We fabricated Josephson vortex flow transistors (JVFTs) with a parallel array of Josephson junctions that were prepared using c-axis-oriented 100-nm-thick YBa2Cu3O7-δ (YBCO) thin films grown on 24bicrystal MgO (100) substrates. We observed clear modulations of the critical current and the flow voltage with DC current input to the control line that was inductively coupled to the array of junctions. From the results, we estimated the parameters of the device, e.g., the mutual inductance and the self-inductance, and calculated the operation frequency at which the device potentially exhibited these parameters. Moreover, the current gain and the transresistance were evaluated and found to be 0.5 and 0.15 Ω, respectively. In addition, we observed the high-frequency responses of the JVFT to the input AC current of the sine wave or the square pulse wave. A clear oscillation of the output voltage could be observed with a 1 MHz sine wave and 250 kHz square pulse wave. We also discussed the feasibility of higher frequency operation by using it as an input interface for a single flux quantum (SFQ) logic circuit.

We are concerned with a CDMA cellular system with unbalanced traffic environment such that a cell with high traffic should be assigned a frequency additional to the common one shared with its neighboring cells. To remove quality-dropping inter-cell hard handoffs, the cell with high traffic was first partitioned into three regions. Then, the common frequency is assigned in the outermost region, and the additional frequency is operated in the innermost region, whereas both the common frequency and the additional frequency are operated in the middle region. This frequency assignment strategy is shown not only to remove inter-cell hard handoffs without requiring extra hardware, but also to reduce intra-cell hard handoffs.