营业厅TD-LTE室内分布系统设计(8)

辽宁科技学院本科生毕业设计（论文） 第 31 页

voice communication time has not yet reflected in the more prominent, but also the requirement of wireless communication system must have some characteristics suitable for transmission of data services, such as high throughput, high burstiness, high reliability etc.. Although the 3G technology has been insufficient for 2G system, made a great enhancement in strengthening the packet data transmission performance, but the rapid growth of market demand will make the peak transmission rate of 2Mbps 3G definition is insufficient. Therefore, in the development process of the third generation mobile communication technology, 3GPP in the R5 version specification were introduced for enhanced technology important, namely HSDPA (high speed downlink packet access) technology.

The HSDPA is a high speed downlink packet access technology is applied to the TD-SCDMA package, in theory it can provide data rates up to 2.8Mbps in each carrier. Adaptive modulation and coding, a new fast scheduling and hybrid automatic retransmission technology greatly improves the user downlink data rate transmission rate and throughput of HSDPA, it means that further improves the utilization rate of equipment and enhance the spectrum efficiency. Therefore, from the operator's perspective, if compared with the existing 3G technology, HSDPA can also provide services to more number of high rate users, effectively reduces the cost per bit. From the user's perspective, the transmission rate, a shorter HSDPA will provide more service response time and shorter delay.

The history and development of HSDPA

TD-SCDMA is the third generation mobile communication standard with independent intellectual property in China in 1999 was adopted by ITU, as the ITU recognized one of the third generation mobile communication wireless transmission technology, included in the ITU-R M.1457. In recent years, follow-up enhanced TD-SCDMA and evolution has been studied and perfected in the industry, and in the form of standards gradually established, the formation of TD-SCDMA technology roadmap to complete: introduced in Release5 high speed downlink packet access (HSDPA, HighSpeedDownlink Packet Access); introduction of multimedia broadcast multicast function in Release6 (MBMS); introduced in Release7 high speed uplink packet access (HSUPA, High Speed Uplink Packet Access).

Introduces the technical characteristics of TD-SCDMA HSDPA

In order to improve the downlink data rate and reduce the time delay, HSDPA mainly adopts the adaptive modulation and coding (AMC, Adaptive Modulation and

辽宁科技学院本科生毕业设计（论文） 第 32 页

Coding), hybrid automatic retransmission (HARQ, Hybrid Automatic Repeat Request), fast scheduling (Fast Scheduling) technology, replacing the R99/R4 in the variable spreading code and fast power control.

Adaptive modulation and coding in AMC

HSDPA is in the original system of fixed modulation and coding scheme based on, introduce more code rate and modulation of the 16QAM, which makes the system can change the encoding and modulation level adaptive tracking of link change.

AMC has two main advantages:

The advantageous position of the user can be higher data rate, improve the cell average throughput;

Link adaptive modulation and coding scheme instead of changing the transmit power based on, in order to reduce the conflict;

Hybrid automatic repeat request HARQ

AMC can provide a rough data rate selection, and H-ARQ based on channel conditions can provide accurate rate adjustment.

H-ARQ has several different ways are called: H-ARQ type, H-ARQ I, type II and H-ARQ type III.

RLC ARQ belongs to the HARQ type I model. In the basic HARQ Type I with CRC, using FEC code. At the receiver to decode the FEC code, and the quality check (CRC). If mistakes are found for retransmission, and the error packet drop. Repeat with the same first code transmission.

H-ARQ Type II is also called the incremental redundancy scheme, data blocks can not retransmission discarded, but with some provided by transmitting redundant information used for decoding. For the H-ARQ Type II, in order to error correction, retransmission of redundant information added to carry. Additional redundancy and the previously received packet are combined together, the code has a higher coding gain. Every retransmission redundancy is different, and retransmission usually only in the first episode and merge the data to be decoded.

With the HARQ Type II, HARQ Type III also belongs to a kind of incremental redundancy coding scheme. Unlike the type- Ⅱ type- Ⅲ, the retransmission information each time has the decoding ability (self decodable).

HSDPA HARQ& scheduling algorithm (MAX C/I, RR, PF)

Retransmission mode HSDPA using the hybrid automatic retransmission (HARQ:

辽宁科技学院本科生毕业设计（论文） 第 33 页

Hybrid Automatic Retransmission Request). In this way, when the Node B retransmission, does not need the original data retransmission complete package, but only need to repeat a part. The receiver can receive the data and previous. The retransmission of the data itself may not be enough to correct solution of the original data, but with the ever sent after binding may can lift the complete data.

Node B creates a HARQ entity responsible for each user, HARQ retransmission management. Each HARQ entity with multiple (maximum 8) HARQ process. Each HARQ process are independent of the work in accordance with HARQ. A plurality of parallel HARQ process, the Node B to the follow-up data is sent before the last packet is sent ACK/NACK back.

Node B can support the MAX C/I, RR, PF three kinds of scheduling algorithm. MAX C/I algorithm always resources allocated to the user with the best channel quality, RR does not consider the channel quality of users, resources among users average distribution. So Max C/I has the maximum cell throughput, RR has access to the absolute fairness.

PF algorithm is a compromise between the two. From the statistical significance of long time on see, more than one user's resource is fair. In the short term, it can cater to the channel quality better user, so as to achieve a higher system throughput than RR.

HSDPA static resource allocation

The maximum transmit power HSDPA can share the static configuration channel in physics by RNC. Node B when scheduling, transmission power will not use HSDPA exceeds the maximum value.

When the time slot DPCH needs more power, transmission power of the Node B can reduce HSDPA, so as to ensure the continuity of the DPCH.

HSDPA access control

Access control based on system resource utilization, access to the user's decision, thus the effective use of system resources, improve the success rate of user access.

According to the network planning and system specification, for each cell /NODEB configure the maximum allowed number of access users. Access process, need to consider the maximum value.

Access process, need to check the IUB interface transmission resources, ensure that HSDPA and R4 coexist, enough to support business needs of QoS.

Access process, set by RNC service rate threshold, according to the service rate

辽宁科技学院本科生毕业设计（论文） 第 34 页

decision request business is carried on HS-DSCH. For the DL streaming services and DL BE services, RNC will use a different threshold.

HSDPA flow control

The HSDPA service in major data users, each user traffic rate is not fixed, the actual rate of each user can be achieved in the empty is not fixed. So, if unchecked, is easy to appear two kinds of system of harmful situations: one is Node B accumulation of a large number of business data, but an actual rate not to send them out, resulting in buffer overflows, Node B, data loss. One is the instantaneous channel when the user's quality is very good, can send data, no data is Node B in the buffer zone, leading to idle resources are wasted.

HSDPA flow control algorithm according to the actual rate of buffer Node B occupancy rate and empty, the capacity allocation frame control RNC down the transmission data rate. When the empty rate high, when Node B empty buffer to speed up the transmission speed, and reduced RNC, can effectively avoid the above two kind of situations, to ensure the full use of idle resources, availability of system.

HSDPA mobility management

HSDPA mobility management is responsible for the HSDPA user in the moving process, to ensure that the user can choose to the new HSDPA cell or R4 cell. Mobility management is needed to ensure that HSDPA users in the selection of new area, as far as possible to avoid service interruptions.

Similar, and R4 HSDPA, switching is also based on the measurement report by the network side UE side reported, performs a handoff decision. Switch types include: HSDPA cell to HSDPA cell switching, HSDPA cells and R4 cells, switching between HSDPA cells and 2G cells, switching between INTER_RNC switching.

Switching between HSDPA cells:

For the same frequency area, when the user moves from one cell to another cell HSDPA, update the best cell through the 1G event. For the pilot area, update the best cell by 2A measurements. The network side based on user handoff decision reporting measurement.

Switching between HSDPA cells and R4 cells:

When the users of HSDPA mobile from HSDPA cells to R4 cells, according to the user to report measurement, if the target R4 cell for the same frequency cell is the same frequency switching judgment; if the target area for different frequency cell is inter-frequency handoff decision. The admission decision target user service rate.

辽宁科技学院本科生毕业设计（论文） 第 35 页

When the user moves from R4 cells to HSDPA cells, can be switched through D2D, by the target cell rate adjusted according to the user's ability; or, in the user support capacity and current business allowable bearing in the HS channel, switch can realize direct D2HS. By switching strategy implementation process of algorithm to determine the actual use of the switch.

Switching between HSDPA cells and 2G cells:

When the users of HSDPA mobile from HSDPA cells to 2G cells, according to the different system measurement, system support area by HSDPA cell to 2G switch. Whether the HSDPA service speed reduction processing specific switching algorithm is realized by the side of decision system.

INTER_RNC switch:

If switching occurs in between the different RNC, SRNC migration process is realized by switching between RNC. By a cell update message triggers the process.

Comparison of HSDPA and R4 business coverage

HSDPA and R4 coverage compared theoretically can be made simple comparative analysis through link budget, we can know from the principle of link budget, for the R4 business, link loss calculation of a business, must know the sensitivity of transmit power transmitter and receiver, the difference is the maximum link loss. R4 service receiving sensitivity, and the channel environment in other words, the receiving sensitivity and the environment of R4 business is the one one corresponding, thus corresponding to different environmental business coverage radius and area of different. HSDPA link calculation principle and the R4 service is not exactly the same, because the first HSDPA receiving sensitivity about not receiving end, but throughput problems; secondly the HSDPA transmission power is fixed. The throughput of the HSDPA and the received signal quality, UE periodically by the uplink HSSICH channel to the Node-B channel CQI, Node-B to determine the transmission blocks the next frame based on CQI. Cover the distance calculation HSDPA must first determine the expected throughput of downlink, in order to get C/I, determine the downlink receiving threshold (here no longer mention the receiving sensitivity). For HSDPA, C/I and the environment is no longer a one one corresponding relation, namely an environment corresponds to a unique C/I, to calculate the HSDPA of the environment in the distance, HSDPA C/I is a set (see table 2-1), ranging from 0.4 to 16dB, with different category UE, the same as the corresponding C/I, the RTBS is different, namely the throughput of different.

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