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We investigate the bit-error rate (BER) of linear block codes. The BER is a function of the encoder realization of the code. We express the BER in terms of the weight profiles of the subspaces of the code. We also discuss the relation between the Hadamard transform and the BER  相似文献   
2.
We give a general procedure for constructing shaping codes from costly constrained graphs. The codes have finite-state encoders and sliding-block decoders. The shaping codes are in the spirit of Calderbank and Ozarow (1990), where shaping is achieved by nonequiprobable signaling on T subconstellations of a signal constellation Ω. We show how nonequiprobable signaling relates to a costly constrained channel. Khayrallah and Neuhoff developed a procedure for constructing codes with rates close to the capacity-cost function of the general cost-constrained channel, and we use their procedure to construct asynchronous (variable-length to fixed-length) shaping codes. Comparisons are made with shaping codes having comparable gain. The codes presented here are less complex and have lower peak-to-average power and lower constellation expansion ratio  相似文献   
3.
BACKGROUND AND METHODS: Trials of antidepressant medications for smoking cessation have had mixed results. We conducted a double-blind, placebo-controlled trial of a sustained-release form of bupropion for smoking cessation. We excluded smokers with current depression, but not those with a history of major depression. The 615 subjects were randomly assigned to receive placebo or bupropion at a dose of 100, 150, or 300 mg per day for seven weeks. The target quitting date (or "target quit date") was one week after the beginning of treatment. Brief counseling was provided at base line, weekly during treatment, and at 8, 12, 26, and 52 weeks. Self-reported abstinence was confirmed by a carbon monoxide concentration in expired air of 10 ppm or less. RESULTS: At the end of seven weeks of treatment, the rates of smoking cessation as confirmed by carbon monoxide measurements were 19.0 percent in the placebo group, 28.8 percent in the 100-mg group, 38.6 percent in the 150-mg group, and 44.2 percent in the 300-mg group (P<0.001). At one year the respective rates were 12.4 percent, 19.6 percent, 22.9 percent, and 23.1 percent. The rates for the 150-mg group (P=0.02) and the 300-mg group (P=0.01) -- but not the 100-mg group (P=0.09) -- were significantly better than those for the placebo group. Among the subjects who were continuously abstinent through the end of treatment, the mean absolute weight gain was inversely associated with the dose (a gain of 2.9 kg in the placebo group, 2.3 kg in 100-mg and 150-mg groups, and 1.5 kg in the 300-mg group; P= 0.02). No effects of treatment were observed on depression scores as measured serially by the Beck Depression Inventory. Thirty-seven subjects stopped treatment prematurely because of adverse events; the frequency was similar among all groups. CONCLUSIONS: A sustained-release form of bupropion was effective for smoking cessation and was accompanied by reduced weight gain and minimal side effects. Many participants in all groups were smoking at one year.  相似文献   
4.
We address the problem of finite-state code construction for the costly channel. This channel model is a generalization of the hard-constrained channel, also known as a subshift. Adler et al. (1986) developed the powerful state-splitting algorithm for use in the construction of finite-state codes for hard-constrained channels. We extend the state-splitting algorithm to the costly channel. We construct synchronous (fixed-length to fixed-length) and asynchronous (variable-length to fixed-length) codes. We present several examples of costly channels related to magnetic recording, the telegraph channel, and shaping gain in modulation. We design a number of codes, some of which come very close to achieving capacity  相似文献   
5.
The expansion factor of error-control codes   总被引:2,自引:0,他引:2  
We investigate the expansion factor Δ(C) of an (n, k, d) linear block code. Δ(C) indicates how well the code preserves and expands the distance relations of the input. We relate Δ(C) to n, k, d, the total weight, and the weight distribution, and we find bounds on Δ(C)  相似文献   
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