Mobile Communications Overview Trong chương này, một tổng quan về truyền thông di động được trình bày để hiểu các nguyên tắc chức năng của mình và giới thiệu các thuật ngữ cần thiết cho phần còn lại của cuốn sách này. | 5 CHAPTER 2 Mobile Communications Overview In this chapter a brief overview of mobile communications is presented to understand its functional principles and introduce the necessary terminology for the rest of this book. GENERAL DESCRIPTION All communication systems have fundamentally the same goal to pass along the maximum amount of information with the minimum number of errors 19 . Modern digital wireless communications systems are no exception. These systems can usually be separated into several elements as indicated by Fig. . Given any digital input the source encoder eliminates redundancy in the information bits thus maximizing the amount of the useful information transferred in the communications system 19 . The output of the source generator is processed by the channel encoder which incorporates error control information in the data to minimize the probability of error in transmission. The output of the channel encoder is further processed by the Digital Signal Processing unit in order to allow simultaneous communication of many users. An example of this would be digital beamforming which by using the geometric properties of the antenna array is able to concentrate signals from multiple users in different desired directions allowing more users to be served by the system. The generated data stream is then processed by the modulator which is responsible to shift the baseband signal at its input into the band-pass version at the output due to the bandwidth constraints of the communication system 19 . The information sequence generated at the output of the modulator is then fed into the antenna array and transmitted through the wireless channel. On the other end of the radio channel the reverse procedure takes place. The demodulator down converts the signals from different users collected by the receiver antenna into their baseband equivalent. The Digital Signal Processor then separates the different signals that come from different users. The channel .
