What Is an HSDPA Network?

High Speed Downlink Packet Access (HSDPA) is a key new feature included in the R5 specification. It is a collection of wireless enhancement technologies. Using HSDPA technology can make the downlink data peak rate based on the existing technology. Great improvement. HSDPA technology is applicable to three different modes of WCDMA FDD, UTRA TDD and TD-SCDMA. The implementation in different systems is very similar.

From a technical perspective, HSDPA is mainly accomplished by introducing a high-speed downlink shared channel (HS-DSCH) to enhance the air interface, and adding corresponding functional entities in UTRAN. From the bottom, it is mainly introduced

3GPP describes three stages of HSDPA development: basic HSDPA, enhanced HSDPA, and new air interface.

1. The first stage-basic HSDPA

The functions of the first phase of HSDPA are specified by 3GPP R5, and its goal is to achieve a peak rate of 10.8 Mbit / s. HSDPA shares the paired frequency band with the channel used by the 3GPP R99 specification through code division multiple access multiplexing technology. Compared with the 3GPP R99 specification, the main changes in the first phase of HSDPA are: 3 new physical channels are added, HS-PDSCH uses adaptive modulation (QPSK / 16QAM) and Turbo coding technology, and a new MAC entity MAC- hs to control HS-DSCH and HARQ protocols.

2. The second stage-enhanced HSDPA

The functions of the second phase of HSDPA are defined by the 3GPP R6 specification, and its goal is to increase the peak data rate to about 30Mbit / s. In order to further improve the coverage, system output and spectrum efficiency of HSDPA, a variety of new multi-antenna transmission technologies are required. Some of these technologies are already included in the 3GPP R5 specifications, while others are still under 3GPP research. It is possible Appears in 3GPP R6 and later specifications.

The second phase of HSDPA mainly uses three multi-antenna transmission technologies: antenna beamforming technology, transmit diversity and space-time coding, and multiple-input multiple-output (MIMO) system.

3. Phase III-New Air Interface

In order to achieve higher average rates, HSDPA technology will be further combined with OFDM, MIMO, etc. to provide higher rates. The air interface determines the performance and complexity of the system, so its choice is critical to increasing the capacity and speed of the network. The goal of the third phase of HSDPA is to provide a rate of 100 Mbit / s to 1 Gbit / s. This requires additional spectrum and improved signal processing technologies, which mainly include improved signal processing technologies and the selection of OFDM as the main technology for OFDMA. . ^[1]

AMC High-Speed Downlink Packet Access Adaptive Code Modulation (AMC)

AMC is based on the fixed modulation and coding methods of traditional systems, and introduces adaptive technologies such as higher coding rates and higher-order modulation methods to enable the system to adaptively track link changes by changing coding methods and modulation levels. The main advantages of AMC are: users in advantageous positions can get higher data rates and increase the average cell throughput; link adaptation is based on changing the modulation and coding scheme instead of changing the transmission power to reduce collisions.

HARQ High-speed downlink packet access hybrid automatic repeat request (HARQ)

The so-called automatic retransmission request (ARQ) is a transmission mechanism that requires retransmission when a data transmission fails. ARQ includes: stop and wait (SW, Stop and Wait) retransmission, step N (GBN, Go Back N) step retransmission, selective (SR) selective retransmission, and N-channel AW retransmission.

Fast packet scheduling algorithm for high-speed downlink packet access

The scheduling algorithm controls the allocation of shared resources and largely determines the behavior of the entire system. The metrics of the packet scheduling algorithm are system efficiency and service fairness. Packet scheduling algorithms include Round Robin algorithm, maximum C / I algorithm, and fairness algorithm.

Round Robin algorithm uses round-robin scheduling without considering channel conditions. It is a blind algorithm. It simply distributes wireless resources evenly among users and has the highest fairness. The maximum C / I algorithm can also be called the highest performance scheduling. Algorithm, because using this algorithm can make the cell get the highest throughput; fair algorithms are divided into fair throughput algorithms, fair time algorithms, and fair power algorithms.

High-speed downlink packet access and fast link adjustment technology

Data services and voice services have different service characteristics. Voice communication systems usually use power control techniques to offset the effects of channel fading on the system to obtain a relatively stable rate, while data services can tolerate delays and can tolerate short-term changes in rate. Therefore, HSDPA does not try to improve the channel condition, but adopts the corresponding rate according to the channel condition. Since the HS-DSCH updates the channel status information every 2ms, the link layer adjustment unit can quickly track the channel change and adjust the rate by using different coding and modulation schemes.

High-speed downlink packet access for fast cellular selection

FCS is recommended for HSDPA. Using FCS, the UE can indicate a best cell for the downlink. Determining the "best" cell is not only based on the conditions of wireless signal propagation, but also considers the power of the cell and the resources of the codeword space in the active set. Generally speaking, there are many cells in the active set at the same time, but only the most suitable cell base stations are allowed to send, which can reduce interference and increase system capacity.

MIMO High-speed downlink packet access MIMO technology

Multiple-input multiple-output (MIMO) systems use multiple antennas at the transmitting and receiving ends simultaneously, which has more benefits than using multiple antennas at the transmitting end only. In MIMO systems, peak throughput can be improved through code multiplexing. ^[2]