You are asked to determine the signal-to-interference ratio (SIR or C/I) on the forward link of a cellular system, when the mobile is located on the fringe of its serving cell. Assume that all cells have equal radii, and that base stations have equal power and are located in the centers of each cell. Also assume that each cell transmits an independent signal, such that interfering signal powers may be added. Let us define a "tier" of cells as being the collection of co-channel cells that are more-or-less the same distance away from the mobile in the serving cell. This problem explores the impact of the cluster size (i.e., frequency reuse distance), the number of tiers used in the calculation of C/I, and the effect of the propagation path loss exponent on C/I.
What is the average distance (in terms of R) between the mobile on the fringe of the serving cell and the first tier of co-channel cells? (These cells are called the "nearest neighbors.") How many cells are located in the first tier? Solve for the case of N = 1, N=3, N=4,N=7, and N= 12 cluster sizes.
How does the average distance compare to the value of D = QR, where .
What is the average distance (in terms of R) been the mobile on the fringe of the serving cell and the second and third tier of co-channel cells, and how many cells are in the second and third tier of co-channel cells for the cases of N= 1, N= 3. N= 4, N= 7, and N= 12 cluster sizes?
Determine the forward link C/I for the following frequency reuse designs: N = 1, N = 3, N = 4, N = 7, and N = 12. Assume that the propagation path loss exponent is 4, and evaluate the S/I contribution due to just he first tier, and then due to additional outer tiers of co-channel cells. Indicate the number of tiers at which there is a diminishing contribution to the interference at the mobile.
Repeat part (c), except now consider a line-of-sight path loss exponent of n = 2. Notice the huge impact that the propagation path loss exponent has on C/I. What can you say about the cluster size, path loss exponent, and the C/I values which result? How would this impact practical wireless system design?