Link Margin Research Articles

Digital video broadcasting‐return channel via satellite linear modulation with turbo coding

SUMMARYThe digital video broadcasting, return channel via satellite second generation (DVB‐RCS2) linear modulation scheme offers significantly better performance than that of the first generation (DVB‐RCS) both at the physical layer and at the link layer. The DVB‐RCS2 design allows for optimizing the link margin by implementing adaptive coding and modulation (ACM) in the return link, controlled by the central system controller, resembling the ACM as supported for the DVB‐S2‐based forward link. The gain of the return link ACM complements performance improvements at layers 1 and 2. The performance enhancement of the DVB‐RCS2 comes with a higher computational complexity compared with that of the DVB‐RCS but mainly at the gateway, whereas the computational load increase of the terminal is minimal. Copyright © 2013 John Wiley & Sons, Ltd.

Modelling of free space optical link for ground‐to‐train communications using a Gaussian source

The demand for access to broadband data services in high-speed trains is increasing as more people are travelling to and from work, which is not met by the existing radio frequency technology. Therefore an alternative technology known as free space optics (FSO) could be readily adopted that could overcome the bandwidth bottleneck problem. The study presents a mathematical model of an FSO link for ground-to-train communications link and analyses the system performance in terms of the signal-to-noise ratio and the bit error rate (BER). The authors show that the simulated BER is in good agreement with the predicted results for bit rates up to 50 Mbps. The link budget analysis for the proposed system is also presented showing a link margin of 17.75 dB.

Wavelength Division Multiplexing Network over Polymer Optical Fiber Using Fabricated Couplers for Informatics Communications

Abstract The implementation of three channels wavelength division multiplexing (WDM) network using a low cost and all POF components are developed. A low cost and high performance of 1x3 POF fused coupler/splitter using POF polymethyl methacrylate (PMMA) is fabricated as the multiplexer/de-multiplexer. Three visible LED light source transmitters; 470 nm, 520 nm and 650 nm are utilized in sending three data inputs; the CCTV and DVD video and audio signal. The optical lights are multiplexed into a single POF link and de-multiplexed back at the receiver end. The unwanted wavelengths are performed using thin color film filter before the receivers. With link margin 5 dB, the maximum POF link length is 25 meters which is suitable for informatics, infotainments, triple play in the field of last miles communications.

Improved lower bounds on ranging accuracy of rectangular template-based UWB correlation radar for vital sign monitoring

This paper proposes and investigates low-power rectangular ultra wideband (UWB) correlation-based radars for vital sign monitoring with a target ranging accuracy of 0.08 mm. The lower bounds on the time-of-arrival estimation error are studied. In particular, we study and compare the improved Ziv-Zakai lower bound of rectangular template-based estimators to the corresponding optimal estimators via semi-analytic simulations in the UWB IEEE 802.15.6a CM #3 channel and a simulated channel model based on actual on-body measurements. We show that the investigated radar achieves the target ranging accuracy at a signal-to-noise-ratio (SNR) = 40 dB. Also, we study the effect of template pulse misalignment on the proposed estimators. We provide theoretical as well as numerical results based on semi-analytic simulations in the IEEE 802.15.6a UWB channels. A link budget is designed for the achievement of the target SNR with a link margin = 3 dB.

47-km 125-Gbps transmission using a self-seeded transmitter with a modulation averaging reflector

We demonstrate an extended-cavity (1-km round trip) transmitter employing a reflective-semiconductor optical amplifier (RSOA) self-seeded by spectrally-sliced passive modulation-averaging reflector. We show that using modulation averaging reflectors in self-seeded transmitters improves link margin, allows a wider range of bias conditions for the RSOA by removing the modulation in the seeding light and consequently allows operation with higher extinction ratios. We furthermore demonstrate 47 km transmission at 1.25 Gbps with a 16-channel fully passive remote node. This type of transmitter is suitable for application in colorless WDM-PON systems.

A 20 Gb/s triple-mode (PAM-2, PAM-4, and duobinary) transmitter

Increasing data rates over electrical channels with significant frequency-dependent loss is difficult due to excessive inter-symbol interference (ISI). In order to achieve sufficient link margins at high rates, I/O system designers implement equalization in the transmitters and are motivated to consider more spectrally-efficient modulation formats relative to the common PAM-2 scheme, such as PAM-4 and duobinary. This paper reviews when to consider PAM-4 and duobinary formats, as the modulation scheme which yields the highest system margins at a given data rate is a function of the channel loss profile, and presents a 20Gb/s triple-mode transmitter capable of efficiently implementing these three modulation schemes and three-tap feed-forward equalization. A statistical link modeling tool, which models ISI, crosstalk, random noise, and timing jitter, is developed to compare the three common modulation formats operating on electrical backplane channel models. In order to improve duobinary modulation efficiency, a low-power quarter-rate duobinary precoder circuit is proposed which provides significant timing margin improvement relative to full-rate precoders. Simulation results of the proposed transmitter in a 90nm CMOS technology compare operation with the different modulation schemes over three backplane channels with different loss profiles.

Differential Fade Margin and Handoff Gain in Wireless Cellular Networks

Communication links in a wireless cellular network are subject to random slow fading. Thus a link margin is required to guarantee a certain level of link reliability. It is well known that the required link margin is reduced due to mobile handoff at the cell edge. This is the handoff gain. Traditionally the handoff gain considers only the reduction of the link margin requirement due to the presence of multiple random slow fading paths; the error rate requirement is not taken into account. However, in the case of soft handoffs, when multiple links are available to the receiver simultaneously, for a given target overall error rate, a higher error rate target per link is allowed. This increases the handoff gain, but the possibility of imbalance at the handoff links requires an additional margin. This is the differential fade margin, which reduces the handoff gain. We show how to numerically calculate the differential fade margin and the overall handoff gain without resorting to simulations. Several illustrative examples are given. The approach is used to show that the benefit of being able to allow a higher per link error rate in the soft handoff far outweighs the drawback of requiring the additional differential fade margin. We show that the soft handoff gain is more than 3 dB higher than the traditional soft handoff gain widely used in the radio frequency (RF) design community. This approach also allows us to quantify the link budget gain when the target error rate is relaxed. In addition to quantifying the gains in theoretical Gaussian and Rayleigh channels, we have also shown that in CDMA2000 3G1× systems, regardless of whether the carrier frequency band is at 1900 MHz (PCS), 850 MHz (cellular), or 450 MHz, relaxing the target frame error rate (FER) from one percent to two percent provides a 1 dB gain in the link budget, while relaxing the target FER from one percent to five percent provides a 2 dB gain in the link budget. © 2012 Alcatel-Lucent.

Geodesy instrument package on the Moon for improving our knowledge of the Moon and the realization of reference frames

The use of passive Laser reflectors on the lunar surface has been the most attractive in the Apollo era among alternative measurement techniques, but the laser link margin is very small, permitting only very few stations to obtain valid measurements. Therefore the next generation of the LLR (Lunar Laser Ranging) technique should aim for a substantial improvement. We propose a one-way ranging concept involving Laser transponders. A particular strength of this proposed experiment is given when several stations are ranging to the Moon simultaneously and/or when several geodetic stations on the Moon are used simultaneously, as this is expected to improve the modeling geometry and data quality. The proposed experiment may well initiate the installation of new observing stations on Earth – perhaps within the infrastructure of existing astronomical observatories. At the same time it allows many more SLR (Satellite Laser Ranging) stations from the existing network to obtain measurements from the Moon. In the case of the beacon mode, only passive optical receivers are needed on the ground. In addition, we propose to deploy and operate a microwave receiver/transmitter with precisely known mechanical local ties to the laser beacon/receiver, which will permit observations of the tangential position of the Moon with respect to the celestial frame. We also propose to include a GNSS microwave transmitter into the equipment realizing a “GPS/Galileo satellite on the Moon” that is tracked together with GNSS satellites by receivers on the ground and possibly on a future generation of GNSS satellites. The ultimate objectives of our proposal are threefold, the improvement of the reference frames for the Earth, a better understanding of the Moon's interior, and a better determination of the parameters of General Relativity.

Error performance of terrestrial free space optical links with subcarrier time diversity

In this work, the performance of binary phase shift keying (BPSK) subcarrier intensity-modulated terrestrial free-space optical (FSO) communication link is analysed in the presence of noise and atmospheric turbulence. To ameliorate channel fading caused by the atmospheric turbulence, we propose a subcarrier time delay diversity (STDD) scheme in which the delayed versions of the original data are re-transmitted on different subcarriers. In short range links, a single re-transmission scheme results in an estimated gain of up to 4.5 dB in received irradiance. With sufficient link margins, short range FSO links might be able to cope without the use of any diversity techniques but for links spanning over 1 km, turbulence induced fading effect must be compensated for. In this study, the authors show that the subcarrier STDD is a viable scheme for this purpose.

Measurements and prediction of outage intensity owing to rain attenuation

Measured data of rain attenuation from 19 terrestrial line-of-sight links, operating in frequencies from 14.5 to 83.5 GHz, were analysed to provide statistics of fade durations as a function of the attenuation threshold. From these results, an empirical method for predicting outage intensity owing to rain attenuation was derived, that shows good agreement with the measurements and allows the calculations of required link margins.

High-sensitivity DPSK receiver for high-bandwidth free-space optical communication links

A high-sensitivity modem and high-dynamic range optical automatic gain controller (OAGC) have been developed to provide maximum link margin and to overcome the dynamic nature of free-space optical links. A sensitivity of -48.9 dBm (10 photons per bit) at 10 Gbps was achieved employing a return-to-zero differential phase shift keying based modem and a commercial Reed-Solomon forward error correction system. Low-noise optical gain was provided by an OAGC with a noise figure of 4.1 dB (including system required input loses) and a dynamic range of greater than 60 dB.

Next-generation access network: A wireless network using E-band radio frequency (71-86GHz) to provide wideband connectivity

The expected explosion in capacity requirements associated with Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX) networks has led to an interest in the use of millimeter wave (specifically E-band) equipment for backhaul. Initially deployed for campus networks, such technology could also become a convenient solution for carrier applications offering the multi-gigabit backhaul capacity needed for future cellular networks. In the fixed point-to-point 70 GHz to 80 GHz radio frequency band, an unprecedented 10 GHz bandwidth is allowed, far exceeding the spectrum allocations in any given lower licensed frequency band. The 71 GHz to 76GHz bands are paired with 81 GHz to 86 GHz, yielding 5 GHz of spectrum in each direction. The vast amount of bandwidth available in this band makes it ideal for offering multi-gigabit transmission rates. This paper aims to characterize a wireless transmission channel operating in the 70 GHz to 80 GHz band, considering the propagation limits and the rain attenuation impairments on transmission link availability. Our objective is to define specific parameters and constraints which can be used to define an optimum topology for an access network. We use point-to-point systems with a transport capacity up to 10 Gb/s per single carrier using high-level modulation schemes. We also propose a specific interference mitigation analysis to enhance understanding of the angular discrimination needed to avoid any degradation of the total link margin and the signal-to-interference ratio.

Coherent Polarization Shift Keying Modulated Free Space Optical Links Over a Gamma-Gamma Turbulence Channel

Problem statement: The optical signal propagating through the Free Spa ce Optical (FSO) channel suffers from irradiance and phase fluctuati ons caused by the atmospheric turbulence, which results in Bit Error Rate (BER) performance degrada tion. Approach: In this study the performance of the Multilevel Coherent Polarization Shift Keying ( M-POLSK) based FSO communication system operating over the gamma-gamma turbulence channel is investigated. To mitigate the turbulence induced fading, the convolutional coding and spatia l diversity techniques are employed. The upper BER bounds are derived using the transfer function technique. Results: For example, with a SNR of 30 dB, the BERs for uncoded and coded M-POLSK are 0.047 and 1.4 ×10 -4 , respectively in the weak turbulence regime. When the Maximum Ration Combining (MRC) technique employing four detectors are used in the receiver, the power gains of ~31.4, ~29.5 and ~57.9 dB are achieved for weak, moderate and strong turbulence regimes, respectivel y. Conclusion: We have also shown that the spatial diversity offers increased link margin as t he scintillation level rises. Compared to the angul ar modulation, the proposed M-POLSK scheme offers high immunity to the phase noise, thus reducing the power penalties.

달 탐사를 위한 우주통신에서 텔레메트리 링크에 대한 최대 전송속도 성능분석

Telemetry link requires high data rate to transmit the multimedia data for lunar explorations in space communications. In this paper, we analyze a data rate with the modulation and channel coding schemes based on Consultative Committee for Space Data Systems (CCSDS) in S, X, Ku and Ka bands, respectively. Then, we suggests modulation and channel coding schemes to meet the link margins and have a maximum data rate for lunar explorations in telemetry links.

Hybrid Channel Codes for Efficient FSO/RF Communication Systems

Conventional hybrid RF and optical wireless communication systems make use of parallel Free Space Optical (FSO) and Radio Frequency (RF) channels to achieve higher reliability than individual channels. True hybridization can be accomplished when both channels collaboratively compensate the shortcomings of each other and thereby improve the performance of the system as a whole. In this paper, we propose a novel coding paradigm called Channel Coding that not only optimally achieves the capacity of the combined FSO and RF channels but also can potentially provide carrier grade reliability (99.999%) for hybrid FSO/RF systems. The proposed mechanism uses non-uniform and rate-compatible LDPC codes to achieve the desired reliability and capacity limits. We propose a design methodology for constructing these Hybrid Channel Codes. Using analysis and simulation, we show that by using Hybrid Channel Codes, we can obtain significantly better availability results in terms of the required link margin while the average throughput obtained is more than 33% better than the currently existing systems. Also by avoiding data duplication, we preserve to a great extent the crucial security benefits of FSO communications. Simulations also show that Hybrid Channel Codes can achieve more than two orders of magnitude improvement in bit error rate compared to present systems.

Hybrid Channel Codes for Efficient FSO/RF Communication Systems

Conventional hybrid RF and optical wireless communication systems make use of parallel Free Space Optical (FSO) and Radio Frequency (RF) channels to achieve higher reliability than individual channels. True hybridization can be accomplished when both channels collaboratively compensate the shortcomings of each other and thereby improve the performance of the system as a whole. In this paper, we propose a novel coding paradigm called "Hybrid Channel Coding" that not only optimally achieves the capacity of the combined FSO and RF channels but also can potentially provide carrier grade reliability (99.999%) for hybrid FSO/RF systems. The proposed mechanism uses non-uniform and rate-compatible LDPC codes to achieve the desired reliability and capacity limits. We propose a design methodology for constructing these Hybrid Channel Codes. Using analysis and simulation, we show that by using Hybrid Channel Codes, we can obtain significantly better availability results in terms of the required link margin while the average throughput obtained is more than 33% better than the currently existing systems. Also by avoiding data duplication, we preserve to a great extent the crucial security benefits of FSO communications. Simulations also show that Hybrid Channel Codes can achieve more than two orders of magnitude improvement in bit error rate compared to present systems.

Antenna with optimized pattern for simultaneous reception of terrestrial signals and signals of geostationary satellites

Abstract. The link margin for satellite communication services targeting mobile users is tight. This leads to reception problems in areas with strong fading scenarios like urban areas or forested areas with dense foliage. In order to avoid loss of service in urban areas with week coverage by satellite signals, terrestrial repeaters are used. Therefore in the design of antennas for mobile reception of satellite services, an optimized characteristics for the satellite constellation, as well as an adequate coverage of the terrestrial repeaters has to be accounted for. In this paper an antenna with optimum shaped pattern for the satellite mode and adjustable gain for vertical polarization is investigated. Beside constraints regarding the radiation pattern, measurements concerning the dependence of the antenna on noise temperature and therefore the behavior in real noisy environments are carried out. A comparison with a conventional antenna shows the high performance of the new antenna in combination with a very low volume requirement.

Advanced Modulation Schemes for Short-Range Optical Communications

The performance of advanced modulation schemes for spectrally efficient data transmission is reviewed, targeting short-range intensity-modulated optical channels with direct detection. Hereby, the focus lies on the performance of multilevel pulse-amplitude modulation combined with electronic equalization and, as an alternative modulation scheme, discrete multitone. A comprehensive statistical analysis of clipping noise is presented and exact expressions for the performance of symmetrically clipped discrete multitone are derived. It is shown that the clipping noise is impulsive and obeys a generalized Laplace distribution. The bit-error probability due to clipping is studied in detail, and it is found that the impact of clipping noise is reduced for an increasing number of subchannels. Finally, the optical link margins of multilevel pulse-amplitude modulation in combination with electronic equalization and that of discrete multitone in combination with margin-adaptive bit loading are compared. It is found that even symmetrically clipped discrete multitone suffers from its large crest factor in the peak-power-limited channel and that, in many instances, pulse-amplitude modulation provides higher link margins for the same target bit-error probability.

Impact of the Receive Antenna Arrays on Spatio-Temporal Availability in Satellite-to-Indoor Broadcasting

This contribution presents the results of our study on spatio-temporal availability in satellite-to-indoor broadcasting. We compare the performance of single and multiple antenna arrays consisting of theoretical and measured antennas with various polarimetric radiation patterns and coupling effects for different satellite elevation angles. The spatial satellite to indoor channels are obtained by a 3D ray tracing engine and by a geometry-based channel modeling tool. The temporal fluctuations of the channels are modeled by the PDF of a truncated normal distribution and are based on satellite-to-indoor measurements. The additional antennas at the receiver reduce both the spatial and the temporal variability of the received power, leading to a significant reduction of the transmit power required to achieve the same target availability. The simulation results suggest that the spatial correlation in the line-of-sight room area is higher than in the non-line-of-sight room area. In the line-of-sight areas, the best performance is achieved by multiple circularly polarized receive antennas. For elevations higher than 50 in the non-line-of-sight areas, a combination of horizontally and vertically (orthogonal) polarized antennas shows the best performance, especially if high availabilities are considered. Furthermore, the influence of coupling effects between closely spaced receive antennas on the availability is studied. In general, antenna coupling effects should be handled by increasing the required link margin. The influence of the temporal changes due to a person movement on the availability is found to be not very significant.

달 탐사를 위한 한국형 심우주 지상국

세계 각국은 이미 우주 개발을 위한 치열한 경쟁에 돌입하였으며, 우리나라도 2020년에 달 탐사선 발사 및 2025년에 달 착륙선 발사를 계획하고 있다. 우리나라 달 탐사 계획을 성공적으로 수행하기 위해서는 심우주 통신 기술 및 지상국 설치등과 같은 심우주 관련 기술 개발이 필요하다. 이를 위하여 심우주 관련 선진국들과의 협력을 통하여 축적된 경험 및 기술을 바탕으로 한국형 달 탐사 임무에 적합한 심우주 통신 방식을 개발하고 독자적인 지상국을 확보하여야 한다. 본 논문에서는 우리나라의 DSN을 성공적으로 정착시키기 위하여 국외 DSN과 심우주 통신 기술에 대해서 살펴보고, 이를 바탕으로 링크 마진을 비롯한 여러 가지 기술적 요구사항을 제시하며 우리나라의 달 탐사 계획을 위해 필요한 최적의 지상국 확보 전략을 제안한다. Many countries of the world have been launched the competition of space development and Korea also has a plan for the launch of Lunar orbiter in 2020 and Lunar lander in 2025 for Lunar explorations. For the success of the planned Lunar exploration, we need to enhance the required deep space communication technologies. To achieve our goals, we should develop space communications system and Korean DSN (deep space network) based on experiences and technologies through cooperation with the advanced countries in the field of deep space exploration. In this paper, we investigate overseas DSNs and deep space communication systems, and present the link margin and other technical requirements for successful DSN deployment. In addition, we propose a best strategy to secure domestic ground stations for the Korean Lunar exploration missions.