A NEW CS BASED TRANSMISSION METHOD FOR VEHICULAR COMMUNICATION Sangeetha Gopinath M.Tech student Communication Engineering Department of ECE RCET, Akkikavu sangethagopinath@gmail.com Abstract— Orthogonal frequency division multiplexing (OFDM) is mainly divided to three types. cyclic prefix OFDM (CP-OFDM), zero padding OFDM (ZP-OFDM), and time domain synchronous OFDM (TDS-OFDM). Compared to CP OFDM, TDS-OFDM have higher spectral efficiency and faster synchronization. But TDS-OFDM cannot support higher order modulation like 256QAM in low-speed vehicular channels and there will be performance loss over fast time-varying vehicular channels. This paper introduce how efficiently use the compressive sensing (CS) theory to solve those problems. Here First, cancelling the interferences if present, and use the idea of inter-block-interference (IBI)-free region of small size to reconstruct the high-dimensional multipath channel. Second, propose the parameterized channel estimation method based on priori aided compressive sampling matching pursuit (PA- CoSaMP) algorithm to achieve reliable performance over vehicular channels. TDS-OFDM have Partial channel priori, so by using this performance can be improved and reduce the complexity of the algorithm. Keywords—Time domain synchronous OFDM (TDSOFDM), mutual interferences, compressive sensing (CS), compressive sampling matching pursuit (CoSaMP). I. INTRODUCTION Vehicular communications is an emerging technology. Efficient transmission of information is the key component of vehicular communications. OFDM plays an important role in vehicular communication because of it’s high spectral efficiency and excellent robustness to multipath fading channels. There are basically three types of OFDM-based block transmission schemes: cyclic prefix OFDM (CP-OFDM), zero padding OFDM (ZP-OFDM), and time domain synchronous OFDM (TDS-OFDM). The standard CP-OFDM is commonly used, which utilizes the CP to eliminate the inter-block- interference (IBI) and inter-carrier-interference (ICI). The CP is replaced by zero samples in ZP-OFDM to overcome the channel null problem. TDS-OFDM uses a known PN sequence based on the concept of joint time-frequency processing. This can be used as the guard interval and training sequence (TS) for synchronization and channel estimation. CPOFDM and ZP- OFDM requires many number of pilots, but this can be saved in TDS-OFDM. Thus, TDS-OFDM has higher spectral efficiency than CP-OFDM and ZP-OFDM. Also this TDS- OFDM have fast and reliable synchronization compared to the others. This can also used in digital television terrestrial broadcasting (DTTB) standard called digital terrestrial multimedia/television broadcasting (DTMB). TDS-OFDM consists of TS & OFDM data block. This TS and the OFDM data block cause mutual interferences to each other. To achieve reliable time-domain channel estimation and frequency-domain data detection in TDS-OFDM systems, interference cancellation method must be used . This results in two problems of TDS-OFDM: First, in low-speed vehicular channels, it is difficult to completely cancel the residual interference when the channel delay spread is large, that problem will lead to the difficulty of supporting high-order modulations like 256QAM (currently, TDS-OFDM can support 64QAM at most); Second, due to the mutual condition of accurate channel estimation and reliable data detection, the performance degradation will occur. This cause to performance loss over fast fading channels. Many methods are used to solve those problems, but the improvement is not obvious. To solve that problems first find the unique word OFDM (UW-OFDM) scheme, which use redundant pilot within the OFDM data block to generate the TS, thus it can remove the remove the interference from the TS to the OFDM data block, but this solution does not solve the interference from the OFDM data block to the TS, and the inserted pilots suffer from very high average power as well. So another method is find, that is the dual-PN OFDM (DPN-OFDM) scheme, here as name implies there is an extra PN sequence is inserted. This extra PN sequence is used to avoid the interference from the OFDM data block to the second PN sequence, this also have a problem, that it leads to reduction in spectral efficiency, especially when the guard interval length should be long in vehicular communications. Here adopt theory of compressive sensing (CS) to solve those two problems of TDS-OFDM. The main contributions of this paper are first, cancelling the interferences if present, and use the idea of inter-block-interference (IBI)- free region of small size to reconstruct the high-dimensional multipath channel. In this way TDS-OFDM system model was developed. Then Based on the classical CS algorithm called compressive sampling matching pursuit (CoSaMP), here propose the priori aided CoSaMP (PA-CoSaMP) algorithm by exploiting the joint time-frequency processing feature of TDS- OFDM, where by the contaminated TS in TDS OFDM is used to acquire partial priori of the channel. Compared with CoSaMP, the proposed PA-CoSaMP algorithm have many advantages, it reduces the required number of observations and the complexity is also reduced. Based on the PA-CoSaMP algorithm channel estimation can be effectively done. Thus transmitted data can be correctly received, this is useful in vehicular communication. To receive data perfectly accurate channel estimation is required, different techniques are used.