K7SF5D9230-4Wireless G Plus MIMO Router

Belkin Ltd. 7 Bowen Crescent, West Gosford NSW 2250, Australia +61 (0) 2 4372 8600 +61 (0) 2 4372 8603 fax Belkin B.V. Boeing Avenue 333 1119 PH Schiphol-Rijk, The Netherlands +31 (0) 20 654 7300 +31 (0) 20 654 7349 fax Belkin Tech Support US: 877-736-5771 310-898-1100 ext. 2263 Europe: 00 800 223 55 460 Australia: 1800 235 546 New Zealand: 0800 235 546 Singapore: 800 616 1790 Belkin Corporation 501 West Walnut Street Los Angeles, CA 90220, USA 310-898-1100 310-898-1111 fax Belkin Ltd. Express Business Park, Shipton Way Rushden, NN10 6GL, United Kingdom +44 (0) 1933 35 2000 +44 (0) 1933 31 2000 fax © 2006 Belkin Corporation. All rights reserved. All trade names are registered trademarks of respective manufacturers listed. The mark Wi-Fi is a registered mark of the Wi-Fi Alliance. The “Wi-Fi CERTIFIED” logo is a certification mark of the Wi-Fi Alliance. Mac, Mac OS, Apple, and AirPort are trademarks of Apple Computer, Inc., registered in the U.S. and other countries. P74880 Wireless G Plus MIMO Router User Manual F5D9230-4 Share your broadband Internet connection Wireless G Plus MIMO Router ������� ��� � � ������� ������ ����� ��� � � ������� ������ ����� ���� ������� ���� ������� ���� ������� ���� � � ����� ����� ����� ����� ����� ������� ����� ������� User Manual ����� Table of Contents 1 Introduction Advantages of a Wireless Network. . . . . . . . . . . . . . . . . . . .1 Placement of your Wireless G Plus MIMO Router. . . . . . . . .2 2 Product Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Product Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 3 Knowing your Router . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 Package Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 System Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 Easy Install Wizard Software System Requirements. . . . . . .9 4 Connecting and Configuring your Router. . . . . . . . . . . . . . . .16 5 Alternate Setup Method . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 6 Using the Web-Based Advanced User Interface . . . . . . . . . .42 Changing LAN Settings. . . . . . . . . . . . . . . . . . . . . . . . . . . .43 Viewing the DHCP Client List Page. . . . . . . . . . . . . . . . . . .45 Configuring the Wireless Network Settings. . . . . . . . . . . . .46 Setting WPA Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52 Setting WEP Encryption . . . . . . . . . . . . . . . . . . . . . . . . . . .53 Using the Access Point Mode. . . . . . . . . . . . . . . . . . . . . . .56 Setting MAC Address Control. . . . . . . . . . . . . . . . . . . . . . .57 Configuring the Firewall . . . . . . . . . . . . . . . . . . . . . . . . . . .59 Using Dynamic DNS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63 Utilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65 Restarting the Router. . . . . . . . . . . . . . . . . . . . . . . . . . .66 Updating the Firmware . . . . . . . . . . . . . . . . . . . . . . . . .71 7 Manually Configuring Network Settings . . . . . . . . . . . . . . . .79 8 Recommended Web Browser Settings . . . . . . . . . . . . . . . . .84 9 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86 10 Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103 Table of Contents 2 1 3 4 5 6 7 8 9 10 section Introduction Thank you for purchasing the Belkin Wireless G Plus MIMO Router (the Router). Following are two short sections—the first discusses the benefits of home networking, and the other outlines best practices that maximize your wireless home network range and performance. Please be sure to read through this User Manual completely, and pay special attention to the section entitled “Placement of your Wireless Networking Hardware for Optimal Performance” on the next page. By following our simple setup instructions you will be able to use your Belkin Home Network to: • Share one high-speed Internet connection with all the computers in your home • Share resources, such as files and hard drives among all the connected computers in your home • Share a single printer with the entire family • Share documents, music, video, and digital pictures • Store, retrieve, and copy files from one computer to another • Simultaneously play games online, check Internet email, and chat Advantages of a Wireless Network Mobility – you’ll no longer need a dedicated “computer room”—now you can work on a networked laptop or desktop computer anywhere within your wireless range Easy installation – Belkin’s Easy Installation Wizard makes setup simple Flexibility – set up and access printers, computers, and other networking devices from anywhere in your home Easy Expansion – the wide range of Belkin networking products let you expand your network to include devices such as printers and gaming consoles No cabling required – you can spare the expense and hassle of retrofitting Ethernet cabling throughout the home or office Widespread industry acceptance – choose from a wide range of interoperable networking products 1 32 Introduction 32 Placement of your Wireless G Plus MIMO Router Important Factors for Placement and Setup Your wireless connection will be stronger the closer your computer is to your Router (or access point). Typical indoor operating range for wireless devices is between 100 and 200 feet. In the same way, your wireless connection and performance will degrade somewhat as the distance between your Router (or access point) and connected devices increases. This may or may not be noticeable to you. As you move farther from your Router (or access point), connection speed may decrease. Factors that can weaken signals simply by getting in the way of your network’s radio waves are metal appliances or obstructions, and walls. If you have concerns about your network’s performance that might be related to rang…

Text truncated - open the document above for the full version.

501W.WalnutStreet- Compton- California90220USA FCCID:K7SF5D9230-4 Date:February10,2006 FEDERALCOMMUNICATIONSCOMMISSION AuthorizationandEvaluationDivision ConfidentialitvReauest PursuanttoSections0.457and0.459oftheCommission'sRules,theapplicantherebyrequests confidentialtreatmentofinfonnationaccompanyingthisapplicationasoutlinedbelow: Schematics BlockDiagram Theabovematerialscontaintradesecretsandproprietaryinfonnationnotcustomarilyreleasedto thepublic.Thepublicdisclosureofthesemattersmightbeharmfultotheapplicantandprovide unjustifiedbenefitstoitscompetitors. TheapplicantunderstandsthatpursuanttoRule0.457,disclosureofthisapplicationand allaccompanyingdocumentationwillnotbemadebeforethedateofthegrantforthisapplication. Sincerely, TacPham InternationalRegulatoryComplianceManager Tel:310-604-2448 Fax:310-604-2220 E-mail:[email protected]

BelkinCorporation 501WestWalnutStreet,Compton,CA90220 TEL:310-604-2448,FAX:310-604-2220 AGENCYAUTHORIZATIONLETTER FCCID:K7SF5D92304 Date:February10,2006 Towhomit mayconcern: We,theundersigned,herebyauthorizeAdvanceDataTechnologyCorp. (ADT)ofTaiwantoactonourbehalf,asouragent,inthefollowingmatters relatedtotheFCCapprovalofourproducts:reportsubmittal,related correspondence,thesigningofalldocumentsrelatingtothesematters,and anyotherlawfulactivitynecessarytoobtainsuchcertification.Anyactcarried outbyADTwithinthescopeofthisauthorizationshallhavethesameeffects asourown. Thisauthorizationshallexpire6 monthsfromoriginaldate.If youhaveany questionsregardingtheauthorization,pleasedon'thesitatetocontactus. Thankyou. Sincerely, TacPham InternationalRegulatoryComplianceManager BelkinCorporation TEL:310-604-2448 FAX:310-604-2220 E-mail:[email protected]

Dear Andrew, Please see Belkin’s explanation below, and please let us now if further info is required. Thanks. ######################################################### Re: FCC ID: K7SF5D9230-4 Applicant: Belkin Corporation Correspondence Number: 28430 731 Confirmation Number: TC753002 Date of Original E-Mail: 05/03/2006 Subject: MIMO?? 1) This device appears to have a single TX and a diversity receiver. However you call it a MIMO device in the description field, user's manual, and several exhibits. The Test Report has data only for a single transmitter and does not meet the testing requirements for MIMO as presented in the TCB training material. Please explain how this device has MIMO capabilities and update any exhibits accordingly. ######################################################### <Response> MIMO (Multiple-Input Multiple-Output) is not narrowly restricted to multiple streams operations, the solution we used in this product is Ralink MIMO XR RT2600 that combines signals from both antennas using MRC algorithm on the receiver and uses selected beam algorithm based on statistic of received signal strength on the transmitter. Please see enclosed “MIMO Clarification” for our claim in detail, and the other four documents are supporting references. All of the references support Ralink’s claims on the MIMO techniques used in the products. Overall, MIMO is divided into two classes: those who use MRC and transmit diversity to mitigate multi-path effects for longer range; others who take advantage of multi-path effects as in spatial multiplexing for higher throughput. Therefore our product should be entitled to MIMO XR TM PCI Adapter. Best regards, Steve Cheng Curtis-Straus LLC

528 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. SAC-2, NO. 4, JULY 1984 Optimum Combining in Digital Mobile Radio with Cochannel Interference JACK H. WINTERS, MEMBER, IEEE Abstract -This paper studies optimum signal combining for space diver- sity reception in cellular mobile radio systems. With optimum combining, the signals received by the antennas are weighted and combined to maxi- mize the output signal-to-interference-plus-noise ratio. Thus, with cochan- ne1 interference, space diversity is used not only to combat Rayleigh fading of the desired signal (as with maximal ratio combining) but also to reduce the power of interfering signals at the receiver. We use analytical and computer simulation techniques to determine the performance of optimum combining when the received desired and interfering signals are subject to Rayleigh fading. Results show that optimum combining is significantly better than maximal ratio combining even when the number of interferers is greater than the number of antennas. Results for typical .cellular mobile radio systems show that optimum combining increases the output signal- to-interference ratio at the receiver by several decibels. Thus, systems can require fewer base slation antennas and/or achieve increased channel capacity through greater frequency reuse. We also describe techniques for implementing optimum combining with least mean square (LMS) adaptive arrays. I. INTRODUCTION S PACE diversity provides an attractive means for im- proving the performance of mobile radio systems. With space diversity, the signals from the receiving anten- nas can be combined to combat multipath fading of the desired signal and reduce the relative power of interfering signals. Previous studies of mobile radio systems (e.g., [l]) have considered space diversity only for combating multipath fading of the desired signal. Interference at each receiving antenna is assumed to be independent in these studies. Under this condition, maximal ratio combining' [l, p. 3161 produces the highest output signal-to-interference-plus- noise ratio (SINR) at the receiver. However, in most sys- tems (in particular, cellular mobile radio systems [l]) the same interfering signals are present at each of the receiving antennas. Thus, the received signal5 can be combined to suppress these interfering signals in addition to combating desired signal fading and thereby achieve higher output SINR than maximal ratio combining. The output SINR can be maximized by using adaptive This paper was presented at the International Conference on Communica- Manuscript received February 25, 1983; revised November 23, 1983. tions, Boston, MA, June 1983. The author is with the Radio Research Laboratory, AT&T Bell Labora- tories, Holmdel, NJ 07733. . 'In maximal ratio combining, the received signals are weighted pro- portionately to their signal-voltage-tenoise-power ratios and combined in phase. array techniques at the receiver (e.g., [2]-[4]). We will not analyze the performance of the various adaptive array techniques in this paper, but only study the performance of the optimum combiner that maximizes the output SINR. Although the adaptive array (i.e., optimum combiner) has been studied extensively, it has not been previously analyzed with the fading conditions of digital mobile. radio., This paper studies the performance of the optimum combiner in digital mobile radio systems. We assume flat Rayleigh fading across the signal channel and independent fading between antennas. The average bit error rate (BER) of the optimum combiner is studied for coherent detection of phase shift keyed (PSK) signals. Analytical and com- puter simulation results show that optimum combining is significantly better than maximal ratio combining even when there are more interferers than receive antennas. Results for typical cellular mobile radio systems show that the optimum combiner can increase the output SINR several decibels more than maximal ratio combining. In Section I1 we describe the optimum combiner. Section I11 studies the BER of the optimum combiner when the desired and interfering signals are subject to Rayleigh fading. We discuss analytical results for one interferer and Monte Carlo simulation results for multiple interferers. In Section IV we consider the optimum combiner perfor- mance in cellular mobile radio systems. Section V discusses the possible methods for implementing the optimum com- biner in mobile radio with a least mean square (LMS) [3] adaptive array. A summary and conclusions are presented in Section VI. 11. OPTIMUM COMBINER A. Description and Weight Equation Fig. 1 .shows a block diagram of an M element space diversity combiner. The signal received by the ith element yi(t) is split with a quadrature hybrid into an in-phase signal xIi(t) and a quadrature signal XQi(t). These signals are then multiplied by a controllable weight wIi(t) or wQi(t). The weighted signals are then summed to form the array output s,(t). The space diversity combiner can be described mathe- matically using complex notation [5]. Let the weight vector w be given by 0733-8716/84/0700-0528$01.00 01984 IEEE WINTERS: OPTIMUM COMBINING IN DIGITAL MOBILE RADIO 529 I GENERhTION I WEIGHT ~ Fig. 1. Block diagram of an M element space diversity combiner. and the received signal vector x be given by The received signal consists of the desired signal, thermal noise, and interference and, therefore, can be expressed as L x=xd+x,+ xj (3) j=l where xd, x,, and xi are the received desired signal, noise, and jth interfering signal vectors, respectively, and L is the number of interferers. Furthermore, let sd( t) and si( t) be the desired and jth interfering signals as they are transmitted, respectively, with E[s,2(t)] =1 (4) ~[s:(t)] =I forl<j<L. (5) and Then x can be expressed as L x =udsd(t)+x, + ujsj(t) (6) where ud and uj are the desired and jth interfering signal propagation vectors, respectively. The received interference-plus-noise corr…

Text truncated - open the document above for the full version.

IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 21, NO. 3, APRIL 2003281 From Theory to Practice: An Overview of MIMO Space–Time Coded Wireless Systems David Gesbert, Member, IEEE, Mansoor Shafi, Fellow, IEEE, Da-shan Shiu, Member, IEEE, Peter J. Smith, Member, IEEE, and Ayman Naguib, Senior Member, IEEE Tutorial Paper Abstract—This paper presents an overview of recent progress in the area of multiple-input–multiple-output (MIMO) space–time coded wireless systems. After some background on the research leading to the discovery of the enormous potential of MIMO wireless links, we highlight the different classes of techniques and algorithms proposed which attempt to realize the various benefits of MIMO including spatial multiplexing and space–time coding schemes. These algorithms are often derived and analyzed under ideal independent fading conditions. We present the state of the art in channel modeling and measurements, leading to a better understanding of actual MIMO gains. Finally, the paper addresses current questions regarding the integration of MIMO links in practical wireless systems and standards. Index Terms—Beamforming, channel models, diversity, mul- tiple-input–multiple-output (MIMO), Shannon capacity, smart antennas, space–time coding, spatial multiplexing, spectrum efficiency, third-generation (3G), wireless systems. I. INTRODUCTION D IGITAL communication using multiple-input–multiple- output (MIMO), sometimes called a “volume-to-volume” wireless link, has recently emerged as one of the most sig- nificant technical breakthroughs in modern communications. The technology figures prominently on the list of recent technical advances with a chance of resolving the bottleneck of traffic capacity in future Internet-intensive wireless networks. Perhaps even more surprising is that just a few years after its invention the technology seems poised to penetrate large-scale standards-driven commercial wireless products and networks such as broadband wireless access systems, wireless local Manuscript received June 1, 2002; revised December 5, 2002. The work of D. Gesbert was supported in part by Telenor AS, Norway. D. Gesbert is with the Department of Informatics, University of Oslo, Blin- dern, 0316 Oslo, Norway (e-mail: [email protected]). M. Shafi is with Telecom New Zealand, Wellington, New Zealand (e-mail: [email protected]). D. Shiu is with Qualcomm, Inc., Campbell, CA 95008 USA (e-mail: [email protected]). P. J. Smith is with the Department of Electrical and Computer Engi- neering, University of Canterbury, Christchurch, New Zealand (e-mail: [email protected]). A. Naguib was with Morphics Technology, Inc., Campbell, CA 95008 USA. He is now with Qualcomm, Inc., Campbell, CA 95008 USA. Digital Object Identifier 10.1109/JSAC.2003.809458 area networks (WLAN), third-generation (3G) 1 networks and beyond. MIMO systems can be defined simply. Given an arbitrary wireless communication system, we consider a link for which the transmitting end as well as the receiving end is equipped with multiple antenna elements. Such a setup is illustrated in Fig. 1. The idea behind MIMO is that the signals on the transmit (TX) antennas at one end and the receive (RX) antennas at the other end are “combined” in such a way that the quality (bit-error rate or BER) or the data rate (bits/sec) of the communication for each MIMO user will be improved. Such an advantage can be used to increase both the network’s quality of service and the operator’s revenues significantly. A core idea in MIMO systems isspace–timesignal processing in which time (the natural dimension of digital com- munication data) is complemented with the spatial dimension inherent in the use of multiple spatially distributed antennas. As such MIMO systems can be viewed as an extension of the so-calledsmart antennas, a popular technology using antenna arrays for improving wireless transmission dating back several decades. A key feature of MIMO systems is the ability to turn multi- path propagation, traditionally a pitfall of wireless transmission, into a benefit for the user. MIMO effectively takes advantage of random fading [1]–[3] and when available, multipath delay spread [4], [5], for multiplying transfer rates. The prospect of many orders of magnitude improvement in wireless communi- cation performance at no cost of extra spectrum (only hardware and complexity are added) is largely responsible for the suc- cess of MIMO as a topic for new research. This has prompted progress in areas as diverse as channel modeling, information theory and coding, signal processing, antenna design and mul- tiantenna-aware cellular design, fixed or mobile. This paper discusses the recent advances, adopting succes- sively several complementing views from theory to real-world network applications. Because of the rapidly intensifying efforts in MIMO research at the time of writing, as exemplified by the numerous papers submitted to this special issue of JSAC, a complete and accurate survey is not possible. Instead this paper forms a synthesis of the more fundamental ideas presented over the last few years in this area, although some very recent progress is also mentioned. 1 Third-generation wireless UMTS-WCDMA. 0733-8716/03$17.00 © 2003 IEEE 282IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 21, NO. 3, APRIL 2003 Fig. 1. Diagram of a MIMO wireless transmission system. The transmitter and receiver are equipped with multiple antenna elements. Coding, modulation, and mapping of the signals onto the antennas may be realized jointly or separately. The article is organized as follows. In Section II, we attempt to develop some intuition in this domain of wireless research, we highlight the common points and key differences between MIMO and traditional smart antenna systems, assuming the reader is somewhat familiar with the latter. We comment on a simple example MIMO transmission technique revealing the unique nature of MIMO benefits.…

Text truncated - open the document above for the full version.

MIMO stands for Multiple-Input Multiple-Output that is not narrowly restricted to multiple streams operations, as evidenced in the proposed IEEE 802.11n specification 1 . In the Appendix A, “Modulation and Coding Schemes” of single steam are defined as MCS0-MCS7. Ralink's MIMO XR system is based on single-stream technology, utilizing both antennas for RX MRC and TX diversity in a time-sharing fashion, described in detail in a published white paper 2 . In summary, Ralink MIMO XR combines signals from both antennas using MRC algorithm on the receiver and uses selected beam algorithm based on statistic of received signal strength on the transmitter. The classical MIMO concept started in1984, with credit to Jack Winters; at that time multiple streams approach did not exist. ( http://en.wikipedia.org/wiki/Multiple-input_multiple- output_communications#History_of_MIMO_in_radio_communications ). Jack Salz, of Bell Laboratories, published a paper 3 on MIMO in 1985, taking a cue from Winters' research, that Tx diversity and Rx MRC form the foundation of the classical MIMO implementation. In addition, in an IEEE paper 4 describing MIMO overview, it is quoted "Now, we consider the use of diversity at both transmitter and receiver giving rise to a MIMO system. For N TX and M RX antennas, we have the now famous capacity equation [1], [3], [21] .... ". There are many other generally accepted MIMO viewpoints, e.g., Netgear’s website (http://www.netgear.com/products/details/WPN824.php “What is MIMO?”) 5 . Dr. A. Paulraj of Stanford University stated, “The multiple antennas at each end of a MIMO link can be used in different modes such as transmit- receive diversity, beam-forming, antenna subset selection and spatial multiplexing... Different aspects of MIMO will find their unique niches in the plethora of products now entering the market.” All of the references support Ralink’s claims on the MIMO techniques used in the products. Overall, MIMO is divided into two classes: those who use MRC and transmit diversity to mitigate multi-path effects for longer range; others who take advantage of multi-path effects as in spatial multiplexing for higher throughput. 1 IEEE 802.11-05/1102r04, IEEE P802.11 Wireless LANs 2 Ralink Technology, “MIMO technology primer: Understanding MRC-OFDM”, JAN, 2006 3 Jack H. Winters, “Optimum Combining in Digital Mobile Radio with Cochannel Interference”, IEEE JOURNAL ON SELECTEDA REAS IN COMMUNICATVIOONLSS,A. C-2,N O. 4, JULY 1984 4 David Gesbert, Member, IEEE, Mansoor Shafi, Fellow, IEEE, Da-shan Shiu, Member, IEEE, Peter J. Smith, Member, IEEE, and Ayman Naguib, Senior Member, IEEE “From Theory to Practice: An Overview of MIMO Space–Time Coded Wireless Systems”, IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 21, NO. 3, APRIL 2003 5 Dr. A. Paulraj & Dr. Heath, “What is MIMO?”, Netgear web site

MIMO technology primer: Understanding MRC-OFDM Ralink Technology White Paper December 2005 Page 2 Understanding MRC-OFDM: a first step in MIMO technology INTRODUCTION The market for wireless LANs, particularly in the consumer and small business segments, has grown significantly in recent years. By all accounts, annual growth in wireless LAN device shipments has increased from threefold to fivefold since 2001. With huge opportunities for wireless LANs looming in home entertainment, Voice over IP (VoIP), and public access, the biggest market growth may yet lie ahead. Next generation wireless LANs will include new technology to enable these exciting applications. Market adoption of wireless LANs has been spurred by the growing popularity of the broadband access in the home. Twenty-nine percent of North American households connected to the Internet using broadband connections in 2004, up from 19 percent in 2003. Networks can be found in 8.8 percent of US households, and these tend to be dominated by homes with multiple PCs and broadband access to the Internet. Access to music, video and online gaming becomes possible when the network can interface seamlessly with entertainment centers, laptops, and handheld devices. The wireless medium is ideal for these applications, but today’s wireless LANs need improved performance to meet the challenge. The typical user experiences three basic qualities of a wireless connection: speed, range and reliability. Prior to the development of MIMO-OFDM, the three parameters were interrelated according to strict rules. Speed could be increased only by sacrificing range and reliability; while range could be extended only at the expense of speed and reliability. And reliability could be improved by reducing speed and range. MIMO OFDM has redefined the tradeoffs, clearly demonstrating that it can boost all three parameters simultaneously. While MIMO will ultimately benefit every major wireless industry including mobile telephone, the wireless LAN industry is leading the way in exploiting MIMO innovations. Multiple Input/Multiple Output (MIMO) is an area of intense development in the wireless industry because it delivers profound gains in range, throughput and reliability. As a result, manufacturers of wireless local area network (WLAN), wireless metropolitan area network (WMAN), and mobile phone equipment are embracing MIMO technology. This White Paper describes how MIMO-OFDM (Multiple Input Multiple Output- Orthogonal Frequency Division Multiplexing) technology delivers significant performance improvements for wireless LANs, enabling them to serve existing applications more cost-effectively as well as making new, more demanding applications possible. It also explains how manufacturers and end-users can benefit by deploying MIMO-OFDM products today without sacrificing compatibility with the popular 802.11a and 802.11g standards. NEXT GENERATION WIRELESS CHALLENGES: Overcoming Multipath Often, Wi-Fi transmission is limited by a phenomenon called multipath: In an obstacle-rich environment the signal bounces off the obstacles (for example, brick walls, office furniture, etc.), in the process generating reflected signals which degrades the reception of the signal. At the receiver, the signal loses quality because the obstacles cause the signal path lengths to be unequal, which results in several Ralink Technology White Paper December 2005 Page 3 time-delayed copies of the information signal arriving at the receiver, as depicted in Figure 1. The total signal is the sum of all signals according to their phase relationships; and in general, the received signal is spread out in the time domain. The receiver is designed to correct signal distortion, but can only do so to within certain limits. For example, if two signal paths are received out of phase, the total signal may cancel out entirely. Places where this happen in a typical user setting, such as a corner room away from the transmitter (AP), are called “dead spots”. Wi- Fi users may also experience locations at home where the signal strength is weak, or where dropouts occur intermittently. Performance fluctuations like this are frustrating for the user, and, indeed, unacceptable for future applications that require stable, high throughput connections. In a home environment, the user may find he can only use a laptop a limited range; while in the workplace several APs may be required to eliminate dead spots and allow wireless access to cover the entire floor. Of course there has been much research and development in recent years to overcome such factors limiting the stability and range of wireless broadband links. Presently, the IEEE standards committee is working on the next generation of the existing IEEE 802.11g standard that will include advanced technologies to enhance performance of broadband wireless LANs. Figure 1: Multipath phenomena in wireless communication WIRELESS TECHNOLOGIES FOR ENHANCED PERFORMANCE The multipath problem is a longstanding issue in wireless communications. To reduce the multipath, the earliest Wi-Fi standard (802.11b) uses a technique called spread spectrum. Using this modulation, the data is spread signal out in the frequency domain to reduce the possibility of destructive interference totally wiping out a connection. This technique is effective, and is still used in current 802.11g modems, but it can provide limited throughput because it uses only a single channel for communication. Other approaches to improving signal quality involve using multiple receiver antennae. Antenna diversity is method by which the receiver switches between two antennae to select the one with best signal strength, as shown in Figure 2. More advanced versions…

Text truncated - open the document above for the full version.