High-level Modulation Schemes Research Articles

LDPC-Coded Generalized Frequency Division Multiplexing for Intensity-Modulated Direct-Detection Optical Systems

In this paper, a low-density parity check (LDPC) coded GFDM with high-level modulation scheme is proposed for more flexible and advanced multicarrier modulation in intensity-modulated/direct-detection (IM/DD) optical systems. Then, we experimentally demonstrate an LDPC-coded GFDM with 16-quadrature amplitude modulation (16QAM) system transmitted over 20-km standard single-mode fiber at different symbol rates to verify the applicability of the proposed scheme. Furthermore, the proposed scheme with trellis-coded 32-quadrature amplitude modulation (TC-32QAM) has also been investigated and compared with the bit error rate (BER) performance with 16QAM-modulated condition. The results indicate that TC-32QAM-modulated GFDM method has a better performance than the 16QAM-modulated case. But with LDPC coding module added, the performance of the proposed system with TC-32QAM gets worse than that with 16QAM modulation. We also experimentally compare the proposed LDPC-coded scheme and the Turbo-coded scheme in the QAM-modulated GFDM IM/DD optical system. The results show the LDPC-coded optical (LCO-) GFDM scheme has lower power penalties and better BER performance. Moreover, the proposed LCO-GFDM scheme is applied in multiband transmission by optical simulation software, and the results show that multiband LCO-GFDM scheme has a better performance than that of LCO-OFDM scheme.

Multi‐carrier transmission of vectorial modulation schemes using electronic transceivers at 588 GHz

A reported is presented on the first communication system using vectorial modulation schemes above 500 GHz. Using Schottky-based electronic technologies at 588 GHz, potentialities of high-level multi-carrier modulation schemes for wireless links are analysed. The wireless link is composed of an emitter with a sub-harmonic mixer for up-conversion from 294 to 588 GHz and carrier modulation. A pumped zero-bias detector is used at reception. Mono-carrier signalling is realised using an up to 32-symbol modulation scheme and multi-carrier terahertz transmission is also achieved using several modulation schemes in parallel.

Investigation and Analysis of SNR Estimation in OFDM system

Estimation of signal to noise ratio (SNR) of received signal and to transmit the signal effectively for the modern communication system. The performance of existing non-data-aided (NDA) SNR estimation methods are substantially degraded for high level modulation scheme such as M-ary amplitude and phase shift keying (APSK) or quadrature amplitude modulation (QAM).In this paper SNR estimation proposed method which uses zero point auto-correlation of received signal per block and auto/cross- correlation of decision feedback signal in orthogonal frequency division multiplexing (OFDM) system. Proposed method can be studied into two types; Type 1 can estimate SNR by zero point auto-correlation of decision feedback signal based on the second moment property. Type 2 uses both zero point auto-correlation and cross-correlation based on the fourth moment property. In block-by-block reception of OFDM system, these two SNR estimation methods can be possible for the practical implementation due to correlation based the estimation method and they show more stable estimation performance than the earlier SNR estimation methods.

A Single Symbol Maximum-Likehood Decoder for Four Transimit Antenna QOSTBC

This letter proposes a very low-complexity maximum likelihood (ML) detection algorithm for the quasi-orthogonal space-time block code (QOSTBC) with four transmits antennas. The low-complexity single-complex-symbol detection is based on QR decomposition and the expansion of equalization via a diagonal matrix transformation. The proposed strategy enables the QOSTBC to achieve ML performance with significant reduction in computational load for any high-level modulation scheme.

SNR Estimation in OFDM System by the Correlation of Decision Feedback Signal

In the channel-varying environment, it is very important to estimate the signal to noise ratio (SNR) of received signal and to transmit the signal effectively for the modern communication system. The performance of existing non-data-aided SNR estimation methods are substantially degraded for high level modulation scheme such as M-ary amplitude and phase shift keying or quadrature amplitude modulation. In this paper, we propose a SNR estimation method which uses zero point auto-correlation of received signal per block and auto/cross-correlation of decision feedback signal in orthogonal frequency division multiplexing (OFDM) system. Proposed method can be studied into two types; Type 1 can estimate SNR by zero point auto-correlation of decision feedback signal based on the second moment property. Type 2 uses both zero point auto-correlation and cross-correlation based on the fourth moment property. In block-by-block reception of OFDM system, these two SNR estimation methods can be possible for the practical implementation due to correlation based the estimation method and they show more stable estimation performance than the previous SNR estimation methods. Also, we mathematically derive the SNR estimation expression according to computational difference of auto/cross-correlation. Finally, Monte Carlo simulations are used to verify the proposed method.

6$\,\times\,$128-Gb/s Nyquist-WDM PDM-16QAM Generation and Transmission Over 1200-km SMF-28 With SE of 7.47 b/s/Hz

The Nyquist wavelength-division multiplexing technique enable a solution to achieve high spectral efficiency in long-haul transmission system. Compare to polarization division multiplexing quadrature-phase-shift-keying, even high-level modulation scheme such as polarization division multiplexing 16-quadrature-amplitude-modulation is much more sensitive to intra-channel noise and inter-channel linear crosstalk caused by Nyquist wavelength-division multiplexing. We experimentally demonstrated the generation and transmission of the 6 × 128-Gb/s Nyquist wavelength-division multiplexing sixteen quadrature amplitude modulation signal over 1200-km single-mode fiber (SMF)-28 with Erbium-doped fiber amplifier only amplification with a net SE of 7.47 b/s/Hz, which is so far, to our knowledge, the highest SE for the signal with the bit rate above 100-Gb/s using the polarization-division multiplexing 16-quadrature-amplitude-modulation format. This experiment was successfully enabled by digital-signal-processing (DSP) pre-equalization of transmitter-side impairments and DSP post-equalization of the channel and receiver-side impairments. Nyquist-band is considered in the pre- equalization to enhance the tolerance of the polarization-division multiplexing 16-quadrature-amplitude-modulation to the aggressive spectral shaping. The bit error rate for each of the 6 channels is smaller than the limitation of the forward-error-correction limit of 3.8 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> after 1200-km SMF-28 transmission.

Next-generation access network: A wireless network using E-band radio frequency (71-86GHz) to provide wideband connectivity

The expected explosion in capacity requirements associated with Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX) networks has led to an interest in the use of millimeter wave (specifically E-band) equipment for backhaul. Initially deployed for campus networks, such technology could also become a convenient solution for carrier applications offering the multi-gigabit backhaul capacity needed for future cellular networks. In the fixed point-to-point 70 GHz to 80 GHz radio frequency band, an unprecedented 10 GHz bandwidth is allowed, far exceeding the spectrum allocations in any given lower licensed frequency band. The 71 GHz to 76GHz bands are paired with 81 GHz to 86 GHz, yielding 5 GHz of spectrum in each direction. The vast amount of bandwidth available in this band makes it ideal for offering multi-gigabit transmission rates. This paper aims to characterize a wireless transmission channel operating in the 70 GHz to 80 GHz band, considering the propagation limits and the rain attenuation impairments on transmission link availability. Our objective is to define specific parameters and constraints which can be used to define an optimum topology for an access network. We use point-to-point systems with a transport capacity up to 10 Gb/s per single carrier using high-level modulation schemes. We also propose a specific interference mitigation analysis to enhance understanding of the angular discrimination needed to avoid any degradation of the total link margin and the signal-to-interference ratio.

OFDM 시스템에서 Decision Feedback 신호의 상관 관계를 이용하는 SNR 추정

채널의 상태가 변하는 전송 환경에서 수신된 신호에 대한 잡음비를 추정하여, 보다 효율적으로 신호를 전송하는 것은 현대 통신 시스템에서 중요한 기술이다. 기존 NDA(Non-Data-Aided) SNR 추정 방법은 M진 APSK 또는 같은 고차원 신호의 SNR 추정 성능이 떨어진다. 본 논문에서는 OFDM 시스템에서 블록 단위 수신 신호의 영점 자기 상관과 decision feedback 신호의 자기 상관 및 상호 상관을 이용하는 SNR 추정 방법을 제안한다. 본 논문에서 제안한 방법은 decision feedback 신호의 2차 모멘트인 영점 자기 상관을 이용하여 SNR을 추정하는 Type 1 방식과 4차 모멘트 성질을 갖고 있는 영점 자기 상관과 상호 상관을 이용한 Type 2 방식이다. 이 두가지 SNR 추정 방식은 OFDM 시스템에서 블록 단위 수신을 할 때, 신호의 상관 관계에 기반을 두고 있어 SNR 추정 방법의 실용적인 구현이 가능하게 하고, decision feedback 신호를 사용함으로써 QAM 신호에서도 종전의 SNR 추정 방식들보다 비교적 안정적인 추정 성능을 보인다. 또한, decision feedback 신호를 사용할 때 자기 상관과 상호 상관의 오차에 따른 SNR 추정 식을 수식적으로 유도한다. 그리고 Monte Carlo 시뮬레이션을 통해 제안한 SNR 추정 방법의 성능을 확인한다. In the channel-varying environment, it is very important to estimate the signal to noise ratio(SNR) of received signal and to transmit the signal effectively for the modern communication system. The performance of existing non-data-aided (NDA) SNR estimation methods are substantially degraded for high level modulation scheme such as M-ary APSK or QAM. In this paper, we propose a SNR estimation method which uses zero point auto-correlation of received signal per block and auto-/cross- correlation of decision feedback signal in OFDM system. Proposed method can be studied into two Types; Type 1 can estimate SNR by zero point auto-correlation of decision feedback signal based on the second moment property. Type 2 uses both zero point auto-correlation and cross-correlation based on the fourth moment property. In block-by-block reception of OFDM system, these two SNR estimation methods can be possible for the practical implementation due to correlation based the estimation method and they show more stable estimation performance than the previous SNR estimation methods. Also, we mathematically derive the SNR estimation expression according to computational difference of auto-/cross-correlation. Finally, Monte Carlo simulations are used to verify the proposed method.

Enhancing Data Rates of TH-UWB Systems Using M-ary OPPM-BPSM Modulation Scheme: A System Perspective

This paper proposes and studies a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio system based on orthogonal pulse position modulation (OPPM) and biorthogonal pulse shape modulation (BPSM). The proposed scheme offers a high data rate with satisfactory system performance by using high-level multi-dimensional modulation schemes. It allows one to increase the number of orthogonal pulses in each pulse position and, consequently, be able to adopt shorter pulse repetition intervals than those used in conventional M-ary OPPM or M-ary biorthogonal PPM (BPPM) modulation schemes. The performance is analyzed by using characteristic function and Gaussian approximation in additive white Gaussian and multipath scenarios, respectively. The proposed scheme reduces multiple access interference considerably in multi-user environments. Finally, simulation results are provided to validate the theoretical results.

A Refined Channel Estimation Method for STBC/OFDM Systems in High-Mobility Wireless Channels

In this paper, we investigate channel estimation for orthogonal frequency division multiplexing (OFDM) systems with space-time block code (STBC) in mobile wireless channels. Our proposed method consists of two-stage processing and is developed on the basis of the classical discrete Fourier transform (DFT)-based channel estimation method. In the initialization stage, we employ a multipath interference cancellation technique to estimate multipath delays and multipath complex gains. In the tracking stage, we develop a refined decision-feedback (DF) DFT-based channel estimation method in which a few pilot tones inserted in OFDM data symbols are applied to form an optimal gradient vector at the first iteration such that the error propagation effect is mitigated. In order to reduce computational complexity, an approximate weighting matrix is adopted to avoid matrix inversion. We demonstrate the proposed method through computer simulation of an STBC/OFDM system with two transmit antennas and a single receive antenna. The results show that our method outperforms the classical DFT-based method, the STBC-based minimum mean square error (MMSE) method, and the Kalman filtering method as well, and that significant signal-to-noise ratio (SNR) performance improvement can be achieved, especially when a high-level modulation scheme, e.g. 16QAM, is adopted in high-mobility environments.

Downlink transmission of broadband OFCDM systems-part III: turbo-coded

Orthogonal frequency and code-division multiplexing (OFCDM) systems have been introduced for high-speed data transmission in future wireless mobile communications. In this paper, a hybrid multicode interference cancellation (MCI) and minimum mean-square error (MMSE) detection scheme is presented for the turbo-coded OFCDM systems. Channel estimation based on a code-multiplexed pilot channel is employed. The weights of the hybrid detection are derived theoretically and an effective method to generate the weights in practical applications is proposed. By means of computer simulation, the effects of system parameters on the performance are studied extensively. It is shown that the hybrid detection outperforms pure MMSE detection in various channel conditions, especially for high-level modulation schemes. To carry out interference regeneration for the hybrid detection, the conventional turbo decoding algorithm which only decodes systematic bits should be extended to decode parity bits as well. Moreover, two iterations in turbo decoding are sufficient to provide good performance for the system with the multistage hybrid detection. Finally, given time-domain spreading factor N/sub T/, the system performance improves with frequency-domain spreading factor N/sub F/. However, the frequency diversity gain is saturated when N/sub F/ is large (i.e., N/sub F//spl ges/16).

Low-Complexity Maximum-Likelihood Decoder for Four-Transmit- Antenna Quasi-Orthogonal Space–Time Block Code

This letter proposes a very low-complexity maximum-likelihood (ML) detection algorithm based on QR decomposition for the quasi-orthogonal space-time block code (QSTBC) with four transmit antennas, called the LC-ML decoder. The proposed algorithm enables the QSTBC to achieve ML performance with significant reduction in computational load for any high-level modulation scheme.

Enhancement of Data Throughput in the AMC-Employed DS-CDMA Systems through Suppression of Channel Frequency Selectivity by a MTMR Antenna System

SUMMARY In this paper, a new algorithm for MTMR adaptive array antenna (AAA) system combined with analog-type transmit power control (TPC) is proposed for DS-CDMA systems in order to employ high level modulation schemes like 64 QAM in wireless multimedia services. A conventional AAA system considering the strongest path as a target path cannot work effectively when angular dispersion between the strongest path and other delayed paths is large, that is, beam selectivity is so small due to severe frequency selective multipath fading. So, in order to solve such a beam selectivity problem, a beam directivity control scheme using a path manipulation technique is introduced for the BS and MS AAA combining in this paper, along with analog-type TPC. It utilizes virtual delay profiles which are modified from the measured complex delay profile and selects a desired path giving the maximum DUR with an optimized weight vector for BS and MS beamforming. We will show through computer simulation that the proposed scheme is very effective in enhancing the data throughput at the downlink of wideband DS-CDMA systems as compared with the conventional system.

Frequency reuse scheme for cellular OFDM systems

A new frequency reuse scheme for coherent orthogonal frequency division multiplexing (OFDM) cellular systems using high level modulation schemes, whereby both data and pilot parts can have different frequency reuse factors, is described. The capacity increase is investigated by simulations.

Degradation of availability performance in dual-polarized satellite communications systems

Dual-polarized operation of satellite communications channels allows for an efficient use of the radio spectrum. A method for evaluating the availability of Ku- and Ka-band dual-polarized digital systems is described. It is based on long-term measurements of slant-path attenuation and depolarization caused by the troposphere and of their joint occurrence. The additional degradation of dual-polarized system availability performance with respect to single polarization operation is assessed, and its dependence on major link and system parameters is highlighted. It appears that satellite links characterized by high-frequency, low elevation angle, circular polarization, and high-level modulation schemes are particularly affected by the depolarization-induced interference. In that case, doubling their capacity by dual-polarization frequency reuse reduces dramatically their availability, assuming a fixed link margin, or alternatively requires prohibitive link margins to meet a given availability objective.

Transmission of SDH signals through future satellite channels using high-level modulation techniques

The authors discuss the possibility of transmitting synchronous digital hierarchy (SDH) signals through two-link nonlinear satellite channels. Transmitting such high bit rate signals through a standard 54 MHz or 36 MHz transponder bandwidth requires the use of high-level modulation schemes. The techniques and technologies needed to make the use of 16-ary quadrature amplitude modulation (QAM) and 64-ary QAM transmissions feasible for future satellite communication systems are examined. It is shown that it is possible to transmit a synchronous transport module-level 1 (STM-1) signal through a standard 54 or 36 MHz transponder bandwidth using 16-ary QAM or 64-ary QAM transmission, respectively, for the 6/4 GHz band. However, for higher frequency bands, due to high fade margins needed to achieve the high availability and performance for SDH systems, is not practical to transmit the STM-1 signal through such standard transponder bandwidths.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparison of High-Level Modulation Schemes for High-Capacity Digital Radio Systems

This paper presents a comparative study of four 2n-state quadrature amplitude modulation techniques, namely, 16, 32, 64, and 128 QAM, in a digital radio system environment. The effects of filtering, interference, amplifier nonlinearities, and selective fading are investigated using computational and simulation methods. Increase of the carrier-to-noise ratio (CNR) at a fixed symbol error probability (10^{-3} ) is taken as a robustness criterion.