Research On Direct Model In Broadband Trunking Communication System

Trunking system is an important part of national private network system.With the demand of large data transmission and high bandwidth increasing dramatically for trunking communication system,higher requirements of performance indexes such as transmission delay and capacity has also been proposed these years.When the communication environment is harsh such as earthquake,whose general ability of communication totally lost caused by the destruction of infrastructure and obstruction of arrival of communications rescue vehicle,trunking system requires another simplified work mode based on these conditions: direct communication between terminals without base stations,which is called off-line direct mode.Although the broadband trunking industry alliance proposed a broadband trunking communication standard B-TrunC(Broadband Trunking Communication),the off-line direct mode is still in pre-research stage,and there has not formed a unified standard yet.Based on the background above,this article first studies the requirements and current situation,analyzes the overall architecture and the time index of broadband trunking system,and elaborates the technology and related protocols used in the off-line direct scheme.After that,the time slot structure,burst structure and call process of TETRA(Terrestrial Trunked Radio)Direct Mode Operate(DMO)are analyzed,and the general rules of call establishment and physical layer burst structure are obtained.Combined with the TETRA DMO and TD-LTE frame structure,the frame structure in broadband trunking direct mode is designed,and the performance of frame structure is tested with voice service and data service.According to the characteristics of short-range communication distance and slow moving speed of the terminal,the DMO burst structure based on OFDM technology is designed.In virtue of the software radio technology,this paper investigates a scheme on the basis of both GNU Radio platform and Universal Software Radio Peripheral(USRP)platform to detect the rationality of the burst structure.Through the in-depth analysis of Session Initiation Protocol(SIP)protocol,the SIP protocol is used as a signaling protocol for the call establishment in the off-line direct scheme of broadband trunking system.And the call establishment processes of single call,group call and broadcast call in direct mode are designed based on SIP protocol.Finally,the data transmission and call establishment process are tested to obtain the data packet loss rate and call setup time.Compared with the WLAN packet acceptance rate index and the voice session establishment in the broadband trunking system,the burst structure of the off-line direct mode is reliable and voice set-up time meets the target requirements.