| With the rapid development of Internet of Things(IoT) and Machine to Machine(M2M)communication, rich application requirements for the communication system have brought great challenges to the traditional communication technology, unified standards of IoT become the urgent needs of major manufacturers. IEEE802.11 ah standard is proposed by the IEEE for IoT, M2 M application of the wireless LAN standard. It works in the Sub-1GHz unauthorized frequency bands, on the basis of the physical layer(PHY) and media access layer(MAC) of IEEE802.11 and improved to support a large number of node involvement(over 8000), a wide range of coverage(more than one kilometer), ultra-long standby(greater than one year). IEEE802.11 ah standard is still in the draft stage, and it is one of the most competitive solutions in the future field of IoT. Study IEEE802.11 ah standards can help us understand the key technologies of the IoT, well prepared for the era of IoT.This thesis started from the IEEE802.11 ah standard, researched the transmission specification and new feature of IEEE802.11 ah standard, focusing on the PHY layer of IEEE802.11 ah standard and its key technology. The main contents are as follows:(1)IEEE802.11 ah standard of the PHY layer is researched, and a transmitter baseband simulation mode which is in accordance with the standard is built. The model includes PLCP preamble sequence generating module, a scrambling module, error correction coding module, two times repeated data module, interleaving module, constellation mapping module, a fixed pilot and mobile pilot generated module, IFFT module, CP module, add window module and so on.(2)The physical layer synchronization algorithm suitable for IEEE802.11 ah standard is studied. According to the specific MCS0-rep2 model of standard, proposed the corresponding synchronization algorithm, including frame capture, coarse frequency offset estimation, fine timing synchronization, fine frequency offset estimation algorithm. In order to solve the frame capture timing metric instability problem under different signal to noise ratio, the frame capture algorithm normalized the timing metric values, thereby achieved a stable autocorrelation peak and improved the frame capture accuracy. In order to improve the frequency offset estimation range and accuracy, the frequency offset estimation algorithm took full advantage of the multiple long training sequence frame structure peculiar to standard, through combinations of two different long training sequence, and estimation and compensation by stages, to obtain better frequency offset estimation effect. Moreover, simulation analysis about the proposed synchronization algorithm is conducted. The results show that the autocorrelation peak is stable under different SNR. When the SNR is-5dB, carrier frequency offset is 40 MHz, residual carrier frequency offset is lower than 540 Hz.(3)The channel estimation algorithm of PHY layer of IEEE802.11 ah standard is analyzed. The performance of the channel estimation algorithm based on the pilot and training sequence is compared. For the MCS0-rep2 model, studied and compared the method of channel estimation based on pilot and training sequence. For the severe Doppler frequency offset under outdoor channel environment, focusing on analysis of Traveling Pilot solution mentioned by IEEE802.11 ah standard, and compared the performance of fixed guide frequency and Traveling Pilot under the Doppler frequency offset. The results show that Traveling Pilot can effectively reduce the influence of Doppler frequency offset on channel estimation.(4)The overall scheme of IEEE802.11 ah baseband receiver is proposed. The scheme is suitable for MCS0-rep2 mode, which is composed of synchronization module, channel estimation module, SNR estimation module, data repeat module, Traveling Pilot sub carrier mapping module and so on. The bit error rate performance of the receiver under different channel models and modulation coding modes is simulated and analyzed. |
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