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This part of the chapter presents actual measurement results showing the performance of DECT when combined with LMDS radio equipment. The goal of the experiment is to study the actual BER performance and frequency tolerance of the integrated system. Figure 7-15 shows the setup for the reference experiments, which consist of connecting the DECT modulator and demodulator back to back without going through the LMDS system.²⁷ The BER analyzer generates pseudorandom data. The data from the BER analyzer are modulated and then subsequently demodulated by the DECT demodulator. The demodulated data are then fed back to the BER analyzer. Figure 7-16 shows BER versus frequency offset over selected received power levels.²⁸ As expected, it can be seen that frequency offset tolerance is higher for a higher received power level. For voice applications, a BER of better than 10^-3 is appropriate. Figure 7-16 shows that the frequency tolerance ranges from 30 kHz at a received power of -69.3 dBm to approximately 100 kHz at received power of -57.3 dBm. This result indicates that an expensive frequency drift compensation circuit is not needed.

LMDS/LMCS Market Drivers

Since completion of the FCC spectrum auctions, local multipoint distribution services (LMDS) have been proposed for the delivery of a wide range of services. A point-to-multipoint radio access system is capable of providing services ranging from voice to high-speed data (up to 155 Mbps) and serving customers ranging from small to large businesses. In this brief overview, let's take a look at the LMDS market drivers, where it can satisfy a market need, the characteristics of the market, and its impact on the technology.

LMDS: A Transport System

As mentioned previously, LMDS differs from ordinary transport systems in the way a train differs from a pipeline. Both are transport systems, but a pipeline can transport only one product from one place to another. A train, on the other hand, can transport many different products over the same infrastructure. LMDS, implemented with a multiservice protocol such as Asynchronous Transfer Mode (ATM), can transport, among others, voice, Internet, ethernet, video, computer files, and transaction data.

It is the multipoint radio technology, combined with the appropriate protocol and access method, that gives LMDS the tremendous potential to transform society. With transport technologies such as fiber in place, how can a newcomer compete? LMDS has some overwhelming advantages: reliability; as a transport system, LMDS can be engineered to provide 99.999 percent availability, rivaling that of the best fiber backbones; and speed of deployment. Once a hub is installed (a matter of days), new customers can be added in a matter of hours, future proof that LMDS provides data rates from T1 to OC-3c per user interface.

Managed Investment

An LMDS hub can provide service to all buildings visible from the hub site. Physical technologies such as copper or fiber require individual rights of way to each building, as well as physical placement of the transport medium.