- 1 What is Mobile Computing?
- 1.1 Mobile communication
- 1.2 Mobile Hardware
- 1.3 Mobile software
- 1.4 Technologies
- 1.5 Multiplexing : Code Division Multiplexing (CDM)
What is Mobile Computing?
Mobile Computing is a technology that allows transmission of data, voice and video via a computer or any other wireless enabled device without having to be connected to a fixed physical link. The main concept involves –
• Mobile communication
• Mobile hardware
• Mobile software
The mobile communication in this case, refers to the infrastructure put in place to ensure that seamless and reliable communication goes on. These would include devices such as protocols, services, bandwidth, and portals necessary to facilitate and support the stated services. The data format is also defined at this stage. This ensures that there is no collision with other existing systems which offer the same service.
Mobile hardware includes mobile devices or device components that receive or access the service of mobility. They would range from portable laptops, smartphones, tablet Pc’s, Personal Digital Assistants.
These devices will have a receptor medium that is capable of sensing and receiving signals. These devices are configured to operate in full duplex, whereby they are capable of sending and receiving signals at the same time. They don’t have to wait until one device has finished communicating for the other device to initiate communications.
Above mentioned devices use an existing and established network to operate on. In most cases, it would be a wireless network.
Mobile software is the actual program that runs on the mobile hardware. It deals with the characteristics and requirements of mobile applications. This is the engine of the mobile device. In other terms, it is the operating system of the appliance. It’s the essential component that operates the mobile device.
Since portability is the main factor, this type of computing ensures that users are not tied or pinned to a single physical location, but are able to operate from anywhere. It incorporates all aspects of wireless communications.
Since the introduction of first commercial mobile phone in 1983 by Motorola, mobile technology has come a long way. Be it technology, protocols, services offered or speed, the changes in mobile telephony have been recorded as generation of mobile communication. Here we will discuss the basic features of these generations that differentiate it from the previous generations.
1G refers to the first generation of wireless mobile communication where analog signals were used to transmit data. It was introduced in the US in early 1980s and designed exclusively for voice communication. Some characteristics of 1G communication are –
- Speeds up to 2.4 kbps
- Poor voice quality
- Large phones with limited battery life
- No data security
2G refers to the second generation of mobile telephony which used digital signals for the first time. It was launched in Finland in 1991 and used GSM technology. Some prominent characteristics of 2G communication are –
- Data speeds up to 64 kbps
- Text and multimedia messaging possible
- Better quality than 1G
When GPRS technology was introduced, it enabled web browsing, e-mail services and fast upload/download speeds. 2G with GPRS is also referred as 2.5G, a step short of next mobile generation.
Third generation (3G) of mobile telephony began with the start of the new millennium and offered major advancement over previous generations. Some of the characteristics of this generation are
- Data speeds of 144 kbps to 2 Mbps
- High speed web browsing
- Running web based applications like video conferencing, multimedia e-mails, etc.
- Fast and easy transfer of audio and video files
- 3D gaming
Every coin has two sides. Here are some downsides of 3G technology –
- Expensive mobile phones
- High infrastructure costs like licensing fees and mobile towers
- Trained personnel required for infrastructure set up
The intermediate generation, 3.5G grouped together dissimilar mobile telephony and data technologies and paved way for the next generation of mobile communication.
Keeping up the trend of a new mobile generation every decade, fourth generation (4G) of mobile communication was introduced in 2011.
characteristics of 4G Technology are –
- Speeds of 100 Mbps to 1 GBPS
- Mobile web access
- High definition mobile TV
- Cloud computing
- IP telephony
Multiplexing in Mobile Computing
- Multiplexing is a technique in which, multiple simultaneous analog or digital signals are transmitted across a single data link.
- The concept behind it is very simple: Proper Resource Sharing and its Utilization.
It can be classified into four types. These are:
1)Space Division Multiplexing
2)Code Division Multiplexing
3)Time Division Multiplexing
4)Frequency Division Multiplexing
Multiplexing: Frequency Division Multiplexing (FDM).
- In Frequency Division, the frequency dimension spectrum is split into bands of smaller frequency.
- FDM is used because of the fact that, a number of frequency band can work simultaneously without any time constraint.
Advantages of FDM
- This concept is applicable on both analog signals as well as digital signals.
- Simultaneous signal transmission feature.
Disadvantages of FDM
- Less Flexibility.
- Bandwidth wastage is high and can be an issue.
For Example : Frequency Division Multiplexing can be used for radio station in a particular region as every radio station will have their own frequency and can work simultaneously without having any constraint of time.
Multiplexing: Time Division Multiplexing (TDM)
- Time Division is used for a particular amount of time in which the whole spectrum is used.
- Time frames of same intervals are made such that the entire frequency spectrum can be accessed at that time frame.
Advantages of TDM
- Single user at a time.
- Less complex and more flexible architecture.
Disadvantages of TDM
- Difficult to implement.
For Example: ISDN(Integrated Service for Digital Network) telephonic service.
Multiplexing : Code Division Multiplexing (CDM)
• In Code Division Multiplexing, every channel is allotted with a unique code so that each of these channels can use the same spectrum simultaneously at same time.
Advantages of CDM
- Highly Efficient.
- Less Inference.
Disadvantages of CDM
- Less data transmission rates.
- Complex in nature.
For Example : Cell Phone Spectrum Technology(2G, 3G etc.).
Frequency Division Multiple Access (FDMA)
- FDMA is the basic technology for advanced mobile phone services. The features of FDMA are as follows.
- FDMA allots a different sub-band of frequency to each different user to access the network.
- If FDMA is not in use, the channel is left idle instead of allotting to the other users.
- FDMA is implemented in Narrowband systems and it is less complex than TDMA.
- Tight filtering is done here to reduce adjacent channel interference.
- The base station BS and mobile station MS, transmit and receive simultaneously and continuously in FDMA.
Time Division Multiple Access (TDMA)
- In the cases where continuous transmission is not required, there TDMA is used instead of FDMA. The features of TDMA include the following.
- TDMA shares a single carrier frequency with several users where each users makes use of non-overlapping time slots.
- Data transmission in TDMA is not continuous, but occurs in bursts. Hence handsoff process is simpler.
- TDMA uses different time slots for transmission and reception thus duplexers are not required.
- TDMA has an advantage that is possible to allocate different numbers of time slots per frame to different users.
Code Division Multiple Access (CDMA)
- Code division multiple access technique is an example of multiple access where several transmitters use a single channel to send information simultaneously. Its features are as follows.
- In CDMA every user uses the full available spectrum instead of getting allotted by separate frequency.
- CDMA is much recommended for voice and data communications.
- While multiple codes occupy the same channel in CDMA, the users having same code can communicate with each other.
- CDMA offers more air-space capacity than TDMA.
Space Division Multiple Access (SDMA)
- Space division multiple access or spatial division multiple access is a technique which is MIMO (multiple-input multiple-output) architecture and used mostly in wireless and satellite communication. It has the following features.
- All users can communicate at the same time using the same channel.
- SDMA is completely free from interference.
- A single satellite can communicate with more satellites receivers of the same frequency.
- The directional spot-beam antennas are used and hence the base station in SDMA, can track a moving user.