20-09-2009, 04:18 PM
CORDECT Wireless Access System
Abstract
corDECT is an advanced, field proven, Wireless Access System developed by Midas Communication Technologies and The Indian Institute of Technology, Madras, in association with Analog Devices Inc., USA. corDECT provides a complete wireless access solution for new and expanding telecommunication networks with seamless integration of both voice and Internet services. It is the only cost-effective Wireless Local Loop (WLL) system in the world today that provides simultaneous tollquality voice and 35 or 70 kbps Internet access to wireless subscribers corDECT is based on the DECT standard specification from the European Tele communication Standards Institute (ETSI). In addition, it incorporates new concepts and innovative designs brought about by the collaboration of a leading R & D company, a renowned university, and a global semiconductor manufacturer. This alliance has resulted in many breakthrough concepts including that of an Access Network that segregates voice and Internet traffic and delivers each, in the most efficient manner, to the telephone network and the Internet respectively, without the one choking the other.
Conceptual Access System
In this conceptual model, there is a Subscriber Unit (SU) located at the subscriber premises The SU has a standard two-wire interface to connect a telephone, fax machine, PCO(PublicCallOffice), peakerphone, cordless phone, or modem. It also provides direct (without a modem) Internet connectivity to a standard PC, using either a serial port (RS-232 or USB) or Ethernet. The Access System allows simultaneous telephone and Internet connectivity. The SUâ„¢s are connected to an Access Centre (AC) using any convenient technology like wireless, plain old copper, DSL on copper, coaxial cable, optical fibre, or even power lines.
Conceptual Access System providing simultaneous voice and Internet connectivity (SU: Subscriber Unit ; AC: Access Centre)
corDECT Wireless Access System
Following the conceptual model, the corDECT Wireless Access System uses a similar architecture to provide telephone and Internet service to a subscriber, as shown in Figure.
corDECT Wireless Local Loop
The subscriber premises equipment, Wallset IP (WS-IP) or Wallset (WS), has a wireless connection through a Compact Base Station (CBS) to an Access Switch, called a DECT Interface Unit (DIU). The air interface is compliant to the DECT standard specified by ETSI. The DIU switches the voice traffic to the telephone network using the V5.2 protocol to connect to an exchange. The DIU also switches the Internet calls to a built-in Remote Access Switch (RAS) which then routes the traffic to the Internet network. The RAS has an Ethernet interface, which is connected to the Internet using any suitable routing device. The CBS is normally connected to the DIU using three twisted-pair wires, which carry signals as well as power from the DIU to the CBS Alternatively, it can be connected to the DIU through a Base Station Distributor (BSD). The BSD is a remote unit connected to the DIU using a standard E1 interface (on radio, fibre, or copper) as shown in Figure. A BSD can support up to four CBSâ„¢s. For long-range communication, a WS-IP or WS can also be connected to the CBS using a two- hop DECT wireless link, one between WS-IP or WS and a Relay Base Station (RBS) and another between the RBS and CBS, as shown in Figure bellow. The wireless range supported between a WS- IP or WS and the CBS or RBS is 10 km in Line- of-Sight (LOS) conditions. The range supported between a CBS and RBS is 25 km in LOS conditions.
CBS remoted to DIU through BSD
Sub-systems of corDECT Wireless Access System
1 Wallset IP and Wallset
As shown in Figure, the Wallset with Internet Port (WS-IP) provides voice connectivity to the subscriber using a RJ-11 interface, enabling one to connect a standard DTMF or decadic telephone, G3 fax machine, PCO (battery reversal and 12/16 kHz metering are standard features), speakerphone, cordless phone, or modem. In addition, the WS-IP has a RS-232 port to directly connect a PC (obviating the need for a telephone modem). The PC establishes a dial-up PPP (Point-to-Point Protocol) Internet connection using a standard dial-up utility. Internet access is supported at 35 or 70 kbps. In fact, the WS-IP can support simultaneous voice and 35 kbps internet connection.
WS-IP (Wallset with Internet Port)
2 Multiwallset
The Multiwallset (MWS), shown in Figure provides simultaneous voice
service to four subscribers. It has all the features of the WS, but at a significantly lower per-line cost. The Multiwallset has a DECT Transceiver Module (DTM), which is an outdoor unit with a built-in antenna with 7.5 dB gain. It isconnected to an indoor SubscriberInterface Module (SIM) unit, which has four RJ-11 ports for telephones. Each port supports all the terminals a WS supports. The connection between the DTM and the SIM uses a single twisted-pair wire, obviating the need for RF cable and connectors. The MWS has a built-in battery for backup and is powered through the AC mains.
3 Multiwallset IP
The Multiwallset with Internet Port (MWS-IP) is a MWS with four telephones and an additional Ethernet interface to provide dial-up Internet connectivity. Multiple PCâ„¢s can be connected to the Ethernet port and provide a shared 35/70 kbps Internet connection. The PPP-over-Ethernet protocol is used to set up individual connections It is to be noted that at any time, either four simultaneous telephone calls with no Internet connection, or three telephone calls and a 35 kbps shared Internet connection, or two telephone calls and a shared 70 kbps Internet connection, can be made. Depending on usage, this may introduce some blocking for voice calls.
4 Compact Base Station
The Compact Base Station (CBS), shown in Figure, provides the radio interface between the DIU and the corDECT subscriber terminal. It supports up to 12 simultaneous voice calls. It is a small, unobtrusive, weatherproof unit that is remotely powered from the DIU or a BSD.
Compact Base Station
The CBS has two antennas for diversity. A directional antenna with significant gain can be used when coverage is required to be confined to certain directions.
5. DECT Interface Unit
The DECT Interface Unit (DIU) shown in Figure implements the functions of a switch (or a Remote Line Unit), Base Station Controller, and the Operations and Maintenance Console (OMC) System reliability is guaranteed by a redundant, hot standby architecture. The OMC allows exhaustive real-time monitoring and management of the entire corDECT system. A fully-configured DIU with an in-built Remote Access Switch (RAS) only occupies a single 28U, 19? cabinet and consumes less than 600 W.
DECT Interface Unit (DIU) with in-built RAS Up to 20 CBSâ„¢s can be supported by a DIU, directly or through the BSD. The DIU provides up to eight E1 links to the telephone network and/or RAS. The signaling protocol used is either V5.2 which parents the DIU (as an RLU) to an exchange, or R2-MF, in which case the DIU acts as a 1000- line exchange.
6. Relay Station Distributor
A Relay Base Station (RBS), as shown in Figure extends the range of the corDECT system by relaying DECT packets between the CBS and subscriber units. The RBS can handle 11 calls simultaneously.
The RBS consists of two units. The RBS Air Unit is typically mounted on a tower/mast and houses the baseband and the RF sub-system. The RBS Ground Unit supplies power and provides maintenance support to the Air Unit and is mounted at the bottom of the tower.
corDECT Access Centre
Functionality and Interfaces
The corDECT Access Centre, consisting of a DIU and iKON RAS, is designed to provide interfaces to the telephone network and to the Internet.
1 The Telephone Connection
.2 Internet Connection
corDEC Deployment Applications
The corDECT DIU can be deployed as an access system, parented to an exchange using either the V5.2 access interfaces. Alternatively, the corDECT DIU itself can act as a Local Exchange, or even as a direct- in-dialing PBX. This chapter presentsa few deployment scenarios for the corDECT Wireless Access System.corDECT Deployment with DIU in Exchange Premises In one of the most widely deployed scenarios, the corDECT DIU is placed in the local exchange premises, parented to an exchange in a transparent manner or using the
V5.2 protocol, or as an independent Local Exchange. This scenario will be widely used by an incumbent operator with existing infrastructure. The exchange building (usually one of the taller buildings in the area) would have a tower to deploy Figure. DIU in exchange premises with collocated CBS The tower could be a short 15 m rooftop mast,
but in some cases, could be a self-supporting 25 - 35 m tower on the ground. Multiple CBSâ„¢s could be mounted on this tower using omni directional antennas, but more often, using directional antennas providing sectorization plan provides sixsector coverage as shown in Figure protocol, or transparently using twowire Compact Base Stations as shown in sectorized coverage. A commonlyused
Remote Location of CBS
At times, it may be desirable to cover a distant locality using the same DIU. It is possible to connect a CBS remotely from the DIU using three pairs of twisted-pair wires, whichcarry the voice signaling, as well as power, to the CBS. The CBS could be as far as 4 km away, when 0.4 mm diameter copper wire is used. If the buried cable plant in an area is three/six/nine pairs of these wires and mount one/ two/three CBSâ„¢s remotely, a few kilometers from the DIU. The CBSâ„¢s could then be mounted on a tall building using a 3 - 6 m pole on the roof and provide coverage to 30 - 150 subscribers in the neighborhood of this remote location. It is important, however, that the buried not fail during rain, if this option is to be used. It is to be noted that remoting of Base Stations enables better frequency reuse.
The CBSâ„¢s mounted at the exchange tower and the CBSâ„¢s mounted remotely can often use the same DECT channels simultaneously. serviceable, it is easy to take cable plant be in reasonable shape and
Internet Connection
An iKON RAS, integrated with the DIU, terminates the PPP connections for all Internet
Rural Deployment
Providing telecom and Internet service to subscribers in rural areas is a major application of the corDECT Wireless Access System. It can costeffectively provide this service to areas where subscriber density is as low as 0.2 subscribers per sq. km. For a subscriber density lower than this, corDECT may not be the most costeffective system. Further, subscribers in rural areas may not have reliable power and solar panels may have to be used. A compact solar panel can be connected to the WS or WS-IP to power the unit and charge the built-in battery, with solar power taking over when the mains is off/low.
corDECT Features at a Glance
The corDECT WLL system provides features and services comparable to the best wireline systems. In the Switch (Local Exchange) Mode, it boasts of all the features of a large digital exchange. The Wallset IP provides simultaneous voice and Internet access (like an ISDN line) as a basic feature that all subscribers can have Base Stations can be deployed in a multitude of ways, some suited to an incumbent operator, some to a greenfield operator, and others that enable coverage of sparsely populated rural areas. The system also has sophisticated Operations and Maintenance support and a Network Management System for managing a corDECT network. The next few sections describe some key features of the corDECT system..
Conclusion
The DECT standard proposed by the European Telecommunication Standards Institute ETSI) is meant for providing wireless access to networks of various types, from the PSTN to LANâ„¢s. It deals only with the task of defining the air interface between subscriber terminal and Base Station The mode of connecting the DECT-based Wireless Local Loop left to the service provider. system to the PSTN and Internet is
