BACKGROUND OF INVENTION In orthogonal frequency division multiplex (OFDM) systems which have been used in recent wireless communication systems, Peak-to-Average Power Ratio (PAPR) is the main drawback. High PAPR causes the degradation in power efficiency of the system and hence the increase to the system cost and also fast depletion of battery power. Several prior arts have attempted to reduce PAPR, which is done by determining an optimum phase sequence.

KR 20030084291 (A) describes a method to exactly reconstruct data at the receiving end by transmitting additional information related to the partial transmission sequence (PTS). Though this solution achieves a good spectrum efficiency and bit error rate (BER), but the complexity of the solution is still a main drawback. This causes the solution to be not applicable in actual systems.

WO2006/012306 describes a solution where predistortion is applied in OFDM systems by modifying frequency domain symbols used to modulate individual subcarriers. Then the frequency domain symbols are modified in such a way to compensate for the amplifier's nonlinearity. This invention did not consider the PAPR reduction and hence it could not achieve maximum efficiency. US 20090310705 describes a solution where an apparatus uses amplitude extraction section that extracts amplitude of an OFDM-modulated wave. A power-amplifier control section sets the power supply of a power amplifier to exceed the rated power when the extracted amplitude exceeds specific amplitude to expand the saturation point of the power amplifier. A compensation-value-selection control section compensates the nonlinear characteristic of the power amplifier, by expanding the saturation point of the power amplifier. This method involves many components that increase the complexity and hence the cost of the system. The effects of the PAPR reduction are not clear in this invention. The solution is thus very complicated and increases the complexity and cost.

There is a need in the field for a solution that determines an optimum phase sequence in a less complex and cost efficient manner.

SUMMARY OF INVENTION

Accordingly there is provided a method of reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplex (OFDM) systems, wherein the method includes the steps of generating a matrix of random phase sequence based on interleaved formation, adding of a dummy sequence to an input signal, partitioning the input signal with dummy sequence into sub blocks, multiplying the matrix of interleaved phase sequence with an input signal, performing a search for optimum phase sequence, comparing the minimum PAPR with a threshold and retrieving the signal at receiver.

The present invention consists of several novel features and a combination of parts hereinafter fully described and illustrated in the accompanying description and drawings, it being understood that various changes in the details may be made without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:

Figure 1 illustrates a block diagram of a method of reducing peak-to-average power ratio (PAPR) in accordance with a preferred embodiment of the present invention;

Figure 2 illustrates a block diagram of a simplified predistortion block with memory compensation, CGMP in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to method of reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplex (OFDM) systems. Hereinafter, this specification will describe the present invention according to the preferred embodiment of the present invention. However, it is to be understood that limiting the description to the preferred embodiment of the invention is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications and equivalents without departing from the scope of the appended claims.

The following detailed description of the preferred embodiment will now be described in accordance with the attached drawings, either individually or in combination. Figure 1 illustrates a block diagram depicting a method of reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplex (OFDM) systems. The method includes the steps of generating a matrix of random phase sequence based on interleaved formation, adding of a dummy sequence to an input signal, partitioning the input signal with dummy sequence into sub blocks, multiplying the matrix of interleaved phase sequence with an input signal, performing a search for optimum phase sequence, comparing the minimum PAPR with the threshold and retrieving signal at receiver.

The method decreases computational complexity of conventional partial transmit sequence (C-PTS) technique. First a matrix of interleaved phase sequence is generated which is then multiplied with the input signal with addition of dummy sequence after partitioning into sub blocks. The matrix can be in random, adjacent or interleaved formats in which the interleaved format has the lowest complexity and PAPR reduction among them. Here the interleaved phase sequence is applied due to lesser complexity, however its PAPR performance is slightly inferior compared to random and adjacent phase sequences. After an orthogonal frequency division multiplex (OFDM) signal is generated and Inverse Fast Fourier transform (IFFT) is performed for each subblocks, the phase sequences are multiplied and the searching for optimum phase sequence is performed. The optimum phase sequence is determined as the phase sequence which results in the lowest PAPR. Index of the phase sequence is transmitted as side information with the signal in order to recover the signal at the receiver. By defining a new phase sequence matrix, the number of searches for optimum phase sequence is reduced which results in significant reduction in the complexity and hence reduction of the hardware resources, while the PAPR performance remains unaffected. By combining the proposed PAPR scheme with complex gain memory predistortion (CGMP), which is a technique of adaptive digital predistortion, the power amplifier (PA) becomes more linear and the power efficiency will be enhanced. The CGMP technique is capable of compensating memory effects due to the behavioral changing of the PA. Figure 2 illustrates a block diagram depicting a method of digital predistortion named complex gain memory predistortion (CGMP). The conventional predistortion techniques such as memory polynomial, have the main drawback in which its complexity rises by increasing the memory length in order to compensate the dynamic memory effects. The current method has the capability to overcome the dynamic memory effects by inversing the input complex signal and updating the predistortion samples in the lookup table (LUT) in order to compensate the dynamic memory effects of the power amplifier. The main impacts of dynamic memory effects or electrical memory effects are spreading the spectrum and in-band distortion. The complexity of CGMP technique will not be changed by increasing the memory length compared to the memory polynomial technique in which the complexity dramatically increases by adding the memory length. By applying the CGMP technique all the memory contents of the power amplifier can be compensated.

The CGMP technique compared with memory polynomial and conventional digital predistortion techniques, has demonstrated acceptable results. Both memory polynomial and conventional predistortion techniques have their own disadvantages. For example, in memory polynomial predistortion, the complexity of extracting coefficients of predistortion function diminishes the capability of linearization, while in complex gain predistortion method, the memory effects that cause dynamic AM-AM and AM-PM are not considered which means that only thermal memory effects can be compensated by this technique. It should be noted that memory effects are of two types, electrical and thermal. The thermal effects can be overcome by means of simple feedback, but electrical memory effects cannot be compensated by feedback only. The CGMP technique that is applied here can compensate the dynamic memory effects of the PA with less hardware resource. The joint PAPR and predistortion are first designed and simulated separately and then the combination of PAPR and CGMP is designed. The present invention discloses a unit that combines Enhanced PTS (EPTS) and CGMP techniques that outperforms the conventional techniques in terms of PAPR reduction, complexity and power added efficiency.

A main advantage of the present invention over prior art is a significant reduction in complexity together with good PAPR performance. By combining the enhanced PTS technique with predistortion, power efficiency increases which results in prolonged battery life. The power amplifier works at maximum efficiency and the out-of-band distortion that causes adjacent channel interference is suppressed. Moreover the higher power efficiency compared to prior art is achieved by applying a predistortion capability to linearize the power amplifier. The immediate impact in practical applications is a significant reduction in total cost of multicarrier systems while overall performance is kept optimal. The main reason for the dramatic drop in system cost is because it does not require expensive high power amplifiers for transmission in the multicarrier systems.

By increasing the bandwidth, the power amplifier exhibits more memory effects. The method is able to combat the memory effects by use of adaptive techniques and a new method based on memory polynomial. The combined PAPR and predistortion method shall significantly enhance several performance parameters in the OFDM systems, namely power added efficiency (PAE), PAPR, bit error rate (BER), error vector magnitude (EVM), power spectral density (PSD) and complementary cumulative distributive function (CCDF). The digital predistortion is low in complexity which requires only look-up table (LUT) and complex divider for it to be implemented.

The method achieves both PAPR reduction and predistortion with low complexity whereas in prior arts, these considerations were not met in one unit. For example, in prior art these cases were studied separately, and though both issues were discussed, it lacks complexity reduction.

The disclosed invention is suitable, but not restricted to, for use in broadband wireless communication systems, specifically worldwide interoperability for microwave access (WiMAX), long term evolution (LTE), digital video broadcasting (DVB) and 4G, which makes mobile devices with higher efficiency, longer battery life and less costly.