Wireless Broadband IST 220, Dr. Abdullah Konak 4/27/2005 500 Blake Drive Reading, PA 19601 Prepared by: Dennis DeFrancesco 1
Table Of Contents 1. Wireless Broadband Overview... 3 1.1. Beginnings... 3 1.2. Defined... 3 2. Wireless components... 3 2.1. Encompassed Hardware... 3 2.2. Local Multipoint Distribution System (LMDS)... 4 2.3. Multichannel Multipoint Distribution System (MMDS)... 5 2.4. Direct Broadcast Satellite (DBS)... 5 2.5. (3G)... 6 2.6. Ultra-Wideband (UWB)... 6 3. Technological Advantages and Disadvantages... 7 3.1. Advantages... 7 3.2. Disadvantages... 7 4. Wireless How and Where?... 8 4.1. Wireless model... 8 4.2. Time Division Multiple Access (TDMA)... 8 4.3. Code Division Multiple Access... 9 4.4. Global System for Mobile Communications (GSM)... 10 5. Wireless Costs... 11 6. Future trends and Implementations... 12 7. Conclusion... 12 8. List of References... 13 2
1. Wireless Broadband Overview 1.1. Beginnings The origins of wireless can be traced back to James Maxwell's treatise on electromagnetism, published in 1873 and later on to the experimental work of Heinrich Hertz, who in 1888 produced the first radio wave communication. Wireless, however, really came to light during the Internet revolution. It started as an exchange mechanism for data transfer and has sparked a worldwide demand for fast, anywhere, anytime communication and computing. 1.2. Defined What is wireless broadband? It is a bundle of overlapping technologies that enable highspeed communication without the use of a physical medium. Local Multipoint Distribution System (LMDS), Multi-channel Multipoint Distribution System (MMDS) Direct Broadcast Satellite (DBS), 3G, and Ultra-Widebase (UWB) form some of the technologies necessary for the global wireless infrastructure needed to deliver high-speed communications and Internet access to the world. In essence, the term wireless broadband encompasses the full range of wireless technologies and applications both fixed and mobile. 2. Wireless components 2.1. Encompassed Hardware Wireless is segmented into three different markets based on the spectrum allocation of the service. These markets are the Local Multipoint Distribution System (LMDS), the Multi-channel Multipoint Distribution System (MMDS), and the Direct Broadcast Satellite (DBS). 3
Figure 2-1 is an architectural reference for fixed wireless systems. It depicts some common components to these systems. In addition to the physical equipment such as antennas, base station, indoor and outdoor units, the figure depicts the different interfaces required for fixed wireless systems. As shown, the RF specifications for MMDS, LMDS, and DBS defines the interface between a base station and a receiving antenna. Figure 2-1: Wireless fixed reference architecture 2.2. Local Multipoint Distribution System (LMDS) An LMDS system can be built on an Asynchronous Transfer Mode (ATM) infrastructure. The typical system consists of the following; base station or hub and a base radio unit that has upstream and downstream channels to the microwave equipment (see Figure 2-2). It includes a network operation center (NOC) where all the network management systems and all the different feeds from other networks. The customer equipment consists of a radio unit and an antenna system. Figure 2-1: LMDS architecture 4
2.3. Multichannel Multipoint Distribution System (MMDS) An MMDS system consists of a head end where all the digital and analog services converge, a base station for broadcasting the signal, the customer equipment, and the return channel (see Figure 2-3). The customer equipment consists of a wireless modem that has a LAN interface (usually Ethernet), a radio, and an antenna. The antenna (or dish), which is usually about a foot in diameter, is mounted on the outside of the building. The hub (base station and antenna tower) is usually located in a place that provides the widest unobstructed coverage of the coverage area. Signals are fed to the tower from the head end through a direct wire connection. Figure 2-3: MMDS architecture 2.4. Direct Broadcast Satellite (DBS) DBS uses geostationary satellites operating with a 12 GHz downlink and a 14 GHz uplink. The architecture of the service for broadband wireless is very straightforward. It uses what is known as a bent-pipe approach, a term used to describe the signal path when satellites are used: signals go up and are reflected to the target earth station. The basic architecture of the service is very similar to cable: a head end receives feeds from the different services and networks and encodes them into MPEG for digital transmission (see Figure 2-4). The composite signal is transmitted to a geostationary satellite, which in turn broadcasts it to the subscriber antennas. The subscriber antenna is connected to a receiver that connects to the television set. 5
Figure 2-4: DBS architecture 2.5. (3G) (3G) refers to a family of new air interfaces. Access networks are currently the European UMTS and North American CDMA2000 systems. These networks are beginning to offer users higher data rates, up to 384 kbit/s. They also include better quality of service support for data, including real-time applications, such as video, and new applications, such as location-based services. 2.6. Ultra-Wideband (UWB) Ultra-wideband is a relatively new technology. The term UWB was introduced by the US Defense Advanced Research Project Agency (DARPA) in the late 1980s. Until recently, its development has been targeted at radar-and location-based applications. This is because the short pulse of the signal transmission results in very high-resolution timing information. However, ultra-wideband can also transmit large amounts of data (10-100 Mbit/s) over a very wide frequency spectrum of a few GHz with a restricted power level over short distance of a few meters. As UWB grows, the systems will eventually be able to transmit data over a very high speed ranging from 400 Mbit/s to 500 Mbit/s. UWB circuits need very little power to achieve these data rates which will be between one tenth and one hundredth of the power required by devices such as mobile telephones and existing wireless LANs for the equivalent data rate 6
3. Technological Advantages and Disadvantages 3.1. Advantages Wireless broadband has distinct advantages over it physical medium dependant counterparts. It is at least 10 to 20 times faster than dial-up connections and can be left on all day, allowing users to use their phone while on the internet. The bandwidth, is measured in bits per second. A dial-up service has around 56,000 bits per second (56Kb). The slowest broadband services have around 512Kb, while one million bits (1Mb) or higher are becoming standard. Another advantage is that wireless can be sent to areas that other networking services can not. Experiments in the United Kingdom are currently looking into providing Wireless Broadband access (WBA) to its rural communities where other broadband technologies are not economical 3.2. Disadvantages A disadvantage is the issue of unobstructed line of sight". This is the key in setting up a wireless Internet feed. That, and a high-powered transmitter to bounce the radio-enabled Internet signal miles away to a receiver, which will in turn, direct it toward businesses and homes. Depending on the technology, leaves, branches, trees, buildings, and topography can block or attenuate signals. In a Point To Point network, a clear line of sight is needed between the hub and the sub. This fact limits the coverage area of a given cell in any urban area. Wireless broadband is also susceptible to what s known as rain fade, as raindrops absorb the waves of the signal. This makes it less suitable in areas with heavy rainfall or snow. The effect of rain fade however, can be diminished through the use of Forward Error correction (FEC) and adaptive power control. 7
4. Wireless How and Where? 4.1. Wireless model All wireless communication systems can be modeled using a few basic blocks as shown in Figure 4.1. Communication starts with an information source that can be audio, video, e-mail, image files, and more. The transmitter converts the information into a signaling format (coding and modulation) and amplifies it to a power level that is needed to achieve successful reception at the receiver. The transmitting antenna converts the transmitter's power to electro-magnetic (EM) waves that propagate in the directions determined by the design and orientation of the antenna. The propagation channel shown in Figure 4.1 is not a physical device but rather represents the attenuation, variations, and any other distortions that affect the EM waves as they propagate from the transmitting antenna to the receiving antenna. Figure 4.1: Block diagram of a basic wireless communications system. There are three core radio technologies in commercial global service today: TDMA, CDMA, and GSM. 4.2. Time Division Multiple Access (TDMA) 8
TDMA is a narrowband digital radio technology. TDMA time division multiplexes a radio signal into 30-KHz slices. Each slice is dedicated to a subscriber on a call. Figure 4.2 is an illustration of the TDMA waveform. Figure 4.2: TDMA Waveform 4.3. Code Division Multiple Access CDMA was standardized in North America by the Telecommunications Industry Association (TIA), and became known as IS-95. Physically, a CDMA carrier system looks like any other wireless system. However, CDMA introduced a concept that requires a Mobile Switching Center (MSC) to monitor and maintain communications between all base stations. CDMA divides the radio spectrum into 1.25-MHz slices taking a signal and multiplexing it across the entire 1.25-MHz slice concurrently with other signals. Whereas TDMA and GSM keep the signal restricted to a specific frame in a sequence of frames, CDMA spreads the signal among multiple frames and at the same time encodes each frame. Figure 4.3 is a representation of a CDMA waveform. 9
Figure 4.3: CDMA Waveform 4.4. Global System for Mobile Communications (GSM) The air interface (radio) and fixed-network specifications known as Global System for Mobile Communications (GSM) are a European suite of standards designed to address the 900-MHz and 1800-MHz needs of the European market. Unlike radio standards developed in North America, GSM standards were developed with an end-to-end perspective. In North America, radio standards and network message sets associated with the fixed or wireline portion of call setup and processing were developed independently of each other. The GSM traffic channel is 200 KHz. GSM enables multiple users to use this 200-KHz channel. GSM time division multiplexes the channel into eight distinct time slots. These slots, like the TDMA system, support both control and traffic channels. Figure 4.4 shows a GSM system. 10
Figure 4.4: GSM System 5. Wireless Costs The frequency range of an LMDS system allows for the design of much smaller antennas with excellent directivity. These focused antennas limit, even eliminate, multipath, because fewer signals are dispersed; equating to less to reflect. This allows more energyefficient modulation techniques such as QPSK (quadraphase phase-shift keying) to be used. The antenna direction also translates to lower power levels that promote frequency reuse. This translates to lower costs. QPSK impacts the affordability of the equipment. It is supported by mass-produced ASIC-based demodulators and effects the most productive frequency reuse plan for deployment. There is, however, a trade-off in the cost in that LMDS systems usually use an ATM or Frame Relay switching technology that provides high performance but makes it more expensive on a subscriber basis. To limit the subscriber equipment costs, lower power levels are used, limiting the effective range of the transmission to about 2.5 miles. LMDS uses many small microcells that are similar to those used for cellular phone communication. The antennas within each cell are fixed within the cell and do not roam 11
from cell to cell in the way a cellular phone does. The use of cells allows for frequency reuse, which is the process in which a frequency can be reused in another cell within the coverage area. This is an important aspect of LMDS, as it allows a more efficient use of the available bandwidth. The spectrum is a limited resource that comes at a steep price for most commercial networks The use of microcells also promotes flexibility in the use of bandwidth, which can be effectively increased by decreasing the size of the cell and multiplied by increasing the number of cells. 6. Future trends and Implementations Southern Railway and T-Mobile will soon unveil details of the world's first train wireless broadband service. The T-Mobile HotSpot service will allow up to 8,000 daily commuters on the London to Brighton route to access the internet. It will be launched in the summer. The city of Philadelphia will become the largest U.S. Internet "hot spot" next year under a plan to offer wireless access at about half the cost charged by commercial operators. The "Wireless Philadelphia" network is expected to be up by late summer 2006 and available to computer users paying up to $20 a month. Commercial Wi-Fi services run about $40 monthly. The network, based on devices attached to city streetlight poles, is expected to cost the city $15 million to set up. The city hopes the plan will get 80 percent of Philadelphia households connected to the Internet within five years, up from the current level of 58 percent. 7. Conclusion Compared to wired alternatives, wireless technologies offer substantially more flexibility in choosing how and where services are deployed and the types of applications that can be supported. The ability to more readily modify, reconfigure and enhance wireless networks compared to wired networks ensures a significant and growing future for fixed broadband wireless communications technology. 12
8. List of References Books: Carty, Glen. Broadband Networking. McGraw-Hill/Osborne 2002 Anderson, Harry R. Fixed Broadband Wireless System Design. John Wiley & Sons (UK) 2003 Smyth, Peter. Mobile and Wireless Communications: Key Technologies and Future Applications. Institution of Electrical Engineers 2004 Internet: BroadBand Wireless: The New Era in Communication. Intel Coorporation 2004 http://wireless.ittoolbox.com/browse.asp?c=wirelesspeerpublishing&r=http%3a%2f %2Fwww%2Eintel%2Ecom%2Fnetcomms%2Fbbw%2F30202601%2Epdf Philadelphia going wireless April 8, 2005 http://money.cnn.com/2005/04/08/technology/philadelphia.reut/ Broadband Revolution speeds up April 11, 2005 The Daily Telegraph. Source: Financial Times Information Limited - Europe Intelligence Wire. http://www.wirelessweek.com/article/nee0411893.7iw?verticalid=110&vertical=wi reless+internet ElectronicsWeekly.com, Melanie Renolds, 04/06/05 13