2. a) OFDM is used in 4G mobile networks. The time-domain structure of the 4G radio interface is shown in Fig.2. Based on Fig.2, answer the following five questions: One frame -10 m One 05mg The -667204873 - p12--107 Fig.2 Evender Of i) In the radio interface, the normal cyclic prefix scheme and the extended cyclic prefix scheme are defined. Explain the main reasons behind the definition of these two cyclic prefix schemes. In the normal cyclic prefix scheme, how many cyclic prefix samples are defined in the first OFDM symbol? And how many cyclic prefix samples are defined in the remaining OFDM symbols? In the extended cyclic prefix scheme, how many cyclic prefix samples are defined in each OFDM symbol? [3+2+2=7] ii) If a signal modulation format of 32-QAM is taken on 1024 subcarriers and a signal modulation format of 64-QAM is taken on all of the remaining subcarriers, work out the raw signal bit rates for both the normal cyclic prefix scheme and the extended cyclic prefix scheme. [4+3=7] iii) A resource block is defined to contain 12 consecutive subcarriers in the frequency domain over a 0.5ms time slot. Assuming that 64-QAM is taken on all the subcarriers, work out the minimum raw signal bit rate that can be allocated to a user for both the normal cyclic prefix scheme and the extended cyclic prefix scheme. [2+2=4] iv) A one-cell frequency reuse scheme is adopted in LTE. Describe the key advantages and disadvantages associated with the scheme. Which technique is widely adopted in practice to avoid the occurrence of worst-case interferences between neighbouring cells? v) Briefly explain why OFDM can reduce the multi-path propagation effect. [2+2=4] [4]