Research And Improvement On The OFDM-OVCDMA System

Sprectrum efficiency is one of the most important objectives in the design of mobile communication system in the future. Based on this reason, D.B. Li proposed a novel high data rate transmission scheme, named generalized parallel transmission based on Overlapped Multiplexing. Overlapped Code Division Multiple Access (OVCDMA) is a key technology especially. Based on introducing overlapping among adjacent symbols, which can form an encoding constraint, it can promote system's sprectrum efficiency and performance, compared with ISI free system under the condition of the same spectrum efficiency. Besides, combining conventional OFDM and OVCDMA technology originally proposed by Li in Urban Macro channel, OFDM-OVCDMA system is presented. It can cancel the adjacent cells'interference perfectly under the quasi-asynchronous condition. And the channel estimation can impact the spectrum, efficiency and system performance directly, so the research on it has great significance.This dissertation focuses on the two parts mentioned above. Some topics are covered as follow:1) Improvement of coded OFDM-OVCDMA coding systemOverlapping Code Division Multiplexing (OVCDM) is new technology based on the information theory. It can substitude the conventional coding and modulation scheme in the single user system and promote spectrum efficiency; or each user is assigned a unique code sequence and realize multi-user parallel transmission. When one channel is occupied by many sources, it's called multiplexing problem; while by many users, it's called multiple access problem. Although "multiplexing" and "multiple accesses" are different names objected to different things, they have the same essence, all about the sharing and distributing of the same channel. This dissertation focuses on the design of RS code as a pre-coding scheme and simulates them using MATLAB to test the improvement of coded OFDM-OVCDMA system's performance.2) Channel estimation of OFDM-OVCDMA systemThis dissertation introduces a new continuous broadband positive and negative LS (Loose Synchronized) code division pilot scheme. Broadband code division pilot scheme means, in multi-carrier system, pilot channels occupy system's whole bandwidth; pilots are isolated by noninterference free broadband code division method; pilot channel's bandwidth is far broader than the single traffic channel (TCH). Since the continuous pilot has many advantages:it only occupies some power resources instead of frequency resources; based on the adding of continuous pilot, it's no need to know the received data's statistic features; can be well used in the multi-carrier and single carrier transmission system; can resist the traffic channel's interference by using the LS code. So, the research and application on it make sense and have a great value.