With two spatial streams, the MRC gain is halved, that is the MRC gain is reduced by 3 dB. This is because
the system has 10 log (3/2 SS) instead of 10 log (3/1 SS). If there were to have been 3 SS with 3 RX, then
the MRC gain would have been zero.
Note
• Number of backhaul hops is limited to eight but we recommend three to four hops.
The number of hops is recommended to be limited to three or four primarily to maintain sufficient
backhaul throughput, because each mesh access point uses the same radio for transmission and
reception of backhaul traffic, which means that throughput is approximately halved over every hop.
For example, the maximum throughput for 24 Mbps is approximately 14 Mbps for the first hop,
9 Mbps for the second hop, and 4 Mbps for the third hop.
• Number of MAPs per RAP.
There is no current software limitation on how many MAPs per RAP you can configure. However,
it is suggested that you limit the number to 20 MAPs per RAP.
• Number of controllers
◦ The number of controllers per mobility group is limited to 72.
• Number of mesh access points supported per controller.
ClientLink Technology
Many networks still support a mix of 802.11a/g and 802.11n clients. Because 802.11a/g clients (legacy clients)
operate at lower data rates, the older clients can reduce the capacity of the entire network. Cisco’s ClientLink
technology can help solve problems related to adoption of 802.11n in mixed-client networks by ensuring that
802.11a/g clients operate at the best possible rates, especially when they are near cell boundaries.
Advanced signal processing has been added to the Wi-Fi chipset. Multiple transmit antennas are used to focus
transmissions in the direction of the 802.11a/g client, increasing the downlink signal-to-noise ratio and the
data rate over range, thereby reducing coverage holes and enhancing the overall system performance. This
technology learns the optimum way to combine the signal received from a client and then uses this information
to send packets in an optimum way back to the client. This technique is also referred to as MIMO (multiple-input
multiple-output) beamforming, transmit beamforming, or cophasing, and it is the only enterprise-class and
service provider-class solution in the market that does not require expensive antenna arrays.
The 802.11n systems take advantage of multipath by sending multiple radio signals simultaneously. Each of
these signals, called a spatial stream, is sent from its own antenna using its own transmitter. Because there is
some space between these antennas, each signal follows a slightly different path to the receiver, a situation
called spatial diversity. The receiver has multiple antennas as well, each with its own radio that independently
decodes the arriving signals, and each signal is combined with signals from the other receiver radios. This
results in multiple data streams receiving at the same time. This enables a higher throughput than previous
802.11a/g systems, but requires an 802.11n capable client to decipher the signal. Therefore, both AP and
client need to support this capability. Due to the complexity of issues, in the first generation of mainstream
802.11n chipsets, neither the AP nor client chipsets implemented 802.11n transmit beamforming. Therefore,
the 802.11n standard transmit beamforming will be available eventually, but not until the next generation of
chipsets take hold in the market. We intend to lead in this area going forward.
Cisco Mesh Access Points, Design and Deployment Guide, Release 7.3
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Design Considerations
ClientLink Technology
