Gaussian Minimum Shift Keying System Research Articles

Design and analysis of optimized CORDIC based GMSK system on FPGA platform

The Gaussian minimum shift keying (GMSK) is one of the best suited digital modulation schemes in the global system for mobile communication (GSM) because of its constant envelop and spectral efficiency characteristics. Most of the conventional GMSK approaches failed to balance the digital modulation with efficient usage of spectrum. In this article, the hardware architecture of the optimized CORDIC-based GMSK system is designed, which includes GMSK Modulation with the channel and GMSK Demodulation. The modulation consists of non-return zero (NRZ) encoder, an integrator followed by Gaussian filtering and frequency modulation (FM). The GMSK demodulation consists of FM demodulator, followed by differentiation and NRZ decoder. The FM Modulation and demodulation use the optimized CORDIC model for an In-phase (I) and quadrature (Q) phase generation. The optimized CORDIC is designed by using quadrant mapping and pipelined structure to improve the hardware and computational complexity in GMSK systems. The GMSK system is designed on the Xilinx platform and implemented on Artix-7 and Spartan-3EFPGA. The hardware constraints like area, power, and timing utilization are summarized. The comparison of the optimized CORDIC model with similar CORDIC approaches is tabulated with improvements.

Rényi Entropy-Based Spectrum Sensing in Mobile Cognitive Radio Networks Using Software Defined Radio.

A very important task in Mobile Cognitive Radio Networks (MCRN) is to ensure that the system releases a given frequency when a Primary User (PU) is present, by maintaining the principle to not interfere with its activity within a cognitive radio system. Afterwards, a cognitive protocol must be set in order to change to another frequency channel that is available or shut down the service if there are no free channels to be found. The system must sense the frequency spectrum constantly through the energy detection method which is the most commonly used. However, this analysis takes place in the time domain and signals cannot be easily identified due to changes in modulation, power and distance from mobile users. The proposed system works with Gaussian Minimum Shift Keying (GMSK) and Orthogonal Frequency Division Multiplexing (OFDM) for systems from Global System for Mobile Communication (GSM) to 5G systems, the signals are analyzed in the frequency domain and the Rényi-Entropy method is used as a tool to distinguish the noise and the PU signal without prior knowledge of its features. The main contribution of this research is that uses a Software Defined Radio (SDR) system to implement a MCRN in order to measure the behavior of Primary and Secondary signals in both time and frequency using GNURadio and OpenBTS as software tools to allow a phone call service between two Secondary Users (SU). This allows to extract experimental results that are compared with simulations and theory using Rényi-entropy to detect signals from SU in GMSK and OFDM systems. It is concluded that the Rényi-Entropy detector has a higher performance than the conventional energy detector in the Additive White Gaussian Noise (AWGN) and Rayleigh channels. The system increases the detection probability (PD) to over 96% with a Signal to Noise Ratio (SNR) of 10dB and starting 5 dB below energy sensing levels.

Performance Realization of CORDIC based GMSK System with FPGA Prototyping

The Gaussian Minimum Shift Keying (GMSK) modulation is a digital modulation scheme using frequency shift keying with no phase discontinuities, and it provides higher spectral efficiency in radio communication systems. In this article, the cost-effective hardware architecture of the GMSK system is designed using pipelined CORDIC and optimized CORDIC models. The GMSK systems mainly consist of the NRZ encoder, Integrator, Gaussian filter followed by FM Modulator using CORDIC models and Digital Frequency Synthesizer (DFS) for IQ Modulation in transmitter section along with channel, the receiver section has FM demodulator, followed by Differentiator and NRZ decoder. TheCORDIC algorithms play a crucial role in GMSK systems for IQ generation and improve the system performance on a single chip. Both the pipelined CORDIC and optimized CORDIC models are designed for 6-stages. The optimized CORDIC model is designed using quadrature mapping method along with pipeline structure. The GMSK systems are implemented on Artix-7 FPGA with FPGA prototyping. The Performance analysis is represented in terms of hardware constraints like area, time and power. These results show that the optimized CORDIC based GMSK system is a better option than the pipelined CORDIC based GMSK systems for real-time scenarios.

Design of Efficient LDPC Coded Non-Recursive CPE-Based GMSK System for Space Communications

We consider a low-density parity-check (LDPC) coded non-recursive Gaussian minimum shift keying (GMSK) scheme for space communications subject to low signal-to-noise ratio (SNR), limited power, and spectrum resources. First, we design a non-recursive continuous-phase encoder (NRCPE)-based GMSK modulator to alleviate the impact of the error propagation existed in a recursive CPE (RCPE)-based one. Then, a corresponding pilot-aided quasi-coherent demodulation algorithm (PA-QCDA) is developed for improving the performance of the non-coherent demodulation and the impact of the Doppler shift in the coherent demodulation, whose basic principle is that a modified Bahl, Cocke, Jelinek, and Raviv (BCJR) algorithm-based detection performs on the received signals with initial and ending trellis-states being determined using the very small pilot overhead. Finally, we choose proper modulation parameters for the NRCPE-based GMSK signaling according to the tradeoffs between power and spectral efficiency. The simulation results show that the proposed system using the PA-QCDA can achieve excellent performance and can also work well in the presence of the large Doppler shifts and some burst errors.

Noise-robust feedforward synchronisation for resource-constrained Gaussian minimum shift keying system in wireless body area network

As Gaussian minimum shift keying (GMSK) modulation scheme is adopted for wireless body area network (WBAN) applications, simple and noise-robust synchronisation algorithms for GMSK are desired to meet the limited resources of power, storage and size in WBAN. However, the current synchronisation algorithms for GMSK are either too complicated or have unsatisfactory performance for low signal-to-noise ratio (SNR), especially for coded GMSK systems. The authors will propose the synchronisation algorithms for general GMSK systems with three unknown synchronisation parameters, namely, timing, frequency and phase offsets estimation. By incorporating noise/interference-reduction methods, the authors propose low-complexity synchronisation algorithms for GMSK that can achieve satisfactory performance in low SNR region. Furthermore, their new feedforward timing and frequency recovery algorithms can provide much better performance than those in the literature by using reliability-measuring mechanism for timing estimation and two-phase frequency estimation. The data-aided Cramer–Rao bounds (CRBs) for the joint estimation of GMSK synchronisation parameters are also derived. The numerical results show that the performance of their proposed synchronisation algorithms is close to the CRBs. The overall bit error rate performance for both uncoded and Bose-Chaudhuri-Hocquenhem BCH-coded GMSK systems are examined. The performance loss owing to synchronisation errors can be reduced to about 1 dB with their proposed algorithms.

BER analysis of a GMSK system using decision feedback

There are considerable literatures on the Bit Error Rate (BER) evaluation of Differential Detection of Gaussian Minimum Shift Keying (DDGMSK) system using Decision Feedback (DF), but most of them give the performance based on the Monte Carlo Error Counting (MCEC) technique. From the probability distribution of the phase angle between two vectors perturbed by Gaussian noises, the formulae of BER are derived for the performance analysis of DDGMSK system with DF in this letter. Considering the m-bit dock-tailed sequence, the new formulae of Gaussian Minimum Shift Keying (GMSK) modulated phase and the Time-Varying Signal to Noise Ratio (TVSNR) of the demodulated signal are presented, and it is proved that the relationship between the TVSNR of the demodulated signal and the size of eye opening is not inevitable. Simulation results show that the theoretical investigation gives analogous results with the MCEC technique. The formulae presented are useful for the performance analysis of systems using GMSK as modulating and demodulating method, for instance, the analysis of synchronous performance of frequency-hopping communication system.

Effects of ACI and nonlinearities on the performance of differentially detected GMSK signals

The effects on the performance of differentially detected Gaussian minimum shift keying (GMSK) signals operated in the presence of adjacent channel interference (ACI), modulator impairments, amplifier nonlinearities and additive white Gaussian noise is investigated. By means of computer simulation, the bit error rate (BER) performance of 1- and 2-bit conventional and decision feedback differentially detected (C-DD and DF-DD) GMSK systems in the presence of static and Rayleigh faded ACI is obtained. It is found that the best performance is achieved by the 2-bit DF-DD receiver and has resulted in BER performance improvements for the static ACI channel and error floor reductions for the Rayleigh faded ACI channel. The effects on the BER performance of a cascade of imperfect GMSK quadrature modulators and a nonlinear amplifier in conjunction with the resulting ACI are also investigated. The combination of 'typical' and 'extreme' operating conditions for the modulator are considered. For all combinations, it was found that the DF-DD receivers perform better than the C-DD receivers. However, for systems operating under 'typical' operating conditions, the 2-bit DF-DD receiver exhibits the best performance.

Optimization of coded GMSK systems

In this article, block and convolutional coding for Gaussian minimum shift keying (GMSK) in additive white Gaussian noise (AWGN) channels is investigated. The performance improvement that can be obtained without an increase in bandwidth is found for block and convolutional codes with various block lengths and constraint lengths, respectively, when a simple suboptimal demodulation scheme is used. For a fixed system transmission bandwidth, the tradeoff between the percentage of bandwidth to use for coding and the percentage to use for modulation is examined and optimized for various values of bandwidth.

Turbo equalization for GMSK signaling over multipath channels based on the Gibbs sampler

We consider the problem of Bayesian data restoration for Gaussian minimum shift keying (GMSK) signals over unknown multipath channels. As an alternative to the linear approximation method employed in the conventional finite impulse response (FIR) model, we develop a nonlinear signal model for this system. A Bayesian equalizer based on the Gibbs sampler, a Markov chain Monte Carlo (MCMC) procedure, is developed for estimating the a posteriori symbol probability in the GMSK system without explicit channel estimation. The basic idea of this technique is to generate ergodic random samples from the joint posterior distribution of all unknowns, and then to average the appropriate samples to obtain the estimates of the unknown quantities. Being soft-input soft-output in nature, the proposed Bayesian equalization technique is well suited for iterative processing in a coded system, which allows the Bayesian equalizer to successively refine its processing based on the information from the decoding stage, and vice versa.

Effect of nonlinearities on outage performance of fiber-fed microcellular networks for GMSK systems

Application of fiber for remoting the complex RF signal processing and control procedures in a microcellular system has attracted much attention. This paper investigates the effect of the laser diode nonlinearities on the outage performance of a Gaussian minimum shift keying (GMSK)-based system in a Rician channel. The analysis presented assumes that in contrast to the rapid (or short-term) fluctuations modeled by the Rician distribution, the slow (or long-term) fluctuations due to shadowing or near-far effects are compensated (in an exact sense) by power control schemes. The nonlinearity of the laser diode is shown to create a tradeoff between the outage and system parameters such as radio capacity and threshold bit-error rate (BER). The optical noises, such as shot noise, thermal noise, and relative intensity noise, are shown to degrade the outage of the system. Also, in addition to the usual improvement of outage with a strong specular component, it is observed that the specularity of the channel in a small measure mitigates the effective nonlinearity of the system and thus increases the dynamic range of the system. Design equations are provided for optimal performance.

Pilot tone aided coherent GMSK systems for sound/data mobile broadcasting

A Gaussian minimum-shift keying (GMSK) modem with built-in fade canceler is proposed narrowband mobile digital broadcasting systems. The proposed scheme combines DC suppressing line code and high-pass filters to create a spectral null at the carrier frequency of the transmit GMSK signal spectrum. This enables an unmodulated carrier pilot tone to be transmitted with the digital broadcast signal without mutual interference. In the receiver, the recovered pilot is used to coherently demodulate the received signal without phase ambiguity. The pilot can be also be used to track and cancel out the random phase noise induced by fast fading. The scheme is applied to a 16 kb/s BT=0.25 GMSK signal with B/sub v/=800 Hz, and its performance over a fast Rayleigh fading channel is investigated using computer simulation. The results demonstrates that the proposed coherent modem is capable of significantly outperforming conventional differential detection in fast fading environments such as a broadcasting channel for mobile reception.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>