Висновок

Проведений порівняльний аналіз показує, що застосування прототипів з хорошою частотно-часовою локалізацією дозволяє обійтись без використання захисних часових інтервалів після кожного OFDM символу. Відповідно отримаємо виграш в спектральній ефективності OFDM/OQAM системи, у порівнянні із OFDM/QAM з використанням захисного інтервалу.

Дослідження варінтів локалізації вузькосмугових прототипів може стати перспективним напрямком розвитку сучасних безпровідних систем в рамках концепції Long Term Evolution.

Література

[1] Strohmer T., Beaver S. Optimal OFDM Design for Time-Frequency Dispesive Channels. /T. Strohmer, S. Beaver // IEEE Transactions on Communications, Jul. 2003 – vol. 51 – pp. 1111-1123.

[2] Benedetto J., Heil C., Walnut D. Differentiation and the Balian–Low Theorem. // Journal of Fourier Analysis and Applications, 1994. – vol. 1, № 4 – pp. 355–402.

[3] 3GPP TR 25.892 Feasibility Study for OFDM for UTRAN enhancement // Release 6, 2004 – V2.0.0.

Signal frequency effect on precision of surface acoustic wave devices

Andrii Melnychuk

Electronic means of information and computer technology department, Lviv Polytechnic National University, UKRAINE, Lviv, S. Bandery street 12, E-mail: andriimelnychuk@gmail.com

In this paper effect of signal frequency on surface acoustic wave (SAW) devices is described. As example of SAW device SAW filter was chosen.

Main characteristic of SAW filters is base frequency, as it is known depth of surface wave propagation depends on it’s frequency and velocity (1). The mechanical properties of surface differ from properties of solid material. This difference will affect not only SAW propagation parameters, but also processes which are taking part in SAW generation. All these effects can generate inaccuracy. Based on this the formula of frequency depending on depth propagation and SAW velocity (2) is provided (3). As mechanical stresses are effecting elastic properties and structure of material, formula for counting base frequency of SAW filter in first approximation is provided (4).

As in silicon wafers depth of damaged layer can be up to 20 µm [5] accountings where done in a range from 0 to 20 µm. Based on mechanical stresses distribution, which are showed on fig. 1, using euations (3) and (4) dependency between frequency (propagation depth) and inaccuracy was designed fig. 2.

Basing on received characteristic fig. 2 following conclusions where done. With grow of operating frequency inaccuracy of SAW devices is growing too. Source of this inaccuracy is presence of mechanical stresses, so if stresses will be reduced inaccuracy will also decrease. It will be good to notice that in case the bandpath filter will be created on chosen wafer with frequency band from 100 to 300 MGz the inaccuracy on lower border will be 20 times less then inaccuracy on higher frequency border.

As operational frequencies are growing with evolution of microelectronics the currency of considering mechanical stresses during SAW device manufacturing is growing as well.