The fading machine, and its use for the investigation of the effects of frequency-selective fading
8
Citation
2
Reference
10
Related Paper
Abstract:
The function of the fading machine is to simulate the frequency-selective fading which is characteristic of long-distance short-wave radio channels. Fading of this type is usually due to interference between waves which have traversed multiple paths between sender and receiver, and its effect is often to produce distortion of the modulation of radio waves. Many radio transmission systems have been devised with the object of minimizing the effects of selective fading; the fading machine enables different systems to be compared in the laboratory under precisely controlled fading conditions. The equipment described in the paper incorporates three transmission paths, the group time-delay differences between which may be varied in steps from 0 to 2 milliseconds. The phase differences between the paths may be varied manually (“static” fading) or continuously (“dynamic” fading), with fading rates ranging from 0.1 to 10 fades per second. Random noise, either fading or non-fading, may be included so as to synthesize a complete short-wave radio channel. The fading machine may also be used to simulate diversity reception obtained by spaced aerials. Examples are given of the use of the equipment to assess the merits of double-sideband, single-sideband and frequency-modulated transmission systems with telephony or telegraphy modulation, under conditions of severe selective fading and high noise level.Keywords:
Fading distribution
Channel state information
Diversity scheme
The fading number of a noncoherent two-user Rician fading channel is derived. The fading number is the second term in the high-SNR expansion of the sum-rate capacity of this multiple-access channel. It is shown that the fading number is identical to the fading number of the single-user Rician fading channel that is obtained when the user seeing the worse channel is switched off.
Rician fading
Fading distribution
Channel state information
Cite
Citations (1)
Fading characterizes the effect of random superposition of signal copies received from different propagation paths. These signal replicas may add together constructively or destructively, which leads to a large variation in received signal strength. Multipath fading manifests itself in a much smaller spatial scale than path loss and shadowing, and therefore, is called the small-scale effect of wireless channel. In this chapter, we first develop the general model for multipath fading channels. Then, we discuss the classification of fading channels based on their time domain and frequency domain characteristics. Finally, we present simplified models for two important types of multipath fading channels, which are widely used in the design and analysis of digital wireless transmission systems.
Fading distribution
Channel state information
Cite
Citations (0)
Polarization Diversity (PD) is a favorable option for compact Base Station (BS) and Mobile Station (MS) antennas while offering the benefits of Space Diversity (SD) for wireless systems. The large bandwidth of future networks is more likely to cause frequency-selective fading yet compactness is desired irrespective of terrain. Therefore, in this paper, performance of PD for flat-fading and frequency-selective fading is investigated based on the Symbol Error Rate (SER) with emphasis on frequency-selective fading. Nakagami-m fading is employed as it can represent a wide range of multipath channels raging from line-of-sight (LoS) to non-line-of-sight (nLoS). SER of PD and SD are compared based on SNR. The dependence of SER of flat as well as frequency-selective fading on SNR, PD factors and fading parameter m is presented. SER of frequency-selective Rayleigh and Rician fading is also compared in this work.
Rician fading
Fading distribution
Diversity scheme
Non-line-of-sight propagation
Nakagami distribution
Channel state information
Antenna diversity
Cite
Citations (2)
Multipath effect is an important factor that affects capability of TTC system at low elevation angles.The principle of multipath effect and the mathematical model of multipath fading are introduced in this paper.While electromagnetic wave travels between transmitting and receiving antennas,it has one direct path and several reflective paths.It will produce multipath fading when reflective signal counterbalances direct signal.Based on the mathematical model,the conditions in which the multipath fading appears and the influences of multipath fading on TTC system are analyzed in this paper.The position where multipath fading appears depends on the altitudes of the both antennas and the distance between them.The intensity of multipath fading depends on the reflectance of surface.Some methods are summarized to avoid and overcome multipath fading.
Fading distribution
Rake receiver
Cite
Citations (2)
We propose the Optimum Power Allocation (OPA) scheme for Distributed Antenna Systems(DAS) in the time-varying Rayleigh fading channel. Recently, the OPA schemes which uses the Channel State Information (CSI) including a small scale (fast) fading have been proposed. However, the channel is changing vary fast over time due to small scale fading, therefore Bit Error Rate (BER) increases. Because of this reason, we derive the OPA for minimizing BER in DAS, which only uses a large scale fading to CSI and excepts a small scale fading. The simulation results show that the proposed OPA achieves better BER performance than conventional OPA considering a small scale fading in time-varying Rayleigh fading channel, and also has similar performance in Rayleigh flat-fading environment. The BER performance of proposed OPA which derived in Rayleigh fading channel is similar to minimum BER of Ricean fading channel which has small Line-of-Sight (LOS).
Channel state information
Fading distribution
Cite
Citations (5)
Due to surface and bottom space constraints of the underwater acoustic channel, multi-path fading occurs and causes degradation of communication. Multi-path fading depending on the maximum delay time(Tm) and symbol period(Ts) can be divided into two kinds of channels. In this paper, we propose Anti-Multipath Fading Underwater Acoustic Communication(AMF-UAC) System. This system estimates the kind of channel and distinguishes flat fading (Tm<Ts) from frequency selective fading (Tm>Ts) under the ocean environmental variability. After checking the channel status, this system selects a mitigation technique depending on the type of multipath fading. In order to verify AMF-UAC system performance, we test transmission of image using 43.2kbit of gray image through the multi-path fading channel. Test results show that the number of bit errors is reduced from 300 to 10 under flat fading channel and from 20,000 to 90 under frequency selective fading channel when the reference SNR is 14dB.
Fading distribution
Channel state information
Underwater acoustic communication
Cite
Citations (0)
In this paper, we consider the fast and slow multipath fading scenarios in which the coherence time of the channel between primary transmitter and secondary receiver is compared to the sensing time. We formulate the detection problem under fast fading, then we show that there are situations in which the detection performance under the fast fading scheme outperforms that of the non-fading case (AWGN) slightly. Also, using Markov inequality, we propose a simple method in order to solve the optimization problem in the slow fading scenario, since the average probability of detection has no closed form. Finally, we observe that in low SNR rgimes the performance of detection under fast fading is significantly better in comparison to slow multipath fading.
Fading distribution
Channel state information
Diversity scheme
Cite
Citations (0)
We derive the optimal power control strategy to maximize the sum rate of a multiple access channel with two time-scale fading, where transmitters have access to each of the other users' 'slow' fading information and the statistics of the 'fast' fading, but no knowledge of the instantaneous fast fading states. Assuming identical fast fading distributions for all users, it is found that the optimal strategy is to let at most one user transmit, with the user transmitting the one with the 'best' slow fading condition. An example with users undergoing lognormal shadowing and Rayleigh fast fading is considered, and capacity comparisons are made. Simple sub-optimal power control schemes which provide close to optimal performance in certain favorable channel conditions are also proposed and analysed.
Channel state information
Fading distribution
Log-normal distribution
Diversity scheme
Rician fading
Cite
Citations (3)
본 논문에서는 time-varying Rayleigh fading channel에서 분산 안테나 시스템의 최적 전력 분배 기법을 제안한다. 기존 관련 연구에서는 각 기지국으로부터 수신되는 전력의 차이를 기지국간 전력 분배에 고려하지 않았으나, 최근 들어 빠르게 변하는 small scale fading까지 Channel State Information (CSI)로하여 전력 분배를 하는 경우에 대한 연구가 진행되었다. 하지만, 실제 무선통신 환경에서 송수신단간의 거리 차이 때문에 피드백이 반영된 신호가 수신될 때의 페이딩 채널은 피드백을 하는 시점과는 차이가 있고, 이로 인한 성능저하가 나타난다. 본 논문에서는 이러한 성능저하를 극복하고 CSI 피드백의 부담을 경감시키기 위하여 small scale fading을 제외하고, 느리게 변하는 경로손실과, 섀도잉에 의한 large scale fading값만을 피드백하는 분산 안테나 시스템을 제안하고 Bit Error Rate (BER)을 최소화하기 위한 최적 전력 분배 공식을 유도했다. 빠른 페이딩 환경에서, 제안된 최적 전력분배 기법이 small scale fading까지 고려한 전력 분배 기법보다 월등히 좋은 성능을 보이며, 피드백 지연이 없는 환경에서도 1dB 이내의 성능을 보이는 것을 확인했다. 또한, 본 논문에서 Rayleigh fading channel을 가정하여 유도한 전력 분배 기법이 Line-of-Sight(LOS) 성분의 크기가 작은 Ricean fading channel에서도 최소의 BER과 거의 비슷한 값을 달성함을 보였다.
Channel state information
Fading distribution
Rician fading
Cite
Citations (0)