By Topic

Wireless Communications, IEEE

Issue 2 • Date April 2003

Filter Results

Displaying Results 1 - 9 of 9
  • Guest editorial - Optical wireless communications

    Publication Year: 2003 , Page(s): 6 - 7
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | PDF file iconPDF (185 KB) |  | HTML iconHTML  
    Freely Available from IEEE
  • Short-range wireless infrared transmission: the link buoget compared to RF

    Publication Year: 2003 , Page(s): 8 - 14
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB) |  | HTML iconHTML  

    First Page of the Article
    View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Indoor broadband optical wireless communications: optical subsystems designs and their impact on channel characteristics

    Publication Year: 2003 , Page(s): 30 - 35
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (474 KB) |  | HTML iconHTML  

    With proper system design, infrared multispot diffusing (MSD) configuration communications links promise several orders of magnitude higher bit rates than radio links. Essential to the communications system are the optical subsystems: transmitter and receiver optics. Preliminary experiments on fabrication of beamshaping optical elements for the transmitter and receiver optical front-end have been conducted. The impact of optical subsystems on channel characteristics is investigated, and the results undoubtedly prove the great potential of MSDC. Use of holographic optical elements at both transmitter and receiver increases the signal-to-noise ratio by at least 11 dB and at the same time significantly improves the power budget of the system by reducing path loss by more than 6 dB. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Wireless infrared communications with edge position modulation for mobile devices

    Publication Year: 2003 , Page(s): 15 - 21
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (569 KB) |  | HTML iconHTML  

    Driven by the Infrared Data Association, wireless infrared communication has become a very popular and widely used method for short-range data transmission between mobile devices like laptops, PDAs, and mobile phones. Especially in ad hoc connection applications, IrDA excels over radio-based solutions like Bluetooth or cable-based solutions like USB, due to the point-and-shoot characteristic of infrared communication. The quality and speed of infrared communications are mainly limited by the bandwidth of infrared transceivers. Therefore, it is important to use a modulation technique with high bandwidth efficiency, while simultaneously maintaining a low bit error rate and high power efficiency. Consequently, the IrDA has continuously improved the modulation techniques of its standards by introducing return to zero inverted (RZI) for the serial infrared (SIR) mode, 4-PPM for the fast infrared mode, and HHH(1,13) for the latest very fast infrared mode. This article presents a new modulation scheme called edge position modulation (EPM) with RLL coding, which offers increased bandwidth efficiency over the previous methods and attractive power efficiency. Since the novel modulation technique can be optimized to the characteristics of the wireless infrared channel, it also maintains low bit error rates. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Experimental characterization of rate-adaptive transmission and angle diversity reception techniques

    Publication Year: 2003 , Page(s): 36 - 44
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (685 KB) |  | HTML iconHTML  

    Ambient light is the main impairment in indoor wireless optical communication systems for data rates up to several megabits per second. Its wide dynamic range, associated with the strong directivity of wireless optical signals, produce large variations on the received signal-to-noise ratio. This article discusses experimental results obtained from a testbed developed to compare different techniques for SNR improvement. The two techniques analyzed are rate-adaptive transmission, which introduces adaptive levels of redundancy in the transmitted signal to improve connectivity, and angle diversity reception, which exploits the inherent directionality of both signal and noise to improve the SNR at the receiver. Furthermore, systems employing both techniques simultaneously were also considered. The testbed replicated a typical indoor environment with both natural and artificial light, containing incandescent and fluorescent light sources. Both the SNR and the associated coverage areas were determined for all considered techniques. Our results show that the combined use of angle diversity based on maximal ratio combining and rate adaptation through the use of repetition coding achieves very good performance with only moderate complexity, allowing connectivity at all locations with data rates close to the maximum possible. In particular, with incandescent illumination and without angle diversity, the data rate had to be decreased down to 2 and 1 Mb/s in 25.9 and 7.7 percent of the room, area, respectively, whereas with maximal ratio combining a decrease to 2 Mb/s was only needed in 0.7 percent of the room area. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • IrDA infrared wireless communications: protocol throughput optimization

    Publication Year: 2003 , Page(s): 22 - 29
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB) |  | HTML iconHTML  

    The delivery of the maximum data rate to users from IrDA IR wireless links depends not only on the physical layer, but also on higher-layer protocols being optimized. This article reviews the IrDA link layer protocol, IrLAP, and examines how to maximize its throughput performance. Simple equations yield to simple rules for the optimization of IrLAP. The analysis presented can also be employed in studying the physical layer requirements of the predicted future data rate increases (40 Mb/s and 100 Mb/s) of the IrDA 1.x standard. The model gives insights for the optimum control of the infrared connection for high performance. Simple formulas are derived for the optimum values of the window and frame size link layer parameters that maximize throughput. Results show that, for the proposed 16 Mb/s extension, significant throughput increase is observed if optimum link layer parameter values are employed. At high error rates, the significance of the minimum turnaround time (a physical layer parameter) and of the transmission control passing mechanism is studied. When the links are adapted to using the optimum window and frame size, combined with low minimum turnaround values and an efficient transmission control passing scheme, we observe performance improvements even at high error rates. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A feature extraction and pattern recognition receiver employing wavelet analysis and artificial intelligence for signal detection in diffuse optical wireless communications

    Publication Year: 2003 , Page(s): 64 - 72
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (638 KB) |  | HTML iconHTML  

    Optical wireless diffuse indoor infrared communication systems have as yet large unrealized bandwidths that are not subject to the same regulatory control as radio frequency systems. Usually, well established RF techniques are used to combat channel imperfections for IR implementations. Here, we introduce a novel receiver system based on the multiresolution time-frequency feature extraction capabilities of wavelet analysis, coupled with the well recognized pattern recognition performance of artificial neural networks for mitigating the effects of bandwidth limiting channel-induced distortion. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Spread spectrum techniques for indoor wireless IR communications

    Publication Year: 2003 , Page(s): 54 - 63
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (667 KB) |  | HTML iconHTML  

    Multipath dispersion and fluorescent light interference are two major problems in indoor wireless infrared communications systems. Multipath dispersion introduces intersymbol interference at data rates above 10 Mb/s, while fluorescent light induces severe narrowband interference to baseband modulation schemes commonly used such as OOK and PPM. This article reviews the research into the application of direct sequence spread spectrum techniques to ameliorate these key channel impairments without having to resort to complex signal Processing techniques. The inherent properties of a spreading sequence are exploited in order to combat the ISI and narrowband interference. In addition, to reducing the impact of these impairments, the DSSS modulation schemes have strived to be bandwidth-efficient and simple to implement. Three main DSSS waveform techniques have been developed and investigated. These are sequence inverse keying, complementary sequence inverse keying, and M-ary biorthogonal keying (MBOK). The operations of the three systems are explained; their performances were evaluated through simulations and experiments for a number of system parameters, including spreading sequence type and length. By comparison with OOK, our results show that SIK, CSIK, and MBOK are effective against multipath dispersion and fluorescent light interference because the penalties incurred on the DSSS schemes are between 0-7 dB, while the penalty on OOK in the same environment is more than 17 dB. The DSSS solution for IR wireless transmission demonstrates that a transmission waveform can be designed to remove the key channel impairments in a wireless IR system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High-availability free space optical and RF hybrid wireless networks

    Publication Year: 2003 , Page(s): 45 - 53
    Cited by:  Papers (18)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (690 KB) |  | HTML iconHTML  

    We introduce hybrid free-space optical and RF wireless links as potential technology for designing next-generation broadband wireless networks. We present various design challenges and potential solutions for real-time link performance characterization and adaptation for enhanced performance during adverse weather conditions. First, we introduce the hybrid wireless architecture and emphasize its significant role in achieving ubiquitous carrier-grade wireless connectivity. Second, we propose a link monitoring scheme that accurately reflects the performance of optical wireless links under various weather conditions. In addition, we examine the role of known link performance restoration schemes - power and data rate control. Third, we propose two novel link restoration schemes that efficiently utilize the hybrid architecture: dynamic load switching and multihop routing. Finally, the article describes an elaborate field testbed based on the hybrid architecture and various link restoration techniques. The dynamic load switching scheme is shown to have a profound impact on the overall hybrid link availability. The results, recorded from the experiments during extreme weather conditions, validate the impact of the hybrid architecture concept and conclusively prove the availability and reliability of the architecture in achieving sustained highspeed wireless connectivity. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IEEE Wireless Communications Magazine deals with all technical and policy issues related to personalization, location-independent communications in all media.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Hsiao-Hwa Chen
Cheng Kung University, Taiwan