Cordect

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Cordect

  1. 1. corDECTWireless Access System December 2000
  2. 2. Copyright (C) 2000 Midas Communication Technologies Private LimitedNo. 15, First Avenue, Shastri Nagar, Adyar, Chennai, India 600020http://www.midascomm.comNo material from this publication may be used in full or in part without the prior written permission ofthe copyright holder.
  3. 3. Table of ContentsChapter 1 IntroductionChapter 2 Wireless Access Network: Some Key Issues2.1 Introduction .......................................................................................................................................................... 2 - 12.2 Access Network ................................................................................................................................................... 2 - 12.3 The Internet Tangle ............................................................................................................................................. 2 - 22.4 Wireless Local Loop Vs. Mobile Wireless Access System ...................................................................................... 2 - 42.5 Capacity and Spectral Efficiency ........................................................................................................................... 2 - 42.6 Summary ............................................................................................................................................................. 2 - 6Chapter 3 corDECT Wireless Access System3.1 Introduction .......................................................................................................................................................... 3 - 13.2 Conceptual Access System .................................................................................................................................. 3 - 13.3 corDECT Wireless Access System ....................................................................................................................... 3 - 23.4 Sub-systems of corDECT Wireless Access System ............................................................................................... 3 - 33.5 corDECT Access Centre Functionality and Interfaces ........................................................................................... 3 - 8Chapter 4 corDECT Deployment Examples4.1 Introduction .......................................................................................................................................................... 4 - 14.2 corDECT Deployment with DIU in Exchange Premises ........................................................................................ 4 - 14.3 DIU Integrated with Access Centre ....................................................................................................................... 4 - 44.4 Rural Deployment ............................................................................................................................................... 4 - 54.5 Franchise Access Provider .................................................................................................................................. 4 - 7Chapter 5 corDECT Features at a Glance5.1 Introduction .......................................................................................................................................................... 5 - 15.2 Voice Quality ........................................................................................................................................................ 5 - 15.3 Data Services ...................................................................................................................................................... 5 - 15.4 Internet Access Speed ......................................................................................................................................... 5 - 15.5 Payphone/PCO ................................................................................................................................................... 5 - 15.6 System Capacity ................................................................................................................................................. 5 - 15.7 Air Interface Transmit Power ................................................................................................................................ 5 - 15.8 Typical CBS Coverage ........................................................................................................................................ 5 - 15.9 Typical RBS Coverage ........................................................................................................................................ 5 - 25.10 Authentication and Subscription .......................................................................................................................... 5 - 25.11 Major Subscriber Services ................................................................................................................................. 5 - 25.12 Major Switch Features ....................................................................................................................................... 5 - 35.13 OMC Features .................................................................................................................................................. 5 - 35.14 Maximum CBS-DIU Copper Distance ................................................................................................................ 5 - 45.15 Maximum CBS-BSD Copper Distance ............................................................................................................... 5 - 45.16 DIU Power Supply ............................................................................................................................................ 5 - 45.17 Wallset and Multiwallset Power Supply ............................................................................................................... 5 - 45.18 Wallset and Multiwallset Talk Time/Standby Time ................................................................................................ 5 - 45.19 RBS Power Supply ........................................................................................................................................... 5 - 45.20 BSD Power Supply ........................................................................................................................................... 5 - 45.21 Other Features .................................................................................................................................................. 5 - 5
  4. 4. Chapter 6 System Dimensioning in corDECT6.1 Introduction .......................................................................................................................................................... 6 - 16.2 System Capacity .................................................................................................................................................. 6 - 16.3 Traffic Capacity of CBS ........................................................................................................................................ 6 - 16.4 Traffic Capacity of the DIU ................................................................................................................................... 6 - 26.5 Traffic Dimensioning from RAS to Internet ............................................................................................................. 6 - 36.6 Re-Use Efficiency in corDECT ............................................................................................................................. 6 - 36.7 Capacity of Multi-Cellular Tower-Mounted CBS Cluster ........................................................................................ 6 - 36.8 How High Capacity is Achieved ........................................................................................................................... 6 - 46.9 Capacity in High-Rise Metropolitan Deployment ................................................................................................... 6 - 56.10 Capacity of RBS ................................................................................................................................................ 6 - 66.11 Summary ........................................................................................................................................................... 6 - 6Chapter 7 Air Interface Link Budgets and Cell Planning7.1 Introduction .......................................................................................................................................................... 7 - 17.2 corDECT Enhancements ..................................................................................................................................... 7 - 17.3 Link Budgets with corDECT ................................................................................................................................. 7 - 37.4 Path Loss Models ................................................................................................................................................ 7 - 37.5 Fade Margins in corDECT .................................................................................................................................. 7 - 37.6 Cable Losses ...................................................................................................................................................... 7 - 47.7 Link Analysis for corDECT ................................................................................................................................... 7 - 47.8 Installation and Survey Tools ............................................................................................................................... 7 - 77.9 Summary ............................................................................................................................................................. 7 - 7Chapter 8 Operation and Maintenance8.1 Introduction .......................................................................................................................................................... 8 - 18.2 corDECT OMC in Switch Mode ........................................................................................................................... 8 - 18.3 corDECT OMC in RLU Mode .............................................................................................................................. 8 - 38.4 RAS Management ............................................................................................................................................... 8 - 48.5 corView User Interface ........................................................................................................................................ 8 - 48.6 NMS for Multiple DIUs ......................................................................................................................................... 8 - 58.7 Data Management ............................................................................................................................................... 8 - 7Chapter 9 Future Roadmap9.1 Introduction .......................................................................................................................................................... 9 - 19.2 Towards Always-on Internet Access .................................................................................................................... 9 - 19.3 Packet-Switched High Speed Internet Downloading ............................................................................................. 9 - 19.4 More Integration for Cost-Effectiveness ................................................................................................................. 9 - 29.5 New Multiwallset Developments ........................................................................................................................... 9 - 29.6 Increased Scalability ............................................................................................................................................ 9 - 29.7 VoIP in corDECT ................................................................................................................................................. 9 - 29.8 New Air Interface ................................................................................................................................................. 9 - 29.9 Installation Planning ............................................................................................................................................. 9 - 29.10 Summary ........................................................................................................................................................... 9 - 3Appendix Digital Enhanced Cordless TelecommunicationsA.1 DECT: Some Salient Features ............................................................................................................................ A - 1A.2 Dynamic Channel Selection ................................................................................................................................ A - 3A.3 corDECT Physical Layer Specifications .............................................................................................................. A - 5Abbreviations
  5. 5. corDECTChapter 1 IntroductioncorDECT is an advanced, field proven, Wireless Chapter 3 contains a brief description of theAccess System developed by Midas various corDECT sub-systems that make itCommunication Technologies and the Indian scalable and modular. Next, Chapter 4 describesInstitute of Technology, Madras, in association the several ways in which corDECT can bewith Analog Devices Inc., USA. deployed to cater to a wide variety of subscriber densities and teletraffic levels, to suit bothcorDECT provides a complete wireless access incumbent and greenfield operators.solution for new and expanding tele-communication networks with seamless Chapter 5 presents at a glance the key featuresintegration of both voice and Internet services. It and services provided by the corDECT system.is the only cost-effective Wireless Local Loop The topic of Chapter 6 is the dimensioning of the(WLL) system in the world today that provides corDECT system to cater to the required voicesimultaneous toll-quality voice and 35 or 70 kbps and Internet traffic levels. Chapter 7 highlightsInternet access to wireless subscribers. the coverage achieved by different configurations.corDECT is based on the DECT standard A system with active elements at each subscriberspecification from the European Tele- location, apart from several Base Station sites,communication Standards Institute (ETSI). In requires a sophisticated and user-friendly Networkaddition, it incorporates new concepts and Management System (NMS) for monitoring andinnovative designs brought about by the maintenance. Chapter 8 discusses the NMScollaboration of a leading R & D company, a available for corDECT. Chapter 9 gives a glimpserenowned university, and a global semiconductor of the future, as corDECT evolves to a full-fledgedmanufacturer. This alliance has resulted in many 3G+ system with advanced features such as fastbreakthrough concepts including that of an download from the Internet.Access Network that segregates voice and Finally, there is an Appendix that gives a briefInternet traffic and delivers each, in the most overview of the DECT standard. The main aspectsefficient manner, to the telephone network and of DECT are dealt with here, in particular MC-the Internet respectively, without the one choking TDMA medium-access and Dynamic Channelthe other. Chapter 2 discusses this. Selection. A short list of key DECT physical parameters is also included.corDECT Wireless Access System 1-1 5
  6. 6. corDECT This page has been intentionally left blank 6 corDECT Wireless Access System
  7. 7. corDECTChapter 2 Wireless Access Network: Some Key Issues2.1 Introduction shown in Figure 2.1, the AN now consists of an optical fibre from an exchange to a Remote LineTill around the mid-eighties, a local loop or an Unit (RLU) and typically a 3 - 4 km copper loopAccess Network (AN) used to consist of a pair from the RLU to the subscriber premises. Theof copper wires connecting the subscriber at signals carried on the fibre are time-multiplexedhome or office to the nearest exchange. The local digital voice and signaling information. A RLUloop length in urban areas would be typically as typically serves 1000 to 4000 subscribers andlong as 6 to 8 km and the diameter of the copper the links from RLU to exchange consist ofused was 0.5 mm to 0.6 mm. The loop was 4 - 16 E1’s. Since the loop length is reduced todesigned to carry 0 - 4 kHz voice and was difficult 3 - 4 km, a wire gauge of 0.4 mm is sufficient andto maintain, with almost 85% of all faults found this brings down the cost considerably. The risingin the local loop. Above all it was expensive, as cost of copper, however, continues to push upwell as difficult and time-consuming, to deploy. the cost of even this solution every year. Today,With copper and digging costs increasing every the per-line copper cost (3 - 4 km long, includingyear, if one were to continue with such an laying charges) and the shared cost of fibre andapproach, the per-line local loop cost itself would RLU, again amounts to almost two-thirds of thetoday amount to over 80% of the total cost of total per-line cost.putting up a telecom network. The signaling protocol on the AN (in the signaling2.2 Access Network slots on the E1 links between the RLU’s and exchange) initially remained proprietary. However,Fortunately, an uncelebrated but major access signaling was standardized internationallytechnological innovation changed the Access in the early nineties, in the form of the V5.1 andNetwork from the mid-eighties onwards. As V5.2 protocols. The V5.2 interface makes the Figure 2.1 Access Network in the 90’scorDECT Wireless Access System 2-1 7
  8. 8. corDECTAN appear as an RLU to any exchange, Even as the issue involving interface to theovercoming the earlier restriction of having a telecom network was resolved, another importantproprietary RLU for each exchange. issue cropped up about three years ago. Today a telecom network can no longer just focus onTelephone traffic is concentrated at the AN- providing telephone service at homes and offices,exchange interface and one channel is not but must provide Internet service too. We nowrequired for every subscriber line. The examine some of the factors involved in providingdimensioning of the links from the AN to the Internet connections using the existing telephoneexchange is determined by an estimate of the network.traffic. For example, 1000 subscribers with anestimated traffic of 0.1 E per subscriber requireno more than four E1 links (120 channels) to the 2.3 The Internet Tangleexchange at 0.5% GOS (Grade of Service). This The Internet has emerged as second only to thenot only implies savings in bandwidth, but also telephone in connecting people and mayimplies that only four E1 interfaces are required tomorrow subsume the telephone network. Butat the exchange (as compared to the 1000 two- today, Internet access at homes and officeswire interfaces that would have been required if largely rides on the telephone network. Internetall 1000 lines were brought to the exchange), thus access appears to be simple: just get a telephonereducing the cost. line, connect a modem and computer and dial an Internet Service Provider (ISP). The ISP has aThe open V5.2 interface permits the AN to be bunch of telephone lines and an equal number ofprocured and deployed independently of the modems connecting the users to a router asexchange vendor. The AN can use innovative shown in Figure 2.2. This router is connected totechnologies on media like fibre, wireless, Digital other routers on the Internet. A dial-up connectionSubscriber Line (DSL) on copper, hybrid fibre- to an ISP’s router gives a user access to everyonecoaxial cable, or even power-lines. As the AN and everything on the Internet.dominates the cost, is the most fault-prone, andis the most time consuming to deploy, availability This straightforward-looking approach toof new access solutions is becoming the key to accessing the Internet, is however, beset withcost-effective expansion of the telecom network. problems. The telephone network is typicallyWireless AN’s, just like any other access network designed to handle 0.1 E traffic per subscriberof today, must connect to an exchange using on the average. This is generally adequate forthe V5.2 access protocol. voice telephony. However, Internet sessions are Figure 2.2 Internet access using the telephone network2 -8 2 corDECT Wireless Access System
  9. 9. corDECTusually of longer duration, often even exceeding of computer-to-computer communications is thatan hour. As a significant percentage of telephone the connection is not in continuous use, but inusers start accessing the Internet, the load on bursts. Packets are transmitted to and from thethe telecom network will far exceed 0.1 E per Internet in bursts, with the link remainingsubscriber, resulting in severe congestion and practically idle most of the time. A circuit-switchedeventual network collapse. If this has not connection on a telephone network, however, ishappened yet, it is because only a small unable to take advantage of this and dedicatespercentage of telephone users are also accessing network resources throughout the duration of thethe Internet. connection thereby congesting the network.The second problem is associated with the local An ideal solution to this problem is to have packet-call charges for accessing the Internet in this switched access. However, the local loop is oftenmanner. In many countries the telephone call a separate physical line to each subscriber andmade for accessing the Internet is usually packet access on this dedicated line gives littlecharged based on the call duration. In addition, a advantage, as no one else can use this resourcesubscriber may also have to pay the ISP for anyway. In such a situation, it is advisable toconnection to the Internet. separate the Internet data at the network node nearest to the subscriber, where data fromThirdly, the analog modem-to-modem link multiple subscribers can be multiplexed. This isbetween the subscriber and the ISP is often shown in Figure 2.3, where separation of Internetunreliable. One does not always get connected data and voice traffic takes place at the Accessat 33.6 kbps and the speed can go down to Centre (AC), located typically at a street-corner.9.6 kbps and even 4.8 kbps at times, especiallyin rural areas. Further, the connection often drops. As shown in the figure, both wired and wirelessFinally, an ISP with N telephone lines, N modems interfaces to the AC are possible. DSLand a N-port router could serve at most N technology and narrowband ISDN equipment cansubscribers at a time. If the connection drops, provide reliable, high-speed, simultaneous, voiceone may not get an immediate reconnection and Internet access on a single copper pair. Ifduring busy hours. wired access is used, there is strictly no restriction on the bitrate between the subscriberThis Internet tangle requires a new approach in and the AC, as long as the physical medium canorder to support future growth. Though an Internet support it.connection is kept on for long hours, a peculiarity Figure 2.3 Access Centre (AC) separates voice and Internet data; SU1 and SU2 provide simultaneous voice and Internet services to subscribers using wired and wireless connectivity respectivelycorDECT Wireless Access System 2-3 9
  10. 10. corDECTHowever, wireless access makes use of an will normally be email and web browsing withimportant shared resource, namely, the frequency small displays. The data rate needed is muchspectrum. It is this resource which limits the less than for accessing the Internet from a desktopcapacity of a wireless system. Thus, access PC. Finally, the traffic per subscriber will not bestrategies which assign a channel to a subscriber high: typically, it will be only 0.02 E traffic peronly when he/she wishes to transmit a packet subscriber. Additional air-time charges for suchwould significantly enhance capacity for Internet value-added services are generally acceptable toaccess. Wireless access networks which can users.share the frequency spectrum and utilize itefficiently during packet bursts are obviously very 2.4.2 Wireless Local Loop Systemattractive candidates for rapid expansion of A Wireless Local Loop (WLL) system, on theInternet access in the future. other hand, is meant to serve subscribers at homes or offices. The telephone provided must2.4 Wireless Local Loop Vs. be at least as good as a wired phone. Voice Mobile Wireless Access System quality must be good — a subscriber carrying onToday, there is little doubt that wireless access a long conversation must feel comfortable. Onesystems should provide digital and not analog must be able to use speakerphones, cordlessaccess. Wireless connectivity to subscribers phones and parallel phones. The telephone musttoday is provided by mobile communication support fax and modem communications andsystems as well as wireless local loop systems. should be usable as a Public Call Office (PCO). The ability to support at least medium-speedThese two appear to be similar and are often (about 64 kbps) Internet access is a must.confused with each other. However, the Further, the traffic supported should berequirements for the two systems are significantly reasonably high — at least 0.1 E per subscriber.different. Besides, the ability to support a large number of subscribers in an urban area (high teledensity)2.4.1 Mobile Telephone System with a limited frequency spectrum is required.Mobile telephone systems, often called “cellular” Finally, for the system to be viable, the cost ofsystems, are meant to provide telephony for providing this wireless access should be less thanpeople on the move. The handset is primarily that of a wired telephone connection. Air-timemeant to keep the subscriber connected while charges are totally unacceptable.he/she is away from the home or office. The key Therefore, even though mobile communicationhere is total coverage of the city/state/country. systems and WLL systems appear to be similarThe mobile telephone must be reachable wherever and are sometimes even referred tothe subscriber is — in the car, on the street, or in interchangeably, the requirements in the twoa shopping mall. Other requirements are applications are quite distinct.secondary. Modest voice quality is acceptableas the user may often be speaking from a location 2.5 Capacity and Spectralwith high ambient noise, such as a street or a Efficiencycar. Data communication is not very important.Fax communication is highly unlikely to be used. Having looked at the PSTN-AN interface and the requirements that a WLL system has to fulfill, letInternet access will be provided on the next- us now take up the most important issue thatgeneration systems. The important applications governs the choice of a WLL technology. One2 - 10 4 corDECT Wireless Access System
  11. 11. corDECThas to recognize that the frequency spectrum to be carried out on air between the subscriberavailable will always be limited. Since a telephone equipment and the Base Station. Signaling is anor an Internet connection is not used overhead that takes away part of the frequencycontinuously, channels must obviously be resources but plays an important role in improvingassigned to a subscriber on demand. But this is the overall efficiency of spectrum usage.not enough. The key focus has to be efficient iii. Modulation Efficiencyuse and spatial re-use of the spectrum. The modulation technique employed has a directWhat governs the re-use of spectrum? The use bearing on the efficient use of spectrum. Highlyand re-use of spectrum is governed by multiple spectrum-efficient techniques have beenfactors including: developed over the years. For example, 16-QAMi. channel pay load (bitrate) is more spectrally efficient than 8-QAM, whichii. signaling overhead in itself is more efficient than QPSK and MSKiii. modulation efficiency modulation techniques. But more efficient techniques are usually expensive to implementiv. cell radius (range) and may sometimes require larger powerv. multiple access method margins. For a WLL system, cost is an importantvi. interference reduction techniques consideration and the power margin available is usually not large. QPSK, MSK or even BFSKvii. spatial diversity and space-time processing techniques are often used, even though theiri. Channel Pay Load spectral efficiency is modest.It is obvious that a higher payload will require iv. Cell Radiusmore frequency resources. Therefore, for voice Cell radius is perhaps the most important factorcommunication on wireless systems, it may be governing spectrum utilization in a wirelessdesirable to have efficient voice compression and system. Let there be N independent channelslower bitrate voice codecs. The resulting reduction available for use in a cell of radius r. It is the re-in quality, however small, is quite acceptable for use efficiency which determines the re-use ofmobile communications. But for telephones at channels in neighboring cells. Leaving this issuehomes and offices, toll-quality voice aside for the moment, let us concentrate on thecommunications at 32 kbps/64 kbps (ADPCM/PCM) is desirable. Besides, PCM and ADPCM N channels available within a cell. Let us also assume that the traffic per subscriber is eare transparent to other communication services Erlangs. The number of subscribers that can belike fax. For Internet access, high bitrate served in the cell works out to N/e and thecommunication is obviously desirable. As the Subscriber Density (SD) that can be served infrequency resource used per channel is directly this cell is approximately,*proportional to the payload, high bitrate Internetaccess implies use of more frequency resources.ii. Signaling Overhead Thus, subscriber density is inversely proportional to the square of the cell radius. The implicationAs signaling is the key to the setting up, of this can be seen by an example. If N = 200monitoring, and tearing down of a call, it needs * For a large number of servers N, from the Erlang-B formula, at 1% blocking probability, the offered load can be nearly N Erlangs.corDECT Wireless Access System 2-5 11
  12. 12. corDECTand e = 0.1 E, the capacity (subscriber density) re-use factor varies from 0.25 to 0.5 per sector.varies with cell radius as follows: vi. Interference Reduction Techniques r (km) SD (per sq. km) The re-use distance is primarily determined by 25 1 the minimum Signal to Interference Ratio (SIR) 10 6 requirement. The target SIR is based on the 3 70 minimum sensitivity required at the receiver input 1 640 in order to obtain a particular Bit Error Rate (BER). 0.5 2550 The required BER is typically 10-3 for voice applications (and 10 -6 or lower for dataTherefore, cell radius plays the dominant role in applications, obtained by using error controldetermining the subscriber density given a certain coding and/or ARQ). Depending on the choice ofamount of frequency spectrum. In other words, a multiple access technique, the modulationsmaller cell radius (microcell) is the key to scheme, and the particular application (mobileefficient use of spectrum and one may have to or fixed wireless), the target SIR will differ.have cells as small as 500 m in radius, if a highsubscriber density is desired. Interference reduction techniques are widely used in wireless systems to increase re-use efficiencyv. Multiple Access Technique while retaining the target SIR requirement.A key parameter determining the efficient re-useof spectrum is the multiple-access technique 2.6 Summaryused. The access technique defines how A Wireless Access System today must providefrequency spectrum is divided into channels and simultaneous voice and medium-rate (at least)affects re-use. FDMA, TDMA, CDMA, and MC- Internet connectivity at homes and offices. ToTDMA are different multi-access techniques serve dense urban areas, the system shouldwhich affect the re-use factor (extent to which support a microcellular architecture, whereas forthe spectrum can be re-used in every cell). Re- rural areas, larger range is desirable. At theuse further depends on the number of sectors Access Unit, the voice and Internet traffic fromused in a cell and also on whether Fixed Channel subscribers should be separated and delivered to the telephone and Internet networksAllocation (FCA), or Dynamic Channel Selection respectively.(DCS) is used. For CDMA and MC-TDMA, the2 - 12 6 corDECT Wireless Access System
  13. 13. corDECTChapter 3 corDECT Wireless Access System3.1 Introduction street corner, serving a radius of 700 m to 1 km. This small radius in urban areas is important forThe corDECT Wireless Access System (WAS) wireless access, in order to enable efficient re-is designed to provide simultaneous circuit- use of spectrum. When cable is used, the smallswitched voice and medium-rate Internet radius ensures low cost and higher bitrateconnectivity at homes and offices. The Access connectivity. However in rural areas, the distanceSystem model, which the corDECT emulates, is between the AC and the SU could easily beshown in Figure 3.1. 10 km and even go up to 25 km in certain situations.3.2 Conceptual Access System The AC is thus a shared system catering toIn this conceptual model, there is a Subscriber multiple subscribers. The voice and Internet trafficUnit (SU) located at the subscriber premises. to and from subscribers can be concentrated hereThe SU has a standard two-wire interface to and then carried on any appropriate backhaulconnect a telephone, fax machine, PCO (Public transport network to the telephone and InternetCall Office), speakerphone, cordless phone, or networks respectively.modem. It also provides direct (without a modem)Internet connectivity to a standard PC, using At the AC, the telephone and Internet traffic iseither a serial port (RS-232 or USB) or Ethernet. separated. The telephone traffic is carried to theThe Access System allows simultaneous telephone network on E1 links using accesstelephone and Internet connectivity. The SU’s are protocols such as V5.2. The Internet traffic fromconnected to an Access Centre (AC) using any multiple subscribers is statistically multiplexed,convenient technology like wireless, plain old taking advantage of the bursty nature of Internetcopper, DSL on copper, coaxial cable, optical traffic, and carried to the Internet network. Asfibre, or even power lines. use of Voice-over-IP (VoIP) grows, voice traffic from subscriber units could also be sent to theThe AC must be scalable, serving as few as 200 Internet, gradually making connectivity to thesubscribers and as many as 2000 subscribers. telephone network redundant. However, forIn urban areas, the AC could be located at a connecting to the legacy telephone network, the Figure 3.1 Conceptual Access System providing simultaneous voice and Internet connectivity. SU: Subscriber Unit ; AC: Access CentrecorDECT Wireless Access System 3-1 13
  14. 14. corDECT Figure 3.2 corDECT Wireless Local Loopvoice port of the AC may be required for some calls to a built-in Remote Access Switch (RAS)time to come. An AC could also incorporate which then routes the traffic to the Internetswitching and maintenance functions when network. The RAS has an Ethernet interface,required. Further, it is possible to co-locate which is connected to the Internet using anyInternet servers with the AC. suitable routing device. The CBS is normally connected to the DIU using3.3 corDECT Wireless Access three twisted-pair wires, which carry signals as System well as power from the DIU to the CBS.Following the conceptual model, the corDECT Alternatively, it can be connected to the DIUWireless Access System uses a similar through a Base Station Distributor (BSD). Thearchitecture to provide telephone and Internet BSD is a remote unit connected to the DIU usingservice to a subscriber, as shown in Figure 3.2. a standard E1 interface (on radio, fibre, or copper) as shown in Figure 3.3. A BSD can support upThe subscriber premises equipment, Wallset IP to four CBS’s.(WS-IP) or Wallset (WS), has a wirelessconnection through a Compact Base Station For long-range communication, a WS-IP or WS(CBS) to an Access Switch, called a DECT can also be connected to the CBS using a two-Interface Unit (DIU). The air interface is compliant hop DECT wireless link, one between WS-IP orto the DECT standard specified by ETSI. The WS and a Relay Base Station (RBS) and anotherDIU switches the voice traffic to the telephone between the RBS and CBS, as shown in Figurenetwork using the V5.2 protocol to connect to 3.4. The wireless range supported between a WS-an exchange. The DIU also switches the Internet IP or WS and the CBS or RBS is 10 km in Line- Figure 3.3 CBS remoted to DIU through BSD3 - 14 2 corDECT Wireless Access System
  15. 15. corDECT Figure 3.4 WS-IP connected to DIU using a two-hop radio link through a Relay Base Stationof-Sight (LOS) conditions. The range supported subscriber using a RJ-11 interface, enabling onebetween a CBS and RBS is 25 km in LOS to connect a standard DTMF or decadicconditions. telephone, G3 fax machine, PCO (battery reversal and 12/16 kHz metering are standard features),A typical system consists of one DIU with one speakerphone, cordless phone, or modem. Inor two RAS units, up to 20 CBS’s, and up to a addition, the WS-IP has a RS-232 port to directly1000 WS-IP’s or WS’s. The BSD and RBS units connect a PC (obviating the need for a telephoneare used as required by the deployment scenario. modem). The PC establishes a dial-up PPP (Point-to-Point Protocol) Internet connection3.4 Sub-systems of corDECT using a standard dial-up utility. Internet access Wireless Access System is supported at 35 or 70 kbps. In fact, the WS-IPBefore we get into more details at the system can support simultaneous voice and 35 kbpslevel, we take a brief look at each of the sub- Internet connections.systems. Besides these two user interfaces, the WS-IP has an antenna port where either a whip antenna,3.4.1 Wallset IP and Wallset or an externally mounted antenna (throughAs shown in Figure 3.5, the Wallset with Internet cable), can be connected. The power to the WS-Port (WS-IP) provides voice connectivity to the IP is provided by a 12 V adaptor connected to Figure 3.5 WS-IP (Wallset with Internet Port)corDECT Wireless Access System 3-3 15
  16. 16. corDECT Figure 3.6 Multiwallsetthe AC mains and optionally by a solar panel connectivity. Multiple PC’s can be connected towhich can be connected in parallel. The WS-IP the Ethernet port and provide a shared 35/70 kbpshas a built-in battery and battery charger. The Internet connection. The PPP-over-Ethernetbuilt-in battery provides 16 hours stand-by time protocol is used to set up individual connections.and more than 3 hours talk time for voice calls. It is to be noted that at any time, either four simultaneous telephone calls with no InternetA Wallset (WS) is a similar terminal without the connection, or three telephone calls and a 35Internet port. kbps shared Internet connection, or two telephone calls and a shared 70 kbps Internet3.4.2 Multiwallset connection, can be made. Depending on usage,The Multiwallset (MWS), shown in Figure 3.6, this may introduce some blocking for voice calls.provides simultaneous voice service to foursubscribers. It has all the features of the WS, 3.4.4 Compact Base Stationbut at a significantly lower per-line cost. The Compact Base Station (CBS), shown inThe Multiwallset has a DECT Transceiver Module Figure 3.7, provides the radio interface between(DTM), which is an outdoor unit with a built-in the DIU and the corDECT subscriber terminal. Itantenna with 7.5 dB gain. It is connected to an supports up to 12 simultaneous voice calls. It isindoor Subscriber Interface Module (SIM) unit, a small, unobtrusive, weatherproof unit that iswhich has four RJ-11 ports for telephones. Each remotely powered from the DIU or a BSD.port supports all the terminals a WS supports The CBS has two antennas for diversity. A(see section 3.4.1). directional antenna with significant gain can beThe connection between the DTM and the SIM used when coverage is required to be confineduses a single twisted-pair wire, obviating the need to certain directions. For example, if the coveragefor RF cable and connectors. The MWS has a area is divided into sectors, each sector can bebuilt-in battery for backup and is powered through covered by a different Base Station withthe AC mains. directional antennas. For 3600 coverage using a single CBS, omni-directional antennas are used.3.4.3 Multiwallset IP More than one CBS can be deployed to serve a single sector or a cell.The Multiwallset with Internet Port (MWS-IP) isa MWS with four telephones and an additional The maximum LOS range between a subscriberEthernet interface to provide dial-up Internet unit and a CBS is 10 km. An isolated CBS3 - 16 4 corDECT Wireless Access System
  17. 17. corDECT Figure 3.7 Compact Base Stationsupports approximately 5.8 E of traffic with a Remote Line Unit), Base Station Controller, andGrade of Service (GOS) of 1%, typically serving the Operations and Maintenance Console (OMC).30 - 70 subscribers. Multiple CBSs serving the System reliability is guaranteed by a redundant,same sector or cell increase the traffic in Erlangs hot stand-by architecture. The OMC allowshandled by each CBS (see Chapter 6). exhaustive real-time monitoring and management of the entire corDECT system. A fully-configuredThe CBS is connected to a DIU or a Base Station DIU with an in-built Remote Access Switch (RAS)Distributor (BSD) with three twisted-pair copper only occupies a single 28U, 19" cabinet andwires, each of which carry voice/data traffic, consumes less than 600 W.signaling and power. The maximum loop length,with a 0.4 mm diameter wire, can be 4 km Up to 20 CBSs can be supported by a DIU,between the DIU and the CBS and 1 km between directly or through the BSD. The DIU provides upthe BSD and the CBS. to eight E1 links to the telephone network and/or RAS. The signaling protocol used is either V5.2,3.4.5 DECT Interface Unit which parents the DIU (as an RLU) to an exchange, or R2-MF, in which case the DIU actsThe DECT Interface Unit (DIU) shown in Figure as a 1000-line exchange. There is a third option,3.8, implements the functions of a switch (or a Figure 3.8 DECT Interface Unit (DIU) with in-built RAScorDECT Wireless Access System 3-5 17
  18. 18. corDECT Figure 3.9 iKON RASwherein the corDECT system, using additional (with power feed). The E1 interface between aequipment, appears to an exchange simply as a DIU and the BSD can be on copper, fibre, or radionumber of twisted-pair lines (see section 3.5.1.2.). and link distance depends only on the link design.Multiple DIU’s are managed through a centralized The BSD is designed to extend corDECTNetwork Management System (NMS). coverage to pockets of subscribers located far away from the DIU.3.4.6 iKON Remote Access Switch 3.4.8 Relay Base StationThe iKON Remote Access Switch (RAS), shownin Figure 3.9, is a 19" 1U unit normally integrated A Relay Base Station (RBS), as shown in Figurewithin the DIU cabinet. It terminates the PPP 3.11, extends the range of the corDECT systemconnections from Internet subscribers using by relaying DECT packets between the CBS andcorDECT WS-IP or MWS-IP. It is connected to subscriber units. The RBS can handle 11 callsthe DIU using up to two E1 ports and does IP- simultaneously.based routing for up to 60 simultaneous corDECT The RBS consists of two units. The RBS Air UnitInternet calls. The RAS has a 10BaseT Ethernet is typically mounted on a tower/mast and housesport to connect to the Internet. It supports the baseband and the RF sub-system. The RBSRADIUS for accounting and authentication, PAP Ground Unit supplies power and providesfor user authentication and is managed using maintenance support to the Air Unit and isSNMP. mounted at the bottom of the tower.3.4.7 Base Station Distributor The RBS uses three antennas. One antenna (usually a directional antenna with high gain),The Base Station Distributor (BSD) is a compact, referred to as the RBSWS antenna, pointsremotely located, locally powered, rack- towards the CBS with which the RBS ismountable unit that supports up to four CBS’s communicating. The other two antennas, called Figure 3.10 Base Station Distributor3 - 18 6 corDECT Wireless Access System
  19. 19. corDECT Figure 3.11 Relay Base StationRBSBS antennas are used for communication management. Figure 3.12 depicts the corViewwith the subscriber units (two antennas are used GUI for configuring the DIU. Commands rangefor diversity). These antennas are similar to those from a bird’s-eye view of the operational statusused by the CBS. of a network of corDECT systems to probing the internals of an individual Wallset.The maximum LOS range between a CBS and aRBS is 25 km, while the maximum LOS range This easy-to-use, menu-driven console can bebetween the RBS and corDECT subscribers is run either locally or remotely. When used10 km. remotely, a single corView workstation serves as an NMS for a number of corDECT systems.3.4.9 Network Management corView can also be used with the CygNet NMS to provide integrated management of a networkcorDECT provides comprehensive operation and of corDECT and other systems.maintenance through the corView OMC console.Its repertoire includes hardware and software corView supports the SNMP protocol and canconfiguration, subscriber administration, be connected to the corDECT system by any IPaccounting, fault notification, and traffic network. In the future, corView will also support Figure 3.12 corView 200 GUI for configuring the DIUcorDECT Wireless Access System 3-7 19
  20. 20. corDECTTMN/Q3. When used as a switch, detailed billing The numbering and all subscriber facilities arerecords are maintained and can be exported to provided by the exchange and billing too is carriedthe billing centre via several media. out at the exchange. The DIU does some limited subscriber administration, such as authenticating3.5 corDECT Access Centre a subscriber (as per the DECT standard). The Functionality and Interfaces DIU console, however, provides management functions for managing corDECT DIU, CBS, RBS,The corDECT Access Centre, consisting of a DIU BSD, WS, WS-IP, MWS and MWS-IP, and alsoand iKON RAS, is designed to provide interfaces carries out wireless traffic monitoring. Theto the telephone network and to the Internet. management functions can also be carried out centrally for multiple DIU’s, as discussed in3.5.1 The Telephone Connection Chapter 8. The 1000-line DIU in this modeThe telephone connection provided to a corDECT consists of three 6U 19" racks in one cabinet,subscriber is a circuit-switched one. The DIU leaving additional space for up to three RAS units.switches the connection to the telephonenetwork. The interface to the telephone network 3.5.1.2 Transparent Modeis provided in three different ways: In this mode, the DIU is parented to an exchangei. RLU mode, with V5.2 protocol on E1 using two-wire interfaces. Each subscriber line interfaces to a parent exchange, is mapped to an unique two-wire port on the exchange. Hook status and digits dialed at WS/ii. Transparent mode, with two-wire interface to WS-IP/ MWS are mapped by the DIU to reflect a parent exchange and at the corresponding exchange port. All servicesiii. Switch mode, with R2-MF protocol on E1 of the exchange are available to the subscriber. interfaces to the telephone network. Billing is carried out at the exchange. However, as in the RLU mode (section 3.5.1.1), the DIU3.5.1.1 RLU Mode carries out subscriber authentication and system management functions.The DIU has up to six E1’s that can be connectedto a parent exchange using V5.2 signaling. The To provide two-wire interfaces at the DIU, aDIU in this case works as a 1000-line Remote Concentrating Subscriber Multiplexer (CSMUX)Line Unit of the parent exchange, as shown in is used. Each CSMUX, housed in one 6U 19"Figure 3.13. Even calls between two corDECT rack, can provide up to 240 two-wire portssubscribers belonging to the same DIU are (grouped as 2 x 120 two-wire ports). The CSMUXswitched by the parent exchange. is connected to the DIU typically using two E1 Figure 3.13 DIU parented to an exchange in RLU mode3 - 20 8 corDECT Wireless Access System
  21. 21. corDECT Figure 3.14 DIU parented to exchange in transparent modeports, providing 4:1 concentration. Thus, using as well as the DIU is much smaller and the powereight E1’s and four CSMUX units and a DIU required is also less when compared to theintegrated in two cabinets, one can serve up to transparent mode.960 subscribers in transparent mode, as shown A more serious problem in the transparent modein Figure 3.14. A concentration of 4:1 is normally comes from a signaling anomaly that can emergeacceptable since wireless channels are anyway in some specific situations. For example, whenbeing shared. Sharing an E1 port among 120 an incoming call comes to the exchange for asubscribers, one can serve nearly 0.2 Erlang subscriber, the exchange signals ring-back to thetraffic per subscriber at 1% GOS. However, it is calling subscriber if it finds from its database thatpossible to avoid concentration at CSMUX and the called subscriber is free. The exchangeconnect eight E1’s to a single CSMUX rack. In simultaneously feeds ring to the correspondingthis case, one DIU will be limited to serve a two-wire port. This is detected by the CSMUX inmaximum of 240 subscribers. the DIU and the DIU then attempts to page theThe transparent mode is the quickest way to corresponding WS/WS-IP and ring theinterconnect corDECT to an existing telephone subscriber. However as wireless channels arenetwork. However, it is not a preferred mode for shared, it is possible that sometimes the DIUoperation. In order to serve 960 subscribers, 960 finds no free channel and fails to feed ring to thetwo-wire ports are required on the exchange side subscriber. The anomaly develops when theconnected to four CSMUX units. In contrast, only called port gets ring-back tone, but the calledfour to six E1 ports are required at the exchange party does not get a ring. Such a situation canin the RLU mode and the CSMUX is avoided. sometimes become problematic. The transparentThus, in the RLU mode, the size of the exchange mode is therefore not the most desirable mode Figure 3.15 DIU as an independent medium-sized exchangecorDECT Wireless Access System 3-9 21
  22. 22. corDECTof operation. Nevertheless, it is the quickest way links between the CBS and the DIU and betweento integrate a wireless system to the existing the DIU and the RAS. Since the BER on thetelephone network anywhere in the world. wireless link could occasionally be high, the PPP packet is fragmented and transmitted with an3.5.1.3 Switch Mode error detection code on the link from the WS-IP to the DIU. ARQ is performed on this link to obtainThe DIU is designed to be a 1000-line, full-fledged, error-free fragment transmission. The PPPmedium-sized exchange for corDECT wireless packets are re-assembled from these fragmentssubscribers. It interfaces to the telephone network before transmitting it to the PC (on the WS-IPon up to six E1 lines using R2-MF protocol as side) and to the RAS (on the DIU side).shown in Figure 3.15. All the exchange functions,including subscriber administration, billing, and The connection between the WS-IP and the DIUmanagement, are carried out at the DIU itself. To is at 32 kbps or 64 kbps (using one or two DECTserve 1000 subscribers in this configuration, a slots on air). The start/stop bits received at theDIU uses three 6U 19" racks. The advantage of RS-232 port are stripped before transmission onthis mode is that the cost of an exchange is air. This enables 35 kbps Internet throughputtotally saved. between the user PC and the RAS on the 32 kbps connection in an error-free situation.The DIU can also serve as a Direct In-Dialing Similarly, 70 kbps Internet throughput is possible(DID) PBX. between the user PC and the RAS on the 64 kbps connection. Bit errors on the link will3.5.2 Internet Connection temporarily bring down the throughput.A corDECT subscriber connects to the WS-IP Each RAS has two E1 ports for connecting tousing a PPP dial-up connection on the RS-232 the DIU and thus can support Internet connectionport. The port is programmed at 38.4 kbps rate for for up to 60 subscribers at a time. The PPPa 35 kbps Internet connection and at 115.2 kbps connections are terminated at the RAS and IPrate for a 70 kbps Internet connection. The PC packets are routed to the Ethernet port of theconnected to the RS-232 port on WS-IP dials a RAS for onward transmission to the Internet. Thepre-designated number using a standard dial-up Ethernet ports from multiple RAS’s wouldroutine. The DIU sets up a circuit-switched normally be connected to an Ethernet switch.connection between the WS-IP and the iKON The Ethernet switch in turn would be connectedRAS connected to the DIU on an E1 port. to an Internet router, completing the connectionThe Internet connection employs the wireless link to the Internet.between the WS-IP and the CBS and the wired3 - 22 10 corDECT Wireless Access System
  23. 23. corDECTChapter 4 corDECT Deployment Examples4.1 Introduction The tower could be a short 15 m rooftop mast, but in some cases, could be a self-supportingWe saw in Chapter 3 that the corDECT DIU can 25 - 35 m tower on the ground. Multiple CBS’sbe deployed as an access system, parented to could be mounted on this tower using omni-an exchange using either the V5.2 access directional antennas, but more often, usingprotocol, or transparently using two-wire directional antennas providing sectorizedinterfaces. Alternatively, the corDECT DIU itself coverage. A commonly-used sectorization plancan act as a Local Exchange, or even as a direct- provides six-sector coverage as shown in Figurein-dialing PBX. This chapter presents a few 4.2(a) and Figure 4.2(b). Figure 4.2(c) shows adeployment scenarios for the corDECT Wireless close up of a CBS and directional antennas.Access System. One or more CBS’s are mounted with antennas4.2 corDECT Deployment with having a typical gain of 12 dB to provide coverage DIU in Exchange Premises in a 600 sector. However as discussed in Chapter 6, one or two CBS’s with omni directionalIn one of the most widely deployed scenarios, antennas could be additionally mounted on thethe corDECT DIU is placed in the local exchange same tower, enabling these CBS’s to handlepremises, parented to an exchange in a overflow traffic from all sectors. All these CBS’stransparent manner or using the V5.2 protocol, are connected to the co-located DIU usingor as an independent Local Exchange. This twisted-pair cables.scenario will be widely used by an incumbentoperator with existing infrastructure. The These CBS’s provide connectivity to subscribersexchange building (usually one of the taller as far as 10 km away in Line-of-Sight (LOS)buildings in the area) would have a tower to deploy conditions. However depending on the built-upCompact Base Stations as shown in Figure 4.1. environment and in order to re-use the spectrum Figure 4.1 DIU in exchange premises with co-located CBScorDECT Wireless Access System 4-1 23
  24. 24. corDECT (a) (b) (c) Figure 4.2 Six sector coverage by CBSmore often, coverage should normally be limited provide coverage to 30 - 150 subscribers in theto 1 to 1.5 km radius in urban environments (see neighborhood of this remote location. It isChapter 7). Wallsets would typically require an important, however, that the buried cable plantexternal (rooftop or window-mounted) antenna, be in reasonable shape and not fail during rain, ifbut in some cases, within a 400 m radius, an this option is to be used.internally-mounted antenna could also be used. A more appropriate way of connecting a multi- CBS cluster remotely is to use the Base Station4.2.1 Remote Location of CBS Distributor (BSD). A BSD is connected to theAt times, it may be desirable to cover a distant DIU by a standard E1 link, using an optical fibre,locality using the same DIU. It is possible to point-to-point microwave radio, or even copperconnect a CBS remotely from the DIU using three (for example, using HDSL). The BSD with a smallpairs of twisted-pair wires, which carry the voice, 48 V power supply unit could then be placed in asignaling, as well as power, to the CBS. The CBS remote building (say, under a staircase landing)could be as far as 4 km away, when 0.4 mm where an optical fibre connection or a cable linkdiameter copper wire is used. If the buried cable with HDSL, is available. Up to four CBS’s canplant in an area is serviceable, it is easy to take now be connected to the BSD and mounted on athree/six/nine pairs of these wires and mount one/ pole or small tower on the building as shown intwo/three CBS’s remotely, a few kilometers from Figure 4.4. These CBS’s could provide coveragethe DIU, as shown in Figure 4.3. to almost 200 subscribers in the vicinity.The CBS’s could then be mounted on a tall Alternatively, the tower could also support thebuilding using a 3 - 6 m pole on the roof and antenna for a digital microwave point-to-point E1 Figure 4.3 Remote CBS connected using copper twisted-pair wire4 - 24 2 corDECT Wireless Access System
  25. 25. corDECT Figure 4.4 Remote CBS deployment using BSDlink from the exchange and the BSD could be an Intel 9300 or a CISCO 2610) could beconnected to it. Again, up to four CBS’s could connected to the LAN as shown in Figure 4.5.be mounted on this tower and provide service in The Internet router is connected to the Internetits neighborhood. using any convenient leased connection. The router could also carry Internet traffic from otherIt is to be noted that remoting of Base Stations access systems.enables better frequency re-use. The CBS’smounted at the exchange tower and the CBS’s Alternatively, the traffic between the Internet andmounted remotely can often use the same DECT RAS could be carried on n x 64 kbps switchedchannels simultaneously. (or leased) circuits. This option can be used only if the DIU is connected to the telephone network4.2.2 Internet Connection on E1 lines (using V5.2, or as an independent LE). The circuits are established between theAn iKON RAS, integrated with the DIU, DIU and a remote router using the telephoneterminates the PPP connections for all Internet network. The RAS traffic (IP packets) could thensubscribers at WS-IP (see section 3.5.2, Chapter be routed on such a connection through the DIU,3). The IP packets are then routed to the Internet as shown in Figure 4.6. Since the RAS isby the RAS. The RAS could be connected to the connected to the DIU on E1 lines, a few 64 kbpsInternet in two different ways. The RAS could be slots could be used for this. The maximumconnected to a Local Area Network (LAN), or to number of subscriber connections that a RASa switched LAN, on its 10BaseT Ethernet (with two E1’s) could then support would be lessInterface. A small Internet router (for example, than 60. Figure 4.5 Internet connection using a local router at the exchangecorDECT Wireless Access System 4-3 25
  26. 26. corDECT Figure 4.6 n x 64 kbps Internet connection between RAS and remote routerIn certain situations, it is possible to locate the 4.3 DIU Integrated with AccessRAS remotely, using E1 links to the DIU. This is Centreuseful if an operator wishes to install all Internet-related equipment at one place and optical fibre In an alternative deployment scenario, an Accessis available between different exchanges and the Centre (AC) is deployed to provide the last-mileISP location. While the DIU’s could be located connectivity to the subscriber. The AC is deployedat different exchanges, all the RAS’s connected away from the exchange and near theto various DIU’s could be at one place along with subscribers.the routers, servers, and other equipment used The DIU along with the RAS acts as an AC,by the Internet Service Provider. providing wireless telephone and Internet servicesThe advantage accruing from the RAS statistically to the subscribers. It could also be integratedmultiplexing bursty traffic from different with other similar access equipment using DSLsubscribers is not availed here. This may not on copper, cable modem, or even plain old analogpose a constraint as fibre typically provides telephony on copper to provide service tosufficient bandwidth between exchanges at subscribers in the vicinity. In a typical deployment,marginal cost. Figure 4.7 shows this scenario. the DIU and RAS would be placed at a street Figure 4.7 Co-location of RAS’s4 - 26 4 corDECT Wireless Access System
  27. 27. corDECT Figure 4.8(a) Fibre backhaul carrying voice and Internet trafficcorner to serve urban subscribers in a 1 to 2 km of the corDECT Wireless Access System. It canradius, or placed in the centre of a small town to cost-effectively provide this service to areas whereserve subscribers in a 10 km radius. subscriber density is as low as 0.2 subscribers per sq. km. For a subscriber density lower thanThe voice and Internet traffic are separated at this, corDECT may not be the most cost-effectivethe DIU and the voice traffic is carried on E1 lines system.to an exchange using the V5.2 access protocol(the DIU acting as a RLU). The Internet traffic is Line-of-Sight (LOS) between a subscriber antennastatistically multiplexed at RAS and carried on and Base Station/Relay Base Station isE1 lines to the Internet network. Both these necessary for the corDECT system to provideconnections are provided using a backhaul service to subscribers in sparse (low subscribernetwork built using optical fibre or point-to-point density) areas. It is therefore necessary to choosemicrowave links, as shown in Figures 4.8(a) and sites for CBS and RBS towers carefully, so that4.8(b) respectively. subscribers in a 10 km radius can be provided service. Similarly, antennas have to be mountedIt is possible for the Access Centre to extend its at subscriber premises using poles, so that LOSreach by remoting some Base Stations using to CBS/RBS is available. The availability of lighteither twisted-pair wires or using the BSD, just and compact antennas for the Wallset makesas described in section 4.2.1. This approach, this task somewhat easier.while increasing the subscriber reach of the AC,also enables better re-use of frequency spectrum Further, subscribers in rural areas may not haveby creating more CBS sites. reliable power and solar panels may have to be used. A compact solar panel can be connected4.4 Rural Deployment to the WS or WS-IP to power the unit and charge the built-in battery, with solar power taking overProviding telecom and Internet service to when the mains is off/low.subscribers in rural areas is a major application Figure 4.8(b) Microwave digital radio backhaul carrying voice and Internet trafficcorDECT Wireless Access System 4-5 27
  28. 28. corDECT Figure 4.9 Deployment for a subscriber density greater than 1 subscriber per sq. kmA DIU along with a RAS could be located either If such E1 links are not available, a cost-effectivein a rural exchange building or a RLU building, rural deployment would use Relay Baseadjacent to a tower (typically 15 m to 35 m high). Stations. The RBS could be mounted on a towerCBS’s mounted on the tower can directly serve up to 25 km away from the CBS tower, providingrural subscribers in a 10 km radius (or 300 sq. km a LOS link between the RBS and the CBS. Toarea), as shown in Figure 4.9. This deployment overcome the problem of larger propagation delayscenario is adequate for a subscriber density from the RBS to the CBS, the RBS transmissionhigher than 1 subscriber per sq. km. is appropriately advanced as discussed in section 7.2.2 of Chapter 7.To serve a pocket of subscribers in a remote area,a BSD could be used. The BSD could then Each RBS serves subscribers in a 10 km radius,connect to up to four CBS’s on a remote tower as shown in Figure 4.11. The RBS has 11and serve subscribers in a 10 km radius around channels and can be used to establish 11it, as shown in Figure 4.10. The BSD requires simultaneous calls. The two-hop radio linkpower back-up at the remote location. This provides the same voice and Internet services todeployment could be cost-effective for a the subscribers as a single-hop link. To thesubscriber density as low as 0.2 subscribers per subscriber, the connection through the RBS issq. km, provided a digital microwave or fibre link transparent. The RBS does require a powerto the BSD is available. supply with appropriate back-up, which is provided Figure 4.10 Rural deployment using BSD4 - 28 6 corDECT Wireless Access System
  29. 29. corDECT Figure 4.11 RBS serving remote subscribers in a 10 km radiusby a mains supply or a solar panel. The RBS rural subscribers in an area with a very lowcan effectively cater to a subscriber density as subscriber density.low as 0.2 subscribers per sq. km.Use of the RBS therefore enables a corDECT 4.5 Franchise Access Providersystem to provide service in a 25 km radius. With As the Access Network is the most difficult partthe DIU (along with the RAS) deployed at the of the telecom network to deploy, and the mostcentre of a circle, the CBSs would be typically expensive and difficult part to maintain, it maydeployed in six sectors. While subscribers in a make sense for an operator to use Franchise10 km radius would be served directly by these Access Providers (FAP’s) to install and maintainCBS’s, an RBS tower deployed in each of the the last-mile access network. A FAP wouldsurrounding cells, as shown in Figure 4.12, would provide service in a locality and would connectenable 25 km coverage. One or more RBS’s to the operator’s backbone network.could be deployed in each cell, depending on The corDECT system could provide an idealthe number of subscribers that need to be served solution for such FAP’s. The DIU acts as an in-in the cell. dialing PBX, with billing and subscriberThus, we see that by properly engineering the management available at the DIU itself. The DIUdeployment, it is possible to cost-effectively would be given a level in the numbering plan forprovide telephone as well as Internet service to switching incoming calls to it. The connection to Figure 4.12 Sectorized RBS deploymentcorDECT Wireless Access System 4-7 29
  30. 30. corDECTthe Local Exchange (of the FAP) would be an E1 to the RAS. The statistically-multiplexed IP traffictrunk with R2-MF signaling for incoming calls. at the RAS is then output to an Internet routerAll the incoming calls meant for the DIU would through the Ethernet interface at the RAS andbe switched by the LE on this trunk interface. one of several possible ways of establishing aThe DIU would then complete the switching to leased connection from the Ethernet port to thethe subscriber. For outgoing calls, either the trunk Internet router could be used.lines with R2-MF signaling, or subscriber lines A FAP could also connect Internet servers at the(using CSMUX), could be used. Ethernet interface (co-located with the RAS andIn all other ways, this deployment scenario DIU) and provide services such as mail server,appears similar to that of an Access Centre. The web-server, etc. It is also possible to co-locate aCBS’s would typically be co-located with the DIU; RADIUS server, used for Internet billing andyet some CBS’s could be remotely mounted accounting, at this place. An integrated billingusing either twisted-pair wires or a BSD. The software for voice calls and Internet service isInternet traffic is separated at the DIU and is sent available (see Chapter 8).4 - 30 8 corDECT Wireless Access System
  31. 31. corDECTChapter 5 corDECT Features at a Glance5.1 Introduction but with a double slot connection V.34 and V.90 modems can operate at full speed.The corDECT WLL system provides features andservices comparable to the best wireline 5.4 Internet Access Speedsystems. In the Switch (Local Exchange) Mode,it boasts of all the features of a large digital Internet Access is possible simultaneously withexchange. The Wallset IP provides simultaneous a voice call using the Wallset IP. There are twovoice and Internet access (like an ISDN line) as access rates: 35 kbps and 70 kbps, using onea basic feature that all subscribers can have. and two time slots respectively.Base Stations can be deployed in a multitude ofways, some suited to an incumbent operator, 5.5 Payphone/PCOsome to a greenfield operator, and others that The system supports payphone with batteryenable coverage of sparsely populated rural reversal as well as 12 kHz/16 kHz meteringareas. The system also has sophisticated pulses. The pulses are provided by the WallsetOperations and Maintenance support and a for an external charge meter. The system alsoNetwork Management System for managing a supports a CCB payphone (battery reversal only).corDECT network. The next few sectionsdescribe some key features of the corDECTsystem. 5.6 System Capacity Each corDECT system supports up to 10005.2 Voice Quality subscribers. Its Base Stations can evacuate more than 150 E of traffic and funnel it to the telephonecorDECT delivers the same toll-quality speech network and Internet using up to eight E1 links.performance as a good copper-based local loop.Toll-quality voice is ensured by using 32 kbpsADPCM for voice digitization as per the ITU-T 5.7 Air Interface Transmit PowerG.726 standard. ADPCM also ensures The power transmitted by a Wallset or Basetransparency to DTMF signals for Interactive Station nominally is 250 mW during the burst, orVoice Response Systems. about 10 mW on the average. This ties in with the need for small cells to enhance frequency5.3 Data Services re-use and also conserves battery power.The employment of 32 kbps ADPCM permits allvoice-band data services available from a 5.8 Typical CBS Coverageconventional wired connection. It is also possible The coverage achieved by corDECT is 10 km into occupy a double time slot on air to transmit at Line-of-Sight (LOS) conditions, made possible64 kbps with error correction. This can be used by enhanced receiver sensitivity, a patentedfor data connectivity at speeds similar to the best timing adjustment feature and compact high gainwireline speed. The speed of a modem/G3 fax antennas. The non-LOS (NLOS) coverage variessupported using 32 kbps ADPCM is 9600 bps,corDECT Wireless Access System 5-1 31

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