Testbed Implementation – On the performance of channel assembling in cognitive radio networks.
In a cognitive radio (CR) system, a secondary user (SU) accesses to a primary user’s (PU) radio spectrum without interfering with PU’s activity. More specifically, SU only has access to the channel when the PU is not present, and will immediately vacate the channel when the PU appears.
Channel aggregation, which combines multiple channels in to one channel, has been utilized in CR technology. Although numerous studies have been carried out in physical layer and MAC layer for channel aggregation in CR systems, the testbed based flow level investigation is still open. Therefore, the main objective of this project is to create a CR testbed for studying a flexible channel allocation scheme where channel aggregation capabilities is enabled from the perspective of the Transmission Control Protocol (TCP), which is designed for reliable data transfer over an unreliable network.
During this project, the physical and MAC layer is constructed, tested and verified. Using National Instrument hardware (NI-USRP) and software (LabView Communication Suite), every channel is handled by a separate NI-USRP (including a host computer) running a version of the LTE Stack that we modified to accept cognitive concept. More specifically, if a PU appears in the channel the system, SU is told to vacate the channel. In addition, this process (a control program) takes care of the PU emulation and the initial setup (bandwidth, guard bands etc.) of all the NI-USRPs (therefore also the channels), making it easy to scale. Performance tests show that with no PU present the raw data rate per channel is about 75Mbit/s (given ideal conditions). When PU are introduced to the channel, the performance expectedly drops in accordance to the PUs behavior.
Future work: As the NI-USRPs and their controllers only accept UDP traffic, and the goals is to evaluate TCP traffic over the CR channels, the use of encapsulation would allow for TCP traffic inside of the UDP. NS-3 (a discrete event network simulator) would be suitable for the encapsulation process and for testing the reliable TCP communication over the link.