HSDPA

High-Speed Downlink Packet Access (HSDPA) is an enhanced 3G (third-generation) mobile telephony communications protocol in the High-Speed Packet Access (HSPA) family, also dubbed 3.5G, 3G+, or Turbo 3G, which allows networks based on Universal Mobile Telecommunications System (UMTS) to have higher data-transfer speeds and capacity. As of 2013 HSDPA deployments can support down-link speeds of up to 42.3 Mbit/s. HSPA+ offers further speed increases, providing speeds of up to 337.5 Mbit/s with Release 11 of the 3GPP standards

Capacity

• It is the maximum throughput that the RBS can deliver to one cell. The capacity is shared by all HSDPA users.

System Capacity

• It is the average capacity per cell for a cluster of cells. For system capacity calculation it is assumed that the load is homogenously distributed and HSDPA is deployed in all cells.

Dedicated Channel Traffic

• DCH traffic is defined as the traffic carried by dedicated transport channels such as speech, PS or CS radio bearers i.e. on channels other than HSDPA.

RBS Load

• It is the percentage of the maximum available RBS power that is used in the downlink.

Power Margin

• Power margin saves a part of the RBS power to cater for power variations, due to the dynamic UE behavior when users move and experience varying channels conditions.

• For HSDPA it is assumed that no power margin is needed and RBS may use 100% of the available power in a system with HSDPA.

Shared Channel Transmission

• Shared channel transmission means that a set of radio resources are dynamically shared among multiple users.

• The sharing is done in time and code domain

Fast Radio Dependent Scheduling

• Scheduling is the function that determines which UE to transmit to at a given time instant.

• Three scheduling algorithms are implemented.

1. Proportional Fair Scheduling

2. Round Robin Scheduling

3. Maximum Channel Quality Indicator

Proportional Fair Scheduling

• The algorithm uses information about fading peaks to prioritize users with good radio conditions

• It also takes delay into account promoting users that have not been given any data for a long time

Round Robin Scheduling

• The algorithm gives every user same amount of radio resources (TTI).

• The algorithm is fair for all users from a resource point of view but bit rate varies.

Max CQI (Channel Quality Indicator)

• UE sends CQI in the UL to aid rate adaptation and scheduling

• The algorithm maximizes system throughput by prioritizing users with good radio channels

• The CQI report estimates the number of bits that can be transmitted to the UE using a certain assumed power with a block error rate of 10%

High-order Modulation

• HS-DSCH uses 16 QAM if the UE category permit.

• This allows twice as high data rates to be transmitted as compared to QPSK

2 ms TTI

• Transmission Time Interval for HSDPA is short when compared to R99

• It is 2 ms for HS-DSCH for R99 it is 10-40 ms

Fast Link Adaptation

• As opposed to R99 RBs, HS-DSCH is transmitted with constant power within the TTI.

• Transmission rate is controlled by adaptive channel coding.

• Data rate depends on radio conditions (CQI)

Fast Hybrid ARQ with soft combining

• In hybrid automatic repeat request scheme, the received blocks that cannot be decoded are buffered and soft combined with later received transmissions of same information bits. Hybrid ARQ protocol terminates in Node B which means short RTT (typically 12 ms

HSDPA Power

• The RBS power available for HSDPA is determined dynamically, depending on R99 power usage

• At least 25% of the average power can be used for HSDPA

HSDPA Channel Structure

New Physical and Transport channels are introduced in HSDPA:

 Transport Channel

• High Speed Downlink Shared Channel (HS-DSCH)

Physical Channels

• High Speed Physical Downlink Shared Channel (HS-PDSCH)

• High Speed Shared Control Channels (HS-SCCH)

• High Speed Dedicated Physical Control Channel (HS-DPCH)

• Associated Dedicated Channel (A-DCH)