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Digital Modulation Techniques for Software Defined Radio Applications
Published in Rajeshree Raut, Ranjit Sawant, Shriraghavan Madbushi, Cognitive Radio, 2020
Rajeshree Raut, Ranjit Sawant, Shriraghavan Madbushi
GMSK has been widely used in mobile wireless communication due to its constant envelope signal feature, which ceases the requirement for power amplifier linearity. In this case, the phase of the carrier is instantaneously varied by “Modulating” signal. It is used as modulation standard of GSM system. It can be regarded as two-level FSK modulation with modulation index of 0.5. Jagadeesh Gurugubelli et al. have used the linear approximated GMSK in SDR environment because it gives a common I/Q modulator that can be used for all second-generation systems. The generalized parametrizable modulator for a reconfigurable radio can perform GMSK and QPSK modulations. GMSK is the underlying modulation scheme for global system for mobile (GSM) standard, while QPSK technique is the basic scheme for code division multiple access (CDMA) standard. Harada and Masayki presented SDR that can realize global positioning service (GPS) navigation system, vehicle information and communication system (VICS), electronic toll collection system (ETC), AM/FM radio broadcasting services, and FM multiplex broadcasting system. It also served modulation schemes such as BPSK, QPSK, GMSK, ASK, and π/4 QPSK. The SDR realizes simultaneous multiple services when user would like to use several communication services in driving situations.
The Pan-European Cellular System
Published in Jerry D. Gibson, The Communications Handbook, 2018
The widely employed partial response GMSK scheme is derived from the full response minimum shift keying (MSK) scheme. In MSK the phase changes between adjacent bit periods are piecewise linear, which results in discontinuous-phase derivative, i.e., instantaneous frequency at the signalling instants, and hence widens the spectrum. Smoothing these phase changes, however, by a filter having a Gaussian impulse response [6], which is known to have the lowest possible bandwidth, this problem is circumvented using the schematic of Fig. 80.8, where the GMSK signal is generated by modulating and adding two quadrature carriers. The key parameter of GMSK in controlling both bandwidth and interference resistance is the 3-dB down filter-bandwidth x bit interval product (B ■ T), referred to as normalized bandwidth. It was found that as the B ■ T product is increased from 0.2 to 0.5, the interference resistance is improved by approximately 2 dB at the cost of increased bandwidth occupancy, and best compromise was achieved for B ■ T = 0.3. This corresponds to spreading the effect of 1 b over approximately 3-b intervals. The spectral efficiency gain due to higher interference tolerance and, hence, more dense frequency reuse was found to be more significant than the spectral loss caused by wider GMSK spectral lobes.
Wireless Data
Published in Jerry D. Gibson, Mobile Communications Handbook, 2017
Allen H. Levesque, Kaveh Pahlavan
The Mobitex interface standard is maintained by the Mobitex Association, and all networks implement the same standard-base specification. Currently, Mobitex networks operate at 400–450 MHz in Europe and 900 MHz in the United States. The Mobitex protocol is a packet-switched data-only service transmitting half-duplex at 8000 b/s in 12.5 kHz channels. The multiple-access scheme is Slotted-Aloha, and useful user-data throughput is typically about half the raw transmission rate. The modulation technique is Gaussian Minimum Shift Keying (GMSK) and demodulation is noncoherent. The transmission protocol is best suited for short-burst traffic, using a maximum packet size of 512 bytes and a 24-bit address field. Forward error-correction, as well as retransmission, is used to ensure the quality of delivered data packets.
Modulation signal identification and classification based on the OA algorithm model
Published in International Journal of Electronics, 2023
Shaofei Wang, Zuliang Wang, Ting Zhang
In the field of modulators, a Gaussian minimum shift keying using in-phase and quadrature phase elements (IQ-GMSK) is a special form of continuous-phase frequency-shift keying (CPFSK) modulators (Linz & Hendrickson, 1996). With the advancements in modulation technologies, GMSK demodulators have been used in satellite communications (Govindaiah, 2012). Two categories of auto-modulation recognition algorithms have emerged in the literature, depending on the likelihood function and the feature of the received signal (Dobre et al., 2007). Wong and Asoke (2008) reported on maximum likelihood classifiers for phase amplitude modulation in coherent environments. An improved QPSK signal modulation and demodulation algorithm has been proposed by Zhou et al. (2014), who used numerical simulations to analyse the feasibility of the algorithm. Chen et al. (2016) presented a new multi-carrier joint detection algorithm exhibiting good demodulation performance for time hopping m-ary phase position shift keying (TH-MPPSK) signals. Daimei and Mathews (2016, 2017) proposed a likelihood-based Phase Shift Keying and Quadrature Amplitude Modulation signal identification algorithm in additive white Gaussian Noise channel. They showed that the modulated signal type can be accurately identified without assuming any prior knowledge of the signal or channel, especially for high-order Quadrature Amplitude Modulation. Based on the research on DBSCAN and OPTICS, a simple Automatic Modulation Classification method was proposed by Jacques et al. (2020), which is then performed in an additive white Gaussian noise channel with M-QAM and M-PSK Evaluate.
Mitigation of DME interference in LDACS1-based future air-to-ground (A/G) communications
Published in Cogent Engineering, 2018
The future communications study (FCS) (Future Communications Study Operational Concepts and Requirements Team, 2007) has preselected two technology decisions for the LDACS, specifically LDACS type 1 (LDACS1) and LDACS type 2 (LDACS2), as the most promising candidates for future aeronautical communications. LDACS1 is a broadband candidate technology using orthogonal frequency-division multiplexing (OFDM) for the future A/G and air-to-air (A/A) mode communication system (Sajatovic et al., 2009). Due to the limited amount of available spectrum in L-band, the transmission bandwidth for LDACS1 is limited to the 500 kHz spectral gap between the two adjacent distance measuring equipment (DME) channels of bandwidth 1 MHz, for each forward and reverse link (FL/RL). The frequency-division duplex (FDD) is applied to split up this limited bandwidth between FL and RL. The second choice, named LDACS2 (Fistas & Phillips, 2007), is a narrowband single-carrier technology with 200 kHz transmission bandwidth. It uses a Gaussian minimum shift keying modulation (GMSK). For duplexing, time-division duplex (TDD) is chosen. One of these two candidates (LDCAS1 or LDACS2) will be selected for deployment in aeronautical communications.