Transmit Power Control, TPC ( for discussion)

A WiMax mobile station may use TPC for ensuring link quality and the satisfactory reception of the signal at the base station. It is used to maximize the usable modulation level, which achieves the highest throughput, while at the same time controlling interference to adjacent cells by reducing unnecessary transmitting power. However, the importance of TPC in WiMax mobile standard slightly reduces due to the some advance technologies like Adaptive Modulation and Coding (AMC), Dynamic Link Adaptation (DLA), OFDMA, subcarriers permutation and fractional frequency reuse. Since in WiMax, the users are assigned, few sub-channels, a small fraction of the channel bandwidth therefore the potential cell edge interference problem can easily be addressed by using such sub-channel segmentation and permutation zone instead of TPC.
The mobile unit located at the cell edge is typically vulnerable as it is operating within the sensitivity level, in which case the mobile terminal will transmit at full power so consequently TPC in such location is not applicable. However, if the mobile terminal comes closer to the base station the received downlink SNR will increase and reciprocally the received uplink SNR at the base station will also increase. In this situation, WiMax mobile terminal can reduce its unnecessary transmitting power in different ways: to switch a high order modulation and low order coding rate, or to remain at the same modulation and coding but to decrease the number of sub-carriers through DLA.

It is to my personal experience that a beamforming / adaptive array / smart antenna array ... BS also work the output power. The receivers, most likely all, will not have type of beamforming or smart antenna but will adjust the RF power to the antenna. This could go in negative db gain, ie. -2db ( TX attenuation ) of RF power or could go to a full power to say 30db.
Alcatel - Lucent is an OEM product from Navini, now Cisco and they incorporate those functions as a standard in all BS.

Receiver side: You means the receiver transmit (output) power ranging from -2 dB to 30 dB. Yes, according to the specification this could be right but I am thinking more realistic one. In situation, the receiver can adjust below 20 dB ( let say 18, 15 dB etc). My understanding was as Mobile supports DLA, AMC, OFDMA it is always possible to adjust the link by reducing the number of subcarriers or increasing the number of subcarriers. The trasnmit power is calculated based on per MHz.
What is the typically maximum output power at WiMax mobile terminal (receiver)?

My personal guess, it's more easy and functional to do it on the subscriber ( Changing modulation ), but then again, if for any reason the subscriber signal is not receiving the BS signal in a decent way, I would change the OFDMA QAM to something lower of even QPSK modulation. Power output would also be adjusted. This is where it get complicate. If for any reason you have one weak subscriber, it will affect with out a doubt the total thought put of that BS. Let me be more specific, If the BS sector has capacity for 33Mbps and with in that sector it has a weak subscriber, the base will change modulation, just for that subscriber, the base will transmit the packets and then switch back to, say QAM64. The modulation change for what ever short time it did, say milliseconds, lowered the total thought put of the Base Sector. Then changing the modulation type QAM64, QAM16 or QPSK , you are then changing the total number of subcarriers. This would be in a TDD. The scenario would be different on a FDD.

To answer the question on output power of the subscriber, I would say most will do less than 1 watt 30dBm, AirSpan MiMax 22dBM, ZyXel MAX-200M1 27dBm, Navini RipWave 30dBm, Telsima 3100 20dBm, .... They are all adjustable according to WiMax Specs.

Yes, this is also my understaidng, assuming TDD, transmit power 22 dBm ( to observe the cases the subscriber will reduce the power below 22dBm)

----if a subscriber is located at cell egde or near cell edge or received weak downlink signal, in that case, the subscriber will transmit at full power ( let say 23 dBm) with lower oder modulation ( say QPSK) in order to reduce the sensitivity level.
---- if a subscriber is located at the middle of the cell ( adequate received DL signal), the subscriber switch to higher modulation ( 16 QAM) and transmit at full power ( 22 dBm) [as the sensitivity level will be reduced then therefore no need to reduce the transmit power]- in that case slightly power adjustment may necessary ( 0-3 dB)
- If a subscriber with 16 QAM or 64QAM is located near the base station ( strong received power), then subscriber need to reduce the power becuase it is already using higher order modulation, in that case, it can reduce number of sub-carriers ( bandwidth) in order to adjust the received power. Then trasnmit again at full power

So, power reducing is not so optimistic for WIMax Capacity or networks

How TDD is better than FDD? My undersatding TDD is better than FDD, however, there are some countries may require FDD. But technical point of view, i see TDD is much better than FDD. TDD has one main disadvantage is that it needs proper system-wide syncronization to counter interference.

Speed is the main disadvantage of TDD, Time. If you have the license, spectrum, and money is no object, then with out a doubt I would choose FDD.
All aspects of the payload must very synchronized on TDD. Reusing the same spectrum to transmit different packets at the same time could be done on a TDD but you loose time, time is proportional to speed in networking. If you are into voice, telephony and you have the spectrum use FDD. All real commercial license in the USA are blocks of two pairs, cellular and now data, because of several reason.
How can you have wire line speeds in TDD, .1usec ( 0.1 micro seconds)? You can switch all you want between TX and RX, but the fact is, If it's good switching time, It will always be better in a real full duplex world.
Now, don't get me wrong, the combination of TDD and FDD is great. Satellite data transmission uses a similar type, but because the stationary satellite is so far away it's hard to se the beauty of it. Digital cellular/mobile devices uses something similar, but it's aimed 99% for voice.
I will always say, "If you have the spectrum, and the standard supports it, use FDD", you will get more packets per second".
For the internet world where one downloads more data than it's uploaded then the second block could use a combination of TDD and FDD, but I don't think that's in the new FDD mobil WiMax standard!
Back to the original subject, in a TDD environment, output power must be taken under good consideration in two way TX/RX. In a FDD, from the base to the subscriber, the base could be screaming out and attenuation in the receiver could fix that, but it get more complicated than that and it's a new complex discussion for the RF engineers.
The only problem with FDD at the moment is cost and complexity.

Yes, You are also right from time point of view. However, I should also consider the FDD as FDD already approved in Mobile WiMax. Could you please help me to provide some information concerning the FDD channel bands and UL and DL separations. This there any data where I can find this information.

Actually, I will detect the UL signal ( i will know the UL frequency) and at the same time without detecting the downlink signal I want to know the DL frequency. For TDD is very easy as same channel bandwidth. But how can i preditc DL frequenc by FDD? Do you have any idea? or any relation between DL and UL frequency band/ separation in FDD?. I know it will vary from country to country?

I was going to answer "Look at the block assignment" but like you said, It will vary from country to country. Best practice is to obtain the country regulation for the spectrum you are checking. This could be a challenge in 3rd world country and consider "TOP SECRET"! yeah, right!
In practice get your analyzer, locate a BS, set it to the band, max hold, and wait! This will give you the DL block. Check users (SM), to know who's who.
I've done this, one can actually see the output power control that the devices have. But unfortunately I've done this on a TDD block, I'll wait for the FDD equipment and check it out.

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