S-mode Link Layer Design

Secondary Surveillance Radar (SSR) is a key equipment in Air Traffic Control (ATC) and military Identification Friend or Foe (IFF) ,SSR is a hot issue in radar signal processing .With the development of international civil air industry and the increasing of the number of airplanes, there are many factors which restrict the development of SSR. To overcome the restriction, Mode S SSR was put forward. Mode S also has many functions that traditional SSR doesn't have.This paper will explain the SSR, and Monopulse SSR, and Mode S Monopulse SSR. It also explains their characteristics, development, actuality, and theories. The most important content is the concepts of Mode S data link, communication formats, types and application. The paper will introduce the structure of the SSR Mode S air-ground data link. It details the work courses of the DCE (data circuit-terminating equipment), XDCE(gournd/air data circuit-terminating equipment), Reformatting process, SSE (Mode S specific services Entity), and SNME(Mode S subnetwork management entity) . And it details the process of uplink and downlink frame. And the interface of data exchange within the subnetwork.Based on the data ,the simulation of the system function and timing were finished, the simulation includes four parts: GDLP uplink processing, GDLP downlink process, ADLP uplink process and ADLP downlink process.Each part includes SLM frame and ELM frame.At last, the paper details the Mode S signal generator based on DSP & CPLD. The generator comprises DSP, CPLD, two pieces of FIFO, two pieces of DAC, and EEPROM, power chip. The soft development is based on CCS, using the EMIF and EDMA of the DSP. The generator can output the required signal of the Mode S data link.