WiMAX Benefits Applications & Solutions
This paper provides guidelines for network providers on how best to take advantage of the IEEE 802.16 standard for wireless broadband equipment, which will be certified by the WiMAX Forum, to grow their business while managing risks. We begin by identifying the key challenges currently facing service providers, and providing a brief introduction to WiMAX technology. We go on to describe some of the ways in which WiMAX can help service providers meet those challenges and the main risks involved in making the move to WiMAX. We then provide detailed recommendations on how and when service providers should transition to WiMAX so as to further their business goals while minimizing the risks.
What Network Service Providers Need Most
Network service providers currently face a situation in which revenues from traditional sources are either declining or stagnating. The market for services delivered via wired infrastructure is saturated, and opportunities for growth in that market are extremely limited. By contrast, demand for services beyond the reach of wired infrastructures is potentially huge, but the wireless technology required to support the delivery of broadband to those market sectors has until now been largely proprietary and marked by either poor performance (at the low end) or prohibitive cost (at the high end).
Network service providers need a cost-effective solution that would allow them to satisfy the demand for broadband-based services beyond the reach of wired infrastructures. They need a solution with a rapid ROI and the promise of steadily increasing revenues. They need to move more quickly than their competitors in order to achieve a dominant position in these new markets. In addition, they need to minimize the risks associated with timely deployment of new wireless technologies.
WiMAX Benefits for Service Providers
Enter IEEE 802.16, or “WiMAX”—the emerging wireless standard that promises to substantially reduce the costs required to further expand the reach of broadband delivery systems while delivering performance that exceeds that of most wired technologies. WiMAX technology offers several key benefits to network service providers. It will:
Allow service providers to profitably deliver high-throughput, broadband-based services like VoIP, high-speed Internet access and video to business and residential users who previously could not be economically served
Facilitate equipment compatibility, allowing all of the components of WiMAX-based broadband systems to form a cohesive network, further reducing deployment and maintenance costs
Facilitate equipment interoperability, allowing service providers to avoid having to commit to single vendors, diversifying vendor-dependent deployment risks
Reduce the initial and incremental capital expenditures required for network expansion
Provide vastly improved performance and extended range compared to existing wireless technologies
Overcome many technical limitations of current wireless technology—for example, it will support service to customers that could not be economically served by legacy “line of sight” wireless technologies
Allow service providers to achieve rapid ROI and maximize revenues
The potential for providers to achieve a faster ROI by deploying emerging wireless technologies than they could by deploying wired networks has been widely recognized. For example, a recent Gartner Research study describes the business advantage of emerging wireless succinctly:
“Looking at the basic pricing mode, a leased T1 line can cost $7,200 per year ($600 per month). Basic wireless point-to-point metropolitan-area network equipment ranges from $1,000 to $10,000 per unit (not including towers, additional routers, shelters, cables or installation, which can add less than $5,000 to the project), depending on speed needed. An enterprise can get a return on investment in less than a year on many systems, and in less than 18 months for most systems.“
Source: P. Redman, Research Note, Gartner Research Inc., July 2003
The following section is excerpted from Can WiMAX Address Your Applications?, published by the WiMAX Forum
The WiMAX standard has been developed with many objectives in mind. These are summarized below:
Flexible Architecture: WiMAX supports several system architectures, including Point-to-Point, Point-to-Multipoint, and ubiquitous coverage. The WiMAX MAC (Media Access Control) supports Point-to-Multipoint and ubiquitous service by scheduling a time slot for each Subscriber Station (SS). If there is only one SS in the network, the WiMAX Base Station (BS) will communicate with the SS on a Point-to- Point basis. A BS in a Point-to-Point configuration may use a narrower beam antenna to cover longer distances.
High Security: WiMAX supports AES (Advanced Encryption Standard) and 3DES (Triple DES, where DES is the Data Encryption Standard). By encrypting the links between the BS and the SS, WiMAX provides subscribers with privacy (against eavesdropping) and security across the broadband wireless interface. Security also provides operators with strong protection against theft of service. WiMAX also has built-in VLAN support, which provides protection for data that is being transmitted by different users on the same BS.
WiMAX QoS: WiMAX can be dynamically optimized for the mix of traffic that is being carried. Four types of service are supported:
Unsolicited Grant Service (UGS) UGS is designed to support real-time data streams consisting of fixedsize data packets issued at periodic intervals, such as T1/E1 and Voice over IP.
Real-Time Polling Service (rtPS) rtPS is designed to support real-time data streams consisting of variable-sized data packets that are issued at periodic intervals, such as MPEG video.
Non-Real-Time Polling Service (nrtPS) nrtPS is designed to support delay-tolerant data streams consisting of variable-sized data packets for which a minimum data rate is required, such as FTP.
Best Effort (BE) BE service is designed to support data streams for which no minimum service level is required and which can be handled on a spaceavailable basis.
Quick Deployment: Compared with the deployment of wired solutions, WiMAX requires little or no external plant construction. For example, excavation to support the trenching of cables is not required. Operators that have obtained licenses to use one of the licensed bands, or that plan to use one of the unlicensed bands, do not need to submit further applications to the Government. Once the antenna and equipment are installed and powered, WiMAX is ready for service. In most cases, deployment of WiMAX can be completed in a matter of hours, compared with months for other solutions.
Multi-Level Service: The manner in which QoS is delivered is generally based on the Service Level Agreement (SLA) between the service provider and the end-user. Further, one service provider can offer different SLAs to different subscribers, or even to different users on the same SS. Interoperability: WiMAX is based on international, vendorneutral standards, which make it easier for end-users to transport and use their SS at different locations, or with different service providers. Interoperability protects the early investment of an operator since it can select equipment from different equipment vendors, and it will continue to drive the costs of equipment down as a result of mass adoption.
Portability: As with current cellular systems, once the WiMAX SS is powered up, it identifies itself, determines the characteristics of the link with the BS, as long as the SS is registered in the system database, and then negotiates its transmission characteristics accordingly.
Mobility: The IEEE 802.16e amendment has added key features in support of mobility. Improvements have been made to the OFDM and OFDMA physical layers to support devices and services in a mobile environment. These improvements, which include Scaleable OFDMA, MIMO, and support for idle/sleep mode and hand-off, will allow full mobility at speeds up to 160 km/hr. The WiMAX Forumsupported standard has inherited OFDM’s superior NLOS (Non-Line Of Sight) performance and multipath-resistant operation, making it highly suitable for the mobile environment.
Cost-effective: WiMAX is based on an open, international standard. Mass adoption of the standard, and the use of low-cost, mass-produced chipsets, will drive costs down dramatically, and the resultant competitive pricing will provide considerable cost savings for service providers and end-users.
Wider Coverage: WiMAX dynamically supports multiple modulation levels, including BPSK, QPSK, 16-QAM, and 64- QAM. When equipped with a high-power amplifier and operating with a low-level modulation (BPSK or QPSK, for example), WiMAX systems are able to cover a large geographic area when the path between the BS and the SS is unobstructed.
Non-Line-of-Sight Operation: NLOS usually refers to a radio path with its first Fresnel zone completely blocked. WiMAX is based on OFDM technology, which has the inherent capability of handling NLOS environments. This capability helps WiMAX products deliver broad bandwidth in a NLOS environment, which other wireless product cannot do.
High Capacity: Using higher modulation (64-QAM) and channel bandwidth (currently 7 MHz, with planned evolution towards the full bandwidth specified in the associated IEEE and ETSI standards), WiMAX systems can provide significant bandwidth to end-users.
StarPlus Hybrid Approach to Avoid and Reduce the Impact of Interference in Congested Unlicensed Radio Bands
EION Wireless Engineering: D.J. Reid, Professional Engineer, Senior Systems Architect
In licensed frequency bands, use of synchronization is accepted as a preferred method to deal with interference problems associated with; numerous base stations and CPEs. Generally speaking, competing operators respect each other’s “space” and frequencies by implementing frequency planning techniques, to reduce the effects of interference. In WiMax implementations, operators prefer to use GPS based synchronization methods. In short, GPS synchronization allows all base station radios to transmit simultaneously and listen for CPE receive signals when the base station is not transmitting. It is the high level of frequency planning and signal synchronization inherent in WiMAX system implementation which provides for an order and less disruptive communication methodology.
In unlicensed frequency bands, the rules for communication are not so clear. Frequency planning is typically not implemented. Power levels are also not usually coordinated. Channel bandwidths are not coordinated. Some systems may use bandwidths as narrow as 3.5 MHz, while others may use much larger bandwidths. Given that in most cases, there is a mix and mash of disparate radio systems operating in dissimilar fashion, the rules for “playing nice” are usually non-existent. This usually makes it impossible to synchronize communications effectively.
There are other inherent problems, some of which include; fixed WiMAX 802.16d, systems use fixed polling of CPEs for traffic often with synchronization, while WiFi, 802.11a and 802.11n systems, use CSMA-CA – and employ on demand schemes to serve CPEs where the CPE will transmit a Request to Send whenever a quiet slot appears on the frequency. On a larger scale, when there are unsynced stations, whether WiFi or other systems, base station or AP and CPE transmissions are quite random and in-system collisions, as well as collisions with same-space 802.16d synchronized signals, are inevitable. Given these factors as well as years of experience in both the licensed and unlicensed wireless communications, EION Wireless would like to proceed as documented in the next few pages.
Hybrid Solution for overcoming Adjacent and Co-Channel Interference in Crowded Unsynchronized Radio Bands
Interference consists essentially of two major elements. The first is from adjacent channels activity affecting the performance of a radio system when standard isolation techniques are notadequate. The second is from co-channel interfering signals that directly impact the desiredradio system. To successfully mitigate the effects on a service both adjacent and co-channel interference must be addressed with appropriate techniques. EION’s solution uses a hybrid approach through application of segment filters combined with a Trade Marked, robust protocol, working in tandem - to reduce the overall detrimental impact on channel availability and system performance.
Techniques Reducing Adjacent Channel Interference problems
Even though the offending station(s) are not on the same channel, the broadband design of contemporary radios makes them susceptible to high-level adjacent channel signals. The mechanism that creates the interference is the Low Noise Amplifier or LNA in the analog front end of the receiver. This is very sensitive and covers a wide frequency range. As a direct result any signal(s) within the band the amplifier covers if too high in level will overload the amplifier resulting in the creation of spectrum by-products that will interfere with the desired signal also being received by the radio but at a much lower level. The spectral by products disrupt the desired signal and at the same time produce inter-modulation “noise” which contributes to the morass of distorted signals making the carrier to interference ratio unacceptable ( C/I < 6 dB).
Much of the offending signals that will impact a radio’s performance are usually located in the immediate vicinity of the Base Station being impacted. In fact it can be the other operators’ radios or sector radios in the same network mounted on the same tower. Several methods used singly or in combination can effectively reduce adjacent channels levels to an acceptable level.
Radio-Antenna Placement, Antenna Alignment and Frequency Co-ordination
Before adding hardware such as filters to an installation, several tactics should be employed as standard operating procedure or SOP in the establishment of a base radio. In order of application the radio and antenna placement, antenna alignment and frequency co-ordination should be done to ensure minimal adjacent channel levels impinging on the radio. These techniques have been field tested and demonstrated a number of times successfully eliminating any impairments from adjacent channel radio systems co-located on the tower.
Separation of at least 1 to 2 meters between antennas is the first tactic to improve C/I levels. This effectively reduces the impact of interfering side lobes from the adjacent antenna. Also use of sector antennas in stead of Omni –directional units greatly increases isolation. Alignment is another important consideration. The sector antenna constricted antenna pattern can be utilized to null out the side lobes of adjacent channel radiation from another close by antenna. These tactics will be able to mitigate most interference when used along with good performing radio with good IF channel response.
Though difficult to do in unlicensed bands, ensuring that there is no co-located radio on using an immediately adjacent channel is good avoidance tactic to prevent excessive C/I. This requires at least one channel spacing between the co-located radios frequency assignments. In doing this, both radios benefit with less in band interference occurring. The adjacent channel C/I has to be quite low ( 3 dB or less) before interference to be significant. Weaker adjacent channel interference form more distant co-located radios should not cause any significant issues
Using filters to block out the adjacent signals for example effectively eliminates the impact of co-located radios or near-by Base Stations operating in the same band. The filters in deployment split the operating radio band into segments so interfering signals can be effectively blocked (>30 dB stop-band) from impeding the desired weaker signals from remote CPEs. The use of channel or segment filters is common in microwave systems and filters are available with the required characteristics. This is a tactic reserved for difficult situations where all other tactics have failed to adequately reduce interference and can be used uniquely or in combination with other tactics.
Connecting Communities: A Rugged Approach to Remote Communication
There has always been a great divide between wealthy, developed nations and poor, underdeveloped ones. This divide spans from economic wealth to social conditions, and it has now reached the communications and information technologies. This is what is now known as the digital divide.
In today’s economy, connecting remote communities through broadband communication is the heart of the digital revolution - and critical to global long-term health and prosperity. It is believed that bridging the digital divide, and providing communications technologies to remote communities in developing countries can improve the lives of more than 80% of their population.
At the same time, these remote communities have very stringent constraints which make it economically unattractive to connect them. Many government agencies and businesses are left wondering how they can participate and take advantage of the technological advancements which are helping economies in the developed world thrive. They are now aware that in order for any community to become productive and prosperous, it must first be connected to the rest of the world through these communications technologies.
The traditional approach of extending urban-centric communication infrastructures to remote applications is no longer adequate, as governments and social organizations increasingly focus on providing communications services. Instead, these communities need a remote-centric business-oriented approach.
Technologies such as the Internet, personal computers and wireless telephony allow individuals, businesses, schools and governments to communicate and interact with each other, regardless of geographic limitations.
This paper provides the solutions needed to effectively provide a remote-centric rugged communication solution, while helping business and government executives achieve the highest possible return on their information infrastructure investment.
The Business Perspective
Applications through information technology (IT) are the driving forces behind every global business operation or government remote community initiative. Today, it is cost prohibitive for businesses and governments to dispatch human resources to collect information in order to make business decisions. For example, in the energy resources industry, the resource extraction takes place in a remote area or worksite for a defined period of time. However, the business decisions using the information gathered from these remote locations is done in a central office far from the energy resource location. In these situations, the information is required in real-time and becomes critical from the business perspective. The same concept applies for remote community sensor applications - from environment monitoring to security surveillance.
In addition, connecting remote communities through IT networks for social, educational, and information sharing purposes enables huge gains on economic growth and prosperity for the regions, specifically in developing and emerging markets. There is a high demand for data sharing and integrated communications for making intelligent business decisions and intelligent information sharing. All is required in real-time. Simply stated, a global business or government agency cannot afford to ignore real-time IT communication for remote communities. Business and government leaders are keenly aware of the cost and importance of the application and the services they support. Not all, however, are aware of the appropriate technologies needed to make cost-effective information access that will reflect a significant business and economic return. In fact, most remote community projects assume that urban-centric IT infrastructure can be easily extended to their application. In many cases, urban-centric IT infrastructure is an over-kill for remote community applications. It is also an inadequate fit for the extreme environmental and operating conditions. Choosing the appropriate infrastructure makes a significant business impact on the outcome of the enterprise’s and community projects.
The Community Perspective
Typically, people relate remote community application to rural community information access. However, the scope also extends to various enterprises providing business transactions to inaccessible communities, such as offshore energy exploration and surveillance services. In addition, areas of dense population where the terrestrial IT infrastructure is cost prohibitive are also treated as inaccessible remote communities.
Over the past few decades, geographically-challenged remote and rural communities focused on providing basic needs for the population, while proactively, and in many cases, reactively emphasizing the catastrophic health epidemics. Similarly, global energy resource industries focused on identifying and exploring these resources in various remote locations. These are the intuitive steps that are required by the governments and businesses to establish a social and business base-line. At the same time, technology has been advancing at a phenomenal pace. Where IT communication was once considered a luxury, it has become a necessity forming the fabric of day-to-day living.
Business Opportunities Created by Wireless VoIP
This paper introduces Wireless Voice over Internet Protocol (WVoIP) to enterprises and service providers who want to identify and take advantage of the substantial business opportunities presented by this new technology.
We begin by describing the benefits of standard (wired) VoIP compared to traditional telephony, and the benefits of wireless networking. We point out that by combining VoIP and wireless technologies, companies and organizations can realize the benefits of both. We go on to introduce some of the important technical aspects of VoIP and WVoIP technology, and describe the main challenges involved in delivering VoIP services—challenges that have been addressed by EION’s own wireless VoIP solutions. Next, we describe the opportunities created by the new technologies for both enterprises and service providers. Finally, we describe how EION, a leader in wireless IP-based networking, is spearheading the movement to wireless VoIP.
WVoIP—the Benefits of both VoIP and Wireless
VoIP’s momentum is no doubt part of a larger movement to move all communications to IP-based networks. Driving this move is the fact that delivering everything over IP can be both more economical and allow the delivery of more advanced services.
By now, the benefits of VoIP are probably familiar:
Earlier technical challenges regarding quality of service (QoS) and performance have been addressed, making VoIP a serious alternative to traditional PSTN-based communications systems, and placing VoIP on a level playing field with traditional technologies.
VoIP systems are capable of delivering a substantially richer array of services than PSTN-based networks. In addition to those services with which consumers are currently familiar (such as call display, call waiting, and so on), VoIP supports advanced new services that integrate Internet and telephony applications—such as integrated email and voice mail.
Implementing and maintaining VoIP networks costs much less than traditional PSTN, allowing enterprises with high call volumes to reduce their telecommunications costs, and service providers to add more subscribers and deliver more diverse services for a relatively low rate.
The benefits of wireless communications are also widely recognized:
Wireless networking has allowed many companies, organizations, and even countries to make telephony widely available to both urban and remote rural areas without having to lay cable lines or copper wires.
Wireless technology has advanced to the point where the quality of the services delivered over wireless networks is equivalent to or surpasses that of wired alternatives.
Nonetheless, it is less widely recognized how wireless technology can now be combined with IP-based networking to deliver telephony wirelessly—simultaneously achieving the benefits of both VoIP and wireless technology
What is WVoIP?
Before going on to describe the components of WVoIP, it is important to understand the basic features of VoIP networks and how they differ from PSTN-based networks. With a PSTN (Public Switched Telephone Network), analog voice data is transmitted over copper wires on a network whose parts are owned and controlled by traditional telephone companies (called Incumbent Local Exchange Carriers or Telcos). With VoIP, voice calls are converted to a digital format that can be transmitted over an IP network (the Internet, a private intranet, or a Virtual Private Network [VPN]). Analog calls can be converted to IP format locally via VoIP gateway devices, transmitted to remote destinations over the Internet for little or no cost, and then enter the remote PSTN via a remote gateway. Wireless VoIP calls are also transmitted over the Internet, but they rely on wireless access to the Internet—through proprietary wireless protocols, or potentially, WiMAX-based technology.
Wideband Orthogonal Frequency Division Multiplexing (W-OFDM)
Orthogonal Frequency Division Multiplexing (OFDM) has been successfully applied to a wide variety of digital communications applications over the past several years and has been adopted as the wireless LAN standard. This paper presents the challenges associated with implementing OFDM for high speed wireless data communication and how Wide-band OFDM (W-OFDM), a variation of OFDM improves bandwidth and noise tolerance.
Just what is OFDM, and what makes it better? To answer this question, we need to review some basic ideas about wireless telecommunications systems, and how OFDM fits into the overall picture.
In what follows, we will review the following concepts needed to understand OFDM; digital messages, carrier waves, modulation and multiplexing. Then we will explain OFDM and why it is used.
Wireless communications systems are used to send messages between two locations using radio waves which travel across free space. Messages of all types (voice, music, image, video, text) are usually converted to digital form and are represented as a stream of 1's and 0's called bits (binary digits). Voice messages can be represented by about 10,000 bits per second, CD quality music needs about 100,000 bits/sec, and TV quality video messages require about 1,000,000 bits per second, plus or minus. Text messages can be sent at any speed, depending on how long you are willing to wait.
Radio waves are electromagnetic waves used to carry a message over a distance. Thus radio waves are also called a carrier waves. A carrier wave looks like a sine wave, and moves like a train at the speed of light. The frequency of the carrier wave is the number of times per second that the wave train goes up and down and back up as it moves past you, and is measured in units of cycles per second or Hertz.
Carrier (electromagnetic) waves of different frequencies and wavelengths have different properties. For example, radio waves can travel through walls, but light waves cannot. Lower frequency waves tend to travel further, and can bend around corners. Higher frequency waves travel more or less only via line of sight. Thus certain parts of the radio spectrum are better suited for certain types of telecommunications. For indoor wireless communications through walls over a distance of several hundred feet, or outdoor communications over several miles mostly over line of sight with perhaps some trees in the way, carrier frequencies in the range of 1 to 5 GHz (gigahertz or billion cycles per second) are used.
Modulation is the process whereby a carrier wave of a particular frequency is modified or modulated by the message signal, so that the modulated carrier wave can be used to carry the message over a distance. For digital messages (a stream of 1's and 0's), there are three basic kinds of modulation:
Amplitude Shift Keying (ASK) (digital AM) in which the amplitude of the carrier wave is modulated in step with the message signal.
Frequency Shift Keying (FSK) (digital FM) in which the frequency of the carrier wave is modulated in step with the message signal.
Phase Shift Keying (PSK) (digital PM) in which the phase of the carrier wave is modulated in step with the message signal.
ASK and PSK may also be used at the same time on one carrier, which is called Quadrature Amplitude Modulation (QAM) or Amplitude/Phase Keying (APK). The receiver is designed to receive the carrier wave, detect these amplitude and phase shifts in the carrier (demodulation), and thus retrieve the digital message.
When a carrier wave is modulated, it is no longer a single frequency but is spread out over a range of frequencies. The bandwidth of the modulated carrier wave is the range from lowest to highest frequency, with the original carrier frequency in the center. The bandwidth is approximately equal to the speed of the digital message, e.g. 10,000 Hz (10 KHz) for voice or 1,000,000 Hz (1 MHz) for video.
OFDM (Orthogonal Frequency Division Multiplexing) is a method of using many carrier waves instead of only one, and using each carrier wave for only part of the message. OFDM is also called multicarrier modulation (MCM) or Discrete Multi-Tone (DMT). We first describe Multiplexing, then Frequency Division and then Orthogonal. It is important to stress that OFDM is not really a modulation scheme since it does not conflict with other modulation schemes. It is more a coding scheme or a transport scheme.
Multiplexing is a way to split a high speed digital message into many lower speed ones. A useful analogy is a highway with a toll collection point. Where each car is one bit of the message, and the number of cars passing a given point in one second is the speed of the message, which represents bits per second. The single lane highway may be split into 10 different lanes for paying tolls. At a point beside the single lane highway, the cars will pass at high speed, whereas at the toll booths, the cars will pass slowly. Thus the single high speed message (flow of cars past a point of single lane highway) is divided into many low speed messages (flow of cars past many toll booths). In a perfect system, the first car will take the first toll lane, the second car takes the second toll lane, etc. The 11th car takes the first toll lane again, and follows the first car. A multiplexer is a switch that assigns each car to one of the many toll booths.
Demultiplexing is the opposite, where many low speed messages are combined into one high speed message. Following the analogy, demultiplexing is where the many low speed messages (cars) passing slowly through the toll booth lanes are merged back into a high speed message travelling quickly on a single lane highway.
Wide-Band Orthogonal Frequency Multiplexing (W-OFDM) Technical
Orthogonal Frequency Division Multiplexing (OFDM) is a multi carrier transmission technique whose history dates back to the mid1960's. Although, the concept of OFDM has been around for a long time, it has recently been recognized as an excellent method for high speed bidirectional wireless data communication. The first systems using this technology were military HF radio links. Today, this technology is used in broadcast systems such as Asymmetric Digital Subscriber Line (ADSL), European Telecommunications Standard Institute (ETSI) radio (DAB:Digital Audio Broadcasting) and TV (DVBT:Digital Video Broadcasting---Terrestrial) as well as being the proposed technique for wireless LAN standards such as ETSI Hiperlan/2 and IEEE 802.11a. There is also growing interest in using OFDM for the next generation of land mobile communication systems.
OFDM efficiently squeezes multiple modulated carriers tightly together reducing the required bandwidth but keeping the modulated signals orthogonal so they do not interfere with each other. Any digital modulation technique can be used on each carrier and different modulation techniques can be used on separate carriers. The outputs of the modulated carriers are added together before transmission. At the receiver, the modulated carriers must be separated before demodulation. The traditional method of separating the bands is to use filters, which is simply frequency division multiplexing (FDM). Fig. 1 shows a representative power spectrum for three sub channels of a FDM system.
In a classic FDM system, the sub channels are non-orthogonal and must be separated by guard bands to avoid inter channel interference. This results in reduced spectral efficiency.
Another method to achieve frequency separation, but is more spectrally efficient than FDM is to overlap the individual carriers, yet ensuring the carriers are orthogonal is to use the discrete Fourier Transform the (DFT) as part of the modulation and demodulation schemes. This is where the name orthogonal FDM (OFDM) arises. High speed, fast Fourier transform (FFT) chips are commercially available, making the implementation of the DFT a relatively easy operation. Fig. 2 shows the spectrum of an OFDM signal with three sub carriers. The main lobe of each carrier lies on the nulls of the other carriers. At the particular sub carrier frequency, there is no interference from any other sub-carrier frequency and hence they are orthogonal. In Fig.2, the sub carriers are 300 Hz apart.
The orthogonal nature of the OFDM sub channels allows them to be overlapped, thereby increasing the spectral tightly efficiency. In other words, as long as orthogonality is maintained, there will be no inter channel interference in an OFDM system. In any real implementation, however, several factors will cause a certain loss in orthogonality.
Designing a system which will minimize these losses therefore becomes a major technical focus. Another advantage to OFDM is its ability to handle the effects of multipath delay spread. In any radio transmission, the channel spectral response is not flat. It has fades or nulls in the response due to reflections causing cancellation of certain frequencies at the receiver. For narrowband transmissions, if the null in the frequency response occurs at the transmission frequency then the entire signal can be lost.
Multipath delay spread can also lead to inter symbol interference. This is due to a delayed multipath signal presents overlapping with the following symbol. This problem is solved by adding a time domain guard interval to each band OFDM symbol. Inter carrier interference (ICI) can be width avoided by making the guard interval a cyclic extension of, the OFDM symbol. There are, however, certain negatives associated with this technique. It is more sensitive to carrier frequency offset and sampling clock mismatch than single carrier systems. Also the nature of the orthogonal encoding leads to high peak to average ratio signals: or in other words, signals with a large dynamic range. This means that only highly linear, low efficiency RF amplifiers can be used.
We present here WOFDM technology, which is less sensitive to inherent OFDM problems such as frequency offset, sample clock offset, phase noise and amplifier non-linearities. WOFDM is also able to tolerate strong multipath and fast changing selective fading by using a powerful equalization scheme combined with a forward error correction scheme.
Broadband Fixed Wireless Solutions—An Enabler for Service Providers
Today there is an increasing demand for access bandwidth that is being fueled by high utilization applications such as those associated with the Internet. In the past only traditional wireline access had been available to consumers and businesses, but recent advancements in wireless technology now allow wireless local loop LL services to compete with Digital Subscriber Lines (DSL), coax, and fiberbased architecture solutions. This White Paper explores these advancements and the opportunities that Broadband Wireless technologies enable for service providers.
Organization of Document
The remainder of this White Paper is organized as follows:
Section 2 describes the use of Broadband Wireless technologies to provide customer highspeed data access to homes and businesses. This use of radio spectrum is referred to as a Broadband Wireless Local Loop or Fixed Wireless Access.
Section 3 describes the market opportunity for FWA service providers.
Section 4 examines some value-added services that can be offered to customers using FWA.
Section 5 discusses some of the advantages of EION's technologies over other wireless technologies. EION's technologies help make the dual Broadband Wireless Local Loop (described in Section 2) competitive with wirein based technologies (described in Section 7).
Section 6 continues the discussion from Section 5 by exploring additional INTERNET characteristics of fixed wireless architectures that provide advantages over RGE wireline technologies.
Section 7 provides an overview of wirebased technologies, including Digital Microwave Subscriber Lines, Hybrid Fiber Coax, and others.
Section 8 identifies new opportunities that EION’s solutions create for various types of service providers.
Section 9 summarizes the key findings of this White Paper.
2 The Broadband Wireless Local Loop
Many service providers are looking for alternative methods, such as fixed wireless local loop, to provide data services. Their interest is a result of a number of factors, which are listed below.
Increasing demand for broadband speeds on the local loop. This demand has been largely fueled by growth in Internet usage, businesstobusiness and business-to-consumer ecommerce, and value-added IP services including Virtual Private Networks (VPNs),Voice over IP (VoIP), and hosted application ice services.
The introduction of competition into local telecommunications services, and the desire of competing service providers to bypass the facilities of the incumbent local exchange carriers.
Improvements in wireless technology (e.g., WOFDM solutions) which have d resulted in costeffective CPE and network equipment..
The allocation of new spectrum.
A number of last mile technologies, including DSL and cable modems, are technically feasible to provide broadband access. One set of technologies with unique benefits is the Broadband Wireless Local Loop (BWLL). The BWLL uses radio spectrum to provide high speed data access. One example of a BWLL architecture is illustrated in Figure 1. The data rates for the service depend on frequency, modulation techniques, protocol, and equipment supplier, but leading suppliers support peak data rates of 30 Mbps.
A BWLL can be used to provide data access for converged services. Consequently, a customer can use a single broadband wireless pipe for any combination of data services, including Internet access, access to an Applications Service Provider (ASP), telecommuting, and Voice over IP. Due to the flexibility of the architecture, BWLL customers include consumer and business users in rural, suburban, and urban areas. In addition, BWLL can be used to provide a highspeed pipe to a multitenant unit, where the inbuilding wiring is used as the data transport medium to the individual units. (For example, an ADSLlike service can be provided bed by placing a DSLAM in the building's basement and using BWLL between the DSLAM and the service provider's backbone.)
Service providers are interested in BWLL for a number reasons. Some of these are described below.
BWLL captures new customers: BWLL allows service to be offered in areas where other broadband technologies are not available. These include rural areas where there is limited wired infrastructure. It also includes densely populated suburban areas where long loops or Digital Loop Carrier (DLC) Systems preclude the use of DSL.
BWLL creates new revenue opportunities: Due to recent technological advancements, BWLL offers data rates that are competitive with other access technologies at lower startup and operating expenses. This allows a service provider to compete with wirebased competitors in urban and suburban areas where wired technologies traditionally dominated. There are in several advantages to a service provider in using a wireless technology to bypass the incumbent's wired facilities, even when access to those facilities can be obtained via local loop unbundling. In order to use the incumbent's loops, a service provider must lease not only the loop but also collocation space in the central office. This creates a monthly recurring expense that wireless providers avoid. In addition, gaining access to an unbundled loop introduces several weeks, of delays into the service provisioning process. Wireless providers are able to quickly deploy service with a minimum upfront investment in equipment. Lastly, addition, in areas where cable, rather than copper, is the dominant method of broadband the access, new service providers’ only option may be BWLL, as cable companies do not provide unbundled access to their hybrid fiber coax plant.
Rapid service deployment: Many DSL service providers require a number of weeks to install a new DSL line, assuming they have a DSL Access Multiplexer NET (DSLAM) in the wire center. If the wire center is not equipped, then the customer may need to wait many months until a DSLAM is installed. Since BWLL PointsOfPresence (POPs) can be deployed readily, and new customers within a POP's circumference can be activated quickly, the wireless provider has an advantage in attracting customers. In markets that are not currently adequately served, the wireless providers can attract and establish relationships with customers before other providers are prepared to compete.
It should be noted that not all wireless technologies are able to support a BWLL with the necessary cost and performance characteristics to compete with wireline technologies. One wireless technology that is uniquely effective in this regard is Wideband Orthogonal Frequency Division Multiplexing (WOFDM), which is described in Section 5.