Performance analysis of simultaneous collision-free transmission duplexing method based on propagation delay in wireless link system

Abstract

In this thesis, we propose a new simultaneous collision-free transmission duplexing method which can be used in wireless communication environment. Duplexing methods used in conventional communication systems are time division duplexing, frequency division duplexing and full duplexing which has been recently studied. If the link distance between the two communication nodes becomes long and time division duplexing is applied to this long propagation link, a very long time between data transmission and reception must be wasted without any action, thus the efficiency of the link becomes very poor. In case of frequency division duplexing, the inefficiency due to the propagation delay time is reduced, but the wireless radio hardware should be doubled to realize this method. In addition, since it is necessary to use twice frequency resources, the efficiency of the frequency division duplexing is very low in terms of the frequency spectrum. Finally, in case of full duplexing, the inefficiency by propagation delay time is also reduced. However, the self-interference suppression function requires a very complicated calculation process. If this function is inaccurate, the efficiency of the full duplexing may be lowered compared with the time division duplex or frequency division duplex. In order to overcome the disadvantages of the conventional schemes mentioned above, we propose a simultaneous collision-free transmission duplexing method that is highly efficient at long propagation delay time, simple to implement, and does not require additional hardware. In the simultaneous collision-free transmission duplexing method, a time interval slightly shorter than the propagation delay time, is set as the uplink and downlink slot times. Thereafter, when two communication nodes simultaneously radiate radio waves toward each other, there is no interference between the uplink and the downlink, so that communication can be successfully performed. We performed theoretical analysis and simulation to show the superiority of the proposed simultaneous collision-free transmission duplexing scheme. In order to reflect more realistic situation, we considered the situation where the synchronization of two nodes does not match exactly. Next, we consider the asymmetric traffic environment. The asymmetric traffic indicates an environment in which the amounts of uplink and downlink data are not the same. The asymmetric traffic environment is supposed to be a very common environment in current networks as well as in future networks. Therefore, we propose a method to adjust the slot length of the up-down link and to find the data transmission timing to apply the simultaneous collision-free transmission duplexing scheme to the asymmetric environment. In order to verify the performance of the proposed scheme, we assumed the asymmetric traffic situation and conducted the simulation. Simulation results showed that our proposed scheme is superior to the conventional time division duplexing in various environments. Finally, a study on the simultaneous collision-free transmission duplexing applied to the point-to-multipoint environment was conducted. In point-to-multipoint environments, link-to-link interferences have a significant impact on performance. In order to alleviate such inter-link interference, conventional dynamic time division duplexing is used to allow multiple links to only transmit uplink or downlink simultaneously. However, the simultaneous collision-free transmission duplexing scheme cannot use this method because of interference. We compared the performance of the simultaneous collision-free transmission duplexing with high efficiency and interference with that of dynamic time division duplexing with low efficiency and less interference. Through theoretical analysis, the upper bounds of the performance of each system was derived, and the minimum inter-link isolation level for the simultaneous collision-free transmission duplexing was applied to the point-to-multipoint environment. Then, it was confirmed that the simultaneous collision-free transmission duplexing outperformed dynamic time division duplexing in realistic isolation level and propagation delay time environment.