Pulse or digital communications – Spread spectrum
Reexamination Certificate
2002-04-01
2003-10-28
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
C375S285000, C375S296000
Reexamination Certificate
active
06639937
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a method and to an apparatus for producing spread-coded signals, in particular spread-coded mobile radio signals.
Telecommunication is one of the fastest developing technologies. In the mobile radio field, work is currently being carried out on the standardization and development of what is referred to as third-generation mobile radio, which is referred by the term UMTS (Universal Mobile Telecommunications System) and envisages a world-wide uniform mobile radio standard.
According to the UMTS mobile radio standard, what is referred to as CDMA (Code Division Multiple Access) is used as the multiple access method. This is a multiple access method in which all the subscribers to the corresponding mobile radio system are allowed to use the entire available system bandwidth at the same time. In order to make it possible, despite this, to avoid collisions between the individual subscribers, the individual subscriber signals are provided with different code sequences which thus allow unique association of the received signals. During this process, the individual signals are spread, as a result of which the bandwidth is multiplied, so that this technique is also referred to as the spread-spectrum technique. In particular, the subscriber data that will be transmitted is multiplied or spread using a code sequence which is independent of the data that will be transmitted. The band-spread signal obtained in this way is then modulated onto a radio-frequency carrier, and is transmitted to a corresponding receiver. The receiver demodulates this band-spread signal and carries out despreading, using a code sequence which is synchronized to the transmitter. The receiver admittedly receives not only the desired signal from the transmitter, but also additional signals from other transmitters, transmitting in the same frequency band. However, the despreading process ensures that the only signal which is despread and whose bandwidth is reduced is that which uses the same and synchronous spread code as the receiver, so that, after the despreading process, the desired signal can easily be filtered out.
While transmission apparatus for digitally producing mobile radio transmission signals for different mobile radio standards, in particular, for example, for the currently normally used GSM (Global System for Mobile Communication) mobile radio standard, are already known, the problem of producing spread-modulated signals in mobile terminals for third-generation mobile radio has not yet been solved.
The UMTS standard “Ultra physical layer description FDD parts”, Ovesjö Fredrik, European Telecommunication Standard, XX, XX, Jun. 25, 1998 (1998-06-25), pages 1 to 41, describes a method for producing spread-coded signals, in which a signal is subjected to spread coding and to subsequent scrambling. The band-spread and scrambled signal is then filtered in an RRC filter.
The technical article “Transmit pulse shaping filters and CORDIC algorithm based precompensation for digital satellite communications”, M. Vandermaar et al., IEEE Proceedings of the 39th Midwest Symposium on Circuits and Systems (Cat. No. 96CH35995), AMES, IA, USA, Aug. 18-21, 1996, pages 1219 to 1222, Vol. 3, 1996, New York, N.Y., USA, IEEE; USA ISBN: 0-7803-3636-4) describes an algorithm for precompensation for non-linearities that occur in a signal amplifier. The compensator has two CORDIC (Coordinate Rotation Digital Computer) stages, which carry out a coordinate transformation on the signal from cartesian coordinates to polar coordinates, and vice versa. The computation steps for the actual signal compensation are carried out between the two CORDIC stages.
U.S. Pat. No. 5,838,733 describes a transmitting device, in which a digital signal that will be transmitted is subjected to programmable amplification and to amplitude limiting.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an apparatus and a method for producing spread-coded signals which overcome the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular, it is an object of the invention to provide an apparatus and a method for producing spread-coded signals that can be used, in particular, in third generation mobile radio transmitters.
Furthermore, it is an object of the invention to enable spread-coded signals to be produced in accordance with different mobile radio standards, for example, in accordance with the UMTS or IS-95 standard.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing spread-coded signals that includes steps of: coding and band-spreading transmission data using a spread code to obtain band-spread transmission data; coding the band-spread transmission data using a scrambling code to obtain band-spread and scrambled transmission data and then pulse shaping the band-spread and scrambled transmission data; subjecting the band-spread and scrambled transmission data to frequency correction; and in a signal path downstream from the frequency correction, subjecting the band-spread and scrambled transmission data to an operation selected from the group consisting of a DC offset operation and an amplitude compensation operation.
In accordance with an added mode of the invention, the pulse shaping is performed by Root Raised Cosine filtering using a roll-off factor of approximately 0.22.
In accordance with an additional mode of the invention, during the pulse shaping, the band-spread and scrambled transmission data is oversampled using a specific oversampling factor.
In accordance with another mode of the invention, the oversampling factor is four.
In accordance with a further mode of the invention, digital frequency offset correction is used for the frequency correction; a rotation angle is used for the frequency correction that is represented as a linear combination of microrotations; and the microrotations are performed as a function of a frequency offset by selectively using a CORDIC algorithm.
In accordance with a further added mode of the invention, the method includes: performing both the DC offset operation and the amplitude compensation operation; performing the DC offset compensation by adding a specific DC offset compensation value to the band-spread and scrambled transmission data; and performing the amplitude compensation by multiplying the band-spread and scrambled transmission data by a specific amplitude compensation value.
In accordance with a further additional mode of the invention, before the transmission data is coded using the spread code, the transmission data is weighted by multiplying the transmission data by a weighting factor. Subsequently, the transmission data is oversampled.
In accordance with yet an added mode of the invention, the method includes using an over-sampling factor to perform the step of oversampling the transmission data such that when the subsequent step of coding the transmission data using the spread code is performed, a maximum chip rate is obtained.
In accordance with yet an additional mode of the invention, the method includes performing the step of coding and band-spreading the transmission data, the step of coding the band-spread transmission data using the scrambling code, the step of pulse shaping the band-spread transmission data, the step of frequency correction, and the step of oversampling the transmission data by:
obtaining the transmission data from a plurality of physical channels, each providing first transmission data;
for each one of the plurality of the physical channels and separately from others of the plurality of the physical channels, weighting, oversampling, and coding the first transmission data using a channel-specific spread code;
after being coded using the spread code, combining the first transmission data of the plurality of the physical channels to form an I branch carrying second transmission data and a Q branch carrying third transmission data;
scrambling the se
Doetsch Markus
Jung Peter
Kella Tideya
Plechinger Jörg
Schmidt Peter
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Pham Chi
Stemer Werner H.
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