Modulation Symbols Research Articles

Performance of opportunistic relaying with truncated ARQ over Nakagami‐m fading channels

ABSTRACTOn the basis of the decode‐and‐forward protocol, the opportunistic relaying scheme selects the best relay out of the N available relays with the correct data copy of the source. The best relay forwards the data of source to the destination in the second time slot. While in the truncated automatic repeat request scheme, the relay will cooperatively do the data transmission only when the original signal is erroneously received by the destination. Through combining these two conceptions, the system throughput can be improved without sacrificing the space diversity. The performance of traditional noncooperative and such cooperative schemes with M‐ary phase‐shift keying and M‐ary quadrature amplitude modulation symbols over Nakagami‐m fading channels is analysed in terms of packet error rate, symbol error rate and throughput. In addition, we suppose that the destination either combines the previous and retransmitted packets using maximal ratio combining technique or simply (SIM) discards the previous wrong packet and uses the current packet alone (SIM). Monte Carlo simulations are included to verify the accuracy of analytical results. Copyright © 2011 John Wiley & Sons, Ltd.

Very Simple BICM-ID Using Repetition Code and Extended Mapping with Doped Accumulator

This paper proposes very simple bit-interleaved coded modulation with iterative detection (BICM-ID) as a spectrally efficient signal transmission scheme, where irregular repetition code and extended mapping with rate-1 doped accumulator (ACC) are combined to achieve a clear turbo-cliff. Doped ACC is used for close matching of the demapper and decoder’s extrinsic information transfer curves. Although the proposed BICM-ID system is very simple, it can achieve excellent performances and completely eliminate bit-error-rate floor. An exemplifying result for extended non-Gray mapped 4-quadrature amplitude modulation symbol shows that with 0.916 bits/channel use, turbo-cliff happens at 1.27 dB away from the Shannon limit.

수중 센서 네트워크에서 저전력 통신을 위한 변조기법의 적용성 연구

In this paper, we propose the result of PSSK(Phase Silence Shift Keying) modulation scheme that is mixed PSK(Phase Shift Keying) modulation and PPM(Pulse Position Modulation) method. The performance of underwater communication systems are influenced underwater channel characteristics. In particular, delay spread can make ISI(Inter Symbol Interference) because of reverberation and multi path. It degrade the performance of the communication system. Also underwater sensor networks consider about power efficient due to the particularities of their operating environment. PSSK modulation method transmit two orthogonal symbol and using silence period in a period so it can reduce the power. Increasing the distance of between modulation symbols, to enhance the performance of BER(Bit Error Rate) as well as to improve power efficient. The result of sea trial, QPSK modulation BER is and PSSK modulation BER is .

Structured Optical Receivers to Attain Superadditive Capacity and the Holevo Limit

Attaining the ultimate (Holevo) limit to the classical capacity of a quantum channel requires the receiver to make joint measurements over long code-word blocks. For a pure-state channel, we show that the Holevo limit can be attained by a receiver that uses a multisymbol unitary transformation on the quantum code word followed by separable projective measurements. We show a concatenated coding and joint-detection architecture to approach the Holevo limit. We then construct some of the first concrete examples of codes and structured joint-detection receivers for the lossy bosonic channel, which can achieve fundamentally higher (superadditive) capacity than conventional receivers that detect each modulation symbol individually. We thereby pave the way for research into codes and structured receivers for reliable communication data rates approaching the Holevo limit.

A combined resource management and admission control scheme for optimizing uplink performance of M-WiMAX systems

According to the AMC (Adaptive Modulation-Coding) mechanism of the M(obile)-WiMAX, the amount of data per modulation symbol depends on the perceived Signal-to-Noise Ratio, while, based on the OFDMA (Orthogonal Frequency Division Multiple Access) technique, each communication entails multiple concurrent transmissions. Therefore, in the uplink case, where each terminal has a maximum power limitation, the assignment of additional subcarriers does not always correspond to a proportional datarate increment, since the power dispersion over a larger set of symbols can cause the transition to a lower AMC level. In this framework, the present paper introduces a novel RRM (Radio Resource Management) algorithm that dynamically alters the number of subcarriers to be allocated to each connection so as to achieve spectrum saving via augmenting the bits per symbol ratio. Furthermore, in order to mitigate the extensive fluctuations imposed by the novel RRM scheme, an adequate minimum-complexity CAC (Connection Admission Control) scheme is proposed, which succeeds in accurately estimating the bandwidth requirements of the active flows by incorporating theoretical calculations along with a sampling process. It is proven analytically as well as through simulations that the new combined RRM-CAC strategy increases substantially the system capacity, without violating the Quality-of-Service guarantees.

Multicarrier-Based QAPM Modulation System for the Low Power Consumption and High Data Rates

Low power consumption and high data rate are the most important requirements for the communication system. Especially, very low power consumption modulation method is required for the short range communication systems such as the medical implantable communication devices or capsule endoscope, and so on. For the higher data rate, we like to combine the OFDM system into the QAPM since the OFDM system has higher bandwidth efficiency than a single-carrier system. In this paper, we like to propose a QAPM (Quadrature amplitude position modulation) method combined with the orthogonal frequency-division multiplexing (OFDM) system. Next, we analyze the performance of three low-power-consumption modulation schemes: the phase shift position modulation (PSPM), phase silence shift keying (PSSK), and QAPM using orthogonal frequency-division multiplexing (OFDM) system in the multi-path channel. These schemes have lower bandwidth efficiency and the higher power efficiency than the existing phase-shift keying (PSK) and quadrature amplitude modulation (QAM) schemes. It can be shown that they can achieve greater power efficiency because every modulation symbol has a zero-envelope period as in pulse-position modulation (PPM) techniques. Finally, we compare the performances of the PSPM, PSSK, and QAPM modulation combined with the OFDM system with regard to bit error rate performance and throughput.

Blind symbol rate estimation of satellite communication signal by Haar wavelet transform

As the raised cosine shaping filter is often employed in practical satellite communication system, the envelope fluctuation at the symbol transition point is decreased which leads to the failure of the common wavelet algorithm under low SNR. Accordingly, a method of blind symbol rate estimation using signal preprocessing and Haar wavelet is proposed in this paper. Firstly, the effect of filter shaping can be reduced by the signal preprocessing. Then, the optimal scale factor is searched and the signal is processed and analyzed by the Haar wavelet transform. Finally, the symbol rate line is extracted and a nonlinear filter method is inducted for improving the estimation performance. Theoretical analysis and computer simulation show the efficiency of the proposed algorithm under low SNR and small roll-off factor.

Scattered Random Network Coding for Efficient Transmission in Multihop Wireless Networks

Packet error rate dramatically increases when transmissions go over multiple hops in wireless networks, leading to substantial throughput performance degradation. However, in real wireless channels, bit error probabilities vary across different bit positions in one modulation symbol, and corruption of the packet is largely due to the incurred errors on those “bad” bit positions. To improve the throughput performance in multihop wireless networks, in this paper, we propose a novel scattered random network coding (which is referred to as S-RNC) scheme, which further exploits the usefulness of random network coding and takes advantage of error position diversity. In S-RNC, the random-network-coded blocks are classified into different groups, and certain groups of blocks are selected as protected blocks. The sender and relays always scatter the bits of these protected coded blocks on “good” bit positions (with low error probability) and the rest on “bad” bit positions (with high error probability). Rather than sharing the same error rate across all blocks in the conventional transmission scheme, the error probabilities of protected blocks in S-RNC significantly decrease, even over multiple hops, which is helpful in achieving overall higher throughput, particularly under poor channel conditions. Corroborating our intuition, our extensive simulation results show that S-RNC substantially improves throughput performance in multihop mode of wireless networks.

Modulation Classification Based on Constellation Shape Using TTSAS Algorithm and Template Matching

The automatic recognition of the modulation format of a detected signal, the intermediate step between signal detection and demodulation, is a major task of an intelligent receiver, with various civilian and military applications. Obviously, with no knowledge of the transmitted data and many unknown parameters at the receiver, such as the signal power, carrier frequency and phase offsets, timing information, etc., blind identification of the modul ation is a difficult task. This becomes even more challenging in real-world. In this paper I develop a novel algorithm using TTSAS algorithm and pattern recognition to identify the modulation types of the communication signals automatically. I have proposed and implemented a technique that casts modulation recognition into shape recognition. Constellation diagram is a traditional and powerful tool for design and evaluation of digital modulations. In this paper modulated signal symbols constellation utilizing TTSAS clustering algorithm, and matching with standard templates, is used for classificatio n of QAM modulation. TTSAS algorithm used here is implemented by Hamming neural network. The simulation results show the capability of this method for modulation classification with high accur acy and appropriate convergence in the presence of noise.

Performance analysis and simulations of 32‐ary cyclic code‐shift keying

AbstractCyclic code‐shift keying (CCSK) is the baseband 32‐ary symbol modulation scheme used by the Joint Tactical Information Distribution System (JTIDS), the communication terminal for Link‐16. CCSK is not orthogonal and an analytic expression for the probability of symbol error for CCSK has thus far been elusive. In this paper, an analytic upper bound on the probability of symbol error of CCSK is derived for the 32‐chip CCSK starting sequence chosen for JTIDS. The analytically obtained probability of symbol error is compared with two different Monte Carlo simulations for additive white Gaussian noise. The results of both simulations match the analytic results very well and show that the analytic method yields a tight upper bound. A new 32‐chip CCSK starting sequence which has a smaller maximum off‐peak cross‐correlation value than the current JTIDS starting sequence is proposed and evaluated both analytically and by simulation. The results obtained for the new CCSK starting sequence compare favorably with the CCSK starting sequence chosen for JTIDS. Published in 2010 by John Wiley & Sons, Ltd.

A Low-PAPR Differential Frequency Shift Orthogonal Keying Transceiver for Multi-Carrier Spread Spectrum System over High Mobility Multipath Channels

A new differential transceiver with a frequency-shift orthogonal keying (FSOK) technique is proposed for the multi-carrier spread spectrum (MC-SS) system over high mobility multipath fading channels. The design of the transceiver involves the following stages. First, the data stream is mapped into MPSK-FSOK symbols and spreaded by the frequency-shift orthogonal sequences. Second, the differential block encoder is exploited to combat the mobile channels. The Chu sequence is adapted for initial differential encoding, making the post-IFFT transmit signals with a low peak-to-average power ratio. Next, for the receiver, the maximum ratio combining technique is used for the block-based differential frequency-domain equalizer, which can overcome the multipath fading channel effect without requiring channel estimation. Finally, an efficient maximum likelihood despreading and demapping scheme is used to detect the modulation symbols. Furthermore, the differential MC-SS transceiver can be easily re-configured for a MISO differential MC-SS system with high link quality. Simulation results show that, under high mobility multipath channels, the proposed SISO differential MC-SS system can outperform the conventional MC-SS system. The proposed MISO differential MC-SS system with space-time diversity gain and M-ary modulation gain also exhibits excellent performance.

Hybrid detectors for wireless orthogonal frequency division multiplexing with code division multiplexing systems based on reliability information

Orthogonal frequency division multiplexing with code division multiplexing (OFDM-CDM) is attractive for the next generation high-speed wireless systems due to the fact that the performance of OFDM-CDM systems can be considerably improved by employing a joint detection scheme such as the maximum likelihood (ML) detector. However, the complexity of the ML detector increases rapidly as the number of orthogonal spreading codes and/or the number of bits per modulation symbol increase. In this study, the authors introduce a unified detection model and propose two hybrid detectors, which combine zero forcing (ZF) with successive interference cancellation (SIC) and sphere detection (SD) algorithms, respectively. After obtaining the initial solution from the front-end ZF receiver, the proposed back-end algorithms are adopted to extend the potential solution list and search for the final result. The objective is to utilise the combination of a simplified linear equaliser and a comprehensive detection scheme to achieve enhanced performance and offer alternatives to the more complex and channel-estimation-sensitive minimum mean squared error (MMSE) scheme. The results show that the proposed hybrid detectors are able to achieve superior performance compared to the MMSE scheme and provides a significant performance improvement compared to the conventional OFDM counterpart.

A Low-PAPR Multiplexed MC-CDMA System with Enhanced Data Rate and Link Quality

Recently, a new multi-carrier CDMA (MC-CDMA) system with cyclic-shift orthogonal keying (CSOK) has been proposed and shown to be more spectral and power efficient than conventional MC-CDMA systems. In this paper, a novel extension called the multiplexed CSOK (MCSOK) MC-CDMA system is proposed to further increase the data rate while maintaining a low peak-to-average power ratio (PAPR). First, the data stream is divided into multiple parallel substreams that are mapped into QPSK-CSOK symbols in terms of cyclic shifted Chu sequences. Second, these sequences are repeated, modulated, summed, and placed on IFFT subcarriers, resulting in a constant-modulus multiplexed signal that preserves the desired orthogonality among substreams. The receiver performs frequency-domain equalization and uses efficient demultiplexing, despreading, and demapping schemes to detect the modulation symbols. Furthermore, an alternate MCSOK system configuration with high link quality is also presented. Simulations show that the proposed MCSOK system attains lower PAPR and BER, as compared to conventional MC-CDMA system using Walsh codes. Under a rich multipath environment, the high link quality configuration exhibits excellent performance with both diversity gain and MCSOK modulation gain.

Nonlinear Blind Equalizers: NCMA and NMCMA

This paper proposes two nonlinear blind equalizers: the nonlinear constant modulus algorithm (NCMA) and the nonlinear modified constant modulus algorithm (NCMA) by applying a nonlinear transfer function (NTF) into constant modulus algorithm (CMA) and modified constant modulus algorithm (MCMA), respectively. The effect of the NTF on CMA and MCMA is theoretically analyzed, which implies that the NTF can make their decision regions much sharper so that the proposed two nonlinear blind equalizers are more robust against the convergency error compared to their linear counterparts. The embedded single layer in NCMA and NMCMA simultaneously guarantees a comparably speedy convergency. On 16-quadrature amplitude modulation (QAM) symbols, computer simulations show that NCMA achieves an 8dB lower convergency mean square error (MSE) than CMA, and NMCMA achieves a 15dB lower convergency MSE than MCMA.

Turbo decoding of concatenated channel coding and trellis shaping for peak power controlled single-carrier systems

Trellis shaping (TS) has found its application in the peak power control of band-limited single-carrier signals. Our recent work has demonstrated that a well-designed TS can control the symbol transitions such that the output signal has almost constant envelope, which significantly alleviates the linearity requirement of power amplifiers. Compared to transmission without constellation shaping, however, the TS involves signal constellation expansion exclusively for peak power control. Therefore, unlike trellis coded modulation (TCM) that increases the minimum Euclidean distances (MED), the TS decreases the MED, thus incurring the increase in signal-to-noise power ratio (SNR) required for achieving a certain error rate. In this letter, in order to overcome this drawback, we propose a serial concatenation of coding and shaping together with an effective decoding algorithm that utilizes the memory effect (i.e., error correcting capability) of the shaped symbols. The achievable performance of the proposed system is analyzed in terms of the average mutual information. The simulation results demonstrate that the iterative decoding of the proposed concatenated system with outer convolutional codes and inner trellis shaping offers a significant performance gain.

A low complexity hierarchical QAM symbol bits allocation algorithm for unequal error protection of wireless video transmission

A low complexity hierarchical quadrature amplitude modulation (QAM) symbol bits allocation algorithm for unequal error protection of video transmission over wireless channels is proposed in this paper. An unequal error protection (UEP) scheme using hierarchical QAM, which takes into consideration the non-uniformly distributed importance of intracoded frame (I-frame) and predictive coded frame (P-frame) in a group of pictures (GOP), is first proposed. In order to optimally allocate the hierarchical QAM's high priority (HP), medium priority (MP) and low priority (LP) symbol bits to the H.264/AVC video, a generic solution for optimal allocation of hierarchical QAM's high priority (HP), medium priority (MP) and low priority (LP) symbol bits to the H.264/AVC video is then proposed. Finally, a low complexity symbol bits allocation algorithm, namely ranking search algorithm, which reduces the computational complexity of the proposed optimal symbol bits allocation algorithm, is proposed. Simulation results show that our proposed UEP scheme outperforms the classical equal error protection (EEP) scheme and also the previous UEP scheme.

Jittery Signal Generation for High-Speed Interconnect Simulation

By generating clock and data waveforms in the frequency domain through a truncated Fourier series, absolute control over both voltage noise and symbol transition timing is achieved. A parameterized Fourier series signal model is derived and used to form clock and data waveforms exhibiting arbitrary noise and jitter characteristics. The method not only facilitates more accurate interconnect modeling in tools like Matlab and Simulink, but also provides a simple means for generating realistic signals that may be imported into Spice-based simulators.

Quadrature Amplitude Modulation for Differential Space-Time Block Codes

Differential Space-Time Block Codes (DSTBC) do not require any radio channel measurement and channel state information neither on the transmitter nor at the receiver side. Therefore, they are an attractive alternative to coherent Multiple-Input Multiple-output (MIMO) systems. The classical technical proposal for differential techniques is based on M-ary phase shift keying (M-PSK) modulation schemes for DSTBC (PSK-DSTBC). One advantage of this scheme is the constant envelop of the transmit signal, but it is well known that higher-order PSK is less efficient due to the small distance between adjacent points in the constellation diagram. Therefore, in this paper an alternative modulation technique for DSTBC is discussed, which is based on quadrature amplitude modulation (QAM-DSTBC). The signal envelope of the transmit signal is not any more constant in this case. Therefore, the technical challenge of integrating QAM into the DSTBC system design is to control the transmit power in order to avoid an increase or a decrease in transmit power to some extreme values. The mechanism, which is used in this paper to control the transmit power is based on an extension of the original QAM constellation diagram. The additional points, which are integrated into the constellation diagram are used in this case for the mapping procedure to select one of the modulation symbols with high or alternatively low signal power. This means for each single bit pattern there are almost always two modulation symbols available in the mapping procedure one with low and one with high signal power, which gives the basis for a signal power control algorithm. The resulting bit-error-rate (BER) performance of QAM-DSTBC is compared finally to the performance figures of the original proposal of PSK-DSTBC.

Distributed QAM-Based Space-Time Block Codes for Efficient Cooperative Multiple-Access Communication

Distributed space-time block coding schemes based on quadrature amplitude modulation (QAM) symbols are introduced that enable users in a wireless multiple-access relay channel to cooperate with each other in order to improve the reliability of their information in a fair, rate-efficient manner. The distributed coding schemes are designed for a system that consists of m users that need to send their information to a common destination. Each user is equipped with only one antenna and a half-duplex transceiver so that it can transmit to the destination or any other user at one time and also receive signals from any other user at another time. The destination is equipped with one or more receive antennas. The goal is to design cooperative schemes which achieve the maximum diversity order (which is equal to the diversity order of the outage probability) while being fair to the users in terms of rate allocation. Two cooperative coding schemes are proposed that meet these requirements-a two-phase cooperative scheme and a single-phase self-information canceling linear (SCL) scheme. The two-phase scheme is of lower decoding complexity and it requires the users to only transmit QAM symbols. The SCL scheme is of higher complexity with the users transmitting linear combination of QAM symbols but it also achieves better performance. Both schemes incorporate new classes of cooperation rules for deciding whether or not a user acts as a relay for another user. The usual outage-based cooperation rule, whereby a user cooperates with another user provided the mutual information of the channel between them is greater than the rate, is sufficient for deriving information-theoretic limits but it cannot be used directly for analysis of a particular coding scheme. Even though the decoder used by the destination in the proposed coding schemes assumes that the inter-user communication is always successful, our performance analysis does not make this assumption. In fact, it rigorously accounts for the decoding errors arising from the information exchange between users. Consequently, it sheds light on precisely what cooperation rules (among the class of rules analyzed) lead to maximal diversity.

Adaptive Concurrent Equalization Applied to Multicarrier OFDM Systems

Receivers for wireless Orthogonal Frequency Division Multiplexing (OFDM) systems usually perform the channel estimation based on pilot carriers in known positions of the channel spectrum. Interpolation is applied between pilot carriers to determine the channel transfer function in all carrier frequencies. Channel variations along time are compensated by means of interpolation between successive channel estimates on the same carrier frequency. However, not rarely do fast channel variations exceed the time interpolator capability, as is the case for mobile operation. In this article we propose a new technique based on concurrent de- convolution, as a mean to further increase the time interpolator capability. Concurrent deconvolution, also known as concurrent equalization, is based on the concurrent operation of two stochastic gradient time-domain algorithms. One gradient-based algorithm minimizes a cost function that measures the received signal energy dispersion and the other minimizes the Euclidean distance between the received digital modulation symbols and the ones in the reference constellation which are assigned to each OFDM sub-channel. Results show that the proposed technique, when subsequently applied to the time interpolation stage, improves the system robustness for fast varying channels. The whole channel compensation computational cost is increased by the cost of a two coefficient multirate adaptive FIR filter, added only to those subcarriers at the FFT output to which a pilot sequence has not been assigned.