**3. Coverage determination factors**

#### **3.1 Incumbent coverage determination**

The coverage of primary DTT signal is the area between the transmitter and the points at which the received signal has the minimum receivable quality. At these points the signal power is considered to be of minimum value for a primary receiver below which it cannot have a viewable quality [2]. The determination of coverage area is essential in primary system deployment in order to avoid interference [3]. It can be determined by using noise limited contour or interference limited contour. The former method formulates the coverage area to be the area under the points where the signal carrier to noise ratio is less than the difference of minimum receivable signal value and noise floor. The later method is based on similar formulation where it uses interference instead of noise floor [15].

#### **3.2 Terrestrial TV network frequency**

The cellular system for DTT planning uses different planning system [2]. The frequency assignment for each transmitter can be of single channel or multiple channels. If the transmitter broadcasts with two or more channels in its coverage range, it is multiple frequency transmission. Otherwise, it is single frequency transmission. For Ethiopian case, the responsible body, Ethiopian Broadcasting Authority, plans which form of transmission should be deployed in one place. Dominantly, multiple frequency transmission is deployed in the country. The authority is also responsible for other planning strategies for terrestrial TV. The single frequency transmission uses only one frequency and there must be sharp gap between neighboring cells in order to avoid interference. It is usual to use in digital TV transmission. Multiple frequency transmission on the other hand relies on using different channels in the licensed range of frequency for TV all over the country. Different transmitters can use different channels for broadcasting. DTT and analog terrestrial TV (ATT) can use this method. The planning body is responsible for allocation of frequency for each transmitter. The power limit and the coverage should be planned in proper way, so that the secondary use is also facilitated well [16]. There must be a reference for the planning which is derived according to ITU recommendation. Regional conference decisions have also their own contribution in planning of national terrestrial TV [17, 18]. The planning includes fixing the outdoor receivers of antenna height 10 m and indoor mobile receivers to be 1.5 m. In Ref. planning configuration, reference values for receivable field strength, location probability and maximum interference level are set [6].

### **3.3 DTT protection**

The primary transmission system must be kept from different interference sources which can result from white space use also [3]. The protection level for which the receiver of incumbent system kept unaffected is known to be protection ratio. It is the allowed level of signal quality determined by the deference of primary signals and interfering signals. It can be given as carrier to noise ratio, carrier to interference or interference to noise ratio [6]. It is limited by the national regulatory body. For Ethiopian case, since it is in region one, means its bandwidth is 8 MHz, the protection ratio is given by the following **Table 1**. **Table 1** below, illustrates the co-channel and adjacent channel protection ratio at 8 MHz channel bandwidth.

#### **3.4 Propagation models**

The frequency for terrestrial TV is different from radio frequency range which are used for other services. Although most of the propagation models developed and being modified are for mobile technology, there are also some propagation models which can cover the frequency range of terrestrial TV broadcasting.

**ITU-R P.1546–5** [2, 3, 20]: This propagation model gives a point to area prediction of signals in the frequency range from 30 MHz to 3GHz with in a distance up to 1000 km and effective antenna height up 3000 m. It is statistical model for land, sea and mixed paths. The value of field strength is given in a graphical and tabulated form for some fixed values of frequency, effective antenna height and distance from the transmitter. To find the value of field strength with factors of different values from the givens, it is advisable to use interpolation (when the required value is between given values) or extrapolation (when the required value is out of the given values in the table or graph). The field strength interpolation (formulas for different parameters are given [3] as:

For distance, *d*, the interpolated field strength ð Þ *Ed* can be obtained as

$$E\_d = E\_{\inf} + \frac{\left(E\_{\sup} - E\_{\inf}\right) \log \left(d\_{\bigvee\_{\inf}}\right)}{\log \left(d\_{\sup} \big|\_{\inf}\right)} \, dB\left(\mu \frac{V}{m}\right) \tag{1}$$


**Table 1.** *Protection ratios [2, 3].* *Coverage Determination of Incumbent System and Available TV White Space Channels… DOI: http://dx.doi.org/10.5772/intechopen.98784*

*For frequency* [3] *f, the interpolated field strength E <sup>f</sup> can be obtained as*

$$E\_f = E\_{\rm inj} + \frac{\left(E\_{\rm sup} - E\_{\rm inf}\right) \log\left(f\_{\langle \, f\_{\rm inj} \rangle}\right)}{\log\left(f\_{\rm np}/\_{f\_{\rm inj}}\right)} \, dB\left(\mu \frac{V}{m}\right) \tag{2}$$

and

For antenna height (*h*1), the interpolated field strength *Eh*<sup>1</sup> can be obtained as value [2],

$$E\_{h\_1} = E\_{\inf} + \frac{\left(E\_{\sup} - E\_{\inf}\right) \log \left(\hbar\_{\left\|\cdot\right\|\_{\text{inj}}}\right)}{\log \left(\hbar\_{\text{up}\left\|\cdot\right\|\_{\text{inj}}}\right)} \, dB\left(\mu \frac{V}{m}\right) \tag{3}$$

Here, the subscripts *inf* and *sup* indicates the values of respective parameters given in the graph or table directly below and above the required value, respectively. In this model there are other factors like time percentage and location probability to be taken into account.

**Okumura Hata Model** [8]**:** Covers distance (d) up to 100 km. The operating frequency (f) ranges from 150 MHz up to 1.5GHz.

The loss for urban areas (*Lurban*Þ is given by:

$$L\_{turban} = 69.55 + 26.16 \log \left( f \right) - 13.82 \log \left( h\_t \right) - a(h\_r) + \left( 44.9 - 6.55 \log \left( h\_t \right) \right) \log \left( d \right) \tag{4}$$

The correction factor a(hr) for middle and small cities is given by:

$$a(h\_r) = (\mathbf{1}.\mathbf{1}\log\left(f\right) - \mathbf{0}.\mathbf{7})h\_r - (\mathbf{1}.\mathbf{5}\mathbf{6}\log\left(f\right) - \mathbf{0}.\mathbf{8})\tag{5}$$

For open or rural areas (*Lrural*Þ, it become:

$$L\_{\rm ram} = L\_{\rm turban} - 4.78(\log\left(f\right))^2 + 18.33\log\left(f\right) - 40.94\tag{6}$$

**Longley Rice/Irregular Terrain Model** [21]**:** It is a model covers a frequency range from 20 MHz to 20GHz. The analysis uses several parameters and contains complex equations where it is simplified by a software called, Signal Propagation, Loss and Terrain Analysis Tool, SPLAT! It takes in the real terrain data and gives the output in coverage map or report in text format. Here we use point to point analysis, where the real data of the terrain is considered.

**Hata Devidson Model** [22]**:** The model uses frequency 30 MHz–1500 MHz, distance 1 km–300 km, Tx HAAT 20 m–2500 m and Rx antenna 1-10 m.

$$\text{PL}\_{\text{HD}} = \text{PL}\_{\text{Hatt}} + \text{A}(h\_1, d\_{km}) - \text{S}\_1(d\_{km}) - \text{S}\_2(h\_1, d\_{km}) - \text{S}\_3\left(f\_{\text{MHz}}\right) - \text{S}\_4\left(f\_{\text{MHz}}, d\_{km}\right) \tag{7}$$

Where,

$$PL\_{\text{Hatt}} = 69.55 + 26.16 \log \left( f \right) - 13.82 \log \left( h\_1 \right) - a(h\_2) + (44.9 - 6.55 \log \left( h\_1 \right)) \log \left( d \right) \tag{8}$$

and the correction factor for receiver antenna is the same as that for Hata model above. *A* and *S1* are factors that extend distance up to 300 km. *S2* is correction factor


#### **Table 2.**

*Terms in the Hata Devidson model.*

for HAAT to cover up to 2500 m. And *S3* and *S4* are correction factors for frequency to cover up to 1500 MHz. Hata Devidson Model terms are described in **Table 2** for different distance ranges.

*And for other correction factors, S1(h1,dkm) = 0.00784/log10(9.98/dkm)/(h1–300), h1 > 300 m, S3(fMHz)=fMHz/250log10(1500/fMHz) and S4(fMHz,dkm) = [0.112log(1500/ fMHz)](dkm-64.38), dkm > 64.38 km.*

**Egli Model** [10]**:** A model for UHF and VHF in frequency range of 40 MHz–900- MHz. It calculates point to point link path loss for urban and rural as well. It is developed to include irregular terrains and its loss formula is given by:

$$PL\_{\rm Egli} = \begin{cases} 20\log\left(f\right) + 40\log\left(d\right) - 20\log\left(h\_t\right) - 10\log\left(h\_r\right) + 76.3, h\_r \le 10m\\ 20\log\left(f\right) + 40\log\left(d\right) - 20\log\left(h\_t\right) - 10\log\left(h\_r\right) + 83.9, h\_r > 10m \end{cases} \tag{9}$$

Where *hr* is receiver antenna height AGL in meter, *ht* is transmitter antenna height AGL in meter, *d* is the distance between transmitter and receiver in kilometers and *f* is the frequency in MHz.
