ADVANCED MOBILE PHONE SYSTEM (AMPS)
Advanced Mobile Phone System (AMPS) was an analogmobile phone system standard developed by Bell Labs, and officially introduced in the Americas in 1983 and Australia in 1987. It was the primary analog mobile phone system in North America (and other locales) through the 1980s and into the 2000s. As of February 18, 2008, carriers in the United States were no longer required to support AMPS and companies such as AT&T and Verizon have discontinued this service permanently. An AMP was discontinued in Australia in September 2000. The signals received from a transmitter cover an area called a cell. As a user moves out of the cell’s area into an adjacent cell, the user begins to pick up the new cell’s signals without any noticeable transition. The signals in the adjacent cell are sent and received on different channels than the previous cell’s signals to so that the signals don’t interfere with each other.
DIGITAL AMPS (D-AMPS)
D-AMPS (Digital-Advanced Mobile Phone Service), sometimes spelled DAMPS, is a digital version of AMPS (Advanced Mobile Phone Service), the original analog standard for cellular telephone phone service in the United States. Both D-AMPS and AMPS are now used in many countries. D-AMPS adds time division multiple access (TDMA) to AMPS to get three channels for each AMPS channel, tripling the number of calls that can be handled on a channel.
D-AMPS use existing AMPS channels and allows for smooth transition between digital and analog systems in the same area. Capacity was increased over the preceding analog design by dividing each 30 kHz channel pair into three time slots (hence time division) and digitally compressing the voice data, yielding three times the call capacity in a single cell. A digital system also made calls more secure because analog scanners could not access digital signals.
TIME DIVISION MULTIPLE ACCESS (TDMA)
Time division multiple access (TDMA) is digital transmission technology that allows a number of users to access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel. The TDMA digital transmission scheme multiplexes three signals over a single channel. The current TDMA standard for cellular divides a single channel into six time slots, with each signal using two slots, providing a 3 to 1 gain in capacity over advanced mobile-phone service (AMPS). Each caller is assigned a specific time slot for transmission.
The two major (competing) systems that split the RF are TDMA and CDMA. CDMA is a spread- spectrum technology that allows multiple frequencies to be used simultaneously. CDMA codes every digital packet it sends with a unique key.
A CDMA receiver responds only to that key and can pick out and demodulate the associated signal. The TDMA system is designed for use in a range of environments and situations, from hand portable use in a downtown office to a mobile user traveling at high speed on the freeway. The system also supports a variety of services for the end user, such as voice, data, fax, short message
services, and broadcast messages. TDMA offers a flexible air interface, providing high performance with respect to capacity, coverage, and unlimited support of mobility and capability to handle different types of user needs.
“TDMA also provides the user with extended battery life and talk time since the mobile is only transmitting a portion of the time (from 1/3 to 1/10) of the time during conversations.”
TDMA relies upon the fact that the audio signal has been digitized; that is, divided into a number of milliseconds-long packets. It allocates a single frequency channel for a short time and then moves to another channel. The digital samples from a single transmitter occupy different time slots in several bands at the same time.
TDMA is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2Gcellular systems such as Global System for Mobile Communications (GSM).
CODE – DIVISION MULTIPLE ACCESS (CDMA)
In CDMA systems your encoded voice is digitalized and divided into two packets. These packets tagged with “codes.” The packets then mix with all of the other packets of traffic in the local CDMA network as they are routed towards their destination. The receiving system only accepts the packets with the codes destined for it. Analog systems are FDM. Digital systems can utilize either
TDMA or CDMA.FDM systems typically allow one call per 10Khz or 30Khz of spectrum. Early TDMA systems tripled the capacity of FDM systems. Recent advances in TDMA promise to provide forty times the carrying capacity of FDM systems. CDMA promises to improve on the results of TDMA.
CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. There are trillions of possible frequency-sequencing codes, which enhance privacy and makes cloning difficult. Code Division Multiple Access (CDMA) is a digital air interface standard, claiming eight to fifteen times the capacity of traditional analog cellular systems. It employs a commercial adaptation of a military spread-spectrum technology. Based on spread spectrum theory, it gives essentially the same services and qualities as wire line service. The primary difference is that access to the local exchange carrier (LEC) is provided via a wireless phone. Though CDMA ̳s application in cellular telephony is relatively new, it is not a new technology. CDMA has been used in many military applications, such as:
- Anti-jamming (because of the spread signal, it is difficult to jam or interfere with a CDMAnsignal).
- Ranging (measuring the distance of the transmission to know when it will be received).
- Secure communications (the spread spectrum signal is very hard to detect).
CDMA is a spread spectrum technology, which means that it spreads the information contained in a particular signal of interest over a much greater bandwidth than the original signal. With CDMA, unique digital codes, rather than separate RF frequencies or channels, are used to differentiate subscribers. The codes are shared by both the mobile station (cellular phone) and the base station, and are called pseudo-random code sequences. Since each user is separated by a unique code, all users can share the same frequency band (range of radio spectrum). This gives many unique advantages to the CDMA technique over other RF techniques in cellular communication. CDMA is a digital multiple access technique and this cellular aspect of the protocol is specified by the Telecommunications Industry Association (TIA) as IS-95. In CDMA, the BSSAP is divided into the DTAP and BSMAP (which corresponds to BSSMAP in GSM).
GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS (GSM)
In 1989, GSM responsibility was transferred to the European Telecommunication Standards Institute (ETSI), and phase I of the GSM specifications were published in 1990. Commercial service was started in mid1991, and by 1993 there were 36 GSM networks in 22 countries, with 25 additional countries having already selected or considering GSM In addition to Europe, South Africa, Australia, and many Middle and Far East countries have chosen to adopt GSM. By the beginning of 1994, there were 1.3 million subscribers worldwide. The acronym GSM now (aptly) stands for Global System for Mobile telecommunications.
From the beginning, the planners of GSM wanted ISDN compatibility in services offered and control signalling used. The radio link imposed some limitations, however, since the standard ISDN bit rate of 64 Kbps could not be practically achieved. The digital nature of GSM allows data, both synchronous and asynchronous data, to be transported as a bearer service to or from an ISDN terminal. The data rates supported by GSM are 300 bps, 600 bps, 1200 bps, 2400 bps, and 9600 bps.
The most basic teleservice supported by GSM is telephony. A unique feature of GSM compared tonolder analog systems is the Short Message Service (SMS). Supplementary services are provided on top of teleservices or bearer services, and include features such as international roaming, caller identification; call forwarding, call waiting, multiparty conversations, and barring of outgoing (international) calls, among others.The most widely accepted standard for mobile communication is the GSM-network. GSM stands for Global System for Mobile communications and uses a dedicated two-way radio infrastructure for cellular telephony and also data applications.
The GSM technology is based on TDMA (Time Division Multiple Access) which allows for very large numbers of subscribers on a cellular and micro-cellular approach. The GSM standard allows for voice, messaging and data services. The predecessor of GSM is AMPS, Advanced Mobile Phone System. We will not discuss this technology extensively in this study, but from a point of completeness, it is included in figure. GSM (Global System for Mobile communication) is a digital mobile telephony system that is widely used in Europe and other parts of the world. GSM uses a variation of time division multiple access (TDMA) and is the most widely used of the three digital wireless telephony technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data,
then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1800 MHz frequency band. GSM, together with other technologies, is part of the evolution of wireless mobile telecommunications that includes High- Speed Circuit-Switched Data (HCSD), General Packet Radio System (GPRS), Enhanced Data GSM Environment (EDGE),
“Since many GSM network operators have roaming agreements with foreign operators, users
can often continue to use their mobile phones when they travel to other countries. SIM cards
(Subscriber Identity Module) holding home network access configurations may be switched to
those metered local access, significantly reducing roaming costs while experiencing no
reductions in service.”
W-CDMA (WIDEBAND CODE-DIVISION MULTIPLE ACCESS)
W-CDMA (Wideband Code-Division Multiple Access), an ITU standard derived from Code- Division Multiple Access (CDMA), is officially known as IMT-2000 direct spread. W-CDMA is a third-generation (3G) mobile wireless technology that promises much higher data speeds to mobile and portable wireless devices than commonly offered in today’s market.
W-CDMA can support mobile/portable voice, images, data, and video communications at up to 2Mbps (local area access) or 384 Kbps (wide area access). The input signals are digitized and transmitted in coded, spread-spectrum mode over a broad range of frequencies. A 5 MHz-wide carrier is used, compared with 200 KHz-wide carrier for narrowband CDMA. W-CDMA has been developed into a complete set of specifications, a detailed protocol that defines how a mobile phone communicates with the tower, how signals are modulated, how data grams are structured, and system interfaces are specified allowing free competition on technology elements.
CDMA is short for code division multiple access. It is the technology used for transferring data, voice and signal information between cellular sites and cell phones. 1xRTT is a version of CDMA that uses a pair of 1.25MHz radio channels. CDMA was originally used during World War II by the British allies for foiling the German from jamming transmissions. Qualcomm was the companies that had created the chips for CDMA and were then later able to develop this technology as we know it and commercialize it.
CDMA is not as fast as EVDO but is a very efficient method of transferring signals both voice and data. Peak data speeds are up to 144Kbps. 1xRTT is used in the United States by a variety of carriers such as Sprint and Verizon, and in Canada by Telus Mobility and Bell Mobility. Also Known As: 3G1X, IMT-CDMA, Multi-Carrier, IS-2000, 2.5G
CDMA 2000 specification was developed by the Third Generation Partnership Project 2 (3GPP2), a partnership consisting of five telecommunications standards bodies: ARIB and TTC in Japan, CWTS in China, TTA in Korea and TIA in North America. Cdma2000 has already been implemented to several networks as an evolutionary step from CDMA One as cdma2000 provides full backward compatibility with IS-95B. Cdma2000 is not constrained to only the IMT-2000 band, but operators can also overlay acdma2000 1x system, which supports 144 kbps now and data ratesup to 307 kbps in the future, on top of their existing CDMA One network.
EDGE (ENHANCED DATA RATES FOR GSM EVOLUTION)
EDGE is a new air-interface technology, to offer third-generation data rates for the global evolution of GSM and TDMA to 3G. EDGE uses 8 Phase Shift Keying Modulation (8-PSK), rather than normal GSM Gaussian Minimum Shift Keying (GMSK). This will offer 48 Kbits/s per GSM timeslot.
The catch is that EDGE requires higher radio signal quality than that found in an average GSM network before higher data throughput can be reached. This means more base stations (especially indoor) and infrastructure build-out for established GSM operators that wish to migrate to EDGE which enables services like multimedia emailing, Web infotainment and video conferencing to be easily accessible from wireless terminals. EDGE is designed for migration into existing GSM and TDMA networks, enabling operators to offer multimedia and other IP-based services at speeds of up to 384 Kbits/s (possibly 473 Kbits/s in the future) in wide area networks. An important attraction of EDGE is the smooth evolution and upgrade of existing network hardware and software, which can be introduced into an operator’s current GSM or TDMA network in existing frequency bands.
GENERAL PACKET RADIO SERVICE (GPRS)
GPRS is expected to profoundly change the mobile data services that GSM, CDMA and DMA (ANSII36) network operators can offer. GPRS will increase opportunities for higher revenues and enable new, differentiated services and tariff dimensions to be offered (such as a charge for the number of kilobytes of data transferred). GPRS combines mobile access with Internet protocol (IP)-based services, using packet data transmission that makes highly efficient use of radio spectrum and enables high data speeds. It gives users increased bandwidth, making it possible and cost-effective to remain constantly connected, as well as to send and receive data as text, graphics and video.
GPRS (general packet radio service) is a packet-based data bearer service for wireless communication services that is delivered as a network overlay for GSM, CDMA and TDMA (ANSI-I36) networks. GPRS applies a packet radio principle to transfer user data packets in an efficient way between GSM mobile stations and external packet data networks. Packet switching is where data is split into packets that are transmitted separately and then reassembled at the receiving end. GPRS supports the world’s leading packet-based Internet communication protocols, Internet protocol (IP) and X.25, a protocol that is used mainly in Europe. GPRS enables any existing IP or X.25 application to operate over a GSM cellular connection. Cellular networks with GPRS capabilities are wireless extensions of the Internet and X.25 networks.
GPRS gives almost instantaneous connection set-up and continuous connection to the Internet. GPRS users will be able to log on to an APN (Access Point Name) and have access to many services or an office network (without the need to dial-up) and remain continuously connected until they log off, only paying when data is actually transmitted. A physical end-to-end connection is not required because network resources and bandwidth are only used when data is actually transferred. This makes extremely efficient use of available radio bandwidth.
Therefore, GPRS packet-based services should cost users less than circuit-switched services since communication channels are being shared and are on a ̳as-packets-are-needed‘ basis rather than dedicated to only one user at a time. It should also be easier to make applications available to mobile users because the faster data rate means that middleware currently needed to adapt applications from fixed line rates to the slower speed of wireless systems will no longer be needed. The key drivers for operators to evolve to GPRS networks are to:
- increase revenues by moving into the mobile data market, especially since the voice market has had profit margins squeezed with the commoditization of voice services
- gain new subscribers who require mobile data services or do not want to invest in a PC to gain Internet access
- retain current subscribers by offering new services
- reduce costs due to the efficient use of network resources
- Ease of adapting applications for mobile users because high data speeds mean that middleware is no longer required to convert fixed applications for mobile use.
The overall benefits of GPRS networks for mobile operators are discussed below. GPRS is based on GSM communication and will complement existing services such as circuit-switched cellular phone connections and the Short Message Service (SMS). It will also complement Bluetooth, a standard for replacing wired connections between devices with wireless radio connections. GPRS stands for General Packet Radio Services and it is a technology that is built on top of GSM, allowing traffic to be sent and received at a speed of approximately 170 Kbps (kilobit per second). This is a whole lot faster than the current GSM possibilities but only time will learn if it will be enough. GPRS supports Packet Switched networks. Packet switching means that GPRS radio resources are used only when users are actually sending or receiving data.
Rather than dedicating a radio channel to a mobile data user for a fixed period of time, the available radio resource can be concurrently shared between several users. This efficient use of scarce radioresources means that large numbers of GPRS users can potentially share the same bandwidth and be served from a single cell. The actual number of users supported depends on the application being used and how much data is being transferred. Because of the spectrum efficiency of GPRS, there is less need to build in idle capacity that is only used in peak hours. GPRS therefore lets network operators maximize the use of their network resources in a dynamic and flexible way, along with user access to resources and revenues.
PERSONAL DIGITAL CELLULAR (PDC)
Personal Digital Cellular (PDC) is a 2Gmobiletelecommunications standard developed and used exclusively in Japan. After a peak of nearly 80 million subscribers to PDC, it had 46 million subscribers in December 2005, and is slowly being phased out in favour of 3G technologies like W-CDMA and CDMA2000. At the end of October 2008, the count had dwindled down to 10.4 million subscribers.
The present invention relates to a communication controlling apparatus in a local area radio system using a PDC (Personal Digital Cellular) portable terminal unit, in particular, to an audio/non-audio PDC communication controlling apparatus that is connected to a private branch exchange (PBX), that has the same service as a public PDC system, and that provides the service of the PBX. A first aspect of the present invention is a PDC communication controlling apparatus, comprising an audio processing means for converting a digital audio signal that has been encoded at a transmission rate of a personal digital cellular (PDC) into a digital audio signal at a transmission rate of a digital exchange network, a small radio base station controlling means accommodating a plurality of small radio base stations that are connected to PDC portable terminal units through radio circuits and that have different radio cover areas, the small radio base station controlling means managing the radio cover areas of the PDC portable terminal units, controlling calls, and controlling and managing the radio circuits, a network-side adaptor used in non-audio communications with the PDC portable terminal units, a PDC/network interface means connected to a private branch exchange through a plurality of communication paths, a time division switch for connecting the PDC/network interface, the audio processing means, the radio base station controlling means, and the network-side adaptor and for switching the connection state thereof under the control of the small radio base station controlling means on time division basis, wherein the small radio base station controlling means separates the PDC/network interface means from the network-side adaptor in the case that a termination call is an audio communication, places the network-side adaptor between the PDC/network interface means and the audio processing means in the case that the termination call is a non-audio communication, and loops back the communication path for an extension communication in the case that the termination call is a communication performed between the PDC portable terminal units.
LONG TERM EVOLUTION (LTE)
Long Term Evolution (LTE) is a 4G wireless broadband technology developed by the Third Generation Partnership Project (3GPP), an industry trade group. 3GPP engineers named the technology “Long Term Evolution” because it represents the next step (4G) in a progression from GSM, a 2G standard, to UMTS, the 3G technologies based upon GSM. LTE provides significantly increased peak data rates, with the potential for 100 Mbps downstream and 30 Mbps upstream, reduced latency, scalable bandwidth capacity, and backwards compatibility with existing GSM and UMTS technology. Future developments could yield peak throughput on the order of 300 Mbps. The upper layers of LTE are based upon TCP/IP, which will likely result in an all-IP network
similar to the current state of wired communications. LTE will support mixed data, voice, video and messaging traffic. LTE uses OFDM (Orthogonal Frequency Division Multiplexing) and, in later releases, MIMO (Multiple Input Multiple Output) antenna technology similar to that used in the IEEE802.11n wireless local area network (WLAN) standard. The higher signal to noise ratio
(SNR) at the receiver enabled by MIMO, along with OFDM, provides improved coverage and throughput, especially in dense urban areas.
LTE is scheduled to be launched commercially in 2010 by Verizon Wireless and AT&T Wireless. T-Mobile and Alltel have also announced plans to roll out 4G capabilities based on LTE. These networks will compete with Clearwire’sWiMAX for both enterprise and consumer broadband wireless customers. Outside of the US telecommunications market, GSM is the dominant mobile standard, with more than 80% of the world’s cellular phone users.
As a result, HSDPA and then LTE are the likely wireless broadband technologies of choice for most users. Nortel and other infrastructure vendors are focusing significant research and development efforts on the creation of LTE base stations to meet the expected demand. When implemented, LTE has the potential to bring pervasive computing to a global audience, with a wire-like experience for mobile users everywhere.
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