###### Abstract  
Power line communication (PLC) is an important interconnection technology for the smart grid, but the robustness of PLC transmission is faced with a great challenge due to strong non-Gaussian noise and interference. In this paper, a narrowband interference (NBI) resistant preamble is designed, and an effective timing and frequency synchronization method is proposed for OFDM-based PLC systems in the smart grid, which is capable of simultaneously conveying some bits of transmission parameter signaling (TPS) as well. In the time domain, the cyclic extension of the training OFDM symbol is scrambled, which makes it feasible to combat against NBI contamination. More accurate timing detection and sharper correlation peak can be implemented under the power line channel and the AWGN channel in the presence of NBI, compared with the conventional [PERSON]'s and [PERSON]'s methods with the same preamble length. Furthermore, the TPS transmitted using the proposed method is also immune from the NBI. The proposed method is capable of improving the synchronization performance of the PLC transmission significantly, which is verified by theoretical analysis and computer simulations. p 202  
there have been some methods that are aimed at preamble design and synchronization. The cyclic prefix (CP) is utilized in [15] to implement the classical sliding auto-correlation (SAC) method. A preamble design structure with two identical sequences, which was applied in WLAN IEEE 802.11g [1] and WMAN IEEE 802.16e [19], was proposed by [PERSON] [16]. However, a broad plateau around the correct timing position would be generated in the result of the SAC using [PERSON]'s design, so it is difficult to estimate the accurate timing position. To solve this problem, a preamble structure as denoted by \([\mathbf{A}\ \mathbf{A}-\mathbf{A}-\mathbf{A}]\) was proposed by [PERSON] et al. to cut down the plateau and sharpen the peak of the SAC results [17]. However, [PERSON]'s design would cause several sub-peaks in the SAC result, which makes it highly probable to obtain false detection when the signal-to-noise ratio (SNR) is small. Moreover, commonly, there exists prevailing intensive NBI, contaminating the channel of OFDM systems, having serious impacts on the system stability and effectiveness [20]. Unfortunately, the state-of-the-art methods of synchronization could be seriously impacted by the NBI [21; 22]. The existing synchronization methods are neither practical nor effective as far as the NBI contamination is concerned. For instance, the impacts of the NBI on the performance of the existing synchronization methods in practical PLC channels are shown in [23]. Hence, in this context, proposing an effective preamble design as well as the synchronization method for OFDM systems impacted by NBI is in desperate need, which is one of the major contributions of this paper. In addition, different symbol constellation types and channel coding rates should be supported in OFDM systems so as to satisfy different requirements of quality of service (QoS) [24]. Exploiting the transmission parameter signaling (TPS) is a common and effective approach to facilitate the subsequent channel estimation [25], and crucial in correctly demodulating the transmitted data for the receiver. The TPS is transmitted separately following the preamble in the existing commercialized systems, such as IEEE 802.11g and IEEE 802.16e. After finishing the timing and frequency synchronization processes, then the signaling part could be handled and decoded. However, the TPS is dependent on the accurate timing synchronization, which seriously suffers from the impacts of the NBI, making the decoding of TPS inaccurate. Besides, this process is spectrum inefficient since a dedicated resource is required to transmit the TPS part following the preamble. If, as designed in this paper, the TPS is integrated into the sub-carriers of the preamble, the process of the TPS acquisition can be independent of the timing synchronization and meanwhile the NBI is mitigated.