CPM 编码调制系统的基本性能限

针对CPM系统的信道容量研究结果进行了综述,并推导计算了Rayleigh衰落信道下CPM的容量分析方法与计算结果。首先回顾了CPM系统的基本概念及其有限状态马尔可夫模型,并对AWGN信道下CPM的可达信息速率计算方法进行了讨论;然后将其推广到Rayleigh衰落信道,推导出在该信道下计算CPM容量的算法。考虑了接收端已知信道状态信息及未知信道状态信息2种情况。在导出容量计算的算法后,通过Monte Carlo仿真给出了在AWGN及Rayleigh衰落信道下几种典型CPM方案的容量曲线。     

LSB coded 8PSK signals

An 8PSK scheme with the least significant bit (LSB) Golay coded is proposed and its performance is analyzed. With hard decision decoding, the proposed scheme can achieve 1 dB asymptotic coding gain and also save 26% bandwidth, as compared with uncoded QPSK scheme     

On noncoherent sequence detection of coded QAM

New noncoherent sequence detection algorithms for combined demodulation and decoding of coded linear modulations transmitted over additive white Gaussian noise channels are presented. These schemes may be based on the Viterbi algorithm and have a performance which approaches that of coherent detection for increasing complexity. The tradeoff between complexity and performance is simply controlled by a parameter referred to as implicit phase memory and the number of trellis states     

On the performance of spectrally efficient trellis coded FMmodulation employing noncoherent FM demodulation

The authors analyze the problem of noncoherent FM demodulation of trellis-coded continuous-phase M-ary FSK (frequency-shift keying). The FM demodulation process is divided into two parts, the first being the actual noncoherent FM demodulation and the second being trellis decoding of the data. Upper bounds on the bit error rate as well as the 99% energy bandwidth are determined for the codes under consideration. In particular, the authors consider the trellis codes with rates 1/2 and 2/3 and symmetric and asymmetric signal constellations. Upper bounds on the probability of error are obtained for the symmetric and the optimum asymmetric cases. The optimum asymmetry is one which minimizes the bit error probability. The performance of this system is compared to that of the standard continuous phase modulation techniques employing noncoherent detection     

Asymptotical analysis and comparison of two coded modulationschemes using PSK signaling .I

An asymptotical analysis and comparison of two coded modulation systems using phase-shift keying (PSK) signaling with the transmission taking place over the additive white Gaussian noise (AWGN) channel is provided. In this paper, bounds for the decoding error probability of conventional coded modulation are derived. Both block and trellis coding are considered. The state-complexity error exponent is introduced     

Asymptotical analysis and comparison of two coded modulationschemes using PSK signaling .II

For pt.I see ibid., vol.47, no.7, p.2782-92 (2001). In this paper we analyze a multilevel coded modulation system using phase-shift keying (PSK) signaling and transmitting over the additive white Gaussian noise (AWGN) channel. We reduce the analysis of the overall system to the analysis of each decoding level, considering them as a set of related channels. The concept of a “genie-aided communication system” is introduced to simplify the analysis. A comparison with the conventional coded modulation system, studied in part I of this work, and some results concerning the synthesis and analysis of practical multilevel modulation schemes concludes the paper     

Analysis of coded noncoherent transmission in DS-CDMA mobilesatellite communications

The paper analyzes possible transmission schemes for satellite personal communication systems adopting low/medium-Earth orbit (LEO/MEO) constellations and direct-sequence code division multiple access (DS-CDMA) in the presence of fading and shadowing, the statistics of which are functions of the satellite elevation angle. In particular, the performance of M-ary Walsh-Hadamard orthogonal (MWHO) convolutionally coded DS-CDMA over a Rice-log-normal fading channel is analyzed in depth, and compared to the simpler coded differential BPSK (DBPSK) scheme. Optimization of the performance/complexity tradeoff in the metric computation for soft inputs to the Viterbi (1979) decoder is addressed. Upper bounds on the error probability without or with satellite diversity and equal gain combining are evaluated considering different coding rates. The effect of correlated fading is also taken into account via simulation. Among the various results, it is shown that the optimal coding rate is a function of the satellite elevation angle and of the diversity order, that the loss for using DBPSK instead of MWHO is in the range 1-1.4 dB, and that interleaving depth is a critical parameter     

Iterative decoding of coded and interleaved noncoherent multiplesymbol detected DPSK

A new receiver for coded and interleaved DPSK based on multiple symbol differential detection (MSDD) and iterative (`turbo') decoding is proposed. Performance close to that of coherent detection over an AWGN channel is demonstrated by simulations     

二相编码信号性能分析

二相编码信号应用于低截获自导声纳波形设计,具有较好的性能。本文着重研究了二相编码信号的模糊函数及频谱,仿真实验表明二相编码信号距离分辨力及速度分辨力与信号带宽和信号时宽分别对应相关。信号带宽越大则距离分辨力越高,信号时宽越长则速度分辨力越高。同时信号带宽亦与信号频谱幅度成反比关系。信号带宽越大,信号频谱幅度越低,功率谱密度亦越低。因此,选择适当的时宽、带宽,二相编码信号具有较好的低截获性能。     

Error rate performance of noncoherent detection of duobinary coded MSK and TFM in mobile radio communication systems

Two continuous phase constant envelope modulation schemes are considered for use in digital mobile radio communication systems. These two schemes, duobinary coded minimum shift keying (MSK) and tamed frequency modulation (TFM), use partial response signaling to achieve efficient power spectrum. Therefore, they are suitable candidates for the application of digital data transmission via mobile radio where spectrum efficiency is an important consideration. The mobile communication channel is characterized by fast Rayleigh fading and cochannel interference resulting from the reuse of the channels. The error rate performance of duobinary coded MSK and TFM has been studied under these environments with noncoherent detection. A closed form expression for the probability of error of duobinary coded MSK with discriminator detection has been derived and evaluated for different cases of fast and slow fading and cochannel interference. The probability of error of duobinary coded MSK and TFM with differential detection has been calculated by numerical integrations for different cases of slow and fast fading and cochannel interference.     

Bit-interleaved coded modulation with iterative decoding and 8 PSK signaling

We have suggested bit-interleaved coded modulation with soft decision iterative decoding (BICM-ID) for bandwidth-efficient transmission over Gaussian and fading channels. Unlike trellis coded modulation, BICM-ID has a small free Euclidean distance but large diversity order due to bit interleaving. With iterative decoding, soft bit decisions can be employed to significantly improve the conditional intersignal Euclidean distance. This leads to a large coding gain, comparable to that of turbo TCM, over both Gaussian and Rayleigh fading channels with much less system complexity. We address critical design issues to enhance the decoding performance and provide the analytical bounds on the performance with an ideal feedback assumption. We investigate the performance characteristics of BICM-ID through extensive simulations and show that at high signal to noise ratios, the performance of BICM-ID converges to the performance assuming error-free feedback.     

16PSK系统仿真及误码率性能分析

为实现16PSK应用到无线激光通信中,本文对16PSK系统性能进行了理论研究。介绍了16PSK调制解调原理,对两种不同信道的系统性能进行了研究,分析对比了在两种信道下的系统误码性能。为基于副载波16PSK无线激光通信系统的研究奠定了理论基础。     

The error probability of M-ary PSK block coded modulation schemes

A tight upper bound on the decoding error probability is derived for block-coded modulation structures where an M-ary phase shift keying (M-PSK) signal constellation is employed. This bound, called a tangential sphere bound, is tight for very low (as well as for high) signal-to-noise ratios (SNRs). Berlekamp's tangential union bound, previously derived for binary codes, can be derived for an M-PSK block coded modulation structure as well. However, it is proven that our tangential sphere bound is tighter than Berlekamp's (1980) tangential bound. For particular schemes, it is shown that for low SNRs our bound is considerably tighter than the tangential bound. As one of the examples, a multistage decoder is considered     

Distance measures for viterbi decoding of coded and bandlimited 8PSK signals

The paper studies a digital modem that transmits a convolutionally encoded eight-phase-shift keyed (CE8PSK) signal over a satellite channel and employs a near-maximum-likelihood decoder at the receiver. Several different earth-stations are assumed to have simultaneous access to a given transponder in the satellite as an arrangement of frequency-division multiple access. Adjacent channel interference (ACI) is neglected here. The high-power amplifier (HPA) at the earth-station transmitter and the satellite transponder are assumed to be linear. The channel distorts the data signal, through the bandlimiting introduced by the equipment filters, and it adds stationary white Gaussian noise to the data signal at the receiver input. The resulting noisy and distorted data signal is coherently demodulated. Four different bandwidths of the transmitted CE8PSK signal are considered, together with three different demodulation processes. The decoder uses the Viterbi algorithm, together with one of six different distance measures to determine the costs of the stored vectors (survivors). The paper describes the various techniques involved in the modem, and presents the results of an extensive series of computer-simulation tests to measure the performances of the system with all appropriate combinations of the signal bandwidth, demodulation process and distance measure. The results of the tests are then used to determine the preferred modem design.     

The development of a coded 8 PSK modem using digital signal processors

A prototype 64 kb/s coded eight phase shift key (C8PSK) modem has been successfully developed using a combination of conventional analogue circuitry and software-based digital signal processing. The C8PSK scheme is fully compatible regarding interference criteria with existing satellite FDMA access requirements and offers more efficient use of the satellite resource than conventional quaternary PSK (QPSK) systems. The C8PSK unit may either maintain channel performance with a lower satellite power requirement or improve the user bit error rate (BER) without the need for extra satellite power or bandwidth. The prototype modem was developed in a general way so that other PSK modulation schemes could be accommodated by replacing PROM units. Software processing also allows adaptive operation which adjusts the processing technique to optimize operation for a degraded signal-to-noise environment.     

A Reed-Solomon coded DS-CDMA system using noncoherent M-aryorthogonal modulation over multipath fading channels

The performance of Reed-Solomon (RS) coded direct-sequence code division multiple-access (DS-CDMA) systems using noncoherent M-ary orthogonal modulation is investigated over multipath Rayleigh fading channels. Diversity reception techniques with equal gain combining (EGC) or selection combining (SC) are invoked and the related performance is evaluated for both uncoded and coded DS-CDMA systems. “Errors-and-erasures” decoding is considered, where the erasures are based on Viterbi's (1982) so-called ratio threshold test (RTT). The probability density functions (PDF) of the ratio associated with the RTT conditioned on both the correct detection and erroneous detection of the M-ary signals are derived. These PDFs are then used for computing the codeword decoding error probability of the RS coded DS-CDMA system using “errors-and-erasures” decoding. Furthermore, the performance of the “errors-and-erasures” decoding technique employing the RTT is compared to that of “error-correction-only” decoding refraining from using side-information over multipath Rayleigh fading channels. As expected, the numerical results show that when using “errors-and-erasures” decoding, RS codes of a given code rate can achieve a higher coding gain than without erasure information     

Theoretical performance limits on tropospheric refractivityestimation using point-to-point microwave measurements

Ducted propagation above the ocean surface can seriously impact shipboard radar and communications. Point-to-point microwave measurements have been proposed as a means of estimating tropospheric refractivity for the purposes of characterizing surface-based ducts. This paper addresses the theoretical performance of refractivity estimates that can be made by combining field measurements at different frequencies with prior statistics of refractivity variation. Parameterizing the refractivity profile using empirical orthogonal functions derived from a historical database, both Cramer-Rao performance bounds and the maximum a posteriori (MAP) estimate are discussed using coherent or incoherent signals. Results obtained using a realistic model of refractivity conditions off Southern California suggest that multifrequency propagation measurements can significantly improve the estimation of refractivity and propagation loss profiles     

空时格码和OFDM系统联合建模及性能分析

发射端分集、编码和调制结合空时格码，可以有效地提高信号在无线衰落信道中传输的有效性和可靠性；在正交频分复用调制OFDM(Omiogonal Frequency Division Multiplexing)系统中应用空时格码可以有效地对抗多径干扰，提高系统容量，适合于在高速无线数据通信中采用。本文详细地说明了它们结合的基础，进而构造了一个基于空时格码的OFDM系统模型，并分析了在高斯信道下的系统性能。     

Maximum likelihood decoding of uncoded and coded PSK signalsequences transmitted over Rayleigh flat-fading channels

The problem of maximum likelihood (ML) detection for uncoded and coded M-PSK signals on Rayleigh fading channels is investigated. It is shown that, if the received signal is sampled at baud-rate, a ML receiver employing per-survivor processing can be implemented. The error rate performance of this receiver is evaluated by means of computer simulations and its limitations are discussed. In addition, it is shown that, on a fast fading channel, the error floor in the BER curve can be appreciably lowered if more than one received signal sample per symbol interval is processed by the receiver algorithm, Finally, a sub-optimum two-stage receiver structure for interleaved coded PSK systems is proposed. Its error rate performance is assessed for simple trellis-coded modulation schemes and compared to that provided by other receiver structures     

编码掩模红外成像的建模与性能分析

针对编码掩模红外成像系统提出了一种建模方法。该模型将成像系统视为由两个功能部分组成,一部分为编码掩模与理想聚焦透镜的理想成像,另一部分为实际透镜自身的非理想成像。据此,系统点扩散函数可以由掩模结构的衍射模式和实际透镜的点扩散函数联合表示。此外,文中对视场内倾斜入射平面波的成像结果进行分析,从而得到了视场内的点扩散函数的变动情况。由码型及相应点扩散函数的指标评价结果可以看出,文中提出的基于Dammann阵列的码型结构对直接成像和图像还原处理具有较为平衡的性能。实验表明,对于编码掩模直接成像系统的码型中应当具有较多的随机性结构,而对于能够做进一步图像还原处理的系统码型中应当具有较多的周期性结构。