Research Of Collided Signal Recovery In MIMO-OFDM System

In recent years, the growing demand of wireless communication systems for the communication performance and system capacity has lead to the rapid development of wireless communication technology. MIMO(Multiple input multiple output) technology exploits the spatial degrees of freedom between transmitting and receiving antenna pairs to obtain spatial multiplexing gain and diversity gain, thereby exponentially improve the system capacity as well as spectral efficiency without increasing the bandwidth.OFDM technology divide the frequency selective fading channel into several parallel flat fading sub-channels, which can effectively avoid inter-carrier interference and inter-symbol interference. OFDM technology has a strong anti-frequency selective fading capability. Multiple input multiple outputorthogonal frequency division multiplexing(MIMO-OFDM) system combines the advantages of both MIMO and OFDM technology and achieve maximum spectrum efficiency by using space and frequency diversity, which greatly improves the capacity and data transfer rates of the wireless communication system.Due to the advantages of high transmission rate, low cost, flexible networking, and easy to extend, Wireless LAN(WLAN) system has been widely used.MIMO-OFDM technology has become a key technology in several wireless LAN standards, such as IEEE 802.11 n.Besides, space-time/frequency coding technology has been introduced to the WLANstandard to further enhance the wireless transmission rate. Carrier sense multiple access /collision avoidance(CSMA / CA) protocol is commonly used in IEEE 802.11 WLAN standard to avoid the signal collision at the receiver. However, when the hidden terminal exists, CSMA / CA protocol can’t efficiently solve the signal collision problem. So it is important to study the signal collision issues in MIMO-OFDM system.In this paper, the common MIMO detection algorithms are summarized at the beginning. And we compare the performance of several detection algorithms with simulation. Then Turbo iterative signal processing principles and iterative MIMO detection techniques are introduced and simulated.For signal collision problem caused by hidden terminal in MIMO WLAN system, we propose an iterative collided signal recovery algorithm based on MIMO detection(ICD-MIMO).Based on the continuous collision signal at the receiver, ICD-MIMO algorithm recover theoriginal transmit signal in three steps, which are collision signal reconstruction, interference cancellation and MIMO signal detection. Further on, we apply Turbo iterative signal processing to the receiver design. The soft information is exchanged between the collided signal recovery module and channel decoding module to improve the system recovery performance.Simulation results show that ICD-MIMO algorithm can be applied to solve the signal collision problem in real MIMO WLAN system.Then we take space-time/frequency coding technology into consideration. In this paper, we propose a new collision recovery algorithm(SCD-MIMO) for SFBC MIMO-OFDM system. In SFBC MIMO-OFDM system, the transmit data symbols have been space-frequency encoded. So different from ICD-MIMO algorithm, the collided signal is recovered by collision signal reconstruction, received signal estimation and space-frequency decoding for SCD-MIMO algorithm.Simulation results show that SCD-MIMO algorithm can effectively solve the signal collision problem in SFBC MIMO-OFDM systemsand the error rate can reach 10-4 magnitude in high SNR situation.