Talk:Orthogonal frequency-division multiple access

This is perhaps the lowest quality page I've seen on Wikipedia in some time. It obviously needs to be completely cleaned up. user:209.166.211.66 02:17, 17 August 2005

I have rewritten it. Some illustrations would help. Mange01 13:11, 15 November 2006 (UTC)

Different reader: I would be interested in understanding how OFDMA actually works. A graphic would be nice too. user:212.117.152.156 14:22, 15 November 2006

Perhaps the OFDM explains it all? But that article would also need some illustrations. Mange01 13:11, 15 November 2006 (UTC)

For SOFDMA page is redirected to here. But it's not mentioned at all!!! —Preceding unsigned comment added by Damithad (talk • contribs) 14:44, 8 October 2007 (UTC)

Cell breathing

Per the clarification request; no I don't think OFDMA suffers from cell breathing. In a CDMA system, cell breathing is caused by an increased interference floor as more users start transmitting, so the cell radius decreases. In OFDMA, the users are orthogonal, so the intra-cell interference is constant. Oli Filth^{(talk|contribs)} 14:46, 1 June 2010 (UTC)

Hi Oli. CDMA does not "suffer" from cell-breathing - it is an advantage of CDMA. To my understanding, it is a traffic-adaptive behaviour, making it possible for CDMA cells to easily borrow resources from each other, for example if the traffic load is higher near one basestation than near adjacent basestations.

In 1G and 2G systems, you also had a simple form of cell breathing, based on traffic-adaptive handover thresholds. A cell with low load may grow and attract traffic from the overlap area of adjacent overloaded cells.

OFDMA may be combined with dynamic channel allocation, and then cells can borrow resources from each other in a similar fashion, resulting in a form of cell breathing. Am I right?

Should we remove cell breathing from the list of OFDMA advantages? Mange01 (talk) 15:29, 1 June 2010 (UTC)

Cell-breathing is definitely not an advantage. Cell planning becomes more difficult because effective cell radius is not fixed, and therefore handovers, etc. are not predictable; instead they're determined by the instantaneous loading.

For OFDMA, I don't see how dynamic channel allocation affects intra-cell interference, and therefore how it affects cell radius! Oli Filth^{(talk|contribs)} 16:05, 1 June 2010 (UTC)

Cell breathing in the sense traffic adaptive handover increases the throughput. So from spectral efficiency point of point, it is an advantage. Regarding DCA+OFDMA, I was probably wrong.Mange01 (talk) 20:24, 2 June 2010 (UTC)

Ok, but that's not what people usually mean when they talk about "cell breathing"! Oli Filth^{(talk|contribs)} 20:46, 2 June 2010 (UTC)

Boosted subcarriers

From the image of the OFDMA subcarriers, does this mean, that pilot subcarriers have more power? In Fundamentals of WiMAX on the page 282: "The power in the pilot subcarriers, as shown here, is boosted by 2.5 dB, allowing reliable channel tracking even at low-SNR conditions." This chapter is about OFDMA used in WiMAX, so I think piot subcarriers have more power, than the other subcarriers. — Preceding unsigned comment added by Csolaszol86 (talk • contribs) 01:55, 13 December 2010 (UTC)

Typically yes. Also in OFDM systems like DVB-T, pilot subcarriers are boosted. Mange01 (talk) 16:06, 17 January 2011 (UTC)