Grandstream Networks GWN7610 Quick reference guide

Grandstream Networks, Inc.
GWN7610/GWN7600/GWN7600LR
Wireless Access Points
Deployment Guide
GWN7610
Enterprise 802.11ac
WiFi Access Point
GWN7600
Mid-Tier 802.11ac Wave-2
WiFi Access Point
GWN7600LR
Outdoor Long Range 802.11ac
Wave-2 WiFi Access point

DP750 User Manual
Table of Contents
OVERVIEW.....................................................................................................................4
WLAN Technical Features .....................................................................................................................4
WLAN Product Introduction ...................................................................................................................4
WLAN PLANNING AND DEPLOYMENT .......................................................................5
The Importance of Planning...................................................................................................................5
How to Plan Deployment .......................................................................................................................6
First Step: Plan Efficient Channel Multiplexing and Minimize Channel Sharing ............................6
Second Step: Improve the Air Interface Efficiency in a Single Channel Coverage Cell.................8
Significance of Radio Signal Parameter ................................................................................................9
SNR (Signal-to-Noise Ratio).........................................................................................................10
Channel Utilization........................................................................................................................12
Impact of Client Performance ..............................................................................................................19
How to Deploy with 802.11ac...............................................................................................................22
Advantages and Features of 802.11ac.........................................................................................22
How to Deploy with 802.11ac Wireless Products .........................................................................26

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Table of Figures
Figure 1: Positions of Access Points deployed on the Floor Plan ................................................................5
Figure 2: Schematic Diagram of Efficient Channel Multiplexing ...................................................................7
Figure 3: WiFi SNR APP ............................................................................................................................. 11
Figure 4: Acrylic Wi-Fi Professional Software .............................................................................................12
Figure 5: Channels overlapping on the 2.4GHz..........................................................................................14
Figure 6: GWN SSH Menu..........................................................................................................................14
Figure 7: Band utilization.............................................................................................................................15
Figure 8: External interference caused by other wireless appliances ........................................................16
Figure 9: Control cellular size of the AP by lowering the transmission power ............................................18
Figure 10: Required SNR value in the 256QAM modulation mode ............................................................23
Figure 11: 5GHz channel numbers and distribution maps (GWN US model).............................................24
Figure 12: Diagram of downlink transmission of SU-MIMO and MU-MIMO ...............................................25
Figure 13: SU-MIMO Omnidirectional antenna vs MU-MIMO beamforming ..............................................26
Figure 14: 2.4G Channel Distribution map..................................................................................................28
Figure 15: Spectrum of the 20MHz channel ...............................................................................................28
Figure 16: Spectrum of the 40MHz channel ...............................................................................................29
Figure 17: 5G primary and secondary channels .........................................................................................30
Figure 18: Selection of 5G 20MHz primary channel ...................................................................................35
Table of Tables
Table 1: GWN76xx Features and Applications..............................................................................................4
Table 2: Transmission power of some smart phones..................................................................................20
Table 3: 802.11ac implementation speed boost factors ..............................................................................22
Table 4: Signal and energy detection threshold for the primary and secondary channels .........................31

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Grandstream Wireless Product Deployment Guide
OVERVIEW
WLAN Technical Features
The growth of WLAN technology began in the mid-1980s, and its technical standards were mainly
developed by the IEEE 802.11 working group. So far, the group has successively introduced many
standards such as 802.11a/b/g/i/e/k/n/ac, and those standards has been perfected in terms of user
bandwidth, wireless security, and manageability.
According to the latest commercial 802.11ac standard, the WLAN physical bandwidth can theoretically
reach 1.7 Gbps. Currently, 802.11ac mainstream products can achieve a bandwidth of up to 866 Mbps (2
spatial streams) / 1.3 Gbps (3 spatial streams), and the APs with 802.1ac support have become the first
choice for WLAN deployment.
This document describes the problems encountered in the deployment of 802.11ac enterprise-class
wireless networks and provides solutions from the perspective of 802.11ac technical details.
This document applies to people: enterprise wireless network integrator, wireless network operation and
maintenance administrator.
WLAN Product Introduction
Grandstream offers 802.11ac series wireless products, including GWN7610, GWN7600 and GWN7600-LR
product features and applications as shown in Table 1 below:
Table 1: GWN76xx Features and Applications
Product
Model
Indoor/Outdoor
Feature Description
Application
GWN7610
Indoor, ceiling
installation
Support 802.11ac-wave1
Dual-band 3x3:3 MIMO, up to 1.75Gbps
Support 802.3af and 802.3at Power-over-
Ethernet (PoE/PoE+)
Indoor installation for
enterprise office,
hotel, and etc.
GWN7600
Indoor, ceiling
installation
Support 802.11ac-wave2
Dual-band 2x2:2 MIMO, up to 1.27Gbps
Support 802.3af and 802.3at Power-over-
Ethernet (PoE/PoE+)
Indoor installation for
enterprise office,
hotel, and etc.
GWN7600LR
Outdoor, pole
installation
Support 802.11ac-wave2
Dual-band 2x2:2 MIMO, up to 1.27Gbps
Support 802.3af and 802.3at Power-over-
Ethernet (PoE/PoE+)
Outdoor installation
for squares, park and
etc.

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Grandstream Wireless Product Deployment Guide
WLAN PLANNING AND DEPLOYMENT
The Importance of Planning
With the tremendous growth of WiFi clients and mobile Internet applications, wireless LANs have evolved
from pursuit of connectivity and coverage to the goal of high-capacity access.
High capacity is meant to support as many wireless clients as possible, and guarantees the experience of
its key business applications. This is not easy to do.
The process of wireless network deployment as planning → construction deployment → network
optimization → operation and maintenance is very different from our previous experience on the wired
network. In the actual deployment, there is such a typical case:
Figure 1 is a floor plan of an Internet company (totally they have 3 floors), each floor has about 100
workstations, each station uses 2-3 terminals, including smart phones, APP tests and office laptops, etc.
By conservatively estimation, there could be 250 terminals per layer.
The company requires wireless deployment for all office phone and laptops, and requires seamless
roaming. In order to achieve the strongest signal coverage, the administrator deployed access points with
full coverage of all workstations (shown by red dots), and added access point installation for outdoor
terraces, elevator halls and corridor (shown by blue dots).
As the result, Wi-Fi signal strength can be detected with over -50dBm at any location on this single floor.
Figure 1: Positions of Access Points deployed on the Floor Plan

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Before the network deployment is delivered, people ran test at night time after work, and network speed
can always reach to the full speed of their ISP bandwidth.
However, after the wireless network is put into use at daytime, the user experience is unexpected terrible,
and employees continuously complain the slow network. However, the measured export bandwidth
utilization on the ISP router is low. So, what is the problem?
Signal strength (dBm) is the basic requirement for guaranteed service. However, the service is not
guaranteed to be good, even the signal quality is strong. Signal strength will finally be converted to SNR
(signal-to-noise ratio, ie the difference between signal and noise, in dB), and then reflect on user
experience.
How to understand the signal-to-noise ratio? For example, when you are at home, you can talk softly and
whispering, but in a pop concert, you have to talk loudly to the person even next to you. The reason is,
often times, and even if the signal is strong, but the background noise is also high, communication is still
hard. Even more, this company has three floors, and all floors are deployed in a high density, while no RF
power and channel planning were done!
When the network is put into operation, where does the noise come from?
Some of them come from some wireless devices, such as microwave ovens, Bluetooth phones, and non-
Wi-Fi co-frequency networks such as frequency hopping wireless networks, and radar interference, but
many of them are derived from the "Friends Wi-Fi Network" and the system in the system. The same-
frequency and adjacent-frequency interference of the manufacturer's Wi-Fi network can also be subdivided
into inter-AP interference, inter-terminal interference, and interference between terminals and APs,
especially in multi-user and multi-path environments.
How to Plan Deployment
How to carry out reasonable planning and design?
For wireless LAN, the key is to increase the channel multiplexing efficiency and air interface utilization
efficiency, thereby reducing media competition and radio frequency interference. The specific operation
requires two steps:
First Step: Plan Efficient Channel Multiplexing and Minimize Channel Sharing
What is channel multiplexing?
Channel multiplexing is the use of non-overlapping channels for coverage to reduce the behavior of co-
channel interference. Since the wireless spectrum resources are not infinite, it is necessary to use the
channel (or channel combination) multiple times when implementing full coverage of the wireless network
in enterprise deployment.

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In the United States, for example, there are only 3 non-overlapping channels (CH1/CH6/CH11) in the 2.4
GHz band, and the resources are more abundant in the 5 GHz band. Under normal circumstances, there
are 9 non-overlapping channels, respectively CH36/CH40/CH44/CH48, and CH149/CH153/CH157/
CH161/CH165.
However, in a high-density deployment, more than usual numbers of APs are required to offer connection
to a large number of clients in a certain area.
In this case, efficient channel multiplexing is basically impossible to achieve on the 2.4GHz spectrum and
can only be realized at 5 GHz with rich spectrum resources. Therefore, in a high-density environment, in
order to improve the user experience, the 2.4G frequency band is often shut down to prevent user
access.
Figure 2 below is a schematic diagram of efficient channel multiplexing. AP1 and AP2 use the same
frequency CH42 channel (that is, the center channel frequency of the 80MHz channel width). If the two APs
can detect each other, they share the same channel and cannot transmit data at the same time.
However, the coverage of the two APs does not overlap, so the two APs will not hear each other. Therefore,
the client connected to AP1 and Client2 connected to the same frequency of AP2 can simultaneously send
to their respective APs. Data does not affect each other.
This picture down below is also a good example of channel multiplexing. In real deployment, channel
usages should be planned in such principle.
Figure 2: Schematic Diagram of Efficient Channel Multiplexing

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How to achieve an efficient channel multiplexing of dense microcells deployment? There are few methods:
•Control the transmit power of the AP on a minimum level, as long as AP transmit power can cover
the size of the planned cell.
•Turn off low data rates support, that is turning off 1, 2, 5.5, 11Mbps (without 802.11b) data rates. In
a scenario where it is particularly necessary to control the size of the coverage cell, in addition to
turning off the 802.11b rate, the number of 11ag management frames is limited to a minimum of 18
Mbps (or even 24 Mbps). It is actually limiting the AP's cell size by controlling the lowest data
connection rate (this feature will be supported in GWN future version).
It should be noted that this feature will affect the connection efficiency of clients from a distance away of
the AP. This should only be considered when deploying the network at a high-density case without far
distance connection requirement. Generally, the Wi-Fi network does not need to do this.
•In some specific scenarios, we can use buildings (eg, concrete thick walls, elevator shafts, pillars,
or natural partitions such as large landscapes) to control the main lobe energy radiation of the
wireless channel and let unintended direction of the target's wireless energy attenuates rapidly, in
order to complete the efficient multiplexing of the channel, prevent the omnidirectional antenna
from spreading the signal everywhere, and reduce the possibility of co-channel interference.
Second Step: Improve the Air Interface Efficiency in a Single Channel Coverage Cell
To improve the efficiency of the air interface is actually to establish a higher data rate connection between
the client and AP.
The client does not always establish the highest data connection rate anywhere within the coverage cell.
Since 802.11 protocol dynamically adjusts the data rate established between client and AP to adapt the
changing wireless environment. The farther the client is away from the AP, the lower the data rate can be
established. Modulation mode always considers redundancy prior to performance.
Therefore, the most important thing for this case is to examine the location and behavior of target clients,
and plan a reasonable AP installation place, so that clients can get as close as possible to the AP.

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Grandstream Wireless Product Deployment Guide
Significance of Radio Signal Parameter
Wireless networks have been closely integrated with people's lives, work, and entertainment. However,
users of WLAN wireless networks may think that wireless network should have the same stable as wired
networks.
In fact, evaluating the performance of a wireless network is very different from evaluating the performance
of a wired network. For example, if your laptop is connected to a wired network switch through a network
cable, the data connection rate between the links is 1000Mbps, then you will use the performance test tool
to test the throughput of the physical link will basically get the same result, the physical layer efficiency is
above 90%, and very stable. However, if your laptop is connected to the AP wirelessly, the data rate of the
link may show 1300Mbps, but what the result will be if you run a throughput test tool?
You may only get about 65%, and this throughput result is only based on 1 on 1 connection between AP
and client. As the number of terminals/clients increases, the aggregate throughput of all clients will continue
to decline. The reasons for this phenomenon are:
1. Objective factors such as unstable and unreliable air media;
2. The wireless network uses the CSMA/CA mechanism for access, and data collision and access
retreat are common events;
3. The MAC layer uses an acknowledgment mechanism so that data retransmission is inevitable;
4. In order to be compatible with old terminals such as 802.11a/n, the physical layer design increases
the overhead of the leader
The 802.11 protocol exchanges a large amount of system overhead for reliability of the data transmission.
In addition, the diversity of the clients will also cause a huge difference in system throughput.
Let’s say we have an 802.11ac supported AP with three spatial streams is deployed on the 80MHz channel,
and when the client also with three spatial streams (usually a laptop) connected, a 1300 Mbps connection
data rate can be negotiated. But when a client (a smartphone or tablet) with single spatial stream connects
to the AP, you can only establish a connection with data rate of 433 Mbps. Obviously, the huge difference
in peak throughput between the two will affect the performance of the entire system.
In short, to ensure the performance and user experience of the wireless network. Its planning, design, and
maintenance are very different from wired networks. So what parameters or key factors we need to focus
on in wireless deployment?

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SNR (Signal-to-Noise Ratio)
For the client, the most important indicator to evaluate its performance is the signal-to-noise ratio (SNR).
Following SNR, we can focus on the received signal strength and retransmission rate.
The signal-to-noise ratio is the difference between the signal and the noise floor. The larger the difference
is, the better the signal quality will be. For example, if a client receives a signal strength of -65dBm, while
the noise floor is -92dBm, the signal-to-noise ratio is -65dBm-(-92dBm)=27dB.
If the received signal strength of the client is -60dBm, the noise floor is -80dBm, and the signal-to-noise
ratio is -60dBm-(-80dBm)=20dB. Although the received signal strength of the second example is stronger,
its signal quality is poor.
We often encounter a misunderstanding that the stronger the signal, the better the signal quality, which is
a wrong impression. The stronger signal does not necessarily mean a better performance, and at the same
the noise is often stronger. The result is poor signal-to-noise ratio and poor signal quality.
It’s SNR that determines what channel bandwidth can be used, how many spatial streams, and what
modulation method is going to be used. All these will determine the data rate of your connection. That is,
the use of 80MHz channel width requires a much higher signal-to-noise ratio than the 20MHz channel width.
Establishing three-space stream communication requires a higher signal-to-noise ratio than establishing a
single spatial stream. And the same applies to the modulation method upon SNR requirement.
Furthermore, to establish a high data connection rate for traditional 802.11a/g clients and APs, 20 dB of
SNR is generally required; 25 dB is required for 802.11n; and 30 dB or more is required for 802.11ac.
In general, you can follow the following guidelines to determine your SNR number readings:
1. SNR > 40 dB, signal quality is excellent, client can always associate with AP, and the highest data
connection rate can be established;
2. SNR between 25-40 dB, signal quality is good, client can always associate with AP to establish a
high data connection rate.
3. SNR between 15-25 dB, signal quality is OK, client can always be associated with AP, and a good
data connection rate can be established;
4. SNR between 10-15 dB, signal quality is fair, client can be associated with AP but with a low data
connection rate;
5. SNR between 0-10 dB, signal quality is poor, client and AP can hardly associate each other.

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How to effectively achieve high signal-to-noise ratio?
It is obviously not a good idea to simply increase the AP transmit power. The non-overlapping channels (or
channel combinations) are limited. If more APs are deployed and the signal strength is increased, the
chance of same-frequency interference will be increased. As a result, the overall network performance will
be reduced. So, the most effective way is to reduce the noise.
Here is something you can consider:
•For the impact from neighborhood Wi-Fi, it is necessary to record the installation location of those
access point, channel distribution, channel bandwidth and coverage field. All this will be used for
your planning reference to avoid their interference.
•Plan and design your own network. Plan the installation location, channel frequency, and
bandwidth, and transmit power accordingly. The goal is to avoid co-channel interference and
adjacent-frequency interference.
•For interference from non-WiFi devices, use spectrum scanning equipment to discovery and
remove them if necessary.
•Run survey after deployment and do optimization accordingly.
Some third-party cellphone app can be used to measure SNR: WiFi SNR.
Figure 3: WiFi SNR APP

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Besides, Acrylic_WiFi_Professional is a Windows software to run measurement through your PC/laptop:
Download link the software: https://www.acrylicwifi.com/en/wlan-wifi-wireless-network-software-tools/wifi-
analyzer-acrylic-professional/wifi-network-scanner-windows/
Figure 4: Acrylic Wi-Fi Professional Software
Channel Utilization
For coverage cells formed by APs, the most critical indicator for assessing their performance is Channel
Utilization. Channel utilization reflects the busyness of the RF spectrum and the overall availability of the
AP channel. Channel utilization is generally expressed as a percentage, and the larger the percentage
value, the busier the channel. A channel utilization below 40%-50% indicates that the network performance
is within an acceptable range.
The reason why channel utilization is important is that the channel utilization reflects all the influence of co-
channel interference, adjacent-channel interference and non-WiFi network interference on the AP's current
channel. It also reflects the intensity of media competition and data transmission in the channel. This is a
comprehensive indicator. When channel utilization is high (>70% or more), this channel is too crowded.

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Grandstream Wireless Product Deployment Guide
1. Where does channel utilization come from?
First, Wi-Fi client’s data transmission will occupy channel. The larger the data packet to be sent, the longer
the time that the sender occupies the channel. Also, the slower the transmission rate is, the longer the time
that the sender occupies the channel.
When the client is away from the AP, for example on the edge of the cellular coverage, the data negotiation
rate drops to a lower value in order to compensate for the degradation of the signal strength. Although, this
helps to improve the reliability of packet delivery, at the same time, it reduces the throughput of the device
and results in an extra air time consumption, which cuts the air time that can be used for higher speed
device transmission.
Therefore, if you want to improve channel utilization, effort of establishing a high data connection rate
between the client and the AP is important.
Secondly, as the demand for high capacity wireless network, high density usage of APs and client devices
causes more same-frequency interference and adjacent-channel interference. The channel utilization of
this channel will also increase.
•Co-channel interference
When an AP is deployed on a particular channel, this AP will compete for the usage of the channel with all
other Wi-Fi devices on the same channel within its radio range. However, Co-channel interference is
relatively manageable compared to adjacent-frequency interference.
APs on the same channel can "hear" each other's signals and will have to compete for transmitting on the
channel. This limits the throughput that each AP can provide. What we need to do is to lower the signal
impact between APs with a reasonable planning so that they do not affect the AP's Clear Channel
Assessment (CCA) process
•Adjacent frequency interference
The neighbor channels on the 2.4GHz spectrum overlap with each other, and the adjacent channel
interference on the 2.4GHz spectrum is particularly serious. The transmission of data on channel CH1 is
unreadable for the adjacent channel CH4, which is equivalent to garbled (noise), and this will increase the
background noise of CH4.

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Figure 5: Channels overlapping on the 2.4GHz
The adjacent channel interference in the 5GHz spectrum is mainly reflected in the interference between
channels of different channel widths.
•Non-WiFi Interference (Other wireless appliances)
Non-WiFi Interference can come from Bluetooth devices, microwave ovens, digital enhanced cordless
communication (DECT) phones, surveillance cameras, or any other device that uses the same RF
frequency as the Wi-Fi channel but does not use the 802.11 protocol. This can also greatly increase channel
utilization.
2. Where does channel utilization come from?
The channel utilization of 2GHz and 5GHz can be extracted through the GWNmenu program as follows:
a) SSH login by WebUI user name and password. After login, "GWNmenu" will be shown as Figure
6 down below;
Figure 6: GWN SSH Menu

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b) Enter “9” to select Maintenance. After entering the page, enter “99” again, select “[99] Band
Utilization”, wait for 10~15 minutes of channel scan time, and get channel utilization of 2GHz and
5GHz support channels. Rate information, as shown in Figure 7 below.
Figure 7: Band utilization
•Non-WiFi Interference (Other wireless appliances)
Specify the channel to view its utilization in real time. It can also indicate the wireless rate used by the
802.11 frame in the current channel. When the low-speed frame is large and the channel utilization is high,
the external interference problem needs to be considered.

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Grandstream Wireless Product Deployment Guide
Figure 8: External interference caused by other wireless appliances
3. How to reduce high channel utilization
Usually, channel saturates when utilization is between [40%, 50%]. In this range, wireless network is still
OK for most applications. But for latency-sensitive applications, such as VoIP, channel utilization above
30% may affect the user experience.
In general, the main methods to reduce high channel utilization are:
1. Reduce the number of total SSIDs
Each additional SSID in the wireless network will bring a lot of air interface overhead. For example, if an
SSID is enabled on an AP, the SSID has an own beacon frame plus its other management frames. The
expense of occupying the channel is about 3% at a data connection rate of 1 Mbps. If an AP enables 3
SSIDs, the expense of the 1Mbps data connection rate will rise to about 9%. When you continuously cover
the network, if the AP is in a contention collision domain with the co-channel AP, the channel utilization rate
will be as high as 27%.
In addition, another reason for reducing the number of SSIDs is that some clients cannot handle a large
amount of SSID information due to their own limitations. These devices may be locked during scanning a
large number of SSIDs, and results in an association failure with targeting wireless network.

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2. Turn off the low rate connection (feature pending on GWN APs)
When the client is far away from the AP, the data connection rate is reduced by one or several levels, which
causes same data amount will consume a longer period of time, and a higher channel utilization. Forbidding
the low data rate force the wireless client to roam to a nearby reliable access point, so that this wireless
client can communicate in a high data rate, which will reduce the channel utilization when same amount of
data is transmitted.
The data rate determines the expense of the management frame occupied by the beacon. An example of
same amount of data transmission. If the data rate is 1 Mbps, the channel expense is about 3%. If the
data connection rate below 6 Mbps is turned off, and negotiated speed increases to 6 Mbps, the channel
expense reduces to about 0.6%. Furthermore, if the data connection rate below 12 Mbps is turned off,
then expense will be about 0.3%.
3. Access control of clients and applications
High channel utilization also reflects the number of clients and application behavior.
If the client uses P2P software, it may results in a higher channel utilization than browsing simple web
applications. These can be limited by features such as "client speed limit"
4. Adjust the size of AP radio coverage cell
Adjusting the AP's cell size can be achieved by reducing the transmit power of the AP or by forbidding the
low-speed management frame. Reducing the transmission power of APs can reduce the visibility, and
mutual interference between APs, and indirectly reduce the channel utilization for neighbor APs on the
same channel. Another benefit of lowering APs’ transmission power is to balance the uplink and downlink
signal strength. Usually AP’s downlink signal is much stranger than mobile end device’s uplink, and this will
cause a phenomenon that mobile device can hear AP while AP can’t hear mobile device.
Another function of "turning off the low connection rate" mentioned in previous paragraph can also
effectively control the cellular size of the AP. The figure below is an example:

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Figure 9: Control cellular size of the AP by lowering the transmission power
In this scenario, the access point has the connection rate below 24 Mbps closed. (18 Mbps and 24 Mbps
are relatively stable connection rates. Please do not close it in real deployment.) By standing at the
position of -80dbm, the probability of beacon being detected is reduced by a lot. So, it reduces the range
indirectly. However, this feature will affect the client connection from the coverage edge and is only
suitable for high-density AP deployment scenarios.
5. Planning of channel multiplexing
Efficient channel planning, by avoiding the co-channel and adjacent channel interference, can greatly
reduce the channel utilization of the working channel (see the section on co-frequency interference and
adjacent-frequency interference mentioned above).
6. Eliminate illegal devices or non-Wi-Fi devices in the same spectrum
Non-WiFi Interference is hard to eliminate during wireless network planning and designing, and it is also
difficult to find, usually by capturing packets or spectrum scanning.
In real situation, you can first test in a near-end and then far-end for a throughput value. In the case of low
throughput or abnormal fluctuations, make a comprehensive judgment of the integrated SNR and
Channel Utilization data, and run wireless capture, if necessary, to confirm.

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Grandstream Wireless Product Deployment Guide
Impact of Client Performance
When designing and deploying and verifying wireless networks, we often focus only on the capabilities of
offered wireless network on APs’ side and ignore the very important element of the wireless network - the
wireless client.
Therefore, we must consider the capabilities and device behavior of target Wi-Fi clients when designing
and deploying and verifying wireless networks.
The main differences in client capabilities (example):
•Does the client use a built-in network card or USB?
•Does the client support 2.4 GHz and 5 GHz dual bands?
•Which of 5 GHz channels does the client support?
•Client transmission power.
•Client receiving sensitivity.
•Does it support 40MHz, 80MHz channel width?
•The number of antennas for sending and receiving on client, and the number of supported spatial
streams.
•Client antenna gain, antenna installation position.
•The number of the client can scan.
•Client support for air interface encryption?
The main differences in client behavior (example):
•Algorithm to select AP on initial connection?
•Roaming decision algorithm?
Among all these, the most related factors that need to be consider during Wi-Fi deployment planning is
client's transmission power.
Considering limited battery life of mobile device, the wireless client's transmission power is usually set to
low. In addition, the size of the wireless client is very small, which limits the space for antenna very much.
As a result, the antenna gain of many clients is 0, and the transmission power is very small, which is as
shown below:

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Table 2: Transmission power of some smart phones
The Wi-Fi system is bidirectional. If the transmit power of the AP is higher than that of the client, the downlink
signal of the AP can reach the wireless client smoothly. However, the uplink signal of the wireless client
cannot reach the AP effectively. Even the air signal reaches the AP, AP may not have enough signal-to-
noise ratio to recognize the content.
Although the uplink traffic is the major direction in the wireless network communication, Wi-Fi uses a Layer
2 acknowledgment mechanism, such as acknowledgment (Ack) messages need to be transmitted on the
reverse direction. If ACK fails, and the entire communication fails. In this case, the access point will be
retransmitted until the retransmission limit is reached, and then the upper application will drop packets or
even be interrupted.
In addition, for real-time voice and video application, the uplink and downlink traffic are basically the same,
so application will be interrupted by this kind of mismatch between the transmission power of the access
point and the client.
It's like an adult talking to a child over a long distance. The adult's voice is loud enough for child, but the
child's reply cannot be hear by the adult. Adult could only keep on repeating until he gives up.
In this case, AP's strong transmit power is useless. It is critical to balance the uplink and downlink
bidirectional links. Unfortunately, the first adjustment people are likely to take, when Wi-Fi communication
goes bad, is to increase AP transmission power, and this doesn’t help at help.
Even worse, increasing power will not only increase the interference level of the entire network, but also
easily cause all clients on this AP sticky from roaming. This is because many clients rely on the strength of
the received signal for connection and roaming decisions. Furthermore, the sticky clients will cause much
clients connection than expected, and may lead to system capacity overload on the AP.