WCDMA: =>Mobile Phone Glossary(1)

Thursday, July 31, 2008

=>Mobile Phone Glossary(1)

Mobile Phone Glossary
1G
In mobile telephony, first-generation systems were analog, circuit-switched. Voice links were poor, handoff unreliable, capacity low, and security non-existent. 1G systems are not now under active development – indeed, in some areas 1G spectrum is being auctioned for 2G and 3G use.

2G
In mobile telephony, second-generation protocols use digital encoding and include GSM, D-AMPS (TDMA) and CDMA. 2G networks are in current use around the world. These protocols support high bit rate voice and limited data communications. They offer auxiliary services such as data, fax and SMS. Most 2G protocols offer different levels of encryption..

2.5G
In mobile telephony, 2.5G protocols extend 2G systems to provide additional features such as packet-switched connection (GPRS) and enhanced data rates (HSCSD, EDGE).

3G
In mobile telephony, third-generation protocols support much higher data rates, measured in Mbps, intended for applications other than voice. 3G networks trials started in Japan in 2001. 3G networks are expected to be starting in Europe and part of Asia/Pacific by 2002, and in the US later. 3G will support bandwidth-hungry applications such as full-motion video, video-conferencing and full Internet access. http://www.3gpp.org/

AMPS
Advanced Mobile Phone System: a 1G standard which operates in the 800-900MHz-frequency band. It is still widely used in the United States.
Analog The simple way to transmit speech, which is translated into electronic signals of different frequency and/or amplitude. The first networks for mobile phones, as well as broadcast transmissions, were analog. Due to being longer established in some countries, analog networks may offer better coverage than digital networks, however analog phones are less secure and suffer more from interference where the signal is weak. Analog systems include AMPS, NMT and ETACS.

API
Historically, "application programming interface". Practically, an API is any interface that enables one program to use facilities provided by another, whether by calling that program, or by being called by it. At a higher level still, an API is a set of functionality delivered by a programming system, and as such the mix of APIs in a particular system tells you what that system can do.
Bluetooth An open specification for seamless wireless short-range communications of data and voice between both mobile and stationary devices. For instance, it specifies how mobile phones, computers and PDAs interconnect with each other, with computers, and with office or home phones. The first generation of Bluetooth permits exchange of data up to a rate of 1 Mbps per second, even in areas with much electromagnetic disturbance. It transmits and receives via a short-range radio link using a globally available frequency band (2.4 GHz ISM band).
bps Bits per second: a way of quantifying data transmission throughput. It is the number of pieces of information (bits) transmitted or received per second.
C++ An industry standard object-oriented compiled language, formally standardized in 1998, but tracing its history to the early 1980s, with an heritage in C and Simula. C++ is a general-purpose programming language with a bias towards systems programming. C++ runs on most computers from the most powerful supercomputers to the ubiquitous personal computers. Symbian OS is written in C++.

CDMA
Code Division Multiple Access: a digital wireless telephony transmission technique. 1. CDMA allows multiple frequencies to be used simultaneously (Spread Spectrum). The CDMA idea was originally developed for military use over 30 years ago. 2. The CDMA standards used for second-generation mobile telephony are the IS-95 standards championed by QUALCOMM.
Cellular Radio The technology that has made large scale mobile telephony possible. Current cellular networks reuse the same radio frequencies by assigning them to cells far enough apart to reduce interference. A cell is the geographical area covered by one radio base station transmitting/receiving in the center. The size of each cell is determined by the terrain, transmission power, and forecasted number of users. Service coverage of a given area is based on an interlocking network of cells, called a cell system.
Circuit-Switching Means of creating a connection by setting up a dedicated end-to-end circuit, which remains open for the duration of the communication.

History of spread spectrum and CDMA

This brief historical explanation begins with a look at Spread Spectrum (SS)
principles, since they are fundamental to the multiple access principle known as
CDMA.
The frequency bandwidth needed to transmit a given amount of information is directly
related to the information rate – the amount of information transmitted per unit of
time. The term “bandwidth” is now often used interchangeably with “bit rate” so this
appears intuitively clear to most people.
SS techniques are methods by which more frequency bandwidth is deliberately used
than motivated by the actual information rate (spectrum spreading). On one hand,
this implies a certain waste of valuable frequency spectrum; but on the other hand,
these techniques have advantages such as increasing the resistance to interference,
jamming and interception.

Technologies in WCDMA

In this section we describe some of the important innovations that constitute the WCDMA standard, developed in response to the challenging 3G requirements placed on it. We also include descriptions of how the technologies differ from those used in the IS-95 family of standards. In particular we discuss functions related to the air interface, which is the interface between the mobile device and the network.

Asynchronous network operation
Several of the requirements for WCDMA did not exist in legacy standards, including IS-95. One such requirement is asynchronous network operation. Early on, one of the fundamental technical principles shared by the Japanese and European WCDMA concepts (including CoDiT) was asynchronous operation; that is, the base stations should not have to be synchronized to each other. This was an opposite requirement to that of the IS-95 (and later Cdma2000) standard, which relies on GPS (Global Positioning System) for its proper operation. The UMTS requirement for an asynchronous system was fundamentally important because it led to a standalone and easily deployable system attractive to operators around the world. But it also gave rise to several new technological challenges for WCDMA, including cell search and handover, described below.

Cell search
Before engaging in any kind of communication with the network, a mobile device must first synchronize to the signals sent from base stations. Mobile devices need to find out which base station code to look for and then synchronize to it. Searching for all possible base station codes at all possible times is an arduous task that could potentially affect the time from power-on to placing a call. Being asynchronous, WCDMA could not employ the principle adopted in the IS-95/Cdma2000 standards, where a common base station code with unique GPS time-shifts was used throughout the system. Clearly there was a need for innovation in this area. The early Japanese version of WCDMA included a structure based on dual synchronization channels, but it was generally considered too complex. Extensive research was conducted to find an information encoding principle that would minimize the cell search time while still keeping the complexity of the search at a negligible level. Solutions were progressively proposed to the standard and soon the goals had been achieved [13]. One of the early major technical challenges of asynchronous CDMA-based 3G had been overcome.

Soft handover
In most older mobile systems, the mobile devices are connected to one base station at a time and handover is the process of seamlessly shifting a mobile device’s connection from one base station to another. In “soft handover” however, mobile devices communicate the same information through two or more base stations simultaneously (see Figure 7). In practice, soft handover is a prerequisite for any high-capacity DS-CDMA-based system operating with the same carrier frequency in neighboring cells. As early as 1988, Jan Uddenfeldt et al., of Ericsson, pioneered the fundamental principles of soft handover in some of Ericsson’s early patents in the digital cellular field [14].

Compressed mode

Already from the beginning, virtually all WCDMA mobile devices were expected to bedual-mode (to support GSM) as the initial WCDMA coverage would probably not beas wide as that of GSM. Therefore, handover of ongoing connections betweenWCDMA and GSM was crucial for a smooth early rollout of WCDMA4. For a securehandover from WCDMA to GSM, the mobile device needs to perform signalmonitoring on potential GSM target base stations in the area, even during an activecall on the WCDMA system. The problem is to find time for this, because the mobiledevice is “busy all the time” with sending and receiving on a given WCDMA carrierfrequency. A technology denoted “Compressed Mode,” originally developed in CoDiT[9, 16], was adopted in WCDMA to solve this problem.

WCDMA

Thursday, July 31, 2008

=>Mobile Phone Glossary(1)

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History of spread spectrum and CDMA

Early spread spectrum and CDMA development

Technologies in WCDMA

Compressed mode

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