upsangel wrote:
1tac大大我得出了和你不一樣的結論，一齊討論: 全球除了華碩的PCI e 68之外，沒有任何一款接收設備支持Turbo QAM...(恕刪)
Smallnetbuilder這篇文章提到
Broadcom responded with the following:
TurboQAM is a Broadcom technology incorporated into our 11ac chips which allow you to transmit and receive at 256 QAM while operating in the 2.4 GHz band.
All of the Broadcom 11ac chips support the TurboQAM feature including:
-1x1ac combo chips (used in HTC One and Galaxy S4)
-2x2 11ac
-3x3 11ac
-Enterprise 11ac solutions.
當然, 這是B社的說法, 從硬體的角度來看應該正確, 只是軟體不知有無被封印; 小弟財力有限，沒有辦法買這些高檔貨來實證
至於TurboQAM有無用處, 小弟以RT-AC68U舉個很粗略的例子來說明
假設一個2.4G的Client位於一面水泥磚牆後, 訊號已衰減了39dB(如下圖), throughput仍維持為120M(代表仍運行TurboQAM, 註1), 若同樣位置換上一個5G的Client, throughput會變多少?
出處已知Free Space下5G會比2.4G多 loss 6dB
出處穿過水泥磚牆後, 5G平均又會比2.4G多衰減8dB --- (10+30)/2-(6+18)/2=8
出處(註2)故5G的client在同樣位置上, 會比2.4G多衰減 6+8=14dB, 2.4G已衰減39dB, 由此推算5G會衰減39+14=53dB
對照下圖, 5G client在衰減53dB的情況下, throughput別說連100M都不到, 甚至有可能根本連不上
出處這個例子並非特例, 日常生活都有機會遇到; 而這個例子告訴我們, 在5G已經衰減到不可用的情況下, 2.4G的訊號並不差, 若加上2.4G較佳的繞射折射反射等效應, 2.4G是大有機會維持滿速
因此TurboQAM並非只是噱頭, 它的確能在不犧牲coverage的情況下增加throughput(註3)
(註1)在此圖上各家2.4G下傳最高速大概都是120Mbps, 似乎看不到AC68U的TurboQAM有所發揮, 這是因為作者使用的client是不支援TurboQAM的ASUS PCE-AC66, 因此TurboQAM根本沒啟動, 若client是使用支援TurboQAM的ASUS PCE-AC68, 估計最高速還可以再加個20M~30M
(註2)一般認為5G的頻率較高,能量較高,因此"直線"穿透力較好, 其實這是不一定的, 主要還是要考率穿透物質對不同頻率的衰減係數, 以此圖來看, 不只水泥磚牆, 其他物質對5G也是情有獨鍾(衰減係數高), 造成5G通過時的衰減比2.4G還要多
(註3) 256QAM@2.4GHZ本來就規範在802.11AC, 並不是Broadcom自己定義的, Broadcom只是先實作出來並取了個"TurboQAM"的響亮名字而已, 其他公司也承認TurboQAM是有好處的並打算跟進
Since 256-QAM isn't proprietary to Broadcom, it is possible that other chipmakers could choose to support it in their 802.11ac devices. In fact, when I asked Qualcomm whether they plan to support 256-QAM in its 802.11ac VIVE products, they said:
We think there’s advantage to be gained when 256 QAM in 2.4 GHz is on both the client and router sides of the link, and of course, there’s the growing marketing check box that we must address. We will enable the feature in a complete ecosystem near-term.
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