Optimum bandwidth-distance performance in partial response CPMsystems

The problem of optimizing the baseband pulse shape in order to obtain the minimum effective bandwidth for a prescribed value of minimum Euclidean distance is treated for partial response CPM. Some comparisons with standard pulses are performed and the results are presented in the form of bandwidth-distance and spectral density plots     

Effective bandwidth optimization for noncoherent full-response CPMsystems

The optimization of the baseband pulse shape for full response CPM signals, when a noncoherent lowest complexity receiver is used, is carried out. The effective bandwidth is chosen as the objective of the optimization. In order to obtain the minimum error probability for high signal-to-noise ratio, orthogonal signaling is taken into consideration. A closed form for the optimum pulse shape, the value of the optimum modulation index and of the optimum effective bandwidth is determined. The power spectral density and the fractional out-of-band power have been compared with some phase functions considered in the literature     

Distance properties of finite-impulse response channels

High-speed data communication over channels with limited bandwidth gives rise to intersymbol interference at the receiver usually resulting in a poor receiver error performance. An important parameter that determines the receiver error performance is the minimum Euclidean distance between two received sequences. Channel properties that maximize this distance are investigated. It is shown that maximum distance channels exist for any length of interference     

Multistream Faster than Nyquist Signaling

We extend Mazo?s concept of faster-than-Nyquist (FTN) signaling to pulse trains that modulate a bank of subcarriers, a method called two dimensional FTN signaling. The signal processing is similar to orthogonal frequency division multiplex (OFDM) transmission but the subchannels are not orthogonal. Despite nonorthogonal pulses and subcarriers, the method achieves the isolated-pulse error performance; it does so in as little as half the bandwidth of ordinary OFDM. Euclidean distance properties are investigated for schemes based on several basic pulses. The best have Gaussian shape. An efficient distance calculation is given. Concatenations of ordinary codes and FTN are introduced. The combination achieves the outer code gain in as little as half the bandwidth. Receivers must work in two dimensions, and several iterative designs are proposed for FTN with outer convolutional coding.     

Noncoherent detection of convolutionally encoded continuous phasemodulation

The authors consider the error probability at large signal-to-noise ratios of rate-1/2 convolutionally encoded CPFSK (continuous-phase frequency-shift keying) with an optimum noncoherent detector on an additive white Gaussian noise channel. The performance is given in terms of a parameter called the minimum squared normalized equivalent Euclidean distance which plays the same role mathematically as the minimum squared normalized Euclidean distance used for coherent detectors. It is shown that by introducing convolutional coding the error performance is significantly improved. The authors propose a decoding algorithm for these convolutionally encoded CPM schemes which is based on a limited tree search algorithm and uses the maximum-likelihood decision rule for noncoherent detection. Computer simulations show that the degradation in error performance compared to the performance of the optimum coherent Viterbi detector is less than 1 dB with a relatively simple noncoherent detector on an additive white Gaussian noise channel for most of the schemes considered     

On the existence of the Mazo-limit on MIMO channels

Mazo, in 1975, showed that the signaling rate of a linear modulation can be significantly higher than the maximum rate for orthogonal signaling without any loss of minimum square Euclidean distance. In subsequent literature the highest such rate is referred to as the Mazo-limit. In this letter we ask whether there exists a Mazo-limit also on MIMO channels. The answer is yes, but it applies to the largest pairwise error probability rather than to minimum square Euclidean distance. Moreover, it occurs at exactly the same rate as in the AWGN case. As a special case results for single-input single-output fading channels are obtained.     

A simple way to compute minimum Euclidean distance for synchronouscoded multiuser systems

We show that the minimum squared Euclidean distance for a synchronous multiuser system using convolutional codes is no less than the product of the free distance of the code and the minimum Euclidean distance for the corresponding uncoded synchronous multiuser system. When all users use an identical convolutional code, equality holds. Thus the relationship can be used to compute the minimum squared Euclidean distance for a coded system. The results also indicate that in terms of maximizing the minimum squared Euclidean distance, it is better if all users use nonidentical error control codes     

Exploiting faster-than-Nyquist signaling

Faster-than-Nyquist signaling introduces intersymbol interference, but increases the bit rate while preserving the signaling bandwidth. For sinc pulses, it has been established that with a small increase in the signaling rate beyond the Nyquist rate, there is no reduction in the minimum Euclidean distance for binary signaling. We generalize these observations to the family of raised-cosine pulses. The structure of the error events that reduce the minimum distance is examined, and constrained coding ideas are suggested that theoretically allow even faster signaling. Then we propose ways of achieving these gains practically by designing appropriate constrained codes and through equalization and iterative joint equalization and decoding (turbo equalization).     

Minimum-Bandwidth Optical Intensity Nyquist Pulses

The indoor diffuse wireless optical intensity channel is bandwidth-limited due to multipath distortion, and all transmitted signal amplitudes are constrained to be nonnegative. In order to control the impact of intersymbol interference (ISI) on this channel, pulse shaping is required. This paper derives the minimum bandwidth, ISI-free Nyquist pulse which satisfies the amplitude nonnegativity constraint. The minimum bandwidth required is twice that of conventional electrical channels. With the addition of excess bandwidth, the optimal bandlimited optical intensity pulse, in the sense of minimizing average optical power, is shown to be a squared double-jump pulse. Thus, a bandwidth versus optical power efficiency tradeoff in pulse design is quantified. The impact of timing jitter on the probability of symbol error for various excess bandwidths is quantified via simulation. Further, it is shown that there are no bandlimited root-Nyquist pulses satisfying the amplitude nonnegativity constraint. In fact, all practical optical intensity root-Nyquist pulses are shown to be necessarily time-limited to a single symbol interval     

Multi-H phase-coded modulations with asymmetric modulationindexes

Multi-H phase-coded modulation (MHPM) is a bandwidth-efficient modulation scheme which offers substantial coding gain over conventional digital modulation schemes. MHPM with asymmetric modulation indices corresponding to the bipolar data +1 and -1 is considered, and numerical results for the minimum Euclidean distances are provided. It is shown that performance improvements on the error probability over conventional MHPM are gained with essentially the same bandwidth and a very slight modification in implementation. The upper bounds on the error probabilities as functions of observation intervals and received E_b/N₀ are also investigated in detail. It is concluded that the concept of asymmetric modulation indices for MHPM is attractive for bandwidth and power-efficient modulation     

Some block- and trellis-coded modulations for the Rayleigh fadingchannel

The error performance of a modulation code over a channel depends on several distance parameters and the path multiplicity of the code. For the AWGN channel, the error performance of a modulation code depends mainly on its minimum squared Euclidean distance and path multiplicity. For the Rayleigh fading channel, however, the error performance of a modulation code depends strongly on its minimum symbol distance, minimum product distance, and path multiplicity. It depends on the minimum squared Euclidean distance in a lesser degree. This paper is concerned with the construction of block and trellis MPSK modulation codes for the Rayleigh fading channel. In each construction, the distance parameters are chosen to achieve good error performance with reduced decoding complexity     

Minimum Euclidean distances of partial response multi-h phase-coded modulations with asymmetric modulation indices

A new concept of asymmetric modulation indices has recently been proposed and applied on full-response multi-h phase-coded modulations (MHPM) and improved error probability performance has been found. In this letter, a similar concept is applied to partial response MHPM and the minimum Euclidean distances for linear phase pulse function are evaluated to show further improvements.<>     

Minimum Euclidean distance for combinations of short rate 1/2 convolutional codes and CPFSK modulation

Continuous phase frequency shift keying (CPFSK) is a constant amplitude modulation method with good spectral sidelobe properties. Good error probability properties can be obtained with coherent maximum-likelihood detection. In this paper we study the Euclidean distance properties of signals formed by a conventional rate1/2convolutional encoder followed by a binary or4-level CPFSK modulator. The minimum Euclidean distance is calculated for these signal sets as a function of the modulation index and the observation interval length. The optimum detector is discussed for rational modulation index values. The best obtainable codes are found for the case of short rate1/2codes with binary or4-level CPFSK modulation. Lists of the best codes are given. Among the results are that the noncatastrophic rate1/2convolutional codes with optimum free Hamming distance do not in general give the best Euclidean distance with CPFSK.     

大气无线光通信系统中数字脉冲间隔调制研究

基于光强闪烁的大气无线光通信系统模型,研究了数字脉冲间隔调制(DPIM)方式的差错性能,分析了符号结构、发射功率、带宽需求等问题,并与 OOK(开关键控)和 PPM(脉冲位置调制)调制方式进行比较。理论和仿真研究结果表明,DPIM 调制方式较 PPM 方式有较高的功率效率和较少的带宽需求,特别是在系统实现上相对于 PPM 大大简化。因此 DPIM 应用于无线光通信系统具有一定优势。     

Rice-Lognormal衰落信道中不同译码度量特性的比较

本文推导出了Ｒｉｃｅ－Ｌｏｇｎｏｒｍａｌ衰落信道中没有信道状态信息和具有信道状态信息两种情况下的最大似然译码度量,并同传统欧氏距离度量的错误概率进行了比较,数值计算结果表明：对于ＴＣ－ＭＰＳＫ方案,信道衰落特征（ｆＤＴ）对度量特性打电话几乎可以忽略。最后,讨论了Ｒｉｃｅ－Ｌｏｇｎｏｒｍａｌ衰落信道中的最小交织深度。     

一种多符号网格码与差分空时分组码级连方法

我们提出了一种多符号网格码(MTCM)与差分空时分组码级连的传输方法,研究了在传输信道是慢时变平坦瑞利衰变的条件下,并采用理想交织时系统的性能。导出了这个级连系统的成对错误概率上限表达式,分析表明,系统的性能主要受到不同信号序列间的最小汉明矩离和信号星座间的平方欧几里德矩离的影响。仿真结果表明,在相同的频谱有效性和信号星座条件下,这种级连的系统比非级连差分空时编码系统有更好的性能。     

A new approximation to the symbol error probability for codedmodulation schemes with maximum likelihood sequence detection

The power efficiency of coded modulation schemes in additive white Gaussian noise depends on the signal space distribution of their most common error events. Symbol error probability calculation allowing for the pairwise interaction of these error events is discussed. Two optimality criteria are considered for detectors. The first minimizes the probability of symbol error for each symbol decision. This is called the symbol-to-symbol detector. The second (which is superior) is the maximum likelihood sequence detector (MLSD). A lower bound for the symbol-to-symbol detector and an approximation to the MLSD symbol error probability are described. The theoretical performance difference between these two detectors is given. The results are more accurate than minimum squared Euclidean distance predictions, especially at low and intermediate signal-to-noise ratios. The MLSD symbol error probability approximation is obtained for considerably less cost than computer simulation and gives more insight into the signal space structure of the scheme being analyzed. Numerical results are presented for a continuous phase modulation (CPM) example     

Trellis codes for the optical direct-detection channel

It is observed that the reduced complexity minimum distance search method of Zehavi and Wolf (1987) can be extended from codes designed using the squared Euclidean distance measure to any measure which is additive over the code branches. C.N. Georghiades (1989) has derived such a metric for codes for the direct-detection optical channel. The search method is applied to find codes for four- and eight-point overlapping pulse position modulation (OPPM), with large minimum distance and a small number of codewords at that distance     

An optimal signal design for band-limited asynchronous DS-CDMAcommunications

An optimal signal design for band-limited, asynchronous, direct-sequence code-division multiple-access (DS-CDMA) communications with aperiodic random spreading sequences and a conventional matched filter receiver is considered in an additive white Gaussian noise (AWGN) channel. With bandwidth defined in the strict sense, two optimization problems are solved under finite bandwidth and zero interchip interference constraints. First, a chip waveform optimization is performed given the system bandwidth, the data symbol transmission rate, and the processing gain. A technique to characterize a band-limited chip waveform with a finite number of parameters is developed, and it is used to derive optimum chip waveforms which minimize the effect of multiple-access interference (MAI) for any energy and delay profile of users. Next, a joint optimization of the processing gain and the chip waveform is performed, given the system bandwidth and the data symbol transmission rate. A sufficient condition for a system to have lower average probability of bit error for any energy profile is found, and it is used to derive some design strategies. It is shown that the flat spectrum pulse with the processing gain leading to zero excess bandwidth results in the minimum average probability of bit error. Design examples and numerical results are also provided