Wimax standards and Security The Wimax

System Performance

Service providers are in an intensive phase of trials and performance eval- uations for fixed WiMAX systems and services. Initial technical evaluation showed promising data rates and a number of more wide-scale trials were conducted on a larger customer base throughout the world—in Europe, Asia, and the Americas.

1. 
   Data Rates
   

IEEE 802.16 and WiMAX profiles allow for several radio channel bandwidths, which lead to very different data rates. In a given profile, physical layer data rate of a WiMAX system is determined by the type of modulation and coding: from BPSK 1/2 to QAM64 3/4. Theoretical data rates are quoted in standards or by manufacturers but actual throughput vary with suppliers: a degrada- tion of 40%–50% is often observed. Table 5.6 summarizes typical data rates observed in a 3.5 MHz FDD channel (also see Figure 5.6). That seemingly large difference is mainly due to timing delays necessary for scheduling and collision avoidance between users. Actual data results vary with suppliers, and interoperability between suppliers introduce even greater variations. Nevertheless, the great value of WiMAX-certified products is to guarantee some minimum performance: a service provider may rely on the fact that WiMAX-certified products will work well with other suppliers certified for the same profile.
These results are for one direction 3.5 MHz channel, a full duplex FDD sys-
tem may see up to twice as much throughput in the total 7 MHz bandwidth. Of course, different profiles and channel widths lead to different through- put results. An unlicensed TDD 10 MHz channel profile for instance has the advantage of adapting to asymmetrical data demand. Similar benchmark tests show that such a system is also capable of throughputs of around 8 Mbps (see Figure 5.7).


TABLE 5.6
WiMAX 3.5 MHz Channel Maximum Theoretical and Actual Measured Throughput (at 3.5 GHz)