3G Distributed model
With the advent of 3G, many of the main RAN ( radio access network) vendors such as Nokia, Ericsson and Huawei began to adopt a distributed BTS model. This meant that the radio, that in previous generations was housed within the BTS cabinet, became a Remote Radio Head (RRH). This overcame the issue of loss between antenna and radio because for the first time the radio could be mounted at the top of the tower (because in 2G the RF signal had to travel over a long cable). In the 3G network the link could be a few hundred meters or even a few kilometers because it consisted of fibre with a transceiver at each end using a transmission protocol known as CPRI (common public radio interface).
The logical evolution of this model is C-RAN, cloud or centralised RAN which allows for a fully centralised model where BBUs can be pooled across many RRU and uses virtualisation techniques from the data centre to allow much more flexible management of the network in real time. It also relies on technologies from the fixed line world such as CWDM and DWDM to transport the data to where it is needed over much longer distances. In this model the distance between RRH and BBU can be 20km or more and so transceivers are used in much greater quantity than before,
Common public Radio Interface defines the standards to be used in such environments. It is an industrial collaboration between Ericsson, Huawei, NEC and Nokia (see: http://www.cpri.info/ for details). It provides detailed standards in relation to communication between the radio equipment and the control equipment. Standards include line bit rates which include 1228 Mbit/s, 2457 Mbit/s, 3072 Mbit/s, 4915 Mbit/s 6144 Mbit/s plus more.
Of course with the advent of 5G, the developments set out above are set to continue which means more and more fibre based architectures in the RAN. It also means that inevitably the way in which the network is managed will be based on the principles of SDN (software defined networking).
TXO Optics for RAN use
Mobile / Wireless operators have come to the same conclusion as those in the fixed line. That is that there are enormous benefits in selecting a vendor who can provide a quality compatible transceiver for CPRI use or indeed compatible cable for connecting BBU to RRU. The benefits are significantly reduced cost for comparable quality and in addition a much reduced lead time which from time to time can be a challenge facing operators.
Quality Compatibles for RAN use
TXO Optics already has RAN equipment inside our testing lab which means that the optic can be tested before shipment. Platforms in scope right now are Huawei BBU 3900 and Nokia Flexi Stack for WCDMA.