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Communications, IET

Issue 5 • Date March 27 2012

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Displaying Results 1 - 14 of 14
  • Guest Editorial: Special Section on Photonic and Free Space Optics Networks

    Publication Year: 2012 , Page(s): 471 - 472
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (80 KB)  

    Since the growth of mobile communications, in particular mobile broadband, the need for high bandwidth infrastructure has become increasingly necessary. Recent developments in wireless radio frequency (RF) technologies have yielded channels which are able to provide high rates with a great deal of user mobility. View full abstract»

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  • Comprehensive modelling of wave propagation in photonic devices

    Publication Year: 2012 , Page(s): 473 - 477
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (315 KB)  

    A simple and powerful modelling method in the time domain is established to resolve travelling waves inside photonic devices. The basic idea is to transform usual space-time coordinates (z, t) into a mixed grid (u, v) in which waves propagate along their characteristic lines, resulting in an inherent numerical stability, as well as easy interpretation of all parametric variables and their derivatives. In this study, the authors will demonstrate, for the first time, how the effect of gain dispersion can be dealt with using an efficient fourth-order algorithm, which attains high precision, high speed as well as very large stepsize. Excellent agreement with existing analytical results is obtained. View full abstract»

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  • Repetition rate and wavelength-tunable all-optical actively mode-locked fibre ring laser based on a reflective semi-conductor optical amplifier

    Publication Year: 2012 , Page(s): 478 - 483
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (607 KB)  

    A repetition rate- and wavelength-tunable fibre ring laser that utilises a reflective semi-conductor optical amplifier as both a gain and mode-locking element is presented. Moreover, 10.3 ps pulses at 10 GHz repetition rate are obtained across a 30 nm tuning range covering the entire C-band. The repetition rate is tunable up to 30 GHz via rational harmonic mode-locking. A comparison is made using a conventional semi-conductor optical amplifier as the gain and mode-locking element. It is shown that the reflective semi-conductor optical amplifier requires in excess of 5 dB less average pump pulse power in order to achieve the optimum mode-locking condition, for achieving the narrowest output pulse width, thereby relaxing the requirement for a complex and expensive pump pulse source. View full abstract»

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  • Optimised non-uniform biasing technique for a highspeed optical router to achieve uniform semiconductor optical amplifier gain

    Publication Year: 2012 , Page(s): 484 - 491
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (509 KB)  

    In this study, we propose applying non-uniform biasing current technique to improve the gain uniformity of the semiconductor optical amplifier (SOA) for high-speed optical routers. The output pulses will have high-gain deviation because of the high-speed input pulses and the slow SOA gain recovery, thus resulting in a high system power penalty. The theoretical SOA operation principle is demonstrated using a segmentation model that employs the rate and propagation equations with third-order gain coefficients. The impact of the bias current on the SOA gain responses owing to the input packet of 1 mW input Gaussian pulses at a wavelength of 1550 nm is analysed in order to optimise the proposed non-uniform bias current shape. The uniform and the optimised non-uniform bias current techniques are investigated in terms of the SOA gain uniformity and the average output power for high-speed data rates from 10 to 160 Gb/s. The impact of the average bias current applied to the SOA on the non-uniform shape is also investigated at all input data rates. Results obtained show a significant improvement in the gain standard deviation of 4.6, 6.3, 8.7, 10.1 and 10.2 dB for the data rates of 10, 20, 40, 80 and 160 Gb/s, respectively, when applying 150 mA average non-uniform biasing and these values reaches 15.2, 16.3, 17.7, 18 and 17.4 dB at 200 mA. The proposed technique also offers an increase in the average output power for the input pulses compared with uniform biasing. View full abstract»

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  • Comparing the cloud effects on hybrid network using optical wireless and GHz links

    Publication Year: 2012 , Page(s): 492 - 498
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1037 KB)  

    Free space optic communication (FSOC) can be considered as high data rate providing communication link between optical ground stations and satellites. However, clouds offer significant attenuation causing several tens of decibels of attenuation and even complete blockage of the link. The hybrid network of FSO/radio frequency (RF) can improve cloud influence reduced availability. In this study, the performance of different FSOC wavelengths has been analysed under different clouds attenuation using Mie scattering theory approach, as well as visibility approach. The different cloud-specific attenuation analysis has also been performed for different RF bands used for satellite communication. View full abstract»

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

    Publication Year: 2012 , Page(s): 499 - 506
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (402 KB)  

    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. View full abstract»

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  • Free-space optical links for latency-tolerant traffic

    Publication Year: 2012 , Page(s): 507 - 513
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    Peer-to-peer (P2P) traffic and other latency-tolerant data sources form a large portion of present-day backbone traffic. Traffic shaping has been introduced to reduce the amount of P2P traffic at the expense of the end-user experience. In this work, free-space optical (FSO) links are proposed as a means to connect internet service providers to the backbone to carry latency-tolerant traffic. Although FSO links are less reliable than fibre, they are inexpensive and able to provide high throughput for traffic, which is able to tolerate delay. Single and adaptive modulation schemes are designed with the goal of maximising the throughput of the FSO link over a period of time rather than maximising the instantaneous reliability. Real world weather and visibility data from a major Canadian city are used to evaluate various techniques in terms of throughput, availability and outage. For a fixed modulation FSO system, four-pulse amplitude modulation (PAM) supports a yearly average rate of near 1.5 Gbps for a 1 km range, whereas conventional on off-keying (OOK) achieves 880 Mbps. With additional channel feedback data, adaptive modulation has over double the average throughput of OOK using four different PAM modulation schemes. View full abstract»

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  • Channel modelling and performance of non-line-of sight ultraviolet scattering communications

    Publication Year: 2012 , Page(s): 514 - 524
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1579 KB)  

    The solar-blind ultraviolet (UV) spectrum has useful properties for wireless communication and sensing. Strong atmospheric scattering in the UV spectrum enables non-line-of-sight (NLOS) communication. The authors present recent experimental and analytical results in NLOS UV channel modelling, including impulse response and path loss. The authors further study the NLOS UV link performance for short-range communication scenarios based on our theoretical modelling results. Relations between power limitation and channel bandwidth limitation are examined. Some link budget results are analysed for long-range communication links up to 5 km. View full abstract»

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  • Network solutions for the line-of-sight problem of new multi-user indoor free-space optical system

    Publication Year: 2012 , Page(s): 525 - 531
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    Recent developments in solid-state light-emitting diode (LED) materials and devices are driving a resurgence in the use of free-space optics (FSO) for wireless broadband communication. This technology uses the visible spectrum provided by `white` LEDs, which are becoming ubiquitous in lighting and has some desirable properties competitive with existing radio-frequency communications. By leveraging the low-cost nature of LEDs and lighting units there are many opportunities to exploit this medium for widespread optical communication deployment. The optical medium, however, has distinct characteristics that must be managed, such as directionality and susceptibility to noise sources in the visible spectrum. In this study, the authors present a new indoor FSO communication system, also known as a visible-light communication system that achieves satisfactory data rates while supporting multiple access under line-of-sight constraints. A hexagonal device design is proposed and investigated in the context to two communication protocols designed to manage point-to-point and point-to-host cases. Theoretical analysis and simulation of the two protocols using this hexagonal transceiver design indicate suitability for addressing high data-rate communications between peer devices; or between multiple devices using the peer-to-host model. A new medium access control scheme will also discussed. View full abstract»

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  • Channel estimation for asymmetrically clipped optical orthogonal frequency division multiplexing optical wireless communications

    Publication Year: 2012 , Page(s): 532 - 540
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (575 KB)  

    A novel channel estimation method for asymmetrically clipped optical orthogonal frequency division multiplexing-based optical wireless communications systems is proposed. Different from the superimposed sequence used in traditional methods, the local matrix and superimposed periodic training are designed rationally. Furthermore, the channel impulse response coefficient of indoor optical wireless diffuse channel can be estimated exactly. The proposed method is not only accurate and simple, but can also allocate time and power flexibly, and improves the bandwidth efficiency. View full abstract»

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  • Indoor optical wireless system dedicated to healthcare application in a hospital

    Publication Year: 2012 , Page(s): 541 - 547
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (629 KB)  

    In this study, the authors deal with a wireless healthcare monitoring solution based on a secure technology in hospital context. Actually, radio frequency (RF) networks can present electromagnetic disturbances in hospital environments. The authors thus investigate an alternative solution based on infrared (IR) technology. As patient mobility is inevitable, they focus on mobile IR communications considering line-of-sight (LOS) propagation between the transmitter coupled with medical sensors and the receiver. The authors study different mobility scenarios, one in two dimensions (2D) for a fixed transmitter height and another in three dimensions (3D) by considering transmitter height variations. In each case, they analyse the distributions of channel gain state to find the statistical model of the mobile IR channel for a given distribution of the patient locations within the room (uniform or gaussian). By calculating the outage probability from statistical analysis, they investigate the impact of the mobility on data rates and quality of service needed for this application in the case of an on-off keying (OOK) modulation before concluding on the reliability of the studied mobile healthcare monitoring system. View full abstract»

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  • Physical-layer network coding with limited feedback in two-way relay channels

    Publication Year: 2012 , Page(s): 548 - 556
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    In this study, the authors introduce the limited feedback technique into the physical-layer network coding which is the most spectrally efficient protocol for two-way relay channels, consisting of one relay and two end (source) nodes. In amplify-and-forward strategy, each source node obtains full channel state information (CSI) of the channel between relay and itself from training sequences and partial CSI of the channel between relay and the other node by means of a limited number of feedback bits provided by the relay. In the decode-and-forward strategy, the authors completely remove training sequences and the source nodes provide the partial CSI of the link between relay and themselves from limited feedback bits, the CSI of the other link being useless for this strategy. Tight upper bounds on the bit error probability depending on the number of feedback bits are derived for binary phase shift keying (PSK) and quadrature-PSK modulations for both strategies. It is shown via computer simulations that the bit-error-rate performance of the system with full CSI at all nodes is achieved for both strategies by using a few number of feedback bits. Moreover, the computation complexity is reduced for the proposed scheme with a single antenna at all nodes. View full abstract»

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  • Accurate simulation of non-isotropic fading channels with arbitrary temporal correlation

    Publication Year: 2012 , Page(s): 557 - 564
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (815 KB)  

    The accurate simulation of wireless channels is important since it permits the realistic and repeatable performance measurement of wireless systems. A new technique is proposed for simulating Rayleigh fading channels with isotropic or non-isotropic scattering and with arbitrary temporal correlation. Fading samples are generated by passing Gaussian samples through a spectrum shaping filter. A new iterative algorithm is then presented for designing stable complex infinite impulse response (IIR) filters with quantised coefficients. The algorithm utilises a least-squares cost function augmented with a barrier function to ensure filter stability and to reduce quantisation noise. The performance of the proposed filter design algorithm is verified with 18-bit fixed-point simulations of different fading channel scenarios including isotropic and non-isotropic scattering and the IEEE 802.11n model F fading spectrum. View full abstract»

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  • Quality of service assurance in multi-antenna relay-assisted networks

    Publication Year: 2012 , Page(s): 565 - 575
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (682 KB)  

    This study concerns two-hop communication over a relay-assisted wireless network, including L point-to-point communication links and a multi-antenna relaying node. It is assumed the relay is equipped with Nr antennas and the amplify-and-forward strategy is employed at this node, considering the second-order statistics of channel coefficients are merely available at the relay. To this end, each source sends its desired signal to the relay during the first hop. Thus, the relay simultaneously receives a faded version of L transmitted signals corrupted with an additive white Gaussian noise in a vector form. Then, the relay applies a weight matrix of dimension Nr×Nr to the received vector and transmits the resulting vector to the destinations throughout the second hop. In this regard, the task of finding the best weight matrix at the relaying node under two different criteria, that is, minimising the relay's transmit power to have a minimum signal-to-interference noise ratio (SINR) at destinations and maximising the worst-case SINR for a given relay's transmit power, is investigated. Accordingly, it is demonstrated that the corresponding problems can be formulated as optimisation problems which are not convex in general. This motivated the authors to propose suboptimal solutions through using the so-called semidefinite relaxation method to translate original problems into semidefinite programming problems. Numerical results are provided, showing the superiority of the proposed methods as compared to the best known method. View full abstract»

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