Tuesday, September 25, 2018

Confusing Tech - USB Standard


Confusing Tech - Fast Charging


Confusing Tech - WiFi Standard

Now we live in a world where we have to use internet everyday and to do so many of us rely on Wi-Fi. Even if my desktop is not connected via wireless means my many other devices are. As time goes by improvements in this field has made it kind of confusing. So I am hoping to clear some up with this post. Note that I will be very brief here because otherwise this post will become extremely long and boring.

So what is Wi-Fi? 

Wi-Fi is a technology for radio wireless local area networking. It is like it's wired counterpart acts as a medium to get your device networked but unlike using wire it simply uses radio link. In simplest term Wi-Fi enabled devices can connect to a Wireless Access Point and provide Internet(or local network whatever the case may be).

What is what?

If we look at the market we will see many devices have many different specification regarding Wi-Fi. Wi-Fi n, Wi-Fi ac, Dual Band Wi-Fi and so on. So let's put them in lists and see what we can get.

IEEE 802.11

This is a set of Media Access Control and Physical Layer specification for implementing Wireless network in difference frequency bands. Wi-Fi ac that you might see on some product specification is actually just 802.11ac which specifies many aspects of that particular technology. I will list out some of the most common ones now to give you a better idea which came out when. Note that in the list very uncommon ones will be omitted.

802.11-1997 (Legacy)

This was pretty much the dawn of Wi-Fi, it worked at a whopping 1Mbps/2Mbps on 2.4GHz ISM band. Some used 900MHz as well.

802.11a OFDM
At 5.8GHz 802.11a solved the issue of crowded 2.4GHz space and could theoretically get up-to 54Mbps. But with higher frequency it lost some of its range. Currently devices still support this standard at 5GHz 54Mbps. Although real speed achievable was about 20Mbps. Which was a lot during 1999.

802.11b
It uses the same ISM 2.4GHz band like legacy Wi-Fi but raw data rate gone up to 11Mbps.

802.11g
This one also works on 2.4GHz but uses OFDM just like 802.11a. It has a maximum bit rate of 54Mbps and real world speed was around 20Mbps.
During this time Wi-Fi started to gain popularity and many devices came at that time supported 802.11a/b/g at both 2.4GHz/5GHz. However using such a device with older hardware say 802.11b will result in reduced throughput.

802.11n 
Probably the most used Wi-Fi standard now(when I am writing this post). It uses both 2.4GHz/5GHz and can get bit rate from 54Mbps to 600Mbps. However without using specialized hardware at both ends do not expect to get 600Mbps speed. From this time things started to get real murky with manufacturers claiming many things and throwing many different numbers at us the customers.

802.11ac
Another very popular network of this time. This was an improvement over the 802.11n using higher frequency 5GHz compared to more common 2.4GHz of n, wider channel, higher-order modulation and thus achieving 433Mbps per stream. Add couple streams together and you will get over gigabit theoretical speed. It also has features like Multi User Multi input multi output. Wi-Fi n only had the Multiple input Multiple output feature.
Vendors also released a so called 802.11ac Wave 2 devices that supports 160MHz channel as opposed to 80MHz of standard 802.11ac(note that n has 20 or 40MHz channel).
However ac has less range compared to n as it uses a higher frequency.

802.11ad
To make a short range high speed communication possible even higher frequency is being used, 60GHz. It drastically reduces the range from a house to maybe a room but improves the speed upto 7Gbps. You might find this type of products under the marketing name WiGig.


There are many more other standards but they are not that common so I will leave them for now.

Frequency:
So another thing we found is the frequency.We got

900MHz
2.4GHz
3.6GHz
5GHz
60GHz

2.4GHz and 5GHz being the most common ones. 2.4GHz is not as fast as 5GHz but it has more range, it is also a very crowded space so interference might be a problem for this frequency. Not as much for 5GHz which also has higher data transfer capability.



Confusions:

So there are a lot of confusion over many things now, specially with the Wi-Fi n and Wi-Fi ac. If a devices says it runs on 5GHz doesn't make it Wi-Fi ac. It can be Wi-Fi n 5GHz.

Another confusion can be with speed, we often see ridiculous speeds printed on devices like 1800Mbps or 3200Mbps, don't expect to get that on a single device. Modern routers often has the capability to work on both n and ac(and previous iterations as well but let's stick to n and ac) so what they usually do is add up all the numbers. If it can get up-to 300Mbps on Wi-Fi n and 867Mbps on Wi-Fi ac they will market it as 300+867 or 1167 or roughly 1200Mbps router. But if your devices is a single antenna Wi-Fi n you would probably get around 72.2Mbps-150Mbps from this router.

Antenna Matters

Both for n and ac number of antennas play a very important role.

For Wi-Fi n single antenna will give you anywhere between 54Mbps to 150Mbps. Add another antenna on both side you will get up-to 300Mbps, add another and get 450Mbps and so on. Although there is a limit at 600Mbps with four antennas in 40MHz mode.

Wi-Fi ac can get much better speed even with a single antenna, 433Mbps. Using 2 antennas will provide around 867Mbps.

The most important catch here for both this is that you need support on both ends. So to get Wi-Fi ac working at 867Mbps you need a router that has two antennas and a device that has two antennas, if one device is a single antenna one your speed will be down to 433Mbps. Same goes for n as well. To get 300Mbps you will be needing two antenna AP and two antenna device.

Some confusing terms:

MIMO

Multiple-input Multiple-output.
Using multiple transmit and receive antennas capacity can be increased with this technology. So with MIMO data can be transferred at a higher speed to any certain device.

MU-MIMO

Multi-user MIMO
This allows data to be transmitted to multiple user at a time improving the latency for all users. However it requires more signal processing.

Beamforming

This is a signal processing technique for directional signal transmission or reception. It can help with focusing more power to a certain device on a certain direction.






Monday, September 24, 2018

How to apply for MRP in Bangladesh

UNDER CONSTRUCTION


মেশিন রিডেবল পাসপোর্টের জন্য অনলাইনে আবেদন করাই সবচেয়ে সহজ। 

প্রথম ধাপঃ ব্যাংকে টাকা জমা দেওয়া। 

দ্বিতীয় ধাপঃ অনলাইনে আবেদনপত্র পূরণ করা।

তৃতীয় ধাপঃ আবেদনপত্রটি প্রিন্ট করা। 
মনে রাখা জরুরী উভয়পাতায় প্রিন্ট করতে হবে। সাদাকালো হলেও চলবে।
অন্তত দুইসেট প্রিন্ট করতে হবে।
ব্যাংকে জমা দেওয়ার রশিদ আঠা দিয়ে সংযুক্ত করতে হবে। 

চতুর্থ ধাপঃ ছবি এবং জাতীয় পরিচয়পত্রের কপি(যদি দেওয়া হয়) সত্যায়িত করা লাগবে। অন্য কোন সনাক্তকারী দলিলাদি সাথে থাকলে তাও সত্যায়িত করা লাগবে।
পরিচিত কোন গ্যাজেটেড অফিসার দ্বারা প্রত্যয়ন লিখা লাগবে এবং তাঁর জাতীয় পরিচয়পত্রের নম্বর দেওয়া লাগবে।

পঞ্চম ধাপঃ আঞ্চলিক পাসপোর্ট অফিসে গিয়ে লাইনে দাঁড়াতে হবে। ছবি তুলে ফেলার পরে আপাতত কাজ শেষ।

ষষ্ঠ ধাপঃ পরবর্তীতে পুলিশ এসে তথ্যাবলি নিশ্চিত করবে এবং এর পর পাসপোর্ট হাতে পাওয়ার অপেক্ষা শুধু।