Raptor code for wireless ad hoc vehicular safety broadcast

Abstract

Abstract-This paper proposes an implementation of systematic Raptor code in an ad hoc V2V (vehicular-to-vehicular) environment for post-crash safety broadcast. This is to address the latency problem caused by use of repetition code in a high speed vehicular environment for time-sensitive safety applications. The highly dynamic topology and challenging RF behavior of vehicular networks necessitate the use of a robust error control mechanism even with the use of spatial diversity techniques such as STBC-MIMO scheme. A crosslayer simulator model is used to evaluate the delay performance of Raptor codes against a low complexity repetition code. The numerical analysis demonstrates that the end-toend delay performance is significantly reduced when Raptor codes are used, especially at higher distances from the source node. This is true in the case of single antenna as well as multiple antenna schemes.

Systematic raptor codes for safety broadcast in an unsaturated vehicular highway environment

“…In Figure 7, we included the performance evaluation of repetition codes based on packet fragmentation at MAC layer and raptor codes implementation at APP as recommended in the 3GPP standard [11]. The evaluation is performed for the SISO scheme in the low density scenario.…”

“…However, it is inefficient when dealing with lossy channels such as vehicular environments. In this article, we propose an implementation of a low complexity coding scheme that is suitable for broadcast channels, known as raptor codes which has been adopted in the 3GPP MBMS and the DVB-H standards [11,16]. We define the ACN warning average end-to-end delay for the FEC schemes as: In the simulation, the τ SS repetition(APP) refers to latency of a 574B PSDU similar to uncoded scenario, τ SS repetition(MAC) refers to 72B PSDU, τ SS raptor refers to 72B if they are applied at the MAC layer or 126B if they are applied at the APP layer.…”

“…Users which do not observe the systematic symbols are still able to reconstruct the set of the intermediate symbols by exploiting the redundant packets in the raptor encoded bit stream. Our multi-layered simulator is designed based on the systematic raptor codes in the 3GPP MBMS standard [11]. In the standard, the precode scheme itself is a concatenation of LDPC (Low-Density Parity Check) code (of length S symbols) and high-density parity check from binary Gray sequence (of length H symbols).…”

“…Raptor codes have been adopted in a number of standards, namely the 3GPP MBMS [11] and the DVB-H standard [16]. In these standards, raptor codes are implemented as the application layer forward error correction (FEC) mechanism.…”

“…Firstly, we propose a novel coding approach for V2V automatic collision notification (ACN) warning using a systematic raptor code as implemented in the 3GPP MBMS (Multimedia Multicast/Broadcast Service) standard [11]. This code is optimised for short source symbols (SSs) length as are expected in a safety broadcast application.…”