I'm in process of preparing to CWNA and a little bit lost with beamforming. When beamforming enabled on AP, we deliver more RF energy to the client using less TX power on access point, and that's fine. At the same time, beamforming does not increase RX sencitivity on access point. So my conclution is that beamforming has the same effect as increasing TX power on access point. But what's the reason to reach out to far-away clients if we still cannot hear them?
Another thought: while AP transmits frames to one client using beamforming, other clients around AP don't hear this communication and thus can start their own transmition, at that's the problem. So RTS/CTS is a must for beamforing to work well?
I must be wrong somewhere, please point me out.
There are a couple of good 'beamforming' marketing pamphlets from Ruckus and Cisco here.
Ruckus seem to be confusing 802.11n TxBF with switched sector antennas but the Cisco paper is closer to a conventional phased array beamformer.
In effect TxBF is inverse MRC for the transmit chain.
Physical antennas offer reciprocal passive gain at their areas of maximum lobe gain at the expense of less reciprocal passive gain at their null gain points. The additional gain is exactly the same regardless whether a transmitter or receiver is attached to it. For a PtP link given that the TX power remains the same the RX SNR will improve at BOTH ends with additional antenna gain even if the high gain antenna is only at one end. The receiver's Minimum Discernible Signal (MDS) or sensitivity is dependent on the Bandwidth and Noise Figure and does not change with antenna gain. So it is correct to say an RX's sensitivity (MDS) doesn't change with a high gain antenna, however the SNR and thus the range and or data rate will improve at both ends even if only one high gain antenna is installed.
Phased array beamforming creates a virtual stearable antenna that will increase the range of both the TX and RX on an AP to both a non-beamforming and beamforming client STA RX due to improving the SNR at both ends of the link if implemented correctly.
Thank you very much, Karlenr! Good reading!
This particular Cisco paper seems to have been written about the time "n" technology way first being pushed. In it, Cisco makes a big deal of their one sided, implicit beamforming technology - and how they work better than systems like Ruckus.
Since the promotion of 802.11ac, it seems as if most manufacturers are saying that implicit beamforming never really worked. But now we have explicit beamforming which uses sounding frames and bidirectional communication between AP and Client (as well as more CPU power in both devices) and standards based algorithms to insure interoperability.
I saw some of the Ruckus hardware, during a CWNP travelling show back then and it was outstanding. Back then at least, I'd say that the Ruckus performance was better.
I was impressed with the coverage in this Cisco paper, but given the technology time frame, I think it was more of a "lets bash the competition" paper, than a fair comparison.
IMHO, Ruckus still makes great gear.