I would like to know what is the approved scheduling scheme used in V2V mode 4 (out-of-coverage communications). I have read the 3GPP standards on PHY (update December 2016) and MAC (update September 2016) but what I have been able to grasp does not give me a complete view of the scheme.
In my understanding, upon successful discovery and synchronization of neighboring vehicles, through some unknown mechanism each vehicle self-allocates to itself a set of RBs from a predefined pool of resources in a semi-persistent and distributed fashion. It also seems that the MAC is some sort of TDMA where the synchronization signals are dictated by a vehicle that acts as a master node. From this succinct information I cannot infer how the scheduling algorithm really works.
Can someone please elaborate on the employed scheduling scheme and possibly refer me to the exact parts of the 3GPP standards that discuss this method (although I have already checked)?
Also, I have the following question. In V2V multicast what is the maximum number of supported receivers? Is it 150? I recall this number as I saw it in one of the RAN proposals but I cannot say if this modification was approved.
As far as I know, the scheduling process is no clearly defined by the 3GPP standard for V2V communications at the time. As you state, the current specification establishes that the VUEs have a pre-defined set of resources (resource pool) and can access that pool in a distributed manner. Personally, I don't think this is gonna be de definitive solution, as it would require an access mechanism such as CSMA/CA which is not very efficient. My advice is to check periodically the 3GPP for new updates on specifications series 36 for LTE-Advanced Pro. There should be a new update in the coming days since a new set of specifications is expected from 3GPP RAN 1 (In charge of layer 1, layer 2 specs)
Thank you for your replies Abdullah Bin Shams and Andres Burbano.
Andres Burbano, do you believe that CSMA would be used? Would then the sidelink become more like IEEE 802.11p? What I can infer from the 3GPP specs covering PHY and MAC, a framework to support a time-slotted approach is provided, for example TDMA or MS-Aloha. Synchronization would be dictated by satellite signals.
A solution is presented in the Communications Standard Magazine paper with title: Vehicle-to-Everything (v2x) Services Supported by LTE-based Systems and 5G, providing an SPS (semi-persistent scheduling) used for mode 4 (out of coverage) D2D SL and more likely for mode 3 (in coverage) too.
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