共查询到20条相似文献,搜索用时 15 毫秒
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2.
Xiupu Zhang Peixuan Jiang 《Lightwave Technology, Journal of》1992,10(8):1127-1131
The performance of a coherent optical M -ary continuous-phase frequency-shift-keying (CPFSK) receiver using limiter-discriminator (L-D) detection is investigated. It is shown that L-D detection of CPFSK optical signals offers the best performance for a large normalized IF beat spectral linewidth, ΔνT . When the modulation index is unity, the receiver is immune to laser phase noise and can produce (M /4) exp (-SNR) symbol error probability, which may be considered as the upper bound if the optimal modulation index is used (SNR is the signal-to-noise ratio per symbol). Optimum modulation indexes are 0.8 and 1 at ΔνT =1% and ΔνT =2%, respectively, for M =4, 8, and 16 相似文献
3.
The application of the nonredundant error correction (NEC) technique to the North American and Japanese digital cellular modulation standard, π/4-shift differential quadrature phase shift keying (DQPSK), in a combined additive white Gaussian noise (AWGN) and cochannel interference (CCI) environment is proposed, analyzed, and theoretically evaluated. The performance for NEC receivers with single, double, and triple error correction capability is theoretically analyzed and evaluated. For the CCI, the general model, which includes M statistical independent interferers also employing the π/4-shift DQPSK modulation format, is adopted. The theoretical symbol error probability versus carrier-to-noise ratio have been obtained with M and the carrier-to-interference ratio (C /I ) as parameters. The results indicate significant performance improvements over conventional differentially detected systems. Some of the results have been verified by computer simulation. The gains offered by the NEC receivers increase as C /I decreases and/or M increases. Significant error floor reductions have been observed 相似文献
4.
The authors consider frequency-hopped spread-spectrum multiple-access communications using M -ary modulation and error-correction coding. The major concerns are multiple-access interference and the network capacity in terms of the number of users that can transmit simultaneously for a given level of codeword error probability. Block coding is studied in detail. The authors first consider the use of Q -ary Reed-Solomon (RS) codes in combination with M -ary modulation with mismatched alphabets so that Q >M . It is shown that the network capacity is drastically reduced in comparison with the system with matched alphabets. As a remedy, the use of matched M -ary BCH codes is proposed as an alternative to mismatched RS codes. It is shown that when the number of users in the system is large, a BCH code outperforms an RS code with a comparable code rate and decoding complexity. The authors consider the use of a robust technique for generation of reliable side information based on a radio-threshold test. They analyze its performance in conjunction with MFSK and error-erasure correction decoding. It is shown that this nonideal ratio-threshold method can increase the network capacity in comparison with the system with perfect side information 相似文献
5.
Honkala H.S. Hamalainen H.O. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1991,37(2):372-375
The normality of binary codes is studied. The minimum cardinality of a binary code of length n with covering radius R is denoted by K (n ,R ). It is assumed that C is an (n ,M )R code, that is, a binary code of length n with M codewords and covering radius R . It is shown that if C is an (n ,M )1 code, then it is easy to find a normal (n ,M )1 code by changing C in a suitable way, and that all the optimal (n ,M )1 codes (i.e. those for which M =K (n ,1)) are normal and their every coordinate is acceptable. It is shown that if C is an abnormal (n ,M ) code, then n ⩾9, and an abnormal (9118)1 code which is the smallest abnormal code known at present, is constructed. Lower bounds on the minimum cardinality of a binary abnormal code of length n with covering radius 1 are derived, and it is shown that if an (n ,M )1 code is abnormal, then M ⩾96 相似文献
6.
Formulas are derived for the error probability of M -ary frequency shift keying (FSK) with differential phase detection in a satellite mobile channel. The received signal in this channel is composed of a specular signal, a diffuse signal, and white Gaussian noise; hence, the composite signal is fading and has a Rician envelope. The error probability is shown to depend on the following system parameters: (1) the signal-to-noise ratio; (2) the ratio of powers in the specular and diffuse signal components; (3) the normalized frequency deviation; (4) the normalized Doppler frequency; (5) the maximum normalized Doppler frequency; (6) the correlation function of the diffuse component, which depends on the normalized Doppler frequency and the type of the antenna; (7) the number of symbols; and (8) the normalized time delay between the specular and diffuse component (t d/T ) where 1/T is the symbol rate. Except for T d/T , all normalized parameters are the ratios of the parameter value and symbol rate. The Doppler frequency depends on the velocity of the vehicle and the carrier frequency. The error probability is computed as a function of the various parameters. The bit error probability is plotted as a function of signal-to-noise ratio per bit and other system parameters 相似文献
7.
The asymptotic (M →∞) probability of symbol error P e,m for M -ary orthogonal modulation in a Nakagami-m fading channel is given by the incomplete gamma function P (m , mx ) where x =In 2/(E b/N 0) and E b is the average energy per bit. For large signal-to-noise ratio this leads to a channel where the probability of symbol error varies as the inverse m th power of E b/N 0. These channels exist for all m ⩾1/2. The special case of m =1 corresponds to Rayleigh fading, an inverse linear channel 相似文献
8.
On the Hamming distance properties of group codes 总被引:1,自引:0,他引:1
Forney G.D. Jr. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1992,38(6):1797-1801
Under certain mild conditions, the minimum Hamming distance D of an (N , K , D ) group code C over a non-abelian group G is bounded by D ⩽N -2K +2 if K ⩽N /2, and is equal to 1 if K >N /2. Consequently, there exists no (N , K , N -K +1) group code C over an non-abelian group G if 1<K <N . Moreover, any normal code C with a non-abelian output space has minimum Hamming distance equal to D =1. These results follow from the fact that non-abelian groups have nontrivial commutator subgroups. Finally, if C is an (N , K , D ) group code over an abelian group G that is not elementary abelian, then there exists an (N , K , D ) group code over a smaller elementary abelian group G '. Thus, a group code over a general group G cannot have better parameters than a conventional linear code over a field of the same size as G 相似文献
9.
A low-complexity pseudo-analog speech transmission scheme is proposed for portable communications. It uses a speech coder based on adaptive differential pulse code modulation (ADPCM) in combination with a multilevel digital modulation technique such as M -ary DPSK or M -ary FSK and features low quantization noise, bandwidth efficiency, and robustness to transmission errors. A nonsymmetric M -ary DPSK scheme called skewed M -ary DPSK is proposed to enhance the noisy channel performance. Comparison to conventional analog FM and a digital speech transmission scheme using adaptive predictive coding and forward error correction (FEC) based on convolutional coding shows that the pseudo-analog system has the best objective signal-to-noise ratio performance under most channel conditions. Informal subjective evaluations rate the digital system superior to the pseudo-analog scheme for bad channels and conversely for good channels. It is concluded that the pseudo-analog system can be designed with low delay and high speech quality for good channels with high spectral efficiency 相似文献
10.
Error probability analyses are performed for a coded M -ary frequency-shift keying system (MFSK) using L hops per M -ary word frequency-hopping spread-spectrum waveforms transmitted over a partial-band Gaussian noise jamming channel. The bit error probabilities are obtained for a square-law adaptive gain control receiver with forward-error-control coding under conditions of worst-case partial-band noise jamming. Both thermal noise and jamming noise are included in the analyses. Performance curves are obtained for both block codes and convolutional codes with both binary and M -ary channel modulations. The results show that thermal noise cannot be neglected in the analysis if correct determinations of the optimum order of diversity and the worst-case jamming fraction are to be obtained. It is shown that the combination of nonlinear combining, M -ary modulation, and forward-error-control coding is effective against worst-case partial-band noise jamming 相似文献
11.
A formula is derived for the error probability of M -ary phase-shift keying (PSK) in the satellite mobile channel when the signal is accompanied by a pilot tone which is used in the receiver for coherent detection of the signal. The author computes the error probability as a function of the signal-to-noise ratio, the ratio of powers in the specular and diffused signal component, the ratio of bandwidth in the pilot tone and signal extraction filters, and the numbers of symbols, i.e. M , while optimizing the ratio of powers in the pilot tone and signal. He computes results when the diffused component is not delayed with respect to the specular component, as well as for the opposite case, i.e. when the symbol in the diffused component is independent of the symbol in the main component 相似文献
12.
It is shown that for worst-case partial-band jamming, the error probability performance (for fixed E b/N I) becomes worse with increasing M for (M >16). The asymptotic probability-of-error is not zero for any E b/N I(>ln 2), but decreases inverse linearly with respect to it. In the fading case, the error-probability performance (for fixed E b/N 0) improves with M for noncoherent detection, but worsens with M for coherent detection. For large E b/N 0 the performance of the Rayleigh fading channel asymptotically approaches the same limit as the worst case partial-band jammed channel. However, for values of M at least up to 4096, the partial-band jammed channel does better. While it is unlikely that an M -ary orthogonal signal set with M >1024 will be used in a practical situation, these results suggest an important theoretical problem; namely, what signal set achieves reliable communication 相似文献
13.
Baseband pulse shaping is proposed to improve the performance of M -ary FSK with limiter discriminator integrator detection in a satellite mobile channel. Numerical results obtained for binary, quaternary, and octonary signaling with a Gaussian and a third-order Butterworth IF filter indicate that pulse shaped signals perform significantly better than frequency shift keying (FSK) signals. The error rate floor in the presence of a Doppler shift is also analyzed. Numerical results indicate that the error rate floor of pulse-shaped signals is significantly lower than that of FSK signals 相似文献
14.
Wang Q. Gulliver T.A. Bhargava V.K. Felstead E.B. 《Communications, IEEE Transactions on》1990,38(10):1786-1798
The performance of fast-frequency-hopped M -ary frequency-shift keying with a fixed hop rate is evaluated, utilizing the Chernoff union bound method. The performance criterion used is a throughput measure i.e., an information rate sustained by a system for a given bit error rate, normalized by the hop rate. Both uncoded and coded systems are considered. It is shown using the cutoff rate argument that coding can provide a few dB gain in throughput. This is confirmed by the performance evaluation of various convolutional and block codes. Both partial-band noise jamming and multitone jamming with one tone per M -ary band are considered. Jamming parameters are assumed to be the worst case against the coding channel. Determination of the optimum M is also addressed 相似文献
15.
Gutman M. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1989,35(2):401-408
The decision problem of testing M hypotheses when the source is K th-order Markov and there are M (or fewer) training sequences of length N and a single test sequence of length n is considered. K , M , n , N are all given. It is shown what the requirements are on M , n , N to achieve vanishing (exponential) error probabilities and how to determine or bound the exponent. A likelihood ratio test that is allowed to produce a no-match decision is shown to provide asymptotically optimal error probabilities and minimum no-match decisions. As an important serial case, the binary hypotheses problem without rejection is discussed. It is shown that, for this configuration, only one training sequence is needed to achieve an asymptotically optimal test 相似文献
16.
Consideration is given to the problems related to the design of M -ary continuous-phase frequency-shift keying (CPFSK) systems with modulation index h =J /M , combined with eternal rate r binary convolution encoders. The following questions are raised and answered: (1) how should different encoder-modulator systems be compared and how can comparable systems be recognized from the system parameters, i.e. M , h , and r ?; (2) what are the limits on the information rate per unit bandwidth, versus signal-to-noise ratio, when reliable transmission is required?; (3) how does one choose the system parameters M , h , and r when the overall system has to achieve a specified performance?; and (4) how does one design the external rate r binary convolutional encoder to put in front of the M -ary CPFSK modulation system with h =J /M ? A simple approximation for the bandwidth of a CPFSK signal is given and shown to be sufficiently accurate for system design purposes. The design of the external convolutional encoder is carried out in a novel way that leads to fewer states in the combined encoder-modulator system and thus yields improved performance for a given demodulation-decoding complexity compared to previous approaches for the design of coded CPFSK systems 相似文献
17.
Wende Chen Honkala I.S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1990,36(3):664-671
The authors prove combinatorial lower bounds for K q (n ,R ), the minimal cardinality of any q -ary code of length n and covering radius R . Tables of lower bounds for K q(n ,R ) are presented for q =3, 4, 5 相似文献
18.
It is shown how to derive formulas for the error probability for M -ary differential phase shift keying with differential phase detection (DPD) and M -ary frequency shift keying with DPD, limiter-discriminator detection and limiter-discriminator-integrator detection in the satellite mobile channel (SMC) with narrowband receiver filter if such formulas are available for the Gaussian channel. The modification of the formulas involves only a redefinition of the noise power and autocorrelation function. Since the SMC contains as special cases the land mobile (Rayleigh) channel and the Gaussian channel, the derived formulas are valid for these channels as well. In fact the formula for the land mobile channel is in many cases reduced to a closed form, which does not contain an integral. The author computes the error probability for the four systems, and compares their performance assuming a third-order butterworth filter and M =2,4,8 symbols 相似文献
19.
An expression is derived for the error probability of M -ary frequency shift keying with a limiter-discriminator-integrator detector and a narrowband receiver filter in the satellite mobile channel. This channel contains, as special cases, the Gaussian and Rayleigh (land mobile) channels. The error probability is computed as a function of various system parameters for M =2, 4, 8 symbols and a third-order Butterworth receiver filter 相似文献
20.
Honkala I.S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1991,37(4):1203-1206
The concept of a (k , t )-subnormal covering code is defined. It is discussed how an amalgamated-direct-sumlike construction can be used to combine such codes. The existence of optimal (q , n , M ) 1 codes C is discussed such that by puncturing the first coordinate of C one obtains a code with (q , 1)-subnorm 2 相似文献