Wireless Access

What is the best practice or recommended distance in between AP to build mesh network? For Aruba AP 228

Do you mean the maximum distance?

Yes, i mean real life environment. 

Since the AP 228 uses external antennas, the max distance will be determined by the antennas chosen and how they are installed.

If use maximum dBi antenna, can up to how many meters?

There is not a best practice or recommendation on maximum distance, as outside environmental issues will play significant role in the overall system performance (antenna installation height, obstructions, etc), in addition to local regulatory restrictions.

There are online link budget tools that can be used to calculate the the receive signal level at a given distance based on radio transmit power combined with the antenna gain. Once you know the receive signal level on the link, the AP288's data sheet (found here: http://arubanetworks.com/assets/ds/DS_AP228.pdf) can help determine what MCS data rate would be possible.

AP-228 with 2m cables or less, should be able to support 3-4mi in PtP with clean RF environment using the ANT-4x4-5314 antennas. Longer antenna cables will result in more loss, and lower distance. If you want numbers, the Outdoor VRD has some graphs to show Rate v Range. If your environment has high noise, if your cables are poor, if your alignment is bad, etc, then all bets are off.

Aruba 228 mesh network is for LNG plant. wireless signal need to cover all the way of the road of the LNG plant.

I have heard the mesh network the distance in between AP can't more than 50 meter or 30 meter. Some said advisible within 50 meter (5GHz radio), if more than 50 meter will be a problem.  Please advise.

How many mesh points are you anticipating in the network? The extra background about the LNG plant deployment helps us to understand the context, and that max distance for a point-to-point mesh link may not be applicable for your use case. Knowing more details; how many APs, expected coverage, bandwidth, etc will help get more meaningful info to you. What are you needing to accomplish?

Why the AP-228 and not the AP-275? Are you requiring C1DX enclosures?

AP-228/275 with 5dBi omnis with clear line of sight can easily support 250-500m spacing between APs in most all environments. Your throughput and latency requirements will ultimately dictate what spacing and how many APs you can support. Note that single channel AP multi-hop mesh has significant per-hop throughput and latency consequences (each 'hop' cuts throughput in half and double the latency). So you need to clearly outline the topology, provide a map with the number and locations of the APs, etc for us to provide any more clarity around what your options are.