RE: stds-80220-eval-criteria: Joint UL/DL simulations?
As Farooq's msg says, a joint UL/DL simulation
will capture some important
interdependencies between UL and DL.
Some are traffic related .. DL traffic modified
by UL activity. Some are protocol related ..
any abnormal behavior in delivery of TCP ACKs
on the UL can affect the DL. There would certainly
be PHY/MAC level interdependencies in terms
of multiple access on UL and scheduling on DL.
I am familiar with some DL-only simulations. These were
usually for systems where the DL is the limitation
(highly asymmetric data flow) and the UL constraints
(TCP ACK issues) are knowingly ignored.
I would lean towards a joint DL/UL simulation
if the PHY/MAC, protocol, and traffic model
are to be simulated with good fidelity.
Separate DL/UL may make sense if the simulation
fidelity has already been restricted to some
aspect of the system.
In some sense joint DL/UL seems to be the de facto mode.
If this poses a huge burden, then perhaps
someone should explain why they would
not want to do it.
I would also note that some traffic models have
implicit UL/DL dependencies. There may be no good way
of separating the UL and DL without violating the
spirit of the model. However, in an aggregate sense,
we may get acceptable results with some assumptions.
- Shankar
-----Original Message-----
From: Khan, Farooq (Farooq) [mailto:fkhan1@lucent.com]
Sent: Tuesday, August 05, 2003 11:12 AM
To: stds-80220-eval-criteria@ieee.org
Subject: stds-80220-eval-criteria: Joint UL/DL simulations?
Another issue that I would like to discuss over tomorrow's conference
call is whether the system simulations for the downlink and uplink be
done separately or jointly. We need to determine this in order to move
forward on specifying different simulation models in the Evaluation
criteria.
In the joint UL/DL simulations, both the uplink and downlink are
simulated simultaneously in the same simulation run. Statistics on both
uplink and downlink performance can be collected at the end of the
simulation run. In the joint simulations, both directions of the traffic
are simulations. For example, in case of web browsing application, HTTP
requests would be simulated on the UL and HTTP response on the DL.
Similarly, TCP segments in one direction and the TCP ACKs in the other
direction. This would also apply to any MAC layer signaling etc. For
example, MAC PDUs transmission in one direction and ACK/NACKs in the
other direction.
In the separate uplink/downlink simulations, the uplink and downlink are
simulated in separate simulation runs and statistics are collected from
these separate runs. For example, in case of web browsing application,
HTTP response would be modeled in the DL simulations and HTTP request
separately in the uplink simulations. One of the issues with separate
DL/UL simulations is that some delay/bandwidth and error models would be
needed for the traffic part on the link direction not simulated. Again
assuming a web browsing application, HTTP request delay and error needs
to be modeled on the UL for web browsing simulations on the DL.
The separate UL/DL simulations may provide the benefit of faster
simulation times (separately) because the details of only a single
direction are simulated. However, two sets of simulations would be
needed, one for the UL direction and other for the DL direction. In the
joint simulations, details of both directions are simulated
simultaneously and therefore the simulation run time can be longer. But
the benefit is that a single set of simulations would be required.
Therefore, in terms of total simulation time, both approaches can be
equivalent. However, the joint approach provide a more realistic
scenario and does not require additional delay/error models.
Comments and suggestions are welcome,
Farooq