part0009

Mobile communication technology allows you to communicate with others using a wireless network system. Radio waves are used within a radiotelephone creating a mobile communication system. This system involves different types of facilities. Public land mobile radio, a mobile two-way radio, amateur radio, and mobile phone are examples of different types of mobile communication systems.

Public land mobile radio is used in fire agencies, police and municipal agencies including a two way FM (Frequency Modulation) radio system. The capability of this system is restricted within a small geographical area.

A mobile two-way radios help to create a one-to-many communication system to operate within a half-duplex mode. CB (citizen band) radio is one of the most common examples of this type of radios and it utilizes AM (amplitude modulation) to operate within the frequency ranging from 26.271 MHz to 10 kHz involving 40 channels. It utilizes a press-to-talk switch as it is not a commercial service. It may be available as amplitude modulated with a single-sideband or double sideband suppressed carrier.

Amateur (HAM) radios can cover a broad frequency band ranging from 1.8 MHz to 30 MHz including CW (continuous wave), FM, AM, HF slow-scan still picture TV, facsimile, radio teleprinter, UHF or VHF slow scan or fast-scan TV, amplitude-shift keying and frequency-shift keying.

The mobile telephone provides full-duplex transmission. It involves a one-to-one system to permit two simultaneous transmissions. Every mobile unit includes a specific number to maintain privacy.

From the year of 1983, the commercial application of AMPS (advanced mobile phone system) has enhanced the growth of the mobile communication system. The cellular concept was a great breakthrough.

The advent of cellular operation has developed exponential growth within the personal communication system involving different advancements such as wireless access, integrated circuits, digital signal processing, increased battery life, and so on. The cellular system acts by following the steps below.

The Cellular telephone had stated involving two-ways analogue, communication system with frequency modulation due to the involvement of transporting voice and frequency-shift keying to control transportation and signal information. Examples of another end of the cellular system are cordless telephony, a digital cellular system, paging, and satellite mobile. Analogue cellular system is considered as the 1G (1st generation) category of cellular concept. The digital cellular low-power wireless is considered as 2G (2nd generation) category of cellular concept.

Analogue Cellular Phone: In New Jersey, Bell Labs placed a proposal for a cellular telephone considering as an AMPS (advanced mobile phone system) within the year 1970. The operation of AMPS was started on 13th October 1983 as standard cellular telephone service. It utilizes narrow land FM including usable 300-3 kHz audio frequency band and positive and negative 12 kHz maximum frequency deviation for 100 percent modulation. It corresponds to 3 kHz considering Carson’s rule.

AMPS utilizes FDMA (frequency direction multiple access) within the area where transmission is divided within the frequency domain. A pair of voice channels involving forward as well as reverse for the duration of the call is allowed to the subscribers. Analogue cellular channels include both voices utilizing digital signaling information and FM by following binary FSK.

Digital Cellular System : It allows development within both performance and capacity. FDMA utilizes a frequency canalization approach to manage spectrum whereas time-division multiple access (TDMA) uses an approach of time-division. The complete available cellular RF spectrum is divided into subdivision classes within narrow-based channels and these are utilized between base stations and mobile points as a one-way communication link.

A specific amount of frequency spectrum is usually issued to a cellular system. A user can share easily the available spectrum as multiple access methods are utilized. Multiplexing can be followed by three dimensions for wireless communication and these three dimensions are TDMA (time-dimension multiple access), CDMA (Code-dimension multiple access) and FDMA (frequency-dimension multiple access) and its various OFDMA.

The available spectrum is separated into frequency channels or narrow frequency bands within TDMA. These are also separated within many time slots. Each frequency channel of frequency 30 kHz is separated within three slots according to American digital cellular standard IS 136. On the other hand, each frequency channel of 200 kHz is separated within eight-time slots according to the European digital cellular system. GSM Guard bands are essential both time slots and frequency channels.

The users share the available spectrum within a frequency band within FDMA named traffic channels. Different users are allotted different channels considering frequency band contains the user’s signal power. All the analogue cellular systems involve FDMA. A data stream is followed involving several lower-rate subcarrier tones within a multi-cellular transmission method named OFDM. The mobile communication system includes OFDM to control hostile frequency selective fading. Wireless network standard is also maintained by incorporating OFDM.

OFDM offers the advantages of OFDM modulation and coherent identification. It also has several qualities that are complicated for high-speed transmission in the future. The need for electrical bandwidth can be decreased to a great extent by involving up-down conversion for the OFDM transceiver. It is very effective for high-speed design as electrical bandwidth involves the cost. Moreover, the advantages of an effective algorithm of FFT (fast Fourier transform) or inverse FFT are established when signal processing is involved within the OFDM transceiver.

Generally, communication systems have modulation of a carrier to create a band pass waveform. A digital signal can help to modulate the frequency amplitude or phase of the sinusoidal carrier making three different digital modulation forms such as FSK (frequency-shift keying), ASK (amplitude-shift keying) and PSK (phase-shift keying). Additionally, some modulation schemes are also involved in engaging a combination of phase modulation and amplitude modulation. It is also important to note PSK transmission is polar whereas the ASK signal is non-polar. PSK represents a non-linear modulation scheme whereas ASK represents a linear modulation. PSK works better than Ask.

The above-mentioned methods of digital modulation are not spectrally efficient as the available channel bandwidth is not completely utilized. OPSK helps to improve spectral efficiency. It involves two types of message sources. In this method, modulation carriers create the output waveform by combining within the quadrature phase. In QPSK, modulation gains and the amplitude of the modulator waveform are formed about equally.

There is no need to involve synchronous carrier for identification of PSK signals within OPSK modification of PS. It is an igneous method in which the derivation of carrier reference is made from the received waveform within the foregoing bit interval by an application of a 1-bit delay.

Digital cellular networks such as GSM, EDGE, IS-136 and PDC (packet data service) support short message service which is one of the most common packet services. It represents a store-and-forward or packet mode service and it offers inter-working involving the different services and applications within a fixed network. Signaling and control channels are usually utilized for data transmission due to message transfer between applicable network services.

GPRS is very important to represent add-on capabilities regarding the basic voice-optimized cellular network system to handle important properties of radio-access technology.

You will have to modify the radio-access part when you want to enhance the capabilities for the data handling of 2G service. EDGE is the form of modification and it has evolved in Europe. It helps to adopt a mechanism for link selecting the best modulation combination and encoding schemes considering the time varying quality of the link. EDGE concept involves both packet mode as well as circuit mode and is also enough generic to use within other digital cellular systems. It acts within the bandwidth of 200 kHz including at least one high-level modulation scheme and specific efficient coding systems.

A spread spectrum is a specific communication method that involves more radio frequency purposefully than the essential transmission of a signal. It is essential to improve the signal-to-noise ratio. It helps to prevent intentional jamming and to secure communication.

In the frequency hopping method, the transmitted frequency is converted pre-assigned channel by spreading the narrowband signal as a function of time. The pre-assigned channels are identified by following the order of pseudo-random.

In the direct sequence method, the signal is expanded over a broadband part of the radio band to spread the signal. It encodes for being the transmission of digital data by using PN (pseudo noise) code generated locally.

Spread spectrum signals have a large number of different signaling formats and they are used to communicate data symbols. As a result of this, although the receiver can identify one of these formats, it fails to detect any other formats through a single message. The spread spectrum is known as the multiplicity factor of a communication link as it contains many formats.

CDMA is a type of direct sequence involving spread spectrum technology. It helps many users to engage the same frequency and time allocations within a mentioned space band. CDMA differentiates signals from different signals within the same spectrum by assigning unique spreading code for each user to layout base band data before transference. Considering this platform, 2G and 3G services have been made. Chip rate represents a signal spreading rate. CDMA offers more analogue capacity than AMPS and more calling capacity than TDMA and GSM systems.

PCS involves a combination of intelligent networks and cellular networks. It represents SST (super simple transfer) into office protocol. It helps to distinguish physical components of switching networks such as signal control point, signal service point and signal transfer point from the services which SST network offers. As the North American implementation, PCS follows the European GSM standard. GSM involves its own TDMA techniques and offers expanded capacity and specific services such as call forwarding, caller ID and short messaging. A critical quality was roaming seamlessly allowing subscribers to move across the boundaries of the provider. A secondary frequency band was specialized in 1990. This band comprises two domains ranging from 1710 MHz to 1785 MHz and from 1805 MHz to 1880 MHz respectively.

ETSI (European Telecommunication Standards Institute) had developed DECT which is a type of PCS. It was developed as a PABX data LAN of wireless communication. It requires minimal access to open cordless representing a closed environment. It involves a TDD or TDMA frame structure using 24 slots equally allocating to operate uplink and downlink. It helps to specify both duplex and simplex operation. It utilizes multilevel modulation to achieve a high level of data rates.

The Group Special Mobile developed GSM and it is considered an initiative of the CEPT (Conference of European Post and Telecommunication) administration. The primary band of GSM involves 900 MHs band including two sub-bands of 25 MHz. GSM systems, such as ICO, Globalstar, and Iridium utilize LEO (low-earth orbit) constellations or MEO (medium-earth orbit) satellites and continue operations for spreading networks for existing PCS networks and cellular networks. These systems extend the network services to any location of the earth’s surface utilizing dual-mode.

PCSS (personal communication satellite service) incorporates QPSK modulation and both TDMA and FDMA to utilize LEO satellite repeaters. The international roaming and features such as frequency hopping, short message service, privacy and encryption, and discontinuous transmission are the major advantages of GSM. Other benefits are waiting, forwarding, hold, barring and teleconferencing. The basic architecture includes base station sub-system, system interworking, network sub-system, mobile stations, and system interfaces. The activation and operation of a GSM terminal require SIM (subscriber identity module).

GPS helps in reliable navigation within any position of the earth and the operation is allowed within all kinds of weather conditions of a day. Airborne, marine and land users can utilize the GPs system which was developed in 1983. It includes three segments such as space segment, user segment, and control segment.

GPS involves 24 NAVSTAR satellites including three spare satellites that are positioned within the orbit at a distance of 20,200 km. considering six circular orbital planes involving a 12 hour orbital period for each orbit. These satellites broadcast continuously navigational signals named coarse acquisition code by operating an L1 band with 1.5 GHz frequency. Anyone can receive these codes to decode and find navigational parameters such as latitude, velocity, longitude and time.

The control segment has an MCS (master control system) and many smaller earth stations named monitoring stations positioned at various places within the world. MCS receives measured data which is delivered by monitoring stations by tracking satellites. MCS returns satellite parameters to the satellite by computing them. As a result of this, all GPs receivers get broadcast service.

The user segment includes all stationary and moving objects along with GPS receivers. As GPS receiver computes its velocity and position in every second as it is a multi-channel satellite.

Bluetooth technology can be compared to WLAN technology. It aims to piconets that are within the local-area network involving limited coverage and eliminating the requirement of infrastructure. A collection of Bluetooth devices termed as piconet and synchronized to the same hopping sequence. One Bluetooth device within the piconet performs as master and all other Bluetooth devices perform under it. The master device selects the hopping pattern and other Bluetooth devices synchronized to the selected pattern. The master device uses the device ID, which 48 bit a unique identifier in the world, to select the hopping pattern. It also assigns the address of a 3-bit active member for all active devices.

All parked devices utilize the address of an 8-bit parked member and there is no need for an address when the devices are in standby mode. The aim of Bluetooth development was to utilize a low-cost, single-chip and radio-based technology for wireless networks for headsets, laptops, notebooks, and so on. Bluetooth operates within the ISM band with 2.4 GHz. For modulation, Bluetooth transceivers utilize Gaussian FSK and they are categorized within three power classes such as Class 1 with a maximum power of 100mW, Class with a maximum power of 2.5mW and Class 3 with a maximum power of 1mW.

In 1990, the 1G feature was released for use in GSM. 1G system represents analogue systems like AMPS which divides the bandwidth by using FDM within significant frequencies for being assigned to individual calls.

The 2G system represents a second-generation digital mobile system utilizing either CDMA or TDMA method. Digital cellular systems have many benefits over analogue by utilizing digital modulation. They also include more privacy, better application of bandwidth and incorporation of error identification and correction.

By adding the latest bandwidth technology, the 2G system has been converted into a 2.5G system. It allows the transmission of high-data-rate for Web browsing and it also allows WAP (wireless application protocol) which is a new format language of browsing. The various upgrade paths include GPRS, HSCSD (high-speed circuit-switched data) and EDGE. HSCSD develops the data rate of available application to 14.4 kbps comparing to available data rate GSM to 9.6 kbps. HSCSD can offer a raw transmission rate maximum of 57.6 kbps to individual users.

EDGE represents 8-PSK which is a new digital modulation and involves octal phase-shift keying. It is famous as a coding scheme and multiple modulations by allowing nine various air interface formats including the changeable degree of error control as well as protection. These formats are quickly and automatically selectable. The coverage range of EDGE is smaller than GRPS and HSCSD.

The 3G system has been developed to overcome the defects of the 2G system and 2.5G system. It involves a wideband wireless network to offer developed clarity within conversations. Different countries within the world are recently selecting new radio spectrum bands for the accommodation of the 3G network system. ITU has built 1700 to 1855 MHz, 2500 to 2690 MHz and 806 to 960 MHz bands. In this system, 2 Mbps is the targeted data rate. Packet switching is used to send data and circuit switching is used to interpret voice calls.

UMTS (universal mobile telecommunication system) or W-CDMA convinces backward compatibility by using TDMA technologies of 2G and 2.5G. W-CDMA has been made for packet-based always-on wireless network service maintaining an air interface standard. As a result of this, computers and entertainment devices can share and a similar wireless network system and make a connection to the internet system anywhere and anytime. W-CDMA allows a data rate maximum of 2.048 Mbps when the user is in a stationary position and allowing high-level data, streaming audio, multimedia, and broadcast type services to the consumers.

The time slots within W-CDMA help in periodic function but don’t help to separate users. The range of bandwidth per W-CDMA channel is from 4.4 MHz to 5 MHz. The 3G system is used within multimedia communication devices and personal mobile phones. It allows video conferencing and also helps in position-based services.