Introduction: From Phase-Locked Loop to Costas Loop

The WiMax (Worldwide Interoperability for Microwave Access) is a technology in<strong> </strong>broadband wireless access, which employs OFDM (Orthogonal Frequency Division Multiplexing) as an alternative transmission to enable high speed data in communication system. This research aim is to analyze the performance system of the OFDM-Based WiMAX, which used the cyclic prefix. The model was designed in four schemes of simulation method, the BPSK (Binary Phase Shift Keying, QPSK (Quadrature Phase Shift Keying), 16 QAM (Quadrature Amplitude Modulation) and 64 QAM. Each scheme was investigated BER (Bit Error Rate) on AWGN (Additive White Gaussian Noise) channel and multipath Rayleigh fading channel, which had applied the cyclic prefix. By simulation of the cyclic prefix was produced the modulation measurement of the BPSK, QPSK, 16 and 64 QAM. The performance result of Eb/No 15 dB was obtained the BER of BPSK and QPSK of 1.11E-11, the BER of 16 QAM and 64 QAM of 8.69E-06 and 0.00333 respectively. Those results indicated much smaller BER value than EbNo 0 dB which BPSK and QPSK of 1 BER, 1.5 and 1.75 BER for 16 QAM and 64 QAM respectively. In conclusion, a higher value of EbNo, hence the BER value would be lower.

In this study, the authors study the modulation classification of linearly modulated signals including amplitude shift keying (ASK), phase shift keying (PSK) and quadrature amplitude modulation (QAM) signals. The authors consider an unknown frequency non-selective slowly fading channel with an unknown variance additive white Gaussian noise. The authors treat this classification problem as a multi-hypotheses test which is invariant under the complex scale. In such a case, the authors objective is to find uniformly most powerful (UMP) test in the class of invariant decisions. However, the authors find out that the UMPI test does not exist; instead, they provide a most powerful invariant (MPI) PSK signal classifier for known signal to noise ratio and use it as the upper performance bound for any invariant classifier. The authros also propose a hybrid likelihood ratio test (HLRT) solution which can be employed for the classification of linearly modulated signals, inter-family and intra-family. The authors also explain the efficient implementation of these algorithms in some steps. In order to reduce the computational cost, the authors propose quasi-HLRT classifiers for PSK signals. Some simulation examples are provided that show the power of the proposed algorithms in the classification of linearly modulated signals.

As for the single-channel overlapped signals, in which the modulation parameters of the component signals are identical or similar, it is still a great challenge to extract the component signals. Aiming at this problem, a single-channel blind source separation (SCBSS) algorithm, constrained by constant modulus, is proposed for the overlapped Gaussian minimum shift keying (GMSK) signals and this algorithm also applies to other overlapped signals with constant modulus (CM), such as binary phase shift keying (BPSK) signals and quadrature phase shift keying(QPSK) signals. By tracking the channels of the component signals, the algorithm can effectively estimate their symbol sequences. Simulation results show that the proposed algorithm can work more robustly and reduce the frame error rate (FER), comparing with the competing algorithms.

In this study, we have presented that Higher Order Cummulants (HOC) based modulation recognition scheme for Pulse Amplitude Modulation (PAM), Quadrature Amplitude Modulation (QAM) and Phase Shift Keying (PSK) modulated signals having orders of 2 to 64. Modulation recognition is a process to recognize the signal modulation type which is received by the receiver in the presence of channel noise. The HOC based MR is accomplished in two modules. First is feature extraction using higher order cummulants. These features are distinct for different modulated signals. Second is recognition process which gives decision based upon the features extracted from higher order cummulants. The Probability of Correctness (POC) curves shows the recognition accuracy for sample size and number of iterations. The Additive White Gaussian Noise (AWGN) is considered throughout the simulations.

This paper presents a novel combination of two fully integrated phase-locked loops (PLLs) to control the oscillation frequency and modulation frequency of a switched injection-locked oscillator (SILO). The SILO is used as an active reflector transponder in a frequency-modulated continuous wave (FMCW) radar system. A fractional-N PLL (RF-PLL) with a tri-state phase-frequency detector (TSPFD) sets the oscillation frequency of the voltage controlled oscillator (VCO) to 2.45 GHz. Another integer-N PLL (modulation PLL) switches the tail current source of the VCO to achieve SILO behavior at the time when the RF-PLL is not controlling the VCO. The RF-PLL supports division ratios from 64 to 511 with a frequency resolution of 0.2 Hz. Reference spur levels are below -48 dBc while the out-of-band phase noise is -103 dBc/Hz at a 1MHz frequency offset. The modulation PLL is based on a Maneatis-cell ring-oscillator supporting modulation frequencies between 6MHz and 20 MHz. Furthermore, the duty cycle of the modulation signal can be set in steps of 0.8 %. Due to the novel TSPFD, the oscillation frequency of the SILO changes only by 36MHz within 10 minutes when the RF-PLL is inactive. The complete circuit is manufactured in a 180nm SiGe BiCMOS process and consumes a total power of 128mW.

Remote monitoring of patients using wireless capabilities increasingly plays an important role in healthcare and the communication with implanted medical devices (IMDs). In the case of IMDs, transmission is characterized by low peak power and low duty cycle to reduce the potential for adverse bio-effects. Currently, most IMDs use radio-frequency (RF) electromagnetic waves to communicate through the body. The corresponding maximum bandwidth allowed is 300 kHz as regulated by the FCC, which inherently limits the communication rates of these devices (limiting to maximum data rates of 50 kb/s). Beyond bandwidth restrictions, the main limitation for using RF electromagnetic waves in the body is loss of signal because of attenuation in the body. For these reasons the output power of RF devices is limited to 25 µW, which also limits data rates to 50 kb/s. In this study, an ultrasonic communication channel is explored for IMD communications as an alternative to EM transmission. We demonstrate the ability to communicate through tissues using the ultrasonic communications channel while maintaining data rates necessary for streaming of high definition video. In our experiments we used a matched pair of 5-MHz f/3 single-element transducers operating in a pitch-catch configuration in a tank of degassed water. Between the transducers was placed either a slab of pork tenderloin or a slab of beef liver (each more than 2 cm thick). Quadrature amplitude modulation (QAM) and quadrature phase shift keying (QPSK) signals were coded for transmission into the transmitting transducer using an arbitrary waveform generator. Signals were transmitted and captured by sending 10 snapshots (packets) of 50,000 samples (10,000 training / 40,000 decision-directed) using a fractionally-spaced (2 samples per symbol) decision feedback equalizer with up to 40 taps in the feed forward section, and 40 taps in the feedback section. Signals were successfully decoded through the samples using QPSK, 16QAM and 64QAM codes with bit error rates of (BER) < 1e-4. A maximum data rate of 30 Mbps using the 64QAM was achieved through both the pork tenderloin and the beef livers. These experiments successfully demonstrate that communications through the ultrasonic channel can provide data rates capable of streaming high definition video.

In this paper, a scheme for optical modulation format conversion from one 20Gbps quadrature phase-shift keying (QPSK) signal to one 20Gbps binary phase-shift keying (BPSK) signal with information integrity is proposed and verified by simulation. The theory of degenerate phase-sensitive amplifier (PSA) employed as a phase de-multiplexer is derived in detail and used to decompose the in- (I) and quadrature- (Q) phase components of QPSK. Then the I and Q components are parallel-to-series converted into one BPSK. The constellations show that the phase noise of the original signal is effectively restrained by the conversion system through use of the PSA. The error vector magnitude and bit-error rate (BER) of the QPSK, converted BPSK, and a back-to-back BPSK are measured and compared with each other. We find that the BER performance of the converted BPSK is better than QPSK and maintains the original information integrity with different input signal quality. Some potential issues are also discussed as to practical implementation of the scheme. This modulation-format-conversion scheme has potential applications in improving the signal BER performance and flexible transmitters and receivers in software-defined networks.

Synchronization plays an important role in wireless communication systems when tracking a phase-shift keying (PSK) signal, especially when the initial frequency error is comparable to the loop bandwidth. In order to improve frequency acquisition, an automatic frequency control (AFC) augmentation is used. This paper presents a composite AFC/Costas loop by combining both the AFC loop with a phase-locked loop (PLL) Costas loop for carrier frequency recovery. Therefore, pull-in from both frequency and phase errors is feasible using the composite AFC/Costas loop. The AFC/Costas loop combination filter coefficient setting is evaluated by a theoretic analysis. Improved frequency and phase acquisition can be realized by changing the first order AFC/Costas loop to the second order. First, the structure of the composite AFC/Costas loop is shown. This structure makes use of phase detectors to obtain the phase differences between the received signal and reference signal, where the phase differences can be used to generate the phase and frequency control signals. Difference equations are proposed to describe the composite AFC/Costas loop. Then, the theoretic analysis for both frequency and phase control are derived in a linearized model of the composite loop. The phase error variance is simulated to show the performance of the composite AFC/Costas loop. Moreover, the frequency and phase synchronization performance for different signal to noise ratio (SNR) and loop filter bandwidth are shown to demonstrate the effectiveness of the composite AFC/Costas loop. Finally, the Quadrature Phase Shift Keying (QPSK) data is demodulated and decoded through the composite AFC/Costas loop. Extensive simulations are implemented to show that the demodulated data matches the transmitted data, which proves that differential QPSK can effectively reduce the phase ambiguity and increase frequency pull-in range, especially for the low SNR region (E b /N 0 < 3 dB). The proposed composite AFC/Costas loop sheds insights on the design of frequency and phase synchronization in wireless communication systems.

An all-optical format conversion (AOFC) scheme of star-m-ary quadrature amplitude modulation (star-mQAM) based on a nonlinear Mach-Zehnder interferometer (MZI) with nested-pump assisted nonlinear optical loop mirror (nested-PA-NOLM) is proposed and numerically simulated. In this scheme, input multi-Gbps star-8QAM signals can be converted into three quadrature phase shift keying (QPSK) signals (namely QPSK-A, -B and -C) through the PA-NOLM under different input power of the signal and the pump. The nonlinear MZI is formed by two PA-NOLMs of the upper and the lower arms, the former and the latter 3-dB optical couplers (OCs), a directional variable optical attenuator (VOA) in the upper arm and a directional variable phase shifter (VPS) in the lower arm. A VOA and a VPS are used to adjust the power ratio (PR) and relative phase shift (RPS) between any two of QPSK-A, -B and -C. When any two adjusted signals in QPSK-A, -B and -C are coherently superposed, the aggregated star-8QAM signal can be extracted again. Furthermore, the proposed scheme can also be used to convert the 20 Gbps bipolar 4-ary pulse amplitude modulation (PAM4) signal into two 10 Gbps BPSK signals and a 20 Gbps QPSK signal. When the proposed scheme is combined with the phase-sensitive amplification (PSA), it can also be used to convert one 16QAM into two QPSK signals. The scheme performance is analyzed via constellation diagrams, power waveforms, the error vector magnitude (EVM) and the bit error rate (BER) of the optical signals. The scheme can not only be deployed in optical gateways to connect optical networks using different modulation formats, but also has a potential applied advantage in security information transmission between different optical networks.

Two chip-sets have been developed for Digital Video Broadcasting (DVB) applications. One chip-set') is optimized for demodulating Quadrature Phase Shift Keying (QPSK) signals received from a satellite. The other diip-se+) is developed for receiving Quadrature Amplitude Modulated (QAM) signals in a cable environment.

On the basis of analyzing the mathematical models of Costas loop, a method to model and simulate it by Simulink is put forward. In order to reduce the complexity of translating model to HDL (hardware description language), the model is realized by MATLAB code; the digital design of LPF (low-pass filter), LF (loop filter) and VCO (voltage-controlled oscillator) are mainly researched. At last, we accomplish the functional simulation by Verilog HDL code on Modlesim platform, finish the logic synthesis by synplify, and implement the hardware verification on the Cyclone series FPGA device EP1C6Q240C8 of Altera company. The final results are applied to the ASIC(application specific integrated circuit) design of BPSK (Binary Phase Shift Keying)signal’s demodulation. Results show that the Costas loop could correctly realize BPSK signal’s carrier recovery and data demodulation. Results of theoretical simulation and practical engineering experiments are the same. The method is proved simple, convenient and hardware resource saving.

The typical subcarrier modulation schemes used in orthogonal frequency division multiplexing (OFDM) system includes; binary phase shift keying (BPSK), quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM). This paper analyses the performance of OFDM system that uses various number of modulation QAM constellation points over various fading channels. Simulation is done for various numbers of QAM (8 to 64-points) and with various Doppler frequency values (5 to 500 Hz) over flat and frequency selective fading channels. Results show that the best performance of OFDM system is with the number of QAM of 8 and maximum Doppler shift (MDS) of 5 Hz at all channels.

Improving tracking accuracy with subcarrier assistance and code monitoring for BOC modulated signal

Conversion between multilevel modulation formats is one of the key functions for flexible networking aimed at high spectral efficiency in optical fiber transmission. The authors previously proposed an all-optical conversion system from quadrature phase shift keying signal to simultaneous two binary phase shift keying (BPSK) signals by using four-wave mixing and interference. Since the converted BPSK signals are spatially separated, there is an issue that they cannot be transmitted at the same time through a single fiber core when redirected to the same destination. In this paper, therefore, we consider to solve the issue by converting to a symbol rate doubled single BPSK signal using a pulse width compression technique. Numerical simulation reveals that the location of the pulse width compressor affects the system performances evaluated by bit error rate and constellation diagram.

We propose a novel multi-dimensional optical transmission system based on a direct detection system. In the proposed system, quadrature phase shift keying (QPSK), binary polarized intensity rotational frequency shift keying (PIRBFSK), and binary differential phase shift keying (DBPSK) signals modulated by optical intensity, polarization, and phase are simultaneously transmitted for optical multi-dimensional transmission. The signal transmission performance of the proposed modulation technique and the possible interference of each dimension modulation were numerically and experimentally analyzed. The performance of the proposed system was verified using the bit error rate (BER), eye diagram, and spectrum of the received multi-dimensional signal.