Mobile communication (モバイル通信) is how a smartphone or similar device uses radio waves to make calls and exchange data on the move.
Device
Base station
Carrier's network
Other party
The data reaches the other party.
4 / 4
A device links by radio to a nearby base station (the equipment that serves as the radio-side front desk), and the carrier's network takes things from there to the other party. 4G and 5G name the generations of this technology. Tethering, which lets a PC or other device share a smartphone's line, also runs on top of it.
AnalogyA landline only works as far as its cord reaches. Mobile communication is like unplugging only the cord at your end and taking the phone out into town.
How to remember"Mobile" means able to be moved. Japanese calls a phone you carry around モバイル after the same word.
Exam points
ExamIn tethering (テザリング), the smartphone takes the role of a router (ルータ, a device relaying between networks). A PC gets online with no second router added.
A base station (基地局) is radio equipment that exchanges signals with mobile devices and relays them to the carrier's network.
It has antennas and radio gear and looks after the devices within its radio range, called a cell. One station's cell only goes so far, so the cells of many base stations are laid side by side to cover a whole region.
AnalogyThink of the post office in each town. The nearest branch takes your letter, and the delivery network between branches gets it to the other person's town.
How to rememberThe character 局 in 基地局 also appears in the Japanese words for broadcaster and post office, marking a site in charge of a service.
Exam points
Mix-upMobile communication (モバイル通信) is not necessarily wireless all the way. Radio mainly covers the stretch between the device and the base station (基地局), and much of the route beyond it is wired.
AP is an abbreviation built from the initials of Access Point, and it means the same thing as the access point (アクセスポイント) coming up next.
In a wireless LAN (a LAN that links places such as a building's interior by radio), it is the name for the equipment a device connects to first, and you will see it in manuals and network diagrams. The next term explains what it does.
How to remember"Access" means getting at or using something, and "point" means a spot. Read it as the spot for using the network and the meaning comes back with it.
An access point (アクセスポイント) is the connection-point device that takes in wireless LAN devices by radio and bridges them to a wired network.
Wireless LAN device
Access point
Wired network
Internet
It sits in homes, offices, shops and the like, and devices within range reach the network through it. Each one is identified by a name called an SSID, which you pick from the list your device displays.
AnalogyIt is like an office receptionist, who takes a visitor's (device's) request and passes it on to the staff deeper in the building (the wired network).
Exam points
Mix-upA base station (基地局) is a connection point of the mobile phone network (携帯電話網), while an access point (アクセスポイント) belongs to a wireless LAN (無線 LAN), so they sit on different networks.
The platinum band (プラチナバンド) is the popular name for the easy-to-connect 700 MHz to 900 MHz bands among the frequencies mobile phones use in Japan.
Low frequency
High frequency
Behind obstacles
Bends around and gets through
Has trouble getting through
Data it can carry
Hard to increase
Easy to increase
Example band
Platinum band
Bands of a few GHz
Frequency is how many times a radio wave oscillates in 1 second, measured in MHz or GHz. Since 1 GHz equals 1000 MHz, the platinum band sits below 1 GHz. That low range is what helps the signal reach spots behind buildings and indoors.
AnalogyStand behind a wall and you can still catch a deep voice from the far side, while a high one is harder to hear. Radio waves show a similar tendency.
How to rememberThe name comes from platinum, likening these frequencies to a rare and highly valued metal.
Exam points
ExamThe platinum band (プラチナバンド) spans the 700 MHz to 900 MHz bands, and the unit is MHz, not GHz.
ExamThe lower a wave's frequency (周波数), the better it bends into shadowed areas and gets past obstacles. This property explains why the platinum band connects so readily.
Handover (ハンドオーバー) moves a traveling device's connection to another base station so that communication carries on unbroken.
Connected to base station A
A's signal weakens
Switch to base station B
Communication continues
Communication goes on with no action from the user.
4 / 4
One station's cell only goes so far, so a device that keeps moving eventually enters the next cell. The switch can happen in the middle of a call or data session, and users often do not notice.
AnalogyPicture the baton in a relay race. The runner (base station) changes, but the baton (communication) keeps moving without stopping.
How to rememberIn everyday English, "hand over" literally means passing something across by hand.
Exam points
Mix-upOnly the connected base station changes. The device and the user's contract stay as they are.
In mobile communication, roaming (ローミング) lets you use communication services outside your own carrier's coverage by borrowing a partner carrier's network.
Leave your carrier's coverage
Join the partner's network
Communicate on the same contract
Calls and data work under your original contract.
3 / 3
The classic example is international roaming, where you use your own smartphone abroad as it is. Your contract stays with the original carrier, and the charges usually come from that carrier as well.
AnalogyIt is like withdrawing from your own account at a partner bank's ATM in a place where your bank has none.
How to remember"Roam" means to wander about. Picture yourself wandering past the edge of your carrier's signal.
Exam points
Mix-upHandover (ハンドオーバー) changes the base station, while roaming (ローミング) brings in another carrier's network, so what gets swapped is different.
Handover vs. Roaming
Aspect
Handover
Roaming
When it happens
When the current base station's signal weakens
When you leave your carrier's coverage
Key differenceNetwork used
Normally still your own carrier's
The partner carrier's
Everyday example
A phone call on a moving train
Using your phone on a trip abroad
Key points
In mobile communication, radio waves link the device and the base station, and the carrier's network carries things on to the other party.
AP stands for access point, the device that bridges wireless LAN devices to a wired network.
The lower the frequency, the more readily radio waves bend behind obstacles, which is why the platinum band of 700 MHz to 900 MHz connects so well.
When movement weakens the signal, handover changes the connected base station and communication continues.
Outside your carrier's coverage, roaming borrows a partner's network so that communication services stay available.