Concern to the cell site antennas explain start up configuration and abnormal antenna configuration of start up systems?
3. Concern to the cell site antennas explain start up configuration and abnormal antenna configuration of start up systems?
For Coverage Use: Omnidirectional Antennas
High-Gain Antennas: There are standard 6-dB and 9-dB gain omnidirectional antennas. The antenna patterns for 6-dB gain and 9-dB gain are shown in Fig.3.1
Start-Up System Configuration: In a start-up system, an omnicell, in which all the transmitting antennas are omnidirectional, is used. Each transmitting antenna can transmit signals from N radio transmitters simultaneously using a N-channel combiner or a broadband linear amplifier. Each cell normally can have three transmitting antennas which serve 3N voice radio transmitters simultaneously
%206%20dB%20(b)%209%20dB.PNG "High-gain omnidirectional antennas (a) 6 dB (b) 9 dB")
%20for%203N%20channels;%20(b)%20for%206N%20channels.PNG "Cell site antennas for omni cells (a) for 3N channels; (b) for 6N channels")
Each sending signal is amplified by its own channel amplifier in each radio transmitter, or N channels (radio signals) pass through a broadband linear amplifier and transmit signals by means of a transmitting antenna (see Fig.3.2a).
Two receiving antennas commonly can receive all 3N voice radio signals simultaneously. Then in each channel, two identical signals received by two receiving antennas pass through a diversity receiver of that channel. The receiving antenna configuration on the antenna mast is shown in Fig.3.2.cFor serving 6N voice radio transmitters from six transmitting antennas is shown in Fig.3.2(b).
Abnormal Antenna Configuration: Usually, the call traffic in each cell increases as the number of customers increases. Some cells require a greater number of radios to handle the increasing traffic. An omnicell site can be equipped with up to 90 voice radios for AMPS systems. In such cases six transmitting antennas should be used as shown in Fig. 3.2b. In the meantime, the number of receiving antennas is still two. In order to reduce the number of transmitting antennas, a hybrid ring combiner that can combine two 16-channel signals is found. This means that only three transmitting antennas are needed to transmit 90 radio signals. However, the ring combiner has a limitation of handling power up to 600 W with a loss of 3 dB.
