This diagram allows you to compare the systems we've mentioned in this lesson. The horizontal-axis uses a logarithmic scale to show the bit rate a system offers. The vertical-axis shows the amount of coverage a system offers, from a single room to the whole world.
As you can see, those systems with the lowest mobility, the wireless LAN solutions, offer the highest bit rates, whilst those with higher mobility, such as GSM, offer lower bit rates. The red lines indicate the future developments. For example, GSM currently offers coverage spanning the globe and a bit rate of 9.6kbps. Enhancements, such as GPRS and HSCSD will increase this bit rate.
AMPS offers coverage in several countries across the world with a bit rate similar to that found in GSM. Future enhancements, such as circuit switched data, will offer higher bit rates than are currently available. Metricom's system, which was discussed earlier offers a higher bit rate than current GSM or AMPS systems, but only provides mobility at the metropolitan level.
Universal Mobile Telecommunications System, UMTS, will offer a much higher bit rate than any of today’s systems. Because of the expense of introducing mobile networks, the first implementations will offer patchy coverage. As time progresses, hopes are that UMTS will cover the globe.