Diversity combining circuits and cellular base stations including such diversity combining circuits

Abstract

A cellular base station comprises a cellular radio having first and second radio ports, the cellular radio configured to perform diversity combining using a first diversity combining technique on first and second received uplink signals that are passed to the cellular radio through the first and second radio ports; and a diversity combining circuit that is configured to select the first and second received uplink signals from a larger group of received uplink signals and to pass the selected first and second received uplink signals to the cellular radio through the first and second radio ports.

Description

M / COMM-106-PC DIVERSITY COMBINING CIRCUITS AND CELLULAR BASE STATIONS INCLUDING SUCH DIVERSITY COMBINING CIRCUITS FIELD

[0001] The present invention generally relates to radio communications and, more particularly, to diversity combining circuits and to cellular base stations that include such diversity combining circuits. BACKGROUND

[0002] Cellular communications systems are well known in the art. In a cellular communications system, a geographic area is divided into a series of regions that are referred to as "cells" which are served by respective base stations. Each base station includes baseband equipment, radios and base station antennas that are configured to provide two-way radio frequency ("RF") communications with subscribers that are positioned throughout the cell served by the base station. The base station antennas are often mounted on a tower or other raised structure, with the radiation pattern ("antenna beam") that is generated by each antenna directed outwardly to serve a respective sector. Typically, a base station antenna includes multiple phase- controlled arrays of radiating elements, with the radiating elements arranged in vertically- extending columns that are referred to as "linear arrays." Herein, "vertical" refers to a direction that is generally perpendicular relative to the plane defined by the horizon. References will also be made herein to the "azimuth" plane, which refers to a horizontal plane that bisects the base station antenna that is parallel to the plane defined by the horizon.

[0003] Most cells are divided into a plurality of "sectors." A very common base station configuration is the "three-sector" configuration in which a cell is divided into three 120º "sectors" in the azimuth (horizontal) plane. In some cases, a cellular operator will deploy aM / COMM-106-PC separate base station antenna for each sector, with each base station antenna including one or more linear arrays that provide coverage (service) to users within its respective sector. Each linear array may be designed to generate antenna beams that provide good service throughout its^^^^ ^^^^^^ ^^ ^^^ ^^^^^^^ ^^^^^ ^^^ that have relatively low "spillover" of RF energy into thetwo other sectors of the cell. In many cases, a cellular operator will deploy three base station antennas in each cell that has a three-sector configuration, with each base station antenna positioned to generate antenna beams that cover its respective sector. In other cases, a single base station antenna may be provided that includes a triangular backplane with at least one linear array on each face of the triangular backplane, where the linear array(s) on the three faces provide coverage (service) to the respective three sectors. The signals transmitted from a base station antenna to users devices are referred to herein as "downlink" signals and the signals transmitted from user devices to a base station antenna are referred to as "uplink" signals.

[0004] The linear arrays of radiating elements typically operate using second, third and / or fourth generation cellular network protocols. The radiating elements of each linear array may be aligned along a vertically-extending axis, or may be "staggered" to a degree in the horizontal plane in order to narrow the azimuth HPBW of the antenna beams generated by the linear arrays. Most modern base station antennas include both "low-band" linear arrays of radiating elements that support service in some or all of the 617-960 MHz frequency band and "mid-band" linear arrays of radiating elements that support service in some or all of the 1427- 2690 MHz frequency band. These linear arrays are typically formed using dual-polarized radiating elements, which allows each linear array to transmit and receive RF signals at two orthogonal polarizations. When linear arrays of dual-polarized radiating elements are used, each linear array is coupled to two ports of a radio and the linear array generates antenna beams at each polarization. An RF signal that is to be transmitted by a linear array is passed from the radio port to the antenna where it is divided into a plurality of sub-components, with each sub- component fed to a respective subset of the radiating elements in the linear array. The sub- components of the RF signal are transmitted through the radiating elements to generate an antenna beam that covers a generally fixed coverage area, such as a sector of a cell. Since the antenna beams generated by the above-described 2G / 3G / 4G linear arrays generate static antenna beams, they are often referred to as "passive" linear arrays. The base station antennas may optionally also include multi-column "beamforming" arrays of radiating elements thatM / COMM-106-PC support fifth generation ("5G") cellular service. The shape, size and pointing direction of the antenna beams generated by the beamforming arrays can be dynamically changed, allowing the formation of narrower, higher gain antenna beams that can provide enhanced service. SUMMARY

[0005] Pursuant to embodiments of the present invention, cellular base stations are provided that comprise a cellular radio having first and second radio ports, the cellular radio configured to perform diversity combining using a first diversity combining technique on first and second received uplink signals that are passed to the cellular radio through the first and second radio ports; and a diversity combining circuit that is configured to select the first and second received uplink signals from a larger group of received uplink signals and to pass the selected first and second received uplink signals to the cellular radio through the first and second radio ports.

[0006] In some embodiments, the cellular base station may further comprise a base station antenna that includes first and second arrays of dual-polarized radiating elements, where the larger group of received uplink signals comprises a first polarization received uplink signal that is received at the first array, a second polarization received uplink signal that is received at the first array, a first polarization received uplink signal that is received at the second array, a second polarization received uplink signal that is received at the second array.

[0007] In some embodiments, the diversity combining circuit is configured to use selection combining to select the first and second received uplink signals from the larger group of received uplink signals. In some embodiments, the diversity combining circuit comprises a first coupler and a second coupler that are configured to tap RF energy from the first polarization received uplink signal that is received at the first array and from the first polarization received uplink signal that is received at the second array, respectively, to provide first and second tapped signals. In some embodiments, the diversity combining circuit further comprises a third coupler and a fourth coupler that are configured to tap radio frequency ("RF") energy from the second polarization received uplink signal that is received at the first array and from the second polarization received uplink signal that is received at the second array, respectively, to provide third and fourth tapped signals.

[0008] In some embodiments, the diversity combining circuit includes a first diversity selector circuit that is configured to receive the first and second tapped signals and to determineM / COMM-106-PC at least one characteristic of the first and second tapped signals. In some embodiments, the determined characteristic comprises a received signal strength. In some embodiments, the determined characteristic comprises a presence of an intermodulation product within an uplink operating frequency band of the cellular radio. In some embodiments, the diversity combining circuit further includes a first switch that is configured to couple an output of one of the first and second couplers to the first port of the cellular radio. In some embodiments, the diversity selector circuit is configured to set the first switch to couple either the output of the first coupler or the output of the second coupler to the first port of the cellular radio based on one or more measured characteristics of the first and second tapped signals.

[0009] In some embodiments, the diversity combining circuit further comprises a first low noise amplifier that is coupled in between an output of the first switch and the first port of the cellular radio. In some embodiments, the diversity combining circuit further comprises a first low noise amplifier that is coupled in between the first array of dual-polarized radiating elements and the first coupler and a second low noise amplifier that is coupled in between the second array of dual-polarized radiating elements and the second coupler.

[0010] In some embodiments, the diversity combining circuit comprises a tower mounted diversity combining circuit that is connected to the cellular radio via a first plurality of cables and to the base station antenna via a second plurality of cables.

[0011] In some embodiments, the first diversity combining technique comprises a maximal ratio diversity combining technique.

[0012] Pursuant to further embodiments of the present invention, diversity combining circuits are provided that comprise a first input port; a second input port; a first output port; a first coupler that has a first coupler input that is coupled to the first input port, a first coupler output, and a first tap port; a second coupler that has a second coupler input that is coupled to the second input port, a second coupler output, and a second tap port; a first switch that has a first switch input that is coupled to the first coupler output and a second switch input that is coupled to the second coupler output, and a first switch output that is coupled to the first output port; and a first diversity selector circuit that is coupled to the first and second tap ports, the diversity selector circuit including a diversity selector output port that is coupled to a control port of the first switch.M / COMM-106-PC

[0013] In some embodiments, the diversity combining circuit further comprises a first low noise amplifier.

[0014] In some embodiments, the first low noise amplifier is coupled between the first switch output and the first output port.

[0015] In some embodiments, the diversity combining circuit further comprises a second switch that has a third switch input that is coupled to the first tap port and a fourth switch input that is coupled to the second tap port, and a second switch output that is coupled to the first diversity selector circuit.

[0016] In some embodiments, the diversity combining circuit further comprises a first diplexer and a second diplexer, where the first diplexer is coupled between the first input port, the first coupler input and the second diplexer, and the second diplexer is coupled between an output of the low noise amplifier, the first output port and the first diplexer.

[0017] In some embodiments, the diversity combining circuit further comprises a first low noise amplifier that is coupled between the first input port and the first coupler input and a second low noise amplifier that is coupled between the second input port and the second coupler input.

[0018] In some embodiments, the first diversity selector circuit has first and second diversity selector inputs that are coupled to the respective first and second tap ports.

[0019] In some embodiments, the diversity combining circuit further comprises a first diplexer and a second diplexer, where the first diplexer is coupled between the first input port, the first coupler input and the second diplexer, and the second diplexer is coupled between the first switch output, the first output port and the first diplexer.

[0020] In some embodiments, the diversity combining circuit further comprises a second switch that has a third switch input that is coupled to the first tap port and a fourth switch input that is coupled to the second tap port, and a second switch output that is coupled to the first diversity combiner circuit.

[0021] In some embodiments, the diversity combining circuit further comprises a first diplexer and a second diplexer, where the first diplexer is coupled between the first input port, the first coupler input and the second diplexer, and the second diplexer is coupled between the first switch output, the first output port and the first diplexer.M / COMM-106-PC

[0022] In some embodiments, the diversity combining circuit further comprises a third input port; a fourth input port; a second output port; a third coupler that has a third coupler input that is coupled to the third input port, a third coupler output, and a third tap port; a fourth coupler that has a fourth coupler input that is coupled to the fourth input port, a fourth coupler output, and a fourth tap port; a third switch that has a third switch input that is coupled to the third coupler output and a third switch input that is coupled to the third coupler output, and a third switch output that is coupled to the second output port; and a second diversity selector circuit that is coupled to the third and fourth tap ports, the second diversity selector circuit configured to couple control signals to the third switch.

[0023] Pursuant to yet additional embodiments of the present invention, cellular base stations are provided that comprise a cellular radio that includes X ports, where X is an integer that is greater than or equal to 2, the cellular radio configured to perform diversity combining using a first diversity combining technique on X received uplink signals that are passed to the cellular radio through the X ports; and a diversity combining circuit that is configured to select the X received uplink signals from a larger group of Y received uplink signals and to pass the selected X received uplink signals to the cellular radio through the X ports.

[0024] In some embodiments, the cellular base station may further comprise a base station antenna that includes Y / 2 arrays of dual-polarized radiating elements, where the Y received uplink signals comprise a first polarization received uplink signal and a second polarization received uplink signal from each of Y / 2 arrays. In some embodiments, Y is equal to 2*X.

[0025] In some embodiments, the diversity combining circuit is configured to use selection combining to select the X received uplink signals from the larger group of Y received uplink signals. In some embodiments, the diversity combining circuit comprises Y couplers that are configured to tap RF energy from the Y received uplink signals to provide Y tapped signals. In some embodiments, the diversity combining circuit includes a diversity selector circuit that is configured to receive a first of the Y tapped signals that was tapped from a first of the Y received signals that was received at a first of the arrays of dual-polarized radiating elements and configured to receive a second of the Y tapped signals that was tapped from a second of the Y received signals that was received at a second of the arrays of dual-polarized radiating elements. In some embodiments, the diversity combining circuit further includes a first switch that isM / COMM-106-PC interposed between first and second of the Y couplers and the cellular radio. In some embodiments, the diversity selector circuit is configured to set the first switch to couple the cellular radio to one of the couplers based on one or more measured characteristics of the first and second of the Y tapped signals.

[0026] In some embodiments, the diversity combining circuit includes a first sub-circuit and a second sub-circuit, and the first sub-circuit is configured to pass first polarization downlink signals that are received from the cellular radio exclusively to a first of the Y / 2 arrays of dual- polarized radiating elements and the second sub-circuit is configured to pass second polarization downlink signals that are received from the cellular radio exclusively to a second of the Y / 2 arrays of dual-polarized radiating elements.

[0027] In some embodiments, the diversity combining circuit includes a first sub-circuit and a second sub-circuit, and the first sub-circuit includes a first low noise amplifier, and a switch circuit that routes first polarization uplink signals from a selected on of the Y / 2 arrays of dual-polarized radiating elements to the cellular radio.

[0028] Pursuant to other embodiments of the present invention. cellular base stations are provided that comprise a two-port cellular radio having a first radio port and a second radio port; a base station antenna having a first array of dual polarized radiating elements and a second array dual polarized radiating elements; and a diversity combiner circuit coupled between the two-port cellular radio and the base station antenna. The diversity combiner circuit is configured to route downlink signals output from the first radio solely to the first array of dual polarized radiating elements and to route downlink signals output from the second radio solely to the second array of dual polarized radiating elements.

[0029] In some embodiments, the diversity combiner circuit is configured to pass either first polarization uplink signals received at the first array of dual polarized radiating elements or first polarization uplink signals received at the second array of dual polarized radiating elements to the first radio port. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG.1A is a schematic view of a conventional cellular base station that includes an omnidirectional three-sector antenna.

[0031] FIG.1B is a schematic shadow perspective view of the base station antenna of FIG.1A that various several of the internal components of the antenna.M / COMM-106-PC

[0032] FIG.2 is a schematic shadow perspective view of a base station antenna that may be used with the diversity combiner circuits according to certain embodiments of the present invention.

[0033] FIGS.3-6 are block diagrams illustrating diversity combiner circuits according to embodiments of the present invention that are each coupled between a two-port radio and a pair of linear arrays.

[0034] FIGS.7A-7C are schematic diagrams illustrating how the techniques according to embodiments of the present invention may be used to support higher order MIMO communications techniques. DETAILED DESCRIPTION

[0035] Cellular communications networks may experience a variety of impairments that degrade the quality of the wireless signals transmitted between the base station antennas and user devices. These impairments, which may be referred to herein generically as "fading", include multipath propagation effects, obstacles along the line-of-sight path between the transmitter and receiver, atmospheric effects and the like, each of which may lower the strength of the received signal. As the received signal strength is reduced, the data rate that can be supported while maintaining a desired quality of service level is also reduced. As fading can often be severe (e.g., 20 dB or more on a given channel), it can adversely impact communication performance.

[0036] Communication performance can also be adversely impacted by interfering RF signals that are within the operating frequency band of a desired communication signal. The RF interference can be from any source, but in many cases may be from other cellular equipment. The range of frequencies used for cellular communications, which includes the above-described low-band frequency range and mid-band frequency range, are sub-divided into different frequency bands e.g., the 1920-2170 MHz frequency band, the 2300-2690 MHz frequency band, etc.) that support different types of cellular service, and these frequency bands are typically further sub-divided into downlink and uplink frequency bands (e.g., the 2110-2170 MHz downlink frequency band and the 1920-1980 MHz uplink frequency band). The downlink and uplink frequency bands are then further subdivided with specific portions (e.g., 20 MHz blocks) of each band being allocated to a particular cellular operator in a particular region.

[0037] The transmit and receive frequency bands for a specific cellular service are widely separated in order to prevent the high power transmit signals at a base station fromM / COMM-106-PC interfering with the much lower power signals (from user devices) that are received at the base station antenna. However, the receive frequency bands for different cellular operators may have little or no guard band therebetween (e.g., the uplink frequency band for a first cellular operator may be the 1940-1960 MHz frequency band, while the uplink frequency band for another cellular operator that operates in the same region may be the 1960-1980 MHz frequency band). As such, sidebands of uplink signals transmitted by users in a first uplink frequency band may interfere with the uplink signals of users in a second uplink frequency band, as the sidebands of the uplink signals in the first uplink frequency band will appear as RF noise to the uplink signals in the adjacent uplink frequency band. Thus, interference from other RF sources such as cellular users operating in adjacent frequency bands may raise the noise floor experienced by the uplink signals, thereby reducing the signal-to-noise ratio. This may further adversely impact communications performance.

[0038] One technique that can be very successful in overcoming fading and / or interference is the use of multi-input-multi-output ("MIMO") communication techniques. When MIMO communications techniques are used, a baseband data stream is sub-divided into a plurality of sub-streams that are used to generate respective RF signals that are transmitted through multiple different arrays of radiating elements. The different arrays are, for example, spatially separated from one another (typically by at least a wavelength corresponding to the center frequency of the operating frequency band) and / or at orthogonal polarizations so that the transmitted RF signals will be sufficiently decorrelated. The transmitted RF signals are recovered at a receiver and demodulated and decoded to recover the original data sub-streams, which are then recombined using a diversity combining technique, where maximal ratio combining is most typically used. The use of MIMO transmission techniques may help overcome the negative effects of multipath fading, and may be particularly effective in urban environments where reflections may increase the level of decorrelation between the RF signals. Since the transmitted RF signals are decorrelated, the presence of fading on the wireless channel for one transmitted RF signal is not predictive as to whether or not the wireless signals on the other MIMO channels will experience fading. The more sub-streams used in a MIMO communications scheme, the more robust that the communications will be with respect to fading and interference. The number of sub-streams is typically referred to as the "order" of the MIMO communications technique. For example, if four channels are provided on both transmit andM / COMM-106-PC receive communications, the MIMO communications may be referred to as a 4xMIMO communications technique. In some instances, the number of sub-streams on the uplink (R) and downlink (T) may be different. Accordingly, the terminology XT / YR is often used to specify the order of a MIMO communications technique, where "X" refers to the number of sub-streams on the downlink and "Y" refers to the number of sub-streams on the uplink.

[0039] In many cases, base stations that were deployed many years ago may operate using lower order MIMO communications technique than comparable systems that are currently being deployed because interference was typically lower years ago than it is today. For example, a cellular operator may have deployed a base station having a single, three-sector base station antenna in which each sector was served by a single linear array of mid-band radiating elements. Three two-port radios would also be provided at the base station, with a radio coupled to each linear array. Such a base station would operate as a 2T / 2R base station in each sector, as the two polarizations supported by each linear array could be used as separate MIMO channels on both the uplink and the downlink.

[0040] Such a base station may not perform well today, as the increased levels of interference may require higher order MIMO communications to support desired levels of quality of service. A cellular operator can remedy this situation by replacing the base station antenna with a base station antenna that includes two mid-band linear arrays per sector, and by replacing each two-port radio with a four-port radio. This would allow the base station to support 4T / 4R MIMO communications in each sector. Unfortunately, however, this can be an expensive replacement, as replacing three four-port radios can be quite expensive.

[0041] The present invention is based, in part, on the realization that by using hybrid diversity combining techniques it is possible to support 2T / 4R communications while using two- port radios. Base stations where the communication performance problems are on the uplink can benefit from the use of such hybrid diversity combining techniques, as the uplink performance will be improved. Moreover, since existing two-port radios can be used with these techniques, it is only necessary to upgrade the base station antenna to an antenna that has two columns per sector, which is much less expensive than replacing three two-port radios with three four-port radios.

[0042] In some embodiments of the present invention, the base station antenna may have two linear arrays of dual-polarized radiating elements per sector for a particular frequency bandM / COMM-106-PC (e.g., for the mid-band or for a portion of the mid-band). The base station antenna may be a single sector antenna that provides coverage to a single sector, or may be an omnidirectional antenna that provides coverage to multiple (e.g., three) sectors in the azimuth plane. The base station antenna may have four ports for a given frequency band since each linear array is used to transmit and receive at two different polarizations (i.e., two ports are provided for each array to support communications at the two orthogonal polarizations).

[0043] As described above, most MIMO techniques perform maximal ratio combining within the radio to combine the outputs of the different MIMO sub-streams. Pursuant to embodiments of the present invention, cellular base stations are provided in which a radio is coupled to a base station antenna that includes at least two arrays of dual polarized radiating elements that are configured to operate in a first operating frequency band. The at least two arrays of dual polarized radiating elements are operatively coupled to the radio via a first plurality of RF ports on the antenna. The first plurality of RF ports provided on the antenna includes more ports than the radio. For example, the first plurality of RF ports may include twice as many ports as the radio (e.g., the antenna includes four RF ports that are coupled to the at least two arrays and the radio only has two ports). A diversity combiner circuit is provided that connects the first plurality of RF ports to the ports of the radio. The diversity combiner circuit includes a diversity selector circuit that selects which of the uplink signals that are received through the at least two linear arrays are passed to the ports of the radio using a first diversity combining technique. The radio then uses a second diversity combining technique to combine the uplink signals that are passed to the radio.

[0044] In some embodiments, the diversity combiner circuit may use a selection combining technique as the first diversity combining technique. When selection combining is used, the diversity combiner circuit samples the received uplink signals and determines which of the received uplink signals has (or is expected to have) the best performance, and the best received signal is passed to the radio. For example, if the base station antenna includes two dual polarized linear arrays of radiating elements, and the four RF ports of the antenna that are connected to those two linear arrays are connected to two radio ports via the diversity combiner circuit, the diversity combiner circuit may be configured to pass the "better" of the two first polarization uplink signals received at the respective arrays to the first port of the radio, and the better of the two second polarization uplink signals received at the respective arrays to theM / COMM-106-PC second port of the radio. It will be appreciated, however, that the diversity combiner circuit may use a different diversity combining technique such as, for example, switch and stay combining in other embodiments.

[0045] Before discussing the diversity combiner circuits and associated cellular base stations according to embodiments of the present invention it is helpful to discuss the design of a conventional cellular base station.

[0046] FIG.1A is a schematic view of a conventional cellular base station 10 that include an omnidirectional three-sector antenna 20. FIG.1B is a schematic shadow perspective view of the antenna 20 that illustrates several of the internal components of the antenna 20. Referring first to FIG.1B, the base station antenna 20 includes a triangular backplane 22 that is contained within a protective radome 28. The triangular backplane 22 has first through third faces 24-1 through 24-3. Each face 24 of the backplane 22 may be a generally planar metal surface. The base station antenna 20 includes three linear arrays 30-1 through 30-3 of radiating elements 32, with a linear array 30 mounted on each respective face 24 of the backplane 22. The faces 24 of the backplane 22 serve as a reflector and ground plane for the linear arrays 30 of radiating elements 32. The radiating elements 32 are shown as being implemented as dual- polarized cross-dipole radiating elements 32 that each include a first dipole radiator 34-1 that isconfigured to transmit and receive -^^^ ^^^^^^^^ ^^^^^^^^^ ^^ ^^^^^^^ ^^^ ^ ^^^^^^ ^^^^^^ ^^^^^^^^34-2 ^^^^ ^^ ^^^^^^^^^^ ^^ ^^^^^^^^ ^^^ ^^^^^^^ ^^^^ ^^^^^^^^ ^^^^^^^^^ ^^ ^^^^^^^^ It should benoted that herein like elements may be referred to individually by their full reference numeral (e.g., linear array 30-2) and may be referred to collectively by the first part of their reference numeral (e.g., the linear arrays 30).

[0047] The base station antenna includes a total of six RF ports 26, where a pair of RF ports 26 (one for each polarization) are connected to each of the three linear arrays 30. The base station antenna 20 may be mounted on a raised structure 40 such as a utility pole of antenna tower (FIG.1A). Each linear array 30 may generate a pair of antenna beams (one for eachpolarization^ ^^^^ ^^^^^^^ ^^^^^^^^ ^^ ^ ^^^^^^^^^^ ^^^^ ^^^^^^ ^^ ^^^ azimuth (horizontal) planeso that base station antenna 20 provides "omnidirectional" ^^^^^^^^ ^^^^^^ ^^^^ ^^^^ ^^^^^^^^ ^^the azimuth plane). The radiating elements 32 may comprise, for example, mid-band radiating elements that are configured to provide service in all or part of the 1427-2690 MHz frequencyM / COMM-106-PC range. It will be appreciated that the base station antenna 20 can include additional linear arrays of radiating elements (e.g., low-band linear arrays) that are not shown in FIG.1B.

[0048] Referring again to FIG.1A, the cellular base station 10 further includes baseband units 50 and cellular radios 60. Three baseband units 50 are shown that are connected to respective ones of the three cellular radios 60. While the cellular radios 60 are shown as being co-located with the baseband units 50 at the bottom of the antenna tower 40 for ease of illustration, it will be appreciated that in most cases the cellular radios 60 will be implemented as so-called "remote radio heads" which refer to cellular radios that are configured to be mounted on the antenna tower 40 adjacent the base station antenna 20, as this configuration reduces RF losses. The baseband units 50 receive data from another source such as, for example, a backhaul network (not shown) and process this data and provide baseband data streams to the respective cellular radios 60. The cellular radios 60 generate RF signals that include the data encoded therein and amplify and deliver these RF signals to the antenna 20 for transmission via respective cabling connections 42. The base station 10 of FIGS.1A-1B will typically include various other equipment (not shown) such as, for example, a power supply, back-up batteries, a power bus and the like.

[0049] As discussed above, there are existing deployed base stations that may no longer exhibit acceptable performance levels because, for example, the base stations now need to support a larger number of users, the communications capacity required by a typical user has increased, and / or because of increased RF interference levels. In this situation, a cellular operator will typically either (1) add new base stations to the network while decreasing the size of the coverage areas of selected base stations or (2) upgrade the equipment at the existing base stations to support higher level MIMO communications, active beamforming or the like. Both of these options, however, can be expensive.

[0050] As an example, a cellular operator may have previously deployed a large number of base stations that each include a three-sector omnidirectional antenna that includes a single linear array of mid-band radiating elements per sector. Three two-port radios are provided at each base station, with the ports of each radio connected to a respective one of the three linear arrays so that each sector operates using 2T / 2R MIMO communications techniques. Over time, the performance of the base station has degraded as the amount of traffic on the uplink increases and / or as the interference levels increase due to increased amounts of traffic on directly adjacentM / COMM-106-PC uplink channels of other cellular operators. While the performance on the uplink could be improved by replacing the base station antenna with another antenna that had two mid-band linear arrays per sector and by replacing the two-port radios with four-port radios so that 4T / 4R MIMO communications techniques could be used, such changes are expensive.

[0051] Pursuant to embodiments of the present invention, the uplink performance of the above-described base station can be improved at much lower cost by replacing the base station antenna with another antenna that has two mid-band linear arrays per sector and by providing diversity combiner circuits that are coupled between each two-port radio and the base station antenna. The base station may communicate with user devices on the downlink using standard 2xMIMO communications techniques, transmitting a MIMO sub-stream at each of two orthogonal polarizations. These uplink signals, however, will be received at both linear arrays, so that a total of four uplink signals will be received at the base station antenna. Since the two linear arrays are separated by a distance that is more than one center wavelength (where the center wavelength is the wavelength that corresponds to the center frequency of the mid-band operating frequency band), the uplink signals received at the two linear arrays may be highly decorrelated, particularly with respect to multipath fading, and may be decorrelated (typically to a lesser extent) with respect to RF interference (since the RF interference typically is also impacted by multipath effects). The diversity combining circuit may include two identical sub- circuits that operate on the received signals at the two respective polarizations. Each sub-circuit may tap a small amount of RF energy from the two received uplink signals at a given polarization and pass the tapped signals to a diversity selector circuit that identifies the "better" of the two tapped signals. While different diversity selection techniques may be used, one common technique is to heavily filter the tapped signals to remove RF energy outside the uplink frequency band and to then select the tapped signal having the higher received signal strength as being the "better" of the two tapped signals. The two uplink signals from which the RF energy was tapped may be fed to the inputs of an RF switch, and the diversity selector circuit may control this RF switch so that the received uplink signal that corresponds to the better of the two tapped signals is passed to the output of the RF switch and from their to the radio. By selecting the uplink signal (for each polarization) that is less impacted by multipath fading and / or RF interference, the performance may be improved on the uplink. The selected RF signal at eachM / COMM-106-PC polarization are input to the two ports of the radio, and a different diversity combining technique (e.g., maximal ratio combining) may be used to recover the uplink baseband data stream.

[0052] In some embodiments, the diversity combiner circuit may be implemented as a separate circuit element that is interposed on the electrical path between the radio and the base station antenna. Moreover, the low noise amplifier(s) may be integrated into the diversity combiner circuit. In many cases, the diversity combiner circuits may be mounted on the antenna tower in close proximity to the base station antenna to reduce RF losses. It will also be appreciated that the diversity combiner circuit may be integrated into the base station antenna in some embodiments.

[0053] FIG.2 is a schematic shadow perspective view of a base station antenna 100 that may be used with the diversity combiner circuits according to embodiments of the present invention. As shown in FIG.2, the base station antenna 100 includes a triangular backplane 122 that is contained within a protective radome 128. The triangular backplane 122 has first through third generally planar metal faces 124-1 through 124-3 that each act as a reflector and ground plane for the linear arrays of radiating elements that are mounted on each face 124. The base station antenna 100 includes six linear arrays 130-1 through 130-3 of cross-dipole radiating elements 132, with a pair of linear arrays 130 mounted on each face 124 of the backplane 122.

[0054] FIG.3 is a block diagram illustrating a diversity combiner circuit 200 according to embodiments of the present invention coupled between a two-port radio 50 and a pair of linear arrays 130-1, 130-2 of a base station antenna (e.g., the base station antenna 100). The two linear arrays 130-1, 130-2 provide service to a sector of a base station such as base station 10. The diversity combiner circuit 200 includes two sub-circuits 202-1, 202-2. Only the details of the first sub-circuit 202-1 are illustrated in FIG.3. The two sub-circuits 202-1, 202-2 may be contained in a common housing or may be implemented as two separate units that each have their own housing.

[0055] As shown in FIG.3, the first sub-circuit 202-1 is coupled between a first port 52-1 of the cellular radio 50 and the first polarization radiators (e.g., the -^^^ ^^^^^^^^^^^^ ^^^^^^^^^^of the radiating elements 132 in linear arrays 130-1, 130-2. It will be appreciated that the second sub-circuit 202-2 may be identical to the first sub-circuit 202-1 and may be coupled between asecond port 52-2 of the radio 50 ^^^ ^^^ ^^^^^^ ^^^^^^^^^^^^ ^^^^^^^^^ ^^^^^^ ^^^ ^^^^ ^^^^^^^^^^^^radiators) of the radiating elements 132 in linear arrays 130-1, 130-2. The block diagrams ofM / COMM-106-PC FIGS.4-6 similarly only illustrate the details of one of the two sub-circuits of the diversity combiner circuits according to further embodiments of the present invention depicted therein.

[0056] As shown in FIG.3, the first sub-circuit 202-1 of diversity combiner circuit 200 includes a pair of diplexers 210-1, 210-2. Each diplexer 210-1, 210-2 includes a downlink port 212, an uplink port 214 and a combined port 216. For purposes of illustration, it is assumed that the cellular operator is licensed to use the 2130-2150 MHz portion of the mid-band frequency range for transmitting downlink signals from the base station antenna 100, and is licensed to use the 1940-1960 MHz portion of the mid-band frequency range for receiving uplink signals at the base station antenna 100. As shown in FIG.3, the combined port 216 of diplexer 210-2 is coupled to the first port 52-1 of the radio 50, typically by a coaxial cable, although any suitable RF interface may be used. The downlink port 212 of diplexer 210-2 is coupled to the downlink port 212 of diplexer 210-2. Again, any suitable RF connection may be used. In some cases, the connection between the two downlink ports 212 may be within a cavity filter that is used to implement both diplexers 210-1, 210-2. The uplink port 214 of diplexer 210-2 is coupled to the output of a low noise amplifier 260 (discussed below) and the combined port 216 of diplexer 210-1 is coupled to the first polarization radiators of the radiating elements 132 of linear array 130-1. The uplink port 214 of diplexer 210-1 is coupled to the input 232 of a first directional coupler 230-1. The directional couplers 230 that are included in the diversity combiner circuits according to embodiments of the present invention may be implemented using any coupler that can split an RF signal input thereto. Preferably, the directional couplers will only tap off a small amount of the RF energy.

[0057] Downlink signals that are output from the first port of radio 50 are passed to the combined port 216 of diplexer 210-2. The downlink signals are routed within diplexer 210-2 to the downlink port 212 and passed to the downlink port 212 of diplexer 210-1. The downlink signals are routed within diplexer 210-1 to the combined port 216 and passed to the first polarization radiators of the radiating elements 132 of linear array 130-1. Note, that the downlink signals that are passed to the first sub-circuit 202-1 through the first port 52-1 of cellular radio 50 are only transmitted through the first linear array 130-1. In some embodiments, the downlink signals that are passed to the second sub-circuit 202-2 through the second port 52-2 of cellular radio 50 may only be transmitted through the second linear array 130-2. This can improve the cross-polarization performance of base station antenna 100.M / COMM-106-PC

[0058] Still referring to FIG.3, uplink first polarization signals that are received at the first linear array 130-1 are passed to the combined port 216 of diplexer 210-1 and routed to the uplink port 214 thereof, which passes the received uplink signals to the input 232 of the first directional coupler 230-1. The first diplexer 210-1 will attenuate RF energy that is outside the uplink frequency band (such RF energy may be referred to herein as out-of-band RF energy). The first directional coupler 230-1 taps off a small amount of RF energy (e.g., 5-10%) from each uplink signal and passes this tapped RF signal to a tap port 236 of the first directional coupler 230-1. The remainder of the RF energy of each uplink signal is output through an output 234 of the first directional coupler 230-1. Similarly, uplink first polarization signals that are received at the second linear array 130-2 are passed through a first filter 220-1 that attenuates out-of-band RF energy, and are passed from the first filter 220-1 to an input 232 of a second directional coupler 230-2. The second directional coupler 230-2 taps off a small amount of RF energy (e.g., 5-10%) from each uplink signal and passes this tapped RF signal to a tap port 236 of the second directional coupler 230-2. The remainder of the RF energy of the received uplink signal is output through an output 234 of the second directional coupler 230-2. The portion of the received uplink signals that are output through the outputs 234 of the directional couplers 230 may be referred to herein as the "primary" uplink signals as these signals contain the vast majority of the RF energy of the two received uplink signals. The outputs 234 of the directional couplers 230 are connected to the respective input ports 242, 244 of a first 2x1 switch 240-1.

[0059] The tapped signals that are output from the tap ports 236 of the directional couplers 230 are passed to the respective input ports 242, 244 of a second 2x1 RF switch 240-2. The second RF switch 240-2 may be a relatively low power switch as it passes tapped signals that may be, for example, only 5--10% of the received uplink signals (and the uplink signals are much lower power than the downlink signals). The second RF switch 240-2 may be programmed to periodically switch between connecting the first input port 242 and the second input port 244 to an output port 246 of the second RF switch 240-2. In this manner, the second RF switch may alternating pass samples of the first tapped signals and the second tapped signals to the output port 246 of the second RF switch 240-2. The signals output from the second RF switch 240-2 are passed to a high selectivity filter 220-2 that may have a passband that is the same as (or even slightly less than) to the bandwidth of the uplink operating frequency band. The filter 220-2 may remove almost all out-of-band RF energy. The filtered signals are passedM / COMM-106-PC from the second filter 220-2 to a diversity selector 250. The diversity selector 250 may be configured to measure one or more characteristics of the tapped uplink signals that are input thereto, and then based on these measured characteristics determine which linear array 130-1, 130-2 is currently receiving "better" uplink signals. For example, the diversity selector 250 may measure a received signal strength of each tapped signal that is input thereto, and may determine that the tapped signal having the higher received signal strength is the "better" uplink signal. Operation of the second RF switch 240-2 and the diversity selector 250 may be coordinated so that the diversity selector 250 alternates between measuring characteristics of the tapped signal that was received at the first array 130-1 and the tapped signal that was received at the second array 130-2. The diversity selector 250 compares the measured characteristics of the tapped signals to identify which of the first and second linear arrays 130-1, 130-2 is receiving higher quality uplink signals at any given point in time.

[0060] It should be noted that the base station antenna 100 may be operated as a frequency division duplex ("FDD") sector antenna in this embodiment and in the various other embodiments described herein. Thus, the uplink signal received at each linear array 130-1, 130- 2 will typically be a combination of all of the uplink signals that are simultaneously being received on different channels of the uplink operating frequency band. Thus, it will be appreciated that references to the "best" or "higher quality" uplink signal refer to the uplink signal across the full uplink operating frequency band. which will typically include a large number of individual uplink signals.

[0061] The diversity selector 250 includes an output port that is coupled to a control port 248 of the first RF switch 240-1. The diversity selector 250 sends control signals to the control port 248 of the first RF switch 240-1 that are used to control the setting of the first RF switch 240-1 (i.e., which input 242, 244 is connected to the output 246). In particular, the diversity selector 250 may set the first RF switch 240-1 so that it passes the uplink signals that are received at the one of the first and second linear arrays 130-1, 130-2 that is receiving higher quality uplink signals at the given point in time to the low noise amplifier 260. The uplink signals that are passed to the low noise amplifier 260 are amplified and then passed through the first diplexer 210-2 to the first port 52-1 of the cellular radio 50.

[0062] As discussed above, a second identical sub-circuit 202-1 may be used to pass the higher quality of the second polarization uplink signals that are received at the first linear arrayM / COMM-106-PC 130-1 and the second linear array 130-2 to the second port 52-2 of the cellular radio 50. The cellular radio 50 may then use a diversity combining technique to demodulate and combine the received uplink signals.

[0063] A separate diversity combiner circuit 200 (which may include a sub-circuit 202 for each polarization) may be provided for each sector of the base station in order to connect each two-port radio to a respective pair of linear arrays. In some cases, all six linear arrays may be included in a single base station antenna, such as the base station antenna 100 of FIG.2. In other cases, three base station antennas may be provided (e.g., conventional base station antenna panel antennas that provide service to a single sector) and a diversity combiner circuit 200 may be provided for each base station antenna.

[0064] Referring again to FIG.3, it can be seen that, pursuant to some embodiments of the present invention, cellular base stations are provided that include a cellular radio 50 that has first and second radio ports 52-1, 52-2. The cellular radio 50 is configured to perform diversity combining using a first diversity combining technique on first and second received uplink signals that are passed to the cellular radio through the first and second radio ports. The base station further comprises a diversity combining circuit 200 that is configured to select the first and second received uplink signals from a larger group of received uplink signals and to pass the selected first and second received uplink signals to the cellular radio 50 through the first and second radio ports 52-1, 52-2 thereof. The cellular base station may also include a base station antenna 100 that includes first and second arrays 130-1, 130-2 of dual-polarized radiating elements 132. The larger group of received uplink signals comprises a first polarization received uplink signal that is received at the first array 130-1, a second polarization received uplink signal that is received at the first array 130-1, a first polarization received uplink signal that is received at the second array 130-2, a second polarization received uplink signal that is received at the second array 130-2.

[0065] The diversity combining circuit 200 may be configured to use selection combining to select the first and second received uplink signals from the larger group of received uplink signals. The diversity combining circuit 200 may include a first coupler 230-1 and a second coupler 230-2 that are configured to tap RF energy from the first polarization received uplink signal that is received at the first array 130-1 and from the first polarization received uplink signal that is received at the second array 130-2, respectively, to provide first and secondM / COMM-106-PC tapped signals. The diversity combining circuit 200 may further includes a first diversity selector circuit 250 that is configured to receive the first and second tapped signals and to determine at least one characteristic of the first and second tapped signals. The diversity combining circuit 200 further includes a first switch 240-1 that is configured to couple an output 234 of one of the first and second couplers 230-1, 230-2 to the first port 52-1 of the cellular radio 50. The diversity selector circuit 250 may be configured to set the first switch 240-1 to couple either the output 234 of the first coupler 230-1 or the output 234 of the second coupler 230-2 to the first port 52-1 of the cellular radio 50 based on one or more measured characteristics of the first and second tapped signals. The diversity combining circuit 200 may further comprise a first low noise amplifier 260 that is coupled in between an output 246 of the first switch 240-1 and the first port 52-1 of the cellular radio 50.

[0066] Still referring to FIG.3, it can also be seen that, pursuant to further embodiments of the present invention, a diversity combining circuit 200 is provided that includes a first sub- circuit 202-1 that includes a first input port 204-1, a second input port 204-2, a first output port 204-2, a first coupler 230-1 that has a first coupler input 232 that is coupled to the first input port 204-1, a first coupler output 234, and a first tap port 236, and a second coupler 230-2 that has a second coupler input 232 that is coupled to the second input port 204-2, a second coupler output 234, and a second tap port 236. The first sub-circuit 202-1 further includes a first switch 240-1 that has a first switch input 242 that is coupled to the first coupler output 234 and a second switch input 244 that is coupled to the second coupler output 234, and a first switch output 246 that is coupled to the first output port 206, as well as a first diversity selector circuit 250 that is coupled to the first and second tap ports 236. The diversity selector circuit 250 includes a diversity selector output port that is coupled to a control port 248 of the first switch 240-1.

[0067] The first sub-circuit 202-1 may further include a first low noise amplifier 260. which may, for example, be coupled between the first switch output 246 and the first output port 206. The first sub-circuit 202-1 may further comprise a second switch 240-2 that has a third switch input 242 that is coupled to the first tap port 236 and a fourth switch input 244 that is coupled to the second tap port 236, and a second switch output 246 that is coupled to the first diversity selector circuit 250. The first sub-circuit 202-1 may also include a first diplexer 210-1 and a second diplexer 210-2, where the first diplexer 210-1 is coupled between the first input port 204-1, the first coupler input 232 and the second diplexer 210-2, and the second diplexerM / COMM-106-PC 210-2 is coupled between an output of the low noise amplifier 260, the first output port 206 and the first diplexer 210-1.

[0068] The diversity combining circuit 200 may also include a second sub-circuit 202-2 that includes a third input port, a fourth input port, a second output port, a third coupler that has a third coupler input that is coupled to the third input port, a third coupler output, and a third tap port, a fourth coupler that has a fourth coupler input that is coupled to the fourth input port, a fourth coupler output, and a fourth tap port, a third switch that has a third switch input that is coupled to the third coupler output and a fourth switch input that is coupled to the fourth coupler output, and a third switch output that is coupled to the second output port, and a second diversity selector circuit that is coupled to the third and fourth tap ports, the second diversity selector circuit configured to couple control signals to the third switch. The second sub-circuit 202-2 may be identical to the first sub-circuit 202-2 and may be coupled between the second port 52-2 of the cellular radio 50 and the remaining two of four RF ports that feed the first and second linear arrays 130-1, 130-2 of base station antenna 100.

[0069] FIG.4 is a block diagram illustrating a diversity combiner circuit 300 according to further embodiments of the present invention coupled between a two-port radio 50 and a pair of linear arrays 130-1, 130-2 that provide service to a sector of a base station. The diversity combiner circuit 300 is similar to the diversity combiner circuit 200 that is discussed above with reference to FIG.3, so the discussion below will focus on the differences between the two diversity combiner circuits 200, 300.

[0070] As shown in FIG.4, the sub-circuits 302 of diversity combiner circuit 300 do not include the second RF switch 240-2 that is provided in diversity combiner circuit 200. Instead, each sub-circuit 302 includes a pair of the second filters 220-2 (instead of a single filter 220) that receive and filter the tapped signals that are tapped by the respective first and second couplers 230-1, 230-2. Each sub-circuit 302 also includes a more capable diversity selector circuit 350 that is capable of simultaneously measuring one or more characteristics of both receive uplink signals that are fed to the diversity selector circuit 350 through the two second filter circuits 220- 2. The diversity selector circuit 350 then compares the measured characteristics of the uplink signals received from the two different arrays 130-1, 130-2 and determines which array 130-1, 130-2 is receiving higher quality uplink signals. The diversity selector circuit 350 then controlsM / COMM-106-PC the first switch 240-1 to pass the higher quality uplink signals in the same manner described above with reference to FIG.3.

[0071] Each sub-circuit 302 of diversity combiner circuit 300 also includes first and second low noise amplifiers 260-1, 260-2 as opposed to the single low noise amplifier 260 included in the sub-circuits 302 of the diversity combiner circuit 200 of FIG.3. Additionally, in diversity combiner circuit 300 the low noise amplifiers 260-1, 260-2 are positioned on the respective uplink paths between the antenna 100 and the couplers 230-1, 230-2.

[0072] Diversity combiner circuit 300 will typically be more expensive to implement than diversity combiner circuit 200 because of the addition of a second low-noise amplifier 260. Diversity combiner circuit 300 also includes an upgraded diversity selector circuit 350 that can simultaneously measure characteristics (e.g., received signal strength) of two received uplink signals, although the diversity combiner circuit 300 omits the second switch 240-2 of diversity combiner circuit 200. It is anticipated that the diversity combiner circuit 300 will provide improved performance as compared to the diversity combiner circuit 200 since the higher power tapped signals that are fed to the diversity selector circuit 350 of diversity combiner circuit 300 (since the uplink signals are amplified prior to being tapped by the couplers 230-1, 230-2) can improve the performance of the diversity selector circuits 350. In addition, in fast fading environments diversity combiner circuit 300 may more quickly switch which of the linear arrays 130 is connected to the radio 50 on the uplink since the diversity selector circuit 350 continuously measures the characteristic of both uplink signals, whereas diversity selector circuit 250 of FIG.3, alternatingly measures a characteristic of the two uplink signals.

[0073] FIG.5 is a block diagram illustrating a diversity combiner circuit 400 according to additional embodiments of the present invention coupled between a two-port radio 50 and a pair of linear arrays 130-1, 130-2 of a base station antenna 100. Diversity combiner circuit 400 combines features of diversity combiner circuits 200 and 300 so the discussion below will focus on the differences between diversity combiner circuit 400 and diversity combiner circuits 200 and 300.

[0074] As can be seen by comparing FIG.5 to FIGS.3 and 4, diversity combiner circuit 400 includes a pair of low noise amplifiers 260-1, 260-2 and positions the low noise amplifiers between the antenna and the couplers 230, in the same manner described above with respect to diversity combiner circuit 300. Diversity combiner circuit 400, however, uses the diversityM / COMM-106-PC selection design of diversity combiner circuit 200, namely the tapped signals are fed to a second RF switch 240-2 that alternatingly feeds the tapped signals corresponding to the uplink signals received at the first and second linear arrays 130-1, 130-2 to a diversity selector circuit 250, that alternatingly measures a characteristic of the tapped uplink signals to determine which linear array is currently receiving higher quality uplink signals, and the diversity selector 250 than controls the first switch 240-1 so that the higher quality uplink signal is fed to the radio 50.

[0075] FIG.6 is a block diagram illustrating a diversity combiner circuit 500 according to still further embodiments of the present invention. The diversity combiner circuit 500 is coupled between a two-port radio 50 and a pair of linear arrays 130-1, 130-2 of a base station antenna 100. Diversity combiner circuit 500 is identical to the diversity combiner circuit 200 that is discussed above with reference to FIG.3, except that diversity combiner circuit 500 does not include any low noise amplifiers. Thus, further discussion of diversity combiner circuit 500 will be omitted.

[0076] FIGS.7A-7C are schematic diagrams illustrating how the techniques according to embodiments of the present invention may be used to support higher order MIMO communications techniques.

[0077] Referring first to FIG.7A, a base station 600 is illustrated which includes a base station antenna 610 that includes first and second linear arrays 612-1, 612-2 of dual-polarized radiating elements 614. The linear arrays 612 provide coverage to a sector of base station 600. The base station antenna 610 has four RF ports 616, where each RF port 616 feeds either the first polarization radiators or the second polarization radiators of the radiating elements 614 of a respective one of the linear arrays 612. The base station 600 further includes a MIMO radio 620 that includes first and second radio ports 622-1, 622-2. An external diversity combining circuit 630 is interposed between the radio 620 and the base station antenna 610. The diversity combining circuit 630 includes first and second sub-circuits 632-1, 632-2. The sub-circuits 632 may be implemented, for example, using the sub-circuits of diversity combiner circuits 200, 300, 400 or 500 that are depicted in FIGS.3-6 above. Each sub-circuit 632 includes a pair of input ports 634 that are coupled to the two RF ports 616 of base station antenna 610 that are connected to a respective one of the linear arrays 612. Each sub-circuit 632 further includes an output port 636 that is coupled to a respective one of the ports 622 of radio 620. The base station 600 may operate as a 2T / 4R base station (for linear arrays 612-1, 612-2).M / COMM-106-PC

[0078] FIG.7B illustrates a base station 700 that shows how the above concepts may be expanded to allow for the use of higher order MIMO techniques. As shown in FIG.7B, the base station 700 includes a base station antenna 710 that includes four linear arrays 612 of dual- polarized radiating elements 614 that all provide coverage to the same sector of base station 700. The base station 700 further includes a MIMO radio 720 that includes four radio ports 622. An external diversity combining circuit 730 is interposed between the radio 720 and the base station antenna 710. The diversity combining circuit 730 includes four sub-circuits 632, each of which may be, for example, the sub-circuits of diversity combiner circuits 200, 300, 400 or 500. Each sub-circuit 632 includes a pair of input ports 634 that are coupled to a pair of the RF ports 616 of base station antenna 710 that feed a respective one of the linear arrays 612. Each sub-circuit 632 further includes an output port 636 that is coupled to a respective one of the ports 622 of radio 720. The base station 700 may operate as a 4T / 8R base station.

[0079] FIG.7C illustrates a base station 800 that includes the base station antenna 710 of FIG.7B and the MIMO radio 620 of FIG.7A. An external diversity combining circuit 830 is interposed between the radio 620 and the base station antenna 710. The diversity combining circuit 830 includes two sub-circuits 832, each of which may be similar to the sub-circuits of diversity combiner circuits 200, 300, 400 or 500. The sub-circuits 832, however, tap RF energy from four uplink signals (i.e., the first or second polarization uplink signals from each of the linear arrays 612) and have a diversity selector circuit that selects the highest quality of the four uplink signals. Each sub-circuit 832 includes four input ports 634 that are coupled to four corresponding RF ports 616 of base station antenna 710. Each sub-circuit 832 further includes an output port 636 that is coupled to a respective one of the ports 622 of radio 720. The base station 800 may operate as a 2T / 8R base station.

[0080] As shown in FIGS.7A-7C, the cellular base stations according to embodiments of the present invention may include a cellular radio 620, 720 that includes X ports (e.g., two or four ports), where X is an integer that is greater than or equal to two, and the cellular radio 620, 720 is configured to perform diversity combining using a first diversity combining technique on X received uplink signals that are passed to the cellular radio 620, 720 through the X ports. The base station further comprises a diversity combining circuit 630, 730, 830 that is configured to select the X received uplink signals from a larger group of Y received uplink signals and to pass the selected X received uplink signals to the cellular radio 620, 720 through the X ports.M / COMM-106-PC

[0081] The cellular base station may further comprise a base station antenna 610, 710 that includes Y / 2 arrays 612, 712 of dual-polarized radiating elements 614, where the Y received uplink signals comprise a first polarization received uplink signal and a second polarization received uplink signal from each of Y / 2 arrays 612, 712. Y may, for example, be equal to 2*X or to 4*X. The diversity combining circuit 630, 730, 830 may be configured to use selection combining to select the X received uplink signals from the larger group of Y received uplink signals.

[0082] In the above-described embodiments of the present invention, the measured characteristic of the uplink signals that is compared to determine the "best" uplink signal was described as being the received signal strength as an example. It will be appreciated, however, that various other parameters may be used such as, for example, signal-to-noise ratio or vector magnitude error.

[0083] The above-described embodiments of the present invention have been presented with reference to base station antennas that include mid-band linear arrays of radiating elements. It will be appreciated, however, that the same techniques described herein can be used with low- band arrays of radiating elements or with arrays of radiating elements that operate in higher frequencies than the mid-band operating frequency range. It will also be appreciated that while the base stations shown herein are only shown as including mid-band linear arrays, the base station antennas may also include additional arrays of radiating elements that operate in other frequency bands or even in other portions of the mid-band operating frequency range. Moreover, while the discussion above focuses primarily on three-sector base station antennas that are designed so that a single base station antenna can provide coverage to a full cell of a cellular communications network, it will be appreciated that all of the above-described embodiments of the present invention are equally applicable to base stations that include three separate base station antennas that provide service to the respective sectors. It will also be understood that the concepts disclosed herein are equally applicable to base stations having a different number of sectors than three (e.g., six-sector base stations).

[0084] Embodiments of the present invention have been described above with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that thisM / COMM-106-PC disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

[0085] It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0086] It will be understood that when an element is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (i.e., "between" versus "directly between", "adjacent" versus "directly adjacent", etc.).

[0087] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0088] Herein, the term "substantially" means within + / - 10%.

[0089] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" "comprising," "includes" and / or "including" when used herein, specify the presence of stated features, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, operations, elements, components, and / or groups thereof.M / COMM-106-PC

[0090] Aspects and elements of all of the embodiments disclosed above can be combined in any way and / or combination with aspects or elements of other embodiments to provide a plurality of additional embodiments.

Claims

M / COMM-106-PC CLAIMS:

1. A cellular base station, comprising: a cellular radio having first and second radio ports, the cellular radio configured to perform diversity combining using a first diversity combining technique on first and second received uplink signals that are passed to the cellular radio through the first and second radio ports; and a diversity combining circuit that is configured to select the first and second received uplink signals from a larger group of received uplink signals and to pass the selected first and second received uplink signals to the cellular radio through the first and second radio ports.

2. The cellular base station of Claim 1, further comprising a base station antenna that includes first and second arrays of dual-polarized radiating elements, where the larger group of received uplink signals comprises a first polarization received uplink signal that is received at the first array, a second polarization received uplink signal that is received at the first array, a first polarization received uplink signal that is received at the second array, a second polarization received uplink signal that is received at the second array.

3. The cellular base station according to any one of the preceding Claims, in particular Claim 2, wherein the diversity combining circuit is configured to use selection combining to select the first and second received uplink signals from the larger group of received uplink signals.

4. The cellular base station according to any one of the preceding Claims, in particular Claim 3, wherein the diversity combining circuit comprises a first coupler and a second coupler that are configured to tap radio frequency ("RF") energy from the first polarization received uplink signal that is received at the first array and from the first polarization received uplink signal that is received at the second array, respectively, to provide first and second tapped signals.

5. The cellular base station according to any one of the preceding Claims, in particular Claim 4, wherein the diversity combining circuit further comprises a third coupler and a fourth coupler that are configured to tap radio frequency ("RF") energy from the secondM / COMM-106-PC polarization received uplink signal that is received at the first array and from the second polarization received uplink signal that is received at the second array, respectively, to provide third and fourth tapped signals.

6. The cellular base station according to any one of the preceding Claims, in particular Claim 4, wherein the diversity combining circuit includes a first diversity selector circuit that is configured to receive the first and second tapped signals and to determine at least one characteristic of the first and second tapped signals.

7. The cellular base station according to any one of the preceding Claims, in particular Claim 6, wherein the diversity combining circuit further includes a first switch that is configured to couple an output of one of the first and second couplers to the first port of the cellular radio.

8. The cellular base station according to any one of the preceding Claims, in particular Claim 7, wherein the diversity selector circuit is configured to set the first switch to couple either the output of the first coupler or the output of the second coupler to the first port of the cellular radio based on one or more measured characteristics of the first and second tapped signals.

9. The cellular base station according to any one of the preceding Claims, in particular Claim 1, wherein the diversity combining circuit further comprises a first low noise amplifier that is coupled in between an output of the first switch and the first port of the cellular radio.

10. The cellular base station according to any one of the preceding Claims, in particular Claim 8, wherein the diversity combining circuit further comprises a first low noise amplifier that is coupled in between the first array of dual-polarized radiating elements and the first coupler and a second low noise amplifier that is coupled in between the second array of dual-polarized radiating elements and the second coupler.

11. The cellular base station according to any one of the preceding Claims, in particular Claim 2, wherein the diversity combining circuit comprises a tower mounted diversityM / COMM-106-PC combining circuit that is connected to the cellular radio via a first plurality of cables and to the base station antenna via a second plurality of cables.

12. The cellular base station according to any one of the preceding Claims, in particular Claim 6, wherein the determined characteristic comprises a received signal strength.

13. The cellular base station according to any one of the preceding Claims, in particular Claim 6, wherein the determined characteristic comprises a presence of an intermodulation product within an uplink operating frequency band of the cellular radio.

14. The cellular base station according to any one of the preceding Claims, in particular Claim 1, wherein the first diversity combining technique comprises a maximal ratio diversity combining technique.

15. A diversity combining circuit, comprising: a first input port; a second input port; a first output port; a first coupler that has a first coupler input that is coupled to the first input port, a first coupler output, and a first tap port; a second coupler that has a second coupler input that is coupled to the second input port, a second coupler output, and a second tap port; a first switch that has a first switch input that is coupled to the first coupler output and a second switch input that is coupled to the second coupler output, and a first switch output that is coupled to the first output port; and a first diversity selector circuit that is coupled to the first and second tap ports, the diversity selector circuit including a diversity selector output port that is coupled to a control port of the first switch.

16. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 15, further comprising a first low noise amplifier.M / COMM-106-PC 17. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 16, wherein the first low noise amplifier is coupled between the first switch output and the first output port.

18. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 17, further comprising a second switch that has a third switch input that is coupled to the first tap port and a fourth switch input that is coupled to the second tap port, and a second switch output that is coupled to the first diversity selector circuit.

19. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 17, further comprising a first diplexer and a second diplexer, where the first diplexer is coupled between the first input port, the first coupler input and the second diplexer, and the second diplexer is coupled between an output of the low noise amplifier, the first output port and the first diplexer.

20. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 15, further comprising a first low noise amplifier that is coupled between the first input port and the first coupler input and a second low noise amplifier that is coupled between the second input port and the second coupler input.

21. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 20, wherein the first diversity selector circuit has first and second diversity selector inputs that are coupled to the respective first and second tap ports.

22. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 21, further comprising a first diplexer and a second diplexer, where the first diplexer is coupled between the first input port, the first coupler input and the second diplexer, and the second diplexer is coupled between the first switch output, the first output port and the first diplexer.

23. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 20, further comprising a second switch that has a third switch input that is coupled to the first tap port and a fourth switch input that is coupled to the second tap port, and a second switch output that is coupled to the first diversity combiner circuit.M / COMM-106-PC 24. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 23, further comprising a first diplexer and a second diplexer, where the first diplexer is coupled between the first input port, the first coupler input and the second diplexer, and the second diplexer is coupled between the first switch output, the first output port and the first diplexer.

25. The diversity combining circuit according to any one of the preceding Claims, in particular Claim 16, further comprising: a third input port; a fourth input port; a second output port; a third coupler that has a third coupler input that is coupled to the third input port, a third coupler output, and a third tap port; a fourth coupler that has a fourth coupler input that is coupled to the fourth input port, a fourth coupler output, and a fourth tap port; a third switch that has a third switch input that is coupled to the third coupler output and a third switch input that is coupled to the third coupler output, and a third switch output that is coupled to the second output port; and a second diversity selector circuit that is coupled to the third and fourth tap ports, the second diversity selector circuit configured to couple control signals to the third switch.

26. A cellular base station, comprising: a cellular radio that includes X ports, where X is an integer that is greater than or equal to 2, the cellular radio configured to perform diversity combining using a first diversity combining technique on X received uplink signals that are passed to the cellular radio through the X ports; and a diversity combining circuit that is configured to select the X received uplink signals from a larger group of Y received uplink signals and to pass the selected X received uplink signals to the cellular radio through the X ports.

27. The cellular base station according to any one of the preceding Claims, in particular Claim 26, further comprising a base station antenna that includes Y / 2 arrays of dual-M / COMM-106-PC polarized radiating elements, where the Y received uplink signals comprise a first polarization received uplink signal and a second polarization received uplink signal from each of Y / 2 arrays.

28. The cellular base station according to any one of the preceding Claims, in particular Claim 27, wherein Y is equal to 2*X.

29. The cellular base station according to any one of the preceding Claims, in particular Claim 26, wherein the diversity combining circuit is configured to use selection combining to select the X received uplink signals from the larger group of Y received uplink signals.

30. The cellular base station according to any one of the preceding Claims, in particular Claim 28, wherein the diversity combining circuit comprises Y couplers that are configured to tap radio frequency ("RF") energy from the Y received uplink signals to provide Y tapped signals.

31. The cellular base station according to any one of the preceding Claims, in particular Claim 30, wherein the diversity combining circuit includes a diversity selector circuit that is configured to receive a first of the Y tapped signals that was tapped from a first of the Y received signals that was received at a first of the arrays of dual-polarized radiating elements and configured to receive a second of the Y tapped signals that was tapped from a second of the Y received signals that was received at a second of the arrays of dual-polarized radiating elements.

32. The cellular base station according to any one of the preceding Claims, in particular Claim 31, wherein the diversity combining circuit further includes a first switch that is interposed between first and second of the Y couplers and the cellular radio.

33. The cellular base station according to any one of the preceding Claims, in particular Claim 32, wherein the diversity selector circuit is configured to set the first switch to couple the cellular radio to one of the couplers based on one or more measured characteristics of the first and second of the Y tapped signals.

34. The cellular base station according to any one of the preceding Claims, in particular Claim 26, wherein the diversity combining circuit includes a first sub-circuit and aM / COMM-106-PC second sub-circuit, and the first sub-circuit is configured to pass first polarization downlink signals that are received from the cellular radio exclusively to a first of the Y / 2 arrays of dual- polarized radiating elements and the second sub-circuit is configured to pass second polarization downlink signals that are received from the cellular radio exclusively to a second of the Y / 2 arrays of dual-polarized radiating elements.

35. The cellular base station according to any one of the preceding Claims, in particular Claim 26, wherein the diversity combining circuit includes a first sub-circuit and a second sub-circuit, and the first sub-circuit includes a first low noise amplifier, and a switch circuit that routes first polarization uplink signals from a selected on of the Y / 2 arrays of dual- polarized radiating elements to the cellular radio.

36. A cellular base station, comprising: a two-port cellular radio having a first radio port and a second radio port; a base station antenna having a first array of dual polarized radiating elements and a second array dual polarized radiating elements; and a diversity combiner circuit coupled between the two-port cellular radio and the base station antenna, wherein diversity combiner circuit is configured to route downlink signals output from the first radio solely to the first array of dual polarized radiating elements and to route downlink signals output from the second radio solely to the second array of dual polarized radiating elements.

37. The cellular base station according to any one of the preceding Claims, in particular Claim 36, wherein the diversity combiner circuit is configured to pass either first polarization uplink signals received at the first array of dual polarized radiating elements or first polarization uplink signals received at the second array of dual polarized radiating elements to the first radio port.

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