GMSK frequency detection using decision feedback equalisation

Frequency detection of GMSK signals using one-bit decision feedback equalisation (DFE) in conjunction with offset decision instant is presented. Experiments on a 16kbit/GMSK signal reception with a premodulation filter bandwidth-bit duration product (Bb T) of 0-25 (typical for mobile radio applications) show that, compared to MSK signal reception, a bit error rate (BER) of 10-2 is obtained with a loss of about 4dB in the signal energy per bit/noise power density ratio (Eb/N0) in the additive white Gaussian noise (AWGN) channels. In the cochannel interference limited channels, a BER of 10-2 is obtainable at a signal/interference power ratio (SIR) about 5-5 dB larger than in the case of MSK signal reception.     

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.     

Performance of offset receiver diversity for GMSK and spread spectrum GMSK with one-bit differential detection using decision feedback in fast Rayleigh channels

This paper introduces the application of three techniques to improve the performance of one-bit differential detection (DD). The Gaussian minimum shift keying (GMSK) modulation technique is employed. The proposed techniques are spread spectrum, offset receiver diversity and decision feedback (DF). A comparative study shows that when applying the direct sequence spread spectrum (DS-SS), the performance is improved by 9.3 dB at a bit error rate (BER) of 10^–3 and the processing gain is equal to 10 relative to that given by Elnoubi [IEEE Trans. Veh. Tech. VT-35(1986)162–167]. When using the offset receiver diversity technique, the corresponding relative improvement is 13 dB. When employing both SS and offset diversity at the same BER, 22 and 25.7 dB improvements are attained for DS and frequency hopping (FH), respectively. A further improvement of about 1 dB is obtained when DF is used.     

带判决反馈的GMSK差分解调算法研究与实现

在超短波电台通信中,由于GMSK调制算法前后码元之间的相关性,码元之间存在码间串扰,传统的GMSK1比特差分解调算法性能不够理想。在分析GMSK信号特性的基础上,提出一种带判决反馈的1比特差分检测算法。在对两种解调算法进行研究比较后对其进行了仿真,仿真结果表明带判决反馈的1比特差分检测算法在满足解调性能时获得了3 dB的解调增益。最后使用VHDL语言在FPGA芯片中实现了该算法,并已成功用于超短波电台通信系统中。     

Adaptive iterative multiuser decision feedback detection

Adaptive iterative receivers which combine multiuser decision-feedback detection with maximum a posteriori (MAP) decoding and soft feedback are presented for synchronous coded direct sequence-code-division multiple access. Both successive and parallel demodulation of users are considered. Optimal filters are derived using both minimum mean squared error and least squares (LS) criteria. The latter assumes short (repeated) spreading codes and that the users to be demodulated simultaneously transmit training sequences. The LS criterion does not require prior knowledge or estimates of spreading codes and channels. Simulation results show that the adaptive receiver can perform significantly better than the standard (soft) interference canceller, since the adaptive algorithm attempts to measure and exploit the second-order statistics between the input and output of the MAP decoder. With limited training, successive feedback and decoding performs significantly better than parallel feedback. The effect of code rate on performance is examined, and reduced-rank versions of the adaptive LS algorithms, which can reduce training overhead, are also presented.     

Differential detection of GMSK signals with low BtTusing the SOVA

A noncoherent Gaussian minimum phase-shift keying (GMSK) detector using differential phase detection combined with the soft-output Viterbi algorithm (SOVA) is presented. This approach overcomes the severe intersymbol interference (ISI) of GMSK signals with low B_tT. Unlike conventional detectors the SOVA produces soft-decision bits resulting in larger coding gains in subsequent convolutional decoders     

Design of block transceivers with decision feedback detection

This paper presents a method for jointly designing the transmitter-receiver pair in a block-by-block communication system that employs (intrablock) decision feedback detection. We provide closed-form expressions for transmitter-receiver pairs that simultaneously minimize the arithmetic mean squared error (MSE) at the decision point (assuming perfect feedback), the geometric MSE, and the bit error rate of a uniformly bit-loaded system at moderate-to-high signal-to-noise ratios. Separate expressions apply for the "zero-forcing" and "minimum MSE" (MMSE) decision feedback structures. In the MMSE case, the proposed design also maximizes the Gaussian mutual information and suggests that one can approach the capacity of the block transmission system using (independent instances of) the same (Gaussian) code for each element of the block. Our simulation studies indicate that the proposed transceivers perform significantly better than standard transceivers and that they retain their performance advantages in the presence of error propagation.     

Performance of GMSK frequency detection with soft decision decoding of block codes using Chase's second algorithm in mobile radio channel

Investigates bit error rate (BER) performance of a GMSK frequency detection system. The channel measurement information (CMI) for a bit in the received block is calculated from samples of the received signal envelope (R/sub s/) and the demodulator output (eye level). The CMIs of eye level*R/sub s/ and of R/sub s//sup 2/ are investigated, and the decoding performances for the CMIs are compared using the Hamming (7, 4) code in nonfading (static) and fading channels in laboratory experiments.<>     

BER improvement of PRCPM in mobile radio channels withdiscriminator detection using decision feedback equalization

The authors investigate the bit error rate (BER) improvement of partial-response continuous-phase modulation (PRCPM) signals in mobile radio channels, when decision feedback equalization (DFE) to cancel the effect of intersymbol interference (ISI) of one adjacent bit is added to the limiter discriminator. A closed-form expression for the average probability of error as a function of the Doppler shift is derived for discriminator detection with decision feedback. Numerical results are presented to compare the BER performance of discriminator detection with and without feedback equalization     

基于符号判决反馈均衡的联合检测算法

传统的联合检测算法使用的块线性均衡和块判决反馈均衡,它们是以整个数据块为单位进行均衡和检测的,导致系统矩阵比较庞大,计算复杂度较高.本文将系统矩阵分成可检测的最小单位--数据符号,来进行逐个符号的联合检测,产生基于符号线性均衡的联合检测.并且将块判决反馈均衡原理应用其中,得到基于符号判决反馈均衡的联合检测算法.此算法系统矩阵尺寸小得多,因此复杂度也小得多.符号判决反馈均衡既能减小噪声项,又能减小前一符号判决误差项,因此总体的性能接近于块判决反馈均衡.仿真实验表明了这一点.本文还讨论了不同用户不同扩频因子情形下该算法的改造,并提出按用户扩频因子大小排列用户数据符号的改进,仿真实验验证了这个改进的好处.     

Fractionally spaced decision feedback joint detection for multitoneCDMA systems

We consider a fractionally spaced decision feedback joint detector (FS-DFJD) for multitone code division multiple access (CDMA) systems. We first derive the structure of the receiver for an minimum mean-squared error (MMSE) criterion. Then we investigate the bit-error rate (BER) performance achieved by this detector for binary phase-shift keying (BPSK) modulation in steady-state conditions. We consider an asynchronous scenario where the signal of each user propagates over a two-path channel. The resistance of the detector against timing errors is studied, and the resistance against a near-far scenario is also demonstrated     

Adaptive ordering for imperfect successive decision feedback multiuser detection

A method for selecting the order in which the users are detected in communication systems employing adaptive successive decision feedback multiuser detection is proposed. Systems employing channel coding without the assumption of perfect decision feedback are analyzed. The method is based on the mean squared error (MSE) measurements during a training period for each user. The analysis' shows that the method delivers BER performance improvement relative to other previously proposed ordering methods.     

An analysis of decision feedback detection of differentiallyencoded MPSK signals

A decision feedback detection scheme for differentially encoded MPSK signals based on the maximum likelihood algorithm is proposed. The performance on the symbol error rate of the system for an AWGN channel is derived by taking the error propagation into account. The error propagation can be stopped by introducing an error propagation detection technique     

Modified decision feedback differential detection fordifferentially encoded 16 APSK signals

In 1996, a version of decision feedback differential detection (DFDD) was proposed for detecting differentially encoded 16-level amplitude/phase shift keying (16 DAPSK) signals. The authors propose two modified DFDD methods, each of which uses an amplitude-state indicator. Both DFDD methods provide an improved error performance compared with the original DFDD     

Multiple-symbol differential detection of GMSK for mobilecommunications

A new multiple differential detection (MDD) sequence estimator is described which uses a decision feedback for the demodulation of a GMSK signal. This technique is based upon a maximum-likelihood sequence estimation of the transmitted phases rather than on a symbol-by-symbol detection. An upper and a lower bound on the bit error probability of the described detector in the case of an AWGN channel and a two-ray Rayleigh fading channel are derived. The performance of the detection algorithm in a mobile radio communication system is obtained through computer simulation. Comparisons with the coherent detection algorithm show that the proposed detection algorithm is quite attractive both in an AWGN and in a multipath channel     

Asymptotic Bayesian decision feedback equalizer using a set of hyperplanes

We present a signal space partitioning technique for realizing the optimal Bayesian decision feedback equalizer (DFE). It is known that when the signal-to-noise ratio (SNR) tends to infinity, the decision boundary of the Bayesian DFE is asymptotically piecewise linear and consists of several hyperplanes. The proposed technique determines these hyperplanes explicitly and uses them to partition the observation signal space. The resulting equalizer is made up of a set of parallel linear discriminant functions and a Boolean mapper. Unlike the existing signal space partitioning technique of Kim and Moon (1998), which involves complex combinatorial search and optimization in design, our design procedure is simple and straightforward, and guarantees to achieve the asymptotic Bayesian DFE.     

Transmit antenna selection for decision feedback detection in MIMO fading channels

In this paper, we investigate a transmit antenna selection (TAS) approach for the decision-feedback detector (DFD) over Rayleigh fading channels. In particular, for a multipleinput multiple-output (MIMO) channel with M transmit and N (N ⩾ M) receive antennas, we derive a lower bound on the outage probability for the TAS approach. The selected transmit antennas are those that maximize the post-processing signalto- noise ratio (SNR) at the receiver end. It is shown that the proposed TAS approach achieves a performance close to optimal selection based on exhaustive search, introduced in the literature, but at a lower complexity. Simulation results are presented to validate and demonstrate the performance gain of the proposed TAS approach.     

Further results on differential detection of GMSK signals

We evaluate the performance, in terms of bit-error rate, of 1- and 2-bit differential detectors for Gaussian minimum-shift keying (GMSK) signals by using a very fast numerical technique which makes use of the saddle point approximation. Moreover, the performance of each detector is optimized by using a closed-form expression of the optimum threshold in the slicer     

Code-aided iterative carrier phase estimation using selective soft decision feedback

A code-aided iterative carrier phase estimator using selective soft decision feedback is proposed. Based on the reliability metric defined, soft decisions provided by the soft-in/soft-out channel decoder with higher reliabilities are selected to perform carrier phase estimation iteratively. Simulation results demonstrate the performance improvement of the proposed algorithm in both the unbiased estimation range and the estimation precision. The overall bit error rate performance of the coded systems with different phase estimators is also compared.