The Oversaturated Complex-valued Orthogonal Multiplexing System:a High-Efficiency Extend Of The Traditional Orthogonal Multiplexing System

Mobile communication can provide a reliable service at any palace with any person with a low price. With the kernel technology of TDMA (Time Division Multiple Access), the Second Generation Mobile Communication System uses the digital cellular technology with the core business of transmitting voice signal. The Third Generation Cellular Communication System based on the CDMA (Code Division Multiple Access) technology had increased the system capacity and elevated the rate of voice and data signal. OFDM (orthogonal frequency division multiplexing) Technique is the key technology of the LTE (Long Time Evolution) project which is proceeding in a full swing just now. The LTE project is famous as its high spectrum efficiency and high transmission rate.TDMA and orthogonal CDMA system belongs to a Multiple Access system and the OFDM is a technique of Multi-Carrier Modulation. Though they belong to different kinds of knowledge, they all use the orthogonal technique, so we conclude the TDMA, CDMA and OFDM as the Orthogonal Multiplexing System. In this paper, we also give the mathematic model of the Orthogonal Multiplexing System. As we all know the advantage of the Orthogonal technique:enhance the spectrum efficiency; decrease the multiuser interference; increase the system capacity; ease the near-far effect; lower the complexity of the receive, but at the same time, the system capacity is limited strictly. If using the non-orthogonal technique, the system capacity can be extend easily without the strength of orthogonal technique. There might be a badly multiuser interference, so it needs a strict power control and a more complicated receiver. In this paper, we propose a hierarchical tree structure to produce new carriers for the oversaturated users by simple addition of the existing carriers. These systems do not need any changes on the hardware, then they can get a nearly twice oversaturated system capacity with a certain transmission efficiency. At this time, though the carrier matrix is not completely orthogonal, it retains a certain mutual information, so that the signal can be correctly detected in the receiver.Multiuser detection effectively uses the mutual information between the users, rather than simply take the multiple access interference as a noise, so it has a good performance than the traditional detector. Though the optimal multiuser detector has the most minimum error probability, but due to its exponential growing computational complexity, this kind of detection can not be used in the system with a larger number of users. Then variety of sub-optimal multiuser detection have been proposed based on different optimal algorithm with a low complexity, which is equivalent to a balance between the algorithm complexity and precision of detection. Some scholars have also put forward some optimum multiuser detection algorithm with a polynomial complexity for some multiple access system with some special features. This paper proposes a polynomial complexity optimal multiuse detector for the proposed oversaturated orthogonal multiplexing system, making it possible of the optimal multiuser detector.