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Introduction to Mobile Terminals

1.1 Introduction to Mobile Terminals

A mobile communication device is a small, portable electronic device, with wireless communication capabilities, which is easy to carry around. There are several types of mobile communication devices, like cell phones or mobile phones, WLAN devices, and GPS navigation devices, but it is the mobile phone that has adopted the term “mobile device,” and gradually its purpose has shifted from a verbal communication tool to a multimedia tool.

A mobile phone, which is also known as mobile terminal (MT), cellular phone, cell phone, hand phone, or simply a phone, is a device that can send and receive telephone calls over a radio link while being connected to a cellular base station operated by a cellular network operator. It provides user mobility around a wide geographic area. A feature phone is a low‐end mobile phone with limited capabilities and it provides mainly voice calling, text messaging, multimedia, and Internet functionality. In addition to telephone calls, modern multifunctional mobile phones with more computing capabilities, which support a wide variety of other applications and services like SMS, MMS, e‐mails, Internet, Web browsing, news, gaming, playing music, movies, calendar management, contact, video, photography, short‐range connectivity, location‐specific information, WLAN connectivity, and GPS connectivity, are considered as smartphones. Smartphones offer all these services in single device, so they are becoming increasingly important as work tools for users who rely on these services. Today, they have become universal replacements for personal digital assistant (PDA) devices. Typically, a smartphone incorporates handheld computer functionalities along with the communication capabilities of a cell phone by providing support of multimodal, multi‐RAT connectivity and user customized applications. Personal digital assistants / enterprise digital assistants, tablet computers, ultramobile PCs, and a lot of wearable devices also provide mobile communication capabilities by integrating communication modems in them. Various types of these devices are shown in Figure 1.1.

Figure 1.1 (a) PDA, (b) smartphone (c) tablet (d) wearable device

1.1.1 Building Blocks of a Smartphone

A system‐level block diagram of a smartphone is shown in Figure 1.2. Smartphones are equipped with various functional blocks as given below:

• Mobile terminal modem unit. This unit (cellular systems modem) interfaces with the cellular base stations, and sends / receives user information (voice, data) generated by the application unit. So it interacts with a base station using different cellular air interface standards like GSM, WCDMA, LTE etc. to send / receive information to distantly located called party or server. It also interacts locally with its application units, like speech, video, and data transfer applications for getting / providing the user application data. This is discussed in Chapters 2, 3 and 4. This consists of two main submodules: Radio Frequency (RF) unit and Baseband (BB) unit.
  • RF unit. The RF analog front‐end unit’s transmitter circuit helps to upconvert the low‐frequency baseband signal to a high‐frequency amplified RF signal for transmission, and the receiver circuit helps to downconvert the analog amplified received high‐frequency signal to a low‐frequency baseband signal. The RF unit is discussed in detail in Chapter 6.
  • Baseband unit. The baseband unit helps for digital bit detection, system protocol processing for proper and reliable communication with the network. These are discussed in detail in Chapter 4 and 5.
  • SIM. A subscriber identification module (SIM) is an integrated circuit that securely stores the international mobile subscriber identity (IMSI) and the related key used to identify and authenticate subscribers on mobile telephony devices. A SIM circuit is embedded into a removable plastic card, called “SIM card.” This is discussed in detail in Chapter 5.
• Application unit. This unit is in charge of running various applications. It interacts with the modem and connectivity modules to send / receive information from remote devices, and uses that data to drive various applications. It provides the functions that users want to execute on the smart phone and these may include speech, audio playback, fax transmission / reception, Internet, e‐mail, Web browsing, image reproduction, streaming video, games, and so forth. This unit also handles the interface functions such as keyboard, display, and speech recognition, and it interfaces and manages other connectivity modules such as GPS and WLAN. Depending on the smartphone device complexity, there could one or several application processors in a mobile phone. The architecture design and selection details are provided in Chapter 5 and 7. The application processor consists of components like the processor core and device interfaces, which communicate with other peripheral devices attached to the application processor like the LCD screen, camera, keypad, universal serial bus (USB), and multimedia card (MMC) via interfaces. These are discussed in detail in Chapter 5.
  • Peripheral devices. There are several peripheral devices placed in the smart phone for different purposes. Like, for data transfer with other devices or PC, an USB device is placed in the phone. Similarly, UART, I2S etc. are used for intermodule or interdevice communication. The other devices are like, SD / MMC, LCD display, keyboard, microphone, and speaker are also used in a mobile phone. These are discussed in detail in Chapter 5.
  • Multimedia modules. It performs multimedia related functions like, speech encoding /decoding, audio encoding / decoding, video encoding / decoding by employing various multimedia standards (MP3, JPEG, MPEG, and so forth). As multimedia‐related functions are time consuming, so these are generally implemented in dedicated hardware block. Also, smartphone contain graphics processing unit (GPU) for rapid processing of multimedia functions. These are discussed in detail in Chapters 5 and 7.
  • Various sensors and actuators. A sensor is a device that measures a physical quantity and converts it into a signal (electrical or optical) by an instrument. They sense the changes in the environment and send them to the application processor. The commonly used sensors in handsets include accelerometers, gyroscopes, proximity sensors, ambient light sensors, barometers, and so forth. On the other hand, an actuator is a type of motor that is responsible for moving or controlling a mechanism or a system. These are discussed in detail in Chapter 5.
  • Vibrator. A vibra alert device is used to give a silent alert signal to the phone user. Generally the vibration is made using an improperly balanced motor and controlled with a pulse width modulation (PWM) signal via the battery terminal. These are discussed in detail in Chapter 5.
  • Connectivity modules. Apart from cellular system modem, the smart phone also houses several other wireless connectivity modules like, Geo Positioning System (GPS), Bluetooth (BT), FM radio, ZigBee, Wireless LAN (WLAN), and so forth. These individual submodules have RF and digital baseband processing unit and interact with the other devices, peripherals like, headset or server through radio interface. These are discussed in detail in Chapter 5.
• Power management module. This unit is responsible for distributing the regulated battery power among various modules, conversion of the battery voltage (generally 3.6 V) according to the different voltage level needed by different modules, which means up or down conversion to various voltages (such as 4.8 V, 2.8 V, 1.8 V and 1.6 V) using, for example, a DC‐DC converter, a battery power consumption control device, sleep‐related functionalities management, battery‐charging control. The battery‐charging component is responsible for charging the battery of the smartphone. These are discussed in detail in Chapter 8.
• Clock distribution module. This distributes a clock signal to the mobile phone. The clock signal is required in every digital blocks in the system and also it is required in RF unit for scheduling transmission and reception at a specific time. These are discussed in detail in Chapter 5.
• Memory. Various types of memory are used in the mobile phone for storing code and data. Generally, Flash memory, EPROM, and DRAM memory are used in a mobile phone. These are discussed in detail in Chapter 5.

Figure 1.2 System‐level block diagram of a typical smartphone

Apart from all these hardware blocks, firmware and software components reside in the memory and are executed by processors to configure, control, and process different hardware modules, applications, and protocols. These are discussed in Chapter 7.

1.2 History of the Mobile Phone

Prior to 1973, mobile telephony was limited to phones installed in cars, trains and other vehicles, mainly due to the larger size and weight of the equipment. On April 3, 1973, Martin Cooper, a senior engineer at Motorola, made the first mobile telephone call from...