tailieunhanh - Radio network planning and optimisation for umts 2nd edition phần 3

Chuyên dụng kênh điều khiển (DCCH), một kênh điểm-điểm hai chiều để truyền thông tin điều khiển chuyên dụng giữa mạng và UE (được thành lập thông qua các thủ tục thiết lập kết nối RRC). TCHs có thể được mô tả như:. Kênh giao thông chuyên dụng (DTCH), một kênh điểm-điểm dành riêng cho một UE cho chuyển nhượng của người sử dụng | WCDMA Radio Network Planning 99 Shadowing Margin and Soft Handover Gain Estimation The next step is to estimate the maximum cell range and cell coverage area in different environments regions. In the radio link budget the maximum allowed isotropic path loss is calculated and from that value a slow fading margin related to the coverage probability has to be subtracted. When evaluating the coverage probability the propagation model exponent and the standard deviation for log-normal fading must be set. If the indoor case is considered typical values for the indoor loss are from 15 to 20 dB and the standard deviation for log-normal fading margin calculation ranges from 10 to 12 dB. Outdoors typical standard deviation values range from 6 to 8dB and typical propagation constants from to 4. Traditionally the area coverage probability used in the radio link budget is for the single-cell case 6 . The required probability is 90-95 and typically this leads to a 7-8 dB fading margin depending on the propagation constant and standard deviation of the log-normal fading. Equation estimates the area coverage probability for the single-cell case F -J1- erf a expp 21a Í1- f 1 a b n Fu 2 s 1 erf a Texp I b2 Ị 1 erf I b Ị I 3 15 where xo - Pr a ----ffiffi- Ơ -fl and b 10 n log10 e Ơ 2 where Pr is the received level at the cell edge n is the propagation constant x0 is the average signal strength threshold Ơ is the standard deviation of the field strength and erf is the error function. In real WCDMA cellular networks the coverage areas of cells overlap and the MS is able to connect to more than just one serving cell. If more than one cell can be detected the location probability increases and is higher than that determined for a single isolated cell. Analysis performed in 7 indicates that if the area location probability is reduced from 96 to 90 the number of BSs is reduced by 38 . This number indicates that the concept of multi-server location probability should be