Research On Key Technologies Of Power Line Communication

Data communication via power line is not a new idea.The cost of power line communication(PLC)is very low since the lines are already there and widely distributed.Power line is not designed for communication,and is a challenging medium for signal transmission.It suffers from frequency-selective fading,impulsive noise and limited frequency band.Furthermore,in order to ensure low electromagnetic interference,the power and frequency bandwidth of the PLC signal are limited,which makes it hard to use power line for signal transmission.Recently,new achievements in PLC and worldwide popularization of smart grid lead to renewed interest in PLC.Some new technologies,such as multi-conductor multi-input and multi output(MIMO),PLC physical layer network coding,are applied,but the problem mentioned above are still not solved,there are still a lot of problem needed to be studied.In this thesis,the problems and key techniques mentioned above are studied.The main contributions are as follows.(1)Suppressing Co-channel interference(CCI)by spatial multiplexing is an effective method.But traditional signal multiplexing in MIMO PLC is achieved by different transmission mode.In this thesis,it is proved that spatial multiplexing can be achieved not only in different feeding paths but also in same feeding path.With this result,a co-channel interference CCI suppression method based on oblique projection for multi-conductor PLC is proposed.In this method,the oblique projection operator which maps the received signal to the signal space along the interference space is estimated based on second order statistics of the received data and the estimated channel,and then,the CCIs from different multiplex channels are able to be suppressed by the oblique projection operator.Besides,power line impulsive noise(IM)is another kind of interference which can severly corrupt power line channel.In this thesis,STBC is jointed with OFDM iterative IM suppressing method,which can further improve the performance of OFDM iterative IM suppressing method.(2)The changes of load impedance cause the varying of channel taps,which leads to more difficult in channel taps associations between adjacent time slot.In order to solve this problem,a power line channel tracking algorithm based on random finite set(RFS)is proposed.In the algorithm,the power line channel is modeled as RFS,compress sensing technique is applied to calculate the instantaneous parameters of the RFS,and the Gaussian mixture probability hypothesis density(GM-PHD)filter is emploied to tracking the parameters of the RFS.Besides,the GM-PHD filter is improved,in the Gaussian components pruning process,the components which could be generated by new birth channel taps are reserved to the next time slot,in this way,the undetection of new birth channel taps is able to be avoided.(3)In traditional physical layer networking coding(PLNC)system,the redundanrt information of channel code cannot be used by symbol detection process.In this thesis,a joint detection and decoding algorithm for two way relay physical-layer network coding PLNC in PLC is proposed.The proposed algorithm is an iterative algorithm base on belief propagation,it combines detection,PLNC and channel decoding together by a joint factor graph,and optimizes the joint factor graph by redesigned the PLNC modulation method to improve the efficiency of the belief propagation.Besides,the update rule of the nodes in the joint factor graph is designed according to the channel code and Bayesian theory.The proposed algorithm is further modified to a hard-decision algorithm,which makes a balance between the performance and computational complexity.(4)A low complexity delay and channel estimation method for frame asynchronous PLNC in PLC channel is proposed.In this method,the discrete Fourier transform extended properties are exploited to design the pilots,which makes the pilots from different nodes orthogonal in frequency domain,then delay can be estimated in frequency domain.In PLNC system,usually carrier offset cannot be compensated,thus channel and delay estimation will be corrupted by inter carrier interference(ICI).In order to suppress the ICI,first,the ICI is restricted by the estimated channel,pilots and the frequency offset,then the ICI is able to be substracted from the received signal.Operating the above two steps iteratively,the influence of ICI will be cancelled.This method can greatly reduce the computational complexity with little loss of performance.(5)In the PLC routing algorithm,there are usurally more than one nodes in each forwarding process,which increases the probability of channel conflict.In order to solve this problem,in this thesis,a physical topology routing(PTR)algorithm for PLC network is proposed.It takes both the static of the PLC network physical topology and the dynamic of the logical topology into consideration.Physical topology information is used to narrow the range of the routing,and competitive mechanism is applied for adaptively choosing relay nodes to combat the dynamic of the logical topology.Comparing to other algorithms,the PTR algorithm can reduce the number of multi-hops and the probability of conflicts.