Research On Key Techniques Of Power Line High Rate Data Communication Based On Adaptive OFDM

As a kind of widely distributed, no wiring and facilitate-connecting communication media, power line has a unique advantage and immeasurable market potential in the smart home networking and broadband access. Orthogonal Frequency Division Multiplexing (OFDM) received extensive attention in recent years, because of its advantages, such as anti-multi-path delay, anti-fading channel, high spectrum utilization, simple hardware implementation et al. Combining adaptive technologies with OFDM, will be more effective to deal with complex PLC environment, so as to realize reliable and high-speed data communication. The key problems of adaptive OFDM technology are accurate real-time channel estimation and efficient adaptive modulation and power allocation of OFDM. Based on the research on channel models, according to the transient characteristic estimation results of the user channels, this paper used dynamic allocation of data rate and transmission power to optimize the system performance effectively, and used constructed general channel simulation platform to test the performance of designed system. The main tasks are as follows:First, through analyzing the test samples of low voltage grids in different regions and different time, based on the existing transmission models, this paper proposed that particle swarm algorithm was applied to multi-path transmission model parameter identification of power line communication. That will shorten the identification time, improve the precision, and lay a good foundation for the research and design of low-voltage modulation carrier communication network.Second, it researched on implementation mechanism of adaptive OFDM communication system, discussed the system structure, OFDM signal frame structure and carrier control method, as well as analyzed system performance, and established parameter options adapted to low-voltage power line channel characteristics.Third, standard Kalman filter equations don't apply to non-linear power-line channel, extended Kalman filter's calculation is substantive, and is of high complexity. In view of these characteristics, this paper put forward non-pilot Kalman filter algorithm based on comb-pilot frequency, in which linear weighted sampling point method was used to replace Taylor formula of linear truncation method for time-domain channel estimation. At the same time, the channel correlation function of inter-carrier frequency domain and the covariance matrix of the Kalman filter estimates error were used to estimate the filtering results at the sense of the minimum mean square error (MMSE) in the frequency domain, and the joint time-frequency domain estimation algorithm was used to make further improving estimation accuracy.What's more, in the multi-user OFDM system, the realization of iterative based channel allocation and bit and power allocation algorithm is very complicated. The packet distribution method can reduce the computational complexity, but it makes the system performance degrade. According to the characteristics presented above, from the view of optimization, this article proposed that used the particle swarm optimization algorithm which has the capacity of global optimization, and combined the channel allocation with the bit allocation to implement the multi-user OFDM sub-carrier adaptive bit and power allocation in power line channel, which would save the computing time, reduce the transmission power and improve the spectrum efficiency.Finally, the situation that low voltage power line channel is complicated and changeable causes carrier communication researchers are lack of comprehensive test environment for testing and assessing the design, meanwhile the on-site testing which they rely on would influence the development speed.Due to above situation, this paper established a blocking and open architecture simulation platform with intergrating software and hardware to simulate the low voltage PLC communication channel characteristics. Taking RC passive components as the core, we built the base simulation modules of resistive, inductive or capacitive loads, and achieved different topologies by way of computer-controlled relays.It enables the users to access different channels of the simulated environment according to the specific need. Hopefully ,it can be introduced by related researchers for developing PLC communication equipments .