Mobile vs Wireless

Following from the title of this blog site, I seek to clarify the differences between “mobile” and “wireless”. These two terms are often used interchangeably, in a rather loose way. Much of this is justified because they are closely related. In fact, many products share the characteristics of both so that any distinction that we may try to bring about becomes rather difficult without referring to specifics.

Yet another reason for the confusion is that “mobile” has multiple connotations. In the good old days before mobile telephony and cell phones, “mobile” meant not fixed, ie. portable. These days we often mean a mobile phone when we say “mobile”.

Here lies the clue to our clarification. In strict terms, “mobile” means portability. “Wireless” means connectivity. That’s just a definition. What are the characteristics? Some examples will make this apparent.

A UMTS Node-B is a wireless device but it is not mobile. A digital camera of the 1990’s is mobile but it is not wireless. Today’s digital cameras are not only mobile but also wireless because they have Bluetooth, infrared and possibly Wi-Fi connectivity. The iPod has always been a mobile device but only with the most recent release of iPod Nano has it become wireless with Wi-Fi connectivity.

Portability requires that the device has a suitable form factor. It must be durable from the consumer’s perspective with some ability to withstand rough transport or fall. It must have a feel-good factor. The device must be power efficient and must have a long battery life. No one talks about battery life for the Node-B because it’s not a mobile device. In some sense, the nature of service provided by the device makes it mobile and requires it to be mobile.

On the other hand, a connected device enables services to be delivered in collaboration with those around it. For example, a conventional laser printer is of little use if it’s not connected to a computer via a parallel port. Thus, connectivity is often linked to services obtained or offered in a collaborative environment. Connectivity implies an environment in which devices are physically separate entities.

Connectivity can be wired or wireless – we are interested in the latter. A modern printer connected to a PC via Bluetooth is a fixed device but it is wireless. For the printer, the PC acts as a data source. For the PC, the printer provides a printing service. A mobile phone is both mobile (in the strict sense) as well as wireless. A mobile device may be self-complete. A wireless device is likely to be incomplete by itself. It needs to get connected.

These days, the term “wireless” when used specifically for mobile phones, laptops or PDAs generally refers to connectivity to the Internet. In other words, the specific service that the term eludes to is the conglomerate of all services that the Internet can offer. While the “wireless” component of a mobile phone enables it to connect to the base station, the term has come to mean the end service as perceived by the user. The man on the street does not want to connect to the Node-B. He wants to access his e-mails from his office mail server.

A cellular phone is obviously both mobile and wireless. It is portable and at the same time it has to stay connected to the base station. Special considerations are in play here in addition to what has already been mentioned. The device must be capable of many or all of these:

• Resilience and recovery in a fast-fading environment
• Ability to make continuous measurements of the radio environment
• Support seamless handover to stay connected
• Dynamic power control
• Adaptive Modulation and Coding (AMC)
• Incremental Redundancy (IR)
• Support Automatic Repeat Request (ARQ) across the wireless access

It will be apparent that a device that is both mobile and wireless, is a fairly complex one. However, this is true only for a subset such as a cellular phone. Other devices are much simpler. For example, a digital camera is a mobile device. It may have Bluetooth connectivity to transfer images to the laptop. However, while such an image transfer is in progress it is likely to be non-mobile w.r.t to the laptop or at worst, mobile at pedestrian speeds (such as the user moving the laptop around during the image transfer). A logical representation of device categories is given in Figure 1.

Figure 1

So far I have looked at the issue from a telecom perspective. Let us look at it from the world of IP (Internet Protocol). This is important as telecom and IP are building bridges with the building blocks of IMS, SIP and all the services that they enable. “Mobile” for IP means that designers have to tackle issues such as addressing, address translations and packet routing. “Wireless” for IP is nothing more than an access mechanism. On the other hand, “wireless” means a lot more for TCP/IP. The performance of TCP/IP on a wired network is different from a wireless network. In a future article, I will cover the performance of TCP/IP over wireless.