PROSPECT OF WIRELESS MAN IN RURAL NETWORK INFRASTRUCTURE OF BANGLADESH

Transcription

1 PROSPECT OF WIRELESS MAN IN RURAL NETWORK INFRASTRUCTURE OF BANGLADESH Abdul Hasib Lecturer, Institute of Information and Communication Technology ABSTRACT The Consumption of IT in Bangladesh is rapidly increasing both in public and private sectors. But our communication network infrastructure is not yet ready to serve the customer requirement to every corner of the country. We believe the rapidly deployable, scalable, distance-insensitive nature, and emerging low costs associated with wireless solutions make broadband wireless a highly viable technology in a developing country like Bangladesh. High frequency point-to-point wireless solutions can serve as urgent backhaul network and point-to-multipoint solution can be last mile broadband access network. These technologies will enable high speed Internet, open new ways of doing business like Telemedicine, Distance Learning, Electronic Service Delivery and Information Sharing. In first step, targeted group of users are core public service organizations, educational institutes and health care organization across the country. We hope that rapid investment on broadband wireless infrastructure will connect every town, even rural area, of Bangladesh with high-speed communication link and minimize the digital divide between rural and urban communities. 1. INTRODUCTION The Consumption of IT in Bangladesh is rapidly increasing both in public and private sectors. The Government's policy on ICT is also very positive. Bangladesh s National ICT Policy aims to harness and utilize the immense potentialities of IT for the overall welfare of Bangladesh. Government has already taken several steps like signing agreement for connectivity to Submarine Cable Network, setting up Software Technology Park etc. to attain that goal. But our communication network infrastructure is not yet ready to serve the customer requirement to every corner of the country. Even more, in a very near future, when Bangladesh will be connected to Intercontinental Fiber optic super high way, to utilize immensely available bandwidth, we need broadband last mail access network. Other than broadband access, any other access technology will be a burden to us. This paper will try to give a guideline on which last mile broadband access network infrastructure, government or private investor should emphasis on and invest to attain the insatiable bandwidth demand of potential users. Here, an urgent solution for backbone network, in absence of fiber-optic network backbone, is also discussed. These technologies will enable high speed Internet, open new ways of doing business like Telemedicine, Distance Learning, Electronic Service Delivery and Information Sharing. In first step, targeted group of users are core public service organizations, educational institutes and health care organization across the country. The possible outcomes are lower telecommunications costs, minimize the digital divide between rural and urban communities and improve government service delivery to small and rural communities. 2. INVESTMENT OPPORTUNITIES Bangladesh has a very few communication network infrastructure. To meet the near future demand of an IT society, we need to invest on broadband technologies. Broadband is characterized by high speed, always-on connection and two-way capability and can support applications in e-commerce, education, health care, entertainment and e-government. Bangladesh has limited broadband setup mainly in big cities and at IT organization level. Most of the Internet user use Dial-up connection with wire line modem of 56 kbps. For an optimal investment on network infrastructure, considered technology should have following characteristics: Reliable and assure quality of service Affordable to ensure its acceptance Excellent Value Effectively connect people with respect to coverage and bandwidth capacity Re-locatable technology with simple installation and maintenance

2 3. COMPETITIVE AND COMPLEMENTARY BROADBAND SOLUTIONS We now have the capability to generate and process massive amounts of data from our desktop. An alwaysgrowing range of applications leaves us craving more capacity. That is the underlying reason of broadband development. Between the desktop and the fiber backbone is that stretch of the information highway known as the last mile or access portion of the network. Broadband access can be served by several broadband technologies, mentionable, PSTN xdsl ISDN or Private/Leased Line Cable Modem Fixed Wireless etc PSTN The biggest network infrastructure laid on Bangladesh is Public Switched Telephone network (PSTN). Most Internet access has been gained through traditional telephone lines. Copper infrastructure is widespread, readily available, and easy to commission. Copper can competently handle bandwidth speeds up to 56 Kbps. However, the public demands for higher connectivity is dramatically increasing, and the imbedded copper cable plant is becoming the bottleneck Digital Subscriber Line (xdsl) A digital subscriber line (DSL) provides broadband service by converting an existing analog telephone line into a digital voice and data circuit. DSL is available in various alternatives, including HDSL (high data-rate DSL), which operates at 1.54 Mbps symmetric, ADSL (asymmetrical DSL), which is faster than HDSL with greater downstream than upstream capacity - benefit for residential use; and VDSL (very high data-rate DSL), which runs faster than ADSL but can only operate over short distances. The always-on connection and maximum speed allure of 8 Mbps downloading and 1 Mbps upstream, combined with a cost much lower than other more high-speed leased lines such as T-1 lines, make DSL a frequent choice of high speed accessibility for small to medium enterprises (SMEs). But to provide mass IT literate people, DSL has major limitations. First, the home or business fixed-line service must be located no more than 18,000 feet from a telephone company switch. Secondly, DSL requires a digital subscriber line access multiplexer (DSLAM) to be installed in a phone company switch, which requires large user group in an area to prove it economically viable ISDN or Private/Leased Lines Integrated services digital network (ISDN) offers a digital telephone line that provides access two to five times faster than traditional analog phone lines. ISDN provides capacity for , video conferencing, faster Internet browsing, and other digital services by operating at 128 Kbps. It also allows multiple stations to be online, so it provides options for business use. The obstacles for ISDN include its cost, which is usually considerably higher than telephone service, and difficulty of installation. The advantage of E-1 or E-3 is very large capacity that is dedicated to the use of the subscriber for multiple uses. The primary problem for the leased lines is expense. A E-1 line can cost $2,000-$3,000 to install, with the average monthly cost between $500 and $1,000. Wireless highspeed access, DSL, and cable all other option will cost less than E Coaxial Cable The greatest benefit of cable is its speed, which can deliver data at speeds up to 100 times faster than telephone modems. However, cable was built as a one-way transmission pipe and must be upgraded to handle twoway capacity. The cost for the upgrades is estimated to run up to $1,000 or more per home. Because of this cost, the build-out is progressing slowly and the service cannot be offered in many areas. Another drawback from the user s standpoint is that it is a shared resource. The technology puts a group of nearby users served by the same node into what is essentially a network, with the bandwidth shared by all users online. As more users go online, there is a reduction of throughput in data and consistent speed. From a practical standpoint, the first user to sign on may find the speeds very fast, but they drop as soon as the next user signs on. As more users log on, the system continues to split the bandwidth among all users, resulting in inconsistent service Fixed Wireless Fixed-wireless systems can be used for almost anything that wire line or fiber is used for, whether the connection is an E-1 circuit, a cable television connection, an Ethernet connection, or a fiber-optic connection. It is designed to emulate wireline and fiber-optic connections, and they use the same type of interfaces and protocols, such as E-1, frame relay, Ethernet, and ATM. The technologies can deliver data rates from less than E-1 up to and beyond 155 megabits per second (Mbps). Broadband wireless allows: a) High Capacity: Broadband wireless solutions use spectrum with a powerful dynamic bandwidth allocation mechanism to support the exponential growth in data

3 communications and the tremendous demand for low-cost circuit services. b) Fast Rollout and Early Market Capture: Broadband wireless solutions are easy and quick to implement, giving the first-mover the opportunity to cherry pick the most profitable customers. c) Low Start-Up Costs: With no cables to lay or DSLAM (for xdsl) access fees to negotiate and pay, deployment costs are kept low. d) On-Demand Build-Out: When demand increases, the broadband wireless access solutions scale simply by increasing sectorization or adding more cells, allowing a business to expand. e) Fast Payback: Since the initial investment is comparatively low and deployment is fast, operators start seeing a return on investment sooner. f) Greater flexibility: One of the major driving forces for broadband wireless will be the simplicity and re-locate ability it provides. Once the technology become obsolete is one group of user, it will be repositioned to a less demanding group of user. Considering the above reasons, when both wireless and wire line options exist, number of companies are deploying or planning to deploy wireless networks. Wireless communication offers tremendous flexibility and ever-improving performance, but it does have some limitations. First and foremost, wireless uses radio spectrum, a finite resource. This limits the number of wireless users and the amount of spectrum available to any user at any moment in time. The amount of spectrum available equates almost directly to data bandwidth, with 1 Hz of spectrum typically yielding between 2 bps and 8 bps of throughput depending on various factors such as the type of modulation used and environmental factors. The amount of spectrum actually available varies from radio band to radio band, but suffice it to say that fiber-optic cable offers far greater overall capacity. Despite this capacity limitation, wireless offers more than sufficient bandwidth for many applications. Another limitation is that fixed- wireless systems operate at frequencies that almost always require line-of-sight and that are restricted to distances that vary from a few miles to tens of miles. New wireless technologies are developing to overcome the limitations. Considering all of these characteristics, broadband wireless can be a potential tool to reach people at remote places of Bangladesh. 4. RADIO SPECTRUM The spectrum needs for broadband radio access networks vary with the application and the environment in which they are deployed. Different prominent broadband wireless systems are: Private Licensed Links (Microwave) Private Unlicensed Links (Spread Spectrum) 2.5GHz and 3.5GHz MMDS (Multichannel Multipoint Distribution Service) UNII (Unlicensed National Information Infrastructure); Broadband Radio Access Network (BRAN) LMDS (Local Multipoint Distribution Service) 38 GHz fixed wireless system The lower the frequency, the farther the signal travels and the better it can penetrate obstacles. For carriers, lower frequencies mean cheaper network build-outs and greater reach than higher frequencies. In addition, mobile services tend to work better at frequencies lower than 3 GHz (cellular is at 800 MHz, and PCS is just less than 2 GHz). At frequencies higher than 3 GHz, wireless services providing substantial range performance usually require a fixed antenna rather than a mobile one. Most higherbandwidth systems use frequencies greater than 10 GHz. Antennas at these frequencies are smaller due to the smaller wavelengths, making systems easier to deploy. But with higher frequency, components demand more sophisticated technology, so systems typically cost more. Also, propagation distance for reliable communications decreases, and the signal is more susceptible to weather conditions like rain and fog. Higher-frequency systems, those greater than approximately 30 GHz, are sometimes referred to as millimeter wave because the wavelength of these signals is on the order of 1 millimeter. Both private and carrier systems have a choice of using licensed or unlicensed spectrum. The main advantage of unlicensed spectrum is being able to deploy a system without applying for a license from the FCC (or equivalent body in other countries). The disadvantage is that user could experience or cause interference, though the type of technology used in these frequencies minimizes this possibility. 5. THE BROADBAND WIRELESS INDUSTRY SEGMENTATION AND SPECTRUM The market for wireless access systems is diverse and changing. There are generally two types of fixed wireless solutions, one in which one terminal station is dedicated to another terminal station, known as point-to-point, and the other that enables transmissions between multiple terminal stations and a single base station, known as point-tomultipoint. A point-to-multipoint wireless system enables a single base station located at the center of a cell to support a few hundred to thousand terminal stations all located at the premises of different customers within that cell, similar to a cellular phone network. This allows a carrier to spread the cost of a base station, the most

4 expensive portion of the wireless link, across many users, providing cost-effective broadband wireless services. Breaking the last-mile bandwidth barrier using broadband wireless is an ideal business opportunity, especially as a cost-attractive alternative to fiber, which can be priced at more than $100,000 per mile. Holders of valuable Table 1: Broadband Wireless Market Segments FSO Figure 2: Broadband Wireless MAN [2] Figure 1: Last Mile Broadband Access Technology [1] spectrum are in an optimal position to build and grow profitable businesses quickly by providing the evolutionary services necessary to keep pace with pervasive demand. PtP products are targeting application where data link rates range from T-1 up to OC-3 with a high degree of spectral efficiency; whereas, PtMP application of wireless is typically targeting a lower shared bandwidth and multiple distributed users in an area. High - Freq. Low- Freq. Point-to-Point High Capacity (OC-3 [155 Mbps], OC-12 in future) Narrowband (T1 [1.5 Mbps] to DS3 [45 Mbps]) Microwave and Bridge market (OC-3 [155 Mbps] to fractional T-1s [sub- 1 Mbps]) Point-to-Multipoint High Capactity (FDMA [>40 MBPS]) Medium Capacity or Wideband (TDMA 1-40 Mbps) 10, 24, 26, 28, and 31 (LMDS); and 38GHz Medium Capacity (fractional T-1 to >10 Mbps) Unlicensed (2.4 GHz and 5 GHz ), MMDS and 3.5 GHz 5.1. Point-to-Point Wireless Broadband Access Fixed-wireless systems have a long history. Point-to-point microwave connections have long been used for voice and data communications, generally in backhaul networks operated by phone companies, cable TV companies, utilities, railways, paging companies, and government agencies, and will continue to be an important part of the communications infrastructure to support constant bandwidth requirement to single locations. An alternative to a microwave link is to use spread-spectrum bridging products. Many wireless LAN vendors offer such products because they incorporate much of the required technology within their access points. These wireless bridges, mostly operating in the 2.4 GHz band, offer rates of 1 Mbps through 11 Mbps and distances up to 10 or 25 miles (16 to 40 kilometers) depending on the type of antenna used. For longer distances, a user may not be able to achieve as high a throughput. The above-mentioned technologies are already available in Bangladesh. Technology has continued to advance, allowing higher frequencies, and thus smaller antennas, to be used, resulting in lower costs and easier-to-deploy systems for private use and for a whole new generation of carriers that use broadband wireless as their last mile of communication.

5 Figure 3: Elements of a Point-to-Point Broadband Wireless System [1] At a minimum, any PtP link will contain two terminals where each terminal consists of an OutDoor Unit (ODU) and InDoor Unit (IDU). The ODU is typically the antenna and RF functions, while the IDU is the modem and a variety of network interfaces. PtP is connecting the tremendous bandwidth available on the long-haul backbones and metropolitan fiber rings to buildings and their business tenants. These networks now form a reliable, sophisticated data infrastructure that can also serve as the basis for Voice over IP. In many cases, DSL technology on copper wiring inside customer buildings can be combined with fixed-wireless networks outside the buildings to provide a lower-cost, entry-level data service for smaller companies. Four critical characteristics differentiate the leading companies in this equipment category from previous microwave suppliers. First, instead of starting with lowcapacity radios and trying to work up to higher data rates to meet the demand for capacity, engineers designed highcapacity systems in the SONET OC-3/SDH STM-1 range. So the baseline systems already offer capacity more than three times greater than the DS-3 rate that was the maximum previously available. Second, they have selected modulation schemes (16 QAM, 64 QAM, 128 QAM, and 256 QAM) that are much more spectrally efficient than those of their predecessors. This provides OC-3 (155 Mbps) in the same 50 MHz channel that otherwise accommodated at best a single DS-3 (45 Mbps). Third, they have integrated very flexible multiplexers into their indoor units that offer carriers interface options of: Direct fiber or copper OC-3/STM-1 Three times DS-3/E base T Fast Ethernet + DS-3/E-3 or Two times 100baseT Fast Ethernet This flexibility offers carriers the very significant benefit to directly provision for all key voice and data formats (e.g., IP and ATM over SONET) and associated broadband data rates as required for various customer applications. And last, lower capacity systems are also offered using even higher order modulation (64 QAM) to allow carriers to deploy DS-3 service in much smaller channel bandwidths (12.5 MHz) than previously possible. Single 100baseT Fast Ethernet circuits are also available in that same narrow bandwidth. With the transmission capacity up to 155 Mbps, PtP can satisfy customers at distance places quickly and cheaply compared to fiber lay down. Wireless service provider risked no significant sunken costs; if their customers terminated service or moved, the radio link is easily moved and reused elsewhere. Wireless carriers believe that their large spectrum holdings are ideal for such higher-capacity services Point-to-Multipoint (PtMP) Wireless Broadband Access Where broadband wireless customers are geographically dispersed, PtP is not appropriate because of the need for many antennas at a central location and the lack of ability to spread costs, or more importantly, for users to share bandwidth. We believe the benefits of PtMP are best leveraged when the number of connection points is increased to justify the cost of the controlling hub, and when the data demands are not as high as what PtP solutions provide or when data allocation adaptation is necessary on the fly between a few nodes. PtMP systems are, of course, being developed for numerous bands; they are intended to offer diverse, flexible capacity services to a multitude of end-users. The point-to-multipoint common objectives include the following: Low cost with simple installation/deployment procedures (i.e., it must be consumer installable for the residential target market) and scalable deployment architectures; Efficient coverage capabilities (potentially including in-building coverage); Spectrially efficient delivery of high data rates and overall throughput (relative to the frequency bandwidth available); and Low-cost continuation support and management.

6 years away from having either DSL or fiber nearby, need access to this technology. Figure 4: Elements of a Point-to-Multipoint Broadband Wireless System [1] PtMP system has minimum of nine elemental functions: Computer, television, or telephone at the customer s premise to interact with the desired data, audio, or video; A modem to encode and decode information; A transceiver and antenna to convert the information to and from radio frequency (RF); A centralized base station antenna; Transmitters, receivers, and switches for the base station; A wireless hub that encodes and decodes information for and from all users; Network management tools to monitor the network s health and manage all users; A gateway and router to effectively connect to other networks and distribute and receive information for all customers; and finally, A connection to an information network or source-in this case the Internet. Deployment of a nationwide PtMP system would provide an information pipe to several under-served segments, including: Residential customers-especially those in rural areas where it is cost-prohibitive cable companies to build systems or for telephone companies to supply DSL service. Schools-all learning institutions, from kindergarten through universities, need data. Branch offices-small to mid-sized public and private offices must have a network to transmit among their locations. Businesses in urban sprawl-those businesses not located in the primary business district, and are thus System Deployment Architecture The system deployment architecture refers to the technological approach used in the actual field deployment of the equipment (i.e., the positioning of the wireless base stations or hubs to adequately cover a service area). In general, there are three different architecture strategies, each with different implications for the product design and system function. The first strategy is an ad hoc approach, where base stations are simply positioned where coverage is needed. This approach is typically the most inefficient relative to coverage and scalability in that it does not employ an overall plan on delivering service to a large number of customers over a broad area. It can, therefore, be quite problematic. In particular, the uniformity of coverage can be inconsistent (i.e., in-building coverage close to the base station and not in areas further away), and interference issues can result as additional base stations are added. This technique is still used, however, in situations where customer density is low and where performance/interference issues can be managed in detail. An incrementally better architecture is the supercell approach in which a plan is derived to cover a given geographic area (typically a large area) with a few largediameter cells (typically miles in diameter for 2.5/3.5 GHz frequencies), i.e., supercells. This approach is better than an ad hoc architecture in that it reduces interference issues with an overall plan detailing where base stations should be located. Each base station is designed to cover a large area and thus typically uses high antenna towers. The supercell architecture is ideal for areas with low customer density and situations where a very cost-effective deployment is required. In addition, a supercell architecture can be a very cost-effective way to initially enter a marketplace because a large area can be covered and initial customers (typically a small number of customers) can be added quickly. In this situation, as customers increase, supercells can be augmented with smaller cells on different frequencies as long as the overall system and frequency availability support this scalability. The disadvantage of supercells is in quality of coverage because base station signal strengths may vary considerably from the inner portion of the cell to the outer edge of the cell. This can result in dramatically inconsistent data rate capabilities from one area to the next and non-existent in-building coverage in most areas. The last architecture strategy is the cellularized approach, which ultimately is very similar to the cellular infrastructure used for mobile wireless communications. A cellular approach uses much smaller cells (typically three to five miles in diameter for 2.5/3.5 GHz frequencies) and offers more uniform coverage capabilities and even inbuilding coverage penetration

7 (Depending on the power output of the transceivers and the modulation techniques used). A cellular approach is the highest-capacity architecture (in terms of customers and aggregate data throughput) and is thus typically used in customer-dense areas. Like mobile cellular infrastructures, frequencies must typically be coordinated on an overall planning basis between base stations to avoid interference. In addition, due to the smaller cell size, base station density is much higher and thus results in a higher infrastructure deployment cost. 6. STANDARDS Very few standards exist for broadband wireless systems, and users need to purchase equipment from the same vendor for both sides of the connection to ensure interoperability. In some vertical markets, interoperability and standards are moot because the entire system, from application to access point to user device, is sold as a package. The broadband wire-less access industry has numerous suppliers for the various elements of the infrastructure throughout the world and will, therefore, require standardization to attain all of the benefits of interoperability IEEE Broadband Wireless Access Systems The IEEE 802 standard [3] covers local and metropolitan area networks whereas Part 16 specifies the standard air interface for fixed broadband wireless access systems under The overall purpose of this standards body is to: 1) Enable rapid worldwide deployment of innovative, cost-effective, and interoperable multivendor broadband wireless access products; 2) To facilitate competition in broadband access by providing alternatives to wireline broadband access; and 3) To facilitate coexistence studies, encourage consistent worldwide allocation, and accelerate the commercialization of broadband wireless access spectrum. This standard specifies the medium access control layer and physical layers of the air interface of interoperable, fixed point-to-multipoint broadband wireless access systems. The specification enables transport of data, video, and voice services. Physical layers are specified for both licensed and license-exempt bands. It will identify techniques to tolerate interference in the unlicensed bands and facilitate strategies for coexistence with other unlicensed band systems such as and It will encourage consistent worldwide spectrum allocation and accelerate the commercialization of unlicensed broadband wireless access spectrum. Utilization of unlicensed frequencies will address a market that includes residences, small office/home office (SOHO), telecommuters, and small and medium enterprises (SMEs) DOCSIS+ The Data Over Cable System Interface Specification (DOCSIS) [4] was developed by a consortium of equipment manufacturers and CATV operators with ratification in August The specification establishes a clear standard for cable modems and the cable modem termination system (CMTS) to allow interoperability of products from various manufacturers. It specifies the RF physical layer, with specific modulation types and symbol rates. The protocols for initialization, data control, and security aspects are also defined. DOCSIS is a standard that has several advantages: lower costs, multiple knowledgeable sources, add-ons, and plug-ins from third parties. DOCSIS was conceived and is designed for the CATV hybrid-fiber/coax plant. DOCSIS+ (a wireless version of the DOCSIS specification) builds on the specification by adding several enhancements. Specifically, it adds a superset of features to the DOCSIS specification. These features extend the frequency tolerance, add more signal path equalization, increase the dynamic range, and support multiple modulation types and modulation symbol rates. These enhancements improve, among other things, the signal-to-noise margin for robust performance under the less-than-ideal conditions of broadband wireless operation. The new DOCSIS 1.1 features quality of service (QoS), data and voice/video application, service flows, classifiers, scheduling types, and dynamic service establishment Broadband Radio Access Network (BRAN) Project The Broadband Radio Access Network project [5] has defined three types of broadband radio networks: HIPERLAN/2, HIPERACCESS, and HIPERLINK. HIPERLAN/2, a complement to HIPERLAN/1, ETSI s high-speed wireless LAN, is a local access network that provides communication between portable computing devices and broadband core networks aimed at telecommunications access and capable of supporting the multimedia applications of the future. User mobility is supported, but only within the local service area, which ranges from 50 meters indoors to a few hundred meters outdoors. HIPERACCESS is an outdoor, high-speed radio access network that provides fixed radio connections to customer premises (other technologies such as HIPERLAN/2 might be used for distribution within the premises). HIPERACCESS will allow an operator to rapidly roll out a wide area broadband access network to provide

8 connections to residential households and small businesses. It will be an attractive alternative to wired access technologies such as digital subscriber loop or cable modems, especially in the competitive market of the future where no one operator will have the certainty of monopoly. The third category is HIPERLINK, which is a very highspeed radio network for small-scale interconnections. A typical use is the interconnection of HIPERACCESS networks and/or HIPERLAN Access Points into a fully wireless network. With this standardized solutions, we believe customer premise equipment pricing less than $200 to $400 will be necessary instead of the $1,500 to $4,000 and multi-hour installation currently being experienced. 7. CONCLUSION The development of broadband wireless is no different from any other new market: the explorers have mapped the terrain, and now the settlers are moving in for growth and expansion. We believe the rapidly deployable, scalable, distance-insensitive nature, and emerging low costs associated with wireless solutions make them a highly viable broadband access technology in a developing country like Bangladesh. We hope that rapid investment on broadband wireless infrastructure will connect every town, even rural area, of Bangladesh with high-speed communication link and ensure that rural and urban communities have the same opportunity to participate in the digital economy. REFERENCE [1] Michael A. Helgeson, Broadband Wireless: The Worldwide Assessment. Institutional Research, DAIN RAUSCHER WESSELS, I May 17, 2001 [2] [3] [4] [5]