Difference Between CDMA and WCDMA

CDMA vs WCDMA

Code Division Multiple Access (CDMA) and Wideband Code Division Multiple Access (WCDMA) are multiple access technologies used in telecommunication networks for users to access the network resources and services. Since the spectrum is a scarce resource, which is directly related to capacity, efficient use of the spectrum is a major concern in most theoretical proposals for air interface. Other than CDMA, different multiple access methods are used around the world in radio network. Even though, these access methods are developed in different time periods, combinations of these technologies are used for efficient use of spectrum. When comes to CDMA, North American version of third generation technology is called cdma2000, which is an extension of TIA/EIA-95B based CDMA, while European version of third generation CDMA is called WCDMA.

CDMA

In general, CDMA is a multiple access technology that was introduced after the TDMA and FDMA. CDMA serves the different users with separate code sequences, while there are other multiple access technologies that use time, frequency, space, and polarisation for user access separation. When we consider the CDMA system design, multiple access and interference handling are totally different from the narrowband systems. In CDMA, each user spread his signal over the entire bandwidth using the direct sequence spread spectrum, whereas for other users, it is shown as pseudo white noise.

WCDMA

WCDMA was selected as the Universal Mobile Telecommunication Systems (UMTS) terrestrialair interface scheme for the Frequency Division Duplex (FDD) frequency bands by the European Telecommunications Standards Institute (ETSI) in 1998. WCDMA uses 5MHz, 10MHz or 20MHz channel bandwidth to send the data signals over the air interface. WCDMA mixes original signal with a pseudo random noise code, which is also known as Direct Sequence WCDMA. Therefore, each user ends up with a unique code, where only users with correct code can decode the message. Using the pseudo signal, original signal is modulated into a higher bandwidth, where original signal’s spectral components sink in the noise. Therefore, without the code, jammers can only see the signal as noise.

WCDMA根据国际电信联盟（ITU）（ITU）为3G网络规定的原始标准使用正交相移键控（QPSK）作为调制方案，该标准可以支持移动环境中的384 kbps，而平稳环境中的2MBP。

What is the difference between CDMA and WCDMA?

WCDMA是3G UTRAN建议的解决方案，而CDMA是一种访问技术。WCDMA使用直接扩散（DS）作为正向链接RF通道结构，而CDMA使用DS或多载波。不同版本的CDMA技术是从不同大陆进化的，而WCDMA是CDMA技术的欧洲发展版本。两种技术都将扩散调制作为正向链接中的平衡qpsk，而反向链接中的双通道qpsk。基于CDMA的访问方法的唯一性是通用频率重复使用，在同一单元格中的所有用户都可以以相同的频率传输和接收。CDMA技术引入了核心优势，例如分别为每个用户的选择性解决功能，消息安全性和干扰拒绝。正确选择具有低跨相关性的代码会导致用户之间的最小干扰，在这种情况下，我们可以在基于CDMA的技术中获得更高的光谱效率。

When compare the CDMA evolution in different European, US, and Japanese based systems, most of them have similar principle, while differ in the chip rate, and in channel structure. WCDMA is considered as a European evolution of CDMA technology for 3rd generation ITU specification.