- A A Mobile Radio Channel Consists Of Three Rays Fig 1 The First Ray Is A Direct Ray From The Base Station 2 Km Aw 1 (54.87 KiB) Viewed 15 times
will give a big thumb.
(a) A mobile radio channel consists of three rays (Fig. 1). The first ray is a direct ray from the base station, 2 km away due west. The second ray bounces off an obstacle 1.5 km away from the user and 2.5 km away from the base station, and arrives from due north. The third ray bounces off a building 500 m to the south-east from the user, 2.38 km from the base station. The situation is shown in the following diagram. 2.5 km 1.5 km 4 Base Station TX km Mobile Station 2.38 450 500 Fig. 1: Three-Ray model Consider a propagation model where the variation in received power with distance is given by the formula Received Power (dBm) = 20 - 30logo(d) where d is the total distance that the energy has travelled in metres. Also assume that the reflection coefficients from the obstacle and the building are both one. The carrier frequency used by the system is 1800 MHz O Determine and sketch the impulse response of this channel. (1) Hence, determine the delay spread of the channel. There is a rule of thumb that states that if the symbol period is greater than five times the delay spread, then an equaliser is not required. According to this rule, what is the minimum symbol period that could be used in this channel without an equaliser? (8 Marks) (8 Marks)