Distribution network for telecommunications services for subscribers of express train

Authors: 
D.E. Bezlyudnov, I.S. Kubasov, K.S. Sunduchkov

NTUU KPI

This article describes the new concept of providing multimedia services, which require bandwidth 12 Mbit/sec, for mobile subscribers moving at speed of 250-350 km/h on train express. This concept is called – interactive heterogeneous telecommunication system (IHTS). Also describe a place of a satellite channel in this network. There are advantages and disadvantages of satellite trunk line in architecture IHTS are also observed in this paper. We consider the signal at the transmitting and receiving side. Defined restrictions on group channel and OFDM symbol separately. Calculate the following parameters of OFDM symbol that will be used in downlink channel from base station to central station on the railway express:
1. Bandwidth of one subcarrier.
2. Pulse length.
3. Pulse widening factor.
4. Maximum number of services in 400 MHz bandwidth.
5. Maximum number of subcarriers in one OFDM-symbol.
6. Bandwidth of one OFDM-symbol.
Also calculated the total number of OFDM-symbols which require for transmit the whole traffic for 200 subscribers. We have composed those OFDM-symbols in 1 GHz group channels and calculate the total bandwidth. We calculate that parameters for 12Mbit/sec for one service and for two hundred subscribers. It is proposed part of the scheme for the receiver of the OFDM signal for central station on train car. Defined the key operations that should be done for receive complex signal. That scheme will receive OFDM-symbols, unpack it, multiplex sub-channels and produce prepared for future distribution services. Also discuss the principles of construction of distribution network services to subscriber’s railway express. Define some key feature of placing routers in the train cars. Proposed 2 different model of distribution network, using Wi-Fi technology, and pros and cons of them are considers. Questions of electromagnetic compatibility for distribution system information from a base station to express subscribers are considered. Problem that reduces the power of the signal at the receiving side are represented. Proposed the following solutions:
1. Use carrier frequency 5 GHz for Wi-Fi 802.11n technology.
2. Decrease radiant power of routers at the central station that transmit signal to routers at train car.
3. Rationally allocate frequencies for Wi-Fi technology.
4. Use a protective coating on the train car roof to reduce the multipath signal. The formula for calculate the length of protective coat from receiver router are offered.
5. Use protective shields on the train car roof to reduce the multipath signal. The formula for calculate the height of protective shields and length, at which the protective shield should be placed from receiver router are offered. Described other possible negative impacts on distribution system.