The fifth generation (5G) of cellular networks aims at providing connectivity for a large number of applications. To achieve this goal, 5G has been designed considering three main service categories, known as enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communications (URLLC). The target for URLLC support in 5G is to deliver small packets within a short time (up to 1 ms) with high probability of success (at least 99.999%). The support of URLLC, along with other services, brings new challenges that should be addressed. This thesis studies some of the challenges and proposes practical solutions to them.
The research in this thesis considers the resource allocations for hybrid automatic repeat request (HARQ) transmission schemes for the efficient support of URLLC. The HARQ-based transmissions can achieve a high transmission rate while ensuring the communication reliability. It is, however, essential to consider different types of errors for resource allocations. This motivates employing a new link adaptation scheme, which considers jointly the errors of the data and the control channels. Time allocation is another concern for ensuring the end-to-end communication latency for two users operating in cellular mode. Conventionally, the time budget is divided equally and assigned to the uplink and downlink. This approach is not efficient for URLLC due to the stringent latency budget. Instead, two novel time allocation schemes are proposed that outperform the conventional approach. The communication between two users can be facilitated by device-to-device (D2D) communication when they are in close vicinity. The performance of D2D can be enhanced by exploiting the diversity for the data retransmissions.
The design of the control channel is another important topic that is considered. The accuracy of control channels directly affects overall communication reliability. Generally, higher accuracy can be achieved by allocating more radio resources to the control channels. However, this approach can significantly reduce the communication efficiency of URLLC, as the amount of resources for the control channels becomes comparable to that allocated to the data channels. Instead, non-trivial solutions can be exploited to improve the performance of control channels for URLLC support.
Blind-transmission schemes can reduce the communication latency and achieve high reliability without relying on a feedback channel. These are achieved by transmitting replicas of the data message using different resources in both time and frequency domains. The reliability of different types of blind-transmissions are evaluated.
|Translated title of the contribution||Enabling Ultra-Reliable Low-Latency Communications in 5G Networks|
- , Supervisor
- Sassan Iraji, Advisor
|Publication status||Published - 2019|
|MoE publication type||G5 Doctoral dissertation (article)|
- 5G, control channels, machine-type communications, radio resource allocations, ultra-reliable low-latency communication