APPARATUS, SYSTEM AND METHOD FOR TESTING RADIO EQUIPMENT

TECHONOLOGICAL FIELD

The invention relates to the field of radio communication systems, and more specifically to testing of radio equipment.

BACKGROUND

SIEMENS is developing innovative test systems for ASIC and FPGA verification and validation in the areas of simulation, hardware emulation, Field Programmable Gate Array (FPGA) pro totyping, and real time (post-silicon, manufacturing) envi ronments. Such test systems may comprise one or more test ap paratus that can be utilized in a variety of high tech fields, ranging from cellular base stations to the automotive industry. For example, a radio equipment test system or test apparatus, e.g. from the X-Step product line, allows stimula tion and tracing of all the digital interfaces in a modern radio equipment such as a radio equipment control (REC) and/or radio equipment (RE) modules (also known as baseband unit, BBU, and remote radio head, RRH, respectively) . The digital interface protocols supported by such a test appa ratus may include JESD204B, CPRI, OBSAI RP3 , and 10G Ether net. A test apparatus may further comprise in register- transfer level (RTL) simulation and hardware emulation and may also work with FPGA prototyping, real-time post-silicon board debugging and final product testing. The test apparatus may cover every phase in a radio base station product devel opment cycle, ranging all the way from very first RTL simula tions to post-production. The same tests can then be re-used in every phase of the product development cycle. Also, thanks to the parameterized test case building block architecture, the porting of test cases from one project to another is fa cilitated . SUMMARY

Implementation of 5G networks will change the technology landscape for all the concerned stakeholders from equipment manufacturers to telecom operators. The radio interface for example is switching from analog over to digital which means that traditional ways of developing and testing the equipment will no longer be possible. Also, the network set-up is be coming more complex. When, for example, a 3G network used six antennas and a 4G network used 36 antennas, then a 5G system may have more than 200 antennas.

It is thus an object of the present invention to improve testing of radio equipment.

According to a first aspect the object is achieved by a meth od of testing radio equipment. The method comprising: receiv ing, by way of a radio channel test apparatus, a baseband signal representing I/Q data of one or more radio channels. The method further comprising processing, by way of the radio channel test apparatus, the baseband signal representing I/Q data according to one or more radio channel models. The meth od further comprising transmitting, by way of the radio chan nel test apparatus, the processed baseband data representing I/Q data to a radio equipment under test.

According to a second aspect the object is achieved by a ra dio channel test apparatus operative to perform any one of the method steps of the first aspect.

According to a third aspect the object is achieved by a radio channel test apparatus comprising a first interface for re ceiving a baseband signal comprising I/Q data. The radio channel test apparatus further comprising a processor config ured to process the received baseband signal according to one or more radio channel models. The radio channel test appa- ratus further comprising a second interface for transmitting the processed baseband signal.

According to a fourth aspect the object is achieved by a sys tem comprising a physical or virtual radio equipment control unit, preferably a physical or virtual base band unit, and one or more physical or virtual radio equipments, preferably one or more physical or virtual remote radio heads, and a ra dio channel test apparatus according to the second or third aspect .

BRIEF DESCRIPTION OF DRAWINGS

Examples of embodiments herein will be described in more de tail with reference to attached drawings, wherein:

Figure 1 shows an illustration of a fronthaul network.

Figure 2 shows an illustration of a fronthaul data transmis sion using different protocols.

Figure 3 shows an illustration of a functional split within a fronthaul network.

Figure 4a shows an illustration of multiple possible func tional splits within a fronthaul network.

Figure 4b shows a table of the functional splits of Figure 4a also listing the different requirements and advantages.

Figure 5 shows an illustration of a testing environment.

Figure 6 shows another illustration of a fronthaul network. Figure 7 shows an illustration of first testing environment comprising a radio channel test apparatus.

Figure 8 shows an illustration of a second testing environ ment comprising a radio channel test apparatus.

Figure 9 shows an illustration of a third testing environment comprising a radio channel test apparatus.

Figure 10 shows an illustration of a fourth testing environ ment comprising a radio channel test apparatus.

Figure 11 shows an illustration of a fifth testing environ ment comprising a radio channel test apparatus. Figure 12 shows an illustration of a testing environment com prising modeling of multiple radio channels.

Figure 13 shows an illustration of a radio channel test appa ratus .

Figure 14 shows exemplary steps according to a method of a first embodiment.

Figure 15 shows exemplary steps according to a method of a second embodiment.

Figure 16 shows exemplary steps according to a method of a third embodiment.

Figure 17 shows exemplary steps according to a method of a fourth embodiment.

Figure 18 shows exemplary steps according to a method of a sixth embodiment.

Figure 19 shows exemplary steps according to a method of a seventh embodiment.

Figure 20shows an exemplary step according to a method of an eighth embodiment.

Figure 21 shows exemplary steps according to a method of a ninth embodiment .

Figure 22 shows exemplary steps according to a method of a tenth embodiment.

Figure 23 shows an exemplary step according to a method of an eleventh embodiment.

Figure 24 shows an exemplary step according to a method of an eleventh embodiment.

Figure 25 shows exemplary steps according to a method of a thirteenth embodiment.

Figure 26 shows an exemplary step according to a method of a fourteenth embodiment.

Figure 27 shows an exemplary step according to a method of a fifteenth embodiment.

In Figure 1 a radio communication system is illustrated. The traditional monolithic base transceiver station (BTS) archi tecture is increasingly being replaced by a distributed BTS architecture in which the functions of the BTS are separated into two physically separate units - a baseband unit (BBU) and a remote radio head (RRH) . The BBU performs baseband pro cessing for the particular air interface that is being used to wirelessly communicate over one or more radio frequency channels. The RRH performs radio frequency processing to con vert baseband data output from the BBU to radio frequency signals for radiating from one or more antennas coupled to the RRH and/or to produce baseband data for the BBU from ra dio frequency signals that are received at the RRH via one or more antennas. The RRH is typically installed near the one or more antennas, often at the top of a tower, and the BBU is typically installed in a more accessible location, often at the bottom of the tower. However, as the case may be RRH and BBU may be collocated, e.g., in a lab. The BBU and the RRH are typically connected through one or more fiber optic links. The interface between the BBU and the RRH is defined by fronthaul communication link standards such as the Common Public Radio Interface (CPRI) family of specifications, the Open Base Station Architecture Initiative (OBSAI) family of specifications, and the Open Radio Interface (ORI) family of specifications .

In the 5G architecture, a new frequency domain fronthaul in terface will be specified. The frequency domain fronthaul is a functional split where the IFFT/FFT (Inverse Fast Fourier Transform/ Fast Fourier Transform) may be moved from the BBU to the RRH. Frequency domain samples instead of time domain samples are sent over the fronthaul. The RRH will have infor mation through a communication channel about the resource al location for different UEs. The new eCPRI interface specifi cation "eCPRI Specification VI .0 (2017-08-22)" is already available .

For the deployment scenario where the remote radio head, RRH, (sometimes also denoted as Radio Remote Unit, RRU) and the baseband unit, BBU, (sometimes also denoted as radio equip ment controller, REC) are separated, the signals received from one or more antennas have to be transported over the me dia that is connecting the RRH with the BBU as normally the signal combination is done at the BBU. In general, the inter face that is used for the connection between the BBU and the RRH is called the fronthaul. The signals over the fronthaul could be complex time domain samples such as specified in the legacy Common Public Radio Interface, CPRI . Digitized wave forms may be transported over the fronthaul from the BBU to the RRH, and vice versa, via one or more radio aggregation units (RAU) .

The user equipment's, UE, signals are power limited and as the path loss varies with the distance to the UE a large dy namic range is encountered when those signals are represented digitally, it may be assumed that for the complex frequency sample a large number of bits will be required and in the case of MIMO (Multiple Input Multiple Output) /diversity lay ers the required fronthaul capacity will multiply with the number of antennas. Furthermore, it is desired to model such propagation of radio signals in order to test the functional ity of the radio system and its components. As the capacity on the fronthaul is limited it is desired to find methods that optimize the usage of the fronthaul.

The BBU may be connected to a core network, Core, and possi bly to other BBUs (not shown) via one or more backhaul or crosshaul connections.

In Figure 2 fronthaul data transmission using different pro tocols is illustrated. As mentioned, the different protocols employed have different bandwidth capacities. Hence, the CPRI streaming supports up to 10.1 Gbps, whereas CPRI v7.0 sup ports 25Gbps, and eCPRI supports up to 25Gbps, e.g., between the RRH and the BBU.

I/Q data, i.e. in-phase and quadrature components data, is digitalized air-interface data. The sample rate in 5G is 122.88MHz. Thus, especially in case of multiple radio chan nels, a high amount of data needs to be transmitted via the fronthaul. It should be understood that I/Q data transmission may occur in uplink and downlink direction for each radio channel .

In order to improve data transmission a functional split be tween the components of the BBU and the RRH may be intro duced. Such a functional split is illustrated in Figure 3.

The concept of a functional split is, e.g., described in sec tion 2.3 of eCPRI Specification VI .0 (2017-08-22) . According to this, a radio base station is divided into two nodes, one called REC (Radio Equipment Control), e.g. the BBU, and the other called RE (Radio Equipment), e.g. the RRH. The 'Fron thaul Network' may thus be understood as the interface be tween the REC and RE. The different functions of the base station, e.g. as listed in Table 1 of eCPRI Specification VI .0 (2017-08-22), can be located either in the REC or in the RE, that is to say BBU or RRH respectively.

Functional split can be summarized as determining how much data is processed in different components, e.g., different parts of an eNodeB/or gNodeB. For example, in CPRI the I/Q data is typically in the time domain, but may be in the fre quency domain, e.g., when FFT processing is made to I/Q sam ples. Such processing reduces the amount of data for trans mission via the fronthaul link. In general however, data may be processed, e.g., according to one or more radio channel models, in the frequency domain, or data can be transformed to the time domain and processing may be performed in the time domain.

In Figure 4a multiple possible functional splits within a fronthaul network are illustrated. Figure 4a shows the proto col stack layers for a 3GPP 4G (LTE) or 5G (NR) radio base station. Five inter-layer functional splits numbered A to E are depicted in Figure 4a. One additional set of intra-PHY splits named {ID;IID;IU} is also shown. More details are de- scribed in section 2.3.1 of eCPRI Specification VI .0 (2017— 08-22) .

In Figure 4b, a table listing the different requirements and advantages of the functional splits according to figure 4a is illustrated. Figure 4b shows how different splits will set different relative capacity- and latency-requirements on the fronthaul network.

Even though reference is being made to one or more BBUs and one or more RRHs throughout the present disclosure, it should be understood that different names are in use throughout the industry, e.g., for the different parts of a base station.

For example, the expression Distributed Unit, DU, and Central Unit, CU, are used for parts equivalent to a RRH and a BBU, respectively, and that the present disclosure also relates those parts.

In Figure 5, a testing environment for testing radio equip ment is illustrated. A channel model is a (test-)model for the behavior of one or more radio signals transmitted over the air interface. This channel model enables to test radio equipment in lab environments or even on-site. Testing may be operationally performed as illustrated in Figure 5. For exam ple, a channel model test apparatus may be used that performs the processing of the radio frequency signals, e.g., in the form of I/Q data, according to one or more channel models.

All connections, e.g., between the base station and/or the test apparatus and/or the UE, may be made by coaxial cables.

Implementation of 5G networks may change the technology land scape for all the concerned stakeholders from equipment manu facturers to telecom operators. Also, the network set-up is becoming more complex. According to 2G, 3G, and 4G testing, channel modeling may be done by connecting multiple mobile phones, also called UEs, to a single antenna via coaxial ca ble. The move to 5G networks may make this method of testing redundant primarily for two reasons. First of all, new 5G an tennas (e.g. employing massive MIMO) do not have an analog coaxial interface. Therefore, new emulators will have to be developed to support the 5G radio equipment, and in particu lar antenna, testing. Second of all, the number of new anten nas needed to provide 5G coverage means that it is not cost effective to test each antenna.

Now turning to Figure 6, a fronthaul network for the purpose of testing one or more radio equipments is illustrated. The base station is separated into a virtual BBU and a (physi cal/real) RRH, wherein between the virtual BBU and the RRH a fronthaul network is provided. The RRH may be operatively coupled to the UE in order to transmit and/or receive radio signals .

According to Figure 7, channel modeling is provided for with in the fronthaul network. The UE may be collocated with the RRH in a test chamber in which radio signals are exchanged between the RRH and the UE . The channel modeling of the radio signal propagation however is performed in the fronthaul net work, e.g. by way of a radio channel test apparatus. That is to say, propagation of radio signals via the air interface according to one or more radio channel models is modeled, e.g. by way of said test apparatus. The test apparatus may be operatively connected to the BBU and the RRH via fronthaul network. That is to say, the test apparatus is inserted in the fronthaul network. Baseband signals representing I/Q data may be exchanged between the RRH and the BBU via the test ap paratus. At the same time channel models may be applied to the I/Q data, i.e. processing the I/Q data and, thereby mod eling the behavior of radio signal propagation between the RRH and the UE .

As illustrated in Figure 8, instead of a physical RRH, a physical UE and/or a test chamber a virtual UE may be used as a testing environment. Thereby, the channel models and/or the virtual UE may reflect properties of the propagation of radio signals via the air interface. Such a set-up is particularly applicable in the case of testing a BBU. Virtual or other ad ditional test apparatus can replace real UE and real RRH in this test setup. Alternatively, the virtual UE and virtual RRH and the channel models may be incorporated into a single test apparatus. The test setup of Figure 8 is thus particu larly useful when the implementation of a BBU is to be test ed. Also, load testing is possible in this setup.

In Figure 9 a testing environment comprising a virtual BBU is used and the channel modeling is performed via a section of the fronthaul communication link connecting the virtual BBU to the RRH. In this testing environment a physical RRH is collocated with a (physical) UE in a testing chamber, cf. Figure 7. The virtual BBU can also emulate core network com ponents, e.g. when a mobile call is made. In this setup, RRH and/or UE may be under test. The digital connection can also be virtual when virtual components (virtual BBU) is used thereby connecting the virtual BBU to channel models.

Yet another testing environment is illustrated in Figure 10. In a UE or an antenna test case, the RRH can be replaced by Software Defined Radio, SDR. The channel model connection protocols can also be different ones, e.g., CPRI and

JESD204C. That is to say, instead of the fronthaul channel protocols such as (e)CPRI or JESD204C another protocol may be used for transmitting and/or receiving I/Q data between the radio channel test apparatus and the device under test, e.g., the SDR apparatus. In addition, as can be seen in Figure 10 for the different sections of the connection between (virtu al) BBU and (virtual) RRH different protocols may be used. In Figure 10 for example CPRI is used to connect the radio chan nel test apparatus to the virtual BBU whereas the JESD204C protocol is used for communicating with the SDR device. In Figure 11 a testing environment comprising multiple RRH which are operatively connected to one or more UEs is illus trated. The multitude of RRHs are connected to the channel modeling (apparatus) via a fronthaul communication network or fronthaul communication link. Again, a virtual BBU as de scribed in the above may be employed. Via CPRI or an alterna tive digital interface data from/to multiple antenna and RRH may be transmitted.

In Figure 12 multiple, different channels/data paths are il lustrated. Basically, every antenna may have a separate data path/data channel to the BBU in both directions, i.e. down link and uplink, although only the uplink data paths are de picted in Figure 12. Hence, every channel depicted may carry radio channel information relating to one or more radio chan nels between the RRH and the UE . Each of these channels may thus be processed according to a radio channel model in order to model radio signal propagation. In addition each radio channel may be subject to the same or to (mutually) different radio channel models. A corresponding radio channel test ap paratus will be described in the following.

In Figure 13 a radio channel test apparatus is illustrated. The radio channel test apparatus may comprise a housing in which one or more of the modules represented by the solid lines in figure 13 are arranged. Communication to or from the radio channel test apparatus may be achieved via a first and/or a second fronthaul protocol. Instead of the fronthaul protocol any other digital protocol may be used in order to transmit and/or receive one or more baseband signals repre senting I/Q data of one or more radio channels. Thus, the ra dio channel test apparatus may be communicatively coupled to one or more BBU on one hand and to one or more RRHs on the other hand. To this end, one or more corresponding interfaces may be provided, that implement the respective protocols. The radio channel test apparatus may thus receive data according to a functional split chosen between the BBU and the RRH. The functional split may be chosen according to the predetermined requirements and/or the design chosen by the network operator and/or network equipment manufacturer.

Thus, the radio channel test apparatus may be communicatively coupled to a real/physical or virtual BBU, e.g., as described in any one of the embodiments of Figures 1 to 12, via a first interface. On the other hand, the radio channel test appa ratus may be communicatively coupled to one or more re al/physical RRHs, e.g. as described in any one of the embodi ments of Figures 1 to 12.

Now, as shown in Figure 13, by way of a channel model for the uplink and/or the downlink of a respective radio channel, I/Q data received by the radio channel test apparatus (belonging to that radio channel) may be processed according to a radio channel model and subsequently the I/Q data processed accord ing to the channel model may be transmitted by the radio channel test apparatus. That is to say, I/Q data received from one or more RRHs is processed and subsequently transmit ted by the radio channel test apparatus to a (virtual) BBU via digital protocol, e.g., a fronthaul protocol. The same is true for the other way around, i.e. in case I/Q data received from a (virtual) BBU is processed and forwarded by the radio channel test apparatus to one or more RRHs. Of course in this case as well, the different testing environments comprising real/physical RRHs and BBUs, respectively, as described in Figures 1 to 12 applies.

As can be seen in Figure 13, different channel models may be employed for the uplink or downlink of a radio channel. How ever, the same channel model may be used for uplink or down link. Furthermore, different channel models can be used for each of a plurality of radio channels. Again, the same chan nel model may be used for a plurality of radio channels. The one or more channel models employed may be chosen according to the test scenario. That is to say, one or more first chan- nel models may be chosen in order to test a UE, whereas one or more second radio channels may be chosen to test the RRH and/or the BBU.

As illustrated in Figure 13 I/Q data received via a first in terface implementing a fronthaul protocol or another digital protocol may be subject to a channel model, i.e. the I/Q data is processed according to that channel model and the pro cessed I/Q data is forwarded via a second interface imple menting a fronthaul protocol or another digital protocol. It should be understood, that the I/Q data of multiple radio channels may be received and that the I/Q data of each radio channel may be subject to a different channel model. The channel model may reflect information including a multipath profile of the channel, spatial signature of the various paths; fading model; mobility pattern.

By way of a radio channel test apparatus it is possible to process uplink and downlink I/Q data at the same time. Fur thermore, a single FPGA may be used to execute the one or more channel models and process the I/Q data. Furthermore, multiple of the proposed radio channel test apparatus may be combined, e.g., stacked, in order to provide the test setup needed, for example in case of multiple BBUs, RRH, and/or UEs. Thus, a method for emulating one or more radio channels that can improve the efficiency of testing, eliminate the need for multiple cables, and allow new RF front-end designs to be easily built, is proposed.

According to an aspect of the present disclosure data and signal processing for testing radio equipment is performed in the digital domain (only) . That is to say, the channel model ing (by way of the radio channel test apparatus) is performed according to a functional split in the fronthaul. This means that one or more radio signals received by one or more anten nas (or one or more antenna arrays) need to be transformed first into the digital domain, e.g. by way of an Analog-to- Digital converter. Thereafter, the sampled data may be pro cessed digitally and the one or more channel models may be employed. For example, after sampling the radio signal re ceived by the one or more antennas. The data may be processed according to JESD204C. The JESD204C can be configured as transmit or receive, using either 64B66B or 8B10B linecoding, and can be used to realize links requiring more than eight lanes .

Thus, received radio signals may be digitally processed by a digital front end (DFE) processor, e.g., with a programmable receive signal processing path for each receive antenna. Each receive signal path is formed, e.g., with a receive signal processor and an associated serialized interface and RF transceiver/receive front end that is connected to a receive antenna or even multiple antennas. The receive signal proces sor may include one or more processors (e.g., vector proces sors) and associated memory (e.g., RAM) for performing re ceive signal processing on I/Q data samples received from the front end over a receive interface, e.g., one of the JESD re ceive interface. To facilitate transfer of received signal information between the receiver front end and DFE, the transceiver/receiver front end may include a serialized in terface (e.g., JESD204B TX 261) for transfer to the received signal information over I/Q data signal lines. At the DFE, the signal information is received at a corresponding serial ized interface (e.g., JESD204B RX) . Once receive signal pro cessing of the signals received over I/Q signal lines is com pleted, the receive signal processor may send the processed samples to the baseband modem, e.g., as by using an (e)CPRI interface module. In this way, separate receive signal paths may be formed for each of the receive antennas. Such a setup is for example described in United States patent publication US8964791 B2.

Now, testing of radio equipment may comprise testing a base station according to 3GPP TS 36.104 V15.3.0 (2018-06) . Of course other radio equipment may be tested by way of the testing environment proposed and as described in the above, e.g. the device under test may be a UE . In particular, 3GPP TS 36.104 V15.3.0 (2018-06) provides inter alia an interfer ence model among others in Table 8.2.6-1. Still further test parameters for testing proper functioning of radio equipment is provided throughout the specification of 3GPP TS 36.104 V15.3.0 (2018-06), in particular in Annex B of 3GPP TS 36.104 V15.3.0 (2018-06) . This allows for testing components of the RRH, such as antennas. Hence, the channel model may comprises for example the interferer model as described in B.6 of 3GPP TS 36.104 V15.3.0 (2018-06) and the I/Q data received (by the radio channel test apparatus) may be processed as if such in- ter-cell interfering UE transmissions occurred.

In another embodiment the functional split in the downlink may be different than the functional split in the uplink.

Furthermore, the configuration of the radio channel test ap paratus, e.g. selection of the radio channels to be processed and/or selection of the one or more channel models, may be way of an external control. The radio channel test apparatus may comprise and additional interface as shown in Figure 13 for receiving corresponding user input.

In Figure 14 exemplary method steps according to an aspect of the present invention are illustrated. As explained in the above channel modeling is performed by processing I/Q data of one or more radio channels. Thus in a step SO a baseband sig nal representing I/Q data of one or more radio channels is received by way of a radio channel test apparatus. The I/Q data may be received from a RRH and/or a BBU, for example de pending on the test environment. Reception of I/Q data may occur via one or more interfaces implementing a digital pro tocol such as JESD204C and/or (e)CPRI. The protocol employed may depend on the functional split between the BBU and the RRH. In a step SI the baseband signal received representing I/Q data may be processed according to one or more radio channel models by way of the radio channel test apparatus. As ex plained in the above, in particular in connection with Figure 13, radio signal propagation may be subject to fading, inter ference or the like. Other test parameters by way of which proper functioning of radio equipment may be tested have also been provide in the above, e.g. Table 8.2.6-1 of 3GPP TS 36.104 VI5.3.0 (2018-06) .

After applying the channel model to the I/Q data, the pro cessed baseband data representing I/Q data is transmitting, by way of the radio channel test apparatus, to a radio equip ment under test. As the case may be this may be a RRH, a BBU and/or a UE or any combination thereof. It should be under stood that such transmission occurs using further radio equipment such as a radio aggregation unit, RAU.

In Figure 15 further exemplary method steps are illustrated. In a step S3 the baseband signal representing I/Q data is re ceived, by way of the radio channel test apparatus, via a communication link according to a functional split of a fron- thaul communication link. It should be understood that func tional split refers to fronthaul transport network, e.g. ac cording to eCPRI Specification VI .0 (2017-08-22), i.e. inter nal interface of radio base stations. Thus radio channel test apparatus is operationally arranged between the BBU and the RRH, or to use the terms of eCPRI Specification VI .0 (2017— 08-22), between the eREC and the eRE .

However, it should be understood that the baseband signal representing I/Q data may be received via another digital protocol in the same data path as the fronthaul network. Tha is to say, the baseband signal representing I/Q data may be received via an interface implementing the JESD204C protocol or another interface of the digital front end, DFE . In a step S4, the baseband signal representing I/Q data is transmitted, by way of the radio channel test apparatus, via a communication link according to a functional split of a fronthaul communication link. The functional split according to which the baseband signal representing I/Q data is trans mitted may correspond to the functional split according to which baseband signal representing I/Q data is received. Al ternatively, the radio channel test apparatus may itself per form certain processing in addition to applying one or more channel models to the baseband signal representing I/Q data. Thus, for example a baseband signal representing I/Q data is received at functional split B but is transmitted according to functional split E, cf. Figures 4a and 4b. The radio chan nel test apparatus may thus e.g. perform the steps of RLC,

MAC and (at least in part) PHY.

In Figure 16 further exemplary steps are illustrated. In a step S5 the I/Q data is converted into the frequency domain. For example (e)CPRI or another digital protocol based on car rying time domain baseband IQ samples between RRH and BBU may be used.

One of the major objectives of a functional split between RRH and BBU or other eREC and eRE is to lower the bit rates on the fronthaul interface. When looking at the different pro cessing stages performed in the PHY-layer (cf. Figure 32, eCPRI Specification VI .0 (2017-08-22)) in downlink direction, three processes will mostly increase the bit rate. These three processes are modulation, the port-expansion being done in combination with the beam-forming process and the

IFFT+cyclic-prefix-process, i.e. going from the frequency do main to the time domain, wherein IFFT refers to Inverse Fast Fourier Transformation. By moving the split upwards (into the direction of the MAC layer) the fronthaul bit rate will be lowered and vice versa. In particular, split IID and Iu as described in eCPRI Specification VI .0 (2017-08-22) may be used in connection with the other aspects and embodiments de scribed herein.

The I/Q data is, e.g., typically in CPRI, in the time domain, but in some case it could be in frequency domain, e.g., when FFT processing is made to I/Q samples. It's reduces data amount for transmission. The I/Q data may thus be modified in the frequency domain, or change data to time domain and make processing in there.

One or more IQ sample pairs (I, Q) , also referred to as I/Q data, may be in frequency domain or time domain and may com prise associated control information. Frequency domain I/Q data or time domain I/Q data may depend on the selected func tional split, e.g., between RRH and BBU and/or other eCPRI nodes, and in particular may be vendor specific.

The bit width of an I/Q sample, the number of I/Q samples in a message, and the format of I/Q samples (e.g. fixed point, floating point, block floating point), etc. may also be ven dor specific and the participating one or more trans

mit/receive BBUs and RRHs or other eCPRI nodes need to know the actual format in advance. In case of time domain func tional split, an eCPRI message carries I/Q data. In case of frequency domain functional split, the information associated with an I/Q sample is contained in a set of N packets, e. g. frequency domain I/Q data for one OFDM symbol and optionally related control information or user data for one OFDM symbol and as the case may be related control information. It should be understood that the conversion of the I/Q data preferably is taking place by transforming the I/Q data from the time domain into the frequency domain, and more particularly said conversion is taking place in the uplink direction.

Subsequent to the conversion of the I/Q data into the fre quency domain one or more channel models may be applied to the I/Q data. Hence, the I/Q data is processed in the fre quency domain in a step S6.

Now turning to Figure 17, further exemplary steps are illus trated. In a step S7 the I/Q data is converted into the time domain. Thus, for example I/Q data may be received in the downlink via fronthaul connection or a fronthaul protocol such as (e)CPRI. For transmission or for modeling transmis sion via the air interface, the I/Q data in the time domain is, preferably in the downlink direction, converted into the frequency domain.

Hence, in general the RF signal received is sampled and I/Q data in the time domain is produced. This time domain I/Q da ta is then converted e.g. by way of a FFT (module) into the frequency domain. In the frequency domain mapping of the I/Q data to OFDM-QAM symbols or other modulation scheme may be made. Subsequently resource mapping may be done and finally frames may be composed. When a RF is to be transmitted the steps outline in this paragraph are executed in reverse or der .

In the downstream direction, the data from the MAC layer is processed to form PHY frames and mapped to OFDM resource lo cations, which are then converted to frequency domain QAM I/Q symbols based on the modulation and coding schemes. The QAM I/Q symbols are then IFFT transformed to obtain the complex time domain samples. These time domain samples are then con verted to an analog RF signal for transmission.

Hence, channel modeling takes place in the time domain, by converting I/Q samples from the frequency domain into the time domain. The time domain I/Q dat is then processed in a step S8 according to the one or more radio channel models.

In Figure 18 further exemplary method steps are illustrated. I/Q data, either in the time or frequency domain may be transmitted in a compressed form in order to save resources of the fronthaul network. Hence, in a step S9 the I/Q data received in a compressed format is uncompressed. In a subse quent step S10 the uncompressed I/Q data is processed accord ing to one or more radio channel models. After the processing the I/Q data according to the one or more channel models, the processed I/Q data may be compressed again in a step Sll and transmitted in a subsequent step S12, e.g. over the fronthaul communication link according to a functional split. It should be understood that the steps S9, S10 and Sll are applicable for downlink and/or uplink transmission.

In Figure 19 further exemplary steps are illustrated. In a step S12 the I/Q data may be monitored, preferably with re spect to the time (mis ) alignment of the I/Q data. Furthermore the I/Q data resulting after the being processed according to one or more channel models may be monitored, e.g., by analyz ing the resulting RF signal, e.g. by way of a spectrum ana lyzer .

Based on said monitoring a condition of the radio equipment under test may be determined in a step S13. It should be un derstood that steps S12 and S13 may be performed, for exam ple, after step S10 of Figure 18. For example, the time mis alignment of in-phase/quadrature (I/Q) data may be monitored. By monitoring I/Q data signal and interference analysis can be performed. Modulation testing can be performed, e.g., in the downlink direction, based on I/Q data to verify correct BBU operation, CPRI levels and compliance of the digital sig nal with the RRH capability. Since user equipment (UE) has much lower transmit power compared to an RRH, interference has the biggest system impact in the uplink. The uplink is also susceptible to interference from passive intermodulation (PIM) . PIM detection and distance to PIM source can all be readily analyzed in the digital domain using I/Q data. Fur thermore, the I/Q data (before and/or after processing ac cording to one or more channel models) and/or the correspond- ing spectrum may be displayed and/or one or more threshold may be set in order to perform a diagnostic analysis and is sue one or more alarms if desired. Hence, monitoring and analysis of the interference of user equipment in the uplink, as well as the radio's signal analysis in the downlink is en abled in addition to applying the one or more channel models to the one or more radio channels. Furthermore, signal quali ty may be assessed.

In Figure 20 another exemplary method step is illustrated.

In a step S14 propagation of radio signals of one or more ra dio channels via an air interface is modeled by way of the radio channel test apparatus. A radio channel may be modeled according to one or more mathematical functions describing the propagation of radio waves. The channel models may com prise and/or be based on a recorded impulse responses and may comprise a model of a physical propagation environment. This modeling may further comprise processing the I/Q data accord ing to the one or more channel models, e.g. according to step SI. The step of modeling may also comprise the step of stor ing or retrieving the corresponding radio channel model from a memory. The memory may for example be located within the radio channel test apparatus. The modeling, i.e. the one or more channel models, may furthermore comprise parameters re garding coherence time, coherence bandwidth, delay spread, and/or angular spread.

In Figure 21 further exemplary steps S15, S16 and S17 are illustrated. Thus, in a step S15 baseband data is received, e.g. by the radio channel test apparatus, via a first section of the fronthaul communication link. Said first section con necting the radio channel test apparatus to the BBU or the RRH, respectively, as the case may be. Subsequently in a step S16 the baseband data is processed according to a first radio channel model, preferably a downlink channel model of the first radio channel model. In an optional subsequent step S17 the processed baseband data is transmitted via a second sec- tion of the fronthaul communication link. The second section of the fronthaul communication link connecting the radio channel test apparatus to the RRH or the BBU, respectively, as the case may be. The first and/or second section of the fronthaul communication link may correspond to one of the functional splits as described with respect to the embodiment in the above .

In Figure 22 still further exemplary steps S18, S19 and S20 are illustrated. Here, in a step S18 baseband data is re ceived, e.g. by way of the radio channel test apparatus, via the second section of the fronthaul communication link. The second section may correspond to the one mentioned in accord ance with Figure 22. In a step S19 the baseband data may be processed according to the first radio channel model, prefer ably an uplink channel model of the first radio channel mod el. Hence in this case the same radio channel model for up link and downlink transmission. However, in step S19 a chan nel model different to the one used in step S16 may be used. After processing the baseband data, which preferably is in the form of I/Q data, the processed baseband data may be transmitted via the first section of the fronthaul communica tion link. Thus, the scenario in Figure 22 described may correspond to an uplink data transmission, whereas the sce nario described in Figure 23 may correspond to a downlink data transmission, or vice versa.

In Figure 23 a further exemplary step S21 is illustrated.

The baseband data received via the first section and received via the second section of the fronthaul link may be pro cessed, by way of the radio channel test apparatus, in paral lel or in a cascaded manner. That is to say, uplink or down link data may be processed at (essentially) the same time, e.g. by one or more processors operative to perform digital processing. For example one or more FPGAs may be used for this purpose. Furthermore, those one or more processors may be arranged in one or more radio channel test apparatus. The multiple radio channel test apparatus may in such a case be operationally arranged in parallel in order to process the baseband signal (s) at (essentially) the same time or may be operationally arranged in a consecutive order in order to process the baseband data in a cascaded manner.

In particular the baseband data, e.g. in the form of I/Q da ta, belonging to a first group of radio channels may be pro cessed by way of a first radio channel test apparatus, where as the baseband data belonging to a second group of radio channels may be processed by way of a second radio channel test apparatus operationally arranged in parallel or in con secutive order to one another.

Thus the I/Q data may take the form of baseband data and may be processed according to one or more channel models (for the respective one or more radio channels) as described in con nection with Figure 21 In addition, a first radio channel test apparatus may be used for processing uplink data whereas a second radio channel test apparatus may be used for pro cessing downlink data.

In Figure 24 another exemplary method step 22 is illustrat ed. According to step 22 the radio channel test apparatus may be operated in a fronthaul communication link between a phys ical or virtual radio equipment control and one or more phys ical or virtual radio equipments. As described in connection with the embodiments of Figures 1 to 13 the radio channel test apparatus may be employed in different test environ ments. Those test environments comprising real, physical equipments and virtual, emulated radio equipments. Thus, a test environment may comprise a physical or a virtual radio equipment control, such as one or more physical or virtual BBU. The test environment may further comprise one or more physical or virtual radio equipments, such as one or more physical or virtual RRH. The radio channel test apparatus may then be operationally arranged between the a physical or vir- tual radio equipment control and one or more physical or vir tual radio equipments in order to process the baseband data, preferably I/Q data, transmitted between the physical or vir tual radio equipment control and physical or virtual radio equipments .

In Figure 25 further exemplary steps 23 and 24 are illus trated. According to step 23 the baseband signal comprising I/Q data of each of multiple radio channels which are pro cessed, by way of the radio channel test apparatus, according to a radio channel model associated with each of the radio channels. One or more radio channels may be subject to the same channel model. However, different radio channel model may be employed for different radio channels. For example as described in the above a first group of radio channels may be subject to processing according to a first channel model whereas a second group may be subject to processing according to a second radio channel model. Furthermore, different chan nel model may be used when processing the baseband signal by way of multiple radio channel test apparatus.

In a subsequent step S24 the processed baseband signal com prising I/Q data may be transmitted, by way of the radio channel test apparatus, a the fronthaul communication link.

Now turning to Figure 26, another exemplary step S25 is il lustrated. Here, as already described in connection with step S21 of Figure 23, the baseband data of each of the multiple radio channels is processed in parallel or in a cascaded man ner, by way of the radio channel test apparatus. To this end, one or more processors may be arranged in a radio channel test apparatus. Each of the processors operative to process the baseband data of one or more radio channels assigned for processing by a respective processor.

Finally, in Figure 27 another exemplary method step S26 is illustrated. According to step 26 baseband signal comprising I/Q data of each of the multiple radio channels, is pro cessed, by way of the radio channel test apparatus. In such a case the radio channel test apparatus comprises consecutively interconnected devices for processing the baseband signal comprising I/Q data of the multiple radio channels, wherein each device processes baseband signal of at least one radio channel. That is to say the radio channel test apparatus may itself comprise multiple device for processing the I/Q data of the one or more radio channels.

Any steps described herein are merely illustrative of certain embodiments. It is not required that all embodiments incorpo rate all the steps disclosed nor that the steps be performed in the exact order depicted or described herein. Furthermore, some embodiments may include steps not illustrated or de scribed herein, including steps inherent to one or more of the steps disclosed herein. Any appropriate steps, methods, or functions may be performed through a computer program product that may, for example, be executed by the components and equipment illustrated in the figure above. For example, a memory, e.g. of the radio channel test apparatus, may com prise computer readable means on which a computer program can be stored. The computer program may include instructions which cause one or more processors and any operatively cou pled entities and devices, to execute methods according to embodiments described herein. The computer program and/or computer program product may thus provide means for perform ing any steps herein disclosed. Any appropriate steps, meth ods, or functions may be performed through one or more func tional modules. Each functional module may comprise software, computer programs, sub-routines, libraries, source code, or any other form of executable instructions that are executed by, for example, a processor. In some embodiments, each func tional module may be implemented in hardware and/or in soft ware. For example, one or more or all functional modules may be implemented by one or more processors, possibly in cooper ation with a memory. Processors and memory thus may be ar- ranged to allow processors to fetch instructions from the memory and execute the fetched instructions to allow the re spective functional module to perform any steps or functions disclosed herein.

Certain aspects of the aspects disclosed have mainly been de scribed above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, em bodiments other than the ones disclosed above are equally possible and within the scope of the inventive concept. Simi larly, while a number of different combinations have been discussed, all possible combinations have not been disclosed. One skilled in the art would appreciate that other combina tions exist and are within the scope of the inventive con cept. Moreover, as is understood by the skilled person, the herein disclosed embodiments are as such applicable also to other standards and communication systems and any feature from a particular figure disclosed in connection with other features may be applicable to any other figure and or com bined with different features.