Ever seen a walkie talkie? Well if you have or not, it is a handheld portable two way radio used for communication. However with walkie talkies you can either speak or listen at a particular time. This type of communications are called Half Duplex(HD) communications. Today’s base stations work similar to a walkie talkie, in which they can either transmit or receive at a given time and frequency.
Consider a train and a train track as the data and the frequency at which the data has to be transferred. Now consider the train is moving along the track and another train comes from the opposite direction by the same track at the same time. Obviously the trains will crash. In the case of radio waves it is called Interference. This happens due to the principle of reciprocity – the tendency of radio waves to travel both forward and backward along the same frequency If a user wishes to transmit and receive information at the same time without interference, two separate frequencies have to be used. Another way is to reroute the signals so that they don’t collide. Both of these ways are considered as Full Duplex(FD) communication. The first method is used in our cell phones today and it reduces latency compared to Half Duplex. 5G uses the second method as it not only reduces latency but also doubles the capacity, because it enables a transciever to transmit and receive data at the same time on the same frequency.
Realizing FD in practical systems :
Anything interesting is never one sided. Full Duplex communication also faces a number of challenges. One of the major challenges faced by FD systems is Self Interference(SI). Self Interference is a phenomena where the performance of a receiver is degraded by unrelated emissions, also known as noises at the same or similar frequency to the desired signal. In Full Duplex systems, self interference reduces the FD gain. This occurs when the transmitted signal is so large that it overwhelms the smaller received signal. Your own signal acts as an interfernce to the received signal – hence the name self interference. Excessive SI may reduce the capacity of FD systems to a level that falls below that of HD systems. Hence it is critical to perform SI suppression or SI cancellation while implementing radical FD communication systems. Other challenges involve hardware limitations, unable to invoke sophisticated receiver combining and more.
Full Duplex in Small Cells:
Small cells are small sized cellular radio access nodes that cover a samll geographical area. In the context of 5G, a number of these small sized wireless transcievers are installed to improve the capacity and coverage of networks. The deployment of FD transceivers on low power small cell base stations are proven possible. Therefore studies have been performed to verify the capacity offered by the FD communications in a single SC, which included the challenges faced by the SCs. The main challenge single SC faces is Co- Channel Interference(CCI) from uplink to downlink transmission besides the residual SI after SI cancellation. Therefore addressing the problem of CCI is also needed for FD systems to work properly in small cell environment.
Although FD techniques can significantly improve the network throughput and the total system capacity, numerous open challenges need to be tackled before implementing them. Engineers and researchers are putting a great effort to overcome these challenges and unlock the full potential of Full Duplex wireless communications.
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