MODULATION, DETECTION AND CODING docx

[...]... spreading code completely vanishes and the message signal resumes its original shape and bandwidth The bandwidth of interfering signals, on the other hand, become larger than or equal to the double chip rate Subsequent bandpass filter is adjusted to the bandwidth of the message signal and cuts off most of the power from the unwanted signals The ratio between wanted and unwanted signal powers will then... of information or the entropy of the source are therefore treated Perhaps demands go beyond the capacity of the channel The book describes fundamental methods of doing the source coding and how the efficiency of the coding is calculated Furthermore, it describes how error-correcting and error-detecting coding can be done and the capacity, in terms of bit-error rate, which can be obtained Different... proportion to the bandwidth expansion and is called processing gain; e.g a bandwidth expansion of 100 times gives a processing gain of 20 dB The combination of multiplier and bandpass filter can be seen as a correlator since the filter bandwidth is narrow in relation to the double chip rate A model for a CDMA system with several users can then look like the one shown in Figure 1.11 The bandwidth of the... the other hand, each modulator in the figure can usually be seen as a radio transmitter and each bandpass filter with demodulator as a receiver The addition of the signals is done in the space between the transmitter and the receiver If the transmitters are at different locations and the receivers at the same location the model can be modified so that each transmitter has its own channel and the addition... Hardware and software solutions are only treated sporadically, and it is therefore recommended that the student has completed basic courses in electronics and digital systems in order to be able to make the connection between real systems and the block diagrams and methods treated here The material has a theoretical base which makes it possible for the student to continue with both deeper studies and design... coding, channel coding, modulation and demodulation Adaptive channel equalisation, the signal processing aspects of adaptive antennas as well as multi-user detectors for CDMA are also included Shorter sections on link budget, synchronising and cryptography are also included Network aspects are not discussed and very little is given about wave propagation The book aims to give the reader an understanding... control, i.e as in wire-bound telephony TDM and FDM are often used, corresponding to TDMA and FDMA FDMA Each user, or message, has its own frequency band At the transmitting end the messages are transferred to the respective frequency bands through modulation of different carrier waves Figure 1.6 shows an example with seven different messages, each with a bandwidth of 2 W (Hz) Each carrier wave is a... along the frequency axis Each signal has a bandwidth of 2 W and must therefore take up at least the corresponding bandwidth on the frequency axis MULTIPLE USER SYSTEMS Figure 1.7 Structure of an FDM A system for N different messages BFP is a bandpass filter It should be remembered that Figure 1.7 is primarily a model of the system, which is useful when understanding of, or calculations on, the properties... CERN, they were in need of a system for document handling Development and standardisation of protocol and text formats was started, which resulted in the World Wide Web (WWW), which is an efficient way to use the Internet In 1993 a further milestone was reached when the computer program Mosaic was presented The program gave a simple interface to the WWW and made the resources of the network accessible... treated in this text Completed courses in basic signal processing and probability theory are necessary for the understanding of the material presented here The book includes: text where theory and methods are presented, completely solved examples, exercises with answers, where the reader can test his/hers understanding of the content, and short presentations of some communication systems This page .