From Phase-Locked Loops for Wireless Communications: Digital, Analog and Optical Implementations, Second Edition
Synchronization of digital waveforms is an area of active research. For the latest information, the reader is encouraged to review the latest issues of IEEE Transactions on Communications. Several references exist that can provide a larger theoretical foundation than provided in this chapter [1] ? [5]. Today's demand for wireless services promises to exceed the available frequency spectrum, necessitating more efficient modulation techniques. Waveforms such as Continuous Phase Modulation (CPM) or Trellis Coded Modulation (TCM) provide more efficient spectral usage, but synchronization is significantly more difficult than traditional Phase Shift Keying (PSK) or Frequency Shift Keying (FSK).
In this chapter, we will begin with an explanation of the synchronization problem. Traditional methods of synchronizing BPSK will be presented. Because of the current research in combined modulation and coding, it is inevitable that today's advanced synchronization will soon be inadequate for the new waveforms. Because of this, our primary emphasis is to develop the general principles of synchronization so the reader can apply them to new waveforms as they are developed.
11.1 The Synchronization Problem
Figure 11.1 begins the problem definition with the transmitter sending a signal, ?( t 1) e j ?( t 1), and the receiver attempting to remove the information from the signal after it has passed through the noisy channel. Typically the receiver and transmitter are not geographically co-located, so there an inherent problem in time synchronization. In some instances a nanosecond of timing ambiguity between timing references t 1
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