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A very high bandwidth efficiency of wireless transmission of digital modulation design

In Electronic Infomation Category: A | on April 13,2011

Existing analog channels in order to improve data transmission efficiency under various transmission technology is widely used, and HCPL-0501 datasheet and explore new to increase the bandwidth by compressing data transmission efficiency of the method of much attention. In recent years, very small frequency shift keying (VMSK) modulation technology developed rapidly, the bandwidth efficiency has reached 15 bit / (s Hz). 2001, Sayhood KH and HCPL-0501 price and nan proposed adoption of a new class of sine wave modulation VMSK, this VMSK higher bandwidth efficiency, higher SNR and HCPL-0501 suppliers and lower bit error rate. The smallest difference keying waveform (VWDK) is the class of sine wave modulation from the VMSK; development onwards, an ultra narrowband (UNB) carrier modulation techniques. It does this by regulating the parameters of a waveform, the bandwidth efficiency and to achieve a compromise between demodulation performance. Based on the VWDK

-Depth study of principles, theory and simulation results show the consistency, which proves the feasibility of utilization of VWDK high frequency band, and gives VWDK transmission system design.

1 VWDK Theory and Simulation

1.1 VWDK modulation theory sources

To improve bandwidth efficiency, it is necessary to transmit a higher frequency in the unit of digital rates. The narrowest bandwidth of the signal form is a sine wave. A pure sine wave, is a non-zero in the frequency domain spectral lines, a high concentration of energy, in theory, the bandwidth is 0, of course, can not pass any useful information. Assuming that the sine wave frequency remains unchanged, a slight jitter waveform, its energy spectrum is still highly concentrated in the carrier frequency of the spectrum, but both sides will appear with random jitter corresponding continuous spectrum, in addition to the harmonics at the carrier frequency discrete spectral lines will appear, this is the result of signal analysis. Relatively small because the jitter waveform, continuous spectrum and discrete spectrum of harmonic energy well below the carrier frequency energy. If the carrier wave is controlled by the small jitter of useful information, you can achieve high spectral efficiency modulation. Therefore, "the smallest difference keying waveform" (Very-minimum Waveform. Difference Keying referred VWDK) the resulting high-modulation.

1.2 VWDK Modulation Theory and Implementation

VWDK is the probability of binary information such as the minimum waveform difference keying modulation technique. Principles are summarized as follows: encountered logic "1" to send in the time interval T, the waveform g1 (t), while the encounter logic "0", then sent within T wave g2 (t). Which, g1 (t) = g (t, ), g2 (t) = g (t, T,-), g (t, ) defines the waveform shown in Figure 1.

Figure 1 VWDK waveform model

Where, T is the signal waveform of the cycle, but also the information symbol symbol width and width; and f = 1 / T was the signal waveform frequency, the value is also equal to the symbol transmission rate; waveforms in two segments are defined, each half cycle sine wave is class, but the magnitude was, a period of 2 and 2 (T-).

1.3 VWDK and simulation of the power spectrum map

Power spectrum modulation signal directly determines the transmission bandwidth and bandwidth efficiency. If so = ? T, and " ? "as a waveform control parameters directly affect the VWDK power spectrum of the modulated wave shape and the corresponding transmission bandwidth. When the ? 0, wave energy has been transferred more and more decentralized, more and more wide-bandwidth; and when ? 1, has been transferred more and more concentrated wave energy, bandwidth narrowing. Expression of the power spectrum, such as type (2) as shown in Figure 2 is to take different values ??VWDK modulated wave power spectrum estimation.

Figure 2 ? time in the 0.2-0.9 and simulation of the power spectrum VWDK map

2 VWDK transmission system

VWDK transmission system is divided into Modulation and demodulation system, respectively, as shown in Figure 3 and Figure 4. Modulation system works: the sender directly from the expression in Figure 1 has been transferred within a period of the waveform g (t, T) and g (t, T-) for discrete samples stored in memory in advance, and then want to transfer under the control of the information sequence provided in accordance with the sampling frequency of the clock generator to select the corresponding g (t, ) or g (t, T-) waveform samples; selected modulation waveform filtered by the filter, directly from the DAC into a modulated wave output of the simulation.

Figure 3 VWDK modulation system

Figure 4 VWDK demodulation system

Demodulation system works: distortion VWDK received signal amplified by the necessary converted into digital signals by the ADC, digital filtering through the inverse filter, the demodulator into coherent, complete the corresponding "0", " 1 "sequence demodulation

3 Numerical Analysis

The VWDK is a carrier modulation, the information rate can be equal to the carrier frequency, in theory, the RF carrier frequency can be achieved. Even in the relatively easy processing on the IF, it can get tens of kb s-1, hundreds of kb s-1 transmission rate. Bandwidth efficiency, that is, the unit band digital transmission rate, in units of b / (s Hz). If the signal frequency f = 1 / T = 15 kHz, the digital rate of 15 kb s-1, if the signal bandwidth of 200 ~ 300 Hz, the bandwidth efficiency = digital rate / bandwidth, the bandwidth efficiency can be achieved 50 ~ 75 bit / (s Hz). When f = 20 kHz, the modulation efficiency can be 100 bit / (s Hz), even higher.

4 Conclusion

VWDK is a carrier modulation, the information rate can be equal to the carrier frequency, and because the transmitted signal waveform is very close to sine wave, a very narrow bandwidth, can achieve high-speed data transmission over narrowband. Since the sender directly to the digital modulation waveform samples by D / A conversion output, while the receiver directly through the A / D output, after demodulation, the system for full digital processing and easy integration. For VWDK modulation, just change a parameter, you can control the signal bandwidth, and the same modulation and demodulation, system control flexibility. Although VWDK modulation efficiency can be greatly improved than in the past, with a wide range of applications.

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