Frequency Planning
Which is the best plan for frequency reuse in wimax. Moreover how important is the synchronization of BTS.
What kind of equipments -BST do u use TDD or FDD?
"Synchronized TDD"
As PMP networks are built out and carriers obtain a larger mass of customers, channels within each
base station will need to be reused for maximum capacity to serve a growing customer base. Once the
same frequency begins to be reused in a given base station (or FR greater than 1), additional complexities
for RF planning must be considered. Although both TDD and FDD suffer greater interference issues in
this more built-out network, the unique pattern for TDD of base station- base station interference
becomes much more acute. The solution is to implement intrahub and interhub synchronization.
In addition, with TDD, no guard bands are required to separate upstream and downstream frequency
traffic. Usually as much as 200 to 300 MHz frequency separation is needed between transmit and receive
frequencies for cost-effective modem designs in FDD.
I would suggest a BS with 4 sectors, each 90 deg. (180deg. antennas are expensive and difficult to obtain).
What do you meen with "different polarity" - I assume you meen polarization. Is that right?
I also added a pic to explain the frequency reuse plan.
Regards
Harald
Attachments
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FrequencyPlan.JPG, 37 KB
Are you not concerned about working with different polarizations in the same network on one BTS? I think for mobile you should stick to vertical polarization. What planning tool are you using? CINR statistics will be needed to analyze your network performance, deploying this frequency plan.
I have the same doubts like Aleks about separating sectors only by polarization:
Imagine if sector A and sector C are transmitting on the same frequency (even with different polarization) the antenna in sector A with its finit front-to-back ratio will fire also into sector C. This will effect CINR in sector C. The same will happen also on sector A.
Typical values for a 90deg antenna are:
gain: 15.5dBi
hor plane: 90deg
ver plane: 6.7deg
front ot back ratio: 25dB
CINR will be affected considerably, taking into account these typical values.
I have one question a little out if this discussion, but it may be useful. What are the typical values of which I can put between the adjacent frequencies as described in the screenshot? Also, how can I calculate the separation in dB needed between the adjacent carrier frequencies?
I will need it when I input the frequency plan in order to get a correct CINR analysis.
Thank you in advance for your time and consideration.
Kind regards,
Aleks
Attachments
- carriers.JPG, 41 KB
The table gives you an overview how modulation, bandwidth, FEC and minimum receive level are related. Data are derived from Source: WiMAX Forum
Conformance Testing to IEEE Std 802.16-2004—Part 3: Radio Conformance Tests (RCT) for WirelessMAN-OFDM™ and WirelessHUMAN (OFDM)™ Air Interface
Now it is up to you to provide this SNR!
Check your transmit spectrum and then deside how far you have to separate your carrier frequencies.
Kind regards
Harald
Attachments
- SNR.JPG, 71 KB
RX-Selecitivity.JPG, 42 KBin the Specification Data Sheet from a WiMAX Vendor I found that the attenuation from
channel n to channel n+1 (the adjucent channel) is 31dB, and from
channel n to channel n+2 is 50dB.
Well, in all mobile networks I have seen vertical polarization is used. This is based on the specifics of radio propagation in this frequency band and antennas. As you know the propagation method for frequencies above 1800 MHz is reflection, not diffraction. I can send you a document, describing the reasons for what I am saying.
Also, mixing polarization typed in one network is not adviseable, according to my understanding and what I have been taught in university and training courses. And I am pretty sure that vertical polarization is well enough for a mobile network.
Actually, there is no need for a certain polarisation in areas potentially covered with mobile WiMAX, as there is no notable difference in propagation for such small cell footprints. Also, you can't expect any mobile device to operate with only one polarisation. To tackle it, you have various diversity schemes, so called x-polarisation being the most popular in mobile networks. With MIMO, and somewhat elaborated antennas, it is all dealt with in a convenient way,and you don't have to worry about it ;)
the amount of bandwidth you need depends on you services.
What type of services have you planned?
Depending on your type of service for example, latency varies from vendor to vendor within the same configuration significantly.
Our round trip delay measurement results are
Vendor A: min. 28ms, max. 45ms (useful for VoIP)
Vendor B: min. 146ms, max. 509ms (not useful for VoIP, caused by high delay and jitter)
So you have to find out if you can live with it or not.
ATPC:
Automatic Transmit Power Contrrol (ATPC) is a feature that allows the system to self-optimize the transmit power and provide for the best overall link performance. The ATPC function automatically will adjust the output power level of remote-end systems to match a pre-specified signal strength value.
When ATPC is enabled, the system will attempt to establish the wireless link and exchange performance information. Once the wireless link is established, the master-end system will dynamically adjust the remote-end systems transmit power to maintain optimum link characteristics while minimizing power output. In short, ATPC optimizes the transmission power for best operation, while minimizing excess power and interference with other devices.
Practical examples:
Vendor X: BS adjustable from +13dBm to +28dBM, CPE adjustable from -30dBm to +20dBm
Vendor Y: BS adjustable from +22dBm to +35dBM, CPE adjustable from -27dBm to +24dBm
I just wanted to add to my previous message that apart from output power adjustment
the dynamic range of ATPC is around 40dB to 45dB depending on vendors specification.
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