HSDPA vs HSUPA
HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access) are 3GPP specifications published to provide recommendations for downlink and uplink of the mobile broadband services. Networks that support both HSDPA and HSUPA are called as HSPA or HSPA+ networks. Both specifications introduced enhancements to the UTRAN (UMTS Terrestrial Radio Access Network) by introducing new channels and modulation methods, so that, more efficient and high speed data communication can be achieved in the air interface.
HSDPA was introduced in year 2002 in 3GPP release 5. The key feature of HSDPA is the concept of AM (Amplitude Modulation), where the modulation format (QPSK or 16-QAM) and effective code rate are changed by the network according to system load and channel conditions. HSDPA was developed to support up to 14.4 Mbps in a single cell per user. Introduction of new transport channel known as HS-DSCH (High Speed-Downlink Shared Channel), uplink control channel and downlink control channel are the major enhancements to UTRAN as per the HSDPA standard. HSDPA selects coding rate and modulation method based on the channel conditions reported by user equipment and Node-B, which is also known as AMC (Adaptive Modulation and Coding) scheme. Other than the QPSK (Quadrature Phase Shift Keying) used by WCDMA networks, HSDPA supports 16QAM (Quadrature Amplitude Modulation) for data transmission under good channel conditions.
HSUPA was introduced with the 3GPP release 6 in year 2004, where Enhanced Dedicated Channel (E-DCH) is used to improve the uplink of the radio interface. Maximum theoretical uplink data rate that can be supported by a single cell as per the HSUPA specification is 5.76Mbps. HSUPA relies on QPSK modulation scheme, which is already specified for WCDMA. It also uses HARQ with incremental redundancy to make retransmissions more effective. HSUPA uses uplink scheduler to control the transmit power to the individual E-DCH users to mitigate the power overload at Node-B. HSUPA also allows self-initiated transmission mode that is called as non-scheduled transmission from UE to support services such as VoIP that need reduced Transmission Time Interval (TTI) and constant bandwidth. E-DCH support both 2ms and 10ms TTI. Introduction of E-DCH in HSUPA standard introduced new five physical layer channels.
What is the difference between HSDPA and HSUPA?
Both HSDPA and HSUPA introduced new functions to the 3G radio access network, which was also known as UTRAN. Some vendors supported the upgrade of WCDMA network into a HSDPA or HSUPA network by software upgrade to the Node-B and to the RNC, while some vendor implementations required hardware changes as well. Both HSDPA and HSUPA use Hybrid Automatic Repeat Request (HARQ) protocol with incremental redundancy to handle re-transmission, and to handle error free data transfer over the air interface.
HSDPA enhances the Downlink of the radio channel, while HSUPA enhances the uplink of the radio channel. HSUPA does not use 16QAM modulation and ARQ protocol for uplink which, is used by HSDPA for downlink. TTI for HSDPA is 2ms in other words re-transmissions as well as changes in modulation method and coding rate will take place every 2ms for HSDPA, whereas with HSUPA TTI is 10ms, also with the option of setting it as 2ms. Unlike HSDPA, HSUPA does not implement AMC. Goal of packet scheduling is completely different between HSDPA and HSUPA. In HSDPA aim of scheduler is to allocate HS-DSCH resources such as time slots and codes between multiple users, while with HSUPA aim of scheduler is to control the overloading of transmit power at Node-B.
Both HSDPA and HSUPA are 3GPP releases that aimed to enhance the downlink and uplink of the radio interface in mobile networks. Even though HSDPA and HSUPA aim at enhancing the opposite sides of the radio link, user experience of speed is inter-dependent on the both links due to request and response behaviour of data communication.