A High - Gain Cell Enhancer

Cell enhancers, or broadband on-frequency repeaters (OFRs), offer radio network operators a cost-effective means of improving service quality in areas of low signal strength, or even extending coverage into new areas. Their ability to simultaneously receive and transmit in the same frequency band provides maximum spectral efficiency and renders them transparent to the rest of the network. For stable operation however, the repeater’s receiver and transmitter must be isolated by a factor greater than its active gain. The maximum gain of current all enhancers is limited by relatively low transmitter/receiver isolation, while output powers are limited by the poor linearity of the multichannel amplifier. In situations where high gain and/ or high output powers are required, novel solutions must be sought. An enhanca offering these features is under development at the Univenrity of Bristol. Introduction On-frequency repeaters (OFRs) provide an important means of enhancing the service quality of any mobile radio network. Their mode of operation renders them transparent to the rest of the network, and so provides a relatively cheap and easy means of extending radio coverage into new or badly shadowed areas. This is in contrast to conventional fnquency-translating or demodulating repeaters, which am spectrally inefficient. Figure 1 represents dua different ways of supporting a fullduplex link between a base station and a mobile. The ‘normal’ situation is for the mbile and base to communicate directly on two simplex channels, (3.1 & (3.2. If the mobile now moves into an area served by a frequencytranslating repeater, two additional simplex channels (3 & 4) are required to support the link. If an on-frequency repeater were employed instead. IY) further channels are required, and there is no need for any mechanisms to control hand-off and hand-back. figure 1 : Channel Allocation in Repeater Systems Repeaters may be grouped into two distinct categories: those that provide amplification for a single channel and those that boost multiple channels. The latter group may be further subdivided into repeaters that provide multichannel operation by summing the output of many singlechannel boosters using a high-power combiner (here designated Class I repeaters), and those that boost a contiguous group of channels using a single linear multichannel amplifier (Class 11 repeaters). Single-channel repeaters are of little use in the context of multi-user mobile radio networks so are considered no further here except as the component parts of Class I multi-channel repeaters. A complete bidirectional repeater consists of two broadband amplifiers (Class 11) or sets of amplifiers (ClassI), one for the forward link and the dher for the reverse link. Of the two methods of providing multi-channel operation. Class I is less efficient and physically large1 than its Class Il counterpart, with one power amplifier per channel and a large, inefficient mechanical combiner. Also this combiner is tuned to a fixed frequency band, and