In OFDM the overall network resources are distributed to the users through resource blocks (RB's). Each individual RB is assigned to the user with the highest SINR for that corresponding RB. If that is the case then in still case, a user in the vicinity of the base station (BS), with the required shadow fading, will achieve the highest SINR for all the RB's available for a particular bandwidth and the same will happen for all TTI's . But surely this can't be the case.
Therefore, in OFDM how are the available RB's allocated among the users, such that more than one user receives at least a single RB?
Hello,
the scheduling in LTE is a key issue. There are some allocation method, which take into account the SINR or not, e.g proportional fair or round robin.
You can see this paper:
http://publik.tuwien.ac.at/files/PubDat_221879.pdf
and references therein. Also, matlab code can be found here:
https://www.nt.tuwien.ac.at/research/mobile-communications/vienna-lte-a-simulators/
Vincent
Dear,
In LTE macrocell, the coherence bandwidth of the signal is in the order of 1 MHz. Within the LTE carrier bandwidth of up to 20 MHz there are some sub-carriers that are faded and other are not faded. Transmission is done using those frequencies that are not faded. The transmission can be scheduled by Resource Blocks (RB) each of which consists of 12 consecutive sub-carriers, or 180 kHz, for the duration of one slot (0.5 ms). This granularity is selected to limit signaling overhead. A Resource Element (RE) is the smallest defined unit which consists of one OFDM sub-carrier during one OFDM symbol interval. Each Resource Block consists of 12 · 7 = 84 Resource Elements in case of normal cyclic prefix (72 for extended CP).
For more information about RESOURCE ALLOCATION TECHNIQUES
FOR THROUGHPUT MAXIMIZATION IN DOWNLINK LTE , check this link:
http://www.jatit.org/volumes/Vol58No2/21Vol58No2.pdf
As far as I know, the LTE standard does not describe how the scheduling should be performed. The reason is that every company that builds base stations should be able to select their own optimized scheduling algorithm - which may or may not be better than the competitors' algorithms.
There are many things to take into consideration in the scheduler, such as maximum throughput, SINRs, user fairness, packet sizes, etc.
I would suggest to use some kind of proportional fairness scheduler, which makes sure that everyone gets approximately the same amount of transmission resources. But the users with good SINRs will still get higher data rates out of those resources.
But if I want to allocate RB's then how would I do that? I will use a particular scheduler, once I determine who will receive which RB's. I know that if I allocate 1 RB to a user I will not be able to share it with anyone in the same TTI. Is it that during the same time also I am not allowed to assign another RB to the same user?
You are surely allowed to assign another RB to the same user also. As Emil said, there is no one standardized scheduling algorithm and you may start with some of the state of the art ones like round robin, proportional fair or max throughput etc.
In this paper the author provided an equation to calculate the SINR of individual subcarriers, refer to eq. (1).
Can anyone tell me how to estimate the parameters H and p in the formula?
In practice, you cannot estimate H and p independently, but p(t).H(t) is the instantaneous received power. You can estimate the mean power by averaging over the time, or in OFDM, over a block of received OFDM symbols.
More clearly, if you add a third index (say q such that t = qTs, where Ts is the OFDM symbol duration):
Power = \sum_q |p_{k,n,q}.H_{k,n,q}|2
Hello Vincent,
Thank you for the sensible answer. In a single TTI, do you mean to say that the average power is:
mod( p(k,n) . H(k,n) )2
The instantaneous power can be found from: Pr = Pt - Pl, where Pl is the path loss.
According to the formula instantaneous power is a function of time, p(t)*H(t). If I now simulate for users with velocity (5 Kmph) then I get very similar instantaneous power at all TTI's for a a particular user-RB pair due to similar path losses. But this creates a problem, I end up with same RB's being received by the same users at all TTI's.
Is there something I am missing or should I modify the approach?
I think the average power is rather:
mean(abs(p(k,n) . H(k,n))2),
where p and H are vectors.
From my point of view, the path loss must included in the instantaneous power. But verify this assumption with other colleagues.
In fact, the path loss, as well as the multipath channel, do not vary that much during one TTI, that why block error rate (BLER) are assessed over sereval TTIs. However, I do not clearly understand your problem.
Thank you Vincent. You helped me a lot. I will share further information here once I overcome this hurdle.
Refer to the LTE Visualization tool, which provides the resource block and throughput calculations.
http://www.lte-bullets.com/visualisation_tool.html
Following papers will also help your understanding regarding this topic:
A.B.Shams, S.R.Abied, and M.A. Hoque, "Impact of User Mobility on the Performance of Downlink Resource Scheduling in Heterogeneous LTE Cellular Networks." 3rd International Conference on Electrical Engineering and Information & Communication Technology (iCEEiCT), Dhaka, 22-24 September 2016.
Link: Conference Paper Impact of User Mobility on the Performance of Downlink Resou...
A. B. Shams, S. R. Abied, and M. F. Hossain, "Performance comparison of network layouts with mobile users under different resource scheduling techniques in downlink LTE." 5th International Conference on Informatics, Electronics and Vision (ICIEV), 2016.
Link: Conference Paper Performance Comparison of Network Layouts with Mobile Users ...
- Badges
- Science topic
- Similar topics
- Computer Communications (Networks)
- Simulators