corDECT(Digital Enhanced Cordless Telecommunications)

ABSTRACT

The traditional wired local loop used to connect each telephone subscriber to the nearest exchange is expensive and unreliable. Wireless Local Loop (WLL) systems largely eliminate these copper wires using wireless technologies and could provide a cost effective solution. corDECT is one such WLL system, based on the DECT (Digital Enhanced Cordless Telecommunications) standard, that provides toll-quality voice and data capability at a cost below that of a wired local loop. Using micro-cells and Dynamic Channel Selection (DCS), it can handle high subscriber densities without frequency planning. corDECT is gaining commercial acceptance in India and a number of other countries.Using a simple Queueing Network Model (QNM), we find that the 1,000-line corDECT system could achieve a Busy Hour Call Attempt (BHCA) of 36,000 calls/hour, which is far greater than its requirement of 20,000 calls/hour. We show how the system could be expanded to a 10,000-line exchange with a BHCA of over 2,10,000 calls/hour. We also investigate the feasibility of implementing 64 kbps data service along with voice. It is shown that this requires modest hardware improvements.

INTRODUCTION

Traditionally, a pair of copper wires is used to connect each telephone subscriber to the nearest exchange. Such a wired local loop poses the following problems:

 The laying and maintenance of copper cable up to the subscriber’s premises incurs high cost. Also, this cost is increasing with time as the cost of copper increases.

The per-line cost for rural areas is significantly higher due to the large amount of cabling          infrastructure required to take even a few telephone lines to remote villages.

Most faults are in the local loop, due to water-logging, damage or theft of cables.

Rapid deployment is difficult owing to the regulatory and other problems in laying buried cables.

Wireless technology can provide a cost-effective solution to the local loop problems. The wireless service facilitates easy expansion of the network as installation is easier. Further, the cost of wireless technologies is primarily in electronics and is expected to come down with time. In order to be useful in urban areas of developing countries such as India, the wireless local loop technology must cater to high subscriber densities of 1,000–10,000 subscribers/sq.km. It must also provide toll-quality voice and data and FAX capability on par with a wired telephone.

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 toll-quality 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.

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 LAN’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 system to the PSTN and Internet is left to the service provider.

DECT has been specified to make possible low-cost subscriber terminals, high subscriber density with heavy call-traffic levels, wireline- quality voice, modem/fax capability, 32/64 kbps and higher-rate data services, all with a modest spectral allocation of 20 MHz. The key technical advances incorporated in DECT when compared to prior standards that make all this possible are:

(i) dynamic channel selection

(ii) microcellular architecture

(iii) channels with multiple data rates

(iv) cost-effective modulation/demodulation techniques.

ADVANTAGES AND LIMITATIONS

Voice Quality

corDECT delivers the same toll-quality speech performance as a good copper-based local loop..

Data Services

The employment of 32 kbps ADPCM permits all voice-band data services available from a conventional wired connection. It is also possible to occupy a double time slot on air to transmit at 64 kbps with error correction.

Internet Access Speed

Internet Access is possible simultaneously with a voice call using the Wallset IP. There are two access rates: 35 kbps and 70 kbps, using one and two time slots respectively.

System Capacity

Each corDECT system supports up to 1000 subscribers.

FUTURE SCOPE

Packet-Switched High Speed Internet Downloading

It is highly desirable for a user to have the ability to download from the Internet at a high peak bitrate, even if the download-channel is shared by many users, each accessing it when needed.

More Integration for Cost-Effectiveness

A next-generation subscriber terminal is under development which is more integrated and compact. It will provide several options: one voice line, two voice lines, or one voice line + one Internet port.

New Multiwallset Developments

Under development is a MWS that will permit one to serve 8/12/16 subscribers, with blocking whenever four simultaneous calls are in progress. This will reduce the per-line cost dramatically and enable an operator to serve the hitherto unviable low-usage subscribers.

Increased Scalability

The corDECT system is unique today in the respect that the cost of the DIU, representing the up-front investment, is a small fraction of the total cost. A new cost-effective, highly integrated mini-DIU will be available soon for a 50-line system and also for a 150-line system. These versions will also reduce significantly the physical infrastructure requirements for housing the DIU.