AskUbuntu's answer recommended that this console app called wavemon to check your Wifi adapter signal strength. Basically, this app "is an ncurses-based monitoring application for wireless network devices." Installation is plain straightforward in Ubuntu 13.04. Just type these two lines.
$ sudo apt-get install wavemon $ sudo wavemon
Screenshot below shown the movement of the signal level of my lappy wifi connection, which was quite poor. Went to Low Yat and bought two antennas to boost the signal from 5dBi to 8dBi. Still, nothing much changed. In the end, switch to plain old cable and ethernet, specifically ethernet over power lines.
What next ? There are three other possibility to restore back my Wifi speed. First, replace and upgrade my wireless router with some other brand like Asus RTAC66U which support thousand assorted features and most importantly, Quality of Service (QoS). You cannot prevent people from watching or downloading movies 24x7, but at least you control their usage. As to be fair for everyone else. Second, buy a high gain wireless USB adapter to replace my lappy internal Wifi adapter. Third, add a few wireless repeaters around several strategic points in the house.
Let's see how this goes.