Pulse shaping which compensates for component distortion

Abstract

A method is provided for defining a pulse function shape for acting on a data stream for transmission in a telecommunication system which compensates for distortion by a component of the transmitter. The method comprises defining desired cost parameters (e.g. error functions for amplitude, BER, bandwidth, energy, AFC) and defining the shape of the pulse function in dependence of the desired cost parameters and the distortion to be compensated for. A pulse generator, modulator and communications device providing such a pulse function are also provided. Application in dual mode TDMA / CDMA system.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. patent application Ser. No. 09 / 625,201, filed Jul. 21, 2000 which is a continuation of PCT Application PCT / GB99 / 00201, filed Jan. 21, 1999 which are hereby incorporated herein in their entirety by reference.BACKGROUND OF THE INVENTION [0002] The present invention relates to a communication device which is provided with pre-distortion to compensate for distortion introduced by components in the device, and a method of such pre-distortion. [0003] In particular, the present invention relates to the compensation of distortion by components in a transmitter. [0004] Components in the transmitter cause an information signal to be distorted prior to transmission to differing degrees. Two major factors affect this distortion, namely ramp up and ramp down, and component tolerances. Whilst individually such distortions may not affect the signal to be transmitted significantly, there is a possibility that ...

AI Technical Summary

Benefits of technology

"The present invention provides a method for compensating for distortion in a telecommunications system by using a pulse function to act on a data stream in a transmitter. This method allows for the selection of components in the transmitter that are more efficient, and can be easily adapted to different telecommunications systems. The method also enables the use of a single pre-distortion compensation pulse function for a range of frequencies, which simplifies the design process and reduces the need for testing and modification of individual devices during manufacture. The invention also provides a modulator and a communication device that use the defined pulse function for shaping a data stream in the transmitter. The method can be used in both TDMA and CDMA telecommunications systems, and the pulse function can be shaped based on the cost parameters and distortion by the transmitter components. The invention also allows for a dual mode communication device that can operate at different data rates for voice and data applications."

Problems solved by technology

Whilst individually such distortions may not affect the signal to be transmitted significantly, there is a possibility that the superposition of such signals is unacceptable as it is outside the limits defined by the appropriate telecommunication standard.

For example, such distortion may cause a signal in the frequency domain to extend outside the bandwidth defined by a standard.

As will be appreciated, this increases manufacturing costs, and results in a reduction in yield over a given time.

However, this increases the complexity of the transmitter and the power consumption.

However, this is not possible for cases where the distortion varies over a frequency range such as in non-linear devices (for example non-linear power amplifiers).

For example, GMSK (used in GSM) is spectrally inefficient but power efficient, whereas on the other hand QPSK (used in CDMA systems) is spectrally efficient but power inefficient.

Distortion by components in the transmitter of a communication device can reduce the benefits of these schemes in practice.

However, in practice, distortion of the signal by components in a GSM transmitter will cause variation in the amplitude envelope and thus a variation in power efficiency, so negating at least to some extent the advantages for which GMSK was chosen.

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