Unformatted text preview: 11.8 (1) MMDS signals have larger wavelengths (greater than 10 cm) and can travel
farther without losing significant power. Hence MMDS can operate in
considerably larger cells, thereby lowering base station equipment costs. (2)
Equipment at lower frequencies is less expensive, yielding cost savings at both the
subscriber and base station. (3) MMDS signals don't get blocked as easily by
objects and are less susceptible to rain absorption.
11.9 802.16.1 is targeted at the 10 to 66 GHz spectrum and is considered a millimeter
wave system. It is designed to support data rates above 2 Mbps. The target market
is small and medium size businesses. 802.16.2 is concerned with coexistence of
multiple systems in the same area. 802.16.3 is targeted at the 2 to 11 GHz spectrum
and is a microwave system. It is designed for data rates below 2 Mbps. The target
market is residential and small business. A N SWERS
NSWERS TO PROBLEMS 11.1 A straightforward way to do this is to double the bandwidth of each individual
channel (using half as many channels), double the data rate, and use TDD on each
channel. So, the channel bandwidth becomes 400 kHz with a bit rate of 541.6 kbps.
Total number of TDD channels = 125.
11.2 a. First, we need the attenuation from rain. We use Equation 11.3, namely A = aRb.
From Table 11.8, we get R = 32 mm/hr. For the parameters a and b, we use
Table 11.7 and interpolate for ah and bh at 38 GHz, yielding a = 0.3152 and b =
0.955. With these parameters A = 0.3152 x (32)0.955 = 8.63 dB/km.
Total attenuation = 8.63 x 12 = 103.56 dB
b. At 99.9%, R = 10 mm/hr. A = 0.3152 x (10) 0.955 = 2.84 dB/km
Total attenuation = 2.84 x 12 = 34.08 dB
At 99%, R = 2 mm/hr. A = 0.3152 x (2) 0.955 = 0.61 dB/km
Total attenuation = 0.61 x 12 = 7.32 dB
The 99.99% requirement would be difficult to meet.
Source: [FREE98] -55- ...
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- Fall '11
- Frequency, Bit rate, base station, total attenuation, MMDS signals