HS-DPCCH (High speed dedicated control channel)
High-speed dedicated control channel (HS-DPCCH) is a channel that is used in the Universal Mobile Telecommunications System (UMTS) to provide high-speed data transfer and control information between the User Equipment (UE) and the NodeB. It is a dedicated uplink channel that is used to transmit control information such as power control, acknowledgement and retransmission requests for high-speed data channels, and to carry dedicated control information for the associated high-speed data channels.
In this article, we will explore the characteristics and features of HS-DPCCH and how it is used in UMTS networks.
HS-DPCCH Overview:
In UMTS, the HS-DPCCH is a dedicated uplink channel that is used to transmit high-speed data control information between the UE and the NodeB. It is a narrowband channel with a bandwidth of 1.28 MHz, and it is allocated to the UE based on its data rate requirement. The HS-DPCCH is always transmitted in the uplink direction, and its data rate is directly proportional to the data rate of the associated high-speed data channel.
The HS-DPCCH is designed to carry control information that is required for the reliable transfer of high-speed data over the air interface. The main types of control information that are carried on the HS-DPCCH include power control commands, acknowledgement and retransmission requests for high-speed data channels, and dedicated control information for the associated high-speed data channels.
HS-DPCCH Transmission:
The HS-DPCCH is transmitted in the uplink direction, and it is transmitted along with the high-speed data channels that it is associated with. The HS-DPCCH is always transmitted at a fixed power level, and its power level is determined by the UE based on the power control commands that it receives on the HS-SCCH (High-speed Shared Control Channel).
The HS-SCCH is used to carry power control commands for the HS-DPCCH, and it is a shared control channel that is allocated to multiple UE simultaneously. The UE monitors the HS-SCCH to receive power control commands for the HS-DPCCH, and it adjusts its transmit power accordingly to maintain a target signal-to-interference ratio (SIR) on the NodeB.
The HS-DPCCH is also used to carry acknowledgement and retransmission requests for the associated high-speed data channels. When the UE receives a high-speed data packet, it checks the packet for errors and generates an acknowledgement or a retransmission request as necessary. The acknowledgement and retransmission request are then transmitted on the HS-DPCCH, along with the high-speed data channel that the packet was received on.
HS-DPCCH Modulation and Coding:
The HS-DPCCH uses the same modulation and coding scheme as the dedicated physical control channel (DPCCH) in UMTS. The DPCCH is a dedicated control channel that is used to carry control information such as power control commands, timing advance information, and handover requests.
The DPCCH uses a fixed modulation scheme of Quadrature Phase Shift Keying (QPSK), and it employs a rate 1/2 convolutional code with a constraint length of 9. The HS-DPCCH uses the same modulation scheme and convolutional code as the DPCCH, but its coding rate is variable and is determined based on the UE's data rate requirement.
The HS-DPCCH can use one of four coding rates: 1/4, 1/2, 3/4, and 4/4. The coding rate is selected based on the UE's data rate requirement, and it determines the number of bits that are transmitted per HS-DPCCH symbol.
HS-DPCCH Power Control:
The HS-DPCCH power control is an important aspect of the channel's operation. As mentioned earlier, the UE adjusts its transmit power on the HS-DPCCH based on the power control commands that it receives on the HS-SCCH. The goal of the power control is to maintain a target signal-to-interference ratio (SIR) on the NodeB.
The target SIR is determined by the NodeB based on the channel conditions and the quality of the received signal. The NodeB periodically sends a power control command on the HS-SCCH to instruct the UE to adjust its transmit power up or down by a certain amount. The UE responds to the power control command by adjusting its transmit power accordingly.
The power control command is a binary value that indicates whether the UE should increase or decrease its transmit power. If the power control command is '1', the UE increases its transmit power by a fixed amount, and if the power control command is '0', the UE decreases its transmit power by a fixed amount.
The power control algorithm is designed to maintain a target SIR on the NodeB, while also minimizing the interference caused by the UE to other users on the same frequency band. The algorithm takes into account the channel conditions, the UE's transmit power, and the interference caused by other users on the frequency band.
HS-DPCCH and High-Speed Data Channels:
The HS-DPCCH is closely associated with the high-speed data channels in UMTS. The high-speed data channels are used to carry user data at high speeds, and they are divided into several channels based on the user's data rate requirement.
The HS-DPCCH is used to carry control information for the associated high-speed data channels. This control information includes power control commands, acknowledgement and retransmission requests, and dedicated control information for the high-speed data channels.
The HS-DPCCH is also used to indicate the start and end of a high-speed data transmission. When a UE begins transmitting data on a high-speed data channel, it sends a Start Indicator (SI) on the HS-DPCCH to notify the NodeB that it is starting a data transmission. When the UE has finished transmitting data, it sends a Stop Indicator (SO) on the HS-DPCCH to indicate that the transmission has ended.
The HS-DPCCH is also used to carry dedicated control information for the associated high-speed data channels. This control information includes channel quality feedback, which is used by the NodeB to adjust the modulation and coding scheme of the high-speed data channel based on the channel conditions.
Conclusion:
In conclusion, the high-speed dedicated control channel (HS-DPCCH) is a critical component of the Universal Mobile Telecommunications System (UMTS). It is a dedicated uplink channel that is used to transmit high-speed data control information between the User Equipment (UE) and the NodeB.
The HS-DPCCH is used to carry control information such as power control commands, acknowledgement and retransmission requests, and dedicated control information for the associated high-speed data channels. It is also used to indicate the start and end of a high-speed data transmission and to carry channel quality feedback.