EP2941915A1

EP2941915A1 - Method and system for testing base stations of a mobile telecommunications network

Info

Publication number: EP2941915A1
Application number: EP13802933.5A
Authority: EP
Inventors: François Hamon; Yiqi Jiang; The Phuong NGUYEN; Damien Pouessel; Frédéric RIBLE
Original assignee: Ercom Engineering Reseaux Communications SAS
Current assignee: Ercom Engineering Reseaux Communications SAS
Priority date: 2013-01-04
Filing date: 2013-12-06
Publication date: 2015-11-11
Also published as: WO2014106561A1; US20150341809A1; FR3000856A1; US9819425B2; FR3000856B1

Abstract

The present invention concerns a laboratory test method for testing base stations (10, 11, 12) of a mobile telecommunications network (20) comprising a plurality of cells (40, 41, 42), characterised in that it comprises the followings steps: • connecting a base station (10), at the antenna (50) of said station, to a testing system (100) by means of a radio-frequency cable (60); • emulating mobile terminals (30, 31, 32) of a cell (40), said mobile terminals (30, 31, 32) transmitting data and transmitting/receiving calls in said cell (40) via a base station (10); and • in that there is a separate channel emulator for each emulated mobile terminal. The present invention also concerns a laboratory test system (100) for testing base stations (10, 11, 12) of a mobile telecommunications network (20) comprising a plurality of cells (40, 41, 42).

Description

METHOD AND SYSTEM FOR TESTING BASE STATIONS IN A MOBILE TELECOMMUNICATIONS NETWORK

Field of the invention

The present invention relates to the field of telecommunications.

The present invention relates more particularly to a method and system for emulating mobile terminals for testing base stations of a mobile telecommunications network.

The present invention applies to base stations called "eNodeB" as part of the fourth generation of mobile telecommunications: LTE or "Long Term Evolution".

State of the art

PCT Application No. WO 03/069814 (Dyaptive Systems Incorporated), which describes a simulator for mobile terminals in a wireless telecommunications network, for the purpose of testing the stations is known in the state of the art. basic.

The effect of Doppler velocity on SINR degradation (Signal to Interference plus Noise Ratio) was addressed in the following publication:

[1] M. Speth, S. Fechtel, G. Fock, H. Meyr, "Optimum Receiver Design for

Wireless Broadband Systems Using OFDM - Part 1 ", IEEE Transactions on Communications, Volume 47, Number 1 1, Nov. 1999

The effect of the multipath channel on SINR compression has been addressed in the following publications:

[2] E. Tuomaala and H. Wang, "Effective SINR Approach to System-mapping in OFDM / Multi-carrier Mobile Network", in Mobile Technology, Application and Systems, 2005 2 ^nd International Conference on, Nov. 2005 [3] X. He, K. Niu, Z. He, and J. Lin, "Link Layer Abstraction in MIMOOFDM System," in Proc. International Workshop on Cross Layer Design, 2007

[4] R. Sandanalakshmi, T. Palanivelu, and K. Manivannan, "Effective SNR Mapping for Link Error Prediction in OFDM-based Systems," in Proc. IET-UK International Conference on Information and Communication Technology in Electrical Sciences ICTES, 2007

Presentation of the invention

The present invention intends to overcome the disadvantages of the prior art by providing a method for emulating a large number of mobile terminals to test base stations of a telecommunications network. The present invention reduces the computational complexity of a mobile multi-channel emulator.

The present invention relates, in its most general sense, to a method of laboratory testing of base stations of a mobile telecommunications network comprising a plurality of cells, characterized in that it comprises the following steps:

• connection of a base station at its antenna to a test system using a radio frequency cable;

Emulating mobile terminals of a cell, said mobile terminals transmitting data and transmitting / receiving calls in said cell through a base station; and

In that there is an independent channel emulator for each emulated mobile terminal.

Advantageously, said method applies to eNodeB-type base stations for LTE (Long Term Evolution) type networks. According to one embodiment, said method implements a plurality of uplink multipath channels based on a single time-frequency transform processor. Advantageously, said time-frequency transform processor is of the fast Fourier transform type.

According to one variant, said multipath channels are finite impulse response filters whose complex coefficients vary over time.

According to one embodiment, said multipath channels are applied in the so-called frequency domain before the time frequency transform.

Thus, the emulation of the channel is inserted inside the modulator which is made possible by the OFDMA waveform of the LTE (see Figure 2).

Preferably, said multipath channels are frequency multiplexed before being applied to the signal transmitted by the mobile terminals. This frequency multiplexing step makes it possible to apply a plurality of multipath channels associated with a plurality of mobile terminals by using a single vector multiplication operation. If one considers a temporal spread of FILTER_SIZE samples, this step of process makes it possible to obtain a gain of FILTER_SIZE ^* NB_UES.

According to one embodiment, said method implements an emulation of a plurality of variable distances between the base station and the independent mobile terminals on the basis of a single FFT (Fast Fourier Transform) processor.

Advantageously, the distance simultaneously emulates a delay of propagation and the weakening of the signal with regard to a law describing the decrease of the power of the signal. According to one variant, said distance emulation is implemented in the form of a phase ramp in the frequency domain.

According to a variant, said method implements an emulation of a variation of the Doppler conditions on the basis of a single set of multipath path realizations, the Doppler speed being induced by the sub-sampling of this set of multipath channel embodiments, and a channel embodiment being associated with a temporal spread which varies according to the subsampling chosen.

According to a particular mode of implementation, said method ensures the continuity of the channel by symmetrical transposition of the channel embodiments, allowing a loopback without discontinuity. According to one embodiment, said method further comprises a SINR (Signal to Interference plus Noise Ratio) compression step taking into account the Doppler effect, the estimation noise, the fading and the noise factor. of the receiver.

This method makes it possible to transpose standard block error rate plots under BBAG (Gaussian additive white noise) channel to the block error rate under multipath and Doppler channel conditions. The innovation of this process is due to its implementation described below and also in that it combines the Doppler effect and the multipath channel in the SINR compression step (see Figures 2 and 3).

Advantageously, said method is implemented on the basis of a LUT (Look-Up Table) of the SINR (Signal to Interference plus Noise Ratio) compression emulation for the calculation of the BLER (Block Error Rate) in a downlink. (downlink) and CQI (Channel Quality Indicator) downlink.

According to one embodiment, said method comprises a step of emulation of a channel MIMO (Multiple-lnput Multiple-Output) in process Downlink LTE (Long Term Evolution) by interacting on the return of Channel Quality Indicator (CQI), Rank Indicator (RI), Precision Matrix Index (PMI), and BLER (Block Error Rate) information. According to one embodiment, for the continuation of CQIs (Channel

Quality Indicators): at each iteration, we use the pair of ^. ^ Of the previous iteration and we test the N pairs of ^ι , ^{0 (2} adjacent, the best of these N couples being used as base pair to the next iteration, the expression

1 SINR '\ k]

SINR _e ' _ff = -, ln (£ exp (

EESM ^Nb >" ⁼ ° ^{a ?,} using N pairs of values ^ι , ^{0 (2} associated with N CQIs (Channel Quality Indicators), said EESM expression converging to the correct value if it has been calibrated with the right pairs of values of" i , ⁰ ^.

Thus, the computation complexity is limited to the test of (N "15) pairs and we suppose a convergence of the algorithm towards the optimal pair.

According to a variant, said method also comprises a step of coherent propagation of the Tx power (transmission power), Tx fading (transmission fading), Channel Quality Indicator (CQI), Precoding Matrix Index (PMI), and Rank Indicator (RI) parameters. ), Doppler, BLER (Block Error Rate) downlink based on a delay line channel model and a distance profile.

Advantageously, said method implements uplink power dynamics on a respectively digital and analog partition of the dynamics specific to said mobile terminals and the cell-specific dynamics.

The present invention also relates to a laboratory test system of base stations of a mobile telecommunications network comprising a plurality of cells, characterized in that it comprises means for:

• connect a base station at its antenna to said test system by means of a radio frequency cable;

• Have an independent channel emulator for each emulated mobile terminal.

Brief description of the drawings

The invention will be better understood by means of the description, given below purely for explanatory purposes, of one embodiment of the invention, with reference to the figures in which:

Figure 1 illustrates the system according to the present invention in one embodiment;

Figure 2a shows a modulator and an external channel emulator, according to the state of the art;

Figure 2b illustrates a modulator including a channel emulator according to the present invention;

Figures 3 and 4 show the SINR compression step (Signal to Interference plus Noise Ratio), in the context of the method according to the present invention;

FIG. 5 illustrates the frequency multiplexing of a plurality of multipath channels, in the context of the method according to the present invention; and

Figures 6 and 7 show the system according to the present invention in one embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

The system 100 and the method according to the present invention make it possible to emulate several hundred LTE compatible mobile terminals 30, 31, 32.

According to the invention, the method makes it possible to test in the laboratory base stations 10, 11, 12 of a mobile telecommunications network 20 comprising a plurality of cells 40, 41, 42,

The method according to the present invention comprises the following steps: • connection of a base station 10 at its antenna 50 to a test system 100 by means of a radio frequency cable 60

· Emulation of mobile terminals 30, 31, 32 of a cell 40, said mobile terminals 30, 31, 32 transmitting data and transmitting / receiving calls in said cell 40 through a base station 10.

We have an independent channel emulator for each emulated mobile terminal.

The emulated mobile terminals 30, 31, 32 stimulate the base station 10: they transmit calls, transmit data, in particular by means of an VoIP protocol ("VoIP"). The base station 10 is thus stimulated in the laboratory, as it would be in a real environment.

The emulated mobile terminals 30, 31, 32 are contained in a chassis

80. We try to emulate the reality of the radio environment. The buildings, the movements of the mobile terminals 30, 31, 32 are simulated (for example in an automobile, or carried by a walking pedestrian). The system 100 and the method according to the present invention make it possible to simulate:

• a multi-path channel model:

• a propagation model (waves); "A Doppler model (linked to mobility).

The system 100 and the method according to the present invention make it possible to represent a realistic environment, taking into account the speed of the mobile terminals 30, 31, 32, their distance from the base station 10 and the environment (buildings, etc.)

Figure 1 illustrates the system 100 according to the present invention: a base station 10 communicates with mobile terminals 30, 31, 32 emulated. The system 100 according to the present invention makes it possible to test in the laboratory base stations 10, 11, 12 of a mobile telecommunications network 20 comprising a plurality of cells 40, 41, 42. This system 100 comprises means for:

Connecting a base station 10 at its antenna 50 to said test system 100 by means of a radio frequency cable 60; and

Emulating mobile terminals 30, 31, 32 of a cell 40, said mobile terminals 30, 31, 32 transmitting data and transmitting / receiving calls in said cell 40 through a base station 10.

Figure 2a shows a modulator and an external channel emulator according to the state of the art.

Figure 2b illustrates a modulator including a channel emulator according to the present invention. Figures 3 and 4 show the SINR compression step (Signal to Interference plus Noise Ratio), in the context of the method according to the present invention. Figure 5 illustrates the frequency multiplexing of a plurality of multipath channels as part of the method of the present invention.

Figures 6 and 7 show the system according to the present invention in one embodiment.

In the system according to the present invention, there is an independent channel emulator for each emulated mobile terminal. Thus, for each emulated mobile terminal, the perceived channel is different. The system according to the invention takes into account the possible buildings (and associated signal reflections) and the distance of each mobile terminal to the base station. This makes it possible to represent a realistic environment.

In one embodiment, an IFFT-type function is shared for all emulated mobile terminals.

In one embodiment, a FFT-type function is shared for all emulated mobile terminals.

Uplink

In one embodiment, a plurality of channel responses are applied in the frequency domain, taking advantage of the fact that in the LTE the resources used by the users are orthogonal in frequency, and a term-to-term multiplication is applied before application of a function of the IFFT type.

The method implements a plurality of uplink multipath channels based on a single Fast Fourier Transform (FFT) processor.

This is achieved through a mapping of the different channels. In one embodiment, for each user, the responses are stored at the initialization of the system, in the presence of Doppler.

The channel instances that correspond to the lowest speed that you want to emulate are stored in memory. The storage is performed so as to represent sufficient statistics of the channel.

In a particular mode of implementation, fifty coherence times are stored. In one embodiment, the Doppler is emulated by subsampling the channel. This subsampling is performed according to the speed of the mobile terminal which has been parameterized.

In one embodiment, the method according to the present invention provides continuity of the channel by symmetric transposition of channel realizations.

In one embodiment, the method according to the present invention implements uplink power dynamics on a respective digital and analog partition of the dynamics specific to said mobile terminals (30, 31, 32) and the dynamics. cell-specific (40).

Downlink In one embodiment, information is reported by the mobile terminal to the base station so that the latter can make decisions. The emulation of the channel is then performed by disregarding the channel at the physical level, and emulating the measurements reported on the base station (eNodeB). From channel realizations, we try to model the parameters that are supposed to be reported by the mobile terminal on the base station (eNodeB). Among these parameters are BLER (Block Error Rate), CQI (Channel Quality Indicator), PMI (Precoding Matrix Index) and RI (Rank Indicator). These parameters are directly dependent on the channel, and make it possible to model said downlink channel. In one embodiment, the method according to the present invention is implemented on the basis of a Look-Up Table (LUT) of the SINR (Signal to Interference plus Noise Ratio) compression emulation for the calculation of the BLER. (Block Error Rate) downlink and CQI (Channel Quality Indicator) downlink.

In one embodiment, said method further comprises a SINR (Signal to Interference plus Noise Ratio) compression step taking into account the Doppler effect, the estimation noise, the fading and the noise factor. of the receiver.

In a first step (Figure 3), the SINR is compressed to account for Doppler velocity.

The SINR compression induced by the Doppler effect can be expressed according to the following formula [1] in the particular case of a SISO transmission:

H

SINR -

P x Â

p _N +

H, P x Â A

Or A is expressed as follows SIR = - - = A _dcp

f f

V

Ps is the power of the signal and PN the power of the thermal noise and H00 the channel gain on the subcarrier. This expression can be extrapolated for the MIMO case by the following formula:

Or

Q _mNr = inv {HW) = {{HW) ^H {HW) Y ^l {HW) ^H = {W ^H H ^H HWy ¹ {W ^H H ^H )

W being the precoding matrix defined in 3GPP specification TS3621 1.

In order to reduce the complexity induced by these methods, the present invention proposes to pre-calculate and store in LUT (Look-Up Table) the following terms:

Σ ¾

For each realization of multipath channel.

In a second step, the method called "Exponential Effective Signal to Interference and Noise Ratio Mapping" (EESM) (described in documents [2] [3] [4] cited above) is used to compress the SINR.

1 SINR '\ k]

SINR- = -a, ln (- £ exp (^))

J where / is the OFDM time index, k is the index of the subcarrier, N _b i is the total number of subcarriers to be averaged (in time / and frequency k) α ^ are the calibration parameters.

In order to reduce the complexity of the second step, the present invention proposes the following method: -Replace the log calculation of the exponential sum by the Jacobian algorithm with the additive correction term stored in a LUT.

Channel averaging by reducing the calculation of instantaneous SINRs for each subcarrier and each time index to one SINR per subset of subcarriers and time indexes.

-Parallelize the calculation of SINR using one or more "threads" per mobile terminal. The number of mobile terminals processed for each millisecond is equal to two or more times the number of available CPUs for the system.

In one embodiment, the method according to the present invention comprises a step of emulation of a downlink (LTE) channel (LTE) by interacting on the return of the information. Channel Quality Indicator (CQI), Rank Indicator (RI), Precision Matrix Index (PMI), and BLER (Block Error Rate).

To calculate the PMI (Precoding Matrix Index), we use a state-of-the-art method based on the calculation of the mutual information [2] [3] [4] described below:

In order to reduce computational complexity, this implementation proposes to pre-calculate and store in LUT (Look-Up

Table) the following elements: = 1 ° g 2det (/ _M ^ _r + pW ₁ ^H H " _n H ^ W _i ) = log 2 (1 + p ² (e ₀ e ₃ -e> -e ₂ ² ) + p (e ₀ + <¾)) ₍₃₎ where and ^e " ^{+ é} ¾ can be stored as real scalar values. With:

Moreover in order to avoid proceeding with the K ^* N computation of log2 expressed in (1) the arguments of (3) are factored using the expression ^l08 ^ ⁼ i ° g ₂ W + iog ₂ (y) _ which allows to replace evaluations of log2 functions by multiplications.

The term EESM uses N pairs of values ^ι , ^{0 (2} which are associated with N CQIs (Channel Quality Indicators) .This expression converges to the correct value if it has been calibrated with the good pairs of values of ^.

In the state of the art, we proceed as follows: to report the correct CQI, we test the pairs in descending order of their associated CQI value. We are looking for the largest value of which the SINReff guarantees that BLER is less than 0.1, so in the worst case, it takes fifteen attempts corresponding to the fifteen CQIs of the LTE to find it.

In the context of the present invention, the procedure is as follows: at each iteration, the pair of the previous iteration is used and the N pairs of adjacent pairs are tested. base pair at the next iteration Thus the computational complexity is limited to the test of (N "15) pairs and we suppose a convergence of the algorithm towards the optimal pair.

The invention is described in the foregoing by way of example. It is understood that the skilled person is able to realize different variants of the invention without departing from the scope of the patent.

Claims

Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) comprising a plurality of cells (40, 41, 42), characterized in that it comprises the following steps :

Connecting a base station (10) at its antenna (50) to a test system (100) using a radio frequency cable (60);

Emulating mobile terminals (30, 31, 32) of a cell (40), said mobile terminals (30, 31, 32) transmitting data and transmitting / receiving calls in said cell (40) through a mobile station (40); base (10); and

Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to claim 1, characterized in that it applies to eNodeB base stations for LTE type networks (Long Term Evolution).

Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to claim 1 or 2, characterized in that it implements a plurality of multipath channels on the way uplink based on a single time-frequency transform processor.

4. Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to claim 3, characterized in that said time-frequency transform processor is of the fast Fourier transform type.

Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to claim 3 or 4, characterized in that said multipath channels are finite impulse response filters whose Complex coefficients vary over time.

Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to claim 3, 4 or 5, characterized in that said multipath channels are applied in the so-called frequency domain before the transformed frequency time.

Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to claim 3, 4, 5 or 6, characterized in that said multipath channels are frequency multiplexed before their application on the signal transmitted by the mobile terminals (30, 31, 32).

Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to at least one of the preceding claims, characterized in that it implements an emulation of a plurality of variable distances between the base station (10) and the independent mobile terminals (30, 31, 32) based on a single FFT (Fast Fourier Transform) processor.

9. Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to claim 8, characterized in that the distance simultaneously emulates a delay of propagation and weakening of the signal under a law describing the decay of the signal power.

A laboratory test method of base stations (10, 11, 12) of a mobile telecommunications network (20) according to claim 8, characterized in that said distance emulation is implemented in the form of a phase ramp in the frequency domain.

1 1. Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to at least one of the preceding claims, characterized in that it implements an emulation of a variation of the Doppler conditions on the basis of a single set of embodiments of multipath channels, the Doppler speed being induced by the sub-sampling of this multipath embodiment set, and a channel embodiment being associated with a temporal spread that varies according to the subsampling chosen.

12. Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to at least one of the preceding claims, characterized in that it ensures the continuity of the channel. by symmetrical transposition of the channel embodiments allowing a loopback without discontinuity.

13. A laboratory test method of base stations (10, 11, 12) of a mobile telecommunications network (20) according to at least one of the preceding claims, characterized in that it also comprises a step SINR (Signal to Interference plus Noise Ratio) compression ratio taking into account the Doppler effect, the estimation noise, the fading and the noise factor of the receiver.

14. A laboratory test method of base stations (10, 11, 12) of a mobile telecommunications network (20) according to at least one of the preceding claims, characterized in that it is implemented on the base of a Look-Up Table (LUT) of the SINR (Signal to Interference plus Noise Ratio) compression emulation for the calculation of the BLER

(Block Error Rate) downlink and CQI (Channel Quality Indicator) downlink.

15. A method of laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to at least one of the preceding claims, characterized in that it comprises a step of emulation of a multiple-lnput multiple-output (MIMO) channel downlink LTE by interacting on the return of Channel Quality Indicator (CQI), RI (Rank Indicator), PMI ( Precoding Matrix Index) and BLER (Block Error

Missed).

16. Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to at least one of the preceding claims, characterized in that, for the continuation of the CQIs ( Channel Quality Indicators): at each iteration, we use the pair of ^ of the previous iteration and we test the N pairs of a ^{0 (2} adjacent, the best of these N couples being used as a base pair at the iteration following, the term EESM

1 SINR ^l \ k \

SINR _e ' _ff = -, ln (£ exp (

^Nb >" ⁼ ° ^a? Using N pairs of values ^ι , ^{0 (2} associated with N CQIs (Channel Quality Indicators), said EESM expression converging to the correct value if it has been calibrated with the right pairs of values of ', ^{0 (2} .

17. A laboratory test method for base stations (10, 11, 12) of a mobile telecommunications network (20) according to at least one of the preceding claims, characterized in that it also comprises a step coherent propagation of Tx power (transmission power), Tx fading, Channel Quality Indicator (CMI), Precoding Matrix Index (PMI), Rank Indicator (RI), Doppler, Block Error Rate (BLER) downlink based on a delay line channel model and a distance profile.

18. Method for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) according to at least one of the preceding claims, characterized in that it implements a dynamic uplink power on a respective digital and analog partition of the dynamics specific to said mobile terminals (30, 31, 32) and the cell-specific dynamics (40).

19. System (100) for laboratory testing of base stations (10, 11, 12) of a mobile telecommunications network (20) having a plurality of cells (40, 41, 42), characterized in that it includes means for:

• connect a base station (10) at its antenna (50) to said test system (100) by means of a radio frequency cable (60);

Emulating mobile terminals (30, 31, 32) of a cell (40), said mobile terminals (30, 31, 32) transmitting data and transmitting / receiving calls in said cell (40) through a mobile station; base (10); and

• Have an independent channel emulator for each emulated mobile terminal.