Wimax Books

[chacho.morales]

I am new on the forum, and also new in the art of rf planning, I start working on a new wimax E y D network so i will like to share some books I have.

i hope you like :)

http://www.4shared.com/file/118310125/c4b15d8e/wimaxbooks.html



Add thanks!!!:D

[Mazari]

Good, reputation added

[Mazari]

Does anybody know how is WiMAX being deployed?? for example, is it using the GSM cell concept (different cells use different channels); or a CDMA cell concept??

[wolverine]

Although it is possible to have a frequency re-use of 1 in a WiMAX network it will lead to interference issues at the cell edge. In order to overcome this a typical deployment will use the same sub-carriers at the centre of the cell but different sub-carriers at the cell edge. Although this will lead to less bandwidth being available it overcomes the interference problem.

The same technique will be used in LTE networks as well as LTE is based on OFDMA as well.

[chacho.morales]

Although it is possible to have a frequency re-use of 1 in a WiMAX network it will lead to interference issues at the cell edge. In order to overcome this a typical deployment will use the same sub-carriers at the centre of the cell but different sub-carriers at the cell edge. Although this will lead to less bandwidth being available it overcomes the interference problem.

The same technique will be used in LTE networks as well as LTE is based on OFDMA as well.

Markos: I have a question regarding the image, each circle represent on BTS ( Base Station)? this is a cell site?

I ask you this because the wimax network that I Work each BTS work only with one OFDMA Carrier, maybe I understand wrong you explanation, can you explain a little more about the center and edge of the cell..

:)

[Mazari]

What do you mean chacho?? Each BTS uses a unique set of frequencies??

Thanks Markos for the explanation...the way I understand is that each circle is a BTS. At the center of the circle the same carriers are used at a lower power lever then different carriers are used at maximum power for the cell edges to avoid co-channel interference.

[chacho.morales]

What do you mean chacho?? Each BTS uses a unique set of frequencies??

Thanks Markos for the explanation...the way I understand is that each circle is a BTS. At the center of the circle the same carriers are used at a lower power lever then different carriers are used at maximum power for the cell edges to avoid co-channel interference.

Let my explain a little more (sorry if I don't use a good English, isn't my native language), you have a Cell Site, it has 3 BTS on It, Each BTS use a carrier ( for me Carrier is a Frequency (F), like 3,575 Mhz). so you have for BTS1= F1, BTS2=F2 and BTS3=F3.

because the coverage of the BTS are Aprox 1 miles, you can re-use the frequency in other Cell site on the network, but not the neighbor cell site of the one you already use. ( the BTS from cell site 1 can't use the same frequency from the BTS cellsite 2).

When the CPE (receiver) is near the BTS they use a high modulation 64QAM, and when the cpe is at the edge they use a low modulation QPSK, an also the BTS change the PA Power from the Lowest modulation and the highest for the edge.

the difference between the LTE and the wimax is the Return of the CPE, on LTE they use SCFDMA and wimax OFDMA, but both use OFDMA in the downlink.

[wolverine]

Yes, each circle represents a cell.

See below for some more info on the subject taken from Wireless Moves..

The air interface of next generation wireless networks such as WiMAX is based on orthogonal frequency division multiple access (OFDMA). This technology divides a channel into many sub-channels which can be used by several terminals independently at the same time. Fractional frequency re-use, which I describe in more detail below, can reduce interference caused by neighboring base stations using the same frequency block and can thus help to increase user throughput and overall network capacity.

Due to the limited frequency bands available and the high bandwidth per cell (e.g. 5 or 10 MHz) of future wireless broadband networks, base stations of an operator use the same frequency band. Using the same frequency band for all base stations, however, creates interference for subscriber terminals when they receive signals from more than one base station at a time. This is the case for example for a subscriber located just in the middle between base station A and base station B. If the subscriber listens to base station A, the signal of base station B is seen as unwanted interference. Thus, from the point of view of the subscriber, the output power of base station B should be as low as possible in order to create as little interference as possible. For another subscriber in a similar location but listening to base station B the situation is just the opposite. Thus, a compromise has to be found to adjust the output power of the base stations to a value which enables subscribers at the cell edge to still communicate at a decent speed while not creating too much interference in neighboring cells.

For distant subscribers a base station has to use more transmission power in order to reach them. Subscribers close to the base station on the other hand require much less transmission power to receive the signal. As client devices only transmit and receive on some but not all sub-channels of the frequency band, transmission power of sub-channels used by clients close to a base station can be lower than the transmission power of sub-channels used by clients at the cell edge. In practice, the reduced transmission power for sub-channels used by clients close to a base station thus creates less interference for users close to other base stations.

Using a combination of high and low power sub-channels can be exploited to increase the overall capacity of the network compared to networks which use the same transmission power for all sub-channels. Base stations can be organized in a way to use the same set of sub-channels to serve subscribers close to them with a low transmission power. The rest of the sub-channels are used with a higher transmission power and can be used by both distant and close subscribers. To minimize interference of high power sub-channels for clients of neighboring base stations the cells are further organized in a way that two adjacent cells do not use the same high power sub-channels. Thus, both close and distant clients of a base station will not see the high power sub-channels of a neighboring base station as interference. This approach is known as “fractional frequency re-use” (FFR) as all base stations use the same frequency band, the same low power sub-channels, but only a fraction of the high power sub-channels.

It is worth to note that fractional frequency re-use can not be used in UMTS, as all subscribers use the complete bandwidth instead of sub-channels. Thus, OFDMA networks implementing FFR suffer less from interference problems which translates into higher spectral efficiency compared to UMTS, i.e. the overall bandwidth available in the network is higher.

[chacho.morales]

this a Better explanation and a good one, thanks, all the knowledge i can learn for me at this moment is good, i came from Ip network and for me all this is new. thanks again.

[dexterhaba]

so we also make freq plan for Wimax,, as explained above ,, how about the important parameters of a cell? is it distinguished like CID in GSM and Scrambling code in WCDMA? Please help,, thanks...

[dsdd]

Wimax uses preamble index.



so we also make freq plan for Wimax,, as explained above ,, how about the important parameters of a cell? is it distinguished like CID in GSM and Scrambling code in WCDMA? Please help,, thanks...

[dexterhaba]

Wimax uses preamble index.

Hi there,, can you expound the planning of preamble index,, thanks.....