E DPCCH (Enhanced Dedicated Physical Control Channel)

Introduction:

The Enhanced Dedicated Physical Control Channel (E-DPCCH) is a part of the WCDMA (Wideband Code Division Multiple Access) air interface used for the uplink in 3G mobile communication systems. E-DPCCH is an extension of the DPCCH (Dedicated Physical Control Channel) and is introduced in the HSPA (High-Speed Packet Access) specification to improve the uplink data rate and reduce power consumption. In this essay, we will discuss the E-DPCCH in detail, including its functions, structure, and usage in HSPA.

E-DPCCH Functions:

The E-DPCCH is used to transmit control information related to the uplink data transmission from the mobile station (MS) to the NodeB (base station). It carries the power control information, which is used by the NodeB to adjust the transmission power of the MS. The E-DPCCH also carries the ACK/NACK (acknowledgment/non-acknowledgment) signals, which are used to indicate whether the transmitted data is received correctly or not. The NodeB uses these signals to adjust the modulation and coding scheme (MCS) and retransmission strategy for the next transmission. The E-DPCCH also carries other control information, such as channel quality indicator (CQI), which indicates the channel quality of the uplink, and the sounding reference signal (SRS), which is used for channel estimation.

E-DPCCH Structure:

The E-DPCCH has a variable structure, which means that it can be configured to transmit different types of control information depending on the system requirements. The basic structure of the E-DPCCH consists of several symbols that are transmitted at a fixed rate of 1500 symbols per second. Each symbol has a duration of 0.667 milliseconds, which is equal to the duration of one chip in the spreading code used in WCDMA.

The E-DPCCH symbols are modulated using a Quadrature Phase Shift Keying (QPSK) modulation scheme. QPSK is a digital modulation scheme that encodes two bits of data into each symbol by changing the phase of the carrier signal. The QPSK modulation is chosen because it provides a good balance between the data rate and the signal-to-noise ratio (SNR) performance.

The E-DPCCH can be configured to use different spreading factors, which determine the number of chips used to transmit each symbol. The spreading factor can be set to 16, 32, 64, or 128. The spreading factor is chosen based on the system requirements, such as the data rate and the channel conditions.

The E-DPCCH can also be configured to use different power levels, which determine the transmit power of each symbol. The power level can be set to one of four levels: -3 dB, -4.77 dB, -6 dB, or -8.45 dB. The power level is chosen based on the system requirements, such as the power consumption and the channel conditions.

E-DPCCH Usage in HSPA:

The E-DPCCH is a key feature of the HSPA specification, which is an evolution of the WCDMA system. HSPA includes two modes of operation: High-Speed Downlink Packet Access (HSDPA) and High-Speed Uplink Packet Access (HSUPA). HSDPA is used for downlink data transmission, while HSUPA is used for uplink data transmission.

HSUPA uses the E-DPCCH to improve the uplink data rate and reduce power consumption. The E-DPCCH is used to transmit the power control information, which is used by the NodeB to adjust the transmission power of the MS. The power control mechanism is based on the closed-loop power control algorithm, which adjusts the transmit power of the MS based on the feedback received from the NodeB. The feedback includes the received signal-to-interference-plus-noise ratio (SINR) and the ACK/NACK signals.

The E-DPCCH is also used to transmit the ACK/NACK signals, which indicate whether the transmitted data is received correctly or not. The NodeB uses these signals to adjust the MCS and retransmission strategy for the next transmission. The ACK/NACK signaling mechanism in HSUPA is based on the Hybrid Automatic Repeat reQuest (HARQ) protocol, which combines both ARQ (Automatic Repeat reQuest) and FEC (Forward Error Correction) techniques.

In addition to the power control and ACK/NACK signaling, the E-DPCCH is also used to transmit other control information, such as the CQI and SRS. The CQI is used to indicate the channel quality of the uplink, which is used by the NodeB to select the appropriate modulation and coding scheme (MCS) for the uplink transmission. The SRS is used for channel estimation, which is used by the NodeB to optimize the uplink transmission.

Conclusion:

The Enhanced Dedicated Physical Control Channel (E-DPCCH) is a key feature of the WCDMA air interface used in the HSPA specification. It is used for the uplink data transmission and carries the power control information, ACK/NACK signals, and other control information such as the CQI and SRS. The E-DPCCH has a variable structure and can be configured to transmit different types of control information depending on the system requirements. The E-DPCCH plays a critical role in improving the uplink data rate and reducing power consumption in the HSUPA mode of operation.