Data receiver having means for minimizing interference and method used in such a receiver

The present invention relates to a data receiver (5) for receiving user data and reference data (CPICH) coming from a transmitter 5 via at least a channel. This receiver comprises means for unscrambling (39,66,64) and means for despreading (40,68) received data, means for analyzing the characteristic of the channel (35), means for evaluating the contribution of interference of data caused by the channel (IEP1Fj-IEPKFj) and a substracter means intended for cancelling the contribution of interference in the user data, said substracter means (62) being placed before said unscrambling means.

FIELD OF THE INVENTION

The present invention relates to a data receiver having means for minimizing interference.

BACKGROUND OF THE INVENTION

This kind of data receiver is used in mobile phones, which comply with the UMTS standard. For data transmission, this standard proposes to use spreading codes having orthogonality properties.

An important problem faced by such mobile phones is that the effect of propagation paths of the data is to be eliminated. A known solution for eliminating this interference is the use of the CPICH channel, which transmits 256 “1”, transformed into “1+j” after modulation. So, at the receiver side in the mobile, the channel can be estimated in an easy way. The following references can be consulted as prior art considerations.

“CPICH interference cancellation as a means for increasing DL capacity”

“CPICH interference cancellation as a mean for increasing DL capacity”

“Further results on CPICH interference cancellation”

SUMMARY OF THE INVENTION

The invention proposes to improve the cancelling of a certain amount of interference with respect of the prior art cited above. According to the invention, a data receiver is defined in the following way:

A data receiver for receiving user data and reference data coming from a transmitter via at least a channel, comprising means for unscrambling and means for despreading received data, means for analyzing the characteristic of the channel, means for evaluating the contribution of interference of data caused by the channel and a subtracter means intended for cancelling the contribution of interference in the user data, said subtracter means being placed before said unscrambling means.

These and other aspects of the invention are apparent from and will be elucidated, by way of non-limitative example, with reference to the embodiment(s) described hereinafter.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a system in which the invention is applied. The system is a CDMA system and concerns a cellular radio mobile system. Reference1shows a base station comprising a transmitter2having a high-frequency part3and the reference5a mobile station. The link from the base station to the mobile station or mobile is determined by a given scrambling code. The arrows P1, P2, P3. . . indicate various paths, providing various delays τ1, τ2, τ3. . . , by which the waves are propagated from an antenna6connected to the output of the high-frequency part3to an antenna8that the mobile5comprises. The mobile station can be interfered by links that have a different scrambling code.

FIG. 2shows, the transmitter2in a schematic way. It comprises the high-frequency part3the output of which is connected to the antenna6and an input connected to a data multiplexer12, via a transmitting filter13. This multiplexer12receives, notably data from the user, which is indicated by a user box15, and data coming from the CPICH. The CPICH data are formed by a “1” sequence. Before transmission, theses data are scrambled by a scrambling sequence Scr thanks to a scrambling device17; a spreading code Sp is also applied, as is known.

FIG. 3shows a mobile station5in a schematic way. As usual, it comprises a screen25, a speaker26, a microphone27and a keyboard28. A general electronic part29manages all the tasks not specially covered by the invention. This Fig. shows a receiver part30in more detail. This part30comprises a high-frequency head31from which data are provided, after a high-rate receiving filter32elaborated by an over-sampling device34. The high-frequency head31also supplies data to a channel estimator35and to a delay estimator38, which determines the delays τ1, τ2, τ3. . . , of the cited paths P1, P2, P3. . . . Scrambling codes are delivered by a scrambling code generator39and spreading codes by a spreading code generator40. All the codes provided by the elements35,38and39can be used by a Rake type receiver42. The output of this receiver42is connected to the input of the electronic part29. The receiver42comprises a plurality of fingers RF1, . . . RFj, . . . RFk, . . . and RFJ as is usual for this kind of receiver. A combining device45combines all the information coming from the fingers to provide symbols.

FIG. 4shows the structure of the Rake finger RFj cooperating with the other parts of the receiver. The finger RFj comprises a plurality of interference estimators allocated to each path respectively. IEPIFj is the interference estimator of the path1on finger1. IEPkFj is the interference estimator of the path k on finger j and so on. The outputs of these estimators are added together by the adding device60. The estimations of the interference are subtracted from the data signal provided by the head31thanks to a subtracter62. The data signal are delayed by the delay device61which delays the data by an amount which has a relation to the delay of the path concerned. After this operation, an unscrambling operation is performed by the multiplier64, which provides data from the scrambling code coming from generator39. As the data are in complex form, a conjugate device66evaluates the conjugate of the scrambling code. This scrambling code is the scrambling code assigned to the link. Finally the data are despread by the multiplier68taking into account the code provided by the generator40.

InFIG. 4the interference estimator IEPkFj is shown in more detailed. It comprises a plurality of correlators COR1. . . CORJ−1 the number of which is dependent on the number of paths. The output signals of these correlators are added together by the adder70and from here sent to the adder60.

FIG. 5shows the structure of the correlator CORJ. This correlator receives the scrambling codes Scrj of the other links which contribute to the interferences to be cancelled. Note that there are J−1 such correlators for each finger, as it is possible to eliminate the interference of all j paths with j≠k, with k being the finger under consideration. For this purpose, the estimate ĥ j of the link and the delay τj of the other paths are considered. All these parameters are not the parameters of the main link but those of the parasitic ones. A multiplier80performs an operation concerning ĥ and the value of the CPICH i.e. “1+j” in complex form. 2 N multipliers M(−N) to M(+N) perform an operation with the scrambling code of the parasitic link delayed in accordance with the delay τj s of these links. The output signals of these multipliers are applied to the operators ρ(−N) to ρ(+N). N is taken into consideration in relation to the number of interference coefficients ρ, each coefficient being generated by the cross-correlation of the transmitting and the receiving filter, as in the formula below (where for example value N=8, but this may vary as a parameter). An adder85sums all the signals at the output of these multipliers before they are applied to the adder70.

The working of the channel estimator is facilitated by the “1” sequence formed, coming from the CPICH and transformed into “1+j” considered in complex form. In this way, the coefficients ĥ of the impulse response of the channel are defined in an easy way. From these received data, the delay τ1, τ2, τ3provided by the various paths P1, P2, P3, . . . are also estimated in the delay estimator38.

Finally, the interference estimator carries out the following formula:

r⁡(n)=∑k=Δj,i-8Δj,i+8⁢ρ⁡(k*Tc-(τj-τi))*h^j*Sc,n+k*Tc*Sp,n+k*tc*(1+j)
In this formula:

ρ is the cross-correlation between the transmit and receive filter,

ĥjis channel coefficients of the path j,

Sp,nis the spreading sequence of the pilot channel,

1+j is the CPICH symbol,

Tc is the duration of a chip (time slot obtained after scrambling),

τj−τiis the delay between the path i and the path j,

τ1-τ0=Δ1,0·Tc+Ω1,0·TcOS⁢⁢Ω1,0<OS
OS is an integer that represents an over-sampling factor. Δ1,0is an integer which measures the delay in Tcunit and Ω1,0the number of over-sampling periods. It is to be understood that the invention covers the case for which the realization of all the embodiments disclosed is made by a processor and convenient software.