Cdma

Cell phones have come a long way. When they first hit the market, a phone could make and receive phone calls with poor voice quality, little security, and frequent dropped calls. Now, we have great voice quality, we can send text messages and multimedia messages, we can browse the web, stream videos, and much more without needing to be connected to WiFi. This is made possible by a great variety of cellular technology which has evolved over time, and have their roots all across the world. In this article, we'll be breaking down these technologies, which contributed to the evolution of cell phone communication and helped the transition from analog to digital modulation. For Commercial Different Cell Phone Technologies The following technologies have helped mobile communication evolve from the earliest 1G cell phones of the 1980s to the high speed 4G LTE and • Advanced Mobile Phone Systems (AMPS)- A cell phone standard used to define the first generation of analog mobile communication. • Code Division Multiple Access (CDMA)- A method used to manage the users accessing a frequency channel on CDMA-based networks. • Code Division Multiple Access 2000 (CDMA2000)- A cell phone standard used to define the third generation of CDMA mobile communication. • Digital Advanced Mobile Phone Systems (DAMPS)- The second-generation successor to AMPS. • Evolution Data Optimized or Evolution Data Only (EVDO)- A mobile broadband technology used to provide the CDMA2000 network with high-speed int...

Device Compatibility and SIM Cards It's easy to swap phones on a GSM network because GSM phones use removable SIM cards to store information about the user on the GSM network, while CDMA phones do not. Instead, CDMA networks use information on the carrier's server to verify the same type of data that GSM phones have stored in their SIM cards. An easy transition is typically not possible with most CDMA phones, even if they do have removable SIM cards. Instead, you typically need your carrier's permission to perform such a swap. Since GSM and CDMA are incompatible with one another, you can't use a Sprint phone on a T-Mobile network, or a Verizon Wireless phone with AT&T. The same goes for any other mix of device and carrier that you can make out of the CDMA and GSM list from above. Simultaneous Voice and Data Usage Most CDMA networks do not allow voice and data transmissions at the same time. This is why you may get bombarded with emails and other Internet notifications when you end a call from a CDMA network like Verizon. The data is basically on pause while you're on a phone call.

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GSM and CDMA are the two most popular networking standards for mobile connectivity. While CDMA is older and now entering a legacy stage, it remains a staple for specific device variants and geographic regions. GSM is the bedrock of advanced cellular networks, fueling the rise of 4G and 5G. This article explains the difference between CDMA and GSM and their relevance in the IoT era. Table of Contents • • • • GSM is a digital cellular technology that provides mobile data and voice services across devices. Global System for Mobile Communication ( GSM) is one of the second-generation telecommunication standards (2G). GSM simply is a wireless network for transmitting data across mobile devices. It has been misunderstood as a mobile phone in some countries and still is even today. However, GSM is not a mobile phone but a means of communication across digital cellular devices. GSM is simply for wireless data transmission. It was established in 1982 and replaced the 1st generation of telecommunication NMT (1G). GSM is not only used for voice calls; one can also use it for sending text messages and computing data. For instance, a user can connect his GSM-enabled phone with his laptop to send and receive emails and faxes, browse the internet, check security, etc. The benefits of GSM include a secure network, extensive coverage, and compatibility with a broad range of accessories and handsets. On the other hand, one of the most significant disadvantages of the GSM is that many users ...

目录 • 1 一般信息 • 2 類型 • 3 優點 • 4 技術細節 • 5 參考資料 • 6 参看 • 7 参考文献 • 8 外部链接 一般信息 [ ] 一般来说（作为 CDMA经常被广泛和不严格地用来称呼使用CDMA技术实现的 这里需要注意： • CDMA（分碼複存技术）理论被应用于 • WCDMA无线接口被应用于国际3G标准 • CDG、TIA和3GPP2等制订的俗称为CDMA的系列标准族（包括 部分CDMA网络和手机支持个人定位功能，简易的方法是通过 類型 [ ] CDMA有兩種類型，分別為 正交型與 偽隨機碼型。 1.正交型（Orthogonal Type） CDMA最常使用的正交轉換為 (1) Walsh Transform的運算量很少，因為不需要乘法而只需要加法的運算。 (2) Walsh Transform的基底（Basis）有正交的特性。 (3) Walsh Transform也有快速演算法。 例子：假設現在要使用8點Walsh Transform來傳送兩組資料A = [1, 0, 1]和B = [1, 1, 0]，步驟如下 調變（modulation） (1)先將資料的0轉成 -1 A = [1,-1,1], B = [1,1,-1] • 好處是在解調時，更能夠區別0和1，而使解調錯誤率下降。 (2-1) A使用Walsh Transform的第一個channel [1,1,1,1,1,1,1,1]（即其第一個basis,矩陣的第一個row）來做調變 A_m = [1,1,1,1,1,1,1,1,|-1,-1,-1,-1,-1,-1,-1,-1,|1,1,1,1,1,1,1,1,]。 (2-2) B使用Walsh Transform的第二個channel [1,1,1,1,-1,-1,-1,-1]（矩陣的第二個row）來做調變 B_m = [1,1,1,1,-1,-1,-1,-1,|1,1,1,1,-1,-1,-1,-1,|-1,-1,-1,-1,1,1,1,1,]。 (3)將調變的結果相加M = A_m + B_m M = A_m + B_m = [2,2,2,2,0,0,0,0,0,0,0,0,-2,-2,-2,-2,0,0,0,0,2,2,2,2] (4)最後傳送出去的信號為M,共有24個bit。 解調（demodulation） (1)將接收到的資料分別和channel做內積 (1-1) M和 第一個channel [1,1,1,1,1,1,1,1]做內積得到 前八碼內積：[2,2,2,2,0,0,0,0] ⋅ [1, 1, -1] (3)最後，將 -1還原回0 (3-1)因此，第一個channel成功還原信號為[1, 0, 1] (3-2)因此，第二個channel成功還原信號為[1, 1, 0] 注意事項： (1)使用N點Walsh Transform時，總共可以有N個channels，但是N必須是2的次方倍。 (2)除了Walsh Transform以外，其他的Orthogonal Transform也可以使用。 (3)使用Orthogonal Transform共通的問題是需要同步Synchronization 2.偽隨機碼型 （Pseudorandom Sequence Type） 優點：不需要同步 （asynchronous） 缺點：Capacity較小 優點 [ ] 雖然已有 ⑴運算量相對於頻分多工減少很多 ⑵可以減少雜訊及干涉的影響 ⑶可以應用在保密和安全傳輸上 ⑷就算只接收部分的信號，也有可能...

• العربية • বাংলা • Català • Čeština • Deutsch • Eesti • Español • فارسی • Français • 한국어 • हिन्दी • Bahasa Indonesia • Italiano • עברית • ქართული • Latviešu • Magyar • მარგალური • မြန်မာဘာသာ • Nederlands • 日本語 • Polski • Português • Română • Русский • Sunda • Suomi • Svenska • தமிழ் • ไทย • Türkçe • Українська • اردو • Tiếng Việt • 吴语 • 中文 • v • t • e Code-division multiple access ( CDMA) is a CDMA optimizes the use of available bandwidth as it transmits over the entire frequency range and does not limit the user's frequency range. It is used as the access method in many It can be also used as a channel or medium access technology, like In these schemes, the message is modulated on a longer spreading sequence, consisting of several chips (0es and 1es). Due to their very advantageous auto- and crosscorrelation characteristics, these spreading sequences have also been used for radar applications for many decades, where they are called For space-based communication applications, CDMA has been used for many decades due to the large path loss and Doppler shift caused by satellite motion. CDMA is often used with History [ ] The technology of code-division multiple access channels has long been known. USA [ ] In the US, one of the earliest descriptions of CDMA can be found in the summary report of Project Hartwell on "The Security of Overseas Transport", which was a summer research project carried out at the USSR [ ] In the [ clarification needed] The technology of CDMA was used...

Verizon and Sprint are CDMA carriers in the US. What is CDMA? CDMA (or code-division multiple access, if you don't want to be lazy about it) is a network technology that along with GSM were once the two main types of networks in the US. Both CDMA and GSM (in their own ways) make it possible for for multiple calls and internet to be transmitted in one radio signal. The technology helped support the boom of cellular phone usage in the 90s. Is CDMA better than GSM? Not necessarily. The quality of a network tends to be more dependent on how the network was built. Keep in mind, that Verizon is a CDMA carrier, and they have been known for the quality of their networks for a long time. How do I know if I have a CDMA phone? If you have a phone that doesn't have a SIM card it is a CDMA phone. That's a pretty easy answer, no? Of course, there's more. Some smartphones with SIM cards while using 4G networks to connect you to the internet, might still be using GSM to connect to 2G CDMA networks for talk. Remember, if your phone is on Verizon or Sprint, it could be a CDMA phone. Do I really need to know about CDMA? For now, knowing if you have a CDMA or GSM phone is still somewhat relevant. However, both network technologies are getting phased out for the more superior 4G and incoming 5G networks. Still, while relics of the old technology are still in rotation, and CDMA networks are still being used, it can beneficial for you to know a little about it, and whether your phone is compatib...