CN103181094B - Radio base station and method for estimating Doppler spread therein - Google Patents

Abstract

Embodiments herein relate to a method in a radio base station (12) for estimating the doppler spread of a signal transmitted by a user equipment (10) over a channel in a radio communications network. The radio base station 12 and the user equipment 10 are comprised in a radio communication network. The radio base station (12) receives a first signal and a second signal from the user equipment (10), wherein the first signal and the second signal are based on a signal transmitted by the user equipment (10). The first and second signals are separated in space, time and/or polarization. The radio base station (12) estimates a first channel estimate for the received first signal by comparing the received first signal to a known signal and estimates a second channel estimate for the received second signal by comparing the received second signal to the known signal. The radio base station (12) determines a ratio of the first channel estimate to the second channel estimate and estimates an autocorrelation function of a function of the determined ratio. The radio base station (12) then estimates the doppler spread based on the estimated autocorrelation function.

Description

Radio base station and method for estimating Doppler spread therein

technical field

Embodiments herein relate to radio base stations and methods therein. In particular, embodiments herein relate to estimation of Doppler spread in radio communication networks.

Background technique

In today's radio communication networks, a user equipment communicates information via a radio link to a radio base station in so-called uplink (UL) transmissions, and the radio base station communicates in the other direction to a radio base station in so-called downlink (DL) transmissions. The user equipment communicates the information. Doppler shift is the shift in frequency of radio signals encountered by a receiver as the transmitter and receiver move relative to each other. Doppler spread is the spread of the Doppler shift of multiple incoming signaling rays from the transmitter to the receiver. Doppler spread causes a change in the propagation channel between the transmitter and receiver. The knowledge of Doppler extension finds many applications in mobile communication systems. Such applications include: receiver algorithms, such as smoothing filters for channel estimation; and radio resource management algorithms, such as link adaptation, scheduling, and selection of closed-loop or open-loop spatial multiplexing. The Doppler spread of a radio link is inversely proportional to the channel coherence time. The channel coherence time is the duration for which a channel impulse response is considered to be correlated, ie a channel impulse response is correlated with another channel impulse response that takes place during the channel coherence time. Long channel coherence times allow receivers, e.g. radio base stations, to follow the effects of small-scale fading for scheduling and link adaptation, e.g. for using mobile communication systems such as the Evolved Universal Terrestrial Radio Access (E-UTRA) system Time-dependent scheduling in and closed-loop spatial multiplexing in the downlink. The period for transmitting channel quality information reports from the user equipment to the radio base station should be shorter than the channel coherence time in order to provide downlink channel state information that is accurate during the reporting period. Similarly, the periodicity of the transmitted channel sounding reference signals in the uplink should be shorter than the channel coherence time in order to enable efficient uplink channel quality estimation between sounding reference signal transmissions.

Doppler spread can be estimated in many ways using a Doppler spread estimator. A class of Doppler spread estimators is based on the temporal nature of the channel estimate of the received signal. In the time domain, the propagation channel can be modeled as a tapped delay line with time-correlated channel taps. Assuming that channel tap C is a Rayleigh fading channel tap, the Doppler spread can be estimated from the measured level crossing ratio of channel tap C. Several estimators rely on the autocorrelation function R _c of the channel taps C:

in

E is the expected value operator,

c ^* means complex conjugate,

t is time, and

τ is the delay.

Theoretically, another autocorrelation function R _c of Rayleigh fading channel taps is expressed as

in

C is a constant,

J0 is a _zero -order Bessel function of the first kind, and

f _D is the Doppler spread.

From the estimate of the autocorrelation function and the known form of the autocorrelation function, the Doppler expansion can then be obtained, for example, from when The second derivative of and The ratio:

Or estimated from maximum likelihood estimation,

in Indicates the Doppler spread estimate.

Doppler spread estimation It can also be derived from the autocovariance function of the function of the channel taps. An example of such a function of channel taps is the squared magnitude of the channel taps.

The channel estimate for a certain time instance is usually derived from the transmission of pilot or reference signals. The channel estimator is simplified and more efficient if there are continuous or periodic transmissions on a fixed frequency. The shorter the periodicity of the transmission, the higher Doppler spread or shorter channel coherence time can be estimated, resulting in a better resolution of the estimate.

Accurate channel estimation requires that the transmitted signal be known at the receiver. In general, the transmitted reference or pilot signal is known, except for amplitude and phase which are constant during a single transmission. In several mobile communication systems, such as E-UTRA, a mobile station can vary the transmit power between subsequent transmissions. This alteration changes the magnitude and possibly also the phase of the transmitted signal. The radio base station estimates the composite channel consisting of the transmitter gain (ie magnitude and phase) and the propagation channel. The composite channel is relevant for compensation in the receiver, but not for estimating the propagation of the transmission. The autocorrelation function and other temporal properties of the composite channel may be very different from those of the propagation channel, and thus Doppler spread estimates based on channel estimates may be wrong. In general, the Doppler spread estimator incorporates temporal properties related to the time of the received signal at the receive antenna, leading to erroneous Doppler spread estimates leading to inefficient transmission schemes.

Contents of the invention

It is an object of the embodiments herein to provide a mechanism to estimate the Doppler spread in a reliable way leading to better performance of the radio communication network.

According to an aspect of the embodiments herein, the object is achieved by a method in a radio base station for estimating the Doppler spread of a signal transmitted by a user equipment over a channel in a radio communication network. Radio base stations and user equipment are comprised in a radio communication network. The radio base station receives a first signal and a second signal from a user equipment, wherein the first signal and the second signal are based on signals transmitted by the user equipment. Additionally, the first and second signals are separated in space, time and/or polarization.

The radio base station estimates a first channel estimate of the received first signal by comparing the received first signal with a known signal, and estimates a channel estimate of the received second signal by comparing the received second signal with the known signal. Second channel estimate. Furthermore, the radio base station determines a ratio of the first channel estimate to the second channel estimate, and estimates an autocorrelation function of a function of the determined ratio. The radio base station then estimates the Doppler spread based on the estimated autocorrelation function.

In order to perform the method, a radio base station is provided for estimating the Doppler spread of a signal transmitted by a user equipment over a channel in the radio communication network. A radio base station is arranged to be included in a radio communication network. Furthermore, the radio base station comprises a receiving circuit configured to receive the first signal and the second signal from the user equipment. The first signal and the second signal are based on signals transmitted by the user equipment, wherein the first signal and the second signal are separated in terms of space, time and/or polarization. Additionally, the radio base station comprises a first estimation circuit configured to estimate a first channel estimate of the received first signal by comparing the received first signal with known signals. In addition, the radio base station comprises a second estimation circuit configured to estimate a second channel estimate of the received second signal by comparing the received second signal with a known signal.

The radio base station further comprises a determining unit configured to determine a ratio of the first channel estimate to the second channel estimate. In addition, the radio base station comprises an estimated autocorrelation circuit configured to estimate an autocorrelation function of a function of the determined ratio. The radio base station also includes estimated Doppler spread circuitry configured to estimate the Doppler spread based on the estimated autocorrelation function.

The estimation of the Doppler spread is based on the ratio of the channel estimates of two separate received signals, where the signals are based on the same transmitted reference signal. This is performed using eg two receive antennas. Thus, variations in the amplitude and phase of the transmitted reference signal have no effect when estimating the Doppler spread. Consequently, the Doppler spread estimation is more accurate, leading to more efficient transmission schemes, link adaptation, scheduling, etc., which lead to improved performance of the radio communication network. Additionally, higher throughput and data rates can be achieved in radio communication networks through more accurate Doppler spread estimation.

Description of drawings

Embodiments will now be described in more detail with respect to the accompanying drawings, which include:

Figure 1 is a block diagram illustrating a radio communication network,

Figure 2 is a schematic diagram showing a combined flow diagram and signaling scheme in a radio communication network,

Figure 3 is a block diagram showing a radio base station,

FIG. 4 is a schematic diagram showing a graph of a curve of an autocorrelation function,

Figure 5 is a block diagram of a method in a radio base station, and

Fig. 6 is a block diagram of a radio base station.

detailed description

1 shows a schematic diagram of a radio communication network, such as Long Term Evolution (LTE), LTE-Advanced, Third Generation Partnership Project (3GPP) Wideband Code Division Multiple Access (WCDMA) system, Global System for Mobile Communications/Enhanced Data Rates GSM Evolution ( GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax) or Ultra Mobile Broadband (UMB), to name just a few possible options for implementing the embodiments disclosed herein.

A user equipment (UE) 10 served by a radio base station 12 communicates with the radio base station 12 via a radio link, wherein the communication is a so-called uplink (UL) transmission. The radio base station 12 communicates with the user equipment 10 in so-called downlink (DL) transmissions. The Doppler shift is the frequency shift of the radio signal encountered by the radio base station 12 when the user equipment 10 and the radio base station 12 move at a velocity v relative to each other. That is, the radio base station 12 may be fixed or mobile, and the user equipment 10 may be stationary or mobile, and the difference in velocity between them is v in one direction.

The user equipment 10 transmits an original signal to the radio base station 12 in UL. As the signal is propagated and reflected along its route to the radio base station 12, different signals (ie first and second signals) originating from the original signal will be received at the radio base station 12 . Thus, the radio base station 12 receives the first signal and the second signal from the user equipment 10 . The first and second signals are based on the original signal, but separated eg in terms of space, time and/or polarization. As the transmission power of the user equipment 10 affects the magnitude and phase, varying transmission power of the user equipment 10 will change the channel autocorrelation properties as obtained from a single received signal. The current embodiments herein provide mechanisms that are not affected by varying transmission power of the user equipment 10 . The radio base station 12 estimates a first channel estimate of the first signal by comparing the received first signal with an initial signal, also called a known signal. Furthermore, the radio base station 12 estimates a second channel estimate for the second signal by comparing the received second signal with the initial signal. For example, reference signals comprised in the received first and second signals may be compared with known reference signals stored in the radio base station 12 .

The radio base station 12 then determines the ratio of the channel estimates by dividing the first channel estimate by the second channel estimate. This ratio is a dimensionless parameter that cancels out the transmitted amplitude and phase correlation of the Doppler spread estimate. The ratio of the channel estimates is then used in the function to estimate the autocorrelation function. This estimated autocorrelation function is then used to estimate the Doppler spread.

Such a more accurately estimated Doppler spread can be used for multiple-input multiple-output (MIMO) modes, modulation and coding of DL transmissions, link adaptation, frequency selective scheduling, etc.

Figure 2 shows a schematic combined signaling and flow diagram in a radio communication network. The radio communication network comprises radio base stations 12 and user equipment 10 which move between each other.

Step 201. The user equipment 10 transmits a signal s to the radio base station 12 . The signal may comprise reference or pilot symbols known at the radio base station 12 . The signal is split into a first signal s1 and a second signal s2 along the route to the radio base station. The first and second signal s1, s2 thus originate from the same transmitted signal, ie the originating signal, and are separated in terms of space, polarization and/or time. The spatially separated signals are distinguished by the receiving antennas by the distance between them. Signals that are separated in polarization are distinguished by cross-polarized receive antennas. Signals separated in time are distinguished in a channel estimator. Additionally, combinations thereof can be used to distinguish between the first and second signals.

In the example shown, the radio base station 12 receives a first signal s1 at a first antenna and a second signal s2 at a second antenna.

Step 202. The radio base station 12 estimates the Doppler spread by first estimating a first channel estimate for the first signal and a second channel estimate for the second signal. The radio base station then determines a ratio of the first channel estimate to the second channel estimate and estimates an autocorrelation function of the function of the determined ratio. The radio base station 12 then estimates the Doppler spread based on the estimated autocorrelation function.

The radio base station 12 removes transmitter effects by basing the estimate of the Doppler spread on the ratio of the channel estimates of the first and second signals. That is, the influence of the magnitude and phase of the transmitted signal on the estimated Doppler spread has canceled out.

In Fig. 3 a block diagram of a radio base station 12 in a radio communication network is shown. In the example shown, the radio base station 12 includes a first antenna and second antenna . baseband equivalent signal is through the antenna Composite representation of the received signal. antenna The baseband equivalent signal of the received sampled signal Due to the transmission of the reference signal S from the user equipment 10 is denoted as

(equation 1)

in

k represents the sample,

l means delayed index,

t means time,

A is the number of receiving antennas,

is the composite channel coefficient,

C is the propagation channel, and

n is noise and interference.

is through the antenna the received baseband equivalent signal, and is through the antenna The received baseband equivalent signal, i.e., in this example .

The transmitted signal is the reference signal S and is constant during the transmission of the reference signal for one channel estimation of the channel but may differ between subsequent transmissions with amplitude and phase The compound gain factor of product of .

It should be noted that the synthetic channel coefficient pass to include the composite gain factor . Because is unknown at the receiver, so the channel estimate is an estimate of the synthesized channel.

For any pair of synthetic channel coefficients, e.g. an antenna with delay l ₁ The synthetic channel coefficient of and an antenna with delay l ₀ The synthetic channel coefficient of , both composite channel coefficients are related to the transmitted composite gain factor proportional. Ratio of two independent composite channel coefficients The autocorrelation of will reflect the coherent nature of the channel excluding changes in the gain factor, so that the estimation of the Doppler spread can be independent of the amplitude and phase changes of the transmitted reference signal. In particular, according to some embodiments herein, the radio base station 12 comprises at least two receive antennas, enabling spatial and/or polarization separation, whereby at least two channel coefficients are always provided, one for each receive antenna. In the example shown, the first channel estimator 303 pairs via antenna Received baseband equivalent signal Perform channel estimation. Therefore, the first channel estimator 303 will include the baseband equivalent of the reference signal A comparison is made with known reference signals stored in the radio base station 12 . This produces the first channel estimate . The second channel estimator 305 pairs through the antenna Received baseband equivalent signal Perform channel estimation. Therefore, the second channel estimator 305 will include the baseband equivalent of the reference signal A comparison is made with known reference signals stored in the radio base station 12 . This produces a second channel estimate . In the embodiments herein, a normalized ratio g(t) of the synthesized channel coefficients is considered. The normalized ratio g(t) can be expressed as

(Equation 2).

The ratio estimate is calculated in the channel tap radio calculator 307, also known as the determination circuit . ratio estimate is the estimate of g(t), and is estimated from the channel according to and come and get

(Equation 3).

In some embodiments, , and l ₀ , l ₁ are two antennas and The minimum value of l such that .

The autocorrelation function of g(t) is expressed as , and by the normalized autocorrelation function and the Doppler spread f _D expresses:

(equation 4)

in

is the delay, i.e., the time difference between two time instances t ₀ and t ₁ in the argument of g(t), and thus The dimension of is time.

Assuming separation of the first and second signals of the and is an independent and identically distributed random variable, inferred from the symmetry is a real number. Furthermore, R _g (0) is equal to 1 by definition.

In the autocorrelation function estimator 309, the estimate of the autocorrelation function of g(t)—expressed as - is first obtained from the channel estimate of the signal. sampling delay Evenly spaced delays of (k=0, 1, ..., K-1) Estimate the autocorrelation function from

(equation 5)

in

K is the amount of sampling delay,

L is the number of estimated channel samples,

is the rate estimate of the normalized rate g and is obtained from the channel estimate according to (Equation 3),

is the delayed sampling interval,

l is a delay index related to the reception time of the first and second signals,

Indicates a ratio estimate The complex conjugate of , and

K indexes delayed samples.

Once an estimate of the autocorrelation function is obtained , the Doppler spread can be estimated in analyzer 311 . In one embodiment, the Doppler spread may be a maximum likelihood estimate, ie the maximum likelihood estimate is the Doppler spread that gives the greatest probability of the estimate of the autocorrelation function.

gap function can be computed as the estimated autocorrelation function with the precomputed ideal autocorrelation function The mean squared error between sets of :

in

The Doppler spread is estimated as such that the gap function is the minimum f _D value.

Embodiments herein allow for robust Doppler spread estimation in systems where the magnitude and phase of the transmitted signal vary between transmissions due to changes in transmit power. Composite gain factors from different channel estimates can be eliminated by using a ratio of channel estimates .

The above normalized autocorrelation function can be calculated numerically for uncorrelated Rayleigh fading channel coefficients and is plotted in FIG. 4 . normalized autocorrelation function The value of is defined along the y-axis, and x is defined along the x-axis. Autocorrelation functions for different Doppler spreads (i.e. A scaled version of ) can be compared to the estimated autocorrelation function, and the Doppler spread is estimated from the autocorrelation function most similar to the estimated autocorrelation function. That is, the Doppler spread with the autocorrelation function most similar to the estimated autocorrelation function is the estimated Doppler spread.

Method steps in a radio base station 12 for estimating the Doppler spread of a signal transmitted by a user equipment 10 over a channel in a radio communication network according to some general embodiments will now be described with reference to the flowchart shown in Fig. 5 . The steps do not have to be performed in the order described below, but may be performed in any suitable order. The radio base station 12 and the user equipment 10 are comprised in a radio communication network.

Step 501. The radio base station 12 receives the first signal and the second signal from the user equipment 10 . The first signal and the second signal are based on the signal transmitted by the user equipment 10, and the first signal and the second signal are separated in terms of space, time and/or polarization. In some embodiments, a first signal may be received at a first antenna and a second signal may be received at a second antenna. By being received at a different point in space than the second signal, by being polarized in a different manner than the second signal, and/or by being delayed in time compared The second signal is separated.

Step 502. The radio base station 12 estimates a first channel estimate of the received first signal by comparing the received first signal with known signals.

Step 503. The radio base station 12 estimates a second channel estimate of the received second signal by comparing the received second signal with known signals.

Step 504. The radio base station 12 determines a ratio of the first channel estimate to the second channel estimate. In some embodiments, the ratio may be a normalized ratio.

Step 505. The radio base station 12 estimates an autocorrelation function as a function of the determined ratios.

Step 506. The radio base station 12 estimates the Doppler spread of the transmitted signal based on the estimated autocorrelation function. Doppler spread may be estimated by comparing the estimated autocorrelation function with at least one pre-calculated autocorrelation function. Furthermore, in some embodiments, the Doppler spread may be estimated by minimizing a gap function, where the gap function may be calculated as the mean squared error between the estimated autocorrelation function and at least one pre-computed autocorrelation function.

In order to perform the method, a radio base station is provided. Fig. 6 is a block diagram illustrating a radio base station 12 for estimating the Doppler spread of a signal transmitted by a user equipment 10 over a channel in a radio communication network. The radio base station 12 is arranged to be included in a radio communication network. The radio base station 12 comprises a receiving circuit 601 configured to receive the first signal and the second signal from the user equipment 10 . The first signal and the second signal are based on the signal transmitted by the user equipment 10, and the first signal and the second signal are separated in terms of space, time and/or polarization. The receiving circuit 601 may comprise a first antenna α ₀ arranged to receive a first signal and a second antenna α ₁ arranged to receive a second signal. In some embodiments, the first signal can be separated from the second signal by being received at a different spatial point _than the second signal, and can be distinguished by the antennas _α0 and α1 by the distance between them. Alternatively or additionally, the first signal may be separated from the second signal by being received with a different polarization than the second signal, and may be distinguished by the cross-polarized antenna. Therefore, the _first antenna _α0 and the second antenna α1 may be cross-polarized. Alternatively or additionally, the first signal can be separated by being delayed in time compared to the second signal, and these signals are then differentiated in the channel estimator. It should be understood that any combination of separations is also possible.

The radio base station 12 further comprises a first estimation circuit 602, which corresponds to the first channel estimator 303 of FIG. 3 and is configured to estimate the received first signal by comparing the received first signal with a known signal The first channel estimate of . The radio base station 12 comprises a second estimation circuit 603, the second estimation circuit 603 corresponding to the second channel estimator 305 of FIG. Second channel estimate. Furthermore, the radio base station 12 comprises a determination circuit 604, corresponding to the channel tap ratio calculator 307 of Fig. 3, configured to determine the ratio of the first channel estimate to the second channel estimate. In some embodiments, the ratio may be a normalized ratio.

The radio base station 12 further comprises an estimated autocorrelation circuit 605, corresponding to the autocorrelation estimator 309 of Fig. 3, configured to estimate the autocorrelation function of the function of the determined ratio. In addition, the radio base station 12 comprises an estimated Doppler spread circuit 606, which corresponds to the analyzer 311 of Fig. 3, configured to estimate the Doppler spread based on the estimated autocorrelation function. In some embodiments, the estimated Doppler spread circuit 606 may be configured to estimate the Doppler spread by comparing the estimated autocorrelation function with at least one pre-calculated autocorrelation function. Additionally, the estimated Doppler spread circuit 606 may be configured to estimate the Doppler spread by minimizing a gap function, where the gap function is calculated as the mean squared error between the estimated autocorrelation function and at least one precomputed autocorrelation function .

The current mechanism for estimating the Doppler spread of a signal transmitted by a user equipment may be implemented by one or more processors such as the processing circuit 607 in the radio base station 12 shown in FIG. The computer program code of the function of example realizes together. The program code described above may also be provided as a computer program product, for example in the form of a data carrier carrying computer program code for executing the present solution when loaded into the radio base station 12 . One such carrier may take the form of a CDROM disc. However, it is possible to use other data carriers such as memory sticks. The computer program code can also be provided as pure program code on a server and downloaded to the radio base station 12 .

Furthermore, the radio base station 12 may comprise a memory circuit 608 arranged for storing estimates, data, applications to perform embodiments herein, etc.

It should be noted here that the radio base station 12 may also be referred to as eg a NodeB, an evolved NodeB (eNB, eNodeB), a base transceiver station, an access point base station, a base station router or be capable of communicating with user equipment in the cell served by the radio base station 12 Any other network element, depending on e.g. the radio access technology and terminology used. User equipment 10 may be represented by, for example, a wireless communication terminal, mobile cellular telephone, personal digital assistant (PDA), wireless platform, laptop, computer or any other kind of device capable of wireless communication with radio base station 12 .

In the drawings and specification, there are disclosed exemplary embodiments of the invention. However, many changes and modifications may be made to these embodiments without substantially departing from the principles of the invention. Accordingly, while specific terms are employed, they are used in a generic and descriptive sense only and not in a limiting sense, the scope of the invention being defined by the following claims.

Claims (12)

1. the method for the doppler spread of the signal being transmitted by the channel of radio circuit by subscriber equipment (10) for estimation in radio base station (12), described radio base station (12) and subscriber equipment (10) are included in described radio circuit, and described method comprises

-receive (501) first signal and secondary signal from described subscriber equipment (10), the signal that described first signal and secondary signal transmit based on described subscriber equipment (10), wherein said the first and second signals are separating aspect space, time and/or polarization

-by received first signal and known signal are compared, estimate the first channel estimating of (502) first signal that receives,

-by received secondary signal and described known signal are compared, estimate that the second channel of (503) secondary signal that receives is estimated,

The ratio that-definite (504) described first channel estimating and described second channel are estimated,

-estimate (505) the auto-correlation function of definite ratio, and

-estimate (506) described doppler spread based on estimated auto-correlation function.

The method of claim 1, wherein described first signal the first antenna () receive, and described secondary signal the second antenna () receive.

3. the method as described in any one in claim 1-2, wherein, by comparing in different spatial point and receive from described secondary signal, by polarizing by different way compared with described secondary signal, and/or by postponing in time compared with described secondary signal, described first signal is separated with described secondary signal.

4. the method as described in any one in claim 1-2, wherein, described ratio is normalization ratio.

5. the method as described in any one in claim 1-2, wherein, by estimated auto-correlation function and at least one precalculated auto-correlation function are compared, estimates described doppler spread.

6. method as claimed in claim 5, wherein, by making gap function for minimum, estimates described doppler spread, and described gap function is calculated as the mean square error between estimated auto-correlation function and described at least one precalculated auto-correlation function.

7. the radio base station (12) of the doppler spread of the signal being transmitted by the channel of radio circuit by subscriber equipment (10) for estimation, described radio base station (12) is arranged to be included in described radio circuit, and described radio base station (12) comprising:

Receiving circuit (601), be configured to receive first signal and secondary signal from described subscriber equipment (10), the signal that described first signal and secondary signal transmit based on described subscriber equipment (10), and wherein said the first and second signals are separating aspect space, time and/or polarization

The first estimating circuit (602,303), is configured to the first channel estimating by received first signal and known signal being compared to estimate received first signal,

The second estimating circuit (603,305), is configured to by received secondary signal and described known signal being compared estimate that the second channel of received secondary signal estimates,

Determine circuit (604,307), be configured to determine the ratio of described the first channel estimating and the estimation of described second channel,

Estimate auto-correlation circuit (605,309), be configured to estimate the auto-correlation function of definite ratio, and

Estimating Doppler expanded circuit (606,311), is configured to estimate described doppler spread based on estimated auto-correlation function.

8. radio base station as claimed in claim 7 (12), wherein, described receiving circuit comprise be configured to receive described first signal the first antenna () and be configured to receive described secondary signal the second antenna ()。

9. the radio base station (12) as described in any one in claim 7-8, wherein, by comparing in different spatial point and receive from described secondary signal, by polarizing by different way compared with described secondary signal, and/or by postponing in time compared with described secondary signal, described first signal is separated with described secondary signal.

10. the radio base station (12) as described in any one in claim 7-8, wherein, described ratio is normalization ratio.

11. radio base stations (12) as described in any one in claim 7-8, wherein, described estimating Doppler expanded circuit (311,606) is configured to by estimated auto-correlation function and at least one precalculated auto-correlation function are compared estimating Doppler expansion.

12. radio base stations as claimed in claim 11 (12), wherein, described estimating Doppler expanded circuit (311,606) being configured to by making gap function is that minimum is carried out estimating Doppler expansion, and described gap function is calculated as the mean square error between estimated auto-correlation function and described at least one precalculated auto-correlation function.