Since digital video broadcasting via satellite (DVBS) signals are “inefficient”, regarding the amount of information they convey on the bandwidth they occupy, a joint broadcasting and ranging system would constitute a unique platform for future digital video broadcasting satellite services effecting the essential tasks of satellite navigation system and direct to home (DTH) services, in terms of both spectrum efficiency and cost effectiveness. In this paper, the design of dual frequency Mary position phase shift keying (MPPSK) system which is suitable for, respectively, performing both data transmission and range measurement is proposed. The approach is based on MPPSK modulation waveforms utilized in digital video broadcasting. In particular, requirements that allow for employing such signals for range measurements with high accuracy and high range are investigated. Also, the relationship between the frequency difference of dual frequency MPPSK system and range accuracy is discussed. Moreover, the selection of MPPSK modulation parameter for data rate and ranging is considered. In addition to theoretical considerations, the paper presents system simulations and measurement results of new systems, demonstrating the high spectral utilization of integrated broadcasting and ranging applications.
Direct to home (DTH) services via satellite are particularly affected by power limitation, which weakens its ability of antinoise and antiinterference. Traditionally, power limitation is the main design objective rather than spectrum efficiency, so DVBS system uses QPSK modulation [
Compared to EBPSK [
In the paper, a dual frequency MPPSK system is creatively proposed to overcome the ranging ambiguity. At the same time, the system is used for the digital video broadcasting satellite services. Such a kind of platform would offer unique possibilities for novel system concepts and applications. Even more important, by using the dual frequency MPPSK waveform for both applications, the occupied spectrum would be used very efficiently and both applications could be operated, respectively, which would guarantee availability of both functions, and help to partially overcome the limitation of spectral resources. Such a system will provide two functions on a single hardware platform of MPPSK modems.
The rest of this paper is organized as follows: Section
The modulated MPPSK signals are defined by [
4 PPSK modulated waveforms.
The modulation waveform for symbol “0” is sinusoidal wave as shown in Figure
MPPSK modulation generator is a new analogdigitalmixed type. Pulse train MPPSK modulator is illustrated by [
Block diagram of pulse train MPPSK modulator.
The next step is to explain the processes more clearly, and the output of a sinewave oscillator with frequency
The impacting filter (IF) is a special digital infinite impulse response (IIR) filter, with the feature of “notchfrequency selection” in an extremely narrow passband [
Consider
Block diagram of source, modulated signal, amplitude impacting, and envelope of amplitude impacting.
The coefficient for the
Nonzero symbols, that is, “1” to “
Dual frequency CW ranging technique can compute very adequate fine range resolution [
Solving for
Such a system with zerointermediate frequency (ZIF) receiver is shown in Figure
Block diagram of a CW Ranging system with single frequency.
After heterodyning (mixing) with the carrier frequency, the phase difference between the two received signals is
Again
Broadcasting and ranging transmitter equipment is mainly composed of two pulse train MPPSK modulation generators, as shown in Figure
Block diagram of broadcasting transmitter equipment.
Two working modes are designed which depend on the original data source. For digital video broadcasting, the data rate and the bit error rate (BER) are the most stringent parameters. Pulse train MPPSK modulator 1 transmits MPPSK signals, which is efficient regarding the amount of information they convey on the bandwidth they occupied. And pulse train MPPSK modulator 2 will stop working when satellite is particularly affected by power limitations.
For the ranging function, the waveform should be robust against interference, noise, and distortion due to multipathpropagation. The pulse train MPPSK modulator 1 transmits MPPSK signals, which are modulated by the original data symbol “1” constantly and is sinelike waveform. Pulse train MPPSK modulator 2 transmits CW, which may be considered to be a special kind of MPPSK signals, the system signals are denoted by
Consider
Consider
Broadcast and ranging reception equipment is made by two kinds of receivers, and one is mainly composed of phase discriminator (PD), and the other is mainly composed of variable bit rate MPPSK (VBRMPPSK) demodulation. As shown in Figure
Block diagram of dual frequency demodulation receiver.
Not only the employed waveform but also the general parameters have to be chosen according to the requirements derived from both applications. For broadcasting, digital video signals are demodulated by VBRMPPSK demodulator alone. From (
For ranging, theoretically, the maximum unambiguous range of MPPSK system must correspond to
Due to the increase in carrier frequency
In this section, the performance of the proposed dual frequency MPPSK system is simulated. Firstly, we consider the dual frequency MPPSK system shown in Figures
Simulation parameter for ranging.
Parameter value  

Carrier frequency: 

Modulation: 

Modulation parameter: 

Receiver distance: 600 km 
As shown in Figure
The PSD of MPPSK ranging signal.
The simulation experiment is in the AWGN channels (
Simulation the rough range value.
From Figure
The simulation result and CR bound.
We also consider the system shown in Figures
Simulation parameters for broadcasting.
Parameter value  

Carrier frequency 

Modulation 

Modulation parameters: 

bit rate: 300 Mbps 
Figure
The PSD of 8PPSK and QPSK.
Figure
Comparative SER results of 8 PPSK, dual frequency 8 PPSK, QPSK and 16QAM.
The result of the dual frequency MPPSK system and single frequency MPPSK system just have less than 1 dB difference in order to obtain the same SER performance, which is caused by the detection method and the selection of the decision threshold in the simulation. Simultaneously, research on the optimal modem method is underway; the system performance still has room for improvement.
The SER performance of the dual frequency MPPSK system is better than that of QPSK in such case, and its occupied bandwidth is much narrower than QPSK. QPSK tries to spread as much power as possible to the sidebands. On the opposite side, MPPSK allocates most power in the carrier to keep sideband energy emissions negligible, and dual frequency MPPSK system also provides an augmentation service, that is, the ranging function. After data integration between PD receiver and VBRMPPSK demodulator, system would provide high precision ranging and extend maximum unambiguous range as well. The dual frequency MPPSK system is illustrated in block diagram, which is advantageous MPPSK signal generator and integrated receiver architecture, PD and impacting filter that essentially determine dual frequency signal demodulation are emphasized in the paper and correlation receiver distance simulation are made. The future work will continue with the research on dual frequency MPPSK system, including selection and combinations of other impacting filter and ranging algorithms. Different channel environment profile, as well as channel coding will be further considered.
The authors thank all of the reviewers for their valuable comments, which have considerably helped in improving the overall quality of the work presented in the revised paper. This work was supported by the National Natural Science Foundation of China (61271204).