines signals of the OLT and signals of the RF/Optic converter for communication over the PON with at least one optical network unit (ONU) at a location of one or more of the network subscribers, so that signals of the OLT and converted wireless base station signals are carried together over the PON. 
         [0008]    A fiber mounted wireless antenna unit (FMCA) has an optical interface and a wireless antenna, and communicates wireless signals of the wireless antenna with the ONU, including performing conversions between wireless RF signals and optical signals. The FMCA obtains the converted wireless base station signals from the PON and converts them back to provide reconverted RF signals for transmission by the FMCA using the wireless antenna, and obtains wireless RF signals from the wireless antenna and converts them to provide optical signals for communication over the PON to the wireless base station at the CO. In this manner, the system provides wireless coverage at subscriber locations. 
         [0009]    According to one embodiment, the FMCA and the ONU are integrated together. 
         [0010]    Other embodiments involve whether the frequencies used over the PON are dedicated to the wireless communication signals or shared between the wireless signals and other signals carried over the PON. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0011]    The invention will be more easily understood by reference to the enclosed drawing figures, in which many specificities have been omitted so as to avoid obscuring the central principles of the invention. In the drawing figures: 
           [0012]      FIG. 1  shows in highly simplified schematic form a prior art PON architecture. 
           [0013]      FIG. 2  shows in highly simplified schematic form a PON with wireless support according to one embodiment of the invention. 
           [0014]      FIG. 3  describes the spectrum of a downlink wavelength which is shared by a CATV application and two wireless bands: GSM900 and GSM1800, according to one embodiment of the invention. 
           [0015]      FIG. 4  describes the spectrum according to an embodiment of the invention in which signals are be shifted from the air frequency to a frequency which is not used by the PON application. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    The invention will be described in principle with respect to certain concrete embodiments mentioned below. Although the discussion will serve to teach the reader the principles of the invention, it is not practical to describe any and every possible embodiment that might be thought of as part of the invention. Accordingly, the exemplary embodiments are provided for teaching the invention and the appended claims are provided to define the scope of subject matter that falls within the spirit of the invention. 
         [0017]    Returning now to the discussion of PONs, two types of transmissions are used over PON: Digital Transmissions and RF Transmissions. Digital transmissions are typically used for internet access where the IP packets are carried over either ATM (e.g. APON, BPON and GPON) or Ethernet (e.g. EPON, GPON, GePON). Digital transmissions are typically bi-directional transmissions, where each direction is carried over a different wavelength. Typical wavelengths are 1310 nm for Upstream and 1490 nm (APON, BPON and GPON) or 1550 nm (EPON and GePON) for downstream. Another option, although less common, is to use a different fiber for each direction. 
         [0018]    RF Transmissions are usually used for CATV transmissions at the downstream direction. The CATV RF signals are converted to optical signals, typically at wavelength of 1550 nm, and are forwarded along the PON to the ONU, which converts the optical signals back to RF signals. The RF output of the ONU is connected to the RF input of the CATV set-top box, allowing transmission of CATV signals over PON while using the existing CATV headend equipment and set-top boxes. 
         [0019]    The following section describes a system in which the PON infrastructure is used to provide in-building wireless coverage. Even though the main application of such a system is in-building coverage, the system may be used for outdoor coverage as well, at locations where PON is deployed and the existing outdoor wireless coverage is insufficient. 
         [0020]    According to the suggested invention, the native wireless signals are forwarded over the PON between the CO and each of the network&#39;s subscribers. A wireless base station is installed at the CO, preferably co-located with the OLT. The base station RF signals are converted to optical signals using an RF/Optic converter. The optical signals are combined with the OLT optical signals and propagated along the PON to the ONU. A small CPE, called FMCA (Fiber Mounted Cellular Antenna) equipped with an optical interface and a wireless antenna is installed at the subscriber home, preferably co-located or even integrated with the ONU. The FMCA separates the optical signals originated from the RF signals of the wireless base station and converts them back to RF signals. These RF signals are transmitted by the FMCA using a wireless antenna, providing a wireless coverage at the proximity of the FMCA. 
         [0021]    At the upstream direction, the wireless signals are received by the FMCA and converted to optical signals. These signals are combined with the optical signals generated by the ONU and forwarded to the CO over the PON. Note that at the upstream direction the PON passive splitter acts as a combiner, combining optical signals generated by several FMCAs. The combined optical signal is received at the CO, where the optical signal originated from the FMCAs is converted back to RF signals. These signals are forwarded to the RF input of the wireless base station. In this way the base station receives all the signals that are received by the antennas of each one of the FMCAs. 
         [0022]    The following sections describe several methods for combining the wireless signals with other signals of the PON. Note that each one of the methods can be implemented either at the upstream direction or the downstream direction and each direction can be implemented using a different method. 
       Dedicated Wavelength, Air Frequencies 
       [0023]      FIG. 2  shows a PON with wireless support. 
         [0024]    As described previously, PON signals are carried over several wavelengths. Typically, wavelength of 1490 nm and 1550 nm are used for downstream traffic and wavelength of 1310 is used for upstream traffic. According to the proposed invention, the wireless signals are carried over additional wavelength which is not used by the PON. If the PON is implemented using a single fiber for both directions, then two wavelengths should be used—one for the wireless downstream signals and the other for the wireless upstream signals. The downstream wavelength carries downstream traffic of all the PON subscribers and the upstream wavelength carries the upstream traffic from all the PON subscribers. In the case of PON which is implemented using two fibers, one for each direction, the same wavelength can be used for both directions. Note that the wavelengths used for the wireless application should be in the range supported by the PON passive splitter. For example, in an EPON, which do not use the wavelength of 1490 nm, this wavelength can be used to carry the wireless traffic of one of the directions. 
         [0025]    The RF signals are converted to optical signals at the dedicated wavelength as is, at the same frequencies that are used over the air, without any frequency conversions or any other processing. Since different technologies (e.g. UMTS, GSM) and different wireless (e.g. cellular) operators are using different frequencies, signals of different wireless networks (either same technology or different technologies, same operator or different operators) can be combined together and propagated over the same PON without any overlaps between the networks. 
       Dedicated Wavelength, Shifted Frequencies 
       [0026]    The combining method described here is similar to the combining method described above. At both methods the RF signals are carried over a dedicated wavelength, however, in this method the frequency of the RF signals is shifted (or converted) in frequency, usually to lower frequency. Conversion of complete wireless band, such as GSM or UMTS band, from RF to optic and vice versa, requires expensive wideband RF/Optic converters. Since a wireless operator uses only small portion of the band (e.g. 10 MHz), this portion of the band can be shifted to a lower frequency, converted to optical signals, converted back to RF frequency at the other end of the network and shifted back the original frequency. In this way narrower band and cheaper components can be used. This method can also support multiple wireless networks by shifting the actual band of each network to a different frequency band at one end of the PON and shift it back to the original air frequency at the other end of the PON. 
       Shared Wavelength, Air Frequencies 
       [0027]      FIG. 3  describes the spectrum of a downlink wavelength which is shared by a CATV application and two wireless bands: GSM900 and GSM1800. 
         [0028]    In some cases, a single wavelength can be shared by the existing PON application and the wireless application. If the wireless RF frequency range is below or above the frequency range used by the existing PON application, then the two signals can be combined before the conversion from RF to optic. This is actually a Frequency Division Multiplexing (FDM) where each application uses its own frequency range. The combined signal is converted from optic to RF and RF to optic at the other end of the network using a single RF/Optic converter. 
         [0029]    For example, in some BPON or GPON network the 1550 nm wavelength is used to carry CATV signals in the frequency range of 50 MHz to 860 MHz. Since GSM900 networks utilize frequencies above 900 MHz for downlink signals, the GSM900 downlink signals may be combined with the CATV RF signals before the conversions from RF to optic at the headend/CO. At the remote end of the network, after the conversion from optic to RF, the signals can be separated using filters. The lower band below 860 MHz is routed to the CATV receiver (e.g. set-top box) and the upper band above 900 MHz is routed to the FMCA for transmission over the air. Note that multiple wireless networks can be supported at this met-hod as well, as long there is no overlap between the frequency range used by the wireless network and the frequency range used by the existing PON application. For example, a wavelength used for CATV cannot be shared with a wireless network that uses frequency range below 860 MHz. 
       Shared Wavelength, Shifted Frequencies 
       [0030]    As mentioned above, converting a wideband RF signal to optic signal and vice versa requires expensive wideband RF/Optic converters. The method introduced in “Shared Wavelength, Air Frequencies” requires RF/Optic conversion of the combined range of the existing PON application and the wireless network. Considering the example described in that section, the frequency range used by the CATV application starts at 50 MHz and ends at 860 MHz. Combining this signal with a UMTS signal will result with total bandwidth of more than 2 GHz. In order to reduce the bandwidth (and the cost) of the RF/Optic converters, the UMTS signals can be shifted from the air frequency to a frequency which is not used by the PON application. See  FIG. 4 . The frequency shift can take place on the entire wireless band (e.g. the entire UMTS band) or on a portion of the band which is actually used by the wireless operator (e.g. 5 MHz per carrier within the UMTS band). In the case of multiple networks, the signals of each network can be shifted to a different, unused frequency range. The following diagram describes the spectrum of a downlink wavelength which is shared by a CATV application and four wireless networks, two GSM networks and two UMTS networks. The total bandwidth used by these networks is 25 MHz. 
         [0031]    As one familiar with this field will appreciate, many variations and modifications can be made without departing from the scope and spirit of the invention. Various alternatives have been presented above and others will occur to the interested reader.