An Introduction to Wireless Technology, Second Edition

Figure 18. ARDIS Network Structure

The connections to customer host systems of Value Added Networks (VANS) are

made at the RF/NCP level, while the message switches control routing between

regions.

The following table compares the parameters associated with MDC4800 and

RD-LAP.

Table 2. MDC4800 and RD-LAP Compared

MDC4800 RD-LAP

Channel bit rate 4800 bps 19,200 bps

FM signalling 2-level FM 4-level FM

Bit/symbol speed 4800 bps 9600 bps

Information per block 6 bytes 12 bytes

Block length 23.3 ms 7.2 ms

Logical message length 256 bytes 512 bytes

Channel access method ASYNC NP-DSMA Slotted NP-DSMA

FEC coding Rate 1/2 convolutional Rate 3/4 trellis

2.6 Summary

In this chapter we have reviewed some principles of physics in order to

understand how radio waves and infrared light behave and can be generated.

These basic principles have provided an understanding of the electromagnetic

spectrum and the relationship between various forms of electromagnet radiation.

An important aspect of any radio system is the antenna and we have looked at

some of the more common types and discussed their relative merits for different

applications. A section on how RF and IR LANs are implemented completes the

first part of this chapter.

54 An Introduction to Wireless Technology

The second part of the chapter discusses the various wide area wireless network

technologies and includes:

•

Analog cellular networks

•

Digital cellular networks

•

CDPD

•

Packet networks

Chapter 2. Wireless Methodologies 55

56 An Introduction to Wireless Technology