Re: 802.16 MAC

On Wed, 30 Jan 2008 08:22:35 -0800 (PST), karthikbalaguru
<karthikbalaguru79@gmail.com> wrote:

>On Jan 30, 4:52*pm, karthikbalaguru <karthikbalagur...@gmail.com>
>wrote:
>> Hi,
>> I find that 802.16 MAC supports both TDD and FDD.
>> But, which is the best option ?
>> Any link/doc that talks in detail about these ?
>>
>
>Is it purely because some countries only allow either FDD or TDD,
>while some allow only FDD ?
>
>Thx in advans,
>Karthik Balaguru

Some operators own spectrum that is split for FDD, and some don't, so
having both available (at least in the standard) covers all bases.
Most equipment will be made to do one or the other, not both.



Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org

On Wed, 30 Jan 2008 10:39:22 -0800 (PST), "PARTICLEREDDY (STRAYDOG)"
<particlereddy@gmail.com> wrote:

>On Jan 30, 10:38 pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote:
>> On Wed, 30 Jan 2008 08:22:35 -0800 (PST), karthikbalaguru
>>
>> <karthikbalagur...@gmail.com> wrote:
>> >On Jan 30, 4:52 pm, karthikbalaguru <karthikbalagur...@gmail.com>
>> >wrote:
>> >> Hi,
>> >> I find that 802.16 MAC supports both TDD and FDD.
>> >> But, which is the best option ?
>> >> Any link/doc that talks in detail about these ?
>>
>> >Is it purely because some countries only allow either FDD or TDD,
>> >while some allow only FDD ?
>>
>> >Thx in advans,
>> >Karthik Balaguru
>>
>> Some operators own spectrum that is split for FDD, and some don't, so
>> having both available (at least in the standard) covers all bases.
>> Most equipment will be made to do one or the other, not both.
>>
>> Eric Jacobsen
>> Minister of Algorithms
>> Abineau Communicationshttp://www.ericjacobsen.org
>
>well, there was this question when linkskog of beceem visited india,
>he delivered a seminar on wimax..there this question was as to why
>preference is to TDD, why not FDD ?. well, there was this clear
>answer, (i dont remember the reasoning now), TDD is most preferable
>for MIMO and beamforming..dspexperts in this group..should let us
>know..as to why MIMO and beamforming go well with TDD and not FDD??
>
>particle (filter) reddy

TDD is a little easier for adaptation because the channel estimated at
either receiver will also be the same channel at the receiver at the
other end of the link (ignoring interference). In other words, the
channel propagation is symmetric in TDD, while it is not in FDD.

So for things like subcarrier adaptation or beamforming this can be
helpful, but, often, the fact that interference is NOT symmetric can
screw that up.

And in FDD it just means that you have to transmit channel information
in a side channel for adapation. That takes up some bandwidth, but
is doable (and I don't know whether 16e accounts for that or not).

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org