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1.
In Digital TV Broadcasting, the Scheme of Single Frequency Network (SFN) has nontrivial advantages. By forming a SFN, a broadcasting system is able to serve an arbitrary large area with the same program within the same frequency block. At the mean time, the SFN structure provides the receiver with a potential of yielding the space diversity gain, while the power in every single transmitter is not increased. However, there are heavy artificial multipath propagation in the area covered by the SFN broadcasting. Traditionally, a transversal equalizer is used at the receiver to remove the SFN interference. The equalizer always cannot converge properly due to the over-long time delay and the over-large magnitude of the different paths from each transmitter of the SFN. To solve the problem, a new model based on the MIMO structure of the SFN is proposed in this paper, where the signal's space information is exploited. With the model in mind, a new receiving scheme is derived. By using a beamformer, signals with different incident angles are separated, so the problem caused by the over-long delay and the over-large magnitude is avoided. A bank of parallel sub-filters are used to remove the residual multipath spread. The space diversity gain is obtained at the output of a combiner. 相似文献
2.
In systems using Orthogonal Frequency Division Multiplexed (OFDM) all transmitters in a radio broadcasting network may transmit identical signals in the same frequency block, forming a so called Single Frequency Network (SFN). The simultaneous transmission creates a severe artificial multipath propagation causing interference at the receiver. This interference consists not only by intersymbol interference (ISI), but also interchannel interference (ICI) due to orthogonality losses between OFDM scheme's subcarriers. A method that is often used to counter the self-interference is to insert a guard interval between consecutive OFDM frames combined with an increased symbol duration. The receiver in an SFN is normally experiencing a diversity gain of receiving several signals. Doubts concerning the performance has been raised due to the OFDM scheme's sensitivity to frequency errors. If the received signals are exposed to different carrier offsets it will lead to ICI, resulting into reduced coverage. In this paper we apply pulse shaping to reduce the effects of ISI and ICI. Pulse shaping of the transmitted OFDM signal is shown to give significant reductions in self-interference. It is hereby possible to achieve the same coverage with a reduced amount of transmitters. The system also becomes less sensitive to time and frequency synchronisation errors. A method to analyse the performance for time limited pulse shapes is presented using weight functions describing the amount of useful and interfering powers. In the receiver analysis, generalised expressions are given using Fourier transforms and series. 相似文献
3.
Göran Malmgren 《Wireless Personal Communications》1995,2(4):307-319
A receiver in an ODFM based broadcasting system allows all transmitters in a radio network to simultaneously broadcast the same information in the same frequency block. This procedure generates an artificial multipath environment at the receiver. Since the receiver is designed to overcome these problems, such a Single Frequency Network (SFN) provides good coverage and frequency economy in national applications. However, the efficiency in local SFN has been questioned. The network planning of local SFNs is a mixture of conventional frequency reuse planning and planning to avoid excessive propagation delays caused by the artificial delay spread. In this paper we propose some rules of thumb to be considered in the design of local SFNs. The coverage properties in SFNs are strongly dependent on the transmitter density which determines the degree of diversity of receiving signals from several transmitters. Results indicate that required coverage can be attained in local networks using three OFDM frequency blocks, provided that seven transmitters are used to cover each regional service area. The results also indicate that the duration of the guard interval between two consecutive OFDM signals has to be chosen with some care dependent on the size of the service area. Furthermore, we show that there exists an optimal antenna height for a given coverage area and guard interval. 相似文献
4.
数字移动电视广播系统是我国广播电视综合覆盖体系中的重要组成部分,单频网(SFN)是目前地面数字电视广播系统覆盖最好的方法之一。介绍数字移动电视单频网建设中的一些经验和心得,包括合理指配单频网数字台站、选择合适的单频网传输模式、单频网时延的合理设置等。 相似文献
5.
《Broadcasting, IEEE Transactions on》2008,54(4):799-805
6.
A method for designing a terrestrial digital audio broadcasting single frequency network (T-DAB SFN) for a mountainous region is proposed. A computer database and the digital terrain elevation data are used in designing the network. Two fundamental approaches are compared; first, utilization of the existing transmitter sites is maximized by applying the initial cost constraint; then, the coverage percent of the service is forced to approach to 100% by applying the coverage efficiency constraint. Finally, a T-DAB SFN hybrid design procedure optimizing both constraints is proposed. The three design approaches are illustrated on the coverage of the mountainous Istanbul-Ankara highway. The results are compared using a reference cost look up table. The hybrid approach is shown to optimize the initial cost and the coverage efficiency, and can be applied to similar networking problems 相似文献
7.
Cutoff rate and outage probability performance comparisons between DVB-T and DMB-T systems under mobile multipath channels 总被引:1,自引:0,他引:1
Zi-Wei Zheng Zhi-Xing Yang Chang-Yong Pan Yi-Sheng Zhu 《Broadcasting, IEEE Transactions on》2003,49(4):390-397
As an effective technique for combating multipath fading and for high-bit-rate transmission over wireless channels, orthogonal frequency-division multiplexing (OFDM) is extensively used in modern terrestrial digital television broadcasting systems to support high performance bandwidth-efficient multimedia services. Cutoff rate and outage probability are two important criteria to evaluate the performance of a practical communication system in radio engineering. In this paper, the cutoff rate and outage probability performance are compared between two important terrestrial digital television broadcasting systems, the cyclic prefix OFDM based DVB-T system and the time domain synchronous OFDM based DMB-T system, under different mobile multipath channel conditions. The DVB-T system and the DMB-T system are summarily introduced. The cutoff rate and outage probability expressions are developed, and simulation results are given for both the DVB-T system and the DMB-T system. 相似文献
8.
Hsiao-Chun Wu Xiaozhou Huang 《International Journal of Wireless Information Networks》2005,12(3):169-177
Orthogonal frequency division multiplexing (OFDM) has been applied in the current wireless local-area networks and digital video broadcasting since it is robust against the frequency-selective channels. However, there is still a crucial intercarrier-interference (ICI) problem due to Doppler effect, local frequency drift and sampling clock offset, associated with OFDM systems. Recently ICI self-cancellation schemes have been proposed to significantly reduce the ICI and empirically they greatly outperform the convolutional coding schemes adopted by the IEEE 802.11 standard. However, all existing ICI self-cancellation receivers are still sensitive to the phase and amplitude ambiguities due to the phase offset, the local oscillator frequency drift and the multipath reflections. Therefore, in this paper, a novel receiver design integrating the ICI self-cancellation with a proposed dynamic phase and amplitude estimation mechanism is introduced, which can well solve the ambiguity problem. The Monte Carlo simulation results show that our phase and amplitude estimators can greatly decrease the error probability for the final symbol detection in the ICI self-cancellation OFDM receivers. 相似文献
9.
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11.
Analysis and characterization of intercarrier and interblock interferences for wireless mobile OFDM systems 总被引:2,自引:0,他引:2
Hsiao-Chun Wu 《Broadcasting, IEEE Transactions on》2006,52(2):203-210
OFDM has been applied in a wide variety of wireless communications in recent years since it has the advantage over the conventional single-carrier modulation schemes when enduring the frequency-selective fading. However, intercarrier-interference (ICI) and interblock interference (IBI) due to the Doppler effect, carrier frequency drift of local oscillators and multipath fading limit the capability of OFDM systems. In this paper, a new generalized mathematical model for intercarrier and interblock interferences is derived for wireless mobile OFDM systems, in which Doppler frequency drift, local carrier frequency offset, multipath fading, and cyclic prefix coding are all present in reality. Such a new ICI/IBI model can be applied for OFDM performance evaluation in different environments. This new formulation of IBI and ICI provides a generalized framework which includes special ICI models appearing in the previous literature. Besides, the derived OFDM performance evaluation analysis in this paper can greatly benefit OFDM designers for wireless multimedia networks and digital video broadcasting technologies. 相似文献
12.
Zi-Wei Zheng Zhi-Xing Yang Chang-Yong Pan Yi-Sheng Zhu 《Broadcasting, IEEE Transactions on》2004,50(2):148-153
As an effective technique for combating multipath fading and for high-bit-rate transmission over wireless channels, orthogonal frequency-division multiplexing (OFDM) is extensively used in modern digital television terrestrial broadcasting (DTTB) systems to support high performance bandwidth-efficient multimedia services. In this paper, novel synchronization schemes, including timing, frequency offset estimation, and phase error tracking, are proposed for the time domain synchronous OFDM (TDS-OFDM) based DTTB systems. Simulations under different channel situations verify the efficiency of the proposed schemes. 相似文献
13.
Radio transmission signals are distorted by multipath propagation and signal level fading in the channel. In the case of digital transmission systems, the distortion of signals causes a degradation of bit error performance. It is an especially severe problem with digital outside-broadcasting-link (OBL) which has to transmit, for example, digital HDTV signals at more than about 45 Mbps. The OFDM modulation scheme can mitigate the adverse effects of multipath fading. An experimental OFDM modem has been developed to enable stable transmission of digital HDTV sources in an OBL. The experimental modem distributes transmitting digital data to 688 carriers in a bandwidth of about 13.5 MHz using the 16DAPSK for each OFDM carrier. A combination of 8DPSK and 2DASK is adopted as the 16DAPSK and another combination of 8DPSK and coherent 2ASK instead of 2DASK is also considered. Indoor transmission experiments confirmed that the 16DAPSK-OFDM is feasible for transmitting high bit rate signals, even under severe propagation conditions 相似文献
14.
FPGA Synthesis of VHDL OFDM System 总被引:1,自引:0,他引:1
M. A. Mohamed 《Wireless Personal Communications》2013,70(4):1885-1909
This paper presents a novel Field Programmable Gate Array (FPGA) technique to gain approach in the problem of OFDM system implementation. The actual and next communication schemes tend to use OFDM systems in order to provide high baud rates, less intercarrier interference (IC), and less intersymbol interference (ISI). Some examples are IEEE-802.11, IEEE-802.15, IEEE-802.16, 3GPP, MC-CDMA, digital video broadcasting (DVB), wireless USB, and/or wireless firewire among others. Trying to provide a solution to the new devices emerging, slow standard adoption, poor spectrum use, etc. This work presents an FPGA design; validation, and implementation of an OFDM modulator for IEEE-802.16e using a high level design tool, also reports the resources requirements for the presented system. The proposed design is synthesized using high level design tools. The design flow is optimized for fast prototyping which is implemented on the latest generation of FPGA chips. Such an FPGA implementation has the added advantage to modify for changes and improved system performance, e.g. reducing propagation delay. 相似文献
15.
In single frequency network (SFN), there exist some special long delay spread channels as well as conventional multipath channels.
For pilot-aided orthogonal frequency division multiplex (OFDM) systems, channel estimation is usually accomplished by interpolation
with pilots. However, few pilot sub-carriers exist within the coherent bandwidth of the long delay spread channels in SFN.
In this case, conventional frequency domain interpolation methods cannot work properly. In a narrowband channel, this paper
indicates that both the real and the imaginary parts of channel frequency response can be accurately approximated as a sine-wave
with DC offset. For many practical pilot-aided OFDM systems, the bandwidth of the narrowband channel mentioned before is comparable
with the interval between several adjacent pilot sub-carriers. Then this paper proposes a sine-wave based frequency domain
interpolation method for the channel estimation of pilot-aided OFDM systems in SFN. As simulation results show, the proposed
method performs well in the long delay spread channel, whereas the mismatched Wiener interpolation filter (WIF) estimates
channel response inaccurately. Moreover, the proposed method gives accurate channel estimation in conventional multipath channels,
especially for the systems which adopt high order modulations. 相似文献
16.
Moriyama S. Tsuchida K. Sasaki M. Yamazaki S. 《Broadcasting, IEEE Transactions on》1996,42(3):266-271
A study on digital broadcasting systems has been conducted for the multimedia era. Regarding program production, a digital outside-broadcasting-link (OBL), in particular, from mobile source is required to gather digital video and audio sources in severe multipath environments. The orthogonal frequency division multiplexing (OFDM) modulation scheme is robust under multipath fading conditions. A digital OFDM modem for OBL in the 800 MHz band has been developed to enable stable transmission of digital sources from moving vehicles. In the experimental OFDM-OBL, the compressed digital video and audio data are distributed to 572 carriers in the 9 MHz bandwidth, using differential quadrature phase shift keying (DQPSK) modulation for each carrier. In computer simulation and indoor/outdoor experiments, it is confirmed that digital OFDM-OBL can stably transmit signals, even under severe multipath fading conditions, while pictures transmitted with conventional FM-OBL are seriously degraded. This paper describes the features of the OFDM modem for the digital OBL which transmits program sources from moving vehicles, and also discusses aspects of gathering digital program sources 相似文献
17.
This paper investigates the design and performance of a digital on‐channel repeater (DOCR) for use in Advanced Television Systems Committee (ATSC) digital television (DTV) broadcasting. The main drawback of a DOCR is the echo interference caused by coupling between transmitter and receiver antennas, which induces system instability and performance degradation. In order to overcome this problem, an echo canceller based on the adaptive echo channel estimation (ECE) technique has been researched and applied for a DOCR. However, in the case of ATSC, the pilot signal, which is used for carrier synchronization, may cause a DC offset error and reduce the isolation performance of the echo canceller for a DOCR in an ATSC network. Moreover, since the multipath fading effect of a radio channel usually occurs in a real environment, it should be minimized to improve the overall performance of a DOCR. Therefore, due to the limited isolation performance of echo canceller and the multipath fading effect, an interference cancellation system (ICS) is proposed for a DOCR in an ATSC network. The performance of the proposed DOCR with an ICS is evaluated by software simulation and hardware test results. 相似文献
18.
Phoong S.-M. Yubing Chang Chun-Yang Chen 《Signal Processing, IEEE Transactions on》2005,53(1):182-192
The orthogonal frequency division multiplexing (OFDM) transceiver has enjoyed great success in many wideband communication systems. It has low complexity and robustness against multipath channels. It is also well-known that the OFDM transceiver has poor frequency characteristics. To get transceivers with better frequency characteristics, filterbank transceivers with overlapping-block transmission are often considered. However these transceivers in general suffer from severe intersymbol interference (ISI) and high complexity. Moreover costly channel dependent post processing techniques are often needed at the receiving end to mitigate ISI. We design discrete Fourier transform (DFT) modulated filterbank transceivers for multipath fading channels. The DFT modulated filterbanks are known to have the advantages of low design and implementation cost. Although the proposed transceiver belongs to the class of overlapping-block transmission, the only channel dependent part is a set of one-tap equalizers at the receiver, like the OFDM system. We show that for a fixed set of transmitting or receiving filters, the design problem of maximizing signal-to-interference ratio (SIR) can be formulated into an eigenvector problem. Experiments are carried out for transmission over random multipath channels, and the results show that satisfactory SIR performance can be obtained. 相似文献
19.
Guerra G. Angueira P. Velez M.M. Guerra D. Prieto G. Ordiales J.L. Arrinda A. 《Broadcasting, IEEE Transactions on》2005,51(2):171-179
This paper presents a study developed to obtain several parameters of the small scale fading of the wideband propagation channel applied to the portable and mobile reception of Digital Terrestrial Television (DTV) services in an urban Single Frequency Network (SFN) environment. The study is focused on the calculation of some relevant parameter values related to the multipath behavior of the channel, using field data collected in a real network. Mean values for the Root mean square Delay Spread (RDS) and the frequency domain Level Crossing Rate (LCR) are given, together with an analysis of the influence of the specific environment and network (SFN) features. 相似文献
20.
一般的MIMO系统,MIMO-OFDM系统和MIMO MC-CDMA系统是未来宽带无线通信业务发展的候选技术,MIMO技术的研究已经成为通信理论的前沿领域。多径传输会引起频率选择性衰落,码间干扰等许多问题,分别在单用户和多用户条件下,检验多径信号传输对MIMO系统信道容量的影响。 相似文献