4G, LTE, HSPA+

1. 4G 的标准为 IMT-advanced。要求高速下载达到 100Mbps，低速可以达到 1Gbps。且为 IP-packet. 
2. LTE 和 4G 都采用了 OFDM 和 MIMIO，但 LTE 并非基于 IP-packet. 所以 LTE 不能称为 4G，只不过目前在部署的和已经商用的LTE 都按照4G进行宣传。 
3. LTE-advanced （LTE的演进版本）和 WiMax-advanced 是4G标准，满足要求。

LTE 分为 TDD 和 FDD，都是采用 OFDM和MIMO，差别是双工的方式。
TD-LTE 是移动抗的大旗，但是从技术上说和 即TD-SCDMA 没啥关系。

联通的演进是 FDD LTE。电信未知。

An advanced HSPA network can theoretically support up to 28 Mbit/s and 42 Mbit/s with a single 5 MHz carrier for Rel7 (MIMO with 16QAM) and Rel8 (64-QAM + MIMO), in good channel conditions with low correlation between transmit antennas. An alternative method to double the data rates is to double the bandwidth to 10 MHz (i.e. 2x5MHz) by using DC-HSDPA. Additionally, some diversity and joint scheduling gains can also be expected[3] with improved QoS for end users in poor environment conditions where existing techniques such as MIMO spatial multiplexing cannot be used to increase data rates. In 3GPP a study item was completed in June 2008. The outcome can be found in technical report 25.825.[4] New HSDPA User Equipment categories 21-24 have been introduced that support DC-HSDPA. DC-HSDPA can support up to 42 Mbit/s, but unlike HSPA, it does not need to rely on MIMO transmission.

LTE:
OFDMA for the downlink, SC-FDMA for the uplink to conserve power

LTE 漫游：

LTE 在不同地区和网络下可能具有不同的频带和双工，但是由于其无线部分工作方式一致，可以预见，若终端支持支持多种频带以及TDD/FDD，则可以进行全球漫游。只要运营商愿意打破相互之间的壁垒。

后续：
1. 截止 12年7月，移动正大力推进 TD-LTE建设，实测下行有 50Mbps 的样子（理想情况）
联通的思路是暂且升级 HSPA+，刚推出标称（理论值） 21Mbps 的上网卡，后续还能升级
电信思路是按兵不动，我刚买了一个电信上网卡，标称 3.1Mbps

2.