A scheme of the superimposing additional data signal in the time domain for orthogonal frequency division multiplexing (OFDM) system is proposed. The proposed scheme has a tradeoff between the degree of freedom for data transmission and inter-carrier interference (ICI), which provides the flexibility of data rate decision when the finite number of modulation and coding levels are available for the given channel condition. A performance analysis of the bit error rate (BER) confirms this tradeoff. In simulation on the practical environment which experiences multipath fading and error of channel estimation, the results show that much improvement of spectral efficiency has been achieved while keeping as nearly good bit error rate as the conventional OFDM. Moreover, the single carrier transmission of the superimposed additional data in the time domain also gives an opportunity of boosting the signal power up to the peak to average power ratio (PAPR) margin of the OFDM system.

In this paper, a new large spreading code set with a uniform low cross-correlation is proposed. The proposed code set is capable of (1) increasing the number of assigned user (capacity) in a multicarrier code division multiple access (MC-CDMA) system and (2) reducing the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) system. In this paper, we derive a new code set and present an example to demonstrate performance improvements of OFDM and MC-CDMA systems. Our proposed code set with code length of N has K=2N+1 number of codes for supporting up to (2N+1) users and exhibits lower cross correlation properties compared to the existing spreading code sets. Our results with subcarrier N=16 confirm that the proposed code set outperforms the current pseudo-orthogonal carrier interferometry (POCI) code set with gain of 5 dB at bit-error-rate (BER) level of 10-4 in the additive white Gaussian noise (AWGN) channel and gain of more than 3.6 dB in a multipath fading channel.

Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitted signal. This study introduces a low-complexity selected mapping (SLM) OFDM scheme based on discrete Fourier transform (DFT) constellation-shaping. The DFT-based constellation-shaping algorithm applied with conventional SLM scheme usually requires a bank of DFT-shaping matrices to generate low-correlation constellation sequences and a bank of inverse fast Fourier transforms (IFFTs) to generate a set of candidate transmission signals, and this process usually results in high computational complexity. Therefore, a sparse matrix algorithm with low-complexity is proposed to replace the IFFT blocks and the DFT-shaping blocks in the proposed DFT constellation-shaping SLM scheme. By using the proposed sparse matrix, the candidate transmission signal with the lowest PAPR can be achieved with lower complexity than that of the conventional SLM scheme. The complexity analysis of the proposed algorithm shows great an improvement in the reduction of the number of multiplications. Moreover, this new low-complexity technique offers a PAPR that is significantly lower than that of the conventional SLM without any loss in terms of energy and spectral efficiency.

In this paper, we propose a simple peak power reduction (PPR) method based on adaptive inversion of parity-check block of codeword in BCH-coded OFDM system. In the proposed method, the entire parity-check block of the codeword is adaptively inversed by multiplying weighting factors (WFs) so as to minimize PAPR of the OFDM signal, symbol-by-symbol. At the receiver, these WFs are estimated based on the property of BCH decoding. When the primitive BCH code with single error correction such as (31,26) code is used, to estimate the WFs, the proposed method employs a significant bit protection method which assigns a significant bit to the best subcarrier selected among all possible subcarriers. With computer simulation, when (31,26), (31,21) and (32,21) BCH codes are employed, PAPR of the OFDM signal at the CCDF (Complementary Cumulative Distribution Function) of 10-4 is reduced by about 1.9, 2.5 and 2.5 dB by applying the PPR method, while achieving the BER performance comparable to the case with the perfect WF estimation in exponentially decaying 12-path Rayleigh fading condition.

The performance of an orthogonal frequency division multiplexing (OFDM) system is degraded if the peak-to-average power ratio (PAPR) is high. In general, in order to obtain optimal PAPR reduction using the partial transmitted sequence (PTS) technique, an exhaustive search of the possible subblocks and rotation factors must be done. As the number of subblocks and rotation factors increases, PAPR reduction improves, but the computational load becomes impractical. In order to reduce the complexity while still improving the OFDM system performance, a new method using a genetic algorithm (GA) is proposed to find a set of rotation factors that reduces both the PAPR and the computational load. A comparison is made between the proposed method and previously developed techniques such as exhaustive and gradient descent PTS methods. The superiority of the proposed method is demonstrated as a reduction in computational load compared with exhaustive PTS and the gradient method, and an improvement in performance compared with the iterative and gradient methods.

We propose the P-SLM (Partitioned-SeLected Mapping) scheme with low complexity for PAPR reduction of OFDM signals. In the proposed scheme, a symbol sequence in the frequency domain is partitioned into several sub-blocks which are multiplied by different orthogonal phase sequences whose length and number are shorter and smaller than those used in the conventional SLM. Then, among various sequences in the time domain generated after the IFFT for the SLM sub-blocks, the sub-block combination with the lowest PAPR is selected and transmitted. Simulation results show that the proposed P-SLM scheme significantly reduces the number of IFFT calculation and multiplication than the conventional SLM without loss of PAPR reduction performance.

One of the disadvantages of using OFDM is the larger peak to averaged power ratio (PAPR) in its time domain signal as compared with the conventional single carrier modulation method. The larger PAPR signal would course the fatal degradation of bit error rate (BER) performance due to the inter-modulation noise occurring in the non-linear amplifier. To overcome this problem, this paper proposes a simple PAPR reduction method by using dummy sub-carriers, which can achieve the better PAPR performance with less computational complexity than the conventional method. This paper presents various computer simulation results to verify the effectiveness of proposed method as comparing with the conventional method in the non-linear channel.

A companding technique using the hyperbolic tangent transform is proposed for reducing the peak-to-average-power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. This technique is practical and can be implemented easily in integrated circuit design. The PAPR value of an OFDM system and the optimal companding coefficient to attain the minimum quantization error are derived. Error probability performance of the system after the companding is evaluated. Our simulation results exhibits that the system with the suggested scheme has nearly the same performance as the systems with the µ-law or A-law companding techniques.

The combination of deliberate clipping and an adaptive symbol selection scheme (ASSS) can be used to reduce the peak to average power ratio (PAPR) for Orthogonal Frequency Division Multiplexing (OFDM) signals. The probability density function (pdf) of a sample's amplitude of an adaptively selected OFDM signal without over-sampling has been considered to be approximately equal to the Rayleigh pdf. In this letter, we derive the exact pdf showing the relationship between the probability distribution of the sample's amplitude and the number of candidate OFDM symbols for ASSS. The use of the newly derived pdf can measure the effect of deliberate clipping on the adaptively selected OFDM signal more accurately.

We propose an adaptive SLM scheme based on peak observation for PAPR reduction of OFDM signals. The proposed scheme is composed of three steps: peak scaling, sequence selection, and SLM procedures. In the first step, the peak signal samples in the IFFT outputs of the original input sequence are scaled down. In the second step, the sub-carrier positions where the power difference between the original input sequence and the FFT output of the scaled signal is large, are identified. Then, the phase sequences having the maximum number of phase-reversed sequence words only for these positions are selected. Finally, the generic SLM procedure is performed by using only the selected phase sequences for the original input sequence. Simulation results show that the proposed scheme significantly reduce the complexity in terms of IFFT and PAPR calculation than the conventional SLM, while maintaining the PAPR reduction performance.

In order to improve OFDM (Orthogonal Frequency Division Multiplexing) PAPR (Peak-to-Average Power Ratio) reduction performance of the conventional SLM (SeLective Mapping), we propose an effective SLM-PRSC (PAPR Reduction Sub-Carrier) hybrid scheme. In the proposed scheme, after performing the SLM for the frequency domain OFDM symbol excluding pre-determined PRSC positions, the SLM-PRSC hybrid sequence with the lowest PAPR, which is generated by adding the time domain PRSC sequence to the results of the SLM, is selected as the transmitted OFDM signal. Since the identical PRSC sequences generated a priori are repeatedly used for every OFDM symbol, excessive IFFT (Inverse Fast Fourier Transform) calculation is avoided. Simulation results reveal that the proposed scheme significantly improves the PAPR reduction performance of the conventional SLM, while avoiding excessive increase of IFFT and PAPR calculation.

In this paper, we propose a new modulation named parallel combinatory/high compaction multi-carrier modulation (PC/HC-MCM) using the techniques of parallel combinatory orthogonal frequency division multiplexing (PC-OFDM) and high compaction multi-carrier modulation (HC-MCM). Two types of PC/HC-MCM systems, which are named as modulated PC/HC-MCM system and (unmodulated) PC/HC-MCM system, can be designed. The modulated PC/HC-MCM system achieves better bit-error rate (BER) performance than that of HC-MCM system with equal bandwidth efficiency (BWE). The PC/HC-MCM system can obtain the better peak-to-average power ratio (PAPR) characteristics by selecting appropriate constellation for each subcarrier. On the other hand, since PC/HC-MCM can divide the PC-OFDM symbol duration into multiple time-slots, the advantages of frequency hopping (FH) can be applied in the PC/HC-MCM system. Therefore, we also combine the PC/HC-MCM and frequency hopping multiple access (FHMA) to propose a novel multiple access (MA) system. It can simultaneously transmit multiple users' data within one symbol duration of PC-OFDM.

Orthogonal frequency division multiplexing (OFDM) systems for mobile applications suffer from inter-carrier-interference (ICI) due to frequency offset and to time-variation of the channels and from high peak-to-average-power ratio (PAPR). In this paper, we revisit symmetric cancellation coding (SCC) proposed by Sathananthan et al. and compare the effectiveness of SCC with a fixed subtraction combining and the well-known polynomial cancellation coding (PCC) over Rayleigh fading channels with Doppler spread in terms of the signal-to-interference plus noise power ratio (SINR) and bit-error-rate (BER). We also compare SCC with subtraction combining and SCC of Sathananthan et al. with maximum ratio combining (MRC). Our results show that SCC-OFDM with subtraction combining gives higher SINR than PCC-OFDM over the flat Rayleigh fading channel and that this superiority is not maintained under multi-path induced frequency-selective fading unless diversity combining is used. A simulation result shows, however, that SCC-OFDM with subtraction combining may perform better than PCC-OFDM for a certain range of Doppler spread when differential modulation is employed. Finally, we also demonstrate that the SCC-OFDM signal has less PAPR compared to the normal OFDM and PCC-OFDM and hence may be more practical.

This paper considers reduction of the peak-to-average power ratio (PAPR) of M-quadrature amplitude modulation (QAM) signals in orthogonal frequency division multiplexing (OFDM) systems. It is known that a 16-QAM or 64-QAM constellation can be written as the vector sum of two or three QPSK constellations respectively. We can then use the Golay complementary sequences over Z4 to construct 16-QAM or 64-QAM OFDM sequences with low PAPR. In this paper, we further examine the squared Euclidean distance of these M-QAM sequences and their variations. Our goal here is to combine the block coded modulation (BCM) and Golay complementary sequences to trade off the PAPR, the code rate, and the squared Euclidean distance of M-QAM OFDM signals. In particular, some 16-QAM and 64-QAM OFDM sequences with low PAPR and large squared Euclidean distance are presented.

The large PAPR of orthogonal frequency division multiplexing (OFDM) transmission is one of the serious problems for mobile communications that require severe power saving. Iterative clipping and filtering is an effective method for the PAPR reduction of OFDM signals. This paper evaluates PAPR reduction effect with a graded band-limiting filter in the iterative clipping and filtering method. The evaluation result by computer simulation shows that the excellent peak reduction effect can be obtained in the fewer iteration numbers by using a roll-off filter instead of the conventional rectangular filter, and the iteration number with the roll-off filter achieving the same PAPR is fewer by twice. The result confirms that the clipping and filtering method by using a graded band-limiting filter can achieve low peak OFDM transmission with less computational complexity.

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) is a multiuser interference-free (MUI-free) CDMA scheme proposed for multipath channels based on the convolution between user data and zero correlation zone (ZCZ) code, and its characteristics depend on the employed ZCZ codes. Although ternary ZCZ codes have more sequences than binary ZCZ codes in general, transmitted signal with ternary ZCZ codes give a slightly higher peak-to-average power ratio (PAPR). In this paper we propose the use of periodic ZCZ codes generated from an M-sequence which not only provides the same user capacity as ternary ZCZ codes but allows more design flexibility. Simulation results show that the new ZCZ code shows stronger robustness against an imperfect transmitter with clipping and enjoys better BER performances when used in CS-CDMA/CP compared to the conventional DS-CDMA with MRC-RAKE.

The main disadvantage of orthogonal frequency division multiplexing (OFDM) is the high time domain PAPR. The larger PAPR signal would fatally degrade BER performance in non-linear channels. This paper proposes an improved DSI method, which can achieve better PAPR and BER performances in the non-linear channel with less computation complexity than the conventional DSI method. The feature of proposed method is to employ the time-frequency domain swapping algorithm in the determination of frequency data for dummy sub-carriers. This paper presents various computer simulation results to verify the effectiveness of proposed DSI method.

We introduce an extension of Golay complementary sequences in which, for each sequence, there exists another sequence such that the sum of aperiodic autocorrelation functions of these two sequences for a given multiple L-shift (L≥1) is zero except for the zero shift. We call these sequences multiple L-shift complementary sequences. It is well-known that the peak-to-average power ratio (PAPR) value of any Golay complementary sequence is less than or equal to 2. In this paper, we show that the PAPR of each multiple L-shift complementary sequence is less than or equal to 2L. We also discuss other properties of the sequences and consider their construction.

AOC-SS (Advanced Orthogonal Code Spread Spectrum) modulation [1] is a flexible scheme that offers multi-rate transmission but causes a PAPR (Peak-to-Average Power Ratio) increase in proportion to the number of AOCs. Our solution to this problem is a new mapping technique. In addition, by combining with STC (Space-Time Coding), AOC-SS can resist multi-path fading. Computer simulations validate the proposed scheme.

One of the key technologies to realize future broadband mobile communications is orthogonal frequency division multiplexing (OFDM) transmission. However, the peak-to-average power ratio (PAPR) in OFDM transmission is so much larger than that in single carrier transmission that its adoption in mobile communication systems is uncertain. This paper evaluates the transmission performance possible with iterative peak reduction to design more efficient OFDM transmitters. The PAPR reduction effect and bit error rate (BER) performance are clarified by computer simulations. We calculate the set PAPR value that achieves a target PAPR in the iterative peak reduction method. The required Eb/N0 performance is evaluated under the calculated PAPR condition. The results are effective in designing the back-off value of a transmission power amplifier given fixed transmission quality and computational complexity.