## 1 Introduction
For the second category, the long term evolution (LTE) system is a typical system in which dual- functional communication and positioning can be considered from the perspective of signal fusion. Because the positioning reference signal (PRS) is discontinuous in the time domain, the receiver confronts the dilemma of signal tracking, which is the major factor about the poor ranging precision [15]. To tackle this discontinuity, a time and code division orthogonal frequency division multiplexing (TC-OFDM) positioning signal is proposed to insert positioning signal into the background noise of the communication signal. Thus, dual functions of communication and positioning can be operated continuously. However, interference exists between the communication signal and the ranging signal. Besides, multi-scale non-orthogonal multiple access (MS-NOMA) scheme is another feasible strategy, in which both the communication signal and the ranging signal are modulated by orthogonal frequency division multiplexing (OFDM). The near-far effect of different positioning users can be overcome by using NOMA, and the signal orthogonality can also be guaranteed by using OFDM. However, the scheme has high computational complexity. Aiming to meet the requirements of the first category, to reduce the cost of the TT&CC network and diminish the burden of the ground segment, we proposed an integrated communication-ranging system (ICRS) in distributed spacecraft networks. Generally speaking, ISC can be completed by different modulation, while ISR can be determined by inter-satellite measurements, such as time-of-arrival (TOA), time-difference-of-arrival (TDOA), round-trip time (RTT), and received signal strength (RSS), which can be obtained from radio signals. Clock offsets among the nodes are nuisances in utilizing TOA measurements. Multiple satellites are required in using TDOA measurements. RSS has limited accuracy in long propagation distance. In asynchronized networks, RTT is a desirable method to solve the problem of clock offset [16]. The propagation time can be estimated by capturing the response frame, then the precision of RTT is restricted because of the limited frame length. However, by using a code early-late loop in the tracking section, the ranging precision of navigation systems can be reduced to the chip level. In this integrated framework, binary phase shift keying (BPSK) modulation is used in ISC, and the GNSS-like signal is used in ISR. Meanwhile, by inserting the previous local distance measurements into the data subframes, the local satellite can ensure that the opposite satellite can obtain its measurements and tracking the receiving signal at the same time. Then, the clock offset can also be estimated as a by-product in our ICRS. To the best of our knowledge, recent investigators have mainly employed PN codes to spread spectrum in both channels, with a short PN code in the communication channel and a long PN code in the ranging channel. However, in our proposed ICRS, high-speed data bits are transmitted in the Q branch of the downlink without using short PN codes. Then, the transmitting data rate can be adjusted flexibly by using the channel coding with different channel coding efficiency. For simplicity, the channel coding technology is not discussed in this paper, and the communication performance is only evaluated by the bit error rate of BPSK modulation. Therefore, a communication scheme using high rate downlink transmission without a spread spectrum is constructed. Subsequently, the relationship between ranging precision and carrier-to-noise ratio (CNR), the relationship between bit error rate (BER) and signal-to-noise ratio (SNR), and the influence of the PWDFs on the system performance are analyzed. The outline of the remainder of this paper is as follows. In Section 2, the system design, proposed algorithm, and underlying theory are presented. Simulations of the ranging precision, BER, and clock offset are described in Section 3. Finally, conclusions are presented in Section 4.