Research On Uplink Key Techniques In Mobile Communication Sysytems

In next generation mobile communication systems, like Super 3G and B3G/4G, Single Carrier-Frequency Division Multiple Access (SC-FDMA) and Cooperative Communication are the two key uplink techniques. As the uplink multiple accessing scheme of Super 3G, SC-FDMA system has Peak-to-Average Power Ratio (PAPR) as high as 6dB in mean, which has a very bad impact on the lasting time of handset battery. In B3G/4G uplink transmitting systems, multiple antennas technique is hard to implement for the size limitation of handsets. As an alternative technique, cooperative technique has attracted many researchers. How to allocate power and how to improve relay users’QoE (Quality of Experience) are two urgent problems in B3G/4G cooperative communication.In order to reduce the PAPR, spectrum shaping is the most frequently used method recently. This method can only reduce the PAPR to 5dB in mean, and even increase the BER. However, this paper proposes a new method based on statistic companding. The proposed method is the first method which combines the statistic feature of SC-FDMA transmitting signal and companding technique. The research result shows the proposed method can not only effectively reduce the PAPR of SC-FDMA to 2dB, but also reduce the BER to a quarter of its original value. The proposed method can be a better choice for PAPR reduction scheme in LTE standardization.In B3G/4G cooperative communication, threshold average allocation is the most frequently used power allocation method. This method doesn’t take the realistic channel state into consideration, so the threshold may not match the channel state. However, this paper proposes a new method based on MCPA threshold, which can not only adapt all kinds of channel state, but also improve the outage probability performance in bad channel state. The proposed method can be a better choice for B3G/4G systems.Furthermore, in cooperative communication, the improvement of source user’s QoE is at the price of decaying of relay uses’QoE. Through searching, we find that nobody has been considered the QoE problem for relay uses. However, this paper proposes Cooperative Contribution to evaluate the contribution relay uses have done at the price of decaying their batteries. Then this paper proposes a power allocation method based on Battery Contribution Power threshold and Battery Remain Power threshold, in order to reserve sufficient power for relay uses’own communication demands. The phrase and method proposed improve QoE of relay uses, which can be used in B3G/4G uplink systems.The future research can be focused on two aspects. First, in SC-FDMA systems, research how the A/D precision impacts the performance of the proposed PAPR reduction method. Second, optimize the proposed power allocation method in cooperative communication systems.