The Novel Frequency Hopping Multiple-Access Systems And Applications In Smart Grid

Frequency-hopping (FH) is one kind of spreading spectrum (SS) communication technologies, where the frequency is hopped randomly from one slot to another within a wide range of spectrum. FH is also considered as a code devision multiple access (FH-CDMA, or FHMA) technology, in which the entire spectrum is seprated and assigned to the different users by using their presigned hopping codes. Due to the inherent advantages of FH technology, such as anti-fading, anti-jamming, multiple-access capacity and so forth, it is desired to combining the FH technology with the exisiting communication system to form novel hybrid communication systems with high security and good performance. One of main insterets in our paper is to design a novel hybrid FH system which could meet the demands in future communication systems. It it well known that multiple-access interference (MAI) is the predominant factor reducing the CDMA system performance. Thus, another interest of our paper is to analysis the performance improvement of FHMA systems with a general orthogonal hoppin sequence. Finally, based on security and QoS requirements, the FH technology is firstly proposed for the wireless transmission scheme in a promising power grid——smart grid. The infrastuacture of the proposed network and the specific FH sequence code, which are suitable to the smart grid, are designed in our paper.In high-speed wireless communication systems, the orthogonal frequency devision multiplex (OFDM) is considered as one of most promisisng technologies due to its advantages of anti-fading and compressing inter-symbol interference. Based on the advantages of FH and OFDM, a novel FHMA system named OFDM-FHMA system is proposed in our paper. The phase shift keying (PSK) modulation and coherent demodulation scheme are usually adopted in this system for the small spectrum width and the low error probability.The study of OFDM-FHMA system in this paper includes the following three sub-parts. Firstly, the theoretical performance of synchronous OFDM-FHMA system with maximum ratio combining (MRC) diversity technique is analysed over AWGN and slow Rayleigh channels. The theoretical results show the relationship between the error rate and other parameters, such as the number of users, the order of diversity, the number of frequency slots and so forth. Our results provide the performance criteria for designing the OFDM-FHMA system. Secondly, due to the presence of AWGN in carrier recovery loop (e.g., phase-locked loop) and the random hopping of the frequency, the resulting steady-state phase error is appreared definitely. The effect of phase error on the OFDM-FHMA system is analysed. MRC diversity technique is proposed in this system to compress the effect of phase error. Finally, the theoretical performance of OFDM-FHMA system with quasi-synchronization multiple-access scheme and random hopping pattern is studied. In order to reduce the MAI effectively, a novel general orthogonal hopping sequence, e.g. no-hit zone (NHZ) code, is proposed into the system. The error probability of the system with the following three classic hopping sequences, i.e., random pattern, NHZ code and Reed-Solomen code, are presented respectively for various multiple-access delays by using the simulation method. Through above three parts of research, the related issues of OFDM-FHMA system have been addressed throughoutly.Most of researches on the theoretical performance of FHMA systems employ the completely random hopping pattern; however, the performances (or MAI) of such systems are uniquely restricted by the size of the frequency slots, which imply that more slots, better performance. It should be noted that the frequency slots could not be incresead without any limitation in wireless communications. Thus, to employing the hopping sequence with the idea Hamming properties in the FHMA system is one of most effective methods to reduce the MAI. In our paper, we propose the NHZ code for the MFSK/FHMA system. Based on the specific NHZ properties, the MAI of MFSK/FHMA-NHZ systems are derived detailedly when the delay is restricted within or slight-outside the no-hit zone. Then the decision variable of the non-coherent MFSK/FHMA-NHZ system is presented, which is utilized to estimate the error probability through semi-analytic Mente Carlo simulations. Subsequently, the theoretical bit error rate (BER) of quasi-synchronous BFSK/FHMA-NHZ system is derived by characteristic function method. The BER expression is the function of cross-correlation value of NHZ code, the relative delay and other system parameters. For comparison, the performance of MFSK/FHMA system with Markov hopping pattern is analyzed as well.Smart grid has been considered as a promising technology in the next generation electric power system, which can smoothly integrate advanced sensing technologies, automated control methods and modern communication technologies into the power grid to address the issues introduced in the exiting power grid. Security and quality-of-service (QoS) are two critical issues in smart grid communication networks. Considering the security in FH technology, we design a novel physical-layer infrasctructure of smart grid communication, which is named the FH-based smart grid communication system. Based on the characteritics of useful data in smart grid, the specific transmission scheme, which occupies small portion spectrum, is proposed in our paper. By using the real measurement, the statistic characteristics of the data collected from power grid is modeled as a general Poisson process. In addtion, to realize the multi-level QoS requirement, we propose a new hopping sequence set, which has multi-level of cross-correlation properties. A design algorithm of sequence set with two-level cross-correlation properties is presented. Finally, by using the proposed sequence set and data model, the theoretical BER of the FH-based smart grid communication system with BFSK modulation over slow Rayleigh fading channel is derived. For reducing the complexity of computation, we use the note of the average hit rate to approximate the real hit rate of the specific sequences. In a word, some critical issues in FH-based smart grid communication network, such as, communication requirements, transmission scheme, sequence design, system performance and so forth are throughoutly analyzed. Moreover, the real simulation and numerical results verify that the FH technology could smoothly integrate with smart grid.