Base station and method for base station

Abstract

The invention relates to a base station and a method for the base station. The base station comprises a first antenna array which is organized into a plurality of first SBFD antenna sub-arrays; the second antenna array is organized into a plurality of second SBFD antenna sub-arrays; a plurality of transmitting RF chains configured to convert the baseband signal into an RF transmitting signal, the plurality of transmitting RF chains having a one-to-one correspondence relationship with the plurality of first SBFD antenna sub-arrays; the plurality of receiving RF chains are configured to convert receiving RF signals into baseband signals, and the plurality of receiving RF chains and the plurality of second SBFD antenna sub-arrays have a one-to-one correspondence relationship; and a plurality of switches having a first configuration for an SBFD mode of operation in which each transmit RF chain is configured to drive a respective first SBFD antenna sub-array with an RF transmit signal of the transmit RF chain and each receive RF chain is configured to receive a receive RF signal of the receive RF chain from a respective second SBFD sub-array.

Description

[0001] This application is a divisional application of the Chinese invention patent application with application date of November 2, 2020 and application number 202080074722.5.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to and the benefit of U.S. Non-Provisional Patent Application No. 17 / 086,368, filed on October 31, 2020, and U.S. Provisional Patent Application No. 62 / 929,853, filed on November 2, 2019, which are both incorporated herein by reference in their entireties as if fully set forth below and for all applicable purposes. Technical Field

[0004] The present application relates to wireless communications, and more particularly to a sub-band full-duplex adaptive base station transceiver. Background Art

[0005] Wireless communication systems are widely deployed to provide a variety of telecommunication services, such as telephony, video, data, messaging, and broadcast. Typical wireless communication systems may employ multiple access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

[0006] These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate at a city, country, regional, and even global level. An example telecommunication standard is 5th Generation (5G) New Radio (NR). 5G NR is part of the continued mobile broadband evolution promulgated by the 3rd Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with the Internet of Things (IoT)), and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB), massive machine type communications (mMTC), and ultra-reliable low latency communications (URLLC). Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There is a need for further multiple access improvements in 5G NR technology. These improvements may also be applicable to other multiple access technologies and telecommunication standards that adopt these technologies. Summary of the invention

[0007] A base station is disclosed, comprising: a first antenna array, organized into a plurality of first sub-band full-duplex (SBFD) antenna subarrays; a second antenna array, organized into a plurality of second SBFD antenna subarrays; a plurality of transmit RF chains, each transmit RF chain being configured to convert a baseband signal into an RF transmit signal, wherein the plurality of transmit RF chains have a one-to-one correspondence with the plurality of first SBFD antenna subarrays; a plurality of receive RF chains, each receive RF chain being configured to convert a receive RF signal into a baseband signal, wherein the plurality of receive RF chains have a one-to-one correspondence with the plurality of second SBFD antenna subarrays; and a plurality of switches having a first configuration for an SBFD operation mode, wherein each transmit RF chain is configured to drive a corresponding first SBFD antenna subarray with an RF transmit signal of the transmit RF chain, and wherein each receive RF chain is configured to receive a receive RF signal of the receive RF chain from a corresponding second SBFD subarray.

[0008] In addition, a base station is disclosed, including: a first transmit RF chain; a first antenna array, including a first sub-band full-duplex (SBFD) antenna subarray and a second SBFD antenna subarray; a first RF signal splitter and combiner; and a switch array, which is configured to couple the transmit RF chain to both the first SBFD antenna subarray and the second SBFD antenna subarray through the first RF signal splitter and combiner in a downlink time division duplex (DL TDD) operation mode, and the switch array is also configured to couple the first transmit RF chain to the first SBFD antenna subarray instead of the second SBFD antenna subarray in the SBFD operation mode.

[0009] Finally, a method for a base station is disclosed, comprising: during a downlink time division duplex (DL TDD) time slot, using a first RF chain to upconvert a first baseband signal to form a first DL radio frequency (RF) signal and sending the first DL RF signal from a first antenna subarray and from a second antenna subarray, the first DL RF signal occupying a frequency band; during an uplink (UL) TDD time slot, using a first antenna subarray and a second antenna subarray to receive a first UL RF signal and using the first RF chain to downconvert the first UL RF signal to form a second baseband signal, the first UL RF signal occupying the frequency band; and during a first sub-band full-duplex (SBFD) time slot, using the first RF chain to upconvert a third baseband signal to form a second DL RF signal and sending the second DL RF signal only from the first antenna subarray, the second DL RF signal occupying a lower subband and an upper subband in the frequency band, the lower subband being separated in frequency from the upper subband by a center subband in the frequency band.

[0010] These and other advantageous features may be better understood through the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1A Some 5G NR time and frequency resources are shown.

[0012] Figure 1B A time slot structure including a conventional TDD one-way time slot and a sub-band full-duplex (SBFD) time slot and a corresponding antenna array configuration of a base station according to aspects of the present disclosure is shown.

[0013] Figure 2

[0013] A wireless communication system including a downlink UE receiving SBFD downlink transmissions and an uplink UE sending SBFD uplink transmissions to a base station according to aspects of the present disclosure is shown.

[0014] Figure 3 The transmit and receive paths of a SBFD base station with 4:1 hybrid beamforming according to aspects of the present disclosure are shown.

[0015] Figure 4A The transmit and receive paths of a SBFD base station with full hybrid beamforming and 4:1 signal combining are shown in accordance with aspects of the present disclosure.

[0016] Figure 4B The transmit and receive paths of a SBFD base station with N:1 hybrid beamforming and R:1 signal combining are shown according to aspects of the present disclosure.

[0017] Figure 5 Two example arrangements of transmit and receive antenna arrays on a circuit board substrate of a SBFD base station according to aspects of the present disclosure are shown.

[0018] Figure 6 A transmit array and a receive array isolated by a pair of conductive first isolation boosters are shown according to aspects of the present disclosure.

[0019] Figure 7 Shows Figure 6 A perspective view of an array and a portion of a conductive first isolation enhancer.

[0020] Figure 8 A portion of a transmit and receive array isolated by a pair of conductive first isolation boosters is shown, where the pair faces the same array.

[0021] Fig. 9 A transmit array and a receive array isolated by a pair of conductive second isolation boosters are shown according to aspects of the present disclosure.

[0022] Fig.10 is a flow chart of an example method of operation of a SBFD base station according to aspects of the present disclosure.

[0023] Embodiments of the present disclosure and their advantages may be best understood by referring to the following detailed description.It should be appreciated that like reference numerals are used to identify like elements shown in one or more of the figures. DETAILED DESCRIPTION

[0024] Compared to previous communication standards, the spectrum options for 5G NR are greatly expanded. For example, the frequency range 2 (FR2) band is extended from about 24 GHz to 60 GHz. Since the wavelength decreases as the frequency increases, the FR2 band is denoted as a millimeter wave band due to its relatively small wavelength. Given this relatively short wavelength, the radio frequency (RF) signals transmitted in the FR2 band behave somewhat like visible light. Therefore, just like light, millimeter wave signals are easily blocked by buildings and other obstacles. In addition, the received power per unit area of ​​the antenna element decreases as the frequency increases. For example, in terms of width and length, a patch antenna element is typically a small fraction of the operating wavelength (e.g., half the wavelength). As the wavelength decreases (and therefore the size of the antenna element decreases), it can be seen that the signal energy received at the corresponding antenna element decreases. Due to the problems of blockage and reduced received signal strength, millimeter wave cellular networks will generally require a relatively large number of base stations. Cellular providers generally have to rent real estate for base stations, making widespread coverage of millimeter wave cellular networks very expensive.

[0025] The electromagnetic properties of radio wave propagation in the sub-6 GHz bands are more adaptable compared to the challenges of FR2. For example, the 5G NR Frequency Range 1 (FR1) band extends from approximately 0.4 GHz to 7 GHz. At these lower frequencies, transmitted RF signals tend to refract around obstacles such as buildings, reducing the problem of obstruction. In addition, the larger size of each antenna element means that FR1 antenna elements intercept more signal energy compared to FR2 antenna elements. Therefore, 5G NR cellular networks operating in the FR1 band will not require as many base stations as were established for 4G and previous networks. Given the favorable characteristics of the lower frequency bands, the sub-6 GHz bands are often denoted as “beachfront” bands due to their desirability.

[0026] One problem with operating in the sub-6 GHz band is that there is only so much bandwidth available. For this reason, the Federal Communications Commission regulates the airwaves and auctions limited bandwidth in the FR1 band. Given this limited bandwidth, it is challenging for cellular providers to achieve the high data rates that are more easily achieved in the FR2 band. To address these challenges, a "Sub-Band Full Duplex" (SBFD) network architecture is disclosed herein that is highly advantageous because it provides users with high data rates that would otherwise require the use of the FR2 band. However, the SBFD network architecture disclosed herein provides these high data rates in more of the FR1 band and reduces costs because fewer base stations per given coverage area can be achieved in the FR1 band than in the FR2 band.

[0027] To better understand the advantages of SBFD networks, we will first refer to Figure 1A Let's review some common 5G NR time and frequency resource structures such as for orthogonal frequency division multiplexing (OFDM) waveforms. In some embodiments, transmissions are organized into frames in the time domain, where each frame consists of 10 subframes of 1 ms each. Figure 1A 1 shows an enlarged view of two exemplary subframes 102. Each subframe 102 can be mapped to an OFDM resource grid 104. However, as will be readily appreciated by those skilled in the art, the PHY transmission structure for any particular application may differ from the examples described herein depending on any number of factors. For the OFDM resource grid 104, time is in units of OFDM symbols in the horizontal direction, while frequency is in units of subcarriers or tones in the vertical direction.

[0028] The resource grid 104 can be used to schematically represent the time-frequency resources for a given antenna port. That is, in a MIMO implementation with multiple available antenna ports, a corresponding plurality of resource grids 104 can be used for communication. The resource grid 104 is divided into a plurality of resource elements (REs) 106. RE, which is 1 subcarrier × 1 symbol, is the smallest discrete portion of the time-frequency grid and contains a single complex value representing data or a signal from a physical channel. A block of twelve consecutive subcarriers defines a resource block (RB) 108, which has an undefined duration in the NR standard. In one implementation, a resource block 108 extends over a symbol duration. A group of consecutive RBs 108 such as shown in the resource grid 104 forms a bandwidth part (BWP).

[0029] Each 1 ms subframe 102 may consist of one or more adjacent time slots. Figure 1AIn the example shown, as an illustrative example, one subframe 102 includes four time slots 110. In some examples, a time slot can be defined according to a specified number of OFDM symbols with a given cyclic prefix (CP) length. For example, a time slot can include 7 or 14 OFDM symbols with a nominal CP. Other examples may include small slots with shorter durations (e.g., one or two OFDM symbols). These small slots may in some cases occupy resources scheduled for ongoing time slot transmissions of the same or different UEs to be transmitted.

[0030] An enlarged view of one of the time slots 110 shows that the time slot 110 includes a control region 112 and a data region 114. In general, the control region 112 may carry control channels, while the data region 114 may carry data channels. The time slot 110 may contain all downlink (DL), all uplink (UL), or at least one DL portion and at least one UL portion. Figure 1A The simple structure shown in is merely exemplary in nature, and different slot structures may be utilized and may include one or more of each of the control region and the data region.

[0031] The SBFD organization of the time and frequency resources of these 5G NRs will now be discussed in more detail. The SBFD resource organization will be discussed with respect to the repeated four-slot structure as previously discussed, but it should be understood that in alternative implementations, the subframe size can be larger or smaller than four slots. In a conventional four-slot structure, the first two slots may be downlink slots, while the last of the four slots is an uplink slot. The third slot is a special slot in which some symbols may be used for uplink transmission and other symbols may be used for downlink transmission. The resulting uplink and downlink traffic is therefore time division duplex (TDD) arranged by dedicated slots and by symbol allocations in special slots. Since there is only a single dedicated slot for the uplink, uplink communications may suffer from excessive delays because the user equipment (UE) is restricted to transmitting in a single dedicated uplink slot and in the resource allocation within the special slot. Since there is only one dedicated uplink slot in the repeated four-slot structure, the resulting delay may be a problem, particularly for low-latency applications such as vehicle-to-vehicle communications. Furthermore, the energy of uplink communication is limited to its single dedicated time slot.

[0032] In order to reduce uplink latency and increase the energy of uplink transmissions, a sub-band full-duplex (SBFD) mode is proposed, in which the second and third time slots are SBFD time slots modified to support frequency duplexing of simultaneous uplink and downlink transmissions. The first and fourth time slots can be retained as traditional time division duplex (TDD) time slots, so that the first time slot is still dedicated to the downlink and the fourth time slot is dedicated to the uplink. However, it should be understood that in alternative embodiments, any time slot can be used in the SBFD mode.

[0033] In the spectrum below 6 GHz, if the mobile phone performs both uplink and downlink transmissions, the relatively limited spacing between the antennas on the mobile phone will generally lead to significant self-interference. The frequency duplexing in the SBFD time slots disclosed herein is therefore implemented only by the base transceiver station (gNB) in some embodiments. In particular, the antenna array for the gNB is subdivided into a first antenna array, which is separated from the second antenna array by an isolation distance such as 10 to 30 cm as an example. During SBFD operation, one antenna array transmits while the other antenna array receives. The self-interference problem is partially solved by the physical spacing between the arrays. To provide additional isolation, conductive shielding can also be implemented between the arrays. However, it should be understood that frequency duplexing can also be implemented by the mobile phone (or more generally, the user equipment (UE)) if the mobile phone implements sufficient self-interference cancellation. However, in other embodiments, the UE is limited to half-duplex transmission, so that the antenna array of the UE is fully dedicated to only transmitting or only receiving in each time slot.

[0034] Example time slot formats for conventional TDD and SBFD communications are given in Figure 1B. The first time slot (SLOT 1) is a traditional TDD time slot dedicated to downlink (DL) transmission. The first time slot can therefore be designated as a DL TDD time slot. It should be understood that DL transmissions can be divided into data and control transmission channels as known in the 5G NR field. Both arrays (array 1 and array 2) in the gNB are used for downlink transmission (Tx (DL)) of SLOT 1. Similarly, both arrays are used to receive uplink transmissions in the fourth time slot (SLOT 4). In the first time slot and the fourth time slot, the transmitted signal can occupy the entirety (or some part) of the time slot frequency band. The second and third time slots (SLOT 2 and SLOT 3) are SBFD time slots. The first antenna array is therefore dedicated to downlink transmission of the SBFD time slot, while the second antenna array is dedicated to uplink reception (Rx (UL)). Note that neither UL nor DL ​​in the SBFD time slot can occupy the entire frequency resource range (frequency band) of these time slots. Instead, the UL occupies the center subband in the frequency band of the SBFD time slot. DL therefore occupies a lower subband ranging from the lower frequency of the frequency band to the lowest frequency of the UL center subband. However, it should be understood that the subbands may be separated by guard bands. DL also occupies an upper subband in the frequency band and extends from the maximum frequency of the UL center subband to the maximum frequency of the frequency band. This is advantageous as will be further explained herein with respect to minimizing or reducing UE-to-UE interference and transmission-to-reception self-interference at the base station. In one embodiment, the UL center subband may be symmetrical about the center frequency of the SBFD time slot. In such an embodiment, the bandwidth of the DL lower subband and the bandwidth of the DL upper subband will be equal. However, in an alternative embodiment, the DL lower subband bandwidth may be different from the bandwidth of the DL upper subband. In some embodiments, the DL upper subband and the DL lower subband may each have a bandwidth that may vary to 10 MHz / 20 MHz / 30 MHz or 40 MHz depending on the downlink data rate.

[0035] Figure 2 An example base station (gNB) 200 in a cell is shown in FIG. In this embodiment, the UEs are as described in Figure 1BThe half-duplex discussed is such that in any given SBFD time slot, one or more user equipments (UEs) 210 (in a particular SBFD time slot) are dedicated to sending UL signals to the base station 200. Similarly, another group or more UEs 205 are dedicated to receiving DL signals from the base station 200 in that SBFD time slot. Note that the UE 205 can act as the UE 210 in other SBFD time slots. Similarly, the UE 210 can act as the UE 205 in other SBFD time slots. The base station 200 sends a downlink symbol (e.g., OFDMA symbol) to each DL UE 205 in the SBFD time slot. Therefore, if the UL UE 210 uses the same central subband as used for downlink transmission to the DL UE 205, there is a possibility of SBFD UE-to-UE interference. For example, assume that the frequency band of the SBFD time slot (time slot frequency resource range) is 100 MHz. Depending on the uplink bandwidth requirements, in some embodiments, the uplink bandwidth may be adjusted from 5 MHz to 10 MHz (or to 20 MHz).

[0036] These uplink transmissions have the potential for substantial SBFD UE-to-UE interference. For example, assume that UL UE 210 is only 1 meter away from DL UE 205. The free space path loss in the 3.5 GHz spectrum for this separation is approximately 43 dB. Since the center frequency of the carrier bandwidth is shifted to DC (0 Hz) when the received signal at DL UE 205 is down-converted to baseband, the receive RF chain in DL UE 205 can utilize adaptive high-pass filtering to resolve interference from UL UE 210. Similarly, UL UE 210 can use an adaptive center frequency to keep UL transmissions centered at DC within the carrier bandwidth.

[0037] With respect to the center frequency below 6 GHz of the carrier, the bandwidth of the upper and lower subbands used for DL ​​transmission from the base station 200 depends on the bandwidth of the center subband of the UL UE 210. For example, assume that the bandwidth of the center subband is 20 MHz. If the SBFD slot bandwidth is 100 MHz, the lower subband occupies a bandwidth from the center frequency minus 10 MHz to the center frequency minus 50 MHz. Similarly, the upper subband occupies a bandwidth from the center frequency plus 10 MHz to the center frequency plus 50 MHz. The DL UE 205 can therefore apply a high pass filter 206 to select DL symbols and exclude UL interference from the UE 210 after the received RF signal is down-converted to the baseband. More generally, the DL UE 205 can use adaptive filtering (high pass, low pass, or complex filtering) to exclude interference from the UL UE 210. For example, instead of transmitting in the center subband, each UL UE 210 can be configured to utilize the lower half of the bandwidth of the SBFD slot. The base station 200 then uses the upper half of the bandwidth of the SBFD slot for DL ​​symbols. In such an embodiment, each DL UE 205 can apply a complex filter 207 to select the upper half of the carrier bandwidth and exclude interference from the UL UE 210. The base station filtering will then be symmetrical so that the lower half of the carrier bandwidth is selected in such a complex filtering implementation.

[0038] The elimination or reduction of SBFD UE-to-UE interference can utilize the existing 3GPP framework to perform UE-to-UE cross-link interference (CLI) measurements to determine the presence of blocked or interfering UEs (such as UL UE 210). For example, each DL UE 205 can be configured with one or more sounding reference signal (SRS) resources, such as time-frequency resources, sequences, cyclic shifts, periodicity, etc., to measure UE-to-UE CLI. With respect to such measurements, SRS-reference signal received power (SRS-RSRP) and received signal strength indicator (RSSI) can be used as metrics for CLI measurements. SRS-RSRP is the linear average of the power contribution of the SRS to be measured on the configured resource elements within the considered measurement frequency bandwidth in the timer resources in the configured measurement opportunity. RSSI is the linear average of the total received power in only certain symbols (e.g., OFDM symbols) of the measurement time resources, in the measurement bandwidth, and on the configured resource elements for CLI measurements performed by the UE.

[0039] By using the measured CLI to establish SBFD UE-to-UE interference, downlink transmissions may be shifted to different subband frequencies to better match filtering in the DL UE 205 with interference symbols from the UL UE 210. Alternatively, the DL UE 205 may use more than one receive RF chain to recover different resource elements in various frequencies of the DL transmission. Thus, one receive RF chain may focus on certain resource blocks for DL ​​transmission, while another receive RF chain may focus on the remaining resource blocks to improve baseband filtering in the DL UE 205 and increase the exclusion of interfering UL transmissions. If the DL UE 205 is configured with knowledge of the direction to the interfering UL UE 210, the DL UE 205 may utilize spatial filtering techniques (e.g., minimum mean square error spatial filtering or similar methods) using multiple receive antennas. In addition, the DL UE 205 may also be configured to send a message to the base station 200 regarding the detection of the CLI. The base station 200 may then instruct the interfering UL UE 210 to resolve the interference by reducing the transmit power of the interfering UL UE 210 or applying a transmit spatial null in the direction of the interfered DL UE 210. In addition, the interfering UL UE 210 may be instructed to use a different time division multiplexing or frequency division multiplexing pattern to minimize CLI.

[0040] The base station 200 transmits downlink symbols through a beamforming transmit antenna array 215. Beamforming can be fully analog, fully digital, or hybrid in the base station 200 and in the UE. This article will assume the use of hybrid beamforming because it effectively utilizes the limited number of baseband to RF transmit chains in the base station 200. For clarity of illustration, a single transmit RF chain 220 is shown. Each transmit RF chain 220 includes one or more mixers (not shown) for up-converting the corresponding baseband signal to RF. The baseband modem 225 includes a baseband transmitter (BB Tx) for generating a baseband signal for each transmit RF chain. Digital beamforming weights 236 are applied to the baseband signal before analog conversion in a digital-to-analog converter (DAC) 230. The baseband signal can also be pre-distorted according to a digital pre-distortion (DPD) 237 before analog conversion to correct nonlinearities in the transmit RF chain 220. The analog signal from the DAC 230 is filtered by a high pass filter 235 before being phased by a phase shifter 240 to perform RF beamforming (RF BF). The filtering 235 may be adaptive to minimize interference to simultaneous uplink transmissions from the UL UE 210. Referring again to Figure 1B, the subband allocation of the SBFD time slots (SLOT 2 and SLOT 3) can be changed so that UL transmissions will occupy the lower and upper subbands, while DL transmissions will occupy the center subband. In such an implementation, the filter 235 in the transmit RF chain 220 can be a high pass filter, while the filter 265 in the receive RF chain 250 can be a low pass filter.

[0041] In the base station 200, each transmit RF chain 220 drives a corresponding antenna subarray within the transmit antenna array 215 (discussed further below). Therefore, in a multiple-input multiple-output (MIMO) manner, one transmit RF chain 220 and the corresponding antenna subarray can beamform the first DL UE 205, while another transmit RF chain and the corresponding antenna subarray can beamform the second DL UE 205. Given the number of antennas that can be utilized in the base station 200, the resulting MIMO can be expressed as a large-scale MIMO. In some embodiments, each individual antenna includes a first polarization port and a second polarization port. In a horizontal / vertical polarization embodiment, the first polarization port can be a vertical polarization port, and the second polarization port can be a horizontal polarization port. Alternatively, the first polarization port can be a positive 45 degree (+45°) polarization port, and the second polarization port can be a negative 45 degree (-45°) polarization port.

[0042] The base station 200 receives UL signals through a receive antenna array (RX array) 245. Similar to the transmit RF chain, the base station 200 includes a plurality of receive RF chains 250. Each receive RF chain 250 is used to down-convert the received RF signal from its corresponding antenna subarray in the receive antenna array 245 from RF to baseband. For clarity of illustration, Figure 2Only a single receive RF chain 250 is shown in FIG. In a massive MIMO approach, each receive RF chain 250 and corresponding antenna subarray may be beamformed to receive UL transmissions from a corresponding one of the UL UEs 210. The phase shifter 255 phase shifts the received RF signal to perform analog beamforming (RFBF). To address self-interference, an analog interference cancellation circuit 260 may be included to subtract the interfering downlink component from the analog phase-shifted RF signal from the phase shifter 255. The low-pass filter 265 low-pass filters the analog phase-shifted RF signal to select for uplink transmission. The analog-to-digital converter (ADC) 270 converts the filtered RF signal from the low-pass filter 265 to form a received baseband signal adjusted according to the digital beamforming weights 275. Self-interference from downlink transmissions and from interfering neighboring base stations 285 or clutter echoes from nearby scatterers 290 may be addressed at baseband by linear interference cancellation (LIC) and / or nonlinear interference cancellation (NLIC) techniques 280. In addition, clutter from scatterers 290 and interference from neighboring base stations 285 may be reduced by beamforming at base station 200. Due to the combination of isolation between receive array 245 and transmit array 215, isolation of received DL signals using low pass filter 265, and interference cancellation 280, reception of the UL at base station 200 may result in a relatively small and acceptable amount of desense. In alternative implementations, the target isolation may be greater or less than 80 dB.

[0043] Figure 3 The example base station 300 is shown in more detail in FIG. The base station 300 includes a plurality of RF chains from the 0th RF chain 305 to the Nth RF chain 305, which is (N+1), where N is a positive integer. Each RF chain 305 includes a plurality of RF chains such as for Figure 2The transmit RF chain and receive RF chain discussed. The base station 300 also includes a first antenna array 315 and a second antenna array 320. Depending on whether the TDD time slot is dedicated to the uplink or the downlink, both the arrays 315 and 320 can be dedicated accordingly. Therefore, for a dedicated downlink TDD time slot, both the first array 315 and the second array 320 can be used to send DL RF signals from the corresponding transmit RF chain. Similarly, for a dedicated uplink TDD time slot, both the first array 315 and the second array 320 can be used to receive UL RF signals. However, the functions of the first array 315 and the second array 320 are bifurcated for the SBFD time slot. For example, the first array 315 can then be dedicated to transmission (TX), while the second array 320 can be dedicated to reception (RX). Although the first array 315 can be used as a receive array in a TDD UL time slot, it is also represented as a transmit array 315 in this article because this is its function during the SBFD time slot. Similarly, although the second array 320 can be used as a transmit array in a TDD DL timeslot, it is also denoted herein as a receive array 320 because this is its function in an SBFD timeslot. To accommodate TDD and SBFD operation, each RF chain is switched via an RF switch 325. In a TDD timeslot, the first throw of each RF switch 325 selects the corresponding TDD transmit channel or path 330. However, in an SBFD timeslot, the second throw of each RF switch 325 selects the corresponding SBFD receive channel or path 351 or SBFD transmit channel or path 350. Note that the 2:1 splitter / combiner 335 is used in Figure 3 305 as separating and combining the corresponding SBFD receive channel 351 and SBFD transmit channel 350. However, it should be understood that each splitter / combiner 335 is conceptual because each transmit RF chain and receive RF chain has its own RF switch 325. Therefore, the second throw of each RF switch 325 of the receive RF chain selects the corresponding SBFD receive channel 351. Similarly, the second throw of each RF switch 325 of the transmit RF chain selects the corresponding SBFD transmit channel 350. Since each RF chain 305 includes a separate transmit RF chain and a separate receive RF chain, each RF chain 305 actually has two RF switches 325, which are shown in FIG. 305 for clarity of illustration. Figure 3 Only one of each RF chain 305 is shown.

[0044] The ability to select between SBFD and TDD operation raises the following question. During TDD operation, each RF chain 305 corresponds to a TDD subarray in one of the first array 315 and the second array 320. For example, in a UL TDD time slot, only the transmit RF chain in a given RF chain 305 is active, while the corresponding receive RF chain is inactive. Conversely, in a DL TDD time slot, only the receive RF chain in a given RF chain 305 is active, while the corresponding transmit RF chain is inactive. For example, the 0th RF chain 305 is active in a TDD time slot to transmit or receive through the corresponding TDD subarray 332. Since there are (N+1) RF chains, there are (N+1) corresponding TDD subarrays 332 on the transmit array 315 and the receive array 320. If the RF chains use the same TDD subarray allocation in the SBFD time slot as used during TDD operation, only half of the transmit RF chains will transmit on the transmit array 315, while half of the receive RF chains will receive on the receive array 320. Therefore, in such an RF chain configuration, there is a 3 dB power loss in both transmission and reception. To prevent this power loss, the correspondence of RF chains to subarrays is changed for SBFD operation so that all transmit RF chains can transmit through the TX array 315 and all receive RF chains can receive through the RX array 320. Each TDD subarray 332 of the antenna is divided into a first SBFD antenna subarray 333 and a second SBFD antenna subarray 334. Since there are (N+1) / 2 TDD subarrays 332 in the transmit array 315, there are a total of (N+1) / 2 first SBFD subarrays 333 and (N+1) / 2 second SBFD subarrays 334 in the transmit array 315. Therefore, half of the transmit RF chains can be transmitted on a one-to-one basis through the corresponding first SBFD subarray 333 in the transmit array 315. Similarly, the remaining half of the transmit RF chains can be allocated on a one-to-one basis for transmission through the corresponding second SBFD subarray 334 in the transmit array 315. Therefore, there is no 3 dB loss in transmitting UL in the SBFD time slot. Receiving the DL is similar: half of the RF chains can each receive from the corresponding first subarray 333 in the receive array 320 on a one-to-one basis. Similarly, the remaining half of the RF chains can each receive from the corresponding second subarray 334 in the receive array 320 on a one-to-one basis. Therefore, there is no 3 dB loss in receiving the UL in the SBFD timeslot. The operation of the base station 300 during the SBFD timeslot is also referred to herein as the SBFD operation mode, and the operation in the TDD timeslot is also referred to herein as the TDD operation mode.

[0045] Since each RF chain 305 corresponds to an SBFD subarray (333 or 334) in the transmit array 315 and there are (N+1) RF chains, the transmit array 315 is formed by (N+1) / 2 first SBFD subarrays 333 and (N+1) / 2 second SBFD subarrays 334. Similarly, there are (N+1) / 2 first SBFD subarrays 333 and (N+1) / 2 second subarrays 334 in the receive array 320. As mentioned above, for the sake of clarity, Figure 3 Only a single RF switch 325 is shown for each RF chain 305. The RF switch 325 of a receive RF chain may thus select the receive SBBD channel 351. Conversely, the RF switch 325 of a transmit RF chain may select the transmit SBFD channel 350.

[0046] During TDD operation, the first array 315 and the second array 320 are used together for uplink or downlink. Each RF switch 325 then selects the corresponding TDD channel 330. Since there are (N+1) RF chains, for TDD operation, there are (N+1) / 2 corresponding TDD sub-arrays 332 in the first array 315 and (N+1) / 2 TDD sub-arrays 332 in the second array 320. In the base station 300, each TDD sub-array 332 includes eight antennas, but it should be understood that in alternative embodiments, the number of antennas in each TDD sub-array 332 can be greater or less than eight. During TDD downlink operation in a TDD DL time slot, the transmit RF signal on the TDD channel 330 of each transmit RF chain is separated by a 2:1 splitter / combiner 340 that drives two RF switches 345. Similar to the RF switch 325, one throw of each RF switch 345 selects the corresponding TDD channel 330, while the other throw of each RF switch 345 selects the corresponding SBFD channel. In particular, each RF switch 345 of the transmit array 315 may select to transmit the SBFD channel 350 during the SBFD time slot. Similarly, each RF switch 345 of the receive array 320 may select to receive the SBFD channel 351 during the SBFD time slot.

[0047] The base station 300 is configured for 4:1 hybrid beamforming. The number of RF chains (and corresponding digital paths in the baseband modem 301) is then one-fourth the total number of antennas in the combination of the TX array 315 and the RX array 320. Each SBFD subarray 333 or 334 has four antennas so that each subarray 333 or 334 receives the same beamforming. Therefore, each subarray 333 or 334 has a phase shifter 355. Each phase shifter 355 is connected to a corresponding transmit / receive RF switch 360. If the subarray 333 or 334 is transmitting, the corresponding transmit / receive RF switch 360 selects the input of the corresponding power amplifier 365. Conversely, if the subarray 333 or 334 is receiving, the corresponding transmit / receive RF switch 360 selects the output of the low noise amplifier (LNA) 370. Each power amplifier / LNA pair is also connected to another transmit / receive RF switch 375. During transmission, each transmit / receive RF switch 375 connects the output of the corresponding power amplifier 365 to the bandpass filter 380 to drive the corresponding sub-array 333 or 334 through the 4:1 splitter / combiner 385. In the receive mode, the splitter / combiner 385 combines the received RF signals from the corresponding sub-array 333 or 334. The combined received RF signal is then filtered by the bandpass filter 380, switched by the transmit / receive switch 375, amplified by the corresponding low noise amplifier 370, switched by the transmit / receive switch 360, and phase shifted in the phase shifter 355 according to the corresponding analog beamforming weight. The path of the signal received from the phase shifter 355 depends on whether the TDD or SBFD mode is active. In the TDD mode, the RF switch 345 selects the splitter / combiner 340 so that the received RF signal for the TDD sub-array can be formed. From the splitter / combiner 340, the combined received RF signal then propagates over the TDD channel 330 and passes through the RF switch 325 so that it can be processed in the corresponding receive RF chain. In the SBFD mode, the RF switch 345 (for the subarray 333 or 334 in the receive array 320) selects the receive SBFD channel 351 so that the received RF signal can propagate through the corresponding RF switch 325 and be received in the corresponding receive RF chain.

[0048] The transmit RF chain in each RF chain 305 receives a digital baseband signal from the baseband modem 301, which is up-converted to a corresponding RF transmit signal. Similarly, the receive RF chain in each RF chain 305 down-converts the received RF signal to provide a corresponding digital baseband signal to the baseband modem 301. Referring again to Figure 2 , the example receive RF chain 250 includes a low pass filter 265 so that DL signals in the lower and upper sub-bands can be filtered out, as described with respect to Figure 1BSpecifically, the center frequency (or approximate center frequency) of the UL center or middle sub-band is down-converted to DC by the receive RF chain 250. The down-converted DL signals from the upper and lower sub-bands are therefore relatively high frequency signals compared to the down-converted UL signals, so that the low pass filter 265 can pass the down-converted UL signals and block the down-converted DL signals. Again, referring to Figure 3 , additional filtering may be further performed in the digital domain using, for example, programmable digital filters in the baseband modem 301 to achieve this spacing between the UL and DL signals. The baseband modem 301 controls the various RF switches through a mode controller interface. In addition, the baseband modem 301 controls the phase shifter 355 using a hybrid beamforming (HBF) control interface.

[0049] It should be appreciated that the 4:1 hybrid beamforming discussed with respect to base station 300 may be modified in alternative embodiments. For example, Figure 4A The base station 400 shown in has full hybrid beamforming. In the absence of any signal combination, there will be a one-to-one correspondence between each RF chain and the corresponding antenna element. This one-to-one correspondence can then lead to an excessive number of RF chains (and the corresponding digital paths in the baseband modem 301). In order to reduce complexity, each RF chain 305 can be associated with a 4:1 splitter / combiner 405. The transmit RF chain portion of the RF chain 305 generates a transmit RF signal, which is divided into four paths by the corresponding 4:1 splitter / combiner 405 to drive four corresponding antenna elements. Each splitter / combiner 405 is also used to combine four received RF signals from four corresponding antenna elements to produce a combined received RF signal that is ultimately received by the corresponding receive RF chain. Therefore, through 4:1 separation and combination, there is a 4:1 reduction from the number of antenna elements to the number of RF chains 305.

[0050] Since the beamforming is 1:1, each individual antenna element has a phase shifter 355. The combination of phase shifter 355, RF switch 360, amplifiers 365 and 370, and bandpass filter 380 is repeated four times for each corresponding 4:1 splitter / combiner 405. For clarity of illustration, only one of the four combinations of these elements is shown for each 4:1 splitter / combiner 405. Each 4:1 splitter / combiner 405 is between the corresponding RF switch 345 and the corresponding phase shifter 355 (note that due to the 4:1 combination and 1:4 separation of the 4:1 splitter / combiner 405, there are actually four corresponding phase shifters 355). In the transmit mode, each 4:1 splitter / combiner 405 is used to separate the transmit RF signal from the corresponding RF switch 345 into four separate transmit RF signals. In the receive mode, each 4:1 splitter / combiner 405 is used to combine the four receive RF signals from the corresponding group of four phase shifters 355 into a combined RF receive signal. The remaining components are as discussed with respect to base station 300. It should be understood that the number of phase shifters 355 in each group in base station 400 depends on the number of antennas in each SBFD subarray. In alternative embodiments, this number can be greater or less than four. The number of antennas in each SBFD subarray determines the number of phase shifters 355 and the order of splitters / combiners 405.

[0051] As the number of antennas increases, full beamforming with some combining as discussed for base station 400, or even 4:1 beamforming without combining as discussed for base station 300, can result in an excessive number of RF chains and corresponding digital paths at baseband modem 301. However, in massive MIMO it is advantageous to have a relatively large number of antennas so that multiple users can be supported, with each user being supported by a corresponding portion of the antenna. As the number of antennas increases, the number of users supported can increase accordingly. In order to provide a relatively large number of antennas in both arrays, Figure 4B4 shows a base station 450 with R:1 combining and N:1 beamforming, where R and N are each positive integers. Therefore, for the base station 450, the reduction from the number of antenna elements to the number of RF chains is a factor of (R*N). The base station 450 includes a top array 405 of antennas, which is used as a receive array 405 in SBFD operation, but can be used as a transmit or receive in TDD operation. Similarly, the bottom array 410 of antennas is used as a transmit array in SBFD operation, but can be used as a transmit or receive in TDD operation. For clarity of illustration, only a single instance of channel 0 (CH0) is shown in the top array 405, but it should be understood that due to 1:R separation and R:1 combining, channel 0 can be instantiated R times. Each instantiation of channel 0 has a first antenna subarray 415 and a second antenna subarray 420. Each subarray 415 and 420 includes a plurality of antennas of N, which are coupled to channel 0 through a corresponding N:1 combiner / splitter 425. After filtering in the corresponding bandpass filter 430, the received and combined RF signal from the subarray 415 or 420 may be switched to the corresponding low noise amplifier 440 through the circulator 435 and the associated switch. The resulting amplified received RF signal may then be phase shifted in the corresponding phase shifter 450 before being attenuated in the digital attenuator and amplified again. Since there are R instantiations of channel 0, there are R resulting RF signals that may be combined in the corresponding splitter / combiner 455. During the DL TDD mode of operation, the received RF signals from the subarrays 415 and 420 are combined in the 2:1 combiner 460 and shifted through the RF switch 465 to the receive RF chain portion of the RF chain 470, which also includes the transmit RF chain.

[0052] Each RF switch 465 has two throws. The first throw selects a TDD path such as just discussed. In the second throw, each RF switch 465 selects a SBFD path. During the SBFD time slot, the receive RF chain in the RF chain 470 receives an RF signal from the subarray 420 due to routing through the corresponding RF switches 445 and 465. In the SBFD time slot, the received RF signal from the subarray 415 passes through the corresponding RF switch 445 and the corresponding RF switch 465 to be received by the receive RF chain in the RF chain 475. With respect to the antenna subarray 485 and the antenna subarray 490, a similar separation of the TDD subarray occurs in the TX array 410. During the ULTDD time slot, the transmit RF chain in the RF chain 475 is driven by the corresponding switch 465 and the 2:1 splitter 460 to jointly drive both the subarrays 485 and 490 as a single TDD subarray. During transmission, each transmit RF signal is amplified by a plurality of amplifiers 441. In SPFD operation, RF chain 470 drives subarray 490, while RF chain 475 drives subarray 485. More generally, all transmit RF chains drive corresponding subarrays in TX array 410, while all receive RF chains receive from corresponding subarrays in RX array 405 during SBFD operation to prevent a 3 dB power loss.

[0053] To provide feedback information about signal strength during transmission and also support digital pre-distortion, each subarray 415, 420, 485 and 490 is associated with a respective transmit feedback circuit (TX fdbk) 491 that samples the transmitted signal strength. The resulting feedback information can then be routed to the receive RF chain through respective switches 445 and 465 so that the transmitted signal strength can be determined.

[0054] In base stations 300, 400, and 450, a plurality of RF switches such as switches 325, 345, 465, and 480 may be represented as a switch array configured to change the mapping from the baseband path in mode 301 to a given subarray of antennas depending on whether the timeslot is a TDD timeslot or a SBFD timeslot. It should be appreciated that the switch matrix may alternatively be implemented in the digital domain rather than the RF domain to provide this subarray mapping capability.

[0055] An example transmit antenna array and an example receive antenna array will now be discussed in more detail. Figure 2As discussed, it is proposed that 80 dB or greater isolation between the two arrays is sufficient for successful SBFD operation. Each antenna array may be arranged in terms of rows and columns. The following discussion will assume that each antenna is a patch antenna, but it will be appreciated that other antenna topologies such as dipole antennas or fractal antennas may be used in alternative embodiments. Similarly, the following discussion will assume that the transmit array and the receive array are each planar arrays that are coplanar with each other, but such coplanarity may be destroyed in alternative embodiments.

[0056] Some example coplanar embodiments are Figure 5 , where the antenna elements are arranged in rows and columns. In the first row-based embodiment 505, the rows are longer than the columns, while in the second column-based embodiment 510, the columns are longer than the rows. Regardless of the array orientation, there is a minimum spacing D that separates the receive array and the transmit array. In a row-based arrangement such as the first arrangement 505, the minimum spacing is between the center of the patch antenna in the bottom row of the upper transmit array (Panel #1 (Tx)) and the center of the corresponding patch antenna in the upper row of the lower receive array (Panel #2 (Rx)). In a column-based arrangement such as the second arrangement 510, the minimum spacing is from the center of the patch antenna in the last column in the transmit array to the center of the corresponding patch antenna in the first column in the receive array. To address the gain loss caused by limiting the transmission and reception to individual arrays rather than using the entire array as is conventional in TDD operation, the spacing of the antenna elements in the row and column directions can be greater than half a wavelength of the desired spectrum.

[0057] The physical spacing D can become impractically large to provide the required 80 dB or greater isolation between the transmit and receive arrays alone. For example, at 3.5 GHz, the physical spacing D requires 70 meters to provide 80 dB of isolation. Since such a physical spacing is difficult to achieve in any real-world base station, this article proposes to use a significantly smaller spacing of at least 20 centimeters (such as 21.5 centimeters). This spacing provides approximately 45 dB of isolation in a cross-polarized transmit-to-receive configuration. For example, the transmit array can be horizontally polarized and the receive array can be vertically polarized. Alternatively, the receive array can have a positive 45 degree polarization (P45) and the transmit array can have a negative 45 degree polarization (N45). In order to achieve the required isolation, such as 80 dB, one or more conductive isolation enhancers are placed between the transmit and receive arrays. Figure 6An example configuration with conductive isolation enhancers is shown in FIG. The TX and RX arrays are row-oriented, so the conductive isolation enhancers 605 and the conductive isolation enhancers are both oriented in the row direction in the space between the two coplanar arrays. The conductive isolation enhancers 610 are adjacent to the last row of antennas in the TX array, while the conductive isolation enhancers 605 are adjacent to the first row of antennas in the RX array.

[0058] The isolation enhancer 610 and a portion of 610 are Figure 7 610 is shown in perspective view. Each isolation enhancer has a U-shaped cross-section. For example, isolation enhancer 605 has a first side 615 of the U-shape extending from the first row of the RX array. For clarity of illustration, the RX array is represented by a single patch antenna. The first side 615 is coplanar with the RX array and extends to a bottom portion 620 of the U-shape extending perpendicular or orthogonal to the plane defined by the RX array (and by the TX array). The second side 625 of the U-shape is arranged parallel to the first side 615 and extends from the bottom portion 620 toward the RX array. The result is that the U-shape is open to the RX array. The isolation enhancer 610 for the TX array is arranged similarly, but its U-shape is open toward the TX array. To enhance isolation, the patch antennas in the RX and TX arrays are arranged to be + / -45° polarized. In alternative embodiments, one of the isolation enhancers may be omitted. Similarly, in some embodiments, each isolation enhancer may be replaced by multiple isolation enhancers. Alternatively, the U-shape of each isolation enhancer may face the same array, such as Figure 8 The width W and height H of each isolation booster are approximately one quarter wavelength of the center frequency in the desired spectrum (e.g., 3.5 GHz). To enhance isolation, the patch antennas in the RX and TX arrays are arranged with + / -45° polarization.

[0059] The similar width W and height H of the RX array isolation enhancer 905 and the TX array isolation enhancer 910 can be obtained by Fig. 9 Each isolation enhancer 905 and 910 has a planar bottom portion 915 similar to the bottom portion 620. However, the upper portion 920 does not protrude perpendicularly from the planar bottom portion, but is at an acute angle to the plane defined by the planar bottom portion 915. The resulting acute angle can vary depending on the implementation, but in one example can be about 45 degrees.

[0060] Now about Fig.10The flowchart of discusses a method of operation of an SBFD base station. The method includes action 1000, which occurs during a downlink time division duplex (DL TDD) time slot and includes using a first RF chain to upconvert a first baseband signal to form a first DL radio frequency (RF) signal, and transmitting the first DL RF signal from a first antenna subarray and from a second antenna subarray, the first DL RF signal occupying a frequency band. DL TDD transmission on a TDD subarray such as TDD subarray 332 is an example of action 1000. The method also includes action 1005, which occurs during an uplink (UL) TDD time slot and includes receiving a first UL RF signal using a first antenna subarray and a second antenna subarray, and using the first RF chain to downconvert the first UL RF signal to form a second baseband signal, the first UL RF signal occupying a frequency band. Receiving a UL TDD RF signal on a TDD subarray such as TDD subarray 332 is an example of action 1005. Finally, the method includes act 1010, which occurs during the first sub-band full-duplex time slot and includes up-converting the third baseband signal using the first RF chain to form a second DL RF signal and transmitting the second DL RF signal from only the first antenna subarray, the second DL RF signal occupying a lower sub-band and an upper sub-band in the frequency band, the lower sub-band being separated in frequency from the upper sub-band by a center sub-band in the frequency band. Transmission of the UL SBFD RF signal on a single SBFD subarray, such as one of the SBFD subarrays 333 or 334, is an example of act 1010.

[0061] It should be understood that many modifications, substitutions and changes may be made to the materials, devices, configurations and methods of use of the equipment of the present disclosure without departing from the scope of the present disclosure. In view of this, because the specific embodiments shown and described herein are only some examples thereof, the scope of the present disclosure should not be limited to the scope of the specific embodiments shown and described herein, but should be fully matched with the scope of the claims attached below and their functional equivalents.

Claims

1. A base station, comprising: The first antenna array is organized into a plurality of first sub-band full-duplex SBFD antenna sub-arrays; a second antenna array organized into a plurality of second SBFD antenna subarrays; a plurality of transmit RF chains, each transmit RF chain being configured to convert a baseband signal into an RF transmit signal, wherein the plurality of transmit RF chains have a one-to-one correspondence with the plurality of first SBFD antenna subarrays; a plurality of receive RF chains, each receive RF chain being configured to convert a receive RF signal into a baseband signal, wherein the plurality of receive RF chains have a one-to-one correspondence with the plurality of second SBFD antenna subarrays; and A plurality of switches having a first configuration for an SBFD mode of operation in which each transmit RF chain is configured to drive a corresponding first SBFD antenna subarray with an RF transmit signal of the transmit RF chain, and in which each receive RF chain is configured to receive a receive RF signal of the receive RF chain from a corresponding second SBFD subarray.

2. The base station according to claim 1, wherein: The first antenna array and the second antenna array are also arranged into a plurality of time division duplexing TDD antenna subarrays having a one-to-one correspondence with the plurality of transmit RF chains, and wherein the plurality of switches have a second configuration for a transmit TDD operation mode, in which each transmit RF chain is configured to drive a corresponding TDD subarray using an RF transmit signal of the transmit RF chain.

3. The base station according to claim 2, wherein: The multiple TDD antenna subarrays have a one-to-one correspondence with the multiple receive RF chains, and wherein the multiple switches have a third configuration for a receive TDD operation mode, in which each receive RF chain is configured to receive a receive RF signal of the receive RF chain from a corresponding TDD subarray.

4. The base station according to claim 2, wherein: Each of the first SBFD antenna subarrays and each of the second SBFD antenna subarrays includes four antennas.

5. The base station according to claim 4, wherein: Each TDD antenna subarray includes eight antennas.

6. The base station according to claim 3, wherein: The base station is also configured for M:1 hybrid beamforming, where M is a positive integer.

7. The base station according to claim 6, wherein: M is equal to 4.

8. The base station according to claim 3, wherein: The base station is also configured for full hybrid beamforming.

9. A base station, comprising: A first transmit RF chain; A first antenna array includes a first sub-band full-duplex SBFD antenna subarray and a second SBFD antenna subarray; a first RF signal splitter and combiner; as well as A switch array is configured to couple the transmit RF chain to both the first SBFD antenna subarray and the second SBFD antenna subarray through the first RF signal splitter and combiner in a downlink time division duplex (DL) TDD operation mode, and the switch array is also configured to couple the first transmit RF chain to the first SBFD antenna subarray without coupling to the second SBFD antenna subarray in an SBFD operation mode.

10. The base station according to claim 9, further comprising: a first receive RF chain; The second antenna array includes a third sub-band full-duplex SBFD antenna subarray and a fourth SBFD antenna subarray; and The switch array is further configured to couple both the first SBFD antenna subarray and the second SBFD antenna subarray to the first receive RF chain via the first RF signal separator and combiner during an uplink UL TDD operation mode, and the switch array is further configured to couple the first receive RF chain to the third SBFD antenna subarray during the SBFD operation mode.

11. The base station according to claim 10, further comprising: A second transmit RF chain; as well as a second receive RF chain; a second RF signal splitter and combiner; and The switch array is further configured to couple the second transmit RF chain to both the third SBFD antenna subarray and the fourth SBFD antenna subarray via the second RF signal separator and combiner in the DL TDD operation mode, and the switch array is further configured to couple the third SBFD antenna subarray and the fourth SBFD antenna subarray to the second receive RF chain via the second RF signal separator and combiner in the UL TDD operation mode.

12. The base station according to claim 11, wherein: The switch array is also configured to couple the second receive RF chain to the fourth SBFD antenna subarray during the SBFD mode of operation.

13. The base station according to claim 9, wherein: The first SBFD antenna subarray and the second SBFD antenna subarray each include a plurality of N antennas, where N is a positive integer, and the base station further includes: a first N:1 splitter and combiner configured to be coupled to the first SBFD antenna subarray; and The second N:1 splitter and combiner is configured to be coupled to the second SBFD antenna subarray.

14. The base station according to claim 11, wherein: The first antenna array is separated from the second antenna array by a spacing of at least 20 centimeters.

15. The base station according to claim 14, wherein: The first antenna array and the second antenna array are arranged in a plane, and the base station further includes: An isolation enhancer is located between the first antenna array and the second antenna array, the isolation enhancer including a conductive bottom portion coplanar within the plane and including a conductive planar upper portion protruding from the plane.

16. The base station according to claim 15, wherein: The planar upper portion protrudes vertically from the plane to define a height of the isolation enhancer that is approximately one-quarter of a wavelength of a center frequency of a transmit RF signal of the base station.

17. The base station according to claim 16, wherein: The bottom portion has a width of approximately one quarter of a wavelength of the center frequency.

18. The base station according to claim 15, wherein: The planar upper portion protrudes from the plane at an acute angle to define a height of the isolation enhancer that is approximately one-quarter of a wavelength of a center frequency of a transmit RF signal of the base station.

19. The base station according to claim 18, wherein: The bottom portion has a width of approximately one quarter of a wavelength of the center frequency.

20. A method for a base station, comprising: During a downlink time division duplex (DL) TDD time slot, upconverting a first baseband signal using a first RF chain to form a first DL radio frequency (RF) signal and transmitting the first DL RF signal from a first antenna subarray and from a second antenna subarray, the first DL RF signal occupying a frequency band; During an uplink UL TDD time slot, receiving a first UL RF signal using the first antenna subarray and the second antenna subarray, and down-converting the first UL RF signal using the first RF chain to form a second baseband signal, the first UL RF signal occupying the frequency band; and During a first sub-band full-duplex SBFD time slot, the first RF chain is used to up-convert a third baseband signal to form a second DL RF signal and the second DL RF signal is transmitted only from the first antenna subarray, the second DL RF signal occupying a lower sub-band and an upper sub-band in the frequency band, the lower sub-band being separated in frequency from the upper sub-band by a center sub-band in the frequency band.

21. The method according to claim 20, further comprising: During a second SBFD time slot, a second UL RF signal is received using the first antenna subarray and down-converted using the first RF chain to form a fourth baseband signal, the second UL RF signal occupying the center subband.

22. The method according to claim 21, further comprising: During the second SBFD time slot, a third UL RF signal is received using the second antenna subarray and down-converted using a second RF chain to form a fifth baseband signal, the third UL RF signal occupying the center subband.

23. The method according to claim 20, wherein: Transmitting the first DL RF signal from the first antenna subarray and from the second antenna subarray comprises: splitting the first DL RF signal in a splitter to form a plurality of RF signals, phase shifting each of the plurality of RF signals according to the beamforming command to form a plurality of phase-shifted RF signals; and The plurality of phase-shifted RF signals are distributed to the first antenna subarray and the second antenna subarray.

24. The method according to claim 21, wherein: Downconverting the second UL RF signal using the first RF chain to form the fourth baseband signal also includes low pass filtering the fourth baseband signal.

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