(a)K=7 Ds/R'= 4.6 mearQ' (c)K=3 R·=R FIGURE 75.1 Four cases of expression of cochannel interference reduction factor Cellular Systems The cellular system [Lee, 1989]is a high-capacity system that uses the frequency reuse concept. The same frequency is used over and over again in different geographical locations. In large cities, the same frequency can be reused over 30 times Key Elements: There are several key elements in the cellular system. Cochannel interference reduction factor q(see Fig 75.1): Two cells using the same frequency channels are called cochannel cells. The required distance between two cochannel cells in order to receive the accepted voice quality is D, and the radius of the cell is R. Then the cochannel interference reduction factor q is q=D,/R There are six co-channel cells at the first tier seen from the center cell as shown in Fig. 75. 1(a). For an analog cellular system g, =4.6, and the cell reuse factor Kis K=9, 23=7. The K=7 means that a cluster of seven cells will reuse again and again in a serving area. The capacity increase in a cellular system can be achieved by reducing both the radius of cell r by one half and the separation D, by one half such at the gs remains constant and the capacity is increasing by four times. The reason is that a cell shown in Figure 75. 1(a)can fit in four small cells shown in Fig. 75.1(b). In Fig. 75.1(c), the size of cells is the same as Fig. 75.1(a),but , =3 is achieved by using an intelligent microcell system. The capacity of Fig. 75. 1(c)is 7= 2. 33 times over that of Fig. 75.1(a). In Fig. 75. 1(d), the radius of the cell is reduced by one half, and K is reduced to 3. The capacity of Fig. 75.1(d)is 4x 2.33=9.32 times over that of 751(a) The value of q is different in different kinds of cellular systems such as analog, TDMA, and CDMA(code Handoff: Handoff is a feature implemented in cellular systems to handoff a frequency of a cell while the mobile unit changes to another frequency of another cell while the vehicle is entering. The handoff is handled by the system and the user does not notice the handoff occurrences c 2000 by CRC Press LLC© 2000 by CRC Press LLC Cellular Systems The cellular system [Lee, 1989] is a high-capacity system that uses the frequency reuse concept. The same frequency is used over and over again in different geographical locations. In large cities, the same frequency can be reused over 30 times. Key Elements: There are several key elements in the cellular system. • Cochannel interference reduction factor q (see Fig. 75.1): Two cells using the same frequency channels are called cochannel cells. The required distance between two cochannel cells in order to receive the accepted voice quality is Ds , and the radius of the cell is R. Then the cochannel interference reduction factor q is q = Ds/R There are six co-channel cells at the first tier seen from the center cell as shown in Fig. 75.1(a). For an analog cellular system qs = 4.6, and the cell reuse factor K is K = qs⅔ = 7. The K = 7 means that a cluster of seven cells will reuse again and again in a serving area. The capacity increase in a cellular system can be achieved by reducing both the radius of cell R by one half and the separation Ds by one half such that the qs remains constant and the capacity is increasing by four times. The reason is that a cell shown in Figure 75.1(a) can fit in four small cells shown in Fig. 75.1(b). In Fig. 75.1(c), the size of cells is the same as Fig. 75.1(a), but qs = 3 is achieved by using an intelligent microcell system. The capacity of Fig. 75.1(c) is  ⁄ = 2.33 times over that of Fig. 75.1(a). In Fig. 75.1(d), the radius of the cell is reduced by one half, and K is reduced to 3. The capacity of Fig. 75.1(d) is 4 ¥ 2.33 = 9.32 times over that of Fig. 75.1(a). The value of q is different in different kinds of cellular systems such as analog, TDMA, and CDMA (code division multiple access). • Handoff: Handoff is a feature implemented in cellular systems to handoff a frequency of a cell while the mobile unit changes to another frequency of another cell while the vehicle is entering. The handoff is handled by the system and the user does not notice the handoff occurrences. FIGURE 75.1 Four cases of expression of cochannel interference reduction factor