1. a) Orthogonal Variable Spreading Factor is used in the Third Generation Mobile Communication Networks. Design an Orthogonal Variable Spreading Factor with Spreading factor = 4 and give examples of which codes are orthogonal and which are not orthogonal. [8 marks] b) In Fourth Generation (4G) mobile systems, Orthogonal Frequency Division Multiplexing (OFDM) is used. With the aid of diagrams critically discuss the difference between Frequency Division Multiplexing (FDM) and OFDM. [5 marks) c) Cloud Radio Access Network (C-RAN) is part of the Fifth- Generation mobile communication (5G). Assume a network with 4 baseband Units (BBU) were each BBU is controlling two remote Radio Head (RRH). BBU1 controlling RRH1= 20 users and RRH2= 25 users, BBU2 controlling RRH3= 15 and RRH4= 35 users, BBU3 controlling RRH5= 10 users and RRH6 = 5 users and BBU 4 controlling RRH7= 20 users and RRH8= 10 users. Assuming each BBU will be able to serve 40 users. Find the number of blocked users. How can one minimise the number of blocked users? Draw the system before and after optimisation. [7 marks]