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In the work, we propose and investigate a real-time optical wireless communication (OWC) system with 1 Gbps on–off keying (OOK) traffic rate for indoor and outdoor transmissions. Here, 1 Gbps OWC traffic with error-free operation can be achieved indoors under the free space transmission length of 500 m based on the simulation and experimental results. In addition, 952, 904, 476 Mbps throughput rates of proposed real-time OWC system are measured outdoors after passing through the wireless transmission lengths of 120, 300 and 500 m, respectively.

In this paper, we propose and demonstrate a free space optical (FSO) communication system with 10 Gbit s−1 on-off keying traffic, which is integrated in a passive optical network (PON) for broadcasting wireless data. After a transmission distance of 25 km of single-mode fiber and a free space transmission length of 6 m, the observed optical sensitivity of the FSO signal can reach −35.2 dBm within the forward error correction level at the bit error ratio of 3.8 × 10−3. Here, according to the obtained results of experiment and simulation, the FSO signal can support 2048 remote optical wireless units (OWUs) for wireless access via the PON network in free space transmission lengths of 0 to 160 m. Moreover, the proposed FSO-PON system also can support 1024, 512 and 256 remote OWUs in free space transmission lengths of 250, 350 and 500 m, respectively.

In time-varying channel, the Doppler effect destroys the subcarrier orthogonality of orthogonal frequency-division multiplexing (OFDM) system which leads inter-carrier interference (ICI). This paper presents a time domain ICI self-cancellation method from the view of equivalent channel time variation mitigation. By utilizing the assumption of linear time-varying channel model, a set of windowing coefficients is derived to mitigate the equivalent channel time variation of the corresponding part into flat. The ICI is therefore reduced by lessening the equivalent channel time variation. The proposed window shape is found as the Franks window. The theoretical ICI power and bit error rate (BER) performance for using the proposed window shape are investigated and validated by simulation results. Comparing to Chang's equivalent windowing method and the 4-step window shape for low-complex windowing method, the proposed method can provide better ICI cancellation performance given with the same criterion.

Based on the standard of digital audio broadcasting (DAB) Eureka 147 system to improve structures of transmitter/receiver, this paper proposes a physical layer transmission technique capable of boosting the spectrum efficiency up to two times of that of the DAB-Eureka 147 system while the backwards compatibility is guaranteed. The proposed transmission technique comprises the development of both the modulation and demodulation schemes. In the developed modulation scheme, differential 16-level amplitude/ phase shift keying (D16 APSK) is adopted to replace the differential quadrature-phase-shift-keying (DQPSK) used in the DAB Eureka 147 system. In the developed demodulation scheme, on the other hand, a detector for two-level differential amplitude-shift-keying (DASK) signal is proposed which can be implemented with rather low hardware costs. The performance is presented by the Simulink platform in multipath fading channel model.

The conventional wireless communication systems are designed to overcome the worst-case channel, using the huge amount of redundant bits to assure communications performance and quality of services. Those systems cannot achieve the optimum spectrum and power efficiency. This paper presents an adaptive coding and modulation scheme used in the user terminals of the third-generation satellite communication system. A three-state photogrammetric channel estimation method is introduced for tracing the variations of large-scale environments. The mobile user terminal dynamically switches the suitable coding and modulation schemes according to the result of photogrammetric channel estimator in order to maximize the power efficiency and data throughput. The real measurement data were used to validate our proposed method. The results show that the proposed method not only reduces the system complexity, but also mitigates the power control requirements and increases the data throughput for the land mobile satellite personal communication systems. Copyright © 2006 John Wiley & Sons, Ltd.

Through the wide deployment of high-speed rails around the world, multimedia services on high-speed trains will be highly demanded in the near future. However, network round trip time and packet loss rate for high-speed rail reception are much higher and also of high variance. To facilitate the delivery of a live video streaming service, our previous research suggests that the video streaming service is transmitted as a file delivery service and the generated streaming files are delivered via a UDP-based file delivery protocol. In this paper, we investigate the potentials of UDP-based file delivery protocols for high-speed rail reception. We propose Reliable FLUTE (R-FLUTE) for reliable UDP-based unicast file delivery by introducing feedback mechanisms into the IETF FLUTE protocol. To get higher throughput and better network utilization, we extend R-FLUTE to support multisession delivery and propose an adaptive session-based rate control mechanism. We further conduct our experiments on a real 802.16e mobile WiMAX network for Taiwan High Speed Rail (THSR). The results show that the proposed scheme in comparison with FTP can provide more stable throughput, thereby requiring smaller buffer level in receivers (i.e., can deliver more real-time live video to receivers).

In Taiwan, because of the Doppler effects and tunnel shading, it is difficult to smoothly receive a live DVB-T channel inside a high-speed train by a laptop equipped with an ordinary DVB-T USB dongle. For providing live TV services inside a high-speed train, we develop a mobile live TV system for Taiwan High-speed Rail (THSR). The proposed system delivers live TV programs to a high-speed train through the mobile WiMAX network deployed along the THSR railway by the WiMAX operator VeeTime. Then, the received live TV programs are delivered to the terminal devices of high-speed rail passengers through Wi-Fi multicast. Using Wi-Fi multicast inside a high-speed train is necessary since there may be several hundreds of concurrent users on the same high-speed train. However, conventionally to provide a scalable Wi-Fi multicast streaming system is difficult because no extra reliability control mechanisms such as ARQ (Automatic Repeat-reQuest) are available for Wi-Fi multicast. Instead we overcome the difficulty of scalable Wi-Fi multicast streaming by using AL-FEC (Application Layer -- Forward Error Correction). Hence, in the demo session of MobiSys 2013, we plan to show the whole mobile live TV system with a live TV input, especially focused on its capability of scalable Wi-Fi multicast streaming over a multi-hop Wi-Fi network that can emulate the real multi-hop Wi-Fi network inside a high-speed train.

A low-cost radio-over-fiber (RoF) based integrated transmission of long term evolution (LTE) and worldwide interoperability for microwave access (WiMAX) signals is proposed to solve the shadowing effect of building envelopes and the complexity of transmitting system in wireless access network services. This scheme is also applied to solve the problems of required fast handover and poor signal penetration in tunnels for high-speed rail mobile connections. We design and demonstrate experimentally a multi-service WiMAX/LTE RoF system that can extend the indoor signal coverage, with an emphasis on the power conversion efficiency and optoelectronic component selections. The designed RoF transceivers and switches are being deployed in both the campus buildings and the tunnels of Taiwan High-Speed Rail system to allow mobile connections.

This paper presents the fading characteristics for wireless communication system in the 2.5GHz band over THSR environment. Based on measurement results, we propose the propagation model and conduct a field trial to investigate the effects of Mobile WiMAX system performances in moving train. The result in downlink TCP throughput shows that the throughput will rise again when the train is passing across bent area. It indicates that the reflecting wave in bent area is disappearing. The propagation loss returns to the free space loss. Our proposed model can not only predict the propagation loss for the cell planning but also observe the effects of wireless communication systems for high-speed railway environments.

AL-FEC (Application-Layer FEC) is already in used for protecting streaming and file delivery services against packet losses in the field of wide-area multimedia broadcasting, such as in DVB-H and 3GPP MBMS (Multimedia Broadcast Multicast Service) mobile TV systems. However, it is still not a well-studied approach for applying AL-FEC to WiFi multicast since guaranteed bandwidth for a multicast service is more difficult to be allocated in a WiFi network in comparison to traditional mobile TV systems. In this paper, we show our experiences of using an AL-FEC code; i.e. the systematic Raptor code as well the IETF FEC Framework to further protect the RTP packets delivered over WiFi multicast carriers inside the cars of a train for high-speed rails, instead of using any feedback and retransmission mechanisms.

For improving the service quality of the Taiwan High-Speed Rail (THSR), a dedicated mobile WiMAX network (based on IEEE 802.16e in the current stage) is planned to be deployed along the railway of THSR. The mobile WiMAX network is not only for providing Internet access over the THSR trains, but also for delivering live entertainment contents to the passengers, such as mobile TV streaming of live programs. In this paper, we show the experiences about the design, implementation and evaluation of the mobile TV streaming service for high-speed rail reception based on AL-FEC (Application-Layer FEC). The experiment results show that AL-FEC can effectively compensate the packet losses in the high-speed reception scenario if the underlying reliability control schemes in IEEE 802.16e cannot provide error free mobile TV streaming delivery.

As high speed rails become more and more popular, providing broadband internet access on high speed rails is not widespread due to the large inter-carrier interference, terrestrial obstacles and inherent carriage shielding. In this paper an integrated Worldwide Interoperability for Microwave Access-Radio over Fiber (WiMAX-RoF) system is proposed and deployed along Taiwan High Speed Rail (THSR) rail tracks. Field trial and laboratory experiment results are presented. According to the field trial results, excessive delay induced by unequal fiber length deteriorates the throughput performance and can be overcome by equalizing the fiber length. On the other hand, rate adaptation for maximum throughput is challenging at high mobility. Careful calibration is needed to tradeoff the throughput gain against robustness to signal fluctuations. Laboratory experiments distinguish the impact of echo channel and remote antenna unit (RAU) distance from others. The results give insights in the analysis of field trial results.

For the sake of satisfying the requirement of different receivers and adapting the network condition, a new video coding scheme appears and is called Scalable Video Coding (SVC). Different from traditional coding scheme i.e. H.264, encoding once by using SVC encoder can generate one bitstream with different resolutions as well as frame rate, and the bitstream can be corresponded with the requirement of different receivers. In this paper, we propose two adaptive SVC layer switching algorithms for dedicated Worldwide Interoperability for Microwave Access (WiMAX) network of Taiwan High Speed Rail (THSR). The adaptive layer switching algorithms are based on network condition to adjust to delivering video data. For the first algorithm, we record the Received Signal Strength Indicator (RSSI) trace at the high speed moving environment of THSR in advance, and measure the available network bandwidth with RSSI trace. Then, Streaming Server can deliver the corresponding SVC layer data by measured network bandwidth. As to the second algorithm, Streaming Server estimates network available bandwidth from static information such as packet loss rate sent by Streaming Client. Streaming Server can select and deliver SVC layer data which are adapted to estimated network bandwidth. Our streaming system is an adaptive streaming system because video layer switching adapts to different network conditions.

A link adaptation scheme for MIMO-OFDM systems over high speed rail environment is addressed in this paper. In this study, a selection method of MIMO transmission mode and the modulation and coding scheme (MCS) according to the Rician channel K-factor from our previous work is considered. A hidden Markov model of time-varying Rician channel K-factor is constructed by using the real measured channel data on the high speed rail train. With the constructed hidden Markov model, the time correlation of Rician channel K-factor can be obtained and the time-varying K-factor value can be generated. By using the hidden Markov model, the K-factor value can be predicted to facilitate link adaptation since the K-factor may vary during feedback, especially in high mobility scenario. Simulation results show an average throughput improvement of 5Mbps.

Wireless broadband access for mobile applications is an area of increasing growth. An international collaboration, led by the Taiwan Industrial Technology Research Institute (ITRI), has been working to implement a dedicated WiMAX network for a user field trial on the Taiwan High Speed Rail (THSR) bullet train system. Continuous wireless coverage at train speeds up to 300km/hr is challenging due to a number of critical issues, including handover at high speeds and coverage in challenging terrain such as tunnels. A Radio-over-Fiber (RoF) Distributed Antenna System (DAS) was developed by Corning Incorporated to address the critical issue of handover and increase the coverage for each WiMAX basestation. For a DAS deployment consisting of multiple discrete antennas, proper signal strength management is required because the maximum delay spread allowed by the WiMAX protocol is easily surpassed at realistic fiber ranges up to 9km. This paper reviews some of the initial results of the RoF DAS experiments in SongShan tunnel in Taipei. Error-free signal transmission was achieved when the difference in received power from two consecutive antennas was greater than 10dB.

In this paper we have presented an OFDM-based channel sounder system. We can use commercial VSG (with arbitrary waveform generator) and real time VSA to conduct channel measurements. The requirement is that both VSG and VSA should have stable oscillator during the time of measurement and the frequency offset between these two equipments can be known in advance. Because the time offset was not calibrated, the power delay profile (PDP) measured does not give the absolute time delay but the relative time delay of multipath components. The frequency offset between the VSA and VSG has little effect on the measurement of single PDP, but will give a constant frequency offset for the Doppler measurement. If the frequency offset is known in advance, the offset can be compensated and the Doppler spectrum can be obtained.

To solve the cell-edge problem (deep and flat fading for long time) of multi-cell MBMS in SFN and reduce PAPR in OFDM systems simultaneously, a novel transmission architecture is proposed. Grid scrambling diversity scheme is adopted in the architecture to increase time and frequency diversity. Several grid scramblers are used and the time domain signal with smallest PAPR is selected for transmission. Some simulation results are provided to demonstrate the efficacy of the proposed architecture.

For orthogonal frequency division multiplexing- based single frequency network systems, such as the terrestrial digital broadcasting systems, the performance of a static/quasi- static receiver at cell edge can be severely degraded by the slow and flat fading effect due to a destructive combination of signals from adjacent transmitters. Recently, the cyclic delay diversity (CDD) and group-wise scrambling diversity (GSD) schemes have been presented to address this issue. However, both the CDD and GSD schemes provide no time diversity against the slow fading nature. Moreover, discontinuities of composite channel responses inherent in the GSD scheme make channel estimation even more difficult. In this paper, a new correlated scrambling diversity (CSD) scheme is proposed that introduces both time and frequency diversities via the time-frequency scrambling independently among transmitters. Continuity of composite channel responses resulting from utilization of correlated scrambling patterns further makes channel estimation easy for receivers.

In this paper, we propose a novel transmission structure with the time-frequency scrambling scheme. The major concept of this technique is coming from combining the Toshiba's approach and our proposed time-dimension group scrambling scheme. In this technique, several OFDM symbols and several sub- carriers can be grouped into a grid structure and then scrambled by a scrambling pattern, the time- frequency dimension diversity gains are both increased after channel decoder. The time-frequency scrambling scheme uses the random behaviors of transmitted signals from multiple cells to create the plentiful time and frequency channel diversity, indeed, control the coherent time and the interleaver length. Hence, the burst error due to the flat fading and the long-term shadowing fading can be mitigated and channel coding will work more efficiently. The simulation results show that the destructive interference can be improved at the cell-edge by the proposed scheme. The SNR gains can be derived by the proposed scheme for mutli-cell MBMS environments (5 dB and 1.5 dB for two equal-gain and TU6 channels, respectively).

In this paper, a novel low-complexity scheme is proposed for cyclic-prefix based OFDM systems to reduce inter-carrier interference (ICI) caused by time-varying channel. Under the assumption that channel delay spread is smaller than the guard interval (GI) of an OFDM symbol, the suitably selected inter-symbol interference (ISI) free received signals are exploited through compensating the corresponding linear phases and taking the average in the frequency domain. Therefore, some ICI terms can be automatically cancelled with less number of FFT operations. Moreover, the theoretical results of bit error rate performance are derived. The simulation results are shown that the ICI effect can be significantly removed by the proposed scheme for high-mobility OFDM systems when the ISI-free region q is adequate. Meanwhile, the proposed scheme has the advantages of increasing the mobile speed up to N/(N

In this paper, a novel low-complexity scheme is proposed for current OFDM systems to reduce inter-carrier interference (ICI) caused by time-varying channel. Under the assumption that channel delay spread is smaller than the guard interval period of an OFDM symbol, the suitably selected inter-symbol interference (ISI) free received signals are exploited through compensating the corresponding linear phases and taking the average in the frequency domain, and in consequence some ICI terms can be automatically cancelled. However, the performance of this self-ICI cancellation scheme is restricted by the inadequate ISI-free region in current OFDM systems. Therefore, a concatenated scheme, which consists of the self-ICI cancellation scheme and a residual ICI reconstruction scheme, is proposed to further improve the BER performance. The simulation results are provided to support that the ICI effect can be significantly removed by the proposed low-complexity concatenated scheme for current high-mobility OFDM systems.

An analytic study applying an M-ary PSK adaptive modulation scheme in a Rayleigh-lognormal fading channel is proposed. The closed-form expressions of the average BER and the average data throughput (BPS) of the proposed adaptive modulation system with constant transmitted power over the fading channel are presented. The effect of shadowing on BER and throughput in the adaptive modulation system is also investigated. The results show analytical expressions for the average BER and data throughput derived for transmission over a Rayleigh-lognormal fading channel. Our analyzed results show good agreement with Monte Carlo simulation ones. The proposed method is useful in enhancing the data throughput of a communication system, such as a third generation wireless communication system, where a huge amount of bandwidth is needed for high-speed multimedia services.