WO2017081522A1

WO2017081522A1 - Simultaneous vswr measurement and coupler calibration at multiple antenna ports

Info

Publication number: WO2017081522A1
Application number: PCT/IB2015/058800
Authority: WO
Inventors: Georgy LEVIN
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2015-11-13
Filing date: 2015-11-13
Publication date: 2017-05-18

Abstract

A method for a radio unit including a plurality of antenna ports configured to transmit a plurality of outbound transmit signals and at least one radio frequency combiner coupled to the plurality of antenna ports is provided. A plurality of incident signals are combined into a combined incident signal. A plurality of reflected signals are combined into a combined reflective signal. Individual incident signals are separated from the combined incident signal. Each separated individual incident signal is associated with a respective antenna port of the plurality of antenna ports. Individual reflected signals are separated from the combined reflected signal. Each separated individual reflected signal is associated with a respective antenna port of the plurality of antenna ports. A voltage standing wave ratio associated with each of the plurality of antenna ports is determined based at least in part on the separated individual incident and reflected signals.

Description

SIMULTANEOUS VSWR MEASUREMENT AND COUPLER CALIBRATION AT MULTIPLE ANTENNA PORTS

TECHNICAL FIELD

The present disclosure relates to multi-antenna base stations and/or radio units, and in particular to a method, radio unit and system for performing simultaneous measurements and calibrations at multiple antenna ports.

BACKGROUND

Wireless radio base stations typically use voltage standing wave ratio

(VSWR)/return loss (RL) measurements to supervise the integrity and connectivity of antennas and antenna feeder cables. A typical configuration of radio unit 10 for taking these measurements is illustrated in FIG. 1 in which respective incident (forward (F)) and reflected (R) signals are one by one fed back for VSWR/RL measurements. In particular, radio unit 10 includes one or more antenna transceiver units 12 for transmitting communication signals to and receiving communication signals from one or more antennas 14a-14d (collectively referred to as "antennas 14") via one or more antenna ports 15a-15d (collectively referred to as "antenna port 15"). Radio unit 10 includes switching unit 16 that is configured to switch individual incident and reflected signals associated with a respective antenna port 15 to measurement unit 18. In particular, switching unit 16 provides switchable feedback loops using multiple directional couplers 20a-20d (collectively referred to as directional coupler 20) for separating and providing incident (forward) and reflected signals, and a network of controllable switches 22a-22c (collectively referred to as switch 22) that are mounted on a radio base station circuit board in the field. In the embodiment illustrated in FIG. 1, N-l dual switches 22 with a control interface are required to individually select N antenna ports 15 for the case of four transmit radios. Each dual switch 22 includes two switches for individually switching incident

(forward) and reflected signals. For example, directional coupler 20a provides an incident signal to switch 22a that provides a switchable path to switch 22c that in turn provides the incident signal to measurement unit 18. A similar switchable path is also provided by switches 22a and 22c in order to feedback an individual reflected signal from port 15a. Therefore, one by one, an incident signal and a reflected signal associated with individual ports 15 are fed back to measurement unit 18 via a network of switches 22 in order to perform VSWR/RL measurements.

There are two main methods for measuring VSWR/RL: analog (scalar) and digital (vector). In the analog method, the incident power (Pine) and reflected power (Pref) at antenna port 15 are measured and the ratio Pinc/Pref is calculated. The RL and VSWR are then obtained according to the below equations:

The analog methods are usually narrow band, i.e., are performed over hundreds of kHz) and have limited accuracy due to directional coupler 20 's finite directivity and port impedance mismatch, i.e., due to the fact that any feasible coupler 20 cannot perfectly separate between incident and reflected signals, and non-zero cross-leakage is always present.

The digital methods are usually preferred when VSWR/RL has to be calculated over a wider band, and high accuracy is required. The digital methods utilize digital signal processing to first calculate complex reflection coefficients (RC) as the ratio of reflected and incident signals, and then to compensate the RC's for the coupler impairments. There are a number of digital methods for measuring

VSWR/RL, e.g., time domain reflectometry, frequency domain reflectometry, spread spectrum reflectometry and noise domain reflectometry. In particular, RL may be calculated from RC as follows:

Both analog and digital methods require directional coupler 20 calibration in production, which is accomplished by selecting individual antenna ports 15 via switching unit 16, and applying a known load to the selected antenna ports. The calibration parameters from the measurement are stored in production database and used during radio base station operation to compensate for coupler 20 impairments. Compared to analog methods, the digital methods are usually more accurate, but require longer measurement/calibration time.

However, as the number of radio base station antennas continues to increase, calibration of antennas 14 during production and measurement of antennas 14 in the field are becoming unacceptably long. Considering that VSWR/RL measurement and directional coupler 20 calibration is done separately at every antenna port using controllable switches 22, increasing the number of antennas/antenna ports also increases the amount of time needed to individually switching through each antenna port 15 for VSWR/RL measurement. Further, network operators require VSWR/RL measurements to be performed for every port, periodically within a predefined time period, irrespective of the number of antennas that has continued to increase.

Therefore, creating a switchable path from each antenna port 15 in FIG. 1 and performing VSWR/RL measurements must be accomplished within the strict time limits prescribed by network operators. This is a task that will become more and more difficult with the massive MIMO 5G systems. Moreover, the expense and complexity of providing and configuring multiple switches 22 on a radio base station board and providing a control system for individually switching each switch 22 will disadvantageously continue to increase as the number of antenna 14 increase. SUMMARY

The present disclosure advantageously provides a method, radio unit and system for performing simultaneous measurements and calibrations at multiple antenna ports.

In one embodiment of the disclosure, a radio unit is provided. The radio unit includes a plurality of antenna ports configured to transmit a plurality of outbound transmit signals. The radio unit includes at least one radio frequency, RF, combiner coupled to the plurality of antenna ports. The at least one RF combiner is configured to combine a plurality of incident signals associated with the plurality of outbound transmit signals into a combined incident signal, and combine a plurality of reflected signals associated with the plurality of outbound transmit signals into a combined reflective signal. The radio unit includes processing circuitry in communication with the at least one RF combiner. The processing circuitry includes a processor and a memory. The memory contains instructions that, when executed by the processor, configure the processor to: separate individual incident signals from the combined incident signal, separate individual reflected signals from the combined reflected signal, and determine a voltage standing wave ratio, VSWR, associated with each of the plurality of antenna ports based at least in part on the separated individual incident and reflected signals. Each separated individual incident signal is associated with a respective antenna port of the plurality of antenna ports. Each separated individual reflected signal is associated with a respective antenna port of the plurality of antenna ports.

According to one aspect of this embodiment, the memory contains further instructions that, when executed by the processor, cause the processor to: determine a degree of correlation between the plurality of outbound transmit signals, determine whether the degree of correlation is greater than a predetermined threshold, and in response to determining that the degree of correlation is greater than the

predetermined threshold, condition the plurality of outbound transmit signals to reduce the degree of correlation. According to another aspect of this embodiment, the conditioning includes one of: adding uncorrected pseudo-noise to the plurality of outbound transmit signals, dithering a phase of each of the plurality of outbound transmit signals, and whitening the plurality of outbound transmit signals.

According to another aspect of this embodiment, the memory further includes instructions that, when executed by the processor, cause the processor to capture a plurality of reference signals. The plurality of reference signals corresponds to the conditioned plurality of outbound transmit signals. The plurality of reference signals are used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal. According to another aspect of this embodiment, the radio unit includes a conditioning circuitry configured to condition the plurality of outbound transmit signals to reduce a degree of correlation of the plurality of outbound transmit signals. The memory contains further instructions that, when executed by the processor, cause the processor to: determine the degree of correlation between the plurality of outbound transmit signals, determine whether the degree of correlation is greater than a predetermined threshold, in response to determining the degree of correlation is greater than the predetermined threshold, cause the conditioning circuitry to condition the plurality of outbound transmit signals to reduce the degree of correlation.

According to another aspect of this embodiment, the memory contains further instructions that, when executed by the processor, cause the processor to: capture reference symbols associated with the plurality of outbound transmit signals. The captured reference symbols is used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal.

According to another aspect of this embodiment, the radio unit includes a plurality of directional couplers in communication with the at least one RF combiner and the plurality of antenna ports. The plurality of directional couplers are configured to provide the plurality of incident signals and plurality of reflected signals to the at least one RF combiner. According to another aspect of this embodiment, the at least one RF combiner includes a plurality of RF combiners in which each of the plurality of RF combiners are configured to output a respective combined incident signal and respective combined reflective signal. At least one RF combiner of the plurality of RF combiners is configured to receive a combined incident signal and combined reflective signal from at least two other RF combiners of the plurality of RF combiners. According to another aspect of this embodiment, the plurality of outbound transmit signals are a plurality of downlink transmit signals.

According to another embodiment of the disclosure, a method for a radio unit including a plurality of antenna ports configured to transmit a plurality of outbound transmit signals and at least one radio frequency, RF, combiner coupled to the plurality of antenna ports is provided. A plurality of incident signals associated with the plurality of outbound transmit signals are combined into a combined incident signal. A plurality of reflected signals associated with the plurality of outbound transmit signals are combined into a combined reflective signal. Individual incident signals are separated from the combined incident signal. Each separated individual incident signal is associated with a respective antenna port of the plurality of antenna ports. Individual reflected signals are separated from the combined reflected signal. Each separated individual reflected signal is associated with a respective antenna port of the plurality of antenna ports. A voltage standing wave ratio, VSWR, associated with each of the plurality of antenna ports is determined based at least in part on the separated individual incident and reflected signals.

According to another aspect of this embodiment, a degree of correlation between the plurality of outbound transmit signals is determined. A determination is made whether the degree of correlation is greater than a predetermined threshold. In response to determining that the degree of correlation is greater than the

predetermined threshold, the plurality of outbound transmit signals are conditioned to reduce the degree of correlation. According to another aspect of this embodiment, the conditioning includes one of: adding uncorrected pseudo-noise to the plurality of outbound transmit signals, dithering a phase of each of the plurality of outbound transmit signals, and whitening the plurality of outbound transmit signals.

According to another aspect of this embodiment, a plurality of reference signals are captured. The plurality of reference signals correspond to the conditioned plurality of outbound transmit signals. The plurality of reference signals are used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal. According to another aspect of this embodiment, reference symbols associated with the plurality of outbound transmit signals are captured. The captured reference symbols are used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal.

According to another aspect of this embodiment, the radio unit includes a plurality of directional couplers in communication with the at least one RF combiner and the plurality of antenna ports. The plurality of incident signals and plurality of reflected signals are provided, by the plurality of directional couplers, to the at least one RF combiner. According to another aspect of this embodiment, the at least one RF combiner includes a plurality of RF combiners. Each of the plurality of RF combiners is configured to output a respective combined incident signal and respective combined reflective signal. A combined incident signal and combined reflective signal are received at at least one RF combiner of the plurality of RF combiner from at least two other RF combiners of the plurality of RF combiners. According to another aspect of this embodiment, the plurality of outbound transmit signals are a plurality of downlink transmit signals.

According to another embodiment of the disclosure, a radio unit is provided. The radio unit includes a plurality of antenna ports configured to transmit a plurality of outbound transmit signals and at least one radio frequency, RF, combiner coupled to the plurality of antenna ports. The at least one RF combiner is configured to: combine a plurality of incident signals associated with the plurality of outbound transmit signals into a combined incident signal, and combine a plurality of reflected signals associated with the plurality of outbound transmit signals into a combined reflective signal. The radio unit includes a processing module that is configured to: separate individual incident signals from the combined incident signal, separate individual reflected signals from the combined reflected signal, and determine a voltage standing wave ratio, VSWR, associated with each of the plurality of antenna ports based at least in part on the separated individual incident and reflected signals. Each separated individual incident signal is associated with a respective antenna port of the plurality of antenna ports. Each separated individual reflected signal is associated with a respective antenna port of the plurality of antenna ports.

According to another aspect of this embodiment, the processing module is further configured to: determine a degree of correlation between the plurality of outbound transmit signals, determine whether the degree of correlation is greater than a predetermined threshold, and in response to determining that the degree of correlation is greater than the predetermined threshold, condition the plurality of outbound transmit signals to reduce the degree of correlation. According to another aspect of this embodiment, radio unit includes a conditioning module configured to condition the plurality of outbound transmit signals to reduce a degree of correlation of the plurality of outbound transmit signals. The processing module is further configured to: determine the degree of correlation between the plurality of outbound transmit signals, determine whether the degree of correlation is greater than a predetermined threshold, and in response to determining that the degree of correlation is greater than the predetermined threshold, cause the conditioning module to condition the plurality of outbound transmit signals to reduce the degree of correlation.

According to another aspect of this embodiment, the processing module is further configured to: capture reference symbols associated with the plurality of outbound transmit signals. The captured reference symbols are used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal. BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is an existing radio unit with switchable antenna port paths for performing individual VSWR measurements;

FIG. 2 is a block diagram of an exemplary radio unit for performing simultaneous antenna port measurements in accordance with the principles of the disclosure;

FIG. 3 is another block diagram of an exemplary radio unit for performing simultaneous antenna port measurements in accordance with the principles of the disclosure;

FIG. 4 is a block diagram of another exemplary radio unit for performing simultaneous antenna port measurements in accordance with the principles of the disclosure;

FIG. 5 is a flow diagram of an exemplary measurement process for separating combined signals and determining VSWR in accordance with the principles of the disclosure;

FIG. 6 is an exemplary block diagram of an n^th downlink (DL) chain of radio unit in accordance with the principles of the disclosure;

FIG. 7 an equivalent block diagram of the n^th downlink (DL) chain of radio unit of FIG. 6 in accordance with the principles of the disclosure;

FIG. 8 is a flow diagram of another exemplary measurement process for separating combined signals and determining VSWR in accordance with the principles of the disclosure;

FIG. 9 is a flow diagram of an exemplary correlation analysis process for reducing the correlation between outbound transmit signals if required for signal separation in accordance with the principles of the disclosure;

FIG. 10 is a flow diagram of an exemplary coupler calibration process for determining and storing calibration parameters to compensate for inherent coupler impairments in accordance with the principles of the disclosure; FIG. 11 is a block diagram of another embodiment of radio unit for performing simultaneous antenna port measurements in accordance with the principles of the disclosure;

FIG. 12 is a block diagram of yet another embodiment of radio unit for performing simultaneous antenna port measurements in accordance with the principles of the disclosure; and

FIG. 13 is graph of the results of a simulation of the radio unit for performing simultaneous antenna port measurements in accordance with the principles of the disclosure.

DETAILED DESCRIPTION

The radio units, methods and systems described herein advantageously provide for simultaneous VSWR/RL measurement at multiple antenna ports. In particular, the instant disclosure advantageously combines incident signals associated with multiple antenna ports and separately combines multiple reflected signals associated with the multiple ports to perform VSWR/RL measurements, thereby avoiding the extensive cost and complexity of switching between antenna ports as described with reference to FIG. 1. Further, in one or more embodiments, special signals such as test or calibration signals are not required to be transmitted during the VSWR/RL measurement. Instead, "live" data traffic transmitted along the downlink path/antenna branch of radio unit may be used, i.e., the plurality of outbound transmit signals are a plurality of downlink transmit signals, thereby increasing data throughput by avoiding having to delay data traffic transmission during VSWR/RL measurement periods. One of ordinary skill in the art would know that VSWR also refers to return loss (RL) or reflection coefficient (RC) and the disclosure is not intended to limit the measurement solely to VSWR/RL measurements. One or more embodiments further allows for the determination whether combined incident and combined reflected signals can be separated in which the inherent properties in reference symbols such as long term evolution (LTE) reference symbols that are part of the data traffic transmission are exploited to separate the combined incident signal and to separate the combined reflected signal. In one or more other embodiments, the instant disclosure deliberately decorrelates the data traffic transmission via one or more methods discussed herein, thereby allowing combined incident and combined reflected signals associated with the correlated data traffic transmission signals to be separated for VSWR measurement. Further, performing simultaneous measurements of multiple antenna ports allows for faster calibration of radio units during manufacturing and when deployed in the field.

Before describing in detail exemplary embodiments that are in accordance with the disclosure, it is noted that the embodiments reside primarily in combinations of apparatus/node/base station/radio unit components and processing steps related to providing simultaneous VSWR/RL measurements. Accordingly, components have been represented where appropriate by conventional symbols in drawings, showing only those specific details that are pertinent to understanding the embodiments of the disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

As used herein, relational terms, such as "first," "second," "top" and "bottom," and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. 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, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. In embodiments described herein, the joining term, "in communication with" and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication.

Referring now to drawing figures in which like reference designators refer to like elements there is shown in FIG. 2 an exemplary system for performing simultaneous antenna port measurements in accordance with the principles of the disclosure and designated generally as "24." System 24 includes one or more base stations 26 for transmitting and receiving transmission signals. Base station 26 includes one or more radio units 28 for performing radio unit functions described herein. In one or more embodiments, base station may be any network node that includes radio unit 28. In that regard, implementations of the disclosure are not limited solely to base stations, such as LTE eNodeBs. Radio unit 28 includes one or more antenna transceivers 30 that are configured to transmit and receive

communication signals. In one or more embodiments, antenna transceiver 30 is configured to transmit one or more outbound transmit signals. As used herein, one or more outbound transmit signals refers to one or more signals output by antenna transceiver 30 towards one or more antenna ports. Outbound transmit signals may include communication signals, calibration signals and/or live data traffic, among other signals.

Radio unit 28 includes combining unit 32 that is configured to combine incident signals associated with multiple antenna ports and combine reflected signals associated with multiple antenna ports as discussed in detail with respect to FIGS. 3 and 9. Radio unit 28 includes conditioning circuitry 34 that is configured to condition outbound transmit signals in order to reduce the degree of correlation between the outbound transmit signals as described herein. In one or more embodiments, functionality of conditioning circuitry 34 is performed by processing circuitry 36 such that conditioning circuitry 34 may be omitted. Outbound transmit signals may include "live" data traffic signals, test signals, calibration signals and/or other signals. Radio unit 28 includes processing circuitry 36 for performing radio unit 28 functions as described herein. In one or more embodiments, processing circuitry 36 includes one or more processors 38 for performing radio unit 28 functions and memory 40 for storing data and/or code such as coupler calibration code 41, measurement code 42 and correlational analysis code 44. For example, coupler calibration code 41 includes instructions that, when executed by processor 38, cause processor 38 to perform the coupler calibration process discussed in detail with respect to FIG. 10. For example, measurement code 42 includes instructions that, when executed by processor 38, cause processor 38 to perform the measurement process discussed in detail with respect to FIGS. 5 and 8. In another example, correlation analysis code 44 includes instructions that, when executed by processor 38, cause processor 38 to perform the correlation analysis process discussed in detail with respect to FIG. 9.

In addition to a traditional processor 38 and memory 40, processing circuitry 36 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry). Processing circuitry 36 may comprise and/or be connected to and/or be configured for accessing (e.g., writing to and/or reading from) memory 40, which may comprise any kind of volatile and/or non-volatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). Such memory 40 may be configured to store code executable by circuitry and/or other data, e.g., data pertaining to communication, e.g., configuration and/or address data of nodes, etc. Processing circuitry 36 may be configured to control any of the methods described herein and/or to cause such methods to be performed, e.g., by radio unit 28 and/or base station 26. In other words, processing circuitry 36 may include a controller, which may include a microprocessor and/or microcontroller and/or FPGA (Field-Programmable Gate Array) device and/or ASIC (Application Specific Integrated Circuit) device. It may be considered that processing circuitry 36 includes or may be connected or connectable to memory, which may be configured to be accessible for reading and/or writing by the controller and/or processing circuitry 36. While radio unit 28 is illustrated as being part of base station 26, radio unit 28 may be separate from base station 26. In one or more embodiments, the measurement process and/or correlation analysis process may be performed before radio unit 28 is transmitting live data traffic in the field such as during manufacturing and testing procedures.

FIG. 3 is a block diagram of an exemplary radio unit 28 for performing simultaneous antenna port 45 measurements. In particular, FIG. 3 illustrates one embodiment of combining unit 32 that is configured to combine incident signals associated with a plurality of outbound transmit signals from antenna transceivers 30a-30d (collectively referred to as antenna transceiver 30) and also configured to combine reflected signals associated with the plurality of outbound transmit signals from antenna transceiver 30, thereby outputting a combined incident signal and a separate combined reflected signal for processing by processing circuitry 36. In one embodiment, antenna transceiver 30 provides or communicates a respective outbound transmit signal to a respective directional coupler 46. For example, antenna transceiver 30a communicates an outbound transmit signal to directional coupler 46a for transmission via antenna port 45a.

Combining unit 32 includes one or more directional couplers 46a-46d (collectively referred to as directional coupler 46) that are configured to separate incident and reflected signals at each antenna port 45a-45d (collectively referred to as antenna port 45) as is known in the art. Combining unit 32 includes one or more radio frequency combiners 48a-c (collectively referred to as combiner 48). In one or more embodiments, each combiner 48 is configured to combine one or more incident signals to form a combined incident signal, and separately combine one or more reflected signals to form a combined reflected signal. For example, combiner 48a combines incident signals received from directional couplers 46a and 46b to output a combined incident signal that is provided to combiner 48c. Further, combiner 48b combines incident signals received from directional couplers 46c and 46d to output a combined incident signal that is provided to combiner 48c, which combines the two combined signals received from combiners 48a and 48b in order to output another combined incident signal, i.e., at least one RF combiner 48 of a plurality of RF combiners 48 is configured to receive a combined incident signal and combined reflective signal from at least two other RF combiners 48 of the plurality of RF combiners 48. The combined incident signal output by combiner 48c includes incidents signals from directional couplers 46a-46d.

A similar and separate process occurs with reflected signals in which combiner 48c will output a combined reflected signal that includes reflected signals from directional couplers 46a-46d. The combined incident signal and separate combined reflected signal are both provided to processing circuitry 36 for processing as described herein. Other configurations of combining unit 32 are possible in accordance with the teaching of the disclosure so long as combining unit 32 outputs a combined incident signal associated with multiple antenna ports 45 and outputs a combined reflected signal associated with multiple antenna ports 45. Further, radio unit 28 is not limited to four transceivers 30, antennas 14 and ports 45, as other quantities of elements may be used in light of the teachings of the disclosure based on specific design and implementation needs.

FIG. 4 is a block diagram an exemplary radio unit 28 for performing simultaneous antenna port 45 measurements. Antenna transceivers 30a-n each include downlink (DL) digital signal generators 50a-50n and downlink (DL) RF circuits 52a-52n for generating RF signals, i.e., outbound transmit signals, for transmission. In one or more embodiment, DL digital signal generators 50 include conditioning circuitry 32 for decorrelating outbound transmit signals as is described herein. In one or more embodiments, DL digital signal generators 50 provide one or more reference signals 53a-53n to processing circuitry 36 for use in separating incident signals from a combined incident signal and reflected signals from a combined reflected signal as described in detail with respect to FIG. 9. Processing circuitry 36 includes one or more receivers 54a and 54b for receiving and down- converting received signals. For example, receiver 54a receives and down-converts a combined incident signal received from combining unit 32. Also, receiver 54b receives and down-converts a combined reflected signal received from combining unit 32.

Processing circuitry 36 includes one or more analog-to-digital converters (ADCs) 56a and 56b that are configured to digitize received signals from receivers

54a and 54b. In one or more embodiments, memory 40 includes N+2 memory blocks where N is the number of antenna ports 45 or antenna branches/paths such that memory 40 may capture N reference signals from N DL digital signal generators 50, and also capture two signals from dual I & Q ADCs 56a and 56b for processing. In one or more embodiments, data capture into the N+2 memory blocks of memory 40 may be triggered by conditioning unit 32, processing circuitry 36 and/or a separate triggering unit (not shown). In one or more embodiments, triggering data capture may also include generating a trigger aligned with the LTE frame structure in the situation where reference symbols of outbound transmit signal are used to separate incident and reflected signals as described in detail with respect to FIG. 9. In one or more embodiments, when a reduction of the degree of correlation of outbound transmit signals is performed by deliberate decorrelation, e.g., dithering, whitening, etc. as described in detail with respect to FIG. 9, a trigger synchronized with the start of decorrelation.

FIG. 5 is a flow diagram of an exemplary measurement process of measurement code 42 for separating combined incident and combined reflected signals in order to determine VSWR for each antenna port 45. It is assumed that processing circuitry 36 has received a combined incident signal and a combined reflected signal from combining unit 32 in which the combined incident signal and the combined reflected signal are based on outbound transmit signals. In one or more embodiments, the outbound transmit signals are downlink data traffic signals generated by antenna transceiver 30 that can be used as reference signals are described herein. Processing circuitry 36 separates individual incident signals from a combined incident signal (Block S100). For example, with reference to FIG. 3, processing circuitry 36 separates individual incident signals from a combined incident signal received from combiner 48c. Each separated individual incident signal is associated with a respective antenna port 45 of a plurality of antenna ports 45.

Processing circuitry 36 separates individual reflected signals from a combined reflected signal (Block S102). For example, with reference to FIG. 3, processing circuitry 36 separates individual reflected signals from a combined reflected signal received from combiner 48c. In other words, radio unit 28 is configured to take simultaneous measurement of multiple antenna ports 45 using a combined incident signal and a combined reflected signal that is communicated to processing circuitry 36. Processing circuitry 36 determines a VSWR for each antenna port 45 based at least in part on the separated individual incident and reflected signals (Block S104). For example, processing circuitry 36 determines VSWR for each antenna port 45 using separated individual incident and reflected signals as discussed in detail with respect to FIG. 6. In one or more embodiments, calibration parameters are considered during the determination of VSWR in order to compensate for coupler 46

impairments. Therefore, radio unit 28 advantageously reduces VSWR measurement time during operation of multiple antennas 14 by combining incident signals and separately combining reflected signals instead of individual switching between these signals as is done in prior art. Further, directional coupler 46 calibration time is reduced as individual switching between antenna ports 45 is advantageously not used. Also, by using combiners 48 instead of controllable switches 22, design of antenna circuit board with multiple antenna ports 45 is simplified while at the same time reducing cost as no interface and switch synchronization are required.

For the purpose of explaining how the combined incident signal and combined reflected signal are used for VSWR measurements, reference will be made to FIGS. 6 and 7. FIG. 6 is an exemplary block diagram of an n^th downlink (DL) chain of radio unit 28 that will be referenced to describe the VSWR/RL measurement calculation process. The equivalent block diagram of n-th DL chain of FIG. 6 is illustrated FIG. 7. "Downlink" as used herein refers to a path from antenna transceiver 30 to antenna port 45. In particular, for clarity purposes, only an n^th DL chain, n = 1...N, of a multi- antenna radio unit 28 with RF load 47, i.e., antenna feeder cable and antenna, connected at antenna port 45 is shown.

are reference, forward and reversed signals respectively in frequency domain, e.g. by applying FFT to the corresponding signals captured in time. The reference signals are captured from the digital circuit. The forward and reversed signals are measured at the outputs of the directional coupler 46.

be the transfer

function from the reference point where is measured to antenna port 45, and

be the transfer function of the feeder cable and antenna from antenna port

45 to the reflection point in antenna 14. Then, the measured reflection coefficient

Using transfer functions, processing circuitry 36 performs simultaneous estimation of for radio unit 28 having multiple antennas 45. For example,

these formulas may be applied to the embodiment of radio unit 28 of FIG. 3 with two combined feedback signals is the combined

incident signal output by combiner 48c and is the combined reflected signal

output by combiner 48c. One may model

where are input noises of observation receivers 54.

There are a number of methods to estimate

observing

, e.g. maximum likelihood, adaptive filtering, Viterbi algorithm, etc. In a Minimum Mean Square Error (MMSE) method, are estimated by such that

where operator E denotes mathematical expectation. Through mathematical manipulations the matrix solution for every frequency

x is the matrix multiplication operator, and superscripts T and * denote vector transpose and complex conjugate respectively.

It is assumed that

_are de-correlated , i.e. the inverse of

exists. If are not inherently de-correlated, there are various well known de

correlation methods, e.g. additive pseudo-noise, phase dithering, etc.

In practice the mathematical expectation can be replaced by averaging the data collected in ^ measurements, i.e.

can be estimated as

where index = 1···Λί denotes the measurement sample. In practice, the measured reflection coefficient only approximates the actual

reflection coefficient

since any real directional coupler 46 has a limited directivity. There are a number of methods to account for the directional coupler 46 impairments. In one embodiment to obtain can be compensated as

where

are functions of the s-parameters of the branch directional

coupler 46.

In production or manufacturing, ABC parameters for each directional coupler can be obtained simultaneously on multiple antenna branches through the steps below in which steps 2-5 are encompassed in coupler calibration code 41. The steps include:

1. Connect standard loads with known, possibly equal,

N antenna ports 45 of radio unit 28.

2. Collect Maples of

frequency domain, e.g. by applying FFT to time domain signals.

3.

Eq. 5 and Eq. 4.

4. Repeat steps

corresponding

5. Based on Eq. 6 mathematical manipulations show that can be

now calculated as

One way to ensure that

exists, is to use standard loads

, of the same magnitude and phase uniformly distributed over Standard

Open, Short, Load approach can be used for

In field operation during transmission of data traffic, VSWR/RL may be measured simultaneousl on multiple antenna branches through the following steps

1. Collect

frequency domain, e.g. by applying FFT to time domain signals.

2. Calculate

using Eq. 6, and find correlation coefficient

using Eq. 5 and Eq. 4 in every antenna branch.

3.

parameters estimated in production as per Eq. 7 to

find the actual reflection coefficient

of every antenna branch as per Eq. 6.

4. Calculate the Return Loss:

5. Calculate VSWR

Therefore, the VSWR/RL are advantageously determined using a combined incident signal and a combined reflected signal which allows for simultaneous measurement of on multiple antenna paths/branches.

FIG. 8 is a flow diagram of another measurement process of measurement code 42 for determining a degree of correlation between outbound transmit signals and separating incident and reflected signals in order to determine VSWR for each antenna port 45. Processing circuitry 36 performs the correlation analysis process of correlation analysis code 44 for separating outbound transmit signals having a degree of correlation as discussed in detail below with respect to FIG. 9 (Block S106).

Processing circuitry 36 performs Blocks S100-S104 as discussed above with respect to FIG. 5. FIG. 9 is a flow diagram of an exemplary correlation analysis process for decorrelating outbound transmit signals that are not sufficiently decorrelated.

Processing circuitry 36 determines a degree of correlation between the plurality of outbound transmit signals (Block S108). In one or more embodiments, the correlation detection may be performed by a cross-correlation computation between each outbound transmit signal and all of the other outbound transmit signals. In one or more embodiments, the signals used for correlation detection are reference signals inside antenna transceiver 30, which are based on outbound transmit signals.

Processing circuitry 36 determines whether the degree of correlation is greater than a predetermined threshold (Block SI 10). The predetermined threshold provides a metric for determining whether individual signals from respective combined incident signal and combined reflected signal output by combining unit 32 can be separated by processing circuitry 36 through digital signal processing techniques. If the degree of correlation of the outbound transmit signals is less than the predetermined threshold, the correlation analysis process may end as the outbound transmit signals are sufficiently uncorrected such that processing circuitry 36 is able to separate respective combined incident signal and combined reflected signal output by combining unit 32.

However, if the degree of correlation between outbound transmit signals is greater than a predetermined threshold, processing circuity 36 determines whether a portion of the outbound transmit signals are uncorrected. The portion of the outbound transmit signals may include frequency and/or time portion(s) of the outbound transit signals. For example, in one or more embodiments, processing circuitry 36 determines LTE reference symbols included in the outbound transmit signals are uncorrected such that these reference symbols may be used by processing circuitry 36 to separate individual signals from respective combined incident signal and combined reflected signal, i.e., the captured reference symbols are used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal. The arrival time and frequency of the reference symbols (CRS) included in the LTE frame are known to radio unit 28 a priory based on LTE standards known in the art. In one or more embodiments, other uncorrected portions of outbound transmit signals may be captured into memory 40 as reference signals for use during signal separation. In one or more embodiment, time synchronization circuitry is used to synchronize data capture such that the captured portions of the outbound transmit signals can be used to separate incident signals from a combined incident signal, and also used to separate reflected signals from a combined reflected signal. In one or more embodiments, other predetermined thresholds may be selected such that the degree of correlation being lower than the predefined threshold leads to Blocks SI 12 and SI 14 being performed.

Referring back to Block SI 12, if portions of the outbound transmit signals are not uncorrelated, i.e., there are no correlated portions of the outbound transmit signals in both time and frequency domains, processing circuitry 36 conditions the plurality of outbound transmit signals to reduce the degree of correlation (Block SI 16). The conditioning of the plurality of outbound transmit signals sufficiently uncorrelates the plurality of outbound transmit signals, i.e., reduces the degree of correlation below the predetermined threshold, such that processing circuitry 36 is able to separate individual signals from the respective combined incident signal and combined reflected signal. In one or more embodiments, the plurality of outbound transmit signals are condition through at least one of adding uncorrelated pseudo-noise to the plurality of outbound transmit signals, dithering a phase of each of the plurality of outbound transmit signals and whitening the plurality of outbound transmit signals. In one or more embodiments, other methods for decorrelating/uncorrelating, i.e., reducing the degree of correlation below the predetermined threshold, may be used. In one or more embodiments, time synchronization circuitry is used for synchronized conditioning such as to allow for separation of combined incident signals and separation of combined reflected signals. In one or more embodiments, time synchronization circuitry generates one or more trigger signals with the start of conditioning or decorrelation to allow for separation of combined incident signals and separation of combined reflected signals.

In one or more embodiments, the modified outbound signals may be captured into memory 40 as a plurality of reference signals, i.e., the plurality of reference signals corresponding to the conditioned plurality of outbound transmit signals. The plurality of reference signals may then be used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal. In an alternative embodiment, processing circuitry 36 triggers conditioning circuitry 32 to condition the outbound transmit signals to reduce the degree of correlation between outbound transmit signals. Conditioning circuitry 32 may include dedicated hardware and/or software for decorrelating one or more outbound transmit signals. In one or more embodiments, Blocks S108-S112 and SI 16 may be omitted such that processing circuitry 36 captures uncorrected portion(s) of outbound transmit signals. For example, radio unit 28 may be configured to use inherently uncorrected portion(s) of outbound transit signals such that processing circuitry 36 does not need to determine a degree of correlation of the outbound transmit signals.

Therefore, the arrangements describe herein determine a degree of correlation between outbound transmit signals in order to determine whether additional processes should be performed to allow for the separation of individual signals from a combined incident signal and a combined reflected signal. Further, if additional processes are triggered due to the degree of correlation of the outbound transmit signals, the instant disclosure advantageously first looks to the outbound transmit signals themselves to determine if any portions of the outbound transmit signals are uncorrected. This helps avoid having to modify the outbound transmit signals for the purpose of uncorrelating the signals. For example, instead of introducing uncorrected pseudo- noise to the plurality of outbound transmit signals, which may slightly degrade these outbound transmit signals since noise is being added, the instant disclosure may use uncorrected portions of the outbound transmit signals for signal separation, thereby avoiding the addition of uncorrected noise to the signals. Therefore, as a last resort in one or more embodiments, the instant disclosure may condition or modify the outbound transmit signals in order to sufficiently decorrelate/uncorrelate these signals to allow for signal separation and subsequent VSWR/RL calculation.

FIG. 10 is a flow diagram of an exemplary coupler calibration process for determining and storing calibration parameters to compensate for inherent coupler impairments. In one or more embodiments, the coupler calibration process is embodied in coupler calibration code 41. Processing circuitry 36 collect ^samples in frequency domain, e.g. by

applying FFT to time domain signals, as discussed above, with respect to FIGs. 6 and 7 (Block SI 18). Processing circuitry 36 calculates

using Eq. 6, as discussed above with respect to FIGs. 6 and 7 (Block S120). Processing circuitry 36 determines as discussed above with

respect to FIGs. 6 and 7 (Block S122). Processing circuitry 36 determines and

c " parameters, i.e., calibration parameters, and stores the parameters in memory 40 for use in calculating the actual reflection coefficient, RL and VSWR as discussed above with respect to FIGs. 6 and 7. Therefore, the coupler calibration process advantageously allows for calibration parameters to be determined through simultaneous measurements of the antenna branches/ports 45, thereby reducing production time and complexity.

FIG. 11 illustrates another exemplary embodiment of radio unit 28. In particular, radio unit 28 includes a different configuration of combining unit 32 than illustrated in FIG. 3. For example, combining unit 32 includes directional couplers 46a-d for separating incident and reflected signal as discussed in FIG. 3, but combining unit 32 in FIG. 11 includes one combiner 42a. Combiner 48a receives respective incident and reflected signals from directional couplers 46a-d, and combines the received incident signals to form a combined incident signal that is provided to processing circuitry 36 for VSWR/RL measurement calculations as discussed above. Also, combiner 48a combines the received reflected signals to form a combined reflected signal that is also provided to processing circuitry 36 for VSWR/RL measurement calculations as discussed above. Therefore, this embodiment of radio unit 28 advantageously further reduces the complexity and cost associated with combiner unit 32 by reducing the number of combiners 48 needed for combining incident signals and combining reflected signals. One of ordinary skill in the art will recognize that other embodiments of combining unit 32 are possible so long as combining unit 32 is able to output a combined incident signal that includes incident signals associated with multiple antenna ports 45 and is also able to output a combined reflected incident signal that includes reflected signals associated with multiple antenna ports 45.

FIG. 12 is a block diagram of another embodiment of radio unit 28. Radio unit 28 includes antenna transceivers 30 and combining unit 32 as discussed above with respect to FIG. 2. Radio unit 28 includes processing module 50 for performing the functions of radio unit 28 as discussed herein. Radio unit 28 includes processing module 50 that is configured to perform the functions described herein with respect to processing circuitry 36 such as the coupler calibration process of coupler calibration code 41, the measurement process of measurement code 42 and the correlation analysis process of correlation analysis code 44. Radio unit 28 includes condition module 52 that is configured to perform functions as described above with respect to conditioning circuitry 34.

FIG. 13 is graph of the results of an exemplary simulation of the radio unit for performing simultaneous antenna port measurements in accordance with the principles of the disclosure. Graph 54 illustrates the mean square error of simultaneous VSWR/RL measurement in a simulated four transceiver (4TX) radio unit 28 with coupler calibration. Theoretical error curves are also shown for a one transceiver (1TX) and thirty-two transceiver (32TX) radio unit 28 for comparison. Uncorrelated outbound transmit signals, directional couplers 46 with lOdB directivity and antenna loads with OdB return loss are assumed in all antenna ports. The

VSWR/RL is calculated using 16k complex samples transmitted by each antenna 14. The error shown is averaged all antenna paths/branches. As illustrated, the

VSWR/RL measurement error increases with the number of antennas 14, since combining signals from multiple antenna ports 45 results in a higher noise level. However, as more antennas are combined, the contribution to VSWR/RL

measurement error by each antenna is less. At SNR=20dB, the VSWR/RL measurement error in 32TX radio unit 28 is less than one percent which is accurate for feeder cable and antenna supervision in most practical cases.

As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, and/or computer program product. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a "circuit" or "module." Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices.

Some embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable memory or storage medium that can direct a computer or other

programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that

communication may occur in the opposite direction to the depicted arrows.

Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the "C" programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination.

It will be appreciated by persons skilled in the art that the disclosure is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings, which is limited only by the following claims.

Claims

What is claimed is:

1. A radio unit (28), comprising:

a plurality of antenna ports (45) configured to transmit a plurality of outbound transmit signals;

at least one radio frequency, RF, combiner (48) coupled to the plurality of antenna ports (45), the at least one RF combiner (48) configured to:

combine a plurality of incident signals associated with the plurality of outbound transmit signals into a combined incident signal; and

combine a plurality of reflected signals associated with the plurality of outbound transmit signals into a combined reflective signal; and

processing circuitry (36) in communication with the at least one RF combiner (48), the processing circuitry (36) including a processor (38) and a memory (40), the memory (40) containing instructions that, when executed by the processor (38), configure the processor (38) to:

separate individual incident signals from the combined incident signal, each separated individual incident signal being associated with a respective antenna port (45) of the plurality of antenna ports (45);

separate individual reflected signals from the combined reflected signal, each separated individual reflected signal being associated with a respective antenna port (45) of the plurality of antenna ports (45); and

determine a voltage standing wave ratio, VSWR, associated with each of the plurality of antenna ports (45) based at least in part on the separated individual incident and reflected signals.

2. The radio unit (28) of Claim 1 , wherein the memory (40) contains further instructions that, when executed by the processor (38), cause the processor (38) to:

determine a degree of correlation between the plurality of outbound transmit signals;

determine whether the degree of correlation is greater than a predetermined threshold; and in response to determining that the degree of correlation is greater than the predetermined threshold, condition the plurality of outbound transmit signals to reduce the degree of correlation.

3. The radio unit (28) of Claim 2, wherein the conditioning includes one of:

adding uncorrected pseudo-noise to the plurality of outbound transmit signals; dithering a phase of each of the plurality of outbound transmit signals; and whitening the plurality of outbound transmit signals.

4. The radio unit (28) of Claim 3, wherein the memory (40) further includes instructions that, when executed by the processor (38), cause the processor (38) to capture a plurality of reference signals, the plurality of reference signals corresponding to the conditioned plurality of outbound transmit signals; and

the plurality of reference signals being used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal.

5. The radio unit (28) of Claim 1, further comprising conditioning circuitry (34) configured to condition the plurality of outbound transmit signals to reduce a degree of correlation of the plurality of outbound transmit signals; and

the memory (40) containing further instructions that, when executed by the processor (38), cause the processor (38) to:

determine the degree of correlation between the plurality of outbound transmit signals;

determine whether the degree of correlation is greater than a predetermined threshold; and

in response to determining the degree of correlation is greater than the predetermined threshold, cause the conditioning circuitry (34) to condition the plurality of outbound transmit signals to reduce the degree of correlation.

6. The radio unit (28) of Claim 1, wherein the memory (40) contains further instructions that, when executed by the processor (38), cause the processor (38) to:

capture reference symbols associated with the plurality of outbound transmit signals; and

the captured reference symbols being used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal.

7. The radio unit (28) of Claim 1 , further comprising a plurality of directional couplers (46) in communication with the at least one RF combiner (48) and the plurality of antenna ports (45); and

the plurality of directional couplers (46) being configured to provide the plurality of incident signals and plurality of reflected signals to the at least one RF combiner (48).

8. The radio unit (28) of Claim 1, wherein the at least one RF combiner (48) includes a plurality of RF combiners (48), each of the plurality of RF combiners (48) being configured to output a respective combined incident signal and respective combined reflective signal; and

at least one RF combiner (48) of the plurality of RF combiners (48) is configured to receive a combined incident signal and combined reflective signal from at least two other RF combiners (48) of the plurality of RF combiners (48).

9. The radio unit (28) of Claim 1 , wherein the plurality of outbound transmit signals are a plurality of downlink transmit signals.

10. A method for a radio unit including a plurality of antenna ports configured to transmit a plurality of outbound transmit signals and at least one radio frequency, RF, combiner coupled to the plurality of antenna ports, the method comprising: combining a plurality of incident signals associated with the plurality of outbound transmit signals into a combined incident signal; and

combining a plurality of reflected signals associated with the plurality of outbound transmit signals into a combined reflective signal;

separating individual incident signals from the combined incident signal, each separated individual incident signal being associated with a respective antenna port of the plurality of antenna ports (Block SI 00);

separating individual reflected signals from the combined reflected signal, each separated individual reflected signal being associated with a respective antenna port of the plurality of antenna ports (Block SI 02); and

determining a voltage standing wave ratio, VSWR, associated with each of the plurality of antenna ports based at least in part on the separated individual incident and reflected signals (Block S104).

11. The method of Claim 10, further comprising:

determining a degree of correlation between the plurality of outbound transmit signals (Block S 108);

determining whether the degree of correlation is greater than a predetermined threshold (Block SI 10); and

in response to determining that the degree of correlation is greater than the predetermined threshold, conditioning the plurality of outbound transmit signals to reduce the degree of correlation (Block SI 16).

12. The method of Claim 11, wherein the conditioning includes one of: adding uncorrected pseudo-noise to the plurality of outbound transmit signals; dithering a phase of each of the plurality of outbound transmit signals; and whitening the plurality of outbound transmit signals.

13. The method of Claim 12, further comprising capturing a plurality of reference signals, the plurality of reference signals corresponding to the conditioned plurality of outbound transmit signals; and the plurality of reference signals being used to separate individual incident signals from the combined incident signal and to separate individual reflected signals from the combined reflected signal.

14. The method of Claim 10, further comprising:

determining whether the degree of correlation is greater than a predetermined threshold (Block SI 10);

in response to determining that the degree of correlation is greater than the predetermined threshold, capturing reference symbols associated with the plurality of outbound transmit signals (Block SI 14); and

15. The method of Claim 10, wherein the radio unit includes a plurality of directional couplers in communication with the at least one RF combiner and the plurality of antenna ports; and

the method further comprising provide, by the plurality of directional couplers, the plurality of incident signals and plurality of reflected signals to the at least one RF combiner.

16. The method of Claim 10, wherein the at least one RF combiner includes a plurality of RF combiners, each of the plurality of RF combiners being configured to output a respective combined incident signal and respective combined reflective signal; and

the method further comprising receiving, at least one RF combiner of the plurality of RF combiners, a combined incident signal and combined reflective signal from at least two other RF combiners of the plurality of RF combiners.

17. The method of Claim 10, wherein the plurality of outbound transmit signals are a plurality of downlink transmit signals.

18. A radio unit (28), comprising:

combine a plurality of reflected signals associated with the plurality of outbound transmit signals into a combined reflective signal;

a processing module (50), the processing module (50) configured to:

19. The radio unit (28) of Claim 18, wherein the processing module (50) is further configured to:

in response to determining that the degree of correlation is greater than the predetermined threshold, condition the plurality of outbound transmit signals to reduce the degree of correlation.

20. The radio unit (28) of Claim 18, further comprising a conditioning module (52) configured to condition the plurality of outbound transmit signals to reduce a degree of correlation of the plurality of outbound transmit signals; and

the processing module (50) being further configured to:

in response to determining that the degree of correlation is greater than the predetermined threshold, cause the conditioning module to condition the plurality of outbound transmit signals to reduce the degree of correlation.

21. The radio unit (28) of Claim 18, wherein the processing module (50) is further configured to: