WO2019245533A1

WO2019245533A1 - Estmating a delay

Info

Publication number: WO2019245533A1
Application number: PCT/US2018/038262
Authority: WO
Inventors: Shavantha Kularatna; Ramasamy Gopalan; Marko FLEISCHER; Linjie LENG
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2018-06-19
Filing date: 2018-06-19
Publication date: 2019-12-26
Also published as: EP3827522A1; WO2019245598A1

Abstract

An apparatus and method are disclosed relating to estimating a delay, and primarily, though not exclusively, to estimating a delay for use in Passive Intermodulation (PIM) cancellation, i.e. for alignment. The method comprises adapting one or more transmit signals within a defined band to improve the autocorrelation properties of the transmit signal. The method may also comprise generating on the basis of at least the transmit signal and a corresponding receive signal a respective passive intermodulation signal comprising a simulated n^th order passive intermodulation product, where n is an odd integer greater than two. The method may also comprise correlating the generated passive intermodulation signal with the receive signal to identify a correlation peak, and determining a time offset (t_deiay) to apply to the generated passive intermodulation signal based on the correlation peak.

Description

ESTIMATING A DELAY

Field

This specification relates to an apparatus, method and computer program product relating to estimating a delay, for example for, but not limited to, alignment in Passive InterModulation (PIM) cancellation.

Background

Passive InterModulation (PIM) is a well-known telecom issue, it is caused if plural signals are transmitted through a non-linear system. A non-linear system may be a system comprising active components, but it may also occur in passive components, e.g. due to corroded connectors etc. Due to PIM, intermodulation products occur at frequencies f corresponding to wherein

.. are the frequencies of the plural signals, and

, , , are integer

coefficients (positive, negative, or 0). The sum

. is denoted as the order of the intermodulation product, denoted as IMP3, IMPS, IMP7 etc. for IMP of 3^rd, 5^th, and 7* order, respectively. The amplitude of the IMPs decreases with increasing order of the IMPs. IMP3 is typically most relevant because it is located close to the input signal and has relatively high amplitude. If a

broadband signal is transmitted through the non-linear system, PIM may cause the occurrence of side-lobes.

Summary

According to one aspect, there is described an apparatus, comprising:

means for adapting one or more transmit signals within a defined band to improve the autocorrelation properties of the transmit signal;

means for generating on the basis of at least the transmit signal and a corresponding receive signal a respective passive intermodulation signal comprising a simulated n^ft order passive intermodulation product, where n is an odd integer greater than two; means for correlating the generated passive intermodulation signal with the receive signal to identify a correlation peak;

means for determining a time offset (tdeiay) to apply to the generated passive intermodulation signal based on the correlation peak.

The adapting means may be configured to add dummy sub-carriers within the defined band.

The adapting means may be configured to add the dummy sub-carriers by means of adding simulated orthogonal channel noise.

The adapting means may be configured to identify one or more resource blocks of the one or more transmit signals which are unused for user traffic, and to add the dummy carriers into at least some of said unused resource blocks.

The adapting means may be configured to add the dummy carriers into substantially all unused resource blocks.

The resource blocks may be LTE or 5G resource blocks.

The dummy sub-carriers may be added within the band with a predetermined minimum frequency separation between resource blocks, sufficient to obtain an accurately measured time offset (t_deiay).

The time offset (tdeiay) determining means may be configured to generate a plurality of reference time offsets t₁ , t₂,..t_n based on a plurality of temporally- spaced samples of the transmit signal and of the receive signal, and to compute the time offset based on an averaging of the reference time offsets.

The determining means may be configured to compute the time offset based on:

(i) computing the median (tmedian) of the reference time offsets t₁ , t₂,..t„ ;

(ii) computing the mean

of the reference time offsets t₁ , t2,..tn ; and

(iii) computing the time offset (tdeiay) as a value between tmedian and t mean·

The time offset (tdeiay) may be computed when abs(tmcdian - tmean) < two or less samples. The generating means may generate the respective passive intermodulation signal comprising either a simulated 3^rd of 5^th order passive intermodulation product The adapting means may be configured to modulate a sub-portion of resource blocks of the one or more transmit signals with a complex mathematical sequence.

One of first and second transmit signals may have a reduced bandwidth than the other transmit signal at a predetermined frequency separation between said transmit signals.

The complex mathematical sequence may be a Zadoff-Chu sequence.

The sub-portion of resource blocks may be unused for user traffic.

The adapting means may be configured to modulate resource blocks having a beneficial frequency spacing to improve the correlation.

The apparatus may further comprise means for applying the determined time offset (tdeiay) to the generated respective passive intermodulation signal and means for applying the resulting signal to the one or more receive signals for mitigating passive intermodulation.

The apparatus may further comprise means for receiving the one or more transmit signals and corresponding receive signals from a remote radio apparatus and for transmitting the time offset (W_ay) to the, or another, remote radio apparatus.

Another aspect provides a method, comprising:

adapting one or more transmit signals within a defined band to improve the autocorrelation properties of the transmit signal;

generating on the basis of at least the transmit signal and a corresponding receive signal a respective passive intermodulation signal comprising a simulated n^tb order passive intermodulation product, where n is an odd integer greater than two;

correlating the generated passive intermodulation signal with the receive signal to identify a correlation peak; and determining a time offset (t_deiay) to apply to the generated passive intermodulation signal based on the correlation peak.

Adapting may comprise adding dummy sub-carriers within the defined band.

The dummy sub-carriers may be added by means of adding simulated orthogonal channel noise.

The method may further comprise identifying one or more resource blocks of the one or more transmit signals which are unused for user traffic, and adding the dummy carriers into at least some of said unused resource blocks.

The dummy carriers may be added into substantially all unused resource blocks. The resource blocks may be LTE or 5G resource blocks.

The dummy sub-carriers may be added within the band with a predetermined minimum frequency separation between resource blocks, sufficient to obtain an accurately measured time offset (tdeiay).

Determining the time offset (tdeiay) may comprise generating a plurality of reference time offsets t₁ , t₂,..t_n based on a plurality of temporally-spaced samples of the transmit signal and of the receive signal, and computing the time offset based on an averaging of the reference time offsets.

Determining the time offset (tdeiay) may comprise:

(i) computing the median (tmedian) of the reference time offsets t₁ , t₂,..tn ;

(ii) computing the mean (tmean) of the reference time offsets t₁ , t₂,..t„ ; and

(iii) computing the time offset (tdeiay) ^ a value between t_media_n and t mean_* The time offset (tdeiay) may be computed when abs(Wuan - tmean) < two or less samples.

The respective passive intermodulation signal may comprise one or more of a simulated 3^rd of 5^th order passive intermodulation product.

The adapting may comprise modulating a sub-portion of resource blocks of the one or more transmit signals with a complex mathematical sequence.

The complex mathematical sequence may be a Zadoff-Chu sequence.

The sub-portion of resource blocks may be unused for user traffic. Adapting may comprise modulating resource blocks having a beneficial frequency spacing to improve the correlation.

The method may further comprise applying the determined time offset (tdeiay) to the generated respective passive intermodulation signal and applying the resulting signal to the one or more receive signals for mitigating passive intermodulation.

The method may further comprise receiving the one or more transmit signals and corresponding receive signals from a remote radio apparatus and transmitting the time offset (tdeiay) to the, or another, remote radio apparatus.

Another aspect may provide an apparatus comprising at least one processor, at least one memory directly connected to the at least one processor, the at least one memory including computer program code, and the at least one processor, with the at least one memory and the computer program code being arranged to perform the method of any of the preceding method definitions.

Another aspect may provide a computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method of any preceding method definition.

Another aspect may provide a non-transitory computer readable medium comprising program instructions stored thereon for performing a method, comprising:

generating on the basis of at least the transmit signal and a corresponding receive signal a respective passive intermodulation signal comprising a simulated n^& order passive intermodulation product, where n is an odd integer greater than two;

correlating the generated passive intermodulation signal with the receive signal to identify a correlation peak; and

determining a time offset (tdeiay) to apply to the generated passive intermodulation signal based on the correlation peak. Another aspect may provide an apparatus comprising: at least one processor; and at least one memory including computer program code which, when executed by the at least one processor, causes the apparatus:

to adapt one or more transmit signals within a defined band to improve the autocorrelation properties of the transmit signal;

to generate on the basis of at least the transmit signal and a corresponding receive signal a respective passive intermodulation signal comprising a simulated n* order passive intermodulation product, where n is an odd integer greater than two;

to correlate the generated passive intermodulation signal with the receive signal to identify a correlation peak; and

to determine a time offset (t_deiay) to apply to the generated passive intermodulation signal based on the correlation peak. Brief description of the drawings

Further details, features, objects, and advantages are apparent from the following detailed description of the preferred embodiments of the present invention which is to be taken in conjunction with the appended drawings, wherein:

Fig. 1 is a graph indicating a delay search peak error, useful for understanding example embodiments;

Fig. 2 shows a measurement arrangement to obtain RX signals and TX signals; Fig. 3 shows another measurement arrangement to obtain RX signals and TX signals;

Fig.4 shows an apparatus according to some embodiments;

Fig. 5 is a schematic diagram showing a frame of the LTE physical layer, useful for understanding example embodiments;

Fig. 6 shows an apparatus according to some embodiments;

Fig. 7 shows a method according to some embodiments;

Fig. 8 shows hardware modules according to some embodiments; and

Fig. 9 shows a non-volatile media according to some embodiments; and Fig. 10 is a graph indicating the correct delay search peak, produced using the methods and apparatus according to some example embodiments.

Detailed Description

Certain example embodiments are described in detail with reference to the accompanying drawings, wherein the features of the embodiments can be freely combined with each other unless otherwise described. However, it is to be expressly understood that the description of certain embodiments is given by way of example only, and that it is by no way intended to be understood as limiting to the disclosed details.

Moreover, it is to be understood that the apparatus is configured to perform the corresponding method, although in some cases only the apparatus or only the method are described. The operations of the method may be embodied in a computer program product on, for example, a non-transitory medium.

Certain abbreviations will be used herein, which are set out below for ease of reference.

Ab i

Cellular base stations may de-sense their own uplink owing to PIM products, for example introduced by passive components such as duplexers, cables, connector interfaces, antennas etc. If PIM is not mitigated, e.g. reduced or cancelled, it may not be possible to decode received signals. Operators may use PIM testers during site visits to measure PIM for mitigation purposes or use PIM cancellation algorithms to improve uplink signal quality.

Example embodiments herein enable to estimate accurately a delay associated with a PIM cancellation system and method, without the need for taking the system being measured off-line. In other words, some example embodiments allow for estimating the delay in real time during normal operations of, for example, a base station (e.g. eNB or MB) using the regular transmitted signal and not a dedicated PIM test signal which would disrupt service. This overcomes issues due to the PIM varying over time, e.g. due to the slow natural degradation of the antenna system resulting from constant exposure to the elements. For example, as the antenna begins to rust over time its PIM performance naturally degrades. This degradation cannot be picked up by a one-time measurement. Some embodiments enable the delay estimation to be performed remotely, e.g. at a server or central network management system remote from the one or more antenna systems under test. P1M measurements may be used for PIM

cancellation or mitigation purposes and/or for quality control purposes.

Passive InterModulation (PIM) is a natural process where transmit signals generate intermodulation products in passive devices. PIM products may be generated at very low power levels, for example due to the aging of antennas, corroded or loose connectors and duplex filters that are passive. Imperfections of cables, combiners and attenuators may also generate PIM. PIM generation with transmit signals is generally harmless due to its low level. However, when PIM products line up with receive signals, issues can arise. Although the level of PIM in a typical radios can range from - 110dBc to -150 dBc (w.r.t to the transmit signal) it can cause the receiver to desensitize. As an example, a transmit signal that is 49dBm of power causes PIM levels that are -81 dBm to -lOldBm. Hence, on some occasions, PIM signals can be higher than the receive signals. When PIM is higher than the receive signal, the receiver decoding process will fail due to negative signal to noise ratio. This may cause a significant throughput loss in the uplink direction (mobile to base station).

Some radios or associated equipment are designed to mitigate, i.e. reduce or avoid, such PIM effects with PIM cancellation algorithms. A PIM cancellation algorithm estimates PIM by comparing the transmit (Tx) and the receive (Rx) signal path. The PIM cancellation algorithm may then build up a model that attempts to cancel, or at least reduce, the PIM products on the receive (Rx) signal.

An aspect of PIM cancellation algorithms is synchronizing (or aligning) the computed third (or other n, where n is an odd integer greater than two) order produces) with the receive (RX) signal. Without the alignment process, the PIM model generated by the algorithm will be wrong and PIM cancellation will not occur. Equations for this synchronizing or aligning process are mentioned below, and the alignment may be referred to generally as estimating a delay or offset in accordance with example embodiments.

The filtered product of, typically, the third order product {third/) of the transmit (TX) signal may be used for the alignment process.

The filter referred to is typically a match filter that is used to match the receive band. Rx is the receive signal.

Upon finding the correlation peak, the delay between Rx and the third/ is adjusted to reflect the correlation peak. The correlation peak indicates the location of the delay offset.

To improve the accuracy of the delay search process, engineers look for:

a) Good auto-correlation properties of the transmit (TX) signal; and/or b) Appropriate processing gain of the signal.

Usually, the above properties are required to obtain a good correlation peak when wide band noise is present in the receive signal. Otherwise, the correlation process may yield incorrect peaks, and thus a wrong delay. Software within the radio under test is usually unaware of the wrong delay and P1M cancellation will occur with a wrong delay offset which may actually worsen the situation. Instead of the required PIM cancellation, the wrong delay may even increase the level of PIM on the receive (Rx) signal, making it almost impossible to decode the receive (Rx) signal. This will result in throughput loss for the receiver.

Another potential issue with PIM cancellation algorithms is the use of transmit (TX) traffic to compute equation (1). The bandwidth of the transmit (TX) signal can be either small or large. For example, a LTE 5MHz signal may comprise transmit (TX) traffic occupying either 180 KHz (minimum) or 4.5 MHz (maximum) of bandwidth. Similarly, Internet of Things (IoT) signals are only 180 KHz wide. Narrow bandwidth signals do not possess good correlation properties. However, wideband signals, such as when LTE 5MHz has 4.5 MHz (90% occupancy of 5MHz) of subcarriers occupied, the correlation properties are preserved, but not at the optimum.

Fig. 1 shows the poor correlation property observed by equation (1), using two narrow band 180 KHz LTE resource blocks, which is the minimum allocation of LTE resource blocks per user. It may be seen that a poor correlation property results. The marker 100 indicates the correct delay. Hence, it is clear from Fig. 1 that the computed or the estimated delay offset is wrong, thus giving a false delay for the PIM cancellation algorithm. Due to a poor correlation property, the estimated delay would have come to the right of the marker 100.

In general, the transmit (TX) signal bandwidth is unknown when the delay search peak is computed.

Example embodiments herein provide more accurate determination of delay search peaks, generally by generating and transmitting a sequence having good auto correlation properties. Further, purging of operator or user data traffic should be minimised or avoided, as traffic purging typically causes a loss of revenue to the radio operator or may cause a loss of emergency calls.

Example embodiments may involve adapting one or more transmit (TX) signals within a defined band to improve the autocorrelation properties of the transmit (TX) signal. Example embodiments may involve generating on the basis of at least the adapted transmit (TX) signal and a corresponding receive (RX) signal a respective passive intermodulation signal comprising a simulated n^ft order passive intermodulation product, where n is an odd integer greater than two. Embodiments may involve correlating the generated passive intermodulation signal with the receive (RX) signal to identify a correlation peak, and determining a time offset (tkiay) to apply to the generated passive intermodulation signal based on the correlation peak. Example embodiments may involve adapting the one or more transmit (TX) signals to add dummy sub-carriers within the defined band. For example, this may involve adding simulated orthogonal channel noise, using for example a orthogonal channel noise simulator (OCNS.)

In some example embodiments, adapting may involve identifying one or more resource blocks of the one or more transmit signals which are unused for user traffic, and adding the dummy carriers into at least some of said unused resource blocks. Dummy carriers may be added into substantially all unused resource blocks.

The resource blocks may be LTE or 5G resource blocks, for example.

The dummy sub-carriers may be added within the band at discrete periods, sufficient to obtain an accurately measured time offset (Way).

The time offset (Way) determination may involve generating a plurality of reference time offsets t₁ , t₂,..t_n based on a plurality of temporally-spaced samples of the transmit signal and of the receive signal, and computing the time offset based on an averaging of the reference time offsets.

An example process may involve computing the time offset based on:

(i) computing the median (Wdian) of the reference time offsets t₁ , t₂,..tn ;

(ii) computing the mean (Wa_n) of the reference time offsets t₁ , t₂,..t„ ; and

(iii) computing the time offset (Way) as value between Wdte_n and t mean» wherein the time offset (Wiay) is computed when abs(tmediun - Wan) < two or less samples.

Allocating just two or more resource blocks per LTE carrier may not be sufficient. At least a signal separation of >= 2 MHz is proposed between the resource blocks. This signal separation between the resource blocks enhances the correlation properties of the transmit signal. Another example embodiment may involve adapting the transmit (TX) signal by modulating a sub-portion of resource blocks of the one or more transmit signals with a complex mathematical sequence, for example a Zadoff-Chu sequence which has good auto-correlation properties. The sub-portion of resource blocks may be those unused for user traffic.

According to some embodiments, the signal output from the transceiver to the antenna and the signal received from the antenna after the receive band filter but before demodulation may be used as TX signal and RX signal, respectively. This is shown in Fig. 2. In some embodiments, instead of these signals, baseband signals may be used.

A corresponding configuration is shown in Fig. 3. In Fig. 3, the impact on RX carrier is based on the transmit carriers, it is still the same PIM Modeling but carrier based. One can predetermine where (at which frequency) the

intermodulation product of the carrier combination will fall.

As shown in Figs. 2 and 3, a composite signal generated by the TX baseband module modulates a RF signal in the modulation unit. The modulated signal may pass through a TX filter (optional) and is transmitted via the antenna system. This signal comprises IMP(s) which may be back-reflected in the antenna system such that it is received by the RX path. The RX path comprises a RX filter to pass substantially only the RX band. Then, the RX signal is demodulated and given to the RX baseband unit The TX and RX signals for the modelling may both be modulated signals (Fig. 2) or both be baseband signals (Fig. 3). The TX and RX signals may be sampled.

The samples (TX signal, RX signal) obtained from these measurements may be input into a basic model of the PIM signal..

Fig.4 shows an apparatus according to an embodiment The apparatus may be an Operation & Maintenance Center or an element thereof such as a PIM estimating unit, which may perform delay estimation in accordance with example

embodiments. The apparatus comprises measuring means lOand adapting means 20. Each of measuring means 10 and adapting means 20 may be a measuring processor and adapting processor, respectively.

The measuring means 10 measures plural transmit signals and corresponding receive signals. Each of the transmit signals is fed into an antenna system, and the corresponding receive signal is received from the antenna system when the respective transmit signal is fed into the antenna system.

The adapting means 20 adapts a basic model describing a relation between each of the plural transmit signals and respective passive intermodulation signal. According to example embodiments, the adapting means 20 may further be configured to synchronize (or align) computed third (or other n, where n is an odd integer greater than two) order product(s) with the receive (RX) signal.

In one example embodiment, this may be performed by adapting the transmit signal (TX) to improve its auto-correlation properties by means of inserting dummy carriers. In some embodiments, the dummy carriers may be provided by adding orthogonal channel noise to the transmit signal (TX) such as by using an Orthogonal Channel Noise Simulator (OCNS). This dummy traffic may be added such that it occupies portions of the transmit signal (TX), however organised at the physical layer, which are unused for operator or user traffic.

For example, Fig. 5 shows a LTE Frequency Division Duplex (FDD) frame which comprises a plurality of resource blocks and subcarriers. For example, for 5 MHz bandwidth, there are 25 resource blocks and 300 uplink subcarriers. At a given time, some of these subcarriers will be used for user traffic. The unused subcarriers may therefore be used to improve the auto-correlation properties of the transmit (TX) signal by the adapting means 40 injecting orthogonal channel noise, as indicated in Fig. 6 schematically, where an OCNS 60 is employed.

The OCNS 60, by means of the adapting means 40, can be selectively turned ON and OFF. When turned ON, all LTE resource blocks are populated, which may yield high auto-correlation results over the full bandwidth, e.g. 5 MHz, with 300 independent subcarriers (full 25 resource blocks). When turned OFF, only the real user traffic will appear.

Fig. 7 is a flow diagram showing processing operations that may be performed in a method according to preferred embodiments. A first operation S10 may comprise adapting one or more transmit signals within a defined band to improve the autocorrelation properties of the transmit signal. A second operation S20 may comprise generating on the basis of at least the transmit signal and a corresponding receive signal a respective passive intermodulation signal comprising a simulated n^tb order passive intermodulation product, where n is an odd integer greater than two. A third operation S30 may comprise correlating the generated passive intermodulation signal with the receive signal to identify a correlation peak. A fourth operation S40 may comprise determining a time offset (tdeiay) to apply to the generated passive intermodulation signal based on the correlation peak.

It will be appreciated that certain operations may be modified or omitted. Further operations may be involved. The numbering of operations is not necessarily indicative of the order of processing.

An algorithm may be activated when the OCNS 60 is turned ON. The algorithm assumes a certain, minimum amount of time to obtain the correct delay result; because the OCNS fills unoccupied resource blocks, the time that it is ON may be kept to a minimum to avoid or minimize cell to cell interference.

The algorithm may assume that the OCNS 60 is turned ON M times per day, or other period, each time period occupying N minutes. M may be operator dependent. N minutes is the minimum period for the algorithm to obtain an accurate delay estimate, which can be determined using routing experimentation. In one operation of the algorithm, the algorithm collects P samples of the receive (RX) and transmit (TX) data. Within the TX data, a 3^rd order model may be computed using any suitable method, including for example that mentioned above, but not limited to such, to compute the delay search procedure outlined in (1) above. The maximum correlation peak may be used as a temporary time alignment pointer, e.g. tl . Depending on the implementation, the P samples may comprise Q blocks of data. The size of Q may be large enough to reduce phase discontinuities. If a block structure is not used, the P samples may be

continuous.

In another operation, the previous operation may be repeated a number of times, e.g. r times. Due to the statistical nature of the data, and other factors such as blockers, phase, thermal noise and other sources of noise, the time alignment pointer may differ at each repetition. The algorithm however collects tl, t2, t3....ti.

In another operation, the collection of time alignment pointers or samples (t1 , t₂, t3.. ,.ti) will be sufficient to obtain an accurate result. The accurate time alignment figure may be computed based on an averaging. For example

The value of Usiay may be any value in between t_Median or t_Mean or vice versa. The parameters that support the algorithm may be N, P, size of Q, and r. These may be specific to a hardware implementation and may be optimized to obtain the correct delay search result from the OCNS 60, for example when a blocker is present in the receiver path.

Particular advantages of the example embodiment of adding additional carriers to fill substantially the whole bandwidth means that an accurate offset figure can be determined. Further, this need not interrupt or purge user traffic and so the operator may incur no revenue loss.

Another embodiment may involve improving the auto-correlation properties of the transmit (TX) signal by using a subset of the transmit signal, e.g. unused resource blocks, with test data that is modulated using a complex mathematical sequence. For example, it is found that by modulating a subset of LTE resource blocks with a Zadoff-Chu sequence, improved offset accuracy is observed, again without purging user traffic.

This embodiment may use two or more LTE resource blocks for the transmit (TX) signal, possibly with a signal separation between resource blocks. For example, the signal separation may be in the order of > 2 MHz on one LTE carrier and 4 MHz on the second LTE carrier. For simplicity, a fixed signal separation of 4 MHz could be used on both LTE carriers. Said figures are given merely by way of example. A distinct frequency spacing between the two or more resource blocks provides benefit, in some embodiments.

As with the previous embodiment, a more accurate offset figure can be determined which need not interrupt or purge user traffic and so the operator may incur no revenue loss.

Fig. 8 shows an apparatus according to an embodiment. The apparatus may provide the functional modules indicated in Fig. 4. The apparatus comprises at least one processor 420 and at least one memory 410 directly or closely connected to the processor. The memory 410 includes at least one random access memory (RAM) 410b and at least one read-only memory (ROM) 410a.

Computer program code (software) 415 is stored in the ROM 410a. The apparatus may be connected to a TX path and a RX path of a base station in order to obtain the respective signals. However, in some embodiments, the TX signals and RX signals are input as data streams into the apparatus. The apparatus may be connected with a user interface U1 for instructing the apparatus and/or for outputting the results (e.g. the estimated delay). However, instead of by a UI, the instructions may be input e.g. from a batch file, and the output may be stored in a non-volatile memory. The at least one processor 420, with the at least one memory 410 and the computer program code 415 are arranged to cause the apparatus to at least perform at least the method according to Fig. 7. The determined offset may be provided from the Fig. 8 apparatus to a local or remote location, such as a radio system, e.g. a cellular base station. The determination and provision may be performed periodically. The Fig. 8 apparatus may be provided in an Operation & Maintenance Center or an element thereof such as a delay estimating unit, which may also be used for storing the data for quality control purposes.

Fig. 9 shows a non-transitory media 130 according to some embodiments. The non-transitory media 130 is a computer readable storage medium. It may be e.g. a CD, a DVD, a USB stick, a blue ray disk, etc. The non-transitory media 130 stores computer program code causing an apparatus to perform the method of Fig. 7 when executed by a processor such as processor 420 of Fig. 8.

Fig. 10 is a graph showing the correct delay search peak, demonstrating improved auto-correlation properties of PIM generated with two resource blocks modulated with a complex mathematical sequence.

One piece of information may be transmitted in one or plural messages from one entity to another entity. Each of these messages may comprise further (different) pieces of information.

Names of network elements, protocols, and methods are based on current standards. In other versions or other technologies, the names of these network elements and/or protocols and/or methods may be different, as long as they provide a corresponding functionality. For example, embodiments may be deployed in 2G/3G/4G/5G networks and further generations of 3GPP but also in non-3GPP radio networks such as WiFi. Accordingly, a base station may be a BTS, a NodeB, a eNodeB, a WiFi access point etc.

A memory may be volatile or non-volatile. It may be e.g. a RAM, a sram, a flash memory, a FPGA block ram, a DCD, a CD, a USB stick, and a blue ray disk.

If not otherwise stated or otherwise made clear from the context, the statement that two entities are different means that they perform different functions. It does not necessarily mean that they are based on different hardware. That is, each of the entities described in the present description may be based on a different hardware, or some or all of the entities may be based on the same hardware. It does not necessarily mean that they are based on different software. That is, each of the entities described in the present description may be based on different software, or some or all of the entities may be based on the same software. Each of the entities described in the present description may be embodied in the cloud. According to the above description, it should thus be apparent that example embodiments provide, for example, a delay estimation device for PIM

cancellation, or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same to well as mediums carrying such computer program(s) and forming computer program produces). Such a delay estimation device for PIM cancellation may be incorporated e.g. in a Nokia Airframe expandable base station.

Implementations of any of the above described blocks, apparatuses, systems, techniques or methods include, as non-limiting examples, implementations as hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. Some embodiments may be implemented in the cloud.

It is to be understood that what is described above is what is presently considered the preferred embodiments. However, it should be noted that the description of the preferred embodiments is gi ven by way of example only and that various modifications may be made without departing from the scope as defined by the appended claims.

Claims

1. Apparatus, comprising:

means for generating on the basis of at least the transmit signal and a corresponding receive signal a respective passive intermodulation signal comprising a simulated n* order passive intermodulation product, where n is an odd integer greater than two;

means for correlating the generated passive intermodulation signal with the receive signal to identify a correlation peak;

means for determining a time offset (Uriay) to apply to the generated passive intermodulation signal based on the correlation peak.

2. The apparatus of claim 1, wherein the adapting means is configured to add dummy sub-carriers within the defined band.

3. The apparatus of claim 2, wherein the adapting means is configured to add the dummy sub-carriers by means of adding simulated orthogonal channel noise.

4. The apparatus of claim 2 or claim 3, wherein the adapting means is configured to identify one or more resource blocks of the one or more transmit signals which are unused for user traffic, and to add the dummy carriers into at least some of said unused resource blocks.

5. The apparatus of claim 4, wherein the adapting means is configured to add the dummy carriers into substantially all unused resource blocks.

6. The apparatus of claim 4 or claim 5, wherein the resource blocks are LTE or 5G resource blocks.

7. The apparatus of any of claims 4 to 6, wherein the dummy sub-carriers are added within the band with a predetermined minimum frequency separation between resource blocks, sufficient to obtain an accurately measured time offset

(tdelay).

8. The apparatus of any preceding claim, wherein the time offset (tdeiay) determining means is configured to generate a plurality of reference time offsets t₁ , t2,..tn based on a plurality of temporally-spaced samples of the transmit signal and of the receive signal, and to compute the time offset based on an averaging of the reference time offsets.

9. The apparatus of claim 8, wherein the determining means is configured to compute the time offset based on:

(i) computing the median (t_media_n) of the reference time offsets t₁ , t2,..t_n ;

(ii) computing the mean (tmom) of the reference time offsets t₁ , t2,..t_n ; and

10. The apparatus of claim 9, wherein the time offset (tdeiay) is computed when abs(tmedian - Wan) < tWO or less Samples.

11. The apparatus of any preceding claim, wherein the generating means generates the respective passive intermodulation signal comprising either a simulated 3^rd of 5^th order passive intermodulation product.

12. The apparatus of claim 1, wherein the adapting means is configured to modulate a sub-portion of resource blocks of the one or more transmit signals with a complex mathematical sequence.

13. The method of claim 12, wherein one of first and second transmit signals has a reduced bandwidth than the other transmit signal at a predetermined frequency separation between said transmit signals.

14. The apparatus of claim 12 or claim 13, wherein the complex mathematical sequence is a

sequence.

15. The apparatus of any of claims 12 to 14, wherein the sub-portion of resource blocks are unused for user traffic.

16. The apparatus of any of claims 12 to 15, wherein the adapting means is configured to modulate resource blocks having a beneficial frequency spacing to improve the autocorrelation.

17. The apparatus of any preceding claim, further comprising means for applying the determined time offset (fo-iay) to the generated respective passive intermodulation signal and means for applying the resulting signal to the one or more receive signals for mitigating passive intermodulation.

18. The apparatus of any preceding claim, further comprising means for receiving the one or more transmit signals and corresponding receive signals from a remote radio apparatus and for transmitting the time offset (Usiay) to the, or another, remote radio apparatus.

19. A method, comprising:

generating on the basis of at least the transmit signal and a corresponding receive signal a respective passive intermodulation signal comprising a simulated n* order passive intermoduiation product, where n is an odd integer greater than two;

correlating the generated passive intermoduiation signal with the receive signal to identify a correlation peak; and

determining a time offset (tdeiay) to apply to the generated passive intermoduiation signal based on the correlation peak.

20. The method of claim 19, wherein the adapting comprises adding dummy sub-carriers within the defined band.

21. The method of claim 20, wherein the dummy sub-carriers are added by means of adding simulated orthogonal channel noise.

22. The method of claim 20 or claim 21 , further comprising identifying one or more resource blocks of the one or more transmit signals which are unused for user traffic, and adding the dummy carriers into at least some of said unused resource blocks.

23. The method of claim 22, wherein the dummy carriers are added into substantially all unused resource blocks.

24. The method of claim 22 or claim 23, wherein the resource blocks are LTE or 5G resource blocks.

25. The method of any of claims 22 to 24, wherein the dummy sub-carriers are added within the band with a predetermined minimum frequency separation between resource blocks, sufficient to obtain an accurately measured time offset

(tdeiay).

26. The method of any of claims 19 to 25, wherein determining the time offset (tdeiay) comprises generating a plurality of reference time offsets ti , t2,..tn based on a plurality of temporally-spaced samples of the transmit signal and of the receive signal, and computing the time offset based on an averaging of the reference time offsets.

27. The method of claim 26, wherein determining the time offset (tdeiay) comprises:

(i) computing the median (tmedian) of the reference time offsets t₁ , t2,..t_n ;

(ii) computing the mean (Wa_n) of the reference time offsets t₁ , t2,..t_n ; and

28. The method of claim 27, wherein the time offset (tdeiay) is computed when abs(tmedian " tmcan) < tWO OG les sasmples.

29. The method of any of claims 19 to 28, wherein the respective passive intermodulation signal comprises one or more of a simulated 3^rd of 5^th order passive intermodulation product.

30. The method of claim 19, wherein the adapting comprises modulating a sub-portion of resource blocks of the one or more transmit signals with a complex mathematical sequence.

31. The method of claim 30, wherein one of first and second transmit signals has a reduced bandwidth than the other transmit signal at a predetermined frequency separation between said transmit signals.

32. The method of claim 30 or claim 31, wherein the complex mathematical sequence is a Zadoff-Chu sequence.

33. The method of any of claims 30 to 32, wherein the sub-portion of resource blocks are unused for user traffic.

34. The method of any of claims 30 to 33, wherein adapting comprises modulating resource blocks having a beneficial frequency spacing to improve the correlation.

35. The method of any of claims 19 to 34, further comprising applying the determined time offset (tdeiay) to the generated respective passive intermodulation signal and applying the resulting signal to the one or more receive signals for mitigating passive intermodulation.

36. The method of any of claims 19 to 35, further comprising receiving the one or more transmit signals and corresponding receive signals from a remote radio apparatus and transmitting the time offset (tde&y) to the, or another, remote radio apparatus.

37. An apparatus comprising at least one processor, at least one memory directly connected to the at least one processor, the at least one memory including computer program code, and the at least one processor, with the at least one memory and the computer program code being arranged to perform the method of any of claims 19 to 36.

38. A computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method of any of claims 19 to 36.

39. A non-transitory computer readable medium comprising program instructions stored thereon for performing a method, comprising: adapting one or more transmit signals within a defined band to improve the autocorrelation properties of the transmit signal;

generating on the basis of at least the transmit signal and a corresponding receive signal a respective passive intermodulation signal comprising a simulated n* order passive intermodulation product, where n is an odd integer greater than two;

determining a time offset (tdeiay) to apply to the generated passive intermodulation signal based on the correlation peak.

40. An apparatus comprising: at least one processor; and at least one memory including computer program code which, when executed by the at least one processor, causes the apparatus:

to correlate the generated passive intennodulation signal with the receive signal to identify a correlation peak; and

to determine a time offset

to apply to the generated passive intermodulation signal based on the correlation peak.