Thursday, September 29, 2011

Wireless antenna technology: SISO, SIMO, MISO and MIMO

The wireless data transmission system consists of 2 parties: the transmitter and the receiver, whereby data is transmitted into the air from the antenna of the transmitter and received by the antenna of the receiver.

In a Single Input Single Output (SISO) system, both the transmitter and the receiver have one antenna, and data transmission over the air is through a single radio frequency (RF) signal chain.

An example of SISO type of wireless is Bluetooth.

Multiple antenna technique has been developed to improve wireless performance.

In a Single Input Multiple Output (SIMO) system, there is one antenna at the transmitter side and multiple antennas (each with an RF chain respectively) at the receiver side.

In a switched diversity or selection diversity implementation, the receiver chooses the best antenna to receive a stronger signal from the transmitter. In a maximal ratio combining (MRC) implementation, the receiver combines signals from all its antennas so that to maximize the Signal to Noise Ratio (SNR).

The Multiple Input Single Output (MISO) system is the other way round, with multiple antennas (each with an RF chain respectively) at the transmitter and a single antenna at the receiver.

A technique known as Alamouti Space Time Coding (STC) is employed at the transmitter with 2 antennas, allowing the transmitter to transmit signals both in time and space. This means data is transmitted by the 2 antennas at 2 different times consecutively.

Multiple Input Multiple Output (MIMO) system is commonly used in today's wireless technology, including 802.11n WiFi, WiMAX, LTE, etc. Multiple antennas (and therefore multiple RF chains) are put at both the transmitter and the receiver.

A MIMO system with same amount of antennas at both the transmitter and the receiver in a point-to-point (PTP) link is able to multiply the system throughput linearly with every additional antenna. For example, a 2x2 MIMO will double up the throughput.

Spatial Multiplexing (SM) technique is used in MIMO to enable signal  to be transmitted across different spatial domains. This is used  to provide additional data capacity.

Therefore, when buying a Wireless-N access point or router, to get a stabler WiFi with higher bandwidth, look for those that support MIMO and with more antennas.

Acknowledgement: the above diagrams are taken from the website.

Thursday, September 22, 2011

Using NetSetMan to change Windows network settings with a single mouse click

If you are using a laptop, you must have faced the problem of having to manually adjust the network settings to connect to the network (either LAN or WiFi) in different places. This is really a tedious thing, isn't it?

Although many places make use of DHCP to automate the IP address assignment (so that you are free from the hassle to manually set the IP address, subnet mask, gateway IP, etc.), you might probably still need to do some adjustment to some other settings, such as the SMTP email server, the DNS server, the default WiFi AP you want to connect with, the default printer, etc. Worse still, there are places that don't make use of DHCP server, and you have to manually change the network settings, especially the IP address, subnet mask and gateway IP, in order to connect and use the network there.

For example, the DHCP server might assign you with the ISP's DNS servers, and you prefer to use Google's DNS servers instead. In some other places, you cannot use Google's DNS servers because the firewall might have blocked DNS request to WAN, and you have to use their internal DNS server.

I found NetSetMan to be a very handy tool allowing you to quickly change your Windows network setting with just a mouse click to connect to the network in different places. It lets you pre-configure the network settings and save them in different profiles. By switching the profile, all the pre-configured settings will be switched over accordingly.

NetSetMan is free for personal non-commercial use. The free version lets you set up to 6 network profiles, while the Pro version lets you set unlimited profiles.

You can customize the settings in each profile for:
  • IP address (to use DHCP or manual setting)
  • DNS servers
  • DNS domain
  • WINS servers
  • Default WiFi AP
  • Default printer
  • Network adapter status (activate, deactivate or restart)
  • Your PC name
  • The workgroup / domain to join
  • SMTP server for email sending
  • Network drive mapping
  • Browser homepage and proxy setting
  • Local "host" file setting for mapping domain names with IP addresses. Normally the setting in this "host" file will supersede the DNS result
  • IPv6 settings
NetSetMan also allows you to run Windows script before and/or after a profile is changed.

It also has feature to allow you to copy-and-paste profile settings from one to another. This is handy to create a new profile where most of the settings are the same with the existing. You just need to make a copy, and modify those settings that need to adjust with.

Sunday, September 18, 2011

The relationship between multi-storey building floor number and the 5 elements of Feng Shui

Nowadays, multi-storey or high rise building is everywhere in urban areas.

You might live in multi-storey building, and you might also work in multi-storey building.

Do you want to know the relationship between multi-storey building floor number and the 5 elements of Feng Shui? With that, you can find out how compatible is the floor you are staying with your own element.

Note that in Chinese floor naming convention, the 1st Floor is the floor that is same level with the ground, which might be known as Ground Floor in certain places. The 2nd Floor is the floor above 1st Floor, which might be known as 1st Floor in buildings that start with Ground Floor.

Before we proceed, please keep in mind that we are using the Chinese floor naming convention here, so do your own adjustment if your building's naming convention is different.

To determine the element of the floor, we look at its last digit. Therefore, 1st Floor, 11th Floor, 21st Floor, 31st Floor, 41st Floor, ... all have the same element. The same concept applies to 2nd Floor, 12th Floor, 32nd Floor, ... and so on. (Remember: use the Chinese floor naming convention!)

And here is the associated elements:

  • Water: 1, 6
  • Fire: 2, 7
  • Wood: 3, 8
  • Metal: 4, 9
  • Earth: 5, 10

There is also a mapping between the 5 elements and your Chinese Zodiac animal. Your Chinese Zodiac animal is determined based on your year of birth. The mapping is as follow:
  • Water: Rat, Boar
  • Fire: Snake, Horse
  • Wood: Tiger, Rabbit
  • Metal: Monkey, Roaster
  • Earth: Cow, Dragon, Goat, Dog

It is a basic Feng Shui concept that:
  • Water produces Wood
  • Wood produces Fire
  • Fire produces Earth
  • Earth produces Metal
  • Metal produces Water
and that:
  • Water destroys Fire
  • Fire destroys Metal
  • Metal destroys Wood
  • Wood destroys Earth
  • Earth destroys Water
Now, you have enough information to evaluate whether the floor your are staying in has positive or negative impact to you.

For example, if you are born in the year of Rabbit (Wood element), and you are staying/working in 5th Floor (in Chinese convention) (Earth element), Wood destroys Earth and therefore Earth suppresses Wood, it seems to be not a good matching. In Feng Shui, this situation is considered Neutral and not as Bad. However, if the floor is Metal (destroys Wood) or Fire (burns up the Wood), that is considered as Bad. If the floor is Water (produces Wood) or Wood (enriches Wood), that is considered as Good.

Hint: Click on the "Older Posts" link to continue reading, or click here for a listing of all my past 3 months articles.