Advanced Cellular Technologies Episode 3: Continuous Packet Connectivity (CPC)

CPC is a large 3GPP R7 work item. What is the motivation for it, what does it do and what should we expect out of it? We'll find out in this post.

Motivation:
When a handset is activated it is usually put in Idle state until the user decides to transmit or receive data, at which point the system transfers the handset from the Idle state to a "connected" state. If the user is inactive for a number of seconds, the handset is put again in Idle state in order to save network resources. This turns out to be problematic with certain types of applications that require continuous connectivity, such as IM, hence the motivation for Continuous Packet Connectivity. The vision is to make the mobile bradband experience similar to the DSL experience in terms of network response time.

The main concern with CPC is the amount of battery power required to maintain connectivity. There are various concepts and schemes that, together, will enable CPC. Some of these concepts are:

DPCCH gating:
DPCCH is a control channel which is typically always on. This will change such that control channels have a discontinuous pattern, which reduces the amount of interference and increases battery life.

Modified HS-SCCH operation:
HS-SCCH is a channel that carries HSDPA signaling in the downlink. This channel typically consumes large amount of power which eats up a part of the cell capacity. Therefore 3GPP came with various suggestions to reduce its effects by restricting it, or eliminate it altogether.

CQI reporting reduction:
CQI stands for Channel Quality Indicator, which is a message sent by the terminal to the bas station reporting the channel quality so that the base station can decide what to send to the terminal. Reducing the rate of CQI signaling will reduce overheads. This means that more bandwidth is available for traffic packets instead of overhead.