## 2 Related Work
This is the most closely related work with ours, but we notice that to carry the resource reservation in the data packet, a cross-layer cooperation is required between the radio layer and the safety application layer. Our work proposes an enhancement within the currently standardized sensing-based SPS framework. [PERSON] et al. is another closely related work with ours. It evaluated the performance of the SPS as proposed in the 3 GPP specification [32]. To lower the collision probability, the authors proposed a cooperative resource allocation and scheduling solution. In the proposal, each UE informs the others of its resource reselection counter (RC) value and resolve any expected collision by forcibly changing the RC values of the UEs that have the same RC value. By reducing the probability of overlapping the reselection windows of the involved UEs, the authors showed that the average collision rate is significantly lowered. Moreover, they proposed to eliminate the randomness in the parameters such as the probability of retaining the same resource in the next streak, and the RC counter. An important finding in this work is that most collisions prevented by this scheme are caused by newly incoming vehicles to the communication range. A deficiency in this work, however, is that the considered resource use level of 25% is rather low to be considered congestion. Moreover, always reselecting other resource when the RC counter reaches zero could raise the collision probability when the use level is high as we will show in Section 5.2.2. In this paper, we consider various levels of resource use including the severe congestion situations. Also, we attempt to broadcast more specific information as to the location of the next resource to be used by a UE instead of the RC counter. [PERSON] and [PERSON] [33] presented a detailed analysis of the performance of LTE-V sidelink Mode 4 and proposes a modification to its distributed scheduling. This work showed that under heavy congestion, the IEEE 802.11p at a high rate transmission [34] can outperform LTE-V in terms of the PDR. The work noticed the differences in the BSM messages as one source of such poor performance by LTE-V. As a solution to this problem, the authors suggested that no subchannels are reserved for a streak when transmitting the larger and less frequent packets (e.g., 300 bytes). [PERSON] et al. analyzed the effect of the Mode 4 resource pool configuration and some of the key SPS parameters on the scheduling performance and found that the resource reservation interval (RRI) significantly influences packet data rate performance, whereas the resource keeping probability has little effect in dense vehicular highway scenarios [35]. The reason is that when the congestion is severe, there remain only a limited amount of available resources. Due to lack of adequate resources, UEs end up choosing the same resources again and this would be equivalent to maintaining the resource reservation without executing the SPS algorithm. The authors showed that that proper configuration of scheduling parameters can significantly improve performance. They concluded that research on congestion control mechanisms is needed to further enhance the SPS performance for many practical use cases. Our work confirms most of their findings, but contrary to this work, we also find that the resource keeping probability parameter has visible effect in a wide range of congestion as we will show in Section 5.2.2.