## 3 PBCS Structure
### Transmitter Structure and Constructing the Glossary  
The sequence of M-bit information is fed into a buffer. According to the size of the glossary, buffer takes the n-bit sequence from this information. This n-bit binary sequence is matched with any n-bit glossary (_i.e._, the binary sequence \"010\" is mapped to second pattern in selected 3-bit glossary). The encoder output is fed into the pattern sequencer. It concatenates these patterns in sequence. The concatenated pattern sequence is transmitted through RF Front-end. As seen, by not requiring any modulation and/or coding layer, the glossary construction algorithm forms the basis of PBCS. Figure 2 shows the transmitter structure of the PBCS. The \"Glossary Selector\" block has the most important role in PBCS performance. This block takes the glossary space information and channel spectral situation as an input. According to these inputs, this block calculates the maximum likelihood value. It uses a hysteresis function to determine the set of most proper glossaries in the glossary space. The reason for the usage of the hysteresis function in the glossary selector block is that the system gives the priority to the active glossary to reduce the  
Figure 2: PBCS transmitter structure. communication costs. The encoder uses the information of the bit stream size at the buffer and it selects the best-fit glossary from the glossary set given by the glossary selector. It is assumed that in order to construct the glossary space, the three fundamental parameters of the communication signal need to be shifted. For that reason, the AFPSK modulation method is used in PBCS. On the other hand, as far as the efficient use of spectral bandwidth is concerned, for an optimum solution this shifting operation needs to be sinusoidal instead of linear. For this purpose, the quarter sinus forms have been used as the basis units in the shift keying. The choice of quarter sinuses as the basis bears the advantage of making the shifts in the signal smooth thus prevents the unexpected extra spectral usage. Moreover, as a fundamental necessity of the RF communication, the constructed signal patterns satisfy the following three conditions: (1) Zero DC component: Average of each symbol and the series of symbols must be zero, so that the RF energy can efficiently be transferred. (2) Continuity: First and Second Derivatives of the symbol and the consequent symbols must be continues in order to prevent non-transferrable harmonics beyond the pass-band. (3) Bandwidth limitation: Spectral distribution of the generated signal should ideally be inside the pre-defined frequency interval. These features also provide a perfect fit during the pattern synchronization. SPEC space defined above is shown in Figure 3. One of the alternatives is shown in bold in the following figure. In Figure 3, the waveform envelope combinations for \(\pm 2\) levels and 6 depth layers are given as an example. All possible outcomes in the SPEC space are formed by the changes in the amplitude, frequency and phase parameters of the signal. The three possible alterations between each depth layer can be a positive or negative quarter sinus or constant level. Since the changes in the signal parameters form the basis of the pattern system, they should be as uncorrelated as possible in the space in which they are located. Therefore, the glossary patterns are constructed so that depending on the number of bits that the glossary should contain, the most uncorrelated number of sinusoidal changes is chosen (_i.e._, for a 4-bit glossary, 16 routes). The vertical levels in the SPEC space represent the maximum and the minimum values that any of the signal characteristics can take. For instance, in a case of phase  
Figure 3: SPEC space for Level: \(\pm 2\) and Depth:6.  
equals to 5 degrees, the spaces defined between the limits \(+\)L2 = +5 and \(-\)L2 = -5; shifting is made between these two values.