TD-SCDMA

Introduction

TDMA's Chinese meaning is the time division multiplexing synchronous code division multiple access, which is proposed by China, on the basis of wireless transmission technology (RTT) Completed and officially became an international mobile communication standard accepted by ITU. This is a creative and contribution to the international mobile communications industry, which is also an unprecedented breakthrough in the mobile communications industry.

TD-SCDMA TD refers to time multiplexing, that is, in the TD-SCDMA system, single user is two-way communication (transceiver) in the same time is TDD (time division duplex), in the same The frequency band is divided into different period (time slots) on the time domain, and the downlink is duplex, which can be easily implemented, and the flexible switch between the downlink. For example, according to different business pairs, the time slots between the downlink are determined, and there is a high efficiency to carry all 3G symmetrical and non-symmetrical services efficiently. Compared to the FDD mode, TDD can operate on unlaminated radio frequency spectrum, so it has a very advantage in current complex spectrum allocation. TD-SCDMA can support rates from 8kb / s to 2Mb / s and higher rates of 3G services from 8kb / s to 2Mb / s and higher rates, and higher rates of spectral, video calls, and Internet.

Development History

Mobile communication is to achieve any time, any location and communication between any communication objects. The development of mobile communications begins with the use of military and certain special fields in the 1920s. By the 1940s, it gradually expanded to civil expansion, and in the past decade, it was the truly thriving period of mobile communications. The development process of mobile communication can be roughly divided into three stages. These three-stage corresponding technologies are also divided into three generations, as shown in the history of mobile communication development.

The development of TD-SCDMA began in early 1998, at the time of the direct leadership of the National Post and Telecommunications Department, the Organization Team organized by the Original Telecom Science and Technology Research on SCDMA technology, study and draft IMT-2000 The draft TDSCDMA is required. The draft standard is based on intelligent antenna, synchronous code division multi-site, relay switching, and time division duplex, the deadline of ITU collection IMT-2000 third-generation mobile communication wireless transmission technology candidate is submitted to June 30, 1998. ITU, thereby becoming one of the 15 candidates of the IMT2000. The ITU combines the assessment results of each evaluation group. At the 18th meeting of the Helsinki ITU-RTG8 / 1 held in November 1999 and the Istanbul ITU-R plenary session held in May 2000, TD-SCDMA was officially accelerated as a CDMATDD model China Wireless Communication Standard Research Group (CWTS) As a regional standardized organization representing China, after the addition of 3GPP in May 1999, after 4 months of adequate preparation, a large coordination of the project coordination group (3 GPPPCG), Technical Specification Group (TSG), TD-SCDMA is recommended to include TD-SCDMA into the work content of the 3GPP standard specification in September of the same year. At the 3GPP meeting held in Nice, France in December 1999, the proposal was accepted by the Wireless Access Network (3 GPPTSGRAN), officially determining the TD-SCDMA into the work plan of Release 200 (subsequent score to R4 and R5), and TD-SCDMA is referred to as a low code rate TDD scheme (LCRTDD).

After more than a year, there have been a discussion of hundreds of working groups to submit a document in March 2001, including TD-SCDMA standards. The 3GPPR4 version specification was officially released, and TDSCDMA fused in 3GPP reached the first target.

To this, TD-SCDMA has been recognized and accepted by the majority of operators, equipment manufacturers, regardless of formula, and has been recognized and accepted by the majority of operators and equipment manufacturers.

Key Technologies

In the TD-SCDMA system, the following main key technologies are used:

(1) time division Duplexing (TIME DIVISION DUPLEXING) );

(2) Joint Detection;

(3) Intelligent Antenna (Smart Antenna);

(4) Upstream Synchronization (Uplink Synchronous;

(5) Software radio;

(6) Dynamic channel allocation;

(7) power Power Control;

(8) relay switching ("High Speed ​​Downlink Packet Access). High Speed ​​Downlink Packet Access.

frame, time slot structure

The air interface between the third generation mobile communication system is the UU interface between the UE and the network, by the physical layer (L1), data link layer ( L2) and the network layer (L3) consist. All physical channels use four-layer structure: system frame (0 ~ 4095), wireless frame (10 ms), subframe (5 ms), and time slot / code. The configuration structure of the subframe or slot / code may vary depending on the different resource allocation schemes. There is a guard interval between each time slot of all physical channels. In the TDMA system, different user signals are distinguished using the time slot on the time domain and code field.

frequency and code planning

TD-SCDMA system takes up 15MHz spectrum, where 2010MHz ~ 2025MHz is a phase of frequency band , small interference, divided into 3 5MHz The frequency band. Each carrier frequency occupies a bandwidth of 1.6MHz, so for 5M, 10M, 15M bandwidth, 3, 6, 9 carrier frequencies can be supported, respectively, can be used in communication groups or unfixable networks. High frequency spectrum utilization rate of the same frequency network, the neighboring area is similar, and the loss of capacity is improved; the foreign frequency group network can effectively reduce the effects of the neighboring interference, improve system performance, but the spectrum utilization is low. More frequent resources are required. At present, the frequency planning of the TD system uses N-band scheme, that is, each sector configures N carriers, including a primary carrier frequency, N-1 supplement frequency. The public control channel is configured to the primary carrier, a secondary carrier frequency configuration service channel. The primary carrier frequency and auxiliary carrier frequency use the same scrambling code and MI-DAMBLE code. The n-frequency scheme can reduce system interference, improve system capacity, and improve system integration network performance.

TD-SCDMA system uses a downlink pilot code having a corresponding relationship, an uplink pilot code, a scrambling code, and a MIDAMBLE code. The 128 basic scrambling code of the TD-SCDMA system is divided into 32 groups in the number sequence, each group, each of which is used for downlink UE distinguishes different cells. In the code plan, first determine the corresponding sequence number of each logical cell downlink code in 32 optional code groups, and then select a suitable scrambling code in the corresponding 4 disturb code according to the location position of the location. . The basic MIDAMBLE code corresponds to the disturb code, which can be determined as the scrambling code is determined. Compared to 512 codewords of WCDMA, TD-SCDMA system code resources are relatively small, so TD scrambling code plans higher than WCDMA network requirements.

Time slot planned

TD-SCDMA system can flexibly configure downlink time slot conversion points to accommodate asymmetivity of downstream traffic on different services. Reasonable configuration The downlink slot conversion point is an effective means of improving system spectral utilization. When the spectral scale plan is specifically performed, the calculation of time slot ratio can be performed according to the BRU ratio of the upper and downlink loads according to the business development status. In the early days of business development, the characteristics of the symmetrical symmetrical in the voice service can be used in 3: 3 (upstream: downward) symmetric slot structure; when the data service is further developed, a slot structure of 2: 4 or 1: 5 can be employed.

Time slot is flexible and configured while increasing resource utilization, it may bring interference caused by inconsistencies between adjacent cells due to the proportion of the upper downstream time slot. Therefore, in the network planning and networking, the assignment of the proportion of the upper and downstream time slot can be adopted, and the interference is appropriately circumvented:

(1) Try to avoid arbitrary allocation of the downlink time slot ratio, but according to different Regional and downstream business flow requirements, the proportion of unified upper and downstream time slots in large sectors, so that this interference only occurs at the junction of two different regions;

(2) At the junction of different time slots, For time slots over downstream of the upper and downstream time slots, the uplink slot capacity loss is serious than the downlink time slot, and the user can carry is less, and therefore, the junction of different gap ratios should be selected in a region with more uplink capacity.

(3) should avoid excessive differences between the downstream time slot of adjacent base stations (such as 1: 5 and 5: 1);

⑷ Upper downlink slot ratio is usually used as The cell parameters are configured, and the proportion of the upper and downstream time slots of all cells under the same sector should be consistent, and the ratio of the slot ratio of the plurality of sectors in the same base station is preferably the same. In special cases, the interference can be avoided by dynamic channel adjustment, spatial isolation, avoiding base station antennas and sacrificial capacity.

Network Planning is a key step in the construction of wireless network construction, mainly based on wireless propagation environments, business, society, etc., from coverage, capacity, and quality three aspects of the network. TD-SCDMA system uses a series of new key technologies and wireless resource algorithms such as intelligent antenna, joint detection, relay switching, dynamic channel assignment, and a wide range of characteristics, and network planning, and the network plan. The coverage of different services has consistency, the cell respiration effect is not obvious, and the upper and downlink channel configuration is flexible.

Cover Plan

The overlay performance of the TD-SCDMA system is mainly dependent, and the first and downlink time slot conversion protection length to the coverage limit, the other is the link budget. TD-SCDMA has 96 codewear-wide protective belts between downlink pilot slots and upstream pilot time slots, limiting the cell coverage of more than 11.25 km. If the first uplink slot is locked by DCA, the theory coverage distance of the base station can be further expanded. The link budget is the key to the TD-SCDMA network coverage plan, which is divided into up and down. The downlink budget is complex, and the transmission power of the general base station is much larger than the mobile phone transmit power, so it is generally determined by calculating the uplink to determine the cell coverage radius, and then estimated the number of base stations from coverage.

TD-SCDMA link budget indicators are affected by key technologies such as its unique frame structure, TDD duplex mode, intelligent antenna, combined detection, and relay switching. According to the unique frame structure of TD-SCDMA, the power allocation, interference reserves, and antenna gain are considered separately, respectively, and interfere with the reserve and antenna gain, respectively, the power distribution of the pilot channel, the BCH channel, etc..

In actual engineering design, the link budget of the TD-SCDMA system should be specific adjusted according to the specific wireless network propagation environment, network design objectives, manufacturers equipment performance, specific engineering parameters settings, etc.

Capacity Plan

TD-SCDMA system adopts a variety of key techniques to make the interference outside the cell and the cells in the cells are basically suppressed, and therefore have greater spectrum utilization and capacity. The TD-SCDMA system capacity characteristics are mainly: all kinds of business basic lanes, the cell respiration effect is not obvious, the relay switch does not have a macro set, and the switching is relatively easy to control, the upper and downlink capacity is related to the time slot ratio and the maximum transmit power.

Adoption of multiple interference suppression techniques, so that the capacity of the TD-SCDMA system exhibits diversity (ie, limited power limited, limited resource resource resource limit), but by resource Limits the Lord. In the intensive urban and complex environments, it will be limited to interference, in the environment and region of general urban, suburban, rural areas, and the TD-SCDMA system capacity planning should be treated differently. At present, the capacity estimation method of TD systems has the following three types: formula method, BRU method and Campbery law. BRU method and Campbella introduced the concept of basic resource units, business resources, etc., suitable for TD-SCDMA resource resource resource resource-limited systems, not suitable for WCDMA interference restricted systems. WCDMA system capacity planning generally uses formula based on interference restricted formula, but the calculation formula and TD-SCDMA are different.