What is HSDPA

HSDPA is a high speed downlink packet access, it is 3GPP in the R5 protocol in order to meet the demand of the upper/lower data business is a modulation and demodulation algorithm, which can not change the already built WCDMA network structure, the downlink data service rate to 10Mbps. This technology is an important technology to improve the downlink capacity and data service rate in the later stage of WCDMA network construction. The application of HSDPA technology can fully meet the implementation of the expansion of operators in the 3G network mature period when the capacity demand is particularly large.

First, HSDPA technology and performance

In order to improve downlink packet data rate and reduce delay, HSDPA mainly uses adaptive coding and modulation (AMC Adaptive modulation and coding), fast hybrid automatic retransmission (HARQ hybrid ARQ) and fast scheduling technology. In fact, the above three kinds of technology belong to the link adaptive technology, can also be regarded as the WCDMA technology variable spread spectrum technology and power control technology to further enhance.

(1) Adaptive Coding and Modulation (AMC)

AMC chooses the appropriate modulation and coding method according to the wireless channel change, the network side according to the user instantaneous channel quality condition and the current resource chooses the most suitable downlink link modulation and the coding way, causes the user to achieve the high data throughput rate. When a user is in a favorable communication location (such as near NodeB or a line-of-sight link), the user data can be sent using high order modulation and high rate channel encoding, such as 16QAM and 3/4 encoding rates, resulting in higher peak rates, and when the user is in a disadvantageous communication location ( If at the edge of the cell or deep fading channel, the network side chooses low order modulation and low rate channel coding scheme, such as: QPSK and 1/4 coding rate, to ensure the quality of communication. (Computer science)

(2) Harq Technology

HARQ technology can improve the performance of the system, adjust the effective encoding rate flexibly, and compensate the bit error caused by the chain is destaged. HSDPA combines AMC with HARQ technology to achieve better link-adaptive effects. HSDPA first through AMC to provide a rough data rate selection scheme, and then use HARQ technology to provide accurate rate mediation, so as to improve the accuracy of adaptive adjustment and improve resource utilization. The HARQ mechanism itself is defined as a kind of error control scheme combining FEC and ARQ, HARQ mechanism has many forms, and HSDPA technology mainly uses three kinds of HARQ mechanism of increasing redundancy: Type-i harq,type-ii HARQ,TYPE-III. The corresponding HARQ mechanism can be selected according to system performance and equipment complexity.

(3) Quick Dispatch

The scheduling algorithm controls the allocation of shared resources and determines the behavior of the whole system to a large extent. The scheduling should be mainly based on the channel conditions, while considering the amount of data waiting to be launched and the priority of the business, and give full play to the capacity of AMC and Harq. The scheduling algorithm should transmit data to users who have the best channel conditions in a moment, so that the highest user data rate and maximum data throughput can be achieved in each instant, but the level and fairness of each user should be taken into account. In order to better adapt to the fast change of the channel, the HSDPA technology puts the dispatching function unit on the NodeB rather than the RNC, and also shortens the TTI to 2ms.

Second, the introduction of the HSDPA

The HSDPA technology is introduced into the R99 system, and the MAC-HS entity is added to the MAC layer, MAC-HS is located in NodeB instead of RNC, which is mainly responsible for handling Harq operation and fast scheduling algorithm. The HSDPA adds three new physical channels to the Utran of R99:

(1) Hs-dsch Channel: downlink, responsible for transmitting user data, channel sharing mode is mainly time division multiplexing and Code Division multiplexing

(2) HS-SCCH Channel: downlink, responsible for transmission of Hs-dsch channel decoding necessary control information

(3) HS-DPCCH Channel: Uplink, responsible for transmission of necessary control information, mainly for ARQ response and downlink quality feedback information

HSDPA function is mainly to modify the NodeB, the RNC is mainly modified algorithm protocol software, hardware impact is very small. If the original equipment in consideration of the HSDPA function upgrade requirements (such as 16QAM, buffer and processor performance, etc.), generally realize the HSDPA function does not require hardware upgrades, as long as the software upgrades can, so now many manufacturers are claiming that the software upgrade to support the HSDPA function. It is not too difficult to achieve this function, the key is to achieve performance, so the real performance of the HSDPA technology needs to be validated.

Third, the performance test considerations

The introduction of HSDPA technology requires a phased functional verification and performance testing, there are two points need operators to note: First, the hardware can be achieved by the processing performance will determine the future HSDPA performance, upgrade the implementation of the HSDPA performance needs to be clear, in addition, to achieve the HSDPA function, The effect of HSDPA technology on network performance. Aiming at the present situation of HSDPA technology, this paper proposes a phased performance test scheme to verify the network performance of HSDPA technology, and to study how to introduce the HSDPA problem through the performance test, and prepare the technology for the development and evolution of WCDMA network capacity and performance in the future.

However, the industry has not yet a manufacturer can provide commercial HSDPA functions, some manufacturers of existing products in the hardware already has the ability to handle HSDPA functions, has been upgraded to the software to HSDPA ready. However, the introduction of the HSDPA function also needs to consider the progress and ability of the terminal, the major manufacturers are also in contact with terminal equipment developers and chip design companies to negotiate research and development timetable for interoperability experiments.

Iv. concluding remarks

HSDPA technology has been formally introduced in the 3GPP WCDMA standard release ' 5, which completes the standardization of HSDPA technology. However, with release ' 5 version of the freeze, also marked the maturity of the HSDPA technical standards. In accordance with the original plan of the 3GPP organization, each release version should be officially released with a yearly cycle.

Through the introduction and analysis of the above HSDPA, we can see that HSDPA technology as WCDMA enhanced wireless technology will improve the system's spectral efficiency and code resource efficiency, is an effective way to improve the performance and capacity of the network. HSDPA not only can effectively support the Non-real time service, but also can be used to support some real-time services, such as streaming media business.