The rapid growth of digitalization in recent years has resulted in billions of devices that interact with one another. As such, Internet of Things (IoT) networks receive great attention during the development of next-generation technologies. In many IoT applications, timely delivery of the information packets is crucial over which the performance of the network is evaluated. In recent years, there has been a growing interest in the optimization of Age of Information in random access channels with a great number of devices. In our research group, we have developed the following ALOHA variants to improve information freshness:
In 2020, we have proposed an age-aware modification on the slotted ALOHA policy. We suggest that instead of having all the nodes eligible for transmission at any time, the age of the nodes shall be greater than a predetermined age threshold before being allowed to make a transmission through the channel. In , we have presented a complete analysis of this Threshold ALOHA policy and showed that the average age of information can be improved by 48% with respect to the slotted ALOHA.
Threshold ALOHA policy provides a great advancement over slotted ALOHA over information freshness; however, the performance of both policies is set back by the low throughput of e-1. Further reduction of age of information can be made possible by reworking the structure of the policy so that the throughput cap of slotted ALOHA can be exceeded. In MiSTA, we affix a mini slot to the time slots for control purposes. In the mini slot, the nodes that wish to use the channel send very small packets before transmitting the actual data, so that the event of a collision is predicted. MiSTA can transmit up to 0.53 packets per time slot and reduce average age of information by 63% compared to slotted Aloha.
Multiple Mini Slotted Threshold ALOHA (MuMiSTA)
In many of the IoT applications, the devices are at a relatively close proximity to the base station and the transmission delay dominates the round-trip time. In such cases, multiple mini slots can be used to fully benefit from the control sequence. In a practical scenario of 5 ms data slots and 10 μs mini slots, data slots can be utilized at a 95% rate. The average age of information is reduced by 79% compared to slotted ALOHA, achieving a very close level of performance to the theoretical upper limit of Round-Robin policy (centralized and by order).
The table below compares the performance improvements of aforementioned policies with respect to the slotted ALOHA.
|Improvement w.r.t. Slotted ALOHA||Threshold ALOHA||SAT||MiSTA||MuMiSTA||Round Robin (theoretical limit)|
|Spectral Efficiency gain||None||None||43%||140%||171%|
|Avg. number of sources in Tx mode in a time slot||0.90||0.36||1|
|Avg. number of sources in Rx mode in a time slot||0.90||1|
 D. C. Atabay, E. Uysal and O. Kaya, “Improving Age of Information in Random Access Channels,” IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS), 2020.
 O. T. Yavascan and E. Uysal, “Analysis of Slotted ALOHA With an Age Threshold,” in IEEE Journal on Selected Areas in Communications, vol. 39, no. 5, pp. 1456-1470, May 2021.
 M. Ahmetoglu, O. T. Yavascan and E. Uysal, “MiSTA: Threshold-ALOHA with Mini Slots,” 2021 IEEE International Black Sea Conference on Communications and Networking (BlackSeaCom), 2021.
 X. Chen, K. Gatsis, H. Hassani and S. S. Bidokhti, “Age of Information in Random Access Channels,” 2020 IEEE International Symposium on Information Theory (ISIT), 2020.