WCDMA vs. HSDPA (3G vs 3.5G)
WCDMA stands for Wideband Code Division Multiple Access, a mobile technology that improves upon the capabilities of current GSM networks that are deployed around the world. People commonly refer to this technology as 3G, or 3rd generation, and it provides newer services like video calling to the traditional call, and text messaging features that are already standard. HSDPA (High Speed Downlink Packet Access) is what is commonly known as 3.5G, as it offers no substantial upgrade to the feature set of WCDMA, but improves the speed of data transmission to enhance those services.
Prior to the introduction of HSDPA, WCDMA networks were only capable of reaching speeds of 384kbps. Although this might be sufficient for most services, people always want faster speeds, especially when browsing the internet or downloading files. HSDPA allowed speeds above 384kbps, the most notable of which is 3.6Mbps and 7.2Mbps, which a lot of telecommunications companies often advertise. In truth, HSDPA is capable of reaching much higher speeds depending on the type of modulation that is being used. HSDPA speeds can even reach a theoretical maximum of 84Mbps.
Aside from increasing the existing data speed provided by WCDMA, HSDPA also improved the latency, or the time it takes between the moment the request is placed and the moment the requested data is received. The lower latencies provided by HSDPA makes the 3G services more real-time, and conversations are more natural. Lower latencies are also good for people who use their connection to play online games, where high latencies result in lag.
Features in HSDPA that make these things possible are Fast Packet Scheduling and AMC (Adaptive Modulation and Coding). Fast Packet Scheduling allows the base station to adjust the amount of data that is being transmitted to a certain device based on the current conditions. AMC also allows the base station to select a better modulation and coding scheme if the signal quality allows it. Initially, users are assigned with QPSK, but can be changed to a lot of other coding schemes that provide better data rates if the signal between the device and the base station is strong enough.
1. WCDMA is commonly referred to as 3G, while HSDPA is commonly referred to as 3.5G.
2. HSDPA provides much higher data rates compared to WCDMA.
3. HSDPA has lower latency times compared to WCDMA.
4. HSDPA has Fast Packet Scheduling and AMC, features that are absent in WCDMA.