Wimax standards and Security The Wimax

FIGURE 5.6
Throughput cumulative distribution statistic measured in a 3.5 MHz FDD channel at 3.5 GHz.


100
80

CDF (%)
60
40
20
0
0 2 4 6 8
Mbps


FIGURE 5.7
Throughput cumulative distribution statistic measured in a 10 MHz TDD channel at 5.8 GHz.

period may be useful in predicting seasonal changes in the radio channel. Typical standard deviations in fixed links over several months vary between 1 and 6 dB; when deciduous trees are present, the value increases in the spring as leaves come out. Trial data also show that the standard deviation tends to

100
80

CDF (%)
60
40
20
0
0 2 4 6 8
Mbps


FIGURE 5.8
Throughput cumulative distribution statistic measured in various foliage conditions for a fixed links in a given area, for a 3.5 MHz FDD channel at 3.5 GHz.
increase with distance. A median value of the standard deviation of path loss is given by
σ_fixed = 2.26 + 0.75 × log(d/d₀) (5.7)
with d₀ = 1 km.
Seasonal variations are especially noticeable as leaves come out. The impact on the link budget has been reported for fixed wireless links [39] and in dif- ferent wind conditions [40]. We measure some variations of the path loss exponent, the intercept, and the log-normal shadowing. In many cases, the wireless system can adapt to these variations, but in some marginal loca- tions where link budget nears the maximum allowable path loss, throughput is affected. As shown on Figure 5.8, low bit rates are affected the most by changes in foliage.

3. 
   Conclusion
   

Modern wireless communications improve continuously in performance and availability, but still require good design methods based on the fundamentals of radio propagation. We reviewed important aspects of propagation model- ing for mobile and fixed wireless access; we quantified performance of fixed WiMAX systems in residential surroundings; and we compared them to other

published trial results and models. Extensive trial results show that WiMAX offers good opportunities for broadband wireless applications.

Analysts and strategists have been announcing ubiquitous broadband wire- less services for years now, yet pessimists claim that these services will never see the light of day. Still, eventually a combination of events will be the cat- alyst for the broadband wireless industry: new technology advances, new spectrum bands, efficient standards like WiMAX, good conformance certifi- cation processes, flexible IP-based network infrastructure, involvement from major chip manufacturers, and global economies of scale are all encouraging signs. One can hope that wireless service providers will deploy these new services in most cities and even in lower-density suburban and rural areas.



References

1. 
   IEEE Std 802.16-2004, IEEE Standard for Local and Metropolitan Area Networks—