Abstract: Methods and apparatus are disclosed for data packetizing in an orthogonal frequency division multiplexing (OFDM) system. In order to improve transmission efficiency, the present invention uses independent packet and OFDDM block boundaries. Therefore, a packet is allowed to go across the OFDM block boundary and packed into two OFDM blocks. To indicate the start of each packet, a Frame Delimiter (FD) with a predefined format is inserted in front of each packet. The predefined format of the FD can be a predefined bit pattern or modulation points of modulation constellation. Idle data can also be inserted into OFDM blocks when no packet is ready. When data of one or more packets and idle data contain the predefined bit pattern of the FD, the data are modified to avoid generating the pre-defined bit pattern.

Abstract: Methods and systems for channel estimation using iterative channel tracking algorithm, in a communication system combined multiple input multiple output (MIMO) technology with orthogonal frequency division multiplexing (OFDM), are disclose. The initial channel estimation of a data packet uses the first preamble inserted in front of the OFDM blocks. After demodulating subsequent one or more OFDM blocks, iterative channel tracking method is used for channel estimation until the next preamble is received. The iterative channel tracking is based on the received signals and the demodulated results of subsequent one or more OFDM blocks.

Abstract: A method and apparatus for admission control in a wireless train communication system with TDMA are disclosed. The method and apparatus according to one embodiment of the present invention identifies neighboring devices within neighborhood of a given device that use the time slot. The frequency and location information for the intended device and the unintended devices are used to determine whether to grant the time slot. In another embodiment according to the present invention, the receive signal strength information at the neighboring devices is used, instead of the distance information, for admission control.

Abstract: A system and method of frequency offset compensation are disclosed for a wireless system between a fast moving radio terminal associated with a locomotive and a stationary radio terminal associated with a base station. The present invention utilizes advanced frequency offset prediction to quickly track Doppler Shift caused by a fast moving locomotive. In one embodiment according to the present invention, the frequency offset prediction is based on a first plurality of coarse frequency offsets, first-order derivatives of the first plurality of coarse frequency offsets, and second-order derivatives of the first plurality of coarse frequency offsets. In another embodiment according to the present invention, the frequency offset prediction is based on a plurality of previous frequency offsets according to a Doppler shift model.

Abstract: A configurable antenna arrangement is disclosed for wireless Positive Train Control system to overcome the deep fading and fast fading issue. The radio channel between a locomotive on-board radio unit and a base station is subject to fast and deep fading. The channel changes rapidly in a short time comparing to the length of the packet. The invention uses a TX antenna and a RX antenna in a time division multiple access (TDMA) radio system associated with control circuits to provide a configurable antenna sub-system. The antenna sub-system is configurable to provide a TX mode, a primary RX mode and a secondary RX mode. In both the TX mode and the primary RX mode, there is substantially no insertion loss. In the secondary RX mode, the TX antenna is used as the secondary RX antenna to overcome fading caused by Doppler shift.

Abstract: A system and method of frequency offset compensation are disclosed for a wireless system between a fast moving radio terminal associated with a locomotive and a stationary radio terminal associated with a base station. The present invention utilizes advanced frequency offset prediction to quickly track Doppler Shift caused by a fast moving locomotive. In one embodiment according to the present invention, the frequency offset prediction is based on a first plurality of coarse frequency offsets, first-order derivatives of the first plurality of coarse frequency offsets, and second-order derivatives of the first plurality of coarse frequency offsets. In another embodiment according to the present invention, the frequency offset prediction is based on a plurality of previous frequency offsets according to a Doppler shift model.