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corDECT –How it works-
The corDECT subscriber terminal, called Wallset, provides an RJ-11 telephone port and an RJ-232 serial port for simultaneous internet access using a PC. The Internet access speed is 35/70 Kbps. The corDECT system has been designed such that it can be easily integrated with the existing network.
In one of the configurations, the corDECT system acts like a switch along with the wireless local loop.
corDECT has been designed to be a modular system. While the basic unit provides service to up to 1000 subscribers, multiple corDECT systems can be connected together using a transit switch. The system has been designed in such a way that the initial investment for the Fixed Part is low. Further, since this scheme does not require frequency planning, the installations need not be coordinated. Coupled with the low cost, it thus makes corDECT one of the most versatile Wireless in Local Loop systems available today. <<<<
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corDECT
The cost-effective Wireless Local Loop technology
corDECT is India's very own Wireless Local Loop technology, jointly developed by Analog Devices Inc., Midas Communication Technologies (P) Ltd. and TeNeT group, IIT Madras. Based on the Digital Enhanced Cordless Telecommunications standard specified by the European Telecommunications Standards Institute (ETSI), corDECT provides cost-effective, simultaneous high-quality voice and data connectivity in both urban and rural areas.This revolutionary new technology provides voice communication using 32 Kbps ADPCM, and Internet connectivity at 35/70 Kbps.
How corDECT works
Employing Multi-Carrier Time Division Multiple Access (MC-TDMA), a technique in which the frequency can change from one time slot to another, DECT defines a wireless communication standard between a Fixed Part (FP) and a Portable Part (PP). Communication takes place using Gaussian Frequency Shift Keying (GMSK) Modulation.
This new system uses a frame of 10 msec in which 24 time slots are defined. Communication between FP and PP is time-division duplex in which 12 time slots are used for a one way transmission. In a 20 MHz frequency spectrum, 10 carriers are defined. Thus, for communication from PP to FP, 10 carriers can be used in each of the 12 time slots, amounting to 120 channels.
In DECT, no channel is permanently assigned to any FP or PP. Which means, any PP can select any of the 120 channels to communicate with a FP using the Dynamic Channel Selection (DCS) algorithm. The algorithm requires the PP to measure Receive Signal Strength (RSSI) on all the 120 channels. It locks to the FP providing the strongest signal and then maintains a RSSI table for all other channels. When a PP tries to establish a connection, it chooses the channel providing lowest interference. Even while a communication process is taking place, the RSSI table is periodically updated and if a channel with less interference than the current one is found, a seamless handover to the new channel takes place.
ETSI has specified the 1880 - 1935 MHz band for DECT. Normally any 20 MHz band out of this spectrum can be chosen for operation. Each DECT channel can carry 32 kbps of payload, and the voice coding employed in DECT is 32 kbps ADPCM. It is also possible for two DECT channels to be combined to provide data communication at 64 kbps between PP and FP.
The corDECT subscriber terminal, called Wallset, provides an RJ-11 telephone port and an RJ-232 serial port for simultaneous internet access using a PC. The Internet access speed is 35/70 Kbps. The corDECT system has been designed such that it can be easily integrated with the existing network. The system interfaces to the network on E1 (2.048 Mbps) lines as per ITU-T G703 standard. In one of the configurations, the corDECT system acts like a switch along with the wireless local loop. The numbering plan is flexible so that it can be modified as per the requirements. The tones, announcements, metering, charging, switching, routing and special services are provided by the `switch part' of the corDECT system. Alternatively, corDECT can also be configured as an Access Network connected to a main exchange using ITU-T specified access protocol V5.2.A transparent version with two-wire analog interface to any exchange is also available for quick rollout.
corDECT has been designed to be a modular system. While the basic unit provides service to up to 1000 subscribers, multiple corDECT systems can be connected together using a transit switch. The system has been designed in such a way that the initial investment for the Fixed Part is low. Further, since this scheme does not require frequency planning, the installations need not be coordinated. Coupled with the low cost, it thus makes corDECT one of the most versatile Wireless in Local Loop systems available today.
After successful field trials by the Department of Telecommunications (DoT) at several sites in India, and by Telebras, the Brazilian counterpart of DoT, at Sau Paulo, Brazil, the technology has now been licensed to a few companies in India, Singapore, Tunisia and Brazil.The system has been deployed in Mumbai and Delhi, and twenty-four other Indian cities are to get the system in 2000. Systems are operational in Madagascar, Figi, Kenya, Tunisia, Argentina and Nigeria. The corDECT system is poised to change the every million of people connect to the world. |
