Android 中telephony 类型 cdma 和 gsm的区别

### Android Telephony CDMA vs GSM Differences In the context of Android telephony, two primary standards are used for cellular communication: Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM). These technologies differ significantly in their architecture, implementation, and features. #### Network Architecture GSM networks use a combination of time division multiple access (TDMA) and frequency division duplexing (FDD), allowing multiple users to share the same carrier frequency by dividing it into sequential time slots. On the other hand, CDMA employs spread spectrum technology where all transmissions occur across an entire allocated bandwidth simultaneously but distinguished through unique codes assigned to each user session[^1]. #### SIM Card Usage One notable distinction between these protocols lies within subscriber identity module (SIM) card usage. Devices operating on GSM require physical insertion of this removable chip containing essential subscription information; meanwhile, traditional North American CDMA carriers did not originally support SIM cards until recent changes towards global interoperability requirements led some providers like Verizon Wireless adopting them partially or fully depending upon device models offered post-2017 period. #### Voice Call Quality & Data Services Historically speaking, voice quality has been perceived better over CDMA due mainly because early implementations provided higher clarity compared against contemporary equivalents found amongst competing alternatives at that point in history – though advancements since then have largely closed any gap which may once existed therebetween today's offerings from either side can generally match one another when considering call fidelity alone without factoring external variables such as network congestion levels impacting real-world performance outcomes experienced end-users might encounter during actual conversations taking place via respective methods employed hereunder discussion points made hereinbefore regarding comparative analysis undertaken concerning said subject matter under examination presently being addressed now within current paragraph structure outlined above accordingly below following immediately after next line break inserted right here: ```java // Example Java code snippet demonstrating how applications interact differently based on whether they operate using CDMA or GSM. TelephonyManager tm = (TelephonyManager)getSystemService(Context.TELEPHONY_SERVICE); if(tm.getPhoneType() == TelephonyManager.PHONE_TYPE_CDMA){ Log.d("Telephony", "Device uses CDMA"); } else if(tm.getPhoneType() == TelephonyManager.PHONE_TYPE_GSM){ Log.d("Telephony", "Device operates on GSM"); } ```