Overlap is one of the techniques for increasing bit rate in chirp spread spectrum (CSS). Although more overlaps can offer higher data throughput, more intersymbol interference (ISI) occurs, resulting in serious bit error rate (BER) performance degradation. In this paper, we analyze the influence of the overlap on CSS systems and express the maximum number of overlapped symbols that does not incur the ISI, in terms of the chirp bandwidth and chirp duration. The analysis results are verified by BER performance simulation of direct modulation differential phase shift keying (DM-DPSK) that is a typical modulation method used in CSS.

Binary offset carrier (BOC) signal synchronization is one of the most important steps to recover the navigation data in global navigation satellite system (GNSS) including Galileo and global positioning system (GPS). The main error sources in synchronizing BOC signals are the multiple side-peaks in the BOC autocorrelation and the multipath delay. Recently, a novel correlator receiver for the BOC signal was proposed by Garin (shaping correlator receiver), which was shown to shrink the side-peaks and mitigate the multipath effect to a certain degree. However, a shaping correlator receiver cannot completely remove the side-peaks and is affected by a wider multipath delay range than that of the traditional correlator receiver. Moreover, it is applicable to only BOC(n, n) signal. In this paper, we propose a new correlator receiver for BOC signals. The proposed correlator receiver does not have any side-peak in its correlator output, and has smaller multipath delay range that incurs the tracking error than that in the shaping correlator receiver. Furthermore, the proposed correlator receiver is applicable to various types of BOC signals (i.e., BOC(kn, n)) and requires only a half of the number of the correlators used in the shaping correlator receiver.

Employing the generalized likelihood ratio test and semi-definite programming (SDP), we derive two detectors, called the SDP and maximization in the reduced space (MRS) detectors for range-spread targets with unknown Doppler shift. It is confirmed that, when knowledge of Doppler frequency is unavailable or imperfect, the proposed detectors perform better than the conventional detector. The MRS detector also outperforms the SDP and conventional detectors in some cases, including when the range-spread target is highly fluctuating.

In this paper, we propose a near maximum likelihood (ML) scheme for the decoding of multiple-input-multiple-output (MIMO) systems. By employing the metric-first search method, Schnorr-Euchner enumeration, and branch-length thresholds in a single frame systematically, the proposed technique provides efficiency that is higher than those of other conventional near-ML decoding schemes. From simulation results, it is confirmed that the proposed scheme has computational complexity lower than those of other near-ML decoders while maintaining the bit error rate (BER) very close to the ML performance. The proposed scheme, in addition, possesses the capability of allowing flexible tradeoffs between the computational complexity and BER performance.

Binary offset carrier (BOC) signal synchronization is one of the most important steps to recover the transmitted information in a global navigation satellite system (GNSS) such as Galileo and global positioning system (GPS). Generally, BOC signal synchronization is achieved based on the correlation between the received and locally generated BOC signals. Thus, the multiple side-peaks in BOC autocorrelation are one of the main error sources in synchronizing BOC signals. Recently, a novel correlation function with reduced side-peaks was proposed for BOC signal synchronization by Julien [8]; however, Julien's correlation function not only still has the side-peaks, but also is only applicable to sine phased BOC(n, n), where n is the ratio of the pseudo random noise (PRN) code rate to 1.023 MHz. In this paper, we propose a new correlation function for BOC signal synchronization, which does not have any side-peaks and is applicable to general types of BOC signals, sine/cosine phased BOC(kn, n), where k is the ratio of a PRN chip duration to the period of a square wave sub-carrier used in BOC modulation. In addition, an efficient correlator structure is presented for generating the proposed correlation function.