幾月之前,我幫自己的好友介紹一位女性友人給他認識,原本是想撮合他們
但現在看起來真是冤家一對飽,男的沒交過女友,不太懂得情趣,也不常打電話約女生出去
那女生方面,又很堅持,事事都要按照他的方式來規劃,明明共同出遊是一件好事情
但總是因為自己的想法,讓現在的處境變的很怪異,看樣子女生是想退出的感覺
但都還沒進一步認識,就開始再放棄,難怪友人說介紹容易但相處難,太龜毛
2009年5月31日 星期日
2009年5月25日 星期一
DECT
什麼是DECT呢? 請先看以下解釋:
數位增強(泛歐式數位)無線電話系統(DECT)
泛歐式數位無線電話系統（DECT）規格發表於1992年，為歐洲的無線電話標準。為了促銷DECT至全世界，歐洲國家將 DECT的「European」一字改成「Enhanced」以沖淡歐區域產的意味。數位或增強無線電話通信系統（Digital Enhanced Cordless Telecommunications, DECT）以超微細（Pico cell）方式在高密度用戶區提供服務，並使TDMA的技術將一個頻道同割成12個語音通道，使用TDD雙工模式，而每一個語音通道的編碼速率為32kb/s。
DECT系統用於不需協調的環境，在該環境下基地台間並不需要同步，且無線通道以動態方式靈活分配。DECT提供手機睡眠模式（Sleep mode）以減少耗電，通話過程干擾太大，還可將通話線路由一個時槽移至另一個時槽，此過程稱之為時槽轉換（Time slot transfer）DECT提供無縫交遞（Seamless handoff）。
(摘錄自中華電信網頁)
DECT or Digital Enhanced Cordless Telecommunications (formerly Digital European Cordless Telephone[citation needed]) is an ETSIstandard for digital portable phones (cordless home telephones), commonly used for domestic or corporate purposes. DECT can also be used for wireless broadband data transfers. DECT is recognised by the ITU as fulfilling the IMT-2000 requirements and thus qualifies as a 3Gsystem. Within the IMT-2000 group of technologies, DECT is referred to as IMT-FT (Frequency Time).
DECT was developed by ETSI but has since been adopted by many countries all over the world. The original DECT frequency band (1880MHz–1900 MHz) is used in all countries in Europe. Outside Europe, it is used in most of Asia, Australia and South America. In the United States, the Federal Communications Commission in 2005 changed channelization and licensing costs in a nearby band (1920 MHz–1930 MHz, or 1.9 GHz), known as Unlicensed Personal Communications Services (UPCS), allowing DECT devices to be sold in the U.S. with only minimal changes. These channels are reserved exclusively for voice communication applications and therefore are less likely to experience interference from other wireless devices such as baby monitors and wireless networks.
Application
The DECT standard fully specifies a means for a portable unit such as a cordless telephone to access a fixed telecoms network via radio, but unlike the GSM standards does not specify any internal aspects of the fixed network itself. Connectivity to the fixed network (which may be of many different kinds) is done through a base station or "Radio Fixed Part" to terminate the radio link, and a gateway to connect calls to the fixed network. In most cases the base station connection is to the public switched telephone network or telephone jack, although connectivity with newer technologies such as Voice over IP has become available. There are also other devices such as some baby monitors utilizing DECT, and in these devices there is no gateway functionality.
The DECT standard originally envisaged three major areas of application:[citation needed]
- domestic cordless telephony, using a single base station to connect one or more handsets to the public telecoms network, which is now available
- enterprise premises cordless PABXs and wireless LANs, using many base stations for coverage. Calls continue as users move between different coverage cells, through a mechanism called handover. Traffic both within the system and to the public telecoms network
- public access, using large numbers of base stations to provide building or urban area coverage as part of a public telecoms network.
Of these, the domestic application (cordless home telephones) has been extremely successful. The enterprise PABX market had some success, and all the major PABX vendors have offered DECT access options. The public access application has not succeeded, since public cellular networks have fulfilled the need better. The one major application of DECT for public access, the Telecom Italia's FIDO network covering major cities in Italy, lasted about a year and was shut in 1997.
DECT has also been used for Fixed Wireless Access as a substitute for copper pairs in the "last mile" in countries such as India and South Africa.[citation needed] By using directional antennas and sacrificing some traffic capacity, cell coverage could extend to over 10 km. In Europe, the power limit laid down for use of the DECT spectrum (250 mW peak) was expressed in ERP, rather than the more commonly-used EIRP, thus permitting the use of powerful directional antennas to produce much higher EIRP and hence long ranges.
VoIP/IP-DECT
In business, DECT has become an essential part of many PABX installations with manufacturer's proprietary methods of supporting PABX features over the DECT standard.[citation needed]Since the onset of the migration from TDM PBXs to VoIP and VoIP hybrid solutions, manufacturers such as Ascom Wireless Solutions, Aastra Technologies, Philips, Avaya and Polycomhave developed IP-DECT solutions where the backhaul from the base station is VoIP (H323 or SIP) while the handset loop is still DECT. These solutions are sometimes restricted by the cost of the base station but may be economic where the concentration of users is high.[citation needed] PBX networking vendors such as Cisco promote the adoption of WIFI-VoIP handsets as the replacement for DECT, but this imposes significant overhead on the design and complexity of the WIFI network in order to provide roaming, coverage and reservation of bandwidth, not to mention QOS.[citation needed] The question of Voice Mobility in commercial environments is still very open. DECT is robust but needs its own radio infrastructure. WIFI is deployed as an ad-hoc network environment. The new entrant into the field will be 3G-nano Cell technology where VoIP sessions would be supported as a private connection onto a 3G handset/PDA.
Technical details
Some DECT properties:[citation needed]
- Audio codec: G.726
- Net bit rate: 32 kbit/s
- Frequency: 1880 MHz–1900 MHz in Europe, 1900 MHz-1920 MHz in China, 1910 MHz-1930 MHz in Latin America and 1920 MHz–1930 MHz in the US
- Carriers: 10 (1,728 kHz spacing) in Europe, 5 (1,728 kHz spacing) in the US
- Time slots: 2 x 12 (up and down stream)
- Channel allocation: dynamic
- Average transmission power: 10 mW (250 mW peak) in Europe, 4 mW (100 mW peak) in the US
The DECT physical layer uses:
- Frequency division multiple access (FDMA),
- Time division multiple access (TDMA) and
- Time division duplex (TDD)
This means that the radio spectrum is divided into physical channels in two dimensions: frequency and time.
The maximum allowed power for portable equipment as well as base stations is 250 mW. A portable device radiates an average of about 10 mW during a call as it is only using one of 24 time slots to transmit.
The DECT media access control layer is the layer which controls the physical layer and provides connection oriented, connectionless and broadcast services to the higher layers. It also provides encryption services with the DECT Standard Cipher (DSC). The encryption is fairly weak, using a 35-bit initialization vector and encrypting the voice stream with 64-bit encryption. There are reports[1] that the security algorithm has been broken.[2]
The DECT data link layer uses LAPC (Link Access Protocol Control), a specially designed variant of the ISDN data link protocol called LAPD. They are based on HDLC.
The DECT network layer always contains the following protocol entities:
- Call Control (CC)
- Mobility Management (MM)
Optionally it may also contain others:
- Call Independent Supplementary Services (CISS)
- Connection Oriented Message Service (COMS)
- Connectionless Message Service (CLMS)
All these communicate through a Link Control Entity (LCE).
The call control protocol is derived from ISDN DSS1, which is a Q.931 derived protocol. Many DECT-specific changes have been made.[specify] The mobility management protocol includes many elements similar to the GSM protocol, but also includes elements unique to DECT.
Unlike the GSM protocol, the DECT network specifications do not define cross-linkages between the operation of the entities (eg Mobility Management and Call Control). The architecture presumes that such linkages will be designed into the interworking unit that connects the DECT access network to whatever mobility-enabled fixed network is involved. By keeping the entities separate, the handset is capable of responding to any combination of entity traffic, and this creates great flexibility in fixed nework design without breaking full interoperability.
DECT GAP is an interoperability profile for DECT. The intent is that two different products from different manufacturers that both conform not only to the DECT standard, but also to the GAP profile defined within the DECT standard, are able to interoperate for basic calling. The DECT standard includes full testing suites for GAP, and GAP products on the market from different manufacturers are in practice interoperable for the basic functions.
DECT for Data Networks
Other interoperability profiles exist in the DECT suite of standards, and in particular the DPRS (DECT Packet Radio Services) bring together a number of prior interoperability profiles for the use of DECT as a wireless LAN and wireless internet access service. With good range (up to 200 m indoors and 6 km using directional antennae outdoors), dedicated spectrum, high interference immunity, open interoperability and data speeds of around 500 kbit/s, DECT appeared at one time to be a superior alternative to Wi-Fi[3]. The protocol capabilities built into the DECT networking protocol standards were particularly good at supporting fast roaming in the public space, between hotspots operated by competing but connected providers. The first DECT product to reach the market, Olivetti's Net3, was a wireless LAN, and German firms Dosch & Amand and Hoeft & Wessel built niche businesses on the supply of data transmission systems based on DECT.
However, the timing of the availability of DECT, in the mid 1990s, was too early to find wide application for wireless data outside niche industrial applications. Whilst contemporary providers of Wi-Fi struggled with the same issues, providers of DECT retreated to the more immediately lucrative market for cordless telephones. A key weakness was also the inaccessibility of the U.S. market, due to FCC spectrum restrictions at that time. By the time mass applications for wireless Internet had emerged, and the U.S. had opened up to DECT, well into the new century, the industry had moved far ahead in terms of performance and DECT's time as a wireless data transport was past.
Ironically, the failure of DECT as a data protocol became a strength when DECT 6.0 phones finally appeared in the U.S. in late 2005. By this time, the ISM bands had become crowded in the U.S., especially the 2.4 GHz band which is used by both the most common variants of Wi-Fi, 802.11b and 802.11g, and many cordless phones; thus interference between unlicensed devices has become common in these bands. However, because Wi-Fi does not operate in the UPCS band and DECT devices negotiate with each other for the available spectrum, not only are DECT 6.0 phones immune from this type of interference, their operation does not impair other nearby devices operating on the same frequency, which is a common issue with 2.4 GHz cordless phones.[citation needed]
[edit]Radio links
DECT operates in 1880-1900 MHz band and defines ten channel from 1881.792 MHz to 1897.344 MHz with band gap of 1728 kHz. Each base station frame provides 12 duplex speech channel with each time slot occupying any of channel. DECT operates in multicarrier /TDMA/TDD structure. DECT also provides Frequency Hopping Multiple Access over TDMA/TDD structure. If frequency hopping is avoided then each base station can provide up to 120 channels in the DECT spectrum before frequency reuse. Each time slot can be assigned to a different channel in order to exploit advantages of frequency hopping and avoid interference from other users in asynchronous fashion.[citation needed]
2009年5月24日 星期日
RF ID Communication System and Frequency Range
- USA: FCC (Federal Communications Commission)
- Canada: CRTC (Canadian Radio-television and Telecommunications Commission)
- Europe: ERO, CEPT, ETSI, and national administrations (note that the national administrations must ratify the usage of a specific frequency before it can be used in that country)
- Malaysia: Malaysian Communications and Multimedia Commission (MCMC)
- Japan: MIC (Ministry of Internal Affairs and Communications)
- China: Ministry of Information Industry
- Taiwan(China): NCC (National Communications Commission)
- South Africa: ICASA
- South Korea: Ministry of Commerce, Industry and Energy
- Australia: Australian Communications and Media Authority.
- New Zealand: Ministry of Economic Development
- Singapore: Infocomm Development Authority of Singapore
- Brazil: Anatel (Agência Nacional de Telecomunicações)
- ISO 14223/1 – Radio frequency identification of Animals, advanced transponders – Air interface
- ISO/IEC 14443: This standard is a popular HF (13.56 MHz) standard for HighFIDs which is being used as the basis of RFID-enabled passports under ICAO 9303.
- ISO 15693: This is also a popular HF (13.56 MHz) standard for HighFIDs widely used for non-contact smart payment and credit cards.
- ISO/IEC 18000: Information technology — Radio frequency identification for item management:
- Part 1: Reference architecture and definition of parameters to be standardized
- Part 2: Parameters for air interface communications below 135 kHz
- Part 3: Parameters for air interface communications at 13.56& MHz
- Part 4: Parameters for air interface communications at 2.45 GHz
- Part 6: Parameters for air interface communications at 860-960 MHz
- Part 7: Parameters for active air interface communications at 433 MHz
- ISO 18185: This is the industry standard for electronic seals or "e-seals" for tracking cargo containers using the 433 MHz and 2.4 GHz frequencies.
- EPCglobal – this is the standardization framework that is most likely to undergo International Standardisation according to ISO rules as with all sound standards in the world, unless residing with limited scope, as customs regulations, air-traffic regulations and others. Currently the big distributors and governmental customers are pushing EPC heavily as a standard well-accepted in their community, but not yet regarded as for salvation to the rest of the world.
- ASTM D7434, Standard Test Method for Determining the Performance of Passive Radio Frequency Identification (RFID) Transponders on Palletized or Unitized Loads
- ASTM D7435, Standard Test Method for Determining the Performance of Passive Radio Frequency Identification (RFID) Transponders on Loaded Containers
Radio-frequency identification
Radio-frequency identification (RFID) is the use of an object (typically referred to as an RFID tag) applied to or incorporated into a product, animal, or person for the purpose of identification and tracking using radio waves. Some tags can be read from several meters away and beyond the line of sight of the reader.
Most RFID tags contain at least two parts. One is an integrated circuit for storing and processing information, modulating and demodulating aradio-frequency (RF) signal, and other specialized functions. The second is an antenna for receiving and transmitting the signal.
There are generally two types of RFID tags: active RFID tags, which contain a battery and can transmit signals autonomously, and passive RFID tags, which have no battery and require an external source to provoke signal transmission.
Today, RFID is used in enterprise supply chain management to improve the efficiency of inventory tracking and management.
Regulation and standardization
There is no global public body that governs the frequencies used for RFID. In principle, every country can set its own rules for this. The main bodies governing frequency allocation for RFID are:
Low-frequency (LF: 125–134.2 kHz and 140–148.5 kHz) (LowFID) tags and high-frequency (HF: 13.56 MHz) (HighFID) tags can be used globally without a license. Ultra-high-frequency (UHF: 868–928 MHz) (Ultra-HighFID or UHFID) tags cannot be used globally as there is no single global standard. In North America, UHF can be used unlicensed for 902–928& MHz (±13 MHz from the 915 MHz center frequency), but restrictions exist for transmission power. In Europe, RFID and other low-power radio applications are regulated by ETSI recommendations EN 300 220 and EN 302 208, and ERO recommendation 70 03, allowing RFID operation with somewhat complex band restrictions from 865–868 MHz. Readers are required to monitor a channel before transmitting ("Listen Before Talk"); this requirement has led to some restrictions on performance, the resolution of which is a subject of current research. The North American UHF standard is not accepted in France as it interferes with its military bands. For China and Japan, there is no regulation for the use of UHF. Each application for UHF in these countries needs a site license, which needs to be applied for at the local authorities, and can be revoked. For Australia and New Zealand, 918–926 MHz are unlicensed, but restrictions exist for transmission power.
These frequencies are known as the ISM bands (Industrial Scientific and Medical bands). The return signal of the tag may still cause interference for other radio users.
Some standards that have been made regarding RFID technology include:
[edit]EPC Gen2
EPC Gen2 is short for EPCglobal UHF Class 1 Generation 2.
EPCglobal (a joint venture between GS1 and GS1 US) is working on international standards for the use of mostly passive RFID and the EPC in the identification of many items in the supply chain for companies worldwide.
One of the missions of EPCglobal was to simplify the Babel of protocols prevalent in the RFID world in the 1990s. Two tag air interfaces (the protocol for exchanging information between a tag and a reader) were defined (but not ratified) by EPCglobal prior to 2003. These protocols, commonly known as Class 0 and Class 1, saw significant commercial implementation in 2002–2005.
In 2004 the Hardware Action Group created a new protocol, the Class 1 Generation 2 interface, which addressed a number of problems that had been experienced with Class 0 and Class 1 tags. The EPC Gen2 standard was approved in December 2004, and is likely to form the backbone of passive RFID tag standards moving forward. This was approved after a contention fromIntermec that the standard may infringe a number of their RFID-related patents. It was decided that the standard itself does not infringe their patents, but that it may be necessary to pay royalties to Intermec if the tag is to be read in a particular manner. The EPC Gen2 standard was adopted with minor modifications as ISO 18000-6C in 2006.
The lowest cost of Gen2 EPC inlay is offered by SmartCode at a price of $0.05 apiece in volumes of 100 million or more[55]. Nevertheless, further conversion (including additional label stock or encapsulation processing/insertion and freight costs to a given facility or DC) and of the inlays into usable RFID labels and the design of current Gen 2 protocol standard will increase the total end-cost, especially with the added security feature extensions for RFID Supply Chain item-level tagging.
Here is the full list of the update on UHF Gen2 Regulation around the world. The list is updated at 2009 January.
Frequency Ranges
Because RFID systems generate and radiate electromagnetic waves, they are justifiably classified as radio systems. The function of other radio services must under no circumstances be disrupted or impaired by the operation of RFID systems. It is particularly important to ensure that RFID systems do not interfere with nearby radio and television, mobile radio services (police, security services, industry), marine and aeronautical radio services and mobile telephones.
The need to exercise care with regard to other radio services significantly restricts the range of suitable operating frequencies available to an RFID system. For this reason, it is usually only possible to use frequency ranges that have been reserved specifically for industrial, scientific or medical applications or for short range devices. These are the frequencies classified worldwide as ISM frequency ranges (Industrial-Scientific-Medical) or SRD frequency ranges, and they can also be used for RFID applications.
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Table: Frequecy ranges used for RFID-systems (August 2006)
Picture: Frequency-ranges used for RFID-systems shown with the corresponding field strength and power levels.
Radio Regulation
The standards drawn up by the ETSI (European Telecommunications Standards Institute) serve to provide the national telecommunications authorities with a basis for the creation of national regulations for the administration of radio and telecommunications.
for more information about radio regulation please have a look at “Standardization”
2009年5月23日 星期六
Wireless system generations
Wireless system generations
1G NMT · AMPS · Hicap · CDPD · Mobitex · DataTAC · TACS ·ETACS
2G GSM · iDEN · D-AMPS · IS-95 · PDC · CSD · PHS · GPRS · HSCSD · WiDEN
2.75G EDGE/EGPRS ·CDMA2000 (1xRTT)
3G UMTS (W-CDMA) · CDMA2000 (1xEV-DO/IS-856) ·
FOMA · TD-SCDMA · GAN/UMA · WiMAX
3.5G UMTS (HSDPA) · UMTS (HSUPA) · CDMA2000 (EV-DO Rev.A)
3.75G UMTS (HSPA+) · CDMA2000 (EV-DO Rev.B/3xRTT)
4G Flash-OFDM · 3GPP LTE
Related articles : Comparison of mobile telecommunications standards
· List of mobile telecommunications standards
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