[e2e] Opportunistic Scheduling.

Detlef Bosau detlef.bosau at web.de
Wed Jul 11 14:05:15 PDT 2007

ksingh at irisa.fr wrote:
> PF scheduler allocates equal share of time slots to all users over long
> term. At the same time it tries to be channel adaptive. Ofcourse, there
> are some assumptions for e.g. it may not hold if a user is moving at 3kmph
> and the another user is moving in car at 90kmph.
> You may look at this paper by Borst:
> http://ftp.cwi.nl/CWIreports/PNA/PNA-R0223.pdf
> Among other interesting results like why a strategy "like PF" is optimal,
> on page 5 you will see that a user gets 1/M time slots by symmetry.
> M is the number of users.

I have a longer answer in preparation. But in the Borst paper, I just see:

"We assume that the feasible rates for the various users vary over time 
according to some stationary discrete-time stochastic process fR1(t); : 
: : ;RM(t)g, with Ri(t) representing the feasible rate for user i in 
time slot t."

The key word is "stationary".

One _can_ make an assumption like this.

However, this does not matsch reality.

It is of course possible  for many propositions to find scenarios where 
the proposition holds. And perhaps we can write those as customer´s 
duties and customer´s responsitibilies in the terms and conditions of 
network operators ;-)

In addition, the paper seems to discuss the distribution of rates. Does 
it discuss, whether a channel is in its local optimum state? Please keep 
in mind, that the C/I ratio exhibits a periodic behaviour.

However, I will have to read the whole paper, which will take some time.

With respect to your very claim, that the sending time is shared in 
equal portions to all channels in the long run, this is plausible when 
the vector of feasible rates moves to some stationary process. However, 
at least at the moment I´m not convinced that this will hold in the 
general case.

Simply spoken: The more I read about HSDPA, the more questions I have 
and the less convincing this whole stuff appears to me.

And the more I read about it, the more rises my strongest objection: 
HSDPA is an excellent example for what Dave Reed critcized here in the 
list: My impression is that there is by far to much complexity and 
"intelligence" in the HSDPA link layer.

Particularly, from an end to end perspective, a link layer should be 
simple and clearly structured.

Just one observation, I made yesterday: In HSDPA, the shared downlink is 
split up into 16 channels using CDMA, 15 of which are used for data 
transport. And a maximum of 4 terminals may be served in the same time 
slot. I don´t yet understand the reason for this. But I see a large and 
complex scheduling algorithm.

Simply spoken: From many posts here in the list, particularly from those 
by David Reed, I learned that networks (and not only networks) shall be 
kept small and simple. When I see HSDPA, this appears to me large and 
complex :-)


Detlef Bosau                          Mail:  detlef.bosau at web.de
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