Investigation of Disturbances in Power Line Communications
In this thesis we investigate disturbances in Power Line Communications that influence data throughput of an orthogonal frequency-division multiplexing (OFDM) based transmissions. We found that data throughput is degraded not only because of low layer problems such as noise or interferences, but also because of high layer problems such as data packet size and the usage of a repeater in between a transmitter and a receiver. The first low layer problem considered in this thesis is Narrow-band Interference (NBI). We proposed an NBI model that is based on statistical properties. We proposed a QPSKOFDM coded modulation that performs well to combat the NBI. We also designed a new simple block code, called permutation code plus (PC+), to be concatenated with a Reed-Solomon (RS) code. Our proposed concatenated error-control code has a lower decoding complexity than the concatenation between RS and Convolutional Code (CC), used in the G3-PLC technology - one of the current OFDM based PLC technologies, while providing comparable error rate level (or performance), for hard decision decoding, in combating the NBI. The second low layer problem of interest in this thesis is impulsive noise (IN). We proposed a way to turn a parametric threshold based IN mitigation scheme into a nonparametric one. We proposed a new simple IN mitigation scheme, called replacement scheme, which delivers a better performance than the known clipping scheme. We also showed that our proposed joint clipping-replacement-nulling scheme delivers the best performance among all simple IN mitigation schemes. Furthermore, we introduced a new idea of combining existing simple IN mitigation schemes. This new combined scheme has a property that cannot be found in the traditional joint IN mitigation scheme, such as the clipping-nulling scheme. It guarantees to deliver the best performance of its individual combined schemes. Beside non-iterative IN mitigation schemes mentioned before, we proposed modifications on the Mengi-Häring iterative IN mitigation scheme that improve significantly the error rate level. We investigated G3-PLC technology performance based on a field trial test conducted in Hamburg (Germany), and identified the high layer problems mentioned before, that inuence its data throughput. We found that in order to have a good data throughput, big size packet transmission must be used instead of small packet size transmission. We also found that the location of a repeater in between a transmitter and a receiver plays an important role. The lack of knowledge to find a good location for a repeater results in data throughput degradation.