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Wb 802.11n position paper
 

Wb 802.11n position paper

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    Wb 802.11n position paper Wb 802.11n position paper Document Transcript

    • POSITION PAPER802.11n in the Outdoor EnvironmentHow Motorola is transforming outdoor mesh networks toleverage full “n” advantages
    • Municipalities and large enterprise customers are deploying mesh networksto provide wireless broadband connections across cities or within campusenvironments. Today, these networks support many different types ofapplications, including video surveillance, meter reading and traffic control,and have demonstrated mesh networks’ ability to deliver a compelling returnon investment as well as enable new services.Many current mesh network deployments are based or building, as well as a wide RF channel with littleon WiFi technology, the common term for wireless interference.services meeting the IEEE 802.11 standards. Up tonow, the best available data speeds leveraging The following 802.11n properties will be explored,802.11a, –b or –g standards reach burst data rates of offering a perspective on their benefits or limitations54 Mbps. However, over the past year, the promise in an outdoor network:and subsequent arrival of 802.11n technology hasgenerated a substantial amount of industry discussion Multiple Input Multiple Output (MIMO)and debate. Adoption of 802.11n WiFi in both the The 802.11n technology standard offers a variety ofenterprise and consumer markets is quickly gaining physical layer diversity mechanisms for achievingground, with many customers upgrading older indoor higher throughput and improved packet receptionnetworks to meet new ‘next generation’ standards. capability. Each 802.11n radio can have multipleThese new high capacity networks promise to deliver transmit antennas and paths. Multiple spatial datasubstantial cost savings in not only infrastructure and streams can be transmitted at the same time, on theoperations, but also in end-user productivity and same channel, but by different antennas. The dataefficiency gains. streams can be combined from multiple receivers using advanced signal processing. When discussingThe use of 802.11n in outdoor network deployments 802.11n or MIMO networks, three numbers are typi-has raised some interesting questions. Based on cally referenced – the first is the number of transmitcurrent network configurations and emerging ROI antennas, the second is the number of receivemodels, the potential benefits are dramatic. However, antennas and the third is the number of spatialthe specific capabilities of 802.11n as applied to streams. For example, a 3x3:2 system has threeoutdoor networks differ significantly from common transmit signals, three receive signals and twoindoor network configurations. Network planners spatial streams.and operators must understand the technologyenhancements 802.11n brings along with the unique Cyclic Shift Diversity (CSD)environmental challenges inherent to outdoor Transmitting from a single antenna can lead todeployments in order to leverage the full advantages areas with unexpectedly poor coverage. Thisof “n” technology. coverage “null” or deep fade can be caused by interference, multi-path errors or general obstruc-This paper will focus on the key 802.11n technology tions. 802.11n allows for multiple transmittingenhancements, specific product design considerations antennas, with each broadcasting the same datafor 802.11n mesh access points, and how to maximize with slight delays. The most effective systems willthe benefits of 802.11n technology in outdoor use multiple antenna polarities to send out differentnetworks. versions of the same signal. The client devices will hear different signals strongest in different partsKey Technical Enhancements of the coverage area, and use the best available signal for communications. This results in moreIEEE 802.11n is the next generation standard for uniform coverage and generally higher data ratesWiFi-based technology, promising high data rates, throughout the coverage area.longer range and more reliable coverage than802.11a/b/g networks. In order to achieve optimized Maximal Ratio Combining (MRC)gains in an outdoor network, the technology will have In public access and municipal networks, clientto account for unique environmental considerations. coverage is often limited by the uplink connectionAs with earlier 802.11a/b/g deployments, 802.11n of the client to the access point. Network clientstechnology was originally designed for indoor hot typically include low powered devices – smartspots. Performance expectations have been derived phones, laptops, and PDAs – limited by thefrom in-building access points that take advantage of strength of their transmitting radios due to size,very short reflective signals bouncing around a room cost and battery life. MRC utilizes multiple receive2 POSITION PAPER: 802.11n in the Outdoor Environment
    • antennas to reconstruct signals, thereby reducing 3. Frame Aggregation error probabilities and re-transmissions, allowing 802.11n provides an option of combining multiple clients to be “heard” better. data frames ready for transmission into an aggregate Spatial Multiplexing frame. This helps channel contention and backhaul Spatial Multiplexing allows data to be split and delays by transmitting the aggregated frame in a transmitted via two independent data streams single transmission on the channel. using spatial separation of signals by antennas, effectively doubling the throughput of a wireless The User Benefits of 802.11n Technology channel. Using different signals mitigates interfer- The key advantages offered by 802.11n lie equally in ence and improves throughput. However, the the high bandwidth applications it enables as well as capability to send parallel data streams depends the vastly improved network performance it delivers. on the environment. Indoor 802.11n gains from The latest applications require higher data rates, Spatial Multiplexing use multi-path from the build- reliable links and predictable performance to realize ing walls to achieve a very high spatial separation their full potential. Video, for example, is having a when the signals arrive at the receiver out of profound effect on the way people communicate and phase. However, in outdoor environments it is consume information and has a dramatic impact on difficult to create enough separation among the public access network infrastructure needs and antenna signals to provide parallel data streams performance. It is estimated that video is now to support Spatial Multiplexing. approximately one-quarter of all consumer Internet traffic. In addition, video is a critical capability in public safety, transportation and industrial markets,2. Channel Bonding with real-time surveillance being the primary driver.802.11n introduces two different channel bandwidths: MIMO technology as well as frame aggregation are20 MHz and 40 MHz. By combining two adjacent 20 beneficial in enabling the transmission of superiorMHz channels into a single 40 MHz channel, 802.11n video quality. MIMO enables faster downloaddoubles the available data rate. Channel bonding is capabilities, reduced interference and enhancedmost effective in the 5 GHz frequency given the connectivity while frame aggregation ensuresgreater number of available channels. 5 GHz has 24 content is combined to support streaming video.non-overlapping channels separated by 20 MHz. Thisallows up to 12 non-overlapping 40 MHz channels. Municipalities stand to benefit greatly from investingThe 2.4 GHz frequency has only 3 non-overlapping in a joint 802.11n network, allowing multiple depart-20 MHz channels. Therefore, bonding two 20 MHz ments – public safety, public works, department ofchannels uses two thirds of the total frequency transportation, etc. – to share access and associatedcapacity in the 2.4 GHz spectrum. costs. A key technology of 802.11n, Spatial Multiplexing, can effectively double the throughput of a wireless channel; allowing more applications3 POSITION PAPER: 802.11n in the Outdoor Environment
    • from multiple departments to run simultaneously. to be capable of the same separation enabled byAdditionally, channel bonding increases the perform- strong client connections.ance of the network. Network users are not requiredto upgrade legacy 802.11a/b/g clients to new 802.11n 3. Higher Mesh Capacityclients, as 802.11n networks are backwards compati- The data rate offered to 11n subscriber units can beble with 802.11a/b/g clients. Some aspects of 802.11 outstanding – it’s possible to provide a 100 Mbpstechnology, such as multi-antenna MRC, can benefit connection or more to a client. But the fastest clientlegacy 802.11 a/b/g client performance as well. connection is worth nothing unless the mesh layer of the network can provide the same or greater speedThe number of devices required to cover an area and connection back to the wired network. Network de-the overall cost to deploy a network are important signers know that the true ‘capacity’ of their networkcriteria as CIOs and IT managers calculate their is determined at the mesh layer, and harnessing thepotential return on the network and total cost of power of 11n connections between nodes is criticallyownership. Increasing the transmit power will lower important.the number of access points required per squaremile and will decrease deployment as well as ongo- Motorola’s Mesh Solution for the Outdooring operational costs. Additionally, designing networks 802.11n Marketfor multiple uses enables costs to be shared among Motorola developed specific technology for our nextmany different departments over the long-term. generation 802.11n access point, the AP 7181. This technology was designed from the ground up toMaximizing 802.11n Benefits Outdoors meet the needs of wide area networks, supportingAs highlighted in the technology enhancement high capacity video and highway-speed mobility.descriptions above, achieving the full benefit of RF Antenna Design802.11n requires a number of elements working Motorola designed an antenna system that takestogether to reach the high data rates and capacities advantage of polarization diversity to increase thepromised by 11n technology. As a result, network probability for parallel data paths in an outdoor en-designers and planners must consider the network vironment. This enables the access point to achieveas well as the capabilities of the access points that higher data rates (up to 300 Mbps) in 802.11n.will be deployed. Without such understanding, the Getting the second data stream to support theinvestment in an 802.11n network may yield only high throughput can only be realized through highminor improvements over 802.11a/b/g offerings. transmit power and a smart antenna design. Most wireless 802.11n access points todayThere are three primary benefits network designers transmit using vertical dipole antennas (sticks).want to achieve: These antennas use only vertically polarized1. Better Client Coverage transmissions, effectively limiting the access pointToday, the number of access points required in a to a single spatial stream. Motorola’s solution usesnetwork is largely determined by the ability of the both vertical and horizontal polarizations to delivernetwork access points to “hear” the client devices. higher data rates and greater range compared toBetter uplinks from clients will reduce the number of a system that uses only a single polarization. Thenodes required, which reduces not only the equipment MRC algorithm in the AP 7181 optimally combinescosts but site acquisition, installation and ongoing signals with different polarizations. The systemmaintenance costs. A network with fewer nodes is can use the dual polarizations to lower interferenceeasier to deploy and maintain. from other networks or to deliver parallel streams in an outdoor environment.2. Stronger Mesh Layer ConnectionsIf better client coverage allows for fewer access Ideally each radio in the access point would havepoints to create the same coverage, then the multiple transmit and receive antennas, with bothconnections between the nodes – the mesh itself – vertical and horizontal polarization. With threeneeds to support the same separation. Without radios, and three antennas per radio, there couldadvancements in the mesh layer technology, the potentially be nine antennas sticking out of themesh nodes will have to be deployed at the same node. Motorola has developed a way to combinedensity as they are today, so there is little to no gain 24 antennas, using no external dipole sticks.from better client connections. The mesh layer has4 POSITION PAPER: 802.11n in the Outdoor Environment
    • High Transmit Power RadiosIndoor access points are limited to 100 mWattscompared to outdoor units that are allowed totransmit as high as 1 watt. The FCC has recognizedthat outdoor networks require increased power levelsin order for access points to effectively supportbackhaul links over increased distances. Higher radiotransmit power enables stronger client connectionsand stronger mesh connections, which result in moreconsistent and faster data speeds. An access pointwith a transmit power of 100 mWatts (20 dBm) willoffer only 10 percent of the power of an access pointwith a transmit power of 1 watt (30 dBm). Lowerpower access points can require two to four timesthe number of nodes to cover a given geographicalarea.Manufacturing radios that transmit clean signals at Figure 1 Traditional OMNI Sticks Antennashigh power rates is difficult. Developing radios thattransmit clean signals at high data rates and high Figure 1 depicts traditional OMNI stick-based accesspower is even more challenging. Most vendors will points resulting in a “self shadowing” coveragetrade data rates for power – the highest power pattern, where nearby antennas shade or notch theoutputs are only seen at the very lowest data rates. desired omni-directional antenna pattern leading toMotorola has developed new radios for the AP 7181 unpredictable coverage holes.that maintain high power transmissions even at thehighest data rates. This enables the full benefits ofstrong connections, especially in meshing layercommunications.Introducing Motorola’s Next Generation Platform,AP 7181Motorola developed the AP 7181 to harness the fullcapabilities of 802.11n technology. Leveraging itsADEPT (ADvanced Element Panel Technology) state-of-the-art antenna technology, AP 7181 achievesmaximum data rates by delivering a reliable dual datastream in an outdoor environment. The integratedADEPT antenna system overcomes the limitations ofmultiple antenna sticks in a typical 11n access point.This improved antenna system takes advantage ofpolarization diversity and increases the probabilityof parallel data paths enabling multiple spatial datastreams – a key design factor for enabling the higher Figure 2 Motorola’s ADEPT Antennasdata rates in 802.11n. ADEPT implements a 3X3MIMO solution that ensures Spatial Multiplexing and Figure 2 highlights Motorola’s ADEPT system, whichhigh data rates while providing a full omni-directional provides true omni-directional coverage for predictablepattern at maximum power levels. deployments and reliable connections.Paired with Motorola’s new high-powered radios, theaccess point offers maximum coverage, throughputand network capacity to support network demandsfor years to come. Figures 1 and 2 compare theperformance of multiple stick antennas to Motorola’sADEPT design.5 POSITION PAPER: 802.11n in the Outdoor Environment
    • Figure 3 802.11g System Coverage Figure 4 Motorola 802.11n System CoverageFigures 3 and 4 show relative coverage for 802.11g and Motorola’s outdoor 802.11n solution. The dark areasin the coverage map depict areas with no usable signal strength. Even when legacy 802.11g access pointsare deployed closer to each other, some areas are left with no coverage. Network designs completed withsophisticated planning tools, such as Motorola’s One Point Wireless Suite, reveal that 802.11g systems require52 percent more access points to cover the same area compared to Motorola’s outdoor 802.11n technology.A Whole New View of Outdoor Wireless About Motorola Wireless BroadbandTechnology evolves rapidly in the wireless space. Motorola’s comprehensive portfolio of reliable andIn 2009, many of the WiFi-enabled clients sold will cost-effective wireless broadband solutions togetherfeature 802.11n-capable radios. Demand for 802.11n with our WLAN solutions provide and extend coveragenetworks will continue to grow as private, enterprise both indoors and outdoors. The Motorola Wirelessand public network operators look to protect their IT Broadband portfolio offers high-speed Point-to-Point,investments for refresh and expansion to new appli- Point-to-Multipoint, Mesh, Wi-Fi and WiMAX networkscations with greater range, simplified deployments that support data, voice and video communications,and AP’s that provide highly reliable, predictable enabling a broad range of fixed and mobile applica-coverage and optimize the performance of legacy tions for public and private systems. With Motorola’sdevices. innovative software solutions, customers can design, deploy and manage a broadband network, maximizingSuccessful 802.11n deployments will require an uptime and reliability while lowering installation costs.in-depth understanding of the outdoor wireless envi-ronment, and advanced RF design tools to ensurelong-term network performance, reliability and costeffectiveness. The expertise and ability to manageindoor and outdoor integrated communicationsnetworks is also a critical capability with the capacitythat 802.11n technology brings.As with any new innovation, the full adoption ofMIMO and 802.11n technology will take time andbring a whole new tier of products and applicationsto market that will fundamentally change the way wework and communicate. Motorola intends to leadthat innovation with products that reflect superiordesign and engineering, deliver reliable performanceat a lower cost, exceed customer expectations anddeliver rapid ROI.6 POSITION PAPER: 802.11n in the Outdoor Environment
    • www.motorola.com/meshMOTOROLA and the Stylized M Logo are registered in the US Patent & Trademark Office. All other product or service names are theproperty of their respective owners. © 2009 Motorola, Inc. All rights reserved.