Research On Wireless Transmission Technology Of Time-frequency Coded Cooperation MC-CDMA In Mine Tunnels

In underground mine tunnels, multipath fading is much more severe than that in the terrestrial wireless channels, which would do harm to the performance of underground wireless communication. However, if the abundant resources such as space, time and frequency could be utilized efficiently and synthetically, the performance of underground wireless communication such as overlay, capacity and data rate could be improved significantly. Under the condition of wireless transmission channels and the confined space structure of underground coal mine, we can take full advantage of open spectrum resources and overcome the severe multipath fading through combining multiple carrier-code division multiple access (MC-CDMA) with cooperative diversity in up-link wireless transmission. We study the wireless transmission technology of time-frequency coded cooperation MC-CDMA in mine tunnels. The mine contributions are as follows:1. Under the condition of wireless transmission channels and the confined space structure of underground coal mine, an up-link wireless transmission schemes which combines MC-CDMA with cooperative diversity was proposed. The coded time-frequency cooperative protocol was designed, the channel capacity was derived and the bit error rate (BER) was simulated by Monte Carlo method for the proposed wireless scheme. Theoretical analysis and simulation results show that the channel capacity and BER performance for the mobile user with poor channel condition are improved significantly by the cooperation between the mobile user with poor channel condition and the mobile user with better channel condition.2. According to the banded structure of underground mine tunnels, a cooperative partner selection protocol was proposed for time-frequency coded cooperation MC-CDMA wireless transmission, which is based on the instantaneous signal to noise ratio (SNR) received by base station (BS) and the location of users. The channel capacity was computed and the BER was simulated by Monte Carlo method. It can be seen that using the proposed cooperation partner selection strategy, we can avoid sharp fluctuations of the BER and the channel capacity between BS and the target user when the target user moves far away from BS.3. Due to the channel relativity for neighboring sub-carriers, it may cause reduced transmission quality for some spread branches of mine MC-CDMA to allocate sub-carriers contiguously, which will affect the performance of wireless transmission. Therefore, a sub-optimal sub-carriers allocation scheme called sub-carriers rotary allocation was proposed, which allocates discrete sub-carriers to spread branches with fixed interval. Simulation results showed that the channel capacity of users are improved significantly with the proposed sub-carriers allocation scheme.4. A channel estimation algorithm based on discrete Fourier transform (DFT) which distribute the transcripts with different delay of the same pilot series to different users was proposed for the multiusers up-link time-frequency coded cooperation MC-CDMA wireless transmission. This algorithm can improve the utilization of pilot resources, at the same time, avoid inter-user interference. Furthermore, through selecting effective path from the impulse response in time domain of each user, in other words, neglecting the invalid path who includes more noise than channel response components, we can optimize the channel estimation algorithm. Finally, we can improve the accuracy of channel estimation. Simulation results showed that the BER performance with the proposed channel estimation algorithm for the multiusers up-link time-frequency coded cooperation MC-CDMA wireless transmission is better than that of LS channel estimation algorithm, and is close to that of ML channel estimation algorithm.The above results show that the overall wireless transmission model of time-frequency coded cooperation MC-CDMA in mine tunnels has been established successfully. And the proposed wireless transmission scheme of time-frequency coded cooperation MC-CDMA in mine tunnels can improve the wireless coverage performance, system capacity and transmission rate of underground wireless communication system through effective and comprehensive utilization of all kinds of resources in mine tunnels, for example, space, time and frequency, etc.